Anti-skid brake control system with a plurality of independently operative digital controllers

An anti-skid brake control system for an automotive vehicle comprising:

• a hydraulic brake system including wheel cylinders, one wheel cylinder associated with each of a driven and undriven vehicle wheels, first and second pressure control valves, each associated with one of the wheel cylinders associated with first and second undriven wheels, and a third pressure control valve associated with the wheel cylinders associated with said driven wheels, each of said first, second and third pressure control valves being operative to increase the fluid pressure in the corresponding wheel cylinder in a first position, to decrease the fluid pressure in said corresponding wheel cylinder in a second position and to hold the fluid pressure in said corresponding wheel cylinder constant in a third position;
• a first wheel speed sensor producing first sensor signal pulses representative of the rotation speed of said first undriven wheel;
• a second wheel speed sensor producing second sensor pulses representative of the rotation speed of said second undriven wheel;
• a third wheel speed sensor producing third sensor signal pulses representative of the average rotation speed of said driven wheels;
• a first controller associated with said first pressure control valve for controlling the latter, said first controller being responsive to said first sensor signal pulses to record an input timing of said first sensor signal pulses, to derive brake control variables including wheel speed and wheel acceleration for anti-skid brake control of said one of the undriven wheels, and to produce a first control signal which actuates said first pressure control valve to one of said first, second and third positions so as to adjust the rotation speed of said first undriven wheel toward an optimal relationship with the vehicle speed;
• a second controller associated with said second pressure control valve for controlling the latter, said second controller being responsive to said second sensor signal pulses to record an input timing of said second sensor signal pulses, to derive brake control variables including wheel speed and wheel acceleration for anti-skid brake control of said the other undriven wheel, and to produce a second pressure control signal which actuates said second pressure control valve to one of said first, second and third positions so as to adjust the rotation speed of said second undriven wheel toward said optimal relationship to the vehicle speed;
• a third controller associated with said third pressure control valve for controlling the latter, said third controller being responsive to said third sensor signal pulses to record an input timing of said third sensor signal pulses, to derive brake control variables including wheel speed and wheel acceleration for anti-skid brake control of said driven wheels, and to produce a third control signal which actuates said third pressure control valve to one of said first, second and third positions so as to adjust the rotational speed of said driven wheels toward said optimal relationship to the vehicle speed;
• and
• means, associated with said first, second and third controllers and responsive to failure of any one of said wheel speed sensors for performing a back-up operation in which the controller corresponding to the failing wheel speed sensor is operated for disabling anti-skid control and allow manual braking control immediately upon failure of the failing wheel speed sensor, and the other controllers are operated for disabling anti-skid control and allow manual braking control when said other controllers complete a current cycle of anti-skid control.

An anti-skid brake control system for an automotive vehicle comprising:

• a hydraulic brake system including wheel cylinders one wheel cylinder associated with each of a driven and undriven vehicle wheels, first and second pressure control valves, each associated with one of the wheel cylinders associated with first and second undriven wheels, and a third pressure control valve associated with the wheel cylinders associated with said driven wheels, each of said first, second and third pressure control valves being operative to increase the fluid pressure in the corresponding wheel cylinders in a first position, to decrease the fluid pressure in said corresponding wheel cylinder in a second position and to hold the fluid pressure in said corresponding wheel cylinder constant in a third position;
• a first wheel speed sensor producing first sensor signal pulses representative of the rotation speed of said first undriven wheel;
• a second wheel speed sensor producing second sensor pulses representative of the rotation speed of said second undriven wheel;
• a third wheel speed sensor producing third sensor signal pulses representative of the average rotation speed of said driven wheels;
• a first controller associated with said first pressure control valve for controlling the latter, said first controller being responsive to said first sensor signal pulses to record an input timing of said first sensor signal pulses, to derive brake control variables including wheel speed and wheel acceleration for anti-skid brake control of said one of the undriven wheels, and to produce a first control signal which actuates said first pressure control valve to one of said first, second and third positions so as to adjust the rotation speed of said first undriven wheel toward an optimal relationship with the vehicle speed;
• a second controller associated with said second pressure control valve for controlling the position of the latter, said second controller being responsive to said second sensor signal pulses to record an input timing of said second sensor signal pulses, to derive brake control variables including wheel speed and wheel acceleration for anti-skid brake control of said other undriven wheel, and to produce a second pressure control signal which actuates said second pressure control valve to one of said first, second and third positions so as to adjust the rotation speed of said second undriven wheel toward said optimal relationship with the vehicle speed;
• and
• a third controller associated with said third pressure control valve for controlling the position of the latter, said third controller being responsive to said third sensor signal pulses to record an input timing of said third sensor signal pulses, to derive brake control variables including wheel speed and wheel acceleration for anti-skid brake control of said driven wheels, and to produce a third control signal which actuates said third pressure control valve to one of said first, second and third positions so as to adjust the rotational speed of said driven wheels toward said optimal relationship with the vehicle speed;
• a first switch interposed between said first wheel speed sensor and said first controller and further connected to said second wheel speed sensor, said first switch being operative to connect said first wheel speed sensor to said first controller in a first, normal position and to connect said second wheel speed sensor to said first controller in a second, back-up state position;
• a second switch interposed between said second wheel speed sensor and said second controller and further connected to said first wheel speed sensor, said second switch being operative to connect said second wheel speed sensor to said second controller in a first, normal position and to connect said first wheel speed sensor to said second controller in a second, back-up state position;
• and
• a detector for detecting a failed one of said first, second and third wheel speed sensors and actuating said first, second and third controllers to operate in a back-up state, said detector operating one of said first and second switches in response to the failed wheel speed sensor to change said one switch from the first position to the second position thereof when said failed sensor corresponds to one of said first and second wheel speed sensors.

An anti-skid method for controlling an automotive hydraulic brake system comprising the steps of:

• detecting rotation speed of a first undriven wheel by means of a first wheel speed sensor;
• detecting rotation speed of a second undriven wheel by means of a second wheel speed sensor;
• detecting rotation speed of third driven wheels by means of a third wheel speed sensor;
• deriving brake control variables for said first undriven wheel on the basis of the output of said first wheel speed sensor, deriving an optimal instantaneous brake pressure to apply to said first undriven wheel and controlling braking pressure to be applied to said first undriven wheel at the derived optimal pressure so that the slippage of said first undriven wheel can be held in an optimal value;
• deriving brake control variables for said second undriven wheel on the basis of the output of said second wheel speed sensor, deriving an optimal instantaneous brake pressure to apply to said second undriven wheel and controlling braking pressure to be applied to said second undriven wheel at the derived optimal pressure so that the slippage of said second undriven wheel can be held in said optimal value;
• deriving brake control variables for said third driven wheels on the basis of the output of said third wheel speed sensor, deriving an optimal instantaneous brake pressure to apply to said third driven wheels and controlling braking pressure to be applied to said third driven wheels at the derived optimal pressure so that the slippage of said third driven wheels can be held in said optimal value;
• and
• detecting a faulty one of said first, second and third wheel speed sensors and performing a predetermined back-up operation including disabling anti-skid brake control for one of said first, second and third wheels by disabling the derivation of the brake control signal based on the output of the faulty wheel speed sensor, continuing an on-going cycle of anti-skid brake control by allowing derivation of control signals based on the outputs of non-faulty wheel speed sensors, and subsequently disabling anti-skid control for all of the wheels, and thus allowing manual braking control when anti-skid control for all of the wheels after said on-going cycle of anti-skid control is terminated.