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. During an expansion stroke, the energy derived from the expansion of the fluid in the piston chamber forces the piston to travel along the length of the cylinder away from that 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 fluid chamber, where the cycle is repeated.

Convention engines of this type are arranged so that the maximum pressure within the cylinder is generated when the piston is at a top-dead-centre position and the crankshaft journal is at a corresponding top centre position, that is to say, at a position closest to the cylinder combustion chamber. The resultant effect of this arrangement is that immediately following ignition at or slightly after the top centre position of the crankshaft, the downward travel of the piston in the cylinder rapidly causes the enlargement of the volume of the cylinder above the upper surface of the piston. A rapid drop in cylinder pressure is thus created and there is a corresponding rapid reduction in the force applied to the piston, and hence to the crankshaft journal for rotation of the crankshaft.

The applicant has observed that such an arrangement inefficiently converts energy from the pressurised fluid within the cylinder to a motive force for turning the crankshaft. Co-pending International Patent Application No.

WO 99/11906, entitled"Coupling Arrangement for Reciprocating Piston Engine"by the applicant addresses this problem by providing a coupling arrangement for interconnecting a gudgeon pin and a crankshaft journal of a reciprocating piston engine. This arrangement comprises 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 transfer means for transforming a rotational movement of the first pivot point about the gudgeon pin into a rotational movement of the crankshaft journal about the crankshaft.

In an engine having these features, the point of attachment of the connecting rod is separated from the gudgeon pin by a connection member pivotally attached between the connecting rod and the gudgeon pin. With such an arrangement, it is possible to create a reciprocating piston engine in which the crankshaft journal need no longer be at a top centre position when the piston is at its top-dead-centre position. The crankshaft journal is able to be located at a position intermediate the top centre position and a bottom centre position so that, shortly after maximum compression of the fluid in the cylinder a greater torque is able to be applied to the crankshaft journal than is possible with conventional reciprocating piston engines.

The applicant has now adapted this principle to a previously unsuspected application in which a first reciprocating piston engine acting as a fluid compressor is connected to a second reciprocating piston engine, acting as a fluid expander. A first torque is applied to the crankshaft of the first reciprocating piston engine, so as to drive the second reciprocating piston

engine and cause the production of a second torque in the crankshaft of that second reciprocating piston engine.

According to the invention there is provided a torque conversion system comprising : a first reciprocating piston engine including a first chamber, a first intake port and a first exhaust port, a second reciprocating piston engine including a second chamber, a second intake port and a second exhaust port, a first reservoir, interconnecting the first intake port and the second exhaust port, for storing fluid at a first pressure, and a second reservoir, interconnecting the second inlet port and the first exhaust port, for storing fluid at a second pressure, the first reciprocating piston engine including a first cylinder, a first piston mounted for movement along a first cylinder longitudinal axis, a first crankshaft journal connected to a first crankshaft by at least a first crankshaft rod, and a first piston gudgeon pin connected to the first crankshaft journal by a first coupling arrangement, the second reciprocating piston engine including a second cylinder, a second piston mounted for movement along a second cylinder longitudinal axis, a second crankshaft journal connected to a second crankshaft by at least a second crankshaft rod, and a second piston gudgeon pin connected to the second crankshaft journal by a second coupling arrangement, at least the first coupling arrangement produces a first angular offset of the first crankshaft rod from the first cylinder longitudinal axis when the first piston is at a top-dead-centre position.

In a torque conversion system having these features, the first reciprocating piston engine acts to draw fluid from the first reservoir into the first chamber during an intake stroke, and to compress the fluid in the first chamber during a compression stroke. The compressed fluid is drawn from the

second reservoir into the second chamber prior to an expansion stroke of the second reciprocating piston engine, the fluid being exhausted from the second chamber to the first reservoir during an exhaust stroke of the second reciprocating piston engine.

Typically, the first pressure at which fluid is stored in the first reservoir is less than the pressure at which fluid is stored in the second reservoir. It has been determined that in such an arrangement, a first value of torque can be applied to the crankshaft of the first reciprocating piston engine to compress fluid in the first chamber. The pressurised fluid is then transferred to the second reservoir, and is introduced into the second chamber of the second reciprocating piston in its pressurised state. As the piston is forced to move within the cylinder due to the expansion of the pressurised gas in the second chamber, the coupling arrangement applies a torque to the crankshaft of the second reciprocating piston engine which is greater than the torque initially applied to the crankshaft of the first reciprocating piston engine.

In one embodiment of the invention, the second coupling arrangement produces a second angular offset of the second crankshaft rod from the second cylinder longitudinal axis when the second piston is at a top-dead-centre position, the first angular offset being different from the second angular offset.

One or both of the first and second coupling arrangements may include 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.

One or both of the first and second coupling means may also include a rotation transfer means for transforming a rotational movement of the first pivot point about the gudgeon pin into a rotational movement of the crankshaft

journal about the crankshaft. The rotation transfer means may comprise a gear chain or like mechanism interconnecting the first pivot point and the crankshaft journal, the gear chain including two or more gears of selected gear ratio.

Conveniently, at least a portion of the gear chain may be mounted to or maintained in position by the connecting rod.

The various 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 torque conversion system of the present invention. To facilitate an understanding of the invention, reference is made in the description to the accompanying drawing where the torque conversion system is illustrated in a preferred embodiment. It is to be understood, however, that the coupling arrangement of the present invention is not limited to the embodiment illustrated in the drawing.

In the drawings: Figure 1 is a schematic diagram illustrating one embodiment of a torque conversion system according to the present invention; and Figures 2 and 3 are respectively front and side view of a reciprocating piston engine forming part of the torque conversion system of Figure 1.

Referring now to Figure 1, there is shown generally a torque conversion system 1 including a first reciprocating piston engine 2, a second reciprocating piston engine 3, a first reservoir 4 and a second reservoir 5. The first reciprocating piston engine 2 includes a piston 6 located within a cylinder 7.

The engine 2 also includes a crankshaft 8 and a crankshaft journal 9 maintained at a position radially displaced from the longitudinal axis of the crankshaft 8 by a crankshaft rod 10. The piston 6 incorporates a piston gudgeon pin 11.

A coupling arrangement, in this case a conventional connecting rod 12 interconnects the piston gudgeon pin 11 and the crankshaft journal 9 of the engine 2. Torque Tin applied to the crankshaft 8 in the direction indicated by the

reference arrow 13 causes rotation of the crankshaft journal 9 about the longitudinal axis of the crankshaft 8 in that direction and, due to the connection of the connecting rod 12 between the piston gudgeon pin 11 and the crankshaft journal 9, the stroking of the piston 6 within the cylinder 7.

The second reciprocating piston engine 3 similarly includes a piston 14 located within a cylinder 15. The engine 3 also includes a crankshaft 16 and a crankshaft journal 17 maintained at a position radially displaced from the longitudinal axis of the crankshaft 16 by a crankshaft rod 18. Thepiston 14 incorporates a piston gudgeon pin 19.

A coupling arrangement interconnects the piston gudgeon pin 19 to the crankshaft journal 17 of the engine 3. This coupling arrangement comprises a connecting rod 20 pivotally connected at a first end to the crankshaft journal 17.

A connection member 21 is pivotally connected at a first pivot point 23,22 to a second end of the connecting rod 20. The connection member 21 is also pivotally connected to the gudgeon pin 19 at a second pivot point 23 distal from the first pivot point 22.

This coupling arrangement also includes rotation transfer means formed by a gear chain-or like mechanism-including in this example two intermeshing gears, respectively 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 17. At least a portion of the gear chain 24,25 is mounted to or maintained in position by the connecting rod 20.

According to such an arrangement, as the piston 14 is driven up and down in the cylinder 15, the gear 24 will be caused to rotate about the piston gudgeon pin 19. As the centre of the gear 24 rotates about the gudgeon pin 19, the intermeshing of the gears 24 and 25 ensures that the rotational movement of the centre of the disc 24 is transferred to the crankshaft journal 17 with the

result that the crankshaft journal is driven in a rotational movement about the crankshaft 16 in the direction indicated by the reference arrow 26. In this example, these two rotational movements are synchronised so that the angular displacement of the first pivot point, or centre of the disc 24, and of the crankshaft journal 17 is the same, each starting and completing a 360° revolution at the same time as the other. The coupling arrangement interconnecting the piston gudgeon pin 19 and the crankshaft journal 17 enables the crankshaft journal to be angularly offset from the longitudinal axis of the cylinder 15 when the piston 14 is in a top-dead-centre position.

Figures 2 and 3 show a second embodiment of a coupling arrangement interconnecting the piston gudgeon pin 19 and the crankshaft journal 17 of the reciprocating piston engine 3. This coupling arrangement comprises a connecting rod including two connecting rod halves 40 and 41 each of which has a first end pivotally connectable to the crankshaft journal 17 via a split bearing arrangement.

A connection member 42, in this case a cam disc, is pivotally connectable at a first pivot point (the center of the cam disc 42, as can be best seen in Figure 3) to a second end of the connecting rod 40,41. The cam disc 42 is also pivotally connectable to the gudgeon pin 19 at a second pivot point distal from the first pivot point, that is to say, that the point at which the cam disc 42 is attached to the piston gudgeon pin 19 is off center from the center of the cam disc 42.

The coupling arrangement also includes rotation transfer means for transforming a rotational movement of the first pivot point about the gudgeon pin 19 into a rotational movement of the crankshaft journal 17 about the crankshaft 16. In the example illustrated in Figures 2 and 3, the rotation transfer means includes a gear train or like mechanism interconnecting the first pivot point (the center of the cam disc 42) and the crankshaft journal 17.

The gear train includes a crankshaft gear 43 centrally located and fixedly held about the crankshaft journal 17 so that it is unable to independently rotate around the longitudinal axis of the crankshaft journal 17. The rotation transfer means also includes a secondary gear 44 mounted to at least one of the connecting rod halves 40,41 by a secondary gear retaining pin 45 and about which the secondary gear is able to rotate. Similarly, an idler gear 46 is mounted to at least one of the connecting rods 40,41 via an idler gear retaining pin 47. A cam disc gear 48 is fixedly attached to the cam disc 42. When mounted in position, the crankshaft gear 43 is positioned so as to interact and mesh with the secondary gear 44, which in turn interacts and meshes with the idler gear 46.

The idler gear 46 interacts with and meshes with the cam disc gear 48.

According to such an arrangement, as the piston 14 is driven up and down the bore of the cylinder 15, the cam disc 42 will be caused to rotate around the piston gudgeon pin 19. As the center of the cam disc 42 rotates around the gudgeon pin 19, the gear train 42,43,44 and 46 ensures that the rotational movement of the cam disc center is transferred to the crankshaft journal with the result that the crankshaft journal is driven in a rotational movement about the crankshaft.

The operation of the torque conversion system 1 will now be described.

Initially, a torque Tin is applied around the crankshaft 8 of the first reciprocating piston engine 2. The crankshaft journal 9 is driven in a circular motion around the crankshaft 8 in the direction indicated by the reference arrow 13. The connection of the connecting rod 12 between the crankshaft journal 9 and the piston gudgeon pin 11 causes a reciprocating movement of the piston 6 within the cylinder 7. During a downward movement of the piston 6, an inlet valve 30, selectively enabling fluid communication between the first reservoir 4 and the first chamber 31 of the engine 2 is opened to so as to draw fluid from the first reservoir 4 into the first chamber 31 during an intake stroke.

The intake valve 30 is then closed, and due to the continued rotational movement of the crankshaft journal 9, the piston 6 is forced upwards within the piston 7 so as to compress the fluid in the first chamber 31 during a compression stroke. At the end of the compression stroke, an exhaust valve 32 selectively enabling fluid communication between the first chamber 31 and the second reservoir 5 is opened to enable the transfer of the compressed fluid into the second reservoir 5. The fluid stored in the second reservoir 5 is maintained at an elevated pressure.

When the piston 14 of the second reciprocating piston engine 3 is at a top-dead-centre position within the cylinder 15 (such as, for example, the position illustrated in Figure 1), an intake valve 33 selectively enabling fluid communication between the second reservoir 5 and a second chamber 34 of the engine 3 is opened. Compressed fluid from the second reservoir 5 is then introduced into the second chamber 34 in a pressurised state. It can be seen from the exemplary configuration illustrated in Figure 1 that whilst the piston 14 is at a top-dead-centre position, the angular position of the crankshaft journal 17 with respect to the crankshaft 16 is offset from the longitudinal axis of the cylinder 15.

Accordingly, the crankshaft journal 17 is no longer at its top centre or uppermost position when the piston 14 is at top-dead-centre, but, as shown, is located laterally from the crankshaft 16. The introduction of the compressed fluid into the second chamber 34 when the piston 14 is at a top-dead-centre position causes a force to be applied, via the coupling arrangement interconnecting the piston gudgeon pin 19 to the crankshaft journal 17, to that crankshaft journal 17 at a position located laterally from the crankshaft 16 so as to cause a torque Tout to be generated about the crankshaft 16 which is significantly greater than the torque Tin applied about the crankshaft 8 of the first reciprocating piston engine 2.

At the end of the expansion stroke, the rotation of the crankshaft journal 17 about the crankshaft 16 causes the piston 14 to be driven vertically upwards within the cylinder 15. The opening of an exhaust valve 35, selectively enabling fluid communication between the first reservoir 4 and the second chamber 34, enables the expanded fluid to be returned for storage in the first reservoir 4 at the end of the exhaust stroke of the second reciprocating piston engine 3.

In one embodiment of torque conversion system 1, the angular offset of the crankshaft journal 17 from the longitudinal axis of the cylinder 15 when the piston 14 is in top-dead-centre position is 90°. The gears 24 and 25 have a one: one gearing ratio and a radius of 30 mm. The length of the stroke of the piston 14 within the cylinder 15 is 65 mm, whilst the length of stroke of the piston 6 within the cylinder 7 is 50% of the stroke of the piston 14, namely 32.5 mm. Fluid is stored within the first reservoir 4 at a pressure of one atmosphere, and in the second reservoir 5 at ten times that pressure. With such a configuration, it has been found that the application of an input torque Tin of 100 Nm results in the production of an output torque Tout of 250 Nm about the crankshaft 16 of the second reciprocating piston engine 3.

Those skilled in the art will appreciate there may be variations and modifications of the torque connection system described herein which are within the scope of the present invention. For example, whilst the torque conversion system 1 illustrated in Figure 1 results in a greater torque output than input, the converse may be produced by inversing the positions of the reciprocating piston engines 2 and 3 in the system.

Similarly, coupling arrangements other than those illustrated in Figure 1 may be used. The present invention is applicable to a variety of applications in which separate mechanisms and coupling arrangements may be used for torque input and torque output. Moreover, a coupling arrangement of the type used in

the second reciprocating piston engine 3 may be used in both reciprocating piston engines 2 and 3, the difference in torque input and output being produced by differently configuring the angular offsets of the crankshaft journals of the respective coupling arrangements from the longitudinal axis of their respective cylinders when the respective pistons are at a top-dead-centre position.