ABSTRACT 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 1 st 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
