Control system for preventing the skidding of vehicles

Claim 2

A control system for preventing the skidding of vehicles provided with a hydraulic brake system including a master cylinder and wheel cylinders operated by a braking hydraulic pressure produced by said master cylinder, said control system comprising: a braking hydraulic pressure modulator having a first position for supplying the braking hydraulic pressure produced by said master cylinder to said wheel cylinders, a second position for stopping the supply of the hydraulic pressure to said wheel cylinders, a third position for reducing the hydraulic pressure in said wheel cylinders while the supply of the hydraulic pressure thereto is stopped and a fourth position for restoring said reduced hydraulic pressure: A wheel speed signal generator for generating a signal corresponding to a wheel speed; means responsive to said wheel speed signal to generate, when a wheel deceleration exceeds a predetermined deceleration, a first set reference wheel speed signal which decreases with a rate of reduCtion corresponding to said predetermined deceleration starting from a level of the wheel speed signal equal to or lower than that at the time when the wheel deceleration exceeds said predetermined deceleration and a second set reference wheel speed signal which is lower than said first set reference wheel speed signal, said means including means for renewing said first and second set reference wheel speed signals when the wheel speed signal exceeds said first set reference wheel speed signal and changes from an increasing state to a decreasing state; and braking hydraulic pressure modulator actuating means responsive to the wheel speed signal for actuating said braking hydraulic pressure modulator a. to said third position for reducing the hydraulic pressure when the wheel speed signal is lower than said second set reference wheel speed signal, b. to said second position for stopping the hydraulic pressure supply to maintain the hydraulic pressure level in said wheel cylinders at the time when the wheel speed signal is higher than said second set reference wheel speed signal but lower than said first set reference wheel speed signal or when the wheel speed signal exceeds said first set reference wheel speed signal and is still increasing, and c. to said fourth position for restoring the reduced hydraulic pressure or said first position for supplying the hydraulic pressure to increase the hydraulic pressure in said wheel cylinders when the wheel speed signal is higher then said first set reference wheel speed signal and is decreasing.

Claim 3

A control system according to claim 1 for use with a said brake system which includes a path through which the braking hydraulic pressure produced by said master cylinder is supplied to the wheel cylinders and wherein said braking hydraulic pressure modulator comprises a stop valve disposed in said path, a fluid chamber located in said path on the side of the wheel cylinders with respect to said stop valve, a pressure control rod moving in and out of said fluid chamber, a diaphragm connected with said rod, two air chambers separated by said diaphragm, a conduit for providing communication between said two air chambers, an electromagnetic valve for stopping, when energized, communication between said conduit and one of said air chambers positioned on the side of said pressure control rod, an electromagnetic change-over valve for switching, when energized, said conduit to be cut off from communication with the other one of said air chambers and to communicate with atmospheric pressure, means for bringing said other air chamber into communication with negative pressure, and a spring for urging said diaphragm to move said pressure control rod into said fluid chamber to open said stop valve by a pushing force of said spring when said two electromagnetic valves are deenergized, whereby said two electromagnetic valves are selectively energized to control air pressures in said two air chambers so that the movement of said pressure control rod is controlled to selectively close said stop valve and to reduce or to restore the braking hydraulic pressure in said path through which the braking hydraulic pressure is supplied to said wheel cylinders.

Claim 4

A control system for preventing the skidding of vehicles provided with a hydraulic brake system including a master cylinder and wheel cylinders operated by a braking hydraulic pressure produced by said master cylinder, said control system comprising: a braking hydraulic pressure modulator capable on actuation of assuming a first position for supplying the braking hydraulic pressure produced by said master cylinder to said wheel cylinders, a second position for stopping the supply of the hydraulic pressure of said wheel cylinders, a third position for reducing the hydraulic pressure in said wheel cylinders while the supply of the hydraulic pressure thereto is stopped and a fourth position for restoring the reduced hydraulic pressure; a wheel speed signal generator for generating a DC voltage corresponding to a wheel speed; set reference wheel speed signal generating means comprising a capacitor, means for charging said capacitor with a voltage of the wheel speed signal, means for discharging said capacitor at a predetermined rate of discharge and means for dividing a terminal voltage across said capacitor, said terminal voltage across said capacitor forming a first set reference wheel speed signal and an output voltage of said dividing means forming a second set reference wheel speed signal; and braking hydraulic pressure modulator actuating means comprising a first comparator for comparing the wheel speed signal with said first set reference wheel speed signal, a second comparator for comparing the wheel speed signal with said second set reference wheel speed signal and a third comparator for detecting whether or not said capacitor is being charged, said actuating means being operable in accordance with the outputs of said three comparators to actuate said braking hydraulic pressure modulator a. to said third position for reducing the hydraulic pressure when the wheel speed signal is lower than said second set reference wheel speed signal, b. to said second position for stopping the hydraulic pressure supply to maintain the hydraulic pressure level in said wheel cylinders at the time when the wheel speed signal is higher than said second set reference wheel speed signal but lower than said first set reference wheel speed signal and said capacitor is being charged, and c. to said fourth position for restoring the reduced hydraulic pressure or said first position for supplying the hydraulic pressure to increase the hydraulic pressure in said wheel cylinders when the wheel speed signal is higher than said first set reference wheel speed signal and said capacitor is not being charged, wherein said capacitor discharging means comprises a constant current discharging circuit and wherein said constant current discharging circuit comprises a parallel connection of said capacitor and a resistor, one end of said parallel connection being negatively biased.

Claim 5

A control system for preventing the skidding of vehicles provided with a hydraulic brake system including a master cylinder and wheel cylinders operated by a braking hydraulic pressure produced by said master cylinder, said control system comprising: a braking hydraulic pressure modulator capable on actuation of assuming a first position for supplying the braking hydraulic pressure produced by said master cylinder to said wheel cylinders, a second position for stopping the supply of the hydraulic pressure of said wheel cylinders, a third position for reducing the hydraulic pressure in said wheel cylinders while the supply of the hydraulic pressure thereto is stopped and a fourth position for restoring the reduced hydraulic pressure; a wheel speed signal generator for generating a DC voltage corresponding to a wheel speed; set reference wheel speed signal generating means comprising a capacitor, means for charging said capacitor with a voltage of the wheel speed signal, means for discharging said capacitor at a predetermined rate of discharge and means for dividing a terminal voltage across said capacitor, said terminal voltage across said capacitor forming a first set reference wheel speed signal and an output voltage of said dividing means forming a second set reference wheel speed signal; and braking hydraulic pressure modulator actuating means comprising a first comparator for comparing the wheel speed signal with said first set reference wheel speed signal, a second comparator for comparing the wheel speed signal with said second set reference wheel speed signal and a third comparator for detecting whether or not said capacitor is being charged, said actuating means being operable in accordance with the outputs of said three comparators to actuate said braking hydraulic pressure modulator a. to said third position for reducing the hydraulic pressure when the wheel speed signal is lower than said second set reference wheel speed signal, b. to said second position for stopping the hydraulic pressure supply to maintain the hydraulic pressure level in said wheel cylinders at the time when the wheel speed signal is higher than said second set reference wheel speed signal but lower than said first set reference wheel speed signal and said capacitor is being charged, and c. to said fourth position for restoring the reduced hydraulic pressure or said first position for supplying the hydraulic pressure to increase the hydraulic pressure in said wheel cylinders when the wheel speed signal is higher than said first set reference wheel speed signal and said capacitor is not being charged, wherein said capacitor discharging means comprises a constant current discharging circuit and wherein said constant current discharging circuit comprises a parallel connection of said capacitor and a resistor, one end of said parallel connection being negatively biased.

Claim 6

A control system according to claim 3, wherein said wheel speed signal generator generates a signal corresponding to a rotational speed of a propeller shaft for driving the wheels.

Claim 7

A control system according to claim 3, wherein said wheel speed signal generator comprises means for detecting a voltage having a frequency proportional to the wheel rotation speed and a frequency-voltage converter for converting said voltage into DC voltage.

Claim 8

A control system according to claim 3, wherein said capacitor charging means comprises a diode.