System Overview

General and components

General




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 gives good fuel economy combined with top-class performance and increased comfort by ensuring smoother gearshifting and lower noise levels.
A control module receives information about the selected gear and driving mode setting. This, together with signals from a number of sensors providing information about the running conditions of the car, is processed by the control module. The control module calculates the optimum gear shifting and lock-up engagement points, depending on the driving mode selected. The control module then controls gearshifting and lock-up engagement by acting on the transmission hydraulic system. The control module also affects the quality of gearshifting by adjusting hydraulic line pressure at the instant of gear shifting.
The transmission's electronic control system receives continuous information from a number of sensors, as well as from the engine management system. Unlike transmissions with exclusively hydraulic control systems, the control system can adapt to extremely small changes in operating conditions. It can control the different transmission functions so that the correct gear for the driving mode selected by the driver, is always selected.
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 faults 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 in the 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 acted on by the gear shift linkage rod are, like other electric components, connected to a connector (9).
The gear-shift position sensor, which informs the control module the gear that 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. Lock-up solenoid SL regulates the torque converter lock-up function. Both the gear shift solenoids S1 and S2 control shifting. These valves are activated by the transmission control module (TCM), as is the line pressure solenoid valve STH, that 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 receives this information and uses it to calculate gear 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 also occurs at approximately 115° C. This reduces slippage and therefore heat generation in the transmission.
The gear-shift position sensor has three separate functions:
- Transmitting an electronic signal to inform the control module which gear has been selected.
- Operating the back-up (reversing) lamp when the gear selector is in position R.
- Preventing the engine from being started unless the gear selector is in the P or N positions.
The transmission and final drive share a common oil pan. A dipstick in the engine compartment is used to check the transmission oil.