EP1336041A1 - Method for injecting fuel during the start phase of an internal combustion engine - Google Patents

Abstract

When an internal combustion engine with fuel injection is started, preliminary injections of fuel (I) are deposited according to a specific preliminary injection strategy, to form a film on the walls of the cylinders and to simultaneously provide an explosive mixture for the first combustion. According to the inventive method, to prevent the preliminary filling during the start phase from being too rich or too lean, the fuel quantities of the preliminary injections (I) vary in their chosen amounts, based on the anticipated filling of the corresponding cylinders.

Description

description

Method for injecting fuel during the starting phase of an internal combustion engine

The present invention relates to a method for injecting fuel into a multi-cylinder internal combustion engine.

It is known to supply the cylinders once with a so-called pre-injector each time a gasoline engine is started in order to wet the cylinder walls and at the same time to provide an ignitable mixture for the first combustion. Since there is no synchronization between the camshaft and the crankshaft at this point in time and the position of the pistons is unknown, a targeted pre-injection strategy is required to minimize the emission of unburned fuel and thus the pollutant emissions during takeoff.

In a method known from EP 0 371 158 B1, the cylinders are divided into a first and a second cylinder group depending on the two different levels of the camshaft signal. The cylinders of the first group are supplied with the pre-injectors (group injectors) immediately after a start detection, while the pre-injectors for the cylinders of the second group are delayed. The fuel quantities of the pre-injector are chosen to be the same.

It has now been shown that due to the gas dynamics in the intake manifold, the air fillings in the cylinders are not the same from the start. As a result of the air column standing in the intake manifold, the first cylinders are not filled as well as the subsequent cylinders, in which the air in the intake manifold has already reached a noticeable flow velocity and corresponding kinetic energy. The result is that the Fuel-air mixtures (Larnbda values) of the first pre-fillings are richer than the subsequent pre-fillings. This leads to increased pollutant emissions in the start-up phase, which should be avoided in particular with pollutant-optimized internal combustion engines.

The present invention is based on the object of specifying a method for injecting fuel into a multi-cylinder internal combustion engine, in which fuel-air mixtures with different lambda values are largely avoided in the starting phase.

The method according to the invention is defined in claim 1.

The present invention is based on the finding that an internal combustion engine always remains at certain discrete positions after being switched off in the disengaged state, the number of discrete positions over two crankshaft revolutions (760 °) corresponding to the number of cylinders. In the case of n cylinders, these are therefore n standstill angular positions which, moreover, have the same angular distances relative to one another. Experiments have also shown that the speed behavior of the internal combustion engine and the timing of the opening of the intake valves to the

Speed during the starting phases are always similar, regardless of which of the discrete positions the internal combustion engine has stopped. This means that each start essentially results in the same sequence of different air fillings for successive pre-injectors.

This makes it possible to estimate the air fillings to be expected for the successive pre-injectors. The fuel quantities of the pre-injectors can therefore be selected depending on the sequence of the pre-injectors and the air fillings to be expected, the air fillings to be expected being determined only once must and the corresponding values can then be used at every start. Since the air fillings primarily depend on the speed in the respective intake phase, the air fillings are preferably determined as a function of the expected speed in the respective intake phases.

In a particularly advantageous embodiment of the method according to the invention, it is provided that the fuel quantities of the pre-injectors are determined by multiplying a standard quantity by weighting factors assigned to a pre-injector in each case. If the weighting factors could also be estimated, they are expediently determined experimentally for each series of an internal combustion engine and then stored in the central control unit.

As mentioned, the present invention takes advantage of the fact that the internal combustion engine always remains at certain discrete positions in the disengaged state after being switched off. However, it should be emphasized that it is not necessary to know these standstill positions in order to carry out the method according to the invention. Rather, it is sufficient for the method according to the invention to know the order of the pre-injectors in order to specify the fuel quantities of the pre-injectors as a function thereof.

It is achieved by the method according to the invention that, in the starting phase, the pre-injectors are deposited in quantities which are at least approximately adequate for the respective air filling. Too rich or too lean fuel-air mixtures are avoided, which results in a corresponding reduction in pollutant emissions.

The method according to the invention is explained in more detail with reference to the drawings. It shows: Figure 1 is a schematic sectional view of an internal combustion engine in the form of a gasoline engine with gasoline injection;

Figure 2 is a graph plotting speed, camshaft, crankshaft, injector, and intake valve signals over time.

FIG. 1 shows a schematic partial section through an internal combustion engine which, in the exemplary embodiment described, is designed for illustration purposes as a four-cylinder gasoline engine with gasoline injection.

A common electronic control unit 1 is assigned to the internal combustion engine 3, which controls the ignition, fuel injection and other processes of the internal combustion engine. At least one inlet valve 6 and at least one injection valve 2 are assigned to each cylinder 7. The injection valve 2 injects fuel into the intake manifold directly onto the valve plate of the intake valve 6.

The crankshaft 8 is assigned a crankshaft sensor 4 with a toothed sensor wheel, which generates a crankshaft signal CRK representing the crankshaft angle (see lower half of FIGS. 2 and 3). The camshaft 5, which controls the intake valves 6 and rotates at half the speed of the crankshaft 8, is assigned a camshaft sensor 9 for generating a camshaft signal CAM (see lower half of FIGS. 2 and 3). The camshaft 5 can be adjustable in angle relative to the crankshaft 8, but this is by no means necessary for the method to be described.

In FIGS. 2 and 3, lower half, the crankshaft signal CRK, the camshaft signal CAM and the speed N are plotted against time. Each pulse of the crankshaft signal CRK corresponds to one tooth of the transmitter wheel, with a double tooth gap after every 60 teeth as synchronization pulse S for one full revolution of the crankshaft. ω CO M> F ¹ F ¹ cπ O Cπ o cπ o Cπ

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The method according to the invention can in principle be used in any pre-injection strategies, for example also in the method according to EP 0 371 158 B1 discussed above, in which the pre-injectors of a first cylinder group are released at the same time and the pre-injectors of the second cylinder group are delayed in time. However, the method according to the invention is used with particularly good success in a pre-injection strategy in which all the pre-injectors are placed one after the other in chronological order. An example of such a pre-injection strategy is explained in more detail below with reference to FIG. 2.

In the lower half of FIG. 2, in addition to the crankshaft signal CRK and the camshaft signal CAM, the speed N of the internal combustion engine is plotted over time. In the upper half of FIG. 2, the control signals IV1 - IV4 for the four injection valves are plotted over time for the four cylinders 1 to 4 of the four-cylinder internal combustion engine, the four pilot injectors I being designated II - 14. In addition, the control signals EV1-EV4 for the four intake valves are plotted over time, the opening pulses for the opening of the intake valves being designated E1-E4. In addition, the top two lines of FIG. 2 show the pulses for the top dead center (TDC1-TDC4) of the four cylinders and the top dead center (TDC1) of the cylinder 1.

As indicated in FIG. 2 in connection with the speed, a starter identification E is provided for starting the internal combustion engine. At this time, the camshaft signal CAM is either high or low, in the example in FIG. 2 low. With this - e.g. as in the method described at the outset according to EP 0 371 158 B1 - the cylinders 1 to 4 are divided into two groups (in the example the

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P- d O 3 Φ Φ 3 *> F cn cn DJ 3 3 Φ er F- 3 F F- F 3 3 rt 3 to 3 DJ 3 3 Ps ¹ • 1 1 Ω 1 Φ cn Φ Φ 1 1 1 1 cn ιQ! • 1 tr F F-

has occurred, the internal combustion engine is synchronized, and thus a defined sequence of the pre-injections occurring after the synchronization pulse S can be determined by the central control unit 1.

As can be seen from FIG. 2, this pre-injection strategy results in a defined sequence of the cylinders supplied with pre-injectors I one after the other, in the illustrated case cylinder 4, cylinder 1, cylinder 2 and cylinder 3. The fuel quantities of the associated pre-injectors 14, II, 12 and 13 become determined by multiplying the standard quantity by the fixed weighting factors.

If the internal combustion engine has stopped at one of the other three possible standstill angular positions, the sequence of the cylinders supplied with the pre-injectors changes. However, since the speed behavior during the starting phase in relation to the intake phases of the successively opening intake valves remains essentially the same, the fuel quantities of the successive pilot injector I can always be determined using the same weighting factors.

The pre-injection method described above is only one example of a pre-injection strategy in which the method according to the invention can be used. In particular, it should again be emphasized that it is not necessary to know the standstill angular positions of the internal combustion engine in order to carry out the method according to the invention.

Claims

claims 1. Method for injecting fuel into a multi-cylinder internal combustion engine at least one injection valve (2) per cylinder (7), a camshaft (5) for actuating the inlet valves (6), which rotates at half the speed of the crankshaft (8), a crankshaft sensor (4) which supplies a crankshaft signal (CRK) representing the crankshaft angle with a synchronization pulse (S) per crankshaft revolution, and a central control unit (1) which controls the injection valves (2) in such a way that, during a starting phase, they each have one fuel pre-injector (I) per cylinder (7) in a certain sequence and then normal fuel quantities determined by the control unit (1) inject sequential injection, That means that the fuel quantities of the pre-injectors (I) are given different sizes depending on the order of the pre-injectors (I) and the expected air fillings of the relevant cylinders (7). 2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the air fillings depending on the expected speed (N) of the internal combustion engine (3) can be determined during the respective intake phases of the cylinders (7) in question. 3. The method according to claim 1 or 2, characterized in that the fuel quantities of the pre-injectors (I) by multiplying a standard quantity with predetermined weighting factors. are agreed, which are each assigned to a pre-injector (I). 4. The method of claim 3, d a d u r c h g e k e n n z e i c h n e t that the weighting factors for each series of internal combustion engines are determined experimentally. 5. The method according to claim 3 or 4, so that the weighting factors of the one or more first to last pre-injectors (I) become increasingly larger.