Overrun of a combustion engine with increased braking effect

Abstract

Method for operating an internal combustion engine which forms at least one cylinder opening in which a piston is moved between a top dead center and a bottom dead center, wherein the piston (delimits a portion of the cylinder opening for use as a combustion chamber, wherein the mobility of the piston is controlled by means of a crankshaft and wherein at least one intake valve is assigned to the combustion chamber, which is actuated by means of a valve train, characterized in that during overrun operation of the internal combustion engine - a first opening phase of the intake valve is carried out, whereby the maximum valve lift (h max ) during a first expansion stroke of the piston, and - a second opening phase of the intake valve is carried out, whereby the maximum valve lift (h max) during a compression stroke following the first expansion stroke or during a second expansion stroke of the piston following the compression stroke.

Description

[0001] The invention relates to an internal combustion engine, in particular in a configuration as a gasoline engine with a four-stroke combustion process, and to a method for operating such an internal combustion engine under overrun.

[0002] Overrun operation of an internal combustion engine is an operation in which it generates negative drive power or braking power. Overrun operation can result, in particular, from a moving motor vehicle, for which the internal combustion engine is intended, driving the internal combustion engine using its kinetic energy, in that the section of the motor vehicle's drivetrain located between the internal combustion engine and the driven wheels of the motor vehicle is not interrupted. The internal combustion engine, which is then usually unfired, is thus dragged along by the moving motor vehicle, with the engine and the components coupled to it, in particular the generator, generating the negative drive power or braking power.

[0003] WO 2015 / 022 071 A1 discloses a variable valve train for an internal combustion engine, by means of which, among other things, a so-called two-phase decompression engine braking operation can be implemented, in which the exhaust valves of the internal combustion engine are opened twice during one working cycle of the internal combustion engine.

[0004] DE 10 2021 211 408 A1 describes a reciprocating piston internal combustion engine which can be operated according to a Miller process with a relatively early closing of the intake valves, wherein an additional opening of the intake valves is provided in the region of the bottom dead center of the piston movement in order to increase the turbulence level of the fresh gas in the combustion chamber, which is relatively low due to the Miller process.

[0005] The invention is based on the object of realizing the highest possible braking effect of an internal combustion engine during overrun operation.

[0006] This object is achieved by carrying out a method according to patent claim 1 and by using an internal combustion engine according to patent claim 12. Advantageous embodiments of the method according to the invention and preferred embodiments of the internal combustion engine according to the invention are the subject matter of the further patent claims and emerge from the following description of the invention.

[0007] According to the invention, a method is provided for operating an internal combustion engine which forms at least one cylinder opening in which a piston is moved between a top dead center (TDC) and a bottom dead center (BDC), wherein the piston delimits a section of the cylinder opening for use as a combustion chamber. The cyclical movement of the piston is controlled by means of a crankshaft. A mixture of fresh gas and fuel can be combusted in the combustion chamber in order to operate the internal combustion engine under load. The mobility of the piston is controlled by means of a crankshaft. At least one intake valve, which can be actuated by means of a valve train, is assigned to the combustion chamber. The valve train can, in principle, be designed as desired. However, a valve train based on one or more camshafts is preferably provided.Alternatively, a fully variable valve train, which may, for example, include electromechanical actuation devices, can also be used advantageously.

[0008] According to the invention, the intake valve is actuated and thus opened at least twice during an operating cycle of the internal combustion engine. During load operation of the internal combustion engine, such an operating cycle can, in a preferred embodiment of the internal combustion engine as a four-stroke engine, comprise an intake stroke in which fresh gas is introduced into the combustion chamber, a compression stroke in which the fresh gas is compressed in the combustion chamber, a power stroke in which a combusting mixture of the fresh gas and fuel expands and work is thereby performed, and an exhaust stroke in which exhaust gas, which was produced by the combustion of the fresh gas-fuel mixture, is expelled from the combustion chamber. Corresponding strokes also occur during overrun operation of such a four-stroke engine, although no fuel is introduced into the combustion chamber and burned therein during overrun operation.In the following, the cycles of an operating cycle in load operation and in overrun operation are therefore referred to the same way.

[0009] "Load operation" of the internal combustion engine is characterized by the fact that it operates under load and consequently generates drive power. In contrast, "overrun operation" is characterized by the fact that no load is required of the internal combustion engine and the engine is self-propelled. In the preferred integration of an internal combustion engine according to the invention into a motor vehicle, such drive of the internal combustion engine occurs in particular by the motor vehicle rolling with the drive train uninterrupted.

[0010] According to the invention, during overrun operation of the internal combustion engine, a first opening phase of the intake valve is performed, which begins with an intake opening of the at least one intake valve and ends with an intake closing of the at least one intake valve. The maximum valve lift in the first opening phase occurs during a first expansion stroke of the piston. This first expansion stroke can correspond to an intake stroke of the operating cycle. Furthermore, a second opening phase of the intake valve is performed, with a period with a closed intake valve between the first opening phase and the second opening phase.The maximum valve lift in the second opening phase occurs during a (first) compression stroke following the first expansion stroke (which may correspond to a compression stroke of the operating cycle), in particular in the second half, preferably in the fourth quarter of this compression stroke, or during a second expansion stroke following the (first) compression stroke (which may correspond to a compression stroke of the operating cycle), in particular in the first half, preferably in the first third of this second expansion stroke of the piston (this should also include a position of the maximum valve lift of the second opening phase at TDC between the first compression stroke and the second expansion stroke). It can preferably be provided that an intake opening takes place during the second opening phase between 50°CA (°CA: angle specification related to the angle of rotation of the crankshaft) and 180°CA after an intake closing of the first opening phase.

[0011] An "expansion stroke" is defined as the piston's movement from TDC to BDC, during which the combustion chamber expands. Accordingly, a "compression stroke" of the piston is defined as the piston's movement from BDC to TDC, during which the combustion chamber shrinks.

[0012] The second opening phase of the intake valve serves to remove gas that was compressed within the combustion chamber during the compression stroke from the combustion chamber in its compressed state through the intake valve. This entails energy loss, resulting in greater braking of the combustion engine during overrun. This energy loss, and thus the desired braking effect, is particularly great when the intake opening of the second opening phase is at TDC or at least between TDC -10°CA and TDC +10°CA, because the highest gas pressure in the combustion chamber can occur at TDC of the piston. When the intake opening is around TDC, the gas is then removed at the highest possible pressure via an intake valve that is not yet fully open and thus a relatively small flow opening, resulting in particularly high flow losses.

[0013] An internal combustion engine suitable for carrying out a method according to the invention forms at least one cylinder opening in which a piston is movably arranged between a top dead center (TDC) and a bottom dead center (UT), wherein the piston delimits a section of the cylinder opening for use as a combustion chamber, wherein the mobility of the piston is controllable by means of a crankshaft and wherein at least one inlet valve is assigned to the combustion chamber, which inlet valve can be actuated by means of a valve train.The valve train is designed such that, during overrun operation of the internal combustion engine, a first opening phase of the intake valve can be carried out, wherein the maximum valve lift occurs during a first expansion stroke of the piston, and a second opening phase of the intake valve can be carried out, wherein the maximum valve lift occurs during a (first) compression stroke following the first expansion stroke and / or during a second expansion stroke of the piston following the (first) compression stroke (this should also include a position of the maximum valve lift of the second opening phase at TDC between the first compression stroke and the second expansion stroke). The internal combustion engine can further preferably comprise a control device which is configured to carry out a method according to the invention in an automated manner.

[0014] According to a preferred embodiment of a method according to the invention, it can be provided that, at least temporarily, even during load operation of the internal combustion engine, the intake valve is actuated and thus opened at least twice during an operating cycle of the internal combustion engine. Specifically, it can be provided that, at least temporarily, during load operation of the internal combustion engine, a first opening phase of the intake valve is carried out during an intake stroke, wherein a first intake closing of the intake valve takes place as part of the first opening phase during the first expansion stroke of the piston and at the latest 20°CA before BDC, preferably at the latest 30°CA or at the latest 40°CA or at the latest 50°CA or at the latest 60°CA before BDC. This can generate those advantages for load operation of the internal combustion engine that are known to be associated with a Miller combustion process.Specifically, by closing the intake valve significantly before the corresponding BDC and thus before the end of the intake stroke, the volumetric efficiency of the internal combustion engine can be reduced during load operation and the pressure in a fresh gas line (boost pressure), via which fresh gas can be supplied to the internal combustion engine, can be increased while maintaining the same fresh gas mass supplied to at least one combustion chamber of the internal combustion engine per operating cycle. This dethrottles the internal combustion engine in the partial load range and, at the same time, lowers the effective compression ratio, which lowers the combustion chamber charge temperature and thus reduces the tendency to knock at higher loads during internal combustion engine operation.

[0015] Internal combustion engines operating according to a Miller cycle generate large-scale gas flow patterns in the combustion chamber earlier than conventional combustion engines, where intake closure occurs around BDC. As a result, the breakup of large-scale flow patterns into small-scale vortices also begins earlier, which can lead to the maximum turbulence level being reached well before ignition and having dropped significantly again by the time of ignition.

[0016] To avoid this disadvantage, a second opening phase of the intake valve can be carried out at least temporarily during load operation of the internal combustion engine, with a second intake opening during the second opening phase occurring at the earliest 20°CA after the intake closing of the first opening phase. During the second opening phase in load operation, additional fresh gas flows into the cylinder opening or into the combustion chamber. This additional fresh gas leads to additional or intensified large-scale flow patterns of the fresh gas in the combustion chamber, with these additional large-scale flow patterns also only dissipating relatively late in the course of the subsequent compression stroke due to their relatively late generation. This can increase the turbulence level during ignition of the fresh gas-fuel mixture, which can occur particularly at the end of the compression stroke.The fresh gas additionally introduced into the combustion chamber during the second opening phase thus at least partially compensates for the negative effect on the turbulence level associated with the early intake closing during the first opening phase according to the Miller combustion process.

[0017] Due to the relatively late actuation of the intake valve during the second opening phase under load, a relatively large pressure gradient across the intake valve can be utilized during the second intake opening, which greatly accelerates the fresh gas flowing into the combustion chamber. Thus, despite the relatively small mass of fresh gas introduced into the combustion chamber during the second opening phase, a relatively strong increase in the turbulence level can be achieved. This pressure gradient is greatest at the piston's bottom dead center (BDC), so it is preferably provided that the second intake opening takes place at BDC, but at least within a range of ±10°CA around BDC.

[0018] The valve train of an internal combustion engine according to the invention can therefore also advantageously be designed such that during load operation of the internal combustion engine, a first opening phase of the intake valve can be carried out, wherein a first intake closing of the intake valve takes place during the first expansion stroke of the piston and at the latest 20°CA before BDC, and a second opening phase of the intake valve can be carried out, wherein a second intake opening takes place at the earliest 20°CA after the intake closing within the scope of the first opening phase.

[0019] In order to prevent the positive effects of the Miller combustion process from being excessively reduced by the second opening phase during load operation, it can preferably be provided that only a relatively small mass of fresh gas is introduced into the combustion chamber during the second opening phase by actuating the intake valve only with a relatively small maximum valve lift, which is at least smaller than the maximum valve lift during the first opening phase and which is preferably no more than 3 mm. For the same reason, it can also be provided that the control width or the opening duration of the second opening phase is no more than 50°CA. Corresponding specifications can advantageously also be implemented with regard to the actuation of the intake valve during overrun operation. Particularly preferably, the maximum valve lift and / or the control width during the second opening phase can be selected to be identical for overrun operation and load operation.Such operation of the combustion engine can have a beneficial effect on the design complexity of the combustion engine's valve train. Furthermore, appropriate actuation of the intake valve during overrun can also have a fundamentally beneficial effect on the desired goal of increasing braking efficiency.

[0020] According to a preferred embodiment of a method according to the invention, it can be provided that when switching between overrun and load operation, the distance between the phase positions of the first opening phase and the second opening phase is changed. This makes it possible to optimize the advantages that can be achieved by the two opening phases, on the one hand during overrun operation and on the other hand during load operation. The phase position of an opening phase is the position of the time of the greatest valve lift in relation to a rotational movement of the crankshaft. The distance between the phase positions therefore refers to the distance (in °CA) between the respective maximum valve lifts of the two opening phases.In order to change the distance between the phase positions of the first opening phase and the second opening phase, the valve train of an internal combustion engine according to the invention can have an intake camshaft assigned to the at least one intake valve, which comprises a cam changing device which makes it possible to change from an actuation of the intake valve by means of a first cam contour to an actuation by means of a second cam contour.

[0021] Alternatively, it can be provided that the phase difference between the first opening phase and the second opening phase is maintained during a change between overrun and load operation. Such a method according to the invention can be implemented using a valve train of the internal combustion engine that has a relatively low structural complexity, which can accordingly have an advantageous effect on the manufacturing costs of such an internal combustion engine.A preferably provided shift in the phase position of the second opening phase for the change, which is preferably provided to optimize the (different) advantages to be realized by means of the second opening phase in the various operating modes, can then also be accompanied by a change in the phase position of the first opening phase when changing between overrun and load operation, which may not be functionally advantageous but also not disadvantageous. In particular, this can result in a first opening phase of the intake valve during overrun operation, the intake opening of which occurs only in or relatively late in the first expansion stroke. However, due to the overrun operation of the combustion engine, this does not necessarily have to be associated with any relevant disadvantages.To change the phase positions of the first opening phase and the second opening phase when switching between overrun and load operation at a constant interval, the valve train of an internal combustion engine according to the invention can have an intake camshaft associated with the at least one intake valve, which includes a phase adjuster. Such a phase adjuster makes it possible to change the relative rotational orientation of a cam track relative to the crankshaft. For optimal implementation of a method according to the invention, the phase adjuster can preferably be configured for an adjustability of at least 180° CA.

[0022] A particularly advantageous variability of the valve train, also with regard to the implementation of a method according to the invention, can be achieved if it comprises both a cam changing device and a phase adjuster for at least the intake camshaft.

[0023] According to a preferred embodiment of a method according to the invention, it can be provided that during overrun operation an (additional) opening phase of at least one exhaust valve which is assigned to the combustion chamber and which can be actuated by means of the valve train is carried out, wherein the maximum valve lift occurs during a compression stroke following the first expansion stroke and / or during a second expansion stroke of the piston following the compression stroke. This opening phase can in particular be additional to a conventional opening phase of the exhaust valve, which takes place during a (second) compression stroke following the second expansion stroke of the piston. It can further preferably be provided that the maximum valve lift of the additional opening phase is smaller than that during the conventional opening phase of the exhaust valve.In this embodiment of a method according to the invention, the exhaust valve is also used to cause additional energy loss and thus a greater braking effect of the internal combustion engine through targeted (especially second) opening. Overall, a particularly strong braking effect of the internal combustion engine can thus be achieved.

[0024] Specific embodiments of the (additional) opening phase of the exhaust valve, particularly with regard to the timing, can correspond in individual and in particular all aspects to the second opening phase of the intake valve provided according to the invention. During load operation, however, it can preferably be provided that only the described conventional opening phase is provided for the exhaust valve.

[0025] To implement the different actuations of the exhaust valve, the valve train of an internal combustion engine according to the invention can preferably have an exhaust camshaft associated with the at least one exhaust valve, which includes a camshaft changer. A phase adjuster can also be associated with the exhaust camshaft (alternatively or additionally).

[0026] According to a further preferred embodiment of a method according to the invention, it can be provided that during overrun operation, the first opening phase of the intake valve is carried out during each expansion stroke of the piston, and the second opening phase is carried out between two first opening phases. Thus, the intake valve is operated in a two-stroke manner during overrun operation, which allows for a correspondingly high braking power.

[0027] A specification of control times (in °CA) refers to a residual lift of a gas exchange valve (inlet or exhaust valve) of 0.2 mm, because a gas exchange valve that is already or still open with such a residual lift can practically be regarded as closed, because then no relevant gas mass flow passes through the gas exchange valve.

[0028] If several, and in particular two, intake valves and / or exhaust valves are assigned to the at least one cylinder opening of an internal combustion engine according to the invention, it can be provided that only one or more of them can be actuated in the manner described or are actuated during operation of the internal combustion engine, while at least one other type of actuation is provided for the other intake valve(s) and / or exhaust valve(s). However, it is preferably provided that all intake valves and / or exhaust valves assigned to the at least one cylinder opening can be actuated or are actuated in accordance with the invention (and in particular in the same way).

[0029] If an internal combustion engine according to the invention has a plurality of cylinder openings or combustion chambers, it can be provided that the intake valve(s) and / or exhaust valve(s) which are assigned to only one or more or, preferably, all cylinder openings, can be actuated or is / are actuated according to the invention.

[0030] An internal combustion engine according to the invention can preferably be operated (at least temporarily) with spark ignition (gasoline engine). Such spark ignition can be achieved by any ignition device, preferably by a conventional (spark-generating) spark plug with or without a prechamber. An internal combustion engine according to the invention can be designed to operate with liquid fuel (in particular gasoline) and / or with a gaseous fuel (in particular natural gas, LNG, or LPG).

[0031] The invention also relates to a motor vehicle, in particular a wheel-based and non-rail-bound motor vehicle (preferably a car or a truck), with an internal combustion engine according to the invention. A method for operating such a motor vehicle is also subject to the invention, wherein the overrun operation of the internal combustion engine is based on propulsion by the rolling motor vehicle with the drive train closed or uninterrupted.

[0032] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the drawings. The drawings show, partly in simplified form: Fig. 1: a top view of an internal combustion engine according to the invention; Fig. 2: the combustion engine in a longitudinal section; Fig. 3: in a diagram, the valve lift curves EV, AV provided for intake and exhaust valves of the internal combustion engine over the angle of rotation α of a crankshaft of the internal combustion engine during load operation of the internal combustion engine according to a first embodiment; Fig. 4: in a diagram, the valve lift curves EV, AV provided for the intake and exhaust valves over the angle of rotation α of the crankshaft during overrun operation of the internal combustion engine according to a first embodiment; Fig. 5: in a diagram, the valve lift curves EV, AV provided for the intake and exhaust valves over the angle of rotation α of the crankshaft during load operation of the internal combustion engine according to a second embodiment, and Fig. 6 shows in a diagram the valve lift curves EV, AV provided for the intake and exhaust valves over the angle of rotation α of the crankshaft during overrun operation of the internal combustion engine according to a second embodiment.

[0033] In the Fig. 1 and Fig. Figure 2 shows an internal combustion engine with an internal combustion engine 1 according to the invention. The internal combustion engine 1 is operable according to the Otto principle and is designed accordingly, ie, as a gasoline engine.

[0034] The internal combustion engine 1 forms a plurality of (e.g., four) cylinder openings 4 in a combination of cylinder housing 2 and cylinder head 3. The cylinder openings 4 are connected on the inlet side via inlet channels 5 formed in the cylinder head 3 to an intake manifold 6 of a fresh gas line 7 of the internal combustion engine, and on the exhaust side via exhaust channels 8, which are also formed in the cylinder head 3, to an exhaust manifold 9 of an exhaust line 10 of the internal combustion engine.

[0035] In a known manner, fresh gas, which consists at least primarily of air, is combusted with fuel in combustion chambers 11, which are defined by the walls of the cylinder openings 4, together with pistons 12 guided in the cylinder openings 4, and the cylinder head 3. The fuel can be introduced directly into the combustion chambers 11 by means of fuel injectors 13 and ignited by spark plugs 14. The exhaust gas produced during the combustion of the fuel-fresh gas mixture is discharged via the exhaust system 10.

[0036] The supply of fresh gas into the combustion chambers 11 and the removal of exhaust gas from the combustion chambers 11 is controlled by four gas exchange valves, specifically two intake valves 15 and two exhaust valves 16 per combustion chamber 11, wherein the gas exchange valves are controlled by a Fig. 1 only partially and in the Fig. 2 valve train of the combustion engine 1 shown in further detail.

[0037] The valve train includes according to the Fig. 2 a crankshaft 17 which forms crank pins 18, wherein the crank pins 18 are connected to the pistons 12 via connecting rods 19. As a result, linear movements of the pistons 12 lead to a rotation of the crankshaft 17, wherein the rotation of the crankshaft 17 in turn causes a periodic change in direction of the linear movements of the pistons 12. The rotation of the crankshaft 17 is transmitted via a timing gear 20, for example a toothed belt gear, to two camshafts 21, each of which actuates two of the gas exchange valves per combustion chamber 11. One of the camshafts 21 is designed as an intake camshaft, i.e. it actuates (directly or indirectly) all of the intake valves 15, while the other is designed as an exhaust camshaft and consequently (directly or indirectly) actuates all of the exhaust valves 16.

[0038] The internal combustion engine also includes an exhaust gas turbocharger (see Fig. 1). This comprises an exhaust turbine 22 integrated into the exhaust line 10 and a fresh gas compressor 23 integrated into the fresh gas line 7. An impeller of the exhaust turbine 22, driven in rotation by the exhaust gas flow, drives an impeller of the fresh gas compressor 23 via a shaft 24. The resulting rotation of the impeller of the fresh gas compressor 23 compresses the fresh gas passing through it.

[0039] Furthermore, an exhaust gas aftertreatment device 25, for example in the form of a three-way catalyst and / or a particulate filter, is integrated into the exhaust line 10, and a throttle valve 26, which is arranged between the fresh gas compressor 23 and the intake manifold 6, is integrated into the fresh gas line 7.

[0040] During load operation of the internal combustion engine 3, the pistons 12 are each moved in an oscillating manner between a top dead center (TDC) and a bottom dead center (BDC) due to the combustion processes in the individual combustion chambers 11. Due to the design of the internal combustion engine 1 as a four-stroke engine, the pistons 12 alternately perform a gas exchange stroke cycle and a power stroke cycle. The gas exchange stroke cycle of each piston 12 comprises an exhaust stroke of the respective piston 12 (corresponding to an exhaust stroke of the cycle occurring in the corresponding combustion chamber 11) and an intake stroke (corresponding to an intake stroke of the cycle occurring in the corresponding combustion chamber 11).The working stroke cycle comprises a compression stroke of the piston 12 (corresponding to a compression stroke of the cyclic process occurring in the corresponding combustion chamber 11) and a working stroke (corresponding to a working stroke of the cyclic process occurring in the corresponding combustion chamber 11). The exhaust stroke and the compression stroke each represent a compression stroke, and the intake stroke and the working stroke each represent an expansion stroke of the piston 12. The four strokes of the pistons 12 or the four corresponding strokes of the cyclic processes occurring in the combustion chambers 11 during load operation each correspond to an operating cycle of the internal combustion engine 1.

[0041] Corresponding stroke movements of the pistons 12 and strokes also occur during overrun operation of the internal combustion engine 1, in which the engine itself is driven. This is particularly the case when a motor vehicle comprising the internal combustion engine 1 rolls with an uninterrupted drive train and the crankshaft 17 of the internal combustion engine 1 is driven in rotation by wheels of the motor vehicle via the closed drive train. During overrun operation, the internal combustion engine 1 does not generate any drive power; rather, it has a braking effect on the motor vehicle through the power required to drive the internal combustion engine 1. The braking effect of the internal combustion engine 1 is based in particular on a cyclical compression of fresh gas within the combustion chambers 11, whereby the compressed gas is expelled from the combustion chambers 11 and expands in the process. The corresponding compression power represents power loss.

[0042] The intake valves 15 and the exhaust valves 16 can be controlled at least temporarily during load operation of the internal combustion engine 1 by means of the camshafts 21 in accordance with the Fig. 3. The intake valves 15 are actuated twice per operating cycle. A first opening phase takes place primarily during the intake stroke (and thus during a first expansion stroke of the respective associated piston 12), whereby the maximum valve lift h max during the intake stroke. This first opening phase begins with the intake opening at approximately 60°CA before TDC, thus still during the preceding exhaust stroke. The first opening phase ends with the intake closing at approximately 70°CA before BDC. This relatively early closing of the intake valves 15 realizes a Miller combustion process with the familiar effects.

[0043] A second opening phase takes place during the compression stroke (and thus during a first compression stroke of the respective associated piston 12 following the first expansion stroke), whereby this second opening phase begins with a second intake opening at BDC and ends with a second intake closing approximately 60°CA after BDC. During the second opening phase, the intake valves 15 are opened with a significantly smaller maximum valve lift h max than during the first opening phase. Specifically, the maximum valve lift h max during the second opening phase according to the Fig. 3 less than one fifth of the maximum valve lift h max during the first opening phase.

[0044] The second opening phase begins at a control time at which the pressure in the respective combustion chamber 11 is at a minimum. This results in a relatively large pressure difference (between the pressures in the intake manifold 6 on the one hand and the respective combustion chamber 11 on the other hand) across the intake valves 15. This, particularly in conjunction with the only relatively small maximum valve lift h maxopening intake valves 15, the highest possible flow velocities are achieved for the fresh gas flowing again into the combustion chambers 11, thereby supporting the generation of large-scale flow patterns of the fresh gas in the combustion chambers 11. Since the generation of large-scale flow patterns is effected relatively late and specifically only at the beginning of the compression stroke, the disintegration of these large-scale flow patterns into small-scale vortices can be delayed until shortly before an ignition point at the end of the compression stroke, which has a beneficial effect on the flame propagation of the igniting fresh gas-fuel mixture quantities. The Fig. The opening phases of the intake valves 15 shown in Figure 3 can achieve an optimum with regard to this goal.

[0045] During overrun of the internal combustion engine 1, the intake valves 15 and the exhaust valves 16 can be opened at least temporarily, preferably always by means of the camshafts 21 in accordance with the Fig. 4 shown valve lift curves EV, AV and therefore also twice per operating cycle. The stroke contours of the opening phases correspond to those during operation under load according to Fig. 3. Both opening phases during overrun operation according to the Fig. 4 are, however, compared to those according to the Fig. 3 retarded. The first opening phase takes place primarily during the intake stroke and begins with a first intake opening at approximately 10°CA after TDC and ends with a first intake closing at approximately 30°CA after BDC. The second opening phase takes place during the power stroke, beginning with a second intake opening at TDC and ending with a second intake closing at approximately 60°CA after TDC. Thus, when switching from load operation according to Fig. 3 to the overrun operation according to the Fig. 4 not only shifted the two opening phases later, but also changed the distance between the two opening phases.

[0046] The second opening phase of the intake valves results in an increased braking effect of the internal combustion engine 1 during overrun because not only is gas contained in the combustion chambers 11 discharged via the exhaust valves 16 opened during the respective power stroke and exhaust stroke, but additionally gas that was compressed in the combustion chambers 11 during the respective compression stroke flows back into the fresh gas line 6 via the intake valves 15 opened again at the beginning of the power stroke and expands there.

[0047] The concrete phase positions of the two opening phases according to the Fig. 4 lead to a particularly high braking effect of the internal combustion engine 1 because the first opening phase is optimized for introducing the largest possible fresh gas mass into the respective combustion chamber 11, while the second opening phase, by beginning approximately at TDC and thus at a time of maximum pressure in the respective combustion chamber, leads to the highest possible pressure difference across the associated intake valves 15 and thus to the highest possible mass flow of fresh gas flowing back into the fresh gas line 7. The valve train of an internal combustion engine 1 operated in this way must therefore have corresponding variability, which, if no fully variable valve train is provided, can be realized by means of a cam changing device 27 or a combination of cam changing device 27 and phase adjuster 28.

[0048] In contrast, the Fig. 5 and Fig. 6 an operation of an internal combustion engine 1 according to the invention according to, for example, the Fig. 1 and Fig. 2, whereby when changing from a load operation according to the Fig. 5 to a push operation according to the Fig. 6, only the two opening phases are shifted later, for which a variability of the valve train is sufficient, which is provided by (only) one phase adjuster 28. However, the stroke contours and their spacing do not change during the change. However, the braking effect of the combustion engine during overrun is not maximized as a result. List of reference symbols 1 combustion engine 2 cylinder housings 3 cylinder head 4 cylinder opening 5 Inlet channel 6 intake manifold 7 Fresh gas line 8 exhaust channel 9 exhaust manifold 10 Exhaust system 11 Combustion chamber 12 pistons 13 Fuel injector 14 Spark plug 15 Inlet valve 16 Exhaust valve 17 Crankshaft 18 crank pins 19 connecting rods 20 control gears 21 Camshaft 22 exhaust turbine 23 fresh gas compressors 24 Wave 25 Exhaust aftertreatment device 26 throttle valve 27 Cam changing device 28 phase adjusters EV valve lift curve of an intake valve AV valve lift curve of an exhaust valve TDC top dead center of a piston movement UT bottom dead center of a piston movement h valve lift h max maximum valve lift α angle of rotation of the crankshaft QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2015 / 022 071 A1

[0003] DE 10 2021 211 408 A1

[0004]

Claims

[1] Method for operating an internal combustion engine (1) which forms at least one cylinder opening (4) in which a piston (12) is moved between a top dead center (TDC) and a bottom dead center (UT), wherein the piston (12) delimits a section of the cylinder opening (4) for use as a combustion chamber (11), wherein the mobility of the piston (12) is controlled by means of a crankshaft (17) and wherein the combustion chamber (11) is assigned at least one inlet valve (15) which is actuated by means of a valve train, characterized by that during overrun of the combustion engine (1) - a first opening phase of the inlet valve (15) is carried out, wherein the maximum valve lift (h max ) during a first expansion stroke of the piston (12), and - a second opening phase of the inlet valve (15) is carried out, wherein the maximum valve lift (h max) during a compression stroke following the first expansion stroke or during a second expansion stroke of the piston (12) following the compression stroke. [2] Method according to claim 1, characterized by that an intake opening of the second opening phase is carried out at TDC or between TDC-10°CA and TDC+10°CA. [3] Method according to one of the preceding claims, characterized by that during load operation of the combustion engine (1) - a first opening phase of the intake valve (15) is carried out, wherein a first intake closing of the intake valve (15) takes place during the first expansion stroke of the piston (12) and at the latest 20°CA before BDC, and - a second opening phase of the inlet valve (15) is carried out, wherein a second inlet opening takes place at the earliest 20°CA after an inlet closing during the first opening phase. [4] Method according to claim 3, characterized bythat when changing between overrun operation and load operation, the distance between the phase positions of the first opening phase and the second opening phase is changed. [5] Method according to one of claims 3, characterized by that when changing between overrun operation and load operation, the distance between the phase positions of the first opening phase and the second opening phase is maintained. [6] Method according to one of claims 3 to 5, characterized by that when changing between overrun and load operation, the phase position of the second opening phase is changed. [7] Method according to one of the preceding claims, characterized by that during overrun operation, the intake is opened during the second opening phase between 50°CA and 180°CA after the intake is closed during the first opening phase. [8] Method according to one of the preceding claims, characterized bythat during overrun and / or load operation the maximum valve lift (h max ) during the first opening phase is greater than the maximum valve lift (h max ) during the second opening phase. [9] Method according to one of the preceding claims, characterized by that during overrun and / or during load operation the control width of the second opening phase is not more than 50°KW. [10] Method according to one of the preceding claims, wherein the combustion chamber (11) is also assigned at least one exhaust valve (16) which can be actuated by means of the valve train, characterized by that during overrun operation an opening phase of the exhaust valve (16) is carried out, wherein the maximum valve lift (h max ) during the compression stroke following the first expansion stroke and / or during the second expansion stroke of the piston (12) following the compression stroke. [11] Method according to one of the preceding claims, characterized by that during overrun operation, the first opening phase of the inlet valve (15) is carried out during each expansion stroke of the piston (12) and the second opening phase is carried out between two first opening phases. [12] Internal combustion engine (1) which forms at least one cylinder opening (4) in which a piston (12) is arranged to be movable between a top dead center (TDC) and a bottom dead center (UT), wherein the piston (12) delimits a section of the cylinder opening (4) for use as a combustion chamber (11), wherein the mobility of the piston (12) is controllable by means of a crankshaft (17) and wherein the combustion chamber (11) is assigned at least one inlet valve (15) which is actuable by means of a valve train, characterized by a design of the valve train such that during overrun of the internal combustion engine (1) - a first opening phase of the inlet valve (15) can be carried out, wherein the maximum valve lift (h max ) during a first expansion stroke of the piston (12), and - a second opening phase of the inlet valve (15) can be carried out, wherein the maximum valve lift (h max ) during a compression stroke following the first expansion stroke and / or during a second expansion stroke of the piston (12) following the compression stroke. [13] Internal combustion engine (1) according to claim 12, characterized by a design of the valve train such that during load operation of the internal combustion engine (1) - a first opening phase of the intake valve (15) can be carried out, wherein a first intake closing of the intake valve (15) takes place during the first expansion stroke of the piston (12) and at the latest 20°CA before BDC, and - a second opening phase of the inlet valve (15) can be carried out, wherein a second inlet opening takes place at the earliest 20°CA after an inlet closing during the first opening phase. [14] Internal combustion engine (1) according to claim 12 or 13, characterized by that the valve train has an intake camshaft (21) assigned to the at least one intake valve (15), which comprises a cam changing device and / or a phase adjuster. [15] Internal combustion engine (1) according to one of claims 12 to 14, wherein the cylinder opening (4) is assigned at least one exhaust valve (16) which can be actuated by means of the valve train, characterized by that the valve train has an exhaust camshaft (21) associated with the at least one exhaust valve (16), which comprises a cam changing device.

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