Design

Design

Transmission, general




The automatic transmission has five forward gears and one back-up (reverse) gear. The fifth gear is an overdrive which saves fuel during highway driving.
The mechanical components of the transmission are enclosed within the torque converter cover, the transmission housing and valve housing.
Gearshifts are controlled by an hydraulic operating system. Gearshifts take place without freewheeling and completely automatically in terms of load and speed.
The solenoid valves are located under the valve housing cover on the transmission, in the valve housing for the hydraulic system. These are activated by the transmission control module (TCM).
The transmission input speed sensor is electro-magnetic and acts on a toothed pulse wheel. By comparing the engine and transmission speeds, the control module can determine the amount of slippage in the torque converter.
The gear-shift position sensor has three separate functions:
- using an electrical route to inform the transmission control module (TCM) of the selected gear position
- to activate the back-up (reverse) light when the gear selector is in R-position
- To allow engine start if the gear selector is in P or N-position. This signal is also transmitted to the engine's control system and is used for drive position compensation of idle.
The transmission and final drive share a common oil pan. A dipstick in the transmission is used to check the oil level in the transmission.

Torque converter




The torque converter is between the engine and the automatic transmission.
When the engine is idling the pump effect is too weak to drive the turbine and the vehicle will not move. As the engine speed (RPM) rises it successively starts to drive in a gradual way. At higher engine speeds (RPM) the power transfer to the turbine can be up to 95%. The torque converter functions as an hydraulic clutch. It also amplifies the torque of the engine at lower engine speeds and therefore an automatic transmission does not require as many gears as a manual transmission.
The torque converter consists of a round metal casing which contains two impeller wheels and is filled with oil. One of the impeller wheels, the pump wheel, is fixed to the casing. Both are connected to the engine crankshaft and rotate with it. The other impeller wheel, the turbine wheel, is connected to the input shaft of the transmission and is driven by the oil which is pumped around by the pump wheel. The rotating impeller wheels and the oil in the torque converter "slip" slightly and creates a slight loss of power, which raises fuel consumption slightly.
Thanks to a third, smaller wheel, the stator wheel, the torque converter also reinforces the engine torque at low engine speeds.

Differential




The differential distributes power equally between the drive wheels, even if they are rotating at different speeds.
The differential consists of the differential housing, large and small side gears, shaft journals and thrust washers.
The differential has 6 gearwheels. The differential housing is completely sealed so that if a drive shaft is removed no dirt can penetrate and no oil can run out.