WO2007081222A1

WO2007081222A1 - Variable compression system for internal combustion engines

Info

Publication number: WO2007081222A1
Application number: PCT/NZ2006/000002
Authority: WO
Inventors: Brian Barradine
Original assignee: Brian Barradine
Priority date: 2006-01-16
Filing date: 2006-01-16
Publication date: 2007-07-19

Abstract

A mechanism for varying the compression ratio of an internal combustion engine while the engine is running comprising a number of beams (1) to which the crankshaft is securely attached by a cradle (2). The cradle (2) and the beams (1) are tilted by the rotation of an eccentric shaft (3) thereby lowering or rising the crankshaft assembly which has the effect of varying the gap between the piston crown and cylinder head thereby lowering or raising the compression ratio accordingly.

Description

TITLE: VARIABlE COMPRESSION SYSTEM f OR INTERNAI COMRUSTION ENCINES

TECHNICAL FIELD

This invention relates to internal combustion engines, and was conceived as an improvement to (over, upon) existing internal combustion engine designs which have fixed compression ratios.

In particular this invention relates to internal combustion engines (especially those designed for use in small cars) which are turbocharged or supercharged, however any size engine could benefit from this invention.

BACKGROUND ART - encompassing the problem which the invention is to solve

Car makers are forever walking a fine line between lowering fuel consumption and exhaust emissions, to comply with government regulations, while at the same time maintaining or improving performance, as demanded by consumers. In the process they are prepared to investigate every option imaginable. Some of these options turn out to be viable, some don't.

One direction that has proven to be feasible, in terms of results, is downsizing engine capacity and making up the performance difference through turbo charging or supercharging. The biggest problem with this concept is that an engine with forced induction requires a lower-than-normal compression ratio to prevent detonation from dangerously high compression pressures when full boost is applied. But a low compression ratio makes the engine inefficient during all phases other than fully boosted - and that's almost all of the time, high compression on the other hand is an excellent way of reducing nitrous oxides (NOx.s) and other noxious fumes from automobile tailpipes since high compression contributes not only to improved fuel economy, but also to clean burning of fuels. An ideal solution then would be an engine which has the capacity to deliver high compression (circa 14:1) when most needed (i.e. during urban driving) and low compression (circa 8:1) at higher speeds to reduce engine loads and prevent detonation PRIOR ART - previously used devices most like the invention

At least six (6) other examples of variable compression ratio systems are known to the author of the system described herein.

However none of these systems feature the same mechanism as the one described herein.

The author of the invention described herein makes no claim suggesting inferiority of previous examples of the art, however advantages of the invention described herein, in its present form may become apparent when compared with prior art relating to the field. (1 ) In one example of prior art relating to the field of the invention described herein - One manufacturer has sought to vary the compression of an internal combustion engine by - tilting the cylinder head to which the cylinders and cylinder liners are affixed, therefore varying the combustion chamber volume. One negative aspect to this solution is that - a flexible membrane must be used around the perimeter of the cylinder head to prevent oil loss from splashing caused by the movement of the reciprocating internal parts of the engine. This flexible membrane (neoprene or similar material) may over the course of time be subject to perishing and fatigue especially in colder climates. Another disadvantage of this system is that the exhaust pipe being connected to the cylinder head (by way of the exhaust manifold) is subject to movement fatigue and possible subsequent cracking which could result in noxious gases leaking out into the engine bay resulting in possible poisoning of the occupants of the vehicle. (2) In a second example of prior art relating to the field of the invention described herein - Another manufacturer has sought to vary the compression of an internal combustion engine by - mounting the crankshaft on eccentric main bearings which form an integrated structural assembly, this assembly is rotated by an electric motor thus raising and lowering the crankshaft axis, this has the effect of varying the gap between the cylinder head and piston crown. (Thus raising and lowering the compression ratio accordingly) One negative aspect of this solution is that - because the crankshaft axis moves up and down (and sideways) the alignment of the crankshaft to the gearbox input shaft and auxiliary drive (timing chain/belt drive) are compromised requiring a variable offset coupling at either end of the crankshaft to compensate for this problem, this makes the engine longer and more difficult to fit in the engine bay. This is especially significant in front wheel drive cars where the engine is mounted transversely.

(3) In a third example of prior art relating to the field of the invention described herein - Another manufacturer has sought to vary the compression ratio of an internal combustion engine by - rotating eccentric crankpins by means of an internally toothed ring gear which is housed in the crankcase.

This not only varies the compression ratio but also varies the length of the stroke of the engine by altering the crankshaft throw.

It works, but mechanical simplicity requires that it be applied only to engines with inline two-cylinder or V4 layouts.

(4) In a fourth example of prior art relating to the field of the invention described herein - Another manufacturer has sought to vary the compression of an internal combustion engine by - raising and lowering small pistons that oppose the main pistons This contra- piston design works but sealing is a problem and the shape of the combustion chamber becomes inefficient when the contra pistons are retracted. A further negative aspect of this solution is that in a four stroke design there is only room for two valves per cylinder as well as the contra pistons which therefore compromises volumetric efficiency. (5) In a fifth example of prior art relating to the field of the invention described herein - Another manufacturer has sought to vary the compression of an internal combustion engine by - varying the height of the piston crown by using a two part piston assembly, The height of the piston being controlled by hydraulic pressure. At first this would seem an ideal manufacturing solution, but this adds undesirable mass to the piston, and raising the piston crown against compression pressure requires very high oil pressure as well as accurate and reliable control of the activating system.

Such a system has been tried but slowness of activation means it is only suitable for compression ignition engines where pre ignition is not a problem. Using a large Bellville-type washer arrangement is also being tried but incurs similar design problems. (6) In yet another example of prior art relating to the field of the invention described herein - Another manufacturer has sought to vary the compression of an internal combustion engine by - using a two part connecting rod which is linked together by an additional wrist pin, the lower link of the connecting rod forming an obtuse capital ^'L' lying on its side.

The longer horizontally orientated leg of this connecting rod (lever arm) has a sliding arrangement by which the fulcrum or pivot point can be shifted, thereby effectively altering the length of the connecting rod. This has the effect of not only varying the compression ratio but also of varying the sweep of the piston therefore altering the capacity of the engine.

This design however is very complex and has problems associated with vibration.

It also suffers from undesirably short conrod lengths and attending angles.

OBJECTIVE OF THIS INVENTION The objective of this invention is to improve the efficiency and performance of the internal combustion engine by mechanically adjusting the compression ratio as required during the running of the engine, thereby making the engine more efficient across a greater range of speeds.

In particular this invention has been conceived to prevent pre ignition or detonation in small petrol (spark ignition) engines which have forced air induction.

(i.e. turbo charging or supercharging) however this invention may prove to be useful on engines of larger capacity and may also prove useful on diesel

(compression ignition) engines, as well as engines that are naturally aspirated. BRIEF DESCRIPTION OF DRAWINGS

To further clarify the present embodiment of this invention reference should be made to the following attached drawings which serve to illustrate both the functionality and form (shape) of the parts which make up the whole of the invention.

Fig 1/4 is a perspective view of the current embodiment of the invention - clearly showing all the parts described herein.

Fig 2/4 is a similar view to Fig 1/4 but on a steeper angle looking down from above - This drawing clearly shows all the parts of the invention insitu.

Fig 3/4 is a perspective drawing of the cradle part (item 2 all 4 figs)

This part may be cast or forged from a suitable alloy of metals before machining bearing surfaces, items 20 & 25 etc.

Fig 4/4 is a two part diagram which clearly shows how the rotating of the cradle part (item 2) increases the gap between the piston crowns and the cylinder head.

Refer reference line 24 (Note: cylinder head is not shown)

Fig 4a maximum compression ratio Fig4b minimum compression ratio

Fig 4/4 is an end elevation view.

Note: all item numbers share a commonality across all figures. (Drawings)

DISCLOSURE OF INVENTION - exemplary embodiment of the present invention According to the preferred embodiment of the present invention - there is a mechanism provided to vary the compression ratio of an internal combustion engine while the engine is running. This mechanism consists of a series of pivoting beams (5 in this case) (running at 90° to the crankshaft) {items 1 FIG 1 , 2,&4) of stout proportions which serve to support the crankshaft at the main bearing positions, the crankshaft being retained to the beams by a cradle structure (item 2 FIG 1 ,3&4) which not only replaces individual bearing caps but also serves to keep the afore mentioned beams on a collinear plane.

This cradle structure is of a substantial and suitable strength to resist torsional and axial loads etc, and is retained to the crankshaft support beams by a series of bolts (20 in this case). The afore mentioned beams (crankshaft support beams) have a common pivot axis {item 10 FIG 2) to one side of the crankshaft centre line (item 21 FIG 4) This axis runs parallel to the crankshaft axis (item 11 FIG 2) and is collinear to the crankcase/sump joint plane (item 22 FIG 4) This pivot axes consists of short stub shafts (item 12 FIG 2) which are an integral part of the crankshaft support beam design. These stub shafts protrude from the crankshaft support beams at right angles and form the bearing surface for the pivot bearing caps (item 13 FIG 2) which are secured to the crankcase by suitable bolts.

The pivoting motion of the crankshaft support beams/and cradle is implemented by the rotating movement of an eccentric shaft (item 3 FIG 1&4) which is secured about its concentric axis by bearing caps (item 4 FIG 1 ) which are in turn secured (bolted) to the engine crankcase.

The eccentric shaft is located on the opposite side of the crankshaft centre line to the crankshaft support beams pivot axis and its axis also runs parallel to the crankshaft axis. The eccentric shafts concentric axis also lies on the crankcase/sump joint line (item 22 FIG 4) The eccentric shaft has a number of lobes (item 5 FIG 1) which are eccentric to the concentric axis of the shaft and form the lever aspect of the shaft. Each eccentric lobe circumference (itemβ FIG 1) on the eccentric shaft forms a bearing surface which is contacted by both the cradle structure and one of the crankshaft support beams.

(The cradle provides a dual function, one of retaining the crankshaft to the crankshaft support beams, and one of retaining the eccentric shaft to the crankshaft support beams) Upon mating each crankshaft support beam to the cradle an oval slot like aperture is formed for each eccentric shaft lobe, thus allowing the eccentric shaft to rotate freely (in one direction) while still bearing the loads of combustion etc. Note: that the forces upon the crankshaft are shared between the pivot axis and the eccentric shaft axis as well as the worm and wheel. When the engine is running at its highest compression setting the lobes of the eccentric shaft point directly upwards but as the eccentric shaft is rotated they begin to defer from the vertical, in doing so they push against the cradle bearing surface (item 20 FIG 3) and rotate the cradle downwards, this also pulls the crankshaft, connecting rods and pistons etc downwards, increasing the gap between the piston crowns and cylinder head thereby reducing the compression ratio accordingly, (refer to fig 4 for clarification)

When the eccentric shaft lobes point vertically downwards the compression ratio is reduced to its minimal limit.

Note: that the eccentric shaft only turns 180° in one direction to lower the compression ratio from its highest setting to its lowest setting, to increase the compression ratio again the eccentric shaft is turned back the opposite way.

Note: also that the eccentric shaft is prevented from rotating more than 180° by a combination of primary hard stops and electronic switching. Rotation of the eccentric shaft is caused by an electronic signal from the ECU (Engine Control Unit) - onboard computer- reaching the electric motor (item 7 FIG 1&4) which is rigidly and solidly mounted to the outside of the crankcase, the electric motor being mounted vertically by way of a flanged base plate (item 23

FIG 4)

The electric motor directly drives a worm shaft (item 8 FIG 1 ) which penetrates through an aperture in the crankcase to engage with a toothed wheel, (item 9 FIG 1 ) the toothed wheel being an integrated feature of the eccentric shaft.

The worm shaft consists of a shaft of stout proportions which has a worm gear

(helix) incorporated into its design.

It has about its centre aspect a flanged shoulder of generous proportions which upon assembly becomes sandwiched between the electric motor base plate and the engines crankcase, this serves to prevent the worm shaft from being forced upwards or downwards by the forces imparted to it by the loads generated from combustion and compression.

The top aspect of the worm shaft has a splined section which plugs into a splined socket in the electric motor; this socket is concentric to the electric motor axis. At the bottom of the worm shaft there is provided a plain section which upon assembly plugs into the sump casting, this bearing socket provides a support for sharing lateral loads upon the worm shaft and ensures full meshing with the eccentric shaft gear when under high load.

Torque derived from the combustion process is transferred from the crankshaft to the clutch via the intermeshing of two gears (cogs), one on the axis of the crankshaft (driver gear) (item 14 FIG 2) which is an integrated feature of the crankshaft design, and the other (driven gear) (item 15 FIG 2) which fits over a stub shaft which protrudes from the flywheel end crankshaft support beam, on the cradle pivot axis. When the cradle is rotated (by the electric motor/eccentric shaft) the crankshaft gear (driver gear) partially orbits about the driven gear axis (as does the crankshaft) thereby maintaining the driven gear axis in the same position.

This planet and sun gear arrangement simplifies torque transmission to the clutch and is a major feature of the design. The driven gear incorporates into its design a flange (item 16 FIG 2) suitable for attaching the flywheel (item 17 FIG 2) by means of appropriate bolts as is the convention, the outer circumference of the flange is of a smooth machined finish to accept a circular oil seal between the later and the crankcase to prevent oil contamination of the clutch plates as is also the convention.

The land between the flange and the gear serves as a bearing surface to additionally support the driven gear, the rear face of the driven gear flange is recessed to accept the gearbox input shaft, this centers the input shaft and acts as a third support for the driven gear.

At the other end of the cradle (and on the same axis) is a freewheeling gear (item

18 FIG 2) which has a sprocket feature, this gear is also driven by a gear keyed to (or part of) the crankshaft (item 19 FIG 2). The purpose of this freewheeling gear is to drive the overhead valve timing gear by way of a suitable chain, the tension of which is unaffected when the cradle pivots due to the fact that the sprocket on the freewheeling gear maintains a constant axis.

The sprocket gear is supported near the sprocket end by a crankcase bearing and at the other end by a stub shaft (which is part of the timing chain end crankshaft support beam) which penetrates into a hole in the rear surface of the sprocket gear.

DESCRIPTION OF HOW THE INVENTION WORKS

Various sensors located in and around the engine relay data (on a continuous basis while the engine is running) to the ECU (engine control unit), which analyzes the data and then orchestrates the movement of the electric motor, (item 7 FIG 1&4) which rotates the eccentric shaft to provide the best possible compression ratio for the engine at any given point in time.

HOLD ALL CLAUSE It will be appreciated that the invention broadly consists in the parts, elements and features described in this specification,

Which when compared to prior art relating to the field, should serve to illustrate the absolute novelty of the invention described herein.

Claims

CLAIMS -what I claim is

1 A variable compression system for internal combustion engines featuring a number of substantial beams to which the crankshaft is securely attached by means of a cradle part and bolts. 2 A variable compression system for internal combustion engines as claimed in claim 1, which consists of a number of substantial beams which support the crankshaft at its main bearing points (stations) and which are pivoted on one side.

3 A variable compression system for internal combustion engines as claimed in claim 1 or claim 2 wherein the cradle part is tilted by the rotation of an eccentric shaft located on the opposite side to the pivot axis. The eccentric shaft being held in place by means of bearing caps which are securely bolted to the engines crankcase. The crankshaft being located between the pivot axis and the eccentric shaft at approximately half the distance between the two.

4 A variable compression system for internal combustion engines as claimed in any preceding claim, wherein there are three (3) main items not normally found in a conventional internal combustion engine.

5 A variable compression system for internal combustion engines as claimed in claim 4, in which these items are: 1 a number of pivoting beams which have a pivot axis to one side of the engines crankshaft, 2 an eccentric shaft located on the opposite side to the pivot axis of the pivoting beams which when turned tilts a cradle part to which the crankshaft is bolted. 3 an electric motor which rotates the afore mentioned eccentric shaft by means of a worm shaft which duly engages in a wheel gear which is part of (or suitably affixed to) the eccentric shaft.

6 A variable compression system for internal combustion engines as substantially described in the text of this document (of which there are 11 pages) and as illustrated in the accompanying drawings. (of which there are 4) fig1/4,fig2/4,fig3/4 and fig4/4.