GB2158534A - Venting compressed air brakes - Google Patents

Abstract

In a dual circuit foot valve assembly for a vehicle compressed air braking system a tendency for foot pedal oscillation to occur is reduced by providing flow restrictor 41 linked to the pedal plunger 9 and which quickly moves into a fluid flow restricting position in the exhaust air passage from both double valves to become effective except for pedal positions at or near full release. <IMAGE>

Description

SPECIFICATION Fluid Pressure Valve Assemblies This invention relates to fluid pressure valve assemblies and relates especially to foot operable brake pressure control valves for air braking systems of vehicles.

It is commonplace to employ compressed air braking systems on heavy commercial and passenger-carrying road vehicles the brakes being controllable by a driver's foot operable valve. The driver's valve is usually designed to provide two separate but nonetheless approximately equal output pressures for independent braking circuits of the vehicie. In some such vehicles relatively soft springing is utilised both in the front vehicle suspension itself and also in the driver's seat mountings and it is found that with certain combinations of such springing and braking force exerted by the driver's foot there is a tendency for oscillation to be set up in the foot valve which manifests itself in a vibration of the foot pedal and pulsed venting of the braking system by the foot valve with resultant loss of air.

The object of the invention is to provide a foot valve with means operable to reduce such pulsed venting and consequent vibration and loss of air.

According to the present invention there is provided a fluid pressure control valve assembly having a housing including input force applying means a double valve arrangement incorporating an inlet valve between an inlet port and an output port a vent valve between the output port and a vent port said double valve being operable by a fluid pressure responsive member moveable in one direction in response to a force applied via resilient means in a sense to open the inlet valve and moveable in the opposite direction in response to pressure at the output port in a sense to open the vent valve the operation thereby being such as to produce delivered output port pressure related in a predetermined manner to said force and characterised by a variable flow restrictor located between the vent valve and the vent port the opening through which restrictor initially increases less rapidly than the opening through the opening vent valve when opening from a closed condition.

In such a fluid pressure valve assembly which includes a further such double valve being operable by a further pressure responsive member the restrictor means may be in a flow path to a common vent port for both said double valves and operable by means coupled to passing through both said valves.

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 the single figure of which illustrates a dual circuit fluid pressure control valve embodying the invention.

Referring to the drawing, the valve illustrated is a dual circuit foot operable control valve for a compressed air braking system of a vehicle. The assembly comprises a cast metal housing denoted by reference 1 which is provided with a first circuit input port 2, a first circuit output port 3, a second circuit input port 4 and a second circuit output port 5. A common vent port 6 is provided at the lower end of the assembly communicating with an inner central space reference 7 via which delivered pressures at the first and second output ports are each dischargeable.

The upper end of the assembly is provided with a pressed metal cap 8 which provides for guiding and retention of an input force applying member in the form of a plunger 9 having a central recess 10 with which a driver's foot pedal assembly is engageable.

Captive between the plunger 9 and a first pressure responsive member in the form of a piston assembly 11 there is resilient means in the form of a pair of springs 12 and 13. Piston assembly 11 also has a weight balancing spring 24a and has first second and third seals 14, 15 and 16 slideable in respective bores of the housing. The seals 14 and 15 slide in bores of different diameters to provide a pressure responsive annular area which communicates with the output port 3 via a passage 17. The input port 2 of a first double valvecommunicates therewith via a region formed between seals 15 and 16. The first double valve comprises a tubular member 18 slideable within the piston assembly and having a valve closure member 19 engageable with an inlet valve seat 20.

The valve member 19 is urged against the valve seat 20 by a light spring 21 and 19 is engageable with an exhaust valve seat 23 formed on a second pressure responsive member in the form of a piston 22. The piston 22 is provided with a weight-balancing spring 24b and at its lower end has a further exhaust valve seat 25 for a second double valve arrangement which is resiliently urged by a spring 48 into engagement with an inlet valve seat 26 retained within the housing, the second double valve member 49 being carried by a tubular member 27.

The piston 22 is provided with double seals 28 and 29 the space between which is vented via passage 30 into the central-vented region 7 in order to avoid the possibility of leakage between the first and second circuits.

The plunger 9 has a downwardly extending stem 31 having an upper reduced diameter portion 32 sliding in a seal 39 and stem 31 is attached to the plunger by a screw 33. The stem passes through exhaust passages for both double valve assemblies and has a reduced diameter lower end portion guided by a spigot 34 carried by vent plate 35 set in position by screws such as 36. An end stop screw 37 is provided in a threaded lower part of the spigot 34 the position of which screw can be adjusted prior to attachment of a snap-on cap 38 which carries vent port 6. Slideable on the guide port 34 there is a further tubular member 40 with an annular lower flange. The member 40 is slideably carried on stem 31 which has a stop 48 against which it is lightly urged by a spring 43 the upper end of which rests against the plunger via a stop ring 44.The flange 41 co-operates with an annular seat 45 to operate as a variable restriction means to close off the main vent aperture 46 of the vent plate 35 leaving only the more restricted vent passage via one or more smaller apertures 47.

In operation of the dual foot valve assembly illustrated in the drawing, input ports 2 and 4 are connected to respective air pressure storage reservoirs. In the rest position of the assembly as shown, the exhaust valve seats 23 and 25 are shown separated from the respective double valve members and output ports 3 and 5 which are connected to respective brake actuators or relay valves controlling such actuators, are vented through the vent port 6 via the central region 7. In order to apply the vehicle brakes, the driver depressed a foot pedal which causes downward movement of the plunger8 carrying the member 41 quickly into closing position over apertures 46.The force exerted by plunger 9 through springs 12 and 13 is exerted directly on piston 11 causing downward movement of this piston and engagement of the double valve member 19 with the exhaust valve seat 23 thereby sealing off the output port 3 from atmosphere. Slight further downward movement causes unseating of the double valve member from the inlet valve seat 20 thereby providing communication between the storage reservoir connected to port 2 and the output port 3 the elevation of pressure acting on the upper surface of the piston 22 causes simultaneous downward movement of the piston 22 to close off the exhaust valve seat 25 and unseat the double valve member 28 from its inlet valve seat thereby providing for equivalent output pressure at the output port 5 and acting on the underside of the piston 22.As pressures at the output ports 3 and 5 build up the resultant upward force against compressed springs 12 and 13 both the double valve settle to a lap condition whereby each is engageable with its inlet and exhaust valve seats.

The output pressures at 3 and 5 therefore stabilise at a value dependent upon the force exerted by the driver's foot pedal on the plunger 9. Upon a slight reduction of the pressure on the driver's foot pedal there is an immediate unseating of each of the exhaust valve seats 23 and 25 due to the upward movement of piston 11. This results in a tendency towards an outward rush of air under pressure via both ports 3 and 5 and in order to counteract this the driver maytend to again depress the plunger 9 and the combination of all the pressures, springs and masses in the system can tend to result in pulsed venting of the brakes through the control valve to atmosphere. In order to alleviate such tendency however, the tubular member 40 which is now moved downwards effecting engagement between flange 41 and seat 45 by virtue of the downward movement of the plunger 9.Even for small such downward movement the main common vent passages 46 are closed off leaving only restricted passage 47. There is therefore only an impeded outflow of air from the brakes via the ports 3 and 5.

Owing moreover to the balanced nature of the piston 22 and the manner in which it controls the double valves of both circuits only balanced and controlled venting occurs in such conditions. Upon full release of the foot pedal pressure on plunger 9 however not only are the valve seats 23 and 25 the more fully separated from their double valve members but the flange 41 is also now lifted from seat 35 by the action of stop 48 to again uncover the main vent passages 46 and substantially unimpeded venting of the first and second circuits occurs for full brake release. Clearly the exhaust way through for such full brake release can be designed to be as large as may be required. By virtue of the foregoing an improved and more stable dual foot valve can be produced.

Moreover, an added benefit results from the provision of a simple adjustable stop-screw 37 adjustment of which on assembly can avoid the necessity for shims or other stop means to iimit the movement of the plunger 9 to a desired amount.

Claims (7)

1. A fluid pressure control valve assembly having a housing including input force applying means a double valve arrangement incorporating an inlet valve between an inlet port and an output port a vent valve between the output port and a vent port said double valve being operable by a fluid pressure responsive member moveable in one direction in response to a force applied via resilient means in a sense to open the inlet valve and moveable in the opposite direction in response to pressure at the output port in a sense to open the vent valve the operation thereby being such as to produce delivered output port pressure related in a predetermined manner to said force and characterised by a variable flow restrictor located between the vent valve and the vent port the opening through which restrictor initially increases less rapidly than the opening through the opening vent valve when opening from a closed condition.

2. Afluid pressure control valve assembly having a housing including input force applying means a first double valve arrangement incorporating an inlet valve between a first inlet port and a first output port a vent valve between said output port and a vent port said double valve being operable by a fluid pressure responsive member moveable in one direction in response to a force applied via resilient means in a sense to open the inlet valve and moveable in the opposite direction in response to delivered pressure at the output port in a sense to open the vent valve a second double valve arrangement incorporating an inlet valve between a second inlet port and a second output port and a vent valve between said second output port and said vent port said second double valve being operable by a second fluid pressure responsive member moveable in one direction in response to a force applied via the resilient means and or said delivered pressure in a sense to open the respective inlet port (of the second double valve arrangement) and moveable in the opposite direction in response to delivered pressure at the second output port in a sense to open the respective vent valve the operation thereby being such as to produce respective delivered pressures at the output ports related in a predetermined manner to the said force and characterised by a variable flow restrictor located between the vent port and the respective vent valves the opening through which restrictor initially increases less rapidly than the openings through the opening vent valves when opening from a closed condition.

3. A fluid pressure control valve assembly as claimed in claim 1 or 2 said variable flow restrictor comprising a restrictormembermoveabletowards a most restricting position upon movement of an actuator member of the assembly away from a full venting position to remain in said most restricting position for further movement of the actuator member over a range of delivered pressures.

4. Afluid pressure control valve assembly as claimed in claim 3 said restrictor member comprising an annular member moveable towards and away from an aperture.

5. Afluid pressure control valve assembly as claimed in claim 4 said annular member having means guiding it on a spigot.

6. Afluid pressure control valve assembly as claimed in claim 4 or 5 the restrictor member being urged by a light spring against stop carried by the actuator member.

7. A dual circuit compressed air control valve assembly substantially as described herein with reference to the accompanying drawing.