GB2180608A

GB2180608A - Dual circuit brake valve

Info

Publication number: GB2180608A
Application number: GB08622228A
Authority: GB
Inventors: Ralph Coupland
Original assignee: Clayton Dewandre Co Ltd
Current assignee: Wabco Automotive UK Ltd
Priority date: 1985-09-19
Filing date: 1986-09-16
Publication date: 1987-04-01
Also published as: SE464859B; GB2180608B; DE3631895A1; DE3631895C2; GB8523198D0; SE8603825D0; GB8622228D0; SE8603825L

Abstract

A dual brake valve of the kind set forth in Patent No. 1466296 is sealed against loss of pressure in the fluid flowing from an accumulator to the primary inlet/exhaust valve assembly (30) by a single sealing element (70) which encircles the primary inlet port (20) and provides a face seal between the relatively movable surface of the primary reaction piston (14) of the bore (16) of the valve housing (10). In the embodiment shown, two O-rings (70) are mounted in grooves (72) surrounding diametrically opposite inlet ports (20). In Fig. 4 (not shown) the O-ring seal is mounted in a housing groove. <IMAGE>

Description

SPECIFICATION Dual brake valve This invention relates to dual brake valves for use in fluid pressure-operated vehicle braking systems having independent primary and secondary braking circuits and is particularly concerned with dual brake valves of the kind comprising a housing having two sets of ports, each associated with a different one of the two braking circuits and each comprising a fluid inlet or supply port and a fluid outlet or delivery port, primary and secondary coaxial valve assembles each associated with a different one of said sets of ports and operative, when actuated, to seal off the delivery ports from exhaust and connect them to their associated inlet ports.

In one such valve forming the subject of the Appiicant's Patent No. 1466296, the input effort exerted on a foot pedal or the like is applied, via graduating means in the form of a coil spring or a resilient block of rubber, to an input system controlling the two valve assemblies and comprising a reaction piston or carrier for the primary valve assembly.

Known valves of this type are usually provided with at least two radially fitted sealing rings arranged on opposite sides of the inlet port of the primary braking circuit so that the fluid applied to the primary valve assembly is maintained at reservoir pressure. The consequent degree of friction depends upon the amount of sealing ring interference, diametral size and bore finish and is relatively high when the sealing rings are stationary for a period of time and varies considerably in dynamic applications.

It is a principal object of the present invention to provide a dual brake valve which is relatively simple and inexpensive to produce, is subject to a considerably reduced degree of friction resulting in lower and more consistent valve hysteresis and has minimum pressure differential between the output circuit delivery pressures.

To this end, according to the invention the usual radially fitted sealing rings are replaced by a single element which encircles the inlet port under minimal initial compression and provides a face seal between the relatively movable surfaces of the reaction piston and housing.

The sealing element is preferably an O-ring which may be much smaller in diameter than the two radially fitted rings used in conventional valves and may be fitted in a groove in either the housing wall or the reaction piston, and in the latter case may be subjected to reservoir pressure which forces it into sealing engagement with the housing wall. In one embodiment of the invention, initial sealing is achieved by a simple spring clip of synthetic plastics material which presses the sealing element against the housing wall. The resultant friction loads are therefore low and very consistent, irrespective of the conditions, which is particularly desirable in the case of dual brake valves of the kind referred to, for the reasons set out above.

Another advantage of the provision of a face seal in accordance with the present invention is that the housing can be made in the form of a single casting having a single bore of mainly uniform diameter and the inlet and outlet ports of each valve element horizontally aligned with one another. This is in contrast to conventional dual brake valves which generally consist of two castings each generally containing a separate valve element centre-joined to allow cores to be provided for delivered fluie from the primary circuit. It will be appreciated, therefore, that the invention facilitates manufacture and yields considerable savings in production costs.

As friction factors, head loads etc, are reduced the risk of valve motorisation increases and it is a further object of the invention to provide adequate damping of all control pressure to ensure no pressure oscillation can be set up.

Known control valves of the kind described in Patent No. 1466296 are already baffled, but because of their design and the space taken up by the radial pressurised sealing rings, it has only been possible to provide a baffle on a reduced area of the reaction piston and such valves are consequently more prone to motorisation especially when used in conjunction with helical coil steel graduating springs.

It is accordingly a further feature of the invention to provide the reaction piston with an internal baffle plate which extends across the whole width of the housing bore and is provided with a small bleed hole which connects the primary delivery port with the space below the reaction piston and provides a slower build-up of fluid pressure which is felt directly at the input plunger.

To balance lateral loading applied to the reaction piston due to face sealing, the housing may have diametrically opposed inlet ports, both connected to the supply of pressure fluid. The outlet or delivery ports may also be diametrically opposed.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-section of a dual-circuit brake valve; Figure 2 is a plan view partly in cross-section taken along line AA in Figure'1; Figure 3 is a cross-section taken on iine BB in Figure 1; and Figure 4 is a detailed cross-section of an alternative valve in whichface sealing is achieved by means of a seal on the valve housing.

The valve shown in Figures 1 to 3 comprises a generally cylindrical housing 10 in one end of which is mounted an input plunger 12 adapted to be actuated by pedal (not shown).

A carrier or reaction piston 14 is slidably received in a bore 16 of the housing 10 and movable in response to actuation of the pedal by means of a travel spring assembly 18 as shown on the left-hand side of the cross-section or, in the alternative, a rubber spring 18' as shown on the right-hand side, acting between the input plunger 12 and the carrier or reaction piston 14.

The housing 10 is formed from a single casting and has through the housing wall, upper and lower sets of input or supply ports 20, 21 and outlet or delivery ports 22, 23, the sets being associated respectively with the primary and secondary braking circuits (not shown). Each set comprises two inlet ports which are diametrically opposed across the bore of the housing and connected to a source of fluid under pressure, usually an air reservoir. The two diametrically opposed delivery ports are connected to the associated braking circuit.

A primary inlet/exhaust valve assembly 30 is carried by the reaction piston 14 and a secondary inlet/exhaust valve assembly 32 is mounted in the lower end of the housing.

Between the two valve assemblies is a tubular piston assembly 34 running in the bore 16 and having an upper stem 36 which is slidably received in a baffle plate 38 integral with the carrier 14. A lower stem 40 of the piston assembly 34 is received in another baffle plate 42 bridging the lower end of the bore 16. The spaces 44,46 above and below the piston assembly 34 communicate respectively with the primary and secondary delivery ports 22,23 via bleed holes 48,50 in the related baffle plate.

The upper and lower ends of the tubular piston assembly form annular exhaust valve elements 52,54 coacting with the heads of the inlet valve elements 56,58 on a smaller diameter than that of the inlet valve seats 60,62.

Although, the illustrated valve differs from conventional valves in many significant respects as will be described below, the principle of operation is much the same and is not described in detail. Briefly, the inlet valve elements 56,58 are normally in engagement with the valve seats 60,62 but are spaced from the exhaust valve elements 52,54 whereby the delivery ports 22,23 are connected to the exhaust via a passage defined by the tubular piston assembly 34 and the middle of the secondary inlet valve assembly 32.

Upon downward displacement of the carrier 14 in response to pedal operation, the primary inlet valve 30 in turn displaces the tubular piston assembly 34 so closing-off connection between the delivery ports 22,23 and the exhaust passage and both inlet valve elements 56,58 are lifted from their seats 60,62 so connecting the supply of fluid under pressure to the delivery ports 22, 23.

O-rings 70 are fitted in grooves 72 in the carrier 14 to provide face seals encircling the primary inlet ports 20. As shown in Figure 2, a spring clip 76 is inserted behind each O-ring 70 to keep it in contact with the bore 16 and provide initial sealing. Also, the groove 72 communicates with the inlet fluid pressure via a passage 78 so that in use the O-ring is urged into its sealing position by the pressure differential across the seal.

To locate the carrier 14 and hence the face seals in the desired angular position relative to the housing 10, a pin 80 is fitted in the carrier to run in a longitudinally extending locating groove 82 formed in the upper end of the bore wall.

Figure 4, illustrates an alternative arrangement in which an O-ring seal 70' providing face sealing around the inlet port 20, is mounted in a plug 84 defining therethrough the inlet port and secured to the valve housing 10 by screws 86. To adjust the force with which the O-ring 70' bears upon the carrier piston (i.e. the O-ring 'nip') shims may be inserted between the flange 85 on the plug 84 and the housing 10.

The valve shown in Figures 1 to 3 includes a baffled reaction piston in a much more compact housing than would be possible with conventional valves. The baffle plate 38 is integral with the reaction piston and output pressure is fed directly to the delivery port 22. A small bleed hole 48 also communicates with the space below the reaction piston. It is the slower build up of air pressure on this area which is felt directly back at the input plunger 12.

As stated above, it is usual to have a single or dual centre piston fitted with '0' rings or sealing rings to provide air operation of the secondary circuit. It is well known that the design of this type of control valve permits a minimum pressure hysteresis between the pressure outputs of the primary and secondary circuits. Rigid constructions generally suffer from air leakage at the valve seats, with tight constraints on machining, concentricities and out of squareness.

The tubular piston assembly 34 however, comprises a flexible double seal arrangement 86 with centre exhaust vent 88 which allows the identical centre pistons 90, 92 to move minutely within the rubber mounting to relieve the concentricity problem. This also enables the pistons to be moulded completely from synthetic plastics material without machining.

Generally known valves having two castings use the uppercasting as a centre piston upper stop. This method prescribes that the exhaust valve lift is subject to the allowed tolerances of the involved detailed parts. The illustrated valve comprising only one casting includes a centre adjustable bolt 94 fixed to a plate 96 beneath the lower inlet/exhaust valve. This enables the stop to be so adjusted to give a minimum value a to the primary circuit exhaust lift and a maximum value b to the secondary circuit exhaust lift (see Figure 1). In effect, this gives a much reduced value to the total exhaust lift as the centre piston will move to compensate the inlet/exhaust valve which is exhausting more slowly.

Inlet/exhaust valves are well known with rubber bonded to metal pressings and having a single moulded lip so that the air inlet pressure may be balanced. However, in the illustrated embodiment, the valve 58 is shown as being moulded with two rubber sealing lips 98, 100 so that the output pressure is fed through a small hole 102 to the area 104 between the sealing lips to give a fully balanced valve. A similar arrangement is shown as being provided on the valve 56 and this provides a very cheap alternative to known designs without resorting to '0' ring sealing and drilling and can be used with a plastics moulded inlet/exhaust guide. Fully balanced valves are essential if the valve travel/pressure hysteresis is to be kept to a minimum.

Claims

1. A dual brake valve of the kind set forth which is sealed against loss of pressure in the fluid flowing to the primary valve assembly by a single sealing element which encircles the primary inlet port and provides a face seal between the relatively movable surfaces of the reaction piston and housing.

2. A valve according to claim 1, wherein said sealing element is an O-ring mounted in one of said surfaces.

3. A valve according to claim 2, wherein the O-ring is mounted under minimal initial compression in a groove formed in the outer surface of the reaction piston and so connected to the primary fluid passage through the valve that, in operation, the pressure of the fluid flowing through the primary braking circuit forces the O-ring into sealing engagement with the housing wall.

4. A valve according to claim 3, wherein the O-ring is maintained in contact with the housing wall by an annular spring clip inserted into the bottom of the groove.

5. A valve according to claim 2, wherein the O-ring is mounted at the inner end of a plug secured in an aperture in the housing wall and having a central bore forming the inlet port.

6. A valve according to claim 5, wherein the plug is formed with an external flange for the passage of screws securing the plug to the housing and the force with which the 0ring bears against the reaction piston is adjustable by the insertion of shims between the flange and the housing.

7. A valve according to any preceding claim wherein each set of ports comprises two diametrically opposed inlet ports and two diametrically opposed outlet ports, with each inlet port encircled by a separate face-sealing element.

8. A valve according to any preceding claim, in which the housing comprises a single casting having a bore of uniform diameter for most of its length, said bore containing both primary and secondary valve reaction pistons, and wherein the inlet and outlet ports of one set are arranged in one horizontal plane and the inlet and outlet ports of the other set are arranged in another horizontal plane.

9. A valve according to any preceding claim, wherein a pin projects radially from the primary reaction piston into a longitudinal groove in the upper end of the housing wall to locate the piston angularly relative to the housing.

10. A valve according to any preceding claim, wherein the head of the primary reaction piston is provided with an integral baffle plate which extends across the whole width of the housing bore and is provided with a bleed hole connecting the primary outlet port to the space immediately below the primary reaction piston.

11. A valve according to claim 10, wherein the primary and secondary valve assemblies have inlet/exhaust valve elements which cooperate with annular valve seats on the primary reaction piston and the housing respectively and with annular exhaust valve elements of less diameter than said valve seats, formed at the upper and lower ends respectively of a central hollow piston assembly arranged in the housing bore between the primary and secondary valve assemblies.

12. A valve according to claim 11, wherein the exhaust valve elements are formed at the ends of tubular stems which pass through the baffle plate on said primary reaction piston and a similar baffle plate bridging the lower end of the housing bore respectively, the latter baffle plate also being provided with a bleed hole connecting the secondary delivery port to the space immediately below the central piston assembly,

13. A valve according to claim 12, wherein said central piston assembly comprises two identical annular piston elements joined together at their peripheries and terminating at their centres in said tubular stems.

14. A valve according to any one of claims 11 to 13, wherein said central piston assembly is formed by moulding from synthetic plastics material.

15. A valve according to claim 14, wherein said central piston assembly is provided, around its periphery with a sealing element of flexible material having two sealing lips on opposite sides of an exhaust vent.

16. A valve according to claim 15, wherein said sealing element is made of rubber.

17. A valve according to any one of claims 11 to 16, wherein an adjustable bolt passes upwardly through the centre of the secondary valve assembly into said hollow central piston assembly and is acted upon by said input system through the medium of a spring to provide a minimum value for the primary circuit exhaust lift and a maximum value for the secondary circuit exhaust lift.

CLAIMS Amendments to the claims have been filed, and have the following effect: New or textually amended claims have been filed as follows:

12. A valve according to claim 11, wherein each inlet/exhaust valve element of said primary and secondary valve assemblies is provided with two rubber sealing lips concentric with the valve axis, the annular space between the lips being exposed to the output pressure through a small hole in order to make the valve fully balanced in all pressure conditions.

13. A valve according to claim 11 or 12, wherein the exhaust valve elements on the central piston assembly are formed at the ends of tubular stems which pass through the baffle plate on said primary reaction piston and a similar baffle plate bridging the lower end of the housing bore respectively, the latter baffle plate also being provided with a bleed hole connecting the secondary delivery port to the space immediately below the central piston assembly.

14. A valve according to claim 13, wherein said central piston assembly comprises two identical annular piston elements joined together at their peripheries and terminating at their centres in said tubular stems.

15. A valve according to any one of claims 12 to 14, wherein said central piston assembly is formed by moulding from synthetic plastics material.

16. A valve according to claim 15, wherein said central piston assembly is provided, around its periphery with a sealing element of flexible material having two sealing lips on opposite sides of an exhaust vent.

17. A valve according to claim 16, wherein said sealing element is made of rubber.

18. A valve according to any one of claims 12 to 17, wherein an adjustable bolt passes upwardly through the centre of the secondary valve assembly into said hollow central piston assembly and is acted upon by said input system through the medium of a spring to provide a minimum value for the primary circuit exhaust lift and.a maximum value for the secondary circuit exhaust lift.