WO2015036094A1

WO2015036094A1 - Internal combustion engine and associated operational method

Info

Publication number: WO2015036094A1
Application number: PCT/EP2014/002355
Authority: WO
Inventors: Tobias BÖCKING; Götz Brachert; Sebastian Donath; Frank Otto; Klaus Rössler; Markus Schilling
Original assignee: Daimler Ag
Priority date: 2013-09-10
Filing date: 2014-08-30
Publication date: 2015-03-19
Also published as: DE102013015012A1

Abstract

Method for operating an internal combustion engine which has at least one outlet valve and at least one inlet valve per cylinder and which has a valve drive for actuating the respective outlet valve according to an outlet valve stroke crankshaft angle curve (1) and for actuating the respective inlet valve according to an inlet valve stroke crankshaft angle curve (2), in which, in a first characteristic diagram region (I) below a low mean pressure (15) and below a mean rotational speed (16), a non-homogenous stratified operation strategy and a first special operating mode (Q2) are selected, wherein the first special operating mode (Q2) has an inlet valve stroke crankshaft angle curve (2) with an inlet start (3) which is shifted in the early direction compared to a standard operating mode (Q1), wherein, in the standard operating mode (Q1), the inlet valve stroke crankshaft angle curve (2) has two inflection points (5, 6) between an inlet start (3) and an inlet end (4) and has a maximum (7) between the two inflection points (5, 6), and the outlet valve stroke crankshaft angle curve (1) has two inflection points (10, 11) between an outlet start (8) and an outlet end (9), and a maximum (12) between the two inflection points (10, 11), and there is a slight, angled overlapping region (13) between the inlet start (3) and the outlet end (9).

Description

Internal combustion engine and associated operating method

The present invention relates to a method of operating an internal combustion engine according to claim 1 and an internal combustion engine according to claim 11, which can be operated according to such a method.

From DE 10 2010 011 681 A1 an internal combustion engine is known, which comprises a plurality of cylinders, each having at least one exhaust valve and at least one

Inlet valve is assigned. The known internal combustion engine is a

spark ignited gasoline engine with direct injection of fuel, with a

Operating strategy, referred to as inhomogeneous stratified charge. In such an inhomogeneous shift operating strategy, multiple layers are generated in the respective cylinder by means of multiple injections, which have different λ values, λ standing in the usual way for the fuel-air ratio. It has been found that with such an inhomogeneous stratified operation strategy, improved pollutant emission values can be achieved by realizing an exhaust gas recirculation, wherein an internal recirculation of hot exhaust gases is particularly advantageous. In order to realize such an internal exhaust gas recirculation, according to the known operating methods, either the respective outlet valve can be closed later to suck exhaust gas out of the exhaust tract at the opening inlet valve, or the respective inlet valve can be opened sooner to allow exhaust gas to flow into the fresh air tract, which in the subsequent intake stroke is sucked in with the fresh air. The shift of the inlet beginning to early or the outlet end to late is realized with the help of special valve lift crankshaft angle curves, which are characterized in that they have four turning points. As a result, within the respective valve lift crankshaft angle curve, in addition to the usual maximum, which characterizes the maximum opening stroke of the respective valve, either a plateau with a constant valve lift or an additional maximum and an additional minimum can be realized. The present invention is concerned with the problem of an improved embodiment of an internal combustion engine or an associated method of operation

which is characterized in particular by reduced fuel consumption and reduced pollutant emissions.

This problem is solved according to the invention by the subject matter of the independent claim. Advantageous embodiments are the subject of the dependent claims.

The present invention is based on the general idea of providing a standard operating mode and several special operating modes for operating the internal combustion engine. Furthermore, the current operating mode is dependent on the current operating state of the internal combustion engine and dependent on the current

Operating strategy can be selected. The current operating state is suitably determined by its position in a medium-pressure speed map. By the

Combination of different operating strategies with different operating modes depending on the current operating state of the internal combustion engine, the fuel consumption and pollutant emissions can be minimized.

In addition to the inhomogeneous shift operating strategy, others can be used

Operating strategies are applied. Other operating strategies are

For example, a homogeneous stratified operating strategy, in which initially a homogeneous base mixture with a constant λ value is generated, in the immediately before

Ignition in the field of the respective ignition an additional

Fuel injection occurs, which locally in the homogeneous base layer, a central core layer with excessive fuel content or with a greatly reduced λ value is generated. In a homogeneous lean operating strategy, a homogeneous, lean mixture is produced in the respective cylinder. In a stoichiometric operating strategy, a stoichiometric mixture with a λ value of 1 is generated in the respective cylinder.

In the operating method according to the invention, a standard operating mode and exactly three special operating modes are expediently provided, as a result of which a particularly high degree of flexibility for realizing different internal efficiency

Exhaust gas recirculation is achieved. The standard operating mode is characterized in that an intake valve lift crankshaft angle curve between a

Beginning of admission and an inlet end only two turning points and between the Turning points has only one maximum, while a Auslaßventilhub- crankshaft angle curve between a Auslassbeginn and an outlet end only two turning points and between the turning points has only one maximum. This corresponds to a usual activation of gas exchange valves, in which there is no or only a slight overlap between the outlet end and inlet start.

A first special mode of operation is characterized in that the intake valve lift crankshaft angle curve has a beginning of intake that is delayed from the standard operating mode. As a result, exhaust gas can enter the fresh air tract, from which it can later be sucked back again. The first special operating mode can be realized particularly simply if the inlet end is selected the same as in the standard operating mode. A further simplification results, even if the maximum is positioned the same as in the standard operating mode. Also, in the first special operating mode, the exhaust valve lift crankshaft angle curve is the same as in the standard operating mode.

A second special mode of operation is characterized by the fact that the

Auslassventilhub-crankshaft angle curve has a relation to the standard mode of operation after retarded outlet end. As a result, exhaust gas can be sucked back from the still open exhaust tract. For ease of implementation of this second special mode of operation, the start of the outlet may remain the same as in the standard mode of operation. Also, for ease of realization, the maximum can remain the same as positioned in standard operating mode. Also in the second special operating mode, the intake valve lift crankshaft angle curve is the same as in the standard operating mode.

In a third special operating mode, the two above-mentioned special operating modes are combined with each other such that the intake valve lift crankshaft angle curve has an intake start shifted from the standard operating mode and the exhaust valve lift crankshaft angle curve is over the standard operating mode postponed

Exhaust end has. In this way, a particularly high internal

Exhaust gas recirculation rate can be realized. Also in this case, it may be expedient to provide the positions of the outlet beginning and the inlet end opposite to the

Standard operating mode to keep constant. Furthermore, the maxima can be maintained. The relative "late" and "early" times refer to the crankshaft angle so that shifting early corresponds to shifting toward smaller crankshaft angles while shifting late to shift to larger crankshaft angles

Crankshaft angles means.

According to an advantageous embodiment, the current operating strategy can be selected depending on the position of the current operating state of the internal combustion engine in the medium-pressure speed map. Thus, depending on the current

Operating state of the internal combustion engine for a suitable one

Operating strategy can be selected. On the other hand, depending on the current operating state and depending on the current operating strategy, the most suitable operating mode for this purpose can be selected. This results in diverse

Adaptation options for operating the internal combustion engine, which can be realized in particular a minimization of fuel consumption and pollutant emissions.

According to an advantageous development can be below a low

Medium pressure and below a medium speed an inhomogeneous

Shift operating strategy can be selected. Particularly useful is a development in which during the inhomogeneous shift operating strategy below a first boundary pressure, which is smaller than the low mean pressure, and below a limit speed, which is smaller than the average speed, the second special operating mode is selected, while above the first boundary pressure and above the limit speed of the third special operating mode is selected. Thus, at least two map areas are defined for the inhomogeneous shift operating strategy within the medium-pressure speed map, in which the current operating state can fall and the different operating modes and in particular to

lead to different special operating modes.

In another embodiment, a homogeneous lean operating strategy or a homogeneous stratified operating strategy may be selected below the average mean pressure, which is greater than the low medium pressure, and below the average speed. In this way, a second map area is defined within the medium-pressure speed map in addition to a first map area, which triggers the inhomogeneous shift operating strategy, a strategy change to the homogeneous

Lean operating strategy or homogeneous shift operating strategy causes. According to an advantageous development can during the homogeneous

Lean operating strategy below a second boundary pressure, which may be speed dependent or constant over the speed, the standard operating mode or an Atkinson modified first special operating mode, while above the second boundary pressure one of the three Operating modes is selected.

Advantageously, the shifting of the inlet start to early in the first and third special operating mode is achieved in that before the maximum opening stroke of the intake valve, the inlet valve opens earlier and remains for a longer period in an opening stroke, which is below the maximum opening stroke. A displacement of the outlet end late in the second and third special operating mode is achieved analogously by the exhaust valve remains after the maximum opening stroke of the exhaust valve over a prolonged period in a stroke range which is smaller than the maximum opening stroke, and accordingly closed later. In a first special mode of operation modified according to the Atkinson principle, the intake start in the intake valve lift crankshaft angle curve is preferably not shifted early, but the same as in the standard operating mode. Alternatively, the residence time of the intake valve may be extended in its maximum opening stroke. Both modifications result in one

Shifting the inlet end to late. With the help of such an Atkinson operating mode, a significant Entschrosselung can be achieved, the one

results in a remarkable reduction in consumption.

Alternatively, below the low mean pressure and below the average speed with the inhomogeneous shift operating strategy, the first special operating mode can be selected.

The first special mode of operation may also be below the first limit mean pressure, which is less than the low mean pressure, and below the limit speed, which is less than the average speed and / or below the mean mean pressure, which is greater than the low mean pressure, and below the average speed and the respective

Shift operating strategies are selected.

According to an advantageous embodiment, below the low mean pressure and below the middle speed and / or below the first limit mean pressure, which is smaller than the low mean pressure, and below the limit speed, which is smaller as the average speed and / or below the average mean pressure, which is greater than the low mean pressure, and below the average speed, a first special operating mode are selected with a modified Auslaßventilhub crankshaft angle curve, wherein the first special mode with the modified Exhaust Valve Stroke Crankshaft Angle Curve has an early shifted exhaust end as compared to the first standard operating mode.

According to another advantageous embodiment, a stoichiometric or substoichiometric operating strategy can be selected above the average mean pressure and / or above the medium speed. It is particularly possible, during the stoichiometric or substoichiometric operating strategy below a third boundary pressure, which is above the average mean pressure, to select the first special operating mode, while above the third

Boundary pressure the standard operating mode is selected.

This results in a total operating method, is selected at high speeds and high loads or mid-pressures of this optimized standard operating mode and this in conjunction with a stoichiometric or

substoichiometric operating strategy. At low to medium speeds and small to medium loads or mean pressures can then be highly dependent on the respective operating strategy between the different special operating modes are selected to always realize a minimum fuel consumption and minimum pollutant emissions.

Suitably, the respective intake valve lift crankshaft angle curve in the first and third special operating mode have exactly four inflection points, with three

Turning points are located in front of the maximum. It can be provided in particular that the intake valve lift crank angle curve between the first and third inflection point has a plateau with a constant intake valve. Alternatively, it is also conceivable that the intake valve lift crankshaft angle curve between the first and third inflection point two more extremes, namely on either side of the second inflection point, a further maximum and a minimum before the

actual maximum intake valve lift owns.

Additionally or alternatively, the Auslaßventilhub crankshaft angle curve in the second and third special operating mode have exactly four inflection points, with three inflection points are located after the maximum. In particular, it can be provided that the Auslaßventilhub crankshaft angle curve between the second and the fourth inflection point has a plateau with a constant Auslaßventilhub. Alternatively, it may also be provided that the Auslassventilhub- crankshaft angle curve between the second and the fourth inflection point has two further extremes, namely a minimum and a further maximum on either side of the third inflection point.

According to another advantageous embodiment, the intake valve lift crankshaft angle curve can have exactly two turning points in a modified first special operating mode or alternatively have a plateau with constant valve lift in the region of the maximum. Further, the inlet start is selected as in the standard operating mode while the inlet end is delayed. In this case, the first special operating mode is modified according to the Atkinson principle.

An internal combustion engine according to the invention, which is preferably used in a motor vehicle, comprises a plurality of cylinders, each having at least one

Exhaust valve and at least one inlet valve is assigned. Furthermore, the

Internal combustion engine, a valvetrain having an exhaust camshaft for driving the exhaust valves and an intake camshaft for driving the intake valves. It will be appreciated that in an internal combustion engine having more than one cylinder bank, multiple exhaust camshafts and multiple intake camshafts may also be provided. Also, the exhaust camshaft is switchable between an exhaust default position for producing the exhaust valve lift crankshaft angle curve of the standard operating mode and an exhaust pending position for generating the exhaust valve lift crankshaft angle curve of the first, second and third special operating modes. Also, the intake camshaft is switchable between an intake default position for generating the intake valve lift crankshaft angle curve of the standard operating mode and an intake discrete position for generating the intake valve lift crankshaft angle curve of the first and third special operating modes.

The internal combustion engine may preferably be a gasoline engine and in particular a gasoline engine with direct injection. Furthermore, the internal combustion engine can optionally be charged, that is to say be equipped with a charging device, in particular with at least one exhaust-gas turbocharger. In an advantageous embodiment, the internal combustion engine is equipped with a control device for operating the internal combustion engine according to the operating method described above.

Further, optionally, an exhaust camshaft phaser for varying the phasing of the exhaust valve lift crankshaft angle curve with respect to

Crankshaft angle may be provided. Additionally or alternatively, a

Intake camshaft phaser for changing the phasing of the

Exhaust valve lift crankshaft angle curve to be provided with respect to the crankshaft angle. For example, with the aid of the intake camshaft phaser in the inlet special position, the modified first special operating mode can be set to realize an Atkinson operating mode.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

It show, each schematically

1 is a valve lift crank angle diagram of a standard operating mode,

2 shows a valve lift crank angle diagram of a first special operating mode,

3 is a valve lift crank angle diagram of a second special

Operation mode,

4 shows a valve lift crank angle diagram of a third special operating mode,

5 shows a medium-pressure speed map,

Fig. 6 is a medium-pressure-speed diagram for a homogeneous

Lean operation strategy 7 shows a valve lift crank angle diagram for a first special operating mode modified according to the Atkinson principle,

Fig. 8 shows another valve lift crank angle diagram for after

Atkinson principle modified first special mode of operation, Fig. 9 is a medium pressure-speed diagram for a stoichiometric

Operating strategy and

10 shows a valve lift crank angle diagram of the first special operating mode with a modified exhaust valve lift crankshaft angle curve.

An internal combustion engine, which is preferably used in a motor vehicle for driving the vehicle, usually comprises a plurality of cylinders, to which at least one outlet valve and at least one inlet valve are assigned. Furthermore, the internal combustion engine is equipped with a valve drive which has at least one exhaust camshaft for actuating the exhaust valves and at least one exhaust camshaft

Having inlet camshaft for driving the intake valves. To that explained in more detail below with reference to Figures 1 to 10 operating method of

To be able to perform internal combustion engine, on the one hand, the exhaust camshaft between an outlet default position for generating a Auslaßventilhub- crankshaft angle curve of a standard operating mode and an outlet special position for generating a Auslaßventilhub crankshaft angle curve of a first, second and third special operating mode switchable , On the other hand, the intake camshaft is switchable between an intake default position for generating an intake valve lift crankshaft angle curve of the standard operating mode and an intake special position for generating an intake valve lift crankshaft angle curve of a first and third special operating mode. Furthermore, the internal combustion engine is equipped with a control device which is designed and / or programmed such that it can operate the internal combustion engine according to the operating method explained in more detail below with reference to FIGS. 1 to 10. In this case, the internal combustion engine can basically be designed as a gasoline engine with spark ignition. Furthermore, the internal combustion engine is preferably equipped with a direct injection, so that the fuel can be introduced directly into the cylinder. Optionally, the internal combustion engine can be charged and accordingly equipped with a suitable charging device, in particular with an exhaust gas turbocharger.

In the diagrams of FIGS. 1 to 4, 7, 8 and 10, an exhaust valve lift crankshaft angle curve is designated 1, while an intake valve lift crankshaft angle curve is designated 1. Crankshaft angle curve is denoted by 2. In addition, a modified intake valve lift crankshaft angle curve can be seen in FIGS. 7 and 8, which is designated by 2 '. In the figure 10 a modified Auslaßventilhub- crankshaft angle curve can be seen, which is designated 1 '. In the diagrams of FIGS. 1 to 4, 7, 8 and 10, the crankshaft angle is abbreviated to "crank angle". For generating the valve lift crankshaft angle curves 1 and 2, the respective camshaft is equipped with corresponding cams having corresponding cams.

The diagram shown in Figure 1 shows the valve lift crankshaft angle curves 1 and 2, which are realized in a standard operating mode Q1. Recognizable possesses the intake valve lift crankshaft angle curve 2 between an inlet start 3 and an inlet end 4 only two turning points 5, 6 and between the two turning points 5, 6 only a maximum 7. The exhaust valve lift crankshaft angle curve 1 has between an outlet start 8 and a Outlet end 9 also two turning points 10, 1 1, between which is exactly a maximum 12. In this standard operating mode Q1, there is usually a slight angular one

Overlap between the inlet beginning 3 and the outlet end 9

corresponding overlapping area is denoted by 13. In this

Intersecting region 13, both the respective inlet valve and the respective outlet valve are open at the respective cylinder. However, the respective valve lift is so small that hardly any exhaust gas can flow back from the exhaust gas tract into the respective cylinder.

FIG. 2 now shows a diagram representing the valve lift crankshaft angle curves 1, 2 for a first special operating mode Q2. The Auslassventilhub- crankshaft angle curve 1 is unchanged, that is identical to the standard operating mode Q1. In contrast to this, in the first special operating mode Q2, the intake valve lift crankshaft angle curve 2 has an inlet start 3 that has been shifted earlier than the standard operating mode Q1. Purely by way of example, according to FIG. 1 in the standard operating mode Q1, the start of intake 3 is about 340 °

Crankshaft angle, while it is according to FIG. 2 in the first special operating mode Q2 at about 280 ° crankshaft angle. Accordingly, the increased

Overlap area 13. In the standard operating mode Q1, the outlet end 9 of FIG. 1 is approximately at 420 ° crankshaft angle, so that in the standard operating mode Q1 the overlap area is above approximately 420 ° -340 ° = 80 ° crankshaft angle extends. In contrast thereto, the overlapping region 13 in the first special operating mode according to FIG. 2 extends over approximately 420 ° -280 ° = 140 ° crankshaft angle.

The diagram of FIG. 3 shows a second special operating mode Q3, in which the intake valve lift crankshaft angle curve 2 is unchanged from the standard operating mode Q1. In this case, in this case, the exhaust valve lift crankshaft angle curve 1 is changed so as to have a late-shifted exhaust end 9 with respect to the standard operation mode Q1. In the example of Figure 3, the outlet end 9 is approximately at 480 ° crankshaft angle. This results in an enlargement of the overlapping region 13, which in this case extends over approximately 480 ° -340 ° = 140 ° crankshaft angle.

Finally, the diagram of Figure 4 shows a third special operating mode Q4, in which both valve lift crankshaft angle curves 1, 2 with respect to those of

Standard operating mode Q1 are changed. In this case, the Auslassventilhub- crankshaft angle curve 1 is modified as in the second special operating mode Q3, such that it has a late-shifted outlet end 9, here again at about 480 ° crankshaft angle. The intake valve lift crankshaft angle curve 2 is modified analogously to the first special operating mode Q2, such that its intake start 3 is shifted to early, so that it is again at about 280 ° crankshaft angle. Overall, this results in a further enlarged overlapping region 13, which in this case extends purely by way of example over approximately 480 ° -280 ° = 200 ° crankshaft angle.

In the first special operating mode Q2, exhaust gas from the respective cylinder can escape into the fresh air tract as a result of the prematurely opening inlet valve. This is sucked in the following suction stroke of the respective piston together with the fresh air, whereby an internal exhaust gas recirculation is realized. In the second special operating mode Q3 exhaust gas can flow back from the exhaust tract into the respective cylinder due to the exhaust valve closing late, whereby a significant internal exhaust gas recirculation is also realized. In the third special operating mode Q4, the two mechanisms leading to internal exhaust gas recirculation are combined, so that both exhaust gas can enter the fresh air tract and exhaust gas can be sucked back out of the exhaust tract. This results in a particularly intensive internal exhaust gas recirculation with a comparatively high exhaust gas recirculation rate.

To these modified curves 1, 2 for the exhaust valve lift and the

Intake valve lift in the special operating modes Q2, Q3, Q4 to realize the respective camshaft may be equipped with a second set of cams, in which case the respective additional or special cam interacts with the respective valve either instead of the standard standard cam or in addition to the standard cam. This can be realized, for example, by means of a so-called "cam-in-cam" camshaft in which two camshafts are arranged coaxially with one another and are rotationally adjustable relative to one another in order to realize the respective standard position or the respective special position.

The exhaust default position of the exhaust camshaft actuates the exhaust valves in accordance with the normal or standardized exhaust valve lift crankshaft angle curve 1, as shown in FIGS. 1 and 2 in the standard operating mode Q1 and the first special operating mode Q2. However, the exhaust camshaft exhaust exceptional position controls the exhaust valves according to the modified or particular history of the exhaust valve lift crankshaft angle curve 1 of FIGS. 3 and 4 as they occur in the second special operation mode Q3 and the third special operation mode Q4. The intake camshaft, in its standard intake position, actuates the intake valves according to the intake valve lift crankshaft angle curve 2 as shown in FIGS. 1 and 3, that is, the standard operating mode Q1 and the second special operating mode Q3. In the inlet special position of the intake camshaft, however, it controls the intake valves according to the particular intake valve lift crankshaft angle curve 2 of Figures 2 and 4, which occur in the first special operating mode Q2 and the third special operating mode Q4. Thus, since both camshafts each have two different positions that lead to different valve lift crankshaft angle curves, a total of four different operating modes can be realized, namely, for example, the aforementioned operating modes Q1, Q2, Q3 and Q4.

According to the map shown in Figure 5, in which a mean pressure is clamped to a speed, different operating strategies for operating the internal combustion engine can be defined or demarcated from each other. The ordinate in the example of Figure 5 plots a calculated mean pressure, referred to as "pme." The mean pressure pme can be calculated from the engine torque output Indicated medium pressure, which is referred to as "pmi". The indicated mean pressure pmi can be determined by means of pressure measurement in the respective cylinder and therefore corresponds to the actual pressure prevailing in the respective cylinder. Usually, the calculated mean pressure pme is smaller than the indexed one

Mean pressure pmi. The difference results from a frictional medium pressure, the may also be termed "pmr." The frictional mean pressure pmr takes into account the pressure drop resulting from friction losses in the

Internal combustion engine results. As a rule, pme = pmi-pmr.

The control of the internal combustion engine selects the current operating mode on the one hand as a function of the current operating strategy and on the other as a function of the position of a current operating state of the internal combustion engine in the medium-pressure speed map, which is designated in Figure 5 with 14. The current operating strategy is preferably also dependent on the position of the current

Operating state of the internal combustion engine in the medium-pressure speed map 14 set.

For example, according to FIG. 5, below a low mean pressure 15, which in the diagram of FIG. 5 is purely exemplary at about 4 bar mean pressure pme, and below a mean rotational speed 16, which in the diagram of FIG. 5 is purely exemplary at about 3000 rpm, a map area I can be defined in which an inhomogeneous shift operating strategy is selected. In such an inhomogeneous

Shift operating strategy is realized in the respective cylinder by means of multiple injection, a layered mixture charge, different layers differ by different λ-numbers from each other. Within this first

Map area I, in which the inhomogeneous stratified operating strategy is selected, by means of a first boundary means pressure 17, which is in the example of Figure 5 at about 2 bar mean pressure pme, and by means of a limit speed 18, which in the example of Figure 5 at about 1500 U / is min, another map area I 'delimited, which is referred to below as a modified first map area Γ. Below the first

Boundary mean pressure 17, which is smaller than the low mean pressure 15; and below the limit speed 18, which is smaller than the average speed 16, the second special mode Q3 is selected, while between the first boundary pressure 17 and the low mean pressure 15 and between the limit speed 18 and the average speed 16, the third special operating mode Q4 is selected. It is noteworthy that the first boundary-pressure 17 in the first map area I speed-dependent, such that the first boundary pressure 17 decreases with increasing speed. In the example of FIG. 5, a substantially linear dependence is shown, so that a connecting straight line 19 has a first state point 20, which is present at maximum first boundary-pressure 17 and at a minimum rotational speed 21 (here about 700 rpm), with a second state point 22 connects, which occurs at maximum limit speed 18 and at a minimum mean pressure 23 (about 0.5 bar). In contrast to this is the low mean pressure 15 across the speed substantially constant. The average speed 16 is independent of the mean pressure.

In the diagram of Figure 5, a mean medium pressure 24 is further indicated, which is also substantially constant over the speed or is independent of the speed. The mean medium pressure 24 is greater than the low mean pressure 15 and is in

Diagram of Figure 5 at about 10 bar pme. Below the average mean pressure 24 and below the average speed 16 is a second map area II, in which either a homogeneous lean operating strategy or a homogeneous

Shift operating strategy can be selected. A homogeneous lean operating strategy is characterized by a homogeneous mixture within the cylinder, in which excess air at a λ value of 1, 2 to 1, 5 prevails. A homogeneous one

Shift operating strategy is characterized by a homogeneous base mixture in that a constant λ prevails, in this homogeneous basic mixture shortly before

Ignition in the area of the respective ignition unit locally by another

Fuel injection is a core with a reduced λ is generated, so quasi an internal fuel layer concentrated with respect to the total content

Shift operating strategy a lean mixture in the cylinder before, i. it lies

Lean operation with stratified charge before.

Within the second map area II, in homogeneous stratified operation in a supercharged internal combustion engine, the third special operating mode Q4 may be preferred when the internal combustion engine is charged with a single exhaust gas turbocharger, while the first special operating mode Q2 is preferred, if the

Internal combustion engine with a mehrflutigen exhaust gas turbocharger, in particular a so-called twin-scroll turbocharger, is charged. It is also conceivable to use two or more multi-flow turbochargers.

It is also conceivable within the first map area I with its inhomogeneous shift operating strategy to select a first special operating mode Q2. The first special operating mode Q2 can also be selected for the modified first map area Γ and / or the second map area II with the respective inhomogeneous or homogeneous shift operating strategies.

It is furthermore conceivable within the first map area I and / or the

Modified first map area Γ and / or the second map area II in the respective selection of inhomogeneous or homogeneous shift operating strategies the In order to explain the first special operating mode with a modified Auslassventilhub crankshaft angle curve Q2 '", reference is made to the explanation below to Figure 10, the first special operating mode with a modified Auslaßventilhub- crankshaft angle curve Q2. The modified

Exhaust valve lift crankshaft angle curve 1 'is characterized by a shorter

Opening phase, which is realized by means of a smaller cam with reduced cam width. In combination with the intake valve lift crankshaft angle curve 2 of the standard operating mode Q1 or special operating mode Q2, with the modified exhaust valve lift crank angle curve 1 'a particularly high internal

Exhaust gas recirculation rate can be achieved.

According to FIG. 6, in the case where the homogeneous lean operating strategy is selected in the second map region II, the respective operating mode can now be selected below a second boundary-line pressure 25, which has a substantially linear dependence on the rotational speed in FIG. For example, the second one has

Boundary medium pressure 25 at 500 rev / min a value of about 4.5 bar pmi. Below the second boundary pressure 25, either the standard operating mode Q1 or a first special operating mode Q2 'modified according to the Atkinson principle can now be selected. On the other hand, above the second boundary-line pressure 25, either the first special operating mode Q2 or the second special operating mode Q3 or the third special operating mode Q4 can be selected.

To explain the first special operating mode Q2 'modified according to the Atkinson principle, reference is made to the explanations below regarding FIG. 7. With the help of the Atkinson operating strategy, a high de-throttling potential can be realized. In combination with a homogeneous and lean combustion process, the application of the Atkinson principle at lower partial loads, for example between 2 and 4 bar pmi, enables a not inconsiderable reduction in fuel consumption.

Coming back to Figure 5 can be found that above the middle

Medium pressure 24 and above the average speed 16, a third map area III is defined within the map 14, which is limited to higher pressures and higher speeds through a maximum allowable speed 26 and a maximum allowable mean pressure 27. For example, the maximum speed 26 has a value of 5500 rpm and the maximum mean pressure 27 has a value of 19 bar. Above the average mean pressure 24 and / or above the average speed 16, ie in the third characteristic area III, a stoichiometric or substoichiometric operating strategy is selected. The stoichiometric operating strategy is characterized by the fact that in the charge a λ-value of 1 prevails, so that in the exhaust gases neither a fuel surplus nor an excess of air prevails. The

sub-stoichiometric operating strategy is characterized by a fuel surplus.

According to FIG. 9, within this third characteristic area III, that is to say during the stoichiometric or substoichiometric operating strategy below a third boundary pressure 28, which in the example of FIG. 9 is essentially constant, that is independent of the rotational speed, and above the mean medium pressure 24 and below of the maximum allowable medium pressure 27, the first special operation mode Q2 is selected, while above this third boundary pressure 28 the standard operation mode Q1 is selected. In the example of FIG. 9, the third boundary pressure 28 is about 9.5 bar pmi.

It is also conceivable stoichiometric or stoichiometric operating strategy of the third map area III on the first map area I, the other

Map area P and the second map area II expand. This means that below the third limit means pressure 28 in the entire remaining map above the minimum speed 21 and above the minimum mean pressure 23 of the first

Special operating mode Q2 is selected.

It is also conceivable the stoichiometric or substoichiometric

Operating strategy of the third map area III with the first special operating mode Q2 below the third Grenzmitteldrucks 28 with one or more operating strategies with their respective operating modes according to the first map area I, the other map area P or the second map area II to combine.

Advantageously, starting from the stoichiometric or

stoichiometric operating strategy of the third map area III with the first special operating mode Q2 below the third boundary pressure 28 a plurality of combinations are formed so that an appropriate application of the various operating strategies are selected with their respective operating modes according to the current operating condition or request to the internal combustion engine Fuel consumption and pollutant emissions can be further reduced. In the first special operating mode Q2 according to FIG. 2 and in the third special operating mode Q4 according to FIG. 4 and in the representation of FIG. 7 and FIG. 10, the intake valve lift crankshaft angle curve 2 has exactly four turning points, namely the two standard turning points 5, 6 and two further inflection points 29, 30, which are both arranged with respect to the crankshaft angle before the maximum 7, so that in this intake valve lift crankshaft angle curve 2 a total of three

Turning points 5, 29, 30 are positioned before the maximum 7. In accordance with their chronological sequence according to the crankshaft angle, these four turning points are also referred to below as the first turning point 29, the second turning point 30, the third turning point 5 and the fourth turning point 6. The maximum 7 is thus between the third inflection point 5 and the fourth inflection point 6. In the case shown here

Embodiments has the respective intake valve lift crank angle curve 2 between the first inflection point 29 and the third inflection point 5, namely in the region of the second inflection point 30, a plateau 31 with a constant intake valve. As a result, the respective inlet valve is held for a specific crankshaft angle range with a constant opening stroke which is smaller than the maximum opening stroke at 7. The plateau 31 can extend over a crankshaft angle range from 40 ° to 80 ° crankshaft angle.

The same applies to the exhaust valve lift crankshaft angle curves 1 of FIGS. 3 and 4, that is to say the second special operating mode Q3 and the third special operating mode Q4. Also there contains the Auslaßventilhub crankshaft angle curve 1 exactly four turning points, namely the two standard turning points 10 and 11 and two other inflection points 32 and 33. Again, the inflection points 10, 1 1, 32, 33 according to their time sequence according to Crankshaft angle hereinafter referred to as first inflection point 10, second inflection point 1 1, third inflection point 32 and fourth inflection point 33. While the maximum 12 between the standard inflection points 10, 11, ie between the first inflection point 10 and the second inflection point 11 remains, follow the additional inflection points 32, 33, ie the third inflection point 32 and the fourth inflection point 33 to the maximum 12 on the second inflection point 11. Again, the Auslaßventilhub crankshaft angle curve 1 is formed in each case so that between the second inflection point 11 and the fourth inflection point 33, ie in the region of the third inflection point 32 forms a plateau 34, in which the respective exhaust valve via a limited crankshaft angle range has a constant opening stroke which is smaller than the maximum opening stroke at 12. The plateau 34 may extend over a crankshaft angle range of 40 ° to 80 ° crankshaft angle.

In order to realize the first special operating mode Q2 'modified according to the Atkinson principle, the phase position of the intake valve lift crankshaft angle curve 2 can now be shifted in accordance with the first special operating mode Q2 with the aid of an intake camshaft phaser. The shift is carried out in the example of Figure 7 so that for the start of intake 3 again about the same crankshaft angle value results as in the standard operating mode Q1. At the same time, the plateau 31 and the maximum 7 shifts late. Alternatively, the intake valve lift crankshaft angle curve 2 can be varied according to the standard operating mode Q1 by widening the intake cam, resulting in the form of the modified intake valve lift crankshaft angle curve 2 'which can be seen in FIG 7 has a plateau 31 '. By the

Phase shift is the initial shift achieved in the first special operation mode Q2, the inlet start converted into early in a shift of the inlet end 4 to late. While the inlet end 4 in the operating modes Q1, Q2, Q3 and Q4 of FIGS. 1 to 4 is in each case approximately 560 °, the position of the inlet end 4 in FIG. 7 is approximately 640 ° crankshaft angle.

8 shows a further alternative modified first special operating mode Q2 ", which in addition to the modified first special operating mode Q2 'is characterized by an exhaust valve lift crankshaft angle curve 1 which corresponds to that of the second special operating mode Q3 modified first special operating mode Q2 "can be used in place of the modified first special operating mode Q2 '.

10 shows the first special operating mode with a modified Auslaßventilhub- crankshaft angle curve Q2 '"This is characterized by the modified Auslassventilhub crankshaft angle curve 1' The modified Auslaßventilhub- crankshaft angle curve 1 'has a shorter opening phase across from

Auslassventilhub crankshaft angle curve 1 of the standard operating mode Q1 and the first special operating mode Q2 on. The shorter opening phase is realized by means of a smaller cam with reduced cam width. In FIG. 10, the

Auslassbeginn 8 with respect to the Auslaßventilhub crankshaft angle curve 1 not changed. In contrast, the outlet end 9 'of the modified Auslaßventilhub- crankshaft angle curve 1' relative to the outlet end 9 of the Auslassventilhub- Crankshaft angle curve 1 shifted to early, whereby the inflection point 1 1 'relative to the inflection point 11 is also moved to early. Due to the smaller cam, the maximum 12 'of the modified exhaust valve lift crankshaft angle curve 1' drops to a lower value than the maximum 12 of the Auslassventilhub- crankshaft angle curve 1. Accordingly, the overlap region 13 'changes to about 380 ° -280 ° = 100 ° crankshaft angle. The turning point 10 remains in

Essentially unchanged.

It is also conceivable that the Auslassventilhub crankshaft angle curve 1 'with its shorter opening phase between the previous Auslassbeginn 8 and the previous outlet end 9 of the Auslaßventilhub crankshaft angle curve 1 runs or the outlet end of the modified Auslaßventilhub crankshaft angle curve 1' with the Outgoing 9 exhaust valve lift crankshaft angle curve 1 coincides. The

Displacement of the modified Auslaßventilhub crankshaft angle curve 1 'can be made by appropriately providing respective additional or special cam in addition to

Standard cams are realized on the camshaft.

It will be appreciated that the engine may optionally also include an exhaust camshaft phaser for varying the phasing of the exhaust valve lift crank angle curve 1 and 1 '.

In the special operating mode with a modified Auslaßventilhub crankshaft angle curve Q2 '"a higher proportion of exhaust gas is retained in the combustion chamber by means of the shorter opening phase of the exhaust valve than in the first special operating mode Q2, so that more exhaust gas for internal exhaust gas recirculation is available whereby a particularly high internal exhaust gas recirculation rate can be achieved.

The smaller cam has a cam width of approximately 150 ° CA with a valve lift of 2 mm.

Claims

Patent claims

1. Method for operating an internal combustion engine which has at least one exhaust valve and at least one intake valve per cylinder and which has a valve train for controlling the respective exhaust valve according to an exhaust valve lift-crankshaft angle curve (1) and for controlling the respective intake valve according to an intake valve lift-crankshaft angle curve. Curve (2), in which an inhomogeneous shift operating strategy and a first special operating mode (Q2) are selected in a first map area I below a low mean pressure (15) and below a medium speed (16), the first special operating mode ( Q2) has an intake valve lift-crankshaft angle curve (2) with an intake start (3) that is shifted early compared to a standard operating mode (Q1), wherein in the standard operating mode (Q1) the

Intake valve lift-crankshaft angle curve

(2) between an entry start

(3) and an inlet end

(4) has two turning points (5, 6) and a maximum (7) between the two turning points (5, 6) and the exhaust valve lift-crankshaft angle curve (1) between an exhaust start (8) and one

Omitting (9) two turning points (10, 1 1 ) and between the two

Turning points (10, 11) have a maximum (12) and a minor one

angular overlap region (13) exists between the inlet start (3) and the outlet end (9) and within the first map region I a modified first map region is delimited, which lies below a first limit mean pressure (17) and below a limit speed (18), where the first limit mean pressure (17) is smaller than the low mean pressure (15) and the limit speed (18) is smaller than the mean speed (16) and the first

Special operating mode (Q2) is selected. Method according to claim 1,

characterized in that

the first limit mean pressure (17) decreases as the speed increases.

Method according to one of the preceding claims,

characterized in that

in a second map area II below a mean mean pressure (24), which is greater than the low mean pressure (15) and below the mean speed (16), a homogeneous shift operation strategy and the first special operating mode (Q2) are selected.

Method according to one of the preceding claims,

characterized in that

for the first map area I and/or for the modified first

Map area I' and/or for the second map area II a first special operating mode with a modified exhaust valve lift-crankshaft angle curve (Q2'") is selected, the first special operating mode having a modified exhaust valve lift-crankshaft angle curve (Q2'") ) one

Intake valve lift-crankshaft angle curve (2) with one versus one

Standard operating mode (Q1) has an early shifted intake start (3), while the modified exhaust valve lift-crankshaft angle curve (1 ') has an early shifted compared to the standard operating mode (Q1).

Has outlet end (9 ').

5. Method according to one of the preceding claims,

characterized in that

in a third map area III above the mean mean pressure (24) and above the mean speed (16) a stoichiometric or

substoichiometric operating strategy is selected.

6. Method according to claim 5,

characterized in that

within the third map area III below a third limit mean pressure (28), the first special operating mode (Q2) and above the third

Limit mean pressure (28) the standard operating mode (Q1) can be selected. Method according to one of claims 1 to 6,

characterized in that

- The intake valve lift-crankshaft angle curve (2) in the first special operating mode (Q2) has exactly four turning points (5, 6, 29, 30), with three turning points (5, 29, 30) being arranged before the maximum (7). , and or

- that the modified exhaust valve lift-crankshaft angle curve (1 ') in the first special operating mode (Q2'") has exactly two turning points (10, 11 '), the turning point (11) being arranged after the maximum (12'), and or

- In particular, it can be provided that the intake valve lift-crankshaft angle curve (2) has a plateau (31) with a constant intake valve lift between the first turning point (29) and the third turning point (5) and/or that the exhaust valve lift-crankshaft angle curve (1) has a plateau (31) with a constant exhaust valve lift between the second turning point (11) and the fourth turning point (33).

Internal combustion engine, in particular in a motor vehicle, operated according to one of the preceding claims 1 to 7,

- with several cylinders, each of which is assigned at least one exhaust valve and at least one inlet valve,

- with a valve train that has an exhaust camshaft to control the

Has exhaust valves and an intake camshaft for controlling the intake valves,

- whereby the exhaust camshaft is between a standard exhaust position

Generating the exhaust valve lift-crankshaft angle curve (1) of the standard operating mode (Q1) and a special exhaust position for generating the exhaust valve lift-crankshaft angle curve (1 ') of the first special operating mode with a modified exhaust valve lift-crankshaft angle curve (Q2' ") is switchable,

- wherein the intake camshaft is between a standard intake position

Generating the intake valve lift-crankshaft angle curve (2) of the standard operating mode (Q1) and a special intake position to generate the

Intake valve lift-crankshaft angle curve (2) of the first special operating mode (Q2) can be switched.