Marine propulsion unit and a valve for a marine propulsion unit

Abstract

A valve for a marine propulsion unit comprises a valve body (11) having an end face (13) and a wall (14) extending from the end face. An aperture (15) is defined in the end face. A valve stem (12) is moveable within and with respect to the valve body, such that, in the closed state of the valve, the valve stem closes the aperture. A maximum width (d.sub.1) of the valve stem is greater than the width (d.sub.2) of the aperture in the end face of the valveso that, if the valve stem should fracture, the detached portion(s) of the valve stem will be retained in the valve body. The valve may for example be used as a cylinder drain valve in a marine propulsion unit.

Claims

1. A marine propulsion unit comprising: a cylinder; a combustion chamber extending from a first end of the cylinder; a spark plug disposed within the combustion chamber; and a piston reciprocably moveable within the cylinder; wherein the unit further includes a user-operable valve, the valve being selectively openable independent of the position of the piston within the cylinder, the valve being positioned such that, in its open state, movement of the piston causes gas within the propulsion unit to flow over the spark plug and subsequently to flow out of the propulsion unit through the valve; wherein the valve includes a valve body having an end face and a wall extending from the end face, an aperture being defined in the end face; and a valve stem moveable within and with respect to the valve body, the valve stem having a sealing portion located within the valve body in both an open state and a closed state of the valve, wherein, in the closed state of the valve, the sealing portion of the valve stem abuts against an inner surface of the end face and thereby closes the aperture; wherein a maximum width of the valve stem is greater than the width of the aperture in the end face of the valve; and wherein in the open state, the sealing portion of the valve stem is spaced apart from the inner surface of the end face of the valve body by a sufficient distance to permit water to drain from the cylinder through the valve.

2. A marine propulsion unit as claimed in claim 1 wherein the sealing portion of the valve stem comprises a sealing face provided on the valve stem, the sealing face abutting against the circumference of the aperture when the valve is in the closed state.

3. A marine propulsion unit as claimed in claim 2 wherein the sealing face is a frusto-conical sealing face.

4. A marine propulsion unit as claimed in claim 1 wherein, when the valve is in the closed state, an end of the valve stem is substantially flush with the outer surface of the end face of the valve body.

5. A marine propulsion unit as claimed in claim 1, wherein, in the closed state of the valve, the valve stem does not project beyond the outer surface of the end face of the valve body.

6. A marine propulsion unit as claimed in claim 2, wherein the valve stem comprises a portion extending beyond the sealing portion, the portion, when the valve is in a closed state, extending into the aperture in the end face.

7. A marine propulsion unit as claimed in claim 1 wherein rotation of the valve stem relative to the valve body causes the valve to change from the closed state to an open state.

8. A marine propulsion unit as claimed in claim 1, wherein the valve is provided within the combustion chamber.

9. A marine propulsion unit as claimed in claim 8, wherein the end face of the valve body is substantially flush with an internal face of a wall of the combustion chamber.

10. A marine propulsion unit as claimed in claim 1, wherein the valve stem includes threads that engage a complimentary thread on the interior of the valve body and that allow for rotation of the valve stem relative to the body and wherein the marine propulsion unit further includes a locking catch for engaging the valve stem to prevent subsequent rotation of the valve stem relative to the valve body, enabling the sealing portion to be locked in either of the open state or the closed state.

Description

(1) Preferred embodiments of the present invention will now be described by way of illustrative example with reference to the accompanying figures, in which:

(2) FIG. 1 is a sectional view of a prior art valve;

(3) FIG. 2 shows the prior art valve of FIG. 1 mounted in the cylinder head of a marine propulsion unit;

(4) FIG. 3 is a schematic illustration of a marine propulsion unit illustrating the process of purging the unit of water after immersion of the propulsion unit.

(5) FIGS. 4 and 5 are schematic sectional view of a valve of the present invention in its closed and open states respectively;

(6) FIG. 6 is a sectional view of another valve of the present invention;

(7) FIG. 7 shows the valve of FIG. 6 mounted in the cylinder head of a marine propulsion unit.

(8) FIG. 4 is a schematic section view of a valve 10 according to an embodiment of the present invention in its closed state, and FIG. 5 shows the valve 10 in an open state.

(9) The valve has a valve body 11 and a stem 12. The valve body has an end face 13 and a wall 14 extending from the end face. An aperture 15 is provided in the end face 13.

(10) The valve stem 12 is provided within the valve body, and is moveable with respect to the valve body. FIG. 4 shows the valve in its closed state, in which the valve stem 12 closes the aperture 15 against the flow of gas or liquid. In the embodiment of FIG. 4 the valve stem 12 has a sealing portion 12a that, when the valve is in its closed state, abuts against an inner surface of the end face 13 of the valve body and thereby closes the aperture 15. To open the valve, the stem is moved relative to the valve body in the direction shown by the arrow in FIG. 4, so that the sealing portion 12a of the valve stem no longer closes the aperture 15 in the end face of the valve body and gas or liquids can pass through the aperture into the interior of the valve body.

(11) In the embodiment of FIGS. 4 and 5 the wall 14 is cylindrical, and the end face 13 and the aperture 15 in the end face are both circular. As described below this may allow for easy fitting of the valve in place, but the invention is not limited to a cylindrical valve body.

(12) As can be seen from FIGS. 4 and 5, the sealing portion 12a of the valve stem 12 is within the valve body in both the closed state of FIG. 4 and the open state of FIG. 5. The sealing portion 12a of the valve stem comprises a sealing face 16 for, when the valve is closed, sealing against the end face of the valve body. In the example of FIGS. 4 and 5 the sealing face is a frusto-conical face (that is, is part of the surface of a cone) that, when the valve is closed, seals against the edge of the aperture in the inside surface of the end face of the valve, but the invention is not limited to this form of sealing face.

(13) The use of a frusto-conical sealing surface has the effect that the maximum width d.sub.1 of the valve stem (for example the maximum diameter in the case of a valve stem that is rotationally symmetric about its axis) is greater than the width d.sub.2 of the aperture 15 (for example the diameter of the aperture in the case of a circular aperture) in the end face of the valve body. This means that the valve stem cannot be removed from the valve body through the aperture. Furthermore the width d.sub.3 of the valve stem is preferably also greater than the width d.sub.2 of the aperture 15 in the end face of the valve body to maximise the likelihood that, if the valve stem should fracture, the pieces would be retained within the valve body. This is advantageous in certain applicationsfor example, if the valve stem of the conventional valve shown in FIG. 2 were to fracture, the broken piece of the valve stem would fall into the cylinder and could potentially cause serious damage to the propulsion unit.

(14) In some applications it may be desirable that the valve, when closed, presents a generally smooth end face. In the embodiment of FIG. 4 the valve stem is arranged such that, when the valve is closed, the end face 17 of the valve stem is in the same plane as, or is substantially in the same plane as, the exterior surface of the end face 13 of the valve body. It may also be advantageous if the difference between the diameter of the end face 17 of the valve stem and the diameter of the aperture is kept small, as this also assists with makes the valve, when closed, presenting a generally smooth end face.

(15) Depending on the thickness of the end face of the valve body and on the taper of the frusto-conical portion of the valve stem, it may be desirable to provide the valve stem with a cylindrical portion 18 so that the aperture 15 in the end face is substantially filled.

(16) As noted, in the embodiment of FIG. 4 the exterior of the valve body is generally cylindrical. This facilitates mounting the valvea hole of the appropriate diameter can be drilled into the component in which the valve is to be mounted. The interior of the valve body may also be cylindrical, and the valve stem may be rotationally symmetric about its axis. However, the invention is in principle not limited to this.

(17) In the embodiment of FIG. 4 the valve stem is positioned substantially along the axis of the valve body and moves along the axis of the valve body, but the invention is again not limited to this.

(18) FIGS. 4 and 5 do not show how the valve stem 12 is mounted in the valve body, but FIG. 6 illustrates one possible way in which the valve stem may be mounted in the valve body. In this embodiment the valve stem is provided with an external screw thread 19 that engages with a complementary screw thread 20 on the interior of the valve body. Rotation of the valve stem causes the valve to move along the axis of the valve body, thereby closing or opening the valve.

(19) FIG. 6 also shows a screw thread 21 provided on the exterior of the valve body. This is one convenient way of securing the valve in positiona hole may be drilled in the component in which it is desired to provide the valve, and threaded to provide a screw thread. The valve body may then be screwed into the threaded hole in the component. Preferably the exterior of the valve body is stepped in diameter, with the length L of the narrower portion 22 of the valve body being made equal or approximately equal to the thickness of the component in which the valve is to be mounted.

(20) FIG. 6 also shows an exhaust passage 23 provided in the valve body such that, when the valve is open, gas or liquid entering the valve body through the aperture 15 can leave the valve body through the exhaust passage 23. The invention is not limited to a single exhaust passage, and one or more further exhaust passages 23a may be provided as indicated in broken lines in FIG. 6.

(21) FIG. 7 illustrates a valve 10 of the invention in use as a drain valve in a cylinder 1 of a marine propulsion unit. FIG. 7 corresponds generally to FIG. 2, except that the conventional valve 6 of FIG. 2 is replaced by a valve 10 of the present invention, and description of components that are common to FIG. 2 and FIG. 7 will not be repeated.

(22) In order to explain the use of the valve as shown in FIG. 7, a description of the process of purging water from a marine propulsion unit as described in GB 2 349 420 will be given with reference to FIG. 3.

(23) The valve 10 of FIG. 7 corresponds to the first valve 32 of FIG. 3. If the marine propulsion unit on which the valve 10 of FIG. 7 is provided should be immersed, water can be drained from the cylinder by opening the valve 10 and reciprocating the cylinder 2 in the manner described above with reference to FIG. 3. Furthermore, the valve 10 of FIG. 7 is positioned near to the spark plug 3 so that, once water has been expelled from the cylinder, continued reciprocation of the piston 2 will cause gases within the top of the cylinder to flow over the spark plug, thereby drying the spark plug.

(24) In the application of FIG. 7, a valve 10 of the present invention provides advantages over the prior valve 6 of FIG. 2. One advantage is that, as described above, the valve stem 12 cannot pass through the aperture 15 in the valve body. Thus, if the valve stem should fracture, the detached portion(s) of the valve stem will be retained in the valve body. In contrast, if the valve stem of the conventional valve 6 of FIG. 2 were to fracture, the detached portion(s) of the valve stem would fall into the combustion chamber and could cause serious damage to the propulsion unit.

(25) Another advantage another benefit of a valve 10 of the present invention is that it provides less resistance to liquid flow from the cylinder through the valve. As can be appreciated from FIG. 2, with the conventional valve 6 it is necessary for water being drained from the cylinder, or for gases being expelled from the cylinder to dry the spark plug, to flow round the head of the valve before leaving the cylinder. When a valve of the present invention is used, however, water or gases can flow into the valve body through the aperture 15 with little resistanceprovided that the length L of the reduced diameter portion of the valve body is chosen correctly, the valve may be such that the end face of the valve body is flush or substantially flush with an internal surface the combustion chamber, as shown in FIG. 7. This provides more efficient drainage of water and/or more efficient drying of the spark plug. Furthermore, making the end face of the valve body flush or substantially flush with an internal surface the combustion chamber minimises the effect on the engine of providing the valve, as the valve has little or no effect on gas flow paths in the cylinder in normal operation of the engine when the valve is closed.

(26) One example of a valve according to the invention has the following dimensions: maximum diameter of valve stem (d.sub.1): 5.3 mm diameter of aperture (d.sub.2): 4.0 mm diameter of valve stem (d.sub.3): 4.0 mm inside diameter of valve body (d.sub.4): 6.5 mm outside diameter of valve body (d.sub.5): 12 mm diameter of end portion 18 of valve stem (d.sub.6): 1.5 mm overall length of valve body: 30 mm

(27) It should be understood that the invention is not limited to the preferred embodiments described above, and that many variations are possible. For example, rather than having the valve stem mounted in the valve body using a screw thread as shown in FIG. 5, the valve stem may be mounted for translational movement relative to the valve body. To open the valve, a user would need to pull the valve body to cause it to move relative to the valve body and thereby open the aperture 15.

(28) A valve of the invention may be biased towards one or other the open or closed state, depending on its intended application. For example, in an embodiment in which the valve stem is mounted for translational movement relative to the valve body, the valve stem may be biased towards a position in which it closes the aperture 15, for example by a spring, eg a coil spring, or other bias member.

(29) If desired, the valve may be provided with a locking means to lock the valve in one or both of its open and closed states. Whether the locking means locks the valve in its open state and/or its closed state will depend on the intended application of the valve where a valve is intended for use a cylinder drain valve as shown in FIG. 7, for example, it is more important that the valve can be locked in its closed state than in its open state, since if the valve were to open when the propulsion unit were running normally this would affect the performance of the propulsion unit. In contrast, if the valve were to close inadvertently when the propulsion unit was being drained of water this would be of lesser consequence.

(30) In the case of a valve that is changed from its closed state to its open state by rotation of the valve, as in FIG. 6, a locking means may be provided to prevent rotation of the valve stem relative to the valve body, for example as a catch 34 that can engage with the valve stem and prevent rotation of the valve stem. To open the valve, a user must first undo the catch so that the valve stem is free to rotate.