DE102007039210A1 - Method for operating an internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine, in particular gasoline engine or diesel engine, in particular a motor vehicle, wherein the closing times of intake valves of working cylinders of the internal combustion engine are selected according to a Miller cycle and wherein a variable turbine geometry of an exhaust gas turbocharger for varying a compression capacity of the exhaust gas turbocharger is actuated , Here, at a speed n [rpm] of the internal combustion engine of 1000 rpm <= n <= 3000 rpm as a function of a load request, the closing times of the intake valves are selected according to the Miller cycle and the variable turbine geometry of the exhaust gas turbocharger set such that an effective engine load m <SUB> eff </ SUB> related to the maximum engine load is obtained according to $ F1.

Description

The The invention relates to a method for operating an internal combustion engine, in particular gasoline engine or diesel engine, in particular of a motor vehicle, the closing times of intake valves of working cylinders the internal combustion engine according to a Miller cycle be selected and where a variable turbine geometry an exhaust gas turbocharger for varying a compression capacity the exhaust gas turbocharger is actuated according to the Preamble of claim 1.

Of the Use of turbochargers with variable turbine geometry (VTG or VGT) also promises great potential for gasoline engines. When using the VTG technology, there are initially two Opportunities for improvement: on the one hand The low-end torque (LET) of the engine over a conventional ATL be significantly improved or used on the other hand, to the significant increase in performance a conventional ATL has a larger VTG ATL, the engine thanks to the VTG technology over a comparable LET has. Especially in the first case can be already realize very high charging levels at low speeds. For such applications are VTG turbochargers, which in addition over have an integrated wastegate, particularly suitable because it optimizes very much to the lower engine speed range can be.

Next VFG technology can be achieved by the well-known Miller / Atkinson process clear advantages with respect to the full load consumption of gasoline engines be achieved. This is by a on the bottom dead center a working piston related late or early Inlet deadline time the internal compression work of the engine reduced. As in the internal compression of the sucked cylinder filling one of the pressure increases in the working cylinder corresponding Heat is generated possesses the compressed mixture at the time of ignition a high temperature. The higher this temperature is, the better more sensitive to knocking is the mixture and the later must it will be detonated. The later, however, the ignition angle must be chosen, the worse is the motor Efficiency, which again leads to higher fuel consumption. Due to the typical Miller timing, the internal compression work reduces the engine, causing less heating and better ignition angle can be realized. In order for the engine to deliver the same power, a higher one must be possible Charge pressure in front of the inlet valves. This external compaction work has the advantage that the charge air in a charge air cooler can be cooled before entering the working cylinder Engines passes. The bigger the positive effect through an applied Miller cycle, the more internal Compaction work must be substituted by external compaction work become. For this purpose, a suitable charging process is necessary.

At the known Miller / Atkinson cycle is the time "intake valve closes "(ES), for example, postponed late. In this way, fresh gas is already in the cylinder z. T. pushed out again. This means a filling disadvantage but with an AH charging with a suitable boost pressure can be compensated. Here is the boost pressure in the volume between Charger output and engine inlet to regulate so that the boost pressure in every Miller operating point, i. H. every operating point in which the "Miller cycle" is used, the theoretical compaction pressure in the working cylinders of the internal combustion engine at the time of intake valve closes corresponds. For the regulation, optionally also control, come pressure and / or temperature and / or mass flow sensors or meaningful combination sensors of the three sensor types mentioned for use.

The positive effect of the Miller / Atkinson cycle on early or late intake valve closure on NO _x emission and homogeneity of the diesel mixture is known. Furthermore, in the case of Otto engine applications, the tendency to knock when being supercharged can be significantly reduced.

at conventional turbocharged engines with standard ATL can the benefits of a Miller cycle, however, only at higher Engine speeds are achieved when sufficient exhaust gas energy available for external compaction work stands. At low engine speeds, the entire, available Boost pressure converted into the effective engine torque. Here arises the possibility of corresponding variability on the inlet side the potential of the Miller cycle in the upper part to tap the speed band.

From the DE 10 2006 003 842 A1 is known an internal combustion engine with a turbocharger with variable turbine geometry, which can also be operated with a Miller cycle. The DE 199 05 636 A1 discloses a method of operating an internal combustion engine according to the Miller cycle, which can also take place in conjunction with a variable turbine geometry.

With Although a mechanically driven loader can also at low engine speeds high boost pressures are realized however, the drive power for the loader is direct branched off from the crankshaft. With increasingly necessary consolidation work on the mechanically driven loader, therefore becomes an increasingly high Drive power dissipated from the crankshaft. This performance Reduces the power effectively delivered by the engine, which, though causes the engine to operate thermodynamically more effectively, externally but no positive effect dissipated can be.

Of the Invention is based on the object, a method of o. G. kind in terms of exploiting the benefits of the Miller cycle This object is achieved by a method the o. g. Art solved with the features characterized in claim 1. Advantageous embodiments of the invention are in the other Claims described.

erzielt wird.For this purpose, it is provided according to the invention in a method of the aforementioned type that at a rotational speed n [rpm] of the internal combustion engine of 1,000 rpm ≦ n ≦ 3,000 rpm as a function of a load request the closing times of the intake valves according to the Miller cycle be selected and the variable turbine geometry of the exhaust gas turbocharger is set such that an effective engine load m _eff based on the maximum engine load m _eff

is achieved.

This has the advantage that even at low speeds with high Motor performances despite low exhaust gas mass flow the advantages of Miller cycle by shifting the compression work from the Working cylinder out, such as low temperature in the combustion chamber and reduced fuel consumption, can be used. This can additionally at low speeds the internal combustion engine of less than or equal to 1,500 rpm one effective engine load of 70% to 100% of the maximum engine load achieved become. With the boost pressure potential of the turbocharger with variable Turbine geometry, the Miller cycle is much more effective than this is the case with conventional charging methods.

erzielt.Conveniently, at a speed n [rpm] of 1,000 rpm ≦ n ≦ 1,500 rpm, the engine load m _eff simultaneously

achieved.

A Expansion of the combustion mixture with appropriate cooling achieved by the fact that the closing time according to the Millerzyklus is chosen such that at least one the intake valves before reaching a bottom dead center in Charge change stroke of a working piston associated with this intake valve is closed.

A Reduction of the effective compression ratio with correspondingly reduced combustion chamber temperature before ignition achieved by the fact that the closing time according to the Millerzyklus is chosen such that at least one the intake valves after reaching a bottom dead center in Charge change stroke of a working piston associated with this intake valve is closed.

In a preferred embodiment is a Phase length of the opening time of at least one Inlet valve 190 ° KW to 220 ° KW.

The The invention will be explained in more detail below with reference to the drawing explained. This shows in the only Fig. A load-speed map an internal combustion engine, which according to the invention Method is operated.

In the only Fig. Is on a horizontal axis 10 a speed n in [rpm] and on a vertical axis 12 a referenced effective engine load is plotted in [%]. A first graph 14 Limits a possible operating range of a conventional engine with the Miller cycle in the direction of lowest engine load and a second graph 16 limits a possible operating range of a conventional burner engine with the Miller cycle in the direction of maximum engine load for the respective speed. The two graphs 14 and 16 close a first area between them 18 in which a conventional internal combustion engine with a Miller cycle can be operated such that the advantages of the Miller cycle, in particular a reduced fuel consumption by outsourcing the compression work out of the working cylinder, are available. It is immediately apparent that the full engine load (m _eff = 100%) is only achieved from a speed of 3,500 rpm. Above the second graph 16 at speeds n of less than 3,500 rpm, the exhaust gas turbocharger does not provide sufficient compression power to compensate for the lower effective compression ratio in the working cylinders of the internal combustion engine through the Miller cycle can.

According to the invention, it is provided that the internal combustion engine is operated with such closing times for respective intake valves of working cylinders of the internal combustion engine according to a Miller cycle and simultaneously with such setting for the variable turbine geometry of a turbine of an exhaust gas turbocharger that in the speed range from 1000 rpm to 3500 rpm min also operating points above the second count 16 in a second area 20 can be achieved.

According to the invention The Miller cycle and VTG technology are optimally connected. By the potential for high boost pressures, which at a corresponding VTG design through more efficient use of exhaust gas energy in comparison to a conventional exhaust gas turbocharger, already off very low engine speeds (<1500 Rpm), it is possible in the entire speed range of the internal combustion engine, the positive effects of the Miller cycle.

For example a camshaft actuator with fixed valve lift is provided on the intake side, the cam shape adapted to the corresponding Millerverfahren is. Preferably, the Miller method comes with late Inlet closing (after UT of the working piston in the charge change stroke) for application, resulting in a phase length of 190 ° KW leads to 220 ° KW. With further variabilities with regard to the inlet-side gas change (phase length to to 240 ° CA, cam switching device, etc.) Further potentials of the Miller cycle can be tapped.

folgt, wobei m_eff eine Motorlast in % der maximal möglichen Motorlast und n die Drehzahl der Brennkraftmaschine ist. In Richtung hohe Motorlast 12 ist der Bereich 20 begrenzt durch die maximale Motorlast bei 100% bzw. durch eine zweite Gerade 24, welche der Gleichung

folgt.According to the invention, the range 20 in the direction of low engine load 12 limited by a first straight line 22 which of the equation

follows, where m _{eff is} an engine load in% of the maximum possible engine load and n is the speed of the internal combustion engine. Towards high engine load 12 is the area 20 limited by the maximum motor load at 100% or by a second straight line 24 which of the equation

follows.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102006003842 A1 [0007]
• - DE 19905636 A1 [0007]

Claims (5)

Method for operating an internal combustion engine, in particular Otto engine or diesel engine, in particular a motor vehicle, wherein the closing times of intake valves of working cylinders of the internal combustion engine are selected according to a Miller cycle and wherein a variable turbine geometry of an exhaust gas turbocharger for varying a compression capacity of the exhaust gas turbocharger is actuated, characterized in that, at a speed n [rpm] of the internal combustion engine of 1,000 rpm ≦ n ≦ 3,000 rpm as a function of a load request, the closing times of the intake valves are selected according to the Miller cycle and the variable turbine geometry of the exhaust gas turbocharger is adjusted in such a way in that an effective engine load m _eff related to the maximum engine load m

is achieved. A method according to claim 1, characterized in that at a speed n [rev / min] of 1,000 rev / min ≤ n ≤ 1,500 rev / min simultaneously the engine load m _eff according to

is achieved. Method according to at least one of the preceding Claims, characterized in that the closing time chosen according to the Miller cycle is that at least one of the intake valves before reaching a bottom dead center in the charge cycle of a this intake valve associated working piston is closed. Method according to at least one of the preceding Claims, characterized in that the closing time chosen according to the Miller cycle is that at least one of the intake valves after reaching a bottom dead center in the charge cycle of a this intake valve associated working piston is closed. Method according to at least one of the preceding Claims, characterized in that a phase length the opening time of at least one inlet valve 190 ° KW up to 220 ° KW.