DE102014207379A1 - Arrangement of internal combustion engine and control unit and method for operating an internal combustion engine - Google Patents

Abstract

The invention relates to an arrangement (1), preferably for a motor vehicle, comprising an internal combustion engine (2), preferably a spark ignition internal combustion engine, with at least one cylinder (3) and at least one inlet valve (4) on the cylinder (3), a variable valve train (3). 5) for adjusting the maximum stroke (24) of the inlet valve (4), a charging device (6), preferably a turbocharger, for increasing the pressure via the inlet valve (4) introducible air, a control device (7) for controlling at least the valve train (5) wherein the controller (7) is configured to: detect whether the engine (2) is operating in a critical map range, the map range being defined by an engine load range and an engine speed range, and wherein in the map range at full stroke (8) predefined pressure gradient limit value (25) of the cylinder pressure gradient in which at least one cylinder (3) is exceeded, and setting de s maximum lift to a reduced maximum lift (9) lower than full lift (8) and wherein the cylinder pressure gradient is equal to or lower than the pressure gradient limit (25) when operating the engine (2) in the critical map area.

Description

The present invention relates to an arrangement of an internal combustion engine and an associated control unit, preferably for a vehicle. Furthermore, the invention relates to a method for operating the internal combustion engine.

In turbocharged internal combustion engines, especially in gasoline engines, with variable valve train, the air inlet duct for a high charge movement (tumble) is designed. This can accelerate the combustion in the partial load and increase the possible residual gas content in order to increase the partial load efficiency. The faster combustion leads to high cylinder pressure gradients at low engine speeds and medium load in the charged area and thus to a hard combustion noise. As a criterion for the evaluation of the acoustics, the maximum cylinder pressure gradient should be used, which should not exceed a limit. A late ignition angle or a late injection start or a double injection can lead to a decrease in the maximum cylinder pressure gradient. However, these measures are associated with significant fuel consumption and high particulate emissions.

It is an object of the present invention to allow operation of the internal combustion engine with the lowest possible noise while optimally fuel consumption and low pollutant emissions and to provide a corresponding method to achieve this goal.

The object is achieved by the features of the independent claims. The dependent claims relate to advantageous embodiments of the invention.

Thus, the object is achieved by an arrangement, preferably for a motor vehicle, comprising an internal combustion engine with at least one cylinder and at least one inlet valve on the cylinder for the charge air. The internal combustion engine is in particular a spark-ignited internal combustion engine, preferably a gasoline engine. The internal combustion engine has a variable valve train. This serves at least for adjusting the maximum stroke of the intake valve. Furthermore, with the variable valve train, the inlet valve can also be actuated according to the angular position of the crankshaft or the phase position. The arrangement further comprises a charging device, preferably designed as a turbocharger or compressor, for increasing the pressure of the inlet valve via the inlet air. It is thus a supercharged combustion engine. In addition, the arrangement comprises a control unit, in particular an engine control unit, for controlling at least the valve train.

Among other things, the control unit can specify the maximum intake valve lift as a function of the engine load and engine speed and limit the maximum cylinder pressure gradient, especially in acoustically critical operating states, by reducing the maximum travel. The acoustically critical operating condition is specified here by a critical map range.

The control unit is designed to: detect whether the internal combustion engine is operated in the critical map area, wherein the map area is defined by an engine load area and an engine speed range, and wherein in the map area at the maximum maximum stroke a predefined Druckgradientgrenzwert the cylinder pressure gradient is exceeded in the at least one cylinder and setting the maximum lift to a reduced maximum lift that is less than the full lift (maximum lift) and wherein the cylinder pressure gradient is equal to or less than the pressure gradient limit when the engine is operating in the critical map range.

The decisive advantage of changing the cylinder pressure gradient by means of a reduction of the maximum lift of the intake valve is that there is little or no functional disadvantage in terms of fuel consumption and pollutant emissions. Thus, it is provided according to the invention that, during operation of the internal combustion engine in the critical map area, the maximum lift of the intake valve is set to a reduced maximum lift. The reduced maximum stroke is less than the full stroke.

The full stroke defined here (also: maximum possible maximum stroke) is the largest maximum stroke occurring in the entire map of the internal combustion engine. In particular, the full stroke is predetermined by the mechanics of the variable valve train.

The cylinder pressure gradient is defined as the change in cylinder pressure over the crankshaft position. As a unit for the cylinder pressure gradient thus results in bar / ° KW, with ° KW as the angular position of the crankshaft.

By reducing the maximum stroke according to the invention, the charge movement is reduced in order to achieve a slower combustion. As a result, the maximum cylinder pressure gradient decreases and the combustion noise becomes quieter.

It is preferably provided that in the control unit, the maximum lift of the intake valve is stored in a characteristic field spanned over the engine load and speed and reduced in the acoustically critical operating ranges. Other parameters that influence the maximum valve lift may be the environmental conditions (temperature, relative humidity, pressure, fuel quality, etc.)

As described above, the acoustically critical map range is at low engine speeds and in the middle load range. Especially in these areas occur the highest cylinder pressure gradient and thus the highest noise. The lower value of the engine speed range of the critical map range is advantageously approximately at the idling speed, in particular at 600 rpm to 1000 rpm. Furthermore, it is preferably provided that the upper value of the engine speed range of the critical map range is at most 60%, preferably at most 55%, of the maximum speed. The maximum speed is the maximum occurring in the entire map of the engine speed. In particular, the speed of the internal combustion engine is limited by the control unit to this maximum speed.

The minimum engine load of the critical map area is preferably the beginning of the charged area with an effective mean pressure of preferably 8 to 12 bar. The upper value of the engine load range of the critical map range is advantageously 2/3 to 3/4 of the full load.

The permissible maximum pressure gradient depends on the acoustic requirements and the specifics of the vehicle. The maximum pressure gradient should not exceed 6 bar / ° CA, preferably 5 bar / ° CA, in the acoustically critical operating range of the engine.

To achieve this goal, it is preferably provided to limit the maximum valve lift in individual operating ranges to 60% to 80%, preferably approximately 70%, of the full stroke. Advantageously, the maximum valve lift is continuously increased until the full stroke the interval limits of the critical map area.

Furthermore, an injection device is preferably provided on the cylinder, so that the internal combustion engine is designed as a direct injection internal combustion engine.

The invention further includes a method for operating an internal combustion engine, in particular of the internal combustion engine just described. The method is used in particular in a motor vehicle. The method includes at least the following steps: (i) detecting whether the engine is operating in a critical map range, wherein the map range is defined by an engine load range and an engine speed range, wherein in the critical map range, the engine is supercharged with charge air, and wherein setting the maximum lift to a reduced maximum lift that is lower than the full lift and wherein the maximum cylinder pressure gradient is equal to or lower than the pressure gradient limit, setting the maximum lift to the maximum cylinder pressure gradient in full cylinder of an intake valve; when the engine is operating in the critical map area.

The advantageous embodiments described in the context of the arrangement and dependent claims find correspondingly advantageous application to the method according to the invention.

In the context of the method, provision is made in particular for the maximum lift to be greater than the reduced maximum lift when the internal combustion engine is operating outside the critical characteristic area. If the engine load is further increased by the increasing charge pressure at low engine speed, the ignition angle must be reduced in order to avoid knocking cycles. Thus, the maximum cylinder pressure gradient is reduced in this operating range anyway and the maximum lift of the intake valve can be increased again. This allows the internal combustion engine to be thermodynamically optimally adjusted in the area of the full load line and achieves the maximum possible torque.

With increasing engine speed, the maximum cylinder pressure gradient decreases because the combustion speed increases disproportionately and the combustion slows down with respect to the angular position of the crankshaft. Accordingly, the maximum stroke can be increased in this area and the maximum possible engine power can be adjusted without throttling by the valve lift on the inlet valve.

In addition to the described reduction of the cylinder pressure gradient by a reduced maximum lift of the intake valve, it is preferably provided to reduce the cylinder pressure gradient by larger valve overlaps and / or by a later ignition angle and / or a double injection.

Further details, features and advantages of the invention will become apparent from the following description and the figures:

1 shows a schematic simplified representation of an inventive arrangement for carrying out the method according to the invention according to an embodiment,

2 shows a characteristic diagram of the internal combustion engine of the arrangement according to the invention according to the embodiment,

3 shows a profile to the cylinder pressure gradient in the internal combustion engine of the inventive arrangement according to the embodiment, and

4 shows valve lift curves in the internal combustion engine of the arrangement according to the invention according to the embodiment.

The following is an arrangement 1 and an associated method for operating the device 1 explained in detail with reference to an embodiment.

1 shows in a schematic highly simplified representation of the arrangement 1 comprising an internal combustion engine 2 for a vehicle. In the internal combustion engine 2 is at least a cylinder 3 educated. In the cylinder 3 an unillustrated piston moves. The piston in turn causes a rotational movement of a crankshaft.

At the cylinder 3 is an inlet valve 4 intended. This inlet valve 4 can by means of a variable valve train 5 be opened and closed. At the inlet valve 4 can air in the cylinder 3 be initiated. This air is supplied via a charging device 6 compacted. The charging device 6 is for example an exhaust gas turbocharger.

Furthermore, there is a control unit 7 for driving the internal combustion engine 2 , in particular the variable valve train 5 , intended. Furthermore, an injection device 10 , a spark plug 27 and an exhaust valve 26 intended. By means of the injector 10 will fuel directly into the cylinder 3 injected.

It is therefore an internal combustion engine 2 with charge air charge and variable valve train 5 ,

In a critical map area, with medium load and low speed, as shown below 2 described in such an internal combustion engine 2 usually a full stroke 8th (maximum possible lift) of the intake valve 4 used. In the context of the invention, however, a reduced maximum stroke is proposed in the specific map area 9 to use.

2 shows an engine speed on the horizontal axis 19 , On the vertical axis is the engine load 21 shown. 2 shows the entire map of the engine 2 with a maximum speed 20 and a full load 22 ,

In the diagram after 2 different cylinder pressure gradients are plotted: 11: cylinder pressure gradient with 1 bar / ° CA; 12: cylinder pressure gradient with 2 bar / ° CA; 13: cylinder pressure gradient with 3 bar / ° CA; 14: cylinder pressure gradient with 4 bar / ° CA; 15: cylinder pressure gradient with 5 bar / ° CA; 16: cylinder pressure gradient with 6 bar / ° CA; 17: Cylinder pressure gradient with 7 bar / ° KW.

The illustrated cylinder pressure gradients 11 to 17 are each the changes in the measured cylinder pressure in the cylinder 3 above the crankshaft position.

Based on 2 It is easy to see that very high cylinder pressure gradients occur in the range of low engine speeds and average engine loads. Usually, in supercharged internal combustion engines in this area the full stroke 8th of the inlet valve 4 set. In the context of the invention is proposed, the reduced maximum stroke 9 to reduce the cylinder pressure gradient in this critical map range.

3 shows on the horizontal the maximum stroke 24 of the inlet valve 4 , On the vertical is the cylinder pressure gradient 23 shown. The course of the drawn curve shows that with increasing maximum stroke 24 also the cylinder pressure gradient 23 increases. Therefore, it is proposed in the invention, at most the reduced maximum stroke 9 to use the cylinder pressure gradient 23 To keep as low as possible and thus to reduce the noise. The reduced maximum stroke 9 will correspond to a desired pressure gradient limit 25 established.

4 shows for the inlet valve 4 Lifting curves with the full stroke 8th and several possible reduced maximum strokes 9 which are used depending on the required reduction of the cylinder pressure gradient.

LIST OF REFERENCE NUMBERS

1

arrangement

2

internal combustion engine

3

cylinder

4

intake valve

5

variable valve train

6

charging

7

control unit

8th

Full stroke (maximum possible maximum stroke

9

reduced maximum lift

10

Injector

11-17

Values of the cylinder pressure gradient

19

Engine speed

20

Maximum speed

21

engine load

22

Full load (maximum load)

23

cylinder pressure gradient

24

maximum stroke

25

Druckgradientgrenzwert

26

outlet valve

27

spark plug

Claims (9)

Arrangement ( 1 ), preferably for a motor vehicle, comprising • an internal combustion engine ( 2 ), preferably a spark-ignited internal combustion engine, with at least one cylinder ( 3 ) and at least one inlet valve ( 4 ) on the cylinder ( 3 ), • a variable valve train ( 5 ) for setting the maximum stroke ( 24 ) of the inlet valve ( 4 ), • a charging device ( 6 ), preferably a turbocharger, for increasing the pressure via the inlet valve ( 4 ) inlet air, • a control unit ( 7 ) for driving at least the valve drive ( 5 ), whereby the control unit ( 7 ) is designed to: • determine whether the internal combustion engine ( 2 ) is operated in a critical map area, wherein the map area is defined by an engine load area and an engine speed range, and wherein in the map area at full stroke ( 8th ) a predefined pressure gradient limit ( 25 ) of the cylinder pressure gradient in the at least one cylinder ( 3 ), and • setting the maximum lift ( 24 ) to a reduced maximum lift ( 9 ), which is smaller than the full stroke ( 8th ) and in which the cylinder pressure gradient ( 23 ) equal to or lower than the pressure gradient limit ( 25 ) is when the internal combustion engine ( 2 ) is operated in the critical map area. Arrangement according to claim 1, characterized in that in the control unit of the critical map area, in the full stroke ( 8th ) the pressure gradient limit ( 25 ) is exceeded, is stored. Arrangement according to one of the preceding claims, characterized in that the lower value of the engine speed range of the critical map area at the idling speed, in particular at 600 to 1000 rev / min, and / or that the upper value of the engine speed range of the critical map area at most 60% , preferably at most 55%, of the maximum speed ( 20 ), lies. Arrangement according to one of the preceding claims, characterized in that the upper value of the engine load range of the critical map area at 2/3 to 3/4 of the full load ( 22 ) lies. Arrangement according to one of the preceding claims, characterized in that the pressure gradient limit ( 25 ) is at most 6 bar / ° CA, preferably at most 5 bar / ° CA. Arrangement according to one of the preceding claims, characterized in that the reduced maximum stroke ( 9 ) at 60% to 80% of the full haul ( 8th ) lies. Arrangement according to one of the preceding claims, characterized by an injection device ( 10 ) for direct injection of fuel into the at least one cylinder ( 3 ). Method for operating an internal combustion engine ( 2 ), preferably in a motor vehicle, comprising the following steps: • detecting whether the internal combustion engine ( 2 ) is operated in a critical map area, wherein the map area is defined by an engine load area and an engine speed range, wherein in the critical map area a charge air charging of the internal combustion engine takes place, and wherein in the map area at full stroke ( 9 ) an intake valve ( 4 ) a pressure gradient limit ( 25 ) of the cylinder pressure gradient in at least one cylinder ( 3 ) of the internal combustion engine ( 2 ), and • setting the maximum lift ( 24 ) to a reduced maximum lift ( 8th ), which is lower than the full stroke ( 9 ) and in which the cylinder pressure gradient ( 23 ) equal to or lower than the pressure gradient limit ( 25 ) is when the internal combustion engine ( 2 ) is operated in the critical map area. A method according to claim 8, characterized in that outside the critical map area of the maximum stroke ( 24 ) is higher than the reduced maximum lift ( 9 ).

Images