Development and Challenges of Electrically Selectable One-Way Clutches

This paper discusses new developments in the field of one-way clutches (OWC). These recent developments involve “Selectable OWC (SOWC)” actuating both hydraulically as well as electrically. The primary focus of this paper is a low-current consuming Electrical SOWC (eSOWC) used in hybrid transmission being designed and developed at Ford Motor Company. Other SOWCs currently being utilized across different applications at Ford are also discussed. Clutching devices represent significant cost, weight, size and drag-loss in automatic transmissions. However, implementation of SOWCs offers the potential to reduce transmission cost, size, weight, and spin loss; eSOWCs may also improve shift quality, reduce shift times, improve shift consistency and reduce OWC-related NVH. In Hybrid applications the electric motor(s) and SOWC create a system that is analogous to a manual transmission synchronizer. Similarly, in automatic transmissions SOWC are analogous to pump-solenoid-valve-friction-clutch system. In conclusion, this paper is intended to educate the reader on the development challenges and benefits associated with SOWC using analytical and empirical data.