Torque Converter
The torque converter is located between the engine and the automatic gearbox and is filled with oil. It consists of a round metal casing that contains three impellers.
- The first impeller, the pump rotor, is attached into the torque converter's casing, which is connected to the engine's crankshaft via a carrier plate. The pump rotor rotates with the crankshaft.
- The second impeller, the turbine rotor, is connected to the transmission's input shaft and is driven by the oil that is circulated by the pump rotor.
- The third impeller, the stator, is located between the pump rotor and the turbine rotor.
There is a hydraulically controlled lock-up clutch with a friction plate in the torque converter. The turbine rotor can be connected with the torque converter's casing via the lock-up clutch. This reduces fuel consumption.
The torque converter functions like a hydraulic automatic clutch. At idle, the pump action is too weak to drive the turbine rotor and thus the vehicle is stationary. When the engine speed increases, the turbine rotor gradually starts to be driven. Thanks to the stator rotor, the torque converter can also reinforce the engine's torque when starting and at low driving speed.
The rotating impellers and the oil in the torque converter "slip" slightly. This gives a certain power loss, which slightly increases fuel consumption.
When the vehicle is moving the torque converter's reinforcement of the engine's torque is not needed. In this situation the lock-up function is activated and, at a certain speed, mechanically connects the transmission's input shaft with the engine. This is automatic and cannot be affected by the driver. The engine speed drops and, since the torque converter's slipping disappears, fuel consumption is also reduced.
For petrol engines, the torque converter has the slipping lock-up function. Lock-up can be used at engine speeds down to approx. 2000 rpm. Slipping lock-up can be used at engine speeds down to approx. 1200 rpm.
For diesel engines, the lock-up function is either fully locked or fully open. Lock-up can be used at engine speeds down to approx. 1200 rpm.
The torque converter's gear ratio and K-value depend on the engine for which the gearbox is designed.
| Engine | Gear ratio | K-value |
| B4204T9/T10 | 2, 13 | 186 |
| B4204T11/T12/T15 | 2.0 | 207 |
The K-value is a measurement of the torque converter's elasticity. The higher the K-value, the higher the stall speed.
| 1. Lock-up-clutch | 5. Stator |
| 2. Casing | 6. Oil pump |
| 3. Turbine rotor | 7. Input shaft |
| 4. Pump rotor |
Flywheel
To left: Flywheel for diesel engine (VED) adapted for the CPA converter (Centrifugal Pendulum Absorber).
To right: Flywheel for petrol engine (VEP) adapted for the STD converter (Super Long Travel Damper).
The flywheel alignment in relation to the torque converter is adapted to the mounting of the nuts against studs.
Oil pump
The oil pump is of "non-crescent" type and is located after the torque converter. It is driven by the engine's crankshaft via the torque converter housing.
The oil pump supplies the hydraulics with oil and supplies the other components of the transmission with oil for lubrication and cooling. Excess oil is routed back to the oil sump.
Cooling of the oil
The oil cooler is a plate oil cooler fitted on the gearbox. The engine's coolant and ambient air work as media for cooling and heating.