DE102010051832B4 - Method for operating a reciprocating internal combustion engine with a swirl combustion process - Google Patents

Abstract

Method for operating a reciprocating internal combustion engine, wherein combustion air is introduced into at least one working cylinder via at least one first intake valve in an intake stroke, wherein the at least one first intake valve is actuated with a predetermined first valve lift curve, which is constant in relation to a time relation to a crank angle of the internal combustion engine is maintained, with the cylinder charge being introduced via the first intake valve in such a way that the cylinder charge in the working cylinder executes a twisting motion, characterized in that the cylinder charge in the at least one working cylinder is additionally fed into the at least one working cylinder via at least one second intake valve with variable phasing with respect to the crank angle of the internal combustion engine second valve lift curve is initiated.

Description

The invention relates to a method for operating a reciprocating internal combustion engine, in particular a spark-ignition engine, wherein combustion air is introduced into at least one working cylinder via at least one first intake valve in an intake stroke, wherein the at least one first intake valve is actuated with a predetermined first valve lift curve, which is relative to a temporal relation to a crank angle of the internal combustion engine is kept constant, the cylinder charge being introduced via the first inlet valve in such a way that the cylinder charge executes a twisting movement in the working cylinder, according to the preamble of patent claim 1.

From Hadler, Jens: "Minimal consumption - maximum power; TST technology in the new 1.21 engine from Volkswagen”, Volumes 1 and 2. Vienna: VDI-Verlag, 2009 (VDI Progress Reports, Series 12, No. 697). - ISBN 978-3-18-369712-0, pages 92 to 116, it is known to operate an Otto engine with a swirling movement of the cylinder charge (swirling combustion process).

From the DE 103 12 961 B3 a device for the variable actuation of gas exchange valves of internal combustion engines is known. In this case, a valve lift curve is influenced in that a position of an axis of rotation of an intermediate member between a cam and a driven member is changed.

From the DE 198 25 308 A1 a variable valve drive for an internal combustion engine is known, with variable valve lifts being set at a constant opening angle. In order to produce variable valve opening angles with particularly small valve lifts, a tilting axis of a rocker arm parallel to a camshaft axis of rotation is dynamically displaced along a path relative to a camshaft.

the DE 10 2010 007 023 A1 discloses an internal combustion engine with at least one cylinder, in which a combustion chamber is delimited between a piston and a cylinder head, and at least one inlet channel, via which combustion air is supplied to the combustion chamber, with a first and a second inlet valve being provided in the combustion chamber, which are The valve control device can be actuated in such a way that, in order to form a swirl flow in the combustion chamber, a different valve lift can be set for the first inlet valve than for the second inlet valve, with a first valve lift being settable for the first inlet valve and a zero lift for the second inlet valve in a part-load range of the internal combustion engine, and wherein in a higher load range of the internal combustion engine the first valve lift from the part-load operating point is maintained for the first intake valve, wherein a second valve lift can be set for the second intake valve.

the DE 101 57 659 B4 describes a method for creating turbulence in an air-fuel mixture in the combustion chamber of a multi-valve engine, the engine having at least first and second intake valves, each independently actuated by an actuator.

The invention is based on the object of providing a measure for reducing fuel consumption for a gasoline engine or diesel engine combustion process with a good cost/benefit ratio.

According to the invention, this object is achieved by a method of the above-mentioned type with the features characterized in claim 1. Advantageous configurations of the invention are described in the further claims.

For this purpose, in a method of the above-mentioned type, the invention provides that the cylinder charge is additionally introduced into at least one working cylinder via at least one second intake valve with a second valve lift curve that is variable with respect to the crank angle of the internal combustion engine.

This has the advantage that through appropriate "phasing" of the second intake valve, a reduction in the air mass is achieved without increasing gas exchange losses in a swirl combustion process, while at the same time underexpansion in the intake stroke is effectively avoided. Surprisingly, this results in an increase in the swirl movement with a correspondingly positive influence on the stability of the combustion process and the homogenization of the cylinder charge.

A mechanically particularly simple and inexpensive variable valve adjustment (VVT) is achieved by keeping the second valve lift curve of the second intake valve constant depending on an operating state of the internal combustion engine and shifting it in time with respect to the crank angle.

A high degree of adjustment flexibility and a variable valve adjustment (VVT) that can be adapted particularly precisely to a wide variety of operating conditions is achieved in that a point in time for opening the second intake valve, a point in time for closing the second intake valve and/or a point in time for a maximum opening stroke of the second intake valve relative to Crank angle is changed depending on an operating state of the internal combustion engine.

A further improvement in the flexibility of the setting is achieved in that a maximum opening lift of the second intake valve is changed as a function of an operating state of the internal combustion engine.

A particularly good adjustability of the high-pressure and gas exchange processes depending on a speed and a load of the internal combustion engine is achieved in that exhaust gas is discharged in an exhaust stroke from at least one working cylinder via at least one first exhaust valve, the at least one first exhaust valve having a predetermined third Valve lift curve is actuated, which is kept constant with respect to a time relation to the crank angle of the internal combustion engine, the exhaust gas being derived from at least one working cylinder additionally via at least one second exhaust valve with a fourth valve lift curve that is variable with respect to the crank angle of the internal combustion engine.

A simplified mechanical configuration of the adjustment of the gas exchange valves is achieved in that the second inlet valve and the second outlet valve are actuated jointly by a camshaft.

A further reduction in the fresh gas mass and an increase in the charge temperature with correspondingly improved ignition and combustion conditions due to hot residual gas being sucked back into the combustion chamber of the working cylinder is achieved in that the fourth valve lift curve of the second exhaust valve and/or a point in time for closing the exhaust valve in such a way is shifted relative to the crank angle so that the second exhaust valve remains open up to an intake stroke of a gas exchange stroke.

A further improvement in the combustion process through additional support for a swirling movement of the cylinder charge is achieved in that the cylinder charge is introduced via the second intake valve in such a way that the cylinder charge executes a swirling movement in the working cylinder.

• 1 eine schematische Darstellung einer ersten beispielhaften Ausführungsform einer Anordnung von Gaswechselventilen einer Hubkolben-Brennkraftmaschine zur Ausführung des erfindungsgemäßen Verfahrens,
• 2 eine schematische Darstellung einer zweiten beispielhaften Ausführungsform einer Anordnung von Gaswechselventilen einer Hubkolben-Brennkraftmaschine zur Ausführung des erfindungsgemäßen Verfahrens,
• 3 eine schematische Darstellung einer dritten beispielhaften Ausführungsform einer Anordnung von Gaswechselventilen einer Hubkolben-Brennkraftmaschine zur Ausführung des erfindungsgemäßen Verfahrens,
• 4 eine graphische Darstellung von Ventilhubkurven über einen Kurbelwinkel gemäß einer bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens und
• 5 eine graphische Darstellung der Drallzahl in Abhängigkeit von einem Kurbelwinkel bei einem bzgl. der Steuerzeiten zeitlich variablen Einlassventil mit Sitzdrallphase für verschiedene Phasenverschiebungen des zeitlich variabel angesteuerten Einlassventils.

The invention is explained in more detail below with reference to the drawings. These show in

• 1 a schematic representation of a first exemplary embodiment of an arrangement of gas exchange valves of a reciprocating internal combustion engine for carrying out the method according to the invention,
• 2 a schematic representation of a second exemplary embodiment of an arrangement of gas exchange valves of a reciprocating internal combustion engine for carrying out the method according to the invention,
• 3 a schematic representation of a third exemplary embodiment of an arrangement of gas exchange valves of a reciprocating internal combustion engine for carrying out the method according to the invention,
• 4 a graphical representation of valve lift curves over a crank angle according to a preferred embodiment of the method according to the invention and
• 5 a graphical representation of the swirl number as a function of a crank angle in an intake valve that is variable in terms of control times with a seat swirl phase for different phase shifts of the intake valve that is controlled in a variable manner in terms of time.

the 1 until 3 each schematically show a working cylinder 10 with a first inlet valve 12, a second inlet valve 14, a first outlet valve 16 and a second outlet valve 18. The inlet valves 12, 14 are fluid-conductively connected to an inlet port 14 and the outlet valves 16, 18 are connected to an outlet port 17 . One intake cam (not shown) and one exhaust cam (not shown) are arranged on a common camshaft (not shown), so that, for example, the first exhaust valve 16 and the first intake valve 12 are controlled by a first camshaft and the second exhaust valve 18 and the second intake valve 14 operated by a second camshaft. For this purpose, the gas exchange valves 12, 14, 16 and 18 are arranged in a star shape as a so-called “valve star”. So that one inlet valve and one outlet valve are arranged one behind the other for actuation by a common camshaft, the valve star is rotated with respect to a parallel 20 to a longitudinal axis of the camshaft. 1 shows a valve star 90°, ie a valve star rotated by 90° relative to the parallel 20, 2 shows a valve star 60° and 3 shows a valve star 120°.

Fresh air is supplied to the working cylinder 10 via the first inlet valve 12 during an intake stroke in such a way that a twisting movement of the fresh air in the working cylinder 10 results. During a twisting movement, the fresh air, cylinder charge or combustion air introduced into the working cylinder 10 via the intake port 13 with at least one intake valve 12 rotates about an axis parallel to a longitudinal axis of the working cylinder 10. This would be in 1 until 3 aligned perpendicular to the plane of the drawing. The first camshaft, each of which is the first one Actuated outlet valve 12 and the first outlet valve 16 of a working cylinder 10 is fixed with respect to the crank angle of a crankshaft of the internal combustion engine, ie not adjustable. The second camshaft, which actuates the second intake valve 14 and the second exhaust valve 18 of a working cylinder, is provided with a camshaft adjuster so that this second camshaft can be adjusted relative to the crank angle or relative to the first camshaft. As a result, an otherwise constant, respective valve lift curve for second intake valve 14 and second exhaust valve 18 can be shifted in time relative to the crank angle.

4 illustrates the valve lift curves for the gas exchange valves 12, 14, 16 and 18 as a function of a crank angle. The crank angle in °KW is plotted on a horizontal axis 22 and a stroke in mm is plotted on a vertical axis 24 . A crank angle of 0°CA corresponds to a "top dead center" (TDC) of the reciprocating piston in the gas exchange stroke between an exhaust stroke and an intake stroke. A first valve lift curve of the first intake valve 12 as a function of the crank angle 22 is denoted by 26 . A family of second valve lift curves of the second intake valve 14 as a function of the crank angle 22 is denoted by 28 . A third valve lift curve of the first exhaust valve 16 as a function of the crank angle 22 is denoted by 30 . A family of fourth valve lift curves of the second exhaust valve 18 as a function of the crank angle 22 is denoted by 32 .

How immediate 4 As can be seen, the second and fourth valve lift curves 28, 32 can be adjusted in terms of time with respect to the crank angle 22 by means of the camshaft adjuster on the second camshaft, as indicated by arrows 34 and 36.

According to the invention, it is provided that in engines or internal combustion engines with at least two intake valves 12, 14 (EV), one is controlled in a phase-shiftable manner. In the present case, this is the second inlet valve 14. In this way, a reduction in the charge can be achieved in adjustment ranges up to a maximum of 120° crank angle by the previously sucked-in charge being partially pushed out in the compression stroke. It is essential that at least a first EV 12 in the timing sequence of opening and closing is not shifted relative to the crank angle, so that under-expansion in the intake stroke is avoided. Overall, a reduction in the air mass is achieved without increasing gas exchange losses. For this purpose, the first and third valve lift curves 26, 30 are kept constant with respect to a time relation to the crank angle of the internal combustion engine.

The expression "valve lift curve, which is kept constant with respect to a time relation to a crank angle of the internal combustion engine" for a gas exchange valve, in particular an intake valve or an exhaust valve, means here that a respective crank angle for the time "gas exchange valve opens" and the time "gas exchange valve closes” and a maximum opening stroke and the crank angle for the point in time of the maximum opening stroke of the gas exchange valve is kept constant.

In engines or internal combustion engines with at least two exhaust valves 16, 18 (AV), one is designed to be shiftable in phase. In the example shown, this is the second exhaust valve 18. The basic control times of this AV 18 are designed in such a way that the event "exhaust valve opens" (AO) is specifically influenced. The aim is to be able to set the optimum in relation to the high-pressure and gas exchange process via variable speed and load: the later AÖ, the better the expansion is used. However, if AÖ is too late, the losses in the form of ejection work increase. The fixed exhaust profile (constant third valve lift curve of the first exhaust valve 16) prevents unintentional residual gas retention, which would otherwise result when the second exhaust valve 18 is "phased". The term "phasing of the gas exchange valve" refers here to the time shift of the valve lift curve 28 or 32 of the respective gas exchange valve 14, 18 relative to the crank angle.

In a preferred embodiment of the invention, the variable intake cam, which actuates the second intake valve 14, and the variable exhaust cam, which actuates the second exhaust valve 18, are arranged on a common, "mixed" camshaft, namely the second camshaft with the phaser. Correspondingly, both gas exchange valves 14, 18 are also jointly actuated synchronously by one phase adjuster.

A preferred valve angle (relative to a cylinder axis, not shown) is in the range of <10° and is advantageous with regard to the inflow/outflow in the case of channels 13, 17 lying one behind the other. Vertical valves are particularly advantageous. For example, the cylinder head of a diesel engine is used.

For example, the charge movement (swirl) is increased in a targeted manner by the phasing 34 of the second intake valve 14. In combination with the low-throttle reduction in the air mass, as described above, this is an essential aspect for increasing the efficiency of gasoline engines at low and medium loads. In this coupling of an outlet event with an intake event (mixed second camshaft with phase adjuster), the corresponding exhaust event is designed in such a way that the exhaust closing (AS) in the basic position is so early that a “normal” AS is achieved with the maximum adjustment range. this is in 4 indicated by the broken fourth valve lift curves 32 .

Alternatively or additionally, the adjustment range for the second intake valve 14 (second valve lift curves 28) and the second exhaust valve 18 (fourth valve lift curves 32) is increased, which leads to an overlap of the exhaust event in the intake stroke. This results in a region 38 of valve overlap and in this additional part of the adjustment region, hot residual gas is sucked back into the combustion chamber. This achieves a further reduction in the fresh gas mass and an increase in the charge temperature, thereby improving the ignition and combustion conditions. A disadvantage is the risk of valve-piston collision. To avoid this, at least one corresponding valve pocket for this one second outlet valve 18 is introduced into the reciprocating piston. The depth of the valve pocket in connection with the design of the trailing edge of the variable exhaust cam is minimized.

Alternatively, the forced coupling between exhaust and intake variability according to arrows 34, 36 (mixed camshaft with phase adjuster) is eliminated and replaced by one or two cam-in-cam variable camshafts. As a result, the second valve cam 28 and the fourth valve cam 32 can be adjusted independently of one another relative to the crank angle 22 .

Optionally, fresh air is also supplied via the second inlet valve 14 to the working cylinder 10 during an intake stroke in such a way that a twisting movement of the fresh air in the working cylinder 10 results. For this purpose, a seat twist phase is formed in the area of the second intake valve 14 . As a result, the fresh air or combustion air flowing in via the second inlet valve is also imparted with a twisting motion, which supports the overall twisting motion of the cylinder charge. The effect of this additional swirl support by the second intake valve 14 is in 5 illustrated. In 5 a crank angle in °CA is plotted on a horizontal axis 40, a swirl number [dimensionless] on a vertical axis 42, and a lift of the second intake valve 14 on a further vertical axis 44. Graphs 46 illustrate second intake valve lift versus crank angle 40.

A first graph 48 illustrates the course of the swirl number 42 over the crank angle when the second inlet valve 14 is opened at a crank angle of 10° CA, i.e. at a 0° phase shift. The first graph 48 is shown with circular support points. An arrow 50 illustrates the point in time at which the second intake valve 14 opens.

A second graph 52 illustrates the course of the swirl number 42 over the crank angle when the second inlet valve 14 is opened at a crank angle of 40° CA, i.e. at a 30° phase shift. The second graph 52 is shown with a dashed line. An arrow 54 illustrates the point in time at which the second intake valve 14 opens.

A third graph 56 illustrates the course of the swirl number 42 over the crank angle when the second inlet valve 14 is opened at a crank angle of 60° CA, i.e. at a 50° phase shift. The third graph 56 is shown with square interpolation points. An arrow 58 illustrates the point in time at which the second intake valve 14 opens.

How out 5 is immediately apparent, with increasing phase shift for the opening time of the second intake valve 14, the swirl of the cylinder charge is increasingly supported and the combustion process is improved as a result.

Reference List

10

working cylinder

12

first intake valve

13

inlet channel

14

second intake valve

16

first exhaust valve

17

exhaust port

18

second exhaust valve

20

Longitudinal axis of the camshaft

22

horizontal axis: crank angle in °CA

24

vertical axis: stroke in mm

26

first valve lift curve of the first intake valve 12 as a function of the crank angle 22

28

second valve lift curve of the second intake valve 14 as a function of the crank angle 22

30

third valve lift curve of the first exhaust valve 16 as a function of the crank angle 22

32

fourth valve lift curve of the second exhaust valve 18 as a function of the crank angle 22

34

Arrows: adjustment of the second valve lift curve of the second intake valve 14

36

Arrows: adjustment of the fourth valve lift curve of the second exhaust valve 18

38

Area of valve overlap

40

horizontal axis: crank angle in °CA

42

vertical axis: twist number [dimensionless]

44

vertical axis: lift of the second intake valve 14

46

Graph: Lift of the second intake valve 14 as a function of KW

48

first graph: progression of the swirl number 42 over the crank angle at 0° phase shift

50

arrow

52

second graph: progression of the swirl number 42 over the crank angle with a 30° phase shift

54

arrow

56

Third graph: course of the twist number 42 over the crank angle with a 50° phase shift

58

arrow

Claims (8)

Method for operating a reciprocating internal combustion engine, wherein combustion air is introduced into at least one working cylinder via at least one first intake valve in an intake stroke, wherein the at least one first intake valve is actuated with a predetermined first valve lift curve, which is constant in relation to a time relation to a crank angle of the internal combustion engine is maintained, the cylinder charge being introduced via the first intake valve in such a way that the cylinder charge in the working cylinder executes a twisting motion, characterized in that the cylinder charge in the at least one working cylinder is additionally fed into the at least one working cylinder via at least one second intake valve with variable phasing with respect to the crank angle of the internal combustion engine second valve lift curve is initiated. procedure after claim 1 , characterized in that the second valve lift curve of the second intake valve is kept constant as a function of an operating state of the internal combustion engine, with the exception of the time relation to the crank angle. procedure after claim 1 , characterized in that a point in time for opening the second intake valve, a point in time for closing the second intake valve and/or a point in time for a maximum opening stroke of the second intake valve is changed relative to the crank angle as a function of an operating state of the internal combustion engine. procedure after claim 1 or 3 , characterized in that a maximum opening lift of the second intake valve is changed depending on an operating state of the internal combustion engine. Method according to at least one of the preceding claims, characterized in that exhaust gas is discharged in an exhaust stroke from the at least one working cylinder via at least one first exhaust valve, the at least one first exhaust valve being actuated with a predetermined third valve lift curve which, in relation to a time relation to the Crank angle of the internal combustion engine is kept constant, the exhaust gas being derived from at least one working cylinder in addition via at least one second exhaust valve with respect to the crank angle of the internal combustion engine variable fourth valve lift curve. procedure after claim 5 , characterized in that the second intake valve and the second exhaust valve are actuated jointly by a camshaft. procedure after claim 5 or 6 , characterized in that the fourth valve lift curve of the second exhaust valve and/or a point in time for closing the exhaust valve is shifted relative to the crank angle in such a way that the second exhaust valve remains open up to an intake stroke of a gas exchange stroke. Method according to at least one of the preceding claims, characterized in that the cylinder charge is introduced via the second inlet valve in such a way that the cylinder charge executes a twisting movement in the working cylinder.

Images