Integrated electronic control of pawl-gear park function of an automatic transmission

An automatic transmission park control system for a wheeled vehicle having a transmission with multiple operating ratio ranges and a park mode, said transmission including a driver-adjustable range selector having a discrete operating position corresponding to said park mode;

• said transmission having a driven shaft, a transmission park means for holding said driven shaft including a movable park mechanism having a transmission park engage position and a transmission park release position;
• first and second redundant reversible electric actuators drivably connected to said transmission park means;
• a source of voltage for said actuators;
• and
• electronic circuit means for controlling power distribution from said voltage source to said actuators whereby said transmission park mechanism is moved into and out-of-park;
• said electronic circuit means including an electronic vehicle powertrain control microcomputer powered by said voltage source comprising output portions connected to said actuators, and input portions connected to said range selector whereby movement of said range selector to said transmission park mode position develops an input signal for said input portions;
• a park switch means actuated by said range selector for developing a redundant park input signal for said input portions;
• means for engaging said transmission park means in the absence of a voltage supply from said output portions connected to said actuators;
• means for disengaging said transmission park means independently of said voltage source;
• said microcomputer comprising means for comparing a park command signal of said range selector to said signal developed by said park switch and for developing an error signal in response to absence of correspondence of said park command signal and said park switch signal,
• each of said actuators including
• a park motion feedback sensor means for monitoring engagements and disengagements of said transmission park mechanism and for developing sensor input signals for said microcomputer whereby a transmission park command indicated by said range selector is compared to a transmission park response;
• and
• means for developing a diagnostic signal indicative of a failure of said actuators to respond to said command by said range selector.