US3741175A

US3741175A - Variable compression ratio internal combustion engines

Info

Publication number: US3741175A
Application number: US00167300A
Authority: US
Inventors: H Rouger
Original assignee: SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1970-08-03
Filing date: 1971-07-29
Publication date: 1973-06-26
Anticipated expiration: 1990-06-26
Also published as: DE2137596A1; FR2102430A5; GB1345074A; DE2137596B2

Abstract

The internal combustion engine comprises at least one main cylinder in which a main piston driving a drive shaft moves, and a cylinder head over the main cylinder. An auxiliary piston slides in an auxiliary cylinder contrived in the cylinder head and communicating with the main cylinder. An actuating mechanism reciprocates the auxiliary piston at half the rate of the main piston piston reciprocation (four-stroke engine) or at the rate of main piston reciprocation (two-stroke engine). Control or adjusting means act on said actuating mechanism so as to vary auxiliary piston travel. The actuating mechanism is so devised that the offset between main piston and auxiliary piston reciprocations is such that the auxiliary piston reaches its inner dead centre position during the exhaust stroke (four-stroke engine) or during the scavenging stroke (two-stroke engine).

Description

ilnited States Patent [1 1 Rouger 1 VARIABLE COMPRESSION RATIO INTERNAL COMBUSTION ENGINES [75] Inventor: Henri Andre Rouger, Courbevoie,

France Assignee: Societe Nationale DEtude Et De Construction De Moteurs DAviation, Paris, France [22] Filed: July 29, 1971 [21] Appl. No.: 167,300

[30] Foreign Application Priority Data Primary ExaminerLaurence M. Goodridge Assistant ExaminerCort R. Flint Attorney-Larson, Taylor and Hinds [57] ABSTRACT The internal combustion engine comprises at least one main cylinder in which a main piston driving a drive shaft moves, and a cylinder head over the main cylinder. An auxiliary piston slides in an auxiliary cylinder contrived in the cylinder head and communicating with the main cylinder. An actuating mechanism reciprocates the auxiliary piston at half the rate of the main piston piston reciprocation (four-stroke engine) or at the rate of main piston reciprocation (two-stroke engine). Control or adjusting means act on said actuating mechanism so as to vary auxiliary piston travel. The actuating mechanism is so devised that the offset between main piston and auxiliary piston reciprocations is such that the auxiliary piston reaches its inner dead centre position during the exhaust stroke (four-stroke engine) or during the scavenging stroke (two-stroke engine).

11 Claims, 7 Drawing Figures PAIENIH] JUN 26 I875 SHEETIN4 VARIABLE COMPRESSION RATIO INTERNAL COMBUSTION ENGINES The invention relates to variable compression ratio internal combustion engines having one or more main pistons which drive a drive shaft by way of a mechanical system of rods and a crankshaft.

The term compression ratio is intended to denote the ratio between, on the one hand, the sum of the volume swept by a main piston (unit cylinder capacity) and of the dead or unswept volume (when the main piston is in its top dead centre position) and, on the other hand, the dead or unswept volume on its own.

The invention is of use more particularly but not exclusively for supercharged internal combustion engines, since this is the field where the invention will probably be most advantageous.

For mechanical strength considerations of some engine parts, it is of course advisable to have a top limit for the combustion pressure, and so, if all other things are equal, the engine compression ration must be reduced on high-power operation and increased for-partial-power operation or for starting.

Many suggestions have been made to vary an engine compression ratio during engine operation and include suggestions using an adjustable linkage or a two-piece piston or a variable-volume combustion chamber.

There have also been suggestions to provide the engine cylinder head with an auxiliary cylinder which communicates with the main cylinder and in which an auxiliary piston moves. An actuating mechanism cyclically imparts to the auxiliary piston a relative movement between an inner dead centre position (disposed on the same side as the communication between the auxiliary cylinder and the main cylinder) and an outer dead centre position (disposed on the side remote from such communication) in this case the actuating mechanism is subject to control means adapted to vary the travel of the auxiliary piston. The auxiliary piston is reciprocated at half the frequency of main piston reciprocation in the case of a four-stroke engine or at the same frequency as main piston reciprocation in the case of a two-stroke engine.

The known engines of this kind have disadvantages which are mainly the size of the auxiliary piston and of its actuating mechanism the appreciable increase in the total inertia of the moving masses the high forces which the auxiliary piston transmits to its actuating mechanism unsatisfactory burnt gas scavenging which worsens in proportion as engine loading increases, and

unsuitability for high-speed operation.

It is an object of the invention to obviate these disadvantages by reducing the size of the auxiliary piston and of its actuating mechanism only very slightly increasing the total inertia of the moving masses reducing the forces transmitted by the auxiliary piston to its actuating mechanism improving burnt gas scavenging, which improves in proportion as engine loading increases, and

making the system suitable for high-speed operation.

In the engine according to the invention, the actuating mechanism is so devised that the offset between main piston and auxiliary piston reciprocations is such that the auxiliary piston reaches its inner dead centre position during the exhaust stroke (or near the exhaust stroke) in the case of a four-stroke engine and during the scavenging stroke (or near the scavenging stroke) in the case of a two-stroke engine.

The outer dead centre position is therefore reached during or near the end of the compression stroke in the case of both a four-stroke and of a two-stroke cycle. Clearly, therefore, altering auxiliary piston travel by action on the control or adjusting means alters the outer dead centre position, thus varying the engine compression ratio by varying the unswept volume between the main piston, the cylinder head and the auxiliary piston. Also, the offset between main-piston and auxiliary piston reciprocations improves scavenging to an extent which increases in proportion as engine loading increases. Advantageously, and more particularly for a fourstroke engine, the inner dead centre position of the auxiliary piston is substantially fixed and is so disposed that the residual volume between the main piston, the cylinder head and the auxiliary piston is very reduced this feature provides a further increase in scavenging efficiency.

Advantageously, the superficial area of the auxiliary piston is less than half the superficial area of the main piston, and the volume swept by the auxiliary piston is less than 10% of the volume swept by the main piston this feature helps to reduce the size of the auxiliary piston and of its actuating mechanism, to only very slightly increase the total inertia of the moving masses, to reduce the forces transmitted by the auxiliary piston to its actuating mechanism and to make the engine suitable for high-speed operation.

Advantageously, the auxiliary cylinder forms an extension of a turbulence chamber contrived in the cylinder head, the fuel being atomized by an injector in the turbulence chamber, the auxiliary piston forming the turbulencechamber end member and being so disposed that its inner dead centre position is very near the passage connecting the turbulence chamber to the corresponding main cylinder the great advantage of this feature is excellent scabenging of the turbulence chamber, since the gases therein are expelled by the auxiliary piston at each stroke thereof when the main piston is on its exhaust stroke (four-stroke cycle) or when the main cylinder is being scavenged (two-stroke cycle).

The invention can in any case be readily understood from the remaining description given hereinafter and from the accompanying drawings, both of which refer to preferred but, of course, non-limitative embodiments of the invention. In the drawings FIG. 1 is a view in section of the top part of a fourstroke engine according to the invention FIG. 2 is a partial section of the top part of a fourstroke engine according to a variant of the invention FIGS. 3 and 4 are each a diagram relating to the kinetics of an actuating mechanism of the engine shown .in FIG. I

FIG. 5 is a diagram showing the operation of a fourstroke engine according to the invention FIG. 6 is a diagram showing the operation of a twostroke engine according to the invention, and

FIG. 7 is a diagram of an alternative form of the kiand 4.

FIG. 1 shows a four-stroke internal combustion engine having a number of in-line cylinders. Each cylinder is called a main-cylinder and has the reference L A-main piston 2 drives a drive shaft (not shown) and slides in the main cyliner 1, above which is a cylinder head 3. The same has an inlet valve (not shown) and an exhaust valve 4 operated by a rocker 5 co-operating with a cam 6 driven by an overhead camshaft 7.

Also forming part of cylinder head 3 is an auxiliary cylinder 8 which communicates with the main cylinder 1 and in which an auxiliary piston 9 can move the same is cyclically operated by an actuating mechanism 10 which reciprocates the auxiliary piston 9 between an inner dead centre position, on the same side as the communication between the auxiliary cylinder8 and the, main cylinderl, and an outer dead centre position on the side remote from such communication.

Since the engine under consideration is a four-stroke engine, the auxiliary piston 9 is reciprocated at half the rate of main piston reciprocation.

The auxiliary piston actuating mechanism 10 is adapted to vary the travel of the auxiliary piston 9 through the agency of control or adjusting means 11.

The offset between main piston reciprocation and auxiliary piston reciprocation is such that the auxiliary piston 9 reaches its inner dead centre position during the exhaust stroke. Such position can either coincide with the top dead centre position of the main piston 2 I at the end of the exhaust stroke thereof or be slightly offset, from the latter position (FIG. 5).

Preferably, the inner dead centre position is fixed and the outer dead centre position is variable.

In FIG. 1, the reference I denotes the inner dead centre position of the auxiliary piston 9, the reference II denotes the outer dead centre position of the auxiliary piston 9, corresponding to engine operation on maximum compression ratio, and

the reference III denotes the outer dead centre position of the auxiliary piston 9 corresponding to engine operation on minimum compression ratio.

The superficial area of the auxiliary piston 9 is less than 50 percent of the superficial area of the main piston 2, and the volume swept by the auxiliary piston 9 is less than 10 percent of the volume swept by the main piston 2. As an exemplary figure, the volume swept by the auxiliary piston 9 is from 4 to 10 percent of the volume swept by the main piston 2.

FIG. 1 relates to a four-stroke fuel-injection engine comprising a turbulence chamber in which an injector l3 atomizes the fuel and which communicates via a flow orifice 14 with the main cylinder 1. The auxiliary cylinder 8 is therefore arranged as an extension of the turbulence chamber 12, the auxiliary piston 9 forming the end member of turbulence chamber 12. Combining a turbulence chamber 12 in this way with the system comprising the auxiliary cylinder 8 and the auxiliary piston 9 according to the invention is very advantageous since the turbulence chamber 12 is scavenged in ve'ry good conditions as FIG. 1 shows, the auxiliary piston 9 expels the gases from the turbulence chamber 12 at each arrival at its inner dead centre position I i.e., whenever the main piston 2 is making its exhaust stroke.

Referring to FIG. 2, where like reference denote the same elements as in FIG. 1, the auxiliary cylinder 8 of a four-stroke fuel injection engine opens directly into the main cylinder 1, the engine injector 15 being disposed at the bottom of the auxiliary cylinder 8 i.e., near the junction thereof with the main cylinder 1.

Advantageously, the actuating mechanism 10 for the auxiliary piston 9 is linkage driven by the engine camshaft 7, to which end the camshaft 7 has a wrist pin 16 for each auxiliary piston 9 mounted on each wrist pin 16 is a rod 17 connected to a lever 18, one end of which pivots around a spindle I9 and the other end of which is connected to the end of a rod 20 pivoted to the auxiliary piston 9.

To vary the outer dead centre position of the auxiliary piston 9 in the required manner, spindle 19 can be moved between, on the one hand, a position P corresponding to the auxiliary piston outer dead centre position II (engine operation on maximum compression ratio), and on the other hand, a position P, corresponding to the auxiliary piston outer dead centre position Ill (engine operation on minimum compres-' sion ratio).

Advantageously, the spindle 19 can be moved by the pivoting of an arm 21, one end of which bears spindle l9 and the other end of which is rigidly secured to a rotatable shaft 22, the angular position thereof being controllable by the control or adjusting means 11.

FIG. 3 shows the integers which make up the actuating mechanism 10 in the positions corresponding to the auxiliary piston 9 being in its inner dead centre position (position I).

FIG. 4 shows the integers which make up the actuating mechanism 10 in their positions corresponding to the auxiliary piston 9 being in its outer dead centre position, corresponding to engine operation on maximum compression ratio (position II) and in the positions for engine operation on minimum compression ratio (position III).

In FIGS. 3 and 4 like reference figures denote the same elements as in FIG. 1.

FIG. 5 is a graph in which time is plotted along the abscissa and the strokes (to difference scales) of the main piston 2 and auxiliary piston 9 are plotted along the ordinate, the graph being for the operation of a four-stroke engine. Curve L represents main piston movement plotted against time for the inlet stroke A, the compression stroke C, the expansion stroke D and the exhaust stroke E consecutively. Curve M represents auxiliary piston travel during engine operation on maximum compression ratio, and curve N represents auxiliary piston travel for engine operation on minimum compression ratio. The offset between main piston reciprocation and auxiliary piston reciprocation is such that the auxiliary piston 9 reaches its inner dead centre position at a time corresponding to an advance of crankshaft angle before the dead centre position of the main piston 2 at the end of the exhaust stroke. Advantageously, the advanceis between 90 and 0.

The internal combustion engine hereinbefore described is a four-stroke engine, but a similar description could be devised for a two-stroke internal combustion engine, the only difference being that, instead of the auxiliary piston actuating mechanism 10 being embodied by linkage driven by a shaft running at half the drive shaft speed (as is the case with the camshaft 7 of the four-stroke engine), the mechanism 10 would have to be driven by a shaft running at the same speed as the drive shaft. A graph such as the one shown in FIG. 6 would then result on this graph time is plotted along the abscissa and main piston travel and auxiliary piston travel are plotted on different scales along the orginate. The curve L represents main piston travel plotted against time for the expansion stroke D scavenging stroke B and compression stroke C consecutively.

The curve M represents auxiliary piston travel for engine operation on maximum compression ratio, and the curve N represents auxiliary piston travel for engine operation on minimum compression ratio. The offset between main piston reciprocation and auxiliary piston reciprocation is such that the auxiliary piston 9 reaches its inner dead centre position at substantially the same time as the main piston 2 reaches its top dead centre position.

As a variant of the actuating mechanism 10, the same canbe devised as shown in FIG. 7 from linkage driven by the engine camshaft 7, to which end the same has a wrist pin 23 for each auxiliary piston 9 disposed on each wrist pin 23 is a rod 24 which is connected to a lever 25 and guided in a link 26. One end of lever 25 is formed with an elongated aperture 27 engaged by a spindle 28, and the other end of lever 25 is connected to the end of a rod 29 pivoted to the auxiliary piston. To vary the auxiliary piston outer dead centre position in the required manner, spindle 28 can be moved between, on the one hand, a position P corresponding to the auxiliary piston outer dead centre position II (engine operation on maximum compression ratio) and, on the other hand, a position P corresponding to the auxiliary piston outer dead centre position III (engine operation on minimum compression ratio).

- The spindle 28'can be shifted through the agency of the control or adjusting means 11.

The auxiliary piston reaches its inner dead centre position (position I) whatever the position of the spindle 28 between its position? and .its position P The control or adjusting means 11 for varying auxiliary piston movement can be directly controlled by the maximum fuel pressure as measured by a-senser in the crown of the auxiliary piston 9.

Whichever embodiment is used, the end result is a variable compression ratio internal combustion engine whichhas a number of advantages including those summarised in the following Ruggedness and simplicity because of a small auxiliary-piston and a simple, low-inertia and small actuating mechanism therefor Improved scavenging, more particularly of the turbulence chamber, and

Good high-speed operation because of the positive low-inertia actuating mechanism.

I claim: 7

1. In a variable compression ratio four-stroke internal combustion engine comprising: at least one main cylinder in which a main piston slides driving a crank-shaft; a cylinder head covering this main cylinder; an auxiliary cylinder arranged in this cylinder head and in which an auxiliary piston slides; a passage between the auxiliary cylinder and the main cylinder; a control mechanism actuating the auxiliary piston in a reciprocating motion between an inner dead center near the main cylinder and an outer dead center remote from the main cylinder; the improvement wherein the reciprocating motion of the auxiliary piston operates at a rate equal to half the rate of the reciprocating motion of the main piston, the relative offset between the reciprocating motions of the main piston and of the auxiliary piston is such that the inner dead center is reached by the auxiliary piston during or at the end of the exhaust stroke, and adjusting means are provided for varying the stroke of the auxiliary piston such that the inner dead center position is fixed and the variable outer dead center position is a function of the compression ratio.

2. An engine according to claim 1, wherein the inner dead centre position is reached at a time corresponding to an advance of from to 0 crankshaft angle before the top dead centre position of the main piston at the end of the exhaust stroke thereof.

3. In a variable compression ratio two-stroke internal combustion engine comprising: at least one main cylinder driving a crank-shaft; a cylinder head covering this main cylinder; an auxiliary cylinder arranged in this cylinder head and in which an auxiliary piston slides; a passage between the auxiliary cylinder and the main cylinder; a control mechanism actuating the auxiliary piston in a reciprocating motion between an inner dead center near the main cylinder and an outer dead center remote from the main cylinder, the improvement wherein the reciprocating motion of the auxiliary piston operates at a rate equal to the rate of the reciprocating motion of the main piston, the relative offset between the reciprocating motions of the main piston and of the auxiliary piston is such that the inner dead center is reached by the auxiliary piston during the scavenging stroke, and adjusting means are provided for varying the stroke of the auxiliary piston such that the inner dead center position is fixed and the outerdead center position varies as a function of the compression ratio.

4. An engine according to claim 3 wherein the inner dead centre position is reached at a time corresponding to the top dead centre position of the main piston.

5. An engine according to claim 1 wherein the superficial area of the auxiliary piston is less than half the superficial area of the main piston, and the volume swept by the auxiliary piston is less than 10 percent of the volume swept by the main piston.

6. A four-stroke engine according to claim 1 wherein the inner dead centre position of the auxiliary piston is arranged to give a very reduced residual volume between the main piston, cylinder head and auxiliary piston.

7. A four-stroke engine according to claim -1 wherein the auxiliary piston actuating mechanism takes the form of linkage driven by the engine camshaft.

8. An engine according to claim 7 wherein the camshaft has for each auxiliary piston a wrist pin fitted with a rod coupled with a lever, one end of which pivots around a spindle and the other end of which is connected to the end of a rod pivoted to the auxiliary piston, the spindle being movable between two end positions, one corresponding to engine operation at maximum compression ratio and the other corresponding to engine operation at minimum compression ratio.

9. An engine according to claim 8 wherein the spindle is moved by a pivoting arm, the spindle being mounted at one end of such arm, the other end thereof being rigidly secured to a rotatable shaft whose angular position is controlled by the adjusting or control means.

10. An engine according to claim 7 wherein the camshaft has for each auxiliary piston a wrist pin on which the other corresponding to engine operation at minimum compression ratio. v

11. An engine according to claim 10 wherein the spindle is displaced through the agency of the control or adjusting means.

* 8 I. I t

Claims

2. An engine according to claim 1, wherein the inner dead centre position is reached at a time corresponding to an advance of from 90* to 0* crankshaft angle before the top dead centre position of the main piston at the end of the exhaust stroke thereof.

3. In a variable compression ratio two-stroke internal combustion engine comprising: at least one main cylinder driving a crank-shaft; a cylinder head covering this main cylinder; an auxiliary cylinder arranged in this cylinder head and in which an auxiliary piston slides; a passage between the auxiliary cylinder and the main cylinder; a control mechanism actuating the auxiliary piston in a reciprocating motion between an inner dead center near the main cylinder and an outer dead center remote from the main cylinder, the improvement wherein the reciprocating motion of the auxiliary piston operates at a rate equal to the rate of the reciprocating motion of the main piston, the relative offset between the reciprocating motions of the main piston and of the auxiliary piston is such that the inner dead center is reached by the auxiliary piston during the scavenging stroke, and adjusting means are provided for varying the stroke of the auxiliary piston such that the inner dead center position is fixed and the outer dead center position varies as a function of the compression ratio.

7. A four-stroke engine according to claim 1 wherein the auxiliary piston actuating mechanism takes the form of linkage driven by the engine camshaft.

10. An engine according to claim 7 wherein the camshaft has for each auxiliary piston a wrist pin on which a rod coupled with a lever and guided in a link is disposed, one end of the lever being formed with an elongated aperture in which a spindle engages, the other end of the lever being connected to the end of a rod pivoted to the auxiliary piston, the spindle being movable between two end positions, one corresponding to engine operation at maximum compression ratio and the other corresponding to engine operation at minimum compression ratio.