4.3. GA8HP transmission: Notes
In the F10, the new automatic transmissions GA8HP45Z and GA8HP70Z with eight forward gears and one reverse gear is used.
Highlights
- Significantly enhanced gearshifts spontaneity
- Greater driving and shifting comfort as a result of a closer gear ratio
- Higher precision control of the converter lockup clutch at low engine loads
- High power transmission of the converter lock-up clutch
- Reduced fuel consumption (-5 to -6 %).
The GA8HP45Z and GA8HP70Z are new developments and will gradually replace the established 6-speed automatic transmissions GA6HP19Z TU and GA6HP26Z TU. The overall gear ratio has been increased from 6.04 to 7.07; the gear to gear ratios have are now closer, thus also reducing the differences in speed when shifting gear. The weight of the transmission has been reduced significantly using a plastic oil pan and other light weight components.
The Electronic Transmission Control (EGS) control unit is integrated in the control unit framework of the electronic immobilizer EWS. This provides better protection against theft.
The operation takes place using the gear selector switch or the shift paddles (option 2TB, sport automatic transmission, via the steering column switch cluster SZL).
In the converter, second-generation mechanical torsional vibration dampers are used:
- Turbine torsional vibration damper (TTD)
- Double-damper converter (ZDW) (Used on diesel X5 and E90 models).
The function and structure of the torque converter are described in the "E70 Automatic transmission" training material available on TIS and ICP.
The vibration isolation reduces the proportion of slip on the converter lockup clutch and enables a larger operating range with the converter lockup clutch closed. This reduces the fuel consumption by 5% to 6% in the consumption cycle (KV01) compared to the TU 6-speed automatic transmission used until now.