The invention relates to internal combustion engines, and more specifically to the configuration of a cylinder head of an engine and of components associated with the, or each, combustion chamber thereof.
In a modern internal combustion engine, the cylinder head has inlet and exhaust passages which communicate with the or each combustion chamber defined between the cylinder head and the respective cylinder space therebeneath. Poppet-type inlet and exhaust valves are reciprocably supported in the cylinder head, and have heads which cooperate with seatings where the passages open into the combustion chamber, the valves being controlled to open and close the respective passages in the required timed relationship.
In addition to the valves and the inlet and exhaust passages controlled thereby, other devices need to be carried by the cylinder head to communicate with the, or each, combustion chamber. These devices are referred to herein using the general term “operating elements”, and the mention of one of these specifically does not necessarily preclude the substitution of one of the other elements in its place. For example, there may be at least one spark plug in the case of a spark ignition engine, a fuel injector in the case of a compression-ignition engine, and some spark-ignition engines have fuel injected directly into each combustion chamber, requiring the provision of both an injector and spark plug for each combustion chamber. Other operating elements, e.g. a sensor, may be required to communicate with the combustion chamber.
It will be appreciated that terms such as “over”, “beneath”, and the like are used herein according to engine design convention, rather than referring literally to the disposition of the respective parts referred to. For example, it is accepted that an engine may have its cylinders disposed horizontally when installed in a vehicle for example, yet still be referred to as having overhead cams, despite the fact that when looking at the installed engine the cams are not physically located above the horizontal cylinders.
In order to achieve currently-desirable characteristics in respect of power output, fuel economy and exhaust emissions, many engines nowadays, especially those for automotive applications, utilise cylinder heads incorporating more than a single inlet and exhaust valve per cylinder, most commonly so-called “four valve” arrangements with two inlet and two exhaust valves per cylinder. A four valve arrangement can provide a greater valve area for flow of both inlet and exhaust gases in relation to the bore of the cylinder, than can fewer valves. The most common arrangement has two inlet valves disposed with their axes of reciprocation lying in a plane inclined to the centreline of the cylinder bore, the valves being spaced from one another in a first direction which may be and usually is, parallel to the engine's crank shaft. The axes of reciprocation of the valves may be parallel to one another, or inclined to one another. The axes of reciprocation of the exhaust valves lie in another plane which is oppositely inclined to the cylinder bore and which intersects the plane of the inlet valves; the exhaust valves being spaced as the inlet valves and parallel or inclined to one another. The exhaust valves themselves are spaced from the inlet valves in a direction which may be, and usually is, transverse of the first direction. The combustion chamber is of shallow pent roof configuration, which is desirable in achieving the required compression ratio.
In a spark ignition such engine, the spark plug typically is disposed centrally or nearly centrally between the heads of the valves to give a combustion process more favourable for fuel economy, exhaust emissions and power characteristics than would be found in alternative arrangements. In a compression ignition such engine, the fuel injector would so positioned to provide even distribution of fuel within the combustion chamber, to achieve a similar effect. In the case of an engine with both injector and spark plug extending into such chamber, it would be desirable for both of them to be centrally mounted to achieve this effect, although the space available for such positioning is severely limited particularly if the size of the valve heads is maximised.
It is broadly the object of the present invention to address the above-described problems of design of a cylinder head having multiple valves and also two or more operating elements communicating with each combustion chamber.
According to a first aspect of the invention, we provide a cylinder head for an internal combustion engine comprising at least one combustion chamber portion for defining, in an engine, a combustion chamber between it and a, or a respective, cylinder space therebeneath;
at least two poppet-type inlet valves associated with the or each combustion chamber portion, having heads which cooperate with seatings in the combustion chamber portion to control flow through respective inlet passage portions, the inlet valves being reciprocably supported in the cylinder head with their axes of reciprocation spaced from one another in a first direction;at least two poppet-type exhaust valves having heads which cooperate with seatings in the combustion chamber portion to control flow through respective exhaust passage portions, the exhaust valves being reciprocably supported in the cylinder head with their axes of reciprocation also spaced from one another in the first direction; andat least two receiving formations for operating elements, the receiving formations opening into the combustion chamber portion in a central region bounded by the heads of the valves;wherein the receiving formations are inclined to one another so as to diverge generally in the first direction as they extend away from the combustion chamber portion.
Preferably, the exhaust valves are spaced from the inlet valves in a second direction transversely of the first direction, and the receiving formations are spaced from one another in the second direction.
Preferably the receiving formations are spaced from one another transversely of the engine relative to the crankshaft.
Preferably, the receiving formations are adjacent one another at their respective ends proximate to the combustion chamber portion.
The axes of reciprocation of the inlet valves may be substantially parallel to one another and lie in a first plane.
The axes of reciprocation of the exhaust valves may be substantially parallel to one another and lie in a second plane.
The first and second planes may be inclined to one another, and may intersect generally in the cylinder space(s).
The axis of intersection between the first and second planes may be substantially parallel to the rotary axis of a crankshaft of an engine wherein the cylinder head is to be used.
The operating elements may comprise a spark plug and an injector.
In the invention, the elements are disposed in the centre section between the valves, allowing the injector and spark plug to be mounted closest to the inlet and exhaust valves respectively. They are disposed in close proximity to one another, to allow minimal effect on valve size. Contrary to existing cylinder head designs where the injector and spark plug are mounted side by side, only the narrower ends of the injector and the spark plug are alongside one another, which allows their tips to be closer together than in other designs. The injector and spark plug are disposed at an opposing angle to one another, so that the wider upper regions of the spark plug and injector bodies are apart.
The invention also provides an internal combustion engine having a cylinder head according to the first aspect of the invention.
The injector may be adapted to distribute fuel in such a way as to compensate for the angle at which it is disposed, and provide a substantially symmetrical distribution of fuel relative to the cylinder centre axis. Thus the injector may have an asymmetrical spray pattern which is provided to compensate for the angle of the injector. This gives the same effect as having the injector in a directly upright position, but avoids the packaging constraints that this creates.