WO1998048158A1

WO1998048158A1 - Three cycle engine

Info

Publication number: WO1998048158A1
Application number: PCT/AU1998/000287
Authority: WO
Inventors: Peter Robert Raffaele; Michael John Raffaele
Original assignee: Peter Robert Raffaele; Michael John Raffaele
Priority date: 1997-04-21
Filing date: 1998-04-21
Publication date: 1998-10-29
Also published as: AUPO633297A0; WO1998048158A9

Abstract

An internal combustion engine comprising a piston (12) constrained for linear sliding in a bore (10), a first crank (22) constrained for rotation about a first axis (24), a second crank (16) mounted on the first crank (22) remote from the first axis (24) for rotation about a second axis (26) and so to have an effective ratio of two thirds, one third or three quarters or half. A connecting rod (14) mounted on the second crank (16) for rotation about a third axis and interconnecting the piston (12) and a follower and constraining means (18) to constrain the second crank (16) to rotate about the second axis (26) as the first crank (22) rotates about the first axis (24).

Description

THREE CYCLE ENGINE

This invention relates to reciprocating piston internal combustion engines and, in particular, to the method of converting the linear motion of the piston into rotary motion. More particularly, it relates to the timing of piston movement.

In conventional reciprocating internal combustion engines, the piston reciprocates in a cylinder and is connected to an offset crank by a connecting rod. Rotation of the offset crank about an axis of rotation causes a generally sinusoidal movement of the piston in the cylinder. The time the piston spends at or near top dead centre is substantially the same as the time it spends at or near bottom dead centre.

In a normal poppet valved engine in which the exhaust and inlet ports to the cylinder are located in the cylinder head, this is not particularly important. However, where the inlet and exhaust ports are located in the cylinder wall, such as in a two stroke engine, the amount of time spent at or near bottom dead centre becomes important. Improved engine performance can be obtained if exhaust gas scavenging is improved and inlet gas intake is improved. If the time that the exhaust or inlet ports are open, or both, can be increased, this will aid in improving engine efficiency.

In an attempt to overcome some of the disadvantages discussed above, the invention, in one broad form, provides a crank device suitable for use in a reciprocating piston device having a piston constrained for linear sliding in a bore, the crank device comprising:

a first crank constrained for rotation about a first axis;

a second crank, mounted on the first crank remote from the first axis, for rotation about a second axis; and

a connecting rod mounted on the second crank for rotation about a third axis and for interconnecting the piston and the second crank; and constraining means to constrain the second crank to rotate about the second axis as the first crank rotates about the first axis.

The constraining means is preferably a ring gear and the second crank is a planetary gear. A conjugate cam arrangement may be utilised instead but other arrangements are also acceptable such as a chain linking two cogs.

The constraining means preferably comprises a pair of gears or cogs which engage with each other, either directly or via a chain. For each pair, one gear or cog is centred on the first axis. The other is centred on the second axis and is connected with or forms part of the second crank, so as to rotate about the second axis with the second crank.

The first gear or cog, hereinafter referred to as the first member, may be fixed relative to the first axis or it may be allowed to rotate relative to the first axis. The second gear or cog, hereinafter referred to as the follower, may be fixed relative to the second crank or may be connected so as to allow rotation of the second crank about the second axis relative to the follower so as to advance or retard the piston.

The first member may be oscillated about the first axis during each cycle or it may be moved to a different "fixed" position. Alternatively, it may be constantly rotated about the axis, albeit with a fixed or varying angular velocity.

In all forms of the invention, after adjusting for any rotation of the first member, preferably the second crank rotates three times, one and one half times or one and one third times for each orbit about the first axis.

When conjugate cams are used, preferably the second crank rotates about the second axis three times or one and one half times for each orbit about the first axis.

The connecting rod may be connected to the crank radially inwardly or outwardly of the follower's effective engagement surface.

When a gear arrangement is used, preferably the diameter of the planetary gear is two thirds, one third or three quarters of the diameter of the ring gear. However, different ratios may be employed when the ring gear is not fixed so as to have an effective ratio of two thirds, one third or three quarters.

One preferred form of the invention provides a reciprocating piston device comprising:

a piston constrained for linear sliding in a bore;

a first crank constrained for rotation about a first axis;

a second crank mounted on the first crank remote from the first axis, for rotation about a second axis; and so as to have an effective ratio of two thirds, one third or three quarters.

a connecting rod mounted on the second crank for rotation about a third axis and interconnecting the piston and the follower; and

constraining means to constrain the second crank to rotate about the second axis as the first crank rotates about the first axis.

Preferably, the device is provided with ports or inlet ports or both, in the cylinder wall.

Alternatively, one of the inlet or exhaust ports may be located in the cylinder head and selectively opened via poppet valves.

The piston device is preferably an internal combustion engine or a compressor. There may be more than one connecting rod and associated piston mounted on a single second crank. For example, a single second crank may have three connecting rods, each piston being spaced 120 degrees from the other.

The invention shall be better understood from the following non-limiting description of embodiments of the invention and the drawings, in which:

Figs. 1 to 3 show schematic cross-sectional views of a first embodiment of the invention at various states of operation. Fig. 4 shows the trajectory taken by the big end of the Fig. 1 device.

Figs. 5A, B and C show a perspective exploded view of a second embodiment of the invention.

Fig. 6 shows a graph of piston displacement against time in a conventional engine and in the present invention.

Fig. 7 shows a schematic cross-sectional view of a second embodiment of the invention.

Fig. 8 shows a schematic cross-section of an in-line three cylinder made according to the Fig. 1 embodiment.

Fig. 9 shows a further embodiment of the invention.

Fig. 10 shows a three cylinder radial engine according to the Fig. 9 embodiment.

Fig. 11 shows an alternate crank arrangement applicable to the Fig. 1 embodiment.

Fig. 12 shows a further alternate crank arrangement.

Referring to the drawings, there is shown, at figure 1 , a single cylinder 10 of an engine according to the invention. The cylinder 10 has a piston 12 positioned for reciprocal movement. The piston 12 is connected by a connecting rod 14 to a first gear 16. This gear member 16 is mounted for rotation within a ring gear 18, with which it engages. The big end journal 20 is mounted on a web to one side of the gear 6 at a radius greater than the gear diameter. This is not essential and the centre of the journal 20 may be located at a radius from the gear centre the same or less than the gear's radius.

The gear 16 is mounted for rotation on a crank 22 which rotates about an axis 24, which is coaxial with the axis of the ring gear 18. Due to the differences in diameter of the gears 16 and 18, the gear 16 is mounted for rotation on an axis 26 offset from the axis 24. Thus, as the gear 16 rotates in a clockwise direction, as indicated by arrow A, its centre, 26, will rotate anticlockwise as it engages with gear 18, as indicated by arrow B. This thus causes the crank 22 to rotate about axis 24. Since gear 16 is rotating clockwise, the journal 20, and hence connecting rod 14 and piston 12 will descend, with the journal initially travelling to the right of axis 26.

The relative diameters of the gears 16 and 18 determine the path that the journal 20 takes. This in turn determines the position and velocity that the piston 12 takes.

Where the gear 16 is half the diameter of the ring gear 18, the journal 20 takes a relatively "up and down" path with little sideways motion. Because the gear 16 is engaged with gear 18, for the contact point 17 between the two gears to move to the bottom of gear 18, gear 16 must complete a full rotation about axis 26. However, this results in the crank 22 rotating 180 degrees and the journal 20 being positioned at the bottom of the gear 16. A further full rotation of gear 16 returns the piston to top dead centre. Thus, the piston tends to follow a path which is similar to that of a conventional engine, in that the time spent at bottom dead centre is similar to that spent at top dead centre.

However, it has been discovered that by utilising particular ratios in the sizes of the gears 16 and 18 an advantageous piston path may be obtained, in which the piston remains at or near bottom dead centre for substantially more time than at top dead centre.

Fig. 1 shows a configuration in which the diameter of gear 16 is two thirds that of gear 18. Thus, one clockwise rotation of gear 16 about axis 26 will cause the contact point 17 between gears 16 and 18 to move anticlockwise two thirds of the way around the circumference of gear 18 to the position shown in figure 2. In doing so, the centre of journal 20 describes a path indicated by line 30 in figure 4. The lower most point of line 30, indicated by line 32 represents bottom dead centre for the piston. This part of the cycle may be considered equivalent to the power stroke of a normal two or four stroke engine as will be explained below.

A further full rotation of gear 16 about axis 26 causes a further movement of the contact point 17 along two thirds of the circumference of gear 8 to the position shown in figure 3. The path described by journal 20 is again shown. It will be seen that the path remains relatively flat with little vertical motion. Thus, assuming a constant rotational velocity of gear 16, for the same time period that the piston takes to travel from top dead centre to bottom dead centre, the piston remains at or near bottom dead centre.

The limited movement piston stroke is in fact a very slight upward and downward stroke but is so small as to be insignificant as far as power generation and compression of gases is concerned. Effectively, the limited movement stroke is a convenient, relatively lengthy, piston dwell period during which evacuation and charging of the combustion chamber may take place. This is best shown in Fig. 6 which plots piston position against time of a conventional engine, shown by line 40, and that of an engine according to the invention, shown by line 41.

A further full rotation of gear 16 about axis 26 again causes the contact point 17 to move along gear 18 to return to the position shown in figure 1. The journal 20 follows the path shown, which is identical to the path taken for the first rotation, albeit reversed.

Thus the piston has three cycles in its movement - a down stroke, a limited movement stroke, at which it remains near bottom dead centre, and an up stroke.

Referring to figures 1 to 3, the motion from the fig. 1 to fig. 2 position represents the power stroke, whilst the motion from the fig. 2 to fig. 3 position represents a combined exhaust/inlet stroke, whilst the motion from the fig. 3 to fig. 1 position represents the compression stroke.

The exhaust/inlet stroke may be further divided into an exhaust stroke and an inlet stroke, if desired, in which both are of equal duration.

Since the piston does not move much during the exhaust/inlet stroke, it cannot be used to drive exhaust gases out of the cylinder or draw inlet gases into the cylinder. Thus, this configuration ideally requires having one or both of the inlet or exhaust ports located in the cylinder wall, such as found in conventional two stroke reciprocating internal combustion engines. Furthermore, because the piston has relatively little vertical motion for 1/3 of the cycle, it is possible to position the exhaust/inlet ports much lower in the cylinder wall compared to a normal two stroke engine. The rise of the piston indicated by 33 in Fig. 4 during the exhaust/inlet stroke is only about 3% of the total piston stroke (this will depend on the offset of the journal 20), so the exhaust or inlet ports may be positioned much lower - a two stroke engine typically has its exhaust ports opening at 65% of the down stroke - i.e. 35% of the down stroke is not available as a power generating portion of the cycle. Because a full 1/3 of the cycle is at or near bottom dead centre, there is much more time for exhaust or inlet gases to flow into or out of the cylinder. This, in turn, means that the vertical height of the ports may be reduced since a lower volume flow per second will still result in a similar total volume flow, due to the greater time available for scavenging. Thus, more of the power stroke is available for power generation. Similarly, the compression stroke will close off the ports earlier, resulting in a higher compression ratio and increased efficiency.

It should be appreciated that the offset at the crankshaft in the present invention need not be as great as that in a conventional crankshaft in order to produce the same torque having regard to the fact that in the present invention the crankshaft ends and hence the offset crank moves laterally (as well as up and down) with respect to the block under the influence of the planetary motion of the pinion wheel attached to the crankshaft.

There are further advantages associated with the present invention which flow from the effective angle which the connecting rod makes with the crank on the crankshaft. In a conventional motor the offset of the crank is simply the offset distance between the big end journal and the rotational axis of the crankshaft whereas in the present invention the offset of the crank with respect to the rotational axis of the crankshaft is only part of the offset which is achieved due to the planetary gears 10 continually moving the axis of the crankshaft ends with respect to the output gear axis, block and pistons. An engine in accordance with the present invention actually moves the crankshaft axis of rotation downwardly during the power stroke such that duration of the period in which the connecting rod makes a near right-angle with the crankshaft is extended. This advantage produced by the present invention is not merely one associated with gearing of the crank but of changing the mechanical advantage which may be exerted by a connecting rod on the crankshaft as compared with a conventional stationary crankshaft configuration.

5 Fig. 5 shows an exploded view of components of a device according to the Figs. 1 to 3 schematic views.

In this embodiment two spaced apart ring gears 118 are provided and a crank member 120 is provided to engage both gears 118. The crank member 120 has two gears 122 at its ends, a central big end journal 124 upon which connecting ιo rod 126 engages and two second journals 128 sandwiched between the big end 124 and the gears 122. Mounted on the second journals 128 are two output gears 130.

The ring gears 118 are mounted coaxially with the output gears 130, which are free to rotate about the common axis whilst the gears 124 engage ring gears 15 118. The output years 130 are connected to an output shaft (not shown) and are caused to rotate about their axes as the gear member 120 rotates about the ring gears 118.

Fig. 7 shows a different embodiment of the invention. Like parts are provided with the same numbers. In this embodiment, the gear 16 is only one third the 20 diameter of ring gear 18.

Thus, a full rotation of gear 16 moves the contact point 17 along one third of the circumference of gear 18, to point B.

A further full rotation moves the contact point to point C, whilst yet a further rotation returns to point A. The path followed by the journal 20 is shown by line 25 30, which is substantially the same shape as that of the first embodiment, i.e. a down-stroke, a "dwell" stroke and an up-stroke. Thus, this configuration provides the same advantages as the first embodiment. It will be noted that the journal 20 travels along path 30 in the opposite direction, compared to the fig. 1 - 3 embodiment. A planetary gear having three quarters the diameter of the ring gear also provides advantages.

Fig. 8 shows an in-line three cylinder engine constructed utilising the arrangements described in relation to the previous embodiments. Each of the three pistons is at 120 degrees to each other in their cycles.

It will be seen that unlike conventional internal combustion engines, the cranks 22 for each cylinder are not connected in a unitary structure. Each crank 22, is joumalled for rotation in the crank case 40 and provided with an output gear 42 on its surface. A linking geared rod, not show, then engages each of the three cranks 22 as an output shaft and to maintain the cranks 22 in synchronisation with each other.

Whilst a movable planetary gear and a fixed ring gear is preferred, if desired a fixed planetary gear and rotating ring gear may be utilised.

Fig. 9 shows one such embodiment 200. The piston 212 is connected via a connecting rod 214 to a ring gear 216, which is mounted on an offset crank 218 at its centre point 220. This crank is mounted for rotation about an axis 222 and has an output gear 224 which engages a take of gear 226.

A planetary gear 228 is fixedly mounted relative to the cylinder with its axis coaxial with axis 222.

Thus, as the piston 212 reciprocates, the ring gear rotates about the planetary gear 228 and causes the crank 218 to rotate about axis 222. With similar ratios as for the earlier embodiments, ie. ring gear to planetary gear diameter ratios of 3:2, 3:1 and 4:3, similar trajectories will be described by the big end 230 of the connecting rod, ie. a power stroke, a combined exhaust/inlet stroke of equal duration and then a compression stroke.

Fig. 10 shows a three cylinder device 300 made according to the Fig. 9 construction in which three cylinder/piston assemblies 310/312 are mounted around the crank assembly at 120 degrees to each other. In this embodiment the connecting rods 314 are mounted on a single big end 316 of the ring gear 318. The ring gear 318 rotates about planetary gear 320 via a crank member, upon which it is mounted for rotation at its centre 322.

Whilst the Fig. 8 embodiment utilises independent crank mechanisms for each piston, it will be appreciated that each crank may have more than one big end on the follower and that if desired the cranks may be joined together, so as to reduce the number of ring gears and "crank" gears. The big ends may be all inline, although this would probably lead to unacceptable vibration or staggered. If staggered, each of the big ends would need to be staggered by an amount appropriate to the planetary gear/ring gear diameter ratios. For instance, Fig. 11 shows a schematic cross-section of an embodiment utilising a unit or crank member.

The crank member 400 comprises a planetary gear 410 at one end and is mounted for rotation on a crank gears 420 about axis 422. The crank gears themselves are joumaled in bearings 424 for rotation about axis 426, the axis of the ring gears. Connecting rods 430 are mounted for rotation about axes 434 on big ends 434. The planetary gear 410 engages the ring gear 440.

If desired two or more connecting rods 430 maybe mounted on each big end 434.

Furthermore, it will be appreciated that an exact one third, two third or three quarter ratio is not essential where the outer gear may rotate relative to the other components. For example, a ring gear of 170mm diameter may be used with a

60mm diameter planetary gear. With no rotation of the ring gear every three rotations of the planetary gear about its own axis will result in the planetary gear rotating about the axis of the ring gear by more than once; by one eighteenth of a rotation. By rotating the ring gear about its axis the planetary gear may arrive at the same position after three rotations. In this case, this requires the ring gear to rotate at an average angular velocity one fifty-fourth that of the planetary gear. In the same fashion, where the ring gear has a greater diameter than the exact ration, it may be rotated in the opposite direction to compensate for the different in ratios. Whilst the embodiments of Figs 1 to 11 utilise a fixed ring gear arrangement, it will be appreciated that the ring gear may be selectively rotatable about its own axis. The ring gear may be rotated to different positions for different operating conditions, so as to alter the "path" taken by the piston and the effective "valve timing". For example, rotating the ring so as to cause the piston to advance from its position will, in the absence of other changes, result in retardation of both valve and spark plug timing and vice-versa. Alternatively, the ring gear may be moved during each cycle so as to extend or contract each portion of the total cycle. For instance, by appropriate movement of the ring gear, one may reduce the slight up and down piston motion during the "dwell" portion of the cycle. Similarly, each of the planetary gears may be constructed that the big end of the connecting rod may be rotated relative to the contact point of the gears. This may be achieved by a two part construction, one part comprising the gear, the other part the big end, mounted for relative rotation about their centre point.

Whilst the embodiments of Figs 1 to 11 utilise a gear arrangement to couple the ring gear and planetary gear, it will be appreciated that the ring gear/planetary gear arrangement may be replaced with other functionally similar arrangements, for instance, a conjugate cam arrangement or a cog and chain arrangement. Use of a conjugate cam arrangement allows further control over the piston motion as the follower travels along the ring's path.

Fig 12 schematically shows a further variation of the invention, in which there is no ring gear.

A first crank 500 is mounted for rotation about a first axis 510. A second crank 512 is mounted on the first crank for rotation about a second axis 514. Secured to the second crank 512 is a cog 516, coaxial with the axis 514. A piston connecting rod (not shown) may be mounted on the big end 513 for rotation about a third axis 515.

Another cog 518 is mounted coaxial with the first axis 510 and a chain 520 extends between the two cogs 516 and 518. As the first crank 500 rotates relative to the cog 518, the chain 520 causes the cog 516 and with it crank 512 to rotate relative to the crank 500. By choosing appropriate diameter ratios of the two cogs 516 and 518, the second crank 512 maybe caused to rotate at the desired amounts for each full rotation of the first crank, or vice versa.

The first cog 518 may be fixed relative to the axis 510 or it may be allowed to rotate about the axis 510. This rotation may be continuous, at a variable or constant angular velocity or it may be a reciprocating motion. Alternatively, the first cog 518 may be moved to different 'fixed' positions to alter the timing for different conditions. When the cog rotates continuously, this may be to adjust for ratios in cog sizes which do not give the exact desired rotational ratios.

It will be apparent that many modifications - variations may be made to the embodiments described herein by those skilled in the art without departing from the spirit or scope of the invention.

For example, the pistons may advantageously be configured in a radial pattern as well as an in-line or "V" pattern. Various methods of charging the combustion chamber may also be utilised. Alternate gfsear ratios between the planetary gears and the annular gears associated with the crankshaft may also be utilised apart from the ratios abovementioned. Further, more than one piston may be mounted on each follower/planetary gear. In a radical configuration, numerous pistons may be mounted on the one planetary gear.

Claims

The Claims:

1. An internal combustion engine comprising:

a piston constrained for linear sliding in a bore;

a first crank constrained for rotation about a first axis;

a second crank mounted on the first crank remote from the first axis and for rotation about a second axis; and so to have an effective ratio of two thirds, one third or three quarters or half;

a connecting rod mounted on the second crank for the rotation about a third axis and interconnecting the piston and the follower; and

constraining means to constrain the second crank to rotate about the second axis as the first crank rotates about the first axis;

Wherein the first member may be oscillated about the first axis during each cycle.