Anti-wheel lock system for tandem axles

Abstract

An anti-wheel lock, system for a vehicle with tandem axles each having a pair of rotatable wheels, the vehicle having a braking system for applying braking forces to such wheels. A brake control device responds to an applied lock signal for controlling the braking system to relieve the braking forces on the wheels. The input circuitry provides for distinct wheel speed signals having values respectively representing the wheel speeds of the four wheels (or wheel sets) carried by the tandem axles. A high wheel gate continuously produces a signal representing the speed of the fastest rotating one of the four wheels by determining the fastest rotating wheel on each pair and then the fastest moving wheel between the pairs. A low wheel gate similarly obtains and continuously provides a signal related to the speed of the slowest moving wheel of the four. An average wheel gate of simplified construction produces a signal simulating the average wheel speed by in effect averaging the outputs of the high and low wheel gates. In a preferred embodiment the speed signals fed to the gates are provided by nonlinear frequency to voltage convertors driven in response to corresponding ones of the four wheels. Logic circuitry provides a locked wheel signal when values of, and changes in, the speed signals from such gates indicate or predict a skid condition.