GB2360079A

GB2360079A - Cooling system pressure control valve assembly

Info

Publication number: GB2360079A
Application number: GB0005554A
Authority: GB
Inventors: William Richard Hutchins
Original assignee: Bayerische Motoren Werke AG; MG Rover Group Ltd
Current assignee: Bayerische Motoren Werke AG; MG Rover Group Ltd
Priority date: 2000-03-09
Filing date: 2000-03-09
Publication date: 2001-09-12
Also published as: GB0005554D0

Abstract

A pressure control valve assembly (28) for the cooling system of a liquid-cooled internal combustion engine is incorporated in the filler cap (25) of an expansion tank (21). A diaphragm (36) and diaphragm support plate (43) are movable in the cap (26) by pressure in the cooling system against the bias of a helical spring (45). A non-return valve (40) acts as an anti-vacuum valve to allow flow into the cooling system if the pressure drops below atmospheric. The non-return valve (40) is also unseated when, at a predetermined pressure in the cooling system, movement of the diaphragm (36) against the spring (46) causes the non-return valve to abut a boss (46) on the cap body. The outer periphery of the diaphragm is preferably trapped in sealing engagement between a retainer (28) and a cylindrical spacer (38). Movement of the support plate (43) under the bias of spring (45) is limited by abutment of rim (44) with flange (41) of the spacer (38).

Description

2360079 Cooling System Pressure Control Valve Assemb This invention

relates to Pressure Control Valve Assemblies for the cooling systems of liquid cooled internal combustion engines. Such assemblies are normally incorporated in a closure cap for an expansion tank. In modern motor vehicles such expansion tanks are usually situated in a convenient underbonnet location away from a radiator of the cooling system. However, in former times such expansion tanks were normally formed as a radiator header tank and such closure caps are still frequently referred to as radiator caps.

For many years radiator caps have evolved around a design in which a spring loaded washer closes an orifice at the base of a filler neck so that at a predetermined pressure the washer lifts against the spring to so limit the pressure in the cooling system. A support plate for the washer would incorporate a so called vacuum valve (more accurately an anti-vacuum valve), to prevent the pressure falling significantly below atmospheric when the cooling system cools. An example of such a cap is shown in US 2, 164,450.

A move towards engine compartments of reduced height has resulted in cross flow radiators and a remote location for the expansion tank, as previously mentioned. Such expansion tanks are frequently made of plastics and these usually require the use of a screw threaded closure cap which incorporates the pressure control valve as an integrated assembly, i.e., these do not rely on there being a seating orifice in the expansion tank filler neck. An example of such an arrangement is shown in GB 1534 318. A problem with such valve assemblies is that there may be long periods of operation in which the pressure in the cooling system rises to that set by the spring loaded washer but there is insufficient rise in temperature or requirement to vent gasses from the cooling system to cause the washer to unseat against the spring bias. As a result the washer tends to stick on its seat and a considerably higher pressure than was originally set by the spring bias load is required to unseat it. The older design of cap as illustrated by US 2,164,450 did not suffer this problem since it was normal practice to remove the cap to inspect the coolant level so the washer and its mating surface did not remain in contact for long periods. Furthermore, imperfect sealing of the cylinder head gaskets would allow minute quantities of combustion gas to escape into the cooling system and this would be vented through the cooling system closure cap.

The present invention has as an object the provision of a valve assembly where the tendency for valve sticking and over pressure is much reduced.

In accordance with a first aspect of the invention there is provided a pressure control valve assembly for the cooling system of a liquid-cooled internal combustion engine, the valve assembly including a housing, an abutment in the housing, a piston movable in the housing by pressure in the cooling system against a spring bias, passage means in the assembly which in use is in a path between the cooling system and atmosphere and a non-return valve which allows flow from the passage into the cooling system, the assembly being arranged such that at a predetermined pressure in the cooling system movement of the piston against the spring bias causes the abutment to unseat the non-return valve and allow venting from the cooling system through the passage means.

Conveniently, the piston comprises a flexible diaphragm and a diaphragm support member, in which case an outer periphery of the diaphragm may be fixed and sealed to the housing. The housing may comprise at least two housing members, the outer periphery of the diaphragm being trapped between adjacent housing members.

The spring bias may be provided by a compression spring acting between the housing and the piston.

Preferably, the non-return valve is in the piston, in which case, the nonreturn valve may comprise a mushroom-shaped valve member. having a stem which extends through an orifice in the piston and a head which can seal against the piston. Where the piston comprises a flexible diaphragm and a diaphragm support member, the head of the mushroom-shaped valve member can abut the diaphragm when the non-return valve is closed.

Where the piston comprises a flexible diaphragm and a diaphragm support member, the diaphragm support member can abut the housing to limit movement of the piston under the action of the spring bias.

In accordance with a second aspect of the invention there is provided a cooling system for a hquid-cooled internal combustion engine, the cooling system including a heat exchanger, passage means for connecting the heat exchanger to the engine, an expansion tank connected to said passage means and a pressure control valve assembly according to said one aspect of the invention. Conveniently, the expansion tank has a closure cap and the pressure control valve assembly is incorporated in the closure cap.

In accordance with a third aspect of the invention there is provided a closure cap incorporating a pressure control valve assembly according to said first aspect of the invention for use in a cooling system according to said second aspect of the invention.

The invention will now be described by way of example and with reference to the accompanying drawings, of which:- Fig. 1 is a diagrammatic representation of the cooling system of a liquid cooled internal combustion engine incorporating a pressure control valve assembly according to the invention; and Fig.2 is a cross section through a pressure control valve assembly according to the invention incorporated in a closure cap of an expansion tank shown in Fig. 1.

Referring to Fig. 1, an internal combustion engine 11 has a pump 12 which can deliver liquid coolant (e.g., a waterlantifreeze mix) through the engine to a delivery hose 13 and a heat exchanger in the form of a conventional air cooled radiator 14.

Flow from the radiator 14 to the pump 12 is through a radiator return hose 15 and a pump return hose 16. A thermostat and bypass control valve 17 operates to control flow in the radiator return hose 15 and in a bypass hose 18 such that until the coolant reaches higher temperatures most of the flow of coolant from the engine 11 is through the bypass hose 18 and there is no flow through the radiator 14. At higher coolant temperatures, most of the flow is through the radiator 14 and not through the bypass hose 18.

An expansion tank 21 has a feed hose 22 connected to the delivery hose 13 and a return hose 23 connected to the radiator return hose 15 (or, optionally, to the pump return hose 16 as shown at 23A). The expansion tank 21 has a filler neck 24 closed by a closure or filler cap 25 which incorporates a pressure control valve assembly 26 as shown in detail in Fig.2.

Referring to Fig.2, the filler cap 25 includes an inverted cup shaped body 27 which is internally threaded to engage corresponding external threads on the finer neck 24. An annular retainer 28 has an outwardly extending flange 29 having a number of outwardly directed tongues 31 on its outward periphery, a cylindrical portion 32 and an inwardly directed flange 33. A number of the tongues 31 are bent upwards so as to space the outwardly directly flange 29 from the adjacent lower face of the body 27. This spacing is also assisted by an L section moulded ring 34 which has castellations 35 where it abuts the retainer 28.

A diaphragm 36 has an outer lip 37 which is retained in sealing engagement with the retainer 28 at the junction of the cylindrical portion 32 and the inwardly 5 directed flange 33 by a generally cylindrical spacer 38. This has slots or castellations 39 at one end where it abuts the base of the filler cap body 27 and an inwardly directed flange 41 at the other end, adjacent the diaphragm 36. A corner recess 42 is provided in the spacer 38 to accommodate the diaphragm lip 37.

A diaphragm support member in the form of a metal support plate 43 has an offset outer rim 44 and is biased away from the base of the filler cap body 27 by a helical compression spring 45 such that in the as assembled condition shown in Fig.2 the rim 44 abuts the flange 41 of the spacer 38. The diaphragm 36 has a central orifice 50 where it is retained by a bent over inner rim 46 of the support plate 43. The diaphragm 36 and support plate 43 carry a non-return valve 40 comprising a mushroom-shaped valve member 47. This comprises a cruciform section stem 48, an integral abutment flange 49 and a separate sheet metal head 51 which is retained on the stem 48 by an integral rivet head 52. A conical com pression spring 53 acts to bias the stem 48 so that a beaded outer rim 54 normally seals against the diaphragm 36 to seal the central orifice 50.

A sealing washer 55 seals between the end of the filler neck 24 and the out-turned flange 29 of the retainer 28 so that in the condition shown in Fig.2 the expansion tank 21 is closed by the retainer 28, the diaphragm 36 and the non-return valve 40.

In use liquid coolant circulates through the expansion tank 21 through the feed and return hoses 22 and 23Following a cold start, the air above the level of liquid coolant is heated and there is a rise in pressure. This causes the diaphragm 36 to move against the spring bias of the compression spring 45 until the abutment flange 49 of the non-return valve 40 abuts an abutment boss 56 extending from the base of the filler cap body 27. Increasing pressure in the cooling system moves the diaphragm 36 upwards away from the non-return valve head 51 so that the beaded outer rim 54 becomes spaced from the diaphragm 36 and air can escape past the non-return valve 40 and through the orifice 50 into the space above the support plate 43. From here air can escape to atmosphere through the slots 39 in the spacer 38, the castellations 35 in the moulded ring 34, between the out-turned flange 39 and the body 27, through gaps between the tongues 31 and between the threads on the fifier cap body 27 and the filler neck 24. Thus the maximum pressure in the cooling system is limited and cannot increase significantly above that at the point where the non return valve 40 opens by abutment of the valve member 47 with the boss 56. It will be appreciated that this maximum pressure is determined by the effective area of the diaphragm 36 which, together with the support plate 43 acts as a spring biased piston, the actual load of the helical spring 45 at the point of valve opening and by the pre-load of the conical spring 53. This means that there is a very much reduced tendency for the non-return valve head 51 to stick onto the diaphragm 36 and that, if such sticking does occur, the increase in pressure required to unstick the non-return.valve 40 is very much lower than is required in a conventional filler cap where the whole of the load of a regulating spring bears against a valve seat.

When the engine 11 is stopped and the cooling system cools down, the nonreturn valve 40 acts as a conventional anti-vacuum valve to prevent the pressure in the cooling system falling significantly below atmospheric. The fact that the non-return valve 40 serves two functions, one as part of the regulation of the maximum pressure and the other as the anti- vacuum valve, means that there is less chance of the head 51 remaining in engagement with the diaphragm 36 for long period and thus becoming stuck.

It will be appreciated that instead of venting to atmosphere past the threads in the filler neck and the filler cap, there may be a separate vent passage to duct 5 any hot air or steam away from the vicinity of the filler cap 25.

Claims

CIAIMS

1. A pressure control valve assembly for the cooling system of a liquidCooled internal combustion engine, the valve assembly including a housing, an abutment in the housing, a piston movable in the housing by pressure in the cooling system against a spring bias, passage means in the assembly which in use is in a path between the cooling system and atmosphere and a non-return valve which allows flow from the passage into the cooling system, the assembly being arranged such that at a predetermined pressure in the cooling system movement of the piston against the spring bias causes the abutment to unseat the non-return valve and allow venting from the cooling system through the passage means.

2. An assembly according to claim 1 wherein the piston comprises a flexible diaphragm and a diaphragm support member.

3. An assembly according to claim 2 wherein an outer periphery of the diaphragm is fixed and sealed to the housing.

An assembly according to claim 3 wherein the housing comprises at least two.housing members and the outer periphery of the diaphragm is trapped between adjacent housing members.

5. An assembly according to any preceding claim wherein the spring bias is provided by a compression spring acting between the housing and the piston.

6. An assembly according to any preceding claim wherein the non-return valve is in the piston.

7. An assembly according to claim 6 wherein the non-return valve comprises a mushroom-shaped valve member having a stem which extends through an orifice in the piston and a head which can seal against the piston.

8. An assembly according to claim 7 when dependent upon claim 2, wherein the head can abut the diaphragm when the non-return valve is closed.

9. An assembly according to claim 2 and any claim dependent thereon wherein the diaphragm support member can abut the housing to limit movement of the piston under the action of the spring bias 10.

10. A cooling system for a liquid-cooled internal combustion engine, the cooling system including a heat exchanger, passage means for connecting the heat exchanger to the engine, an expansion tank connected to said passage means and a pressure control valve assembly according to any preceding claim for controlling the pressure in the cooling system.

A cooling system according to claim 10 wherein the expansion tank has a closure cap and the pressure control valve assembly is incorporated in the closure cap.

12. A closure cap incorporating a pressure control valve assembly according to any of claims 1 to 9 for use in a cooling system according to claim 11.

13. A pressure control valve assembly substantially as described herein with reference to the accompanying drawings.

14. A closure cap substantially as described herein with reference to the accompanying drawings.