Fail safe circuit for vehicle skid control brake system

A vehicle brake control system for selectively controlling the engagement and disengagement of a brake system of a vehicle in accordance with selective braking conditions, comprising in combination:

• first signal means for generating a signal proportional to vehicle wheel speed;
• second signal means responsive to said wheel speed signal for generating a signal representative of vehicle speed;
• comparing means responsive to said wheel speed and vehicle speed signals for generating a first control signal when the relationship therebetween is at a first predetermined condition;
• third signal means responsive to the rate of change of said wheel speed signal for generating a second control signal when the rate of change of said wheel speed signal reaches a first value, and a third control signal when the rate of change of said wheel speed signal reaches a second value;
• fourth signal means responsive to said second and third control signals for generating a fourth control signal proportional to the rate of change of said wheel speed signal when said first and second values are reached;
• logic means selectively responsive to said first, second, third and fourth control signals for disengaging the vehicle brake system when said first predetermined condition and said first value are reached, and sequentially engaging and disengaging the vehicle brake system in response to said fourth control signal when said first predetermined condition and said second value are reached;
• said logic means including
• ramp logic means responsive to said third and fourth control signals for producing signals representing selected speed conditions of the vehicle wheels with respect to vehicle speed for controlling said second signal means,
• oscillator logic means responsive to said second and fourth control signals for producing signals representing selected speed conditions of the vehicle wheels when said first and second values are reached,
• reset logic means responsive to said signals produced by said ramp logic means and the output signals of said system for producing reset signals for resetting the system when the relationship between vehicle wheel speed and vehicle speed reaches a second predetermined condition, said first predetermined condition being reached when said vehicle wheel speed approaches zero, and said second predetermined condition being reached when said vehicle wheel speed approaches vehicle speed, and
• output logic means responsive to said first control signals, said signals produced by said oscillator logic means and said signals produced by said reset logic means for producing a logic means output signal;
• output means responsive to said logic means output signal for selectively controlling the engagement and disengagement of the brake system of the vehicle;
• and
• fail safe means for monitoring the operation of the system and for selevtively providing visual and audible signal indicative of system failure and for disconnecting system power so as to prevent damage to the components thereof.

In an electronic control system of the type that monitors a condition of a mechanical system to provide an input to the electronic control system which generates therefrom output control signals to selectively actuate a means to control the mechanical system, a failsafe system for monitoring the output signal of a power source to said electronic control system and indicating malfunctions therein comprising in combination:

• power source detector means for monitoring the power source to said electronic control system and generating a first control signal upon a selective condition of said power source;
• output detector means for monitoring the output of said electronic control system and for generating second and third control signals upon a selective condition of the output of said control system and upon a first condition of said control means;
• condition detector means for monitoring said condition of the mechanical system and for selectively generating a fourth control signal upon the absence of said condition;
• and
• logic circuit means responsive to said first, second, third and fourth control signals and further responsive to the output of said electronic control system for selectively generating a first logic output signal indicative of either of first and second malfunction conditions of said electronic control system and a second logic output signal indicative of said second malfunction condition only.