One particular application of a valve of the present invention is in relation to a post- immersion restart system for a marine propulsion unit. When a boat capsizes the propulsion unit is submerged and it will flood with water. Even in the case of a vessel provided with a self-righting capability, the engine is generally flooded with water by the time the vessel has righted itself. In order to restart the engine it is necessary to drain each cylinder of water, and also to drain the carburettor or carburettors. A post immersion restart system for draining a carburettor is described in European Patent EP- B-0 219 278, and a post immersion re-start system incorporating crankcase drainage is described in co-pending UK Patent Application No. 9909947.5. The contents of these two documents are hereby incorporated by reference.

The basic principle of operation of the post-immersion restart system of UK Patent Application No. 9909947.5 is illustrated in Figure 1.

The marine propulsion unit shown in Figure 1 is a two-stroke internal combustion engine. Only one cylinder 1 is shown in Figure 1 for clarity and ease of explanation, although the propulsion unit will in general have two or more cylinders.

A combustion chamber 2 is disposed at a first end of the cylinder 1, and a crank-case 3 is disposed at a second end of the cylinder 1. The engine is a crank-case scavenged engine, and a transfer passage 4 connects the crank-case 3 to the combustion chamber 2.

A piston 5 is disposed within the cylinder, and can move reciprocably within the cylinder. A crank-shaft 6 is disposed within the crank-case 3, and the piston 5 is connected to the crank-shaft 6 by a connecting rod 7, so that reciprocating motion of the piston 5 is converted into rotary motion of the crank-shaft 6.

In use, fuel and air are introduced into the crank-case from the carburettor 11 by inlet means (not shown). One or more spark plugs 8 are provided in the combustion chamber to ignite the compressed air/fuel mixture at the completion of the compression stroke, and the resultant combustion of the fuel/air mixture drives the piston 5 away from the combustion chamber 2. An exhaust port E allows the combustion products to exhaust from the cylinder when it is uncovered by the piston.

The post-immersion restart system shown in Figure 1 essentially consists of two ports provided in the cylinder. A first port, or purge port, 9 is provided in the combustion chamber and a second port, or drain port, 10 is provided at the lowest effective drainage point of the propulsion unit. In the propulsion unit of Figure 1, the drain port 10 is located in the transfer passage 4. These ports are additional to the exhaust port E, and they are selectively and independently openable regardless of the position of the piston 5 in the cylinder 1. The ports 9,10 are shown in their open states in Figure 1, but in normal operation of the propulsion unit both ports will be closed since operation of the engine would be adversely affected if one or both of the ports 9,10 were open.

When the vessel fitted with the marine propulsion unit of Figure 1 capsizes, water will enter the propulsion unit through, for example, the air intake or the exhaust. Thus, when the vessel is righted after a capsize, the propulsion unit will typically be flooded with water. If the unit has stopped with the piston 5 blocking the exhaust port E, it will not be possible for the water to leave the cylinder so that the piston 5 is hydraulically locked and so cannot move within the cylinder 1. In a multi-cylinder propulsion unit it is possible that the unit will stop with the crank-shaft in a position such that the exhaust port in one cylinder is uncovered.. However, if just one cylinder in the unit is hydraulically locked this will lock the entire unit and will prevent it from being turned over and re-started.

The first step in the purging process is to open the drain port 10 so that the interior of the cylinder is vented to atmosphere. Water can then drain out of the unit as a result of the action of gravity, through the transfer passage 4 and the drain port 10. Subsequent opening of the purge port 9 enables release of hydraulic pressure above the piston (that is, from the combustion chamber 2). It is then possible to rotate the crank-shaft 6 and so reciprocate the piston 5 within the cylinder 1, and such movement of the piston 5 will cause water within the propulsion unit to be expelled through the drain port 10. The crank-shaft can be rotated either manually or, if the propulsion unit is fitted with a starter motor, using the starter motor. This will drive gas over the spark plug, thereby removing any water lodged in the spark plug and so drying the spark plug.

Once the spark has been dried sufficiently to allow the engine to be restarted, the engine can be restarted, the purge port 9 and drain port 10 are closed, and the engine then operates in a conventional manner.

In an alternative embodiment, the drain port 10 is omitted so that all water in the cylinder has to be expelled through the purge port 9 by turning the engine over. This simplifies the post-immersion restart system, at the expense of increasing the time taken to drain the cylinder and restart the engine.

Where a post-immersion restart system is fitted to an existing boat, or to an existing design of engine, it is desirable that providing the post-immersion restart system has as little effect as possible on the normal operation of the engine. Thus, one requirement is that the compression ratio of the cylinders is not significantly changed when the post- immersion restart system is fitted, and this means that the volume of the combustion chamber should not be changed significantly as a result of providing the purge port 9 in the combustion chamber.

US patent No 5 632 659 discloses a marine propulsion unit in which a conventional poppet valve is fitted in the cylinder head to enable the cylinder to be drained of water.

This valve is provided in a recess, however, so that the volume of the combustion chamber is increased by fitting the valve. This will change the compression ratio of the engine, and so affect the normal operation of the engine. In addition, it is desirable that the valve used as the drain valve can be fitted to an existing engine as simply as possible, with as little as possible modification to the engine. It is also desirable that the valve has a single outlet, so as to facilitate making connections to the valve. US patent 5 632 659 uses a conventional poppet valve having a series of outlets spaced around the circumference of the valve, and this complicates making connections to the valve.

It is also desirable for there to be as little restriction to the flow of fluid through the valve when the valve is open. This ensures that there is little or no compression when the engine is turned over, thus allowing easy rotation of the crankshaft. This is particularly important if it is intended that the engine will be turned over manually.

It is also desirable for the valve to be as simple as possible to open and close, to simplify the restart process and to make it easier to carry out.

Finally, the valve must of course be able to withstand the heat generated when the engine is running normally. Where the valve is used in a water-cooled engine part of the valve may be adjacent the water jacket of the engine, so it is desirable if the valve has a good thermal conductivity so that the cooling due to the water jacket is transmitted to parts of the valve not in direct contact with the water jacket.

A first aspect of the present invention provides a poppet valve having a closure member; wherein the closure member has a hollow interior closed at one end, fluid passing through the hollow interior of the closure member when the valve is open.

Since fluid passes through the interior of the closure member, there is no need for porting leading to the valve to be provided in the valve body or in the cylinder head.

A second aspect of the present invention provides a marine propulsion unit comprising a valve as described above. In a preferred embodiment, the valve is disposed so that, in its open state, it allows fluid communication between the combustion chamber of a cylinder of the engine and the exterior of the cylinder.

In a preferred embodiment the end face of the closure member is substantially flush with the combustion chamber when the valve is closed. Thus, the valve does not alter the volume of the combustion chamber or the compression ratio of the cylinder, so that providing the valve does not affect the performance of the engine in normal operation.

Preferred features of the invention are set out in the dependent claims.

Preferred embodiments of the present invention will now be described, by way of illustrative example, with reference to the accompanying drawings in which: Figure 1 is a schematic view of a marine propulsion unit fitted with a post-immersion restart system; Figure 2 is a schematic view of a valve according to an embodiment of the present invention in a closed state; Figure 3 is a schematic view of the valve of Figure 2 in an open state; Figure 4 is an enlarged schematic view of the valve of Figure 2 in its open state; Figure 5 is an enlarged schematic view of the valve body of the valve of Figure 2; Figure 6 is a schematic sectional view of a valve according to another embodiment of the invention; Figure 7 is a cross-section of the valve of Figure 6; and Figure 8 is a partial enlarged view of a modification of the valve of Figure 6.

Like reference numerals denote like components throughout the drawings.

A valve according to an embodiment of the invention is illustrated in Figure 2, which shows the valve in its closed state, and Figure 3, which shows the valve in its open state.

Figures 2 and 3 show a valve according to one embodiment of the present invention.

These figures show the valve installed in the cylinder head of a marine propulsion unit.

The valve is open in Figure 2, and is closed in Figure 3.

The valve has a valve body 14 (or"valve guide") which, in use, is disposed in a bore 16 provided in the cylinder head 15 of the engine. A bore 23 is provided within the valve body 14, and a closure member 17 (or"valve stem") is disposed within the bore 16 in the valve body 14.

The valve body 14 can be secured in the bore in the cylinder head by any conventional means that will provide a gas-tight seal between the valve body 14 and the combustion chamber of the engine. In the embodiment of Figures 2 and 3, the lower section of the valve body is provided with an external screw thread 27, and a complementary screw thread is provided on the interior of the bore 16 in the cylinder head. If the valve is used in a water-cooled engine and is located so that it passes through the water jacket of the engine, it is also desirable for there to be a substantially water-tight seal where the valve body 14 passes through the water jacket.

The lower end of the closure member 17 is provided with a sealing face 18. When the valve is closed, the sealing face 18 of the closure member 17 abuts against a complementary sealing face 19 provided on the valve body 14 so as to provide a substantially gas-tight seal.

It will be noted that an increase in fluid pressure below the closure member 17 will force the sealing faces 18,19 of the closure member and the valve body together more firmly, thereby improving the gas-tightness of the valve.

The valve 13 is provided with a bias member to bias the closure member 17 into its closed position. In the valve shown in Figures 2 and 3, the bias member is a coil spring 20. The lower end of the coil spring is received in a recess in the valve body 14, and bears against the valve body. The upper end of the coil spring bears against a retaining member 21 fixed to the closure member 17.

The spring 20 is in compression, and so it acts to urge the retaining member 21 upwards and hence urges the closure member 17 upwards so that the valve is normally in its closed state as shown in Figure 3. The valve is opened by applying a force to the closure member to move the sealing faces 18,19 apart from one another.

The construction of the valve 13 as described above is thus far conventional.

According to the present invention, the closure member 17 has a hollow interior. One or more apertures 22 are provided in the lower part of the closure member 17 to provide fluid communication between the interior and exterior of the closure member. In the embodiment shown in Figures 2 to 4, four apertures 22 spaced around the circumference of the closure member are provided, but the invention is not limited to a valve having this number of apertures. In principle any number of apertures can be provided, as long as the total area of the apertures is sufficiently large not to restrict the flow of fluid through the valve but is not so large as to weaken the closure member.

The preferred area of the apertures 22 and the preferred cross-sectional area of the interior of the closure member will depend on the dimensions of the valve, and on the desired fluid flow rate when the valve is open.

The bore 23 through the valve body 14 does not have a constant diameter. This is illustrated in Figure 5, which is an enlarged sectional view of the valve body 14.

The central portion 14a of the valve body has the smallest internal diameter, dl. This is slightly greater than the external diameter of the closure member 17, so that the closure member is a close sliding fit in the central part 14a of the valve body 14. It is not generally necessary for there to be a fluid-tight seal between the valve body and the closure member, since the low resistance flow path through the apertures 22 and the interior of the closure member means that leakage between the valve body and the closure member should be insubstantial.

In the lower part 14b of the valve body 14, the diameter of the bore increases to a diameter d2 which is greater than d,. When the valve is open, gas has to flow between the valve body 14 and the closure member 17 until it reaches the apertures 22 provided within the valve body 17. Increasing the diameter of the bore in the valve body at the lower end of the valve body increases the area of the gas flow passage through the valve, so that gas flow through the valve is not unnecessarily restricted when the valve is open. It is preferable for there to be a smooth transition in diameters as shown in Figures 2 and 3, since this minimises resistance to fluid flow.

Finally, in this embodiment the upper portion 14c of the valve body has an internal diameter d3 which is again greater than ds. This increased diameter portion is provided to receive the spring 20. It should be noted that if another form of bias means where used to bias the closure member relative to the valve body it might not be necessary to provide the increased diameter portion 14c.

The apertures 22 in the closure member 17 are located such that, when the closure member 17 is depressed downwards against the action of the spring 20, the travel of the closure member is sufficiently great that the part of the closure member in which the apertures 22 are provided moves into the lower part 14b of the valve body where the bore has a diameter d2. This is shown in Figure 4, which is an enlarged view of the valve in its open position (the spring 20 and the retaining member 21 are omitted from Figure 4 for clarity).

When the valve of the invention is open, fluid is able to pass between the sealing face 18 of the closure member 17 and the sealing face 19 of the valve body 14, and can thus enter into the bore in the lower part 14b of the valve body 14. The fluid can then pass through the apertures 22 into the interior of the closure member 17. This flow of fluid is indicated by the arrows in Figures 2 and 4.

An exhaust aperture 24 is provided in the upper part of the closure member 17. In the embodiment shown in Figures 2 to 4 the exhaust aperture is provided in the upper face of the closure member 17. However, it can in principle be located in other positions.

Thus, when the valve 13 is open, fluid is able to pass between the sealing faces 18,19 of the valve body 14 and the closure member 17, pass into the hollow interior of the closure memberl7 through the apertures 22, flow through the interior of the closure member, and leave by the exhaust aperture 24. When the valve is in use, a flexible connection (not shown) is provided between the exhaust aperture 24 and a drain or exhaust system so that fluid entering the valve can be removed from the vicinity of the valve.

One use for a valve of the present invention is as the purge port 9 of a post-immersion restart system of the general type shown in Figure 1 of this application. Figure 2 in fact illustrates a valve of the present invention disposed in the cylinder head 15 of a cylinder to act as the purge port of a post-immersion restart system of the type shown in Figure 1. The position of the spark plug 8 is shown in broken lines in Figure 2. When the purge port 9 is required to be open, a downward force is applied to the closure member 17 to force it downward against the pressure of the spring 20, thereby opening the valve 13. The downward pressure can be applied by any suitable actuating means. During the upstroke of the piston 5 in the cylinder, gas above the piston will be expelled through the valve 13. When the boat is righted after a capsize, water in the cylinder may also be expelled through the purge port by turning the engine over.

When an existing engine is modified by providing a post-immersion restart system of the present invention, the purge port 9 should be located so as to ensure a good flow of gas over the contacts of the spark plug when the engine is turned over with the purge port open. This will remove any water lodged in the contacts of the spark plug, thereby drying the spark plug and enabling the engine to be restarted.

When the valve of Figures 2 and 3 is closed, the part of the closure member containing the apertures 22 would be within the central portion 14a of the valve body, and so will be close to the water jacket (where the valve is installed in a water-cooled engine). This will ensure good cooling of the region of the closure member 17 where the apertures 22 are provided, and this could be desirable since this part of the closure member will tend to be weaker than other parts of the closure member.

When a valve of the present invention is used as the purge port in a post-immersion restart system, it is possible that some water removed from the spark plug would become lodged in the bore of the lower part 14b of the valve body 14. When the valve was closed, the part of the closure member containing the apertures 22 would be within the central portion 14a of the valve body, so that the water would effectively be trapped within the bore of the lower part 14b of the valve body. This would present the risk that the trapped water would be heated and eventually vaporised as the engine ran and the cylinder block 15 warmed up. If this were to happen, when the gas pressure became sufficient to overcome the pressure exerted by the spring 20, the valve 13 would open.

In order to prevent the valve 13 from opening in this manner, the valve is preferably provided with means to relieve any pressure generated by fluid trapped within the bore of the lower part 14b of the valve body. In the embodiment of Figures 2 to 5, these means comprise a pressure relief aperture 25 provided in the closure member 17. This aperture passes through the wall of the closure member, and communicates with the interior of the valve member. The pressure relief aperture is located in a part of the closure member that is disposed within the lower part 14b of the valve body even when the valve 13 is closed. Thus, if water should be trapped within the lower part 14b of the valve body and should subsequently be vaporised, the resultant gas will be able to escape through the pressure relief aperture 25 into the hollow interior of the closure member 17, so that unwanted opening of the valve 13 is prevented. The pressure relief aperture can have a small diameter, such as lmm, to minimise the effect of any leaks through the sealing faces 18,19.

In Figure 3, the combustion chamber of the engine is indicated in dashed lines. This figure relates to a water-cooled engine and also shows a water jacket 30, disposed over the cylinder head 15, and a cover member 31 disposed over the water-jacket. (The water-jacket 30 would not be present if the valve were installed in an air-cooled engine.) It will be seen that the volume of the combustion chamber has not been changed by fitting the valve. Thus, a valve of the invention can be used as the purge port when an existing engine is provided with a post-immersion restart system, without affecting the normal operation or performance of the engine. The dimensions of the valve body 14 can be chosen so that the lower face of the closure member 17 is flush with the existing surface of the combustion chamber, simply by varying the length of the complete valve unit below the flange 27 to suit the cylinder head configuration of a particular engine.

In a conventional poppet valve of the type used in US Patent No. 5 632 659, there are a large number of small diameter exhaust ports that extend through the valve body. This means that it is difficult to collect the exhaust gases, since there are a large number of outlets. In contrast, in the present invention there is a single outlet for exhaust fluid, and this makes collection of the exhaust fluid much simpler. Furthermore the use of small diameter exhaust ports in the valve of the type used in US Patent No. 5 632 659 will create a high resistance to fluid flow-in contrast, a valve of the present invention has one, large diameter bore that provides a low resistance to fluid flow, and so allows fluid to be rapidly exhausted from the combustion chamber.

A further avantage of the valve of the engine is that it can be installed and replaced as a single unit. Thus, in order to provide an existing engine with a purge port, it is simply necessary to provide a bore having a suitable diameter in the cylinder head of the engine, so that a valve of the invention can be inserted into the cylinder head. In order to facilitate inserting the valve, the flange 27 on the valve body can be provided with a hexagonal cross section that enables it to be screwed in place using a suitable tool.

Once the actuating mechanism of the valve has been removed, removing and replacing the valve is as straightforward as changing a spark plug on an engine.

The valve body and closure member can be made of any materials having the required properties such as strength, heat resistance, thermal conductivity, and corrosion resistance. Suitable materials include stainless steels, bronzes, stellite and ceramic materials.

A second embodiment of the invention is shown in Figures 6 and 7. Figure 6 is a schematic sectional view of the valve in its open state. The construction of this valve is generally similar to that of the valve shown in Figure 2 to 5, and only the differences will be described.

The principal difference is that the apertures 22 in the closure member 17 are located near the lower end of the closure member, so that the when the valve is open the apertures are disposed below the sealing face 19 of the valve body. Fluid can then flow directly into the apertures 22, and does not need to pass up inside the valve body 14 before reaching the apertures. When the valve of Figures 6 and 7 is installed in a cylinder head, the apertures 22 would be inside the combustion chamber when the valve is open.

Since the apertures 22 are disposed below the sealing face 19 of the valve body when the valve is open, so that fluid can flow directly into the apertures 22, it is not necessary for the diameter of the bore of the valve body to increase at the lower end of the valve body. The valve body shown in Figure 6 has a constant internal diameter, except at its upper end where the diameter of the bore is increased to form a recess for receive the coil spring 20. (As noted above with regard to Figures 2 to 5, if another form of bias member were used instead of a coil spring it might not be necessary to provide the recess.) In Figure 6, a connector 32 is disposed over the upper end of the closure member, for connection to a drain or exhaust system.

Four apertures 22 are provided in the closure member of the valve of Figure 6, as shown in Figure 7 which is a cross-section along the line 7-7 of Figure 6. However, as with the previous embodiment, the invention is not limited to a valve with four apertures, and fewer or more than four apertures could be provided.

In the valve of Figures 6 and 7 there is little dead space inside the valve when it is closed, so the problem of water being trapped inside the valve when it is shut is reduced compared to the valve of Figures 2 to 5. In a modification of the valve of Figure 6, a pressure relief mechanism is provided by a vertically extending groove 33 in the interior of the valve body 14. This modified embodiment is illustrated in Figure 8, which shows only the lower part of the valve (apart from the provision of the groove 33, all features of the valve are substantially the same as the valve of Figure 6 and 7).

The groove 33 starts above the sealing face 19, so as not to impair the integrity of the seal when the valve is shut. It extends upwards so as to communicate with one of the apertures 22. More than one groove can be provided if desired.

Although the invention has been described with reference to preferred embodiments, the invention is not limited to the embodiments described above. For example, although the bore 23 in the valve body 14 and the exterior of the closure member 17 have circular cross-sections in the embodiments described above, the invention is not limited to this.

Furthermore, although the apertures 22 and the pressure relief aperture are circular in the embodiments described above, they could have other cross-sections.

In the embodiments described above where the valve is shown in use, the valve is vertically oriented. The invention is not limited to this. As is shown schematically in Figure 1, the purge port could be placed at an angle, and it would be possible to produce an angled valve that embodies the principles of this invention.