Anti-skid control system for motor vehicle

In an anti-skid control system for a motor vehicle, including a brake fluid pressure reduction-control mode and a brake fluid pressure buildup-control mode, each of which occurs cyclically, wherein in said reduction-control mode, reduction of the brake fluid pressure is started on the basis of detection of an abrupt drop in wheel speed which occurs when a wheel of the vehicle is braked;

• and in said buildup-control mode, valve means is repetitively opened and closed so that brake fluid pressure buildup and holding operations are performed alternately and repetitively, whereby the brake fluid pressure is caused to buildup gradually, the improvement comprising:
• means for determining the length of time period for the first one of said pressure buildup operations in said buildup-control mode, on the basis of variation in the wheel speed occurring during a period of time between a low peak point and a high peak point, said period of time being determined in relation to the difference between the wheel speed at a point of time when reduction-control of brake fluid pressure is to be started, and said low peak point;
• means for determining a point of time when reduction-control of brake fluid pressure is to be started, on the basis of detection of an abrupt drop in the wheel speed which occurs when the wheel is braked;
• means for detecting the wheel speed V.sub.a at said point of time when reduction-control of brake fluid pressure is to be started;
• means for detecting a low peak point when the wheel speed is changed from deceleration to acceleration by the reduction-control of brake fluid pressure which is started from said point of time when reduction-control of brake fluid pressure is to be started;
• means for detecting the wheel speed V.sub.LP at said low peak point;
• means for calculating the speed difference A between said wheel speeds V.sub.a and V.sub.LP ;
• means for detecting a first point of time when said wheel speed is increased from the speed V.sub.LP at the low peak point to a speed V.sub.b which is higher than said speed V.sub.LP by a quantity corresponding to K.sub.1 .times.100% of said speed difference A, where K.sub.1 is a preset value that is greater than zero but smaller than unity;
• means for detecting a second point of time when the wheel speed is increased from the speed V.sub.LP at said low peak point to a speed V.sub.c which is higher than the speed V.sub.LP by a quantity corresponding to K.sub.2 .times.100% of said speed difference A, where K.sub.2 is a preset value that is greater than zero but smaller than unity;
• means for calculating average acceleration (V.sub.c -V.sub.b)/.DELTA.T, where .DELTA.T is the time interval from said first point of time to said second point of time;
• and
• means for determining the length of time period T.sub.x for the first pressure build operation in said brake fluid pressure buildup-control mode, on the basis of said average acceleration.