General System Description
AUTOMATIC TRANSMISSION 096, GENERAL INFORMATIONTransmission
The type 096 automatic transmission has four forward speeds and features electronic control. Engine power is passed on to the transmission by the torque converter, a fluid coupling that multiplies engine torque for better acceleration from rest and at low speeds.
Another feature of the transmission's electronic control unit is self-diagnosis capability-circuitry that monitors the normal range of operating values, detects unusual values and other faults, and stores fault information for later recall. Volkswagen dealer technicians use special electronic test equipment to access the control unit fault memory and display coded fault information.
Torque Converter
The torque converter is a fluid coupling. Curved impeller vanes inside the housing are driven by the engine. They set up a flow of ATF that drives the vaned turbine wheel opposite it, connected to the planetary gearbox in the transmission.
A central set of vanes inside the torque converter, called the stator, provides torque multiplication. Starting out from rest, a one-way clutch keeps the stator stationary. Its curved vanes redirect the impeller's flow of ATF to a different part of the turbine. At higher speeds, when there is little or no speed differential between the impeller vanes and the turbine, the stator freewheels and torque multiplication ceases.
PLANETARY GEARBOX
Operation of the transmission itself is hydro-mechanical. A torque converter alone cannot supply the torque multiplication needed for all driving conditions. The torque converter drives through a planetary gearbox that can transfer power at different drive ratios.
Automatic transmission fluid (ATF), under pressure, actuates and releases a series of hydraulic clutches and brakes in the planetary gearbox to effect changes in gear ratio. Hydraulic pressure in the system is maintained by the ATF pump, and the fluid is directed to act on the various clutches and brakes by the valve body.
VALVE BODY
The valve body controls gear selection in two ways. The selector lever, operated by the driver, is mechanically linked to the valve body and operates a manual valve. The manual valve has some direct control over gear selection. Other other control of gear selection is by electronic control.
ELECTRONIC CONTROL
Electronic control allows transmission to perform differently under different conditions, and provides much greater flexibility. Seven solenoid valves in the valve body route ATF flow and pressure electrically. An electronic control unit, mounted under the rear seat, operates the solenoids and selects drive ratios and shift points in response to inputs such as vehicle speed and engine load.
With the driver's selection of the Sport or Economy modes, the electronic control unit can operate according to two different programs. The Sport mode raises shift points, delaying shifts to the next higher gear to increase torque for better response and acceleration. The Economy mode is programmed to shift to the next higher gear as soon as is practical for the driving conditions, in order to maximize fuel economy.
In the absence of any electronic control, the transmission reverts to a "limp-home" mode controlled by the manual valve in the valve body. It can also be manually shifted into 1st and Reverse gears. In any other Drive position, hydraulic control operates the transmission in 3rd gear only.
CAUTION: - The transmission ECU must be reprogrammed to its basic settings whenever the throttle valve, throttle valve potentiometer or throttle cable is adjusted or replaced, and whenever the trans- mission ECU or the engine are replaced.