Theory Of Operation

The Park Pawl system consists of the Electric Vehicle Control Unit (EVCU), Electronic Shifter Module (ESM), and the Park Pawl Motor. The EVCU sends park pawl motor command signals (Motor PWM1, Motor PWM2, and Enable) to the ESM. The ESM is responsible for controlling the high current Park Pawl Motor and provides feedback to the EVCU. The ESM has the 20 or more amps required for controlling the park-pawl motor operation.

The speed and direction are commanded by the Motor PWM1 and Motor PWM2 signals. The Diagnostic band for the PWM signals is defined as 0 to 5% and 95 to 100%. The motor stop band for both PWM signals is 45 to 55%. The motor speed for the PWM signals increase proportionally from 56 to 90% and from 44 to 10% depending on the direction. If the Motor PWM1 is between 44 to 10% the direction of the Park Pawl is disengage. If Motor PWM1 is between 56 to 90% then the direction of the Park Pawl is engage. Motor PWM2 signal will be the opposite of Motor PWM1 signal. The sum of PWM1 and PWM2 will equal 100%. Example: If PWM1 is equal to 20%, then PWM2 is equal to 80%. The Module Enable signal is used to signal the ESM to begin Park Pawl movement based on Motor PWM1 and Motor PWM2 signals. The ESM provides feedback to the EVCU, via the CAN Bus, of the Park Pawl Motor current, Motor PWM1, Motor PWM2, and Module Enable signals.

The park lock motor has two Hall Effect (Quadrature) sensors (Park Pawl Position Sensor 1 and Park Pawl Position Sensor 2) that measure shaft travel in tic counts. The EVCU will use the tic values of each sensor and then add them together to get an absolute value and the position of the park pawl. The two sensors read at 90 degrees phase shift and provide speed and direction of the move. The software is designed to travel between the tic counts and the hard end stop speeds are designed to be slower (100 tics/second) to prevent damaging the system. The absolute travel between the end-stops is minimum 335 tics up to a maximum of 388 tics.

During each key-up/wake-up cycle, the EVCU will perform an initialization process to identify the park-pawl position. To learn this position the EVCU will command the ESM to run the motor to the park (engage) direction, until it reaches end stop. The EVCU determines the motor has the reached the end stop when the tic counts stop counting and the motor current begins to increase. The motor will then move away from the end stop but stay in the park position. If the brake is applied, and vehicle speed is less than 2 mph, and either Reverse, Neutral, or Drive is selected then the EVCU will command the ESM to run the motor to the other stop end (disengage) and learn the full calibration travel. The subsequent Park Pawl Motor engage/disengage travel will operate at a faster speed, however the motor will not contact the end stops. After every 10th travel, or on a key ON, the system will recalibrate the end stops

If vehicle speed is greater than 2 mph, and the key is turned OFF or park is selected, the lock motor will remain in the disengage or neutral position. If the vehicle slows to below 2 mph and a second request for park position is requested then the vehicle will shift to park.