Anti-lock brake system which calculates exponential changes in wheel brake pressure

Anti-lock brake system for controlling brakes of a wheeled vehicle comprising:

• measurement pick-ups, each for measuring a respective wheel speed and producing a respective wheel speed signal;
• an analysis circuit for receiving the wheel speed signals, the analysis circuit having a determining means for determining an instantaneous wheel brake pressure p.sub.R (t), and using the wheel speed signals and the instantaneous wheel brake pressure to generate respective brake pressure control signals;
• brake pressure control devices which are each activated by the respective brake pressure control signal to vary the brake pressure to prevent wheel lock;
• and
• wherein the determining means uses the brake pressure control signals and stored data and curves characterizing particular hydraulics of the brakes of the wheeled vehicle to determine the instantaneous wheel brake pressure p.sub.R (t), with the determining means including:
• means for calculating the instantaneous wheel brake pressure p.sub.R (t) in accordance with the relationship
• p.sub.R (t)=p.sub.R (t.sub.o)+{p.sub.v (t.sub.o)-p.sub.R (t.sub.o)}(1-e.sup.-(t-t.sbsp.o.sup.)/T.sbsp.2)
• during a pressure reduction phase, and
• p.sub.R (t)=p.sub.R (t.sub.o)-p.sub.R (t.sub.o).multidot.(1-e.sup.-(t-t.sbsp.o.sup.)/T.sbsp.1)
• during a pressure build-up phase,
• where t.sub.o is a starting time for a change of pressure for a control cycle, p.sub.V (t.sub.o) is an admission pressure at the starting time, and T.sub.1 and T.sub.2 are time constants specific to the wheeled vehicle;
• means for deriving the pressure values p.sub.V (t.sub.o) and p.sub.R (t.sub.o) at the starting time for the control cycle, from an instantaneous vehicle deceleration and constants specific to the vehicle;
• means for comparing a pressure value, corresponding to the average lock-up pressure and obtained from the instantaneous vehicle deceleration at the starting time for each control cycle, to an average of calculated instantaneous wheel brake pressures for wheels of a front axle, to produce a correction value;
• and
• means for adjusting the calculated instantaneous wheel brake pressure p.sub.R (t) using the correction value.