Background of the Invention Existing internal combustion engines come in a straight, V, or flat configuration. Straight configuration is where a plurality of pistons are provided in line facing in the same direction with each piston connecting to a crank shaft at a separate location on the crank shaft so that reciprocating motion of the piston towards and away from the axis of the rotation of the crank shaft results in turning of the crank shaft. In a V configuration a first set of pistons are coupled to the crank shaft and a second set of pistons are coupled to the crank shaft at an angle to the first set to form a V shape in end view. In a flat configuration, also known as a boxer engine, the two sets of pistons reciprocate towards and away from the crank shaft with the angle between each of the sets being about 180°.

In each of these cases, each piston is coupled to a separate point on the crank shaft, the result being the pistons are offset from one another relative to the crank shaft.

The present invention provides a new piston arrangement that is believed to provide better performance than existing piston arrangements.

Summary of the Invention In accordance with the present invention there is provided a piston arrangement for an internal combustion engine comprising: a pair of aligned pistons connected to each other and facing in opposite directions, the pistons moveable in a reciprocating motion under the impedous of expanding fluid within a respective chamber housing each piston, wherein the pair of pistons are coupled to a crank shaft extending substantially perpendicular to the pistons by a slot coupling, such that the crank shaft rotates with the reciprocating movement of the pistons. Preferably the crank shaft and slot coupling form a scotch yoke mechanism. Preferably the slot coupling is located mid-way between the pistons.

Preferably the piston arrangement further comprises at least one further pair of aligned pistons connected to each other and facing in opposite directions, the further pistons moveable in a reciprocating motion under the impedous of expanding fluid within a respective chamber housing each further piston, wherein the pair of further pistons are coupled to a second crank shaft member by a second slot coupling such that the further pistons rotate the crank shaft with the reciprocating movement of the further pistons.

Preferably the first mentioned crank shaft is coupled to the second crank shaft member.

Preferably the second crank shaft member is part of a second crank shaft, wherein the first crank shaft is coupled to the second crank shaft of a belt, chain or similar. Alternatively, the second crank shaft member forms a part of the first crank shaft, such that both pairs of pistons are coupled to the same crank shaft.

Preferably the slot coupling includes a bearing coupled to the crank shaft, the bearing slidingly moveable within the guide casing.

Preferably the crank shaft includes a cog for driving a power uptake means.

Preferably at least one of the pistons includes a first piston ring, a second piston ring and an oil seal between the piston rings.

In accordance with a second aspect of the present invention there is provided a pair of aligned pistons connected to each other for use in an internal combustion engine, the pistons provided with a slot coupling for connection to a crank shaft to rotate the crank shaft with reciprocal motion of the pistons.

In accordance with a further aspect of the present invention there is provided a piston having a first piston ring, a second piston ring and an oil seal between the piston rings.

Detailed Description of Preferred Embodiments In order to provide a better understanding, preferred embodiments of the present invention will now be described in greater detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of a plan view of an internal combustion engine incorporating a first embodiment of the piston arrangement of the present invention; Figure 2 shows a side elevation view of a pair of pistons coupled to a crank shaft of the embodiment of Figure 1; Figure 3 shows a schematic representation of a plan view of a second embodiment of a piston arrangement of the present invention with a pair pistons in a central position; Figure 4 shows the piston arrangement of Figure 3 with the pistons moved part way through a reciprocating cycle and the crack shaft rotated 90° from its position in Figure 3; Figure 5 shows the piston arrangement of Figure 3 with the pistons returning to the central position and the crank shaft rotated 180° from its position Figure 3; Figure 6 shows the piston configuration of Figure 3 with the pistons moved further through the reciprocating motion and the crank shaft having rotated 270° from its position in Figure 3; Figures 7A to 7D shows motion of the crank shaft within a slotted coupling as the pistons move through their reciprocating motion (on the right) and rotation of the crank shaft (on the left); Figure 8 is a perspective view of the crank shaft of the present invention; Figure 9 is an upper perspective view of the slotted coupling between the pistons and crank shaft; Figure 10 is an upper perspective view of a head of one of the pistons in accordance with another aspect of the present invention; and Figure 11 shows a schematic representation of an alternative embodiment of the piston arrangement of the present invention.

Referring to Figure 1, there is shown a piston arrangement 10 within an engine block 12 that forms an internal combustion engine. The arrangement 10 includes a pair of pistons 14 and 16 which are in alignment with one another and face in opposite directions.

Pistons 14 and 16 are connected to one another by connecting rod 22. Piston 14 is housed within combustion chamber 18, piston 16 is housed within combustion chamber 20. The combustion chambers 18 and 20 are formed with in the engine block 12. The pistons 14 and 16 are arranged to reciprocate within the space provided within the engine block between combustion chambers 18 and 20. In the internal combustion engine, a fuel intake, exhaust outlet and other standard components would be provided in the combustion chambers as would be understood by the skilled addressee. However, the piston arrangement 10 and block 12 need not form an internal combustion engine. Some other means of fluid expansion within the chambers 18 and 20 could be provided, such as for example, steam or hydraulic fluid.

Another pair of pistons 34 and 36 are housed within combustion chambers 38 and 40 respectively are also contained within the engine block 12. The pistons 14 and 16 via connecting rod 22 are coupled to a crank shaft 32. The crank shaft 32 includes shaft member 24 and shaft member 44. Shaft member 24 is offset from shaft member 44 such that the crank shaft 32 is able to be cranked by an orbital motion of the shaft members 24 and 44 about a central axis of rotation. Both shaft members 24 and 44 are offset by the same amount from the axis of rotation.

Shaft member 24 is slidingly coupled to the connecting rod 22 mid-way between the pistons 14 and 16 by a slotted guide casing 26. Shaft member 24 and guide casing 26 form a scotch yoke mechanism better illustrated in Figure 2. Shaft member 44 is also connected to another guide casing 26 coupled between connecting rod 44 between pistons 34 and 36.

Referring to Figures 2 and 9, the guide casing 26 divides connecting rod 22. Within guide casing 22 a slot 25 is provided that allows shaft member 24 to slide within the guide casing 22. Free rotating device 28 in the form of a bearing fits on the end of the guide member 24 in a similar manner to a cap which then resides within the slot 25. The bearing 28 alleviates wear as it slides back and forth within the slot as the pistons 14 and 16 reciprocate (up and down the page). The result being that with the reciprocating motion of the pistons and side to side motion of the shaft member 24 within the slot moves the shaft member 24 in an orbiting manner thereby rotating the crank shaft 32.

In an alternative arrangement guide casing 26 may be mounted to the side of connecting rod 22 as shown in Figures 3 to 6. In this embodiment the connecting rod 22 is integrally formed with the pistons 14 and 16. This can also be viewed as a double headed piston connected to the crank shaft 32 between the piston heads.

Referring to Figure 3, the crank shaft 32 is in a first position where shaft members 24 and 44 are aligned in plan view, however they are not aligned in end view (not shown). This position corresponds to the pistons 14 and 16 being at the centre of their reciprocating motion. In use they will be moving as indicated by the straight arrows. This in turn will cause the crank shaft 32 to rotate as indicated by the curved arrows. Figure 7A reflects the position of member 44 in relation to the axis of rotation of the crank shaft 32 and within the guide casing 46.

Referring to Figures 4 and 7B, when the crank shaft has rotated 90°, from its position in Figure 3, the piston 14 will be at the peak of its stroke, the piston 16 will be at the bottom of its stroke. Also in addition, the piston 36 will be at the peak of its stroke and piston 34 will be at the bottom of its stroke.

Referring to Figures 5 and 7C, the crank shaft 32 is rotated by another 90°, 180° from its position in Figure 3. Pistons 14 and 16 have returned to midway through their strokes, as have pistons 34 and 36. As can be seen from the arrows, pistons continue to move to positions shown in Figure 6.

In Figures 6 and 7D, crank shaft 32 has rotated a further 90° from than that shown in Figure 5, 270° from that shown in Figure 3. Piston 14 is at the bottom of its stroke, piston 16 is at the peak of its stroke. Furthermore, piston 34 is at the peak of its stroke and piston 36 is at the bottom of its stroke. With a further 90° movement of the crank shaft, the pistons will have returned to the position shown in Figure 3 which will complete a cycle.

Referring to Figure 8, the crank shaft 32 includes in one embodiment a cog 33 to which shaft members 24 and 44 are connected. The cog 33 is provided with teeth 50 which enable it to mesh with another cog of a power uptake means.

Referring to Figure 10, piston 14 is shown in more detail and includes piston ring arrangement 30. The piston ring arrangement 30 includes a first piston ring 52, a second piston ring 54 spaced therefrom. In between the two piston rings 52 and 54 is an oil seal 56. The oil seal includes an aperture 58 to allow oil flow and to provide lubrication.

Referring to Figure 11, an alternative embodiment of the piston arrangement is shown where each pair of pistons, such as the pair 14 and 16, includes its own crank shaft 32.

Likewise, pistons 34 and 36 include their own crank shaft 32'. The crank shafts 32 and 32' may be coupled together by, for example, a chain or a belt 70. In this case, a power uptake means may be yet another chain or belt (not shown). In this case, as in the case of Figures 3 to 6, the guide casing is mounted on the side of the connecting rod 22 rather than bisecting the rod.

It will be appreciated that modifications and variations may be made to the present invention without departing from the basic inventive concept. Such modifications may include providing alternative power uptake mechanism such as passing one of the shaft members 24 or 44 through the connecting rod 22 or 42 and through a goose neck shape to provide a power uptake drive train, the drive train rotating about the axis of rotation of the crank shaft 32. The number of pairs of pistons may be as little as one pair or more than the two pairs shown in the examples.

Such modifications and variations are intended to fall within the scope of the present invention, the nature of which is to be determined from the foregoing description.