EP1521911A1

EP1521911A1 - Method for operating an internal combustion engine

Info

Publication number: EP1521911A1
Application number: EP03763682A
Authority: EP
Inventors: Lothar Herrmann; Oliver Steil
Original assignee: DaimlerChrysler AG
Current assignee: Daimler AG
Priority date: 2002-07-11
Filing date: 2003-07-01
Publication date: 2005-04-13
Also published as: DE10231582A1; US20050224041A1; JP2005532504A; JP4260741B2; WO2004007944A1; US7047946B2

Abstract

The invention relates to a method for forming a fuel/air mixture of a direct-injection internal combustion engine. According to said method, a closing body of the fuel injection nozzle is displaced from a closed position into an operating position in order to adjust an operating stroke by means of a control unit, in such a way that different speeds are realised until the operating stroke is achieved, to permit optimal combustion. The inventive method also permits a uniform concentration of fuel particles that have been introduced into the combustion chamber with an increased impetus, thus creating a border turbulence with a constant symmetry and a uniform fuel distribution.

Description

DaimlerChrysler AG

Method for operating an internal combustion engine

The invention relates to a method for operating an internal combustion engine with direct injection, in particular a spark-ignited internal combustion engine with direct injection, with the features of the preamble of claim 1.

When operating new internal combustion engines with direct injection, improvements in mixture formation are achieved by designing the course of the injection in both the self-igniting and the spark-ignited internal combustion engines. An attempt is made to exert a targeted influence on the combustion and on the formation of emissions by varying the course of the injection.

From the patent DE 198 57 785 C2 a method for mixture formation in a combustion chamber of an internal combustion engine is known, in which a three-stage fuel injection is carried out, in which a main fuel quantity is connected to an ignition fuel quantity via an additional fuel quantity without an interruption in injection. The times of the beginning and end of the injections of the main fuel amount and the additional ignition fuel amount can be chosen flexibly by the additional fuel amount that is injected between the main fuel injection and the ignition fuel injection.

A method for operating a diesel engine is known from DE 100 40 117 A1, in which an especially fast cross-sectional release of an injector valve attempts to achieve a good homogenization of the fuel / air mixture. aim. In this method, the injector valve is suddenly opened to improve the homogenization of the fuel / air mixture by means of a sharp injection course.

Furthermore, from DE 100 12 970 AI a method for forming an ignitable fuel-air mixture is known, in which the fuel is introduced into the combustion chamber of the internal combustion engine in at least two partial quantities, the closure body of an injection nozzle being able to be brought into its closed position after the injection process of a partial quantity. The fuel jet is accelerated up to the outlet by the nozzle opening continuously tapering towards the outlet with a curved or parabolic outlet cross section.

From DE 19636088 a method for controlling the direct injection of fuel into the combustion chamber of an internal combustion engine is known, with which different fuel control cross-sections can be achieved by means of a stroke-dependent actuatable actuator, so that the control cross-section of a control valve in the case of sequential valve positions between the beginning and the End of the injection process always remains above a minimum value that differs from the closed position.

The document DE 19642653 C1 discloses a method for forming a mixture of an internal combustion engine with direct injection, with which an opening stroke of a valve member relative to a valve seat of an injector and the injection time can be variably adjusted during fuel injection, thereby making it possible to influence an injection angle and also the fuel mass flow dynamically. Since different fuel sprays are produced in the injection nozzles due to production, which often lead to misfires due to different mixture formations, hardly any feasible improvements to the respective geometry of the injection nozzle would have to be made before installation in an internal combustion engine.

In contrast, the object of the invention is to design the injection behavior of an injection nozzle in such a way that an optimal injection behavior and accordingly an improved combustion can be achieved despite manufacturing tolerances.

This object is achieved according to the invention by a method with the features of claim 1.

The inventive method is characterized by the formation of an ignitable fuel / air mixture in a combustion chamber of a direct injection internal combustion engine with an injection nozzle having a closure body, in which an operating stroke and a fuel injection time can be variably adjusted. The closure body of the injection nozzle is moved from a closed position to an operating position for setting an operating stroke by means of a control device such that the closure body is moved between the closed position and the operating position with a varying acceleration during a fuel injection process in such a way that up to the setting of the Operating speeds different speeds can be set.

The opening behavior of the injection nozzle is designed in such a way that an increase in the momentum of the injected fuel drops occurs when exiting the injection nozzle and the fuel drop decays after the fuel exits is reinforced from the outlet cross section of the injection nozzle. The closure body of the injection nozzle is preferably brought into an operating position in such a way that a required duration between two operating positions, the closed state also representing an operating position, being less than 200 μsec.

In an embodiment of the invention, the closure body is opened in such a way that the closure body is moved at a high and constant speed up to the operating position, which remains below the level of a maximum achievable speed. Due to the sudden opening and the rapid adjustment of the operating position of the closure body, the fuel flows from the injection nozzle into the combustion chamber with a higher momentum, which results in an increased atomization of the fuel droplets. This allows manufacturing tolerances to be compensated, i.e. The flow behavior of the fuel from the injection nozzle is hardly influenced by the manufacturing errors that occur.

In a further embodiment of the invention, the opening of the injection nozzle is designed in such a way that when the closure body is moved to an operating position, it is first moved at a reduced speed and then with a continuous increase in speed to a maximum value when the operating position is reached. This also increases the atomization properties, which improves the properties of engine combustion, in particular consumption and emissions. Furthermore, the symmetry in the generated spray pattern of the injected fuel is improved and further fluctuations in the spray pattern due to production are compensated for. In a further embodiment of the invention, the opening of the injection nozzle is designed such that the closure body of the injection nozzle is first moved at a reduced speed and then at an increasing speed up to a maximum value when approaching an operating position, the closure body being reached shortly before the operating position is reached is moving at a slowing speed.

According to a further embodiment of the invention, the opening of the injection nozzle is designed in such a way that the closure body of the injection nozzle is moved at an increased constant speed to an intermediate position which corresponds to a stroke which is greater than the operating stroke. If the intermediate position is reached, the closure body is returned to the operating position immediately or after a certain holding time. Alternatively, the closure body can be moved to the intermediate position according to a previous embodiment of the invention, the closure body generally being able to be moved according to a combination of the proposed embodiments.

According to a further embodiment of the invention, the opening of the injection nozzle is designed such that the closure body of the injection nozzle is moved up to an operating position A at an increased and constant speed. If the position A is reached, the closure body is moved after a certain holding time T _AH at an increased and constant speed up to an operating position B, which corresponds to a stroke which is greater than the stroke of the operating position A. If the position B is reached, the closure body is moved into the closed position immediately or after a certain holding time T _BH at an increased and constant speed. In particular, the method according to the invention is suitable for use in direct-injection gasoline engines in which a well-prepared mixture must be present in the area of the spark plug within a very short time, the method according to the invention being suitable for both spark-ignited and self-igniting internal combustion engines with direct injection. Accordingly, the manufacturing-related deviations of the injection jet are compensated for, which has a positive influence on the spray pattern according to the invention. As a result, a uniform distribution of the fuel is achieved in all areas of the injected fuel jet. This leads to the maintenance of a required symmetry of an injected fuel jet in all working cycles, whereby a minimization or elimination of undesired tipping phenomena is realized.

In a further embodiment, the method according to the invention is used particularly in the case of injectors opening outwards, in which the fuel is injected as a hollow cone. Such injection nozzles are preferably used in spark-ignited internal combustion engines in which there is a jet-guided combustion process. In such internal combustion engines, the fuel is injected in such a way that a toroidal vortex is formed at the end of the hollow fuel cone, the electrodes of a spark plug arranged in the combustion chamber being arranged outside the injected hollow fuel cone, but within a fuel / air mixture formed in the form of the toroidal one Vertebrae lie. The method according to the invention maintains a necessary symmetry of the toroidal vertebra and prevents the toroidal vertebra from tilting. This improves the ignition of the fuel / air mixture and prevents the occurrence of misfires. Further characteristics and combinations of characteristics result from the description. Specific exemplary embodiments of the invention are shown in simplified form in the drawings and are explained in more detail in the description below. Show it:

1 is a sectional view of a cylinder of a direct injection spark ignition internal combustion engine,

2 shows a schematic diagram with a stroke curve of a closure body of a fuel injection nozzle of the internal combustion engine from FIG. 1 until an operating position is reached, plotted over time,

3 shows a schematic diagram with a stroke profile of a closure body of a fuel injection nozzle of the internal combustion engine from FIG. 1 until an operating position is reached plotted over time according to a second method example according to the invention,

4 shows a schematic diagram with a stroke profile of a closure body of a fuel injection nozzle of the internal combustion engine from FIG. 1 until an operating position is plotted against time according to a third example of the method according to the invention, and _s

FIG. 5 shows a schematic diagram with a stroke profile of a closure body of a fuel injection nozzle of the internal combustion engine from FIG. 1 until an operating position is plotted against time according to a fourth method example according to the invention.

Fig. 1 shows a cylinder 2 of a spark-ignition internal combustion engine 1 with direct injection, in which a combustion chamber 4 between a piston ^" 3 and a cylinder head 5. In the cylinder 2, the piston 3 is held in a longitudinally displaceable manner, the longitudinal mobility of the piston 3 being limited by an upper dead center and a lower dead center. The internal combustion engine 1 shown in FIG the four-stroke principle, the method according to the invention being equally suitable for both spark-ignited and self-igniting two-stroke internal combustion engines with direct injection. In the first stroke, combustion air is supplied to the combustion chamber 4 through an inlet duct 13, the piston 3 moving downwards to bottom dead center UT In the further compression stroke, the piston 3 moves in an upward movement from the bottom dead center to the top dead center OT, the fuel being injected during the stratified charge mode of the internal combustion engine 1 in the region of the top dead center OT by means of a spark plug 7 the fuel-air mixture is ignited, the piston 3 expanding in a downward movement to bottom dead center UT. In the last stroke, the piston 3 moves upwards to the top dead center TDC and pushes the exhaust gases out of the combustion chamber 4.

The internal combustion engine 1 according to the present exemplary embodiment is operated in such a way that the stratified charge mode is operated in the lower and middle speed and load ranges and the homogeneous mode is operated in the upper load range. In particular, there is a so-called beam-guided combustion process in stratified charge operation. The fuel is injected in stratified charge mode in the compression stroke, preferably in a crank angle range between 40 and 10 ° before TDC. The fuel is preferably injected into the combustion chamber 4 in two subsets. . In such a jet-guided combustion process, an outward-opening injection nozzle 11 is preferably used, with which a hollow fuel cone 8, preferably with an angle α between 70 ° and 100 °, is generated. Since the hollow fuel cone 8 meets combustion air compressed in the combustion chamber 4, a toroidal vortex 10 is formed in the combustion chamber 4 in such a way that an ignitable fuel / air mixture forms in the region of the electrodes 12 of the spark plug 7 _. is achieved. The spark plug 7 is arranged in such a way that the electrodes 12 of the spark plug 7 protrude into the vortex obtained, during the fuel injection they lie outside the lateral surface 9 of the fuel cone 8. As a result, the electrodes 12 of the spark plug 7 are not wetted with fuel. In order to achieve optimal combustion of the injected fuel, it is necessary to design a symmetrical and uniform toroidal vortex 10, that is, the toroidal vortex 10 obtained should have a uniform fuel distribution over the entire area, so that the vortex does not tilt, and furthermore when Mounting the fuel valve 6 a defined rotational position of the fuel valve 6 in the cylinder head 5 can be avoided.

FIG. 2 shows a schematic stroke profile of the closure body, not shown, of the injection nozzle 11 according to FIG. 1 over time T. The fuel is injected in such a way that the opening time T _B ι of the closure body of the injection nozzle 11 until an operating stroke H is set _{B is completed} over a period of approximately 100 μsec to 200 μsec. As a result of the rapid opening of the closure body at a high and constant speed, the fuel from the injection nozzle 11 is accelerated in such a way that the fuel droplets have a higher momentum when they enter the combustion chamber 4, thereby atomization and a quickxex mix with dex combustion air already present in the combustion chamber. The faster opening avoids an uneven fuel distribution in the fuel cone 8 caused by manufacturing tolerances. The aim is to achieve a symmetrical vortex 10 with a uniform fuel distribution without undesired tilting ¹ , i.e. a horizontal 15 through the vortex 10 formed should, as far as possible, be in a position perpendicular to the fuel valve axis 14 in all injection processes during the entire operating time of the internal combustion engine 1 are located. The formation of streaks at the end of the fuel cone 8 or the vortex 10 should also be avoided.

According to FIG. 3, a second example of the method is shown, in which the closure body of the injection nozzle 11 is opened in such a way that it is first started at a reduced or low speed, with a continuous increase in speed up to a maximum value when setting the Operating strokes H _{B is} made. When the closure body is slowly opened, first little fuel flows into the combustion chamber 4, which is braked by the existing counterpressure in the combustion chamber, and then is pulled into the combustion chamber 4 with a higher impulse by the fuel that shoots out further, so that better atomization and uniform distribution of the fuel in the cone 8 is achieved. This avoids that the vertebra 10 is formed asymmetrically and strands are formed in the lower region of the vertebra. Due to the uniform distribution of the fuel in the entire region of the toroidal vortex 10, the fuel particles are transported into the outer region of the vortex 10 in the direction of the electrodes 12 of the spark plug 7 and concentrated there. The already mixed vaporized fuel particles with the combustion air and form an ignitable fuel / air mixture.

4 shows a further exemplary embodiment of the invention, in which first the closure body of the injection nozzle 11 is slowly opened and, after a short time, is opened further at an increasing speed, the speed of the closure body decreasing shortly before the operating stroke H _{B is} reached. Similar to the previous exemplary embodiment, the fuel particles are brought into the combustion chamber 4 with a higher momentum and distributed evenly in the toroidal vortex 10.

5 shows a further exemplary embodiment in which the closure body is brought to an intermediate stroke position H _z at a high speed within a time T _z , the intermediate stroke position H _{z being} greater than the operating stroke H _B. If the intermediate stroke position H _{z is} reached, the closure body is moved back to the operating stroke within the duration T _B2 immediately or after a certain holding time T _ZH . During this opening process, the fuel particles are accelerated out of the injection nozzle in such a way that they are injected into the combustion chamber with a very high impulse. This results in better atomization and thus compensates for manufacturing tolerances. According to this exemplary embodiment, a higher speed is achieved when the injection nozzle is opened, which causes the fuel to decay more intensely.

Referring to FIG. 6, a further embodiment is illustrated, in which the closure body is engaged with ^'a high speed to a lift position _A within a time T H _A. If the stroke position H _{A is} reached, the closure body is opened after a certain holding time T _AH with an l <ώ

high and constant speed in a time T _B to an operating position B which corresponds to a stroke H _B which is greater than the stroke of the operating position A. If position B is reached, the closure body is moved into the closed position immediately or after a certain holding time T _BH at an increased and constant speed. With this course of opening, small drops are initially generated, which lead to the early formation of a toroidal vortex. The large stroke of operating position B generates droplets with great momentum, which enlarge and stabilize the toroidal vortex.

The process examples shown enable optimal combustion and a pronounced toroidal vortex formation is achieved. The fuel particles are concentrated in the edge region of the vortex 10 in such a way that there are more drops in the edge region. This creates a larger contact area with the combustion air. Furthermore, the formation of a vortex 10 with a constant symmetry and a uniform, uniform fuel distribution is achieved. Furthermore, the installation of fuel valves is made easier since a defined rotational position of the fuel valve 6 is not required. Another advantage is the compensation of manufacturing inaccuracies in the manufacture of fuel valves, which generally negatively affect the mixture formation in the direct-injection internal combustion engines.

In all of the process examples shown, the fuel is preferably injected into the combustion chamber in stratified charge mode at a combustion chamber back pressure of approximately 16 bar, which corresponds to a point in time of approximately 30 ° crank angle before TDC. This fuel injection is carried out in stratified charge mode, with the internal combustion engine operating in homogeneous mode 1 the fuel injection can be carried out in the intake stroke of the internal combustion engine. In the process examples shown above, the change in operating position of the closure body of the injection nozzle 11 is to be achieved in less than 200 μsec.

It is also advantageous that the injection pressure of the injector 11 is varied between 100 bar and 300 bar or between 150 bar and 250 bar, the fuel jet 8 emerging from the injector 11 being conical with a jet angle between 70 ° and 100 °.

The invention relates to a method for forming a fuel / air mixture of a direct-injection internal combustion engine, with which a closure body of the fuel injector is moved from a closed position to an operating position for setting an operating stroke by means of a control device such that until the operating stroke is set different speeds are set to allow an optimum combustion ^', and to allow a uniform concentration of the introduced with a higher pulse into the combustion chamber fuel particles in the edge area of the vortex at a torusformigen vortex formation, so that formation of a tip vortex with a constant symmetry and a even distribution of fuel is achieved.

Claims

claims

1. A method for forming an ignitable fuel / air mixture in a combustion chamber of a direct-injection internal combustion engine, in particular a spark-ignition internal combustion engine, with a fuel injection nozzle having a closure body, with which

the closure body of the fuel injection nozzle is moved from a closed position to an operating position by means of a control device, the operating stroke and the fuel injection duration being variably adjustable,

characterized ,

- That during a fuel injection process the closure body is moved between the closed position and the operating position with a varying acceleration in such a way that different speeds are set up to the setting of the predetermined operating stroke.

2. The method according to claim 1, characterized in that the closure body of the fuel injector is moved from the closed position to the operating position such that it moves at a slow speed when starting and then at a continuously increasing speed to a maximum value when reaching the Operating position is moved.

A method according to claim 1, characterized in that the closure body is moved from a closed position to an operating position such that it is moved at a slow speed when moving off and then moved to a maximum value at an increasing speed, whereby it moves forward reaching the operating position with a slower than the maximum set speed.

A method according to claim 1, characterized in that the closure body is moved from the closed position to the operating position in such a way that it is moved at a high and constant speed until reaching a stroke which is greater than the operating stroke, and then with a high and constant speed is returned to the operating position.

A method according to claim 1, so that the closing body is moved from the closed position to the operating position in such a way that it is moved at a high and constant speed until a stroke is reached. The closing body is then moved to an operating position with a higher stroke at a high and constant speed.

Method according to one of the preceding claims, characterized in that the fuel injection nozzle is designed as an outwardly opening injection nozzle, so that the fuel is injected from the fuel injection nozzle in the form of a hollow cone.

7. The method according to claim 6, since you rchgezeichen that at the end of the injected hollow fuel cone a toroidal fuel / Luftgemiseh vortex is formed such that the electrodes of a spark plug arranged outside a lateral surface of the injected hollow cone of the toroidal and ignitable fuel / air mixture -Vortices are included.

8. The method according to any one of the preceding claims, that the control device of the fuel injector is preferably driven piezoelectrically.

9. The method according to any one of the preceding claims, that the fuel injection takes place in homogeneous operation of the internal combustion engine in the intake stroke and / or in the compression stroke.

10. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the fuel injection takes place in the stratified charge mode of the internal combustion engine during the compression stroke.

11. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the fuel injection is carried out in a total amount or in at least two subsets.