Rear pressure control and rear dynamic proportioning in a vehicle brake system

1. A method for controlling a rear brake hydraulic circuit having a fluid storage element and a master cylinder supplying a volume of pressurized brake fluid to the rear brakes during the braking cycle in a pump-less anti-lock brake apparatus controlling the rotational speeds, during a braking cycle, of only the rear brakes of a vehicle having at least one front wheel, at least one rear wheel, and front and rear brakes acting on the front and rear wheels respectively, the method comprising:

determining whether the vehicle is operating lightly loaded at a light vehicle weight (LVW) or heavily loaded at a gross vehicle weight (GVW) as a function of the rotational speed of at least one rear wheel and the rear brake pressure;

providing rear dynamic proportioning (RDP) when a predetermined deceleration rate is exceeded during the braking event with the vehicle operating at LVW;

monitoring rear brake pressure; and

determining a rear brake pressure rate (RBP Rate) from the rear brake pressure; inhibiting RDP when the RBP rate is less than a predetermined value; and

inhibiting RDP when the vehicle is operating at GVW.

2. The method of claim 1 further comprising:

monitoring rear wheel speed;

and

controlling the rear brake hydraulic circuit as a function of the rear wheel speed and the rear brake pressure.

3. The method of claim 1 further comprising:

monitoring rear wheel speed;

determining a vehicle speed (VS Est) as a function of rear wheel speed; and

determining an RDP entry point as a function of the vehicle speed (VS Est).

4. The method of claim 3 further comprising:

determining a vehicle acceleration (VA Est), and a rear wheel acceleration (RWA Est) from the rear wheel speed;

determining an RDP term as a function of the vehicle acceleration (VA Est) and rear wheel acceleration (RWA Est) for a vehicle operating at LVW.

5. The method of claim 4 further comprising determining if the RDP term indicates operation of the vehicle at GVW.

6. The method of claim 5 further comprising:

and

determining if the vehicle is operating at LVW or GVW as a function of rear brake pressure and vehicle acceleration (VA Est).

7. The method of claim 1 further comprising providing rear pressure control (RPC) of the rear brake hydraulic circuit.

8. The method of claim 7 further comprising:

calculating an RPC entry point as a function of vehicle speed (VS Est);

calculating an RPC term as a function of the vehicle speed; and

controlling the rear brake hydraulic circuit as a function of the RPC term and RPC entry point.

9. The method of claim 8 wherein the RPC term is calculated as the proportional and derivative difference between the vehicle speed (VS Est) and the rear wheel speed.

10. The method of claim 9 further comprising:

determining a road surface condition; and

modifying the RPC entry point as a function of the road surface condition.

11. The method of claim 10 comprising determining the road surface condition as a function of variations of the rear wheel speed.

12. The method of claim 1 further comprising controlling the rear brake hydraulic circuit as a function of a volume available in the fluid storage element for receiving fluid supplied by the master cylinder during the braking cycle.