Part 1
Electronic Component Description
General
The electronic control system of the MVA 4-speed automatic transaxle consists of the control listed below.
Construction
The configuration of the electronic control system in the MVA 4-speed automatic transaxle is as shown in the following chart.
Layout of Main Components
Shift Indicator
Solenoid Valves, Speed Sensors and Switches
Solenoid Valves
Solenoid Valves SL1, SL2 and SLT
* In order to provide a hydraulic pressure that is proportion to current that flows to the solenoid coil, the solenoid valves SL1, SL2, and SLT linearly control the line pressure and clutch and brake engagement pressure based on the signals from the ECM.
* The solenoid valves SL1, SL2, and SLT have the same basic structure.
Solenoid Valves S4 and DSL
* The solenoid valves S4 and DSL use a three-way solenoid valve.
* The solenoid valve S4 when set to ON controls the 3-4 shift valve to establish the 4th by changing over the fluid pressure applied to B3 brake and C3 clutch.
* The solenoid valve DSL controls the B2 control valve via the C2 lock valve when the transaxle is shifted in the R or L position.
* During lock-up, the lock-up relay valve is controlled via the C2 lock valve.
Apply Orifice Control
This control is effected by the B3 orifice control valve. The B3 orifice control valve has been provided for the B3 brake, which is applied when shifting from the 4th to 3rd. The B3 orifice control valve is controlled by the amount of the line pressure in accordance with shifting conditions, and the flow volume of the fluid that is supplied to the B3 brake is controlled by varying the size of the control valves apply orifice.
Construction and Operation of Main Components
ATF Temperature Sensor
* The ATF temperature sensor is installed in the lower valve body for direct detection of the fluid temperature.
* The ATF temperature sensor is used for correction of clutch and brake pressure to keep smooth shift quality every time.
Input Turbine Speed Sensor and Counter Gear Speed Sensor
The MVA 4-speed automatic transaxle uses an input turbine speed sensor (for the NT signal) and a counter gear speed sensor (for the NC signal). Thus, the ECM can detect the timing of the shifting of the gears and appropriately control the engine torque and hydraulic pressure in response to the various conditions.
* The input turbine speed sensor detects the input speed of the transaxle. The direct clutch (C2) drum is used as the timing rotor for this sensor.
* The counter gear speed sensor detects the speed of the counter gear. The counter drive gear is used as the timing rotor for this sensor.
Clutch Pressure Control
Clutch to Clutch Pressure Control
A clutch to clutch pressure control is used for shifting from the 1st to 2nd gear, and from the 2nd to 3rd gear. Solenoid valves SL1 and SL2 are actuated in accordance with the signals from the ECM, and this output pressure is guided directly to the control valves B1 and C2 in order to regulate the line pressure that acts on the B1 brake and C2 clutch. As a result, high response and excellent shift characteristics have been achieved.
Clutch Pressure Optimal Control
The solenoid valve SLT is used for optimal control of clutch pressure. The ECM monitors the signals from various sensors such as the input turbine speed sensor, allowing solenoid valve SLT to minutely control the clutch pressure in accordance with engine output and driving conditions. As a result, smooth shift characteristics have been realized.
Line Pressure Control
Through the use of the solenoid valve SLT, the line pressure is optimally controlled in accordance with the engine torque information, as well as with the internal operating conditions of the torque converter and the transaxle.
Accordingly, the line pressure can be controlled minutely in accordance with the engine output, traveling condition, and ATF temperature, thus realizing smooth shift characteristics and optimizing the workload in the oil pump.
Shift Control in Uphill/Downhill Traveling
General
This control helps minimize the gear shifting when the driver operates the accelerator pedal while driving on a winding uphill or downhill road in order to ensure a smooth drive.
Shift Control in Uphill Traveling
When the ECM detects uphill travel, it prohibits upshifting to the 4th after downshifting to the 3rd.
Shift Control in Downhill Traveling
If a signal indicating that the driver has operated the brake pedal is input while the ECM detects downhill travel, it downshifts from the 4th to 3rd.
Uphill/Downhill Judgment
The actual acceleration calculated from the speed sensor signal is compared with the reference acceleration (based on level road travel) stored in the ECM to determine uphill or downhill travel.
Flex Lock-up Clutch Control
* In addition to the conventional lock-up timing control, flex lock-up clutch control is used.
* This flex lock-up clutch control regulates the solenoid valve DSL as an intermediate mode between the ON and OFF operation of the lock-up clutch.
* The flex lock-up clutch control operates during acceleration, in the 3rd and 4th gears in the D position, and during deceleration, in the 3rd and 4th gears in the D position, and in the 3rd gear in the 3 position.
* During acceleration, the partition control of the power transmission between the lock-up clutch and torque converter greatly boosts the transmission efficiency in accordance with the driving conditions, improving the fuel economy.
* During deceleration, the lock-up clutch is made to operate. Therefore, fuel-cut area is expanded and fuel economy is improved.
Flex Lock-up Timing
Diagnosis
* When the ECM detects a malfunction, the ECM makes a diagnosis and memorizes the failed section. Furthermore, the MIL (Malfunction Indicator Lamp) in the combination meter illuminates or blinks to inform the driver
* At the same time, the DTCs (Diagnosis Trouble Codes) are stored in memory.
Fail-Safe
This function minimizes the loss of driveability when any abnormality occurs in each sensor or solenoid.
