GB2368882A

GB2368882A - Valve seats for internal combustion engines formed by filling rebate in cylinder head with weld material

Info

Publication number: GB2368882A
Application number: GB0123252A
Authority: GB
Inventors: Andrew Short; Edward Pye
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-09-27
Filing date: 2001-09-27
Publication date: 2002-05-15
Also published as: GB0023621D0; GB0123252D0

Abstract

A method of forming a valve seat for an internal combustion engine by forming a rebate in the engine and filling the rebate in part or whole with weld material to form the valve seat. The weld material may then be shaped by machining to form the valve seat. A capping member may be located in the rebate prior to the addition of weld material, to cap off the opening of a passage connected to one or more cooling water jackets.

Description

Title: Valve Seats DESCRIPTION This invention concerns an improved valve seat for use in internal combustion engines.

Internal combustion engines provide mechanical energy from thermal energy produced when a suitable fuel, which may be in liquid, gaseous or even solid form, is burned.

A fuel and air mixture is introduced into the engine. The mixture is then compressed in the cylinder of the engine, and is then ignited or detonated. This combustion process thrusts the piston of the engine downwards, which imparts rotary motion to the crankshaft of the engine, thereby providing mechanical energy.

The air is admitted into the cylinder through one or more inlet valves and the resulting combustive gases exit the cylinder via one or more exhaust valves. These valves are opened and closed according to the requirements of the combustive cycle.

The inlet and exhaust valves are usually accommodated in a cylinder head of the engine.

However, a problem exists when the base material of the cylinder head is not suitable to run the valves directly, in that it does not in general have the heat resistant properties or hardness, to facilitate optimum operation of the engine for long periods of time. In order to alleviate this problem, and thus increase the lifetime of the cylinder head, it is known to provide valve seats, against which the valve closes. When the surface of the seat is in contact with the valve, this provides the necessary seal, and further, the seat possesses better heat and wear resistant properties than the cylinder head itself. In general, valve seats are in the form of inserts, and are separately machined items, which are shrink-fitted into the cylinder head of the engine. The inserts may be made from a hard, heat resistant material, such as steel.

However, problems exist with the valve inserts currently in use, in that they are expensive. Furthermore, when the valve seat inserts are shnnk-fitted into the cylinder head, there exists a gap between the underside of the insert itself and the cylinder head, since it is impossible to ensure 100% contact due to warpage and distortion, etc.. This results in a decrease in thermal conductivity, which causes the valve to heat up. In addition, the inserts are susceptible to becoming dislodged from their recesses in the cylinder head, since they are not, in general, permanently attached thereto. If the valve seat insert fails, the whole insert must be removed and replaced.

A further problem exists in that the valve seat inserts currently in use have a tendency to heat up, due to the poor thermal contact between the cylinder head and the valve seat inserts. It is known to cool cylinder heads in general by way of using suitable cooling means, such as water or other suitable liquid flowing through cooling jackets.

However, there is a limit to how close to the valve seat inserts that the water can flow, since there must be a significant amount of cylinder head material between the water cooling jacket and the valve seat-inserts in order to cope with the significant amount of mechanical hoop stress, which may be present. This stress is on account of the method commonly used to insert and secure the valve seat insert into the cylinder head, whereby the cylinder head is first heated up, and then the insert is cooled down and then inserted into the cylinder head. As both of the components return to their normal temperature, there is a hoop stress induced.

It is an object of the present invention to provide an internal combustion engine valve seat and a method for forming a valve seat, which overcomes or at least alleviates the above-mentioned problems.

Accordingly, one aspect of the present invention provides a method of forming an internal combustion engine valve seat, comprising the steps of forming a rebate for the valve seat, infilling the rebate with weld material, and machining the weld material to form the valve seat. Most usually, the valve seat rebate will be formed in the cylinder head of the engine.

A second aspect of the present invention provides a valve seat in an internal combustion engine, which is formed from weld material.

A third aspect of the present invention provides an internal combustion engine having a valve seat formed from weld material.

Preferably, the weld material is welded to the cylinder head by conventional welding means, such as arc welding, TIG welding, or oxyacetylene welding. It is further preferable that the rebate is cast into the cylinder head of the engine. Alternatively, the cylinder head may be machined to form the rebate.

In a preferred embodiment, the weld material is made from a suitable alloy. It is further preferable that the particular alloy to be used as the valve seat may be varied according to the material from which the cylinder head is made. For example, if an aluminium cylinder head is used, then an aluminium alloy may be used as the weld material. Preferably, the hardness of the valve seat is comparable to the hardness of typical prior art inserts, such as steel, and is sufficient to ensure that the valve seat recession rates fall within acceptable limits.

It is preferable that cooling water jackets are cast into the cylinder head of the engine, and capped off with a suitable material prior to the welding of the valve seats.

Preferably, at least part of the cooling water jackets are located adjacent the valve seats. More preferably still, the cooling water jackets communicate with an annular water passage located beneath a capping ring. Casting of the cooling water jackets in this way is not possible if conventional valve seat inserts are used, because of the problem of not being able to maintain a hermatic seal between the cylinder head and the valve seat inserts.

As a result of using the weld material as the valve seat as opposed to an insert slotted into the cylinder head, no gap exists between the cylinder head and the valve seat, which results in there being no drop in thermal conductivity. Accordingly, the valve temperature is significantly reduced. In addition, by using the weld material as opposed to inserts, the cooling water jackets may be situated a lot nearer to the valve seats than is possible if prior art valve seat inserts are used, because the material section of the cylinder head does not have to take account of mechanical hoop stress.

Furthermore, if the valve seat fails for some reason, more weld material may be simply added to the valve seat. By using weld material in this way, the lifetime of the cylinder head may be increased indefinitely. If an insert is used. however, the whole valve seat insert must be replaced if it fails, which significantly increases costs. In addition, by using weld material as the valve seat insert. larger valves may be accommodated.

The present invention will now be described further hereinafter, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic sectional view of a prior art valve seat insert, in situ, Figure 2 is a diagrammatic sectional view of the valve seat, in accordance with one embodiment of the present invention, Figure 3 is a perspective view of a capping member, in accordance with one embodiment of the present invention, and Figure 4 is a fragmentary perspective view of part of the capping of Figure 3 taken on section line A-A.

With reference to Figure 1 of the drawings, part of a cylinder head is illustrated generally by reference numeral 1. A rebate for receiving a valve seat insert is illustrated generally by reference numeral 3. The rebate may be formed by machining the cylinder head, or conversely, it may be cast into the cylinder head. A valve seat insert 2 is located in rebate 3 in the cylinder head 1. In order to secure the insert 2 in the rebate 3 of the cylinder head 1, the insert 2 is shrink-fitted into the rebate 3. In this way, a valve (not shown) closes against a valve seat surface 2a, as opposed to the surface of the cylinder head 1, which may not be suitable for the purpose. The valve seat insert is shown spaced from the rebate for ease of description. In practice, the radial surfaces of the valve seat and the rebate will be in close contact. There may be gap X on the underside of the valve seat insert. Cooling water jackets 5 are located in the cylinder head to reduce the temperature of the valve. As can be seen from this Figure, the jackets 5 are spaced from the valve seat insert 2. The drawing shows a single valve seat insert.

In practice, the cylinder head may have a plurality of valve seat inserts. Figure 2 of the drawings shows part of a cylinder head l'having a valve seat

IS formed in accordance with the present invention. A rebate, shown by hatching 3"is formed in the cylinder head. It may be formed either by machining or during the casting process of the cylinder head. Weld material is welded into the rebate 3"of the cylinder head, to form valve seat 4. In this way, the cylinder head 1 of the internal combustion engine, and the valve seat 4 form an integral component, as opposed to the separate cylinder head 1 and slot-in valve seat insert 2 arrangement of the prior art. Any water jackets can extend up to the location of the rebate.

In accordance with a preferred feature, cooling water jackets 6 communicate with the rebate 3". An annular capping member 8 is inserted in the rebate. It has arcuate walls 8a, 8b (see Figure 4) and an annular water passage 7 defined beneath the capping member, which is also shown in Figure 3. The capping member 8 is used to cap off the cooling water jackets 6 prior to welding of the valve seat 4.

The capping member does this by forming a cavity in the valve seat.

The weld material can include an aluminium alloy or any other suitable material.

Claims

Claims: 1. A method of forming a valve seat for an internal combustion engine, said method including the steps of forming a rebate at a suitable location in said engine for the valve seat, filling the rebate in part or whole with weld material to form the valve seat.
2. A method according to claim 1 wherein the weld material is shaped to form the valve seat.
3. A method according to claim 1 wherein the rebate is formed in a cylinder head of said engine.
4. A method according to claim 3 wherein the rebate is formed in said cylinder head by machining.
5. A method according to claim 3 wherein the rebate is formed in said cylinder head by casting the rebate therein.
6. A method according to claim 1 wherein the weld material is shaped to form the valve seat by machining.
7. A method according to claim 1 wherein a capping member is located in the rebate prior to the addition of welding material to form a cap for an opening of a passage connected to or forming part of one or more cooling water jackets.
8. A valve seat for an internal combustion engine, wherein said valve seat is formed from weld material located in a rebate at a suitable location in said engine, said weld material forming said valve seat.
9. A valve seat according to claim 8 wherein the weld material is machined to form said valve seat.
10. A valve seat according to claim 7 wherein the rebate is formed in a cylinder head in the engine.
11. A valve seat according to claim 9 wherein the rebate is formed in the cylinder head by machining the rebate therein.
12. A valve seat according to claim 9 wherein the rebate is formed in the cylinder head by casting the rebate therein.
13. A valve seat according to claim 9 wherein one or more cooling jackets are located adjacent the valve seat.
14. A valve seat according to claim 12 wherein the one or more cooling jackets communicate with at least a portion of the valve seat.
15. A valve seat according to claim 13 wherein the cooling jackets are provided with one or more capping members, the capping members provided in the valve seat prior to the addition of the welding material to form a cap for an opening of a passage in said valve seat connected to or forming part of one or more cooling water jackets.
16. A valve seat for an internal combustion engine, said engine including at least one cylinder head, said cylinder head including one or more inlet valves for admitting one or more gases for combustion into said cylinder and one or more outlet valves for emitting combustive gases thereform, said inlet and outlet valves having one or more valve seats against which the valves close, said valve seats provided in rebates in said cylinder, and wherein said valve seats are formed from weld material located in said rebate and said weld material shaped accordingly to allow a seal to be formed between said inlet and outlet valves and said valve seats when said valves are closed.
17. An internal combustion engine, said internal combustion engine having a valve seat at a suitable location, wherein said valve seat is formed from weld material located in a rebate at a suitable location in said

e engine, said weld material shaped accordingly to form said ngine, sal 1 9 valve seat.
18. An internal combustion engine, said engine including at least one cylinder head, said cylinder head including one or more inlet valves for admitting oxygen containing gas or gases into said cylinder and one or more outlet valves for emitting combustive gases thereform, said inlet and outlet valves having one or more valve seats against which the valves close, said valve seats provided in rebates in said cylinder, and wherein said valve seats are formed from weld material located in said rebate and said weld material shaped accordingly to allow a seal to be formed between said inlet and outlet valves and said valve seats when said valves are closed.
19. A valve seat substantially as hereinbefore described with reference to figure 2.
20. A capping member substantially as hereinbefore described with reference to figures 3-4.