WO2008015119A1

WO2008015119A1 - Method for operating an internal combustion engine with variable valve mechanism

Info

Publication number: WO2008015119A1
Application number: PCT/EP2007/057569
Authority: WO
Inventors: Christian Trapp
Original assignee: Robert Bosch Gmbh
Priority date: 2006-08-03
Filing date: 2007-07-23
Publication date: 2008-02-07
Also published as: DE102006036219A1

Abstract

Method for operating an internal combustion engine with variable valve mechanism for actuating gas exchange valves (EV1, EV2, AV1, AV2) and an injection of fuel into a combustion chamber (2) and/or an induction pipe (5). In an induction stroke (ANS), the gas exchange valves (EV1, EV2, AV1, AV2) are opened in such a way as to form a stratified charge in the combustion chamber (2), with substantially exhaust gas being present in a lower part of the combustion chamber and an ignitable mixture being present in an upper part.

Description

description

title

Method for operating an internal combustion engine with variable valve train

State of the art

The present invention relates to a method for operating an internal combustion engine with a variable valve train.

Direct injection of fuel into a cylinder allows charge stratification so that only a portion of the combustion chamber in the vicinity of the spark plug contains a combustible mixture having a local air ratio of between 0.8 and 1.3, ideally surrounded by fuel-free air. The load control takes place via the injected fuel quantity, the throttle valve is ideally fully open, the charge exchange losses occurring in a conventional gasoline engine in partial load operation can thereby be drastically reduced. However, the global air ratio of significantly greater than 1 does not allow conversion of the resulting nitrogen oxides in a conventional 3-way catalyst. In order to be able to comply with current and future limits of global emissions legislation (eg Euro 4, Euro 5 in Europe, Ulev, Sulev in the NAFTA market), either a NO _x storage catalytic converter with the associated consumption disadvantages (periodic regeneration by operation with substoichiometric, that is rich mixture) and a much higher application cost or a system with urea or Ammoniakeindüsung for the reduction of nitrogen oxides with a likewise much higher application costs and additional supplies are used. In order to reduce the effort required for this purpose, the nitrogen oxide emissions resulting from the combustion must be reduced. By recirculating exhaust gas into the combustion chamber, the critical temperature level during nitrogen oxide formation can be lowered during the combustion phase. The disadvantage here is the carryover of the combustion The dilution of the mixture, at high exhaust gas recirculation rates leads to partial burns and dropouts associated with high turbulence and significantly increased hydrocarbon emissions.

Fully variable valve trains offer a different approach for reducing the fuel consumption disadvantages of gasoline engines: The cylinder filling required for one operating point is measured by the valve duration, the throttle valve is fully open. The air ratio of 1 allows conversion of all raw emissions (hydrocarbons, nitrogen oxides and carbon monoxide) in a conventional 3-way catalytic converter. Nevertheless, even with an early closing of the intake valves

(FES) a return of exhaust gas advantageous, the charge cycle can be further reduced: internally recirculated exhaust gas increases the cylinder filling and thus reduces the decisive for the throttle losses through the valves pressure difference between the intake manifold and the combustion chamber. At the same time, for a constant flow of fresh air through reduced flow, the inlet valves must be closed later, the

Charge change losses continue to decrease.

Disclosure of the invention

An object of the present invention is to further reduce charge cycle losses as well as nitrogen oxide emissions. Another object of the invention is to allow conversion of NO _x emissions by a conventional 3-way catalyst.

This object is achieved by a method for operating an internal combustion engine with a variable valve train for actuating gas exchange valves and an injection of fuel into a combustion chamber and / or a suction tube, wherein the gas exchange valves are opened in an intake stroke so that a layer charge is formed in the combustion chamber, wherein in a lower part of the combustion chamber substantially exhaust gas and in an upper part is an ignitable mixture. The gas exchange valves are the inlet valve (s) and the outlet valve (s). The variable valve train can be a partially variable valve train with an adjustable camshaft or a fully variable valve train eg with an electrohydraulic valve control. The ignitable mixture is preferably a fresh air / fuel mixture. The fuel can be injected during the intake stroke into the fresh air (both intake manifold and direct injection) or injected in the compression stroke (direct injection).

It is preferably provided that in the upper part of the combustion chamber, a lambda value of about 1, more preferably from about 0.8 to about 1.3, is present. If there is a global lambda value of about one, the resulting nitrogen oxide emissions can be converted by a conventional 3-way catalytic converter.

It is preferably provided that at least one outlet valve is first opened during the intake stroke and is closed again after a certain opening period, then at least one inlet valve is opened and closed again after reaching a certain cylinder charge.

In an internal combustion engine having two exhaust valves, both exhaust valves are preferably opened and closed at the same time. It is preferably provided that a force injection during the opening phase of the intake valve or valves is performed in the intake stroke.

The problem mentioned at the outset is also solved by an internal combustion engine with a variable valve train for actuating gas exchange valves and an injection of fuel into a combustion chamber and / or a suction tube, wherein the gas exchange valves are opened in an intake stroke so that a layer charge is created in the combustion chamber , wherein in a lower part of the combustion chamber substantially exhaust gas and in an upper part is an ignitable mixture. It is preferably provided that the internal combustion engine comprises a partially variable or fully variable valve train.

The problem mentioned above is also solved by a computer program

Program code for performing all the steps according to a method of the invention when the program is executed in a computer. By subdividing the combustion chamber of a gasoline engine into a zone of recirculated exhaust gas or residual gas without fuel and a fresh air zone into which the corresponding air ratio of 1 fuel is injected, the charge exchange losses similar to a conventional stratified charge or early closing of the intake valve in an engine drastically reduce with fully variable valve train.

The advantage compared to a conventional stratified charge with an air ratio significantly greater than 1 lies in the exhaust gas composition. The so-called exhaust gas stratification with a global air ratio of 1 enables the conversion of nitrogen oxide raw emissions during combustion into a 3-way catalytic converter, a complex after-treatment NO _x storage catalytic converter or urea injection is not necessary.

The stratification prevents mixing of the exhaust gas with the fresh mixture and prevents dilution of the fuel-rich charge in the vicinity of the spark plug. As a result, the burning rate remains high, there is no carryover of the combustion to thermodynamically unfavorable long burning times.

At the same time increases the compatibility for recirculated exhaust gas or residual gas through the exhaust stratification, the possible higher cylinder mass lowers the temperature level in the combustion chamber and thus leads to reduced nitrogen oxide emissions and reduced wall heat losses.

The avoidance of the mixing of exhaust gas and fresh air fuel mixture in the method according to the invention leads to a thermodynamically more favorable combustion, the higher compatibility of recirculated exhaust gas or residual gas in turn allows a higher cylinder mass with lowered temperature level in the combustion chamber and thus leads to reduced nitrogen oxide raw emissions and reduced Wandwärmever lusten ,

In addition, the inlet valve can be compared to the previous procedure in a strategy with an early inlet closure, even with respect to a variant with led exhaust, still closed much later and so the charge exchange losses are lowered again.

Brief description of the drawings

Hereinafter, an embodiment of the present invention will be explained in more detail with reference to the accompanying drawings. Showing:

Fig. 1 is a sketch of a cylinder of an internal combustion engine;

FIG. 2 shows a section according to I-I in FIG. 1; FIG.

3 is a diagram of the valve lift of the intake valves;

4 shows a sketch of the intake stroke with an opened exhaust valve;

5 shows a sketch of the intake stroke with two intake valves open;

Fig. 6 is a sketch of the intake stroke with an open inlet valve.

Embodiment (s) of the invention

The technological environment of the invention will first be described with reference to FIGS. 1 and 2. In FIG. 1, a cylinder 1 of an otherwise not shown internal combustion engine, which as a rule consists of a plurality of cylinders, is shown in section as a schematic diagram, in FIG. 2 a section according to II in FIG. 1 is shown. The cylinder 1 comprises a combustion chamber 2, in which a piston 3 with a connecting rod 4 is arranged displaceably. The connecting rod 4 is connected to a crankshaft, not shown. Into the combustion chamber 2 opens a suction pipe 5 with two inlet valves EVI and EV2, of which in Fig. 1, only the inlet valve EVI is shown. Instead of two inlet valves EVI and EV2, only one inlet valve EV can be provided here. Furthermore, opens into the combustion chamber 2, an outlet 7 with two exhaust valves AVL and AV2, of which in Fig. 1, only the exhaust valve AVI is shown. Instead of two exhaust valves AVL and AV2, only one exhaust valve AV can be provided here. Both the intake valves EVI, EV2 and the exhaust valves AV1, AV2 are actuated by electro-hydraulics, so the internal combustion engine is equipped with a so-called electrohydraulic valve control (EHVS). An electrohydraulic valve control allows control of the valves independently of the crankshaft position. Air is sucked from the environment into the combustion chamber 2 via the intake manifold 5. The combustion exhaust gases are discharged via the outlet 7 back to the environment. By means of a suitable opening time of the exhaust valves AV1, AV2, eg opening of the exhaust valves AV1, AV2 during the intake stroke of the internal combustion engine, a so-called internal exhaust gas recirculation can be realized, in that exhaust gas from the outlet 7 flows back into the combustion chamber or is sucked back ,

A spark plug 11 and an injector 12 open into the combustion chamber in a known manner. The injector 12 is preferably a piezoelectric injector or a magnetic injector. The injector 12 is connected via a high-pressure line 10 to a high-pressure rail of the internal combustion engine, not shown. The high-pressure line 10 leads fuel to the injector 12. The injector 12 is electrically controlled by a control unit 9, accordingly, the control unit 9, the spark plug 11 and the intake valves EV 1, EV2 and the exhaust valve 2 AVL, AV2 controlled. In the suction pipe 5, a throttle valve 8 is arranged.

For electrohydraulic, camshaftless valve controls (EHVS), as e.g. From DE 10127205 and DE 10134644 are known, stroke and timing of the gas exchange valves of an internal combustion engine can be freely programmed in principle. The gas exchange valves are the inlet valve (s) EV and the one or more

Exhaust valve (s) AV.

In a first operating mode, the homogeneous operation of the internal combustion engine, the throttle valve 8 is partially opened or closed depending on the desired air mass to be supplied. The fuel is injected from the injector 12 (injector) into the combustion chamber 2 during an intake stroke caused by the piston 3. By simultaneously sucked air, the injected fuel is swirled and thus distributed in the combustion chamber 2 substantially uniform / homogeneous. Thereafter, the fuel air mixture during the compression stroke, in is reduced by the piston 3, the volume of the combustion chamber 2, compressed, in order to then be ignited shortly before reaching the top dead center, the piston 3 of the spark plug 11.

In a second mode, the stratified operation of the internal combustion engine, the

Throttle valve 8 wide open. The fuel is injected from the injector 12 into the combustion chamber 2 during the compression stroke VER produced by the piston 2. Then, as before, with the aid of the spark plug 11, the fuel is ignited, so that the piston 3 is driven in the working phase EN now taking place by the expansion of the ignited fuel. Another possible operating mode is the homogeneous lean operation, in which fuel is injected into the combustion chamber 2 as in homogeneous operation during the intake phase.

Fig. 3 shows a diagram of the valve lift of the intake valves EVI, EV2 and the exhaust valves AVL, AV2 over the crankshaft angle ( ⁰ KW). Valve openings are each shown as ascending lines, the valve closing correspondingly as descending lines and an open valve as a straight line above a solid line, which represents the closed valve respectively. In addition, in the diagram injections are shown as lines or dash-dotted lines, which are identified by the reference symbol E, above the opening course of the injection valves and the ignition Z by means of the spark plug. The individual work cycles are marked with AN for the intake stroke, VER for the compression stroke, ENT for the power stroke, and OFF for deployment. In addition, the ignition top dead center is marked ZOT at 360 degrees crankshaft. As can be seen from FIG. 3, the outlet valve AV 1 becomes between about 10 during the intake phase

Degree crankshaft angle and 100 degrees crankshaft angle open, then either only one of the intake valves, here the intake valve EVI, or both intake valves, ie the intake valves EVI and EV2, opened. By opening an exhaust valve during the intake phase, exhaust gas from the exhaust port or manifold is drawn back into the combustion chamber (swirl) back into the combustion chamber and travels over the piston and along the lower cylinder walls, as shown schematically in FIG. After closing the exhaust valve, either one intake valve or both intake valves are opened quickly during the intake phase. As a result, fresh air with the lowest possible axial velocity in the cylinder sucked, this is shown in Fig. 5 for the opening of both intake valves. The valve opening periods and times are adjusted so that the upper part of the combustion chamber is filled in the spark plug near the fresh air required for the load to be reached at an air lambda value (air ratio) of 1, but the rest of the combustion chamber is filled with exhaust gas. Thus, there is a stratification in the combustion chamber, in which a region F is filled with fresh air and a region A is filled with exhaust gas. The fuel is injected into the fresh air either synchronously with the opening of the intake valves EVI, EV2 or after closing the intake valves EVI, EV2 with pressures corresponding to a conventional stratified charge.

If only one inlet valve is opened during the intake phase, as shown in FIG. 6, the fresh air is drawn in with an increased charge movement (swirl). This leads to a significant increase in the burning rate and thus to a thermodynamically more favorable combustion, but also to a greater instability of the stratification.

After combustion, all the exhaust valves are opened as in previous combustion processes for gasoline engines to push out the exhaust gas.

The method described above can be realized very simply by changing the software of a control unit in gasoline engines with fully variable valve train and gasoline direct injection. A change of the hardware is not necessary. In engines with a conventional cam drive, changes to the cam contour and camshaft adjuster for partially variable valve control are necessary for the combustion method described above. The inventive method is also suitable for increasing the compatibility of recirculated exhaust gas in gasoline engines with direct gasoline injection, which use a beam-guided combustion process for a stratified charge operation. As a matter of principle, this is carried out with the least possible charge movement and therefore allows only low exhaust gas recirculation rates.

Claims

claims

1. A method for operating an internal combustion engine with variable valve train for actuating gas exchange valves (EVI, EV2, AVI, AV2) and an injection of fuel into a combustion chamber (2) and / or a suction tube (5), characterized in that the Gas exchange valves (EVI, EV2, AVl, AV2) in one intake stroke

(ANS) are opened so that a layer charge in the combustion chamber (2) is formed, wherein in a lower part of the combustion chamber is substantially exhaust gas and in an upper part is an ignitable mixture.

2. The method according to claim 1, characterized in that the ignitable mixture is a fresh air / fuel mixture.

3. The method according to any one of claims 1 or 2, characterized in that in the upper part of the combustion chamber (2) has a lambda value of about 1 is present.

4. The method according to claim 3, characterized in that the lambda value in the range of about 0.8 to about 1.3.

5. The method according to any one of the present claims, characterized in that during the intake stroke (ANS) at least one exhaust valve (AVL,

AV2) is opened and after a certain opening period is closed again, then at least one inlet valve (EVI, EV2) is opened and closed again after reaching a certain cylinder charge.

6. The method according to claim 5, characterized in that in an internal combustion engine with two exhaust valves both exhaust valves (AVL, AV2) are opened and closed at the same time.

7. The method according to any preceding claim, characterized in that a fuel injection during the opening phase of the intake valve or valves (EVI, EV2) in the intake stroke (ANS) is made.

8. internal combustion engine with variable valve train for actuating gas exchange valves (EVI, EV2, AVI, AV2) and an injection of fuel into a combustion chamber (2) and / or a suction tube (5), characterized in that the gas exchange valves (EVI, EV2, AVl, AV2) in an intake stroke (ANS) are opened so that a layer charge in the combustion chamber (2) is formed, wherein in a lower part of the combustion chamber (2) is substantially exhaust gas and in an upper part an ignitable mixture.

9. Internal combustion engine according to claim 8, characterized in that the internal combustion engine comprises a partially variable or fully variable valve train.

A computer program with program code for performing all steps according to any one of claims 1 to 7, when the program is executed in a computer.