Hydraulic Control System

HYDRAULIC CONTROL SYSTEM [LA4A-EL]
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 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 follows 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 ranges, 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 Park, Neutral and Reverse ranges. The absence of D21 circuit pressure in Park, Neutral, and Reverse ranges allows for a higher line pressure.

EPC solenoid control





- At a low current, the TV circuit pressure will be higher, resulting in high line pressure.
- At a high current, the TV circuit pressure will be lower, resulting in lower line pressure.
- In a fail-safe mode, maximum TV circuit pressure will be present in maximum line pressure.

Solenoid Circuit
Overview





- The LA4A-EL transaxle has hydraulic circuits to control the scheduling of shifts. The PCM has control of four solenoids (SST, SS2,3-2 T/CSS, and TCC) to do the following things:
- Move shift valves to provide transaxle operation in 1st, 2nd, 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