DE102013015011A1 - Internal combustion engine and associated operating method - Google Patents

Abstract

The present invention relates to a method of operating an internal combustion engine having at least one exhaust valve and at least one intake valve per cylinder and including a valvetrain for driving the respective exhaust valve according to an exhaust valve lift crankshaft angle curve (1) and for driving the respective intake valve according to an intake valve lift Crankshaft angle curve (2), in which in a third map area III above a minimum mean pressure (23) and above a minimum speed (21) a stoichiometric or substoichiometric operating strategy is selected and within the third map area III below a third Grenzmitteldrucks (28 a first operating mode (Q2) and above the third limit means pressure (28) a standard operating mode (Q1) are selected, wherein the first special mode (Q2) an inlet valve lift crankshaft angle curve (2) with respect to the standard -B in the standard operating mode (Q1), the intake valve lift crankshaft angle curve (2) between an inlet start (3) and an inlet end (4) has two inflection points (5, 6) and between the two turning points (5, 6) has a maximum (7) and the exhaust valve lift crankshaft angle curve (1) between an outlet start (8) and an outlet end (9) has two turning points (10, 11) and between the two turning points ( 10, 11) has a maximum (12) and a slight angular overlap area (13) exists between the inlet beginning (3) and the outlet end (9).

Description

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 10, which can be operated according to such a method.

From the DE 10 2010 011 681 A1 an internal combustion engine is known which comprises a plurality of cylinders, each of which is associated with at least one exhaust valve and at least one inlet valve. The known internal combustion engine is a spark ignited gasoline engine with direct injection of fuel, which is operated with an operating strategy, which is referred to as an 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, internal recirculation of hot exhaust gases being 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 providing an improved embodiment for an internal combustion engine or for an associated operating method, 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 to be selected as a function of the current operating state of the internal combustion engine and depending on the current operating strategy. The current operating state is suitably determined by its position in a medium-pressure speed map. By combining different operating strategies with different operating modes depending on the current operating state of the internal combustion engine, the fuel consumption and the pollutant emissions can be minimized.

In addition to the inhomogeneous shift operating strategy, other operating strategies can thus also be used. 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 which immediately before the ignition process in the region of the respective ignition additional fuel injection takes place, whereby 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 expediently a standard operating mode and exactly three special operating modes are provided, whereby a particularly high degree of flexibility for realizing different efficient internal exhaust gas recirculation is achieved. The standard operating mode is characterized in that an intake valve lift crankshaft angle curve has only two turning points between an intake start and an intake end and only one maximum between the turning points, while an exhaust valve lift crankshaft angle curve only has two turning points between an exhaust start and an exhaust end has only one maximum between the turning points. 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. It is particularly easy to realize the first special operating mode when 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 in that the exhaust valve lift crankshaft angle curve has a late-shifted exhaust end relative to the standard operating mode. As a result, exhaust gas can be sucked back from the still open exhaust tract. For ease of realization 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 operation mode, the intake valve lift crankshaft angle curve is the same as in the standard operation 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 early onset shifted from the standard operating mode and the exhaust valve lift crankshaft angle curve is over the standard operating mode having late-shifted outlet end. In this way, a particularly high internal exhaust gas recirculation rate can be realized. Also in this case, it may be expedient to keep the positions of the outlet start and the inlet end constant in relation to the standard operating mode. 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 means shifting to larger crankshaft angles.

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, on the one hand, an operating strategy suitable for this purpose 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 a variety of customization 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, an inhomogeneous shift operating strategy can be selected below a low mean pressure and below a medium speed. Particularly useful is a development in which during the inhomogeneous shift operating strategy below a first Grenzmitteldrucks, 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, for the inhomogeneous shift operating strategy within the medium-pressure speed characteristic map, at least two characteristic map regions are defined into which the current operating state can fall and which lead to different operating modes and in particular 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 rotational speed map in addition to a first map area, which triggers the inhomogeneous shift operating strategy, which causes a strategy change to the homogeneous lean operating strategy or to the homogeneous stratified operating strategy.

According to an advantageous refinement, during the homogeneous lean operating strategy below a second boundary pressure, which may be dependent on the rotational speed or constant over the rotational speed, the standard operating mode or a first special operating mode modified according to the Atkinson principle can be selected, while above of the second boundary pressure of one of the three special modes of operation 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 a Öffnungshubbereich 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, after the maximum opening stroke of the exhaust valve, the exhaust valve remains in a stroke range over a prolonged period of time, 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 a shift of the inlet end to late. With such an Atkinson mode of operation, significant dethrottling can be achieved, resulting in a notable reduction in consumption.

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. In this case, it is possible in particular to select the first special operating mode during a stoichiometric or substoichiometric operating strategy below a third boundary pressure which is above the average mean pressure, while the standard operating mode is selected above the third boundary pressure.

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 inflection points are arranged before 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 basically also conceivable that the intake valve lift crankshaft angle curve between the first and third inflection points has two further extremes, namely a further maximum on both sides of the second inflection point and a minimum before the actual maximum intake valve lift.

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 may 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 exhaust valve lift crankshaft angle curve between the second and the fourth inflection point has two further extremes, namely a minimum and a further maximum on both sides 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, to each of which at least one outlet valve and at least one inlet valve are assigned. Furthermore, the internal combustion engine comprises a valve drive, which has an exhaust camshaft for actuating the exhaust valves and an intake camshaft for actuating 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 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 with a control device equipped to operate the internal combustion engine according to the operating method described above.

Further, an exhaust camshaft phaser may be optionally provided for varying the phasing of the exhaust valve lift crankshaft angle curve with respect to the crankshaft angle. Additionally or alternatively, an intake camshaft phaser may be provided for varying the phasing of the exhaust valve lift crank angle curve with respect to the crankshaft angle. For example, the modified first special operating mode for realizing an Atkinson operating mode can be set with the aid of the intake camshaft phaser in the inlet special position.

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

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

3 a valve lift crank angle diagram of a second special operating mode,

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

5 a medium-pressure speed map,

6 a medium pressure-speed diagram for a homogeneous lean operating strategy,

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

8th a further valve lift crank angle diagram for a Modified according to the Atkinson principle first special operating mode and

9 a medium pressure-speed diagram for a stoichiometric operating strategy.

An internal combustion engine, which is preferably used in a motor vehicle for driving the vehicle, usually comprises a plurality of cylinders, to each of 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 intake camshaft for actuating the intake valves. To the following with reference to the 1 to 9 The exhaust camshaft between an exhaust standard 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 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 that is configured and / or programmed to the internal combustion engine according to the below with reference to 1 to 9 operate operating method explained in more detail. 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 1 to 4 . 7 and 8th is an exhaust valve lift crankshaft angle curve with 1 designated during an intake valve lift crankshaft angle curve with 2 is designated. In the 7 and 8th are each also a modified intake valve lift crankshaft angle curve recognizable with 2 ' is designated. In the diagrams of 1 to 4 . 7 and 8th is the crankshaft angle shortened with "crank angle" designated. For generating the valve lift crankshaft angle curves 1 and 2 is the respective camshaft equipped with corresponding cams having corresponding cams.

This in 1 The diagram shows the valve lift crankshaft angle curves 1 and 2 which are realized in a standard operating mode Q1. Recognizable has the intake valve lift crankshaft angle curve 2 between an inlet beginning 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 owns between an outlet beginning 8th and an outlet end 9 also two turning points 10 . 11 between which is exactly one maximum 12 located. In this standard operating mode Q1, there is usually a slight angular overlap between the start of intake 3 and the outlet end 9 , A corresponding overlapping area is included 13 designated. In this overlap area 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.

In 2 is now a diagram showing the valve lift crankshaft angle curves 1 . 2 for a first special operating mode Q2. The exhaust valve lift crankshaft angle curve 1 is unchanged, ie identical to the standard operating mode Q1. In contrast, in the first special operating mode, Q2 has the intake valve lift crankshaft angle curve 2 a beginning of intake shifted from the standard operating mode Q1 3 , By way of example is according to 1 in standard operating mode Q1, the start of intake 3 at about 340 ° crankshaft angle, while according to 2 in the first special operating mode Q2 is about 280 ° crankshaft angle. Accordingly, the overlap area increases 13 , In standard operating mode Q1, the outlet end is located 9 according to 1 approximately at 420 ° crankshaft angle, so that in the standard operating mode Q1, the overlap region extends over approximately 420 ° -340 ° = 80 ° crankshaft angle. In contrast, the overlap area extends 13 in the first special operating mode according to 2 over about 420 ° -280 ° = 140 ° crankshaft angle.

In the diagram of 3 is shown 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, this is the exhaust valve lift crankshaft angle curve 1 changed, such that they compared to the standard operating mode Q1 a delayed outlet end 9 has. In the example of 3 lies the outlet end 9 at about 480 ° crankshaft angle. This results in an enlargement of the overlapping area in this case as well 13 which extends over about 480 ° -340 ° = 140 ° crankshaft angle here.

Finally, the diagram shows the 4 a third special operating mode Q4, in which both valve lift crankshaft angle curves 1 . 2 are changed from those of the standard operating mode Q1. Here is the exhaust valve lift crankshaft angle curve 1 as modified in the second special mode of operation Q3, such that it has a late-shifted outlet end 9 has, which is 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 beginning of intake 3 moved to early, so that it is again at about 280 ° crankshaft angle. Overall, this results in a further increased overlap area 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 late closing exhaust valve, 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 either instead of the normal standard cam or cooperates with the respective valve 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 each other and are mutually rotatable in order to realize the respective standard position or the respective special position.

The exhaust default position of the exhaust camshaft controls the exhaust valves according to the normal or standardized exhaust valve lift Crankshaft angle history 1 on how he is in the 1 and 2 is present in the standard operating mode Q1 and in 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 the 3 and 4 as they occur in the second special operating mode Q3 and the third special operating mode Q4. The intake camshaft controls the intake valves according to the intake valve lift crankshaft angle curve in their default intake position 2 on how they are in the 1 and 3 is present, ie in the standard operating mode Q1 and in 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 the 2 and 4 which occur in the first special operating mode Q2 and in the third special operating mode Q4. Since both camshafts thus each have two different positions which lead to different valve-lift crankshaft angle curves, a total of four different operating modes can be realized, namely, for example, the abovementioned operating modes Q1, Q2, Q3 and Q4.

According to the in 5 shown map, in which a medium pressure is clamped to a speed, different operating strategies for operating the internal combustion engine can be defined or demarcated against each other. On the ordinate in the example of the 5 a calculated mean pressure called "pme" is plotted. The mean pressure pme can be calculated from the output torque of the internal combustion engine. In the diagrams of 6 and 9 is indicated on the ordinate in each case an indexed mean 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 indicated mean pressure pmi. The difference results from a frictional medium pressure, which can also be called "pmr". The frictional mean pressure pmr takes into account the pressure drop resulting from friction losses in the internal combustion engine. 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 hand depending on the position of a current operating state of the internal combustion engine in the medium-pressure speed map, the 5 With 14 is designated. 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 established.

For example, according to 5 below a low mean pressure 15 that in the diagram of 5 purely exemplary at about 4 bar mean pressure pme, and below a mean speed 16 in the diagram of the 5 purely exemplary at about 3000 rpm, a map area I are defined, in which an inhomogeneous shift operating strategy is selected. In such an inhomogeneous stratified operating strategy, a stratified mixture charge is realized in the respective cylinder by means of multiple injection, different strata differing from one another by different λ-numbers. Within this first map area I, in which the inhomogeneous shift operating strategy is selected, is by means of a first boundary pressure 17 who in the example of the 5 at about 2 bar mean pressure pme, and by means of a limiting speed 18 that in the example of the 5 at about 1500 rpm, another map area I 'is delimited, which is referred to below as a modified first map area I'. Below the first boundary pressure 17 which is smaller than the low mean pressure 15 ; and below the limit speed 18 , which is less than the average speed 16 , the second special operation 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 middle speed 16 the third special operating mode Q4 is selected. It is noteworthy that the first boundary pressure 17 is speed-dependent in the first map area I, such that the first boundary pressure 17 decreases with increasing speed. In the example of 5 a substantially linear dependence is shown, so that a connecting line 19 a first state point 20 that at maximum first border pressure 17 and at a minimum speed 21 (here about 700 rpm), with a second state point 22 connects, which at maximum limit speed 18 and at a minimum medium pressure 23 (about 0.5 bar) occurs. In contrast, the low mean pressure 15 essentially constant over the speed. Also the middle speed 16 is independent of medium pressure.

In the diagram of 5 is also a medium mean pressure 24 indicated, which is also about the speed substantially constant or independent of the speed. The mean medium pressure 24 is greater than the low mean pressure 15 and lies in the diagram of 5 at about 10 bar pme. Below the mean medium pressure 24 and below the middle speed 16 There is a second map area II in which either a homogeneous lean operating strategy or a homogeneous shift operating strategy are selected. A homogeneous one Lean operating strategy is characterized by a homogeneous mixture within the cylinder, in which excess air prevails at a λ value of 1.2 to 1.5. A homogeneous stratified operating strategy is characterized by a homogeneous base mixture in that a constant λ prevails, a core with reduced λ being generated locally in this homogeneous basic mixture shortly before ignition in the region of the respective ignition unit by further fuel injection, that is, with respect to the fuel content concentrated inner layer Overall, the shift operating strategy involves a lean mixture in the cylinder, ie there is a lean operation with stratified charge.

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 is equipped with a multi-engine 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.

According to 6 can now, for the case that in the second map area II, the homogeneous lean operating strategy is selected, below a second boundary pressure 25 who in 6 has a substantially linear dependence on the speed, the respective operating mode are selected. For example, the second boundary pressure has 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. Above the second boundary pressure 25 On the other hand, either the first special operating mode Q2 or the second special operating mode Q3 or the third special operating mode Q4 can be selected.

For an explanation of the first special operating mode Q2 'modified according to the Atkinson principle, reference is made to the explanations below 7 directed. 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 5 can be stated that above the mean medium pressure 24 and above the middle speed 16 a third map area III within the map 14 is defined, the higher pressures and higher speeds through a maximum speed 26 and a maximum allowable medium pressure 27 is limited. For example, has the maximum speed 26 a value of 5500 rpm and the maximum medium pressure 27 a value of 19 bar.

Above the mean medium pressure 24 and / or above the average speed 16 , So in the third map 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 substoichiometric operating strategy is characterized by a fuel surplus.

According to 9 can within this third map area III, ie during the stoichiometric or substoichiometric operating strategy below a third boundary pressure 28 who in the example of the 9 is substantially constant, that is independent of the speed, and that is above the mean center pressure 24 and below the maximum allowable mean pressure 27 The first special operating mode Q2 is selected while above this third boundary pressure 28 the standard operating mode Q1 is selected. In the example of 9 is the third boundary pressure 28 at about 9.5 bar pmi.

It is also conceivable to extend the stoichiometric or substoichiometric operating strategy of the third characteristic area III to the first map area I, the further map area I 'and the second map area II. This means that below the third boundary pressure 28 throughout the remaining map above the minimum speed 21 and above the minimum mean pressure 23 the first special operating mode Q2 is selected.

It is also conceivable stoichiometric or substoichiometric operating strategy of the third map area III with the first special operating mode Q2 below the third boundary mean pressure 28 with one or more operating strategies with their respective operating modes according to the first map area I, the other map area I 'or the second map area II to combine.

Advantageously, starting from the stoichiometric or substoichiometric operating strategy of the third characteristic area III with the first special operating mode Q2 below the third boundary pressure 28 a variety of combinations are formed, so that one needs-based application of the various operating strategies are selected with their respective operating modes according to the current operating condition or requirement of the internal combustion engine, which fuel consumption and pollutant emissions can be further reduced.

In the first special operating mode Q2 according to 2 and in the third special operating mode Q4 according to 4 as well as in the representation of 7 has the intake valve lift crankshaft angle curve 2 exactly four turning points, namely the two standard turning points 5 . 6 as well as two more turning points 29 . 30 , both with respect to the crankshaft angle before the maximum 7 are arranged so that at this intake valve lift crankshaft angle curve 2 a total of three turning points 5 . 29 . 30 before the maximum 7 are positioned. In accordance with their chronological sequence according to the crankshaft angle, these four inflection points will subsequently also be the first inflection point 29 , second turning point 30 , third turning point 5 and fourth turning point 6 designated. The maximum 7 is thus located between the third inflection point 5 and the fourth turning point 6 , In the embodiments shown herein, the respective intake valve lift crankshaft angle curve 2 between the first turning point 29 and the third turning point 5 namely in the area of the second inflection point 30 a plateau 31 with constant intake valve lift. 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 may extend over a crankshaft angle range of 40 ° to 80 ° crankshaft angle.

The same applies to the exhaust valve lift crankshaft angle curves 1 of the 3 and 4 , ie the second special operating mode Q3 and the third special operating mode Q4. Also there contains the exhaust valve lift crankshaft angle curve 1 exactly four turning points, namely the two standard turning points 10 and 11 as well as two more turning points 32 and 33 , Again, the turning points 10 . 11 . 32 . 33 in the following as the first inflection point, according to their time sequence according to the crankshaft angle 10 , second turning point 11 , third turning point 32 and fourth turning point 33 designated. While the maximum 12 between the standard turning points 10 . 11 that is, between the first turning point 10 and the second turning point 11 remains, follow the additional turning points 32 . 33 that is the third turning point 32 and the fourth turning point 33 after the maximum 12 on the second turning point 11 , Again, the shaping of the Auslaßventilhub crankshaft angle curve takes place 1 each so that is between the second inflection point 11 and the fourth turning point 33 , ie in the area of the third turning point 32 a plateau 34 is formed, in which the respective exhaust valve over 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.

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 can now be determined with the aid of an intake camshaft phaser 2 according to the first special operating mode Q2 be delayed. The shift is in the example of 7 so carried out that for the beginning of admission 3 returns approximately the same crankshaft angle value as in standard operating mode Q1. At the same time, the plateau shifts 31 and the maximum 7 after late. Alternatively, the intake valve lift crankshaft angle curve 2 according to the standard operating mode Q1 be changed by a widening of the inlet cam, so that in 7 recognizable shape of the modified intake valve lift crankshaft angle curve 2 ' that results in the range of the maximum 7 a plateau 31 ' having. Due to the phase shift, the shift of the inlet beginning originally achieved in the first special operating mode Q2 is transformed into a shift of the inlet end in advance 4 after late. While the inlet end 4 in operating modes Q1, Q2, Q3 and Q4 of the 1 to 4 each at about 560 °, results for the inlet end 4 now in 7 a position of about 640 ° crankshaft angle.

In 8th is shown another alternative modified first special operating mode Q2 ''. This is characterized by the modified first special operating mode Q2 'additionally by an exhaust valve lift crankshaft angle curve 1 which corresponds to that of the second special operating mode Q3. The alternative modified first special mode Q2 "may be used instead of the modified first special mode Q2 '.

It will be appreciated that the engine optionally also includes an exhaust camshaft phaser for varying the phasing of the exhaust valve lift crankshaft angle curve 1 can have.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102010011681 A1 [0002]

Claims (10)

A method of operating an internal combustion engine having at least one exhaust valve and at least one intake valve per cylinder, and comprising a valve train for driving the respective exhaust valve according to an exhaust valve lift crankshaft angle curve ( 1 ) and for driving the respective intake valve according to an intake valve lift crankshaft angle curve ( 2 ), in which in a third map area III above a minimum mean pressure ( 23 ) and above the minimum speed ( 21 ) a stoichiometric or substoichiometric operating strategy is selected and within the third characteristic area III below a third boundary pressure ( 28 ) a first special mode (Q2) and above the third boundary pressure ( 28 ) a standard operating mode (Q1) are selected, wherein the first special mode (Q2) is an intake valve lift crankshaft angle curve (Q1) 2 ) with a beginning of intake which is delayed in relation to the standard operating mode (Q1) ( 3 In the standard operating mode (Q1), the intake valve lift crankshaft angle curve (FIG. 2 ) between an inlet beginning ( 3 ) and an inlet end ( 4 ) two turning points ( 5 . 6 ) and between the two turning points ( 5 . 6 ) a maximum ( 7 ) and the exhaust valve lift crankshaft angle curve ( 1 ) between an outlet beginning ( 8th ) and an outlet end ( 9 ) two turning points ( 10 . 11 ) and between the two turning points ( 10 . 11 ) a maximum ( 12 ) and a slight angular overlap area ( 13 ) between the beginning of admission ( 3 ) and the outlet end ( 9 ) exists. A method according to claim 1, characterized in that in a first map area I below a low mean pressure ( 15 ), which is greater than the minimum mean pressure ( 23 ) and below a medium speed ( 16 ), which is greater than the minimum speed ( 21 ), an inhomogeneous shift operating strategy and a third special operating mode (Q4) are selected, wherein the third special operating mode (Q4) is an intake valve lift crankshaft angle curve (Q4). 2 ) with a beginning of intake that is delayed to a standard operating mode (Q1) ( 3 ) while the exhaust valve lift crank angle curve (FIG. 1 ) an outlet end shifted later than the standard operating mode (Q1) ( 9 ) having, A method according to claim 2, characterized in that within the first map area I is a modified first map area I 'is delimited below a first boundary pressure ( 17 ) and below a limit speed ( 18 ), the first boundary pressure ( 17 ) is smaller than the low mean pressure ( 15 ) and the limit speed ( 18 ) is less than the average speed ( 16 ) and a second special mode (Q3) is selected, wherein the second special mode (Q3) is an exhaust valve lift crankshaft angle curve (Q3) 1 ) with an outlet end shifted later than the standard operating mode (Q1) ( 9 ) having. Method according to claim 3, characterized in that the first boundary pressure ( 17 ) decreases with increasing speed. A method according to claim 1, characterized in that in a second map area II below an average mean pressure ( 24 ), which is greater than the low mean pressure ( 15 ) and below the average speed ( 16 ) a homogeneous lean operating strategy or a homogeneous shift operating strategy are selected. A method according to claim 5, characterized in that within the second map range II in a supercharged internal combustion engine with a single exhaust gas turbocharger, the third special mode (Q4) is selected. A method according to claim 5, characterized in that within the second map area II in a supercharged internal combustion engine with a multi-flow turbocharger a first special mode (Q2) is selected, wherein the first special mode (Q2) an intake valve lift crankshaft angle curve ( 2 ) with a beginning of intake which is delayed in relation to the standard operating mode (Q1) ( 3 ) having. A method according to claim 5, characterized in that within the second map area II when selecting the homogeneous lean operating strategy below a second boundary pressure ( 25 ) the standard operating mode (Q1) or a modified Atkinson principle first special mode (Q2 ', Q2'') is selected and above the second boundary pressure ( 25 ) the first special mode (Q2) or the second special mode (Q3) or the third special mode (Q4) is selected. Method according to one of claims 1 to 8, characterized in that - the intake valve lift crankshaft angle curve ( 2 ) in the first special operating mode (Q2) and in the third special operating mode (Q4) exactly four turning points ( 5 . 6 . 29 . 30 ), where three inflection points ( 5 . 29 . 30 ) before the maximum ( 7 ), and / or - that the exhaust valve lift crankshaft angle curve ( 1 ) in the second special operating mode (Q3) and in the third special operating mode (Q4) exactly four turning points ( 10 . 11 . 32 . 33 ), wherein three Turning points ( 11 . 32 . 33 ) to the maximum ( 12 ) are arranged, and / or - that in particular can be provided that the intake valve lift crankshaft angle curve ( 2 ) between the first turning point ( 29 ) and the third inflection point ( 5 ) a plateau ( 31 ) with constant intake valve lift and / or that the exhaust valve lift crankshaft angle curve ( 1 ) between the second turning point ( 11 ) and the fourth inflection point ( 33 ) a plateau ( 31 ) with constant Auslaßventilhub, and / or - that in particular can be provided that the intake valve lift crankshaft angle curve ( 2 ) in a modified first special operating mode (Q2 ', Q2'') exactly two inflection points ( 5 . 6 ) and in the range of the maximum ( 7 ) a plateau ( 31 ' ) with constant intake valve lift. Internal combustion engine, in particular in a motor vehicle, operated according to one of the preceding claims 1 to 9, - having a plurality of cylinders, each associated with at least one exhaust valve and at least one inlet valve, - with a valve train having an exhaust camshaft for driving the exhaust valves and an intake camshaft to Driving the intake valves, wherein the exhaust camshaft between an exhaust standard position for generating the exhaust valve lift crankshaft angle curve ( 1 ) of the standard operating mode (Q1) and an outlet special position for generating the Auslassventilhub crankshaft angle curve ( 1 ) is switchable between the second special operating mode (Q3) and the third special operating mode (Q4), the intake camshaft being set between an inlet standard position for generating the intake valve lift crankshaft angle curve ( 2 ) of the standard operating mode (Q1) and an inlet special position for generating the intake valve lift crankshaft angle curve ( 2 ) of the first special operating mode (Q2) and the third special operating mode (Q4) is switchable.

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