GB2251917A

GB2251917A - Gas flow control valve.

Info

Publication number: GB2251917A
Application number: GB9101247A
Authority: GB
Inventors: Keith Ransom
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1991-01-19
Filing date: 1991-01-19
Publication date: 1992-07-22
Also published as: DE69201194D1; EP0496497B1; DE69201194T2; GB9101247D0; EP0496497A1

Description

225,1 ' 17 GAS FLOW CONTROL VALVE The present invention relates to gas

flow control valves and in particular to a valve for controlling a modulated flow of gas in one direction.

In internal combustion engine exhaust systems with catalytic converters, in order to assist catalyst lightoff, air may be pumped to the exhaust manifold of the engine so that the air will react with the engine gases to preheat the catalyst. In sugh systems, air is pumped into the exhaust manifold for several minutes after starting the engine and must then be shut down quickly. In order to avoid possible damage to the pump, for example melting of hoses or plastic components, it is essential to ensure that there is no backflow of hot exhaust gases from the exhaust system. Furthermore, the amount of air mixed with the exhaust gases is critical, too little air prolonging the warming up period and too much air over heating the catalyst so that there is a risk that it will melt. As the volume of exhaust gases will depend upon the engine speed, it is desirable that the flow of air to the exhaust manifold is modulated to maintain optimum proportions of air and exhaust gases at all engine speeds. Hitherto, this has been achieved by controlling the speed of the pump requiring a sophisticated pump motor and control system.

- 2 The present invention provides a gas flow control valve which will provide modulation of gas flow and will also prevent reversal of flow.

is According to one aspect of the present invention a gas flow control valve comprises a valve housing with an inlet and an outlet, the inlet and outlet being interconnected by a valve chamber, said valve chamber defining a valve seat intermediate of the inlet and outlet, the diameter of the valve chamber increasing away from the valve seat; a valve mgmber slidably mounted coaxially of the valve chamber, the valve member having a valve head adapted at one extreme of movement of the valve member to engage and close the valve seat; first and second gas-tight chambers being provided at axially spaced locations coaxially of the valve chamber, the valve member having a valve stem which extends through the first gastight chamber and into the second gas-tight chamber; a first diaphragm being attached at its inner periphery to the valve stem and at its outer periphery to a wall of the first gas-tight chamber, to divide the first gas-tight chamber into a pair of gas-tight compartments; a second diaphragm being mounted at its inner periphery to a plunger located coaxially within said second gas-tight chamber and at its outer periphery to a wall of the second gas-tight chamber, to divide the second gas-tight chamber into a pair of gas-tight compartments, resilient means being provided to urge the 1 1 3 plunger into engagement with the end of the valve stein; one compartment of the first chamber being connected to the inlet and the other compartment of the first chamber being connected to the outlet, such that when pressure at the inlet is in excess of that at the outlet, the pressure differential across the first diaphragm will apply a load to the valve member urging it out of engagement with the valve seat and when the pressure at the outlet is in excess of that at the inlet, the pressure differential across the first diaphragm will apply a load to the valve membe: urging it into engagement with the valve seat; and means being provided to apply a pressure differential across the second diaphragm which will apply a load to the plunger opposing that applied by the resilient means.

With the gas flow control valve described above, when pressure at the outlet is in excess of pressure at the inlet, the pressure differential across the first diaphragm will close the valve and prevent flow of gases from outlet to inlet. When gas under pressure is supplied to the inlet and the pressure at the inlet is in excess of the pressure at the outlet, the pressure differential across the first diaphragm will apply a load to the valve member7opposing that applied by the resilient means acting upon the plunger and will tend to open the valve member. The degree of opening may be controlled by the pressure differential across the second diaphragm which will oppose the load applied by the resilient means. Because of the varying diameter of the chamber between the inlet and outlet, the axial movement of the valve member will control the area of the opening and hence the flow rate of the gas from inlet to outlet. The pressure differential across the second diaphragm may be removed or even reversed, to ensure that the valve member is positively seated when delivery of gas under pressure to the inlet is disrupted.

The invention is now described,_by way of example only, with reference to the accompanying drawings in which:- Figure 1 illustrates diagramatically a gas flow control valve in accordance with the present invention; and Figure 2 shows a sectional elevation of an alternative form of air flow control valve in accordance with the present invention.

In the gas flow control valve 10 illustrated in Figure 1, a valve housing 11 defines a cylindrical valve chamber 12 having an inlet 14 and outlet 15. The valve chamber 12 defines a valve seat 13, the valve chamber 12 increasing in diameter from the valve seat 13 towards the inlet 14.

A valve member 16 is located coaxially of the valve chamber 12, a valve stem 17 being slidably mounted in a bearing 18 mounted at the end of the valve chamber iz remote from outlet 15. A valve head 19 is located at the end of the valve stem 17 adjacent to the seat 13, so that the valve member 16 may be moved between a position in which the valve head 19 engages and closes the valve seat 13 and a position in which the valve head 19 is spaced axially away from the valve seat 13 towards the inlet 14.

A cylindrical gas-tight casing 20 is bolted to the valve housing 11 coaxially of the valve chamber 12. The end of the valve stem 17 remote from valve head 19 extends into the casing 20. The-easing 20 is formed from two parts 22 and 23 which are clamped together in suitable manner. A flexible annular diaphragm 25 is mounted within the casing 20, an outer peripheral bead portion 26 being clamped between parts 22 and 23 of casing 20, to provide a gas-tight seal therebetween and the inner periphery 27 of diaphragm 25 being secured to the valve stem 19 at an axially fixed position. The diaphragm 25 thereby divides the casing 20 into two gas-tight compartments 30 and 31. Compartment 30 is connected to the inlet 14 by means of a bore 32 passing through the housing 11 and casing 20, and compartment 31 is connected via inlet 33, pressure tube 34 and bore 35 to the valve chamber 12 on the side of the seat 13 adjacent to outlet 15.

A second cylindrical gas-tight casing 40 is bolted to casing 20 with sealing means 41 and bearing 42 6 - therebetween. An extension 43 is secured to the end of valve stem 17 in suitable manner and extends through the bearing 42 into casing 40. The casing 40 is formed from two parts 44 and 45, in similar manner to casing 20. The outer periphery 47 of a second diaphragm 46 is clamped between parts 44 and 45 of casing 40 and the inner periphery 48 is secured to a plunger 49 located coaxially within the casing 40. A helical compression spring 50 acts between the end of casing 40 and the plunger 49 to urge the plunger 49 into engagement with an abutment 51 on the end of the extension 43 of valve stem 17. The diaphragm 46 theieby divides the casing 40 into two gastight compartments 52 and 53. A port 54 is provided to compartment 52 by which it is connected to asmosphere and port 55 is provided to compartment 53 by which it may be connected to a controllable vacuum source.

The valve mechanism described above is suitable for use in a secondary air system for an internal combustion engine in which when the engine is started up, air is pumped to the engine's exhaust manifold in order to heat up the exhaust catalyst to its optimum operating temperature. The output of a positive displacement air pump is connected to the inlet 14 of valve 10 and the outlet 15 of valve 10 is connected to the exhaust manifold. The port 55 to compartment 53 is connected via an electronic vacuum regulator to a suitable source of vacuum.

Under normal operation of the engine when the exhaust catalyst is at its optimum operational temperature, the air pump is switched off and the electronic vacuum regulator connects compartment 53 to atmosphere. Compartments 52 and 53 will thus be at equal pressure and there will be no pressure differential across the diaphragm 46. The load of spring 50 acting upon plunger 49 will thus urge the valve member 16 downwardly so that the valve head 19 engages seat 13, as illustrated in Figure 1. The valve 10 will thus be positively closed preventing exhaust gases from flowing from the exhaust manifold to the pump.

When the engine is started from cold, the air pump is switched on and the electronic vacuum regulator connects compartment 53 to vacuum. The pump will deliver air under pressure to the inlet 14 and when the pressure P1 at inlet 14 and in compartment 30 is in excess of the pressure P2 at the outlet 15 and in compartment 31, the pressure differential across diaphragm 25 will apply a load to the valve stem 17 urging the valve member 16 upwardly. Furthermore, the vacuum in compartment 53 will produce a pressure differential across diaphragm 46 applying an upward load on plunger 49, this upward load opposing the downward load applied by spring 50. The load applied to the valve member 16 by diaphragm 25 will thus cause the valve member 16 to move upwardly against the resultant load applied by spring 50 less that applied by diaphragm 46. Upward movement of the valve member 16 will open the valve seat 13 and permit air to flow from inlet 14 through outlet 15 into the exhaust manifold.

The degree of axial movement of the valve member 16 will depend upon the magnitude of the load applied to valve member 16 by diaphragm 25 and load applied to plunger 49 by diaphragm 46. The load applied to plunger 49 by diaphragm 46 may be controlled by the electronic vacuum regulator thereby controlling movement of the valve member 16 which, because of the varying diameter of valve chamber 12 will vary the degree.of opening of the valve seat 13 and thus the flow rate of gas from inlet 14 to outlet 15. If the engine should backfire while air is being supplied to the exhaust manifold and P2 becomes greater than P1, the pressure in compartment 31 will then be in excess of that in compartment 30 and the pressure differential across diaphragm 25 will move the valve member 16 downwardly, so that the valve head 19 will engage and close the valve seat 13, thereby preventing exhaust gases from being fed back to the pump.

Similarly, if the pump is switched off or should fail, the pressure P1 will fall below pressure P2 so that the pressure differential across diaphragm 25 will again close the valve 10 irrespective of the state of the electronic vacuum regulator.

The valve described above will thus provide a variable flow of air to the exhaust manifold whilst positively -1 preventing blow back of exhaust gases to the air pump. Plastics materials may consequently be used in the air pump and/or in the hoses therefrom. Moreover, the sensitivity of the valve to backflow is such that the valve itself may include plastic moulded components, as the establishment of back pressure upon closure of the valve will prevent the exhaust gases from reaching the valve.

The valve illustrated in Figure 2 is of moulded plastic construction. Identical reference numerals to those used in Figure 1 have been used in Figure 2 for similar components. The housing of the valve 10 illustrated in Figure 2 is formed from four plastic mouldings 60, 61, 62 and 63. The mouldings 60, 61, 62 and 63 are held together by angularly spaced clip formations 64 on mouldings 61, 62 and 63 which engage through apertures 65 in the adjoining moulding 60, 61 and 62.

Moulding 60 defines the outlet 15, valve seat 13 and a frustoconical lower portion of valve chamber 12. Moulding 61 which is connected to moulding 60 with a sealing element 66 therebetween, defines the upper part of valve chamber 12, inlet 14 and a bearing formation 67. Moulding 61 also defines the lower part of cylindrical casing 20, bore 32 being provided in the wall between the upper part of valve chamber 12 and lower part of casing 20. Moulding 62 which defines the upper part of casing - 10 20 and lower part of casing 40 is secured to moulding 61 with the outer periphery 26 of diaphragm 25 clamped therebetween to produce a seal. Similarly, moulding 63 which defines the upper part of casing 40 is clamped to moulding 62 with the outer periphery 47 of diaphragm 46 clamped therebetween.

A tubular plastic valve stem 70 is slidingly located through bearing formation 67 to locate valve member 16 coaxially of valve chamber 12 and compartments 30, 31, 52 and 53. A moulded plastic valve head 71 is located on the lower end of valve stem 70 and elastomer ic-o-ring 72 being provided around the periphery of the valve head 71 to provide sealing engagement with the valve seat 13. The inner periphery of diaphragm 25 is secured to a flange formation 73 mounted on valve stem 70 within the casing 20. A radial bore 74 is provided through the wall of valve stem 70 so that it opens into chamber 31. A cap 75 closes the end of valve stem 70 remote from valve head 71 and is abutted by the plunger 49. A diaphragm 76 is trapped at its inner periphery between the end of valve stem 70 and the cap 75 and is secured at its outer periphery to a portion of moulding 62 defining the top of casing 20 and the bottom of casing 40, thereby sealing compartment 31 from compartment 52.

The valve described above will operate in the same manner as that described with reference to Figure 1, compartment - 11 30 being connected to the inlet 14 by bore 32, compartment 31 being connected to outlet 15 via radial bore 74, and the bore of tubular valve stem 70, and port 55 being connected to an electronic vacuum regulator.

Various modifications may be made without departing from the invention. For example, while in the above embodiments compartment 52 is connected to atmosphere while compartment 53 is controllably connected to vacuum, compartment 53 may alternatively be connected to atmosphere while compartment 52 is controllably connected to a source of gas under pressure.

1

Claims

1. A gas flow control valve comprising a valve housing with an inlet and an outlet, the inlet and outlet being interconnected by a valve chamber, said valve chamber defining a valve seat intermediate of the inlet and outlet, the diameter of the valve chamber increasing away from the valve seat; a valve member slidably mounted coaxially of the valve chamber, the valve member having a valve head adapted at one extreme of movement of the valve member to engage and clos.e the valve seat; first and second gas-tight chambers being provided at axially spaced locations coaxially of the valve chamber, the valve member having a valve stem which extends through the first gas-tight chamber and into the second gas-tight chamber; a first diaphragm being attached at its inner periphery to the valve stem and at its outer periphery to a wall of the first gas-tight chamber, to divide the first gas-tight chamber into a pair of gas-tight compartments; a second diaphragm being mounted at its inner periphery to a plunger located coaxially within said second gas-tight chamber and at its outer periphery to a wall of the second gas-tight chamber, to divide the second gas-tight chamber into a pair of gas-tight compartments, resilient means being provided to urge the plunger into engagement with the end of the valve stem; one compartment of the first chamber being connected to the inlet and the other compartment of the first chamber - 13 being connected to the outlet, such that when pressure at the inlet is in excess of that at the outlet, the pressure differential across the first diaphragm will apply a load to the valve member urging it out of engagement with the valve seat and when the pressure at the outlet is in excess of that at the inlet, the pressure differential across the first diaphragm will apply a load to the valve member urging it into engagement with the valve seat; and means being provided to apply a pressure differential across the second diaphragm which will apply a load to the plunger opposing that applied by the resilient means.

2. A gas flow control valve according to Claim 1 in which the valve head engages the valve seat on the side thereof adjacent to the inlet, the compartment of the first gas-tight chamber adjacent to the valve chamber being coniected to the valve chamber on the side thereof adjacent the inlet and the compartment of the first gastight chamber remote from the valve chamber being connected to the valve chamber on the outlet side of the valve seat.

3. A gas flow control valve according to Claim 2 in which the inlet is c onnected to said compartment defined in the first gas-tight chamber by means of a bore through the valve housing.

4. A gas flow control valve according to Claim 2 or 3 in which the outlet is connected to said compartment defined in the first gas-tight chamber by means of an external connection.

5. A gas flow control valve according to Claim 2 or 3 in which the outlet is connected to said compartment defined in the first gas-tight chamber by means of an axially extending bore through the valve member.

6. A gas flow control valve according to any one of the preceding claims in which a helical compression spring acts against the end of the second gas-tight chamber remote from the valve chamber and the plunger, urging the plunger into engagement with the end of the valve stem.

7. A gas flow control valve according to any one of the preceding claims in which the compartment defined in the second gas-tight chamber on the side of the diaphragm remote from the valve chamber is connected to a controllable source of vacuum, the compartment on the side of the second diaphragm adjacent the valve chamber being connected to atmosphere.

8. A gas flow control valve according to any one of the preceding claims in which the valve chamber, first gastight chamber and second gas-tight chamber are formed from four plastics mouldings.

1 - 15

9. A gas flow control valve according to Claim 8 in which a first plastics moulding defines the outlet, valve seat and lower part of the valve chamber, a second plastics moulding defines the inlet, upper part of valve chamber, a bearing formation for the valve stem and the lower part of the first gas-tight chamber, a third plastics moulding defines the upper part of the first gas-tight chamber and the lower part of the second gastight chamber and a fourth plastics moulding defines the upper part of the second gas-tight chamber.

10. A gas flow control valve according to Claim 8 or 9 in which the valve member is formed from a moulded plastic valve stem, a moulded plastic valve head being secured to the valve stem at the end adjacent the valve seat and a cap closing the bore of the valve stem at the end remote from the valve seat, a radial bore extending through the wall of the valve stem to provide communication between the outlet and the compartment of the first gas-tight chamber associated therewith.

11. A gas flow control valve substantially as described herein with reference to, and as shown in, Figures 1 or 2 of the accompanying drawings.