Encoder error detection for an automatic four-wheel-drive vehicle

摘要

A method for controlling a transfer case in a four wheel drive vehicle is provided. The transfer case has a neutral state and a plurality of drive modes. A MSS having a plurality of positions is provided for selecting the drive modes. An upshift relay and a downshift relay energize a motor to effect a shift of the transfer case to the selected drive mode. An encoder detects a value corresponding to the rotational position of the motor. The method senses if the encoder has lost power, and upon sensing the encoder has lost power, compares a current MSS position with a MSS position prior to losing power to the encoder. If the current and prior MSS positions differ, the most recent valid MSS position is determined. Whether the upshift and downshift relays are turned "on" is established. The direction of rotation of the motor is established. The desired motor destination is established. The direction in which to rotate the motor and the maximum time to allow the motor to rotate to achieve the desired destination are established.