Automatic transmissions use one-way clutches and regular clutches to control gear shifts. Regular one-way clutch locks in one direction and free spins (freewheeling) in the other direction and thus provides good shift quality. However, a clutch is needed if the freewheeling direction needs to be locked. The advantage of a selectable one-way clutch (SOWC) is that it can be designed to act like a regular one-way clutch, fully freewheels or locks in both directions. In the GM six-speed transmissions, there is one one-way clutch which is accompanied by a clutch CB1R to control between 1st gear and reverse direction. The study is to replace the one-way clutch and CB1R clutch with simply one selectable one-way clutch in GM 6-speed transmissions (1). This will eliminate one transmission clutch, reduce weight and cost, and improve transmission efficiency. The proposed design of transmission is applied to a GM SUV and a GM passenger vehicle. Different from a regular clutch, which can be applied with force/pressure from high slippage to lock-up between two elements, a selectable one-way clutch can only be applied to a lock-up position when the slippage between two elements is near zero speed. Also, an SOWC can only be released when there is no torque or force carried by the clutch while a regular clutch can be easily released by dropping the applied force/pressure. These requirements impose challenges of the control strategies of the SOWC, especially during the scenarios such as 2–1 engine idle downshift (engine braking) and 1–2 upshift (coasting). This paper reviews hardware design, vehicle implementation, and focuses on control of the selectable one-way clutch. Vehicle results demonstrate static and rolling garage shifts, 1–2 upshifts, 2–1 and coast downshifts. Also demonstrated is the successful application of engaging 1st gear engine braking with the SOWC. This control involves coordination between the engine speed and SOWC slip speed, and the apply/release of the device.

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