Brake Fluid Pressure Controller for Vehicle

1. Field of the Invention

The present invention relates to a brake fluid pressure controller for vehicles that have a brake anti-locking control means.

2. Description of the Prior Art

It is known that a brake fluid pressure control valve, which is called a proportioning valve and decreases the pressure of incoming brake fluid entering the valve at a prescribed rate in order to increase the pressure applied to the brake fluid leaving the valve, is provided in the rear wheel liquid fluid pressure line system of a vehicle in order to approximate the distribution of the front and rear braking force of the vehicle to an ideal one, as disclosed in the U.S. Pat. No. 3,479,095.

Such a proportioning valve is also provided in a vehicle having a brake anti-locking controller, as disclosed in the U.S. Pat. No. 4,652,060. The valve functions so that the braking force applied to the front wheels of the vehicle and that applied to the rear wheels thereof are of equal magnitude, as the braking force in the front and the rear wheels is less than a prescribed magnitude at the initiation of braking of the vehicle. It also functions in such a manner that the braking force applied to the rear wheels is made lower in magnitude than that applied to the front wheels, as the respective magnitudes of braking force are equal to or higher than the prescribed magnitude after the initial stage of the braking, thus approximating and comparing the times for locking the front wheels as well as locking the rear wheels with each other in order to prevent the loss of initial braking force and premature anti-locking control of the rear wheels.

Another such proportioning valve has an inertia member fitted with an inertial valve action element for cutting off the transmission of brake fluid when a prescribed rate of deceleration is applied to the member, as disclosed in the U.S. Pat. No. 4,116,493. As for a vehicle such as a truck, which differs much in ideal distribution of braking force between the loaded and unloaded states of the vehicle, the pressure of brake fluid, which is decreased by yet another proportioning valve, is altered depending on the load in the vehicle in such a manner that the pressure of the brake fluid, which initiates and controls the braking force for the rear wheels of the vehicle, is increased in accordance to an increase in the load on the vehicle, thus providing the valve with a braking force distributing property responsive to the load as shown in FIG. 6 of U.S. Pat. No. 4,116,493.

The brake fluid pipe system of a vehicle provided with the proportioning valve, especially that of a vehicle provided with the deceleration-sensitive, load-responsive proportioning valve having the inertial valve action element, is rather complicated. Also, the proportioning valve is relatively expensive and increases the cost of the vehicle due to the installation of the anti-locking controller.

Therefore, to simplify both the embodiment as well as cost, the present invention comprises a brake anti-locking controlling means, which prevents the wheels of a vehicle from locking while braking on the low-friction coefficient surface of a road, thereby securing the steering capability and stable movement of the vehicle, as well as shorten the braking distance thereof. The brake anti-locking controlling means also includes a modulator which has hold valves, constituted by solenoid valves which apply and maintain pressure of brake fluid in cylinders for application to the wheels of the vehicle, and decay valves constituted by solenoid valves which decrease the pressure of brake fluid applied to the wheels. On the basis of electric signals received from wheel speed sensors, indicative of the speed of the individual wheels, the microcomputer of the controller performs to either open or close the hold valves and the decay valves in order to either increase, maintain or decrease the pressure of the brake fluid in the wheel cylinders.

Accordingly, it is an object of the present invention to provide a brake fluid pressure controller for a vehicle having an anti-locking controller without a proportioning valve yet incurring no reduction of effectiveness.

The brake fluid pressure controller of the present invention includes a control means for opening and closing the hold valves of a rear wheel brake fluid pressure line system at the time of a rise in the brake fluid pressure after the start of braking of the vehicle and before the start of the anti-locking control, thereby keeping the rate of the rise in the brake fluid pressure in the rear-wheel system lower than that of the rise in the brake-fluid pressure in the front wheel brake fluid pressure line system.

FIG. 1 is a schematic view of a brake fluid pressure controller according to the present invention.

FIG. 2 is a block diagram of the control unit of the brake fluid pressure controller.

FIG. 3 is a time chart of the controller to illustrate the operation thereof.

FIG. 4 is a graph of the controller to illustrate the relationship between front wheel braking force and rear wheel braking force.

FIG. 5 is a flow chart of the controller to illustrate the operation thereof.

FIG. 6 is a graph of a conventional brake fluid pressure controller to illustrate the relationship between front wheel braking force and rear wheel braking force.

FIG. 1 is a schematic view of the present invention, a brake fluid pressure controller for a vehicle. For simplification, FIG. 1 shows only a cross-piped brake fluid pressure line system for the right rear wheel and left front wheel of the vehicle. The vehicle includes hold valves HV which are normally open solenoid valves, decay valves DV which are normally closed solenoid valves, a brake pedal 18, a master cylinder 19, which is operated by the pedal and is connected to a wheel cylinder 21 for the left front wheel and a wheel cylinder 22 for the right rear wheel through fluid passages 23 and 24 provided with the hold valves HV and connected to a reservoir 25 through the decay valves DV, and a brake fluid pressure pump 27 provided in a fluid passage 26 between the reservoir and the master cylinder. The brake fluid pressure controller includes a control unit 20 made of a microcomputer in the main.

The opening and closing of the hold valves HV and the decay valves DV are controlled by command signals sent out from the control unit 20. The control unit acts to open and close the hold valves HV and the decay valves DV on the basis of signals sent out from speed sensors 1 and 2 for the left front wheel and the right rear wheel, respectively, and are indicative of the speeds of the wheels. When the brake pedal 18 is depressed, as the hold valves HV and the decay valves DV remain de-energized as shown in FIG. 1, the pressure of brake fluid in the master cylinder 19 is transmitted to the wheel cylinders 21 and 22 through the fluid passages 23 and 24 to increase the pressure of the brake fluid in the wheel cylinders. If the brake anti-locking control of the vehicle is then started, the hold valves HV perform to close the fluid passages 23 and 24 in order to maintain the pressure of the brake fluid in the wheel cylinders 21 and 22. When the decay valves DV thereafter open, the brake fluid in the wheel cylinders 21 and 22 flows therefrom to the reservoir 25 via the decay valves so that the pressure of the brake fluid in the wheel cylinders is decreased.

FIG. 2 is a block diagram of the control unit 20 including calculation circuits 5, 6, 7 and 8, control logic circuits 9, 10, 11 and 12, a computed vehicle speed calculation circuit 13, a differentiation circuit 14, and comparison circuits 15, 16 and 17. Wheel speed sensors 1, 2, 3 and 4 provided for the left front wheel, right rear wheel, left rear wheel and right front wheel of the vehicle, respectively, send out AC signals whose frequencies change in proportion to the rotation speeds of the wheels. The calculation circuits 5, 6, 7 and 8 receive the AC signals from the wheel speed sensors in order to perform calculations to generate signals indicative of the respective wheel speeds VwFL, VwRR, VwRL and VwFR. The electric signals are sent to the control logic circuits 9, 10, 11 and 12 as well as the computed vehicle speed calculation circuit 13, which calculates a computed vehicle speed Vv approximate to the actual speed of the body of the vehicle. The computed vehicle speed is a constant and uniform speed of acceleration or deceleration. For the calculation of the computed vehicle speed Vv, the highest of the four wheel speeds VwFL, VwRR, VwRL and VwFR is selected, and the limit to the rate of the decrease in the other lower wheel speed relative to the highest is set at a prescribed value such as -1 g. The computed vehicle speed Vv is applied to the control logic circuits 9, 10, 11 and 12, which operate, dependent on the basis of the four wheel speeds as well as the computed vehicle speed, to open or close the hold valves HV and decay valves DV of the brake fluid pressure line systems for all the wheels of the vehicle to increase, maintain or decrease the pressure of the brake fluid in the wheel cylinders for all the wheels to perform the anti-locking control of the vehicle in a conventional manner.

The differentiation circuit 14 differentiates the computed vehicle speed Vv to determine the rate VvG (dVv/dt) of the decrease in the speed. The comparison circuit 15 compares the rate VvG with a preset deceleration rate Go. The other comparison circuit 16 compares the left front wheel speed VwFL with the right rear wheel speed VwRR. The remaining comparison circuit 17 compares the right front wheel speed VwFR with the left rear wheel speed VwRL. The outputs from the comparison circuits 15 and 16 are applied to the control logic circuit 10 for the brake fluid pressure lines for the right rear wheel. The outputs from the comparison circuits 15 and 17 are applied to the control logic circuit 11 for the brake fluid pressure lines for the left rear wheel.

The control logic circuits 10 and 11 monitor the outputs from the comparison circuits 15, 16 and 17 throughout a period from a time point t1 which is shown in FIG. 3 and at which the brake pedal 18 begins to be depressed, to a time t4, which is also shown in FIG. 3, and at which time the anti-locking control is started. At time t2, at which the rate VvG of the decrease in the calculated vehicle speed Vv is larger than the preset deceleration rate Go and the rear wheel speed VwR is higher than the front wheel speed VwF, the control logic circuits 10 and 11 act to energize and de-energize the hold valves HV at a preset duty factor to slowly increase the pressure of the brake fluid in the wheel cylinders for the rear wheels. The speeds of the rear wheels are thus controlled in such a manner that the rate of increase in the pressure of the brake fluid in the wheel cylinders for the rear wheels is less than the increase in pressure of brake fluid in the wheel cylinders for the front wheels in order to cause the speeds of the rear wheels to be as near as possible to the speeds of the front wheels. Since it is clear that the time at which the rate VvG of the decrease in the computed vehicle speed Vv becomes larger than the prescribed deceleration rate Go depends on the load on the vehicle, the hold valves HV can thus be caused to perform nearly the same function as the above-mentioned deceleration-sensitive load-responsive proportioning valve.

FIG. 4 shows the braking force distribution property of the brake fluid pressure controller. At a time which the rear wheel speed VwR becomes lower than front wheel speed VwF, the control logic circuits 10 and 11 begin to act to keep the hold valves HV energized or closed in order to maintain the pressure of the brake fluid in the rear wheel cylinders to prevent the anti-locking control of the vehicle from starting too early on the rear wheels.

FIG. 5 is a flow chart of a control routine which is executed through the control logic circuits 10 and 11. In step S1 of the routine, it is judged whether the brake pedal 18 is depressed during the movement of the vehicle or not. If it is judged in step S1 that the brake pedal 18 is depressed during the movement of the vehicle, it is then judged in step S2 of the routine whether or not brake anti-locking control initiation conditions are established. If it is judged in step S2 that the conditions are not yet established, it is then judged in step S3, in terms of the output from the comparison circuit 15, whether or not the absolute value of the rate VvG of the decrease in the computed vehicle speed Vv has become larger than the preset deceleration rate Go. Until it is judged in step S3 that the absolute value has become larger than the preset rate Go, the pressure of the brake fluid in the rear wheel cylinders is increased in a conventional manner in step S4 of the routine while the hold valves HV are kept de-energized or open. After step S4, the brake anti-locking control initiation conditions of step S2 are evaluated once more. When it is judged in step S3 that the absolute value has become larger than the preset value Go, it is then judged in step S5 of the routine whether the rear wheel speed VwR is higher than the front wheel speed VwF or not. If it is judged in steps S3 and S5 that the absolute value has become higher than the preset rate Go and the rear wheel speed VwR is higher than the front wheel speed VwF, the hold valves HV are energized and de-energized at the preset duty factor in the step S6 of the routine to gradually increase the pressure of the brake fluid in the rear wheel cylinders as shown in FIG. 3. After the step S6 is taken, return to step S2. If it is judged in the step S5 that the rear wheel speed VwR has become equal to or lower than the front wheel speed VwF, the hold valves HV are kept energized in step S7 of the routine to maintain the pressure of the brake fluid in the rear wheel cylinders. Step 2 follows step S7. If it is then judged in step S2 that the conditions are established, the brake anti-locking control is started in step S8 of the routine.

According to the present invention, the hold valves of the rear wheel brake fluid pressure line system of a modulator provided for the brake anti-locking control of a vehicle are closed and opened according to a prescribed duty factor before the start of the brake anti-locking control so as to slowly increase the pressure of a brake fluid in the system , thereby enabling the hold valves to function similarly to the above-mentioned proportioning valve. For that reason, the proportioning valve can be dispensed with in order to reduce the cost of the modulator but without sacrificing effectiveness of the brake fluid piping thereof. If the operation of the hold valves is started on the basis of the comparison of the rate of the decrease in a computed vehicle speed and a preset deceleration rate as in the above-described embodiment, there is no loss in function, whatsoever, in comparison to that of the above-mentioned deceleration-sensitive load-responsive proportioning valve. The hold valves are well-suited to create an ideal property of braking force distribution.