MECHANISM WITH TORQUE RESTRAINT MEMBER

FIELD OF INVENTION

The invention relates to improvements in a mechanism for converting linear reciprocating motion, from one or more pistons for example, to rotary motion about an axis parallel or substantially parallel to the axis or axes of linear motion of the piston (s). Alternatively the mechanism may convert rotary motion to linear reciprocating motion. The mechanism may be used in an engine, pump, refrigerator, or compressor for example. BACKGROUND OF INVENTION

In an axial engine linear reciprocating motion from one or more pistons is converted to rotary motion about an axis parallel or substantially parallel to the axes of the linear reciprocating piston motion. Typically multiple pistons are arranged around the axis of the output shaft of the engine. Alternatively in a pump or compressor of a similar configuration, input rotary motion is converted to linear reciprocating motion of one or more pistons or diaphragms, along a parallel axis or axes parallel to that of the rotary input motion.

Swash plate mechanisms are known for converting between linear reciprocating motion and rotary motion. Swash plate mechanisms are extensively used in for example automotive air conditioning pumps, and are used in several forms of Stirling engine (one form of heat engine).

Wobble or 2-crank mechanisms are also known for converting between linear reciprocating motion and rotary motion and can offer better mechanical efficiency in low power applications.

These motion conversion mechanisms require the torque transmitted to the drive shaft to be reacted to a stationary housing to impart a rotating force to a moveable object such as an alternator rotor.

SUMMARY OF INVENTION

It is an object of the invention to provide an improved or at least alternative form of mechanism for converting between linear reciprocating motion and rotary motion.

In a first aspect the invention may broadly be said to comprise a mechanism for converting between linear reciprocating motion and rotary motion about a substantially parallel axis, comprising

a shaft mounted for rotation about the substantially parallel axis,

a wobble member mounted directly or indirectly to the shaft to transmit a torque to the shaft during operation of the mechanism, one or more linkages for coupling substantially linear reciprocating motion to the wobble member, and

a resiliently flexible torque restraint member coupled between the wobble member and at least one non-moving reference point to react torque transmitted to the shaft to the reference point while allowing oscillating movement of the wobble member.

Typically the torque restraint member is coupled to a mechanism housing as the non- moving reference point.

In one form the resiliently flexible torque restraint member is a plate or plate-like in a plane across the mechanism, or substantially transverse to the machine axis, and is formed of a resiliently flexible material such as spring steel.

The resiliently flexible torque restraint member may comprise at least one arm or two or more arms coupled at or towards an outer end or ends to the wobble member, and at least one arm or two or more arms coupled at or towards an outer end or ends to the non-moving reference point. Each arm has a relatively lesser cross-sectional depth in a direction substantially parallel to the machine axis and a relatively greater width transverse to said axis so as to be relatively rigid or stiff in-plane due to the relatively greater width and resiliently torsionally flexible about its length.

In some embodiments the end of each arm coupled to the wobble member and the end of each arm coupled to the non-moving reference point is cranked at an angle to the length of a major portion of the length of the arm. The cranked end of each arm may be fixed to the wobble member or the non-moving reference point through an aperture in the cranked end of the arm.

In a further aspect the invention may broadly be said to comprise a mechanism for converting between linear reciprocating motion and rotary motion about a substantially parallel axis, comprising:

a shaft mounted for rotation about the substantially parallel axis,

a wobble member mounted directly or indirectly to the shaft to transmit a torque to the shaft during operation of the mechanism,

one or more linkages for coupling linear reciprocating motion to the wobble member, and one or more bearings or bushes by which the wobble member is supported on the shaft for motion between the wobble member and the shaft, one or all below the zero moment point of the mechanism.

In this specification, "converting reciprocating motion to rotary motion" includes the opposite conversion— of rotary motion to reciprocating motion, unless the text indicates otherwise. Also, the term "piston" includes, but is not to be limited to: a piston of known type in a single- or double-acting engine; a displacer; a diaphragm; and a reciprocating ram such as can be used as a positioning mechanism. The term 'comprising' as used in this specification and claims means 'consisting at least in part of, that is to say when interrupting independent claims including that term, the features prefaced by that term in each claim will need to be present but other features can also be present. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described with reference to the accompanying drawings, by way of example and without intending to be limiting. In the drawings:

Figure 1 is a perspective view of the z-crank shaft, wobble member, pistons and connecting rods, and torque restraint member of an engine comprising an embodiment of the mechanism, the engine being a four cylinder double acting Stirling engine (other parts of the engine not shown),

Figure 2 is a perspective view of the z-crank shaft, wobble member, and torque restraint member of the mechanism, removed from the engine and separate from the cylinders, pistons and connecting rods, showing however four universal joints carried by the wobble member for coupling to the connecting rods,

Figure 3 is a side view of the mechanism removed from the engine showing the same parts as in Figure 2, and also the pistons and connecting rods, from one side,

Figure 4 is a view of the mechanism from above (as later defined), with pistons and connecting rods removed,

Figure 5 is a cross-section view of the mechanism of Figures 3 and 4 along line A-A of Figure 4,

Figure 6 is a cross-section view of the mechanism of Figures 3 to 5 along line M-M of Figure 5,

Figure 7 is a cross-section view similar to Figure 5 but of the mechanism in place within the casing of an engine-generator also showing the generator in cross-section,

Figure 8 is a perspective view of the torque restraint member of the mechanism of Figures

1 to 7, separate from the rest of the mechanism,

Figure 9 is an exploded view of the wobble member, knuckle joints, z-crank shaft and bearings, and torque restraint member,

Figure 10 is an exploded view of the wobble member, knuckle joints, and torque restraint member,

Figure 11 shows an alternative form of a torque restraint member,

Figure 12 shows a further alternative form of a torque restraint member,

Figure 13 is a perspective view similar to Figure 2 of the z-crank shaft, wobble member, and torque restraint member of an engine comprising another embodiment of the torque restraint member mechanism, the engine being a four cylinder double acting Stirling engine (other parts of the engine not shown), removed from the engine and separate from the cylinders, pistons and connecting rods, showing however four universal joints carried by the wobble member for coupling to the connecting rods,

Figure 14 is a view similar to Figure 4, of the mechanism of Figure 13 from above (as later defined) in the direction of arrow of Figure 13, with pistons and connecting rods removed, and

Figure 15 is a cross-section view similar to Figure 5 of the mechanism of Figure 13 and 14 along line A-A of Figure 14.

DETAILED DESCRIPTION OF PREFERRED FORMS

The linear-rotary motion conversion mechanism shown in Figures 1 to 10 is described as part of an engine and in particular an external combustion/heat engine specifically a Stirling engine, for converting linear reciprocating piston motion to rotary motion of an output shaft of the engine. In this description the terms "upper" or "top" and "lower" or "bottom" or similar are used to describe the mechanism in an orientation in which the output drive end of the z-crank shaft is lowermost and the crank pin of the z-crank shaft is uppermost, but it will be appreciated that the mechanism may be used in an engine (or pump or compressor) in which the output end of the crank shaft is uppermost, or to either side, or in any orientation, and the use of the relative terms upper or top and lower or bottom or similar should not be read as limiting the following description.

The z-crank shaft of the mechanism is indicated at 1 (see Figure 5). It comprises an output drive end 2 and an angled crank pin 3. The z-crank shaft 1 is mounted for rotation about the longitudinal axis of the output drive end 2. In the preferred form shown the z-crank shaft 1 is mounted in an upper bearing 4a provided in an engine casing 5 of the engine (see Figure 7), and in a lower bearing 4b. In the embodiment shown the Stirling engine drives an electrical generator or alternator (herein referred to as a generator for convenience) but alternatively the engine may drive a pump or compressor for example. The rotor assembly 50 of the generator is carried on the output drive end 2 of the z-crank shaft. The rotor assembly can comprise laminations and windings as shown or be of a permanent magnet type interacting with a wound stator. The lower bearing 4b is mounted in a lower part of the casing 5, around the bottom end of the output drive end 2 of the z-crank shaft. The upper bearing 4a is also around the output drive end 2 of the z- crank shaft, below the crank pin 3.

A wobble member 6 is mounted on the angled crank pin 3 via bearings 7a and 7b. The wobble member 6 comprises a central boss portion 6a (see Figure 3) having a cylindrical interior, by which the wobble member is carried on the z-crank shaft 1 through the bearings 7a and 7b such that the z-crank shaft can rotate within the wobble member. Bolt 30 passes through the top of the wobble member 6 and cap 60 and threads into an axial bore in the top of the crank pin 3. Four universal or knuckle joints comprising clevis parts 10 and 11 couple the lower ends of connecting rods 29 from four pistons 19 operating in cylinders to the wobble member 6 equidistantly around the wobble member 6 as shown. In the preferred form the primary parts of each knuckle joint are a clevis 10 which is bolted to the wobble member 6 by two bolts 8 which thread into bores 9 in the wobble member 6, a bearing cross 13 which is pivotally mounted to the clevis 10 about an axis across the clevis 10, and a clevis 11 which is pivotally mounted to the bearing cross 13 about a transverse axis through the clevis 10. Cups 15 fit through apertures 11a in the arms of the clevis 11 and form the outer races of bearings 16 between the ends 13a of the bearing cross 13 and the clevis 11. Cups 18 fit dirough apertures lOa in die clevis 10 and form the outer races of bearings 17 between the ends of 13b of the bearing cross 13 and the clevis 10 (see particularly Figures 10 and 6). The lower end of a connecting rod 29 couples to each clevis 11, in the preferred form by a threaded connection into the upper bridge part of each clevis.

In operation, linear reciprocating motion of the pistons of the engine, in the direction of arrows LM in Figure 3, is converted to rotary motion of the output shaft end 2 of the z-crank member 1 , as indicated by arrow RM (or vice versa in a pump or compressor application for example). The wobble member oscillates as indicated by arrows OM.

As the z-shaft rotates, an equal and opposite torque reaction is imparted on the wobble member 6, which is coupled via torque restraint member 20 to the engine casing 5 as a stationary reference point (to prevent the wobble member from rotating). In accordance with the invention a resiliently flexible torque restraint member 20 is coupled between the wobble member 6 and die engine casing to carry the reaction force from the wobble member 6 to the engine casing.

In the embodiment of Figures 1 to 10 the torque restraint member 20 is a plate or may be otherwise plate-like having a cross-form as shown, and may be formed of spring steel or other resiliently flexible material of sufficient strength. Two opposite arms 21a and 21b are coupled to the wobble member 6 and two other arms 22a and 22b are coupled to the engine casing 5. In the preferred form the wobble member comprises lateral arms 6a, and bolts 31 pass through apertures in the opposed ends of arms 21a and 21b of the torque restraint element 20 into threaded bores in the ends of the arms 6a and 6b to fix the ends of the arms of the torque restraint member to the wobble member. Similarly, bolts (not shown) pass through apertures in the other two arms of the torque restraint member and into the casing 5.

Each arm 21a, 21b, 22a and 22b has a relatively lesser cross-sectional depth parallel to the machine axis and a relatively greater width transverse to the machine axis and is resiliently torsionally flexible (about its length) and across its plane due to its substantially thin cross-sectional depth and relatively rigid or stiff in-plane due to its greater width. This allows the wobble member 6 to wobble or oscillate during operation whilst preventing it from rotating relative to the axis of the engine.

Where the ends of the two arms 21a and 21b and the ends of the arms 22a and 22b of the torque restraint member are coupled to the wobble member 6 and to the engine casing

respectively, flat or shaped washers 31a (rigid or alternatively of spring steel or a resilient engineering plastics material) may be used both between the head of bolt 31 and die torque restraint member and between the torque restraint arm and the wobble member 6. Alternatively in another embodiment the fixing of the torque arm ends to the wobble member and to the casing may allow for a small degree of reciprocal movement in-axis of the length of each arm.

In the embodiment described above the bearings 16 and 17 in the knuckle joints preferably comprise needle roller bearings, and the bearings 4a and 4b which mount the z-crank shaft 1 and the bearings 7a and 7b which mount the wobble member 6 to the top of the z-crank shaft 1 are ball bearings, but alternative bearing types may be used in each case or alternatively bushes (metal or plastic, lubricated or unlubricated) as appropriate for the application of the mechanism.

For coupling the linear reciprocating piston motion to the wobble member, linkages other than the particular form of die knuckle joint units described may be used, such as ball joints for example.

Also, the linear-rotary motion conversion mechanism shown in the drawings is described as part of an engine and in particular a Stirling engine, for converting linear or substantially linear reciprocating piston motion to rotary motion of output shaft of the engine, but in alternative applications the mechanism may convert rotary motion to linear reciprocating piston motion, in a pump refrigerator or compressor for example, and the linear motion may be motion of one or more diaphragms instead of one or more pistons.

Figure 11 shows an alternative form for the torque restraint member 20. In this

embodiment the torque restraint member comprises two cross-shaped elements both formed of spring steel plate or similar which are fixed together at or towards the ends of arms 28a and 29a. The ends of 28b of one of the elements 28 are coupled to the arms 6a and 6b of the wobble member and the ends 29a and 29b of the arms of the other element 29 are coupled to the casing (or vice versa).

Figure 12 shows a further alternative embodiment having a four leaf clover shape as shown, comprising an outer peripheral part 35 and inwardly projecting arms 36 and 37. The ends of the arms 36 are coupled to the wobble member and the ends of the arms 37 to the housing, or vice versa.

Figures 13 to 15 show a mechanism similar to that of Figures 1 to 10 but with a torque restraint member in a further alternative form. In Figures 13 to 15 similar reference numerals indicate similar parts of the mechanism as in Figures 1 to 10, and the mechanism is constructed and operates as previously described for the mechanism of Figures 1 to 10, unless the following description otherwise indicates. In the mechanism of Figures 13 to 15 the outer ends 221c and 22 Id coupled to the wobble members and 222c and 222d coupled to the casing of the torque restraint member, are cranked at an angle to the length of the major portion 221a and 221b and

222a and 222b respectively of each arm. In a preferred form as shown the arm ends are cranked at an approximate right angle to the arm length as shown but the arm ends may be cranked at lesser or greater than 90°. An advantage of this form of the torque restraint member is that the arm at the crank or bend between the major length portion of the arm and the arm end comprises some resilient flexibility, which will accommodate marginal shortening of the arm as it twists about its length and generally will allow for a small degree of reciprocal movement in-axis of the length of each arm, as the mechanism operates. The junction point at which each arm is bent to form the cranked end the bend may be radiused rather than comprise a sharp right angle transition between the length portion of the arm and the arm end, to increase the amount of reciprocal in-axis movement that will be possible in operation of the mechanism.

The cranked arm ends are fixed to the wobble member and to the casing by fasteners such as bolts 331 which pass through an aperture in the arm ends (see apertures 222e in Figure 13 for example), into threaded bores in the ends of the arms 6a and 6b of the wobble member, and into the casing respectively. The apertures in the arm ends may contain collars or simply washers on either surface of the arm end, formed of a resilient material such as rubber for example.

The embodiment of Figures 13 to 15 also comprises balance weights 130 fixed to the top of the z-shaft, by bolt 30 through an aperture in balance weight 130 into the end of the angled crank pin (see Figure 15) and at the lower end of the output shaft by a bolt (not shown) into a bore 2a.

In a yet further alternative embodiment the torque restraint member may comprise only a single arm rather than two arms coupled to the wobble member and similarly a single arm rather than two arms coupled to the casing.

Mechanisms using a resiliently flexible torque restraint member as described can be used in axial pumps, motors, compressors or engines such as hydraulic pumps, hydraulic motors, air motors, gas compressors, Stirling engines and internal combustion engines for example.

Further, in the particular embodiment described above the bearings 7a and 7b by which the wobble member 6 is supported on the z-crank shaft 1 are both positioned below the zero moment point of the mechanism. Referring to Figure 5 this is the point of intersection of all of the longitudinal axis of the output drive end 2 of the z-crank shaft, indicated by Line CS-CS (not shown) in Figure 5, the longitudinal axis of the angled crank pin 3 of the z-crank shaft, indicated by line CP-CP in Figure 5, and line M-M in Figure 5 across the centres of the knuckle joints which point of intersection in the embodiments of Figures 1 to 10 and 13 to 15 is at or in the head of bolt 30. This bearing position offers lower overall transmission height and may also provide lower bearing loading.

Also, the flexible torque restraint member is preferably positioned in a plane along line M-

M and through this zero moment point as shown.

The foregoing describes the invention including preferred form thereof. Alterations and modifications as would be obvious to those skilled in the art are intended to be incorporated within the scope hereof as defined in the accompanying claims.