BMW 3 Owners & Service Manuals

BMW 3: Dual-mass flywheel

In order to reduce fuel consumption and CO2 emissions, high-charged engines are used, the number of cylinders is reduced and the drivable speeds are lowered.

However, with these measures the torsional vibrations of the crankshaft are increased as a result of the acceleration during the work cycle and deceleration during the compression cycle. This irregular rotation is the reason for torsional vibrations in the downstream drive train.

To isolate these torsional vibrations a dual-mass flywheel is used in the automatic transmission of the G20 PHEV. The dual-mass flywheel establishes the mechanical connection between the crankshaft of the combustion engine and the electrical machine. It consists of a torsional vibration damper and a centrifugal pendulum.

The dual-mass flywheel weighs approximately 11 kg/24 lbs and can be replaced separately in the event of a fault.

Automatic transmission
PHEV, dual-mass flywheel of the GA8P75HZ transmission

  1. Torsional vibration damper
  2. Centrifugal pendulum
  3. Dual-mass flywheel

The centrifugal pendulum is integrated in the dual-mass flywheel and can almost fully absorb the occurring torsional vibrations. It comprises a flange, on which masses can move on defined tracks.

Arch-shaped curved tracks are integrated in the flange and in the masses, which serve as running tracks. The masses are connected to the flange via two rollers and can move back and forth along the curved tracks.

Automatic transmission
GA8P75H, structure and operating principle of the centrifugal pendulum

  1. Flange
  2. Mass
  3. Rollers
  1. Oscillating mass
  2. Torsional vibration of the engine

The centrifugal pendulum consists of several oscillating masses (dynamic vibration absorbers). They vibrate contrary to the torsional vibrations of the combustion engine and compensate for these. At low engine speeds, i.e. precisely when the annoying vibrations occur most, the deflection of the dynamic vibration absorbers is particularly big. This also leads to improved acoustics in the vehicle interior.

Electric motor

Another new feature of the GA8P75HZ transmission was the integration of the electrical machine, an additional torsional vibration damper and a separation clutch in the transmission housing. These are located behind the dual-mass flywheel. Together with the dual-mass flywheel, the electrical machine, the torsional vibration damper and the separation clutch occupy the space of the hydraulic torque converter.

Further information on the electrical machine, the additional torsional vibration damper and the separation clutch can be found in the chapter entitled "Electrical Machine".

Automatic transmission
Electrical machine in the GA8P75HZ transmission

  1. Electric motor


     Shift elements

    Brakes and clutches are described as shift elements which make possible the shifting and changing of all gears. Like in the GA8HP70Z transmission, the following shift elements are also used in the G

     Oil supply

    The basic functions of the oil circuit of the GA8P75HZ transmission correspond to those of the GA8HP70Z transmission. The oil has the following tasks: Lubrication Control of the shift elements Co

     Service information

    Electronic emergency gearbox release As with the conventional 8-speed automatic transmission, the GA8P75HZ also has an electrical emergency release option. In conventional vehicles the starter motor


     Setting the speed

    Maintaining and storing the speed Press the rocker switch up or down once while the system is interrupted. The system will be activated. The current speed is maintained and stored as desired speed. The stored speed is displayed on the speedometer. DSC Dynamic Stability Control is switched on, if

     Steering wheel

    Safety information Warning Steering wheel adjustments while driving can lead to unexpected steering wheel movements. Vehicle control could be lost. There is a risk of accident. Adjustng the steering wheel while the vehicle is stationary only. Manual steering wheel adjustment 1. Fold the lever dow

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