Anti-skid control system for motor vehicles

#1. Field of the Invention

#This invention relates to an anti-skid control system for motor vehicles of the type that the drive system thereof is switchable to a direct-coupled four-wheel drive system (referred to as direct-coupled 4WD system hereinafter). More particularly, the invention pertains to such an anti-skid control system which is adapted, during anti-skid control operation, to cause a pressure reduction starting point to occur earlier when the drive system of the motor vehicle is switched to the direct-coupled 4WD system than when the drive system is other than the direct-coupled 4WD system, thereby making relatively small the speed difference between a high peak and a low peak of the wheel speed, and thus making it possible to achieve smooth anti-skid control operation even when the direct-coupled 4WD system is working. The expression "direct-coupled 4WD system" used herein refers to the cases where no center differential gear is provided or the cases where even if a center differential gear is provided, the differential gear is locked so that at least the drive shafts of the front and rear wheels are coupled directly to each other.

#2. Description of the Prior Art

#FIG. 1 is a schematic view illustrating an example of automotive brake apparatus incorporating the anti-skid control system according to an embodiment of the present invention.

#FIG. 2 is a block diagram showing an example of the circuit arrangement adapted for implementing the present invention.

#FIG. 3 is a flow chart useful for explaining the operation of the anti-skid control system according to the present invention.

#Referring first to FIG. 1 of the drawings, there is illustrated an example of automotive brake apparatus incorporating the anti-skid control system according to an embodiment of the present invention, wherein a front right-hand wheel, from left-hand wheel, rear right-hand wheel and rear left-hand wheel are indicated at FR, FL, RR and RL respectively; a front axle and rear axle are indicated at 1a and 1b respectively; a front differential gear and rear differential gear are denoted at 2a and 2b respectively; and a center differential gear is shown at 3. The center differential gear 3 is coupled to a drive apparatus such as engine and so forth (not shown) through a transmission (not shown), as shown by an arrow mark R. Indicated at 4 is a propeller shaft through which the center differential gear 3 is coupled to the front and rear differential gears 2a and 2b. Each of the center, front and rear differential gears 3, 2a and 2b is adapted to be locked. Further, a brake pedal is indicated at 5; a master cylinder is indicated at 6; and brake apparatus wheel cylinders associated with the front right-hand wheel FR, front left-hand wheel FL, rear right-hand wheel RR, and rear left-hand wheel RL are denoted at 7FR, 7FL, 7RR, and 7RL respectively.

#Furthermore, wheel speed detectors (speed sensors) 8FR, 8FL, 8RR and 8RL are provided in association with the front right-hand wheel FR, front left-hand wheel FL, rear right-hand wheel RR, and rear left-hand wheel RL respectively, as shown in FIG. 1. Signals derived from these speed sensors are inputted to a control circuit 9 (referred to as ECU hereinafter) which may generally be constituted by a microcomputer. According to this embodiment of the invention, the ECU 9 may comprise various elements such as contained in a broken-line block 9 in FIG. 2. Indicated at 10 is a modulator, well known in the art, which includes a gate valve, pressure buildup valve, pressure reduction valve and so forth, and adapted to control buildup/reduction of the brake fluid pressure. The modulator 10 may be constructed so as to correspond to the channel type of the brake apparatus and is connected to the master cylinder 6 through a piping 11. The number of pipes constituting the piping 11 depends on the channel type of the brake apparatus and/or the construction of the modulator. The modulator 10 is coupled to the front left-hand wheel cylinder 7FL, front right-hand wheel cylinder 7FR, rear left-hand wheel cylinder 7RL and rear right-hand wheel cylinder 7RR through pipes 12FL, 12FR, 12RL and 12RR respectively. Furthermore, the modulator 10 is adapted, during anti-skid control operation, to be controlled and enabled to perform pressure increasing, decreasing/holding operation with respect to each wheel cylinder in response to a signal provided by the ECU 9 as shown by a broken-line arrow mark 13.

#According to this embodiment of the invention, means 14 is provided which is adapted, when the drive system of the motor vehicle is switched to the direct-coupled 4WD system, to detect such drive system switching and provide a signal indicating that the drive system of the motor vehicle is switched to the direct-coupled 4WD system. The direct-coupled 4WD signal generator 14 is connected to the ECU 9 and which will be described in detail hereinafter.