GB2242962A - Valve assemblies - Google Patents

Abstract

An inlet and/or exhaust valve (14) particularly of an internal combustion engine has a head (28) with a polygonal profile which is generally square. The valve stem (32) has a generally triangular cross-section which slides in a correspondingly shaped valve guide to ensure proper orientation of the valve head (28). Use of the square valve head (28) enables the total valve area of the cylinder head to be increased. <IMAGE>

Description

VALVE ASSEMBLIES This invention relates to valve assemblies, and particularly, although not exclusively, to inlet and exhaust valve assemblies for reciprocating internal combustion engines.

All present-day mass-produced internal combustion engines for automotive use employ valve members having circular valve heads which cooperate with circular seats. This configuration has the advantage of ease of manufacture and assembly, since no measures need to be taken to ensure that the valve member is rotationally located with respect to the seat.

There has been an increasing tendency in recent years for measures to be taken to improve gas flow in internal combustion engines. One way of doing this is to increase the flow cross-sections of the inlet and exhaust ports which, in turn, entails larger valve areas. Where a single inlet and a single exhaust valve is provided in each cylinder, there is a limit to the maximum diameters of the circular valve heads which can be accommodated in the cylinder head. Even if the valve heads have the maximum possible diameter, there is a still a significant area of cylinder head within the combustion chamber which is not utilised by the valves.

In order to increase the utilization of the combustion chamber surface, many engine designers provide more than one inlet and/or outlet valve in each cylinder. Thus, although the valve head of each valve is smaller than would be the case if one inlet or outlet valve were provided, the total valve area is increased. Nevertheless, the valve heads'themselves remain circular.

DE-A-3628466 discloses a valve assembly for an internal combustion engine in which the valve head has the shape of a distorted ellipse. In order to maintain the orientation of the valve head with respect to the correspondingly shaped valve seat, the valve stem has a pin for engagement in a slot in the valve guide.

The purpose of the specific shape of the valve head is to increase the valve area without requiring more than one inlet valve and exhaust valve. The proposed valve shape of DE-A-3628466 has disadvantages arising from the fact that the shape of the valve head has only a single order of symmetry. The consequence of this is that some parts of the sealing surface of the valve head are considerably further from the valve stem than other parts. Consequently, there is a danger that thermal and other stresses in the valve head will cause the valve head to distort, so that sealing contact will fail to be made around the entire periphery of the valve seat.

Another disadvantage arises from the use of the pin and slot guide mechanism for preventing rotation of the valve member. This mechanism is susceptible to wear, with the result that, after a relatively short life, the valve member will be able to rotate in its valve guide to an extent sufficient to prevent reliable sealing between the valve head and the valve seat.

GB-A-339710 also discloses an internal combustion engine having valves utilizing non-circular valve heads. However, these valves are secondary flow control valves, the principal sealing of the combustion chamber during a firing stroke of the engine being achieved by a main, circular, valve member.

According to the present invention there is provided a valve assembly comprising a valve seat, a valve member provided with a valve head and a valve stem, and a valve guide which cooperates with the valve stem to guide the valve member during movement to open and close the valve, wherein the valve seat and the valve head have cooperating sealing surfaces which are polygonal as viewed lengthwise of the valve stem.

Preferably, the valve head has the shape of a regular polygon, with at least two orders of symmetry.

The shape of the valve head may be square.

The term "polygonal", and other terms identifying the shape of the valve head in this specification, are not intended to be interpreted as restricted to shapes having straight sides and sharp angles. In preferred embodiments in accordance with the present invention, the sides of the polygonal valve head are arcuate, with a relatively large radius of curvature, and are interconnected at arcuate corners, having a relatively small radius of curvature. Preferably, the polygonal shape of the valve head is a harmonic shape, with the sides of the polygon forming a continuous curve with the corners. The polygonal shape of the valve head may, for example, take the form of a cycloidal figure.

In a preferred embodiment, the valve stem and valve guide have complementary polygonal crosssections. Preferably, the cross-section of the valve stem has the shape of a regular polygon, with at least two orders of symmetry. The cross-section of the valve stem may be triangular.

Preferably, the polygonal shape of the valve stem cross-section is a non-harmonic shape, with the sides of the polygon being discontinuous with the corners.

The present invention also provides a valve member for use in a valve assembly as defined above.

For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a diagrammatic view of a cylinder head illustrating, in the upper part of the Figure, an inlet and an exhaust valve in accordance with the present invention and illustrating, in the lower part of the Figure, conventional inlet and exhaust valves; Figure 2 is a sectional view taken on the lines A-A in Figure 1; Figure 3 is a side view of a valve member; Figure 4 is a plan view of the valve member of Figure 3; Figure 5 is a perspective view of the valve member shown in Figure 3; Figure 6 is a sectional view taken on the line B-B in Figure 3; Figure 7 represents the configuration of a valve stem; and Figure 8 represents the configuration of a valve head.

Referring to Figures 1 and 2, a cylinder head 2 is provided with two inlet ports 4 and two outlet ports 6 (only one of each is shown in Figure 2).

Each of the ports 4 and 6 opens at a surface 8 which, in use, partially defines a combustion chamber.

Each port 4 and 6 has a respective inlet or exhaust valve. Figure 1 shows an inlet valve 10 and an exhaust valve 12 of conventional form, and an inlet valve 14 and an exhaust valve 16 in accordance with the present invention. It will be appreciated that, in practice, the same combustion chamber would not be provided with both conventional valves and valves in accordance with the present invention; this combination is shown in Figures 1 and 2 for the purpose of comparison.

Referring to Figure 2, the conventional exhaust valve 12 has a circular valve head 18 and a valve stem 20 having a guide portion of circular cross-section.

This guide portion extends to a cylindrical bore in a valve guide 22. The valve stem 20 has a peripheral groove 24 for receiving a collet (not shown). In use, a valve spring acts against the collet to bias the valve member 12 to its closed position, shown in the drawings. A circular valve seat insert 26 is fitted into the cylinder head 2. When the valve member 12 is in the closed position, the periphery of the valve head 18 makes sealing contact with the valve seat insert 26 to prevent the flow of gas through the exhaust port 6.

The inlet valve 14 is disposed in the cylinder head 2 in generally the same way as the exhaust valve 12. Thus, it has a head 28 which engages the valve seat insert 30 when the valve is closed, and it has a valve stem 32 with a guide surface extending through a valve guide 34. Also, it has a groove 36 for receiving a spring-retaining collet.

It will be appreciated from Figure 1 that the difference between the conventional valves 10 and 12 and the valves 14 and 16 in accordance with the present invention is that the valve heads of the valves 14 and 16 (as exemplified by the valve head 28 of the valve member 14) are not circular but have a polygonal shape.

This is apparent more clearly from Figures 3 to 5, which show the valve member 14. A more detailed description of the shape of the valve head 28 is given below with reference to Figure 8. It will be appreciated that the valve seat insert 30 will have a shape complementary to that of the valve head 28.

Another distinguishing feature of the valve members in accordance with the present invention is that the guide surface of the valve stem 32 is generally triangular, as shown in Figure 6. Again, the valve guide 34 will have a complementary generally triangular bore, and the valve guide 34 itself will need to be fitted in the cylinder head 2 in the correct rotational position to ensure that the valve head 28 seats properly on the insert 30.

With reference to Figures 7 and 8, it will be noticed that the shape of the guide surface of the valve stem 32 is a non-harmonic profile, in that the shape of the guide surface is defined by a discontinuous line. This shape is made up of three arcuate lines 38 which are connected to one another by shorter arcuate lines 40. The radius of curvature of the arcuate lines 40 is the same as the radius of the circumscribing circle 42, and is significantly smaller than the radius of curvature of the arcuate lines 38.

A non-harmonic profile, as shown in Figure 7, is appropriate for the guide surface of the valve stem 32 because this profile permits longitudinal sliding movement of the valve stem 32 within the valve guide 34 when torque is applied to the valve stem 32. This is an essential requirement for spring-biased valves, since compression and extension of the spring is accompanied by relative rotation between its ends, which rotation is imparted to the valve member 14.

The profile of the valve head 28 is shown in Figure 8. This is a harmonic profile and is a continuous cycloid curve having four orders of asymmetry. The curve comprises four arcuate sides 44, connected to one another by arcuate portions 46.

As demonstrated by Figure 1, the use of valve head profiles in accordance with the present invention considerably increases the total valve area available in the cylinder head, by comparison with conventional circular valve heads, particularly when multiple inlet and exhaust valves are used. This increase in valve area is achieved without any significant alteration in the total mass of the valve, and without increasing the risk of adjacent valves interfering with each other during operation. Furthermore, because the valve heads of the valve members 14 and 16 have four orders of symmetry, without any re-entrant regions, they are resistant to distortion as a result of thermal or inertial stresses. Consequently, adequate sealing can be maintained by the valve over a relatively long period of operation. Valve grinding may be achieved by ultrasonic techniques, in which the valve head and valve seat are vibrated with a layer of grinding medium between them.

Furthermore, the use of the non-harmonic profile shown in Figure 7 for the guide surface of the valve stem 32 reliably prevents rotation of the valve member 14 without incurring the risk of jamming of the valve stem 32 in the valve guide 34. ALso, guiding contact is achieved over substantially the entire periphery of the guiding surface, with the result that wear takes place evenly, ensuring a relatively long useful life for the valve member 14 and the valve guide 34.

Claims (14)

1. A valve assembly comprising a valve seat, a valve member provided with a valve head and a valve stem, and a valve guide which cooperates with the valve stem to guide the valve member during movement to open and close the valve, wherein the valve seat and the valve head have cooperating sealing surfaces which are polygonal as viewed lengthwise of the valve stem.

2. A valve assembly as claimed in claim 1, in which the sealing surfaces have the shape of a regular polygon.

3. A valve assembly as claimed in claim 1 or 2, in which the sealing surfaces each have at least two orders of symmetry.

4. A valve assembly as claimed in claim 3, in which the sealing surfaces have a square shape.

5. A valve assembly as claimed in any one of the preceding claims, in which the polygonal shape of the sealing surfaces comprises portions which are arcuate, with a relatively large radius of curvature, and which are interconnected at arcuate corners, having a relatively small radius of curvature.

6. A valve assembly as claimed in any one of the preceding claims in which the polygonal shape of the sealing surfaces is a harmonic shape, with the sides of the polygon forming a continuous curve with the corners.

7. A valve assembly as claimed in claim 6, in which the polygonal shape of the sealing surface is in the form of a cycloidal figure.

8. A valve assembly as claimed in any one of the preceding claims, in which the valve stem and the valve guide have complementary polygonal cross-sections.

9. A valve assembly as claimed in claim 8, in which the cross-section of the valve stem has the shape of a regular polygon, with at least two orders of symmetry.

10. A valve assembly as claimed in claim 9, in which the shape of the valve stem is generally triangular.

11. A valve assembly as claimed in any one of claims 8 to 10, in which the polygonal shape of the valve stem cross-section is a non-harmonic shape, with the sides of the polygon being discontinuous with the corners.

12. A valve assembly as claimed in claim 1 and substantially as described herein with reference to, and as shown in, the accompanying drawings.

13. An internal combustion engine having a valve assembly in accordance with any one of the preceding claims.

14. An internal combustion engine as claimed in claim 12, in which more than one inlet and/or exhaust valve is provided per cylinder of the engine.