Dynamic rear proportioning brake system

A brake pressure control method for a vehicle having front and rear wheels, and control means for controlling the pressure at said wheels, said method comprising a sequence of the steps of:

• calculating a rear proportioning mode activation threshold in accordance with the formula;
• ##EQU3## where:
• T is the resultant activation threshold;
• K.sub.0 is a default or nominal offset value;
• K.sub.BRAKE is a constant added when the vehicle brake switch is open;
• K.sub.DRPACT is a constant value subtracted when the rear proportioning mode is active;
• W1 is a factor used to weight the contribution of lateral acceleration;
• LAT.sub.-- ACCEL is the estimated vehicle lateral acceleration;
• AVEL is the estimated vehicle speed;
• MAX.sub.-- AVEL is the maximum estimated vehicle speed at which LAT.sub.-- ACCEL effect is increased;
• W2 is a factor used to weight the contribution of the rear slip variable;
• RSLIP is the estimated and filtered rear slip value;
• W3 is a factor used to weight the contribution of the vehicle deceleration;
• VEH.sub.-- DEC is the estimated vehicle deceleration;
• K.sub.MACEL is a scale factor and gain used on the MACEL variable contribution;
• .SIGMA.MACEL is the sum of the wheel maximum acceleration values;
• initiating a rear proportioning mode of automatic brake pressure control of said rear wheels if the estimated vehicle speed is above a low speed limit and said activation threshold exceeds a predetermined value, to thereby maintain an optimum pressure to said rear wheels;
• terminating said dynamic rear proportioning mode when said threshold is no longer exceeded or a predetermined interval of time after the vehicle speed drops below said low speed limit.

A brake pressure control method for a vehicle having front and rear wheels, wheel speed sensors for sensing the speed of at least one front wheel and at least one rear wheel speed, and a hydraulic brake for each wheel having a brake pressure controllable by an actuable valve, the method comprising a sequence of the following steps:

• estimating vehicle speed based on sensed wheel speed;
• calculating an activation threshold based on the formula;
• ##EQU4## where:
• T is the resultant activation threshold;
• K.sub.0 is a default or nominal offset value;
• K.sub.BRAKE is a constant added when the vehicle brake switch is open;
• K.sub.DRPACT is a constant value subtracted when the rear proportioning mode is active;
• W1 is a factor used to weight the contribution of lateral acceleration;
• LAT.sub.-- ACCEL is the estimated vehicle lateral acceleration;
• AVEL is the estimated vehicle speed;
• MAX.sub.-- AVEL is the maximum estimated vehicle speed at which LAT.sub.-- ACCEL effect is increased;
• W2 is a factor used to weight the contribution of the rear slip variable;
• RSLIP is the estimated and filtered rear slip value;
• W3 is a factor used to weight the contribution of the vehicle deceleration;
• VEH.sub.-- DEC is the estimated vehicle deceleration;
• K.sub.MACEL is a scale factor and gain used on the MACEL variable contribution;
• .SIGMA.MACEL is the sum of the wheel maximum acceleration values;
• initiating a dynamic rear proportioning (DRP) mode of brake pressure control, including the limiting of the brake pressure to at least one rear wheel, if the vehicle speed is above a predetermined speed threshold and said activation threshold value is equal to zero;
• terminating said DRP mode a predetermined period of time after said vehicle speed falls below said predetermined speed threshold.

A method of controlling the rear brake pressure of a vehicle having front and rear wheels, comprising a sequence of the steps of:

• transitioning from an IDLE mode of operation, during which brake pressure applied to the rear brakes is under manual control, to a DRP mode of operation, during which pressure applied to the rear brakes is automatically proportioned relative to the pressure applied to the front brakes to maintain an optimum rear brake pressure based on vehicle conditions including rear wheel slip and vehicle deceleration,
• transitioning from said DRP mode of operation to an ABS mode of operation, in which brake pressure to the rear wheels is initially increased to force a rear wheel departure in response to and incipient skid condition at both of said front wheels,
• transitioning from said ABS mode of operation to said DRP mode of operation, if said ABS mode of operation is terminated prior to said vehicle coming to a complete stop, and
• transitioning from said DRP mode of operation to said IDLE mode of operation a predetermined interval of time after said vehicle speed drops below a predetermined speed.

A vehicle anti-lock braking system (ABS) for controlling the front and rear brakes of front and rear wheels respectively of a vehicle by continually forcing wheel instability in a cyclic manner tending to minimize stopping distance and maximize vehicle stability, said ABS including an integral dynamic rear proportioning (DRP) mode of operation providing control of said rear brakes during braking conditions which do not require an ABS mode of operation, comprising;

• sensor means for developing input signals indicative of the speed of at least on front and one rear vehicle wheel,
• valve means for controlling the brake pressure to the front and rear brakes,
• computer means responsive to said input signals for calculating a DRP activation threshold based on predetermined vehicle parameters,
• said computer means providing output signals to said valve means for initiating said DRP mode if said vehicle speed is above a predetermined speed, and said activation threshold exceeds a predetermined value,
• said computer means providing output signals to said valve means for transitioning from said DRP mode to said ABS mode in response to an incipient skid condition of said rear wheel, for transitioning from said ABS mode to said DRP mode upon rear wheel recovery, and for terminating said DRP mode a predetermined interval of time after said vehicle speed drops below said predetermined value.