This invention relates to linear-rotational motion converters, and to sources of linear and rotational motion using such converters .

Linear-rotational motion converters are well known in the prior art. They are used where it is desired to convert some form of linear motion, typically reciprocating linear motion such as would be obtained from the piston of an internal combustion engine, into rotational motion, for example of a shaft; or from rotational motion, for example of a motor, into reciprocal motion such as of a piston pump, compressors , saws, stamps and so on. One very common example of a linear to rotational converter is the connecting rod and crankshaft found in nearly all internal combustion engines . In this, a connecting rod is connected pivotally to the piston and to the eccentric portion (typically a crank pin) of a crankshaft. The power stroke of the piston forces the crankshaft away from the piston, thus rotating it.

However, this mechanism has some significant drawbacks. Significant side forces are placed on the linearly-moving element; as the connecting rod cannot be parallel to the linear motion of the piston at all positions in the cycle, there will be some sideways pressure of the piston on the cylinder wall. This leads to friction and hence wear. Furthermore, such mechanisms do not easily allow the piston to be double-acting without resorting to a complex articulated connecting rod or crosshead used in both directions of reciprocation.

The scotch yoke is an alternative linear-rotational motion converter, which comprises a yoke having an elongate slot at right-angles to the direction of reciprocating linear motion, and the eccentric portion of a crankshaft passing through that slot. As the yoke reciprocates, the crankshaft will be forced to rotate. However, to date, the scotch yoke has not been widely used in all the situations that a linear-rotational motion converter could be, given issues with friction and wear of the eccentric portion of the crankshaft in the slot in the yoke, and in particular that it relies on only hydrostatic lubrication. For these reasons, scotch yokes have generally only been used in relatively small apparatus such as jigsaws , sanders and small refrigerant compressors.

According to a first aspect of the invention, there is provided a linear- rotational motion converter, comprising an first body, a second body and at least one cylindrical member mounted for rotation relative to the second body about an axis of rotation, the or each cylindrical member supporting the second body relative to the first body such that the second body can slide relative to the first body parallel to the axis of rotation, and in which a drive means is provided arranged to cause rotation of the or each cylindrical member about its axis of rotation.

Thus, by providing a rotating cylindrical member, such as a rod, which supports the first and second bodies relative to one another, the converter can promote the sliding motion of the second body relative to the first body, as the rotational motion will decrease the level of friction due to the motion of the cylindrical member. This is particularly true where a lubricant is used; the motion of the cylindrical member can be used to entrain sufficient lubricant to ensure a smooth and reliable sliding motion.

As such, the side forces (that is, the forces parallel to the axis of rotation) of this linear-rotational motion converter can be reduced compared with prior art converters such as the connecting rod and crankshaft arrangement described above. Each of the first body and the second body may be provided with at least one groove for the or each cylindrical member. The or each groove may be part-circular in cross-section. This ensures that the or each cylindrical members are securely held between the first and second bodies.

The converter may further comprise a crankshaft, where an eccentric portion of the crankshaft engages the second body, such that reciprocating linear motion of the first body causes the second body to rotate the crankshaft or rotation of the crankshaft causes reciprocating linear motion of the first body. The linear motion of the first body may be perpendicular to the or each axis of rotation of the or each cylindrical member. As such, the combination of the linear motion of the first body and the sliding of the second body may cause the second body to move in a circular path.

The drive means may engage the crankshaft, such that rotation of the crankshaft by the second body causes rotation of the or each cylindrical member. The or each cylindrical member may comprise an eccentric cam, offset from the axis of rotation of the cylindrical member, which is engaged by the drive means. The drive means may comprise a drive yoke, which engages the or each eccentric cam of the or each cylindrical member, such that reciprocating linear motion of the drive yoke causes the or each cylindrical member to rotate. The drive means may comprise a drive shaft having an eccentric cam which engages the drive yoke so as to drive the drive yoke for reciprocating linear motion. The drive shaft may engage the crankshaft, typically by a geared connection. Thus, rotation of the or each cylindrical member can be achieved.

Typically, one revolution of the crankshaft will be synchronous with one revolution of the or each cylindrical member. Thus , the path of the or each eccentric cam of the or each cylindrical member will typically be generally elliptical, composed of the reciprocating linear motion of the first member in one direction overlaid with the circular motion of the eccentric cam about the axis of rotation of the cylindrical member. Alternatively, the drive means may comprise means independent from the crankshaft, and may therefore comprise a motor coupled to the or each cylindrical member for rotation thereof.

The converter may comprise two cylindrical members , positioned on opposing edges of the second body. The first body may surround the second body around the two edges ; this gives improved stability as the first body is moved in two opposing directions. The first body may comprise two parts surrounding the second body, each part contacting one side of the body, and the two parts being connected together, typically rigidly. The two parts may be connected by at least one strap, and preferably by a pair of straps.

Such an arrangement is particularly useful in devices having opposed pistons, such as boxer engines , where forces can then be applied in either direction to the second body.

The converter may also comprise a source of lubricant; for example, an oil port, typically for connection to an oil pump. The source of lubricant may be arranged to provide lubrication to the or each cylindrical member. Typically, the source of lubricant will comprise a passage from an oil port to the vicinity of the or each cylindrical member.

Potential uses for the converter include in an internal combustion engine, typically to convert reciprocating linear motion of at least one piston of the engine into rotational motion of the crankshaft of the engine; to convert rotational motion of a motor into reciprocating linear motion in a pump, or in any other situation where it is desired to convert linear (typically reciprocating) motion into rotational motion or vice versa.

According to a second aspect of the invention, there is provided a source of rotational motion, comprising a linearly moving body arranged for reciprocating linear movement, an output shaft and at least one converter according to the first aspect of the invention, in which the first body of the converter is connected to the linearly moving body, and the second body is connected to the output shaft so as to convert reciprocating linear motion of the linearly moving body into rotational motion of the output shaft.

Thus , this source of rotational motion can have reduced side forces on its linearly moving body or bodies as compared with using a connecting rod and crankshaft arrangement.

The source of rotational motion may be an engine, such as a Stirling engine or internal combustion engine. The linearly moving body may be a piston of the engine. Typically, the output shaft will be a crankshaft of the engine.

According to a third aspect of the invention, there is provided a source of linear motion, comprising a rotationally moving body arranged for rotational movement, an output shaft and at least one converter according to the first aspect of the invention, in which the first body of the converter is connected to the output shaft, and the second body is connected to the rotationally moving body so as to convert rotational motion of the rotationally moving body into reciprocating linear motion of the output shaft. The source of linear motion may comprise a motor, with an output shaft of the motor forming the rotationally moving body.

There now follows , by way of example only, embodiments of the present invention described with reference to the accompanying drawings, in which:

Figure 1 shows an exploded perspective view of a linear-rotational motion converter according to a first embodiment of the invention;

Figure 2 shows a further exploded perspective view of part of the converter of Figure 1 ;

Figure 3 shows a non-exploded perspective view equivalent to that of Figure 2;

Figure 4 shows a perspective view of a linear-rotational motion converter according to a second embodiment of the invention; Figure 5 shows a perspective view of a linear-rotational motion converter according to a third embodiment of the invention;

Figure 6 shows a perspective view of the input body of a linear- rotational motion converter according to a fourth embodiment of the invention;

Figure 7 shows a perspective view of the input body of a linear- rotational motion converter according to a fifth embodiment of the invention; Figure 8 shows a perspective view of a linear-rotational motion converter according to a sixth embodiment of the invention; and

Figure 9 shows a cross-sectional view through a linear-rotation motion converter according to a seventh embodiment of the invention, used to drive a pump.

Figure 1 shows a linear-rotational motion converter according to a first embodiment of the invention. It is used to convert linear motion into rotational motion. In this embodiment, a first, input body 1 is provided, having a pair of elongate input shafts 2. In use, a reciprocating linear force, such as that generated by an internal combustion engine, is applied to these input shafts 2, along the length of the shafts. The input body is formed of upper and lower parts la, lb (the lower part lb not being shown in Figure 1 for the sake of clarity) .

There is also provided a second, output body 3. This has a central bore 4, through which passes the eccentric portion 5 of a crankshaft 6. The crankshaft 6 is free to rotate about its axis 7, with the axis 18 of the eccentric portion 5 being offset therefrom. This means that the eccentric portion 5 and so the output body 3 is constrained to follow a circular path as the crankshaft 6 rotates.

In order to allow the circular motion of the output body 3 , that output body 3 can slide relative to the input body 1. This is achieved by using two cylindrical rods 8, one on each of the upper and lower faces 9 of the output body 3. These upper and lower faces 9 of the output body 3 are formed as grooves so as to retain the rods 8. Each of the rods engages either the upper la or lower lb parts of the input body 1. The rods are free to rotate about their axes 10. This arrangement allows the output body 3 to slide relative to the input body 1 in a direction parallel to the axes 10.

In order to secure the converter together, the two parts la, lb, of the input body 1 can be held together by steel straps 24, so as to capture the rods 8 and the output body 3 therebetween.

In order to reduce the friction inherent in the contact between the output body 3 and the rods 8, the rods 8 are driven for rotation about their axes 10 by use of a drive means 11. This drive means is driven off crankshaft 6 by means of a geared coupling 12. In this coupling 12, rotation of the crankshaft 6 causes a drive shaft 13 to rotate. The drive shaft is provided with an eccentric cam 14, which engages a first cam follower 15 in a cam follower body 16, the cam follower body 16 being restricted so as to only be able to move in a linear direction shown by arrows 17 perpendicular to the axes 10 of the rods 8.

The first cam follower 15 is of the form of a loop of material defining an elongate slot of the same internal width as the diameter of the eccentric cam 14. This means that, as the eccentric cam rotates about the axis 19 of the drive shaft 13, the cam follower body 16 will be driven back and forth along direction 17.

This motion can be used to drive the rotation of the rods 8. A second cam follower 20 is provided in the cam follower body 16, which again is formed of material defining an elongate slot. The end of each rod 8 is formed with an eccentric cam 21 which engages the slot of the second cam follower, such that the reciprocating linear motion of the cam follower body caused by the eccentric cam 14 of the drive shaft 13 causes the eccentric cams 21 of the rods 8 to rotate the rods 8 about their axes 10. Even when the cam follower body 16 is stationary at the end of its travel (as it changes direction) , the rods 8 will continue to rotate, due to their rotational momentum.

The rotation of the rods 8 leads to the friction between the output body 10 and the rods being kinetic friction, rather that static friction, which in itself is generally lower in magnitude. However, the greatest decrease in friction can be obtained if a lubricant, such as standard engine oil, is sprayed onto the rods 8, typically by connecting a spray head 21 (shown in Figure 2) by means of an oil conduit 22 to an oil pump 23 of the engine. The rotation of the rods 8 will entrain lubricant into the interfaces between the rods 8 on the one hand and the input 1 and output 3 bodies respectively on the other hand.

This entrained lubricant combined with the rotation of the rods 8 will lead to a consistent reduction in friction in the converter, as the rods will be in constant motion throughout the motion of the converter; there will no point in a rotation of the converter where the rods 8 stop rotating. The rotation causes a lubricant film to be maintained between the rubbing surfaces, thus maintaining hydrodynamic lubrication.

Various different embodiments of the invention are possible that work in the same manner as the embodiment described above. In the embodiment shown in Figure 4 (in which reference numerals for integers equivalent to those of the embodiment of Figures 1 to 3 have been raised by 100) , the converter is for use with a single piston (it being possible to provide multiple converters for an engine having multiple cylinders) .

Only a single input shaft 102 is provided, and a single rod 108 (which will be driven for rotation in the same manner as in the first embodiment) . The other rod is replaced by a plate 125, which is used to hold the output body 103 captive together with the straps 124. Because the forces on the converter from the piston in an internal combustion engine will be in one direction - downwards in Figure 4 - that is the only direction in which force is transmitted from the input body 101 through the rod 108 to the output body 103 ; there will be therefore no load on the output body 103 - plate 125 interface. Similarly, forces transmitted back from the crankshaft (not shown in Figure 4) to the piston will be in a single direction - upwards in Figure 4 - and so will not result in there being any load on the plate 125. Rather than be formed as two separate parts connected by straps, Figures 5 to 7 (in which reference numerals for integers equivalent to those of the embodiment of Figures 1 to 3 have been raised by 150) show that the input body 151 can be a single integral unit. They also show that the number of pistons 176 whose motion is converted by a single converter can vary, being two in Figure 5, three in Figure 6 and four in Figure 7. The skilled man will therefore be able to appreciate that the converter of the present invention can be adapted to the situation in which it is desired to be used; the present invention is flexible and can be conveniently with any desired number of suitably positioned co-acting pistons.

Generally, the input and output bodies can be formed of aluminium or steel for strength and relatively low weight. The straps, where used, can be cast from steel.

One of the advantages of the embodiments of the invention is that there will be very little side force applied to the input shaft due to the converter. This can be used to simplify how a piston is guided. As shown in Figure 8 (which shows a converter akin to that of Figures 1 to 3 and according to a sixth embodiment of the invention, with corresponding reference numerals raised by 200) , rather than relying on the piston rings keeping the piston correctly aligned in the cylinder, the input shaft 202 can be guided by a pair of cylindrical rollers 230, which are arranged for rotation about parallel axes X. These rollers 230 can accurately control orientate the input shaft 202 as it reciprocates linearly. This can be used to control the position of a body, such as a piston, attached to the input shaft 202. In an internal combustion engine, by accurately placing the piston within the cylinder bore, the load of the walls of the cylinder can be reduced, further reducing wear of the cylinder.

A seventh embodiment of the invention shown in Figure 9 of the accompanying drawings takes this advantage even further; reference numerals of integers common to the embodiment of Figures 1 to 3 have been reused, raised by 250) . In this embodiment, the converter is used to convert rotational motion from, for example, a motor, into reciprocating linear motion to run a pump.

In this embodiment, the first body 251 is an output body, and the second body 253 is now an input body. The output of motor is coupled to a crankshaft (not shown) , an eccentric component of which engages the input body 253. The rods 258 are driven for rotation off the crankshaft in the same manner as in the first embodiment. The converter is now acting as a rotational-to-linear movement converter, in that rotation of the input body 253 will cause reciprocating linear motion of the output body 251 and so of the output shaft 252 coupled to the output body 251.

The output shaft can be used to drive a pump. This comprises a pump chamber 283 , with a piston 276 being formed on the end of the output shaft 253 within the pump chamber 283. The piston 276 separates the pump chamber into upper 284 and lower 285 sections . Because the motion of the output shaft 252 is linear along the length of the output shaft 252, with little if any force being applied transverse to the length of the output shaft 252, a simple annular seal 286 can be used to seal the portal for the output shaft 252 into the pump chamber 283. Thus , the pump can pump on both strokes of the piston; it is double-acting. With a prior-art connecting rod and crankshaft, the seal on the lower section where the output shaft 252 enters the pump chamber would be practically impossible to seal, meaning such a pump would generally only be single acting.

In a similar manner to Figure 5 , the converter can have two output shafts 252, with a further pump chamber 285 (not shown) being provided on the lower output shaft 252.