Cross section of an automatic transmission
1 - planetary gear; 2 - clutch; 3 - oil cooler; 4 - torque converter; 5 - tachometer drive; 6 - conical wheels of the differential mechanism; 7 - driven bevel wheel.
Since the start of production of Renault 19, modifications of GTS and TELEX (engine 1.7 l) could be equipped with an electronically controlled 3-speed automatic transmission (internal designation - MB3). Since 1991, for the 1.8S modification, an advanced automatic 4-speed gearbox based on the MB3 gearbox was also offered, which is also controlled by a microprocessor. The designation of this jointly developed «Volkswagen» automatic 4-speed transmission is «AD4». It is controlled by a dual shift program: driver-selectable and microprocessor controlled.
The microprocessor constantly maintains the oil pressure at the optimum level. The gearbox has a mechanical torque converter lock in third and fourth gears. The fourth gear ratio is defined as «Overdrive» (overdrive).
The principle of operation of the automatic 4-speed gearbox AD4
In automatic transmissions, the engine drives the pump sprocket in the torque converter. The fluid of the converter set into rotation is supplied under pressure by means of a guide wheel to the turbine wheel, which is set in motion. There is a certain speed difference between the pump sprocket and the turbine wheel. It is large during acceleration and decreases with increasing speed. In a conventional automatic transmission there is always a so-called «slippage». In the AD4 automatic transmission on the Renault 19, the torque converter in third and fourth gear is converted by mechanically bridging the converter into a fixed two-way drive.
In this way, unwanted slippage is prevented, which leads to increased fuel consumption with a decrease in the transmitted force. An element of an automatic transmission are the so-called planetary gear sets. They are a gear that drives 3 other gears. Above this device is a gear wheel with internal gearing (epicycle). Each of these 2 structural groups is connected to each other and forms its own small two-speed gearbox. The change in gear ratio occurs by fixing or releasing parts of the planetary gear set. Shifting is carried out without interrupting the transmission of traction from the engine to the wheels. Locking and release is provided by hydraulically controlled clutches and brakes.