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.
Overview of the GA8P75HZ transmission
- Dual-mass flywheel
- Electric motor
- Drive chain of the mechanical transmission oil pump
- Gear set 1
- Gear set 2
- Gear set 3
- Gear set 4
- Parking lock
- Multidisc clutch D
- Multidisc clutch C
- Multidisc clutch E
- Common sun gear for gear set 1 and 2
- Multidisc brake B
- 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:
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.
Mechatronics module GA8P75HZ transmission
- Parking lock magnet
- Hydraulic shift unit
- Speed sensor, planet spider, gear set 1
- Electronic control unit
- Output speed sensor
- Electronic pressure control valves and solenoid valves
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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
SEE MORE:
Steptronic transmission: BMW
Digital Key
Concept
BMW Digital Key allows the vehicle to be unlocked
and locked, as well as started, with a
compatible smartphone.
General information
BMW Digital Key varies by country and may be
unavailable.
To unlock and start a vehicle with a compatible
smartphone, a digital key must be installed on
this s
Wireless charging tray
Concept
The wireless charging tray enables the following
functions to be performed without cables:
Charging the rechargeable battery of a mobile
phone with Qi capability and of other mobile
devices, which support the Qi standard.
Charge the BMW Display key, see Owner's
Manual for the vehicle.
