honda m4va and szca cvt pressure pressure controlscontrols · honda m4va and szca cvt pressure...

22 GEARS January/February 2005

Honda M4VA and SZCA CVT

Pressure ControlsHonda M4VA and SZCA CVT

Pressure Controlsby Sean Boyle

W hile some manufac-turers are questioning theirfaith in continuously vari-

able transmissions (CVTs), others arekicking production into high gear (orsomething equivalent). Honda hasalways been a leader in CVT technolo-gy and reliability, but the production ofHondas equipped with CVTs is stillfairly low. Without a doubt, CVTs arerelatively rare transmissions. But withfuel costs rising, the newer, fuel-effi-cient hybrids have recently becomemore attractive to many consumers, andone thing that makes hybrids practicaland fuel efficient is the CVT.

For now there are only two HondaCVTs in production:

• M4VA in the 1996-to-2000Civic HX

• SZCA in the 2001-to-currentHX, Insight, and Civic hybrids

The two models essentially operatethe same way, but there are differencesbetween them. Honda has refined theelectronics, hydraulics, and even themechanical configuration as the CVTevolved from the M4VA to the SZCA.Let’s look at how each of these HondaCVTs achieves the pulley ratio changesand sheave (pulley) pressure.

Pressure TestingFor the most part, pressure testing

a Honda vehicle is difficult. First,Honda doesn’t use conventional pres-sure taps. The pressure tap is an 8 x1.25 metric thread with an aluminumsealing washer.

Second, they put the pressure tapsin the worst possible places. Whenattempting to check pressures, have

plenty of fittingsand adapters onhand to make life alittle easier. I’veresorted to makinghomemade fittingsby drilling a small1/8" hole throughthe center of a boltand welding a 1/8"pipe fitting to it(figure 1).

On a positivenote, Honda pro-vides a pressure tapfor most, if not all,of the circuits in the transmission. Sopressure tests can provide excellentinsight into hydraulic and electronicfailures.

Be careful performing pressuretests on these units: The Honda CVTcan reach more than 500 PSI, so neveruse a conventional 300 PSI gauge.

Consider an electronic pressure trans-ducer, not only because of the rangesavailable, but for its recording capabili-ties. The pressure test shown is on aCVT in failsafe mode (figure 2). Keepin mind, the driven pulley pressure reach-es 540 PSI. All this from a small, chain-driven, positive displacement pump.

Figure 1: While Honda provides pressure taps for nearly every circuit in the unit,connecting your gauge to these taps often requires extensive plumbing.

Figure 2: In failsafe, CVT pressures can exceed 500 PSI.Always use a pressure gauge with adequate range, or better

yet, use a pressure transducer for hydraulic testing.

boyle-CVT.qxd 12/31/04 2:12 PM Page 22

Life1-05.qxd 12/31/04 10:52 AM 3

If the CVT is operating correctly,the normal pressure range isn’t thatalarming (figure 3). In neutral at 1700RPM, you should expect 50 – 92 PSI atthe drive pulley, 92 – 140 PSI at thedriven pulley. In drive, you should have228 – 267 at the forward clutch. Thelube circuit should produce 36 – 58 PSIin neutral, at 3000 RPM.

The service manual doesn’t pro-vide specifications for stall or movingpressure ranges, but look for the start

clutch, drive, and driven pulley pres-sures to increase with engine torque.The relationship between drive anddriven pulley pressures will change asyou drive the vehicle. This changes theeffective ratio of the drive and drivenpulleys (figure 4).

Pressure ControlHonda relies on two pulse width

modulation (PWM) solenoids to con-trol how much pressure each sheave

(pulley) receives. The design andresponsibility of each PWM solenoid isdifferent between the two generationsof transmissions (figures 5A and 5B).

Early CVT (M4VA)A PH/PL solenoid controls overall

line pressure, which is also termed PH(Pressure, High). The PH/PL solenoidalso controls PL (Pressure, Low),which works with PH pressure to estab-lish ratios and sheave pressure. Think


Figure 4: The Honda CVT blends the pressures from the PH/PL solenoid to adjust the width of the sheaves

(pulleys) and control drive ratio.

Figure 3: Under normal operation, pressures are more reasonable, although Honda doesn’t offer a complete set

of pressure specs.

Honda M4VA and SZCA CVT Pressure Controls

HUGE INVENTORY- VOLUME DISCOUNTS

Also: Complete Rebuild Kits with OE quality parts

Manual Transmissions & Transfer Cases

You can order online and use our complete buyers guide at:www.nat ionaldr ivetrain.com

TOLL FREE ORDER LINEWe beatanyone’spublishedprice onRing andPinions

Standard12 MonthUnlimitedMileWarranty.Extended Warranties available

QUALITY REBUILT

INTRODUCING

12M

ON

TH

UN

LI

MITED MILE SILVERW

AR

RA

NTY

QUALITY REBUILT

1-800-507-4327

Platinum Torque is a new productline developed by NationalDrivetrain to usher in a higherstandard of quality parts andrebuilt units at affordable prices.

Take Note:Call and request a credit application today

Member


of the PH/PL solenoid circuit as con-trolling the amount of pressure in theCVT.

The Shift Control Solenoid isresponsible for distributing the PH andPL pressure between the drive and driv-en pulleys. The shift control solenoidacts on the shift control valve to delivera combination of PH and PL pressure toa given pulley. The TCM then monitorsthe speed ratio through one of its fourspeed sensors and adjusts accordingly.

Think of the shift control solenoid ascontrolling the pressure ratio betweenthe drive and driven pulleys.

Late CVT (SZCA)The late model CVT valve body

looks similar to the earlier unit, but thehydraulic functions have changed dra-matically. A separate Drive PressureControl solenoid and Driven PressureControl solenoid replace the PH/PLsolenoid and the shift control solenoid

in the M4VA units, and satisfy all of thepressure and ratio functions. Each sole-noid will determine the amount of pres-sure for its respective pulley, in addi-tion to influencing line pressure.

Here’s how it works:Honda’s PWM solenoids mechani-

cally assist the valves they control.When energized, the solenoid pintleextends, forcing the valve againstspring pressure. Take a look at the

GEARS January/February 2005 25

Figures 5a and 5b: A look at the physical differences between the early (left) and late (right) CVT valve bodies.

1425 STAGECOACH RDSHAKOPEE, MN 55379VOICE 800-800-9274FAX 952-445-0231www.powerpusher.com


hydraulic schematic: each PWM sole-noid works along with regulated pres-sure to move its valve to the right,which cuts off its own fluid supply.

When the PWM duty cycle is high,the mechanical assist from the PWMsolenoid is high, requiring lesshydraulic pressure to move thevalve to the right (figure 6).This creates lower solenoid sig-nal pressure. If power wereinterrupted at the solenoids, thevalves would have no mechani-cal assist from the solenoids, sothey’d require more hydraulicpressure to move the valves tothe right. This would boostsolenoid signal pressure.

In earlier CVTs, the PH/PLsolenoid (6) regulated pressureto the PH control valve (7) andthe PL control valve (5). ThePH control valve, as its nameimplies, controls PH pressure,which is basically line pressure(figure 7). The PL control valvelowers PH pressure, whichhelps control the ratio betweenthe pulleys.


1 Driven Pulley

2 Drive Pulley

3 Shift Control Solenoid

4 Shift Control Valve

5 PL Regulator Valve

6 PH/PL Solenoid

7 PH Control Valve

8 PH Regulator Valve

The changes in pressure between the PHand PL are linear: As the

TCM reduces the dutycycle signal to the PH/PLsolenoids, both PH andPL pressure increase.

Figure 7: On early Honda CVTs, the PH/PL solenoid (6) controls pressure for both pulleys; the shift control solenoid (3) controls regulates how much pressure applies to each pulley.

Figure 6: The TCM controls the PH/PL solenoids with a variable duty cycled signal.As signal on-time increases, pressure decreases.



The Problem Solvers.

We have a transmission solution

for any vehicle.

(Well, almost any)

As the technological leader,

Precision International’s repair kits are truly state of the art.

210 Knickerbocker Ave., Bohemia, NY 11716 (631) 567-2000 • Fax (631) 567-2640 • Toll Free: 800-872-6649 Florida Office:455 Lakeview Drive, Coral Springs, FL 33071(954) 509-9950 • Fax (954) 509-9945E-mail: [email protected]

Name any year, make or model. Give us any transmission problem.

Chances are we’ve got a solution. Not just any solution, but one that

will really work and keep on working – backed by solid engineering, the

latest specs and our reputation for giving you and your customers reliable

performance and the utmost peace of mind. When you

see the Precision International name on one of our

transmission repair kits, you can feel confident you’ve

got the very best. All are cross-checked against OEM

specs. All changes are noted and made. And we always use OE parts or

better. Spaceships? We haven’t helped repair one of those yet. But who

knows what tomorrow will bring!

THE LATEST SOLUTIONFROMTHE PROBLEM SOLVERSRL4F02A/V – RE4F02A/VPROBLEM: Before and/or after rebuilding a transmission, the vehicle has repeated front seal leaks. The front seal may appear to have popped out of the converter housing.

CAUSE: The front pump seal may have been installed toodeeply into the converter housing. This can cause the sealto block off half of the drain back hole in the pump, leadingto an increase in oil pressure behind the seal. Which, in turn,can make the front seal pop out of the housingor oil to blow past the seal between its lipand converter hub.

SOLUTION: Precision International’sredesigned Vamac® front pump seal number 63704. It’s pre-notched and indexedto avoid blocking the drain back hole. You canorder the seal, including complete installationinstructions, under the number Sub-K63704.® Viton is a Registered Trademark of DuPont.

T H I S A D V E R T I S E M E N T P R E PA R E D B Y L o B o & P e t r o c i n eC l i e n t : P r e c i s i o n I n t e r n a t i o n a l J o b # : P R E - N - 2 0 3 A d # : P R E - 0 1 7 A d S i z e : 8 1 2 5 ” x 1 0 8 7 5 ” 4 / C

203PRE017 ALIEN 4C 12/16/04 2:48 PM Page 1

1 Driven Pulley 5 Driven Press Control

2 Drive Pulley 6 Drive Press Control

3 Driven Pulley Control 7 PH Control Valve

4 Drive Pulley Control 8 PH Regulator Valve

The changes in pressurebetween the PH and PL are lin-ear: As the TCM reduces theduty cycle signal to the PH/PLsolenoids, both PH and PLpressure increase. The overallpressure changes in the PH andPL circuits, but the shift controlsolenoid (3) still controls howthose pressures apply to eachpulley.

The shift control solenoidreceives modulator (solenoid)pressure and alters it into shiftcontrol solenoid signal pres-sure. This pressure acts on theshift control solenoid valve,which is responsible for deliv-ering the PH and PL pressuresto the pulleys for ratio control.

When the PWM signal ishigh, shift control solenoid sig-nal pressure is low, moving theshift control valve (4) towardthe left. This delivers more PHpressure to the driven pulley (1)and more PL pressure to thedrive pulley (2). This pressurearrangement moves the pulleysinto a low ratio, such as youmight expect during accelera-tion.

As vehicle speed increases,the shift control valve movestoward the right. This reversesthe blend, sending more PHpressure to the drive pulley, andmore PL pressure to the drivenpulley. This configuration cre-ates a higher ratio, similar tooverdrive on a conventionaltransmission.

The mechanical operationsof the late-model CVT sole-noids are the same as the earlierunit, but the hydraulic functionsare different. Look at the latemodel CVT hydraulic schemat-ic (figure 8): the drive (6) and driven(5) pressure control solenoid signalpressure affects drive and driven pres-sures as well as overall line pressure.

All of the valves in the CVTexcept the reverse inhibit valve are bal-ance-type valves, that regulate circuitpressure by balancing hydraulic pressure, spring force, and, in the caseof the solenoid-operated valves,


Figure 8: On later Honda CVTs, the drive and driven pulleys each have their own PH/PLsolenoid, which also control overall line pressure.



Tradition

Engineering

Innovation

Vision

Leadership

Passion

Performance

Ambition

Dedication

Know How

BorgWarner

makes OEM

quality parts for

over 80 transmissions

world-wide, including

FLEX-BAND ™,

UNI-BAND ™ and

MAJI-BAND ™

transmission bands,

friction plates and

one-way clutches.

ince 1928, the BorgWarner name has been synonymous with pioneering innovation in theworld-wide automotive industry. Our leadership in product development has resulted in animpressive list of “firsts” – from the first mass produced automatic transmission to our recentinnovation of Torque on Demand (TOD)™ systems for all-wheel drive. Today, BorgWarneradvances its long tradition of ambition and vision with new technology dedicated to highenergy applications and full systems product strategies for our OEM customers.

BorgWarner has available for your transmission shop virtually every automatic transmissionpart we manufacture for the world’s leading vehicle makers. That’s more than 450 no-riskOEM quality components for over eighty transmissions world-wide, including our newline of high performance friction products for race-ready transmissions.

Go significantly beyond the competition. Make BorgWarner your one-stop source for auto-matic transmission parts that are competitively priced, readily available and guaranteed to fityour rebuilds. Call your authorized distributor today and ask for the original parts from theleader in automatic transmission technology…BorgWarner Inc.

Go Beyond.

G OS I G N I F I C A N T L Y

B E Y O N DT H E C O M P E T I T I O N.

BorgWarner Inc. Transmission Systems1350 North Greenbriar Drive Unit B Addison, IL 60101 (630) 261-9980

The BorgWarnerIndianapolis 500 Trophyis a registered trademark

of BorgWarner Inc. www.bwauto.com

S

▼

▼

▼

▼

▼

▼

▼

▼

▼

▼

borgWmorsetec.qxd 12/31/04 11:00 AM Page 29

mechanical solenoid force. The late model CVTs havegreater control over how much pressure each pulleyreceives, because they use separate solenoids andhydraulic circuits for the drive and driven pulleys.

Both generations of CVT use low-resistance PWMsolenoids, measuring between 3.8 and 6.8 ohms. At roomtemperature you should measure around 5 ohms. Thereverse inhibit solenoid is the only on/off solenoid in theCVT, with between 11.7 and 21 ohms. The reverse inhib-it solenoid works like other Honda on/off solenoids,hydraulically trapping pressure when it’s de-energized.

Service NotesYou can reach all of the solenoids through the bottom

pan, but be careful with the electrical connectors: Theshift control solenoid and the start clutch solenoid use thesame connectors on early M4VA units. The drive pulleypressure control solenoid and the start clutch solenoidhave the same connector on SZCA units. These solenoidconnecters reach each other easily, and won’t look out ofplace if you cross them (figure 9).

Contamination is an important issue with CVT units: Whateveryou’re doing in a CVT, keep it clean. Take a good look at the springsthat control the valve positions in the CVT: They’re very small andhave very little tension. It wouldn’t take much to hang a valve in thisvalve body, so be careful and be extra clean when rebuilding theseunits.



Contamination is animportant issue withCVT units: Whatever

you’re doing in a CVT,keep it clean.

Figure 9: Be careful reconnecting the solenoids to the electricalharness; the connectors are identical, and can easily be crossed

during reassembly.


honda m4va and szca cvt pressure pressure controlscontrols · honda m4va and szca cvt pressure...

Documents