|Fuel savings with ZF automatic transmissions compared to earlier models. The new 6-speed delivers up to 19% in fuel savings compared to an old 3-speed. Click to enlarge.|
ZF has introduced a new second-generation 6-speed automatic transmission that delivers fuel savings of up to 3% in a gasoline-engine vehicle and up to 6% in a diesel.
The use of a new torque converter in combination with optimized transmission control and hydraulics make the multi-ratio automatic 6-speed transmission of the second generation even more efficient than its predecessor, thereby contributing to the increased fuel savings. BMW began offering the new rapid shift transmission in the 3 Series Coupé and the X3 in September.
Response times have been reduced by up to 50% and, for the first time, direct double shifts without interruption are possible. The rapid shift transmission is designed for an input torque of up to a maximum 850 Nm—i.e. for light-duty vehicles with engines of up to twelve cylinders.
|A new torque converter enables reduced shift times at low fuel consumption while maintaining comfort.|
In order to optimize fuel consumption, ZF has developed a consistent shift strategy for the torque converter lock-up clutch with the objective of closing the clutch completely as soon as possible.
Further development of the hydraulic system enables downshifts of up to four stages to occur without any time losses or noticeable deceleration. A separate pressure regulator directly controls the respectively need clutch so that no additional time is required for jumping a drive stage. Called the target gear finding mechanism, this makes the shift process precise.
On the basis of the data received on load conditions, the driving situation, and the speed of acceleration, the improved control software determines whether one-stage or multiple stage downshifts are required.
ZF reduced the shift time by half compared to its previous transmissions, and response time is rapid whether one gear step or several are shifted. If—at an approximate driving speed of 70 kph in sixth gear—the transmission receives a kickdown signal, it needs just 100 milliseconds to trigger the change from sixth to second gear.
As with earlier ZF transmissions, the planetary transmission system—based on a Lepelletier gear set—is at the center of the new automatic ZF 6-speed transmission. Thus, six gears can be realized with significantly less components. In the past, only three gear sets and six shift elements were needed for the automatic 5-speed transmission; today, a simple planetary gear set suffices as well as a Ravigneaux gear set in combination with five shift elements.
This results in a weight reduction of approximately eleven kilograms (24 pounds) compared to the 5-speed automatic. Increased use of plastics contributes to the reduction of weight and consequently fuel consumption.