GB2406614A

GB2406614A - Variable compression ratio i.c. engine

Info

Publication number: GB2406614A
Application number: GB0323006A
Authority: GB
Inventors: Rik Osmond Alewijnse; James William Griffith Turner; John Westwood Moore
Original assignee: Lotus Cars Ltd
Current assignee: Lotus Cars Ltd
Priority date: 2003-10-01
Filing date: 2003-10-01
Publication date: 2005-04-06
Anticipated expiration: 2023-10-01
Also published as: GB2406614B; GB0323006D0

Abstract

The cylinder block 31,41 is movably mounted relative to the crankcase 32,42 in such a way that any relative movement includes movement of the cylinder block at least partly perpendicularly to the cylinder axis thus varying an offset distance between the cylinder axis and the crank axis. The movement may be purely laterally eg via sliding joints, fig.4. Alternatively, the sliding joints may be inclined or a cam track may be used to cause movement with both lateral and axial components. In a further modification, fig.6, the mounting may comprise a number of links 47,48 that form, with the cylinder block 41 and the crankcase 42, a four-bar chain mechanism. An actuator, eg hydraulic, pneumatic or electrical, may act on the cylinder block directly or via a linkage and may be controlled by an open loop or a closed loop system. The cam shaft may be driven via a swinging idler gear (61, fig.7 or 71, fig.8) to accommodate the relative movement between the cylinder block and the crankcase.

Description

INTERNAL COMBUSTION ENGINE WITH A VARIABLE COMPRESSION RATIO

This present invention relates to an internal combustion engine with a variable compression ratio.

It is well known that it is desirable for an internal combustion engine to have a variable compression ratio.

This is particularly the case for a forced induction engine, i.e. a supercharged or a turbocharged engine. A number of different mechanisms have previously been proposed to facilitate this. The applicant is aware of seven basic types of mechanism, which will now be briefly described with reference to the enclosed schematic drawings, Figures la to lg: 1. as shown in Figure la, a piston can be provided with a variable length, e.g. using hydraulics; 2. a piston can be attached to its connecting rod via an eccentric mounting as illustrated in Figure lb; 3. a connecting rod connecting a piston with a crankshaft can itself have a joint with the crankshaft which includes an eccentric pin as illustrated in Figure lc; 4. a non-standard linkage for connecting the piston with the crankshaft can be provided with a geometry which is variable as illustrated in Figure Id; 5. a cylinder head of the engine can be made movable along the cylinder axis as illustrated in Figure le; 6. the bearings mounting the crankshaft in the engine can form an eccentric mounting for the crankshaft as illustrated in Figure If; and 7. the cylinder can be provided with a side chamber of variable volume as illustrated in Figure lg.

All of the mechanisms proposed have certain advantages and disadvantages. The disadvantages of the mechanisms proposed to date have been such that they have not been widely taken up in the internal combustion engines found in modern-day automobiles.

The present invention provides in a first aspect an internal combustion engine comprising: at least one piston reciprocable along a cylinder axis of a cylinder in a cylinder block; and a crankshaft rotatable about a crank axis and rotatably mounted in a crank case; wherein: the cylinder block is movable relative to the crankcase and actuator means is provided to occasion relative motion therebetween; characterized in that the cylinder block is mounted in the engine by mounting means which ensure that all movement of the cylinder block relative to the crankcase comprises movement of the cylinder block at least partly perpendicular to the cylinder axis whereby all movement of the cylinder block varies an offset distance between the cylinder axis and the crank axis.

The present invention provides in a second aspect an internal combustion engine comprising: at least one piston reciprocable along a cylinder axis of a cylinder in a cylinder block; and a crankshaft rotatable about a crank axis and rotatably mounted in a crank case; wherein: the crank case is movable relative to the cylinder block and actuator means is provided to occasion relative motion therebetween; characterized in that the crank case is mounted in the engine by mounting means which ensure that all movement of the crank case relative to the cylinder block comprises movement of the crank case at least partly perpendicular to the cylinder axis whereby all movement of the crank case varies an offset distance between the cylinder axis and the crank axis.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figures la to lg illustrate prior art mechanisms;

Figure 2 is a schematic drawing illustrating the principle of the present invention; Figure 3 is a graphical representation of the effects of the present invention; Figure 4 is an illustration of a first embodiment of internal combustion engine according to the present invention; Figure 5 is a view of part of the engine of Figure 4; Figure 6 is a view of a second embodiment of internal combustion engine according to the present invention; Figure 7 shows a first example of how a camshaft and a crankshaft can be connected together in an engine according to the present invention; and Figure 8 shows a second example of how a cam shaft and a crankshaft can be connected together in an engine according to the present invention.

Turning first to Figure 2, this figure illustrates the principle of the present invention. It is the principle of the present invention to provide a cylinder block 17 which can be moved laterally relative to a crankshaft 10 in order to provide a variable offset between a central axis of the cylinder 16 (or axes of cylinders including 16)in the cylinder block 17 and a crank axis of the crankshaft 10.

In Figure 2 it can be seen that the crankshaft 10 has a crank axis 11. The crankshaft has throws, e.g. 12, which are connected by connecting rods, e.g. 13 to pistons of the engine, e.g. 14. It can be seen in Figure 2 that the piston 14 is connected to the connecting rod 13 at a point of connection lying on the central axis 15 (or with a small offset, typically 0.5 - 1.5 mm) of a cylinder 16 in which the piston 14 reciprocates. It can be seen that there is a lateral offset between the cylinder axis 15 and the crank axis 11. The cylinder block 17 in which the cylinder 16 is defined is arranged to be movable laterally (in a manner described later) so that can be varied between O and 40 45mm.

As the lateral offset is increased, there are three principle beneficial effects: 1. The compression ratio in each cylinder, e.g.16, is reduced. This results from the fact that there is an increased clearance distance between the end of the cylinder 16 and the top of the piston 14 at the top dead centre position of the piston 14 in the cylinder 16.

2. The volume swept by the piston 14 in each reciprocation IS Increased.

3. By moving the cylinder head 17 to the right of its position in Figure 2 (in which the crankshaft rotates clockwise), the expansion stroke angle is increased while the compression stroke angle is decreased. In other words, - 5 the expansion stroke of the engine becomes longer in duration in terms of degrees of crankshaft rotation, whilst the compression stroke becomes shorter in terms of degrees of crankshaft rotation. This is desirable.

The graph of Figure 3 shows how the compression ratio, the swept volume, the length of the expansion stroke and the length of the compression stroke vary with changes in the crank offset b. The example illustrated is with a cylinder bore of 86mm, a crankshaft throw of 43mm and a connecting rod length of 129mm. The four-cylinder engine of this particular configuration will have a swept volume of 1996cm3 and a compression ratio of 12:1 for part load operation (zero crank offset). In the graph the line 20 illustrates variation in compression ratio with variation in 6, the line 21 illustrates the variation in swept volume with variation in the offset 6, the line 22 shows variation in length of the expansion stroke (in terms of degrees of crankshaft rotation) and the line 23 shows the variation in length of the compression stroke (again in terms of degrees of crankshaft rotation). At full load with the crankshaft offset according to the invention, the compression ratio would typically be reduced to 8:1 and the swept volume would be increased to 2332cm3 Figure 4 shows schematically an internal combustion engine arranged to provide variable lateral offset as described above. The engine is provided with a cylinder block 31 arranged to slide relative to a crank case 32 in which is rotatably mounted a crankshaft 33 for rotation about a fixed crank axis. The cylinder block 31 and the crank case 32 are connected via a plurality of dovetail 6 joints, one of which is illustrated in Figure 5. The crank case 32 is provided with a male member 36 slidable in a matching socket in the cylinder block 31 (the reverse arrangement is also suitable). It is envisaged that, for instance, a pair of sliding joints will be provided one at each end of the cylinder block, or alternatively a sliding joint will be provided between each cylinder. The dovetail sliding joints will be similar to those commonly employed in a machine tool slide. The dovetail sliding joints restrain the cylinder block 31 to move in a direction perpendicular to the cylinder axis. The dovetail sliding joints prevent separation between the cylinder block 31 and the crank case 32 which might otherwise be caused by the compression and combustion in the cylinder.

The cylinder block 31 will be moved relative to the crank case 32 by a suitable actuator. This could be a hydraulic actuator, a pneumatic actuator, an electrical actuator or any other suitable actuator. The actuator may act directly on the cylinder block or via a linkage. The actuator can be controlled by an open loop control system and be slidable between two fixed points. Alternatively, a position sensor could be used to sense the position of the cylinder block relative to the crank case and thus permit closed loop control of the movement. This would allow the cylinder block to moved to any position between the two fixed end stops.

In the example illustrated above, the movement of the cylinder block 31 with respect to the crankshaft 33 is purely lateral. However, it is possible that the lateral motion could be combined with a previously known way to vary - 7 cylinder compression ratio, namely the moving of the cylinder block along the cylinder axis. For instance, this could be achieved by constructing the sliding track of embodiments 4 and 5 to be inclined 1 - 45' relative to a plane perpendicular to the cylinder axis so that the sliding motion of the cylinder block 31 results in movement in a direction which has a component lateral to the cylinder axis and a component parallel to the cylinder axis.

Alternatively, one of the cylinder block 31 and the crank case 32 could be provided with a cam track and the other of the cylinder block 31 and the crank case 32 provided with a cam movable in the cam track so that when the cylinder block 31 is moved laterally relative to the cylinder axis 32 then the cam track gives rise also to movement of the cylinder block parallel to the cylinder axis.

In Figure 6 there is illustrated a further way in which the cylinder block can be moved relative to a crank case in a manner with motion of the cylinder block in a direction with a component parallel to the cylinder axis of the cylinders and also a component perpendicular to the cylinder axis of the cylinders is shown in Figure 6. In Figure 6 connecting rods 47 and 48 connect the cylinder block 41 to the crank case 42 so that the links 47, 48, the crank case 42 and the cylinder 41 form a well-known four-bar chain mechanism. This mechanism permits movement of a cylinder block axially along the axes of the cylinders as well as perpendicularly to the cylinder axes, so adding to the variable compression ratio effect. In the mechanism shown, the cylinder block 41 also tilts its axis relative to the crank case 42. This tilting can be beneficially arranged to reduce the side thrust on the piston 45 which inevitably arises with the use of a cylinder axis offset from the crankshaft axis.

A flexible seal 46 is provided to keep lubricating oil within the crank case 42 and cylinder block 41.

The combination of axial movement, movement perpendicular to the cylinder axes and tilting motion of the cylinder block 41 can be optimised by selecting suitable lengths for the links 47 and 48 as well as optimising the distances between pivot points 49 and 50 on the cylinder block 41 and the distance between the pivot points 51 and 52 on the crank case 42.

As with the first embodiment, in the second embodiment the movement of the cylinder block 41 relative to the crank case 42 can be achieved by any suitable actuator, e.g. a hydraulic actuator, a pneumatic actuator, or an electrical actuator. Again, the movement can be controlled by an open loop control system between fixed end points or a closed loop control system can be used with a position sensor sensing the position of the cylinder block relative to the crankcase in order to allow the cylinder block 41 to be stopped at a range of positions relative to the crank case 42.

One difficulty in providing for movement of the cylinder head relative to a crank case is dealing with the need to provide rotation to the cam shaft of the engine.

The cam shaft of the engine will be mounted to the cylinder block (typically in a cylinder head connected to the cylinder block), but must be driven from the crank shaft within the crank case. An example of a special connecting mechanism which would accommodate the sliding cylinder block relative to the crankshaft is shown in Figure 7.

In Figure 7 it can be seen that there is a crank gear connected to a crankshaft for rotation therewith. The crank gear 60 meshes with a swinging idler gear 61 mounted on a swing arm 62. The swinging idler gear 61 meshes also with an idler gear 63 fixed to the cylinder block. The cam shaft will be driven directly or indirectly from the fixed idler gear 63.

The swinging idler gear 61 is mounted on the swing arm 62 which is part of a carrier pivoted about the crank axis.

It is maintained in contact with the crank gear and the fixed idler 63 by a spring (not shown) or by an actuator (hydraulic, electric, etc.) or a mechanical linkage. As the cylinder block is moved to offset the axis of the cylinder relative to the crank axis, the swinging idler will move around the crank gear 60 whilst maintaining mesh with the idler 63 fixed to the cylinder block. Thus, the drive connection is maintained between the crankshaft and the camshaft.

The rotation of the idler gear 61 on the swing arm 62 about the crank gear 60 will lead to a phase angle change in the drive train. In some cases this may prove in itself an advantage of the mechanism and may be desirable. However, it is always possible to use continuously variable cam phasers fitted to each cam shaft in order to compensate for - 10 or attenuate and/or accentuate the phase angle change occasioned by the movement of the swinging idler 61 about the crank gear 60.

In Figure 8 an alternative mechanism for connecting the crankshaft to the camshaft is shown. In this mechanism, the crank gear 70 is connected by a belt (or chain) to a swinging idler gear 71 which in turn is connected by a belt (or chain) to an idler gear 72 fixed to the cylinder block.

The swinging idler gear 71 is rotationally mounted on a carrier 73 which has one arm 73A pivotable about the rotational axis of the crank gear 70 and another arm 73B pivotable about the rotational axis of the fixed idler gear 72. In this case, phase relationship between the crankshaft and the fixed idler 72 is maintained throughout movement of the cylinder block relative to the crank case. However, there will still be a change in phase relationship between the crankshaft and the stroke of the piston. For this reason, the use of cam phasers may still be desirable.

The engines described above are preferably forced induction engines, e.g. supercharged or turbocharged engines.

The sliding joint described above comprises a dovetail joint, but there are many suitable sliding arrangements.

For instance a box slide could be used or a joint with a linear track, profiled in cross-section, with rolling element bearings running along it.

Claims

1. An internal combustion engine comprising: at least one piston reciprocable along a cylinder axis of a cylinder in a cylinder block; a crankshaft rotatable about a crank axis and rotatably mounted in a crank case; wherein: the cylinder block is movable relative to the crankcase and actuator means is provided to occasion relative motion therebetween; characterized in that: the cylinder block is mounted in the engine by mounting means which ensure that all movement of the cylinder block relative to the crankcase comprises movement of the cylinder block at least partly perpendicular to the cylinder axis whereby all movement of the cylinder block varies an offset distance between the cylinder axis and the crank axis.

2. An internal combustion engine comprising: at least one piston reciprocable along a cylinder axis of a cylinder in a cylinder block; and a crankshaft rotatable about a crank axis and rotatably mounted in a crank case; wherein: the crank case is movable relative to the cylinder block and actuator means is provided to occasion relative motion therebetween; characterised in that the crank case is mounted in the engine by mounting means which ensure that all movement of the crank case relative to the cylinder block comprises movement of the crank case at least partly perpendicular to the cylinder axis whereby all movement of the crank case - 12 varies an offset distance between the cylinder axis and the crank axis.

3. An internal combustion engine as claimed in claim 1 or claim 2 wherein the mounting means comprises a sliding joint connecting together the cylinder block and the crank case.

4. An internal combustion engine as claimed in claim 3 wherein the sliding joint extends perpendicularly to the cylinder axis so that all movement of the cylinder block or crank case is wholly perpendicular to the cylinder axis.

5. An internal combustion engine as claimed in claim 3 wherein the sliding joint extends at an angle to the cylinder axis so that all movement of the cylinder block or crank case is in part perpendicular to the cylinder axis and in part parallel to the cylinder axis.

6. An internal combustion engine as claimed in any one of the claims 3 to 5 wherein the sliding joint comprises a male member of one of the cylinder block and the crank case slidable in a recessed track in the other of the cylinder block and the crank case.

7. An internal combustion engine as claimed in claim 6 wherein the sliding joint comprises a cam track with one of the cylinder block and the crank case having a cam sliding in a profiled cam track provided in the other of the cylinder block and the crank case.

8. An internal combustion engine as claimed in claim 1 or claim 2 wherein the mounting means comprises a plurality of - 13 connecting links connecting the cylinder block to the crank case, each connecting link pivotally connected at a first end to the crank case and each connecting link pivotally connected at a second end to the cylinder block.

9. An internal combustion engine as claimed in claim 8 wherein the connecting links are arranged such that as the cylinder block moves relative to the crank case the offset distance between the cylinder axis and the crank axis is varied, the cylinder block is moved parallel to the cylinder axis and the cylinder block is tilted.

10. An internal combustion engine as claimed in any one of the preceding claims wherein a crank gear is mounted on the crankshaft for rotation therewith, the crank gear meshes with a swinging idler gear mounted on a swinging carrier pivotable about the crank axis and the swinging idler gear meshes with a fixed idler gear rotatably mounted on the cylinder block, the fixed idler gear being connected to a camshaft of the engine to drive the camshaft, and means is provided to act on the swinging carrier to hold the swinging idler gear in mesh with the fixed idler gear, whereby the swinging idler gear can move around the crank gear when the cylinder block moves relative to the crank case with continuity of transmission of drive from the crankshaft to the camshaft.

11. An internal combustion engine as claimed in any one of claims 1 to 9 wherein a crank gear is mounted on the crankshaft for rotation therewith, a first belt connects the crank gear to a swinging idler gear, a second belt connects the swinging idler gear to a fixed idler gear rotatably mounted on the cylinder block, and a swinging carrier is mounted to rotate about the crank axis and the axis of the fixed idler gear, the swinging carrier carrying the swinging idler gear, whereby the cylinder block and the crank case can move relative to each other with continuity of transmission of drive from the crankshaft to the camshaft.

12. An internal combustion engine as claimed in any one of claims 1 to 9 wherein a crank gear is mounted on the crankshaft for rotation therewith, a first chain connects the crank gear to a swinging idler gear, a second chain connects the swinging idler gear to a fixed idler gear rotatably mounted on the cylinder block, and a swinging carrier is mounted to rotate about the crank axis and the axis of the fixed idler gear, the swinging carrier carrying the swinging idler gear, whereby the cylinder block and the crank case can move relative to each other with continuity of transmission of drive from the crankshaft to the camshaft.

13. An internal combustion engine as claimed in any one of the preceding claims wherein the actuator means comprises a hydraulic actuator.

14. An internal combustion engine as claimed in any one of claims 1 to 12 wherein the actuator means comprises a pneumatic actuator.

15. An internal combustion engine as claimed in any one of claims 1 to 12 wherein the actuator means comprises an electric actuator. -

16. An internal combustion engine as claimed in any one of claims 13 to 15 wherein the actuator means is controlled by a closed loop control system which controls the relative position between the cylinder block and the crank case using a position sensor to provide a feedback signal.

17. An internal combustion engine as claimed in any one of the preceding claims having forced induction means for delivering pressurized charge to the/each cylinder.

18. An internal combustion engine as claimed in claim 17 wherein the forced induction means comprises a turbocharger.

19. An internal combustion engine as claimed in claim 17 wherein the forced induction means comprises a supercharger.

20. An internal combustion engine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

492923 AWP/ctf Amendments to the claims have been filed as follows 1. An internal combustion engine comprising: at least one piston reciprocable along a cylinder axis of a cylinder in a cylinder block; a crankshaft rotatable about a crank axis and rotatably mounted in a crank case; wherein: the cylinder block is movable relative to the crankcase and actuator means is provided to occasion relative motion therebetween; wherein: the cylinder block is mounted on the crank case by mounting means which ensure that all movement of the cylinder block relative to the crankcase comprises movement of the cylinder block at least partly perpendicular to the cylinder axis whereby all movement of the cylinder block varies an offset distance between the cylinder axis and the crank axis; and the mounting means comprises a plurality of connecting links connecting the cylinder block to the crank case, each connecting link pivotally connected at a first end to the crank case and each connecting link pivotally connected at a second end to the cylinder block, whereby the connecting links, the crank case and the cylinder block form a fourbar chain mechanism.

2. An internal combustion engine as claimed in claim 1 wherein the connecting links are arranged such that as the cylinder block moves relative to the crank case the offset distance between the cylinder axis and the crank axis is varied, the cylinder block is moved with a component of 1) motion parallel to the cylinder axis; and the cylinder block is tilted.

3. An internal combustion engine as claimed in claim 1 or claim 2 wherein a crank gear is mounted on the crankshaft for rotation therewith, the crank gear meshes with a swinging idler gear mounted on a swinging carrier pivotable about the crank axis and the swinging idler gear meshes with a fixed idler gear rotatably mounted on the cylinder block, the fixed idler gear being connected to a camshaft of the engine to drive the camshaft, and means is provided to act on the swinging carrier to hold the swinging idler gear in mesh with the fixed idler gear, whereby the swinging idler gear can move around the crank gear when the cylinder block moves relative to the crank case with continuity of transmission of drive from the crankshaft to.the camshaft.

4. An internal combustion engine as claimed in claim 1 or claim 2 wherein a crank gear is mounted on the crankshaft for rotation therewith, a first belt connects the crank gear to a swinging idler gear, a second belt connects the swinging idler gear to a fixed idler gear rotatably mounted on the cylinder block, and a swinging carrier is mounted to rotate about the crank axis and the axis of the fixed idler gear, the swinging carrier carrying the swinging idler gear, whereby the cylinder block and the crank case can move relative to each other with continuity of transmission of drive from the crankshaft to the camshaft.

5. An internal combustion engine as claimed in claim 1 or claim 2 wherein a crank gear is mounted on the crankshaft for rotation therewith, a first chain connects the crank lS gear to a swinging idler gear, a second chain connects the Sw;lylly l=- sear in -icy -'e-- Acts- -v' .-eA on the cylinder block, arid a swinging carrier is mounted to rotate about the crank axis and the axis of the fixed idler gear, the swinging carrier carrying the swinging idler gear, whereby the cylinder block and the crank case can move relative to each other with continuity of transmission of drive from the crankshaft to the camshaft.

6. An internal combustion engine as claimed in any one of the preceding claims wherein the actuator means comprises a hydraulic actuator.

7. An internal combustion engine as claimed in any one of claims 1 to 5 wherein the actuator means comprises a pneumatic actuator.

8. An internal combustion engine as claimed in any c,,e Of claims 1 to 5 wherein the actuator means comprises an electric actuator.

9. An internal combustion engine as claimed in any one of claims 6 to 8 wherein the actuator means is controlled by a closed loop control system which controls the relative position between the cylinder block ar,d the crank case using a position sensor to provide a feedback signal.

10. An internal combustion engine as claimed in any one of the preceding claims having forced induction means for delivering pressurized charge to the/each cylinder.

I

11. An internal combustion engir,e as claimed in claim 'O wheer1 the forced illduc=_Grl r-eal-ls GO,,,pl- ses - u.-bocha-ge^.

12. An internal combustion engine as claimed in claim 10 wherein the forced induction means comprises a supercharger.

29. At! Internal combustion engine substantially as hereinbefore described with reference to and as shown in the accompanying figures 6, 7 and 8.