Valve Body: Description and Operation

HYDRAULIC CONTROL COMPONENT DESCRIPTION





COMPONENT LOCATOR





HYDRAULIC CIRCUIT IDENTIFICATION CIRCUIT DESCRIPTION

HYDRAULIC CONTROLS DESCRIPTION





LINE PRESSURE CIRCUITS
The LA4A-EL transaxle has hydraulic circuits to provide filtered fluid under line pressure to the other hydraulic circuits.
The PCM has control of line pressure, using the EPC: Electronic Pressure Control solenoid. This results in a precise control of shift feel and efficient use of pressure for apply component operation.
Changes in the position of the main regulator valve are controlled by TV circuit pressure from the EPC solenoid and by the presence or absence of pressure in the D21 circuit. The main regulator valve controls the amount of fluid exiting the LP circuit in two directions:
- Into the LPX circuit for torque converter operation
- Into the MRX recirculation circuit that returns to the oil pump
The flow of fluid in the LP circuit has this path:
- From the sump through the filter to the oil pump
- From the oil pump in several directions:
- To the manual valve
- To the solenoid regulator valve
- To the EPC solenoid
- To the main regulator valve
The PCM varies the current of the electrical circuit for the EPC solenoid in order to vary TV circuit pressure.
The fluid exhausted at the EPC solenoid flows over the Transaxle Fluid Temperature (TFT) sensor. The TFT sensor input signal is used by the PCM for transaxle control.
In D, 2 or 1 range, the presence of fluid under line pressure in the D21 circuit at the main regulator valve causes line pressure to operate in a lower pressure range than in P, N and R positions. The absence of D21 circuit pressure in P, N, and R positions allow for a higher line pressure.

EPC SOLENOID CONTROL
- At a low current, the TV circuit pressure is higher, resulting in high line pressure.
- At a high current, the TV circuit pressure is lower, resulting in lower line pressure.
- In a fail-safe mode, maximum TV circuit pressure is present, resulting in maximum line pressure.

SOLENOID CIRCUITS





OVERVIEW
The LA4A-EL transaxle has hydraulic circuits to control the scheduling of shifts. The PCM has control of four solenoids: SS1, SS2, 3-2 T/CCS, and TCC to do the following operations:
- Move shift valves to provide transaxle operation in the first, second, third and fourth gear
- Control the timing of a 3-2 shift
- Control the apply and release of the coast clutch
- Control the release, apply, and modulation of the torque converter clutch





SOLENOID FEED/FINAL DRIVE GEAR LUBE CIRCUIT
Fluid under LID circuit pressure flows to the solenoid regulator valve, where it enters the SF circuit at a lower, regulated pressure. The flow of fluid in the SF circuit has the following paths:
- To Shift Solenoid 1 (SS1)
- To Shift Solenoid 2 (SS2)
- To 3-2 Timing/Coasting Clutch Solenoid (3-2 T/CCS)
- To Torque Converter Clutch (TCC) solenoid
- To the final drive gear lube circuit
The flow of fluid in the SF circuit also provides lubrication to the final drive components.





SHIFT SOLENOID 1 (SS1) HYDRAULIC CIRCUIT
Fluid under SF circuit pressure flows through SS1 when the PCM turns it to ON. SSI is at ON in the D, 2 and 1 range/first gear, as well as in D range/fourth gear.
When SS1 is at ON in first gear, fluid under pressure in the S1 hydraulic circuit moves the 1-2 shift valve, but not the 3-4 shift valve. The reason for this is that the fluid under line pressure in the L1 circuit prevents movement of the 3-4 shift valve in the first gear.
When SS1 is at ON in the fourth gear, fluid under pressure in the SI hydraulic circuit moves the 3-4 shift valve, but not the 1-2 shift valve. The reason for this is that the fluid under line pressure in the L34 circuit prevents movement of the 1-2 shift valve in the fourth gear.
When SS1 is at OFF, the SI circuit connects to exhaust while the SF circuit is blocked.





SHIFT SOLENOID 2 (SS2) HYDRAULIC CIRCUIT
Fluid under SF circuit pressure flows through SS2 when the PCM turns it to ON.
When SS2 is at ON in D, 2 and 1 range, fluid under pressure in the S2 hydraulic circuit moves the 2-3 shift valve.
When SS2 is at OFF in D and 2 range, the S2 circuit connects to exhaust while the SF circuit is blocked. Spring force then to move the 2-3 shift valve.





3-2 TIMING/COASTING CLUTCH SOLENOID HYDRAULIC CIRCUIT
The PCM varies the current of the electrical circuit for 3-2 timing solenoid in order to vary pressure in the S3 hydraulic circuit. The following principles of operation apply for the solenoid:
- At zero current, S3 circuit pressure will be exhausted, resulting in the following action:
- The coast clutch valve allows fluid under line pressure in the L123 circuit to enter the CCL circuit, causing the application of the coasting clutch.
- In fail-safe mode: zero current, no S3 circuit pressure will be present, resulting in actions similar to those for zero current operation.





- At a moderate current, S3 circuit pressure varies, resulting in the following actions:
- The 3-2 timing valve provides regulated exhausting of the DC circuit during the first and second gear operation. Exhausting the DC circuit releases the pressure from the direct clutch and from the release side of the 2/4 servo through the 2-3 shift valve.
- The coasting clutch valve does not allow fluid under line pressure in the L123 circuit to enter the CCL circuit, causing the release of the coasting clutch.





- At maximum current, S3 circuit pressure will be high, resulting in the following actions:
- The 3-2 timing valve provides exhaust of the DC circuit during the first and second gear operation. Exhausting the DC circuit releases the pressure from the direct clutch and from the release side of the 2-14 servo through the 2-3 shift valve.
- The coasting clutch valve does not allow fluid under line pressure in the L123 circuit to enter the CCL circuit, causing the release of the coasting clutch.





TORQUE CONVERTER CLUTCH (TCC) HYDRAULIC CIRCUIT
The PCM varies the pulse-width (ON time) of the electrical signal to the TCC solenoid in order to vary pressure in the S4 hydraulic circuit. The following principles of operations apply for the TCC solenoid:
- At low pulse-width, S4 circuit pressure is lower, resulting in release of the torque converter clutch.
- At high pulse-width, S4 circuit pressure is higher, resulting in apply of the torque converter clutch.
- At moderate and varying pulse-width, S4 circuit pressure is varying, resulting in controlled slip of the torque converter clutch.
- In fail-safe mode, (no pulse-width), no S4 circuit pressure is present, resulting in the release of the torque converter clutch.





TORQUE CONVERTER/LUBE CIRCUIT
The LA4A-EL transaxle has hydraulic circuits to provide component lubrication and to operate the torque converter including the torque converter clutch. Fluid entering the LPX circuit from the main regulator valve flows through the converter regulator valve, where it enters the CCX circuit at a lower, regulated pressure.
The flow of fluid in the CCX circuit has the following paths:
- To the bypass valve
- Into the CI circuit, where it flows to the torque converter impeller
- To passages for the front lube and drive chain/differential lube areas.
At the bypass clutch control valve, fluid returning from the torque converter turbine in the CT circuit enters the TC circuit as it flows to the fluid cooler. Fluid from the cooler then reenters the transaxle as it flows to the passages of the rear lube area.
The position of the bypass clutch control valve controls the fluid in the CCX circuit entering the CBY circuit. Fluid in this circuit enters the torque converter to push the torque converter clutch plate away from the cover, releasing it. The PCM varies the pulse-width control of the TCC solenoid to vary S4 circuit pressure, causing the pressure in the CBY circuit to vary.
In R position, fluid under pressure in the R circuit opposes the movement of the bypass clutch control valve, resulting in high CBY pressure and the release of the torque converter clutch.
In D, 2 and 1 range/first gear, fluid under pressure in the L1 circuit prevents the application of the torque converter clutch.

APPLY COMPONENT HYDRAULIC CIRCUITS DESCRIPTION





REVERSE CLUTCH HYDRAULIC CIRCUITS
The LA4A-EL transaxle has a hydraulic circuit to control the apply and release of the reverse clutch. The reverse clutch is applied in the R position at the same time that the low/reverse is applied.
The path of fluid under line pressure during the application of the reverse clutch is as follows:
- From the manual valve to the R circuit
- From the R circuit to the 1-2 shirt valve
- From the 1-2 shift valve to the reverse clutch.
In R position, fluid underline pressure in the R circuit prevents the bypass clutch control valve from applying the torque converter clutch.
When the manual valve moves to a position other than R position, it provides an exhaust path for the R circuit.





LOW/REVERSE CLUTCH HYDRAULIC CIRCUITS OPERATION
The LA4A-EL transaxle has hydraulic circuits for the control of the low/reverse clutch. The low/reverse clutch is applied in the R position and 1 range/first gear.

R POSITION
The path of fluid under line pressure during the application of the low/reverse clutch in the R position is as follows:
- From the manual valve into the R circuit
- From the R circuit in several directions:
- To the bypass clutch control valve to prevent torque converter clutch application
- Through 1-2 shift valve to the RC Circuit
- From the low/reverse valve, through the LRC circuit, to the low/reverse clutch
As pressure in the LRC circuit builds, it first strokes the low/reverse clutch piston and then the pressure buildup is modulated by the accumulator.
If the PCM detects that a shift into the R position is occurring above a specified vehicle speed, it causes a lockout by turning SS1 to ON to move the 1-2 shift valve. When this occurs, the R circuit feed is blocked and the low/reverse clutch and accumulator have a path to exhaust through the 1-2 shift valve until SS1 is turned OFF.
When the manual valve moves from the R position, it provides an exhaust path for the R circuit.





1 RANGE/FIRST GEAR OPERATION
The path of fluid under line pressure during the application of the low/reverse clutch in 1 range/first gear is as follows:
- From the manual valve into the L circuit
- From the L circuit to the LX circuit through the 1-2 shift valve.
- From LX circuit to the low/reverse modulator valve
- As pressure builds in the LX circuit, it moves the low/reverse valve to allow a controlled flow through the LRC circuit to the low/reverse clutch
If the PCM detects that a shift into 1 range is occurring above a specified vehicle speed, it prevent is the first gear operation by turning SS1 to move the 1-2 shift valve to OFF. When this occurs, the L circuit will be blocked.
When the manual valve moves from the 1 range position, it provides an exhaust path for the L circuit.





2/4 SERVO AND DIRECT CLUTCH HYDRAULIC CIRCUITS
The LA4A-EL transaxle has hydraulic circuits to control the apply and release of the 2/4 band and direct clutch. The 2/4 band is applied in D, 2 and 1 ranges/second and fourth gear. The direct clutch is applied in third and fourth gear of the same ranges.

FIRST GEAR OPERATION
The PCM controls first gear operation by turning Shift solenoid 1 (SSI) and Shift solenoid 2 (SS2) ON. This results the 1-2 and 2-3 shift valves move against spring force and the 3-4 shift. valve does not move because of opposing force of fluid under pressure in the L1 circuit. In first gear, the 2/4 band and direct clutch are released.
To prepare for a 1-2 shift, fluid under pressure in the D21 circuit flows to the line modulator valve, where it exits in the LM circuit to the 2/4 accumulator under lower pressure modulated by TV circuit pressure.





1-2 SHIFT OPERATION
The PCM controls a 1-2 shift by turning to Shift solenoid 1 (SS1) OFF while Shift solenoid 2 (SS2) remains ON. This results in spring force moving the 1-2 shift valve to the left side. In second gear, the 2/4 band is applied and the direct clutch is released.
To apply the 2/4 band, fluid under line pressure from the D21 circuit moves through the 1-2 shift valve, 2-3 shift valve and 3-4 shift valve and several circuits. Fluid in the SA circuit from the 3-4 shift valve applies the 2/4 band. Fluid in the circuits to apply the 2/4 band also moves through the 3-2 control valve and into the ACC circuit for the 2/4 accumulator. As pressure builds during band apply, it is modulated by the accumulator.





2-3 SHIFT OPERATION
The PCM controls a 2-3 shift by turning Shift solenoid 2 (SS2) OFF while Shift solenoid 1 (SS1) remains OFF. This results in spring force moving the 2-3 shift valve to the left side. In third gear, the P-14 band is released and the direct clutch is applied.
To release the 2/4 band, fluid under pressure in the D21 circuit moves through the 2-3 shift valve, servo release shuttle valve and 3-4 shift valve and several circuits. Fluid in the SR circuit from the 3-4 shift valve releases the 2/4 band by opposing fluid under modulated line pressure in the SA circuit.
To apply the direct clutch, fluid under pressure from the D21 circuit moves through the 2-3 shift valve. The 3-2 timing and 2-3 shift valve block the exhaust path for the DC circuit through the 34V circuit.





3-4 SHIFT OPERATION
The PCM controls a 3-4 shift by turning Shift solenoid 1 (SS1)ON while Shift solenoid 2 (SS2) remains OFF. This results in fluid pressure in the S1 circuit moving the 3-4 shift valve to the right side without moving the 1-2 shift valve because of the opposing pressure in the L34 circuit. In fourth gear, the 2/4 band and the direct clutch are applied.
To apply the 2/4 band, fluid under pressure in the D21 circuit moves through the 1-2 shift valve, 2-3 shift valve and 3-4 shift valve and several circuits. Fluid in the SA circuit from the 3-4 shift valve applies the 2/4 band. Fluid also moves through the3-2 control valve and into the ACC circuit for the 2/4 accumulator to modulate pressure during band apply.
The direct clutch continues to receive fluid under pressure from the D21 circuit through the 2-3 shift valve. The 3-2 timing valve and 2-3 shift valve block the exhaust path for the DC circuit through the 34V circuit.





4-3 SHIFT OPERATION
The PCM controls a 4-3 shift by turning Shift solenoid 1 (SS1) OFF while Shift solenoid 2 (SS2) remains OFF. This results in the loss of fluid pressure in the S1 circuit moving the 3-4 shift valve to the left side. In third gear, the 2/4 band is released and the direct clutch is applied.
To release the 2/4 band, fluid under pressure in the D21 circuit moves through the 2-3 shift valve, servo release shuttle valve and 3-4 shift valve and several circuits. Fluid in the SR circuit from the 3-4 shift valve releases the 2/4 band by opposing fluid under modulated line pressure in the SA circuit.
The direct clutch continues to receive fluid pressure from the D21 circuit moves through the 2-3 shift valve. The 3-2 timing and 2-3 shift valve block the exhaust path for the DC circuit through the 34V circuit.





3-2 SHIFT OPERATION
The PCM controls a 3-2 shift by turning Shift solenoid 2 (SS2) ON while Shift solenoid 1 (SS1) remains OFF. This results in fluid pressure in the S2 circuit moving the 2-3 shift valve to the right side. In second gear, the 2/4 band is applied and the direct clutch is released.
To release the direct clutch, the 2-3 shift valve blocks the D21 circuit and opens an exhaust path for the 34V circuit. The PCM controls the position of the 3-2 timing valve as it varies the rate of fluid exhaust from the DC circuit into the 34V circuit.
The SR circuit connects through the DCX circuit and servo release shuttle valve to the DC circuit. Pressure in the SR circuit cushions the servo apply.
To apply the 2/4 band, fluid under pressure in the D21 circuit moves through the 1-2 shift valve, 2-3 shift valve and 3-4 shift valve and several circuits. Fluid in the SA circuit from the 3-4 shift valve applies the 2/4 band.





FORWARD CLUTCH HYDRAULIC CIRCUITS
The LA4A-EL transaxle has a hydraulic circuit to control the apply and release of the forward clutch. The forward clutch is applied in D, 2 and 1 range/first, second, third and fourth gear. Although it is applied in fourth gear, the forward clutch does not transmit torque, because the forward one-way clutch overruns.
The path of fluid under line pressure during the apply of the forward clutch is as follows:
- From the manual valve to the FC and D21 circuits
- From the D21 circuit to the main regulator valve, line modulator valve and the 1-2, 2-3 and 3-4 shift valves
- From the FC circuit to the forward accumulator and forward clutch When the manual valve moves to the P, R and N positions, it provides an exhaust path for the FC and D21 circuits.





COASTING CLUTCH HYDRAULIC CIRCUITS
The LA4A-EL transaxle has hydraulic circuits to control the apply and release of the coast clutch. The coasting clutch is applied under the following conditions:
- D range/first, second and third gear (O/D OFF Switch ON)
- 2 range/second and third gear
- 1 range/first and second gear
The PCM controls the apply and release of the coasting clutch by changing the current to the 3-2 timing/coasting clutch solenoid. The result is that S3 hydraulic circuit pressure varies as follows:
- When the current is zero, S3 circuit pressure is too low to move the coast clutch valve, causing coasting clutch to apply.
- During fail-safe mode
- When the current is moderate-to-high, S3 circuit pressure is high enough to move the coasting clutch valve, causing coasting clutch to release.
The path of fluid under line pressure during the application of the coasting clutch is as follows:
- From the manual valve (D21 circuit), through the 3-4 shift valve, to the L123 circuit
- From the L123 circuit, through the coasting clutch valve, into the CCL circuit
- From the CCL circuit to the coasting clutch
When the coasting clutch valve moves to the release position, it blocks the Ll23 circuit and provides an exhaust path for the CCL circuit. In the D range/fourth gear, the movement of the 3-4 shift valve exhausts the L123 circuit, regardless of coasting clutch valve position.

FLUID PASSAGE LOCATION DESCRIPTION





TRANSAXLE CASE





CONVERTOR HOUSING





OIL PUMP





SEAL RINGS





SEAL RINGS BOTTOM VIEW