BMW 3 Owners & Service Manuals

BMW 3: 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 GA8P75HZ transmission:

  • 2 fixed multidisc brakes (brakes A and B)
  • 3 rotary multidisc clutches (clutches C, D and E).

The multidisc clutches (C, D and E) feed the drive torque to the planetary gear. The multidisc brakes (A and B) support the torque against the transmission housing.

The clutches and brakes are closed hydraulically. For this purpose, oil pressure is applied to a piston enabling it to press the disc sets together.

Automatic transmission
Overview of the GA8P75HZ transmission

  1. Dual-mass flywheel
  2. Electric motor
  3. Drive chain of the mechanical transmission oil pump
  4. Gear set 1
  5. Gear set 2
  6. Gear set 3
  7. Gear set 4
  8. Parking lock
  9. Multidisc clutch D
  10. Multidisc clutch C
  11. Multidisc clutch E
  12. Common sun gear for gear set 1 and 2
  13. Multidisc brake B
  14. Multidisc brake A

The shift elements of the GA8P75HZ transmission correspond in number and arrangement to those of the GA8HP70Z transmission. The 8 gears are triggered in the same way.

The following table shows what shift element is closed in what gear:

Automatic transmission

Due to the elimination of the torque converter, the multidisc brake B of the automatic transmission has been modified. In the GA8P75HZ transmission driving off and crawling are realized via the multidisc brake B. For this the number of discs is increased and their diameter enlarged. To guarantee sufficient cooling, transmission oil is passed through the integrated drive-off element (multidisc brake B) as required.

Mechatronics module

The mechatronics module is a combination of the hydraulic shift unit and the electronic control unit.

The control unit is arranged in the lower area of the transmission and is surrounded by the oil sump.

The hydraulic shift unit contains the mechanical components of the transmission control unit such as valves, dampers and actuators.

The mechatronics module was adapted for operation in the GA8P75HZ, for example the slip at the starting clutch (multidisc brake B) is now calculated via the speed signal of the sensor (3). The transmission input speed is determined in the GA8P75HZ transmission with help of the rotor position sensor of the electrical machine.

Automatic transmission
Mechatronics module GA8P75HZ transmission

  1. Parking lock magnet
  2. Hydraulic shift unit
  3. Speed sensor, planet spider, gear set 1
  4. Electronic control unit
  5. Output speed sensor
  6. Electronic pressure control valves and solenoid valves

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