EP1464832A1 - Method for starting an internal combustion engine - Google Patents

Abstract

The internal combustion engine (10) has combustion taking place during the starting phase in the expansion stroke of at least one cylinder (3) and the method involves determining the oxygen concentration in the working cylinder before the starting phase and feeding in a quantity of fuel to be burnt depending on the oxygen concentration. An independent claim is also included for the following: (a) an internal combustion engine, preferably with direct injection and external ignition.

Description

The invention relates to a method for starting an internal combustion engine, preferably an internal combustion engine with direct injection. The invention further relates to an internal combustion engine designed to carry out such a method.

To improve fuel economy in vehicles with internal combustion engines the engine is often switched off completely instead of idling, if no drive power is required. The engine must then be restarted when his performance is needed again. Point for starting conventional internal combustion engines special auxiliary units such as one Starter motor or a generator that can be used as a motor (so-called starter generator) on. These are relatively large and costly Facilities, because a high electrical for starting the internal combustion engine Performance is required.

In addition, it is known to trigger an internal combustion engine Start combustion. This is particularly true with internal combustion engines Spark ignition and direct injection possible. The straight into the combustion chamber injected fuel is ignited by a spark, and the subsequent one Explosion of the air-fuel mixture moves the piston and starts the engine without the crankshaft being moved by an additional auxiliary unit should be. Such direct engine starting requires certain Boundary conditions in order to be carried out successfully. In particular it is necessary or advantageous that the crankshaft at the beginning of Starting in or near a specific position.

With a combination of the above methods, one occurs during the tempering Internal combustion engine with a starter motor early or from the start an injection and combustion in the cylinders, thereby the starter to support.

DE 198 35 045 C2 discloses a method for starting an internal combustion engine by igniting an air-fuel mixture in a cylinder ("Working cylinder"), the pistons of which stop when the internal combustion engine is at a standstill a working cycle position. The should be inside the working cylinder contained air volume can be estimated based on various sensor data. It however, it is not specified in detail how this should be done. It is also with disadvantageous in such a procedure that, for example, due to residual exhaust gases Knowing the amount of air in the cylinder alone is not sufficient for a subsequent one Being able to control combustion optimally. This does not only apply to the im Work cycle located expansion cycle, but also for one in the compression cycle located cylinder, which according to DE0010020325A1 and DE0019955857A1 by ignition of the fuel-air mixture located in this cylinder is used to turn back the internal combustion engine. The Turning back (rotation against the direction of engine rotation) is the actual engine start (Rotation in the direction of motor rotation) upstream and serves to compress the Expansion cylinder air content and thus the improvement of the starting properties.

Against this background, it was an object of the present invention to provide funds for simple and meaningful determination of the starting conditions for the To provide the starting phase of an internal combustion engine.

This object is achieved by a method with the features of claim 1 and solved by an internal combustion engine with the features of claim 10. Advantageous refinements are contained in the subclaims.

The method according to the invention is used to start an internal combustion engine, which in particular can be an internal combustion engine with direct injection of the fuel into the combustion chamber (cylinder) and with spark ignition. In the method, the combustion of an air / fuel mixture is carried out in the first working cycle of the piston of at least one cylinder of the internal combustion engine, which is referred to below as the "working cylinder", which occurs during the starting phase of the internal combustion engine. The method according to the invention is characterized in that the oxygen concentration in the working cylinder is determined before the starting phase of the internal combustion engine, and in that a quantity of fuel to be burned is metered in as a function of the determined value. The oxygen concentration is preferably expressed as a relative quantity which describes the proportion of pure oxygen O ₂ in the gas mixture in the working cylinder, this proportion in mass percentages, volume percentages. Mole percentages can be expressed as partial pressure or as another suitable size. Such a relative value is independent of the volume of the combustion chamber.

By considering the oxygen concentration in the working cylinder in the process, the necessary and sufficient for good combustion Amount of fuel determined very precisely and then z. B. by direct injection be fed to the working cylinder. In this way, on the one hand ensures maximum energy yield because the entire available Oxygen can be exploited for combustion, on the other hand however, avoided harmful emissions from excess fuel would arise. The mechanical energy from the combustion can for example to be used to the internal combustion engine without another auxiliary unit (Starter engine etc.) solely by igniting the air-fuel mixture to start in the working cylinder, whereby the piston of the working cylinder is at The internal combustion engine is at a standstill in one work cycle (expansion cycle) got to. Alternatively, the combustion can only be supportive during the start phase act for starting the internal combustion engine with an auxiliary unit. This made it possible e.g. B., a less powerful and therefore cheaper Auxiliary unit to use.

The acid concentration can also be measured in the compression cylinder with this method are determined, with the help of which the actual starting process upstream reverse rotation according to DE0010020325A1, to improve starting can be initiated.

The determined oxygen concentration is preferably used to from this the absolute amount of oxygen (e.g. as mass value or as number of moles) in Determine working cylinder at the start of the start phase. From the amount of oxygen can then directly supply the amount of fuel for a stoichiometric Combustion can be calculated. For the calculation of the absolute amount of oxygen from the oxygen concentration can advantageously start anyway variables measured in an internal combustion engine, such as the crankshaft angle, atmospheric pressure and / or engine temperature (or coolant temperature) be used.

• Zylinderinnendruck im Arbeitszylinder;
• Ansaugdruck im Ansaugkrümmer der Brennkraftmaschine;
• Luftmassenfluß im Ansaugkrümmer der Brennkraftmaschine.

According to a preferred embodiment of the method, the oxygen concentration in the working cylinder is determined on the basis of the measurement of at least one of the quantities listed below while the internal combustion engine is running down (that is to say in the period from switching off the ignition and / or the fuel supply until the internal combustion engine stops):

• Internal cylinder pressure in the working cylinder;
• Intake pressure in the intake manifold of the internal combustion engine;
• Air mass flow in the intake manifold of the internal combustion engine.

All three sizes mentioned have in common that they are usually at one anyway Internal combustion engine can be measured by appropriate sensors respectively that they can easily be determined from measured variables if necessary are.

The assessment is carried out in order to minimize the effort for data processing the oxygen concentration preferably based on an average and / or due to an accumulated, that is, summed up or integrated value of the sizes mentioned (internal cylinder pressure, intake pressure and / or air mass flow).

To further reduce the effort for data processing, the Measurement of the sizes of the internal cylinder pressure, intake pressure and / or air mass flow only at specified crankshaft positions. Preferably acts these are angular positions of the crankshaft, the lower and / or top dead center of the piston of a cylinder, preferably the working cylinder, correspond. In this way, the sizes mentioned are only too proportionate few, but particularly characteristic points in time during the Run-out phase of the engine is sensed.

In particular, the internal cylinder pressure during the phase-out phase of the internal combustion engine at the top dead center of the piston of the working cylinder, in which during the start phase the first combustion takes place. Furthermore, the measurement of the suction pressure can preferably be carried out at the lower one Dead center of the piston of the working cylinder take place.

The invention further relates to an internal combustion engine, preferably one Internal combustion engine with direct injection and spark ignition, which thereby is characterized in that they carry out a method of the above Art is set up. In particular, the internal combustion engine can be controlled by an engine be equipped, which is programmed so that it the oxygen concentration in the working cylinder of the internal combustion engine for the calculation of the to be metered Amount of fuel for the first combustion in the working cylinder during used in the start-up phase. The internal combustion engine can continue with the Engine control coupled sensors for the air mass flow in the intake manifold, for the intake pressure and / or for the cylinder internal pressure to get out of these Sizes to determine the oxygen concentration.

The invention is explained in more detail below with the aid of the figures.

Fig. 1

schematisch die Komponenten einer Brennkraftmaschine mit Direkteinspritzung, bei welcher das erfindungsgemäße Verfahren durchgeführt werden kann;

Fig. 2

die zeitlichen Verläufe des Ansaugdruckes, der Motordrehzahl, sowie verschiedener Zylinderinnendrücke beim Auslaufen einer Brennkraftmaschine;

Fig. 3

den Zusammenhang zwischen der Sauerstoffkonzentration und dem mittleren Zylinderinnendruck während der Auslaufphase einer Brennkraftmaschine, und

Fig. 4

den Zusammenhang zwischen der Sauerstoffkonzentration und dem mittleren Ansaugdruck während der Auslaufphase einer Brennkraftmaschine.

Show it

Fig. 1

schematically shows the components of an internal combustion engine with direct injection, in which the method according to the invention can be carried out;

Fig. 2

the temporal courses of the intake pressure, the engine speed, and various cylinder pressures when an internal combustion engine runs out;

Fig. 3

the relationship between the oxygen concentration and the mean internal cylinder pressure during the stopping phase of an internal combustion engine, and

Fig. 4

the relationship between the oxygen concentration and the mean intake pressure during the stopping phase of an internal combustion engine.

The internal combustion engine 10 shown in FIG. 1 is a Internal combustion engine with direct injection of petrol into the cylinder 3 leading fuel supply 6. Such a direct injection engine has the Advantage that he by ignition of the air-fuel mixture in the cylinders 3rd can be started directly without an additional starter motor the crankshaft must drive during a starting phase. Alternatively, the (foreign or Self-) ignition of an air-fuel mixture during the starting phase, however also only to support a starter (starter motor) to make the starting process to accelerate ("Quick Start"), to be able to design the starter smaller, and to improve the comfort behavior of the conventional start. at Such a supported start is already from the first revolution or Fuel injected from the first expansion stroke of a piston and ignited.

The internal combustion engine 10 also has an intake manifold 2 for supplying fresh air, the supply rate of which can be adjusted via a throttle valve 1. An air mass flow sensor 8 is arranged upstream of the throttle valve and transmits a signal representing the air mass flow MAF to an engine control unit 7, which can be implemented, for example, by a microprocessor. A pressure sensor 9 for the intake pressure p _{man is} arranged downstream of the throttle valve 1, the signal of which is also passed to the engine control 7. Finally, pressure sensors 4 for the internal cylinder pressure p _{cyl are} provided in the cylinders 3 of the internal combustion engine, which transmit their signals to the engine control 7.

The exhaust gases from the cylinders 3 of the internal combustion engine 10 are from a Exhaust manifold 5 passed into an exhaust system, not shown. Of course can the internal combustion engine with other known components such as for example an exhaust gas recirculation system, an exhaust gas turbocharger, a catalytic converter and the like, which are not shown in FIG. 1 are.

The engine control 7 receives the above and a number of other sensory ones Information (e.g. engine speed, coolant temperature, the ambient pressure etc.) and calculates control commands for different ones Components of the internal combustion engine. In this regard, Figure 1 is only the output of the engine control unit 7 to the fuel injection system 6 is shown, Via which the engine control unit 7 controls the fuel injection (time, duration, fuel quantity, Fuel pressure) can control.

To successfully direct the internal combustion engine 10 after a standstill (i.e. without Auxiliary unit) to start or to start by early ignitions in To be able to support the start phase is compliance Knowledge of a number of boundary conditions required. One of the most advantageous conditions to be known is the oxygen content in the working cylinder 3 or the working cylinders. All cylinders are called "working cylinders" referred to, whose valves are closed at the start of the start phase and whose Valves no longer open until fuel mixture ignition in the respective cylinder become. The pistons of the working cylinders are either in one position (short) behind the top dead center, i.e. in the position of a work or Expansion clock or, with upstream turning back, just before the upper one Dead center, i.e. in the compression cycle. Because of the closed valves remains receive the gas filling in a working cylinder. The absolute amount of oxygen in the working cylinder determines the maximum amount of fuel there can be burned and thus the maximum amount of energy required for movement the crankshaft is used beyond the subsequent top dead center can be.

The absolute amount of oxygen in the working cylinder 3 depends on the volume of the combustion chamber formed by the cylinder walls and the piston (and thus the position of the crankshaft), on the air density, and on the oxygen concentration c _{0 of} the cylinder charge. The absolute crankshaft position can easily be determined by an angle sensor or a similar device. The air density can be determined by the pressure and the temperature in the working cylinder, the pressure being approximately equal to the ambient pressure (atmospheric pressure) and therefore easily predictable, while the temperature can be approximated by the coolant temperature, which is usually monitored by an appropriate temperature sensor.

In contrast, a direct measurement of the oxygen concentration c _o in the working cylinders is not possible in a simple manner. Corresponding robust and simply designed sensors for measuring the oxygen concentration in a combustion chamber are not available. On the other hand, for the success and quality of a direct start without auxiliary units or a supported start with auxiliary units, it is important to know the oxygen content and thus the oxygen concentration in the working cylinder in order to be able to determine the amount of fuel to be injected as accurately as possible. If the oxygen content were underestimated, too little fuel would be injected and the available energy would not be used up. If the oxygen content were overestimated, however, too much fuel would be injected, which would lead to increased emissions of hydrocarbons and carbon monoxide. Furthermore, an incorrect assessment of the amount of oxygen can also lead to a wrong prediction as to whether a direct start is successfully possible or not.

• durchschnittlicher Druckverlauf in den Arbeitszylindern;
• akkumulierter Druckverlauf in den Arbeitszylindem;
• durchschnittlicher Ansaugdruck während der Ansaugphase (Laden der Zylinder);
• akkumulierter Ansaugdruck während der Ansaugphase;
• mittlerer Luftmassenfluß während der Ansaugphase;
• akkumulierter Luftmassenfluß während der Ansaugphase.

To solve this problem, it is proposed _according to the _invention to predict the oxygen concentration c _o in the working cylinder or cylinders 3 on the basis of the measurement of the _internal cylinder pressure p _cyl , the intake pressure p _man and / or the air mass flow MAF. It can be seen that the oxygen concentration c ₀ in the working cylinders 3 is proportional to the parameters listed below, which are simple in the course of the engine running down (i.e. the delay time from switching off the ignition and / or the fuel supply until the engine stops) ) can be measured:

• average pressure curve in the working cylinders;
• accumulated pressure curve in the working cylinders;
• average intake pressure during the intake phase (cylinder loading);
• accumulated suction pressure during the suction phase;
• mean air mass flow during the intake phase;
• accumulated air mass flow during the intake phase.

The continuously recorded measurement data of the cylinder _internal pressure p _cyl , the intake pressure p _man and / or the air mass flow MAF can be used during the stopping phase of the engine. Alternatively, only a few data can be used at predefined positions of the camshaft or crankshaft. Due to the typically limited resources of computing capacity in the engine controller 7 (FIG. 1), a prediction of the oxygen concentration c ₀ by selecting only a few data of the internal cylinder pressure, the intake pressure and / or the air mass flow at predefined crankshaft angles is advantageous, since this can minimize the computing effort.

In this context, FIG. 2 shows the course over time of the intake pressure p _man , the engine speed n and the _internal cylinder pressure p _cyl for a working cylinder (solid line) and the remaining three cylinders (dotted lines) of the internal combustion engine 10 during a phase-out phase that occurred at time 0 ( "off") begins with the switching off of the fuel supply and / or the ignition. The points in time TDC1, TDC2 and TDC3 in the figure are indicated by dashed lines, at which the piston of the working cylinder of the internal combustion engine passes top dead center for the first, second and third (and last) times in the phase-out phase. The preceding passage of the piston through the bottom dead center is marked with BDC1, BDC2 and BDC3. Furthermore, the measured values of the _internal cylinder pressure p _cyl in the working cylinder at the first times TDC1, TDC2 and TDC3 are referred to as p _cyl1 , p _cyl2 and p _cyl3 . An average internal cylinder pressure can then be calculated from these measured values according to the following equation: <p cyl > = (p CYL1 + p CYL2 + p CYL3 ) / (Number of measured values).

This mean _internal cylinder pressure <p _cyl > in the working cylinder 3 is closely related to the oxygen concentration c _o in the working cylinder, so that the latter can be calculated from this. In this regard, Figure 3 shows schematically the relationship between the oxygen concentration c _o and the mean cylinder pressure <p _cyl >. Such a relationship can be determined empirically and, for example, recorded in a lookup table or a mathematical approximation function in order to be available to the engine control system.

In addition or as an alternative to measuring the cylinder pressure at top dead center, this can also take place at other suitable positions of the crankshaft. Furthermore, instead of the average pressure <p _cyl >, the cumulative pressure could be used during all or part of the recorded cycles.

In FIG. 2 it is also indicated that the intake pressure p _man can be recorded each time the bottom dead center BDC1, BDC2, BDC3 _{is passed} during the phase-out of the internal combustion engine. The corresponding measured values p _man1, p _MAN2, p _man3 can turn according to the following formula are combined to form an average value: <p you > = (p man1 + p man2 + p man3 ) / (Number of measured values).

This mean value can then be converted into an oxygen concentration c _o on the basis of the relationship shown schematically in FIG.

In addition or as an alternative to measuring the intake pressure at bottom dead center, this can also take place at other suitable positions of the crankshaft. Furthermore, instead of the average pressure <p _man >, the cumulative pressure could be used during all or part of the recorded cycles.

In order to increase the accuracy of the method, the _internal cylinder pressure p _cyl and the intake pressure p _{man can} also _be used in combination to estimate the oxygen concentration c _o in the working cylinder. In addition or as an alternative to these data, the measured or calculated data of the air mass flow MAF (on average or cumulatively) could also be used.

Claims (10)

Method for starting an internal combustion engine, preferably an internal combustion engine (10) with direct injection and spark ignition, with combustion taking place in the first expansion cycle of at least one cylinder (3) (working cylinder) during the starting phase,
characterized in that
before the starting phase, the oxygen concentration (c _o ) in the working cylinder (3) is determined, and that a quantity of fuel to be burned is metered as a function thereof. Method according to claim 1,
characterized in that
the oxygen concentration in the working cylinder (3) at the beginning of the starting phase is determined from the oxygen concentration (c _o ). Method according to claim 1 or 2,
characterized in that
the oxygen concentration (c _o ) in the working cylinder (3) is estimated on the basis of the measurement of at least one of the following variables during the runout of the internal combustion engine (10): Cylinder _internal pressure (p _cyl ) in the working cylinder (3); Intake pressure (p _man ) in the intake manifold (2); Air mass flow (MAF) in the intake manifold (2). Method according to claim 3,
characterized in that
the oxygen concentration (c _o ) is _estimated on the basis of the mean value (<p _cyl >, <p _man >) and / or an accumulated value of the quantities mentioned. Method according to claim 3 or 4,
characterized in that
the oxygen concentration (c _o ) is determined on the basis of an empirically determined relationship. Method according to at least one of claims 3 to 5,
characterized in that
the measurement of the quantities mentioned (p _cyl , p _man , MAF) takes place only at predetermined positions of the crankshaft, preferably at the bottom (BDC) and / or at the top (TDC) dead center of a piston of the internal combustion engine (10). Method according to claim 6,
characterized in that
the measurement of the _internal cylinder pressure (p _cyl ) at top dead center (TDC) and / or that the intake pressure (p _man ) is measured at bottom dead center (BDC) of the piston of the working cylinder (3). Method according to at least one of claims 1 to 7,
characterized in that
the internal combustion engine (10) is started without an auxiliary unit by igniting an air-fuel mixture in the working cylinder (3), the piston of which is in the position of an operating cycle when the internal combustion engine (10) is at a standstill. Method according to at least one of claims 1 to 7,
characterized in that
the internal combustion engine (10) is started with an auxiliary unit and is supported by the combustion in the working cylinder (3). Internal combustion engine, preferably internal combustion engine (10) with direct injection and spark ignition,
characterized in that
this is designed to carry out a method according to at least one of claims 1 to 9.

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