System Overview

General

General description




The AW 50-42 is an electronically-controlled four-speed automatic transmission with torque converter lock-up of the three highest gears. Because the transmission is controlled by an electronic control module gear-shifting can be controlled to allow the correct gear to be selected for driving conditions, engine load, driver's wishes, speed, etc. This yields good fuel economy combined with top-class performance and increased comfort by ensuring smoother shifts and lower noise levels.
A control module receives information about the selected gear and driving mode setting required. Together with signals from a number of sensors describing the running conditions of the car, this information is processed by the control module, which calculates optimum shifting and lock-up engagement points, depending on the driving mode selected. The control module then controls shifting and lock-up engagement by acting on the transmission hydraulic system. The control module also affects the quality of gear-changing by instantaneously modifying the hydraulic line pressure when shift is made.
The transmission's electronic control system receives continuous information from a number of sensors, as well as from the engine control system. Unlike a transmission with just a hydraulic control system, this enables the control system to adapt to extremely small changes in operating conditions and to control the various transmission functions so that the correct gear is always selected in accordance with the driving mode selected by the driver.
To facilitate fault-tracing, the control module has a built-in on-board diagnostic system (OBD II system) which records any faults in the control system and transmission, these can be read off via the data link connector (DLC).

Components




The transmission's mechanical components are enclosed in the torque converter housing (1), the transmission housing (2), with integrated final drive housing (3) and valve housing cover (4). The transmission speed sensor (5) in the transmission housing, the temperature sensor (6), the vehicle speed sensor (VSS) (7) and the gear-shift position sensor (8), which is affected by the gear selector shaft (control shaft) are, like other electric components, connected to a connector (9). The gear-shift position sensor, which informs the control module which gear has been selected, also contains a back-up (reversing) light and a Park/Neutral Position (PNP) switch.
The solenoid valves (SL, S1, S2, STH) are located in the hydraulic system valve housing (control system), which is located beneath the valve housing cover on the transmission. The lock-up solenoid valve SL regulates the torque converter lock-up function, and shifting valves S1 and S2 control shifting. These valves are activated by the transmission control module (TCM), as is the system pressure solenoid valve STH, which controls the transmission line pressure.
The transmission speed sensor (5) is activated by a toothed impulse wheel. By comparing the engine and transmission speeds, the control module can determine the amount of slippage in the torque converter. The electromagnetic vehicle speed sensor (VSS) (7) is activated by a toothed impulse wheel. The sensor sends vehicle speed status signals to the transmission control module (TCM).
An NTC type temperature sensor (6) measures the oil temperature. The control module uses this information to calculate shifting and lock-up engagement points (temperature controlled lock-up). The lower limit for temperature activated lock-up is at an oil temperature of 20-30 °C. Below this limit there is no lock-up function engagement so the transmission reaches its normal operating temperature faster. An upper limit with enhanced engagement occurs at approx. 115 °C. This reduces slippage and thus heat generation in the transmission. (There is no upper lock-up limit on B5202S and B5204S engines.)
The gear-shift position sensor has three separate functions:
- Transmitting a signal informing the control module which gear has been selected.
- Operating the back-up (reversing) lights when the gear selector is in position R.
- Preventing anyone starting the engine without first selecting position P or N. This signal is also transmitted to the engine management system and is used for drive compensation when the engine is idling.
The transmission and final drive share a common oil pan. A dipstick in the engine compartment is used to check the oil in the transmission.