Hydraulic Control System: Notes
- The hydraulic pressure during gear shifting engages the clutches and applies the brakes. It is regulated by the pressure control valve. The hydraulic pressure that works on the pressure control valve is further regulated by the pressure control solenoid valve which functions under the control of the transaxle control module. The transaxle control module controls the solenoid valve using a duty cycle signal, thus providing appropriate regulation of the hydraulic pressure.
- The transaxle control module decides the timing of the gear-shifting period (during which it performs hydraulic pressure control for gear shifting) according to the change in the kickdown drum rotating speed that it detects. The module identifies the time just before the kickdown brake is applied and uses that as the timing for initiating control of the hydraulic pressure that is to be applied to the kickdown brake.
- TCM detects torque change ratio (turbine speed change ratio in torque converter). If input torque is larger than the pre-set torque in TCM, TCM controls the duty of PCSV and changes oil pressure. Shift shock will be alleviated due to torque control. Torque change ratio is applied differently according to each pattern.
- When the transaxle is cold, the fluid viscosity is high, causing slower oil pressure response. In such conditions, the transaxle control module provides a correction for the oil pressure by changing the control duty of the pressure control solenoid valve. This control is performed when the fluid temperature as indicated by the oil temperature sensor is lower than 60°C (140°F).
- After the engine has been started and the vehicle is in motion, the transaxle control module continues to refine its performance for smoothest possible gear shifting.
The hydraulic control system consists of an oil pump that generates hydraulic pressure for A/T. It also has valves and solenoid valves that control the hydraulic pressure or switch the oil passage. The valves and solenoid valves are all built into the valve body. For better and smoother shift quality, the rear clutch pressure is controlled independently, 4th-->2nd gear skip shift is available and the line pressure at 3rd/4th gear is reduced.
There are 6 solenoid valves are incorporated on the valve body. Two of those are duty-controlled type and the rest are ON/OFF type.
- Duty control type: Pressure control solenoid valve A/B, Damper clutch control solenoid valve
- ON/OFF type: Shift control solenoid valve A/B/C
If the mechanical malfunction such as valve sticking occurred, the fail-safe valve has been adopted to prevent interlock. The line pressure is regulated at the 4th speed to improve the efficiency of power transmission. This function is performed by High-low pressure valve and regulator valve.