Method for Operating an Internal Combustion Engine, in Particular of a Motor Vehicle

Abstract

A method for operating an internal combustion engine includes first operating the internal combustion engine in a first operating state and setting a second operating state, different from the first operating state, by advancing the exhaust camshaft relative to the crankshaft by a value in comparison with the first operating state. The exhaust valve is actuated by the exhaust cam and a decompression lift of the exhaust camshaft, whereupon, in the second operating state, the cylinder assumes a function of a decompression brake by compressing a first cylinder charge in the cylinder within a respective operating cycle of the internal combustion engine and then decompressing it by a decompression travel of the exhaust valve in a region of a charge exchange top dead center. In the second operating state, the intake camshaft is retarded relative to the crankshaft by a value.

Claims

1.-11. (canceled)

12. A method for operating an internal combustion engine, wherein the internal combustion comprises: a cylinder and a piston which is received in the cylinder so as to be movable in translation; an exhaust valve and an intake valve assigned to the cylinder; a crankshaft via which a torque is providable by the internal combustion engine; an intake camshaft which is driveable by the crankshaft and has an intake cam for actuating the intake valve; an exhaust camshaft which is driveable by the crankshaft and has an exhaust cam and a decompression lift for actuating the exhaust valve; and comprising the steps of: first operating the internal combustion engine in a first operating state; and setting a second operating state, different from the first operating state, of the internal combustion engine by advancing the exhaust camshaft relative to the crankshaft by a value (WA) in comparison with the first operating state; wherein the exhaust valve is actuated by the exhaust cam and the decompression lift of the exhaust camshaft, whereupon, in the second operating state, the cylinder assumes a function of a decompression brake by compressing a first cylinder charge in the cylinder within a respective operating cycle of the internal combustion engine and then decompressing it by a first decompression travel (DH1) of the exhaust valve in a region of a charge exchange top dead center (LWOT); wherein in the second operating state, the intake camshaft is retarded relative to the crankshaft by a first value (WE1) which is in a range of greater than 80 degrees crank angle and up to at most 120 degrees crank angle after the charge exchange top dead center (LWOT) or wherein in the second operating state, the intake camshaft is retarded by a second value (WE2) which is in a range of 0 degrees crank angle to 20 degrees crank angle after the charge exchange top dead center (LWOT).

13. The method according to claim 12, wherein a closed position (S) of the exhaust valve following the first decompression travel (DH1) is reached at 40 degrees crank angle to 165 degrees crank angle after the charge exchange top dead center (LWOT).

14. The method according to claim 12, wherein a closed position (S) of the exhaust valve following the first decompression travel (DH1) is reached at more than 80 degrees crank angle and at the latest at 165 degrees crank angle after the charge exchange top dead center (LWOT).

15. The method according to claim 12, wherein the exhaust camshaft is advanced relative to the crankshaft by the value (WA) in a range of 70 degrees crank angle to 110 degrees crank angle before the charge exchange top dead center (LWOT).

16. The method according to claim 12, wherein in the second operating state, a second cylinder charge is compressed in the cylinder within the respective operating cycle of the internal combustion engine and is then decompressed by a second decompression travel (DH2) of the exhaust valve in a region of an ignition top dead center (ZOT).

17. The method according to claim 12, wherein, in the second operating state, a second exhaust valve of the cylinder is opened simultaneously by the exhaust cam and only the first exhaust valve is opened by the first decompression travel (DH1).

18. The method according to claim 12, wherein, in order to set the second operating state, first an introduction of fuel into the cylinder is terminated (step S1), then the intake camshaft is retarded (step S2), and thereafter the exhaust camshaft is advanced (step S3).

19. The method according to claim 12, wherein, in order to set the second operating state, first an introduction of fuel into the cylinder is terminated (step S1), then the intake camshaft is retarded (step S2) and the exhaust camshaft is simultaneously advanced (step S3).

20. The method according to claim 12, wherein, in order to set the second operating state, first an introduction of fuel into the cylinder is terminated (step S1), then the exhaust camshaft is advanced (step S3), and thereafter the intake camshaft is retarded (step S2).

21. The method according to claim 18, wherein, after the steps (S1 to S3), a decompression travel of the exhaust valve is effected (step S4).

22. The method according to claim 19, wherein, after the steps (S1 to S3), a decompression travel of the exhaust valve is effected (step S4).

23. The method according to claim 20, wherein, after the steps (S1 to S3), a decompression travel of the exhaust valve is effected (step S4).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 shows a diagram illustrating a method according to the invention as per a first embodiment for operating an internal combustion engine, in particular of a motor vehicle;

[0036] FIG. 2 shows a diagram illustrating a second embodiment of the method; and

[0037] FIG. 3 shows a flowchart illustrating the method.

DETAILED DESCRIPTION OF THE DRAWINGS

[0038] In the figures, identical or functionally identical elements are provided with the same reference signs.

[0039] FIG. 1 shows a diagram which is used below to illustrate a first embodiment of a method for operating an internal combustion engine of a vehicle. The vehicle is designed, for example, as a motor vehicle, in particular as a commercial vehicle, and can be powered by means of the internal combustion engine, in particular in its fired mode. The internal combustion engine is designed as a reciprocating piston engine and has at least one cylinder and at least one piston which is received in the cylinder so as to be movable in translation. In particular, the internal combustion engine has a plurality of cylinders in which combustion processes take place during the fired mode of the internal combustion engine. For example, first ones of the cylinders form a first cylinder group, with second ones of the cylinders forming a second cylinder group. Thus, for example, the first group of cylinders comprises the plurality of first cylinders and the second group of cylinders comprises the plurality of second cylinders. The respective cylinder group is also referred to as a cylinder bank. In particular, the internal combustion engine can be designed as a V engine, so that the cylinders or cylinder banks can be arranged in a V shape relative to each other. Furthermore, the internal combustion engine can be designed as an inline engine, so that the cylinder banks can be arranged next to each other.

[0040] The respective piston is accommodated in the respective cylinder so that it can be moved in translation, whereby the piston can be moved in translation between a top dead center and a bottom dead center. The internal combustion engine also has an output shaft configured as a crankshaft, via which the internal combustion engine can provide torques to power the motor vehicle. The pistons are connected in an articulated manner to the crankshaft via respective connecting rods, so that the translatory movements of the pistons are converted into a rotary movement of the crankshaft. The cylinders with their respective pistons and a cylinder head each enclose a combustion chamber in which the combustion processes take place.

[0041] A respective operating cycle of the internal combustion engine configured as a four-stroke engine comprises exactly two complete revolutions of the crankshaft and thus exactly 720 degrees of crank angle. During the revolutions, the crankshaft comes into different rotational positions or rotational angles, whereby the rotational positions or rotational angles are also referred to as crank angle degrees. The respective piston moves exactly twice to its top dead center and exactly twice to its bottom dead center within the respective operating cycle, so that the top dead center occurs exactly twice within the respective operating cycle. The first occurrence of the top dead center is, for example, a so-called charge exchange top dead center LWOT. A second of the occurrences is, for example, an ignition top dead center ZOT.

[0042] Since the internal combustion engine is configured as a four-stroke engine, the respective operating cycle comprises exactly four strokes. In or in relation to the fired mode, for example, a first of the strokes is an intake stroke, also referred to as induction stroke, in which the respective piston moves from the charge exchange dead center LWOT to its respective bottom dead center UT and at least ambient air is introduced into the cylinder via the intake valves and thus a cylinder charge is introduced into the cylinder from the intake tract via the intake valves. The first stroke is followed by a second of the strokes. The second stroke is a compression stroke, also referred to as compression phase, in which the piston moves from the bottom dead center UT to its ignition top dead center ZOT. In this way, the cylinder charge previously introduced into the cylinder is compressed by means of the piston. A third stroke that follows the second stroke is a power stroke, in which the piston is driven and is moved from its top dead center ZOT to its bottom dead center UT. This results in the piston being driven as described. The fourth stroke following the third stroke is also referred to as the exhaust stroke or exhaust travel or exhaust phase, since during the fourth stroke the combusted fuel-air mixture or exhaust gas is expelled from the cylinder by means of the piston.

[0043] In addition, the internal combustion engine comprises at least one intake valve or a plurality of, in particular exactly two, intake valves per cylinder, via which, for example, at least ambient air or air or fresh air can be introduced or flow into the respective cylinder as cylinder charge. If the internal combustion engine is configured as a supercharged internal combustion engine, the cylinder charge is introduced into the cylinder via the intake valves, for example by means of a compressor of an exhaust gas turbocharger. In addition to the ambient air, for example, recirculated exhaust gas can also be contained in the cylinder charge, whereby the recirculated exhaust gas is usually mixed with the ambient air compressed by the compressor by means of high-pressure exhaust gas recirculation (HP-EGR) downstream of the compressor and/or is mixed with the introduced ambient air by means of low-pressure exhaust gas recirculation (LP-EGR) upstream of the compressor. In particular, the cylinder charge can flow from an intake manifold via intake ducts of an intake tract of the internal combustion engine into the respective cylinder, in particular when the respective intake valve is open. The internal combustion engine also comprises at least one intake camshaft that can be driven by the crankshaft and has at least one intake cam for actuating the at least one intake valve. Conventional internal combustion engines are designed as V engines or inline engines. An internal combustion engine designed as a V engine can have one intake camshaft for each cylinder bank, by means of which the respective intake valves, in particular of the respective cylinder bank, can be actuated and thus opened. V Engines with only one intake camshaft for the cylinder banks are also conceivable or designed. Typically, an internal combustion engine configured as an inline engine has only one intake camshaft for both cylinder banks.

[0044] At least one exhaust valve of the internal combustion engine is also provided for each cylinder, whereby a plurality of exhaust valves are usually provided for each cylinder and, in this case for example, exactly two exhaust valves. A cylinder charge, such as the aforementioned exhaust gas, can flow out of the cylinder via the respective exhaust valve and flow, for example, into an exhaust manifold and thus into an exhaust tract or on an exhaust side of the internal combustion engine. In this case, the internal combustion engine has at least one exhaust camshaft which can be driven by the crankshaft and has at least one exhaust cam and at least one decompression lift for actuating the at least one exhaust valve. In particular, the internal combustion engine has an exhaust camshaft, in particular for each cylinder bank of a V engine, by means of which the respective exhaust valves, in particular of the respective cylinder bank, can be actuated and thus opened. V Engines with only one exhaust camshaft for the cylinder banks are also conceivable or designed. Typically, an internal combustion engine configured as an inline engine has only one exhaust camshaft for both cylinder banks.

[0045] The at least one intake camshaft and the at least one exhaust camshaft are also collectively referred to as camshafts which can be driven by the crankshaft. In addition, the intake valves and the exhaust valves are also collectively referred to as valves or gas exchange valves. By way of example, in the exhaust tract there is an exhaust gas aftertreatment device, also referred to as an exhaust system, through which the exhaust gas can flow. The exhaust gas can be after treated by means of the exhaust system.

[0046] The diagram shown in FIG. 1 has an x-axis 10 on which the crank angle degrees are plotted. The respective gas exchange valve can be moved in translation and thus performs a respective travel within the respective operating cycle, which travel is plotted on the y-axis 12 of the diagram.

[0047] Within the context of the method, the internal combustion engine is, for example, first operated in a first operating state, in or during which the internal combustion engine is, for example, in its fired mode or in a dragged mode known per se. In or during the first operating state, the respective intake valve is actuated or moved according to a valve lift curve 14 shown in FIG. 1. In the exemplary embodiment illustrated in FIG. 1, exactly two intake valves and exactly two exhaust valves are assigned to the respective cylinder, whereby one of the exhaust valves is also referred to as the first exhaust valve and the other of the exhaust valves is also referred to as the second exhaust valve. By way of example, in the first operating state, both the first exhaust valve and the second exhaust valve are actuated or moved according to a valve lift curve 16 shown in FIG. 1. Thus, for example, the valve lift curves 14, 16 illustrate the movements or actuations of the gas exchange valves during fired mode or in the first operating state.

[0048] In the method, the internal combustion engine is switched from the first operating state to the second operating state so that the second operating state is set. The second operating state is set by retarding the intake camshaft relative to the crankshaft in comparison to the first operating state. Furthermore, in the second operating state, the cylinder is operated as, or in the manner of, a decompression brake by compressing a first cylinder charge in the cylinder within the respective operating cycle of the internal combustion engine and then decompressing it in the manner of a decompression brake by means of a first decompression travel DH1 of the first exhaust valve.

[0049] In order to be able to realize a particularly advantageous operation, in particular a particularly advantageous braking operation, of the internal combustion engine, the at least one intake camshaft is retarded by a first value WE1 in order to set the second operating state, the first value WE1 lying in a range from 80 degrees crank angle to 120 degrees crank angle. The first value WE1 is preferably greater than 80 degrees crank angle and at most 120 degrees crank angle. It is also provided that in the second operating state, the first exhaust valve reaches its closed position S immediately or directly following the first decompression travel DH1 within the respective operating cycle at a crank angle of 40 degrees to 165 degrees after the charge exchange top dead center of the piston. In other words, when the first exhaust valve reaches its closed position S immediately following the first decompression travel DH1, the crankshaft is at 40 degrees crank angle up to 165 degrees crank angle, preferably at a value greater than 80 degrees crank angle up to 165 degrees crank angle at the latest, as shown in in FIG. 1, after the charge exchange top dead center LWOT of the piston. The closed position S denotes the state of the first exhaust valves of the respective cylinders when the first exhaust valves are not open, i.e., the exhaust valve travel is zero or there is zero travel.

[0050] Since the at least one intake camshaft is retarded to set the second operating state, the intake valves, in particular all of the intake valves, assigned to the respective cylinders are moved or actuated during the second operating state in accordance with a valve lift curve 18 shown in FIG. 1. The at least one intake camshaft is adjusted or rotated relative to the crankshaft with a phase adjuster known per se. Of course, the phase adjuster for the at least one intake camshaft can also be used to adjust the intake camshaft in the first operating state.

[0051] It is further provided that for setting the second operating state, the at least one exhaust camshaft is advanced relative to the crankshaft by a value WA in comparison to the first operating state, wherein the value WA is in a range of 70 degrees crank angle to 110 degrees crank angle. In the first operating state, both exhaust valves are actuated or moved according to the valve lift curve 16. The valve lift curve 16 is effected, for example, by means of the respective exhaust cam of a respective exhaust camshaft, so that the respective exhaust valve is actuated in the first operating state by means of the respective exhaust cam.

[0052] In the second operating state, both exhaust valves of the respective cylinder continue to be actuated by means of the respective exhaust cam so that in the second operating state, both exhaust valves are actuated or moved according to a valve lift curve 20 shown in FIG. 1. The valve lift curve 20 corresponds to the valve lift curve 16, with the only difference being that the valve lift curve 20 is advanced or shifted early in comparison with the valve lift curve 16. This results from the advancement of the at least one exhaust camshaft.

[0053] To set the second operating state, for example, an actuating element assigned to the first exhaust valve is moved from the first position into a second position different therefrom, so that the first exhaust valve is actuated by means of the exhaust cam assigned to the first exhaust valve and thereby additionally by means of the decompression lift, different from the first exhaust cam, with the decompression travel DH1. As is known, the decompression lift can be designed as an additional brake cam alongside the exhaust cam or as an additional decompression lift on the exhaust cam. In this case, actuation of the first exhaust valve, effected by the exhaust cam, and simultaneously of the second exhaust valve is carried out according to the valve lift curve 20 in the second operating state. In addition, actuation of the first exhaust valve by the decompression lifts causes the first exhaust valve to be actuated and moved, respectively, to the second operating state according to a valve lift curve 21 and a valve lift curve 22. As a result, within the respective operating cycle, the first exhaust valve performs the decompression travel DH1 according to the valve lift curve 21 as first decompression travel DH1 and a second decompression travel DH2 according to the valve lift curve 22. This is explained in more detail below. Moving the actuating element from the first position to the second position is also referred to as connecting the decompression travels DH1 and DH2. The connected decompression travels DH1 and DH2 are permanently linked to the exhaust travel by their position on the crank circuit. Due to the previously described linkage, the exhaust travel and the respective decompression travel DH1 or decompression travel DH2 are shifted simultaneously, for example by a further phase adjuster, next to the phase adjuster for the at least one intake camshaft. Of course, the further phase adjuster for the at least one exhaust camshaft can be used to adjust the exhaust camshaft in the first operating state. It is also conceivable that in addition to the first exhaust valve, the second exhaust valve is also actuated in the second operating state according to the valve lift curve 21 and the valve lift curve 22, so that the second exhaust valve also performs the decompression travels DH1 and DH2. It is further conceivable that the first exhaust valve performs only one of the two decompression travels DH1, DH2, while the second exhaust valve performs the other of the two decompression travels DH1, DH2, or neither of the decompression travels DH1, DH2.

[0054] In the first embodiment, it is provided that in the second operating state the at least one cylinder is operated as a or the aforementioned decompression brake in such a way that within the respective operating cycle of the internal combustion engine in the cylinder the aforementioned first cylinder charge is compressed and thereafter decompressed by the first decompression travel DH1 of the first exhaust valve. The first cylinder charge is introduced into the respective cylinder by means of the piston via the open first exhaust valve and via the open second exhaust valve during the power stroke, and is at least partially compressed in the cylinder by means of the piston during the subsequent exhaust stroke. Compression of the first cylinder charge can take place as the exhaust valves close before the end of the exhaust stroke and the piston continues to move in the direction of the charge exchange dead center LWOT. Subsequently, the first cylinder charge is decompressed in the manner of a decompression brake by means of the first decompression travel DH1 of the first exhaust valve in the region of charge exchange dead center LWOT. Thereafter, a second cylinder charge is introduced into the cylinder during the intake stroke by means of the piston via the intake valves from the intake tract and then compressed during the compression stroke and then decompressed by the second decompression travel DH2 of the first exhaust valve in the manner of a decompression brake in the region of the ignition dead center ZOT. It is thereby provided that in the second operating state, the second decompression travel DH2 according to the valve lift curve 22 within the respective operating cycle starts at 70 degrees crank angle to 120 degrees crank angle, preferably at more than 90 degrees crank angle to 120 degrees crank angle before the ignition top dead center (ZOT). The first cylinder charge originates substantially from the exhaust tract, whereby the second cylinder charge originates substantially from the intake tract. Thus for the first decompression travel DH1, a so-called reverse charge or reverse supercharging of the respective cylinder is provided, wherein for the second decompression travel DH2, a forward charge or forward supercharging of the respective cylinder is provided.

[0055] FIG. 2 shows a second embodiment of the second operating state. In this case, the at least one intake camshaft is retarded by a second value WE2 which is in a range from 0 degrees crank angle to 20 degrees crank angle, in particular in a range from 1 degree crank angle to 20 degrees crank angle, after the charge exchange top dead center LWOT. The at least one exhaust camshaft is adjusted analogously to the first embodiment.

[0056] In internal combustion engines with, for example, two cylinder banks, each with its own intake camshaft and exhaust camshaft, the second operating state can be set for only one of the two cylinder banks or for both cylinder banks. Each of the two intake camshafts and each of the two exhaust camshafts has its own phase adjuster. It is also conceivable that different values of a phase adjustment can be set with the respective intake camshafts and exhaust camshafts of the two cylinder banks.

[0057] FIG. 3 shows a flowchart that is used to describe a particularly advantageous sequence for switching from the first operating state to the second operating state. By way of example, to set the second operating state, in a first step S1 an introduction, in particular an injection, of fuel into the cylinder is first terminated. Then, in a second step S2, for example, the at least one intake camshaft is retarded. Thereafter, in a third step S3, for example, the at least one exhaust camshaft is advanced. Then, in a fourth step S4, for example, at least one decompression travel DH1, DH2 of the at least one exhaust valve is effected. It is also conceivable in the exemplary embodiment shown in FIG. 3 that the third step S3 is carried out before the second step S2. Furthermore, it is conceivable that the third step S3 and the second step S2 are carried out simultaneously.

LIST OF REFERENCE CHARACTERS

[0058] 10 x-axis [0059] 12 y-axis [0060] 14 valve lift curve [0061] 16 valve lift curve [0062] 18 valve lift curve [0063] 20 valve lift curve [0064] 22 valve lift curve [0065] DH1 first decompression travel [0066] DH2 second decompression travel [0067] LWOT charge exchange top dead center [0068] S closed position [0069] S1 first step [0070] S2 second step [0071] S3 third step [0072] S4 fourth step [0073] UT bottom dead center [0074] WA value [0075] WE1 first value [0076] WE2 second value [0077] ZOT ignition top dead center