Transaxle Electronic Control System
Transaxle Electronic Control System
Overview Electronic Transaxle Control
The electronic transaxle control system includes:
- a Transmission Control Module (TCM)
- a Transmission Range (TR) sensor
- an Output Shaft Speed (OSS) sensor
- 2 input shaft speed sensors each with pre-measured shims.
- 2 shift motors
- 2 clutch motors
- a Brake Pedal Position (BPP) switch
- a Brake Shift Interlock Actuator (BSIA)
- a starter inhibitor relay
- an Transmission Control Switch (TCS)/Grade Assist button
- an TCS/Grade Assist Indicator
Electrical System Components
Transmission Control Module (TCM)
The TCM is an assembly of an electronic module, sensors, and electrical actuators. It combines a control module and two electric motors for gear shifting. The primary function of TCM is to collect incoming data signals to control the transaxle, perform the interpretation of incoming data signals, communicate with the periphery and connect the electrical and mechanical contact to the signal transmitter and actuating elements. Vehicle and transaxle interface is achieved via two connectors; vehicle and transaxle connector. The transaxle connector plug is located at the TCM and is the electrical connection between the TCM and the clutch actuators and the sensors. The vehicle connector is located at the TCM and is the electrical connection between TCM and the vehicle. The TCM is a programmable module.
Transmission Range (TR) Sensor
The TR sensor detects the position of the manual control lever shaft. The TR sensor is mounted on the transaxle. The TR sensor allows the vehicle to start in PARK and NEUTRAL positions. The TR sensor output signal is linear over the measurement range and the TCM receives the selector lever position.
The signals of the TR sensor are used for the following functions:
- to recognize the selector lever position.
- to actuate the starter inhibitor relay.
- to actuate the reversing lamps.
No substitute signal is available for the TR sensor.
If the connection is cut, the vehicle cannot be started.
The TR sensor requires to be calibrated through the adaptive learning procedures.
Output Shaft Speed (OSS) Sensor
The OSS sensor measures the input speed of the output shaft. The rotation direction is not measured.
The OSS sensor is located in the transaxle housing above the rotor in the differential.
The OSS sensor is an inductive sensor which detects the vehicle speed by means of a impulse ring on the differential.
The signal is used for the following functions among other things:
- to determine the shift timing.
- to supply the vehicle speed input signal for the TCM.
Input Shaft Speed Sensors
Input shaft speed sensor 1 measures the input speed and the rotating direction of the input shaft 1. The input shaft can be stationary. Therefore it is necessary, that the sensor system can detect the stationary state of the input shaft accurate. By being stationary the sensor must not indicate speed unequal to 0 (also not, if the motor runs by high speeds). The slow rolling of the car has to be detected safely.
Input shaft speed sensor 2 measures the input speed of the input shaft 2. The rotation direction is not measured.
Shift Motors
Two electric motors are used to shift the gears in the transaxle, one motor for gears 1-3-5 and one motor for gears R-2-4-6. The gear shifting is made by two shift drums connected to shift motor pinion via two ideal gears. The max shifting force is 1500N (337 lb). The motors are integrated in the TCM and work independently of each other.
Clutch Motors
Two electrically commuted motors are used to actuate the double clutch in the transaxle - one motor per clutch. The motors work independently of each other. When the clutch is fully closed, the motor provides the holding torque in addition with spring force. The clutch motors work against a clutch spring and are disengaged when they reach the zero position (rest position) with the spring force.
Brake Pedal Position (BPP) Switch
The BPP switch is mounted on the brake pedal bracket.
The signal of the BPP switch is used by the PCM for the following functions:
- to activate the Brake Shift Interlock Actuator (BSIA) when the brake pedal is pressed in PARK.
No substitute signal is available for the BPP switch.
If the connection to the BPP switch is cut, the selector lever cannot be moved out of PARK.
Brake Shift Interlock Actuator (BSIA)
When the ignition is switched to the ON or RUN position, the BSIA is actuated by pressing the brake (signal from the BPP switch). This retracts the blocker so that the selector lever can be moved out of PARK.
Brake Shift Interlock Override
NOTE: If PARK is selected again, the selector lever is locked again.
If the brake signal should fail due to a malfunction, manual unlocking of the selector lever is possible.
For this, the release of the mechanism must be done by removing the side console panel and using a suitable tool press the BSIA lever until the selector lever can be moved out of PARK.
Starter Inhibitor Relay
The relay prevents the engine starting in selector lever positions R, D and L.
The relay obtains the information about the position of the selector lever directly from the TR sensor.
Transmission Control Switch (TCS) Button
The TCS button is located on the selector lever.
Grade Assist improves vehicle handling in hilly terrain or mountainous areas by providing additional engine braking and extends lower gear operation on uphill climbs. Additional engine braking is provided through the automatic transaxle shift strategy which reacts to vehicle inputs including vehicle acceleration, accelerator pedal, brake pedal and vehicle speed. The transaxle will select gears that will provide the desired engine braking, based on the vehicle inputs, the engine rpm during engine braking will increase. It is recommended to return to DRIVE mode on flat terrain to provide the best fuel economy and transaxle function. The transaxle returns to Overdrive (O/D) and grade assist is cancelled when the TCS is pressed again.
TCS/Grade Assist Indicator
The TCS/Grade Assist indicator is located in the Instrument Cluster (IC).
It tells the driver that shifting into 6th gear is prevented by the transaxle control.
The O/D/Grade Assist light flashes to tell the driver that the transaxle control has switched to the emergency operating mode.
Emergency Operating Program
If correct gear shifting can no longer be guaranteed due to failure of certain signals, the TCM changes to an emergency operating program.
The driver is informed of the operation of the emergency operating program by the illumination of the powertrain warning indicator in the IC.
Continued motoring is guaranteed in the following limited conditions based on the failure:
- 1st, 3rd and 5th gear if a fault with clutch 2 and/or relational components occurs.
- 2nd, 4th, 6th and reverse if a fault with clutch 1 and/or relational components occurs.