|The Zeroshift transmission offers better fuel economy than automatic transmissions while preserving ease of driving. Click to enlarge. Source: Zeroshift.|
Zeroshift, Ltd. launched the second generation of its automated manual transmission (earlier post) at the SAE World Congress. The Zeroshift transmission allows a manual transmission to change gear in zero time, thereby offering potential fuel economy improvements from driveline efficiency and the best possible vehicle acceleration.
The Zeroshift concept is to remove the synchromesh components within a manual transmission and replace them with a ring drive system.
The latest version uses a new drive ring system, combined with other developments, to deliver reductions in cost, weight and packaging volume while improving durability, fuel economy, emissions and refinement.
The first generation Zeroshift was pneumatically operated and used six drive elements—specially contoured metal “bullets”—to engage and disengage the drive gears in a similar manner to dog clutches.
|A simplified rendering showing the rings and bullets (red and blue).|
In the second generation system, these have been replaced by a pair of interlocking rings, each incorporating the three drive elements in a single forged component and operated by shift forks.
When shifting from neutral, ring one is engaged to take up drive while ring two is engaged within a few degrees of revolution to takeup backlash. The next shift is made with ring two taking up the drive and ring one taking the backlash. As ring two is unloaded during the change, it requires less than 1/20th the axial force required by a conventional synchromesh.
The control system, also developed and calibrated by Zeroshift, coordinates gearshift actuation, engine management and clutch operation to provide full control over the driveline during gearshifting.
Zeroshift improved the transmission’s refinement and durability through the design of the working surfaces. Shift forces also have been reduced from around 100N in the first generation system (compared to about 1,000N for a conventional AMT) to 40N. The low forces allow the components to be manufactured from proven light-weight materials.
The second-generation system uses simplified actuators with lighter rails and light weight shift forks. Total packaging volume is also reduced in this version of the AMT.
Compared to a manual transmission, Zeroshift calculates that its transmission can deliver 2% better fuel economy and 5% better acceleration. While the Zeroshift AMT would increase production cost over a manual transmission by about 25%, it is significantly less expensive to manufacture than a 6 speed AT, which, Zeroshift calculates, costs 70% more to manufacture than a manual transmission.
Zeroshift. A Seamless Automated Manual Transmission (AMT) With No Torque Interrupt (SAE 2007-01-1307)