Abstract: A control system or apparatus (10) is provided which is deployed within a four-wheel drive vehicle (12) and which is adapted to automatically control the activation and deactivation (i.e., locking and unlocking) of hub locks (44) according to a certain control strategy. Hub locks (44) are effective to operatively connect and disconnect the front wheels (14) of vehicle (12) to the front axle assembly (16), thereby allowing torque from the front driveshaft (22) of the vehicle to be transferred to the front wheels (14) when the vehicle (12) operates in a four-wheel drive mode. Control system (10) is effective to detect system faults and malfunctions and to selectively alter the hub locks control strategy in response to such a detection, thereby substantially preventing the undesired locking/unlocking of the hub locks (44) resulting in possible ratcheting, binding or damage to the hub locks (44).

Abstract: This invention describes encoding methodology for the encoder assembly 18 which senses position of a shift motor 14 in a shift system 10. The basic motivation is robust operation of the shift system 10 in the event of an open circuit (OC) fault in the encoder output signal bus 20 or any fault in the encoder power supply line 80. It is assumed here that the controller 40 is unable to detect the said faults in a manner that is direct and independent of the sensed position code. The most important aspect of the encoding scheme is that the likely motor positions (main-stop positions) should be assigned as many logically high bits as possible. Next, no main-stop position should look like either Neutral or any of the two adjacent positions when an OC fault takes place in the bus 20. Finally, no position in the complete range of the travel of motor 14 should possess code which is identical to the power loss code (all logical zero's).

Abstract: A system and method are provided for detecting faults in an encoder used for position feedback as part of a transfer case in an electronic-shift 4×4 vehicle. Encoder signal failures including open-circuit, short-to-ground, and short-to-power faults and encoder power line failure with open-circuit or short-to-ground fault are detected. The methodology ensures that no fault is set due to transients seen immediately after the power-set up in the system or after turning a relay off at the end of a shift. If the relays are off and an intermittent physical fault changes the encoder code, the fault flag is reset by the methodology when the fault disappears. The physical encoder faults which are transparent from the encoder code in stationary motor are detected by an intelligent recursive index-based algorithm which works when a shift is commanded.

Abstract: 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.

Abstract: A method for controlling a transfer case in an automatic four-wheel-drive driveline for a motor vehicle includes sensing if the engine is drivably decoupled from the transfer case and setting a first variable to "T" if the engine is decoupled, otherwise setting the variable to "F". The vehicle speed is sensed to determine if the speed is substantially zero and a second variable is set to "T" if the speed is substantially zero, otherwise the second variable is set to "F". Whether the vehicle is braking is sensed, and a third variable is set to "T" if the vehicle is braking, otherwise the third variable is set to "F". If all the first, second and third variables are "T", a shift condition flag is set to "T" to permit a shift of the transfer case through a neutral state, otherwise the shift condition flag is set to "F" and a shift of the transfer case through the neutral state is not permitted.