GB2133469A - A spark-ignition, reciprocating- piston internal combustion engine - Google Patents

Abstract

The oval combustion chamber cavity (9) in the piston (3) widens out in a tapered manner towards the cylinder head (1) and is surrounded on all sides by a squish region (18, 18a). The sparking plug (20) is offset by a distance (s) from the median line (37) of the combustion chamber (9) and is disposed in the half of the combustion chamber which contains the exhaust port. When the combustion chamber (9) is used for a four-cylinder, in-line internal combustion engine the sparking plugs (20) of the two outer cylinders (27, 29, Fig. 5) are positioned offset to the outside by the distance (s) with respect to the combustion chamber median lines (37) and the sparking plugs (20) of the two inner cylinders (26, 28, Fig. 5) are positioned offset to the inside towards the median plane (25) of the engine, in order to achieve equally long air induction paths for all the cylinders and an optimum combustion process. <IMAGE>

Description

SPECIFICATION A spark-ignition, reciprocating-piston internal combustion engine The invention relates to a spark-ignition reciprocating-piston internal combustion engine.

Our co-pending British Patent Application No.

8227208 discloses a spark-ignition, reciprocating-piston internal combustion engine, having overhead valves extending parallel to the piston axis, a flat cylinder head, a combustion chamber cavity which is formed only in the piston head and widens in a tapered manner towards the cylinder head and whose opening area in the piston head forms a squish region, the latter region including one sickle-shaped portion which, with a first circular edge having a first radius of curvature, is opposite the sparking plug and separated therefrom by a substantial part of the combustion cavity, and another portion with a second circular edge concentric with the piston axis and having a second radius of curvature provided in the region of the spark plug, the combustion chamber cavity being disposed eccentrically to the piston axis and being surrounded on all sides by the squish region with the sparking plug being approximately in the centre of the circle of curvature of the first edge.

By means of such an internal combustion engine it is possible to reduce the fuel consumption and the exhaust gas emission, as an intensive turbulence is produced at the end of the compression stroke by the shape of the combustion chamber and the position of the squish surfaces. The favourable results of this combustion chamber are also enhanced in particular by the position of the sparking plug, which is situated between the exhaust port and the inlet port close to the median line of the combustion chamber, i.e. the connection line of the centre of the circle of curvature of the edge of the combustion chamber.

The object of the invention is to reduce the fuel consumption and the exhaust gas emission still further by the optimum choice of the installation position of the sparking plug while retaining the same high performance.

Surprisingly, this object is attained by the sparking plug being disposed in the half of the combustion chamber which contains the exhaust port, offset by a slight distance s from the median line of the combustion chamber. This result was unexpected since it had always been assumed that the sparking plug would have to lie on the median line of the combustion chamber in order to obtain equal paths for the flame propagation towards both halves of the combustion chamber and thus a symmetrical advance of the flame front.

It has now been found that the best results are obtained when the sparking plug is offset by approximately 5 mm with respect to the median line of the combustion chamber and is moved by this amount towards the exhaust valve. In addition to an improvement in efficiency, a higher performance is also achieved, as more space is left for the inlet port by moving the sparking plug.

Since the intake air may flow in unchoked, the improved filling of the cylinders thus achieved results in an increase of torque and performance.

In a further development of the present invention, in a four-cylinder internal combustion engine with an in-line arrangement, the sparking plugs of the two inner cylinders are arranged offset to the inside towards the median axis of the internal combustion engine by the distance s from the median line of the combustion chamber, while the sparking plugs of the two outer cylinders are arranged offset to the outside by the same amount from tha median line of the combustion chamber.

The purpose of this alternate offsetting of the sparking plugs to the left and right with respect to the median line of the combustion chamber is to move the individual suction pipes and inlet ducts in pairs as close together as possible, in order to give their length equal dimensions and to match them uniformly with respect to oscillation charging.

In the accompanying drawings Fig. 1 is a vertical section through a portion of a cylinder head, cylinder block and piston of an internal combustion engine according to the present invention, Fig. 2 is a side view, partly in section, of the piston shown in Fig. 1, Fig. 3 is a plan view of the piston shown in Fig.

2 with the inlet and exhaust ports indicated, Fig. 4 is a diagrammatic view from below of the cylinder head shown in Fig. 1, and Fig. 5 is a plan view of a four-cylinder internal combustion engine according to the present invention.

Referring now to the drawings, there is shown a cylinder head 1, a cylinder block 2 and a piston 3.

The cylinder head 1 has an inlet port 5 cooperating with an inlet valve 4 and an exhaust port 6 cooperating with an exhaust valve (not shown). The inlet valve 4 and the exhaust valve are positioned vertically and extend axially parallel to the piston axis 7.

The combustion chamber of the internal combustion engine is formed by a cavity 9 in the piston 3. This cavity 9 is positioned eccentrically in the piston head 10 and has a tapered shape with a generally elliptical base area 11 and a generally elliptical opening area 1 2. The cavity 9 has a peripheral surface 23 which comprises two tapered portions A and B of different curvature.

One portion B with the centre M is positioned concentric with the piston 3 and the other portion A with the centre M1 is positioned eccentrically in the piston 3. The portions A and B extend approximately in a longitudinal plane 22 which runs parallel to the median longitudinal plane 1 9 of the piston 3 and in which the cavity 9 is at its widest. The inlet valve 4 and the exhaust valve are disposed in the cylinder head 1 in this longitudinal plane 22.

The combustion chamber has a squish region 1 8 and 1 8a which is formed by a portion of the lower surface 14 of the cylinder head 1 disposed at right angles to the piston axis 7 and a corresponding surface 15 of the piston head likewise disposed at right angles to the piston axis 7.

In the present example of embodiment the entire squish region 1 8, 1 8a is formed by a surface which surrounds the elliptical opening area 1 2 of the cavity 9 and which comprises the larger sickle-shaped part 18 and the narrow annular part 1 8a adjoining the latter. This annular area 1 8a extends approximately as far as the longitudinal plane 22 of the piston 3 and then passes into the sickle-shaped area 1 8. The sickleshaped part 1 8 is defined by a circular edge with a radius of curvature 21 and the sparking plug 20 is positioned close to the centre M1 of said circle of curvature.It is offset by the distance s with respect to the median line 37 of the combustion chamber and is positioned with its centre in the half of the combustion chamber which contains the exhaust port 6. The other part 1 8a of the squish region is provided with a circular edge lying concentric with the piston axis 7.

Fig. 5 shows the application of the combustion chamber according to the invention in the case of a four-cylinder, in-line internal combustion engine.

The cylinders 26 and 27 are positioned on the lefthand side of a median plane 25 of the cylinder block 2, and the cylinders 28 and 29 on the right hand side of the median plane 25. On the median plane 25 there is also disposed the centre of a collector intake pipe 30, from both sides of which extend intake pipes 31 and 32 which are bent symmetrically to the median plane 25 and branch off into the individual intake pipes 33, 34 and 35, 36 respectively which open into the internal combustion engine and are connected to the inlet ports 5. In order to be able to make the lengths of all the intake pipes and thus the induction ratios approximately equal, the inlet ports 5 of each of two cylinders 26, 27 and 28, 29 respectively are positioned adjacent to one another. The exhaust ports 6 of cylinders 27 and 28 are therefore to the left of the combustion chamber median lines 37, and the exhaust ports 6 of cylinders 26 and 29 are to the right of the combustion chamber median lines 37.

All the sparking plugs 20 are offset by the distance s with respect to the combustion chamber median line 37 and are disposed in the combustion chamber halves which contain the exhaust ports 6. They are therefore offset outwards relative to the combustion chamber median line 37 in the case of the two outer cylinders 27 and 29, and offset inwards in the case of the two inner cylinders 26 and 28. A distance s of 55 mm has been found to be optimum.

Claims (4)

1. A spark-ignition, reciprocating-piston internal combustion engine, having overhead valves extending parallel to the piston axis, a flat cylinder head, a combustion chamber cavity which is formed only in the piston head and widens in a tapered manner towards the cylinder head and whose opening area in the piston head forms a squish region, the latter region including one sickle-shaped portion which, with a first circular edge having a first radius of curvature, is opposite the sparking plug and separated therefrom by a substantial part of the combustion cavity, and another portion with a second circular edge concentric with the piston axis and having a second radius of curvature provided in the region of the spark plug, the combustion chamber cavity being disposed eccentrically to the piston axis and being surrounded on all sides by the squish region with the sparking plug being approximately in the centre of the circle of curvature of the first edge, wherein the sparking plug is offset from the median line of the combustion chamber and is positioned with its centre in the half of the combustion chamber containing the exhaust port.

2. An internal combustion engine according to Claim 1, with four cylinders arranged in line, wherein the sparking plugs of the two outer cylinders are arranged offset to the outside relative to the median lines of the combustion chambers and the sparking plugs of the two inner cylinders are arranged offset to the inside towards the median plane of the internal combustion engine.

3. An internal combustion engine according to Claim 1 or 2, the distance of the, or each, offset is approximately 5 mm.

4. An internal combustion engine substantially as described with reference to, and as illustrated in, the accompanying drawings.