WO2014137266A1

WO2014137266A1 - Arrangement pertaining to a combustion engine

Info

Publication number: WO2014137266A1
Application number: PCT/SE2014/050163
Authority: WO
Inventors: Henrik Skog; Håkan SARBY
Original assignee: Scania Cv Ab
Priority date: 2013-03-06
Filing date: 2014-02-11
Publication date: 2014-09-12
Also published as: DE112014000858T5; SE1350269A1; SE537013C2

Abstract

An arrangement at a combustion engine (7) with at least three cylinders (1 -6) comprises a first conduit (9) for air supply to the engine for the combustion in the cylinders, a second conduit (18) for leading a part of the exhausts resulting from the combustion in the engine back to the first conduit, to be mixed with fresh air for air supply to the engine. An outlet for exhaust from at least one of the cylinders is connected with the second conduit. All exhaust valves in at least one of the cylinders, having its exhaust outlet connected with the second conduit, is arranged to open at least 5 crank degrees earlier in this cylinder's combustion cycle than at least one exhaust valve in at least one of the other cylinders.

Description

Arrangement pertaining to a combustion engine

TECHNICAL FIELD OF THE INVENTION AND PRIOR ART

The invention pertains to an arrangement at a combustion engine according to the preamble of the enclosed claim 1 and a method according to the preamble of the enclosed independent method claim. The invention pertains to such arrangements for use in all types of combustion engines, such as an otto engine and a diesel engine, but the description below pertains primarily to such arrangements in motor vehicles. Such motor vehicles may be wheeled utility vehicles, such as trucks and buses.

Such an arrangement entails that the engine is equipped with an arrangement for exhaust gas recirculation of the type usually called EGR (Exhaust Gas Recirculation), which consists of a purification method for the reduction of the level of harmful emissions, especially nitrogen oxides (NO_x). It is desirable to achieve a certain size of the share of exhausts being recirculated for mixing with the inlet air, so that the desired size is typically 10% of the total exhausts arising from the combustion in the engine's cylinders. Recirculating this share of the exhausts to the engine's air supply conduit is problematic. In the event such an arrangement has a variable geometry turbocharger

(VGT) arranged in an exhaust conduit from the engine's cylinders, it is possible to control the pressure of the exhausts in the inlet conduit, so that a desired share of exhausts is recirculated to the inlet conduit. However, such a turbocharger is both expensive and complicated. Another disadvantage is that the engine's gas exchange becomes poor as a result of the engine having to work against a higher pressure on its outlet side than on its inlet side, and thus the fuel consumption increases. If, instead, a fixed geometry turbocharger (FGT) is used, this problem would not arise. In addition, such a turbocharger is available at a lower cost and is less complex than a turbocharger of the VGT type. With a turbocharger of the FGT type, the engine's fuel consumption is low, since the pressure in the exhaust manifolds is at the same level as the pressure in the first conduit, but instead it is not possible to drive a sufficient amount of exhausts to the inlet side, since there is a lack of pressure difference required for this purpose. This means that the exhaust pulses arising when the cylinders' exhaust valves are opened must be used to drive the pulsating recirculation of the exhausts. It is desirable to increase the fraction of exhausts which, in such an arrangement, may be recirculated to the air supply to the engine, in order to reduce the level of harmful nitrogen oxides in the exhausts.

In US 4131 095 a prior art arrangement is described, driving the EGR by way of recirculation of exhausts from a cylinder in the engine in the event of a low PTO from the engine, and no EGR at all in the event of a high PTO from the engine. This type of drive of the EGR leaves, however, a lot to be desired in terms of the possibilities of achieving low levels of NO_x in the exhausts.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide an arrangement of the type described above, which is improved in at least one respect in relation to prior art arrangements. This objective is achieved according to the invention by providing an arrangement of the type described in patent claim 1. By opening the exhausts valves earlier in at least one cylinder than in at least one other cylinder, the exhaust pulses from said first cylinder will become more forceful, than if the previously opened exhaust valves in this cylinder had been opened at the same point in this cylinder's combustion cycle as said exhaust valves in said second cylinder. This means that the first cylinder's exhaust pulse will drive a larger share of exhausts for recirculation to the air supply than would otherwise have been the case. An earlier opening of the exhaust valve will entail that a part of the pressure created during combustion may not be converted to mechanical energy, and thus the efficiency of the engine is reduced. The engine's output power may thus not be maintained without a somewhat increased fuel consumption in the cylinder concerned. However, since such earlier opening is not carried out in all the cylinders, fuel consumption may be maintained at a desirably low level. The first cylinder may have several exhaust valves and only one or several or all of these, i.e. any number of them, may be opened earlier in the cylinder's combustion cycle than at least one exhaust valve in said second cylinder's combustion cycle. According to one embodiment of the invention, said exhaust valves in said first cylinder are arranged to open 5-60 crank degrees, 5-30 crank degrees or 10-20 crank degrees earlier than the exhaust valves in the at least one second cylinder. This constitutes potential intervals for an earlier opening of an exhaust valve in said first cylinder, without the fuel consumption of the cylinder becoming unacceptably high. How large an earlier opening of the relevant exhaust valve is selected, may depend on the intended use of the combustion engine.

According to another embodiment of the invention, the at least one second cylinder has its exhaust outlet connected with said second conduit. By thus using several cylinders to drive the EGR, but only one or some to do so through an extra powerful exhaust pulse, the desired fraction of exhausts may be recirculated to the air supply, while the engine's fuel consumption may simultaneously be kept low.

According to another embodiment of the invention, all the cylinders in the engine have their exhaust outlets connected with said second conduit. Since exhaust pulses from all the cylinders are used for recirculation of exhausts to the air supply, this exhaust flow becomes substantially even, while an earlier opening of at least one exhaust valve in one or several first cylinders has a heightening impact on this flow.

According to another embodiment of the invention, said second conduit comprises at least one inlet opening for receipt of exhausts arranged near, such as in front of, and especially aligned with, the exhaust outlet of said one first cylinder. Through such a placement of the inlet opening to the second conduit, the more powerful exhaust pulse from the cylinder in question may be used to a maximum extent to drive the EGR, so that the desired share of recirculated exhausts may be achieved with a minimal extra fuel consumption in the engine.

According to another embodiment, the invention comprises a control device, adapted to control said exhaust valves in said one first cylinder to open at least 5 crank degrees earlier in the cylinder's combustion cycle than the exhaust valves of the at least one second cylinder. Thus the control of the exhaust recirculation becomes simple and reliable. One advantage of using such a control device is that it allows a resetting of the exhaust valve to open earlier only in those cases where exhaust recirculation is required. In certain operating modes, no exhaust recirculation is required, and the relevant exhaust valve may in these operating modes be set to open at the same time as other exhaust valves. The engine will function, in these operating modes, in a conventional manner and without impact by the invention. One advantage of this is that the fuel consumption may be improved, and the operating modes with impaired fuel consumption due to the use of the invention may be limited. According to another embodiment of the invention, the arrangement comprises an exhaust manifold device designed to receive exhausts from several of said cylinders and connected to an exhaust conduit for the removal of exhausts from the arrangement, and the second conduit has at least one opening, debouching in the exhaust manifold device for receipt of exhausts, arranged at one end of the exhaust manifold device in the region of its connection to the exhaust outlet conduit. It is advantageous to arrange an opening in the second conduit at this place in the exhaust manifold device, to avoid exhausts from a cylinder flowing in the opposite direction, toward exhausts from some other cylinder.

According to another embodiment of the invention, the arrangement comprises a turbocharger connected to the first conduit, for

compression of air supplied to the engine with the help of exhausts from the engine. Said turbocharger is advantageously of the type with fixed geometry (FGT). Since the exhaust valves in at least one cylinder connected with said second conduit are opened earlier, so that a more powerful exhaust pulse for driving of the EGR gases is generated, the exhaust recirculation may be driven at a desirably high level in a combustion engine equipped with a fixed geometry

turbocharger. Simultaneously, a low fuel consumption of the engine is obtained, which leads to lower costs and a more robust structure than when using a turbocharger of the VGT type in the arrangement. According to another embodiment of the invention, the engine has at least two said first cylinders, and a control device in the arrangement is adapted to initiate combustion in the engine's cylinders in a sequential order, so that said first cylinders are essentially evenly distributed or evenly distributed therein. By allocating the cylinders with more powerful exhaust pulses evenly, or essentially evenly, in the engine's firing order, the flow of exhausts recirculated to the air supply becomes substantially even, and thus the amount of NO_x resulting from the combustion in the engine becomes minimal.

According to another embodiment of the invention, a control device in the arrangement is adapted to control said at least one exhaust valve in aid one first cylinder, so that it has a fixed opening distance, in crank degrees, to said at least one exhaust valve in aid at least one second cylinder. Thus the control of the EGR becomes simple and reliable. This means that the control device does not actually control said at least one exhaust valve in said first cylinder to open earlier, rather it is not possible to control when it opens at all. The distance in crank degrees between the opening of the exhaust valves in the engine's different cylinders is fixed in this embodiment, i.e. always the same. According to another embodiment of the invention, the combustion engine has six cylinders, and two of the cylinders are first cylinders, both having their exhaust outlet connected with said second conduit, and having exhaust valves, which a control device in the arrangement is adapted to control to open at least 5 crank degrees earlier in the combustion cycle than the exhaust valves in the remaining four second cylinders. By using two of the six cylinders to provide an enhanced exhaust pulse to drive the EGR gases, the level of NO_x formed during the engine's combustion may be kept low, and yet the early opening of the exhaust valves in both these cylinders will only have an insignificant impact on the engine's fuel consumption. It is particularly advantageous if the four second cylinders are connected to aid second conduit and both the first cylinders are evenly distributed in the engine's firing order, i.e. with two other cylinders lit between both the first cylinders.

According to another embodiment of the invention, the combustion engine has eight cylinders, and two, three or four of the cylinders are first cylinders, all having their exhaust outlet connected with said second conduit, and having exhaust valves, which a control device of the arrangement is adapted to control to open at least 5 crank degrees earlier in the combustion cycle than exhaust valves in the remaining said second cylinders. The above reasoning as regards the embodiment with a combustion engine with six cylinders is also applicable here.

The invention also pertains to a method for the control of air supply to a combustion engine with at least three cylinders, according to the enclosed independent method claims. The result of the

implementation of such a method and the advantages of this are very clear in the description above of the arrangement according to the invention.

The invention also pertains to a computer program, a computer program product, an electronic control device and a combustion engine. Other advantageous features and advantages regarding the invention are set out in the description below.

BRIEF DESCRIPTION OF THE DRAWINGS Below are descriptions of example embodiments of the invention, with reference to the enclosed drawings, in which: Fig. 1 is a simplified view of an arrangement at a combustion engine of the type according to the invention,

Fig.2 is, in relation to Fig. 1 , a somewhat more detailed view of a said arrangement according to one embodiment of the invention,

Fig.3shows a diagram which illustrates the exhaust pressure over crank degrees in the three cylinders illustrated at the top of Fig.2, and how this changes in connection with an earlier opening of the exhaust valve in the third cylinder, and

Fig.4 is a diagram of an electronic control device for the

implementation of a method according to the invention. DETAILED DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTION

An arrangement at a combustion engine is schematically illustrated in Fig. 1. The arrangement has a combustion engine 7 equipped with six cylinders 1-6 in the form of a straight, six-cylinder engine, and may be intended for a motor vehicle or for industrial or marine use. The arrangement has an air inlet 8 for fresh air to the engine, from which the air is led via a first conduit 9 to the engine's cylinders, for combustion of fuel mixed therewith in the cylinders. A supercharger in the form of a turbocharger 10 with fixed geometry (FGT) is arranged to compress the air to be supplied to the cylinders. The turbocharger 10 comprises, in a conventional manner, a compressor 11 and a turbine 12. The air, which has been given an overpressure via the compressor 11, is cooled in an intercooler 16, and then continues to an air inlet conduit 17 in the first conduit, leading the air to the cylinders 1-6. The engine comprises two exhaust manifolds 27, 31 (see Fig.2) to which the exhausts are led from the cylinders, where the cylinders 1-3 lead the exhausts to one of the exhaust manifolds 27, and where exhausts from the cylinders 4-6 are led to the second exhaust manifold 31. From the respective exhaust manifolds 27, 32 the exhausts are led further via the exhaust outlet conduits 13, 14 to the turbine 12. The turbine 12 is thus equipped with a double inlet, i.e. a so-called Twin Scroll Turbine. The exhausts driving the turbine 12 exit into the environment via an exhaust conduit 15.

The arrangement also has an EGR system for recirculation of a part of the exhausts, resulting from the combustion in the engine, to the part of the first conduit 9 extending downstream of the intercooler 16, for mixture with fresh air in the air supply to the engine. It is

schematically illustrated how, for this purpose, a second conduit 18 extends with two conduit sections 19, 20 from the exhaust outlet conduits 13, 14 and further along, via a back valve 21 and an EGR cooler 22, to the first conduit 9.

The arrangement has, in an advantageous embodiment, a control device 23 adapted to control at least the opening of the exhaust valves in the cylinders, i.e. at which point in the combustion cycle the respective cylinder's combustion chamber is connected to the cylinder's exhaust outlet for the emission of exhausts. In this regard, this may be the same control device which is adapted to initiate the combustion in the engine's cylinders, and also to control other components in the arrangement. The control of the valves' time of opening may suitably be carried out indirectly, through control of an arrangement intended for this purpose for the control of variable valve times, e.g. one where the engine's camshaft is brought to abut against alternative cam ridges. Alternatives where the valves may be

controlled directly with the help of electromagnets are also possible. Here each cylinder has two exhaust valves 41, 42 controlled by the control device, and two inlet valves 43, 44. Each cylinder could, however, have another number of exhaust valves and inlet valves. For example, one, three or four exhaust valves.

Reference is now made to Fig.2. In the embodiment displayed, the exhaust outlets 24-26 in three of the cylinders 1-3 are connected to one of the exhaust manifolds 27, while the exhaust outlets 28-30 in the remaining cylinders 4-6 are connected to the second exhaust manifold 31. The pressure in the exhaust manifolds 27, 31 will be approximately the same as in the air inlet conduit 17, so that there is no pressure difference which drives the recirculation of exhausts through the second conduit 18, but such drive will instead be provided by the exhaust pulses resulting when the cylinders' exhaust valves open, so that a pulsated EGR flow is obtained. The return valve 21 prevents each respective exhaust pulse from turning back when the pressure in the exhaust manifolds 27, 31 drops.

The control device 23 controls the exhaust valves 41, 42 in a first cylinder 3, 4 connected to the respective exhaust manifolds 27, 31 to open at least 5 crank degrees and at most 60 crank degrees, and here to open approximately 20 crank degrees earlier in this cylinder's combustion cycle than the exhaust valves in both the second

cylinders 1, 2 and 5, 6 respectively, connected to the relevant exhaust manifold device, in those operating modes where exhaust

recirculation should take place. This means that the first cylinders have exhaust valves which open when the cylinder's piston is not at the same position, which means that the fuel consumption in this cylinder increases a little, while the exhaust pulse from said first cylinder becomes significantly stronger (see below the discussion regarding Fig.3) than for said second cylinders and thus operates more strongly driving on the reflux of exhausts in the second conduit 18. The respective conduit sections 19, 20 of the second conduit are arranged with their inlet openings 32, 33 for receipt of exhausts in front of and aligned with the extension of the exhaust outlet 26, 28 in said first cylinders 3, 4, while the cylinders that have their exhaust outlets debouching in the exhaust manifold device, at one end thereof in the region of its connection with the exhaust outlet conduits 13, 14, i.e. at the so-called turbo foot, are those which have been selected to be said first cylinders. Overall, this entails that the exhaust pulse generated thanks to the earlier opening of an exhaust valve is used to a maximum, in order to drive the EGR. All, here two, exhaust valves are advantageously opened earlier in the cylinders 3, 4, arranged facing the inlet openings 32, 33, in order to obtain a strongly driving EGR exhaust pulse. Fig.2 also shows schematically how a small scoop 34, 35 may be arranged to help in using a part of the exhaust pulses from both the second cylinders 1, 2 and 5, 6 respectively, to drive the EGR.

The control device 23 may be adjusted and, in those operating modes where exhaust recirculation is not required, may be set to open the relevant exhaust conduit (exhaust conduits) at the same time as the engine's other exhaust valves. This entails that the work generated at the combustion may be used optimally.

A control device to control the initiation of combustion in the engine's cylinders is adapted to perform this in a sequence, so that both the first cylinders are evenly distributed in this sequence, and for this sake the firing sequence 1 53624 is chosen here, where 3 and 4 are the cylinders with exhaust valves which are opened earlier. Thus a substantially even flow of exhausts is achieved in the second conduit, for mixing with the air in the first conduit, and the share of recirculated exhausts is maintained at a desirably high level in order to achieve a low level of NO_x emanating out of the engine, while a favourably low fuel consumption in the engine is maintained. The more powerful exhaust pulses from the cylinders 3 and 4 do not disturb the other cylinders, thanks to a twin scroll turbine, turbine wheels with double inlets, and an even distribution in the firing sequence.

The diagram in Fig.3 shows how the pressure P at the inlet opening 32 for the EGR output from the cylinders 1-3 develops over the number of crank degrees CP in the cylinders. The three tops 2, 1 and

3 are thus attributable to the opening of exhaust valves in

corresponding cylinders, and the curve A illustrates the cylinder pressure in the cylinder 3, while the curve B illustrates the lifting of the exhaust valves in cylinder 3 in non-displayed length units (mm). It is clear that the exhaust pressure is highest after the exhaust valves on cylinder 3 have been opened, due to the exhaust outlet of this cylinder being aligned with the inlet opening 32. A dashed line B.1 shows that the exhaust valves in cylinder 3 are opened 20 crank degrees earlier, and the dashed line 3.1 shows what happens to the exhaust pressure, which increases considerably, since the cylinder pressure then (curve A) will be higher (ΔΑ) when the opening occurs.

In one alternative embodiment of the invention, the arrangement instead comprises a combustion engine in the form of a V8 engine with eight cylinders, which advantageously have a firing sequence 1 5

426378 and a displayed Twin Scroll Turbo placed at one end of the combustion engine near cylinders 4 and 8. The exhaust valves from cylinders 4 and 8, and potentially also from cylinder 3, may then advantageously be opened earlier in order to obtain an even

distribution in the firing sequence. A computer program code for the implementation of a method according to the invention is suitably included in a computer program, loadable into the internal memory of a computer, such as the internal memory of an electronic control device of a said arrangement, e.g. a motor vehicle. Such a computer program is suitably provided via a computer program product comprising a data storage medium readable by an electronic control device, the data storage medium having the computer program stored thereon. Said data storage medium is e.g. an optical data storage medium in the form of a CD- ROM, a DVD, etc., a magnetic data storage medium in the form of a hard disk drive, a floppy disc, a cassette, etc., or a Flash memory or a ROM, PROM, EPROM or EEPROM type memory. Fig.4 illustrates very schematically an electronic control device 36 comprising execution means 37, such as a central processor unit (CPU), for the execution of a computer software. The execution means 37 communicates with a memory 38, e.g. a RAM memory, via a data bus 39. The control device 36 also comprises a data storage medium 40, e.g. in the form of a Flash memory or a ROM, PROM, EPROM or EEPROM type memory. The execution means 37

communicates with the data storage means 40 via the data bus 39. A computer program comprising computer program code for the implementation of a method according to the invention is stored on the data storage medium 40.

The invention is obviously not in any way limited to the above described embodiments, but a number of potential modifications are possible. For example, the arrangement could lack a turbocharger. Another alternative is, for example, in a combustion engine of the type displayed in Fig.2, to have only the cylinders in one of the exhaust manifold devices, such as cylinders 1-3, connected to the second conduit for EGR, and in this case e.g. the control device may be adapted to control the exhaust valves of the cylinders 2 and 3 to open earlier in their combustion cycle than the remaining cylinders. One single inlet opening to the second conduit could be arranged in front of cylinder 3, and another such opening in front of cylinder 2. It is pointed out again that the definition of the control device is to be interpreted as also comprising the case that adjustability of distance in crank degrees between the opening of the exhaust valves of the combustion engine's different cylinders is lacking, and that this distance is adjusted to be invariable over time.

Claims

Patent claims

1. Arrangements pertaining to a combustion engine (7) with at least three cylinders (1-6), comprising a first conduit (9) for air supply to the engine for the combustion in the cylinders, a second conduit

(18) returning a part of the exhausts resulting from the combustion in the engine to said first conduit to be mixed with fresh air in the air supply to the engine, an outlet (24-26, 28-30) for exhausts from at least one of the cylinders being connected with said second conduit (18), characterised in that all the exhaust valves in at least one first of said cylinders (3, 4), having its exhaust outlet (26, 28) connected with said second conduit (18), are arranged to open at least 5 crank degrees earlier in this cylinder's combustion cycle than all the exhaust valves in at least one second of said cylinders (1 , 2, 5, 6).

2. Arrangement according to claim 1, characterised in that said

exhaust valves in said first cylinder (3, 4) are arranged to open 5- 60 crank degrees, 5-30 crank degrees or 10-20 crank degrees earlier than at least one exhaust valve in the at least one second cylinder (1 , 2, 5, 6).

3. Arrangement according to claim 1 or 2, characterised in that the at least one second cylinder (22) has its exhaust outlet (24, 25, 29, 30) connected with said second conduit (18).

4. Arrangement according to claim 3, characterised in that all the cylinders (1-6) in the engine have their exhaust outlets (24-26, 28- 30) connected with said second conduit (18).

5. Arrangement according to any of the previous claims,

characterised in that said second conduit (18) comprises at least one inlet opening (32, 33) for receipt of exhausts, arranged near, such as in front of or aligned with, the exhaust outlet (26, 28) in said first cylinder (3, 4).

Arrangement according to claim 1, characterised in that a control device (23) is adapted to control said exhaust valves in the at least one first cylinder (3, 4) to open at least 5 crank degrees earlier in this cylinder's combustion cycle than all the exhaust valves in the at least one second cylinder (1, 2, 5, 6).

Arrangement according to claim 6, characterised in that the control device (23) is adapted to control the exhaust valves in the at least one first cylinder (3, 4) to open 5-60 crank degrees, 5-30 crank degrees or 10-20 crank degrees earlier than all the exhaust valves in the at least one second cylinder (1, 2, 5, 6).

Arrangement according to any of the previous claims,

characterised in that it comprises an exhaust manifold device (27, 31), designed to receive exhausts from several of said cylinders (1-6) and connected to an exhaust outlet opening (13, 14) for the removal of exhausts, and that the second conduit (18) has at least one opening (32, 33) debouching in the exhaust manifold device for receipt of exhausts, arranged at one end of the exhaust manifold device in the region of said device's connection to the exhaust outlet conduit.

Arrangement according to any of the previous claims,

characterised in that it comprises a turbocharger (10) connected to the first conduit (9) for compression of air supplied to the engine with the help of exhausts from the engine, and said turbocharger (10) being a turbocharger with fixed geometry.

10. Arrangement according to claims 8 and 9, characterised in that the turbocharger on the engine's exhaust side is connected to the exhaust outlet conduit's (13, 14) opening (32, 33), debouching downstream of the exhaust manifold device.

11. Arrangement according to any of the previous claims,

characterised in that the engine (7) has at least two first cylinders (3, 4), and that one control device (23) in the arrangement is adapted to initiate combustion in the engine's cylinders (1-6) in a sequence, so that said first cylinders are substantially evenly distributed, or evenly distributed, therein.

12. Arrangement according to any of the previous claims,

characterised in that a control device (23) in the arrangement is adapted to control said exhaust valves in said first cylinder (3, 4) to have a fixed opening distance, in terms of crank degrees, to all the exhaust valves in the at least one second cylinder (1, 2, 5, 6).

13. Arrangement according to any of the previous claims,

characterised in that the combustion engine (7) has six cylinders

(1-6), and that two (3, 4) of the cylinders are first cylinders, both having their exhaust outlets (26, 28) connected with said second conduit (18) and having exhaust valves which a control device (23) in the arrangement is adapted to control to open at least 5 crank degrees earlier in the combustion cycle than the exhaust valves of the other remaining four second cylinders (1, 2, 5, 6).

14. Arrangement according to any of the claims 1-12, characterised in that the combustion engine has eight cylinders, and that two, three or four cylinders are first cylinders, all having their exhaust outlet connected with the said second conduit and having exhaust valves which a control device in the arrangement is adapted to control to open at least 5 crank degrees earlier in the combustion cycle than the exhaust valves of the other said second cylinders.

15. Method for the control of air supply to a combustion engine (7) with at least three cylinders (1-6), in which a part of the exhausts resulting from the combustion in the engine is returned and mixed with fresh air for the joint supply thereof to the engine,

characterised in that all the exhaust valves in the at least one first cylinder (3, 4), which has its exhaust outlet (26, 28)

connected with a conduit (18) for leading of exhausts to be mixed with fresh air for air supply to the engine, are opened at least 5 crank degrees earlier in this cylinder's combustion cycle than all the exhaust valves in the at least one second cylinder (1, 2, 5, 6). 16. Computer program, loadable directly into the internal memory of a computer, which computer program comprises a computer program code to bring the computer, for an arrangement at a combustion engine (7) with at least three cylinders (1-6), a first conduit (9) for air supply to the engine for the combustion in the cylinders and a second conduit (18) for leading a part of the exhausts resulting from the combustion in the engine back to said first conduit for mixing with fresh air for the air supply to the engine:

to control exhaust valves in said cylinders (1-6) and

in connection with the control of the exhaust valves, to control all the exhaust valves in at least one first cylinder (3, 4), which has its exhaust outlet (26, 28) connected with said second conduit (18), to be opened at least 5 crank degrees earlier in this cylinder's combustion cycle than all the exhaust valves in at least one second cylinder (1, 2, 5, 6).

17. A computer program product comprising a data storage medium which is readable by a computer, the computer program code of a computer program according to claim 16 being stored on the data storage medium.

18. Electronic control device in an arrangement at a combustion

engine comprising an execution means (37), a memory (38) connected to the execution means and a data storage medium (40) connected to the execution means, the computer program code in a computer program according to claim 16 being stored on said data storage medium.

19. Combustion engine, characterised in that it is equipped with an arrangement according to any of claims 1-14.