SE1530094A1 - Method and arrangement for controlling a combustion engine - Google Patents

Abstract

I\/|ODEO02SE2015-06-22 ABSTRACT The invention relates to a method for optimizing an internal combustion engine with variablecompression ratio for a direct start, the engine comprising a crankcase comprising acrankshaft connected to at least tvvo pistons; and a cylinder block comprising at twocylinders The method involves determining a crank angle adjustment required to achieve acrank angle suitable for ignition in this first cylinder and operating at least one actuator (123)to displace the cylinder block relative to the crankcase for adjustment of compression ratioand cylinder offset (O). This causes a simultaneous displacement of the cylinder block (217)in the direction of the cylinder axis (Y), and transverse to the cylinder axis (Y) and thecrankshaft axis (X). The crank angle adjustment is performing using a mechanism (428; 528;430) connecting the cylinder block and the crankshaft, which mechanism (428; 528; 430) isactuated by the cylinder block displacement. (Figure 4A)

Description

IVIODEOOZSE2015-06-221 l\/IETHOD AND ARRANGEIVIENT FOR CONTROLLING A COMBUSTION ENGINE TECHNICAL FIELD The invention relates to a method and an arrangement for controlling an internal combustionengine for direct start of the internal combustion engine, in particular for start-stop operation, using an arrangement for simultaneous adjustment of compression ratio and cylinder offsetBACKGROUND OF THE INVENTION Using start-stop operation for internal combustion engines is a common way of reducing fuelconsumption, for instance by stopping the engine temporarily at traffic lights. When theengine is re-started it is advantageous to ensure that the crankshaft is positioned so that oneof the pistons is in a suitable position for cranking.

A known device for starting an internal combustion engine is disclosed in WO 91/16538, inwhich an electric motor serving as generator and starter is coupled to a crankshaft. Prior tothe internal combustion engine being started, the crankshaft is brought by means of thestarter into a position in which the pistons are aligned in the most advantageous alignmentfor the next start. The rotational position of the crankshaft is determined via a sensor which isprovided. ln the case of conventional ignition or injection systems of four-stroke engines, sensors foridentifying the top dead center (TDC) of the pistons are provided on the flywheel of thestarting motor. ln addition, a sector identifying means for the sectors 0 - 360 degrees and360 - 720 degrees of the crankshaft is provided. ln order to allow a control unit connected tothe ignition or injection system to determine the current position of the crankshaft from thesensor signals, the starter has to rotate the crankshaft through more than one revolution, andup to a maximum of 660 degrees in the case of a six- cylinder motor. ln the case of modern starting/stopping systems, it is now possible to reach the startingspeed for the engine after a rotational angle of the crankshaft of just 90 degrees. lt istherefore a disadvantage that despite reaching the starting speed, firing cannot be carriedout until the control unit has determined the current position of the crankshaft, since the exactrelative positions between the crankshaft and the pistons is demanded by the control unitbefore ignition takes place.

MODE002SE2015-06-222 During positioning of the crankshaft, the piston arranged to perform the first firing must bedisplaced by the starter/generator towards and past the TDC during a compression cycle.Hence, the rotation of the crankshaft will require a relatively large torque from thestarter/generator, especially for engines operated at relatively high compression ratios.

The object of the invention is to provide an improved method and arrangement for controllingan internal combustion engine for direct start in order to overcome the above problems.

INVENTIONThe above problems have been solved by a method as claimed in the appended claims. ln the subsequent text, the term ”engine” is used to denote an internal combustion engine,which engine can be either a spark ignited engine, a spark-assisted compression ignitionengine, a flash-assisted compression ignition engine, or a conventional compression ignitedengine. Further, when referring to the position of a crankshaft the terms “crankshaft rotational angle”, “crank angle” or the abbreviation CAD may be used interchangeably in the text.

A preferred embodiment of the invention relates to a method for optimizing an internalcombustion engine with variable compression ratio for a direct start. The engine comprises acrankcase comprising a crankshaft connected to at least two pistons; and a cylinder blockcomprising at two cylinders, each provided with intake and exhaust valves. The methodcomprising the steps of: - detecting that the internal combustion engine has stopped; - detecting a current crank angle; - determining which cylinder is next to fire in a predetermined cylinder firing order; - determining a crank angle adjustment required to achieve a crank angle suitable forignition in this first cylinder - operating at least one actuator to displace the cylinder block relative to the crankcase foradjustment of compression ratio and cylinder offset; - causing a simultaneous displacement of the cylinder block in the direction of the cylinderaxis, and transverse to the cylinder axis and the crankshaft axis; and - performing the crank angle adjustment using a mechanism connecting the cylinder blockand the crankshaft, and which mechanism is actuated by the cylinder blockdisplacement.

MODE002SE2015-06-223 According to the invention, the method is carried out when the ignition is turned off, eithermanually by the driver or automatically by a control unit used for controlling a start-stopfunction, e.g. when stopping the engine temporarily at traffic lights. The method is completedprior to engine re-start to ensure that the crankshaft is positioned so that one of the pistons isin a suitable position for direct start.

As indicated above, the method involves detecting the position of the crankshaft when theengine has stopped. This can be performed by means of known sensors connected to a control unit.

According to one example, a flywheel having an outer circumference provided with, forexample, a toothing arrangement can be provided with a position marker for the crankshaft.The position marker reproduces the rotational position of the crankshaft and therefore thecurrent position of each of the pistons of the internal combustion engine can be determined.The ignition in the combustion chambers of the internal combustion engine can be initiated ata suitable time by reference to the current position of the pistons. The position marker isrealized by a relatively large tooth spacing in the toothing arrangement, so that a positionsensor in the vicinity of the toothing arrangement identifies the rotational position of thecrankshaft when the position marker rotates past the position sensor. The sensor can be apulse counter or inductive pickup. lf the signal of a camshaft position sensor of the internalcombustion engine is added, then the position of the pistons can be determined exactly viathe rotational position of the crankshaft. This makes it possible, for example, in the case of aspark-ignited internal combustion engine to identify whether a piston is at the beginning ofignition or at the beginning of induction. However, the invention is not restricted to spark-ignited internal combustion engines. ln the same or modified manner, the invention is alsosuitable for self-igniting internal combustion engines (diesel). lnstead of the toothingarrangement, a perforated disc may also be used.

During the switching-off process of the internal combustion engine, the crankshaft will cometo a standstill in a rest position. When the engine is approaching its rest position thepressures of the previous, last cylinder in the firing order and the next cylinder in turn to firewill attempt to balance out. The previous, first cylinder will be in its expansion stroke whilethe next, second cylinder will be in its compression stroke. The momentum of the system asthe engine revs down will cause the piston in the second cylinder to come to rest at least halfway into the compression cycle, i.e. less than 90 crank angle degrees before top dead center.

MODE002SE2015-06-224 The control unit is connected to one or more suitable sensors for detecting the exact positionof the crankshaft and/or a camshaft when the rotation comes to a stop. Using the crankshaftposition, camshaft position and/or other engine related data, the control unit can determinewhich cylinder is next to fire in the predetermined cylinder firing order for the engine inquestion. The control unit can then determine the crank angle adjustment required forrotating the crankshaft from the current, first crank angle to a desired, second crank anglesuitable for performing ignition during a subsequent direct start. ln a spark ignition (SI) engine a direct start can be carried out by performing a fuel injection inthe next cylinder is to fire in the predetermined cylinder firing order and igniting the air-fuelmixture using a spark plug. ln a compression ignition engine a direct start can be carried outby performing a fuel injection in the next cylinder is to fire in the predetermined cylinder firingorder, as well as into a pre-combustion chamber connected to the cylinder. An ignition isperformed in the pre-combustion chamber in order to ignite the air-fuel mixture in thecylinder. Normal engine operation can then be resumed.

As indicated above the method involves operating at least one actuator to displace thecylinder block relative to the crankcase for adjustment of compression ratio and cylinderoffset. This requires simultaneous displacement of the cylinder block in the direction of thecylinder axis and displacement of the cylinder block transverse to the cylinder axis and thecrankshaft axis. Suitable guides are provided for controlling the relative displacementbetween the cylinder block and the crankcase.

As indicated above, a displacement of the cylinder block will act on a mechanism connectingthe cylinder block and the crankshaft. This causes an adjustment of the crank angle from thecurrent, first crank angle to the desired, second crank angle. Suitable mechanisms for thispurpose can be connected directly to the crankshaft, which will then control the displacementof each camshaft via the transmission provided, or be connected to the transmissionbetween crankshaft and camshaft. Such mechanisms will be discussed in further detailbelow.

According to one example, simultaneous adjustment of compression ratio and cylinder offsetcan be achieved by displacing the cylinder block along planar guide surfaces arranged at anangle to a first plane at right angles to the cylinder axis. The plane along which the cylinderblock is displaced will intersect the first plane located at right angles to the cylinder axis in aline parallel to the crankshaft axis. The angle between the guide surfaces and the first planeis an acute angle within the range 0° to 60°. Further the size of the angle will have direct MODE002SE2015-06-225 effect on the compression ratio and cylinder offset. For instance a relatively large angle, suchas 50-60°, will cause a relatively larger and faster change in compression ratio and arelatively small change in cylinder offset during a displacement. Similarly, a relatively smallangle, such as 5-10°, will cause a relatively smaller and slower change in compression ratioand a relatively large change in cylinder offset. ln practice, a minimum useful anglecorresponds to a slope of approximately 1/20, preferably within a range of 1/7 to 1/3.

The cylinder offset can vary from an initial negative offset or from zero offset, where thecylinder axis intersects the crankshaft axis, and up to a maximum value equal to the crankradius. ln practical use, positive/negative offset up to +/- 2/3 of the crankshaft crank radiuscan be selected. For the purpose of this invention, a positive offset is desired for performinga direct start.

Alternative examples for performing a simultaneous adjustment of compression ratio andcylinder offset can be achieved by displacing the cylinder block along cylindrical guidesurfaces comprising generatrices parallel to the crankshaft axis, or by displacing the cylinderblock at right angles to the crankshaft axis, along a fixed path having a predeterminedcurvature, e.g. by means of an excenter mechanism or guiding tracks (coulisse).

According to a second example, simultaneous adjustment of compression ratio and cylinderoffset can be achieved by displacing the cylinder block along part-cylindrical guide surfacescomprising generatrices parallel to the crankshaft axis. ln this example, operation of eachactuator will cause the cylinder block to slide along the curved guide surfaces until thecompression ratio and cylinder offset for the desired engine operating point is achieved.When the desired displacement has been performed each actuator is locked in position toprevent further displacement. ln the above examples, the guide surfaces can be located at either end of the cylinder blockand/or between individual cylinders between the cylinder block and the crankcase. The guidesurfaces comprise surfaces guiding the cylinder block along the plane of displacement, aswell as additional angled, profiled or interlocking portions arranged to prevent movement ofthe cylinder block in the longitudinal direction of the crankshaft. The guide surfaces can alsocomprise two or more parallel rods, having a cylindrical or profiled cross-section, cooperatingwith guide surfaces arranged to at least partially enclose the rods.

Alternatively, the guide surfaces can be located along the front and rear sides of the cylinderblock, extending parallel to the crankshaft. ln this context, the terms “front” and ”rear” areapplicable to a transverse mounted engine. Such guide surfaces would also be provided with MODE002SE2015-06-226additional angled, profiled or interlocking portions arranged to prevent movement of the cylinder block in the longitudinal direction of the crankshaft.

According to a third example, simultaneous adjustment of compression ratio and cylinderoffset can be achieved by displacing the cylinder block at right angles to the crankshaft axis,along a fixed path having a predetermined curvature. Suitable guide mechanisms for thispurpose can be an excenter mechanism or guiding tracks (coulisse). For instance, anexcenter mechanism can comprise two or more shafts located parallel to the crankshaft axison opposite sides of the cylinder axis. The shafts are provided with cams or cranks and arerotated in the same direction to cause the cylinder block to be displaced relative to thecrankcase along a curved path in the form of a quarter circle until the compression ratio andcylinder offset for the desired engine operating point is achieved. ln the case of an excentermechanism this can be rotated through up to 90° between two end positions. When thedesired displacement has been performed each shaft is locked in position to prevent furtherdisplacement.

For an excenter mechanism, the cranks or cams on the respective shafts are preferably, butnot necessarily of the same size. lt is also possible to provide cranks or cams havingdifferent sizes on each side of the cylinder axis. ln the latter case, the shaft comprising thesmaller cranks or cams is limited to a maximum rotation of 90° between two end positions.Alternatively, if a guide mechanism in the form of guiding tracks or a coulisse is used, thenthe path can be given any suitable constant or variable curvature. This allows the relativechanges in compression ratio and offset to be adapted to achieve the desired properties.

According to a fourth example simultaneous adjustment of compression ratio and cylinderoffset can be achieved by displacing the cylinder block using cooperating first planar guidesurfaces arranged at a first angle to a plane at right angles to the cylinder axis andcooperating second planar guide surfaces arranged at a second angle to a plane parallel tothe cylinder axis. A first actuator, such as an excenter mechanism is connected to andarranged to act on a first wedge that is displaced at right angles to the cylinder axis while incontact with a first planar guide surface on the cylinder block to displace the cylinder blockparallel to the cylinder axis in order to adjust the compression ratio. The first wedge ispreferably arranged substantially below the cylinder block. The first wedge can be arrangedto travel in guides fixed to the crankcase and arranged at right angles to the cylinder axis,wherein displacement of the cylinder block is achieved by angled cooperating first planarguide surfaces between the wedge and the cylinder block. ln this case the wedge will travelin a plane at right angles to the cylinder axis. Alternatively, the first wedge can be arranged to MODE002SE2015-06-227 travel in guides fixed to the crankcase and arranged at an angle to the cylinder axis, whereindispiacement of the cylinder block is achieved by angled cooperating first planar guidesurfaces between the wedge and the crankcase. ln this case the wedge will travel along theangled plane of the guide surfaces, being displaced simultaneously at right angles to, andparallel with the cylinder axis. A second actuator, such as an excenter mechanism isconnected to and arranged to act on a second wedge that is displaced parallel to the cylinderaxis while in contact with a second planar guide surface to displace the cylinder block parallelto the cylinder axis in order to adjust the offset. The first and second angles can be selectedindependently with in the same range of angles in order to provide the desired dispiacementin the respective directions.

The arrangement according to the fourth example allows both simultaneous and independentadjustment of compression ratio and offset, depending on the operating conditions of theengine. For the purpose of the current invention, the crank angle adjustment is performedusing a mechanism connecting the cylinder block and the crankshaft, which mechanism ispreferably actuated by the first actuator controlling the compression ratio. Advantages withthis arrangement is, for instance, that the offset can be set to an optimum value for directstart under conditions where the optimum compression ratio cannot be achieved, and thatthe offset can be controlled under conditions when it is not desired to change the compression ratio. ln the above examples, the plane along which the cylinder block is displaced will intersect thefirst plane located at right angles to the cylinder axis in a line parallel to the crankshaft axis.The angle between the guide surfaces and the first plane is an acute angle within the range0° to 60 °.

The guiding means arranged to guide the cylinder block relative to the crankcase cancomprise guide surfaces located in or on the respective cylinder block and crankcase.Alternatively, an intermediate component comprising guide surfaces or a guide mechanismcan be located between the crankcase and the cylinder block, wherein the intermediatecomponent is attached to the cylinder block and the crankcase respectively.

The guide surfaces described above can be used as described in each example, or ascombinations of several examples. Where suitable, a combination of different guide surfacescan be used, such as planar guide surfaces extending parallel to the crankshaft and planarguide surfaces extending transverse to the crankshaft at each end of the cylinder block to MODE002SE2015-06-228create a continuous guide surface around the periphery of the cylinder block. The latter combination can be applied both to planar guide surfaces and part-cylindrical guide surfaces. ln addition to the cooperation guide surfaces described above, the cylinder block and thecrankcase can be provided with clamping means. The clamping means will allow relativedisplacement of the cylinder block and the crankcase along the plane of desireddisplacement, while preventing separation of the cooperating guide surfaces in the directionof the cylinder axis. ln order to prevent crankcase gases and oil from leaking out of the engine, flexible and/ordisplaceable sealing means are provided between the cylinder block and the crankcase.

Examples of suitable sealing means includes a frame defining a sealing plane around thecircumference of the crankcase, wherein the cylinder block is in contact with and is movablerelative to this sealing plane. The sealing plane can be flat, in the case planar guide surfaces,or curved, in the case of part-cylindrical or curved guide surfaces. Linear seals located alongthe direction of displacement can be attached to or integrated in the guide surfaces and canbe of the same type as used for crankshaft seals. Alternative or additional sealing means canbe of a dual barrier type, a labyrinth seal, or a similar suitable sealing means allowing relativedisplacement between the cylinder block and the crankcase. Depending on the type ofadjustment means used, a combination of different types of sealing means can be applied.An outer seal in the form of a bellows or a similar flexible arrangement can be used forsealing out dust and particles from the ambient environment, as well as sealing in oil mistfrom the crankcase. The sealing means must be sufficient for maintaining a lower than atmospheric pressure in the crankcase.

The one or more actuators used for effecting the relative displacement of the cylinder blockand the crankcase is preferably mounted on the crankcase, but can also be mounted on thecylinder block. Although a single actuator is possible, two or more actuators are preferred inorder to ensure that wedging does not occur between cooperating guide surfaces. Actuatorscan act directly on the respective component to be displaced, or via a force amplifying meanssuch as a suitable gearing. A non-exhaustive list of examples of suitable actuators comprisesdouble acting fluid actuators, lead or ball screws, electric motors and servo motors. Fluidactuators can be provided with a controllable valve allowing movement to be preventedbetween operations. Similarly, screw actuators, electric motors and servo motors can beprovided with a controllable locking means. Alternatively, screw actuators can be self-lockingto prevent movement. A sensor, such as a position or proximity sensor, is provided to detect MODE002SE2015-06-229and monitor the position of at least one actuator, preferably each actuator, in order to allow the current compression ratio and cylinder offset to be monitored. ln operation, an engine control unit can determine a current operating point for the enginebased on available engine related parameters detected by suitable sensors. Examples ofsuch parameters are engine speed, load, fuel type and composition, as well as ambientconditions. This solution allows the compression ratio and offset settings to be adjusted toadapt the engine for wide areas of operation. The engine can be adapted to operate at lowengine speeds and loads using a relatively high compression ratio and small positive and/ornegative cylinder offset. The engine can be adjusted gradually, in steps or continuously, tobe operated at high engine speeds and loads using a relatively low compression ratio andlarger cylinder offset. Also, the displacement of the cylinder block from a high load range to alow load range can be performed faster. For a spark ignition (SI) engine a commoncompression ratio can be in the range 14-15:1. Using an engine according to the inventionthe compression ratio can be lowered to 7-7,5:1 by means of a cylinder block displacement.

This operating condition can be used for compression ignition (Cl) engines, such as dieselengines, homogenous charge compression ignition (HCCI) engines and partially pre-mixedcompression ignition (PPCI) engine. During a cold start or during part load operation it isadvantageous to use high compression ratios to achieve ignition and stable operation withoutmisfire. This is also the case when operating at high exhaust gas recirculation (EGR)volumes at light loads. Under these conditions an engine can be operated at compressionratios of approximately 17-20, in combination with a relatively small negative or positiveoffset. When moving towards operating points where the engine load is higher, the enginecan be adjusted towards reduced compression ratios of approximately 13-15, in combinationwith an increased offset.

By reducing the compression ratio the cylinder volume increases and the work required forturning the crankshaft from the first crank angle to the second crank angle can besignificantly reduced. Also, when a direct start is initiated, the reduced compression ratio willreduce the compression work required for subsequently firing cylinders, making the engineeasier to start. By increasing the offset it is possible to reduce tangential cylinder forces andfriction forces, while at the same time achieving a more effective crank torque arm and crank locaüon.

As described above the method involves determining the crank angle adjustment required todisplace a piston in the first cylinder to fire into a positon after top dead center, where the MODE002SE2015-06-22 crank angle is suitable for direct start. The first crank angle is determined by the control unitas the engine revs down and comes to a stop. The second crank angle is selected between10 crank angle degrees after top dead center and 10 crank angle degrees before exhaustvalve opening. Due to the geometry of the piston and piston pin in relation to the crankshaftaxis and crank pin when a positive offset is used, the second crank angle is preferably set at10 crank angle degrees or more after top dead center. Also, as the starting speed for theengine can be reached after a rotational angle of the crankshaft of just 90 crank angledegrees it is possible to start the engine from a crank angle as late as 10 crank angledegrees before exhaust valve opening. Preferably the crank angle is selected between 30and 60 crank angle degrees after top dead center.

The invention involves controlling the mechanism to connect the cylinder block and thecrankshaft when the internal combustion engine is stopped. ln this text the term “mechanism”is defined as including the component parts required for converting the linear displacement ofthe cylinder block into a rotary motion that can be applied to the crankshaft and/or thecamshaft transmission. Alternatively the mechanism can further be controlled to disconnectthe cylinder block and the crankshaft prior to an engine start. This can be achieved by, forinstance a controllable arm or a rack located on the cylinder block and connectable to acontrol wheel or gear wheel located on the crankcase for rotating the crankshaft directly, viathe flywheel or camshaft pulley, or indirectly, via a chain, belt or intermediate gear wheel. lnthis context a control wheel is defined as a part of the camshaft transmission that ensurescorrect tension in the belt or chain at all times, and which provides a belt geometry thatprovides sufficient friction for the driving and driven shafts. The camshaft transmission cancomprise at least one control wheel. The controllable arm is pivoted or displaced to be indriving connection with the gear during periods when the ignition is off in order to rotate thecrankshaft to a desired crank angle. lf a fixed rack is used, then the control wheel can beoperatively disconnected from the rack by means of a free-wheeling device, a clutch or asimilar controllable device..

Alternatively, a control wheel located on the cylinder block can be in driving connection with arack on the crankcase and with the camshaft transmission, such as a belt or chain, normallydriven by the crankshaft. During a displacement of the cylinder block the relative movementbetween cylinder block and crankcase causes a rotation of the control wheel. The controlwheel will then rotate the crankshaft to a desired crank angle via the camshaft transmission.The control wheel can be provided with a free-wheeling device allowing is to be disconnectedfrom the rack and be driven by the camshaft transmission during normal engine operation.

MODE002SE2015-06-2211 ln both the above cases it is assumed that the available displacement range is sufficient forusing a 1:1 ratio between the mechanism and the control wheel to achieve the desired crankangle. However, if this is not the case then a suitable gearing or similar device can beprovided. According to one example a control wheel comprising two gear wheels side-by-side can be provided for the above control wheel in order to achieve a sufficient gear ratio.For instance, the control wheel can comprise a relatively smaller gear wheel connected tothe cylinder block and a relatively larger gear wheel acting on the crankshaft, camshaft pulleyor the camshaft transmission. The gear ratio betvveen the smaller and larger gear wheels isselected depending on the available displacement range between cylinder block and thecrankcase, and the rotational angle required to achieve the desired crank angle.

Under certain operating conditions, e.g. if the engine is operated at a relatively lowcompression ratio and high offset, the control unit may detect that the current relativeposition between the cylinder block and the crankcase is such that a desired crank anglerotation will not be possible. ln such cases it can be necessary to perform a displacement ofthe cylinder block towards a higher compression ratio and lower offset when the engine isswitched off and is revving down. This operation can also be used for stopping the enginemore rapidly, as the increased compression ratio will assist in braking the engine.

The mechanism for adjusting the crank angle can be designed to reflect the number ofcylinders in the engine. Depending on the number of cylinders the distance, measured incrank angle degrees (CAD), between firing events will vary. ln a four-cylinder, four-strokeengine the distance betvveen two firing events is 180 CAD. ln a four-stroke engine the fourcycles are compression, expansion exhaust and intake, performed during two full revolutionsof the crankshaft and making up a total of 720 CAD. When an engine of this type is runningdown with the ignition off, and stopped the pressures of the previous, last cylinder in the firingorder and the next cylinder in turn to fire will attempt to balance out. The previous cylinderwill be in its expansion stroke while the next cylinder will be in its compression stroke,whereby the momentum of the system will cause the piston in the next cylinder to come torest at least half way into the compression cycle, i.e. less than 90 CAD before top deadcenter (TDC). Hence the distance required to rotate the crankshaft is at least 90 CAD plusthe angle up to the desired firing position for direct start. According to the above examples,the minimum and maximum rotation required could be between 100 CAD (90°+10°) and anangle up to 10 CAD before exhaust valve opening, respectively, depending on the exhaustvalve opening timing. Preferably, the minimum and maximum rotation required could bebetween 120 CAD (90°+30 °) and 150 CAD (90°+60°). Using the known possibledisplacement range required for achieving the desired crank angle it is possible to adapt the MODE002SE2015-06-2212 gear ratio of the mechanism to provide a sufficient range. When performing a displacement,the cylinder block is dispiaced towards the lowest compression ratio possible within therange of desired crank angles. Alternatively the cylinder block is dispiaced towards thecompression ratio available at an optimum crank angle for start.

Similar adaptations are made for, for instance, three- or six-cylinder four-stroke engineswhere the distances between two firing events are 240 CAD and 120 CAD, respectively.Hence, in accordance with the above example the preferred the minimum and maximumcrankshaft rotation required could be between 150 CAD (120°+30°) and 180 CAD (120°+60°)for a three cylinder engine, and between 90 CAD (60°+30°) and 120 CAD (60 °+60°) for a sixcylinder engine.

The invention also relates to an internal combustion engine comprising a crankcase with acrankshaft connected to at least two pistons and a cylinder block comprising at least twocylinders, each provided with intake and exhaust valves. The cylinder block is displaceablerelative to the crankcase by at least one actuator connected between the cylinder block andthe crankcase, wherein guiding means is arranged to guide the cylinder block relative to thecrankcase for simultaneous adjustment of compression ratio and cylinder offset when theactuator is operated. The actuator causes a translator displacement of the cylinder block in adirection at right angles to the crankshaft axis. The engine further comprises a sensorarranged to detect a current, first crank angle when the engine has stopped and a controlunit arranged to determine which cylinder is next to fire in a predetermined cylinder firingorder based on the detected crank angle and to determine a crank angle adjustment requiredto achieve a desired, second crank angle suitable for ignition in that cylinder. ln order toperform the required crank angle adjustment a mechanism is arranged to connect thecylinder block and the crankshaft, so that a predetermined displacement the cylinder block bythe actuator causes turning of the crankshaft to adjust the crank angle to the second crankangle.

The at least one actuator is arranged to displace the cylinder block and perform asimultaneous reduction of the compression ratio and increase of the offset during the crankangle adjustment. This requires simultaneous displacement of the cylinder block in thedirection of the cylinder axis and displacement of the cylinder block transverse to the cylinderaxis and the crankshaft axis. Suitable guides are provided for controlling the relativedisplacement between the cylinder block and the crankcase. A displacement of the cylinderblock will act on a mechanism connecting the cylinder block and the crankshaft. This causesan adjustment of the crank angle from the current, first crank angle to the desired, second MODE002SE2015-06-2213 crank angle. Suitable mechanisms for this purpose can be connected directly to thecrankshaft, which will then control the displacement of each camshaft via the transmissionprovided, or be connected to the transmission between crankshaft and camshaft. Suchmechanisms will be discussed in further detail below. ln connection with a direct start, it is desirable to reduce the compression ratio and increasethe offset simultaneously over at least a portion of a displacement range during the crankangle adjustment. The control unit is arranged to determine the crank angle adjustmentrequired to displace the piston in the next cylinder to fire into a positon after top dead center,where the crank angle is suitable for direct start. According to a first example, the secondcrank angle can be selected between 10 crank angle degrees after top dead center and 10crank angle degrees before exhaust valve opening. According to a second example, thesecond crank angle can be selected between 30 and 50 crank angle degrees after top dead center.

The mechanism performing the crank angle adjustment is arranged to connect the cylinderblock and the crankshaft when the internal combustion engine is stopped. The mechanism isoperatively connected to the crankshaft during periods when the ignition is off in order torotate the crankshaft to a desired crank angle. The mechanism can further be controlled todisconnect the cylinder block and the crankshaft prior to an engine start.

The mechanism can comprise a controllable arm located on the cylinder block andconnectable to a control wheel, or gear wheel located on the crankcase for rotating thecrankshaft directly, via the flywheel or camshaft pulley, or indirectly, via a gear wheel. Thecontrollable arm is pivoted or displaced to be in driving connection with the gear duringperiods when the ignition is off in order to rotate the crankshaft to a desired crank angle.Alternatively, a control wheel located on the cylinder block can be in driving connection with arack on the crankcase and with the camshaft transmission, such as a belt or chain, normallydriven by the crankshaft. During a displacement of the cylinder block the relative movementbetween cylinder block and crankcase causes a rotation of the control wheel. The controlwheel will then rotate the crankshaft to a desired crank angle via the camshaft transmission.The control wheel can be provided with a free-wheeling device allowing is to be disconnectedfrom the rack and be driven by the camshaft transmission during normal engine operation. lf the available displacement range between the cylinder block and the crankcase is notsufficient for using a 1:1 ratio between driving and driven wheels to achieve the desired crankangle then a suitable gearing or similar device can be provided to increase the gear ratio.

MODE002SE2015-06-2214 Simultaneous adjustment of compression ratio and cylinder offset can be achieved bydisplacing the cylinder block along planar guide surfaces arranged at an angle to a first planeat right angles to the cylinder axis. The plane along which the cylinder block is displaced willintersect the first plane located at right angles to the cylinder axis in a line parallel to thecrankshaft axis. The angle between the guide surfaces and the first plane is an acute anglewithin the range 0° to 60 °. The size of the angle can be selected to provide a desired rangefor compression ratio and cylinder offset. Alternative examples for performing a simultaneousadjustment of compression ratio and cylinder offset can be achieved by displacing thecylinder block along cylindrical guide surfaces comprising generatrices parallel to thecrankshaft axis, or by displacing the cylinder block at right angles to the crankshaft axis,along a fixed path having a predetermined curvature, e.g. by means of an excentermechanism or guiding tracks (coulisse).

The invention also relates to a vehicle comprising an internal combustion engine foroptimizing an internal combustion engine with variable compression ratio for a direct start as described above. lt is particularly advantageous that a reliable direct starting of the internal combustion enginecan be carried out with a conventional, and therefore cost-effective, determination of therotational position of the crankshaft. The invention allows simultaneous adjustment of thecrank angle, compression ratio and cylinder offset using a single actuator type. A reducedcompression ratio will reduce the compression work required for subsequently firingcylinders, making the engine easier to start. By increasing the offset it is possible to reducetangential cylinder forces and friction forces, while at the same time achieving a moreeffective crank torque arm and crank location. The same displacement used for theseadjustments is used for performing the crank angle adjustment required to displace a pistonin the first cylinder to fire into a positon after top dead center, where the crank angle issuitable for direct start. By means of the rapid revving-up of the internal combustion enginein less than one complete revolution of the crankshaft, possibly at little as a quarter of arevolution, the crank case of the internal combustion engine can advantageously beprevented from slipping into a natural frequency of the engine assembly.

I\/|ODEO02SE2015-06-22 FIGURES ln the following text, the invention will be described in detail with reference to the attacheddrawings. These schematic drawings are used for illustration only and do not in any way limitthe scope of the invention. ln the drawings: Figure 1 shows a schematically indicated vehicle with an engine suitable for use with amethod according to the invention; Figure 2A-B show a side view of an internal combustion engine with variable compressionand offset; Figure 3 shows a schematic diagram of pressure vs. crank angle degrees; Figure 4A-B show a side view of an internal combustion engine with a mechanism foradjusting the crank angle; Figure 5 shows a side view of an alternative mechanism for the engine in Fig.4B.

DETAILED DESCRIPTION Figure 1 shows a schematically indicated vehicle 111 provided with an internal combustionengine 112 according to the invention. The vehicle 111 is further provided with atransmission arrangement 113 connected to the engine 112. The engine 112 and thetransmission 113 is controlled by an electronic control unit (ECU) 114. The transmission 113is controlled to select a gear ratio between the engine 112 and a pair of driven wheels 115,116. Although the figure indicates a transmission for a rear wheel drive vehicle, the inventionis not limited to any particular type of transmission.

The engine 112 is provided with a position sensor 121, in this example located adjacent aflywheel (not shown) having an outer circumference provided with a toothing arrangement toprovide position markers for the engine crankshaft (not shown). The position markersreproduce the rotational position of the crankshaft and therefore the current position of eachof the pistons of the engine 112 can be determined by the ECU 114. The ignition in thecombustion chambers of the internal combustion engine can be initiated at a suitable time byreference to the current position of the pistons. The position sensor 121 is located in thevicinity of the toothing arrangement that identifies the rotational position of the crankshaftwhen the position markers rotate past the position sensor 121. The sensor 121 can be apulse counter or inductive pickup. An optional, second position sensor 122 connected to theECU 114 can be provided for determining the position of at least one camshaft in the engine MODE002SE2015-06-2216112. lf the signal of a camshaft position sensor 122 of the engine 112 is detected, then the position of the pistons can be determined exactly via the rotational position of the crankshaft.

Figure 2A shows a side view of an internal combustion engine 210 with variable compressionand offset. The internal combustion engine 210 comprises a crankcase 211 having acrankshaft 212 connected to at least two pistons 213 (one shown), via a connecting rod 214.The connecting rod 214 is connected to the piston 213 by a piston pin 215 and to a crank216 of the crankshaft 212. The crankshaft 212 has a central axis X in the longitudinaldirection of the engine 210. The engine 210 further comprises a cylinder block 217comprising at least one cylinder 218 (one shown) in which the piston 213 can perform areciprocating motion. A cylinder block 219, comprising at least one intake valve and at leastone exhaust valve controlled by a respective camshaft 225, 226, is mounted on the cylinderblock 217. The position sensors 121, 122 described in Figure 1 are schematically indicated inFigure 2A.

The cylinder 218 has a central axis Y at right angles to the crankshaft axis X. ln the examplein Figure 2A, simultaneous adjustment of compression ratio CR and cylinder offset can beachieved by displacing the cylinder block 217 along opposed, contacting planar guidesurfaces 221, 222 arranged in an angled first plane P1. A first guide surface 221 is locatedon the crankcase 211 and a second guide surface is located on the cylinder block 217. Thefirst plane P1 is arranged at an angle d relative to a second plane P2 at right angles to thecylinder axis Y, which angle can be selected between 0° and 60°. An actuator 223 forcontrolling the relative displacement of the crankcase 211 and the cylinder block 217 islocated between the crankcase 211 and the cylinder block 217. ln the example shown inFigure 2A, the actuator 223 is mounted onto the crankcase 211 in order to act on the cylinderblock 217. The schematically indicated actuator can be operated by a suitable hydraulic, electric or mechanical means.

Figure 2B shows a side view of the engine in Figure 2A after actuation of the actuator 123.As in Figure 2A the internal combustion engine 210 comprises a crankcase 211 having acrankshaft 212 connected to a piston 213 via a connecting rod 214. The connecting rod 214is connected to the piston 213 by a piston pin 215 and to a crank 216 of the crankshaft 212.The crankshaft 212 has a central axis X in the longitudinal direction of the engine 210. Theengine 210 further comprises a cylinder block 217 comprising at least one cylinder 218 inwhich the piston 213 can perform a reciprocating motion. A cylinder block 219 comprising atleast one intake valve and at least one exhaust valve for each cylinder is mounted on the MODE002SE2015-06-2217cylinder block 217. The cylinder 218 has a central axis Y at right angles to the crankshaft axis X.

As indicated in Figure 2B simultaneous adjustment of compression ratio CR and cylinderoffset has been achieved by displacing the cylinder block 217 along opposed, contactingplanar guide surfaces 221, 222 arranged in an angled first plane P1. The first plane P1 isarranged at an angle a relative to a second plane P2 at right angles to the cylinder axis Y.

This displacement along the first plane P1 can be divided into two components. A firstcomponent causes an upward displacement of the cylinder block 217 in the direction of thecylinder axis Y in the direction of the arrow A1. The upper surface of the piston 213, which islocated in the plane P3 in in Figure 2A, will effectively be located further from the cylinderblock 219, as indicated by the plane P4 in Figure 2B. The clearance volume will thereby beincreased by the volume enclosed between the two planes P3 and P4, causing a loweredcompression ratio. A second component causes a transverse displacement of the cylinderblock transverse to the cylinder axis and the crankshaft axis, in the direction of the arrow A2.This causes a parallel displacement of the cylinder axis Y relative to the crankshaft axis X,resulting in a positive offset O, which is preferably up to 2/3 of the crank pin radius. Theangle oi between the first and second planes P1, P2 and the crank pin radius determines thepossible variation in compression ratio and the required displacement range of the guidingmeans between the cylinder block and the crankcase.

Figures 2A and 2B are used to illustrate the principle of a variable compression ratio engineproviding simultaneous adjustment of compression ratio and cylinder offset. According to theinvention the same displacement is used for simultaneously adjusting the crank angle of thecrankshaft to a position suitable for direct start. The mechanism for achieving this functionwill be described in further detail below.

Figure 3 shows a schematic diagram of pressure vs. crank angle degrees (CAD) for theoperating cycles of the three consecutive firing cylinders in a four-stroke four cylinder engine.ln a four-stroke engine the four cycles are compression, expansion exhaust and intake,performed during two full revolutions of the crankshaft and making up a total of 720 CAD.When the engine is approaching its rest position the pressures of the previous, last cylinderC1 in the firing order and the next cylinder C2 in turn to fire will attempt to balance out. Theprevious, first cylinder C1 will be in its expansion stroke while the next, second cylinder C2will be in its compression stroke. The momentum of the system as the engine revs down willcause the piston in the second cylinder C2 to come to rest at least half way into the MODE002SE2015-06-2218compression cycle, i.e. less than 90 CAD before top dead center TDC2. ln this example, the next cylinder to fire in a subsequent engine start will be the second cylinder C2.

Hence the distance required to rotate the crankshaft into a desired crank angle position forstart is a first crank angle adjustment CA1 of at least 90 CAD plus an additional crank angleadjustment past top dead center TDC2 up to the desired firing position for direct start.According to the example in Figure 3, the additional crank angle adjustment is to beperformed up to at least a second angle adjustment CA2 of 30 CAD, but no more than a thirdangle adjustment CA3 of 60 CAD ln the current example the minimum and maximum rotationrequired would be betvveen 120 CAD (90°+30°) and 150 CAD (90°+60°). Knowing theavailable displacement range at the time of engine stop, a control unit (Figure 1) controls anactuator (Figure 2B) to displace the cylinder block towards the lowest compression ratiopossible within the range of desired crank angles. As indicated in Figure 3, the crankshaftwould be rotated from its rest position at a first crank angle 301 to its starting position at asecond crank angle 302 prior to start.

Figure 4A shows a side view of an internal combustion engine 410 with variable compressionand offset. The internal combustion engine 410 comprises a crankcase 411 having acrankshaft 412 connected to at least two pistons 413 (one shown), via a connecting rod 414.The connecting rod 414 is connected to the piston 413 by a piston pin 415 and to a crank416 of the crankshaft 412. The crankshaft 412 has a central axis X in the longitudinaldirection of the engine 410. The engine 410 further comprises a cylinder block 417comprising at least one cylinder 418 (one shown) in which the piston 413 can perform areciprocating motion. A cylinder block 419, comprising at least one intake valve and at leastone exhaust valve controlled by a respective camshaft 425, 426, is mounted on the cylinderblock 417. The position sensors 121, 122 described in Figure 1 are schematically indicated inFigure 4A.

The cylinder 418 has a central axis Y at right angles to the crankshaft axis X. ln the examplein Figure 4A, simultaneous adjustment of compression ratio CR and cylinder offset can beachieved by displacing the cylinder block 417 along opposed, contacting planar guidesurfaces 421, 422 arranged in an angled first plane P1. A first guide surface 421 is locatedon the crankcase 411 and a second guide surface is located on the cylinder block 417. Thefirst plane P1 is arranged at an angle oi relative to a second plane P2 at right angles to thecylinder axis Y, which angle can be selected between 0° and 60°. An actuator 423 (seeFigure 4B) for controlling the relative displacement of the crankcase 411 and the cylinderblock 417 is located between the crankcase 411 and the cylinder block 417. ln this example MODE002SE2015-06-2219the actuator is to be mounted onto the crankcase 411 in order to act on the cylinder block 417. The actuator can be operated by a suitable hydraulic, electric or mechanical means.

The engine in Figure 4A is further provided with a first and a second camshaft 425, 426 forcontrolling their respective intake and exhaust valves. The camshafts 425, 426 are driven bythe crankshaft 412 via a camshaft transmission, which in this case comprises a belt 424 anda first and a second control wheel 427, 428. The usual function of a control wheel is toensure correct tension in the belt or chain at all times, and to provide a belt geometry thatprovides sufficient friction for the driving and driven shafts. ln Figure 4A, the first control wheel 427 is arranged to ensure that tension is maintained inthe belt 424. The second control wheel 428 is located fixed relative to the crankcase 411 andis in driving connection with a rack 430 on the cylinder block 417. ln this example the rack430 is arranged in the plane P1, at right angles to the crankshaft axis X. During adisplacement of the cylinder block, as shown by the arrow B in Figure 4B, the relativemovement between the cylinder block 417 and the crankcase 411 causes a rotation of thesecond control wheel 428. The second control wheel 428 will then act on the belt to rotatethe crankshaft 412 to a desired crank angle. At the same time the camshafts 425, 426 will berepositioned via the camshaft transmission. The second control wheel 428 is provided with afree-wheeling device 431 allowing is to be disconnected from the rack 430 to be driven bethe camshaft transmission during normal engine operation. The free-wheeling device can bereplaced by a controllable clutch or a similar device for disconnecting the second controlwheel from the rack. ln the case of a clutch, the clutch should be biased to a non-actuatedposition under normal engine operation. During normal operation of the engine the controlwheel 428 is driven by the belt 424 and is disconnected from the above-mentionedmechanism. Consequently, after start the compression ratio and the offset can be controlleddepending on the current operating conditions of the engine, without interfering with themechanism for performing the crank angle adjustment prior to start. ln the above case it is assumed that the available displacement range for the cylinder block417 along the plane P1 is sufficient for using a 1:1 ratio between the rack 430 and thesecond wheel 428 to achieve the desired crank angle adjustment. However, if this is not thecase then a suitable gearing or similar device can be provided. According to an alternativeexample shown in Figure 5, a control wheel 528 comprising two gear wheels 528a, 528barranged side-by-side on the same axis can be provided in order to achieve a sufficient gearratio. For instance, the control wheel 528 can comprise a relatively smaller gear wheel 528aconnected to the crankcase and a relatively larger gear wheel 528b acting on the crankshaft MODE002SE2015-06-22 512 via the camshaft transmission belt 524. The gear ratio between the smaller and largergear wheels is selected depending on the available displacement range between cylinderblock and the crankcase, and the rotational angle required to achieve the desired crankangle. Figure 5 schematically indicates a pair of opposed, contacting planar guide surfaces521, 522 and a rack 530 in contact with displaced with the displacement of the cylinder block(not shown) to act on the smaller gear wheel 528a.

The invention is not limited to the embodiments described above but may be varied freely within the scope of the claims.

Claims (21)

1. Method for optimizing an internal combustion engine with variable compression ratio for adirect start, the engine comprising a crankcase (211 ; 411) comprising a crankshaft (212; 412)connected to at least two pistons; and a cylinder block (217; 417) comprising at two cylinders(218; 418), c h a r a c t e r i z e d b y the method comprising the steps of: - detecting that the internal combustion engine has stopped;- detecting a current crank angle;- determining which cylinder is next to fire in a predetermined cylinder firing order; - determining a crank angle adjustment required to achieve a crank angle suitable forignition in this first cylinder - operating at least one actuator (123) to displace the cylinder block (217; 417) relative tothe crankcase (211; 411) for adjustment of compression ratio and cylinder offset (O); - causing a simultaneous displacement of the cylinder block (217; 417) in the direction ofthe cylinder axis (Y), and transverse to the cylinder axis (Y) and the crankshaft axis (X);and - performing the crank angle adjustment using a mechanism (428; 428'; 430) connectingthe cylinder block and the crankshaft, and which mechanism (428; 428'; 430) is actuatedby the cylinder block displacement.

2. Method according to claim 1, c h a r a c t e r i z e d b y reducing the compression ratioand increasing the offset simultaneously over at least a portion of a displacement range during the crank angle adjustment.

3. Method according to claim 1 or 2, c h a r a c t e r i z e d b y determining a crank angleadjustment required to displace the piston in the first cylinder to fire into a positon after topdead center, where the crank angle is suitable for direct start.

4. Method according to claim 3, c h a r a c t e r i z e d i n that the crank angle is selectedbetween 10 crank angle degrees after top dead center and 10 crank angle degrees before exhaust valve opening.

5. Method according to claim 4, c h a r a c t e r i z e d i n that the crank angle is selectedbetween 30 and 50 crank angle degrees after top dead center. MODE002SE2015-06-222

6. Method according to any one of claims 1-5, c h aracte r i z ed by controlling themechanism (428; 428'; 430) to connect the cylinder block and the crankshaft when theinternal combustion engine is stopped.

7. Method according to claim 6, c h a r a c t e r i z e d b y controlling the mechanism (428;428'; 430) to disconnect the cylinder block and the crankshaft prior to an engine start.

8. Method according to any one of claims 1-5, c h a r a c t e r i z e d b y mechanism (428;428'; 430) is connected to the crankshaft via a free-wheeling device.

9. Method according to any one of claims 1-8, c h aracte r i z ed by displacing thecylinder block (217; 417) along guide surfaces (221, 222; 421, 422) arranged at an angle (d)to a plane (P2)at right angles to the cylinder axis (Y).

10. Method according to claim 9, c h a r acte r i z ed in that the angle between the guide surfaces and the first plane is an acute angle (d) within the range 0°to 60°

11. An internal combustion engine, comprising a crankcase (211; 411) with a crankshaft(212; 412; 212; 412'; 92; 212) connected to at least two pistons; a cylinder block (217; 417)comprising at least two cylinders, which cylinder block is displaceable relative to thecrankcase; and at least one actuator (123) connected between the cylinder block and thecrankcase, wherein guiding means (221, 222; 421, 422) is arranged to guide the cylinderblock (217; 417) relative to the crankcase (211; 411) for simultaneous adjustment ofcompression ratio and offset when the actuator is cylinder operated, c h a r a c t e r i z e d in that the engine further comprises:- a sensor arranged to detect a current, first crank angle when the engine has stopped; - a control unit arranged to determine which cylinder is next to fire in a predeterminedcylinder firing order based on the detected crank angle and to determine a crank angleadjustment required to achieve a desired, second crank angle suitable for ignition in thatcylinder; and - a mechanism (428; 428'; 430) arranged to connect the cylinder block and the crankshaft,so that a predetermined displacement the cylinder block by the actuator causes turning ofthe crankshaft to adjust the crank angle to the second crank angle.

12. An internal combustion engine according to claim 11, c h a r a c t e r i z e d i n that theactuator (223; 423) is arranged to displace the cylinder block and perform a simultaneousreduction of the compression ratio and increase of the offset during the crank angleadjustment. l\/lODE002SE2015-06-22

13. 313. An characterized in internal combustion engine according to claim 11 or 12,that the control unit is arranged to determine the crank angleadjustment required to displace the piston in the next cylinder to fire into a positon after top dead center, where the crank angle is suitable for direct start.

14. An internal combustion engine according to claim 13, c h a r a c t e r i z e d i n that thesecond crank angle is selected between 10 crank angle degrees after top dead center and10 crank angle degrees before exhaust valve opening..

15. An internal combustion engine according to claim 14, c h a r a c t e r i z e d in that thesecond crank angle is selected between 30 and 50 crank angle degrees after top dead center.

16. An characterized in internal combustion engine according to any one of claims 11-15, that the mechanism (428; 428'; 430) is arranged to connect thecylinder block and the crankshaft when the internal combustion engine is stopped.

17. An 11-15,c h a r a c t e r i z e d i n that the mechanism (428; 428'; 430) is arranged to disconnect the internal combustion engine according to any one of claims cylinder block and the crankshaft prior to an engine start.

18. An characterized in internal combustion claims 11-15,that the mechanism (428; 428'; 430) is arranged to turn the crankshaft via a free-wheeling device. engine according to any one of

19. An 11-18,c h aracte r i zed in that the guiding means comprises planar guide surfaces (221, internal combustion engine according to any one of claims222; 421, 422) arranged at a predetermined angle to a first plane at right angles to the cylinder axis.

20. An internal combustion engine according to claim 19, c h a r a c t e r i z e d i n that theangle between the guide surfaces and the first plane is an acute angle (oi) within the range 0°to 60 °.

21. Vehicle c h a r ac t e r i z e d i n that the vehicle comprises an internal combustion engine according to any one of claims 11-20.