fluid power - (me353)- lec7
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Fluid Power Systems (ME353)
Fall 2012
Lecture 7
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Motors in seriesSame flow rate for each motor.
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Motors in parallelDifferent flow rate for each motor
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Motors in parallel with flow control
Different flow rate for each motor with flow control valvefor each one.
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Braking circuits for Hydraulic Motors
Braking circuits are used to slow hydraulic motors to a stop
– Inertia of a heavy rotating load can continue to turn the motor shaft
– Braking occurs when fluid discharged from the motor outlet port is
forced to pass through an adjustable pressure control valve before
returning to the reservoir
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Open-Loop and Closed-Loop HydraulicMotor Systems
An open-loop hydraulic motor system uses a layout typical of a basichydraulic system
– Pump moves fluid from a reservoir, through a directional control valve,
to the motor
– Fluid is then returned from the motor to the reservoir through the same
control valve
Closed-loop hydraulic motor systems continuously circulate fluid between
the pump and the motor without returning it to a system reservoir
These systems use a replenishment circuit to replace fluid lost through
leakage
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Open circuit design
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Hydrostatic Drives
Hydrostatic drive systems consist of the basic components typically found in
other hydraulic motor circuits
When compared to conventional transmissions, hydrostatic drives:
– Have a high power output – to – size ratio
– May be stalled under full load with no internal damage
– Accurately maintain speed under varying load conditions
– Provide an almost infinite number of input/output speed ratios
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Hydrostatic drives provide effective transmission of power and allow easy
adjustment and control of:
– Output shaft speed
– Torque
– Horsepower
– Direction of rotation
Hydrostatic drives may be open or closed circuits – Open circuit has the layout of a basic hydraulic motor circuit
– Closed circuit has the outlet of the pump directly connected to the inlet
of the motor and the outlet of the motor directly connected to the inlet of
the pump
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Open circuit design
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Closed circuit design
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Four combinations of pump/motor arrangements can be used
– Fixed-displacement pump and motor
(Maximum horsepower, torque, and output shaft speed are fixed)
– Fixed-displacement pump and variable-displacement motor
(Maximum horsepower is fixed, Torque and speed are variable)
– Variable-displacement pump and fixed-displacement motor
( Horsepower and output shaft speed are variable, Torque output is fixed) – Variable-displacement pump and motor
(Horsepower, torque, output shaft speed are variable)
Hydrostatic drives are typically considered hydrostatic
transmissions when both the pump and motor have variabledisplacement
This combination allows manual or automatic control of torque,
speed, and power output