INTERNAL COMBUSTION ENGINES

Abstract: The invention relates to a four-valve combustion chamber for an internal combustion engine and to a cylinder head and internal combustion engine incorporating the same. The combustion chamber comprises a pair of adjacent elongate part-spherical cavities or sub-chambers (8', 8") with their longer axes (X', X") converging in a direction from the inlet valve seats (5, 5") of the sub-chambers towards the exhaust valve seats (6', 6") thereof and with a ridge (11) therebetween.

Description: INTERNAL COMBUSTION ENGINES The present invention relates to four-valve combustion chambers for internal combustion engines, to cylinder heads and internal combustion engines incorporating the same, and to methods of forming the same. More particularly, the invention relates to a four-valve combustion chamber for a four-stroke engine of the overhead valve type, which is a development of the combustion chamber design forming the subject of my US Patent No. 3,633,577. In this prior design, the combustion chamber is formed with two elongate cavities or sub-chambers disposed side-by-side, with their longer axes parallel, and with a ridge between the cavities. The cross section of each cavity is substantially arcuate in the direction of its shorter axis, and is arcuate at least at each end zone in the direction of its longer axis. An opening is provided in each end zone which constitutes, or is fitted with, a valve seat which is cooperable with the head of an associated reciprocatory poppet valve. It is beneficial to employ exhaust valves which have a smaller head diameter than that of the associated inlet valves, for reasons that are well known, as discussed, for example in my European Patent No. 0428691 . It is an object of the present invention to provide an improved combustion chamber design of the type disclosed in my US Patent No. 3,633,577, which takes advantage of the above-mentioned difference in inlet/exhaust valve head diameters. According to the present invention, there is provided a four-valve combustion chamber generally of the aforementioned type, wherein the longer axes of the side-by-side cavities or sub chambers, instead of being mutually parallel, mutually converge in a direction from the inlet valve-ends of the sub chambers towards the exhaust valve - ends thereof. In one embodiment of the invention, the included angle between the mutually converging longer axes and the axis of the ridge between the sub chambers is of the order of 5° to 1 2°, for example about 8° to 10° or about 6° to 9°; i.e. the included angle between the longer axes is of the order of 10° to 24°, for example about 16° to 20° or about 1 2° to 18°. The longer axes preferably converge symmetrically about the axis of the ridge between the sub chambers although this is not essential. The median planes of the sub chambers, which are coincident with converging longer axes, may also be coincident with the centres of the inlet and exhaust valve heads, or their valve seats, when the combustion chamber is viewed in plan. However, this is not essential, and it may be preferable, as described later, for the spacing between the median planes/longer axes, in the region of the inlet valve heads/seats, to be greater than (or less than) the spacing between the centres of the inlet valve heads/seats, or for the median planes/longer axes to be disposed asymmetrically with respect to the centres of the inlet and/or exhaust valve heads/seats. Since the longer axes of the side-by-side sub chambers converge, the sub chambers will narrow down in the direction of the exhaust valves. However, the combustion chamber will still retain the two main features of the aforesaid prior type of combustion chamber, namely the ridge separating the two sub chambers, and the squish areas or lands located at opposite ends of combustion chamber between the elongate sub chambers. The resultant combustion chamber is much more compact than my prior design. The distance between the sparking plug and the farthest portions of the combustion chamber is reduced. This makes it easier to design a combustion chamber of much reduced volume, helped by the fact that the presence of the ridge reduces the volume for the same combustion chamber height. Such a reduced volume, which is achieved without having to resort to "bumps" on the piston crown which hamper the efficient "swirl" movement of the incoming charge, is desirable to obtain high compression ratios. High compression ratios increase the efficiency of internal engines, and are also necessary for efficient combustion with some fuels, for example alcohols such as ethanol or methanol. One advantage of the combustion chamber design forming the subject of my US Patent No. 3,633,577 over a conventional four-valve pent-roof chamber was to enhance the "swirl" pattern of flow, particularly in the region of the sparking plug. This type of flow creates a dynamically stratified air-fuel charge, richer in fuel at its periphery, so that the flame front travels at a higher velocity during the crucial first portion of its travel. The effect thereof is to decrease the ignition advance necessary for efficient combustion. A low ignition advance requirement was observed in the engines incorporating my above-mentioned combustion chamber design, for instance in the million and a half motorcycle engines built in the last 20 years in accordance with my aforementioned US patent. The improvement was approximately 5° of crankshaft rotation. In the new combustion chamber design embodying the present invention, the convergence of the longer axes, and therefore of the incoming air-fuel charge streams, further enhances the "swirl" effect. This is believed to be because the two streams emerging from the inlet valve seat openings or ports energise each other in the critical plug region. All the tests carried out with the engines fitted with the new combustion chamber design incorporating converging-stream sub chambers confirm that ignition advances can be reduced by approximately a further 5° compared with engines incorporating combustion chambers according to my aforementioned US patent, with consequential advantages in torque, fuel consumption and exhaust pollution control, particularly noted in the r.p.m. range under 1 500 r.p.m. even at wide open throttle operation. In order that the invention may be more readily understood, one embodiment will now be described with reference to the accompanying drawings in which:- Fig. 1 is a fragmentary section of a cylinder head of an internal combustion engine according to one embodiment of the present invention, taken in a plane including the line l-l shown in Fig. 2; Fig. 2 is a section of the same cylinder head, taken on the line 11-11 shown in Fig. 1 , i.e. in the median plane of one of the cavities or sub chambers of one combustion chamber; Fig. 3 is an underneath plan view of one combustion chamber of the same cylinder head; Fig. 4 is a fragmentary perspective view of the same cylinder head, in an inverted position, showing the combustion chamber embodying the invention; Fig. 5 is a fragmentary side elevation of a cutting tool for machining one of the cavities or sub chambers of the combustion chamber embodying the invention; and Fig. 6 is a view, similar to Fig. 3, of a prior combustion chamber design of the type disclosed in my US Patent No. 3,633,577. Referring to the drawings, the cylinder 1 of an internal combustion engine, is surmounted by a cylinder head 2 into which are fitted valves 3', 3" and 4', 4" respectively, controlling the induction ports 5' , 5" and exhaust ports 6', 6" . 7 is the sparking plug. The or each combustion chamber 8 is formed by two side-by-side, elongated, part-spherical cavities or sub-chambers 8', 8" of radius R. The cavities are divided by a ridge 1 1 . As shown in Fig. 6, in the prior combustion chamber design disclosed in US Patent No. 3,633,577, the longer axes X', X" of the two side-by-side sub chambers 8', 8" are mutually parallel. In addition, as viewed in Fig. 6, these longer axes are coincident with the centres of the heads/seats of the associated inlet and exhaust valves, i.e. the valve/valve seat axes lie in the longitudinal median planes of the sub chambers. The present invention takes advantage of the fact that the exhaust valve heads, and therefore the exhaust valve seats, are of smaller diameter than the inlet valve heads and their associated seats, enabling the locations of the exhaust valves and their seats to be moved closer together whilst still maintaining an adequate gap therebetween. The longer axes X-X', X-X" of the side-by-side sub chambers 8', 8" may be arranged to correspondingly mutually converge in a direction from the inlet valve seat-ends of the sub chambers towards the exhaust valve seat-ends thereof, as clearly shown in Fig. 3. As viewed, in this Figure, the longer axes X-X', X'-X" , and more particularly the median planes of the sub chambers which are perpendicular to the plane of the underside of the cylinder head, may coincide, or approximately coincide, with the centres of the inlet and exhaust valve seats. These axes are symmetrical about the median plane of the combustion chamber, i.e. about the central longer axis X-X coincident with the ridge 1 1 , each making an included angle αwith the central axis X-X (shown as approximately 8° in Fig. 3 as one specific but non-limiting example). The shape of the combustion chamber may be obtained directly during the cylinder head casting operation. It could alternatively be entirely obtained, or the cast combustion chamber could be finished, by milling or otherwise machining when accuracy is needed, more simply than for a classical pent-roof four-valve combustion chamber. In one embodiment, in which milling is involved, the finishing of each sub chamber may be carried out separately by means of left and right-handed rotary cutting tools 9 of the type shown in Fig.5. The cutter 9 is located with its rotational axis at right angles to the longer axis of one of the sub chambers (e.g. 8') as viewed in Fig. 3, centrally of the longitudinal extremities of that sub chamber, with the lateral zone 9' remote from the ridge 1 1 . The cutter is simply traversed towards and away from the face of the cylinder head to mill the sub chamber to the required depth in a single operation. A similar procedure is carried out on the other sub chamber (e.g. 8") with an opposite-handed cutter, or with the illustrated cutter reversed, i.e. with the zone 9' of the cutter on the other side, located with its rotational axis at right angles to the longer axis of that sub chamber. The radius R of the central zone 9" of the cutter shown in Fig. 6 will determine the radius of each part-spherical region of the sub chamber. As shown in Figs. 1 , 3 and 4, each sub chamber includes a part-spherical side surface 12 which blends the part-spherical region of the sub chamber with the face of the cylinder head, so that the edge 13 of the side surface approximately coincides with the upper end of the cylinder bore 1 . These side surfaces are formed by the lateral zone 9' of the cutter. These side surfaces 12 appear as curved zones or segments when the cylinder head is viewed in plan, as shown in Fig. 3. In order to optimise the shape of the side surfaces 12, it may be preferable to provide an included angle (2α) between the convergent longer axes X-X', X'-X" which is greater than the included angle between the median planes common to the centres or axes of the pairs of inlet and exhaust valve heads/seats. In this case, as viewed in Fig. 3, whilst the longer axis of each sub chamber is approximately coincident with the axis of the exhaust valve seat 6', 6", the longer axis is outboard of the axis of the associated inlet valve seat 5', 5". Due to the convergent nature of the longer axes, and the convergent nature of the sub chambers themselves, the volume of the combustion chamber, i.e. the combined volume of the sub chambers 8', 8", will be significantly less than that of the combustion chamber disclosed in US Patent No. 3,633,577, thus giving rise to a higher compression ratio, and a more compact combustion chamber in which the distance between the sparking plug and the farthest extremities of the combustion chamber is reduced. The projected surface of the combustion chamber, seen in Fig. 3, as created by the main cutter radius R" of Fig. 5, which is the region in which the valve seats are situated, is reduced when compared with the same surface as seen in Fig. 6 representing my prior combustion chamber design. Therefore, for a given height of the combustion chamber, the volume is reduced substantially. It will be understood that various modifications may be made without departing from the scope of the present invention. For example, the combustion chamber shape may be incorporated in single or multi-cylinder spark ignition internal combustion engines.

Claims: CLAIMS 1 . A four-valve combustion chamber for an internal combustion engine, comprising two elongate cavities disposed side-by-side with a ridge between the cavities, the cross-section of each cavity being substantially arcuate in the direction of its shorter axis, and being substantially arcuate at least at each end zone in the direction of its longer axis, and an opening in each end zone which constitutes or is fitted with a valve seat, characterised in that the longer axes of the side-by-side cavities mutually converge in a direction from the inlet valve seat-end zones of the cavities toward the exhaust valve seat-end zones thereof. 2. A combustion chamber as claimed in claim 1 , wherein the included angle between the mutually converging longer axes is of the order of 10° to 24°. 3. A combustion chamber as claimed in claim 2, wherein the included angle is of the order of 1 6° to 20°. 4. A combustion chamber as claimed in claim 2, wherein the included angle is of the order of 12° to 18°. 5. A combustion chamber as claimed in any preceding claim, wherein the longer axes converge symmetrically about the axis of the ridge between the side-by-side cavities. 6. A combustion chamber as claimed in any preceding claim, wherein the median planes of the side-by-side cavities, which are coincident with the converging longer axes, coincide or approximately coincide with the centres of the inlet and exhaust valve seats. 7. A combustion chamber as claimed in any of claim 1 to 5, wherein the median planes of the side-by-side cavities, which are coincident with the converging longer axes, are spaced apart in the region of the inlet valve seats by a distance which is greater than the spacing between the centres of the inlet valve seats. 8. A combustion chamber as claimed in any preceding claim, wherein the cavities are of part-spherical configuration. 9. A combustion chamber as claimed in claim 8, wherein the side of each cavity remote from the ridge is formed by a part-spherical side surface extending generally in the direction of the ridge. 10. A combustion chamber as claimed in any preceding claim, wherein a passage adapted to receive a sparking plug opens into the chamber at the apex of the ridge in a substantially central position relative to the valve seats. 1 1. A cylinder head for an internal combustion engine, incorporating one or more combustion chambers as claimed in any preceding claim. 12. An internal combustion engine, incorporating one or more cylinder heads as claimed in claim 1 1 . 13. An internal combustion engine as claimed in claim 12, wherein the longer axes of the cavities of the or each combustion chamber are disposed generally transversely to the axis of rotation of the engine crank-shaft. 14. An internal combustion engine as claimed in claim 13, wherein the centres of the arcs of corresponding end zones of the cavities of the or each combustion chamber lie on a line parallel to the axis of rotation of the engine crank-shaft. 15. An internal combustion engine as claimed in claim 12, 13 or 14 when dependent upon claim 9, wherein the curvature of the part-spherical side surfaces of the cavities of the or each combustion chamber blend with the face of the cylinder head so that the edges of the side surfaces approximately coincide with the upper end of the associated cylinder bore of the engine.

Inventors: PIATTI SANZIO PIO VINCENZO, PIATTI, SANZIO, PIO, VINCENZO
Applicants: PIATTI SANZIO PIO VINCENZO, PIATTI, SANZIO, PIO, VINCENZO
Application year: 1998
Main classification: F02F1
IPC codes: F02B23, F02F1