GB2341891A

GB2341891A - A poppet valve for an internal combustion engine having a protuberance on its valve head

Info

Publication number: GB2341891A
Application number: GB9820596A
Authority: GB
Inventors: John William Hitchman
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1998-09-23
Filing date: 1998-09-23
Publication date: 2000-03-29
Also published as: GB9820596D0

Abstract

A poppet valve 14 for an internal combustion engine comprises a valve stem, a valve head 15 and a protuberance on the side of valve head 15 facing a combustion chamber of the I.C. engine. The protuberance may be in the form of an annular rib 22 that tapers towards the combustion chamber. This annular rib 22 increases the surface area of the valve head 15 exposed to the combustion chamber allowing the valve head 15 to absorb heat faster during start up of the engine in order to reduce the amount of combustion gases deposited on the valve head 15. Reduced deposits reduces the incidence of poor or hesitant running and of increased emissions following cold starts.

Description

2341891 - 1 Internal Combustion Engine The invention relates to internal

combustion engines of the kind which a poppet-type inlet valve has a valve stem which extends through an inlet port and a valve head at one end of the stem to seal the inlet port from an associated combustion chamber. Such inlet valves are in common use in all 5 types of four-stroke piston engines.

It is now common to provide multi-point fuel injection with an individual injector for each cylinder. This has a disadvantage in that there is only a short distance between the injector and the combustion chamber and a correspondingly short time for fuel to vaporise. Consequently, the inlet valve is cooled by the latent heat of vaporisation of the fuel and thus tends to run at a much cooler temperature than in a corresponding carburettor or single point injection engine. Depending on the fuel, lubricating oil and the duty cycle of the engine, there are circumstances where carbonaceous deposits build up on the back face or inlet port side of the inlet valve. These deposits act as a heat insulator and an absorbent of fuel such that during the period immediately following a cold start there can be poor or hesitant running and increased emissions.

Tests indicate that the build-up of deposits on the inlet valve can be reduced if the valve-is relatively hot during normal running of the engine.

Hence, it is an-object of the invention to provide an internal combustion engine of the kind described in which the inlet valve is warmed quickly by the combustion chamber gasses and is operated at a relatively high temperature.

According to one aspect of the invention there is provided an internal combustion engine having a poppet-type inlet valve comprising a valve stem extending through an inlet port and a valve head at one end of the stem to seal the inlet port from an associated combustion chamber, the valve head having a protuberance on the side facing the combustion chamber to increase the surface area of the valve head exposed to the combustion chamber. This increases the heat flow from the combustion chamber.

Since the inlet valve is novel per se, according to a further aspect of the invention there is provided a poppet-type inlet valve for an internal combustion engine piston engine, the inlet valve comprising a valve stem which in use extends through an inlet port of the engine and a valve head at one end of the stem to seal the inlet port from an associated combustion chamber, the valve head having a protuberance on the side facing the combustion chamber to increase the surface area of the valve head exposed to the combustion chamber.

Preferably the protuberance is annular. This makes manufacture relatively easy and helps to reinforce the valve head which can be reduced in thickness to improve heat transfer and compensate for the weight of the protuberance.

The protuberance preferable tapers towards the combustion chamber. This further assists heat flow and helps to reduce any build-up of deposits 5 on the combustion chamber side of the valve head.

The protuberance may have a rounded free end. This helps to reduce the temperature at the tip of the protuberance and thereby avoid pre-ignition or other temperature related problems.

In an internal combustion engine according to said one aspect of the invention there may be two or more inlet ports opening into the combustion chamber, only one or some of the inlet valves having said protuberance. Preferably such an engine comprises means to minimise or eliminate the lift of the inlet valve without said protuberance. Such means may be operational during a short period after a cold start.

The invention will now be described by way of example and with reference to the accompanying drawings, of which:- Fig.1 is a cross-section through part of a cylinder head of an internal combustion engine according to the invention; and I,- -\ 1 -4 Fig.2 is an enlarged cross-section through an inlet valve shown in Fig. 1.

A piston-type internal combustion engine has a cylinder head 11 which includes an inlet port 12 leading to a combustion chamber 13. An inlet valve 14 has a head 15 which is biased into sealing contact with a valve seat insert 16 by a valve spring 17. The valve is unseated by a cam 18 on a camshaft 19 acting through a bucket tappet 21 which incorporates an hydraulic lash adjuster.

As described so far the components are all conventional. However, in accordance with the present invention the valve head 15 has an annular protuberance or rib 22 on the side facing the combustion chamber 13. The rib 22 tapers towards the combustion chamber 13 and has a rounded end 23.

When the engine is started from cold, all of the engine components are at ambient temperature and there is poor vaporisation of the fuel injected upstream of the inlet port 12. To compensate for this, the airlfuel mixture is enriched in the usual way and to an extent necessary to provide an ignitable mixture in the combustion chamber 13. As the engine starts to warm up, the need for mixture enrichment diminishes, the mixture being vaporised by heat from the walls of the inlet port 12 and from the back face of the inlet valve head 15 (i.e. the side facing the inlet port 12). The inlet valve 14 warms up faster than the cylinder head 11 and its water based coolant so that the inlet valve 14 is the main source of vaporising heat in the first few seconds from a cold start. However, heat must be conducted from the combustion chamber side of the valve head 15 to the inlet port side before it can be effective to help vaporise the fuel. The rib 22 increases the surface area exposed to the combustion chamber and thereby increases the rate at which such heat is conducted. Therefore in the crucial few seconds after firing from a cold start there is improved vaporisation of the fuel. This allows the enrichment to be reduced more rapidly and improves drivability, i.e. the manner in which the engine responds when fitted in a vehicle.

Emissions are also reduced.

To compensate for the additional weight of the rib 22, the thickness of the valve head 15 can be reduced, further improving the conduction of heat. By making the rib 22 annular, it becomes a useful structural part of the valve head 15 and thereby compensates for the reduction in valve head thickness. However, other forms of protuberance are possible, e.g. two or more concentric annular ribs, radial ribs or a generally annular wavy or sinusoidal rib.

Once the engine has warmed up to its normal operating temperature, the valve head 15 tends to run hotter than the normal inlet valve. This helps to prevent the-build-up of deposits on the back face of the valve head 15 and thereby further improves the transfer of heat to the mixture during the critical warm up period compared to the conventional engine. However, the increased valve temperature tends to reduce the maximum torque available, particularly at low and medium engine speeds. For this reason it may be better to have a protuberance on only one or some of the inlet valves in the case where there are two or more inlet valves to the combustion chamber. Although it would be feasible to operate the inlet valves conventionally and thereby benefit only proportionally, the valves are preferably controlled so that during the crucial period following start up the conventional valve' remains closed or has a minimal lift (opening).

Individual control of valves can be achieved by known means, e.g. using known electro-magnetic or electro-hydraulic actuation or mechanically or hydro-mechanically by using devices such as described in US 4 336 775 or US 4 615 307.

Claims

-7CLAIMS

1. An internal combustion engine having a poppet-type inlet valve comprising a valve stem extending through an inlet port and a valve head at one end of the stem to seal the inlet port from an associated combustion chamber, the valve head having a protuberance on the side facing the combustion chamber to increase the surface area of the valve head exposed to the combustion chamber.

2. _An engine according to Claim 1 wherein the protuberance is annular.

3. An engine according to any preceding claim wherein the protuberance tapers towards the combustion chamber.

4. An engine according to any preceding claim wherein the protuberance has a rounded free end.

5. An engine according to any preceding claim and comprising two or more inlet ports opening into the combustion chamber and wherein only one or some of the inlet valves have said protuberance.

6. An engine according to Claim 5 and comprising means to minimise or eliminate the lift of the inlet valve without said protuberance.

7. A poppet-type inlet valve for an internal combustion engine piston engine, the inlet valve comprising a valve stem which in use extends through an inlet port of the engine and a valve head at one end of the stem to seal the inlet port from an associated combustion chamber, the valve head having a protuberance on the side facing the combustion chamber to increase the surface area of the valve head exposed to the combustion chamber.

8. An inlet valve according to Claim 7 wherein the protuberance is annular.

9. An inlet valve according to Claim 7 or Claim 8 wherein the protuberance tapers towards the combustion chamber.

10. An inlet valve according to any of Claims 7 to 9 wherein the protuberance has a rounded free end.

11. An inlet valve for an internal combustion engine substantially as described herein with reference to the accompanying drawings.

12. An internal combustion engine substantially as described herein with reference to the accompanying drawings.