GB1587374A - Brake systems for motor vehicles - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO rJRAKE SYSTEMS FOR MOTOR VEHICLES (71) We, ROBERT Bosun GmbH, a German company of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to brake systems for motor vehicles.

Mas present-day motor vehicles have a socalled "fixed brake adjustment" in which the braking forces on the front axle are in a fixed ratio to those on the rear axle. Fixed braking adjustment of this type has the disadvantage that in, for example, a laden vehicle of conventional construction, the pressure at which the rear axle brakes lock is considerably greater than that for the front axle brakes. The necessary locking pressure is in excess of the proportional boosting range of a brake booster which supplies one or more brake circuits with brake pressure medium, with the result that the pedal forces for obtaining a higher brake pressure increase over-proportionally.

This means that, in such a case, a normal driver is not able to fully utilize the possible braking forces on the rear axle.

In addition to this, recent investigation has shown that, in general, a driver does not increase the pedal force during braking when he detects a reaction in the steering. A reaction in the steering is possible when the front wheels lock, and is also possible when the front wheels enter an anti-skid regulating range, since slight reactions in the steering resulting from changes in the braking force cannot be avoided even in efficient anti-skid systems.

Similar factors also apply to drivers who are unable to apply large foot pressures as a result of their physical; constitution. During emergency braking, such a driver is generally not able- to utilize the maximum possible braking force on the front axle.

According to the present invention there is provided a brake system for motor vehicles comprising a brake booster provided with a control valve for supplying brake pressure medium from an accumulator to a brake circuit, and a change-over valve for establishing direct commuricafion between the accumulator and said brake circuit.

In contrast to the above-described prior brake system, a brake system embodying the present invention can have the advantage that the maximum- possible brake pressure from the accumulator and from the booster can be fully utilized when the pressure of brake pressure medium introduced by the control valve exceeds a predetermined leveL The change over can then be effected automatically In this manner full accumulator pressure can be used: for braking even when a driver does not fully depress the brake pedal for reasons of fear or lack of physical strength.

The present invention can be used to advantage in dual-circuit brake system, whereby either one or the two brake circuits can be acted upon by a hi-gher pressure. Preferably operation of the change-over- valve can be prevented if there is a lack of pressure in the accumulator.

The change-over valve can be responsive to a regulating signal device from a control pulse of an anti-skid: system. Preferably the regulating signal of one of two steered front wheels of the vehicle' is: used as a control pulse for causing the change-over valve to place the accumulator in communication with brake cylinders associated with the rear axle of the vehicle.

The invention will be further described by way of example with reference to! the accompanying drawings in which: Fig 1 is a diagrammatic illustration of a brake system having a change-over valve according to a first embodiment: of the inven tion; Fig. 2 is a diagrammatic illustration of a modification of the change-over valve of Fig.

1; and- Fig. 3 is a circuit diagram- of parts of an electronic brake system.

Referring initi-ally/ to Fig 1 of the draw- ings, a brake system has- an hydraulic duals circuit brake booster 1 which is adapted to be actuated by means of a brake pedal 2 and which can feed pressure medium to wheel brake cylinders 6, 61, and 7, 71 selectively by way of an anti-skid system 3 which essentially comprises a multi-position valve 4, a position sensor 5, wheel sensors (not illustrated), and an electronic control device.

The brake cylinders 6, 61 form part of a front axle brake circuit I which is supplied with pressure medium from a master cylinder 8 which is arranged coaxially beyond the brake booster 1 and which has a toppingup container 9, the brake circuit I being a so-called "closed brake circuit".

The brake booster 1 has a booster cylinder 10 in which a booster piston 11 is movable. A pressure chamber 12 is separated from the master cylinder 8 by means of a partition 13 and, by way of a pressure line 14 controlled by a non-return valve, is connected to a hydraulic accumulator 15 and to a pump 17 which is assembled together with the multi-position valve 4 and which, together with the latter, is driven by a common drive motor 16.

A spring 18 is arranged in the pressure chamber 12 and seeks to urge the booster piston 11 towards the pedal 2. The spring 18 is opposed by a cup spring 19 which acts upon the other end of the booster piston 11.

A pedal push rod 20 is movable in the booster piston 11 and can act upon a control valve 23 by way of a spring 22 disposed in a relief chamber 21. The control valve 23 is in the form of a double valve and has an inlet valve 24 and and outlet valve 25.

The outlet valve 25 communicates with the relief chamber 21 which is connected to a topping-up container 26. The container 26 is also connected, by way of an annular recess 27 in the booster piston 11, to a relief line 28 which leads to the pump 17. A valve closure member of the outlet valve 25 and a valve spring are arranged in a pressure-change chamber 29 from which leads a brake line 30 of the brake circuit II. A change-over valve 31 is incorporated in the brake line 30.

A line 32, normally closed by the changeover valve 31, leads from the pressure chamber 12 or from the hydraulic accumulator 15. In the multi-position valve 4, communication exists between the line 30 and a primary chamber 34 of the master cylinder 8 by way of a line 33. Finally, a pressure line 35 leads from the multi-position valve 4 to the pressure line 14 and, monitored by means of a pressure relief valve, from the pressure line 14 to the relief line 28.

A piston 37, subjected to the force of a spring 36, is movable in the change-over valve 31 and has an effective surface which is subjected to the pressure in the brake line 30 A valve closure member 39 is connected to the piston 37 by way of a piston rod 38 and normally closes an inlet 40 of the line 32 which is subjected to accumulator pressure.

The brake system operates as follows: When the brake pedal 2 is actuated, the control valve 23 is charged over and allows pressure medium to flow from the pressure chamber 12 into the brake line 30 of the brake circuit II. The pressure introduced is also effective in the primary chamber 34 of the master cylinder 8 by way of the multiposition valve 4, so that the master cylinder piston produces a corresponding pressure in the brake circuit I. The anti-skid device 3 ensures that the brake pressure at the individual wheels or wheel axles does not exceed the locking limit.

The prevailing brake pressure reacts upon the brake pedal 2 by way of the push rod 20 and thus allows the driver to sense the effective brake pressure. When, during braking, either the front axle anti-skid device operates and the driver detects vibration on the pedal 2, or the driver is not physically able to introduce a higher brake pressure, he no longer further actuates the brake pedal to actuate the brakes. However, in most cases, the braking ability of the rear wheel brakes is not fully utilized and a long braking path results.

This is when the advantageous mode of operation of the present invention takes place in that the change-over valve 31 changes over when the pressure introduced by the control valve 23 exceeds a predetermined level of, for eaxmple, 50 bar. The piston 37 overcomes the force of the spring 36, and the valve closure member 39 opens the inlet 40. Pressure medium can now flow from the accumulator 15 into the brake circuit II under a pressure of approximately 200 bar.

When the brake system is equipped with an anti-skid system of the type described, the brake pressure introduced is also effective in the brake circuit I by way of the line 33, but an introduced pressure of this magnitude is not dangerous since it is monitored in the two brake circuits I and II by means of the anti-skid system.

Without an anti-skid system, the changeover valve 31 operates such that only the rear axle brake circuit II receives the full reservoirs pressure. The rear axle normally tolerates a higher brake pressure without the wheels locking, particularly when it is stressed by a heavy service load.

Fig. 2 shows substantially the same brake system as Fig. 1, except that, in this instance, change-over valve 41 is provided with an additional actuating piston 42 subjected to the pressure stored in the hydraulic accumulator 15. The actuating piston 42 prevents change-over of the change-over valve 41 when the accumulator pressure is too low.

The response pressure should be slightly in excess of the filling pressure or the minimum working pressure of the accumulator 15.

Fig. 3 shows that the automatic admission of accumulator pressure to one or both brake circuits can be initiated not only by the brake pressure introduced.

Regulating signals IGvL IGvB derived in an anti-skid system from control pulses respectively from each of the two front wheels, and a regulating signal IGHA from the rear axle are processed in an electronic switching unit 43, 44, 45. However, only the regulating signals IGvL and IGVB of the front axle act as trigger pulses. The two signals are combined in an OR circuit 46 and are transmitted by way of a line 47, as a control pulse for pressure change, and by way of a line 48 as a control pulse for applying the accumulator pressure to the rear axle brake circuit II, by way of an adjusting member, for example by means of the multi-position valve 4 or by means of a solenoid valve.

In this manner, pressure can be automatically admitted to the rear axle brake circuit by means of a regulating signal of the antiskid system 3.

WHAT WE CLAIM IS:- 1. A brake system for motor vehicles, comprising a brake booster provided with a control valve for supplying brake pressure from accumulator to a brake circuit, and a change-over valve for establishing communication between the accumulator and said brake circuit.

2. A brake system as claimed in claim 1, in which the change-over valve is subjected to the brake pressure in the brake circuit and is responsive to the attainment of a predetermined pressure therein to esetablish said direct communication between the accumulator and the brake circuit.

3. A brake system as claimed in claim 1 or 2, which has a plurality of brake circuits and in which the change-over valve is incorporated in that one of the brake circuits which is associated with the vehicle axle on which the change in axle loading is the greatest.

4. A brake system as claimed in claim 1 or 2, which has a plurality of brake circuits, and in which the change-over valve is incorporated in each brake circuit.

5. A brake system as claimed in claim 1, which has an anti-skid system, and in which the change-over valve is responsive to a regulating signal device from a control pulse of the anti-skid system.

6. A brake system as claimed in claim 5, in which a regulating signal of one of two steered front wheels of the vehicle is used as a control pulse for causing the change-over valve to place the accumulator in communication with brake cylinders associated with the rear axle of the vehicle.

7. A brake system as claimed in any of claims 1 to 6, in which the change-over valve is provided with a further actuating piston which is subjected to the pressure of brake pressure medium in the accumulator whereby operation of the change-over valve may be prevented when there is a lack of accumulator pressure.

8. A brake system for motor vehicles, constructed and arranged and adapted to be operated substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 or Fig. 2 or Fig. 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. excess of the filling pressure or the minimum working pressure of the accumulator 15. Fig. 3 shows that the automatic admission of accumulator pressure to one or both brake circuits can be initiated not only by the brake pressure introduced. Regulating signals IGvL IGvB derived in an anti-skid system from control pulses respectively from each of the two front wheels, and a regulating signal IGHA from the rear axle are processed in an electronic switching unit 43, 44, 45. However, only the regulating signals IGvL and IGVB of the front axle act as trigger pulses. The two signals are combined in an OR circuit 46 and are transmitted by way of a line 47, as a control pulse for pressure change, and by way of a line 48 as a control pulse for applying the accumulator pressure to the rear axle brake circuit II, by way of an adjusting member, for example by means of the multi-position valve 4 or by means of a solenoid valve. In this manner, pressure can be automatically admitted to the rear axle brake circuit by means of a regulating signal of the antiskid system 3. WHAT WE CLAIM IS:-

1. A brake system for motor vehicles, comprising a brake booster provided with a control valve for supplying brake pressure from accumulator to a brake circuit, and a change-over valve for establishing communication between the accumulator and said brake circuit.

2. A brake system as claimed in claim 1, in which the change-over valve is subjected to the brake pressure in the brake circuit and is responsive to the attainment of a predetermined pressure therein to esetablish said direct communication between the accumulator and the brake circuit.

3. A brake system as claimed in claim 1 or 2, which has a plurality of brake circuits and in which the change-over valve is incorporated in that one of the brake circuits which is associated with the vehicle axle on which the change in axle loading is the greatest.

4. A brake system as claimed in claim 1 or 2, which has a plurality of brake circuits, and in which the change-over valve is incorporated in each brake circuit.

5. A brake system as claimed in claim 1, which has an anti-skid system, and in which the change-over valve is responsive to a regulating signal device from a control pulse of the anti-skid system.

6. A brake system as claimed in claim 5, in which a regulating signal of one of two steered front wheels of the vehicle is used as a control pulse for causing the change-over valve to place the accumulator in communication with brake cylinders associated with the rear axle of the vehicle.

7. A brake system as claimed in any of claims 1 to 6, in which the change-over valve is provided with a further actuating piston which is subjected to the pressure of brake pressure medium in the accumulator whereby operation of the change-over valve may be prevented when there is a lack of accumulator pressure.

8. A brake system for motor vehicles, constructed and arranged and adapted to be operated substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 or Fig. 2 or Fig. 3 of the accompanying drawings.