Fluid pressure circuit protection valves

Abstract

 Afluid pressure circuit protection valve is provided which has a closure member biassed by a spring against a seat such that the valve remains dosed to protect other circuits supplied from the same source from effects of appreciable leakage from a circuit on the output side of the valve but wherein the spring is counteracted by a predetermined level of output pressure, the closure member being provided with a small path across it which is closed by resilient deformation due to the spring but which is opened to permit restricted flow through the valve to a service brake circuit reservoir which is required to aquire a recharged condition prior to a parking apring brake circuit despite the possibility of respective circuit protection valves not being identically biassed.

Description

[0001] This invention relates to fluid pressure circuit protection valves especially but not exclusively for use in fluid pressure reservoir charging systems.

[0002] Fluid pressure reservoir charging arrangements are used extensively in road vehicle braking systems wherein it is convenient to provide charging of a plurality of reservoirs from a single source of fluid pressure, typically a compressor. Such braking systems invariably have two service reservoirs for supplying fluid pressure to completely independent.service air brake circuits and in addition, a secondary or parking brake reservoir is usually provided on heavy vehicles for providing hold-off pressures for holding off spring brakes provided for secondary braking and parking. In addition, if a trailer is to be attached to the vehicle, a trailer brake reservoir will also be provided for applying fluid pressure to trailer brakes controlled by signals from the trailer.

[0003] In charging circuits for the respective reservoirs in such an arrangement it is susual to include charging circuit protection valves for the purposes of ensuring that if a failure occurs in the pipes or connections of a circuit connected to one reservoir, the remaining good circuits can nevertheless become charged at least to a working pressure. A problem exists in such an arrangement because of possible inequality between the strength of the springs employed in such protection valves. In normal production these may vary sufficiently for a protection valve associated with a faulty or leaking reservoir to permit the loss of an air supply to such an extent that the other non-faulty circuits do not become charged. In order to overcome such a problem, the Specification of German O.L.S. 2553818 provided in

with each protection valve a check valve a check valve and a restricted flow path which will always ensure that a supply of air reaches non-faulty reservoir circuits despite a small amount of inequality of the springs of the protection valves. It will be appreciated that an accumulation of some air pressure in a non-faulty reservoir then permits any relevant difference in spring forces to be overcome by the established pressure acting on the relevant area of the protection valve.

[0004] Even with a system arranged with parallel restrictive passages such as described in the aforementioned German O.L.S., there is a problem which is not dealt with or solved by the said O.L.S. In such systems, again as a result of inequality of the springs of the protection valves or slightly different effective areas, a spring brake reservoir used for parking and secondary braking may become fully charged before the reservoir or reservoirs supplying the service brakes of the vehicle. As a result, the vehicle may be capable of having its parking brakes released whilst the service brake circuits, not having yet received their charged pressure, may be inoperable. Accordingly, it is an object of the present . invention to substantially overcome this problem.

[0005] According to the present invention there is provided a fluid pressure circuit protection valve having a closure member and seat member biassed towards a closed relationship with one another, the biassing force being counteracted by a predetermined output pressure characterised by one said member being resiliently deformable by a predetermined biassing force to close-off a restricted fluid flow path which exists between the members when in contact but subjected to a next force less than the said biassing force.

[0006] By virtue of the present invention, there can be provided a reservoir charging arrangement for a multi-circuit brake system which by employing such a protection valve for one or some of a plurality of reservoirs to be charged from a single source, that one or some reservoirs are normally assured of becoming charged prior to others.

[0007] In order that the invention may be more clearly understood and readily carried into effect, the same will be further described by way of example with reference to the accompanying drawings of which:-

Fig. 1 illustrates a typical reservoir charging arrangement for a vehicle braking system and

Fig. 2 illustrates a circuit protection valve (cutaway view) embodying protection valves in accordance with the invention and

Fig. 3 illustrates an alternative form of protection valve formed in accordance with the invention and

Fig. 4 shows an enlarged view of the plunger of the protection valve of Fig. 2, and

Fig. 5 illustrates alternative forms of the cutaway in the upstand of the resilient member of Fig. 4.

[0008] Referring to Fig. 1, the reservoir charging arrangement shown therein comprises a compressor to be driven by the internal combustion engine of the vehicle in which the arrangement is installed as part of the braking system. The compressor denoted by reference 1 is controlled by a governor denoted by reference 2 and the output of the compressor in fed to an air dryer 3 of known form, the output of which is connected in common to the supply ports of four circuit protection valves denoted by references 4, 5, 6 and 7. These protection valves precede reservoirs 8, 9, 10 and 11. The reservoirs 8 and 9 are service reservoirs, the outputs of which would be connected to respective sides of a driver's dual circuit foot valve. The reservoir 10 comprises the secondary or parking air reservoir, the output of which would be to a manually operable spring and parking brake control valve in the cab of the vehicle. The reservoir 11 comprises the trailer reservoir source, the output of which would be connected to trailer relay valves for providing supplies to a trailer when connected to the vehicle.

[0009] The protection valves 4 and 5 are valves as shown in Fig. 2. From the cutaway illustration of Fig. 2, the construction of the valve is clearly visible and it will be seen that it comprises a main body denoted by reference 21 having a supply port 22 provided in a screw insert 23 against which a spring-loaded valve closure member 24 'engages through its resilient seat 25, the spring loading is provided by spring 26, the thrust of which is adjustable by-a suitable screw 27 bearing against a pressure plate 28. The output port is denoted by reference 29.

[0010] In operation of the protection valve, when the air pressure at the supply port attains a pressure which is sufficient to compress the spring 26, the member 24 lifts and the supply pressure then acts upon the full area of the stem of 24 embraced by the sliding seal 30, holding the member 24 raised against the effect of the spring. Should a failure in the circuit which is connected to the delivery port occur, the valve closes at a pressure typically about 60 p.s.i. and any remaining circuits connected to the same source of supply are assured of an air supply not less than this pressure.

[0011] In order to ensure that the service reservoirs 8 and 9 of the circuit arrangement of Fig. 1 are given charging preference, the resilient seat 25 of the protection valve of Fig. 2 is provided with a contacting upstanding annular raised portion, having a slight depression which for pressures somewhat below the aforesaid 60 p.s.i., provides a restricted flow path through the valve.

[0012] Fig. 5 shows at a and b, views through sections of the upstanding resilient portion of the valve of Fig. 2, and which is shown more clearly at reference 41 in Fig. 4. A ground cut-out may be as in Fig. 5 at a or a moulded cut-out may be as in Fig. 4 at b.

[0013] For pressures substantially less.than the intermediate pressure, the depression in the resilient raised portion of the valve seat becomes closed owing to the effect of the spring 26 causing compression of the resilient raised portion. At such pressures, the valve operates to completely seal the connection between the supply port 22 and the output port 29. Since the protection valves 6 and 7 are not provided with such restricted flow paths for intermediate pressures, it is always ensured that the reservoirs 8 and 9 are charged preferentially when recharging of a discharged system is commencing.

[0014] An alternative form of protection valve is shown in Fig. 3, and this is very similar to the valve of Fig. 2 with the added feature that an additional check valve with a light spring is provided within the central plunger, and now denoted by reference 34. In this case, the central check valve has a resilient closure member 35 and again the upstonding annuier portion of the seat 35 which bears against the hard valve seat provided on the upper surface of the screw member 33, is provided with a slight depression such that at intermediate pressures as aforesaid, a restricted flow path is provided across the check valve.

[0015] The reason for the added check valve in the valve of Fig. 3 is to inhibit feedback as between one reservoir and another. In this connection, it will be noted that with a reservoir such as the service reservoir 8 connected to the supply via a protection valve such as shown in Fig. 2, with a fully charged reservoir, the plunger 24 is raised and a loss of pressure in one or other of the other reservoirs can be replenished to a certain extent by reverse flow from the reservoir-8 to the depleted reservoir. In the case of the valve of Fig. 3 however, by virtue of the central check valve 35, even though the plunger 34 is raised under the effect of a fully charged reservoir pressure at the delivery port fed via a slot to the underside of the plunger 34, the check valve 35 remains closed when a depression of the pressure at the supply port occurs, thereby preventing feedback from one reservoir to another.

[0016] Typically, whilst the valves 4 and 5 of the arrangement of Fig. 1 may be of the type described with reference to Fig. 2, such as to provide the possibility of feedback, it may be desirable to provide valves not permitting feedback for the protection valves 6 and 7. In general, the question as to whether one or more of the protection valves 8, 9, 10 or 11 are required to prevent feedback will depend upon the vehicle builder requirements.

[0017] The protection valves may all be constructed in a single metal casting.

[0018] From the foregoing it will be appreciated that by virtue of the present invention and whereby the protection valves of a multi-circuit braking system which are provided in the charging paths for reservoirs for the or each service braking circuit, it can be ensured that during recharging of the system, a parking spring brake reservoir does not become recharged before a service reservoir to an extent which can permit release of a parking brake. This is achievable even in cases where the spring of a spring brake protection reservoir is slightly less effective than the spring of a service reservoir due to manufacturing tolerances.

Claims

1. A fluid pressure circuit protection valve having a closure member and seat member biassed towards a closed relationship with one another, the biassing force being counteracted by a predetermined output pressure characterised by one said member being resiliently deformable by a predetermined biassing force to close-off a restricted fluid flow path which exists between the members when in contact but subjected to a net force less than the said biassing force.

2. A fluid pressure circuit protection valve as claimed in Claim 1, said one member having an annular upstanding portion of the area which makes contact with the other member, said upstanding portion having an interruption formed in it to provide said restricted fluid flow path.

3. A fluid pressure circuit protection valve as claimed in Claim 1, the one of said members being provided with a surface depression which with said members in contact provides the restricted fluid flow path but which becomes closed by resilient deformation of the one member.

4. A fluid pressure circuit protection valve as claimed in Claim 1, 2 or 3, comprising a check valve which with less than said predetermined output pressure is biassed into a closed condition by a spring, said spring being counteracted by the output pressure to hold the valve open.

5. A fluid pressure circuit protection valve as claimed in Claim 1, 2 or 3, comprising a check valve biassed into the closed condition by a spring, said spring being counteracted by the output pressure to free the check valve to operate to prevent flow from the output of the valve back to the input of the valve.

Drawing