GB2025552A

GB2025552A - Brake pressure limiting valves

Info

Publication number: GB2025552A
Application number: GB7924453A
Authority: GB
Original assignee: Automobiles Peugeot SA; Automobiles Citroen SA
Current assignee: Automobiles Peugeot SA; Automobiles Citroen SA
Priority date: 1978-07-17
Filing date: 1979-07-13
Publication date: 1980-01-23
Also published as: DE2928866A1; FR2383049A1; FR2383049B1

Abstract

The braking system has two circuits 1 and 13, circuit 1 being provided with a load responsive pressure limiter comprising a valve 2 subject to the control pressure in the circuit 1 downstream (1b) of the valve 2 via a chamber 6. A pressure drop detector 9 for the pressure in the circuit 13, comprises a member 9 which closes a by-pass 15 connecting the upstream and downstream parts 1a, 1b of the circuit 1 when there is pressure in the circuit 13. <IMAGE>

Description

SPECIFICATION Hydraulic circuit braking installations This invention, relates to hydraulic circuit braking installations having dual braking circuits in which braking pressure in one of the circuits of the dual braking circuit installation is limited in dependence on the axle load, while the application of the total pressure to the loaded axle is maintained in the event of failure in the other circuit.

In the known installations, application of the non-limited pressure is possible either by opening a branch duct bypassing the pressure limiter, or by blocking the limiter in the position in which it opens the first circuit.

This invention relates to installations in which a a bypass is produced at the ends of the pressure limiter, this being achieved in a simple manner enabling the limiter and its safety system to be located in a readily manufactured unit which can be installed with the minimum of piping.

To this end, the invention relates to a hydraulic braking installation for a motor vehicle, of the type comprising two separate braking circuits, of which the first, which feeds the braking means of a vehicle axle, is provided with a means of limiting the pressure according to the load of said axle, comprising a valve, the movable member of which is subjected at one of its ends to a counteracting force depending on the said load, while its other end is subject to the control pressure in said first circuit downstream of said valve by means of a chamber in which the said other end moves, in permanent communication with said downstream part of the first circuit, said installation also comprising an abnormal pressure drop detector for the second circuit, comprising a movable element subjected at its ends to the counteracting effects of a resilient return means and of the control pressure in said second circuit acting as the piloting pressure at one of the ends of said movable member, which forms a valve to close a branch duct connecting the upstream and downstream parts of the said first circuit in relation to the said limiter when the effect of said piloting pressure is greater than that of the resilient member.

According to the invention, the said branch duct is disposed between that part of the said first circuit which is situated upstream of the pressure limiter and the said chamber.

In a preferred embodiment, the moving member of the said detector is a grooved spool in which the groove establishes communication between the upstream part of the first circuit and the branch duct when the spool is subjected to the predominant force of the resilient return means, and the movable member of the limiter is also a spool which is mounted for parallel sliding with the spool of the detector in a single body.

The invention will be more readily understood from the following description which is given by way of example without any limiting force and which shows the advantages and secondary features of the invention.

The invention is described with reference to the accompanying drawings wherein: Figure 1 is a diagrammatic section of an installation according to the invention.

Figure 2 is also a section of an industrial embodiment of Fig. 1.

In the figures, like elements have like references.

The figures show a limiter for the pressure in the rear braking circuit 1, for example, part 1 a of which is connected to a pressure fluid source shown in the form of a master cylinder A, while part 1 b is connected to braking means. The pressure limiter consists, in known manner, of a spool 2 having a groove 2aand mounted slideably in a recess formed in a body 3. The end 2b of the spool is in contact with the lever 4 connected to a resilient means 5 which applies thereto a force proportional to the rear axle load of the vehicle. The end 2 C of the spool 2 moves in a chamber 6 formed in the body 3 and permanently connected to part 1 b downstream of the spool 2 of the rear circuit 1 via a duct 7.

A return spring 8 is attached between the end 2cof the spool and one of the walls of the chamber 6, and its forces tend to bring the groove 2a into register with the parts 1 a and 1 b of the circuit leading into the said recess.

The spool 9 of a pressure drop detector is mounted slideably in a recess 10 formed in the body 3. In this recess, by means of a groove 9a in an upper part of the spool, a first chamber 11 is defined and a second chamber 1 2 is defined around a lower part of the spool. The first and second chambers are connected respectively to part 1 a of the circuit 1 and to a branch 1 3a of the front braking circuit 1 3. Spool 9 is therefore subject to the counteracting effects of the fluid pressure in the chamber 1 2 and a return means (spring 14) acting at the other end of the spool.In the absence of any pressure in the chamber 12, the spring 14 brings the spool 9 into contact with the end of said chamber 1 2. In this position the bottom surface of the spool 9 opens the port 1 spa of a branch line 15 connecting the recess 10 to the said chamber 6. Thus in the absence of any pressure in the chamber 1 2 the duct 1 5 is connected to the duct 1 a via the chamber 11.

A hydraulic installation according to the invention operates as follows: It will be assumed that the driver does not actuate the vehicle brakes during the first stage. There is therefore no pressure in the ducts of the installation. As a result of the rear axle load transmitted to the spool 2 via the lever 4 and as a result of the return spring 8 the spool 2 of the pressure limiter is normally in contact with the bottom of chamber 6. In this position, groove 2a is situated in register with the parts 1 a and 1 b of the rear braking circuit. These two parts therefore inter-communicate. The spool 9 of the pressure drop detector is kept in contact with the bottom of chamber 12 by the spring 14. This position of equilibrium is such that the groove 9 a of the spool 9 is situated in register with the ducts laand 15.

In a second stage the driver actuates the vehicle braking means. A pressure produced by the driver, i.e. the control pressure, therefore forms in the two front and rear braking circuits. The pressure in the front circuit is generally equal to the pressure in the rear circuit. Consequently, the pressure forms in the ducts 1 a and 1 3a leading to the chamber 1 2. The pressure in chamber 1 2 moves the spool 9 and its bottom surface closes the port 1 5a The pressure is established in the chamber 6 via the duct 7 and acts on the end 2c of the spool 2.If the force due to the action of this pressure on the spool 2 is greater than the sum of the forces exerted on the spool by the lever 4 and the return spring 8, the spool 2 rises in known manner and the groove 2a shifts with respect to the parts 1 a and 1 b of the circuit and hence, for a control pressure greater than a limiting pressure, the groove 2a moves beyond the parts 1 a and 1 b of the circuit 1 and the circuit is broken. The pressure in the rear braking means is then equal to the limiting pressure, the value of which depends on the rear axle load and is independent of the driver's will. When the driver stops his braking action, the pressure in the chamber 1 2 and the duct 1 a is relieved. The spool 9 goes down again and the duct 1 5 again communicates with the duct 1 a.Pressure in the chamber 6 is thus relieved allowing the spool 2 to go down again and thereby relieving the pressure to the braking means.

In the event of failure in the front braking circuits leak in this circuit will prevent a braking pressure from being produced-all the braking pressure must be applied to the rear of the vehicle independently of the axle load. Thus if there is no pressure in the front circuit the chamber 1 2 connected to it by the duct 1 3a is also pressureless. The spool 9 then remains in its position so that the groove 9a is in register with the spool 15. The latter is then fed directly, as is also the chamber 6.

The spool 2 occupies the position it must occupy according to the load, but the braking pressure is admitted without limitation into the rear brakes from the chamber 6 via the duct 7.

Referring to Fig. 2, it can be seen that the features according to the invention can be embodied in a very compact block 3 by means of easily produced concurrent boreholes at right angles to one another.

The invention has an advantageous application in motor vehicles.

It is not limited to the above description but, on the contrary, covers all variants made thereto, without departing from the scope or spirit thereof.

Claims

1. A hydraulic braking installation for a motor vehicle, comprising two separate braking circuits, of which the first, which feeds the braking means of a vehicle axle, is provided with a means of limiting the pressure according to the load of said axle, comprising a valve, the movable member of which is subjected at one of its ends to a counteracting force depending on the said load, while its other end is subject to the control pressure in said first circuit downstream of said valve by means of a chamber in which the said other end moves, in permanent communication with said downstream part of the first circuit, said installation also comprising an abnormal pressure drop detector for the second circuit, comprising a movable element subjected at its ends to the counteracting effects of a resilient return means and of the control pressure in said second circuit acting as the piloting pressure at one of the ends of said movable member, which forms a valve to close a branch duct connecting the upstream and downstream parts of the said first circuit in relation to the said limiter when the effect of said piloting pressure is greater than that of the resilient member, characterised in that the said branch duct is disposed between that part of the said first circuit which is situated upstream of the pressure limiter and the said chamber.

2. An installation according to claim 1, characterised in that the moving member of the said detector is a grooved spool in which the groove establishes communication between the upstream part of the first circuit and the branch duct when the spool is subjected to the predominant force of the resilient return means.

3. An installation according to claim 2, characterised in that the movable member of the limiter is a spool which is mounted for parallel sliding with the spool of the detector in a single body.

4. A hydraulic circuit braking installation substantially as described with reference to and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.