Skid control system

Claim 1

In a skid control system for controlling the application and release of brake pressure to at least one wheel of a vehicle, the improvement comprising sensing means for sensing the wheel angular velocity, generating means for generating a signal which is an approximation of the vehicle velocity from said wheel velocity signal and comparator circuit means for deriving a slip signal in response to said wheel and vehicle velocity signals, said generating means including means connected to said wheel velocity sensing means for establishing a characteristic of said vehicle velocity curve including establishing a starting point for said signal from said wheel velocity sensing means and means for decreasing said vehicle velocity signal independently of the actual vehicle velocity in accordance with a preselected curve when said curve is below said starting point by a preselected amount, said comparator circuit including differential circuit means for comparing the vehicle velocity signal with the wheel velocity signal during the braked portion of the cycle for stopping the vehicle and deriving an output signal when said wheel velocity signal bears a preselected relationship to the vehicle velocity signal, said vehicle velocity signal being a linearly decreasing ramp, said system further including a charge storage device, said charge storage device being supplied with electrical energy when said wheel velocity signal bears a preselected relationship to the charge on said storage device, said preselected relationship occurring when the wheel velocity signal exceeds the charge on said storage device, said system further including a circuit for discharging said storage device when said wheel velocity signal is less than the charge on the storage device, the discharge circuit causing the discharge of said storage device in accordance with a preselected deceleration relationship to approximate the deceleration of the vehicle, means for giving greater effect to said vehicle velocity signal as compareD to said wheel velocity signal to create a differential between said signals, said differential creating circuit means including a fixed voltage drop circuit in said vehicle velocity signal generating circuit and a fixed voltage drop circuit in said wheel velocity signal generating circuit, the fixed drop of said vehicle velocity circuit exceeding that of said wheel velocity circuit, means for generating an output signal when said wheel velocity signal falls a preselected magnitude below said vehicle velocity signal to create a critical slip signal, an output circuit for controlling the application of brake pressure, said critical slip signal providing an output signal to release brake pressure when a critical value is obtained, and slip circuit disabling means connected in responsive relationship to said output circuit, said disabling means operating to disable the slip circuit when said output signal is generated, said critical slip signal causing a brake relieving condition which relieves brake pressure on the vehicle wheels, said skid control system further including pressure applying circuit means including first signal generating circuit means responsive to said wheel velocity signal for generating a rate of change of wheel acceleration signal and second circuit means for generating a wheel acceleration signal and output gate means correlating said rate of change of wheel acceleration signal and said wheel acceleration signal to control the reapplication of brake pressure to the wheels.