EP1325219A1

EP1325219A1 - Method and computer programme for operating an internal combustion engine and an internal combustion engine

Info

Publication number: EP1325219A1
Application number: EP01974031A
Authority: EP
Inventors: Gernot Wuerfel
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-09-30
Filing date: 2001-09-07
Publication date: 2003-07-09
Also published as: DE10048608A1; US20040025829A1; JP2004510910A; WO2002029222A1; DE10048608C2

Abstract

An internal combustion engine (10) is operated by a method, according to which petrol is directly injected into a combustion chamber (12). The injection takes place at least temporarily in such a way that in association with a corresponding supply of air into the combustion chamber (12), the petrol-air mixture lies in layers in said combustion chamber (12). The aim of the invention is to reduce the petrol consumption of the internal combustion engine (10) by means of an increased compression ratio, without the risk of knocking. To achieve this, the petrol is injected exclusively during the compression phase of the internal combustion engine (12), even at wide-open throttle, by a multihole fuel injection device (22).

Description

Method and computer program for operating an internal combustion engine and internal combustion engine

State of the art

The present invention relates to a method for operating an internal combustion engine in which gasoline is injected directly into a combustion chamber at least temporarily and air is supplied to the combustion chamber at least temporarily such that the gasoline-air mixture is present in stratified form in the combustion chamber of the internal combustion engine.

Such a process is generally referred to as a direct petrol injection (PDC) process. In this method, the gasoline is acted upon by a very high pressure in a fuel collecting line called a rail. High-pressure injection valves are connected to the fuel manifold and inject the gasoline directly into the combustion chamber. The gasoline is injected into the combustion chamber in such a way that there is a rather rich gasoline-air mixture in the immediate vicinity of an ignition device, which is ignitable. In the remaining combustion chamber. the gasoline-air mixture very lean. In extreme cases, pure air can also be present in certain areas of the combustion chamber. Such a "stratification" of the gasoline is preferably present in the combustion chamber in the entire operating or map area of the internal combustion engine.

One operated according to the above-mentioned process B ^'racing engine consumes relatively little gasoline and has a favorable emission behavior. Nevertheless, there is a desire to reduce the fuel consumption of the internal combustion engine, which is operated with the known method, can be reduced even further.

Such an internal combustion engine is known for example from DE 196 02 065 AI. In this, the fuel is introduced into the combustion chamber of the internal combustion engine by means of a main injection and an ignition injection during the compression stroke. This creates a stratification of the fuel in the combustion chamber. The shift operation is with this' internal combustion engine up to max. 80% of full load is provided.

Current internal combustion engines with gasoline direct injection operate with a geometric compression ratio of approximately 12. However, favorable fuel consumption is achieved with a geometric compression ratio of approximately 13 to 16 (under the geometric compression ratio, the sum of the stroke volume and compression volume is divided by the

Compression volume, understood). Analogous to a higher geometric compression ratio, in which there is a higher compression end pressure in the upper ignition dead center position of the piston, the effective pressure ratio (pressure before charging / pressure after charging) can be achieved in internal combustion engines with mechanical charging or with exhaust gas turbocharging or with other charging systems (for example pressure wave superchargers). be increased.

Such a high compression ratio has not been possible so far, since it leads to uncontrolled pre-combustion of the fuel in the combustion chamber, especially in full load operation, i.e. with high engine load, which is usually injected during the intake stroke, with a higher geometric and effective compression ratio located gasoline can come. The pre-burns are caused by extremely heated components and areas in the combustion chamber. Another danger to the durability of the internal combustion engine is a greatly increased "susceptibility to knock". Knocking can damage the internal combustion engine. For this reason, the compression ratio is determined according to the current state of the art in such a way that the engine can be operated safely at full load, without the risk of knocking and without uncontrolled burns. This

Compression ratio is below the optimal compression ratio for consumption.

In addition, especially for engines with pre-compression, i.e. those internal combustion engines that have, for example, a turbocharger, the mixture composition is enriched at least temporarily in full-load operation beyond the stoichiometric mixture composition (lambda = 1) to lambda values of around 0.7, especially for thermal reasons , Such mixture enrichment in the full load range of the internal combustion engine, however, has a serious disadvantage:

Due to the lack of oxygen in the exhaust gas, only nitrogen oxides can be reduced in the catalytic converter using carbon monoxide to nitrogen and carbon dioxide, but there is no oxidation of unburned hydrocarbons. These get into the environment untreated. The cleaning of the exhaust gas in the catalytic converter is therefore not optimal. In order to be able to oxidize unburned hydrocarbons as well, an additional secondary air pump is required, which conveys additional air into the exhaust duct. However, such a pump has a high power requirement and should therefore be avoided if possible. To counteract this, the compression ratio is reduced in today's internal combustion engines. However, a higher compression ratio would be favorable again in idling and in part-load operation.

For the present invention, this results in the object of developing a method of the type mentioned at the outset in such a way that the consumption of gasoline is reduced again, in particular when idling and in part-load operation, and at the same time the emission behavior is also favorably influenced in the upper part-load and full-load range.

This object is achieved in the known method in that the gasoline is injected exclusively and also at full load during the compression phase of the internal combustion engine by a multi-hole fuel injection device.

Advantages of the invention

The fuel is injected into the combustion chamber of the internal combustion engine exclusively, that is to say in the entire possible load range of the internal combustion engine, during the compression phase. Because of this late injection, the internal combustion engine is extremely insensitive to uncontrolled combustion or unwanted self-ignition ("knocking"). With the conventional. The gasoline is injected in the upper part-load range during the intake stroke. Even distant zones of the combustion chamber are wetted with petrol, which form knock-out spots in the event of overheated combustion.

In the late injection according to the invention, on the other hand, the amount of fuel injected concentrates until the controlled ignition in the center of the combustion chamber, while in the Edge zones of almost pure combustion air is distributed without fuel components. So there can be no knocking and no knocking. There can also be no uncontrolled pre-combustion. Even in the presence of hot combustion chamber areas, the combustion in the method according to the invention is triggered by the ignition or injection timing and not by a hot "ignition source", as can be done during an injection during the intake stroke.

Special measures, such as a later firing angle is not necessary in the method according to the invention to avoid knocking. In this respect, the method according to the invention also has the advantage that the full engine torque is available at all times. Furthermore, no enrichment is required. Instead, an essentially stoichiometric mixture of air and gasoline is always present in the combustion chamber at full load. So the full one

Exhaust gas cleaning capacity (NOx reduction and HC oxidation) - based on the principle of the three-way catalytic converter.

Overall, thanks to the method according to the invention, the corresponding internal combustion engine can be designed for significantly higher, ie consumption-optimized compression ratios, which above all favor low-consumption partial-load operation. This is particularly important in the case of internal combustion engines with a larger displacement, since these are generally operated predominantly in the part-load range. In addition, the possible use of devices with which the compression ratio can be varied during the operation of the internal combustion engine can be dispensed with. This saves costs. It should be noted that internal combustion engines with gasoline direct injection according to the current state of the art work according to the wall-guided or air-guided method, or a combination of both. In contrast to the jet-guided combustion process on which this invention is based, these two combustion processes have to be injected during the full-load operation during the intake stroke. Only in the jet-guided combustion process, which is implemented according to the invention by using a multi-hole valve, is it possible to inject into the compression stroke even at full load. Here, the injection can take place immediately shortly before the ignition point or simultaneously with the ignition point, ie the end of the injection can be later than the ignition point.

In the jet-guided method provided according to the invention, the stratification of the gasoline in the combustion chamber takes place through the injection valve itself. In this method, an injector of an injection valve takes over the fuel distribution in the combustion chamber. The stratification is therefore independent of the flow of the fresh air drawn into the combustion chamber, which means that stratification with a mixture that is locally over-greased in the vicinity of the ignition device and a mixture that is heavily emaciated in the rest of the combustion chamber is reliably possible at full load as well as at idle (full load can also be at low Speeds are available when the accelerator pedal is fully depressed and the engine receives the maximum amount of air and the associated stoichiometrically adjusted amount of fuel (lambda = 1).

Advantageous developments of the invention are specified in the subclaims.

First of all, a further development is given in which the injection of the gasoline is in close proximity to one Ignition device takes place. This ensures that an ignitable air-fuel mixture reaches the ignition device and can be ignited by it under all operating conditions, particularly also at full load and a short period between injection and ignition.

With the method according to the invention, it is possible that no throttling takes place when the internal combustion engine is idling. Such throttling is required in idle mode in the conventional method in order to avoid that the ignitable area of the fuel / air mixture is "blown away" by the ignition device due to an unthrottled strong air flow and thus no longer an ignitable mixture in the area of the ignition device at the time of ignition is present. '

Because the gasoline is injected in the invention during the compression phase of the internal combustion engine, that is to say at a much shorter time interval from the ignition point than in the prior art, this risk of "blowing away" the ignitable fuel-air mixture from the injection ignition device no longer exist. Thus, at low operating loads and especially when idling, throttling of the air flow is no longer necessary, so that the internal combustion engine can be operated without the associated throttling losses even under these operating conditions.

The geometric compression ratio of the internal combustion engine is preferably in the range from 12 to 16. With such a compression ratio, there is already a considerable reduction in gasoline consumption. In addition, compression ratios in said area are still technically feasible. The method according to the invention is particularly well suited when the intake air is precompressed, since the operation of the internal combustion engine at full load is not critical even with precompressed intake air.

It is further proposed that the ignition of the mixture by the ignition device takes place after or while the gasoline is being injected into the combustion chamber, preferably after the crankshaft has been rotated from the time of injection by approximately 0 to 30 °. In this case, the injected gasoline still has sufficient time to spread (ie "stratify") in the required manner, on the other hand the period between injection and ignition is also so short that the risk of the fuel cloud "blowing away" from the ignition device is not given away, so there is a reliable ignition. The injection can also take place simultaneously with or during the ignition. Injection and ignition take place at the optimum combustion time.

However, it is also possible for the mixture to be ignited by means of an annealing device. In this case there is no separation between injection and ignition. Instead, the combustion process is initiated by the start of injection. ^' Like in the case of spark ignition on an electrode, flame core formation also occurs selectively, namely in the hot environment of the glow device, since the glow device itself must not be sprayed directly. The glow device preferably comprises a glow plug. The advantage of such an annealing device is its lower price.

The glow device can be operated at a higher speed or engine load with much lower power than at a lower speed and load. This depends together with the fact that when the internal combustion engine is subjected to a higher load, less electrical energy has to be supplied due to the higher fuel energy supplied and its implementation during combustion in order to keep the glow device glowing.

The present invention also relates to a computer program which is suitable for carrying out the above method when it is executed on a computer. The computer program is particularly preferred when it is stored on a memory, in particular on a flash memory.

Finally, the invention also relates to an internal combustion engine with an injection device which injects gasoline directly into a combustion chamber at least at times and with an air supply device which at least temporarily supplies air to the combustion chamber in such a way that the gasoline-air mixture is stratified in the combustion chamber. In order to reduce the consumption of the internal combustion engine, it is proposed that the gasoline is injected exclusively and also at full load during the compression phase of the internal combustion engine by a multi-hole fuel injection device, so that the stratification of the gasoline in the combustion chamber is carried out by the fuel injection device. This enables a higher compression ratio to be achieved.

drawing

An exemplary embodiment of the invention is explained in detail below with reference to the accompanying drawing. The drawing shows: 1: a block diagram of an internal combustion engine with jet-guided injection;

FIG. 2 shows a section through a region of the internal combustion engine from FIG. 1;

FIG. 3: a bar diagram in which various operating parameters of the internal combustion engine from FIG. 1 are compared to a conventional internal combustion engine;

4a-4d: four bar diagrams, in which operating parameters of the internal combustion engine from FIG. 1 are compared to a conventional internal combustion engine;

5 shows a diagram in which injection and ignition times are plotted against the crankshaft angle at low engine speed; and

Fig. 6: a representation similar to Fig. 5 at higher speed.

Description of the embodiment

In Fig. 1, an internal combustion engine bears the reference number 10. It comprises a combustion chamber 12, to which air is supplied via an intake pipe 14. The exhaust gases are discharged from the combustion chamber 12 via an exhaust pipe 16.

The combustion chamber 12 is bounded at the bottom by a piston 18, which works on a crankshaft 20. Gasoline is injected into the combustion chamber 12 via a high-pressure injection valve 22, which is connected to a gasoline manifold 24. The gasoline manifold 24 is also referred to as a "rail". This is ignited in combustion chamber 12 Air-gasoline mixture present through a spark plug 26, which is fed by an ignition system 28.

In the intake pipe 14 there is a throttle valve 30 which is moved by a servomotor 32. The angular position of the throttle valve 30 is detected by a position transmitter 34, which forwards corresponding signals to a control and regulating device 36. This also receives signals from a speed sensor 38, which taps the speed of the crankshaft 20. On the output side, the control and regulating device 36 is connected on the one hand to the servomotor 32 of the throttle valve 30, on the other hand to the ignition system 28 and finally to the high-pressure injection valve 22.

As can be seen from FIG. 2, the high-pressure injection valve 22 is arranged in a cylinder head 39 essentially parallel to a piston longitudinal axis 41. The spark plug 26 is inserted obliquely from the side into the cylinder head 39 in such a way that its electrodes 40 are in the immediate vicinity and below an outlet 42 of the high-pressure injection valve 22. A combustion chamber trough 44 is formed in the boundary wall of the piston 18 facing the high-pressure injection valve 22 and the spark plug 26.

The internal combustion engine 10 is operated as follows:

During an intake phase, in which the piston 18 moves away from the high-pressure injection valve 22 and from the spark plug 26, air flows through the intake pipe 14 and an intake valve (not shown) into the combustion chamber 12 formed between the piston 18 and the cylinder head 39. The servomotor 32 is regulated by the control and regulating device 36 such that the throttle valve 30 is essentially parallel to the longitudinal extent of the intake pipe 14 is aligned. The exact position of the throttle valve 30 is transmitted to the control and regulating device 36 via the position transmitter 34. Position transmitter 34, control and regulating device 36 and servomotor 32 form a closed control loop. Because the throttle valve 30 is fully open during the intake phase, there are no throttle losses. This in turn means that the combustion chamber 12 can fill with air in an optimal manner.

When the piston 18 has reached its bottom dead center, the intake valve is closed and the compression phase of the internal combustion engine 10 begins. This is also shown in FIGS. 5 and 6 (FIGS. 5 and 6 show exemplary embodiments which show a certain optimum at different pressures of the fuel in the gasoline manifold and / or other trained

Injectors (e.g. different spray hole distribution) can shift the time relationships shown).

If the internal combustion engine 10 is running at a low speed, this is transmitted from the speed sensor 38 to the control and regulating device 36. In this case, the air enclosed in the combustion chamber 12 is initially only compressed during the compression phase. As can be seen from FIG. 5, the control and regulating device 36 controls the high-pressure injection valve 22 at an angle of the crankshaft 20 of approximately −61 ° before the top dead center ignition (ZOT) so that it opens. At an angle of the crankshaft 20 of −34 ° ZOT, the high-pressure injection valve 22 is closed again by the control and regulating device 36. According to the low

Performance requirements at low speed therefore only result in a relatively short injection pulse. As can be seen from FIG. 2, the gasoline is injected from the high-pressure injection valve 2-2 into the combustion chamber 12 in such a way that it is stratified in the latter. This means that in particular in the middle of the combustion chamber 12, i.e. also in the area of the electrodes 40 of the spark plug 26 and within a combustion chamber trough, there is an over-rich mixture with a local lambda value <1, whereas in the edge zones of the combustion chamber 12 there is almost pure combustion air is distributed without gasoline components. The gasoline cloud present in the combustion chamber 12 shortly after the injection by the high-pressure injection valve 22 is indicated in FIG. 2 by a dashed line and there bears the overall reference number 46. Although in the middle of the combustion chamber an over-rich mixture with a local lambda value <1 and in a lean mixture with a lambda value> 1 exists in the edge regions, the mixture is stoichiometric globally in the combustion chamber 12 with a lambda value of 1 measured or calculated in the exhaust gas flow of the exhaust pipe 16.

At an angle of the crankshaft 20 of −18 ° ZOT, the control and regulating device 36 controls the ignition system 28 such that an ignition spark is generated at the electrodes 40 of the spark plug 26. Due to the fact that an over-rich mixture is present in the area of the electrodes 40, this can be ignited and ignited reliably. Although the period of time between the closing of the injection valve 22 and the generation of the spark at the spark plug 26 is relatively short, it is sufficient to prepare and layer the mixture in the required manner.

Overall, however, the time is so short that the zones of the combustion chamber 12 remote from the outlet 42 of the high-pressure injection valve 22 are not wetted with gasoline, so that there is no uncontrolled pre-combustion and no knocking in any phase of the operation of the internal combustion engine 10 " can come. Since the mixture in the combustion chamber 12 is altogether stoichiometric, all possibilities of exhaust gas purification by a three-way catalytic converter (not shown in the figure) are available. As can be seen from FIGS. 3 and 4, the internal combustion engine 10 is therefore characterized in operation by low exhaust gas emissions and low gasoline consumption.

At a higher speed (cf. FIG. 6), in the present exemplary embodiment, the high-pressure injection valve is controlled by the control and regulating device 36 in such a way that the start of injection based on the angular position of the crankshaft 20 is earlier than at a lower speed (cf. FIG. 5) , here at an angle of the crankshaft of - 144 ° ZOT. The injection is ended at an angle of the crankshaft 20 of −36 ° ZOT and the ignition takes place at an angle of the crankshaft 20 of −20 ° ZOT. Since the absolute time between the end of injection and the ignition at relatively high engine speeds is relatively short, there is an increase in gasoline consumption of approximately 5% in this operating range compared to an injection of fuel during the induction phase (FIG. 4a). However, this increase in consumption only occurs in the area of full load and can be compensated for by a higher compression ratio and correspondingly optimal ignition angles. As can be seen from FIG. 4d, there is also a higher soot emission at full load, but this is still below 1. By fine-tuning and with higher pressures of the fuel rail 24, however, even lower soot values can be obtained.

Even if this is not shown in the present exemplary embodiment, the internal combustion engine 10 is particularly suitable for use with a turbocharger which pre-compresses the air supplied to the combustion chamber 12. There, like above has been carried out, due to the jet-guided injection only shortly before ignition, an ignitable mixture is only present in the middle of the combustion chamber, there is no risk of "knocking" or of uncontrolled glow ignition even with pre-compressed intake air.

Instead of a spark plug 26, an annealing device could also be used. Such a device, known from diesel engines, is relatively inexpensive and does not require a complex ignition system. In this case, the combustion process is no longer initiated by the ignition of a spark, but by the start of gasoline injection. However, the formation of a flame core also takes place selectively, namely in the area e.g. a glow plug of the glow device, thus ultimately similar to spark ignition on the electrodes 40 of the spark plug 26 in the present exemplary embodiment. At high speed and / or in particular at high load, the glow device can be operated at a lower power.

Claims

Expectations

1. Method for operating an internal combustion engine (10), in which gasoline is injected directly into a combustion chamber (12) at least temporarily and air is supplied to the combustion chamber (12) at least temporarily so that the gasoline-air mixture is present in stratified form in the combustion chamber (12) , characterized in that the gasoline is injected exclusively and also at full load during the compression phase of the internal combustion engine (12) by a multi-hole fuel injection device (22), so that the stratification of the gasoline in the combustion chamber (12) by the fuel injection device ( 22) takes place.

2. The method according to claim 1, characterized in that the fuel is injected into the combustion chamber (12) in close proximity to an ignition device (40).

3. The method according to claims 2 and 3, characterized in that at low operating load, in particular when the internal combustion engine (12) _r, there is no throttling of the intake air.

4. The method according to any one of the preceding claims, characterized in that the geometric compression ratio of the internal combustion engine (10) is in the range from 12 to 16.

5. The method according to any one of the preceding claims, characterized in that the intake air is precompressed.

6. The method according to any one of the preceding claims, characterized in that the ignition of the mixture by the ignition device (40) after the injection of the gasoline into the combustion chamber (12), preferably after a rotation of the crankshaft (20) by approximately 0 to 30 °, and / or during the injection.

7. The method according to any one of claims 1 to 5, characterized in that the ignition of the mixture takes place by means of an annealing device.

8. The method according to claim 7, characterized in that the glow device is operated at a higher speed and / or load with lower power than at a lower speed and / or load.

9. Computer program, characterized in that it is suitable for performing the method according to one of claims 1 to 8 when it is executed on a computer.

10. Computer program according to claim 9, characterized in that it is stored on a memory, in particular on a flash memory.

11. Internal combustion engine 'with an injection device (22) which injects gasoline directly into a combustion chamber (12) at least at times, and with an air supply device (14) which air the combustion chamber

(12) supplies at least at times so that the gasoline-air mixture is stratified in the combustion chamber (12), characterized in that the gasoline is obtained exclusively and also at full load during the compression phase of the internal combustion engine (12) from a multi-hole fuel injection device (22) is injected so that the stratification of the gasoline in the combustion chamber (12) takes place by the fuel injection device (22).