t03 hitachi

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1HH-3-1

SECTION 3

COMPONENT OPERATION

CONTENTS

Group 1 Pump Device

Outline .....................................................T3-1-1

Main Pump1, 2 .........................................T3-1-2

Regulator .................................................T3-1-6

Pilot Pump..............................................T3-1-22

N Sensor (Engine Speed Sensor)...........T3-1-22

Pump Delivery Pressure Sensor.............T3-1-22

Group 2 Swing Device

Outline .....................................................T3-2-1

Swing Motor .............................................T3-2-2

Swing Parking Brake ................................T3-2-3

Valve Unit.................................................T3-2-4Swing Reduction Gear..............................T3-2-6

Group 3 Control Valve

Outline .....................................................T3-3-1

Hydraulic Circuit .......................................T3-3-6

Flow Combiner Valve..............................T3-3-10

Pump Control Valve................................T3-3-12

Main Relief Valve....................................T3-3-14

Overload Relief Valve .............................T3-3-15

Arm Regenerative Valve .... .... ........ .... .... .T3-3-16

Boom Regenerative Valve ......................T3-3-18

Bucket Regenerative Valve.....................T3-3-20

Arm Anti-Drift Valve (Bottom Side)... .... ...T3-3-22

Arm Anti-Drift Valve (Rod Side) /

Boom Anti-Drift Valve ...........................T3-3-25

Bucket Flow Rate Control Valve .............T3-3-26

Travel Flow Rate Control Valve...............T3-3-28

Bypass Shut-Out Valve...........................T3-3-30

Needle Valve..........................................T3-3-32

Group 4 Pilot Valve

Outline .....................................................T3-4-1

Operation .................................................T3-4-2

Group 5 Travel Device

Outline .....................................................T3-5-1

Travel Reduction Gear..............................T3-5-2

Travel Motor .............................................T3-5-3

Travel Brake Valve ...................................T3-5-6

Travel Motor Swash Angle Control..........T3-5-14

Parking Brake.........................................T3-5-19

Group 6 Others (Upperstructure)Pilot Shut-Off Valve ..................................T3-6-1

Shockless Valve .......................................T3-6-2

Solenoid Valve Unit ..................................T3-6-4

Torque Control Solenoid Valve, Pump 2

Flow Rate Control Solenoid Valve ...........T3-6-6

Pilot Relief Valve ......................................T3-6-8

EC Motor ..................................................T3-6-8

Group 7 Others (Undercarriage)

Swing Bearing ..........................................T3-7-1

Center Joint..............................................T3-7-2

Track Adjuster ..........................................T3-7-3

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1HH-3-2

(Blank)

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COMPONENT OPERATION / Pump Device

T3-1-1

OUTLINE

The pump device consists of the transmission, main

pumps, and pilot pump. The transmission transfers

engine power to gears via the coupling and drives the

main pumps and pilot pump. The gear ratio to the main

pumps and pilot pump is 1, and 1, respectively.

The main pump is a bent-axis type variable displace-

ment axial plunger pump. The pilot pump is a gear type.

The engine speed sensor (N sensor) and pump deliv-

ery pressure sensor (P sensor) are provided to control

the engine, pump, and valves.

T173-03-01-003

T173-03-01-001

T173-03-01-002

1 - Main Pump 1 3 - Main Pump 2 5 - Pump 2 Delivery

Pressure Sensor

7 - N Sensor

2 - Pilot Pump 4 - Pump 1 DeliveryPressure Sensor

6 - Transmission 8 - Coupling

7

6

123

5 4

8

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T3-1-2

MAIN PUMP 1, 2

The main pump supplies pressure oil to the hydraulic

actuators such as motors, and cylinders. Shaft (3) is

connected to each pump cylinder block (6) via 7

plungers (4) so that the shaft and the cylinder block

rotate together. When cylinder block (6) is rotated,

plunders (4) reciprocate in the cylinder block, suction-

ing and delivering the hydraulic oil. Each pump is

equipped with a regulator to control the delivery oil flow

rate.

T173-03-01-004

1 - Regulator 3 - Shaft 5 - Valve Plate 6 - Cylinder Block

2 - Housing 4 - Plunger

Shaft6 1

2

3

5

4

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T3-1-3

Operational Principle

Engine torque is transferred to the shaft and the

seven plungers, causing the cylinder block to rotate

while sliding along the valve plate surface. The

plungers reciprocate in the cylinder block bores to al-

ternately draw and deliver hydraulic oil.

T105-02-03-002

Plunger

Valve Plate

Shaft

Cylinder Block

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T3-1-4

Increasing and Decreasing Flow Rate

Changing inclination of the cylinder block, causes the

plunger stroke to increase or decrease depending on

the slant angle which in turn controls the main pump

flow rate. Up-down movement of the servo piston

changes inclination of the cylinder block. The servo

piston is interlocked with the valve plate via the pin.

The one end of the cylinder block is kept in contact

with the surface of the valve plate and slides along it.

T105-02-03-021

T105-02-03-022

T173-03-01-004

Maximum Displacement Angle:

Minimum Displacement Angle

α

α

Plunger

Shaft

Cylinder Block

Cylinder Block

Pin

ServoPiston

Plunger Valve Plate

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T3-1-5

(Blank)

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T3-1-6

REGULATOR

The regulator controls the main pump flow rate in re-

sponse to the various command signal pressures so

that the pump driving power doesn’t exceed the engine

power. Pump 1 and pump 2 are provided with one

regulator each. The major parts of the regulator are

spring (1), sleeve A (2), sleeve B (7), spool A (3), spool

B (6), piston (4), load piston (5), outer spring (8), and

inner spring (9). According to the various command

signal pressures, the regulator opens or closes the

circuit to servo piston (10), causing the inclination of

cylinder block (11) to change, by which the pump flow

rate is controlled.

NOTE: Pilot oil pressure is constantly supplied in

the smaller side chamber of servo piston(10).

T1HH-03-01-018

Pd1 -Pump 1 Delivery Pres-

sure

Pi - Pump Control Pressure


sure

Pps -Torque Control Pressure

Dr - Returning to Hydraulic

Oil Tank

Pg - Primary Pilot Pressure

(From Pilot Pump)

421 3

7

8, 912

65

Increase Decrease

Pd1

Pps

Dr

Pg

Dr

Air BleedingCircuit

Pi

Pd2

10

Cylinder Block Inclination

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T3-1-7

T1HH-03-01-002

T173-03-01-004

1 - Spring 4 - Piston 7 - Sleeve B 10 - Servo Piston

2 - Sleeve A 5 - Load Piston 8 - Inner Spring 11 - Cylinder Block

3 - Spool A 6 - Spool B 9 - Outer Spring 12 - Link

1 2 3 4

5 6 7 8 9

12

11

10

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T3-1-8

Regulator Functions

The regulator has the three following functions:

• Control by Pump Control Pressure

The pump control valve in the control valve controls

pressure in response to the movements of the spool.

The regulator receives this pump control pressure

signal and controls the pump flow rate as follows.

When the control valve spool is moved and the

pump control pressure is increased, the regulator in-

creases the pump flow rate.

When the control valve spool is returned to the neu-

tral position and the pump control pressure is re-

duced, the regulator decreases the pump flow rate.

(Refer to the Control Valve group pages.)

• Control by Pump Delivery Pressure

The delivery pressure of both main pump 1 and

main pump 2 are routed to the regulator. When the

average pressure of the two pumps exceeds the

specified P-Q line, the regulator reduces both pump

flow rates so that the pump performance is returned

to the specified P-Q line. Thus, the engine is pro-

tected from overloads. The designed P-Q line has

been determined based on the two pump perform-

ance. Therefore, both pump flow rates are set to al-

most equal value. Accordingly, the high pressure

pump is loaded heavier than the low pressure pump.Then, the total output of the two pumps is equal to

the engine output (Total Horsepower Control).

• Control by Pilot Pressure from Solenoid Valve Unit

(SD)

The MC (main controller) compares the engine tar-

get speed with the actual engine speed and sends

control signals to solenoid valve unit (SD).

The solenoid valve unit (SD) delivers the pilot oil

pressure in response to control signal from the MC

to the regulator. When the regulator receives the pi-

lot pressure, the regulator reduces the pump flow

rate (Speed Sensing [Horsepower Reduction] Con-trol). (Refer to the Control System group pages.)

Flow Rate (Q)

Pump Control Pressure (Pi)0

Flow Rate Decrease

Pressure Increase

Pressure (P)0

Flow Rate (Q)

Pressure (P)0

Flow Rate (Q)

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T3-1-9

• Control by Pilot Pressure from Flow Rate Control

Solenoid Valve (Pump 2 Side Only)

When the MC receives signals from the work mode

switch, pressure sensor (optional) [auxiliary] or at-

tachment mode switch (optional), the MC send sig-

nals to the maximum pump flow rate control sole-

noid valve. Then, in response to the signals from the

MC, the maximum pump flow rate control solenoid

valve reduces pump control pressure Pi, limiting the

maximum pump flow rate. (Pump Flow Rate Limit

Control)

(Refer to the CONTROL SYSTEM section.)

T1HH-03-01-016

NOTE: This indicates the regulator when the en-

gine stops. Pd1 -Pump 1 Delivery Pressure Pi - Pump Control PressurePd2 -Pump 2 Delivery Pressure Pps -Torque Control Pressure

Dr - Returning to Hydraulic Oil

Tank


(From Pilot Pump)

FlowRate (Q)

Pressure (P)0

FlowRate (Q)


Pd1

Pd2

Pps

PgPi

Dr

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T3-1-10

Control by Pump Control Pressure

• Increasing Flow Rate

1. When a control lever is operated, pump control

pressure Pi increases (Refer to control valve

group).

2. Piston (4) pushes spool A (3) and spring (1) so

that spool A (3) is moved in the direction of the ar-

row.

3. Then, the circuit from the large chamber of servo

piston (10) is opened to the hydraulic oil tank.

4. The pilot oil pressure is always routed into the

small chamber of servo piston (10). Thereby,

servo piston (10) is moved toward the direction of

the arrow. Then, the cylinder block rotated in the

maximum inclination direction, increasing the

pump flow rate.5. The movement of the cylinder block is transmitted

to sleeve A (2) via link (12). Then, sleeve A (2) is

moved in the same direction as spool A (3).

6. When sleeve A (2) is moved by the same stroke

as spool A (3), the circuit from the large chamber

of servo piston (10) to the hydraulic oil tank is

closed so that servo piston (10) is stopped, com-

pleting flow rate increase operation.

T1HH-03-01-018

1 - Spring 4 - Piston

2 - Sleeve A 10 - Servo Piston

3 - Spool A 12 - Link


sure


Pd2 - Pump 2 Delivery Pres-

sure



Oil Tank


(From Pilot Pump)

421 3

10

FlowRate (Q)


12Increase Decrease


Pd1

Pps

Dr

Pg

Dr

Air BleedingCircuit

Pi

Pd2

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T3-1-11

T1HH-03-01-004

T1HH-03-01-005

1

Pump ControlPressure Pi

Primary Pilot PressureTo Hydraulic Oil tank

2 3 4

12

10

1



2 3 4

12

10

ANIMATION

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T3-1-12

• Decreasing Flow Rate

1. When a control lever is returned, the pump control

pressure Pi decreases.

2. Piston (4) and spool A (3) is pushed by spring (1)

so that spool A (3) is moved in the direction of the

arrow.

3. Then, the pilot oil pressure is also routed onto the

large chamber of servo piston (10).

4. Due to the difference in diameter between the

large and small chambers, servo piston (10) is

moved toward the direction of the arrow so that

the cylinder block is rotated in the minimum incli-

nation direction, decreasing the pump flow rate.

5. The movement of the cylinder block is transmitted



6. When sleeve A (2) is moved by the same strokeas spool A (3), the pilot oil pressure circuit to

servo piston (10) through sleeve A (2) and spool A

(3) is closed so that servo piston (10) is stopped,

completing flow rate decrease operation.

T1HH-03-01-018





sure



sure



Oil Tank


(From Pilot Pump)

421 3

FlowRate (Q)


Increase Decrease


Pd1

Pps

Dr

Pg

Dr

Air BleedingCircuit

Pi

Pd2

1210

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T3-1-13

T1HH-03-01-006

T1HH-03-01-007

1



2 3 4

12

10

1



2 3 4

12

10

ANIMATION

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T3-1-14

Control by Own or Opponent Pump Delivery

Pressure


1. When the pump is loaded by operating any of the

control levers, either pump 1 delivery pressure

Pd1 or pump 2 delivery pressure Pd2 increases.

(During operation, pump control pressure Pi is in-

creased.)

2. Load piston (5) moves spool B (6) and inner and

outer springs (8 and 9) toward the direction of the

arrow.

3. Due to the movement of spool B (6), the pilot oil

pressure is routed into the large chamber of servo

piston (10).

4. Due to the difference in diameter between the

large and small chambers, servo piston (10)moved toward the direction of the arrow so that

the cylinder block is rotated in the minimum incli-

nation direction, decreasing the pump flow rate.


to sleeve B (7) via link (12). Then, sleeve B (7) is

moved in the same direction as spool B (6).

6. When sleeve B (7) is moved by the same stroke

as spool B (6), the pilot oil pressure circuit to

servo piston (10) through sleeve B (7) and spool B


completing flow rate decrease operation.

T1HH-03-01-018

5 - Load Piston 9 - Outer Spring

6 - Spool B 10 - Servo Piston

7 - Sleeve B 12 - Link

8 - Inner Spring

Pd1 - Pump 1 Delivery

Pressure


Pd2 - Pump 2 Delivery

Pressure


Dr - Returning to HydraulicOil Tank

Pg - Primary Pilot Pressure(From Pilot Pump)

7

8, 912

65

Increase Decrease


Pd2

Pps

Dr

Pg

Dr

Air BleedingCircuit

Pi

Pd1

FlowRate (Q)

Pressure (P)0

10

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T3-1-15

T1HH-03-01-008

T1HH-03-01-009

5



6 7

12

10

5



12

10

8 9

6 7

8 9

Pump 1 DeliveryPressure Pd 1




ANIMATION

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T3-1-16

• Increasing Flow Rate

1. When the pump load is reduced, either pump 1

delivery pressure Pd1 or pump 2 delivery pres-

sure Pd2 decreases. (During operation, pump

control pressure Pi is kept increased.)

2. Load piston (5) and spool B (6) are pushed by in-

ner and outer springs (8 and 9) toward the direc-

tion of the arrow.

3. Due to the movement of spool B (6), the circuit

from the large chamber of servo piston (10) is

opened to the hydraulic oil tank.

4. Since the pilot oil pressure is constantly routed in

to the small chamber of servo piston (10), servo

piston (10) is moved toward the direction of the ar-

row. Then, the cylinder block is rotated in the


pump flow rate.5. The movement of the cylinder block is transmitted




as spool B (6), the pilot oil pressure circuit to

servo piston (10) through sleeve B (7) and spool B


completing flow rate increase operation.

T1HH-03-01-018




8 - Inner Spring


sure



sure



Oil Tank


(From Pilot Pump)

7

FlowRate (Q)

Pressure (P)0

65

Increase Decrease


Pd1

Pps

Dr

Pg

Dr

Air BleedingCircuit

Pi

Pd2

108, 912

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T3-1-17

T1HH-03-01-010

T1HH-03-01-011

5



6 7

12

10

5



12

10

8 9

6 7

8 9





ANIMATION

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T3-1-18

Control by Pilot Pressure from Torque Control So-

lenoid Valve


1. When the torque control solenoid valve is acti-

vated by the signals from the MC, torque control

pressure Pps increases.

2. Torque control pressure Pps and either own pump

delivery pressure Pd1 or opponent pump delivery

pressure Pd2 are combined and applied to load

piston (5).

3. Load piston (5) pushes spool B (6) and inner and

outer springs (8 and 9) toward the direction of the

arrow.

4. Due to the movement of spool B (6), the pilot oil

pressure is routed into the large chamber of servo

piston (10).5. Due to the difference in diameter between the

large and small chambers, servo piston (10) is

moved toward the direction of the arrow. Then, the

cylinder block is rotated in the minimum inclination

direction, decreasing the pump flow rate.





as spool B (6), the pilot oil pressure circuit to the

large chamber of servo piston (10) through sleeve

B (7) and spool B (6) is closed so that servo piston(10) is stopped, completing flow rate decrease

operation.

T1HH-03-01-018




8 - Inner Spring


sure



sure



Oil Tank


(From Pilot Pump)

7

FlowRate (Q)

Pressure (P)0

65

Increase Decrease


Pd1

Pps

Dr

Pg

Dr

Air BleedingCircuit

Pi

Pd2

10 8, 912

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T3-1-19

T1HH-03-01-012

T1HH-03-01-013

5



6 7

12

10

5



12

10

8 9

6 7

8 9





Torque Contro lPressure Pps

Torque Contro lPressure Pps

ANIMATION

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T3-1-20

Control by Pilot Pressure from Flow Rate Control

Solenoid Valve

• Limiting Maximum Flow Rate (Pump 2 Only)

1. The maximum pump flow rate control solenoid

valve in the pump control pressure Pi circuit is ac-

tivated by the signals from the MC.

2. The maximum pump flow rate control solenoid

valve functions as a reducing valve, limiting pump

control pressure Pi.

3. Piston (4) pushes spool A (3) and spring (1) to-

ward the direction of the arrow.

4. Due to the movement of spool A (3), the circuit

from the large chamber of servo piston (10) is

opened to the hydraulic oil tank.

5. Since the pilot oil pressure is constantly routed

into the small chamber of servo piston (10), servopiston (10) is moved toward the direction of the ar-

row so that the cylinder block is rotated in the


pump flow rate.




7. When sleeve A (2) is moved by the same stroke

as spool A (3), the pilot oil pressure circuit to the

large chamber of servo piston (10) is closed so

that servo piston (10) is stopped, completing flow

rate increase operation.8. As the pump control pressure is restricted, the

maximum flow rate is reduced more than normal.

T1HH-03-01-018





sure



sure



Oil Tank


(From Pilot Pump)

421 3

Increase Decrease


Pd1

Pps

Dr

Pg

Dr

Air BleedingCircuit

Pi

Pd2

FlowRate (Q)

Pressure (P)0

10 12

FlowRate (Q)


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T3-1-21

T1HH-03-01-014

T1HH-03-01-015

1


2 3 4

12

10

1


2 3 4

12

10

Pump Control Pres-sure Pi Regulated byMaximum Pump Flow

Rate Control Sole-noid Valve

Pump Control Pres-sure Pi Regulated byMaximum Pump FlowRate Control Sole-noid Valve

ANIMATION

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T3-1-22

PILOT PUMP

Drive gear (1) is driven by the engine via the transmis-

sion which in turn rotates driven gear (2) as they are

meshed together.

When drive gear (1) rotates, driven gear (2) is also

rotated. The hydraulic oil, routed from the inlet port, fills

the spaces between the teeth on each gear, is trans-

ferred along the inside surface of the housing, and dis-

charged from the outlet port.

1 - Drive Gear 2 - Driven Gear

N SENSOR (ENGINE SPEED SENSOR)

The N sensor detects the engine speed, which is used

to control various operations. The N sensor is located

close to the transmission teeth so that the sensor con-

verts the number of teeth passing by the sensor into

pulse signals, effectively sensing the engine speed.

3 - Tooth 5 - Output

4 - Output

PUMP DELIVERY PRESSURE SENSOR

This sensor detects the pump delivery pressures,

which are used to control various operations. When oil

pressure is applied onto diaphragm (9), the diaphragm

is deformed. The deformation of the diaphragm is de-

tected as electrical signals.

6 - Ground 8 - Power Source (5V)

7 - Output 9 - Pressure Receiving Area

(Diaphragm)

T137-02-03-005

T178-03-01-020

T1HH-03-01-017

2

1Inlet Port

Outlet Port

4

3

5

6 7 8 9

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COMPONENT OPERATION / Swing Device

T3-2-1

OUTLINE

The swing device consists of the valve unit, swing mo-

tor, and swing reduction gear. The valve unit prevents

cavitation in the swing circuit from occurring and pro-

tects the circuit from being overloaded. The swing mo-

tor is a swash plate type axial plunger motor with a

built-in swing parking brake. The swing motor is driven

by pressure oil delivered from the pump, and drives the

swing reduction gear.

The swing reduction gear converts the swing motor

output into slow large torque to rotate the shaft.

Thereby, the upperstructure is rotated.

T1HH-03-02-001

Swing Reduction Gear

Swing Motor

Valve Unit

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T3-2-2

SWING MOTOR

The swing motor consists of the swash plate, rotor,

plungers, valve plate, housing and swing parking brake

(springs, brake piston, plates, friction plates, and

switch valve). The rotor in which the plungers are in-

serted is splined onto the shaft.

When pressure oil is supplied from the pump, the

pressure oil pushes the plungers. Since the swash

plate is inclined, the shoes on top of the plungers slide

along the swash plate, causing the rotor and shaft to

rotate. The shaft tip end is splined into the first stage

sun gear in the swing reduction gear so that shaft rota-

tion is transmitted to the swing reduction gear.

T1HH-03-02-002

Shoe

Shaft

Housing

Swash Plate

Plate,

Friction Plate

Spring

Valve Plate

Rotor

Plunger

Brake Piston

Switch Valve

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T3-2-3

SWING PARKING BRAKE

The swing parking brake is a wet-type multi-disc brake.

The brake is released when brake release pressure

enters into the brake piston chamber (negative brake

type). Brake release pressure is supplied from the pilot

pump only when a front attachment and/or swing op-

eration is made. During operations other than swing

and/or front attachment or while the engine is stopped,

brake release pressure is returned to the hydraulic oil

tank so that the brake is automatically applied by

spring.

Releasing Brake:

1. When the swing and/or front attachment control

levers are operated, the spool in the control valve

is shifted.2. Thereby, the pilot signal circuit is blocked and the

pressure in the pilot signal circuit increases. The

pressure in the pilot signal circuit shifts the switch

valve.

3. Then, the brake release pressure from the pilot

pump flows to brake piston chamber (b) via hy-

draulic oil timer check valve and acts on brake pis-

ton (2).

Consequently, plates (3) and friction plates (4)

are free, so the brake is released.

Applying Brake:1. When the swing and/or front attachment control

levers are released, the spool in the control valve

is returned to neutral so that the pressure of the

pilot signal circuit is reduced.

2. Therefore, the switch valve is shifted by the spring

force. The brake release pressure flows to the hy-

draulic oil tank port via the orifice of the hydraulic

oil timer.

3. Consequently, spring force (1) is applied to plates

(3) and friction plates (4) which are meshed with

the outer diameter of rotor (6) and inner diameter

of motor housing (5) respectively via brake piston

(2). Then, the rotor (6) outer diameter is held withfriction force. While the engine is stopped, no

pressure in the pilot signal circuit is routed, allow-

ing the brake to be automatically applied.

T157-02-04-007

Brake “OFF”

T157-02-04-005

Brake “ON”

T157-02-04-004

1 - Spring 4 - Friction Plate

2 - Brake Piston 5 - Motor Housing

3 - Plate 6 - Rotor

1

2

3

4

5

6

b

SwitchValve

BrakeReleasePressure

Hydraulic OilTimer

OFF

SwingMotor

Spool

SwitchValve

BrakeReleasePressure

Hydraulic OilTimer

ON

SwingMotor

Spool

Pilot SignalCircuit

Pilot SignalCircuit

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T3-2-4

VALVE UNIT

The valve unit consists of the make-up valves and the

relief valves. The make-up valves prevents cavitation

in the circuit. The relief valves prevent surge pressure

and overloads in the circuit.

Make-Up Valve

During swing stop operation, the swing motor is

driven by inertia force of the upperstructure. The mo-

tor is rotated by inertia force more than by pressure

oil delivered from the pump, causing cavitation to de-

velop in the circuit. To prevent cavitation, when pres-

sure in the swing circuit is reduced more than the re-

turn circuit (port C) pressure, the poppets are opened

so that hydraulic oil is drawn into the circuit from the

hydraulic oil tank to compensate for the lack of oil inthe circuit.

T107-02-04-013

T1HH-03-02-003

Control Valve

Port C

Relief Valve

Make-Up Valve

Make-Up Valve

Relief Valve

Make-Up Valve

Poppet

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T3-2-5

Relief Valve

When starting or stopping swing operation, oil

pressure in the swing circuit becomes high. The relief

valve prevents the circuit pressure from rising higher

than the specified pressure. The plunger is pushed to

the left by pressure (Pp) force of the swing circuit in

pressure-receiving area A2.

However, plunger is also pushed back to the right by

spring force and pressure Pg at chamber (g) in

pressure-receiving area A1.

Chamber (g) is routed to port through orifice (m).

When the force acting on the right is higher than that

on the left, the relief valve operates.

T107-02-04-020

g m

Swing Circuit(Pressure Pp)

A2 A1

Return Circuit(Port C)

Plunger

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T3-2-6

SWING REDUCTION GEAR

The swing reduction gear is a two-stage planetary gear

type.

Ring gear (2) is provided on the inside of the housing, it

is fixed and does not rotate.

The motor output shaft of the swing motor drives first

stage sun gear (8).

Then, rotary power is transmitted to second stage sun

gear (6) via first stage planetary gear (1) and first stage

carrier (7). Second stage sun gear (6) rotates shaft

(output shaft)(4) via second stage planetary gear (3)

and second stage carrier (5).

As shaft (4) meshes with the internal gear of the swing

bearing bolted to the undercarriage, the upperstructure

is rotated.

T1HH-03-02-001

1 - First Stage Planetary

Gear

3 - Second Stage Planetary

Gear

5 - Second Stage Carrier 7 - Fi rs t Stage Carrier

2 - Ring Gear 4 - Shaft (Output Shaft) 6 - Second Stage Sun Gear 8 - First Stage Sun Gear

1

2

3

4

7

8

6

5

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COMPONENT OPERATION / Control Valve

T3-3-1

OUTLINE

The control valve controls oil pressure, flow rate and

flow direction in the hydraulic circuit. The major com-

ponents of the control valve are the flow combiner

valve, pump control valve, main relief valve, overload

relief valve, arm regenerative valve, boom regenera-

tive valve, bucket regenerative valve, arm anti-drift

valve (both the bottom and rod sides), boom anti-drift

valve, bucket flow rate control valve, travel flow rate

control valve, bypass shut-out valve, needle valve, and

spools.

The spool arrangement in the 4-spool section (seen

from the front) is the travel (right), bucket, boom 1, and

arm 2. The spool arrangement in the 5-spool section

(seen from the front) is the travel (left), auxiliary, boom

2, arm 1, and swing. Each spool is operated by pilot

pressure oil.

T1HH-01-02-005

Machine Front

Swing

Main Relief Valve

Travel (Right)

Bucket

Boom 1

Arm 2

Arm 1

Boom 2

Auxil iary

Travel (Left)

5-Spool Side

4-Spool Side

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T3-3-2

System Layout

T1HH-03-03-001

1 - Pump Control Valve(In 5-Spool Section) 11 - Overload Relief Valve(Bucket) 21 - Load Check Valve(Arm 2 Tandem Passage) 31 - Arm Anti-Drift Valve:Bottom Side (Switch Valve)2 - Check Valve

(Main Relief Circuit)12 - Load Check Valve

(Boom 1 Parallel Passage)22 - Needle Valve 32 - Arm Anti-Drift Valve:

Bottom Side (Check Valve)3 - Main Relief Valve 13 - Boom Regenerative Valve 23 - Boom Anti-Drift Valve

(Switch Valve)33 - Arm Anti-Drift Valve:

Bottom Side (Relief Valve)4 - Check Valve

(Main Relief Circuit)14 - Boom Anti-Drift Valve

(Check Valve)24 - Orifice 34 - Overload Relief Valve

(Arm)5 - Flow Combiner Valve 15 - Overload Relief Valve

(Boom)25 - Load Check Valve

(Arm 2 Parallel Passage)35 - Arm Anti-Drift Valve:

Rod Side (Check Valve)6 - Check Valve (Flow Com-

biner Valve Circuit)16 - Arm Regenerative Valve 26 - Load Check Valve

(Arm 1 Parallel Passage)36 - Load Check Valve

(Boom 2 Parallel Passage)7 - Check Valve With Orifice

(Bucket Combination)17 - Check Valve (Arm Regen-

erative Valve Circuit)27 - Orifice 37 - Load Check Valve

(Aux. Parallel Passage)8 - Bucket Flow Rate Control

Valve (Poppet Valve)18 - Bucket Flow Rate Control

Valve (Switch Valve A)28 - Load Check Valve

(Arm 1 Tandem Passage)38 - Travel Flow Rate Control

Valve

9 - Bucket Flow Rate ControlValve (Switch Valve B)

19 - Bypass Shut-Out Valve 29 - Load Check Valve (Swing) 39 - Load Check Valve(Travel Tandem Passage)

10 - Bucket Regenerative Valve 20 - Pump Control Valve(In 4-Spool Section)

30 - Arm Anti-Drift Valve:Rod Side (Switch Valve)

Travel Motor (Right)

Bucket

Cylinder

Pump 2 Pump 1

Swing Motor

ArmCylinder

1Travel Motor (Left)

2 3 4 5 6 7

8

12

9

11

20

19

18

23 22 2125

17

16

15

14

29 26

39

38

33 31

34

35

36

30

37

242728

32

13

10

BoomCylinder

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T3-3-3

T173-03-03-050

T173-03-03-051

T1HH-03-03-002

T1HH-03-03-003

T1HH-03-03-004

G

F

E

D

B

C

A

Section C

39

Travel (Right)Travel (Left)

38

7

Machine Front34

20

2223

113

9

7

5

14

1221

24, 25

1530

35

29

27

3233

3638

391

Machine Front

Machine Front

Section BSection A

65

4

2

3

1

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T3-3-4

T1HH-03-03-001

1 - Pump Control Valve(In 5-Spool Section) 11 - Overload Relief Valve(Bucket) 21 - Load Check Valve(Arm 2 Tandem Passage) 31 - Arm Anti-Drift Valve:Bottom Side (Switch Valve)2 - Check Valve

(Main Relief Circuit)12 - Load Check Valve

(Boom 1 Parallel Passage)22 - Needle Valve 32 - Arm Anti-Drift Valve:

Bottom Side (Check Valve)3 - Main Relief Valve 13 - Boom Regenerative Valve 23 - Boom Anti-Drift Valve

(Switch Valve)33 - Arm Anti-Drift Valve:

Bottom Side (Relief Valve)4 - Check Valve

(Main Relief Circuit)14 - Boom Anti-Drift Valve

(Check Valve)24 - Orifice 34 - Overload Relief Valve

(Arm)5 - Flow Combiner Valve 15 - Overload Relief Valve

(Boom)25 - Load Check Valve

(Arm 2 Parallel Passage)35 - Arm Anti-Drift Valve:

Rod Side (Check Valve)6 - Check Valve (Flow Com-

biner Valve Circuit)16 - Arm Regenerative Valve 26 - Load Check Valve

(Arm 1 Parallel Passage)36 - Load Check Valve

(Boom 2 Parallel Passage)7 - Check Valve With Orifice

(Bucket Combination)17 - Check Valve (Arm Regen-

erative Valve Circuit)27 - Orifice 37 - Load Check Valve

(Aux. Parallel Passage)8 - Bucket Flow Rate Control

Valve (Poppet Valve)18 - Bucket Flow Rate Control

Valve (Switch Valve A)28 - Load Check Valve

(Arm 1 Tandem Passage)38 - Travel Flow Rate Control

Valve

9 - Bucket Flow Rate ControlValve (Switch Valve B)

19 - Bypass Shut-Out Valve 29 - Load Check Valve (Swing) 39 - Load Check Valve(Travel Tandem Passage)

10 - Bucket Regenerative Valve 20 - Pump Control Valve(In 4-Spool Section)

30 - Arm Anti-Drift Valve:Rod Side (Switch Valve)


BoomCylinder

Bucket

Cylinder

Pump 2 Pump 1

Swing Motor

ArmCylinder

1 2 3 4 5 6 7

8

12

9

11

20

19

18

23 22 2125

17

16

15

14

29 26

39

38

33 31

34

35

36

30

37

242728

32

13

10

Travel Motor (Left)

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T3-3-5

T1HH-03-03-005

T1HH-03-03-007

T1HH-03-03-006

T1HH-03-03-008

Section F Section G

Arm 2 Arm 1

Section E

Boom 2 Boom 1 23

14

Section D

12

15

15

36

30

35

26

32 3124, 25

21

37

17

Bucket

18

Auxil iary

Swing

9

20

22

16

34

9

29

8

34

11

28

10

33

27

19

13

11

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T3-3-6

HYDRAULIC CIRCUIT

Main Circuit

1. The pressure oil from pump 1 flows to the travel

(right), the bucket, boom 1, and arm 2 spools in

the 4-spool side control valve.

2. The pressure oil from pump 2 flows to the swing,

arm 1, boom 2, auxiliary, and the travel (left)

spools in the 5-spool side control valve.

3. The main circuits in both the 4 and 5-spool sec-

tions have parallel passages to make combined

operations possible.

4. An oil flow combining passage is provided in both

the boom and the arm circuits so that when a sin-

gle operation is made, the pressure oil from both

pump 1 and 2 is supplied to the boom or the arm

cylinder.5. The pump control valves are provided down

stream of the neutral passages in both the 4 and 5

spool sections.

6. The oil pressure in the main circuit (between the

pump and the actuator) is controlled by the main

relief valve preventing the man circuit oil pressure

from increasing higher than the set pressure.

7. The overload relief valves are located in the boom,

the arm and the bucket actuator circuits between

the control valve and the actuator.

The overload relief valve prevents the surge pres-

sure from being developed by the external loadsin the actuator circuit and prevents the pressure in

the circuit from rising more than the set pressure

when the control spool is in neutral.

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T3-3-7

T173-03-03-009

Pump Control Valve

(In 5-Spool Section)

Pump Control Valve

(In 4-Spool Section)

FlowCombiningPassages

Pump 1Pump 2

NeutralPassage

NeutralPassage

Travel (Right)

Swing

Arm 1

Boom 2

Auxil iary

Travel (Left)

Arm 2

Boom 1

Bucket

To the 4-Spool Section.

5-Spool Side ParallelPassage

To the 5-Spool Section.

OverloadRelief Valve

4-Spool Side Parallel PassageMain Relief Valve

OverloadRelief Valves

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T3-3-8

Pilot Control Circuit

The pilot pressure oil (indicated by figures) from the

pilot valve is routed to the end face of each spool in

the control valve so that the spool is operated. While

operating the spools, the pilot pressure oil functions

as follows:

• When raising the boom, pilot pressure oil (1) is

routed to the bucket f low rate control valve (switch

valve B) via the bucket flow rate control valve

(switch valve A) and to the travel flow rate control

valve. Then, both valves are activated.

• When lowering the boom, pilot pressure oil (2) is

routed to activate the boom anti-drift valve (switch

valve).

• When rolling out the arm, pilot pressure oil (3 and

3A) is routed to activate the arm bottom side anti-

drift valve (switch valve).• When rolling in the arm, pilot pressure oil (4) is

routed to activate the arm rod side anti-drift valve

(switch valve) and the bucket flow rate control

valve (switch valve A).

The air bleeder circuit is provided in the upper section

of the control valve so that the air trapped inside the

control valve is automatically exhausted.

Pilot Signal Circuit

The pressure oil from the pilot pump flows through

the control valve as signal pilot pressure. When trav-

eling, the travel spool restricts the signal pilot oil flow,

increasing the circuit pressure. The pressure sensor

(travel) monitors the pressure increase.

When operations other than travel are performed, the

signal pilot pressure circuits other than travel are re-

stricted, increasing the circuit pressure. The pressure

sensor (front attachment) monitors the pressure in-

crease. The flow combiner valve and swing parking

brake switch valve (swing motor) are also operated.

Solenoid Valve Pilot Signal Circuit

• The pilot pressure from solenoid valve unit (SC)

shifts the arm regenerative valve.

• The pilot pressure from solenoid valve unit (SG)increases the pressure setting of the main relief

valve.

(Refer to SYSTEM / Control System group.)

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T3-3-9

T1HH-03-03-009

1 - Boom Raise 4 - Arm Roll-In 7 - Bucket Roll-Out 10 - Left Travel Reverse

2 - Boom Lower 5 - Left Swing 8 - Bucket Roll-In 11 - Right Travel Forward

3 - Arm Roll-Out 6 - Right Swing 9 - Left Travel Forward 12 - Right Travel Reverse

3 A- Arm Roll Out

To SwingParking Brake

Pressure Sensor (Front Attachment) Pressure Sensor (Travel)

From Solenoid Valve Unit (SG)

FromSolenoidValve Unit(SC)

From Pump 1

Air Bleeder Circui t

From Pump 2 From PilotPump

From Pilot PumpFrom PilotPump

Flow Combiner Valve

Arm Anti -Drift Valve(SwitchValve): Bot-tom Side

Arm Anti -Drif t Valve(Switch Valve): RodSide

Arm Regenerat iveValve

Boom Anti-DriftValve(Switch Valve)

Main Relief Valve

Bucket FlowRate ControlValve (SwitchValve A)

12

6

3A3

1413

1211910

5

4

7

8Travel Flow RateControl Valve

Bucket Flow RateControl Valve(Switch Valve B)

Pilot Signal Circuit Other thanTravel

Travel Pilot Signal Circuit

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T3-3-10

FLOW COMBINER VALVE

1. When the front attachment and/or swing function

is operated, the spools in the control valve restrict

the signal pilot pressure oil other than travel so

that the circuit pressure is increased and the flow

combiner valve is activated.

2. At this time, when the travel function is operated,

the pressure oil from pump 1 is routed to the right

travel spool and the left travel spool via the flow

combiner valve and the check valve.

3. Consequently, the pressure oil from pump 1 is

routed simultaneously to both right and left travel

spools. The pressure oil from pump 2 is routed to

the front attachment and swing spools. Therefore,

when a combined operation of the travel and front

attachment, and/or swing is performed, the ma-

chine can travel straight.

T1HH-03-03-010

Pressure Oil from Pump 1

Flow Combiner Valve

Check Valve

Pilot Signal CircuitOther than Travel

To Left Travel Spool

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T3-3-11

T173-02-02-003

Pump 1Pump 2

Arm 2

From thePilot Pump.

Travel (Right)


Travel Motor (Left) Flow Combiner Valve

Travel(Left)

ArmCylinder

Arm 1

Pilot Signal CircuitOther than Travel

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T3-3-12

PUMP CONTROL VALVE

The pump control valves are located down stream of

the neutral passages in both the 4 and 5-spool sec-

tions. (Refer to T3-3-7.)

The pump control pressure is regulated by the pump

control valve and is routed to the pump regulator to

control the pump displacement angle. (Refer to the

pump device group.)

The pump control pressure is monitored by the pump

control pressure sensor. Then, the sensing signals are

used to control the travel motor displacement angle.

(Refer to the Control System group in the SYSTEM

section.)

• When All Control Levers are in Neutral:

1. When all control levers are in neutral, the controlvalve neutral passage isn’t restricted as all control

valve spools are in neutral.

2. All oil flow is routed to the hydraulic oil tank from

the neutral passage via spool (B), acting on the

spool (A) in the pump control valve.

3. The oil flow through spool (B) acts on the spring

chamber via spool (C).

4. All oil flow acts on spool (A) in the pump control

vale, so that the force acting on spool (A) over-

comes the spring force and the pressure acting on

the spring chamber through spool (C).

Therefore, the spool in the pump control valvemoves to the right.

5. As connecting port PC and port DR via the spool

notch, the pump control pressure which was

routed to the regulator is returned to the hydraulic

oil tank via port PC.

6. Thus, the pump control pressure is reduced so

that the regulator reduces the pump displacement

angle to the minimum, saving engine fuel con-

sumption.

• When a Control Lever is Operated:

1. When a control lever is operated, the control valve

spool is moved so that the control valve neutralpassage is restricted.

2. In response to the control valve spool, the oil flow

acted on spool (A) in the pump control valve is re-

duced.

3. When the force acting on spool (A) doesn’t over-

come the spring force and the pressure acting on

the spring chamber through spool (C), the spool in

the pump control valve is returned to the left.

4. Then, port PE is connected to port PC via the

spool notch. Thus, the pilot oil pressure is routed

from port PE to the regulator via port PC.

5. When the pump control pressure increases, theregulator increases the pump displacement angle.

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T3-3-13

T1HH-03-03-013

When All Control Lever are in Neutral:

T1HH-03-03-011

When a Control Lever is Operated:

T1HH-03-03-012

Neutral Passage

DR

PE PCToHydraulicOil Tank

Spring Chamber

(B)

(A) (C)Spool

DR

PE PC

Spring Chamber Spool

Neutral Passage

Spool

Spring Chamber

Spring

Hydraulic Oil Tank

PCPE

(A)

(B)

(C)

DR

(A) (C)

To HydraulicOil Tank

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T3-3-14

MAIN RELIEF VALVE

The main relief valve prevents the main circuit pres-

sure from increasing more than the designed pressure.

When the power boost switch is ON, the relief valve

set pressure is increased. (Refer to the Control System

group in the SYSTEM section.)

Normal Relief Operation

1. The main circuit pressure in port HP acts on pilot

poppet (2) via the orifice in main poppet (1).

2. When pressure in port HP increases more than

the set force of spring B (3), pilot poppet (2) is un-

seated, allowing pressure oil to flow to hydraulic

oil tank port LP via passage A.

3. Then, pressure in the oil chamber is reduced, de-

veloping a pressure difference between port HP

and the oil chamber by the orifice in main poppet

(1). When the pressure difference increases more

than the set force of spring A (6), main poppet (1)is unseated, allowing the pressure oil to flow from

port HP to port LP.

Relief Operation When Set-Pressure is Increased1. When power boost switch is ON, the pilot pres-

sure is routed in port SG.

2. The pilot pressure via passage B in sleeve (5) and

passage C in piston (4) pushes piston (4) to the

left.

3. Therefore, a higher pressure is required to open

pilot poppet (2) as the set force of spring B (3) in-

creases. The relief set pressure increases more

than normal.

Neutral:

T1HH-03-03-014

1 - Main Poppet 4 - Piston

2 - Pilot Poppet 5 - Sleeve

3 - Spring B 6 - Spring A

Normal Relief Operation:

T1HH-03-03-015

T1HH-03-03-016

Relief Set-Pressure is Increased:

T1HH-03-03-017

LP

SG

HP

1 2

64

5

3

Passage BPassage A

Oil Chamber Orifice

LP

HP

1 2 3

Passage A

Orifice

LP

HP

1Orifice

LP

SG

HP

2

45

Passage C

Passage B

6

3

Oil Chamber

Oil Chamber

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T3-3-15

OVERLOAD RELIF VALVE

The overload relief valve prevents the actuator circuit

pressure from increasing more than the designed

pressure. If the actuator pressure becomes negative,

the valve makes up the hydraulic oil from the hydraulic

oil tank.

Relief Operation

1. Pressure in port HP (actuator circuit) acts on pilot

poppet (4) via the orifice in piston (1).

2. When pressure in port HP increases more than

the set force of spring B (5), pilot poppet (4) is un-

seated so that the pressure oil flows to hydraulic

oil tank port LP via the passage.

3. Then, pressure in the oil chamber is reduced, de-

veloping a pressure difference between port HP

and the oil chamber by the orifice in piston (1).

When the pressure difference increases more

than the set force of spring A (3), piston (1) ismoved to the right and main poppet (2) is un-

seated, allowing the pressure oil to flow from port

HP to port LP.

Make-Up Operation

1. When pressure in port HP decreases lower than

port LP, sleeve (7) is moved to the right.2. Then, the hydraulic oil flows from port LP to port

HP so that cavitation is prevented.

Neutral:

T1HH-03-03-018

1 - Piston 5 - Spring B

2 - Main Poppet 6 - Spring C

3 - Spring A 7 - Sleeve

4 - Pilot Poppet

Relief Operation:

T1HH-03-03-019

T1HH-03-03-020

Make-Up Operation:

T1HH-03-03-021

HP

LP

1 2

6

3

PassageOil Chamber

4 5

7

HP

LP

1

Passage

Orifice 4 5

HP

LP

1 2 3

Oil Chamber

Orifice

HP

LP

7

Orifice

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T3-3-16

ARM REGENERATIVE VALVE

The arm regenerative valve regulates the return oil

flow from the cylinder rod side when rolling the arm in.

Thereby, the arm roll-in speed is increased to improve

the arm controllability so that the arm hesitation is pre-

vented.

1. In response to the signal from MC solenoid valve

unit (SC) acts, then the pilot pressure is routed to

the arm regenerative valve from solenoid valve

unit (SC). (Refer to SYSTEM / Control System

group)

2. The return oil from the arm cylinder flows into the

spool from hole A on the arm 2 spool.

Arm Regenerative Valve is in Neutral:3. The pressure oil from hole A flows to the hydraulic

oil tank via orifice A and hole B.

Arm Regenerative Valve is Operated:

4. When the pilot pressure is supplied from port SC,

the arm regenerative valve is activated. Then, the

pressure oil flow from hole A is restricted by orifice

A and hole C, increasing the pressure in the

spool.

5. If the pressure in the arm cylinder bottom side cir-

cuit is lower than that of the spool inside, the

pressure in the spool opens the check valve viaorifice B and flows to the arm cylinder bottom side

circuit.

T173-03-03-049

When Arm Regenerative Valve is in Neutral:

T1HH-03-03-022

When Arm Regenerative Valve is Operated:

T1HH-03-03-023

Hole B

Hole A

To Hydraulic OilTank.

Pilot Pressure fromSolenoid Valve Unit(SC)

Hole B

Hole A


Hole C (Orifice )

Orifice A

Orifice B

Orifice A

Check ValveTo Cylinder Bottom SideCircuit

ArmRegenerativeValve


To Hydraulic OilTank

Arm 2 Spool

ArmCylinder

From4-Spool SectionNeutral Circuit

From4-Spool Side

Parallel Passage


SC

Hole A

Orifice A,Hole C

Orifice B

Orifice A, Hole B

Check Valve

Hole B

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T3-3-17

T1HH-03-03-024

Check Valve

Port SC

Arm Cylinder Arm Regenerat ive Valve

Hole B, Hole C

Tank Passage

Hole A

Cylinder Bottom SideCircuit

Arm 2 Spool

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T3-3-18

BOOM REGENERATIVE VALVE

The boom regenerative valve regulates the return oil

flow from the cylinder bottom side when the boom is

lowered. Thereby, the boom lower speed is increased

to improve the boom controllability so that cavitation is

prevented.

1. When the boom is lowered, the return oil from the

boom cylinder bottom side flows into the spool via

boom 1 spool hole A.

2. If the pressure in the boom cylinder rod side is

lower than the bottom side, the pressure (the

pressure oil in the bottom side) in the spool opens

the check valve 1 and flows into the boom cylinder

rod circuit via hole c.

3. When the pressure in the boom cylinder rod sideis higher than the bottom side during excavation

for example, check valve 2 is unseated so that all

oil flow is returned to the hydraulic oil tank via hole

B.

T1HH-03-03-045

From4-Spool SideParallel Passage

BoomCylinder

Boom 1Spool

To Hydraulic OilTank

Check Valve 1

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T3-3-19

T1HH-03-03-025

Hole A

Hole C

Check Valve 1

Hole B

Check Valve 2

Boom Cylinder

Boom 1 Spool

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T3-3-20

BUCKET REGENERATIVE VALVE

The bucket regenerative valve controls the return oil

from the cylinder rod side when operating the bucket

roll-in. This makes the bucket roll-in operation more

controllable and the occurrence cavitation is pre-

vented.

1. If operating the bucket roll-in at the most retracted

position of the arm cylinder, the pressure in the

bottom side circuit of the bucket cylinder is lower

than that in the rod side because of its own

weight.

2. The return oil from the bucket cylinder rod side is

separated in the bucket spool. One flows back to

the hydraulic oil tank.

The other flows into the spool through hole A onthe spool.

3. The pressure oil (in the rod side) into the spool

opens the check valve and flows to the bucket cyl-

inder bottom side circuit via hole B on the spool.

Thereby the cavitation is prevented.

T1HH-03-03-027

Check Valve


From FlowCombiner Valve

BucketSpool

Hole B Hole A

BucketCylinder

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T3-3-21

T1HH-03-03-026

Hole A

Hole B

Check Valve

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T3-3-22

ARM ANTI-DRIFT VALVE (BOTTOM SIDE)

The arm anti-drift valve is provided to reduce cylinder

drift.

When the control lever is in neutral: Holding Op-

eration

1. The pressure in the arm cylinder bottom side is

routed to port A6B.

2. The pressure in port A6B is routed to spring

chamber A via the spool.

3. Then, the check valve is pushed downward, clos-

ing the oil circuit from the cylinder bottom to the

spool.

4. Thereby, the cylinder drift is reduced.

T173-03-03-024

T173-03-03-028

T1HH-03-03-028

X

Cross Section X-X

Spool

Port A6B

Port A6B

Spring Chamber A

Spool

Check Valve

Spool

ArmCylinder

Port A6B

Check Valve

X

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T3-3-23

When the control lever is operated : Deactivated

1. When the arm is rolled in, the pressure oil from

the arm spool opens the check valve and flows to

the cylinder from port A6B.

2. When the arm is rolled out, the pilot pressure is

supplied to ports PL so that the spool is shifted af-

ter moving the piston.

3. Port D is connected to spring chamber A and the

hydraulic oil tank so that the pressure in spring

chamber A is reduced.

4. Then, the return oil from the arm cylinder bottom

side opens the check valve and flows back to the

arm spool.

T173-03-03-026

T1HH-03-03-029

T1HH-03-03-030

T1HH-03-03-031

When Arm is Rolled-In:

Port A6B

From Arm Spool

Check Valve

When Arm is Rolled-Out:

Pilot Pressure

Piston

Port D

Section Y-Y

Port PL

Drain

Check Valve

Spool

To ArmSpool

Port A6B

To Arm Spool

Spool

ArmCylinder

PortPL

Port A6B

Spool

Check Valve

Port D

Hydraulic Oil Tank

Pilot Pressure

Port D

Piston

Spring Chamber A

Y

Y

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T3-3-24

When the control lever is in neutral: Overload

Prevention

1. When the control lever is in neutral, if the pres-

sure in the arm cylinder bottom side is increased

by an external force, hydraulic components may

be damaged.

2. The pressure in port A6B on the arm cylinder bot-

tom side is routed to spring chamber A through

the spool as when the arm is in the holding posi-

tion.

3. Then, when the pressure increases more than the

set pressure, the poppet is unseated, allowing the

pressure oil to flow into chamber C.

4. Therefore, the piston is pushed downward, the

spool is shifted, allowing the pressure oil in port D

to flow back to the hydraulic oil tank.

5. Port D is connected to spring chamber A and thehydraulic oil tank so that the pressure in spring

chamber A is reduced.

6. Then, the check valve is unseated, the pressure

oil in port A6B on the arm cylinder bottom side

flows to the arm spool and opens the overload re-

lief valve.

7. This makes the pressure in the arm cylinder bot-

tom prevent from increasing abnormally.

T1HH-03-03-033

T1HH-03-03-032

T1HH-03-03-031

Spool Piston

Port D

Drain

Port A6B

Spool

Port A6B

To Arm Spool

Section Y-Y

Poppet

Poppet

Chamber C

Y

Y

Check Valve

Spring

Chamber A

SpoolPort D

Check Valve

SpringChamber A

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T3-3-25

ARM ANTI-DRIFT VALVE (Rod Side) /BOOM ANTI-DRIFT VALVE

The anti-drift valves (on the arm cylinder rod side and

boom cylinder bottom side) are provided to reduce

cylinder drift.

NOTE: The construction of the arm anti-drift valve

is identical to the boom anti-drift valve.

When the control valve is in neutral: Holding Op-

eration

1. The oil pressure in the arm cylinder rod side (the

boom cylinder bottom side) is routed to port B6

(B3).

2. Then, the pressure in port B6 (B3) is routed to oil

chamber A through the spool.3. Thereby, the check valve is pushed to block the oil

flow from the cylinder to the spool so that the cyl-

inder drift is reduced.

When the control valve is operated: Deactivation

1. When the arm is rolled in (the boom is lowered),

the pressure oil from the arm (boom) spool opens

the check valve so that the pressure oil flows to

the cylinder via port B6 (B3).

2. When the arm is rolled out (the boom is raised),

the pilot oil pressure moves the spool.

3. The oil in oil chamber A flows back to the hydrau-lic oil tank through the spool, reducing pressure in

oil chamber A.

4. Then, the return oil from the arm cylinder rod side

(the boom cylinder bottom side) passes port B6

(B3), opens the check valve, and flows to the arm

spool (the boom spool).

T1HH-03-03-034

T1HH-03-03-035

T1HH-03-03-037

T1HH-03-03-036

Deactivation (Arm Roll-In, Boom Lower):

Deactivation (Arm Roll-Out, Boom Raise):

Arm SpoolBoom Spool

Port B6 (B3)

Spool

Oil Chamber A

Check Valve

Holding Operation:

Check Valve

To Arm Cylinder To Boom Cylinder


Arm Roll-Out Pilot PressureBoom Raise Pilot Pressure

To Arm Spool.To Boom Spool.

Spool

Arm SpoolBoom Spool

Port B6 (B3)Check Valve

Pilot Pressure

Arm SpoolBoom Spool

Port B6 (B3)

Spool

Oil Chamber A

Check Valve

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T3-3-26

BUCKET FLOW RATE CONTROL VALVE

The bucket flow rate control valve consists of the pop-

pet valve, switch valve A, and switch valve B.

The bucket flow rate control valve restricts the bucket

oil flow to give priority to the boom raise operation

when the bucket, arm roll-in, and boom raise functions

are simultaneously operated.

1. The pressure oil from the neutral passage flows to

the poppet valve.

When the Bucket is Single-Operated:

2. Normally, the pressure oil opens the check valve

in the poppet valve and flows to port A2 from

chamber A.

3. Both the check valve and poppet in the poppetvalve are supported by the same spring. There-

fore, when the check valve is opened, the poppet

valve is also opened, allowing the pressure oil

from the neutral circuit to directly flow to the

bucket spool.

When the bucket, the arm roll-in and the boom

raise are combined-operated:

4. When operating the arm roll-in, the arm roll-in pilot

pressure shifts the spool in switch valve A.

5. Therefore, the boom raise pilot pressure through

switch valve A shifts the Spool in switch valve B.6. But, when switch valve B spool is moved to re-

strict the pressure oil flow from chamber A to port

A2, pressure in chamber A increases.

7. Then, the poppet is raised to reduce the pressure

oil flow from the neutral passage to the bucket

spool.

8. Accordingly, the pressure oil has precedence to

flow to boom 1 spool via the parallel passage so

that the boom is raised.

When Bucket is Single-Operated:

T1HH-03-03-038

When Bucket the Arm Roll-In and Boom Raise are

Combined-Operated:

T1HH-03-03-039

Bucket Cylinder

Bucket Spool

Check Valve

Poppet Valve

Switch Valve B

Boom RaisePilot Pressure

Arm Roll-In PilotPressure

Check Valve

Poppet Valve

Switch Valve A

Switch Valve B

Bucket Cylinder

Bucket Spool

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T3-3-27

When Bucket is Single-Operated:

T1HH-03-03-040

When Bucket, Arm Roll-In and Boom Raise are Combined-Operated:

T1HH-03-03-041

B2 A2

Chamber A

Poppet Valve

Check Valve

Spring

Neutral Passage

B2 A2

Chamber A

Boom Raise Pilot PressureFrom Switch Valve A

Poppet Valve

Spool

Neutral Passage

Switch Valve B

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T3-3-28

TRAVEL FLOW RATE CONTROL VALVE

When the travel and boom raise combined operation is

performed, the flow combiner valve is opened so that

the pressure oil from pump 1 flows to both right and left

travel motors and the pressure oil from pump 2 flows

to boom 2 spool.

When traveling on a flat or down slope surface, the

travel motor load pressure becomes lower than the

boom cylinder. Accordingly, the pressure oil from pump

2 is routed to the lower pressure side of the travel (left)

spool via parallel passage P2’, reducing the oil flow to

the high pressure side of the boom 2 spool.

The travel flow control valve restricts the passage to

the travel (left) spool from parallel passage P2’ in such

cases and secures oil flow to raise the boom.

1. When the boom is raised, the boom raise pilot

pressure is supplied to the travel flow control

valve, pushing piston to the right to increase the

spring force.

2. Then, the poppet is pushed to the right harder.

3. Therefore, even if the pressure in the travel (left)

neutral passage P2 is reduced lower than the

parallel passage P2’, the poppet does not unseat.

4. Thereby, the pressure oil from pump 2 does not

flow to the travel (left) spool but flows to the boom

2 spool, ensuring boom raise operation.

T173-03-03-043


Travel (Left) Spool

Piston

From Flow

Combiner Valve

Parallel Passage P2’Neutral Passage P2

To Hydraulic Oil Tank

Poppet

Spring

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T3-3-29

T1HH-03-03-042

Neutral PassageP2

Parallel PassageP2’

Travel (Right)Travel (Left)

Piston


Poppet

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T3-3-30

BYPASS SHUT-OUT VALVE

The bypass shut-out valve is provided in the neutral

passage of the 4-spool section control valve. The by-

pass shut-out valve allows the pressure oil from pump

1 to join into the pressure oil from pump 2 when an

attachment is operated by the auxiliary spool in the 5-

spool section control valve.

1. When the attachment is operated, the pilot pres-

sure is routed to port PBC.

2. Then, the bypass shut-out valve spool is moved to

the right, closing the passage from the neutral cir-

cuit to port T2.

3. Accordingly, the pressure oil from pump 1 flows

from the neutral passage to port A4 and is routed

further to the point just before the auxiliary spool

in the 5-spool section control valve where the

pressure oil joins into the pressure oil flow from

pump 2.

T1HH-03-03-043

To AttachmentSpool

Spool

Port PBC

Port A4

Port T2

Pilot Pressure

Neutral Circuit in 4-SpoolSection Control Valve

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T3-3-31

T173-03-03-044

Pump 2

BypassShut-Out Valve

To 5-Spool SideControl Valve To 4-Spool Side

Control Valve

Pilot Pressure

Pump 1

Auxil iary

Spool

To Attachment

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T3-3-32

NEEDLE VALVE

The needle valve is provided for emergencies in order

to lower the boom, in case stopping the engine is nec-

essary.

1. The pressure oil in the boom cylinder bottom side

is routed to port B3 and blocked by the boom anti-

drift valve. (Refer to T3-3-25.)

2. Port B3 is connected to the needle valve through

the inner passages. When the needle valve is

loosen, the pressure oil in port B3 flows to port

DR2 through the needle valve.

3. Consequently, the boom cylinder is retracted and

the boom is lowered because of its own weight.

T1HH-03-03-044

T173-03-03-046

Port DR2

Port B3

Needle Valve

Boom Anti-Drift Valve(Switch Valve)

Boom Anti -DriftValve

(Check Valve)

Boom Anti-DriftValve(Check Valve)

Boom Anti-DriftValve(Switch Valve)

BoomCylinder

Needle Valve

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COMPONENT OPERATION / Pilot Valve

T3-4-1

OUTLINE

The pilot valve controls pilot pressure oil to move the

control valve spools. There are two types of pilot

valves. One is for front attachment / swing operation;the other is for travel operation. Both have four oil ports

as standard. An optional two-port type is available. The

construction of the reducing valves in both the front

attachment / swing and travel pilot valves are identical

except for the pusher cams.

• Front Attachment / Swing Pilot Valve

Port

No.ISO Control Pattern Hitachi Pattern

1 Bucket Roll-Out ←

2 Boom Lower ←

3 Bucket Roll-In ←

RightValve

4 Boom Raise ←

1 Right Swing Arm Roll-In

2 Arm Roll-Out Right Swing

3 Left Swing Arm Roll-Out

Left

Valve

4 Arm Roll-In Left Swing

T105-02-07-020

T178-03-04-001

• Travel Pilot Valve

1 Right Travel Reverse

2 Right Travel Forward

3 Left Travel Forward

4 Left Travel Reverse

T105-02-07-020

T178-03-04-002

HydraulicDiagramSymbol

4231

TP

4

1

2

T

3

2

1

3

T

P

P

4

4

1

3

2

P

T

HydraulicDiagramSymbol

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T3-4-2

OPERATION

Spool (6) head comes in contact with the upper face of

spring guide (3) which is kept raised by return spring

(5).

Neutral (Output Diagram: A to B):

1. When neutral, spool (6) totally blocks pressure oil

port P (from the pilot pump).The output port is

opened to port T (hydraulic oil tank) through the

passage in spool (6). Therefore, oil pressure in

the output port (to the control valve) is equal to

that in port T.

2. When the control lever is slightly tilted, cam (1) is

tilted, moving pusher (2) downward. Then, pusher

(2) compress return spring (5) along with spring

guide (3). At this time, as oil pressure in the outputport is equal to that in port T, spool (6) moves

downward while keeping the under face of the

spool head in contact with spring guide (3).

3. This status continues until hole (7) on spool (6) is

opened to port P.

T522-02-05-001

PilotPressure

FE

D

C

B ALever Stroke

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T3-4-3

T178-03-04-005

T178-03-04-006

T178-03-04-007

T178-03-04-011

1 - Cam 3 - Spring Guide 5 - Return Spring 7 - Hole

2 - Pusher 4 - Balance Spring 6 - Spool

Front Attachment / Swing Pilot Valve

1

2

3

4

6

5

7

Output Port

Port P

Port T

Travel Pilot Valve

1

2

3

4

6

5

7

Output Port

Output Port

Port P

Port T

1

2

3

4

5

7

Output Port

Port P

Port T

1

2

3

4

6

5

7

Output Port

Output Port

Port P

Port T

6

Port P

Port T6

7

Port P

Port T

7

6

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T3-4-4

During Metering or Decompressing (Output

Diagram: C to D)

1. When the control lever is further tilted to move

pusher (2) downward more, hole (7) on spool (6)

is opened to port P, allowing pressure oil in port Pto flow into the output port.

2. Oil pressure in the output port acts on the bottom

face of spool (6) so that spool (6) is pushed

upward.

3. However, until upward force acting on the bottom

face of spool (6) overcomes balance spring (4)

force, balance spring (4) is not compressed. Then,

spool (6) is not raised, allowing oil pressure in the

output port to increase.

4. As oil pressure in the output port increases, force

to push spool (6) upward increases. When, this

force overcomes balance spring (4) force,balance spring (4) is compressed so that spool (6)

is moved upward.

5. As spool (6) is moved upward, hole (7) is closed

so that pressure oil from port P stops flowing into

the output port, stopping pressure oil in the output

port to increase.

6. As spool (6) is moved downward, balance spring

(4) is compressed, increasing the spring force.

Therefore, oil pressure in the output port becomes

equal to the oil pressure acting on the bottom face

of spool (6) being balanced in position with the

spring force.

T522-02-05-001

PilotPressure

FE

D

C

B ALever Stroke

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T3-4-5

T178-03-04-008

T178-03-04-012

T178-03-04-009

T178-03-04-013




1

2

3

4

6

5

7

Output Port

Port P

Port T

1

2

3

4

6

5

7

Output Port

Port P

Port T

Travel Pilot Valve

1

2

3

4

5

7

Output Port

Port P

Port T

6

1

2

3

4

5

7

Output Port

Port P

Port T

6

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T3-4-6

Full Stroke (Output Diagram: E to F)

1. When the control lever is fully stroked, pusher (2)

is moved downward until pusher (2) in the front

attachment / swing pilot valve comes in contact

with the casing shoulder, or cam (1) on the travelpilot valve comes in contact with the casing.

2. At this moment, the bottom of pusher (2) directly

pushes spool (6). Therefore, even if oil pressure

in the output port increases further, hole (7) on

spool (6) is kept open.

3. Consequently, oil pressure in the output port is

equal to oil pressure in port P.

NOTE: Total lever strokes for the front attachment

and swing controls are determined by

stroke dimension (E) of pusher (2). Total

lever stroke for the travel control is

determined by stroke dimension (E) of cam

(1).

T522-02-05-001

PilotPressure

FE

D

C

B ALever Stroke

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T3-4-7

T178-03-04-010

T178-03-04-014

T178-03-04-005

T178-03-04-006




1

2

3

4

6

5

7

Output Port

Port P

Port T

Travel Pilot Valve

1

2

3

4

5

7

Output Port

Port P

Port T6

2

E

E

1

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T3-4-8

(Blank)

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COMPONENT OPERATION / Travel Device

T3-5-1

OUTLINE

The travel device consists of the travel motor, travel

reduction gear, and travel brake valve.

The travel motor for ZAXIS330, ZAXIS350H is a bent

axis-type variable displacement axial plunger motor.

The travel motor for EX370MTH is a swash plate-type

variable displacement axial plunger motor.

The travel motor is equipped with a parking brake (wet

multi-disc negative type), is driven by pressure oil from

the hydraulic pump, and outputs rotary power to the

travel reduction gear.

ZAXIS330, ZAXIS350H:

T173-03-05-001

The travel reduction gear is a third stage planetary

gear type which converts rotary power transferred from

the travel motor into a slow and large torque to drive

the sprocket and track.

The travel brake valve prevents the occurrence of

overloads and cavitation in the travel circuit.

ZAXIS370MTH:

T16J-03-05-001

Travel Reduction Gear

SprocketTravel Brake Valve

Travel Motor Travel Reduction Gear

SprocketTravel Brake Valve

Travel Motor

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T3-5-2

TRAVEL REDUCTION GEAR

The travel reduction gear is a three stage reduction

planetary gear type.

The travel motor rotates propeller shaft (7). This rota-

tion is transmitted to third stage carrier (2) and ring

gear (1) via first stage planetary gear (8), first stage

carrier (6), first stage sun gear (5), second stage

planetary gear (9), second stage carrier (4), second

stage sun gear (3), and third stage planetary gear (10).


T173-03-05-001

Travel motor housing (14) is bolted to the track frame

and is secured to third stage carrier (2) by hub (11).

Ring gear (1) is bolted to drum (13). Drum (13) is

bolted to sprocket (12). Accordingly, when ring gear (1)

is rotated, drum (13) and sprocket (12) are also ro-

tated.

ZAXIS370MTH:

T16J-03-05-001

1 - Ring Gear 5 - First Stage Sun Gear 9 - Second Stage Planetary

Gear

12 - Sprocket

2 - Third Stage Carrier 6 - First Stage Carrier 10 - Third Stage Planetary Gear 13 - Drum

3 - Second Stage Sun Gear 7 - Propel Shaft 11 - Hub 14 - Housing

4 - Second Stage Carrier 8 - First Stage Planetary Gear (Travel Motor)

1 2 3 4 5 6

891011

12

14 13 7

1 2 3 4 5 6

891011 71314

12

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T3-5-3

TRAVEL MOTOR


The travel motor, a bent axis-type variable displace-

ment axial plunger motor, consists of the plate, valve

plate, rotor, plungers, and drive disc. When the pres-

sure oil is supplied from the pump, the plungers in the

rotor are pushed and the force to the direction (F) oc-

curs.

As the plunger leans against the drive disc, vertical

component force (FV) occurs and causes the drive

disc to rotate.

Whether pressure oil from the pump is supplied to port

AM or BM determines travel direction.

T173-03-05-002

T107-03-04-014

Rotor Plate Plunger Valve Plate Drive Disc

Rotor

Port BM

Port AM

Plunger Valve Plate Drive Disc

FR

FFV

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T3-5-4

ZAXIS370MTH:

The travel motor is a variable displacement swash

plate axial plunger type, consisting of swash plate (7),

rotor (16), plungers (4) with shoes, valve plate (1), out-

put shaft (11), tilt pistons (9), casing (8), and so forth.

Four of tilt piston (9) are located in casing (8). The

pressure to change travel speed acts on these tilt

pistons (9) to change swash plate (7) angle.

Rotor (16) is preloaded against valve plate (1) by

spring (14) to prevent oil from leaking at the clear-

ance between them.

Hydraulically released type disc parking brake (3) is

installed in the travel motor.

T16J-03-05-003

1 - Valve Plate 6 - Retainer Plate 10 - Spring 14 - Spring2 - Spring 7 - Swash Plate 11 - Output Shaft 15 - Brake Piston

3 - Parking Brake 8 - Casing 12 - Roller Bearing 16 - Rotor

4 - Plunger 9 - Tilt Piston 13 - Ball 17 - Valve Cover

5 - Holder

1 2 3 4 5 6 7 8 9 10

11

12131415

17

16

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T3-5-5

Pressure oil from the pump flows to port A of valve

plate (1), and enters into one-sided bores in rotor (2)

located just behind the right-side crescent-shaped oil

port (port A side) of valve plate (1).

Then, plungers in the right half side of rotor (2) are

pushed out toward swash plate (5), and slide on the

swash plate to rotate rotor (2) and output shaft (6).

As output shaft (6) rotates, rotor (2) also rotates. Then,

when plungers (3) reach port B, oil is routed to the hy-

draulic oil tank.

Whether pressure oil from the pump is supplied to port

A or port B determines the travel direction.

T183-03-05-009

1 - Valve Plate 3 - Plunger 5 - Swash Plate 6 - Output Shaft

2 - Rotor 4 - Shoe

Port B

Valve Plate

Port APort B

Port A

1

2

3

64

5

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T3-5-6

TRAVEL BRAKE VALVE


The travel brake valve is located on the travel motor

head and consists of the following valves.

Check Valve (1):

assists counterbalance valve (5) operations and pre-

vents cavitation from occurring.

Reducing Valve (2):

reduces the parking brake release pressure and pre-

vents the parking brake from being quickly applied.

Parking Brake Release Shuttle Valve (3):

leads the motor drive pressure to the parking brake.

Overload Relief Valve (4):

prevents overload and surge pressure from occurring

in the motor circuit.

Counterbalance Valve (5):

ensures smooth starting and stopping, and prevents

the machine from running away while descending

slopes.

Servo Piston Control Shuttle Valve (6):

leads the motor drive pressure to the servo piston.

T173-03-05-003

1 - Check Valve 3 - Parking Brake Release

Shuttle Valve

5 - Counterbalance Valve 6 - Servo Piston Control Shut-

tle Valve

2 - Reducing Valve 4 - Overload Relief Valve

A

B

C

A

Cross Section B-B

Cross Section C-C

Cross Section A-A

1

44

2

5

3

6

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T3-5-7

When Traveling:

Pressure oil from the control valve enters port BV,

flows around spool CB in the counterbalance valve,

opens check valve BC, and flows into port BM. On the

other hand, the return oil from the travel motor is

routed to port AM. However, the circuit is blocked by

check valve AC and spool CB. Oil pressure in port BV

is routed into chamber G via orifice F of spool CB so

that when oil pressure in port BV increases further,

spool CB is moved to the left.

Then, the return oil from the travel motor flows to port

AV via port AM and notch H on spool CB. Thus, pres-

sure oil flows through the circuit , enabling the travel

motor to rotate.

When the travel control lever is returned to neutral,

spool CB is returned to the original position by spring

force, blocking the oil circuit. Thereby, the travel mo-tor stops rotating.

When Descending:

While descending a slope, the travel motor is forcibly

rotated by the machine weight (pump operation).

When the travel motor starts sucking pressure oil, oil

pressure in port BV and chamber G is reduced, mov-

ing spool CB to the right. Then, the return oil flow

from the travel motor is restricted, increasing oil pres-

sure in port AM. Therefore, the travel motor is braked.

Once the oil flow is restricted, oil pressure in port BV

increases again, moving spool CB to the left.

This operation (hydraulic brake operation) is repeated

so that machine runaway is prevented.

Circuit Protection:

When circuit pressure increases more than the set

pressure of the overload relief valve, the valve opens,

allowing high pressure oil to relieve to the lower pres-sure side.

Thereby, the travel motor is protected from overloads.

The valve also functions to relieve shock pressure

developed when the travel motor stops.

If the travel motor draws oil due to pump operation,

check valve BC is unseated (makeup operation) so

that cavitation is prevented.

T173-03-05-004BV AV

BM AM

FH G

Spool CB

Check Valve BCCheck Valve AC



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T3-5-8

(Blank)

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T3-5-9

ZAXIS370MTH:

The travel brake valve is located on the travel motor

head and consists of the following valves:

Counterbalance Valve:

ensures smooth starts and stops and prevents

overrunning when traveling down slopes.

Overload Relief Valve:

prevents overloads and surge pressure in the

motor circuit.

Check Valve:

ensures smooth starts and stops, and prevents

cavitation from occurring in the motor circuit by

functioning together with counterbalance valve.

Travel Speed Shift Valve:

controls the tilt pistons when travel mode switch is

operated.

T183-03-05-004

A A AOverload Relief Valve

CounterbalanceValve

Counterbalance

Valve

Overload Relief

Valve

Travel SpeedShift Valve

Check Valve

Cross Section A-A-A

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T3-5-10

Travel Operation

When supply oil from the main control valve is routed

to port P1, supply oil flows around spool CB, opens

check valve BC and is led to motor port BM. However,

return oil from motor port AM is blocked by spool CB

in the counterbalance valve.

As supply oil pressure at port P1 increases, supply oil

is routed to chamber G through orifice F in spool CB,

moving spool CB down against spring force. Conse-

quently, return oil from motor port AM starts to flow

into port P2 through port AM and notch H in spool CB,

allowing the travel motor to rotate.

When the travel levers are returned to the neutral po-

sition, the oil in both ports P1 and P2 are routed to the

hydraulic oil tank through the control valve. Thus, oil

pressure in chamber G decrease, and spool CB ismoved back to the original position by spring force.

Then, the oil flow circuits is blocked, causing the

travel motors to stop rotating.

Descending Operation

When the machine travels down a slope, the travel

motors are forcibly driven by the machine weight so

that the motor draws oil like a pump. When the motor

draws oil, oil pressure at port P1 and chamber G de-

crease, causing spool CB to move upwards to restrict

return circuit from the motor.

Then, the return oil flow from the motor is restrictedby the spool, increasing pressure at port AM.

The increased pressure at port AM brakes the motor.

Thus, the restricted return oil flow from the travel mo-

tor increases the pressure at port P1 again, moving

spool CB back down. This repeated movement of the

spool (hydraulic brake action) prevents the machine

from overrunning.

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T3-5-11

(Travel Operation)

T183-03-05-005

(Descending Operation)

T183-03-05-006

Check ValveBC G Spool CB

P2

P1

Counterbalance Valve AM

BM

Spool CB

From AM

P2

H

To BMP1

F

G

G Spool CB

P2

P1

AM

BM

Spool CB

From AM

P2

To BM

P1

G

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T3-5-12

Circuit Protection

If pressure in the circuit increases over the setting

pressure of the overload relief valve, this valve opens

to relieve peak pressure to the lower pressure side to

protect the motor from overloading. This valve also

functions to release shock pressure caused by inertia

force developed when the motor stops.

T183-03-05-011

Low Pressure

High Pressure

Poppet


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T3-5-13

(Blank)

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T3-5-14

TRAVEL MOTOR SWASH ANGLE CON-TROL


Servo piston (1) is connected to valve plate (6) with link

(5). When servo piston (1) is moved, rotor (7) is tilted

via valve plate (6) so that travel speed is controlled.

• Slow Speed (Maximum Displacement Angle)

When the travel mode switch is turned to the slow

position, the MC (main controller) does not send a

signal to solenoid valve unit (SI). Therefore, pilot

pressure is not supplied to servo piston (1). Then,

spool (3) is kept downward by spring (2).

Pressure oil P from the motor port is routed into

chambers B and C. Due to the difference in area,

servo piston (1) is pushed upward to increase the

swash plate angle of rotor (7).

Consequently, the plunger stroke in the travel motor

is increased, reducing the travel motor rotation

speed.

T157-03-02-001

1 - Servo Piston 3 - Spool 5 - Link 7 - Rotor

2 - Spring 4 - Orifice 6 - Valve Plate

2

1

5

6 7

3

4

B

C

P

Drain

Pilot Pressure

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T3-5-15

• Fast Speed (Minimum Displacement Angle)

When the travel mode switch is turned to the fast

position, the MC sends signals to solenoid valve unit

(SI) in response to travel loads. Then, pilot pressure

is routed into chamber D, moving spool (3) upward.

Thus, section E is opened so that the oil in chamber

C is drained via the passages in spool (3). As pres-

sure oil P from the motor port is routed, servo piston

(1) is lowered, reducing the swash plate angle of ro-

tor (7).

Consequently, the plunger stroke in the travel motor

is reduced, increasing the travel motor rotation

speed.

T157-03-02-002

1 - Servo Piston 3 - Spool 5 - Link 7 - Rotor 2 - Spring 4 - Orifice 6 - Valve Plate

3

67

5

1

2

4

B

D

C

E

P

P

Drain

Drain

After fast mode has been selected:

When fast mode is selected:

Pilot Pressure

Pilot Pressure

1

B

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T3-5-16

ZAXIS370MTH:

Travel speed is changed when tilt piston (5) moves and

the swash angle of swash plate (3) is changed.

• Low speed (Swash angle: Large)

When the slow travel mode is selected, MC doesn’t

send the signals to solenoid valve unit (SI), so pilot

pressure (7) isn’t supplied.

Spring force of spring (2) keeps spool A (8) in travel

speed shift valve (1) the neutral position.

At this time, the pressure oil from the control valve is

shut off by spool A (8) and the passage to tilt piston

(5) is connected to the hydraulic oil tank.

Thus, the swash angle of swash plate (3) is main-

tained at the larger side, the stroke of plunger (6) is

larger and the flow to rotate the travel motor is more,

so that the travel motor rotation is at slow speed.

(Refer to SYSTEM/ Control System group on Con-

trol Circuit)

T1HH-03-05-001

1 - Travel Speed Shift Valve 4 - Ball 6 - Plunger 8 - Spool A

2 - Spring 5 - Tilt Piston 7 - Pilot Pressure (From

Solenoid Valve Unit (SI))

9 - Spool B

3 - Swash Plate

FromControl Valve

Travel Speed Shift Valve


5 6

4 3

5

4

3

7 8 1 29

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T3-5-17

• High Speed (Swash Angle: Small)

When the fast travel mode is selected, in response

to the travel load MC sends the signals to solenoid

valve unit (SI).

When pilot pressure (7) from solenoid valve unit (SI)

is supplied to travel speed shift valve (1), pilot pres-

sure (7) is routed to chamber (a) through the circum-

ference of spool B (9), and moves spool A (8) to the

right. Thereby, the pressure oil from the main control

valve is routed to tilt piston (5) through the circum-

ference of spool A (8).

Thus, the tilt piston pushes swash plate (3) making

the swash angle smaller. Consequently, the travel

motor rotates at fast speed.

(Refer to SYSTEM/ Control System group/ Valve

Controls on Control Circuit.)

T1HH-03-05-002

1 - Travel Speed Shift Valve 4 - Ball 6 - Plunger 8 - Spool A

2 - Spring 5 - Tilt Piston 7 - Pilot Pressure (From Sole-

noid Valve Unit (SI))

9 - Spool B

3 - Swash Plate

FromControl Valve

From Travel SpeedControl Vavle

5 6

4 3

5

4

3

7 8 1 2aTravel Speed Shift Valve

9

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T3-5-18

(Blank)

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T3-5-19

PARKING BRAKE


The parking brake is a wet type multi-disc brake. This

brake is a negative type which is released only when

brake release pressure oil (K) is routed into the brake

piston chamber. Unless the travel function is operated,

the parking brake is automatically applied.

The friction plates and the plates are splined to the

drive disc and the travel motor housing, respectively.

The disk spring pushes the piston, then the parking

brake is applied after the friction plates come in con-

tact with the plates.

• Releasing Brake:

When a travel lever is operated, pressure oil from

the main pump is routed to port AM or BM in thetravel motor via the control valve.

This pressure oil is also routed to chamber (G) at the

end of travel brake valve spool CB. At the same time,

this pressure oil is supplied via the shuttle valve as

brake release pressure oil (K). As long as oil pres-

sure in chamber (G) is low, parking brake release

pressure oil (K) is blocked by spool CB. When oil

pressure in chamber (G) increases, spool CB moves

to the right, allowing parking brake release pressure

oil (K) to flow into parking brake chamber (M) via

notch (I) on the travel brake valve spool CB and the

reducing valve at which pressure is reduced.

• Applying Brake:

When motor drive pressure decreases, parking

brake chamber (M) is opened to the drain circuit via

the orifice in the reducing valve.

Accordingly, the piston is pushed to the right by the

disc spring so that the friction plates and plates

come in contact with each other, applying the park-

ing brake.

T137-03-02-009

T140-03-02-007

T140-03-02-006

T173-03-05-002

When Brake is Applied:

When Brake is Released:K M

M

K

G AM I BMShuttleValve

Drain

Housing DriveDisc

Spool CB

Reducing Valve

DiscSpring

Piston

FrictionPlate Plate

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T3-5-20

ZAXIS370MTH:

The parking brake is a negative type which is released

only when the pilot pressure oil is routed into brake

piston chamber (M). Unless the travel function is oper-

ated, the parking brake is applied. The friction plates

and plates are splined to the rotor and the casing, re-

spectively.

The spring pushes the piston, then the parking brake is

applied after the friction plates come in contact with the

plates.

T16J-03-05-003

1 - Spring 3 - Plate 5 - Casing 6 - Rotor

2 - Piston 4 - Friction Plate

Casing

Friction Plate

Rotor

Plate

M

PistonSpring

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T3-5-21

• Releasing Brake:

When a travel lever is operated, pressure oil from

the main pump is routed to the travel motor via the

control valve.

This pressure oil flows into parking brake chamber

(M) to release the parking brake. After separating

the friction plates from the plates.

• Applying Brake:

When motor drive pressure decreases, the friction

plates and plates come in contact with each other,

applying the parking brake. The pressure oil in brake

chamber (M) flows back to the hydraulic oil tank.

T111-03-04-008

T111-03-04-007

M

FrictionPlate

CasingRotor

Plate

Spring

Spring

FrictionPlate

CasingRotor

Plate

Spring

Spring

M

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T3-5-22

(Blank)

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COMPONENT OPERATION / Others (Upperstructure)

T3-6-1

PILOT SHUT-OFF VALVE

The pilot shut-off valve is a manually operated switch

valve. The spool in the pilot shut-off valve is rotated by

moving the pilot control shut-off lever to turn the pilotoil flow to the pilot valves ON or OFF.

Valve Operation with Pilot Control Shut-Off Lever

in LOCK Position

The pilot shut-off valve is closed so that pressure oil

from the pilot pump does not flow to the pilot valve,

but it is routed to the shockless valve.

Pilot oil on the pilot valve side is routed to the

hydraulic oil tank. Even if the control levers (front

attachment / travel) are operated, the pilot valves do

not operate.

Valve Operation with Pilot Control Shut-Off Lever

in UNLOCK position

The pilot shut-off valve is opened, and the return

passage is blocked so that pressure oil from the pilot

pump flows to the pilot valves and the solenoid valve

unit. Then, when a control lever (front attachment /

travel) is operated, the pilot valves operate.

Section Z-Z

T178-03-07-002

T178-03-07-003

A1 - To Travel Pilot Valve A4 - To Solenoid Valve Unit T1 - From Travel Pilot Valve T4 - To Hydraulic Oil Tank

A2 - To Left Pilot Valve A5 - To Shockless Valve T2 - From Left Pilot Valve

A3 - To Rightt Pilot Valve P - From Pilot Pump T3 - From Right Pilot Valve

To ShocklessValve

FromPilot Pump

T4A4

Z

Z

A3T2T1

A1A2

T3 P

A5

NOTE: The picture indicates that the

shut-off valve is turned OFF.

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T3-6-2

SHOCKLESS VALVE

Beside the shockless valve, a check valve, pressure

sensor (arm roll-in), pressure sensor (boom raise), and

pressure sensor (swing) are provided in the shocklessvalve block.

The shockless valve regulates the return oil from the

control valve spool to the pilot valve, preventing abrupt

and rapid movement of the respective control valve

spools.

The shockless valve regulates the secondary pilot

pressure oil for the arm roll-in operation.

• When a control lever is moved, the pilot valve

delivers pilot oil pressure to the control valve.

When pilot oil pressure is low immediately after the

control lever is moved, pilot pressure oil is routed to

the control valve spool via the orifice and spool. After

pilot oil pressure increases, the check valve is

unseated.

• Pilot return oil from the control valve spool flows

back to the hydraulic oil tank via the spool and orifice.

When the return oil flow rate increases and oilpressure on the pilot valve side increases, the spool

is returned in response to the pressure increase on

the pilot valve side, regulating the return oil flow rate.

T1HH-03-06-001

1 - Pressure Sensor (Arm Roll-In) 4 - Pressure Sensor (Boom Raise)

2 - Shockless Valve 5 - Pressure Sensor

(Swing)

3 - Check Valve 6 - Check Valve

T173-03-06-002

T173-03-06-003

1 2 3 4 5

6

To ControlValve

From PilotValve

SpoolOrifice

Check Valve

FromControl

Valve

To Pilo tValve

SpoolOrifice

Check Valve

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T3-6-3

Warm-Up Circuit

When the pilot shut-off valve is closed (in the LOCK

position), the pilot pressure oil from the pilot pump

flows through the pilot shut-off valve, and is routed to

the shockless valve.Then, the pilot pressure oil is restricted, and is heated

by the orifice provided at the inlet port of the

shockless valve. As the warmed up pilot oil is then

routed to the shockless valve and pilot valve, the

components in the pilot system are warmed.

T1HH-03-06-002

To Pilot Valve

To Pilot Valve

To Pilot Valve

To Pilot Valve

From Pilot Pump

Pilot Shut-Off Valve(Lock Position)

Orifice

To Control Valve

To Control Valve

To Control Valve

To Control Valve

Shockless Valve

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T3-6-4

SOLENOID VALVE UNIT

The solenoid valve unit controls the control valve,

travel motor swash angle control servo piston, and

pump regulator by delivering pilot signal pressure oil inresponse to electrical signals from the MC.

The solenoid valve unit consists of 3 proportional

solenoid valves (SC, SI, and SG.). (Refer to the

Control System and Electrical System group in the

SYSTEM section.)

SC : Controls the arm regenerative valve in the

control valve.

SI : Controls the travel speed shift valve.

SG: Increases the set relief pressure of the main

relief valve in the control valve.

T1HH-01-02-008

SG

SI

SC

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T3-6-5

Proportional Solenoid Valve

The proportional solenoid valve is controlled by a

current signal from the MC, and delivers the oil

pressure in proportion to the current signal value.

• When in neutral:

Spool (1) is pushed to the right by spring (2),

opening delivery port S to tank port T.

• When activated:

Solenoid (3) pushes spool (1) to the left with force in

proportion to the current signal which flows through

solenoid (3). Then, pilot pressure oil is routed from

port P to delivery port S so that pressure in delivery

port S increases.

• Pressure in delivery port S acts on the stepped

flanges in section (a). Due to the difference in areaof the flanges, spool (1) is pushed to the right. When

pressure force to push spool (1) to the right

increases more than solenoid (3) force to push spool

(1) to the left, spool (1) is returned to the right side,

closing the passage between delivery port S and

port P so that pressure in delivery port S stops

increasing.

T107-02-07-005

1 - Spool 2 - Spring 3 - Solenoid

a

a

S PT1 2 3

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T3-6-6

TORQUE CONTROL SOLENOID VALVE,PUMP 2 FLOW RATE CONTROLSOLENOID VALVE

The torque control solenoid valve and the pump 2 flowrate control solenoid valve are placed at the top of the

pilot filter.

ST: Controls the pump regulator.

(Speed Sensing Control)

SB: Controls the pump regulator.

(Pump 2 Flow Rate Control)

• The torque control solenoid valve supplies torque

control pressure Pps to the regulators of pump 1 and

pump 2, reducing the pump delivery flow.

•The pump 2 flow rate control solenoid valve reducesthe pump control pressure to the regulator of pump 2,

controlling the maximum limit of the pump 2 delivery

flow.

Operation:

1. In the neutral position, port P is connected to the

output port via the notch on the spool.

2. When the current from MC (Main Controller) flows

to the solenoid, the solenoid pushes spring 1.

3. As spring 1 pushes the spool, the output port is

connected to port T via the notch on the spool,

reducing the pressure in the output port.

4. The left diameter (A) is larger than the right

diameter (B) of the spool notch, so the spool is

moved back to the left.

5. When the notches on the spool and the sleeve

come in contact with each other, the spool stops

moving and the pressure in the output port stops

decreasing.

T1HH-03-06-003

ST

Pilot Filter

SB

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T3-6-7

At Neutral Position:

T176-03-01-030

At Operating Position:

T176-03-01-031

Spring 1

Spring 1

Solenoid

Solenoid

Spring 2

Spring 2

A

A

Port P

Port P

Sleeve

Sleeve

Spool

Spool

Output Port

Output Port

Port T

Port T

B

B

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T3-6-8

PILOT RELIEF VALVE

The pilot relief valve has a pilot filter incorporated.

Pilot relief valve functions to regulate the pilot pump

pressure oil routed to port P to a set constant pressure.

EC MOTOR

The EC motor is used to control engine speed.

A worm gear is incorporated into the EC motor to

prevent a loss of synchronism from occurring. The EC

sensor is provided to detect the degrees of the EC

motor rotation to calculate the governor lever position.

(Refer to the Control System group in the SYSTEM

section.)

T1HH-03-06-003

T157-02-05-018

PilotRelief Valve

Output Shaft

Sensor Gear

ECSensor

WormWheel

Motor

Worm Gear Output Gear

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COMPONENT OPERATION / Others (Undercarriage)

T3-7-1

SWING BEARING

This bearing is a single-row shear ball-type bearing,

comprising outer race (1), inner race (3), balls (6),

supports (5), and seals (2), (4). Outer race (1) is bolted

to the upperstructure and inner race (3) is bolted to the

undercarriage.

The internal gear of inner race (3) engages with the

output shaft of the swing reduction gear.

T135-03-02-001

1 - Outer Race 3 - Inner Race 5 - Support 6 - Ball

2 - Seal 4 - Seal

1

2

3

4

5

6

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T3-7-2

CENTER JOINT

The center joint is a 360° rotating joint. When the

upperstructure is rotated, the center joint avoids

twisting of hoses and allows hydraulic oil to flow

smoothly to or from the travel motors. Spindle (1) is

attached to the main frame, and body (2) is bolted to

the swing center of the undercarriage.

Hydraulic oil flows to the right and left travel motors via

spindle (1) and the oil ports of body (2). Seals (3)

prevent oil leaks between spindle (1) and body (2) into

adjacent passages.

T157-03-02-004

1 - Spindle 2 - Body 3 - Seal

To Right TravelMotor (Forward)

To Left TravelMotor (Reverse)

To Left TravelMotor (Forward)

Pilot Pressurefor Travel Speed Selection

Pilot Pressurefor Travel SpeedSelection

: Pilot Pressure for Travel Speed Selection

: Reverse

: Forward

Drain

Drain

Drain

Drain

To Right TravelMotor (Reverse)

To Right TravelMotor (Reverse)

To Right TravelMotor (Forward)

To Left TravelMotor (Forward)

To Left TravelMotor (Reverse)

1

2

3

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T3-7-3

TRACK ADJUSTER

The track adjuster located on the side frame is

composed of spring (5) and adjuster cylinder (6).

Spring (5) absorbs loads applied to the front idler.

Adjuster cylinder (6) adjusts track sag.

• Grease is applied through grease fitting into

chamber A of adjuster cylinder (6) as illustrated

below. The pressure of the grease pushes piston

rod (8) out and decreases track sag.

• To increases track sag, loosen valve (1) 1 to 1.5

turns counterclockwise to release grease from the

track adjuster cylinder through the grease

discharge hole.

CAUTION: Do not loosen valve (1) quickly or

loosen too much since high-pressure grease

in the adjusting cylinder may spout out.

Loosen carefully, keeping body parts and

face away from valve (1).

Never loosen grease fitting.

M104-07-119

T135-03-05-001

1 - Valve 3 - Washer 5 - Spring 7 - Flange

2 - Nut 4 - Spacer 6 - Adjuster Cylinder 8 - Piston Rod

1

2 3

Grease Discharge Hole

4

Grease Fitting

5 6 7 81 a

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(Blank)

t03 hitachi

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