GB2103751A

GB2103751A - Adjustable throw crank linkage for piston and cylinder internal combustion engine

Info

Publication number: GB2103751A
Application number: GB08110451A
Authority: GB
Inventors: Zbigniew Kowszun
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-04-03
Filing date: 1981-04-03
Publication date: 1983-02-23

Abstract

An internal combustion engine having at least one cylinder in which a piston reciprocates to turn a crankshaft has means operable to vary the length of the reciprocating stroke so that the engine can be operated over most loads without throttling. In one embodiment (Fig. 1) the connecting rod EI is in two parts, one part IG being pivoted to a curved rocking link GD and the other part EF being movable at end F along the curved rocking link by control means ABC which control engine operation. In a variation (Figs 2 and 3), the action of the control means ABC is modulated by a cam so that the induction stroke is shorter than the expansion stroke giving improved efficiency. In another embodiment (Fig. 11), the connecting rod acts upon a swash plate which is axially movable relative to the crankshaft and of variable tilt so as to provide variable strokes and variable compression and expansion ratios. <IMAGE>

Description

SPECIFICATION Piston and cylinder internal combustion engine The present invention relates to an internal combustion engine of the piston and cylinder type.

A conventional piston and cylinder i.c. engine operates over a fixed working volume and load variations are accommodated by varying the inlet manifold pressure by means of a throttle valve in the case of a gasoline engine or by varying the quantity of fuel provided during the operation of the engine in the case of a compression-ignition engine. In both cases, the efficiency of fuel utilization is best at full load but becomes progressively lower as the load is reduced, particularly in the case of the gasoline engine. Some recent attempts to reduce the shortcomings of the gasoline engine have involved inactivating 2 or 4 cylinders of an 8-cylinder engine at part-load thereby giving a stepwise reduction in swept volume.

The present invention provides an internal combustion engine comprising at least one cylinder having a combustion chamber wherein fuel is at least partially burned, a piston received in the cylnder and connected by connecting means to a rotatable shaft in such a manner that reciprocating motion of the piston in the cylinder causes rotary motion of the shaft, the connecting means comprising means operable to vary the length of the reciprocating stroke of the piston in the cylinder.

The engine may be so arranged and/or constructed that the length of the reciprocating stroke is different for different engine loads, and may further be such that for a given engine load, the stroke may vary for at least two parts of the engine cycle. An engine according to the invention works at substantially constant intake manifold pressure and substantially constant air:fuel ratio, and thereby attains higher fuel use efficiencies than previously known engines.

The invention is now further described with reference to some non-limitative examples thereof and with reference to the accompanying schematic diagrammatic drawings.

With reference to Fig. 1: a conventional piston/cylinder (1) is connected to a conventinoal crankshaft (2) via a split connecting rod El. The conrod is pivoted conventionally to the piston at E and slides freely at F over a curved rocking link DG. The rocking link is pivoted to a mounting on the cylinder block at D and to the continuation of the conrod (GI) at G. A stroke-controlling link ABC is pivoted to the conrod at A and is optionally pivoted to a continuation of itself at B so that the externally adjusted position of C needs to vary linearly only.

in operation, the stroke of piston (and therefore the swept volume) depends on the position of the control link AC: C in its extreme left position (position actually shown in Fig. 1) corresponds to the maximum stroke. As point C moves to the right the base F of the conrod EF moves towards D and, since movement of G is restricted by the crankshaft geometry, the movement of F is decreased, reaching a minimum with C in its extreme right position. The compression ratio can be varied as the swept volume is changed by moving the support pivot D:D can be either (a) fixed so that the compression ratio changes in a pre-determined fashion as the swept volume is changed or (b) the position of D can be adjusted while the engine is running:the movement of D towards E increases the compression ratio.

In a modification of the engine incorporating the principles described with reference to Fig. 1 , the expansion ratio is arranged to be increased at part load, as will be appreciated from Figure 2.

With reference to Figure 2 the length of stroke of the piston (and therefore the swept volume) depends on the position of the control link C'C and also on the degree of rotation of the cam H which rotates at half the engine speed. The position actually shown corresponds to a part load operation at the end of compression stroke. As the combustion and expansion commences, with C'C fixed, the connecting link C'B begins to move towards the left because the follower J follows the cut-away on the cam H. As the end of link C'B moves from B towards B' the other end of control link AB moves towards A' causing the split conrod AF to adopt a longer stroke position AF'. The extreme movement of point F is limited by a stop K so that the greatest benefit would be obtained at part load.The cam H is cut away on one side only so that the movement of F to F' occurs during the expansion stroke only and F' to F during exhaust stroke. During the induction and compression strokes the cam follower J bears against the semicircular face of the cam H, and F remains fixed giving the desired reduction in stroke.

Mechanical limitations (clearance volume, bearing loads, etc.) will tend to limit the maximum stroke reduction to the range of 3:1 to 4:1, but expansion ratios of the order of 30:1 for a gasoline engine and up to 100:1 for large stationary diesels should be possible giving improvements in economy of the order of 30% above that for operation of previously known i.c. engines. Such an improvement will raise the overall efficiency of large diesels from the present maximum of about 42% to 58-60%-i.e., equal to or better than combined cycle efficiency.

In the engine incorporating the principles described with reference to Figure 2, the movement of the base end F of the connecting rod EF along rocking link DG at the beginning of the expansion stroke is limited by a stop at G, which may set up a high deceleration load in the conrod. In order to avoid the necessity to strengthen the con rod and the stop to accommodate a high deceleration load, the cam H may have a profile which varies in the axial direction, and the connecting link C'B and the cam H may be relatively axially moveable so that the link C'B follows a profile which controls the extent of movement of the end F of the conrod EF towards the stop at G.

This principle is illustrated with reference to Figures 3,4 and 5 wherein Figure 5 is a view of the cam H in the axial direction and Figure 4 is a radial cross-section through the cam of Figure 5 showing the axially-varying profile.

Referring to Figures 3, 4 and 5, the cam is rotatably mounted so as to be axially moveable, the axial movement being determined by the movement of the control rod C (e.g. by means of a known collar and fork arrangement). The axial profile of the cam, shown approximately in Figure 4, has a large cut-away for light load operation (C in forward position, F starting at the right hand end) and a progressively smaller cut-away as C moves to the right. At part load, the sequence of operation would be:

induction: short stroke) compression: short stroke) e.g. at compression ratio (C.R.) 8:1 work: long stroke) t C.R. of 30:1 exhaust: long stroke) e.g. a At full power output, a long stroke is utilised for all strokes (e.g. at 8:1 C.R.) and the engine operates in a manner which is equivalent to conventional engine operation.

Since the control cam H is working at half the engine speed, its camshaft can be used for controlling the valve train with the additional benefit of being able to vary the valve timing and length of valve stroke as the camshaft is moved longitudinally; this is illustrated schematically in Figures 6 and 7 in which Fig. 6 depicts a valve V controlled by a rocking link L which follows the profile of a valve cam on the axially-moveable crankshaft, and Figure 7 is a radial sectional view through the valve cam in the plane of A-A of Figure 6 showing the follower of the rocking link L at an intermediate position between the axial extremes of the valve cam.

It will be apparent, by reference to Figure 3, that the position of the fixed pivots and the shape of the rocking link SG determine the clearance volume above the piston and hence the compression ratio, which can be made constant, or be increased or decreased, as F is moved along GS. The position of S may be adjustable if the desired engine characteristics so require.

Although the invention as described with reference to Figures 1 to 7 provides an engine in which the (or each) cylinder is more or less radially outwards of the axis of the crankshaft, the invention is not limited to this type of arrangement. For example, the invention comprehends other relative dispositions of cylinder and the crankshaft's axis, such as, e.g. an arrangement wherein the cylinder(s) may be more or less alongside the crankshaft. This latter type of arrangement is very compact and rigid, and moreover provides advantages from the point of view of driving the camshaft and other ancillaries.

Figures 8 and 9 are PV indicator diagrams respectively illustrating the idealized cycle of a known, conventional gasoline engine at full load (Figure 8a) and part load (Figure 8b) and an engine according to the present invention at full load (Figure 9a) and part load (Figure 9b).

On the four indicator diagrams, all the cycle sequences start at point 0, and: 1-2 is the induction stroke; 2-3 is the compression stroke; 3--4 is the combustion pressure rise; 4-5 is the expansion (working) stroke; and 6-7 is the exhaust stroke, ending at 0.

Comparisons of the two engine cycles in Figures 8 and 9 show that at full load (Figures 8(a) and 9(a)), the conventional 4-stroke cycle and the proposed cycle are substantially the same except that with the proposed cycle it is possible to expand all the way to atmospheric pressure (5' in Figure 9(a)) with a marginal gain of efficiency which tends to offset any losses due to the more complicated linkages. At part load, however, the conventional engine inspires air past a partly closed throttle reducing the mixture pressure to well below atmospheric pressure but needs to exhaust at or marginally above atmospheric pressure: thus area 7-1-2-6 in Figure 8(b) represents a net energy debit which needs to be supplied during the working stroke.No such debit appears in Figure 9(b) apart from a small pumping loss defined by the area between BDC(1) and BDC(2) and the isobars 6-7 and the extension of 1-2 where it intersects the BDC's. Moreover, by expanding the hot gas well past the compression stroke (ideally all the way to atmospheric pressure), the part load proposed cycle is more efficient than full load cycle as shown in Figure 10. A motor-car engine spends most of its working life at part load and the advantage of the cycles and engines according to the invention is clearly apparent.

Reference is now made to Figure 11 which is a schematic illustration of another engine according to the invention which provides a continuously (i.e. progressively or steplessly) variable swept volume operation of a single of multi-cylinder engine as required with no intake throttling throughout the engine load range (although it is contemplated that intake throttling may be practiced for idling operation).

Figure 11 shows, schematically, a two cylinder engine with a swash-plate splined for axial movement and pivoted at A on to a shaft (1). Two positions of swash plate (SP) are shown: the minimum stroke and maximum stroke positions. In the minimum stroke position (BB) the left hand piston (2) is at the top dead centre position while the right hand piston (3) is at the bottom dead centre position. As the SP rotates, points BB will move until at half a revolution they will be at CC when the left hand piston will be at its bottom dead centre (indicated by a dotted line (4) while the right hand piston will be at the top dead centre (indicated by dotted line (5)). Further rotation of the swash plate will complete the cycle.Moving the splined centre of the SP to A' and tilting the plate will alter the top dead centre position of the left hand piston to (6) and of right hand piston to (7) when the plate is in position DD and to positions (9) and (8), respectively, when the swash plate rotates to the position EE.

Pressure in the cylinder transmitted via a respective connecting-rod to the sloping side of the swash plate causes the rotation as shown in Figure 12. Valves, spark plugs, etc, may be conventional, as may also be the carburettor (except that the throttle would not be used, except possibly at idle); these latter items are not shown.

One arrangement of the SP tilting mechanism is shown schematically in section in Figure 13: two concentric collars are splined for axial movement on to each other and onto the shaft (1) so that they are free to move axially but rotate with the shaft. The SP is pivoted to collars (2) and (4) and a slot in its centre portion allows free movement. On the opposite side, the SP is pivoted to the collar (3) by a pin at (5). Controllers (6) and (7) alter the position and angle of the SP: moving (6) and (7) together moves the SP up or down along the shaft while moving (6) relative to (7) alters the tilt of the plate. (6) and (7) are in sliding contact with the SP so that both tilt and position can be adjusted while the SP and the collars are rotating. Restraining bearings and activators for (6) and (7) are not shown since they may be conventional.

It is to be understood that a feature of combination of features referred to in connection with one example or form of the invention may be employed, if feasible, in another example or form of the invention without departing from the invention

Claims

1. An internal combustion engine comprising at least one cylinder having a combustion chamber wherein fuel is at least partially burned, a piston received in the cylinder and connected by connecting means to a rotatable shaft in such a manner that reciprocating motion of the piston in the cylinder causes rotary motion of the shaft, the connecting means comprising means operable to vary the length of the reciprocating stroke of the piston in the cylinder.

2. An engine as in claim 1 in which the connecting means comprises means operable to vary the effective length of the connecting means for varying the length of the reciprocating stroke.

3. An engine as in claim 1 or claim 2 in which the shaft comprises a crank having a crankpin, there being a first connecting rod which, at one end thereof, rotatable engages the crankpin and at the other end thereof is pivotally connected to a first part of a rocking link which is itself pivotally connected, at a second part thereof, to a part of the engine which is permanently or adjustably fixed relative to the cylinder, a second connecting rod pivotally connected at one end to the piston and connected at the other end to the rocking link between the said first and second parts thereof, the connection between the second connecting rod and the rocking link being such that the said other end of the second connecting rod can be caused to move along the rocking link between the first and second parts thereof, and control means for causing the said other end of the second connecting rod to be located at a desired location along the rocking link.

4. An engine as in claim 3 in which the rocking link is curved to present a concave face towards the said one end of the second connecting rod.

5. An engine as in claim 4 in which the rocking link is curved about a point or locus outwards of the pivotal centre of the said one end of the second connecting rod and the said other end of the second connecting rod is connected thereto by a non-pivotable slidable connection.

6. An engine as in any one of claims 3 to 5 in which the control means comprises a linkage for moving the said other end of the second connecting rod along the rocking link.

7. An engine as in any one of claims 3 to 6 comprising a rotatable cam which is interconnected with the shaft in such a manner that it rotates at a predetermined ratio of the shaft speed, the cam acting directly or indirectly to vary the position of connection between the second connecting rod and the rocking link.

8. An engine as in claim 7 in which the cam has a profile such that the compression stroke of the piston is shorter than the expansion stroke.

9. An engine as in claim 7 or claim 8 in which a follower arm is pivoted at one end to the control means and pivoted at the other end to a control link which is connected for causing movement of the said other end of the second connecting rod along the rocking link, the rotatable cam determining the position of the follower arm and the control link.

10. An engine as in any one of claims 7 to 9 in which the interconnection between the cam and the shaft is such that the cam rotates at half the speed of the shaft.

1 An engine as in any one of claims 7 to 10 in which the cam has a profile which comprises a first part which is arcuate about the centre of rotation of the cam and a second part which is arcuate, at least in part, about an axis which is offset from the said centre of rotation of the cam so that the centre of rotation is between the said axis and the second part of the profile, the second part of the profile having a greater radius of curvature than the first part of the profile.

12. An engine as in claim 11 in which the second part of the cam profile has a radius of curvature which is relatively small in one radial plane and relatively large in another radial plane and which increases progressively when passing from said one radial plane to the other radial plane, and wherein the construction and/or arrangement of the cam and/or follower arm is or are such that the relative positions of the cam and/or follower arm can be changed so that the follower arm will move in accordance with a desired radius of curvature of the second part of the cam profile.

13. An engine as in claim 12 in which the cam is mounted for axial movement to vary the radius of curvature of the second part of the cam profile to determine the motion of the follower arm.

14. An engine as in claim 13 in which the or each cylinder is provided with at least one valve which opens and closes in accordance with the rotary motion of a valve cam, and wherein the valve cam is on a common camshaft with the follower arm's cam so that axial movement of the latter causes axial movement of the valve cam, and wherein the maximum radial eccentricity of the valve cam's profile increases progressively from one radial plane thereof to another radial plane whereby the maximum valve opening is determined by the axial position of the camshaft, and wherein the construction and/or arrangement of the valve cam and the follower arm's cam on the camshaft is such that when the second part of the follower arm's cam profile presents a relatively large radius of curvature to determine the position of the follower arm, the valve cam provides a relatively small maximum eccentricity to determine the opening of the valve, and when the second part of the follower arm's camshaft presents a relatively small radius of curvature to determine the position of the follower arm, the valve cam provides a relatively large maximum eccentricity to determine the opening of the valve.

1 5. An engine as in any one of claims 12 to 14 in which relative axial movement of the follower arm and the follower arm's cam is regulated directly or indirectly by said control means.

1 6. An engine as in claim 1 or claim 2 comprising at least one or two cylinders disposed with their axes substantially parallel to, and substantially symmetrically about, the axis of the shaft, respective connecting rods each connected at one end to a piston and the other ends of the connecting rods being operatively associated with a member which engages the shaft in a rotary sense, the member being pivotally connected to the shaft for rotary engagement therewith in such a way that the member can be pivotted over a range of angles relative to the axis of the shaft so as to vary the length of the stroke of each piston, and control means operable to cause the member to be pivotted relative to the shaft's axis at a desired angle to vary the length of the stroke of the pistons to a desired extent.

1 7. An engine as in claim 1 6 in which the member is rotatably engaged with the shaft but is axially movable along the shaft, and means operable for moving the member axially along the shaft to vary the compression and expansion ratios of gas in the cylinders.

1 8. An internal combustion engine substantially as hereinbefore described.

19. An internal combustion engine substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.