From the August 2016 issue
Despite our best efforts, the clutch, that fantastic frictional fuse between engine and transmission that has served us so long, has a dim future. With the manual gearbox critically endangered and an industry-wide focus on efficiency, the smartest minds in engineering are now hellbent on excising energy-sapping friction discs, even those in dual-clutch automatics. Dan Dorsch, a Ph.D. candidate and National Science Foundation Graduate Research Fellow in the mechanical-engineering program at the Massachusetts Institute of Technology, is one of those minds. In April, he won the Lemelson-MIT “Drive it!” grad-student prize, awarded to the design demonstrating the best potential for societal benefit, economic success, and environmental impact.
Model Citizen
This working model only serves to illustrate what Dorsch’s gearbox can do, not how it will look. The finished product will disconnect the engine with a toothed dog-gear coupling (not shown, 001) and speed-match gears with the smaller electric motor (002) while the propulsion motor (003) drives the wheels (004).
Dorsch’s design is a hybrid-vehicle transmission that replaces the traditional clutch or torque converter with a dog gear, using interlocking teeth rather than friction to couple the engine to the gearbox. Dorsch’s design significantly reduces the size, weight, and friction losses of existing transmissions, but the overall concept is geared toward fast cars rather than economy hybrids. An unnamed “leading performance-car company” is currently developing a prototype that could end up in the most exotic hybrids.
The transmission mates the engine with two electric motors, the larger of which is sized to launch the car at the friction limit of the tires. The second electric motor’s job happens inside the transmission, where it spins the engine to perform rev matching during shifts. It also acts as a starter when driving the combustion engine and as a generator when the roles are reversed.
The larger electric motor moves the car off the line, filling the role of first and reverse gears and replacing the need for a clutch or torque converter to smoothly mesh a spinning engine and stationary wheels. As speed increases, the engine fires and the second electric motor joins the party. During gearchanges, the larger motor provides uninterrupted torque to the ground while the smaller one matches engine speed to that of the wheels—faster and more precisely than your feet ever could with declutching and throttle blipping. Dorsch says that with precise enough controls, friction cones on gear synchronizers could be eliminated, too, further streamlining the gearbox. The results, in theory, are perfectly speed-matched shifts, with no lurching and no need for the power-sapping clutches found in dual-clutch transmissions.
Should that unnamed manufacturer bring the transmission to production, it would make torquey all-electric launches fortified by zero-power-loss shifts a reality. We can’t think of a greater societal benefit.
Jenny Krieg
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Porsche’s PDK transmission is one of several available today that use all the components Dorsch’s design eliminates. In the 911, it weighs about 265 pounds. For a vehicle using Dorsch’s streamlined design, subtract key components as follows:
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