EP2191118A1

EP2191118A1 - Method for operating an internal combustion engine

Info

Publication number: EP2191118A1
Application number: EP08784645A
Authority: EP
Inventors: Dirk Hagelstein; Jens Kühlmeyer; Paul Gnegel
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2007-08-20
Filing date: 2008-07-08
Publication date: 2010-06-02
Also published as: WO2009024213A1; DE102007039210A1

Abstract

The invention relates to a method for operating an internal combustion engine, particularly an Otto motor or a diesel motor, particularly of a motor vehicle, wherein the closing times of inlet valves of operating cylinders of the internal combustion engine are selected in accordance with a Miller cycle and wherein a variable turbine geometry of an exhaust gas turbocharger is activated in order to alter a compression output of the exhaust gas turbocharger. At an engine speed n [rpm] of the internal combustion engine of 1,000 rpm ≤ n ≤ 3,000 rpm, as a function of a load requirement, the closing times of the inlet valves are selected in accordance with the Miller cycle and the variable turbine geometry of the exhaust gas turbocharger is set such that an effective motor load meff is attained relative to the maximum motor load in accordance with (I) of the maximum motor load.

Description

description

Method for operating an internal combustion engine

The invention relates to a 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 , according to the preamble of claim 1.

The use of turbochargers with variable turbine geometry (VTG or VGT) also promises great potential for gasoline engines. There are two main ways of improving VTG technology: On the one hand, the low-end torque (LET) of the engine can be significantly improved compared to a conventional ATL, or on the other hand, a significant increase in power compared to a conventional ATL can be achieved. ATL, whereby the engine has a comparable LET thanks to the VTG technology. Especially in the first case, very high charging levels can be achieved even at low speeds. For such applications, VTG turbochargers, which also have an integrated wastegate, are particularly suitable because they can be optimized very strongly for the lower engine speed range.

In addition to the VTG technology, the well-known Miller / Atkinson process offers significant advantages in terms of full-load fuel consumption in gasoline engines. In this case, the internal compression work of the engine is reduced by a late or early intake closing time related to the bottom dead center of a working piston. Since in the internal compression of the sucked cylinder filling one of the pressure increase occurring in the working cylinder corresponding heat arises, the compressed mixture has a high temperature at the ignition. The higher this temperature, the more sensitive the mixture is and the later it has to be ignited. However, the later the ignition angle has to be selected, the worse the engine efficiency becomes, which in turn leads to higher fuel consumption. The typical Miller control times reduce the internal compression work of the engine, resulting in less heating and firing angles. To ensure that the engine delivers the same power, a higher charge pressure must be applied in front of the intake valves. This external compression work has the advantage that the charge air to be cooled in a charge air cooler

n \ anmeldun \ kuker2 (from 11000) \ k15136 doc can, before it gets into the working cylinder of the engines. The greater the positive effect of an applied Miller cycle, the more internal compaction work has to be substituted by external compaction work. For this purpose, a suitable charging process is necessary.

For example, in the familiar Miller / Atkinson cycle, the "intake valve closes" (ES) time is delayed, for example. In this way, already located in the working cylinder fresh gas z.T. pushed out again. This means a filling disadvantage, which can be compensated but via a charge with a suitable boost pressure. In this case, the charge pressure in the volume between the loader outlet and the engine inlet is to be controlled so that the boost pressure at each Miller operating point, i. each operating point in which the "Miller cycle" is used, the theoretical compression end pressure in the working cylinders of the internal combustion engine at the time intake valve closes corresponds. For the control, optionally also control, come pressure and / or temperature and / or mass flow sensors or useful combination sensors of the three types of sensor used.

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.

However, in conventional turbocharged engines with standard ATL, the benefits of a Miller cycle can only be achieved at higher engine speeds, if there is sufficient exhaust gas energy available for external compaction work. At low engine speeds, the total available boost pressure is converted into the effective engine torque. This gives rise to the possibility of opening up the potential of the Miller cycle in the upper part of the speed band by means of corresponding variabilities on the inlet side.

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

With a mechanically driven supercharger, it is still possible to react to high load pressures even at low engine speeds, but the drive power for the supercharger is diverted directly from the crankshaft. With increasingly necessary compaction work on the mechanical driven loader, therefore, an increasingly high drive power is dissipated from the crankshaft. This power reduces the actual power output from the engine, which in turn means that the engine is operated thermodynamically more effectively, but can be dissipated to the outside no positive effect.

The invention is based on the object, a method of o.g. To improve the way of exploiting the benefits of the Miller cycle

This object is achieved by a method of o.g. Art solved with the features characterized in claim 1. Advantageous embodiments of the invention are described in the further claims.

For this purpose, it is provided according to the invention in a method of the aforementioned type 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 according to the Miller cycle are selected and the variable turbine _{geometry of} the exhaust gas turbocharger is set such that an effective engine load m _etf related to the maximum engine load m _etf

m, _ft ≥ n * - - + 10% of the maximum motor load e ^Jf 2000 X _{n is} achieved.

This has the advantage that even at low speeds with high engine outputs, despite low exhaust gas mass flow, the advantages of the Miller cycle can be exploited by shifting the compression work out of the working cylinder, such as low temperature in the combustion chamber and reduced fuel consumption. In this case, an effective engine load of 70% to 100% of the maximum engine load can additionally be achieved even at low engine speeds of less than or equal to 1,500 rpm. With the boost pressure potential of the variable turbocharger exhaust gas turbocharger, the Miller cycle becomes significantly more effective than conventional charging methods.

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

m _ftr ≤ n * - + 10% of the maximum engine load f ^f 500%, "achieved. An expansion of the combustion mixture with appropriate cooling is achieved in that the closing time is selected according to the Miller cycle such that at least one of the intake valves is closed before reaching a bottom dead center in the charge cycle of a working piston associated with this intake valve.

A reduction of the effective compression ratio with correspondingly reduced combustion chamber temperature before ignition is achieved by selecting the closing time according to the Miller cycle such that at least one of the intake valves is closed after reaching a bottom dead center in the charge cycle of a working piston associated with this intake valve.

In a preferred embodiment, a phase length of the opening time of at least one inlet valve 190 is ⁰ KW to 220 ⁰ KW.

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

In the only FIGURE, a rotational speed n in [U / miπ] is plotted on a horizontal axis 10, and a related effective engine load in [%] is plotted on a vertical axis 12. A first graph 14 limits a possible operating range of a conventional engine with the Miller cycle toward lowest engine load, and a second graph 16 limits a possible operating range of a conventional engine with the Miller cycle in the direction of highest engine load for the respective speed. The two graphs 14 and 16 enclose therebetween a first region 18 in which a conventional Miller cycle internal combustion engine can be operated such that the benefits of the Miller cycle, in particular reduced fuel consumption by offloading the compression work from the working cylinder, are usable. 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 with such closing times for respective intake valves of working cylinders of the internal combustion engine according to a Miller cycle and at the same time with such a setting for the variable turbine geometry of a Turbine of an exhaust gas turbocharger is operated, that in the speed range from 1000 rev / min to 3500 rev / min and operating points above the second graph 16 in a second region 20 can be achieved.

According to the invention, the Miller cycle and the VTG technology are optimally interconnected. Due to the potential for high boost pressures, which can be provided at a corresponding VTG design by a more efficient utilization of the exhaust gas energy compared to a conventional turbocharger, even from very low engine speeds (<1500 U / min), it is possible throughout Engine speed range to use the positive effects of the Miller cycle.

For example, a camshaft valve with fixed valve lift is provided on the intake side, the cam shape being adapted to the corresponding Miller method. Preferably, the Miller method comes with late inlet closure (after UT of the working piston in the charge cycle), which leads to a phase length of 19O ⁰ KW to 220 ⁰ KW. With further variabilities regarding the inlet side gas exchange (phase length up to 240 ° CA, cam switching device, etc.) further potentials of the Miller cycle can be developed.

According to the invention, the region 20 in the direction of low engine load 12 is limited by a first straight line 22, which corresponds to the equation

m _eff ≥ n * - - - + 10% for 1,000 rpm <n ≤ 3,000 rpm e ^fr 2000%, "

follows, where m _Θff an engine load in% of the maximum possible engine load and n is the speed of the internal combustion engine. In the direction of high engine load 12, the range 20 is limited by the maximum engine load at 100% or by a second straight line 24 which corresponds to the equation

m _efr <n * - - + 10% for 1,000 rpm <n ≤ 1,500 rpm f ^f 500 < ^/ / .. "

follows.

Claims

claims

1. 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 thereby characterized in that at a speed n [rpm] of the internal combustion engine of

1,000 rpm ≦ n <3,000 rpm in response to a load request, the closing timings of the intake valves are selected according to the Miller cycle and the variable turbine geometry of the exhaust gas turbocharger is set such that an effective engine load m _eff according to the maximum engine load

m -> n * hlθ% of the maximum engine load f ^f 2000% _{m is} achieved.

2. The 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 _etf according to

m ~ ≤ n * hlθ% of the maximum engine load f ^f 500% _{m is} achieved.

3. The method according to at least one of the preceding claims, characterized in that the closing time is selected in accordance with the Millerzyklus such that at least one of the intake valves is closed before reaching a bottom dead center in the charge cycle of this intake valve associated working piston.

4. The method according to at least one of the preceding claims, characterized in that the closing time is selected according to the Miller cycle such that at least one of the intake valves after reaching a bottom dead center in the charge cycle of a valve associated with this intake valve working piston Method according to at least one of the preceding claims, characterized in that a phase length of the opening time of at least one inlet valve 190 is ⁰ KW to 220 ⁰ KW.