Creating a new hybrid-electric transmission (with integrated electric motors) brings up some problems and opportunities; one of the more prosaic ones is the humble parking pawl, that little bit of metal that keeps the car or truck from moving when the transmission is in Park.
Typically, a notched wheel on the output shaft locks up the transmission in Park; but if the transmission controller loses power, the system could default to Neutral when Park is wanted, or vice versa. Having the park pawl drop at speed could be a serious problem, and there would be no way to “limp home” from that. As the patent (filed for FCA US by Abhilash Gudapati, Jayant Chalke, and Ankur Jaiswal from Troy and Auburn Hills) says, “Conventional solutions include additional hardware, such as electric motor(s) and/or redundant power sources, but this increases system costs and complexity.”
Their contribution is a number of new methods for activating the park pawl, moving control from the transmission controller to the engine controller, which communicate regardless. If the engine controller loses power, the transmission controller can still stay out of Park but using hydraulic pressure, avoiding the need for redundant power sources, additional motors, and such. With a hybrid transmission, one of the motors could be activated to provide additional pressure, if needed. Whether the pawl is being engaged or not, the two controllers (engine and transmission) can communicate and double-check the status of the pawl and take corrective action.
Patent #11,358,589 was granted on June 14, 2022.
