T AW55-50SN Initial Engagements - Valve · PDF file10 Transmission Digest AW55-50SN Initial Engagements T he AW55-50SN transmission has been with us now for a little more than a

10 Transmission Digest

AW55-50SN Initial Engagements

The AW55-50SN transmissionhas been with us now for alittle more than a decade,

and judging by the calls I hearcoming to the tech line at ValveBody Pro by people who rebuildtheir own solenoids, it continues tobe somewhat of a mystery to manyof us.

I will try to explain one of themost-common questions beingasked, concerning Drive andReverse engagement problems.Some of this information has beencovered at the ATSG semi-nars, so I will be using someamperage and pressure read-ings taken from a 2005Nissan Altima as a visual aidso we can see how this trans-mission accomplishessmooth, almost-unfelt initialengagements, or garage feelas it is known to some.

This transmission goes bydifferent names. Nissan callsit RE5F22A and GM calls itAF33-5, but all use fiveon/off solenoids and threelinear solenoids to controlshift quality. The main job ofthe five on/off solenoids is toalign the valves in the valvebody so that the three linearsolenoids – SLT, SLS andSLU – can control the rate atwhich the oncoming clutch isapplied and the rate of re-lease of the off-going clutch.

To control the clutch engage-ment and disengagement, AisinWarner uses a system of threephases: servo control, torque andinertia. During the initial engage-ment, the servo-control phase basi-cally primes the apply circuit toensure a quick response of theapply element during the torquephase. The torque phase appliesthe piston in a gradual, progres-sive manner, ensuring a smoothapplication. Finally, the inertiaphase fully applies main line pres-

sure to the piston, ensuring a goodhold. These phases are used duringinitial engagement, or garage feel,and during upshifts.

Let’s look at the Drive engage-ment first (Figure 1). The SLT is re-sponsible for controlling the rate ofapplication of the C1 forwardclutch. When the manual valve isplaced in the Drive position, mainline pressure is directed to the cen-ter of the C1 control valve. At oneend of the C1 control valve is SLT

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•Subject: Drive and Reverse engagement problems

•Unit: AW55-50SN (Nissan RE5F22A, GM AF33-5)

•Vehicle Applications: 2005 Nissan Altima

•Author:Jesse Zacarias

•Essential Reading: Rebuilder

Shop Owner

Center Manager

Diagnostician

R & RTEC

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Copyright © 2012 Valve Body Pro

From oil pump

Drive Circuit

Forward-clutch(C1) accumulator

Main line pressure

Throttle signal

P R N D I L

Manual valve

To forward-clutch(C1) assembly

Line pressurecontrol solenoidvalve (SLT) C1 controlC1 control

continues page 12

12 Transmission Digest

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pressure and at the other end isbalance oil. The SLT pressure hasto gradually push the C1 control

valve against balance pressure,thus controlling the rate at whichmain line pressure enters the cir-

cuit to the C1 forward clutch.In Figure 2 we can see that the

Channel 1 SLT pressure

Channel 2 C1 pressure

SLT amperageduring N-D

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18 Transmission Digest

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moment that the manual valvewas placed in Drive, C1 pres-sure (green) starts to enter theC1-clutch drum, then SLT pres-sure (yellow) starts to increaseand control the rate of apply.Then when both SLT pressureand C1 pressure are about 54psi, SLT pressure is lowered toless than 10 psi and main linepressure is allowed to enterundisturbed the C1-clutchdrum, where it settles at about61 psi.

Now let’s look at how theTCM accomplishes this. You canfollow the amperage activity inFigure 3. The SLT and SLS sole-noids are normally open linearsolenoids that decrease pressureas amperage increases. At 1amp the SLT is adjusted to haveabout 5 psi, and at 0.1 amp youhave about 80 psi. During theinitial Drive engagement, SLTgoes from 1.0 amp to 0.87, thento 0.88. This is the servo-controlphase, allowing fluid to fill theclutch circuit without applyingthe C1 clutch. Then the amper-age is gradually lowered, in incre-ments of hundredths, to 0.78 amp.This is the torque phase that grad-ually applies the C1 clutch withoutbeing felt. Finally, the amperage isspiked to 0.63, which is the inertiaphase, allowing full line pressureto hold the C1 clutch. SLT amper-age is finally raised to 0.93 amp,where it settles, controlling mainline pressure and being ready toraise it during acceleration. All thistakes place in about two seconds.

I have found the SLT to be ad-justed properly – checked in Parkor neutral when the transmission ishot – if set anywhere between 4and 6 psi, but it is more stable ifchecked in Drive and set at 7-9 psi.If you feel a delay double bumpduring initial engagement intoDrive, SLT pressure is probablytoo low. If, on the other hand, youfeel a harsh engagement it is prob-ably too high. I recommend using apressure transducer gauge to ad-just the SLT, but if you use a regu-

lar needle gauge it is better to usethe 0- to 100-psi gauge, as it ismore accurate at low pressure. Ihave found that there are 12 clicksin one complete turn of the SLTadjuster (Figure 4) and that eachclick makes a difference of about 1psi, so 1 turn equals 12 psi.Turning in the adjuster increasesSLT pressure; turning it out de-creases the SLT pressure.

Now let’s look at the initialReverse engagement (Figure 5 onpage 20). When the manual valveis placed in Reverse, main linepressure is routed to the shift-pressure control valve, where it isthen routed to the C2-clutch drumthrough the shift-pressure relayvalve held in position by shift so-lenoid E. The SLS linear-solenoidpressure controls this pressure riseby gradually increasing SLS pres-sure present at the shift-pressurecontrol plunger. This allows theSLS to raise the torque-phase pres-

sure gradually from 17 psi to 75psi (Figure 6 on page 22), thenshift solenoid E turns on, allowingmain line pressure present at theshift-pressure relay valve to be di-rected to the C2-clutch drum; thisis the inertia phase.

Now let’s look at how the TCMaccomplished this smooth engage-ment (Figure 7). SLS amperagewas at 0.67 in neutral. When themanual-lever position sensor no-ticed that the transmission wasplaced in Reverse, the amperagewas raised to 0.75; this is theservo-control phase. Then SLS am-perage is gradually lowered from0.75 amp to 0.54; this is the torquephase. At this stage, shift solenoidE is turned on, resulting in the in-ertia stage, or fully applied. InFigure 6, when you see the drop inC2 pressure at about 3.5 seconds,this is when shift solenoid E isturned on.

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SLU adjustment

SLS adjustment

SLT adjustment

continued from page 12

continues page 20

If you have a double-bump feelor delay in Reverse engagementand a flare on the 2-3 or 3-4 shift,SLS pressure is probably too low.

If, on the other hand, you have aharsh Reverse engagement andharsh 2-3 shift, SLS is probably toohigh. As mentioned previously,

turning in the adjuster increasesSLS pressure, and turning it outdecreases SLS pressure, with each

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Transmission Digest20

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Transmission Digest22

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click equal to 1 psi.I hope this information helps

you understand the role that SLT

SLS amperage duringReverse engagement

Channel 1 SLT pressure

Channel 2 C1 pressure

Channel 3 C2 Pressure

Channel 4 B4 Pressure

plays in the initial Drive engage-ment and the role SLS plays in theinitial Reverse engagement. TD

Jesse Zacarias is the owner of Elec-TranDiagnostics (www.electrandiagnostics.com) inGilroy, Calif.