WO1990006426A1

WO1990006426A1 - Positive displacement fluid machines

Info

Publication number: WO1990006426A1
Application number: PCT/GB1989/001431
Authority: WO
Inventors: Michael Richard Lionel Daniel
Original assignee: Collins Motor Corporation Limited
Priority date: 1988-11-29
Filing date: 1989-11-29
Publication date: 1990-06-14
Also published as: AU4741390A; KR900702189A; GB8827835D0

Abstract

A positive displacement fluid machine such as a 2-stroke internal combustion engine has a set of cylinders (2) having their axes disposed radially with respect to the axis of a crankshaft (3) having an eccentric crankpin (4). A drive block (11) is rotatably mounted on the crankpin (4). Pistons (23) are slidable in respective cylinders (2) and each carries a slider (18) which extends transversely of the axes of both the cylinder and the crankshaft and is slidable but captive in a respective guideway (16) in the drive block. The lengths of each slider (18) and of each guideway (16) exceed twice the throw or eccentricity of the crankpin (4).

Description

POSITIVE DISPLACEMENT FLUID MACHINES

This invention relates to positive-displacement fluid machines of the piston and cylinder type, such as internal coaribustion engines and fluid pumps and motors.

According to the present invention, there is provided a positive-displacement fluid machine cαπprising a shaft mounted for rotation about its axis, a drive block mounted for relative rotation about an eccentric portion of the shaft and at least one piston and cylinder assembly having its axis radial to the shaft axis, the drive block having a guideway transverse to both the shaft axis and the cylinder axis, and a slider captively but slidably engaged with the guideway for reciprocating the reciprocatory element of the piston and cylinder assembly, wherein the slider is connected to the said reciprocatory element in such a manner as to prevent tilting of the drive block relative to the reciprocatory element about the eccentric portion and the length of the slider is greater than twice the eccentricity of the eccentric portion.

This arrangement provides a radially coπpact construction.

Advantageously, the πachine has a plurality of piston and cylinder assemblies having their axes angularly spaced around the crankshaft axis and the drive block has a corresponding plurality of guideways, and each reciprocatory element has a slider captively but slidably engaged with a respective guideway.

Preferably, the or each guideway is formed by a passage of effectively constant cross section in the drive block, the slider is a close sliding fit in the guideway passage and can be introduced into the passage from one end thereof, and connecting means extend from the slider to the reciprocatory element through a slot extending between the passage and an external face of the drive block, the slot being too narrow to permit passage therethrough of the slider.

The invention will now be further described by way of example with reference to the accαrtipaiiying drawings, in which:-

Figure 1 is an isometric view with parts cut away of a four cylinder two two stroke spark-ignition radial internal combustion engine;

Figure 2 is a diagrarmiatic cross-section showing the layout of the cylinders, pistons and their driving elements as the engine shown in Figure 1;

Figure 3 is an isometric e∑qploded view of two of the pistons of the engine and their connection to the crankshaft;

Figure 4 is a longitudinal section taken ttirough the axis of the crankshaft and the axis of one of the cylinders;

Figures 5 to 8 show different forms of piston and connecting rod; and

Figure 9 is a view on the line IX-IX of Figure 8.

The engine shown in the drawings has a stationary crank case 1 supporting four cylinders 2A 2B,2C and 2D which have their axes extending radially from the axis of rotation of a crankshaft 3. The crankshaft 3 is a single-threw crankshaft having its single crank pin 4 connected by webs 5 and 6 to journal portions 7 and 8 which are rotatably supported in plain journal bearings 9 and 10 in the crank case 1. The crank case 1 is divided into sections each formed by an alumini^*um alloy casting, the various sections being bolted together.

A generally square drive block 11 is divided along a diagonal plane 12, (Figures 2 and 3), the two halves being secured together by cap screws 13 having their heads located in recesses 14 in the drive block 11. The drive block 11 has a central bore containing a bearing sleeve 15 by means of which it is rotatably mounted on the crank pin 4.

Parallel to each face of the drive block 11 is a guideway 16 in the form of a cylindrical bore open at both ends and also connected to the outer face of the drive block by means of a slot 17.

A cylindrical slider 18 is a close sliding fit in each of the guides 16 and itself is formed with a slot 19 to receive a widened plate-like portion 20 of a connecting rod 21. The portion 20 is secured to the slider 18 by a set of spaced cross pins 22.

Rigidly connected to the other end of each connecting rod 21 is a piston 23 which is slidable in a cylinder liner 24 of the respective cylinder 2, the cylinder liners 24 being secured in the crankcase 1.

With this arrangement, as the crankshaft 3 rotates abouts its axis, the drive block 11 will undergo an orbital movement about the axis of the crankshaft with components of motion relative to each piston both along the axis of that piston and transversel to it. The interconnection between the drive block 11 and the slider 18 -which is connected to that piston will enforce on that piston the ∞mponent of the motion of the drive block (and thus of the crank pin) along the axis of the piston whereas relative sliding motion will take place between the slider 18 and the guideway 16 to accoππiodate that cαπponent of relative movement between the drive block and the piston which is a right angles to the axis of the piston.

In order to prevent undesired tendencies of the drive block 11 to tip or turn about the crankpin 3 with possible jaπming or heavy wear of the mechanism, the size of the drive block 11 and the length of the sliders 18 is chosen so that in all positions of the mechanism portions of the slider 18 are in contact with portions of the guideway in drive block- 11 on both sides of the plane throuφ the axis of rotation of the crankshaft 3 and throu the axis of the piston. This requires the length of the slider 18 to be greater than twice the throw or eccentricity of the crankpin 4 relative to the axis of rotation of the crankshaft 3.

In order to reduce the tipping moment applied to the piston 23 through the connecting rod 21, and also to provide sufficient area of bearing contact between the guideway 16 and the slider 18, the length of each guideway 16 and thus the length of any side of the drive block 11 should also be greater than twice the throw or eccentricity of the crankpin 3.

The pistons 2A and 2C reciprocate with a simple harmonic motion at a constant spacing from each other. Similarly, the pistons 2B and 2D remain at a constant distance frcm each other and reciprocate with a simple harmonic motion which is in quadrature with that of the pistons 2A and 2C. Thus, the effect of the moving masses coπprising the pistons 23 and connecting rods 21 together with that of the orbiting drive block 11 acts on the crankshaft in the sane manner as a single mass concentrated on the axis of the cranlspin and equal to the su of the mass of the drive block 11 and two piston assemblies each consisting of the piston 23, connecting rod 21 and slider 18. This rotating mass can be readily balanced around the axis of rotation of the crankshaft 3 by extensions 25A, 25B of the crankshaft webs 5 and 6 on the opposite side of the crankshaft axis to form counter balance weights to which additional weights 27 can be secured, if required, by screws 28.

As mentioned above, the engine shown in Figures 1 to 4 is a two-stroke engine so that each cylinder fires once per revolution of the crankshaft. Scavenge air is supplied to the cylinders by means of a super-charger 30 having an air inlet 31 and a tangential outlet 32. Air under pressure from the outlet 32 is delivered to air inlet manifolding 33 supplying inlet passages 34 for each cylinder in register with inlet ports 35 formed in the liners 24 in positions to be uncovered by the respective piston 23 as it approaches its innermost or bottom dead centre position, thereby allowing a fresh charge of air to enter the cylinder.

Continued rotation of the crankshaf results in the crank pin 4 driving the piston 23 towards its radially outermost or top dead centre position, During this movement, the piston 23 first closes off the inlet ports 35 and then compresses the now-trapped charge of air. A charge of fuel is delivered into the cylinder by a fuel injector 36 (Figure 1) and the resulting compressed fuel air mixture is fired at a predetermined instant before the top dead centre postion is reached by means of a conventional spark plug arrangeπent 37.

After the top dead centre position is reached, the burning mixture drives the piston 23 radially inwardly towards the crankshaft axis until, around the position where the piston begins to uncover the ports 35, the burnt mixture is allowed to escape to an exhaust system by opening of a pair of exhaust valves 38 operated by cam shafts 39. As can be seen in Figure 1, exhaust valves 38 operate in the side valve configuration. Each valve 38 is normally held on its seat by a valve spring 40 but is opened by an associated cam 41 on the cam shaft 39. As can be seen in Figure 1, there are only two cam shafts 39 each serving two cylinders and having four cams thereon two, such as the cams 41C, engaging cam followers 42C for the cylinder 2C and the other two 42D for the cylinder 2D. Exhaust gas released by the exhaust valves passes to the exhaust system throuφ exhaust ports 43.

As can be seen with reference to Figure 3, any two guideways 16 which are at right angles to each other must be spaced apart along the crankshaft axis. As it is preferable that the axis of each piston should intersect the axis of its slider, the common axis of the cylinders 2B and 2D is spaced from the common axis of the two cylinders 2A and 2C in the direction of the crankshaft axis and this spacing is reflected in the spacing between adjacent cams 41C and 41D for example.

The two cam shafts 39 are driven by the crankshaft at the same speed as the crankshaft by means of a first gear 45 (Figure 4) keyed to the crankshaft, an idler gear 46 and a cam shaft gear 47 on the cam shaft 39.

Also meshing with the first crankshaft gear 45 is a further gear 48 driving an oil pump (not shown) which draws oil from a sump 49 in the base of the housing 1 and delivers it through a filter 50 to an oil gallery 51 formed in the crankcase and arranged to supply oil under pressure to feed passages 52 in the crankshaft leading from an inlet in the end face of the crankshaft to supply drillings feeding the journal bearings 9,10 and 15 and thence also supplying feed holes 53 in the drive block 11 leading into the guideways 16. The pistons are lubricated by oil mist formed by oil escaping from the various bearings.

The super charger 30 is driven from a second crankshaft gear wheel 54 and appropriate step-up gearing (not shown) which may be epicyclic. In order to prevent leakage of air into the crankcase when the rings of the pistons 23 are radially beyond the inlet ports 35, a rotatary distibutor valve (not shown) may be driven at crankshaft speed from the gearing described above and control the supply of air to the inlet ports in such a manner that only that cylinder whose piston is at any time approaching the innermost or bottom dead centre position is supplied with air.

A coolant circulating pump 56 is driven by means of a further gear wheel 57 meshing with one of the idler gears 46 to circulate coolant through water spaces W and an external radiator (not shown) and an alternator 58 is belt-driven from a pulley 59 conveniently attached to an extension of one of the cam shafts 39.

As can be seen in Figures 3 and 4, each piston 23 has a cut out in its skirt on one side to clear the adjacent balance weight 24.

The driving connection between crankshaft and pistons described above may of course be used in other types of machines such as pumps and four-stroke internal combustion engines. In the latter case, it is preferable to have an odd number of cylinders, for example three, with their axes at angular intervals of 120° around the crankshaft axis and of a -triangular drive block. Alternatively, the axes of the three cylinders may be arranged in an inverted T-shaped formation with two of the pistons opposed to each other and the third having its axis at right angles to the first two. In such a case, to ensure mechanical balance, it would be necessary to double the mass of the third piston and its connecting rod in order to enable the engine to be balanced by means of counter weights on the crankshaft.

In the modified construction shown in Figure 5, the connecting rods 121 are lengthened and formed with stiffening ribs 125 whic increase in height from the portion 120 within the guideway up to end flanges 126 which are secured by cap screws 128 to an annular boss 129 formed integrally on the inner face of the crown of the piston 123.

Figure 6 shows an alternative form of piston which may be used in the engine shown in Figures 1 to 4. The crown 201 of the piston is formed by a ceramic insert in the form of a disc having integrally formed therewith, or fastened thereto, a supporting column 202. The remainder of the piston is formed by an alumirii-um alloy casting or forging 203 in the form of a hollow cone which, adjacent its apex is secured to the connecting rod 221 by cap screws 204 and forms in the interior of its narrow end an abutment surface 205 for the column or strut 202. An integral cyl ndrical flange 206 is formsd with circular grooves 207 to receive piston rings.

In the arrangement shown in Figure 7, the connecting rod 321 is again fixed directly to a central boss 301 formed integrally with the piston 302. The skirt of the piston 302 has arcuate cut out portions to clear the counterbalance portions 324 and 325 of the crankshaft while still presenting a skirt portion 306 for transferring thrust reactions from the drive block 311. This arrangement permits the counter balance weight portions 324 and 325 to be closer together than in the case of Figures 1 to 4 where the inner side faces of the counterbalance weight portions 24 and 25 are cut away to provide clearance for the more extended skirts of the pistons requiring the additional weights 27 which thus extend the clearance space required within the crankcase to accommodate the crankshaft and in turn somewhat increase the length of the engine.

Figures 8 and 9 shown one arrangement whereby the axes of all four cylinders may lie in the same plane at right angles to the crankshaft axis. The guideways 416 are not parallel to this plane but are angled as can be seen in Figure 9 so that for any guideway 416 the two adjacent guideways lie on opposite sides of this guideway near its two ends. Thus, as the slider 418 moves relatively to the guide block 411 up and down its guideway 416, the slider 418 undergoes motion along the axis of the crankshaft since the drive block 411 is prevented from carrying out such axial movement. In order to accommodate this axial movement of the connecting rod 421 attached to this slider 418, a connecting rod is not rigidly attached to the piston 423. Instead, a substantial gudgeon pin 401 is located in the piston 423 by circlips 402 in grooves in a transverse bore in the piston and this bore and thus the gudgeon pin are oriented to have their axes perpendicular to the guideway 416. The end of the connecting rod 421 which is remote from the slider 418 is enlarged and has a transverse bore containing a linear bearing 403 engaged on the exterior of the gudgeon pin 401. This linear bearing may be of the kind having rollers with their axes transverse to the axis of the gudgeon pin 401.

As shown in Figures 8 and 9 the slider 418 and guideways 416 are of rectangular cross section. They could also be of circular cross section. In each of the arrangements shown in Figures 1 to 4 and 5 to 7, the guideways and sliders could also be of rectangular cross section, for example, square cross section.

In a modification (not illustrated) which may be applied to any of the embodiments described above, the sliders have internal guide channels (similar to the guideways in the drive block in the illustrated emboα^*iments) and the guideways are formed by external profiles on the drive block, these profiles being slidable but captive in the guide channels in the sliders which are attacked by the connecting rods or* webs to the pistons.

Claims

1. A positive-displacement fluid machine comprising a shaft mounted for rotation about its axis, a drive block mounted for relative rotation about an eccentric portion of the shaft and at least one piston and cylinder assembly having its axis radial to the shaft axis, the drive block having a guideway transverse to both the shaft axis and the cylinder axis, and a slider captively but slidably engaged with the guideway for reciprocating the reciprocatory element of the piston and cylinder assembly, wherein the slider is connected to the said reciprocatory element in such a manner as to prevent tilting of the drive block relative to the reciprocatory element about the eccentric portion and the length of the slider is greater than twice the eccentricity of the eccentric portion.

2. A machine according to claim 1, having a plurality of piston and cylinder assemblies having their axes angularly spaced around the crankshaft axis and the drive block has a corresponding plurality of guideways, and each reciprocatory element has a slider captively but slidably engaged with a respective guideway.

3. A machine according to claim 1 or 2, wherein the or each guideway is formed by a passage of effectively constant cross section in the drive block, the slider is a close sliding fit in the guideway passage and can be introduced into the passage from one end thereof, and connecting means extend from the slider to the reciprocatory element throuφ a slot extending between the passage and an external face of the drive block, the slot being too narrow to permit passage therethrough of the slider.

4. A machine according to any of claims 1 to 3, in the form of a two-stroke internal combustion engine, the or each cylinder having an inlet port for air from an air supply means driven by the engine or the exhaust thereof, and an exhaust valve.

5. A machine according to any of claims 1 to 3, in the form of a four-stroke engine.

6. A machine according to any of claims 5, having three cylinders two of which are opposed on opposite sides of the shaft axis and the third has its axis at right angles to the axes of the other two, the mass of the third reciprocatory element is twice that of the other two and the crankshaft carries counterbalance mass means.