Abrufbares Fahrzeug-Antriebssystem

An on demand vehicle drive system monitors vehicle performance and operating conditions and controls torque delivery to the vehicle wheels. The system includes a plurality of speed and position sensors, a transfer case (28) having primary and secondary output shafts (40,26) driving primary and secondary drive shafts, differentials and axles and a microcontroller (200). The sensors include a vehicle speed sensor, a pair of primary and secondary drive shaft speed sensors, and brake and driveline status sensors. The transfer case includes a modulating electromagnetic clutch (124) comprising a primary, cone clutch assembly (125) which functions as a pilot device to actuate a secondary, disc pack clutch assembly (150). The electromagnetic clutch is controlled by the microcontroller which is incrementally engaged to transfer torque from the primary output shaft to the secondary output shaft. When the speed of either the front or the rear drive shaft overruns, i.e., exceeds, the speed of the other drive shaft by a predetermined value related to the vehicle speed and other variables, indicating that wheel slip is present, clutch current is incrementally increased to increase clutch engagement and torque transfer to the secondary drive shaft. When wheel slip is reduced below the predetermined value the current to the clutch is incrementally reduced. The system also senses and compensates for the speed differences between the primary and secondary drive axles caused by the use of different, mixed tire, sizes, e.g., a compact spare, at one or more tire locations by adjusting the predetermined value. The method of operating such a system is also described.