MULTI-CIRCUIT FLUID PRESSURE CONTROL VALVE

Abstract: In a dual circuit compressed air foot operable valve for a braking system a first circuit double valve (15) carried by a pressurable input plunger (8) has an exhaust valve seat carried by a piston (24) and a second circuit double valve located in the housing has an exhaust valve seat carried by a piston (25) back to back with piston (24), the arrangement being such that out­ put pressure from the first circuit valve acts via one piston (24) and resilient springs (33, 34) on the other piston (25) to control the output pressure of the second circuit valve the tubular ex­ haust passage (31) through the former piston (24) being con­ structed by a member 30 carried by the latter piston (25) to re­ duce instability.

Description: Multi-Circuit Fluid Pressure Control Valve Assa s4 O i This invention relates to multi-circuit fluid pressure control valve assemblies and relates especially but not exclusively to dual circuit fluid pressure brake control valves. It is common to employ compressed air braking systems on heavy commercial and passenger carrying road vehicles the brake being controllable by a driver's foot operable valve. The driver's foot valve is usually designed to provide two separate but nonetheless usually equal output pressures for independent braking circuits of the vehicle. 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 driver's foot there is a tendency for instability or oscillation to occur in the foot valve which manifests itself in the vibration of the foot pedal and results in pulsed venting of the braking systems by the foot valve with resultant loss of compressed air from reservoirs supplying the valve. The object of the present invention is to provide an improved multi-circuit fluid pressure control valve. According to the present invention there is provided a multi-circuit fluid pressure control valve assembly including a housing, a first double valve for controlling a connection between a firstoutput port and a first input port or a vent port, a second double valve for controlling a connection between a second output port and a second input port or a vent port, the respective output ports being connected opposingly to respective pressurable areas of a pair of mutually resiliently interacting pressure responsive members and characterised by said members carrying mutually relatively displaceable parts which define a variable restriction between at least one said double valve and the respective vent port and which acts in a sense to more appreciably impede venting when the pressure members are uged-together. In order that the present 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 accompanring drawing which illustrates by way of example one embodiment of a dual-circuit fluid pressure control valve assembly in accordance with the invention. Referring to Fig. 1, the multi-circuit fluid pressure control valve assembly comprises a housing denoted by reference 1 having a first fluid pressure input port denoted by reference 2, a first fluid pressure output port 3, a second fluid pressure input port 4, a second fluid pressure output port 5 and a fluid pressure vent port 6. The dual circuit valve is controlled by the force exerted by a driver '5 foot pedal engageable with a socket 7 in an input piston 8 which carries seals 9, 10 and 11 sealingly slideable in the housing and is urged into the position shown by a return spring 12. The region between the seal 9 and the seal 10 provides an annular pressure responsive area on the piston which acts in the same direction as the spring 12 and has communicated therewith fluid pressure from the output port 3 via a passage 13. The input port 2 communicates with the region between the seals 10 and 11 of the input piston for supply of pressure from a reservoir connected to the port 2 to a double valve arrangement carried in the piston. The double valve arrangement consists of a tubular member 14 with a double valve member 15 urged into engagement with an inlet valve seat i6 by virtue of a light spring 17. The tubular member 14 is sealingly slideable in the piston by virtue of a seal 18 which isolates the input pressure from the vent passage. Referring now to the lower part of the valve assembly, a further double valve is provided input pressure to which is derived from the input port 4. This double valve comprises a tubular member 19 carrying a double valve member 20 urged by a spring 21 into engagement with a valve seat 22 retained in the lower part of the housing. Again the tubular member 19 is provided with a seal 23 whereby it is sealingly slideable but separates the input port 4 from the vent passage. Exhaus valve seats for the double valves are identically provided on a pair of mutually opposing resiliently separated pressure responsive members in the form-of pistons 24 and 25 the vent valve seat for the first circuit double valve being denoted by reference 26 and the vent valve seat for the second circuit double valve being represented by reference 27. These pistons feely slide on a guide rod 35 with end stops 36 and 37. These pistons are also mutually sealingly slideable in the bore portion 28 of the housing vented air from port 3 passing over an unseated vent valve member 15 being able to pass down axially through both pistons to reach the vent port 6. The piston 25 carries in its central web 29 an upwardly extending flow restriction member 30 which is mutually co-operable with a downwardly extending tubular portion 31 of the upper piston.24. The upper end of 30 being cut away to form peripheral castellations 32 whereby when the piston 24 and 25 have moved closer together a substantially increasing air flow restriction is provided for air being vented from the port 3 via the first circuit double valve. In operation of the dual circuit valve assembly, the first and second input ports 2 and 4 are respectively connected to separate reservoirs and the output ports 3 and 5 are connected to separate braking circuits of a vehicle. In the normal running position as shown and with no pressure exerted by the driver on the foot pedal, the output port 3 is vented by the valve member 15 unseated from the vent valve seat 26 and the output port 5 is vented by the valve member 20 being unseated from the vent valve seat 27. When the driver wishes to apply the service brakes his foot is pressed against the pedal which urges the piston b in a downward direction whereby the vent valve seat 26 of the first circuit valve is engageable by the valve member 15 thereby sealing off the output port 3 from atmosphere and due to the upward reaction exerted by piston 24 a slight further downward movement of 8 causes unseating of the valve member 15 from the input valve seat 16 to provide communication between the reservoir connected to port 2 and the port 3. The downward force exerted by the valve member 15 and the increasing pressure now acting on the upper surface of the piston 24 causes slight downward movement of this piston and downward force is thereby exerted via the separating springs 33 and 34 to the lower piston 25 which acts in a substantially identical manner to the first circuit double valve to provide output pressure at the port 5 accompanied by an upward reaction on the underside of piston 25. When the opposing pressures on pistons 24 and 25 sufficiently compress the springs 33 and 34 the double valves each lap into a condition where the inlet and vent valves are respectively closed and stable output pressures are produced at ports 3 and 5. Further downward movement of the piston 8 by the driver to increase the braking results in increasing stable pressure at ports 3 and 5. With such pressure applied at ports 3 and 5 it will be appreciated that the pistons 24 and 25 have been moved together against the resilience of springs 33 and 34 and that the upper end of the member 30 will have moved into closer relationship with the downwardly extending portion 31 of piston 24. Accordingly, upon reduction by the driver of the force exerted on the pedal accompanied by a slight upward movement of the piston 8, there is an immediate tendency for compressed air being applied at port 3 to rush in the return direction through the now unseated vent valve 26, 15 of the first circuit double valve. However, by virtue of the close relationship getween the upper end of 30 and the downward extending part 31, such outward rush of air towards the vent port 6 is appreciably impeded and a tendency for instability and possible oscillation of the system is thereby appreciably reduced. However, in the event the driver completely removes the force from the pedal whereby the piston 8 returns to the starting position shown, air is permitted to be vented from the port 3 virtually unimpeded to the output port 6. Similarly, complimentary pressure reduction occurs via the second circuit valve the output pressure from which acts on the underside of piston 25. Furthermore, it will be appreciated that by virtue of the balanced relationship between pistons 24 and 25 and the associated valve seats 26 and 27, by impeding the outflow of air via the first circuit vent valve the outflow of air via the second circuit vent valve tends to be attenuated in sympathy. The precise position of the piston 8 for which the restriction between 30 and 31 becomes effective is determined by the preload which is set into the springs 33 and 34 by the stops on the inner guide rod 33 and this and the component dimensions can be set to enable the choke to be effective down to whatever output pressure may be desired. However, for the purposes of a dual foot valve for a braking system the arrangement may preferably be such that the relative positions of the end of portion 31 and the bases of the castellations 30 are such that they align following some compression of springs 33 and 34, to close the restriction which restriction is maintained down to about 1 bar in a subsequent pressure releasing mode. In an alternative the part 30 could be carried by the piston 24 and the part 31 could be carried by the piston 25. In that case the restriction provided would be in the vent path for air from the output port 5 associated with the lower valve 20.

Claims: CLAIMS 1. A multi-circuit fluid pressure control valve assembly including a housing (1), a first double valve (15) for controlling a connection between a first output port (3) and a first input port (2) or a vent port (6) a seond double valve (20)for controlling a connection between a second output port (5) and a second input port (4) or a vent port (6), the respective output ports (3, 5) being connected opposingly to respective pressurable areas of a pair of mutually resiliently interacting pressure responsive members(24,25) and characterised by said members (24,25) carrying mutually relatively displaceable ports (31,32) which define a variable restriction between at least one said double valve and the respective vent port and which acts in a sense to more appreciably impede venting when the pressure members are urged together. 2. A multi-circuit fluid pressure control valve as claimed in claim 1, characterised by the first double valve (15) being carried by a piston (8) moveable in the housing and an exhaust valve seat (26) for said double valve being carried by a first of said pressure responsive members (24), said restriction being effective in a tubular portion (31) leading from said exhaust valve seat 3. A multi-circuit fluid pressure control valve as claimed in claim 1, characterised by the first double valve being carried by a piston (8) moveable in the housing and an exhaust valve seat for said double valve being carried by a first of said pressure responsive member (24) said second double valve (20) being located in the housing and an exhaust valve seat (27) for said second double valve being carried by the other (25) of said pressure responsive members, said restriction being effective in a tubular portion leading from said latter exhaust valve seat. 4. A multi-circuit fluid pressure control valve assembly as claimed in claims 1, 2 or 3 characterised by one said mutually displaceable part comprising a tubular portion (31) and the other mutually displaceable part comprising a restriction member (30) moveable into the tubular portion. 5. A multi-circuit fluid pressure control valve assembly as claimed in claim 4, characterised by the restriction member (30) having one or more peripheral castellations (32) the bases of which move sufficiently out of the proximity of the tubular portion (31) to substantially alleviate the restriction of the tubular portion (31). 6. A multi-curcuit fluid pressure control valve as claimed in any preceding claim characterised in that the dimensions and a resilient preload (33,34) between said pressure responsive members are such that in operation for increasing output pressures the restriction is defined before opening of a said double valve. 7. Multi-circuit fluid pressure control valve substantially as described herein with reference to the accompanying drawing.

Inventors: BENNETT, MARTIN JOHN, FOGG, STEPHEN WALTER
Applicants: BENDIX LIMITED
Application year: 1985
Main classification: B60T15
IPC codes: B60T15