ZF 6HP26 transmission

This ZF 6HP26 transmission used in Jaguar’s, BMW’s and other cars.

A world first concept goes into production in the middle of July 2001: The ZF 6-speed automatic transmission for passenger vehicles, which has gone from the development to the production stage in just under 4 years, will set standards in drive technology. The new product offers more than just fundamentally better performance than standard 5-speed automatic transmissions; it is also lighter, more compact and significally more economical to drive. This apparent “squaring of the circle” was made possible by ZF engineers by developing a new transmission concept based on the Lepelletier-gear train and achieving improvements in the production process as well as in the Mechatronik, the transmissions electronic control system. The new product comes into service first in the new BMW 7 series.

The 6-speed automatic transmission has considerably more to offer than just an extra gear”, commented Dr Michael Paul, Chairman of the Board at ZF Getriebe GmbH, Saarbrücken, about his current show piece product. “It is a completely new generation of transmission which will also noticeably change driving characteristics of cars for the better. These characteristics range from lower fuel consumption and weight reduction at improved performance levels to a very innovative Mechatronik, E-shifting and standby control.”

High performance – less fuel consumption

In tests simulating normal driving conditions, the 6HP26, the internal ZF name for the new production model, used between 5 and 7% less fuel – and this at higher driving performance levels: Accelerating from 0 to 100 km/h, the 6-speed automatic transmission is achieving improvements of between 2 and 5%. Other than by reason of the sixth gear, the lower fuel consumption is made possible by a low viscosity oil developed at ZF, Stand-by-Control (SBC) and other detailed measures.

The new transmission is designed for an input torque of 600 Newton meters, in other words for high performance cars with 8 to 12 cylinders. The overall gear ratio was selected to achieve comparatively low revolutions in the “long” 6th gear ratio, and also at high speeds. Noise build-up and fuel consumption are favourable compared to a 5-speed automatic transmission.

New gear train

At the heart of the ZF 6-speed automatic transmission is a new gear train concept based on the Lepelletier-gear train. With this new concept, the six gears can be realized with significantly fewer components: For the current 5-speed automatic transmissions, 3 gear trains and six clutch elements were needed; for the six gears, one simple and one Ravigneaux-gear train, in combination with five clutch elements suffice. The result is a significant weight reduction of about 11 kilos in total.

The use of plastic also reduces weight: The oil pan and base body of the Mechatronik are no longer made of metal; in addition, the 6-speed automatic transmission has absolutely no freewheeling features. Their functions are carried out by a substantially improved electronic control system.

Electronic control system

The Mechatronik module is high tech, with a combination of a hydraulic selector unit and electronic components controlling the new 6-speed automatic transmission. The fine tuning of all shifting processes in the transmission is made more precise by the Mechatronik. For the driver of a vehicle with the 6-speed automatic transmission, this means optimal shift quality and increased driver comfort. The shifting electronics not only give signals to the driver, but also receives information about the current driving situation: in this way, it is able to recognize and react to (for example with optimal shift timing) the condition of the transmission, drag resistance (e.g. weight and slope) and driver behaviour. In this way, it caters for many variations, ranging from very sporty to very economical driving styles.

A further new feature for automatic transmissions is made possible by the 6HP26’s electronic control system; the “Stand-by-Control” (SBC). The electronics control the input clutch in the transmission such that the engine is disconnected from the driveline when the vehicle is stationary, even when in gear.

Outlook

The beginning of the 6HP26 series production for upper range cars is only the start. In the medium-term, ZF will offer a complete 6-speed range which will be appropriate for middle-range car engines as well as 4 wheel drive vehicles.