GB2324844A

GB2324844A - Hydraulic dual-circuit brake system for a motor vehicle

Info

Publication number: GB2324844A
Application number: GB9808578A
Authority: GB
Inventors: Siegfried Emmann; Eberhard Lipp; Christian Mosler; Werner Spielmann
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1997-04-28
Filing date: 1998-04-22
Publication date: 1998-11-04
Anticipated expiration: 2018-04-22
Also published as: IT1299440B1; FR2762569B1; ITRM980273A1; DE19717999C1; GB2324844B; FR2762569A1; GB9808578D0; ITRM980273A0

Abstract

A hydraulic dual-circuit brake system comprises a vacuum brake booster 2, 3 for each brake circuit and a vacuum source 8 connected to each of the brake boosters 2, 3 via a connection 9,10. To acquire increased operating reliability so that an additional auxiliary service brake can be dispensed with, a stop valve 11 is provided. When there is an unintentional pressure rise in connection 9 e.g.due to a leak, the pressure increases in passage 23 and causes piston 13 to move to the left to cut off connection 9 from connection 10 and from the vacuum source. The description refers to a hydraulic dual-circuit brake system having two separate vacuum sources formed by a dual-chamber vacuum pump.

Description

1 Hydraulic dual-circuit brake system for a motor vehicle 2324844 The

invention relates to a hydraulic dual-circuit brake system, with a vacuum brake booster for each brake circuit, for a motor vehicle, particularly but not exclusively for a commercial motor vehicle having a permissible total weight of about 5 to 8 t.

Such a brake system is known, for example, from US 5,188,431. In this known arrangement, care is taken to ensure that, if one brake circuit fails on the pressure side of a brake booster, the other brake circuit continues to be operable with full effectiveness. This is not the case, however, if a defect occurs on the vacuum side of the brake booster, that is to say if there is a defect in the region of connection between the vacuum source and the brake booster.

Proceeding from this, the invention deals with the problem of additionally also designing a vacuum-side region between the vacuum source and brake boosters, in such a way that, in the event of a defect, one of the two brake circuits continue to be operable.

According to the present invention there is provided a hydraulic dualcircuit brake system, with a vacuum brake booster for each brake circuit, for a motor vehicle, in each case with a connection of the brake boosters to a vacuum source, wherein the two brake boosters have no pressure-equalizing connection to one another at least in the case of a pressure rise in one of the two connections leading to the vacuum source, the said pressure rise being unintended on the vacuum side and exceeding a predeterminable amount.

The invention, in this case, is based on the idea of also designing the region of connection between the vacuum source and brake boosters in the form of a dual-circuit system, in which a connecting circuit may fail, without the other connecting circuit failing at the same time. Thus, in a hydraulic brake system for a commercial motor vehicle, there is still no need for an additional auxiliary brake, even when, in the event of a failure of the brake booster, it is no longer possible, due to the permissible total weight, to brake purely by using foot power to actuate the service brake. The invention is of particular benefit here, since a brake system without an additional auxiliary service brake can be produced considerably more economically, 2 that is to say more cost-effectively. This is especially due to the fact that, in the case of vehicles having a total weight of more than about 5 t, auxiliary service brakes are, as a rule, actuated by compressed air and therefore require a costly compressed-air generator.

Since an auxiliary service brake is normally actuated by compressed air, if one is needed, the brake systems are usually even designed as a whole as compressed-air brake systems.

US 4,054,327 discloses a compressed-air brake system, in which compressed air is already supplied to a dual-circuit brake system according to a dualcircuit system for safety reasons. A compressed-air generator is used there which is connected to the compressed-air cells of the two brake boosters of the brake system via a stop valve, in such a way that, if one compressed-air supply line fails, the latter is blocked and the other compressed-air supply line is thereby made ready to operate. The disadvantage of this brake system is that, being a compressed-air brake system, it is costly.

In a preferred embodiment, the dual-circuit vacuum supply system is implemented by two separate vacuum sources which are each separately connected to a brake booster. Such separate vacuum sources may be obtained, for example, by using a dual-chamber vacuum pump. Pumps of this type can be produced relatively cost-effectively.

In a further embodiment of the invention, the dual-circuit vacuum supply system is obtained by inserting a stop valve into the vacuum supply lines of the brake boosters. This stop valve is expediently located directly on the vacuum source, so that the region between the compressed-air source and brake boosters, the said region being protected via the dual-circuit vacuum supply system, if possible covers the entire region of connection.

It is advantageous according to the invention, to use such a stop valve in the vacuum supply lines.

An embodiment of the invention is now described and illustrated in the drawing, in which:

Figure 1 shows a diagrammatic illustration of a dual-circuit brake system with a dual-circuit vacuum supply, 3 Figure 2 shows a section through a stop valve from the dual-circuit vacuum supply system according to the illustration in Figure 1.

In the brake system according to Figure 1, braking is triggered via a brake pedal 1 which is to be actuated by a driver's foot. For brake boosting, a vacuumactuated brake booster 2, 3 is inserted in the brake line of each of the two brake circuits.

The brake circuits are connected in such a way that, in each case, a front wheel 4 or 5 is connected to a diagonally opposite rear wheel 6, 7.

Vacuum is supplied for the two brake boosters 2, 3 from a vacuum pump as a compressed-air source 8. The vacuum supply lines 9 and 10 of the brake boosters 2 and 3 open into the pressure source 8 via a stop valve 11 which is provided as near as possible to the vacuum source 8.

The design of the stop valve 11 is explained below with reference to the illustration in Figure 2.

In a valve housing 12, a control piston 13 can be displaced in a cylinder 14 in the direction of the cylinder axis. The piston 13 is shorter than the longitudinal extent of the cylinder 14, so that the end faces of the piston 13 are in each case adjacent to a cylinder chamber 15 and 16. Provided in the cylinder chambers 15 and 16 are compression springs 17 which are supported on the cylinder end faces and which centre in a neutral position the piston 13 serving as an abutment.

The housing 12 of the stop valve 11 possesses, on the one hand, a connection 18 to the pressure source 8 and, on the other hand, connections 19 and 20 for the vacuum supply lines 9 and 10. These connections 18 to 20 lead into a cylinder connecting chamber 21 which is formed by a peripheral groove in the middle region of the piston 13. In this case, the groove in the piston 13 has a width which is dimensioned in such a way that the two connections 19 and 20 can open into this groove next to one another in the longitudinal direction of the cylinder. The opening orifice for the connection 18 into the groove of the piston 13 has a diameter such that it is only somewhat smaller than the width of the groove.

Located in each of the connections 19 and 20 is a non-retum valve 22 which in each case blocks the respective connections 19, 20 against loss of vacuum in the vacuum supply lines 9 and 10. Furthermore, the connections 19 and 20 are also 4 connected to the cylinder chambers 15 and 16 via lines 23 and 24.

The two lines 23 and 24 are, in turn, connected to one another via a small throttle orifice 25.

The stop valve 11, the design of which is described above, functions as follows.

If, for example, the vacuum in the vacuum supply line 9 collapses, excess pressure relative to the cylinder chamber 16 occurs in the line 23 and therefore also in the cylinder chamber 15. The piston 13 is thereby displaced to the left in the drawing, with the result that the connection 19 is closed by the piston 13. In this way, the operating vacuum via the connection 20 remains uninfluenced with regard to the brake booster 3, that is to say this brake circuit continues to be fully operative.

If the vacuum supply line 10 becomes leaky, the piston 13 moves to the right in the drawing, that is to say the connection 20 is blocked, with the result that the operating vacuum at the brake booster 2 continues to remain uninfluenced.

The throttle orifice 25 serves solely for the purpose of making it possible for the piston displaced into a lateral end position to be moved back easily if a vacuum supply line 9 or 10 is defective. Moreover, the throttle orifice 25 must be so small that it does not prevent an operating vacuum from being maintained if only one connection 19 or 20 has a flow passing through it.

Claims

1. A hydraulic dual-circuit brake system, with a vacuum brake booster for each brake circuit, for a motor vehicle, in each case with a connection of the brake boosters to a vacuum source, wherein the two brake boosters have no pressureequalizing connection to one another at least in the case of a pressure rise in one of the two connections leading to the vacuum source, the said pressure rise being unintended on the vacuum side and exceeding a predeterminable amount.

2. A brake system according to Claim 1, wherein the two brake boosters are supplied from two vacuum sources separate from one another.

3. A brake system according to Claim 2, wherein the two vacuum sources separate from one another are formed by a dual-chamber vacuum pump.

4. A brake system according to Claim 1 or 2, wherein the connections of the two brake boosters lead to a common vacuum source via a stop valve, the stop valve blocking the connection to the booster having the lower vacuum in the case of a predeterminable vacuum difference between the two boosters.

5. A brake system according to Claim 4, wherein the stop valve is provided directly adjacent on the vacuum source.

6. A stop valve for a brake system according to Claim 4 or 5, including; a compact piston capable of being subjected to pressure on its two opposite end faces is mounted so as to be longitudinally displaceable in a cylinder of a housing, the cylinder chambers adjacent to the end faces of the said housing being sealed relative to one another by the piston, the piston is subjected to an equal spring force in opposition on its end faces, in each case by a spring supported on the housing, in a neutral position of the piston determined by the springs, there is a flow connection, in a cylinder region acted upon by the piston, between the two supply 6 lines leading to the brake boosters and a compressed-air source, the cylinder chambers adjacent to the end faces of the piston are in each case connected to one of the vacuum supply lines of the brake boosters, in the case of a pressure difference exceeding a predetermined value between the two cylinder chambers, the piston is displaced into a position, in which the supply line having the lower vacuum is simultaneously separated, on the one hand, from the other supply line and, on the other hand, from the vacuum source, the two separate supply lines open into the connecting chamber of the stop valve in each case via a non- return valve blocking these lines relative to higher outside pressure.

7. A brake system according to Claim 6, wherein the two cylinder chambers are connected to one another via a throttle orifice.

8. A hydraulic dual-circuit brake system, substantially as described herein with reference to and as illustrated in the accompanying drawing.