SE544230C2 - Method and arrangement for variable valve timing for inernal combustion engine; vehicle and engine with such arrangement; computer program and computer readable medium for such a method - Google Patents

Abstract

The disclosure concerns a control arrangement and a method for controlling a variable valve timing of a four-stroke ICE (4), the ICE (4) comprising: an exhaust valve (20) and an intake valve (22), an exhaust camshaft (10) arranged to control the opening of the exhaust valve (20) and to control compression release braking of the internal combustion engine (4), and an intake camshaft (12) arranged to control the opening and closing of the intake valve (22). The control arrangement (38) is configured to, upon compression release brake activation: change the timings of the intake and exhaust camshafts. A timing change angle of the intake camshaft (12) and a timing change angle of the exhaust camshaft (10) are selected such that the timing change angle of the intake camshaft is a function of the timing change angle of the exhaust camshaft during the compression release braking.The disclosure also concerns a four-stroke internal combustion engine comprising a control arrangement, a vehicle comprising such an internal combustion engine, a computer program, and a computer-readable storage medium.

Description

TECHNICAL FIELD The invention relates to a control arrangement for controlling a variable valve timing of a four-stroke internal combustion engine, to a four-stroke internal combustion engine comprising acontrol arrangement, to a vehicle comprising a four-stroke internal combustion engine, and toa method for controlling a variable valve timing of a four-stroke internal combustion engine.The invention further relates to a computer program and to a computer-readable storage medium.

BACKGROUND A four-stroke internal combustion engine, ICE, may for instance form a power source of adrivetrain of a vehicle. When fuel is combusted in the ICE, positive torque is provided to thedrivetrain for propelling the vehicle via drive wheels of the vehicle. The driving wheels formpart of the drivetrain and are configured for transmitting torque between the drivetrain and a surface, on which the vehicle is travelling.

When no fuel is combusted in the ICE while the vehicle is travelling along the surface, themomentum of the vehicle rotates the drive wheels. If under such circumstances the drivetrainis closed, i.e. When torque is transferred from the drive wheels to the ICE, the crankshaft ofthe ICE is rotated by the rotating drive wheels. ln such a situation, the ICE may apply anegative torque, i.e. a braking torque, to the drivetrain. The application of the negative torqueto the drivetrain is often referred to as engine braking. That is, the negative torque applied to the drivetrain reduces the speed of the vehicle.

During normal engine braking, occurring for example when a driver of a vehicle releases anaccelerator pedal, no combustion of fuel will take place in the ICE. In this condition, the ICEwill provide some negative torque to the drivetrain due to ICE internal friction and due topumping of air through the ICE. However, as a piston of the ICE travels upward during itscompression stroke, the air that is trapped in the relevant cylinder is compressed. Thecompressed air opposes the upward motion of the piston. However, almost all of the energy stored in the compressed air is returned to the crankshaft on the subsequent expansion stroke of the piston. Thereby, during normal engine braking, the compression stroke togetherwith the subsequent expansion stroke, will not contribute to a significant braking torque of the engine.

The amount of negative torque applied to the drivetrain during engine braking may beincreased by utilising a compression release engine brake. The compression release enginebrake may also be referred to as compression release break, CRB, or Jake brake, or Jacobsbrake, or decompression brake. When activated, the CRB opens the exhaust valve after thecompression stroke, releasing the compressed air to the exhaust system of the ICE.Thereby, the energy stored in the compressed air during the compression stroke will not bereturned to the crankshaft on the subsequent expansion stroke. Accordingly, the negative torque of the engine is increased.

DE102018002015 discloses a four-stroke ICE including an exhaust valve control assemblyhaving a discharge valve phase shifting device configured to control the opening of exhaustvalves during expansion strokes and closing during exhaust strokes in order to achieveengine braking via compression in the cylinders during the exhaust stroke. An intake valvecontrol assembly is configured to control intake valves during the engine braking via compression in the cylinders to be open during at least a portion of expansion strokes.

The use of phase shifting, which may also be referred to as cam phasing, and herein isreferred to as variable valve timing or timing change, during compression release engine braking introduces problems related to the control of such timing changes.

SUMMARY lt would be advantageous to achieve an alternative control arrangement for controlling avariable valve timing of a four-stroke internal combustion engine and/or an alternativemethod for controlling a variable valve timing of a four-stroke internal combustion engine. lnparticular, it would be desirable to enable simplified control of a variable valve timing duringcompressing release engine braking. To better address one or more of these concerns, acontrol arrangement, a four-stroke internal combustion engine, a vehicle, and a method having the features defined in the independent claims are provided.

According to an aspect of the invention, there is provided a control arrangement forcontrolling a variable valve timing of a four-stroke internal combustion engine, the internalcombustion engine comprising: an exhaust valve and an intake valve, an exhaust camshaft arranged to control the opening of the exhaust valve and to control compression release braking of the internal combustion engine, and an intake camshaft arranged to control theopening and closing of the intake valve. The control arrangement is configured to, uponcompression release brake activation: - change the timing of the intake camshaft to delay opening of the intake valve, and - change the timing of the exhaust camshaft to advance closing of the exhaust valve, whereina timing change angle of the intake camshaft and a timing change angle of the exhaustcamshaft are selected such that the timing change angle of the intake camshaft is a function of the timing change angle of the exhaust camshaft during the compression release braking.

According to a further aspect of the invention, there is provided a method for controlling avariable valve timing of a four-stroke internal combustion engine. The internal combustionengine comprises: an exhaust valve and an intake valve, an exhaust camshaft arranged tocontrol the opening of the exhaust valve and to control compression release braking of theinternal combustion engine, and an intake camshaft arranged to control the opening andclosing of the intake valve. The method comprises, upon compression release brakeactivation: - changing the timing of the intake camshaft to delay opening of the intake valve, and - changing the timing of the exhaust camshaft to advance closing of the exhaust valve,wherein a timing change angle of the intake camshaft and a timing change angle of theexhaust camshaft are selected such that the timing change angle of the intake camshaft is afunction of the timing change angle of the exhaust camshaft during the compression release braking.

Since during the compression release braking, the timing change angles of the intake andexhaust camshafts are selected such that the timing change angle of the intake camshaft is afunction of the timing change angle of the exhaust camshaft, there exists a limited number ofcombinations of timing change angles of the intake and exhaust camshafts. Thus, thepresent invention provides simplified control of variable valve timing of an ICE, because thetheoretically large number of available combinations of timing change angles of the intakeand exhaust camshafts during compression release braking has been reduced to thecombinations of timing change angles of the intake and exhaust camshafts provided by the function.

More specifically, there are multiple combinations of intake and exhaust timing changeangles that produce the same engine braking torque during compression release braking.There are also certain combinations of intake and exhaust timing change angles that may put damaging loads on ICE hardware. The control strategy provided by the above mentioned 4 control arrangement and method, utilising during compression release braking that the timingchange angle of the intake camshaft is a function of the timing change angle of the exhaustcamshaft, limits the number of combinations used, and also makes possible to avoidcombinations resulting in large hardware load by suitable selection of the function. Reducingthe degrees of freedom of the control arrangement for the torque control is achieved withoutlimiting compression release braking performance, while making calibration of the control arrangement significantly easier.

The four-stroke internal combustion engine, ICE may be a compression ignition ICE, such asa diesel engine. Herein, the four-stroke ICE alternatively may be simply referred to as an internal combustion engine, ICE, or engine.

The ICE comprises the crankshaft, the exhaust camshaft, the intake camshaft, and thecontrol arrangement. A rotational speed of the crankshaft may herein alternatively bereferred to as a rotational speed of the ICE. Further, the ICE may comprise at least onecylinder arrangement and a compression release brake mechanism, which are known assuch. The cylinder arrangement may comprise the exhaust and intake valves, a combustionchamber, a cylinder bore, and a piston configured to reciprocate in the cylinder bore andbeing connected to the crankshaft. The cylinder arrangement may comprise further exhaust and/or intake valves.

As in any four-stroke ICE, the piston performs an intake stroke, a compression stroke, anexpansion stroke, and an exhaust stroke in the cylinder bore of the cylinder arrangement.The ICE may comprise more than one cylinder arrangement, such as e.g. four, five, six, or eight cylinder arrangements.

The exhaust camshaft is configured to control the opening and closing of the exhaust valvein a commonly known manner with an ordinary cam lobe of the exhaust camshaft controllingthe exhaust valve. ln a known manner, the exhaust camshaft is further arranged to controlcompression release braking of the ICE via the compression release brake mechanism. Forthis purpose, the exhaust camshaft may comprise one or more further cam Iobes, whichcause the exhaust valve to open via the compression release brake mechanism whencompression release braking is activated. The intake camshaft is configured to control theopening and closing of the intake valve in a commonly known manner with a cam lobe of the intake camshaft controlling the intake valve.

During compression release braking without timing change of the exhaust camshaft, thecompression release brake mechanism causes the exhaust valve to open at the beginning ofthe expansion stroke. That is, without any timing change of the exhaust camshaft, thecompressed air in the combustion chamber is released into the exhaust system of the engine around Top Dead Centre fire, TDCfire, of the piston.

The timing change of the exhaust camshaft during compression release braking affects boththe ordinary cam lobe of the exhaust camshaft and the one or more further cam lobes of the exhaust camshaft.

Engine braking torque, braking torque, negative torque, requested engine braking torque,engine braking torque request, etc. discussed herein relate to braking torque produced by the ICE during compression release braking.

The rotations of the exhaust and intake camshafts are synchronized with the crankshaft.However, the timing of the exhaust and intake camshafts is changeable, i.e. the rotationalpositions of the camshafts in relation to the crankshaft are controllable. Herein, this is referred to as timing change and as variable valve timing. ln practice, this means that the crankshaft angle at which a valve controlled by the relevantcamshaft is opened and closed can be changed. The changing of the timing of the camshaftsmay be performed in any known manner. For instance, WO 2017/217908 and US 8714123disclose suitable timing control arrangements to be utilised for changing the timing of the camshafts. lt is to be noted that an angular length of the open period of each of the exhaust and intakevalves remains the same when the timings of the camshafts are changed. This, as opposedto systems Where lost motion mechanisms are utilised for changing closing and/or opening positions of valves, which accordingly will also affect the angular length of the period during which the relevant valve remains open.

As mentioned above, the timings of the exhaust and intake camshafts are controllable by thecontrol arrangement, i.e. the control arrangement is configured to change the rotationalposition of the camshafts in relation to the crankshaft. The control arrangement is configured,upon receiving an engine braking torque request, or upon producing a requested engine braking torque, to activate compression release braking.

A timing change angle of the respective camshaft is the angle by which the timing of thecamshaft is changed in relation to its ordinary angular operating position in relation to the crankshaft.

The function defining the timing change angle of the intake camshaft in relation to the timingchange angle of the exhaust camshaft during the compression release braking may e.g. be expressed as a mathematical function or mapped in a table.

Accordingly, the function is representable by a line in a coordinate system representing thetiming change angle of the exhaust camshaft and timing change angle of the intakecamshaft, wherein e.g. the timing change of the exhaust camshaft is represented along the X-axis, and the timing change of the intake camshaft is represented along the Y-axis.

Along the line represented by the function, different amounts of negative torque, i.e. brakingtorque, are produced by the ICE during compression release braking. By mapping theamount of negative torque produced at the different combinations of timing change angles ofthe intake and exhaust camshafts along the line represented by the function, the controlarrangement may control the amount of negative torque produced by the ICE during compression release braking by changing the timings of the intake and exhaust camshafts.

The function defining the timing change angle of the intake camshaft in relation to the timingchange angle of the exhaust camshaft during the compression release braking, may be anysingle-valued or multi-valued function suitable for the relevant ICE. ln a single-valuedfunction, there exists for each timing change angle of the exhaust camshaft only one timingchange angle of the intake camshaft. ln a multi-valued function, for one or more timingchange angles of the exhaust camshaft there may exist more than one timing change angle of the intake camshaft.

If the cylinder arrangement comprises one or more additional intake valves and/or exhaustvalves, also these valves may be opened and closed in the manner discussed above duringcompression release braking. This will occur if such additional valves are controlled by thefirst and/or second camshafts. Accordingly, if the additional valves are controlled byadditional camshafts, also the timing of any additional camshafts may be changed as discussed herein.

According to embodiments, the control arrangement may be further configured to: - change the timing of the intake camshaft to provide a larger delay in opening of the intakevalve with a lower engine braking torque request during compression release braking, and - change the timing of the exhaust camshaft to provide less advance in closing of the exhaustvalve with a lower engine braking torque request during compression release braking. ln thismanner, the pressure in the combustion chamber during the compression stroke may bereduced due to the intake valve remaining open during a portion of the compression stroke.Accordingly, the pressure may be reduced in the combustion chamber preceding thecompression release during the expansion stroke. The reduced pressure in the combustionchamber may reduce the load on the compression release brake mechanism during compression release braking.

More specifically, generally, a low engine braking torque may be achieved with acombination of timing changes of low advance in the timing of the exhaust valve and a largedelay in the timing of the intake valve, whereas a high engine braking torque may beachieved with a combination of timing changes of a large advance in the timing of the exhaust valve and a low delay in the timing of the intake valve.

Accordingly, the control arrangement may be configured to: - change the timing of the intake camshaft to provide a larger delay in opening of the intakevalve when a low engine braking torque is requested during compression release brakingthan when a high engine braking torque is requested during compression release braking,and - change the timing of the exhaust camshaft to provide less advance in closing of the exhaustvalve when a low engine braking torque is requested during compression release braking than when a high engine braking torque is requested during compression release braking.

Conversely, the control arrangement may be configured to: - change the timing of the intake camshaft to provide a lesser delay in opening of the intakevalve with a larger engine braking torque request during compression release braking, and- change the timing of the exhaust camshaft to provide a larger advance in closing of theexhaust valve with a larger engine braking torque request during compression release braking.

That is, the control arrangement may be configured to:- change the timing of the intake camshaft to provide less delay in opening of the intake valvewhen a high engine braking torque is requested during compression release braking than when a low engine braking torque is requested during compression release braking, and - change the timing of the exhaust camshaft to provide a larger advance in closing of theexhaust valve when a high engine braking torque is requested during compression releasebraking than when a low engine braking torque is requested during compression release braking.

An engine braking torque request may be provided to, or by, the control arrangement. Thecontrol arrangement utilises the engine braking torque request for applying changes to thetimings of the intake and exhaust camshafts in order to provide a negative torque from theICE during compression release braking corresponding to the requested engine braking torque.

According to embodiments, the control arrangement may be further configured to: - determine a braking torque during compression release braking based on a currentrotational speed of the internal combustion engine. ln this manner, the braking torque may bedetermined e.g. during stable engine operating conditions. For instance, the braking torquemay be determined based on the engine rotational speed when the ICE has been operatingunder the same load and with the same rotational speed over a time period sufficient for establishing stable operating conditions prior to activating compression release braking.

Moreover, the current rotational speed of the ICE may be utilised in a vector or matrix fordetermining from the vector or matrix at least one braking torque value that is availableduring compression release braking. Further braking torque values may be determined from the vector or matrix at various timing change angles of the intake and exhaust camshafts.

According to embodiments, the four-stroke ICE may comprise a turbocharger configured toproduce a charge air pressure to be utilised during compression release braking. ln thismanner, the produced charge air pressure may be utilised for charging a combustionchamber of the ICE during compression release engine braking. Thus, the ICE may providea larger negative torque during compression release engine braking than if the ICE would not comprise any turbocharger.

According to embodiments, the control arrangement may be configured to: - determine a braking torque during compression release braking based on a current chargeair pressure provided by the turbocharger. ln this manner, the control arrangement mayutilise the current charge air pressure for determining a braking torque, e.g. for providing arequested braking torque, or for determining intermediate braking torques that in turn may be utilised for providing a requested braking torque.

Moreover, the current charge air pressure may be utilised in a vector or matrix fordetermining at least one braking torque value that is available during compression release braking.

According to embodiments, the control arrangement may be further configured to: - determine a braking torque at an intermediate charge air pressure between two knownbraking torques at two known charge air pressures, based on a linear interpolation orextrapolation between the two known charge air pressures and/or the two known brakingtorques. ln this manner, the control arrangement may avoid storing braking torques for everyconceivable charge air pressure. lnstead, the control arrangement may be configured todetermine the available engine braking torque, thus, simplifying setup of the control arrangement.

The charge air pressure from the turbocharger varies during operation of the ICE. Charge airpressure build-up and reduction are dynamic processes. Also during compression release braking of the ICE, the charge air pressure may vary.

Since the braking torque at an intermediate charge air pressure may be determined by theabove-mentioned linear interpolation or extrapolation, the control arrangement maycontinuously or intermittently determine a currently available braking torque duringcompression release braking, e.g. while the charge air pressure builds up duringcompression release braking. That is, by continuously or intermittently determining thecurrent charge air pressure during charge air build-up, and utilising the current charge airpressure as a value of the intermediate charge air pressure, the currently available braking torque may be determined during the dynamic process of charge air pressure build-up.

Embodiments of the control arrangement for controlling a variable valve timing of a four-stroke ICE discussed herein may be implemented in a corresponding manner inembodiments of the method for controlling a variable valve timing of a four-stroke ICE discussed herein.

According to a further aspect, there is provided a four-stroke internal combustion enginecomprising a control arrangement according to any one of aspect and or embodiments discussed herein.

According to a further aspect, there is provided a vehicle comprising a four-stroke internal combustion engine according to any one of aspect and/or embodiments discussed herein.

According to a further aspect, there is provided a computer program comprising instructionswhich, when the program is executed by a computer, cause the computer to carry out the steps of the method according to any one of aspect and/or embodiments discussed herein.

According to a further aspect, there is provided a computer-readable storage mediumcomprising instructions which, when executed by a computer, cause the computer to carryout the steps of the method according to any one of aspect and/or embodiments discussed herein.

Further features of, and advantages with, the invention will become apparent when studying the appended c|aims and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS Various aspects and/or embodiments of the invention, including its particular features andadvantages, will be readily understood from the example embodiments discussed in thefollowing detailed description and the accompanying drawings, in which: Fig. 1 illustrates embodiments of a vehicle, Fig. 2 schematically illustrates embodiments of an ICE, Fig. 3 illustrates a control arrangement, Fig. 4 schematically illustrates a diagram over timing change angles of an intake camshaft asa function of timing change angles of an exhaust camshaft, Fig. 5a illustrates two exemplified vectors containing braking torques available duringcompression release braking, Fig. 5b illustrates two exemplified vectors containing charge air pressure values, Fig. 6 illustrates diagrams over an internal combustion engine, Fig. 7 illustrates embodiments of a method for controlling a variable valve timing of a four-stroke internal combustion engine, Fig. 8 illustrates embodiments of a computer-readable storage medium.

DETAILED DESCRIPTION Aspects and/or embodiments of the invention will now be described more fully. Like numbersrefer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

Fig. 1 illustrates embodiments of a vehicle 2 configured for land-based propulsion. Thevehicle 2 comprises a four-stroke internal combustion engine, ICE, 4 according to aspectsand/or embodiments discussed herein, such as e.g. the ICE discussed below with referenceto Fig. 2. The ICE 4 comprises a control arrangement, as discussed below with reference toFigs. 2 and 3. ln these embodiments, the vehicle 2 is a heavy load vehicle in the form of a truck. However,the invention is not limited to any particular type of vehicle configured for land-based propulsion.

Fig. 2 schematically illustrates embodiments of an ICE 4. The ICE 4 may be configured to form part of a powertrain of a vehicle, such as e.g. the vehicle 2 shown in Fig. 1.

The ICE 4 is a four-stroke direct injection internal combustion engine, such as a compressionignition ICE 4, e.g. a diesel engine. The ICE 4 comprises at least one cylinder arrangement 6, a crankshaft 8, an exhaust camshaft 10, an intake camshaft 12.

The cylinder arrangement 6 comprises a combustion chamber 14, a cylinder bore 16, apiston 18 configured to reciprocate in the cylinder bore 16, an exhaust valve 20, an intake valve 22. The piston 18 is connected to the crankshaft 8 via a connecting rod 24.

The movement of the exhaust valve 20 is controlled by the exhaust camshaft 10, i.e. theexhaust camshaft 10 is configured to control the opening and closing of the exhaust valve20. The movement of the intake valve 22 is controlled by the intake camshaft 12, i.e. the intake camshaft 12 is configured to control the opening and closing of the intake valve 22.

The intake valve 22 is configured for admitting charge air into the combustion chamber 14,and the exhaust valve 20 is configured for letting exhaust gas out of the combustion chamber14. The timing of the exhaust camshaft 10 is configured to the be controlled by a timingcontrol arrangement 30 as indicated by a double arrow. Similarly, the timing of the intakecamshaft 12 is configured to the be controlled by a timing control arrangement 32 as indicated by a double arrow. ln a known manner, the intake valve 22 comprises an intake valve head configured to sealagainst an intake valve seat extending around an intake opening 26. The exhaust valve 20comprises an exhaust valve head configured to seal against an exhaust valve seat extending around an exhaust opening 28. ln a known manner, the camshafts 10, 12 may rotate at half the rotational speed of thecrankshaft 8 and control the movement of the exhaust and intake valves 20, 22 via camlobes 40, 42 arranged on the camshafts 10, 12. The exhaust camshaft 10 is arranged forcontrolling movement of the exhaust valve 20, and opening and closing of the exhaustopening 28. The exhaust camshaft 10 comprises a cam lobe 40. For instance, by abuttingagainst the cam lobe 40, the exhaust valve 20 will follow a contour of the cam lobe 40. Theexhaust valve 20 may be biased towards its closed position, e.g. by means of a non-shownspring. The movement of the intake valve 22 is controlled in a corresponding manner by the intake camshaft 12 and its cam lobe 42 for opening and closing the intake opening 26.

The piston 18 is arranged to reciprocate in the cylinder bore 16. The piston 18 performs fourstrokes in the cylinder bore 16, corresponding to an intake stroke, a compression stroke, anexpansion or power stroke, and an exhaust stroke, see also Fig. 6. ln Fig. 2 the piston 18 isillustrated with continuous lines at its Bottom Dead Centre, BDC, and with dashed lines at itsTop Dead Centre, TDC. The combustion chamber 14 is formed above the piston 18 insidethe cylinder bore 16.

The cylinder arrangement 6 has a total swept volume, VS, in the cylinder bore 16 betweenthe BDC and the TDC. According to some embodiments, the cylinder arrangement 6 mayhave a total swept volume, VS, of within a range of 0.3 to 4 litres. Mentioned purely as anexample, in the lower range of Vs, the cylinder arrangement 6 may form part of an internalcombustion engine for a passenger car, and in the middle and higher range of Vs, thecylinder arrangement 6 may form part of an internal combustion engine for a heavy load vehicle such as e.g. a truck, a bus, or a construction vehicle.

The ICE 4 comprises a compression release brake mechanism 34. The exhaust camshaft 10is configured to control compression release braking, CRB. For this purpose, the exhaustcamshaft 10 may comprise one or more dedicated lobes 36. Upon activation of compressionrelease braking, the one or more lobes 36 engage with the compression release brakemechanism 34 to control opening and closing of the exhaust valve 20. CRB produces anegative torque, or braking torque, which may be utilised for retarding the vehicle. Whencompression release braking is deactivated, the compression release brake mechanism 34 does not affect the exhaust valve 20.

The ICE 4 comprises a turbocharger 44. The turbocharger 44 comprises a compressor 50 and a turbine 52. The compressor 50 and the turbine 52 of the turbocharger 44 are connected via a common shaft 54. An inlet conduit 46 for charge air, leads from thecompressor 50 to the intake opening 26. For the sake of clarity, the inlet conduit 46 is notshown in its entirety. An exhaust conduit 48 leads from the exhaust opening 28 to the turbine52. The turbocharger 44 produces a charge air pressure in the inlet conduit 46 and at theintake valve 22. More specifically, the gas discharged via the exhaust valve 20 drives theturbine 52, which in turn rotates the compressor 50. Thus, the compressor 50 providescharge air at a charge air pressure to the intake valve 22. The turbocharger 44 may comprisea so-called wastegate (not shown), through which part of a gas flow from the exhaust valve may bypass the turbine 52.

The ICE 4 comprises a fuel injector 56 configured for injecting fuel into the combustion chamber 14 when the ICE 4 produces positive torque, e.g. for propelling the vehicle.

The ICE 4 further comprises a control arrangement 38 according to aspects and/orembodiments discussed herein. The control arrangement 38 is configured for controllingvariable valve timing of the ICE 4. That is, the control arrangement 38 is configured forcontrolling at least the timing of the exhaust camshaft 10 and the timing of the intakecamshaft 12. Accordingly, the timing control arrangements 30, 32 form part of the control arrangement 38.

The control arrangement 38 is configured to, upon compression release brake activation: - change the timing of the intake camshaft 12 to delay opening of the intake valve 22, and- change the timing of the exhaust camshaft 10 to advance closing of the exhaust valve 20.These timing changes of the camshafts 10, 12 are co-ordinated in accordance with afunction. Namely, a timing change angle of the intake camshaft 12 and a timing changeangle of the exhaust camshaft 10 are selected such that the timing change angle of theintake camshaft 12 is a function of the timing change angle of the exhaust camshaft 10 during the compression release braking.

The control arrangement 38 and the timing changes of the camshafts 10, 12 are further discussed below with reference to Figs. 3 - 6.

Fig. 3 illustrates a control arrangement 38 to be utilised in connection with different aspectsand/or embodiments of the invention. ln particular, the control arrangement 38 is configuredfor the control of the timing of the camshafts 10, 12 of the ICE 4 discussed in connection withFigs. 1 and 2. The control arrangement 38 is also indicated in Fig. 2. Accordingly, in the following reference is also made to Fig. 2.

The control arrangement 38 comprises at least one calculation unit 60, which may take theform of substantially any suitable type of processor circuit or microcomputer, e.g. a circuit fordigital signal processing (digital signal processor, DSP), a Central Processing Unit (CPU), aprocessing unit, a processing circuit, a processor, an Application Specific Integrated Circuit(ASIC), a microprocessor, or other processing logic that may interpret and executeinstructions. The herein utilised expression “calculation unit” may represent a processingcircuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of theones mentioned above. The calculation unit 60 may be configured to perform calculations, such as e.g. interpolations and extrapolations as discussed herein.

The control arrangement 38 comprises a memory unit 62. The calculation unit 60 isconnected to the memory unit 62, which provides the calculation unit 60 with, e.g. storedprogramme code, data tables, and/or other stored data which the calculation unit 60 needs toenable it to do calculations and to control the ICE. The calculation unit 60 is also adapted tostore partial or final results of calculations in the memory unit 62. The memory unit 62 maycomprise a physical device utilised to store data or programs, i.e. sequences of instructionson a temporary or permanent basis. According to some embodiments, the memory unit 62may comprise integrated circuits comprising silicon-based transistors. The memory unit 62may comprise e.g. a memory card, a flash memory, a USB memory, a hard disc, or anothersimilar volatile or non-volatile storage unit for storing data such as e.g. ROM (Read-OnlyMemory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), EEPROM(Electrically Erasable PROM), etc. in different embodiments.

The control arrangement 38 is further provided with respective devices 70, 72, 73, 74, 66, 68,69 for receiving and/or sending input and output signals. These input and output signals maycomprise waveforms, pulses or other attributes, which can be detect as information by signalreceiving devices, and which can be converted to signals processable by the calculation unit60. lnput signals are supplied to the calculation unit 60 from the input receiving devices 70,72, 73, 74. Output signal sending devices 66, 68, 69 are arranged to convert calculationresults from the calculation unit 60 to output signals for conveying to signal receiving devicesof other parts of the control arrangement 38. Each of the connections to the respectivedevices for receiving and sending input and output signals may take the form of one or morefrom among a cable, a data bus, e.g. a CAN (controller area network) bus, a MOST (mediaorientated systems transport) bus or some other bus configuration, or a wireless connection. ln the embodiment depicted, only one calculation unit 60 and memory unit 62 are shown, but the control arrangement 38 may alternatively comprise more than one calculation unit and/or memory unit.

Mentioned as examples, the output signal sending devices 66, 68, 69 may send controlsignals to the timing control arrangements 30, 32 of the exhaust and intake camshafts 10,12, and the compression release brake mechanism 34. The input signal receiving devices70, 72, 73, 74 may receive signals from the ICE 4, such as e.g. from a rotational speedsensor 75 of the crankshaft 8 of the ICE 4, a charge air pressure sensor 76, a rotationalspeed sensor 81 of the exhaust camshaft 10, a rotational speed sensor 82 of the intake camshaft 12.

Examples of data tables may be e.g.; - a table containing the function for coordinating the timing change angle of the intakecamshaft 12 with the timing change angle of the exhaust camshaft 10 during CRB, -tables containing ICE rotational speed mapped with braking torque values at differentpositions along the function, the tables may be provided for different charge air pressures orcharge air pressure ranges, -tables containing ICE rotational speed mapped with charge air pressure values at different positions along the function.

The tables may alternatively be referred to as vectors and/or matrixes in the following.Examples of data may be measured, monitored, determined, and/or calculated data, such asrotational speed data, charge air pressure data, timing change angle data. The controlarrangement 38 comprises or is connected to various sensors and actuators in order toreceive input and provide output for performing the various aspects and embodiments of themethod discussed herein. Some of the various sensors are exemplified above. An exampleof actuators may be actuators configured for changing the timing of the camshafts 10, 12 and forming part of the timing control arrangements 30, 32.

The control arrangement 38 may be configured to perform a method 100 according to anyone of aspects and/or embodiments discussed herein, see e.g. below with reference to Fig.7.

Fig. 4 schematically illustrates a diagram over timing change angles of an intake camshaft asa function 90 of timing change angles of an exhaust camshaft during the compression release braking. ln the following reference is made to Figs. 2 - 6.

As mentioned above, upon compression release brake activation, the control arrangement38 is configured to: - change the timing of the intake camshaft 12 to delay opening of the intake valve 22, and - change the timing of the exhaust camshaft 10 to advance closing of the exhaust valve 20,with the following condition fulfilled: - a timing change angle of the intake camshaft 12 and a timing change angle of the exhaustcamshaft 10 are selected such that the timing change angle of the intake camshaft 12 is afunction 90 of the timing change angle of the exhaust camshaft 10 during the compression release braking.

Thus, during compression release braking, the timing change of the intake camshaft 12 is co-ordinated with the timing change of the exhaust camshaft 10 in accordance with the function90. ln Fig. 4, an exemplified function 90 is represented by a bold line. An exemplified furtherfunction 90' is represented by a thin line. Both exemplified functions 90, 90' are shown in acoordinate system representing the timing change angle of the exhaust camshaft, ocexh, alongthe X-axis and timing change angle of the intake camshaft, omm, along the Y-axis. Each of thefunctions 90, 90' may be expressed as a mathematical function and/or may be mapped in atable containing timing change angles of the exhaust and intake camshafts 10, 12. Such amathematical function and/or such a table defining the function may be stored in the memoryunit 62 and utilised by the calculation unit 60 for determining and applying combinations oftiming change angles of the exhaust and intake camshafts 10, 12 in accordance with thefunction 90. The function 90 is one example of a single-valued function. The further function 90' is one example of a multi-valued function.

As mentioned initially, there are certain combinations of intake and exhaust timing changeangles that may put damaging loads on the ICE 4, such as e.g. on the compression releasebrake mechanism 34. ln the diagram of Fig. 4, such damaging combinations of intake andexhaust timing change angles are indicated by the broken line 92. That is, damagingcombinations of the timing change angles are combinations below the broken line 92.Depending on engine operating conditions, the broken line 92 may have different extensions.Suitably, the function 90 may be selected to avoid the area below the broken line 92 at all operating conditions of the ICE 4.

The control strategy provided by the control arrangement 38 in applying intake and exhausttiming change angle combinations in accordance with the function 90 during compressionrelease braking, limits the number of combinations used, thus, simplifying selection andcontrol of intake and exhaust timing change angles, and also making it easy to avoid combinations of timing change angles that Would result in large hardware loads on the ICE 4.

Herein, reference is made to crankshaft angle degrees, CA degrees, e.g. when discussingtiming changes of the camshafts. One full rotation of the crankshaft is 360 CA degrees.Crankshaft angle may be measured e.g. from Top Dead Centre fire, TDCfire, or Top DeadCentre gas exchange, TDCge. Negative timing change angles related to advancing theopening and closing of a relevant valve and positive timing change angles related to delaying the opening and closing of a relevant valve.

According to embodiments, the timing change angle of the intake camshaft 12 to delayopening of the intake valve 22 may be at least within a range of 0.1 - 40 degrees CA, or atleast within a range of 0.1 - 60 degrees CA. ln this manner, negative torque provided by the ICE 4 during compression release braking may be controlled within an adequate range.

According to further embodiments, the timing change angle the intake camshaft 12 to delay opening of the intake valve 22 may be at least within a range of 0.1 - 80 degrees CA.

According to embodiments, the timing change angle of the exhaust camshaft 10 to advanceclosing of the exhaust valve 20 may be at least within a range of -0.1 - -40 degrees CA, or atleast within a range of -0.1 - -60 degrees CA. ln this manner, negative torque provided by the ICE 4 during compression release braking may be controlled within an adequate range.

According to further embodiments, the timing change angle of the exhaust camshaft 10 toadvance closing of the exhaust valve 20 may be at least within a range of -0.1 - -80 degreesCA.

Mentioned purely as an example, in the diagram of Fig. 4 the Y-axis may be graded from aminimum intake camshaft timing change angle, ountmln, e.g. 0 CA degrees to a maximumintake camshaft timing change, oqntmax, e.g. 80 CA degrees. The X-axis may be graded from aminimum exhaust camshaft timing change angle, ßexhmln, e.g. 0 CA degrees to a maximumexhaust camshaft timing change angle, ßexhmax, e.g. -80 CA degrees. Note that since the exhaust camshaft timing is advanced during compression release braking, the maximum exhaust camshaft timing change angle has a lower value than the minimum exhaust camshaft timing change angle.

The function 90 forms a line. Along the line formed by the function 90, braking torqueproduced during CRB may be mapped. For instance, the braking torque produced during CRB may be mapped in one or more vectors as discussed below with reference to Fig. 5a.

Along the function 90, at II a low braking torque may be produced during compressionrelease braking. Mentioned purely as an example and depending inter alia on the size of ICEand available charge air pressure, the braking torque, i.e. the negative torque produced bythe ICE 4, may be -100 Nm at ll. Along the function 90, at lll a high braking torque may beproduced during compression release braking. Again, mentioned purely as an example anddepending inter alia on the size of ICE and available charge air pressure, the braking torquemay be -400 Nm at III.

The two exemplified points ll and lll along the line formed by the function 90 illustrate that, alow engine braking torque may be achieved with a combination of timing changes of lowadvance in the timing of the exhaust valve and a large delay in the timing of the intake valveduring CRB, whereas a high engine braking torque may be achieved with a combination oftiming changes of a large advance in the timing of the exhaust valve and a low delay in the timing of the intake valve during CRB.

The same applies to the line formed by the further function 90', at ll' a low braking torquemay be produced during compression release braking and at III' a high braking torque may be produced during compression release braking.

Fig. 5a illustrates two exemplified vectors 95, 97, each representing e.g. the line formed bythe function 90 in the diagram of Fig. 4. Each vector 95, 97 contains the braking torquesavailable during compression release braking at a particular rotational speed of the ICE 4and at the different timing change angles of the camshafts 10, 12 defined by the function 90.Each vector 95, 97 is graded from 0% to 100%, where 0% represents the low braking torquestarting end, and 100% represents the high braking torque finishing end, of the line definedby the function 90. In each vector 95, 97, a number of braking torque values from a minimumavailable braking torque up to a maximum available braking torque are defined at respectivepositions/percentages along the line. Accordingly, at a particular rotational speed, a certainpercentage of the line defined by the function 90 corresponds to a certain braking torque value.

The number of intermediate braking torques defined between the minimum and maximumavailable braking torques may vary. For instance, there may be 2, 5, 7, 8, 12, 20, or anyother number of intermediate braking torques defined in each vector 95, 97. Further, a linearrelationship may be assumed to prevail between adjacent braking torque values in eachvector 95, 97.

Similarly, there may be provided more than two vectors 95, 97, each vector representingavailable compression release braking torques at a particular rotational speed of the ICE 4.For instance, there may be 5, 7, 8, 10, 12, 20, or any other number of vectors. The vectors 95, 97, and any further vectors may form a matrix, or a table.

At steady operating conditions of the ICE 4, the rotational speed of the ICE 4 correlates witha particular charge air pressure produced by the turbocharger 44 and as mentioned above,the available braking torque produced during compression release braking depends on the charge air pressure.

Accordingly, the vectors 95, 97 and any further vectors may relate to one particular chargeair pressure. Further, corresponding vectors may be provided at one or more different charge air pressures.

The torque and rotational speed values of the vectors 95, 97 of Fig. 5a are only examplesand depend on the relevant charge air pressure, as mentioned above, and inter alia on thetype and size of the ICE 4. The different braking torque values of the vectors 95, 97 atdifferent timing change angles of the camshafts 10, 12 in accordance with the function 90,may be determined for a particular type and size of engine utilising test equipment. Thevectors 95, 97 containing the accordingly determined braking torque values may be stored in the memory 62 of the control arrangement 38.

Thus, the control arrangement 38 may be configured to determine a braking torque duringcompression release braking based on a current rotational speed of the internal combustion engine.

The control arrangement 38 may control the variable valve timing to provide a particular braking torque during CRB in the following manner: A control arrangement of a vehicle, such as the vehicle 2 discussed in connection with Fig.1, provides a requested braking torque. The control arrangement providing the requestedbraking torque may be the control arrangement 38 as such, or a different control arrangement of the vehicle.

The control arrangement 38 determines a current rotational speed of the ICE 4 utilising e.g.the rotational speed sensor 75 and a current charge air pressure produced by theturbocharger 44 utilising e.g. the charge air pressure sensor 76. Utilising the abovediscussed vectors, the control arrangement 38 controls the control arrangements 30, 32 toprovide timing change angles of the exhaust and intake camshafts 10, 12 in accordance withthe function 90 which correspond to the requested braking torque at the current rotationalspeed of the ICE 4 and current charge air pressure, and activates CRB via the compression release brake mechanism 34.

Since the requested braking torque corresponds to a position along the line formed by thefunction 90, that position provides the relevant timing change angles of the camshafts 10, 12.Utilising inter-alia the above discussed vectors, the requested braking torque at a currentrotational speed of the ICE 4 and current charge air pressure, can be applied by the control arrangement 38 during CRB.

Put differently, the control arrangement 38 determines where along the line, e.g. at whatpercentage along the line, the requested braking torque is produced at a current rotationalspeed of the ICE 4 and a current charge air pressure. The function 90 is utilised to determinethe relevant timing changes of each of the camshafts 10, 12 corresponding to the positionalong the line formed by the function 90. The relevant timing changes are applied to the camshafts 10, 12 in order to achieve the requested braking torque during CRB.

Moreover, during CRB the charge air pressure produced by the turbocharger 44 changes.Also, as the vehicle speed is reduced during CRB, the rotational speed of the ICE 4 isreduced. Accordingly, during CRB, the timing change angles of the camshafts 10, 12 mayrequire adjustment. Updated timing change angles of the camshafts 10, 12 are set in acorresponding manner using an updated current rotational speed of the ICE 4 and an updated current charge air pressure.

According to some embodiments, a large number of vectors may be provided, each vectorcomprising a large number of braking torque values. The large number of vectors may be conceived to cover substantially all rotational speeds and charge air pressures within the operating range of the ICE 4. The large number of braking torque values may cover theentire range of braking torques produced during CRB by the ICE 4 with a suitable resolution such as e.g. 2, 5, 10, 25, 50 Nm between adjacent braking torque values. ln such embodiments, the relevant timing change angles of the camshafts 10, 12corresponding to requested braking torque at a current rotational speed of the ICE 4 andcurrent charge air pressure are determined via a vector related to the current rotationalspeed at the current charge air pressure. Rules may be provided for only allowing requested braking torques at the resolution of the braking torque values in the large number of vectors.

Providing the required large number of vectors may be cumbersome and/or difficult.

Accordingly, alternative approaches may be used requiring a smaller number of vectors.

According to some embodiments, a limited number of vectors may be provided, each vectorcomprising a limit number of braking torque values. The limited number of vectors may coverthe rotational speeds and charge air pressures within the operating range of the ICE 4 withan appropriate resolution. For instance, adjacent vectors may relate to rotational speedsdiffering by 5, 10, 25, 50, or 100 rpm. The vectors may be provided over the charge airpressure range of the ICE 4 with a resolution of e.g. 5, 10, 25, 50, or 100 hPa. The limitednumber of braking torque values may cover the range of braking torques produced duringCRB by the ICE 4 with a suitable resolution such as e.g. 5, 10,25, or 50 Nm between adjacent torque values. ln such embodiments, the relevant timing change angles of the camshafts 10, 12corresponding to the requested braking torque at a current rotational speed of the ICE 4 andcurrent charge air pressure are selected from the vector related to the closest availablerotational speed and charge air pressure. The braking torque value of that vector closest tothe requested braking torque is selected for providing the timing change angles of thecamshafts 10, 12.

This approach may prove to be sufficiently accurate during CRB. ln particular so, consideringthat timing change angles of the camshafts 10, 12 require updating as the rotational speed ofthe ICE 4 and the charge air pressure changes during CRB. Thus, the overall compression release braking performance over the duration of a CRB manoeuvre may be satisfactorily.

According to some embodiments, again, a limited number of vectors may be provided, each vector comprising a limit number of braking torque values. The limited number of vectors may cover the rotational speeds and charge air pressures within the operating range of the ICE 4with an appropriate resolution. For instance, adjacent vectors may re|ate to rotational speedsdiffering by 50, 100, or 250 rpm. The vectors may be provided over the charge air pressurerange of the ICE 4 with a resolution of e.g. 50, 100, or 250 hPa. The limited number ofbraking torque values may cover the range of braking torques produced during CRB by theICE 4 with a suitable resolution such as e.g. 25, 50, or 100 Nm between adjacent torquevalues. Thus, a more limited number of vectors and braking torque values may be provided in these embodiments than in the previously described embodiments. ln these embodiments, approximations may be calculated for rotational speeds and/orcharge air pressures and/or braking torque values not available from the vectors. For acurrent charge air pressure, the requested braking torque value from each vector of the twoclosest available charge air pressures may be linearly interpolation or extrapolation in orderto arrive at a position along the function 90 which provide timing changes of the camshafts10, 12 that will produce the requested braking torque during compression release braking.Similarly, if the current rotational speed of the ICE 4 is not available in the vectors, therequested braking torque value from the two rotational speeds closest to the currentrotational speed may be linearly interpolation or extrapolation in order to arrive at a positionalong the function 90 which provide timing changes of the camshafts 10, 12 that will producethe requested braking torque during compression release braking. Also, if the requestedbraking torque is not available in the vectors, the two closest braking torque values for therelevant rotational speed may be linearly interpolation or extrapolation in order to arrive at aposition along the function 90 which provide timing changes of the camshafts 10, 12 that willproduce the requested braking torque during compression release braking. The differentinterpolations or extrapolations may be combined in one or more steps if more than one ofthe rotational speeds, charge air pressures, and braking torque values are not available from the vectors.

Also this approach may prove to be sufficiently accurate during CRB. Again so, consideringthat timing change angles of the camshafts 10, 12 require updating as the rotational speed ofthe ICE 4 and the charge air pressure changes during CRB. Thus, the overall compression release braking performance over the duration of a CRB manoeuvre may be satisfactorily.

Fig. 5b illustrates two exemplified vectors 94, 96, each representing the line formed by thefunction 90 in the diagram of Fig. 4. Each vector 94, 96 contains the charge air pressurevalues produced by the turbocharger 44 at a particular rotational speed of the ICE 4 and at the different timing change angles of the camshafts 10, 12 defined by the function 90. Again, each vector 94, 96 is graded from 0% to 100%, where 0% represents the start and 100%represents the end of the line defined by the function 90. ln each vector 94, 96, a number ofcharge air pressure values from a minimum value up to a maximum value are provided atrespective positions/percentages along the line. Accordingly, at a particular rotational speed,a certain percentage of the line defined by the function 90 corresponds to a certain charge air pressure value.

The number of intermediate charge air pressure values between the minimum and maximumvalues may vary. For instance, there may be 2, 5, 7, 8, 12, 20, or any other number of intermediate charge air pressure values provided in each vector 94, 96.

The charge air pressure values and rotational speed values of the vectors 94, 96 of Fig. 5bare only examples and depend inter alia on the type and size of the ICE 4. The charge airpressure values of the vectors 94, 96 at different timing change angles of the camshafts 10,12 in accordance with the function 90, may be determined for a particular type and size ofengine utilising test equipment. The vectors 94, 96 containing the accordingly determined charge air pressure values may be stored in the memory 62 of the control arrangement 38.

According to embodiments, the control arrangement 38 may be configured to:- determine a braking torque during compression release braking based on a current chargeair pressure provided by the turbocharger 44. Such example embodiments will be discussed in the following.

According to some embodiments, the control arrangement 38 may control the variable valvetiming to provide a particular braking torque during CRB utilising only four matrixes. ln suchembodiments, two braking torque matrixes correspond to the vectors 95, 97 shown in Fig.5a, and two charge air pressure matrixes correspond to the vectors 94, 96 shown in Fig. 5b.Each matrix may comprise only two vectors as shown however, according to someembodiments each of the four matrixes may be a 10x10 matrix, i.e. comprising 10 columns,each related to a specific rotational speeds of the ICE 4 and 10 rows, each related to a specific position along the line representing the function 90.

The four matrixes are of the same size. Each respective element within each of the fourmatrixes corresponds to the same element in all matrixes, i.e. for instance, element 1:1 in allfour matrixes relates to the same position along the function 90 and to the same rotational speed. 24 As mentioned above, the values of the elements of the matrixes have been determined for aparticular type and size of engine utilising test equipment. More specifically, in theseembodiments, the elements of a first braking torque matrix are populated with braking torquevalues, and the elements of a first charge air pressure matrix are populated with charge airpressure values. The braking torque values and charge air pressure values are measuredduring CRB in the test equipment at each rotational speed and each timing change angleposition along the function 90 at a low charge air pressure range. The low charge airpressure range may for instance be provided by throttling the charge air flow and/or by opening a wastegate of the turbocharger 44. ln a similar manner, the elements of a second braking torque matrix are populated withbraking torque values, and the elements of a second charge air pressure matrix arepopulated with charge air pressure values. This time, the elements are populated at a highcharge air pressure range. The high charge air pressure range may be provided by utilising the full capacity of the turbocharger 44 and an unthrottled charge air flow. ln this manner, each element containing a braking torque value within the first braking torquematrix has a corresponding charge air pressure value within the corresponding element of the first charge air pressure matrix. Similarly, each element containing a braking torque valuewithin the second braking torque matrix has a corresponding charge air pressure value within the corresponding element of the second charge air pressure matrix. ln these embodiments, the position along the line representing the function 90 and thus, therelevant timing change angles of the camshafts 10, 12 for providing a requested brakingtorque during CRB may be determined by the control arrangement 38 in the following mannef. ln these embodiments it is assumed that there are linear relationships between adjacentcharge air pressure values, adjacent braking torque values, adjacent rotational speeds, andadjacent positions along the line representing the function 90 and the timing changes of thecamshafts 10, 12.

Again, the control arrangement 38 determines a current rotational speed of the ICE 4 utilisinge.g. the rotational speed sensor 75 and a current charge air pressure produced by the turbocharger 44 utilising e.g. the charge air pressure sensor 76.

Depending on how well the current rotational speed matches the rotational speed values ofthe columns of the matrixes, how well the current charge air pressure matches the charge airpressure values of the elements of the first and/or second charge air pressure matrixes,and/or how well the requested braking torque happens to match a corresponding element inthe first and/or second braking torque matrix either - no, one, or more interpolations or extrapolations are performed.

Should a current charge air pressure at a current rotational speed match an element in oneof the first and second charge air pressure matrixes, and the corresponding element of thecorresponding first or second braking torque matrix contains the requested braking torque,the position along the function 90 and the corresponding timing change angles of the camshafts 10, 12 are directly provided by the relevant element of the matrixes.

Otherwise, the current rotational speed and the current charge air pressure determine a firstset of two corresponding elements in the first and second charge air pressure matrixes. Thebraking torque values of the corresponding two elements of the first and second brakingtorque matrixes are interpolated or extrapolated in order to arrive at the requested braking torque and corresponding position along the line representing the function 90. lf for instance, the current rotational speed finds a match in one of the columns of thematrixes, in the respective columns for the current rotational speed of the first and secondcharge air pressure matrixes, one element is selected for which the respective charge airpressure values are close to the current charge air pressure. The respective charge airpressure values are linearly interpolated or extrapolated and the position of the currentcharge air pressure along this linear interpolation or extrapolation is determined. The brakingtorque values from the corresponding elements of the first and second braking torquematrixes are linearly interpolated or extrapolated and a position along this linear interpolationor extrapolation corresponding to the determined position of the current charge air pressure determines an interpolated or extrapolated braking torque value. lf this first interpolated or extrapolated braking torque value does not correspond to therequested baking torque value, a further element is selected in the first and second chargeair pressure matrixes for which the respective charge air pressure values are close to thecurrent charge air pressure. Again, the respective charge air pressure values are linearlyinterpolated or extrapolated and the position of the current charge air pressure along thislinear interpolation or extrapolation is determined. The braking torque values from the corresponding further elements of the first and second braking torque matrixes are linearly interpolated or extrapolated and a position along this linear interpolation or extrapolationcorresponding to the determined position of the current charge air pressure determines asecond interpolated or extrapolated braking torque value. A further linear interpolation orextrapolation between the first and second interpolated or extrapolated braking torque valuesprovides the requested braking torque at a position along this further linear interpolation orextrapolation. A corresponding position along a linear interpolation or extrapolation betweena first point along the function 90 corresponding to the elements first selected and a secondpoint along the function 90 corresponding to the further elements selected and related timing change angles of the camshafts 10, 12 provide the requested braking torque during CRB. ln one example, for instance, the current rotational speed may be 1800 rpm, and the current charge air pressure may be 1350 hPa. A requested braking torque may be -150 Nm.

Column 6 of the matrixes may relate to 1800 rpm. The first element of column 6, i.e. element1:6, of the first charge air pressure matrix may contain the value 1200 hPa, and element 1:6of the second charge air pressure matrix may contain the value 1500 hPa. lnterpolatingthese two charge air pressure values, the current charge air pressure, 1350 hPa, is found at50% along the interpolation. Element 1:6 of the first braking torque matrix may contain thevalue -100 Nm, and element 1:6 of the second braking torque matrix may contain the value-200 Nm. Performing an interpolation between these two values, at 50% along the interpolation, the requested braking torque -150 Nm is found.

When the requested braking torque is found in an interpolation or extrapolation between twoelements on one and the same row, the position along the function 90 and the correspondingtiming change angles of the camshafts 10, 12 of that row are applicable in order to apply therequested braking torque during CRB. That is, in this example the timing change angles of the camshafts 10, 12 corresponding to those of row 1 of the matrixes is applied during CRB. ln a further example, again, the current rotational speed may be 1800 rpm, and the current charge air pressure may be 1350 hPa. A requested braking torque may be -180 Nm.

Again, column 6 of the matrixes may relate to 1800 rpm, element 1:6 of the first charge airpressure matrix may contain the value 1200 hPa, and element 1:6 of the second charge airpressure matrix may contain the value 1500 hPa. lnterpolating these two charge air pressurevalues, the current charge air pressure, 1350 hPa, is found at 50% along the interpolation.Again, element 1:6 of the first braking torque matrix may contain the value -100 Nm, and element 1:6 of the second braking torque matrix may contain the value -200 Nm. Performing an interpolation between these two values, at 50% along a first interpolated braking torquevalue, -150 Nm is found. Accordingly, further interpolations and/or extrapolations have to be performed in order to arrive at the requested braking torque, -180 Nm.

Element 2:6 of the first charge air pressure matrix may contain the value 1300 hPa, andelement 2:6 of the second charge air pressure matrix may contain the value 1800 hPa.lnterpolating these two charge air pressure values, the current charge air pressure, 1350hPa, is found at 17.5% from 1300 hPa in element 2:6 of the first charge air pressure matrix.Element 2:6 of the first braking torque matrix may contain the value -200 Nm, and element2:6 of the second braking torque matrix may contain the value -400 Nm. Performing aninterpolation between these two values, at 17.5% from -200 Nm in element 2:6 of the first braking torque matrix a second interpolated braking torque value -235 Nm is found.

Finally, an interpolation between the first and second interpolated braking torque values,-150 Nm and -235 Nm, the requested braking torque value -180 Nm is found at 35% from-150 Nm, i.e. between rows 1 and 2 of the braking torque matrixes. Thus, the position alongthe line representing the function 90 is moved 35% from the point on the line correspondingto row 1 towards the point corresponding to row 2. Accordingly, the timing change angles ofthe camshafts 10, 12 are changed a corresponding 35% in order to apply the requested -180Nm during CRB. lf the current rotational speed does not match one of the rotational speeds of the columns ofthe matrixes, columns of interpolated values may be provided for each of the matrixes.lnterpolation or extrapolation of the two closest rotational speed columns and correspondinginterpolations or extrapolations of the respective charge air pressure values and brakingtorque values may be performed. The thus, provided charge air pressure values and brakingtorque values may in turn be used for interpolation or extrapolation in accordance with theabove discussed manner to arrive at a position along the function 90 and the related timing change angles of the camshafts 10, 12, which provide the requested braking torque.

The embodiments discussed above with reference to Figs. 5a and 5b, are examples ofembodiments, wherein the control arrangement 38 is configured to: - determine a braking torque at an intermediate charge air pressure between two knownbraking torques at two known charge air pressures, based on a linear interpolation orextrapolation between the two known charge air pressures and/or the two known braking torques.

Also, the embodiments discussed above with reference to Figs. 5a and 5b, are examples ofembodiments, wherein the control arrangement 38 is configured to:- determine a braking torque during compression release braking based on a current rotational speed of the internal combustion engine.

Fig. 6 illustrates diagrams over the ICE 4 of Fig. 2, and control thereof in accordance withthe discussion above with reference to Figs. 2 - 5b. Accordingly, in the following reference isalso made to Figs. 2 - 5b. Fig. 6 illustrates the four strokes of a piston 18 and themovements of the exhaust valve 20 (full line) and of the intake valve 22 (dash-dotted line)during operation of the ICE 4. The crankshaft 8 of the ICE 4 rotates 720 degrees CA as thefour strokes of the piston 18 are performed. For each stroke, the crankshaft 8 rotates 180 degrees CA as indicated in Fig. 6.

Along line I. the opening and closing of the exhaust and intake valves 20, 22 are shownduring ordinary compression release braking, CRB, of the ICE 4 without variable valvetiming. There the exhaust valve 20 and the intake valve 22 are opened and closed in anordinary manner during the respective exhaust and intake strokes. In addition, thecompression release brake mechanism 34 is activated and engages with the exhaust valve22 and the one or more additional lobes 36 of the exhaust camshaft 10. Thus, in an ordinarymanner the exhaust valve 22 is opened with a CRB lift at the beginning of the expansionstroke and the compressed air in the combustion chamber 14 is released into the exhaustsystem of the ICE 4.

Along line II. the opening and closing of the exhaust and intake valves 20,22 with variablevalve timing applied during CRB is shown. The control arrangement 38 is configured tochange the timing of the intake camshaft 12 to delay opening of the intake valve 22 andchange the timing of the exhaust camshaft 10 to advance closing of the exhaust valve 20. Asdiscussed above, the timing change angle of the intake camshaft 12 and a timing changeangle of the exhaust camshaft 10 are selected such that the timing change angle of theintake camshaft 12 is a function, such as one of the functions 90, 90' exemplified in Fig. 4, of the timing change angle of the exhaust camshaft 10 during the CRB, as discussed above.

Line II. relates to a situation wherein comparatively low braking torque is applied during CRB.For instance, line II. may represent timing changes of the intake and exhaust camshafts 12,10 corresponding to those at point II along the line formed by the function 90 shown in Fig. 4.

Thus, there is applied a combination of a small timing change angle ß for advancing the timing of the exhaust valve 22, and a large timing change angle a for delaying the timing of the intake valve 22.

Since compression release braking is activated, also the CRB lift of the exhaust valve 22 is advanced with timing change angle ß.

Along line lll. the opening and closing of the exhaust and intake valves 20,22, again, withvariable valve timing applied during CRB is shown. As discussed in connection with line ll.above, the control arrangement 38 is configured to change the timing of the intake and exhaust camshafts 12, 10 based on the function 90.

Line lll. relates to a situation wherein comparatively high braking torque is applied duringCRB. For instance, line lll. may represent timing changes of the intake and exhaustcamshafts 12, 10 corresponding to those at point lll along the line formed by the function 90shown in Fig. 4. Thus, applying a combination of a large timing change angle ß for advancingthe timing of the exhaust valve 22, and a small timing change angle a for delaying the timingof the intake valve 22. Since compression release braking is activated, also the CRB lift of the exhaust valve 22 is advanced with timing change angle ß.

Line IV. illustrates embodiments wherein the exhaust camshaft 10 comprises more than onelobe 36 for controlling the compression release brake mechanism 34 and opening andclosing the exhaust valve 20 during CRB. ln these embodiments, the exhaust camshaft 10comprises in total three lobes 36 for controlling the compression release brake mechanism34, and accordingly, provides three CRB lifts during two rotations of the crankshaft 8. Thefirst CRB lift is that provided around TDCfire and also provided in the examples of lines l. ll.and lll. The second CRB lift follows the ordinary exhaust valve 20 opening and closing at theexhaust stroke of the piston 18. This second CRB lift reduces the mechanical strain on theintake valve lifting mechanism during CRB. Namely, when the timing of the exhaust camshaft10 has been advance with a timing change angle ß, the exhaust valve 20 closes before thepiston 18 reaches, Top Dead Centre gas exchange, TDCge, which causes air to becompressed in the combustion chamber 14. Thus, the second CRB lift may release thecompressed air into the exhaust system of the ICE 4 before the intake valve 22 is opened.Moreover, the compressed air is supplied to the turbocharger 44 providing energy to theturbine 52 thereof. The third CRB lift is provided around BDC between the intake and compression strokes. This third CRB lift permits air to be drawn from the exhaust conduit 48 back into the combustion Chamber 14 around BDC, thus, permitting a larger amount of air to be drawn into the combustion Chamber 14 while the intake valve 22 is closing at BDC.

Mentioned as an example, each CRB lift caused by the lobes 36 for controlling thecompression release brake mechanism 34 and opening and closing the exhaust valve 20during CRB may be configured to maintain the exhaust valve open for a duration within arange of 100 - 130 degrees CA.

Mentioned as an example, the three lobes 36 for controlling the compression release brakemechanism 34 and opening and closing the exhaust valve 20 when CRB is activated butwithout any timing change of the exhaust camshaft may control the exhaust valve 20 in thefollowing manner: The first CRB lift provided by the compression release brake mechanism34 may open the exhaust valve 10 approximately 100 - 140 degrees CA before the ordinaryopening of the exhaust valve at the exhaust stroke of the piston 18. The second CRB lift mayopen the exhaust valve 10 approximately 20 - 60 degrees CA after the closing of theexhaust valve at the exhaust stroke of the piston 18. The third CRB lift may open the exhaustvalve 10 approximately 150 - 190 degrees CA after the closing of the exhaust valve at the exhaust stroke of the piston 18.

Fig. 7 illustrates embodiments of a method 100 for controlling a variable valve timing of afour-stroke ICE. The ICE may be an ICE 4 comprising a control arrangement 38 asdiscussed above in connection with Figs. 1 - 6. Accordingly, in the following reference is also made to Figs. 1 - 6.

The method 100 comprises, upon compression release brake activation, steps of: - changing 102 the timing of the intake camshaft 12 to delay opening of the intake valve 22,and - changing 104 the timing of the exhaust camshaft 10 to advance closing of the exhaustvalve 20, wherein a timing change angle of the intake camshaft 12 and a timing changeangle of the exhaust camshaft 10 are selected such that the timing change angle of theintake camshaft 12 is a function of the timing change angle of the exhaust camshaft 10 during the compression release braking.

Embodiments of the control arrangement 38 discussed above are applicable in a corresponding manner in the method 100. 31 According to embodiments, in the step of changing 102 the timing of the intake camshaft 12there may be provided a larger delay in opening of the intake valve 22 with a lower enginebraking torque request during compression release braking, and in the step of changing 104the timing of the exhaust camshaft 10 there may be provided less advance in closing of theexhaust valve 20 with a lower engine braking torque request during compression releasebraking. ln this manner, the pressure in the combustion chamber 14 during the compressionstroke may be reduced due to the intake valve remaining open during a portion of the compression stroke during CRB with lower engine braking torque.

According to embodiments, the method may comprise a step of:- determining 106 a braking torque during compression release braking based on a currentrotational speed of the internal combustion engine. ln this manner, the braking torque may be determined e.g. during stable engine operating conditions.

According to embodiments, the method may comprise a step of. - determining 108 a braking torque during compression release braking based on a currentcharge air pressure provided by the turbocharger. ln this manner, the current charge airpressure may be utilised for determining a braking torque, e.g. for providing a requestedbraking torque, or for determining intermediate braking torques that in turn may be utilised for providing a requested braking torque during compression release braking.

According to embodiments, the method may comprise a step of. - determining 110 a braking torque at an intermediate charge air pressure between twoknown braking torques at two known charge air pressures, based on a linear interpolation orextrapolation between the two known charge air pressures and/or the two known brakingtorques. ln this manner, storing braking torques for every conceivable charge air pressuremay be avoided, and a simplified setup of a control arrangement configured for performing the method may be utilised.

According to a further aspect, there is provided a computer program comprising instructionswhich, when the program is executed by a computer, causes the computer to carry out a method 100 according to any one of aspects and/or embodiments discussed herein.

One skilled in the art will appreciate that the method 100 of controlling timings of an exhaustcamshaft 10 and an intake camshaft 12 of a four-stroke ICE 4 may be implemented byprogrammed instructions. These programmed instructions are typically constituted by a computer program, which, when it is executed in a computer or calculation unit 60, ensures that the computer or calculation unit 60 carries out the desired control, such as the method100, and thereto related steps 102 - 110. The computer program is usually part of acomputer-readable storage medium which comprises a suitable digital storage medium on which the computer program is stored.

Fig. 8 illustrates embodiments of a computer-readable storage medium 99 comprisinginstructions which, when executed by a computer or calculation unit 60, cause the computeror calculation unit 60 to carry out the steps of the method 100 according to any one of aspects and/or embodiments discussed herein.

The computer-readable storage medium 99 may be provided for instance in the form of adata carrier carrying computer program code for performing at least some of the steps 102 -110 according to some embodiments when being loaded into the one or more calculationunits 60. The data carrier may be, e.g. a ROM (read-only memory), a PROM (programableread-only memory), an EPROM (erasable PROM), a flash memory, an EEPROM (electricallyerasable PROM), a hard disc, a CD ROM disc, a memory stick, an optical storage device, amagnetic storage device or any other appropriate medium such as a disk or tape that mayhold machine readable data in a non-transitory manner. The computer-readable storagemedium may furthermore be provided as computer program code on a server and may bedownloaded to the calculation unit 60 remotely, e.g., over an lnternet or an intranet connection, or via other Wired or wireless communication systems.

The computer-readable storage medium 99 shown in Fig. 8 is a nonlimiting example in the form of a USB memory stick. lt is to be understood that the foregoing is illustrative of various example embodiments andthat the invention is defined only by the appended claims. A person skilled in the art willrealize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the invention, as defined by the appended claims.

Claims (13)

1. A control arrangement (38) for controlling a variable valve timing of a four-stroke internalcombustion engine (4), the internal combustion engine (4) comprising: - an exhaust valve (20) and an intake valve (22), - an exhaust camshaft (10) arranged to control the opening of the exhaust valve(20) and to control compression release braking of the internal combustion engine (4), and - an intake camshaft (12) arranged to control the opening and closing of theintake valve (22), wherein the control arrangement (38) is configured to, upon compressionrelease brake activation: - change the timing of the intake camshaft (12) to delay opening of the intakevalve (22), and - change the timing of the exhaust camshaft (10) to advance closing of theexhaust valve (20), wherein a timing change angle (oi) of the intake camshaft (12) and a timingchange angle (ß) of the exhaust camshaft (10) are selected such that the timing changeangle (oi) of the intake camshaft (12) is a function of the timing change angle (ß) of the exhaust camshaft (10) during the compression release braking.

2. The control arrangement (38) according to claim 1, further configured to: - change the timing of the intake camshaft (12) to provide a larger delay inopening of the intake valve (22) with a lower engine braking torque request duringcompression release braking, and - change the timing of the exhaust camshaft (10) to provide a lesser advance inclosing of the exhaust valve (20) with a lower engine braking torque request duringcompression release braking.

3. The control arrangement (38) according to claim 1 or 2, further configured to:determine a braking torque during compression release braking based on acurrent rotational speed of the internal combustion engine (4).

4. The control arrangement (38) according to any one of the preceding claims, wherein thefour-stroke internal combustion engine (4) comprises a turbocharger (44) configured to produce a charge air pressure to be utilised during compression release braking.

5. The control arrangement (38) according to claim 4, further configured to: determine a braking torque during compression release braking based on acurrent charge air pressure provided by the turbocharger (44).

6. The control arrangement (38) according to claim 4 or 5, further configured to: determine a braking torque at an intermediate charge air pressure between twoknown braking torques at two known charge air pressures, based on a linear interpolation orextrapolation between the two known charge air pressures and/or the two known brakingtorques.

7. The control arrangement (38) according to any one of the preceding claims, wherein thetiming change angle (oi) of the intake camshaft (12) to delay opening of the intake valve (22)is at least within a range of 0.1 - 40 degrees CA, or at least within a range of 0.1 - 60degrees CA.

8. The control arrangement (38) according to any one of the preceding claims, wherein thetiming change angle (ß) of the exhaust camshaft (10) to advance closing of the exhaust valve(20) is at least within a range of -0.1 - -40 degrees CA, or at least within a range of -0.1 - -60degrees CA.

9. A four-stroke internal combustion engine (4) comprising a control arrangement (38)according to any one of the preceding claims.

10. A vehicle (2) comprising a four-stroke internal combustion engine (4) according to claim9.

11. A method (100) for controlling a variable valve timing of a four-stroke internal combustionengine (4), the internal combustion engine (4) comprising: an exhaust valve (20) and an intake valve (22), an exhaust camshaft (10) arranged to control the opening of the exhaust valve(20) and to control compression release braking of the internal combustion engine (4), and an intake camshaft (12) arranged to control the opening and closing of theintake valve (22), wherein the method (100) comprises, upon compression release brakeactivation: - changing (102) the timing of the intake camshaft (12) to delay opening of theintake valve (22), and - changing (104) the timing of the exhaust camshaft (10) to advance closing ofthe exhaust valve (20), wherein a timing change angle (oi) of the intake camshaft (12) and a timingchange angle (ß) of the exhaust camshaft (10) are selected such that the timing changeangle (oi) of the intake camshaft (12) is a function of the timing change angle (ß) of the exhaust camshaft (10) during the compression release braking.

12. A computer program comprising instructions which, when the program is executed by acomputer, cause the computer to carry out the steps of the method (100) according to claim11.

13. A computer-readable storage medium comprising instructions which, when executed by acomputer, cause the computer to carry out the steps of the method (100) according to claim11.