GB2044850A - Cylinder intake valve slide for an internal combustion engine - Google Patents

Abstract

The valve slide provides closure on the combustion chamber side of 3 the air passages 1 disposed in the cylinder head 8 and comprises a relatively thin valve disc 2 formed with apertures which in the closed position of the valve slide are concentric with the air passages and have a greater diameter than the respective air passages. A closure plate 10 which is rigid as compared with the disc 2 is disposed in each aperture with a peripheral gap 9, the disc is welded to each closure plate by way of a respective connecting element 11 to provide a gas-tight connection which may yield resiliently in response to thermal expansion 1 and each closure plate is in heat-conductive contact by way of its edge with the surface of the cylinder head when the valve slide is in its closed position. <IMAGE>

Description

SPECIFICATION Valve slide for internal combustion engine The invention relates to a valve slide for an internal combustion engine, particularly for the control of scavenging or charge air in a two stroke internal combustion engine.

It has already been suggested in our British Patent Application No. 80051 37 Serial No.

2043172 to use a valve slide to close air ports in the cylinder head of a combustion chamber side as a means of promoting the formation of a very thorough "displacing airpiston" to clear the exhaust gases from the cylinder of an internal combustion engine with longitudinal scavenging. Endeavours to carry this suggestion out in practice have been faced with constructional difficulties since the valve slides experience extreme temperatures and pressures which, because of thermal expansion and/or high pressure, cause deformation and/or permanent distortions of the air ports and impede, if not making it completely impossible, the serviceability and sealing effect of the slide.

It is the object of the invention to provide a valve slide arrangement for such application, the valve slide being able to withstand the extreme conditions-i.e., not suffering loss of serviceability as a result of deformation.

Accordingly the present invention provides a valve slide for providing a closure on the combustion chamber side of an air port disposed in the cylinder head of a reciprocating internal combustion engine comprising a relatively thin valve seal member formed with an aperture which in the closed position of the valve slide is concentric with the air port and which has a greater diameter than the air port; a closure plate which is rigid as compared with the valve seal member disposed in the bore with a peripheral gap; in which the valve seal member and the closure plate are interconnected in gas-tight manner by way of a connecting element which may yield resiliently in response to thermal expansion; and the closure plate is in heat-conductive contact by way of its edge with the surface of the cylinder head when the valve slide is in its closed position.

The relatively thin valve seal member takes over the sealing of the air port when the valve slide is in the closed state. Such member, being relatively thin, experiences little, if any, heat distortion and can therefore follow distortions of the cylinder head without impairment of its sealing tightness.

The closure plate, which acts as a closure for the air port but does not have to provide any sealing function, withstands the pressures in the cylinder because of its much greater thickness and rigidity. Also, the closure plate is cooled effectively from the edge by its edge surface being in engagement with the cylinder head; conveniently, the extent of contact surface between the cylinder head and the edge of the closure plate can be such, having due regard to the thermal strength of the material used for the closure plate, that the temperature thereof does not exceed a safe upper limit.

The narrow physical contact zone (instead of a direct connection) and the heat-transmission-inhibiting gap between the sealing disc and the closure plate greatly reduce the heat flow therefrom to the sealing disc, so that the same, which has relatively little mass and relatively little heat capacity, is substantially at the temperature of its environment. The "installation" of the disc from the plate can be improved if the connecting element is in the form of a metal angle member enclosing an "insulating air gap". Also, the increased radial extent of the plate in the light connection is intercepted purely resiliently.

Similarly, thermal distortions which are operative towards the combustion chamber and which result in the plate becoming spherical are taken over resiliently by the connecting element, and so the sealing disc continues to seat flat on the cylinder cover.

In order to promote a fuller understanding of the above and other aspects of the present invention, an embodiment will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows part of a valve slide, the view being in plan looking from the combustion chamber of a cylinder, a single axial slide opening and closing all the air ports distributed over the surface of the cylinder head, and Figure 2 is a section on the line ll-ll of Fig.

1.

Air ports 1 are disposed in a cylinder head 8 of each cylinder 1 3 of an internal combustion engine, the centres of the ports 1 being disposed on two pitch circles 4,5 concentric with the cylinder axis 6. For each port 1 a sealing disc 2 of a valve slide is formed with an orifice 7. The disc 2 is formed, between the various orifices 7, with apertures 3 whose centres are disposed on the same pitch circles 4, 5 as the air ports 1 and orifices 7, and whose diameter is greater than the diameter of the associated orifices 7. One such aperture 3 is shown on the circle 5 of Fig. 1 for the right-hand air port 1; this aperture 3 is shown without closure plate 10, to be described hereinafter, and the connection 11 between the same and the disc 2.

A closure plate 10 which, with the valve slide in the closed position (as shown) covers a respective port 1, is received in each bore 3, a peripheral gap 9 being left. The plate 10 is held concentrically of the respective bore 3 by means of a retainer 11 which is of angular annular cross-section and whose narrow edges are welded in gas-tight manner to the disc 2 and the respective plate 10. To reduce heat transfer from the plates 10 to the members 11 and therefore to disc 2, a void 1 5 bounded by each retainer 11 and closure plate 10 is left beside the gap 9. The thickness of the plate 10 (Fig. 2) is approximately from 3 to 4 times that of the relatively thin disc 2. The plate 10 and disc 2 can both be made of steel or of a heat-resistant alloy.

As Fig. 2 shows, the diameter of the bores 3 is such that the closure plate 10 engages by way of its edge zones 12 on the surface of cylinder head 8, the head being cooled by a cooling system (not shown). As already mentioned, the bearing surface of the plate edge 12 is such that, while the engine is operating, plate temperature does not exceed a permissible top limit which depends upon the particular material used for the plate 10.

As described in detail in the previous British Patent Application No. 8005137 hereinbefore referred to, the valve slide is reciprocated intermittently by means of pins 14 secured to disc 2; when the air ports are in the open state and closed state, the pins 1 4 are received in additional bores 1 8 which extend parallel to the air ports 1.

Claims (5)

1. A valve slide for providing a closure on the combustion chamber side of an air port disposed in the cylinder head of a reciprocating internal combustion engine comprising a relatively thin valve seal member formed with an aperture which in the closed position of the valve slide is concentric with the air port and which has a greater diameter than the air port; a closure plate which is rigid as compared with the valve seal member disposed in the bore with a peripheral gap; in which the valve seal member and the closure plate are interconnected in gas-tight manner by way of a connecting element which may yield resiliently in response to thermal expansion; and the closure plate is in heat-conductive contact by way of its edge with the surface of the cylinder head when the valve slide is in its closed position.

2. A valve slide as claimed in Claim 1, in which the connecting element is in the form of a thin annular metal member of angular cross-section having its edges connected to the closure plate and to the valve seal member respectively.

3. A valve slide as claimed in Claim 1 or 2, in which the surface by which the closure plate edge engages with the surface of cylinder head is of a size and design such that closure plate temperature does not exceed in operation of the engine a maximum which is acceptable for the material of which such plate is made.

4. A -valve slide as claimed in any preceding Claim for a cylinder head having a plurality of inlet ports arranged in two circular rows substantially concentric with the axis of the cylinder, the valve seal member being provided with such a closure plate and aperture for each air port.

5. A valve slide substantially as herein described with reference to the accompanying drawings.