Automatic transmission in section
1 - planetary gear row; 2 - friction; 3 - oil radiator; 4 - torque converter; 5 - tachometer drive; 6 - bevel gears of the differential mechanism; 7 - driven bevel gear.
Already from the beginning of production of Renault 19, modifications GTS and TELEX (1.7L engine) could be equipped with an electronically controlled 3-speed automatic transmission (internal designation - MB3). Since 1991, an improved automatic 4-speed transmission based on the MB3 transmission, which is also controlled by a microprocessor, was also offered for the 1.8S modification. The designation of this automatic 4-speed transmission, developed jointly with Volkswagen, is "AD4". It is controlled by a dual shift program: by driver selection and by a microprocessor.
The microprocessor constantly maintains the oil pressure at the optimum level. The gearbox has a mechanical torque converter lock-up in the third and fourth gears. The gear ratio of the fourth gear is defined as "Overdrive" (overdrive).
Operating principle of the AD4 automatic 4-speed gearbox
(Source is located on the website: «renaultbook»)
In automatic transmissions, the engine drives the pump sprocket in the torque converter. The fluid in the converter, which is set in rotation, is supplied under pressure via the guide wheel to the turbine wheel, which is set in motion. There is a certain difference in rotation speed 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 so-called "slippage". In the AD4 automatic transmission on the Renault 19, the torque converter in third and fourth gear is converted by mechanically bypassing the converter into a fixed two-way drive.
This prevents unwanted slippage, which leads to increased fuel consumption with a decrease in the transmitted force. The element of the automatic transmission is the so-called planetary rows. They are a toothed wheel that ensures the rotation of 3 other toothed wheels. Above this device is a toothed wheel with internal engagement (epicycle). Each of these 2 design groups is connected to each other and forms its own small two-speed gearbox. The gear ratio is changed by fixing or releasing parts of the planetary row. Shifting is carried out without interrupting the transmission of traction from the engine to the wheels. Fixing and releasing are provided by hydraulically controlled clutches and brakes.