A method of controlling a vehicle drive system is provided for a vehicle
having an internal combustion engine, free-wheeling steerable front
wheels, driven rear wheels, an infinitely variable transmission (IVT)
transmitting torque from the engine to the rear wheels, and a control
unit for controlling the IVT as a function of sensed parameters and
supplying a speed command to the IVT for commanding a speed of the rear
wheels. The method includes sensing a steering angle of the front wheels,
sensing a front wheel speed, sensing a rear wheel speed, generating a
corrected estimated vehicle speed as a function of the front wheel speed
and the sensed steering angle, and increasing the speed command in
response to a comparison between the corrected estimated vehicle speed
and the rear wheel speed. The infinitely variable transmission is
preferably embodied by a hybrid electric drive system. The estimated
vehicle speed value is determined as a function of a gear ratio of a rear
wheel drive, the front wheel speed, a rolling radius of the front wheel,
a rolling radius of the rear wheel, and the steering angle of the
steerable front wheels. The speed command is increased when the rear
wheel speed is less than 90% of the corrected estimated vehicle speed.