WO2000058612A1

WO2000058612A1 - Coupling arrangement for reciprocating piston engine

Info

Publication number: WO2000058612A1
Application number: PCT/AU2000/000237
Authority: WO
Inventors: Claude Neil Bresland
Original assignee: Bresland C N
Priority date: 1999-03-25
Filing date: 2000-03-23
Publication date: 2000-10-05
Also published as: AUPP943899A0

Abstract

A coupling arrangement for interconnecting a piston gudgeon pin (6) and a crankshaft journal (4) of a reciprocating piston engine, said crankshaft journal (4) being connected to a crankshaft (3) by at least one crankshaft arm, the arrangement comprising: a connecting rod (20) having a first end pivotally connected to the crankshaft journal, a connection member (21) pivotally connectable at a first pivot point to a second end of the connecting rod, and pivotally connectable to the gudgeon pin at a second pivot point distal from the first pivot point, and rotational synchronisation means (24, 25) for synchronising the rotational movement of the first pivot point about the gudgeon pin and the rotational movement of the crankshaft journal about the crankshaft, wherein at least the initial relative angular positions of the crankshaft arm and the connection member, and the relative dimensions of the crankshaft arm, connection member and connecting rod, are selected so as to cause the stroke length to alternate between a first and a second value.

Description

COUPLING ARRANGEMENT FOR RECIPROCATING PISTON

ENGINE The invention relates to reciprocating piston engines, and in particular to coupling arrangements for interconnecting a gudgeon pin and a crankshaft journal of such an engine. The invention is notably applicable to reciprocating two-stroke and four-stroke piston combustion engines and compression engines and it will be convenient to hereinafter describe the invention in relation to that exemplary application, although it should be appreciated that the invention is not limited to the application. Conventional reciprocating piston engines are generally manufactured in two and four stroke designs. A single piston is housed within each cylinder, the piston being connected from a central piston gudgeon pin to a single bearing crankshaft journal by a single solid centre mounted connecting rod. After combustion has taken place in the combustion chamber of the piston, the energy derived from the expansion of the combustible material forces the piston to travel along the length of the cylinder away from the combustion chamber. This translational movement is transferred via the connecting rod to the crankshaft journal and is transformed into a rotational movement as the crankshaft is driven around its longitudinal axis. As the crankshaft completes each revolution, the connecting rod interconnecting the crankshaft journal and the gudgeon pin forces the piston back along the length of the cylinder towards the combustion chamber, where either combustion once again takes place (two-stroke engines) or an intake stroke occurs (four-stroke engines).

Conventional engines of this type are arranged so that the intake and exhaust strokes (two-stroke engines) or the induction, compression, expansion and exhaust strokes (four-stroke engines) are of constant stroke length. This property represents a kinematic limitation in conventional reciprocating piston engines and results in the loss of a considerable amount of thermodynamic energy per cycle. By way of explanation, in a conventional four-stroke reciprocating piston engine, the expansion stroke is equal to the compression stroke. This results in the exhaust valve opening while the pressure inside the cylinder is still well above the barometric value. The pressure differences represents work that is lost by the engine.

It would be desirable to provide a reciprocating piston engine which is able to minimise the thermodynamic energy losses of known reciprocating piston engines.

It would also be desirable to provide a reciprocating piston engine which overcomes or ameliorates one or more of the disadvantages of known reciprocating piston engines.

With this in mind, the present invention provides a coupling arrangement for interconnecting a piston gudgeon pin and a crankshaft journal of a reciprocating piston engine, the reciprocating piston including a piston reciprocating within a cylinder along a stroke length, said crankshaft journal being connected to a crankshaft by at least one crankshaft arm, the arrangement comprising: a connecting rod having a first end pivotally connected to the crankshaft journal, a connection member pivotally connectable at a first pivot point to a second end of the connecting rod, and pivotally connectable to the gudgeon pin at a second pivot point distal from the first pivot point, and rotation synchronisation means for synchronising the rotational movement of the first pivot point about the gudgeon pin and the rotational movement of the crankshaft journal about the crankshaft, wherein at least the initial relative angular positions of the crankshaft arm and the connection member, and the relative dimensions of the crankshaft arm, connection member and connecting rod, are selected so as to cause said stroke length to alternate between a first and a second value.

Preferably, the rotation synchronisation means may comprise a gear train or like mechanism interconnecting the first pivot point and the crankshaft journal, said gear train including two or more gears of selected gear ratio. The gear ratio may also be selected so as to vary the first and second value of said stroke length.

At least a portion of the gear train may be mounted to or maintained in position by the connecting rod. Another aspect of the present invention provides a reciprocating piston engine which includes a coupling arrangement as previously described, wherein the first stroke length value is less than the second stroke length value. The reciprocating piston engine may be a four-stroke engine, the first stroke length corresponding to an induction/compression stroke, and the second stroke length corresponding to an expansion/exhaust stroke.

This and other advantages and features of the invention will be better appreciated from the following description which refers in more detail to the various features of the coupling arrangement of the present invention. To facilitate an understanding of the invention, reference is made in description to the accompanying drawings where the coupling arrangement is illustrated in preferred embodiments. It is to be understood, however, that the coupling arrangement of the present invention is not limited to the embodiments illustrated in the drawings. In the drawings: Figure 1 is a schematic front view of a reciprocating piston engine including a first embodiment of a coupling arrangement according to the present invention;

Figure 2 is a side view of the reciprocating piston engine of Figure 1; Figure 3 is a front view of a reciprocating piston engine including a second embodiment of a coupling arrangement according to the present invention;

Figure 4 is a side view of the reciprocating piston engine of Figure 3; Figure 5 is a side view of a third embodiment of a coupling arrangement according to the present invention; Figures 6 and 7 are respectively a schematic end view and a further side view of the coupling arrangement of Figure 5; and Figure 8 is a graphical representation of the piston position of a reciprocating piston engine including the coupling arrangement of Figures 5 to 7.

Referring now to Figure 1, there is shown generally a single piston within a reciprocating piston engine. The piston 1 is located within a cylinder 2. The engine also includes a crankshaft 3 and a crankshaft journal 4 maintained at a position radially displaced from the longitudinal axis of the crankshaft 3 by crankshaft rods 5. In the position shown in Figure 1, the crankshaft journal is at a top centre position. The piston 1 incorporates a piston gudgeon pin 6. A coupling arrangement is provided for interconnecting the piston gudgeon pin 6 and the crankshaft journal 4 of the engine. This coupling arrangement comprises a connecting rod including two connecting rod halves 7 and 8 each of which has a first end pivotally connectable to the crankshaft journal 4 via a split bearing arrangement. A connection member 9, in this case a cam disc, is pivotally connectable at a first pivot point (the centre of the cam disc 9, as can be best seen in Figure 2) to a second end of the connecting rod 7, 8. The cam disc 9 is also pivotally connectable to the gudgeon pin 6 at a second pivot point distal from the first pivot point, that is to say, that the point at which the cam disc 9 is attached to the piston gudgeon pin 6 is off centre from the centre of the cam disc 9.

The coupling arrangement also includes rotation synchronising means for synchronising the rotational movement of the first pivot point about the gudgeon pin 6 and the rotational movement of the crankshaft journal 4 about the crankshaft 3. In the example illustrated in Figures 1 and 2, the rotation synchronisation means includes a gear train or like mechanism interconnecting the first pivot point (the centre of the cam disc 9) and the crankshaft journal. The gear train includes a crankshaft gear 10 centrally located and fixedly held about the crankshaft journal 4 so that it is unable to independently rotate around the longitudinal axis of the crankshaft journal 4. The rotation synchronisation means also includes a secondary gear 11 mounted to at least one of the connecting rod halves 7, 8 by a secondary gear retaining pin 12 and about which the secondary gear is able to rotate. Similarly, an idler gear 13 is mounted to at least one of the connecting rods 7, 8 via a idler gear retaining pin 14. A cam disc gear 15 is fixedly attached to the cam disc 9. When mounted in position, the crankshaft gear 10 is positioned so as to interact and mesh with the secondary gear 11, which in turn interacts and meshes with the idler gear 13. The idler gear 13 interacts with and meshes with the cam disc gear 15. According to such an arrangement, as the piston 1 is driven up and down the bore of the cylinder 2, the cam disc 9 will be caused to rotate around the piston gudgeon pin 6. As the centre of the cam disc 9 rotates around the gudgeon pin 6, the gear train 15, 13, 11 and 10 ensures that the rotational movement of the cam disc centre is transferred to the crankshaft journal with the result that the crankshaft journal is driven in a rotational movement about the crankshaft 3. Moreover, these two rotational movements are synchronised so that the angular displacement of the first pivot point, or centre of the cam disc 9, and of the crankshaft journal occurs at the same time. In this example, each starts and completes a 360° revolution at the same time as the other, however in other embodiments, this will not be the case. Moreover, in other embodiments of the invention, one of the crankshaft arms and the connection member may complete more than one 360° revolution for every 360° revolution of the other. The cam disc 9 and the cam disc gear 15 are held in position by the connecting rod halves 7, 8 to allow the piston gudgeon pin 6 to pass from one side of the piston 1 through the cam disc 9 and cam disc gear 15 to the other side of the piston 1, securely connecting the piston 1 to the crankshaft journal 4 by means of the above described coupling arrangement. As the cam disc gear 15 and the cam disc 9 rotate, the piston gudgeon pin 6 is forced to rotate also. As the gudgeon pin 20 rotates it can be seen from Figure 2 that the distance between the crankshaft journal 4 and the piston 1 will by cyclically lengthened and then shortened, as the centre of the cam disc 9 rotates around the off centre mounting position of the cam disc 9 on the gudgeon pin 6. Figures 3 and 4 show an alternative embodiment of the coupling arrangement, in which the rotation synchronisation means further include a chain or like mechanism interconnecting two or more gears in the gear train. In this embodiment, the crankshaft journal gear 10, and the cam disc 9 and associated cam disc gear 15, have been retained and are connected respectively to the piston gudgeon pin 6 and the crankshaft journal 4 in the manner previously described. However, in this embodiment, the cam disc gear 15 and the crankshaft journal disc 10 are interconnected by a chain 16. According to this arrangement, the direction of rotation of the cam disc gear 15 and of the crankshaft journal disc 10 will be the same, where as these two gears were caused to rotate in opposite directions in the arrangement shown in Figures 1 and 2. It is to be appreciated that whereas the arrangements in Figures 1 to 4 show the interconnection of various gears and chains, a variety of like mechanisms may be used in the context of the present invention. For example, coupling arrangements using pulleys and belts and other devices for the transfer of rotational movement may easily be envisaged by a skilled worker in this field.

Either of the two embodiments shown in Figures 1 and 2, and Figures 3 and 4, enable the setting of the angular position of the first pivot point (or centre of the cam disc 9) with respect to the gudgeon pin 6, as well as the angular position of the crankshaft journal 4 with respect to the crankshaft, so that, unlike conventional reciprocating piston engines, the top dead centre position of the piston 1 need not necessarily require that the crankshaft journal 4 be located in its top centre or uppermost position.

This can be more clearly seen in Figure 5, which shows schematically the crankshaft journal 4, crankshaft 3 and gudgeon pin 6 of Figures 1 to 4. A connecting rod 20 is pivotally connected at a first end to the crankshaft journal 4. A connection member 21 is pivotally connected at a first pivot point 22 to a second end of a connecting rod 20. The connection member 21 is also pivotally connected to the gudgeon pin 6 at a second pivot point 23 distal from the first pivot point 22. It will be noted that in this case, the connection member 21 is not in the form of a disc, and that the rotation synchronising means are formed by two intermeshing gears only, referenced 24 and 25, which are respectively fixed to the connection member 21 around the first pivot point 22 and fixed around the crankshaft journal 4. From this Figure, it can be seen that whilst the angular position of the first pivot point 22 with respect to the gudgeon pin is approximately 180° with respect to a reference axis 30, the angular position of the crankshaft journal 4 with respect to the crankshaft 3 is approximately 270° with respect to that same reference axis. As ignition occurs, the piston 1 is forced down in the cylinder 2, and force is transmitted from the gudgeon pin through the connecting member 21 and the connecting rod 20 to the crankshaft journal 4. The force applied to the crankshaft journal 4 at the instant just after ignition results in torque being applied to the crankshaft journal 4. As the crankshaft journal 4 is driven anti-clockwise (as shown in Figure 5) around the longitudinal axis of the crankshaft 3, the gear 25 is caused to rotate in the direction shown by the arrow referenced 32. This causes a corresponding rotation of the gear 24 in the direction shown by the arrow 31. This rotation causes the first pivot point 22 of the connection member 21 to be driven in a clockwise direction around the gudgeon pin 6.

It has been found experimentally that the present invention provides several advantages depending upon the relative angular positions of the crankshaft arm connection member during operation of the engine. For example, it is possible to vary the length of the piston travel within the cylinder by changing the initial relative angular positions of the crankshaft arm and the connection member.

It is also possible to vary the speed of travel of the piston within the cylinder at various stages of the cycle of operation of the engine. For example, it is possible to choose initial relative angular positions of the crankshaft arm and the connection member so that the speed of travel of the piston in the proximity of its bottom dead centre position is reduced. In this configuration, the piston spends a large proportion of its time in the bottom of the cylinder, thus allowing an increased amount of time for the exhaust of waste combustion gases when the coupling arrangement of the present invention is used in a reciprocating piston combustion engine. Adjustment of the initial relative angular positions of the crankshaft arm and the connection member advantageously enables the coupling arrangement to determine whether the reciprocating piston engine has a two or four stroke operation Figures 6 and 7 show a reciprocating piston engine in which a piston 41 is located within a cylinder 42. The reciprocating piston engine also includes a crankshaft 43 and crankshaft journal 44 interconnected by crankshaft rods or arms 45. The piston 41 incorporates a piston gudgeon pin 46.

A coupling arrangement is provided for interconnecting the piston gudgeon pin 46 and the crankshaft journal 44 of the engine. This coupling arrangement comprises one or more connecting rods 47 having a first end pivotally connectable to the crankshaft journal 44. A cam disc gear 49 is pivotally connectable at a first pivot point (the centre of the cam disc gear 49) to a second end of the connecting rod 47. The cam disc gear 49 is also pivotally connectable to the gudgeon pin 46 at a second pivot point. The coupling arrangement also includes rotation synchronising means for synchronising the rotational movement of the first pivot point about the gudgeon pin 46 and the rotational movement of the crankshaft journal 44 about the crankshaft 43.

As can be best appreciated from Figure 7, the relative angular positions of the various elements of the coupling arrangement are adjusted so that when the piston is at a bottom dead centre position (as illustrated in Figures 6 and 7), the angular position of the crankshaft journal with respect to the crankshaft is aligned with a first reference direction 51. That is to say, the crankshaft arm is in a vertical orientation, the crankshaft journal being closer to the piston 41 than is the crankshaft 43. Moreover, the cam disc 49 is oriented so that the angular position of the first pivot point with respect to the gudgeon pin is similarly aligned with the reference direction 51. In other words, the first pivot point, gudgeon pin, crankshaft journal and crankshaft are all aligned in a single direction running through the longitudinal axis of the cylinder 42, the gudgeon pin 46 being closer to the crankshaft and crankshaft journal than is the first pivot point. Such an arrangement has been found to provide a reciprocating piston function in which each of the strokes has an equal length. However, it has been found that by offsetting one or other of the discs 49 or 50, for example by 2 to 3 degrees, the lengths of alternate piston strokes can be varied. In particular, it is possible by providing such an angular offset to give the reciprocating piston engine a longer exhaust stroke than compression stroke. Such an arrangement is particularly advantageous for four-stroke reciprocating piston engines in which complete exhaustion of combusted fuel contributes to the efficient operation of the engine.

Figure 8 provides a graphical representation of the varying stroke lengths which can be achieved according to the present invention. This figure plots the position of the piston 1 of Figure 5 within the cylinder 2 against an angle e₄ formed between the crankshaft arm and the longitudinal axis of the cylinder 2 shown in Figure 5. In this example, the length L₂ of the crankshaft arm was 60mm, the length L₃ of the connecting rod 20 was 100mm, the L₄ of the connecting rod 21 was 20mm and the gear ratio between the diameter of the crank gear mounted about the crankshaft journal 4 and the diameter of piston gear mounted about the first pivot point is 0.5. In addition, the initial angular position e₂ of the connection member with respect to the longitudinal axis of the cylinder 2 was 8°, whilst the initial angular position e of the crankshaft arm with respect to the longitudinal axis of the cylinder 2 was -20°. It can be seen from Figure 8 that a coupling arrangement having the characteristics described in the previous paragraph provides an expansion/exhaust stroke which is significantly longer than the induction/compression stroke. Accordingly, the pressure difference between the pressure inside the cylinder 2 and the ambient pressure which occurs in conventional reciprocating piston engines at the end of an expansion stroke is no longer wasted. The coupling arrangement according to the present invention is able to utilise this pressure difference due to the fact that the piston 1 can move further in expansion than in compression, and is therefore more thermodynamically efficient than conventional reciprocating piston engines. It will be appreciated from the foregoing that this principle can be applied to can be applied to situations in which alternating piston stroke lengths may be advantageous. By selecting at least the relative initial angular positions of the crankshaft arm and connection member, and the relative dimensions of the crankshaft arm, connection member and connecting rod, a coupling arrangement is provided which causes the stroke length of the piston within the cylinder to alternate between a first and a second value. Moreover, the stroke lengths may also be affected by the selection of the gear ratio of the two or more gears from which the rotation synchronisation means is formed .

Those skilled in the art will appreciate that there may be variations and modifications of the connection arrangement described herein which are within the scope of the present invention.

Claims

1. A coupling arrangement for interconnecting a piston gudgeon pin and a crankshaft journal of a reciprocating piston engine, said reciprocating piston engine including a piston reciprocating within a cylinder along a stroke length, said crankshaft journal being connected to a crankshaft by at least one crankshaft arm, the arrangement comprising: a connecting rod having a first end pivotally connected to the crankshaft journal, a connection member pivotally connectable at a first pivot point to a second end of the connecting rod, and pivotally connectable to the gudgeon pin at a second pivot point distal from the first pivot point, and rotational synchronisation means for synchronising the rotational movement of the first pivot point about the gudgeon pin and the rotational movement of the crankshaft journal about the crankshaft, wherein at least the initial relative angular positions of the crankshaft arm and the connection member, and the relative dimensions of the crankshaft arm, connection member and connecting rod, are selected so as to cause the stroke length to alternate between a first and a second value.

2. A coupling arrangement according to claim 1 wherein said rotation synchronisation means comprises a gear chain or like mechanism interconnecting said first pivot point and said crankshaft journal, said gear chain including two or more gears of selected gear ratio.

3. A coupling arrangement according to claim 1, wherein at least a portion of said gear chain is mounted to or maintained in position by said connecting rod.

4. A reciprocating piston engine including a coupling arrangement according to any one of the preceding claims, where said reciprocating piston engine is a four stroke engine, and wherein said first stroke length corresponds to an induction/compression stroke, and said second stroke length corresponds to an expansion/exhaust stroke.

5. A reciprocating piston engine according to claim 4, wherein said first stroke length value is less than said second stroke length value.