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OEMs pursue latest Zeroshift transmission
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01/05/2007
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A second generation Zeroshift transmission uses a new drive ring system, combined with other developments which the developers say will reduce cost, weight and packaging volume as well as improving durability, fuel economy, emissions and refinement.
The technology provides a compact, low-cost, fully automatic transmission that changes ratio with zero torque interruption, making it as smooth as a traditional planetary automatic. Applications include passenger cars, commercial vehicles, off-highway vehicles and motorcycles.
The shift mechanism can be built into an existing manual gearbox and can therefore be assembled on existing production lines. Essentially, the normal synchromesh parts are simply replaced with the Zeroshift components.
“The second generation system incorporates the knowledge gained from five years of rigorous development,” said managing director Bill Martin.
At the recent SAE Congress in Detroit, the company confirmed that it was in a “pre-production phase” with a group of OEMs and that the first examples could be on the road by 2009.
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, replacing the synchromesh found in a conventional gearbox.
In the second generation system, these have been replaced by a pair of interlocking rings, each incorporating the three drive elements in a single forged component and operated by shift forks.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 take up backlash. The next shift is made with ring two taking up the drive and ring one taking up the backlash. As ring two is unloaded during the change, it requires less than one-twentieth the axial force required by a conventional synchromesh. The control system coordinates gearshift actuation, engine management and clutch operation to provide full control over the driveline during gear shifting.
Refinement and durability have been further improved through design of the working surfaces. One side of the drive element has a retention angle to take up the drive, while the opposite side has a ramp face to smoothly disengage drive. Shift forces have also been reduced, from around 100N in the first generation system (compared with typically around 1,000N for a conventional AMT) to just 40N. This allows components to be manufactured from lightweight materials with no additional surface treatment.
Future enhancements already in development will include production packaging of the control electronics and electric actuation of the drive rings using brushless DC motors. A system incorporating these and other enhancements is expected to be running in a demonstration vehicle this year.
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Author
Roger Bishop
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