Introduction

Design and Function







The AW 50-42 is an electronically controlled four speed automatic transmission with torque converter lock-up in the three highest gears. The transmission is controlled by an electronic control module, making it possible to control gear shifting so that the correct gear is always selected consistent with 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 concerning the selected gear and driving mode. 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 influencing the transmission hydraulics. 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 module and these can subsequently be read off using the Data Link Connector (DLC). The control module also affects the quality of gear-changing by instantaneously modifying the hydraulic line pressure the moment a shift is made.

The transmission's electronic control system continuously receives information from a number of sensors, as well as from the engine control system. Unlike a transmission with only a hydraulic control system, this enables the control system to accommodate 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 selected shifting mode.

The slippage which normally occurs in the torque converter and in clutches and brakes during engagement is registered and stored in the control module memory. This information is used to calculate the engagement times for the various gears. (This slippage time function has not yet been incorporated in the transmission control system. The function is intended for future use.) By allowing the control module to modulate the system pressure in response to the engagement times, the shifting comfort level is increased, and wear on mechanical components is minimized, thereby significantly reducing the need for service.