EP0046046A1

EP0046046A1 - A power conversion unit

Info

Publication number: EP0046046A1
Application number: EP81303546A
Authority: EP
Inventors: Colin Richard Edwin Read
Original assignee: Winder Controls Hydraulics Pty Ltd
Current assignee: Winder Controls Hydraulics Pty Ltd
Priority date: 1980-08-01
Filing date: 1981-08-03
Publication date: 1982-02-17
Also published as: JPS5762901A

Abstract

The invention relates to a power conversion unit (10) which includes a set of primary pistons (16), reciprocably displaceable in a set of primary cylinders (14), defined in a body, (12) on the internal combustion engine principle. The primary pistons (16) are directly connected, or via a constraining means, to a set of auxiliary pistons (28), reciprocably displaceable in a set of auxiliary cylinders (30), also defined in a body (32). The auxiliary pistons (28) can act upon a hydraulic fluid and the chemical and thermal energy of a combustible fuel, by combustion in the primary cylinders (14) is thus substantially directly converted to nyorauiic energy available from the auxiliary cylinders (30₁ The constraining means may be a non-rotatably wobble plate (18), which can limit displacement of the pistons, and which can be mounted on a rotatable shaft (20) from which mechanical energy can be obtained to assist with the operation of the conversion unit (10).

Description

According to the invention there is provided a power conversion unit which includes

a first cylinder defining means defining at least one primary cylinder;
a primary piston reciprocably displaceable within each primary cylinder and which can be acted upon by an expanding fluid within the cylinder;
at least one auxiliary piston associated with each primary piston, which is connected to its primary piston so that reciprocal displacement thereof is directly transmitted to the auxiliary piston to cause reciprocal displacement of the auxiliary piston;
a second cylinder defining means defining a cylinder for each auxiliary piston and in which cylinder the auxiliary piston is reciprocably displaceable to act upon a hydraulic fluid; and
a constraining means for constraining and regularising reciprocating displacement of the primary and auxiliary pistons.

In particular, the first cylinder defining means may define a plurality of primary cylinders and each primary piston has one auxiliary piston associated therewith.
The primary pistons and auxiliary pistons may be aligned parallel with one another and in one configuration may be axially aligned with one another.
The primary pistons and their associated auxiliary pistons may be in one piece with one another or, alternatively, may be connected to one another by a connecting member. In a particular configuration the connecting member may be the constraining means to which both the primary pistons and their associated auxiliary pistons are connected.
Furthermore, the primary pistons and their associated auxiliary pistons may have the same cross-sectional dimensions or may have different cross-sectional dimensions.
In one embodiment of the invention the constraining means may be a wobble plate to which the primary pistons and their associated auxiliary pistons are connected. The wobble plate may be non-rotationally mounted on a shaft extending centrally from the wobble plate and which is rotatable, in use, by the wobbling action of the wobble plate due to reciprocating displacement of the primary pistons.
The primary pistons and/or the auxiliary pistons may be connected to the wobble plate by universal joints.
In addition, the power conversion unit may include restraining means to restrain rotation of the wobble plate. The restraining means may be a restraining arm secured to the wobble plate and fixed relative to the wobble plate.
Alternatively, the wobble plate may define gear formations and the restraining means is a restraining gear which is fixed relative to the wobble plate and can engage the gear formations on the wobble plate to restrain rotation thereof. The restraining gear may have a solid body which defines the second cylinder defining means.
The rotatable shaft of the wobble plate may be supported in bearings located relative to the first and second cylinder defining means and may serve as a mechanical power take-off.
Further according to this embodiment of the invention the power conversion unit may include a flywheel mounted on the rotatable shaft. Also, the power conversion unit may include a valve inlet arrangement and a valve outlet arrangement for controlling the passage of an expanding fluid into and out of the primary cylinders.
Further according to the invention the expanding fluid may be a combustible fuel, and the unit may include means to initiate the combustion of the fuel within the primary cylinders. The means to initiate the combustion of fuel may be a spark ignition means.
The primary pistons and the primary cylinders may accordingly form an effective internal combustion engine.
The valve arrangements may be operable by a camshafi which is rotatably connected to the rotatable shaft. The camshaft may be connected to the rotatable shaft via a gear arrangement and may operate the valve arrangements via a rocke arrangement.
The power conversion unit may further include a distributor to control operation of the spark ignition means, the distributor being operable from the rotatable shaft.
In an alternative embodiment of the invention the constraining means may be a swashplate rotatable about its owr axis and may be engaged by the primary and the auxiliary pistons. The swashplate may be mounted on a shaft, which shaf may be parallel to the axis of the pistons.
More particularly the primary pistons and their associated auxiliary pistons may be connected together by a connecting member and the connecting member may have a groove therein defined between two opposing slipper pads which slippe pads engage opposing peripheral edges of the swashplate. The shaft of the swashplate may include balancing weights to reduc energy losses resulting from constraining of the motion of the pistons by the swashplate as well as a flywheel for the same purpose.
The power conversion unit, in accordance with the invention, may include a conduit arrangement through which hydraulic fluid can be conveyed in a controlled manner to and from the cylinders in which the auxiliary pistons are displaceable. The conduit arrangement may include connector means for connection to a hydraulic fluid supply and to a hydraulic power take-off.
Conveniently the conduit arrangement may form a part of a hydraulic circuit which hydraulic circuit may be a closed circuit.
The hydraulic circuit may further incorporate a hydraulic motor operable by hydraulic power provided by the operation of the auxiliary pistons on a hydraulic fluid to provide mechanical power. The hydraulic motor may be a variable displacement type motor and more particularly may be a swashplate motor in which the angle of the swashplate is adjustable.
The power conversion unit may include control means for controlling the hydraulic power output of the auxiliary pistons. The control means may be adapted to control the flow of hydraulic fluid displaced by the auxiliary pistons to thereby control the hydraulic power output of the auxiliary pistons.
Further according to the invention there is provided a power conversion unit which includes a first cylinder defining means defining
primary cylinder;

a primary piston reciprocably displaceable within each primary cylinder and which can be acted upon by an expanding fluid within the cylinder;
at least one auxiliary piston associated with each prima: piston, which is connected to its primary piston so that reciprocal displacement thereof is directly transmitted to the auxiliary piston to cause reciprocal displacement of the auxiliary piston;
a second cylinder defining means defining a cylinder for each auxiliary piston and in which cylinder the auxiliary piston is reciprocably displaceable to act upon a hydraulic fluid; and
a conversion means for converting reciprocal motion of tl primary and auxiliary pistons into rotational motion.

The invention also extends to a power unit which includes a power conversion unit in accordance with the invention and which is associated with a hydraulic circuit an< a hydraulic motor included in the hydraulic circuit for providing mechanical power.
The invention is now described, by way of examples, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 shows a schematic three dimensional view of a first embodiment of a power conversion unit in accordance witl the invention;
Figure 2 shows a schematic cross-sectional side view of slightly different arrangement of the embodiment of the power conversion unit of Figure 1;
Figure 3 shows a schematic three dimensional view of a second embodiment of a power conversion unit in accordance with the invention;
Figure 4 shows a schematic three dimensional view of a third embodiment of a power conversion unit in accordance with the invention; and
Figure 5 shows a schematic cross-sectional side view of a fourth embodiment of a power conversion unit in accordance with the invention.

Referring to the drawings, like parts are indicated by the same reference numerals in the different embodiments shown. Also, for the sake of clarity, various parts have been omitted or are shown in an exploded configuration.
Referring particularly to Figures 1 and 2, a power conversion unit, in accordance with the invention, is generally indicated by the reference numeral 10. The unit 10 includes a main body 12 within which cylinders 14 are defined. Primary pistons 16 are reciprocably displaceable within the cylinders 14, displacement of the pistons 16 taking place in accordance with the internal combustion principle by burning a combustible fuel in the cylinders 14.
Each piston 16 is connected to a wobble plate 18, the wobble plate 18 being mounted on a shaft 20 in a non-rotational manner. The pistons 16 are peripherally spaced on the wobble plate ^18, the pistons 16 being spaced an equal radial distance from the centre of the wobble plate 18 and the peripheral spacing between adjacent pistons 16 also being equal. The connection of the pistons 16 to the wobble plate 18 is effected via piston rods 21, the rods 21 being connected to the piston heads 22 by means of a gudgeon pin 24 and universal joint as shown and to the wobble plate 18 via universal spherical joints 26.
On the opposite side of the wobble plate 18, directly opposing each primary piston 16 in an axially aligned manner, there are provided auxiliary pistons 28. The pistons 28 are reciprocably displaceable in auxiliary cylinders 30 defined in an auxiliary body 32, forming a part of the power conversion unit 10 and which may form an integral part of the main body 12. The auxiliary pistons 28 are connected to the primary pistons 16 via the wobble plate 18, universal joints 34 at opposite ends of piston rods 36 connecting the piston heads 38 of the pistons 28 to the wobble plate 18. The auxiliary pistons 28 are adapted to act on an hydraulic fluid such as oil, when being reciprocably displaced as is hereinafter described.
The shaft 20, onto which the wobble plate 18 is mounted, is rotatably mounted via two sets of bearings 40 within the main body 12. It will thus be understood that by the reciprocal displacement of the primary pistons 16, and with the wobble plate 18 secured against rotation, the plate 18 will be forced to wobble about the axis of the shaft 20, the wobbling action of the plate 18 then causing rotation of the shaft 20. As is shown in Figure 2 the wobble plate 18 is mounted onto the shaft 20 by means of bearings 42, permitting the shaft 20 to rotate while the wobble plate 18 cannot rotate. To provide an even wobbling action of the plate 18, the reciprocating action of the pistons 16 are regulated so that their reciprocating strokes occur in an alternate order which enhances the wobbling action of the plate.
The shaft 20 extends through the body 12 and has a gear arrangement 44 mounted thereon whereby a camshaft 46 is rendered rotatable for operating a valve arrangement 48 whereby the fuel supply to the cylinders 14 can be controlled as well as the exhaust of combusted fuel from the cylinders. The actual operation of the valve arrangement 48 is equivalent to that of conventional internal combustion engines, opening and closing of the valves being controlled by rockers 50 which are actuated by the rotation of the camshaft 46. The speed of rotation of the camshaft 46 is controlled by the gear arrangement 44 which includes a pair of bevel gears 52 and a set of mitre gears 54 as shown to provide.the required rotation of the camshaft 46.
The shaft 20 further has a flywheel 56 mounted thereon to enhance the regular rotation of the shaft 20 and to minimize the shock effects which the reciprocating motion of the pistons 16 have on the wobble plate 18. A distributor 58 is further mounted on the shaft 20 from which spark plugs 61 are actuated to ignite fuel in the cylinders 14 when required.
From the above description, it will be understood that reciprocation of the pistons 16 occur as for any conventional internal combustion engine. By controlling the ord of combustion in the cylinders 14 the wobble plate 18 can thu be caused to wobble which action is directly transmitted to t auxiliary pistons 28, thus causing the pistons 28 to reciprocate with an equivalent stroke to the pistons 16, this stroke being constrained by the wobble plate 18.
By providing a hydraulic fluid inlet 60 into the cylinders 30 and an outlet 62 from the cylinders 30, the pistons 28 can thus be made to act on a hydraulic fluid, such as oil, thus providing hydraulic fluid under pressure and, in effect, hydraulic energy. It will be understood from the abo that the unit 10 thus directly converts chemical and thermal energy of a combustible fuel into hydraulic energy, available for use. The cylinders 30 can thus be connected to a hydraul circuit for use of the hydraulic energy, such a circuit being described with reference to Figure 5.
From the above construction it will be clear that t: wobble plate 18 must remain free from rotation. In the embodiment shown in Figure 1 this is further ensured by a torque arm 64 which is secured between the body 12 and the wobble plate 18 to prevent any rotation of the wobble plate 1
Referring now also to Figure 3, the operation of th unit 66 shown therein and its parts are the same as for the unit described above with reference to Figures 1 and 2. However, in order to restrain rotation of the wobble plate 18 the above described torque arm is replaced by a gear arrangement 68. The gear arrangement 68 comprises involute gear formations 70 defined on the wobble plate 18, and a restraining gear 72, which is fixed relative to the wobble plate 18 and which can engage the formations 70 upon wobbling of the plate 18 to restrain rotation thereof. As is shown in the drawing, the restraining gear 72 may also define the auxiliary body 32 within which the auxiliary cylinders 30 are defined.
Furthermore, in this configuration, the auxiliary pistons 28 are not aligned with the primary pistons 16 but are positioned closer to the centre of the wobble plate 18. In this manner, the stroke of the auxiliary pistons 28 are reduced to a more acceptable stroke with a view to generating hydraulic power. By the positioning of the pistons 28, the hydraulic power output is thus controllable. In this configuration, the pistons 28 are secured directly to the wobble plate 18, again by universal joints (not shown clearly in the drawing).
Referring to Figure 4, a unit 66 with a gear arrangement 68 is again provided to restrain rotation of the wobble plate 18 and the auxiliary pistons 28 are again placed nearer the centre of the wobble plate 18 than the pistons 16. To provide further control over the hydraulic power output of the pistons 28 a rotatable port plate 74 is provided at the outlet ends of the cylinders 30. By different positioning of the plate 74, different sized apertures 76 can be aligned with the outlet openings (not shown) from the cylinders 30 and in this way the hydraulic fluid output from the cylinders can'be restrained and thus the hydraulic power output controlled.
It will be understood that the effective hydraulic power output will also depend on the relative cross-sectional areas of the pistons 16 and 28, any variation in the relative sizes of these areas altering the power output.
In Figure 5, a power conversion unit 78 is shown which is equivalent to that shown in Figures 1 and 2 except that the wobble plate 18 is replaced by a rotatably mounted swash plate 80. In particular, the swash plate 80 is disposed between opposing slipper pads 82 defining the free ends of the piston rods 21 and 36 of the pistons 16 and 28 respectively. The slipper pads 82 further form a part of a connecting membe _l 84 joining together the pistons 16 and 28. In use, by the reciprocal displacement of the pistons 16, the pistons 28 are correspondingly displaced, the overall displacement of the pistons 16, 28 being constrained by the swash plate 80, which rotates together with its shaft 84 which is rotatably mounted relative, to the body 12. Such rotation of the swash plate 80 occurs as a result of the displacement of the pistons 16 whicl acts upon the swash plate 80 and forces it to be slidably displaced in a rotational manner between the slipper pads 82. It will be understood that the shaft 84 is equivalent to the shaft 20 onto which the above described wobble plate 18 is mounted. The shaft 84 further has balancing weights 83 and a flywheel 85 mounted thereon to reduce energy losses resulting from constraining of the motion of the pistons by the swash plate 80.
As described above, the conversion units 10, 66, 78 provides hydraulic power and can be associated with a hydraulic circuit in which such hydraulic power is employed.
In a particular such application of the conversion unit 10, 66, 78 the inlets 60 and outlets 62 into and from the cylinders 30 are connected to a closed hydraulic circuit generally shown by reference numeral 90. The hydraulic circuit 90 includes a hydraulic fluid distributor 92 which includes control means for controlling the supply of hydraulic fluid to the cylinders 30. Fluid supplied to these cylinders is hence pumped under pressure again via the distributor 92 to a hydraulic motor 94 forming part of the hydraulic circuit 90. The hydraulic motor 94 has a mechanical energy take-off in the form of, for example, a drive shaft 96 thus providing mechanical energy, while the hydraulic fluid is again returned to the distributor 92. The mechanical energy from the drive shaft 96 may be used for driving a vehicle or for any other suitable purpose.
In a particular arrangement, not shown in detail, the distributor 92 may be rotatably mounted and may have an inlet 98 for receiving hydraulic fluid and outlets 100 for supplying hydraulic fluid to the fluid inlets 60 of the cylinders 30. The frequency with which the distributor outlets 100 are hence brought into register with the inlets 60 upon rotation of the distributor 92, determines the flow rate of hydraulic fluid in the circuit 90. The distributor may also include a suitable drain port for draining hydraulic fluid from the circuit when necessary. The distributor.92 can thus effectively replace the , port plate 74 described with reference to Fiaure 4.
Furthermore, the hydraulic motor 94 may be a swash plate motor in which the angle of its swash plate is adjustable. The mechanical energy output from the motor 94 can hence be adjusted by the operation of the distributor 92 to control fluid flow and by adjustment of the angle of the swash plate of the hydraulic motor 94. The above adjustments thus permit an infinite output variation from the motor 94 in terms of the drive shaft speed of rotation and the torque supplied by the shaft within design limits of the hydraulic motor. Additional adjustment can also be provided by adjustment of the swash plate angle of the swash plate 80 described with reference to Figure 5.
The power conversion unit 10 and hydraulic circuit 90 thus provide a complete power unit which applicant believes can be operated very economically and efficiently due to relatively few moving parts and the infinite adjustment thereof so that it can always be operated under optimum conditions for specific requirements.
From the above description, it will be understood that the conversion unit 10, 66, 78 provides a very compact unit for providing hydraulic power. Also, in all the above embodiments, it will be noted that the same principle of reducing side forces on the pistons 16, 28 applies, the pistons being either axially aligned or acting along parallel lines. It is thus the axial displacement of these pistons that provide for the wobbling action of the wobble plate 18 or rotation of the swash plate 80, whereby the displacements of the pistons ₁₆, 28 are constrained. The above effective reduction in side forces significantly reduce friction and permit weight saving designs of the pistons, and the applicant believes that the overall efficiency of the unit 10, 66, 78 can thus be beneficially effected.
Also, the circular arrangement of the pistons 16 of the effective internal combustion engine, also permits a compact and weight saving design which may be beneficial. By a small increase in the overall size of the unit 10, 66, 78 the number of pistons can be increased for additional power output. It will further be understood that the invention can be performed in various other configurations still employing the basic principles defined in this specification.

Claims

1. A power conversion unit which includes

a first cylinder defining means defining at least one primary cylinder;

a primary piston reciprocably displaceable within each primary cylinder and which can be acted upon by an expanding fluid within the cylinder;

at least one auxiliary piston associated with each primal piston, which is connected to its primary piston so that reciprocal displacement thereof is directly transmitted to the auxiliary piston to cause reciprocal displacement of the auxiliary piston;.

a second cylinder defining means defining a cylinder for each auxiliary piston and in which cylinder the auxiliary piston is reciprocably displaceable to act upon a hydraulic fluid; and

a constraining means for constraining and regularising reciprocating displacement of the primary and auxiliary pistons.

2. A power conversion unit as claimed in Claim 1, in which the first cylinder defining means defines a plurality of primary cylinders and each primary piston has one auxiliary piston associated therewith.

3. A power conversion unit as claimed in Claim 1 or Claim 2, in which the primary pistons and auxiliary pistons are aligned parallel with one another.

'4. A power conversion unit as claimed in Claim 3, in which the primary pistons and their associated auxiliary pistons are axially aligned with one another.

5. A power conversion unit as claimed in any one of the preceding claims, in which the primary pistons and their associated auxiliary pistons are in one piece with one another.

6. A power conversion unit as claimed in any one of Claims 1 to 4, in which the primary pistons and their associated auxiliary pistons are connected to one another by a connecting member.

7. A power conversion unit as claimed in Claim 6, in which the connecting member is the constraining means to which both the primary pistons and their associated auxiliary pistons are connected.

8. A power conversion unit as claimed in any one of the preceding claims, in which the primary pistons and their associated auxiliary pistons have the same cross-sectional dimensions.

9. A power conversion unit as claimed in any one of Claims 1 to 7, in which the primary pistons and their associated auxiliary pistons have different cross-sectional dimensions.

10. A power conversion unit as claimed in any one of the preceding claims, in which the constraining means is a wobble plate to which the primary pistons and their associated auxiliary pistons are connected.

11. A power conversion unit as claimed in Claim 10, in which the wobble plate is non-rotationally mounted on a shaft extending centrally from the wobble plate and which is rotatable, in use, by the wobbling action of the wobble plate due to reciprocating displacement of the primary pistons.

12. A power conversion unit as claimed in Claim 11, in which the primary pistons are connected to the wobble plate by universal joints.

13. A power conversion unit as claimed in Claim 11 or Claim 12, in which the auxiliary pistons are connected to the wobble plate by universal joints.

14. A power conversion unit as claimed in any one of Claims 11 to 13, which includes restraining means to restrain rotation of the wobble plate.

15. A power conversion unit as claimed in Claim 14, in which the restraining means is a restraining arm secured to the wobble plate and fixed relative to the wobble plate.

16. A power conversion unit as claimed in Claim 14, in which the wobble plate defines gear formations and the restraining means is a restraining gear which is fixed relative to the wobble plate and can engage the gear formations on the wobble plate to restrain rotation thereof.

17. A power conversion unit as claimed in Claim 16, in which the restraining gear has a solid body which defines the second cylinder defining means.

18. A power conversion unit as claimed in any one of Claims 11 to 17, in which the rotatable shaft is supported in bearings located relative to the first and second cylinder defining means.

19. A power conversion unit as claimed in any one of Claims 11 to 18, in which the rotatable shaft can serve as a mechanical power take-off.

20. A power conversion unit as claimed in Claim 19, which includes a flywheel mounted on the rotatable shaft.

21. A power conversion unit as claimed in any one of the preceding claims, which includes a valve inlet arrangement and a valve outlet arrangement for controlling the passage of an expanding fluid into and out of the primary cylinders.

22. A power conversion unit as claimed in Claim 21, in which the expanding fluid is a combustible fuel, and which includes means to initiate the combustion of the fuel within the primary cylinders.

23. A power conversion unit as claimed in Claim 22, in which the means to initiate the combustion of fuel is a spark ignition means.

24. A power conversion unit as claimed in Claim 23, in which the primary pistons and the primary cylinders form an effective internal combustion engine.

25. A power conversion unit as claimed in any one of Claims 21 to 24, insofar as they are dependent on Claim 19 or Claim 20, in which the valve arrangements are operable by a camshaft which is rotatably connected to the rotatable shaft.

26. A power conversion unit as claimed in Claim 25, in which the camshaft is connected to the rotatable shaft via a gear arrangement.

27. A power conversion unit as claimed in Claim 25 or Claim 26, in which the camshaft operates the valve arrangements via a rocker arrangement.

28. A power conversion unit as claimed in Claim 23, insofar as it is dependent on Claim 19 or Claim 20, which includes a distributor to control operation of the spark ignition means, the distributor being operable from the rotatable shaft.

29. A power conversion unit as claimed in any one of Claims 1 to 9, in which the constraining means is a swashplate rotatable about its own axis and engaged by the primary and the auxiliary pistons.

30. A power conversion unit as claimed in Claim 29, in which the swashplate is mounted on a shaft, and in which the shaft is parallel to the axis of the pistons.

31. A power conversion unit as claimed in Claim 29 or Claim 30, in which the primary pistons and their associated auxiliary pistons are connected together by a connecting memb and the connecting member has a groove therein defined betwee two opposing slipper pads which slipper pads engage opposing peripheral edges of the swashplate.

32. A power conversion unit as claimed in any one of Claims 29 to 31, in which the shaft of the swashplate include balancing weights to reduce energy losses resulting from constraining of the motion of the pistons by the swashplate.

33. A power conversion unit as claimed in any one of Claims 29 to 32, in which the shaft of the swashplate include a flywheel to reduce energy losses resulting from constrainin of the motion of the pistons by the swashplate.

34. A power conversion unit as claimed in any one of the preceding claims, which includes a conduit arrangement through which hydraulic fluid can be conveyed in a controlled manner to and from the cylinders in which the auxiliary pistoi are displaceable.

35. A power conversion unit as claimed in Claim 34, in which the conduit arrangement includes connector means for connection to a hydraulic fluid supply and to a hydraulic power take-off.

36. A power conversion unit as claimed in Claim 34 or Claim 35, in which the conduit arrangement forms a part of a hydraulic circuit.

37. A power conversion unit as claimed in Claim 36, in which the hydraulic circuit is a closed circuit.

38. A power conversion unit as claimed in Claim 36 or Claim 37, in which the hydraulic circuit incorporates a hydraulic motor operable by hydraulic power provided by the operation of the auxiliary pistons on a hydraulic fluid to provide mechanical power.

39. A power conversion unit as claimed in Claim 38, in which the hydraulic motor is a variable displacement type motor.

40. A power conversion unit as claimed in Claim 39, in which the hydraulic motor is a swashplate motor in which the angle of the swashplate is adjustable.

41. A power conversion unit as claimed in any one of the preceding claims, which includes control means for controlling the hydraulic power output of the auxiliary pistons.

42. A power conversion means as claimed in Claim 41, in displaced by the auxiliary pistons to thereby control the hydraulic power output of the auxiliary pistons.

43. A power conversion unit which includes

a first cylinder defining means defining at least one primary cylinder;

at least one auxiliary piston associated with each primary piston, which is connected to its primary piston so that reciprocal displacement thereof is directly transmitted to the auxiliary piston to cause reciprocal displacement of the auxiliary piston;

a secpnd cylinder defining means defining a cylinder for each auxiliary piston and in which cylinder the auxiliary piston is reciprocably displaceable to act upon a hydraulic fluid; and

a conversion means for converting reciprocal motion of the primary and auxiliary pistons into rotational motion.

44. A power unit which includes a power conversion unit as claimed in any one of Claims 1 to 43, associated with a hydraulic circuit and a hydraulic motor included in the hydraulic circuit for providing mechanical power.

45. A power conversion unit, substantially as described in the specification with reference to and as illustrated in the accompanying drawings.