Importance

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Abstract

A vehicle braking system comprising a controller responsive to wheel speed signals from at least two wheel speed sensors for sensing skid conditions of at least two wheels and for generating skid control instructions; a plurality of wheel brakes responsive to fluid pressure, hereinafter referred to as brake pressure, supplied thereto; a supply device, comprising a common supply valve, for supplying brake pressure to the brakes from a fluid pressure supply in accordance with a brake operating signal; and a skid controller controlled by the skid control instructions for controlling the brake pressure in a plurality of cycles each of which comprises a pressure reduction phase and a pressure increase phase, and a first comparitor to compare the co-efficient of friction of the lower friction surface with a predetermined threshold, and/or a second comparitor to compare the relative values of the co-efficients of friction of the surfaces with which at least two of the wheels are engaged and a device to operate the skid controller in a select low mode if the comparitors determine that a) the co-efficient of friction of the lower friction surface is above a predetermined absolute level, and/or b) the co-efficients of friction of the surfaces with which at least two of the wheels are engaged differ by less than a predetermined amount, and in a select high mode if the comparitors determine that a) the co-efficient of friction of a lower friction surface is at or below a predetermined absolute level, and/or b) the co-efficients of friction of the surfaces differ by at least the predetermined amount.

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First Claim