GB2147963A

GB2147963A - Improvements in or relating to hydraulic brake systems

Info

Publication number: GB2147963A
Application number: GB08425862A
Authority: GB
Inventors: Lothar Kirstein
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1983-10-15
Filing date: 1984-10-12
Publication date: 1985-05-22
Also published as: SE8405117L; SE455076B; FR2553360A1; DE3337545A1; FR2553360B1; GB8425862D0; GB2147963B; JPS6094861A; SE8405117D0

Abstract

A hydraulic brake system is disclosed which includes the combination of an anti-skid brake pressure regulating system and an anti-drive-slip means. A high-pressure pump (16) has the dual function of returning brake fluid from a skidding wheel and charging an accumulator (26), and a low-pressure pump (33) is used to produce an inlet pressure in order to avoid the occurrence of a vacuum and gas bubbles in the suction line of the high-pressure pump (16). The low-pressure pump is located at a topping-up reservoir (28) of a master cylinder (1) and is constructed such that brake fluid can flow therethrough in either direction in a non-pressurised manner. <IMAGE>

Description

SPECIFICATION Improvements in or relating to hydraulic brake systems The present invention relates to hydraulic brake systems.

One form of hydraulic brake system has a master cylinder which is combined with a topping-up reservoir and which is connected to wheel brake cylinders by way of a brake line, and has a combination comprising an anti-skid brake pressure regulating system and an anti-drive-slip means. One such hydraulic brake system is disclosed in German Offenlegungsschrift 32 15 739.

In this known hydraulic brake system, an anti-skid system is combined with a drive slip regulator. When the anti-skid system is operating, the brake pressure at the wheel brakes is varied by means of a brake pressure regulative valve. In order to reduce the brake pressure, pressure medium is discharged into an accumulator chamber by way of the regulative valve, and this discharged pressure medium is returned by means of a return pump into the connection between the master cylinder and the brake pressure regulating valve.

The drive slip regulator has a pressure accumulator into which pressure medium is fed by means of the return pump, the said pressure medium being introduced to actuate the brake during operation of the drive slip regulator.

The drive slip regulator has a solenoid valve which interrupts communication between the master cylinder and the brake pressure regulating valve during drive slip regulation and then connects the pressure accumulator to the inlet of the brake pressure regulating valve by which the brake pressure is varied (controlled by a control circuit) to suppress the drive slip.

However, a pressure accumulator having a high pressure is required for the drive slip regulator. Charging of this accumulator involves the problem that a vacuum can occur during an intake operation and cause gas bubbles in the pump suction line, which can lead to failure of the pump.

According to the present invention there is provided a hydraulic brake system having a master cylinder which is combined with a topping-up reservoir and which is connected to wheel brake cylinders by way of a brake line, and a combination comprising an antiskid brake pressure regulative system and an anti-drive-slip means, in which a high-pressure pump and a low-pressure pump with an accumulator charging valve are used, and the lowpressure pump is disposed in that inlet line of the master cylinder which is connected to the wheel brake cylinders of the driving wheels.

In contrast to the prior art, a brake system embodying the present invention has the advantage that the high-pressure pump is used in combination with a low-pressure pump. A vacuum in the high pressure pump inlet is avoided by virtue of the fact that the highpressure pump is combined with a low-pressure pump. Gas bubbles then cannot occur.

Brake fluid can flow through the low-pressure pump in either direction when the anti-driveslip means is not activated. Hence, the passage of brake fluid is not obstructed when the brake is released and also when the brake is operating normally.

Finally, it is also advantageous that brake lines have a dual use. An additional line to the topping-up reservoir is not required for the charging of the accumulator effected by the high-pressure pump.

The invention will be further described by way of example with reference to the accompanying drawing which illustrates one embodiment of the invention.

A hydraulic brake system has a hydraulic main tandem cylinder 1. Two brake lines lead from the main tandem cylinder, one of which brake lines is connected to the brake cylinders of non-driven front wheels, and the other brake line 2 is connected to two brake cylinders 3 and 4 of two wheels 6 and 7 which are driven by way of a differential 5. The brake line 2 splits up into two line branches 2' and 2" upstream of the wheel brake cylinders 3 and 4, and a three-port, three-position solenoid valve 8 or 9 is fitted as a brake pressure regulating valve in each line branch 2' and 2" respectively, each of the said solenoid valves being by-passable in a flow direction towards the master cylinder 1 by way of a respective non-return valve 10 or 11.

Each three-port, three-position solenoid valve 8 and 9 has on the one hand a respective port 1 2 or 1 3 for a respective return line 14 or 1 5 which is connected to a highpressure pump 1 6 and, on the other hand, a respective port 1 7 or 1 8 for the brake line branches 2' and 2" to which the pressure side of the high-pressure pump 1 6 is connected by way of a pressure line 1 9.

The return lines 14 and 1 5 lead to an accumulator charging valve 21 by way of a common return line 20. The accumulator charging valve 21 is provided with a nonreturn valve 22, a spill valve 23 and a lowpressure accumulator 24.

The brake line 2 incorporates a three-port, two-position solenoid change-over valve 25 which, when in one of its positions (the position illustrated), opens the brake line 2 and which, when in its second position attained after its solenoid has been energized, establishes communication between the brake line branches 2' and 2", connected to the pressure line 19, and a high-pressure accumulator 26 having a pressure responsive switch 27.

The master cylinder 1 is combined in a conventional manner with a topping-up reservoir 28 which is split up into two chambers 29 and 30 which are both connected to the master cylinder 1 by way of separate lines 31 and 32. The line 31 incorporates a lowpressure pump 33 which is driven by an electric motor 33' and which, when stationary, permits brake fluid to flow in either direction in a non-pressurized manner. In order to achieve this, the low-pressure pump is a hydrodynamic pump such as a rotary pump or a centrifugal pump. In practice, the lines 31 and 32 are in the form of passages, the low-pressure pump 33 is fitted directly in the topping-up reservoir 28, and the electric drive motor 33' is disposed outside the topping-up reservoir 28, that is to say, "in the dry".

The system illustrated and described operates as follows: During normal braking, the passage of brake fluid through the low-pressure pump 33 and through the solenoid change-over valve 25 is unaffected.

If one of the wheels 6 or 7 tends to lock, sensors (not illustrated) associated with the wheels apply signals characterising each wheel's rotational behaviour to the corresponding three-port, three-position solenoid brake pressure regulating valve which then switches either to its second position (pressure holding) or to its third position (reduction of pressure). The high-pressure pump 1 6 is also switched on simultaneously with the threeport, three-position solenoid valve in order to return the relief quantity of fluid to the master cylinder 1 by way of the brake line branches 2' and 2".

If one of the wheels 6 or 7, for example wheel 6, spins during a moving-off operation, its sensor detects this fault and applies a signal to the change-over valve 25 and to the three-port, three-position solenoid control valve 9 of the wheel which is not spinning.

The valves change over, whereby, on the one hand, the high-pressure accumulator 26 is connected to the brake line branches 2' and 2" whereas, on the other hand, the threeport, three-position solenoid valve 9 switches to its pressure-holding position, so that the brake fluid can flow to the brake cylinder 3 of the spinning wheel 6 only by way of the nonswitched three-port, three-position solenoid valve 8. The other wheel 7 can then supply torque and move the vehicle. The prevailing pressure head is varied by a control circuit (not illustrated) in dependence upon the extent of drive slip detected.

However, it must be ensured that the highpressure accumulator 26 is charged for the purpose of drive slip regulation. This is achieved in conjunction with the low-pressure pump 33 which is used to produce an inlet pressure in the suction line of the high-pressure pump.

The advantage of this system resides particularly in its operational reliability. The use of the hydrodynamic low-pressure pump 33 avoids the occurence of vacuum in the system in an inexpensive manner. By virtue of its simple construction, the pump 33 itself can also be very inexpensive.

Claims

1. A hydraulic brake system having a master cylinder which is combined with a toppingup reservoir and which is connected to wheel brake cylinders by way of a brake line, and a combination comprising an anti-skid brake pressure regulative system and an anti-driveslip means, in which a high-pressure pump and a low-pressure pump with an accmulator charging valve are used, and the low-pressure pump is disposed in that inlet line of the master cylinder which is connected to the wheel brake cylinders of the driving wheels

2. A hydraulic brake system as claimed in claim 1, in which the low-pressure pump is disposed in the region of the topping-up reservoir and, when stationary, permits brake fluid to flow through in a non-pressurised manner.

3. A hydraulic brake system as claimed in claim 1 or 2, in which the low-pressure pump is a hydrodynamic pump such as a rotary pump or a centrifugal pump through which brake fluid can flow in either direction when the pump is stationary.

4. A hydraulic brake system as claimed in any of claims 1 to 3, in which the topping-up reservoir of the master cylinder is constructed as the housing of the low-pressure pump.

5. A hydraulic brake system as claimed in any of claims 1 to 4, in which the lowpressure pump is driven by an electric motor disposed outside the topping-up reservoir "in the dry".

6. A hydraulic brake system constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in the accompanying drawing.