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Rethinking the Automated Manual Transmission

Dual-clutch gearboxes, which combine the attributes of a manual gearbox with the convenience of an automatic, are as efficient as a pure manual, but at least as expensive as an automatic. This would suggest that automating a manual transmission would be the best of both worlds.

Manual gearboxes are inexpensive to build and can be up to 97% efficient. Automatic transmissions are more expensive to make and just 86% efficient, but they meet the needs of a majority of drivers. Dual-clutch gearboxes, which combine the attributes of a manual gearbox with the convenience of an automatic, are as efficient as a pure manual, but at least as expensive as an automatic. This would suggest that automating a manual transmission would be the best of both worlds, except for the fact that these transmissions, while efficient, shift crudely from gear to gear. Not surprisingly, they have fallen from favor among OEMs.

Not so fast, say the folks at Zeroshift Advanced Transmissions (Milton Keynes, U.K.; www.zeroshift.com). “There’s a simple, relatively inexpensive way to automate a manual transmission without having shifts more suited to a delivery truck than an automobile,” says Tony Child, chief designer at Zeroshift. Oddly, it involves removing the standard synchronizer packs and replacing them with like-size dog rings, a design more suited to racing gearboxes where smoothness takes a back seat to shift speed and robustness. However, by splitting a typical dog ring in half, with the first ring taking up drive while the second moves to engage the next gear when a shift is initiated, Zeroshift engineers were able to eliminate much of the roughness and backlash associated with this design. Since each ring is double-faced it can drive only in the direction opposite its partner, and because the second ring is unloaded at the time of engagement, shift force is claimed to be 1/25 that required to overcome a typical synchronizer.
The Zeroshift transmission uses electric motors to move the clutch and gear selector rods on an as-needed basis, eliminating the need for the hydraulic pump used on most automated manual gearboxes. Torque spikes are handled by a combination of engine and transmission management, clutch control, and system compliance. In addition, Child claims shifts, “are instantaneous, eliminate the torque interruption and pitch of conventional shifts, improve acceleration by 5% with no change in gearing, and the ring assembly can be packaged in existing synchronizer envelopes at a lower cost.” He claims a 4.0-liter V6 Mustang fitted with the system gained an average of five car lengths over a manually shifted version in acceleration tests, showed a marked increase in fuel economy on a typical drive cycle, and lower emissions. Childs estimates a Zeroshift transmission will cost roughly 25% more than its manual equivalent and 55% less than a dual-clutch design in volume production. Not surprisingly, several OEMs are said to be interested in testing the technology.—CAS