Vehicle braking system with proportional poppet valve pressure control strategy

[0011]This invention relates to electrohydraulic braking (EHB) systems for vehicles and in particular to a method (algorithm) for controlling the pressure of brake fluid applied to the wheel brakes thereof. The algorithm interprets a braking pressure command input from any of a variety of braking functions, and controls the electromagnetic poppet valves to achieve the commanded pressure at a vehicle's brakes reliably and with good control in all states of flow (leakage or bulk) through the valves. Additionally, the pressure control system accepts inputs from advanced braking functions, such as ABS, VSC, TC, DRP, ACC, etc. More specifically, the purpose of the pressure control system is to provide adequate wheel pressure control with respect to dynamic response, tracking error, robustness and stability objectives, while taking into account issues such as vibration, noise and flow consumption. The pressure control system is intended for use with base braking functions, such as that described in U.S. Pat. No. 6,226,586, granted May 1, 2001, the disclosure of which is incorporated herein by reference.

[0012]The EHB pressure control system receives a desired wheel pressure command, and with a caliper pressure feedback signal, computes one voltage command for the apply valve and another one for the dump valve, both corresponding to a requested flow from the hydraulics. The voltage command drives current control electronics. The electronics in turn selectively power the apply and dump poppet valves to control flow in or out of the brakes and modulate wheel pressure as required.

A major difference between poppet valves (used herein) and spool valves is that there is significant amount of leakage associated with poppet valves.

One limitation in controlling valves in a closed or near-closed position is that it is difficult to control the change in pressure applied to the brake.