DE102014219483A1 - Method and device for operating an internal combustion engine - Google Patents

Abstract

The invention relates to a method of operating a multi-cylinder internal combustion engine in a four-stroke operation, wherein each of the cylinders is supplied with fresh air via at least one intake valve in an intake stroke and combustion exhaust gas is exhausted from each of the cylinders via at least one exhaust valve in an exhaust stroke, comprising the steps of: Providing an exhaust back pressure indication for each of the cylinders, the exhaust back pressure indication indicating an exhaust back pressure for the respective cylinder during the exhaust stroke; Adjusting at least one valve timing of the intake valve, in particular a valve opening time and / or a valve closing time, based on the exhaust back pressure indications of each of the cylinders.

Description

Technical area

The invention relates to internal combustion engines, in particular internal combustion engines with varying ignition interval. In particular, the invention relates to measures for improving the smoothness of an internal combustion engine.

State of the art

An internal combustion engine operated in four-stroke mode discharges combustion exhaust gases into an exhaust gas discharge path in an exhaust stroke. These directly cause exhaust valves of cylinders of the internal combustion engine exhaust backpressure, which may be subject to considerable fluctuations depending on the operation of the internal combustion engine. In particular, these variations in exhaust backpressure on the exhaust valves occur in internal combustion engines that have an irregular firing interval between consecutive combustion cylinders, such as in cross-plane internal combustion engines such as a V-type engine.

The respective exhaust backpressure in the region of the exhaust valve substantially determines the amount of residual exhaust gas remaining in a respective cylinder after an exhaust stroke. As a result, the amount of fresh air flowing in during a subsequent intake stroke is determined, so that different exhaust gas back pressures lead to different air fillings of the cylinders for a subsequent combustion cycle. In air-driven internal combustion engines, this leads to a non-uniform torque and thereby to a reduced smoothness of the internal combustion engine.

Disclosure of the invention

According to the invention a method for operating an internal combustion engine according to claim 1 and by the device and the motor system according to the independent claims is provided.

• – Bereitstellen einer Abgasgegendruckangabe für jeden der Zylinder, wobei die Abgasgegendruckangabe einen Abgasgegendruck für den betreffenden Zylinder während des Ausstoßtaktes angibt;
• – Einstellen mindestens einer Ventilsteuerzeit des Einlassventils, insbesondere einer Ventilöffnungszeit und/oder einer Ventilschließzeit, für jeden der Zylinder basierend auf den Abgasgegendruckangaben jedes der Zylinder.

Further embodiments are specified in the dependent claims. According to a first aspect, there is provided a method of operating a multi-cylinder internal combustion engine in a four-stroke operation, wherein each of the cylinders is supplied with fresh air via at least one intake valve in an intake stroke and combustion exhaust gas is exhausted from each of the cylinders through at least one exhaust valve in an exhaust stroke following steps:

• Providing an exhaust back pressure indication for each of the cylinders, the exhaust back pressure indication indicating an exhaust back pressure for the respective cylinder during the exhaust stroke;
• Adjusting at least one valve timing of the intake valve, in particular a valve opening time and / or a valve closing time, for each of the cylinders based on the exhaust backpressure indications of each of the cylinders.

One idea of the above method is to set the valve timing of the intake valve of the respective cylinder depending on a desired predetermined air charge depending on a modeled, measured or predetermined exhaust gas backpressure. This ensures that a different air charge in the individual cylinders, which occurs due to an exhaust gas back pressure varying between the cylinders, is compensated by means of a specification or adaptation of the valve timing of the intake valves. By adjusting the valve timing of the intake valves of the torque contribution of the individual cylinders can be matched to each other, so that a higher smoothness of the internal combustion engine can be achieved without this being accompanied by a reduced efficiency of the internal combustion engine.

Furthermore, the exhaust gas backpressure indications can each comprise a firing interval of the relevant cylinder relative to the cylinder previously reaching the combustion stroke or correspond to it.

In particular, the exhaust gas backpressure information can be modeled using an exhaust tract model from an operating state of the internal combustion engine.

According to one embodiment, a maximum air charge for each of the cylinders may be determined based on the exhaust gas backpressure information of the respective cylinder, wherein the valve timing of the intake valve that is in the intake stroke is dependent on the maximum air charges of all cylinders, particularly depending on the smallest of the maximum air charges all cylinders are adjusted.

It can be provided that the valve timing of the intake valves of those cylinders whose exhaust valves during an exhaust stroke, a higher exhaust back pressure than the exhaust back pressure on the cylinder with the smallest maximum air charge are controlled so that their opening times are extended during a subsequent intake stroke.

Furthermore, the valve timing of the intake valves of those cylinders whose exhaust valves lower exhaust back pressure during an exhaust stroke than exhaust back pressure on the cylinder having the largest maximum air charge can be controlled so that their opening times during a subsequent intake stroke are shortened.

According to a further aspect, a device, in particular a control device is provided, which is designed to carry out the above method.

In another aspect, an engine system including an internal combustion engine and the above apparatus is provided.

In other aspects, a computer program for carrying out the above method, a machine-readable storage medium on which the computer program is stored, and a control unit having the machine-readable storage medium are provided.

Brief description of the drawings

Embodiments are explained below with reference to the accompanying drawings. Show it:

1 a schematic representation of an engine system with an internal combustion engine; and

2 a flowchart for illustrating a method for operating the internal combustion engine with variable valve timing for the intake valves.

Description of embodiments

1 shows a schematic representation of an engine system 1 with an internal combustion engine 2 , The internal combustion engine 2 is designed as an air-driven internal combustion engine, in particular as a gasoline engine, which is operated according to a four-stroke operation with intake stroke, compression stroke, combustion stroke and exhaust stroke.

The internal combustion engine 2 has several, for example, eight cylinders 3 on each of which air via an air supply section 4 is supplied. The air supply section 4 spreads to each of the cylinders 3 , wherein at least one inlet valve 5 for each of the cylinders 3 is provided, depending on the valve opening times cylinder-specific in the cylinder 3 to control the intake of air.

The cylinders 3 can on several cylinder banks 11 be distributed. In the embodiment shown are two cylinder banks 11 provided, each four cylinders 3 exhibit. The cylinders 3 are coupled to a common crankshaft (not shown). To the combustion exhaust gas in the exhaust gas removal tract 4 to collect has these subsections 12 on, the individual cylinder banks 11 assigned.

The intake valves 5 are with one or, with several cylinder banks 11 corresponding to a plurality of camshafts (not shown) coupled and may be provided, for example, as per se known electro-hydraulic valves, which provide a coupling with the camshaft or prevent. These valves are also known as valves for fully variable electrohydraulic valve control, eg UniAir ^® valves. By selecting a suitable coupling timing with the camshaft may be an opening time and / or a closing time of each of the intake valves 5 be controlled separately and in particular be delayed with respect to the camshaft movement and the crankshaft angle. In particular, by the choice of the opening times of the intake valves 5 can be in the respective cylinder 3 admitted or sucked amount of fresh air set or controlled fully variable.

Furthermore, exhaust valves 6 provided, the combustion exhaust gases from the cylinders 3 in an exhaust discharge tract 7 omit.

For cylinder-specific supply of fuel injection valves 8th whose opening periods determine the amount of fuel injected and that for each of the cylinders 3 can be controlled individually.

For operation of the internal combustion engine 2 is a control unit 10 provided the intake valves 5 and the injection of fuel through the injectors 8th controls. The control unit receives this 10 via sensors information on a current operating point of the internal combustion engine 2 For example, a speed indication of a speed sensor, an indication of a sucked air quantity from an HFM sensor and the like. The control unit 10 operates the internal combustion engine 2 by setting encoders based on the information on the current operating point and an indication of a drive torque to be provided. The positioners can inject the injectors 8th for fixing in the cylinders 3 amount of fuel to be injected, the electrohydraulic intake valves 5 , a throttle or other in an engine system 1 include usual positioners.

In particular, in internal combustion engines with multiple cylinder banks, especially in internal combustion engines in cross-plane construction, such as For example, in V-engines, the operation at different firing intervals of the individual cylinders on a section 12 the exhaust removal tract 7 to lead. A firing interval is understood to mean the angle of the crankshaft to which it is after the ignition of an air-fuel mixture in one of the cylinders 3 during a combustion cycle until ignition of an air-fuel mixture in a cylinder next entering the combustion cycle according to a predetermined firing order 3 the same cylinder bank 11 rotates. The different ignition distances of the cylinders 3 a cylinder bank 11 can cause different exhaust back pressures on the exhaust valves 6 the single cylinder 3 to lead.

Other effects that result in different exhaust back pressures on the exhaust valves 6 the single cylinder 3 can cause pulsations in the exhaust discharge tract 4 , which lead to standing waves in the exhaust column and thereby speed-dependent pressure differences in the exhaust gas discharge tract 4 in the field of exhaust valves 6 cause.

Pressure differences of the combustion exhaust gas in the area of the exhaust valves 6 the cylinder 3 usually lead to a varying air charge in a subsequent combustion cycle. This is a consequence of the amount of fresh air sucked in from the amount of fuel in the cylinders 3 remaining combustion exhaust gas depends. The higher the exhaust back pressure in the area of the exhaust valves 6 a cylinder 3 is, the higher the amount of combustion exhaust gas in the cylinder in question 3 and vice versa.

In conjunction with the flowchart of 2 hereinafter, a method of operating the internal combustion engine 2 described in detail, preferably in the control unit 10 provided and executed as software.

In step S1, an indication of an exhaust back pressure at each of the cylinders is first provided 3 provided. The indication of the exhaust back pressure at the exhaust valves 6 each of the cylinders 3 may be fixed depending on a speed or modeled using an exhaust tract model. Such an exhaust tract model may be a gas model that dynamically describes the gas flow in the exhaust removal tract. In particular, the indication of the exhaust back pressure to a firing interval of succession of a cylinder bank 11 in the combustion cycle passing cylinders 3 match that of a firing order of the cylinders 3 depends.

The predetermined firing order, especially in a cross-plane engine, such as a V-type engine, results in a cylinder bank 11 to varying firing intervals between the successive reaching into the combustion cycle cylinders 3 (the same cylinder bank). For a V-engine, the cylinders are 3 usually in two cylinder banks 11 arranged, which move in different planes and are thus synchronized to different crankshaft angles. The firing distance of two at a cylinder bank 11 arranged successively in the combustion cycle passing cylinders 3 This varies compared to the firing interval of two at different cylinder banks 11 arranged successively in the combustion cycle passing cylinders 3 ,

Also for the individual cylinder banks 11 Considered separately, the firing intervals vary between two cylinders entering the combustion stroke immediately after each other 3 same cylinder bank 11 , This corresponds, for example, for an eight-cylinder engine usually a crankshaft angle of 90 °, whereas the firing interval between successive reaching into the combustion cycle cylinders 3 the same cylinder bank 11 180 °, if according to the firing order temporally intervening a cylinder 3 the other cylinder bank 11 gets into the combustion cycle. In an eight-cylinder V-engine in cross-plane design, the distance in which is ejected into the exhaust tract on an exhaust bank between 90 ° and 240 ° vary. Generally, in an N cylinder engine, this corresponds to a crankshaft angle of 720 ° / N, with firing intervals between consecutive cylinders entering the combustion cycle 3 vary between 720 ° / N and B * 720 ° / N, where B is the number of cylinder banks 11 equivalent. The different ignition distances can be in the sections 12 the exhaust removal tract 7 to different pressure ratios for the next there in the combustion cycle reaching cylinder 3 to lead.

The unequally distributed ignition intervals between the successive reaching into the combustion cycle cylinders 3 lead to different progressions of the exhaust back pressures in the exhaust gas discharge tract, in particular in the region of the sections 12 near the exhaust valves 6 the cylinder concerned 3 , As the firing interval usually by the fixed default firing order of the cylinder 3 is known, a corresponding exhaust backpressure based on the current speed of the internal combustion engine 2 be modeled and provided for example by means of a map.

Regardless of the caused by the different firing order exhaust back pressures different exhaust back pressures can also speed dependent, based on existing vibrations and resonances in the exhaust discharge tract 7 , be generated. The vibrations in the exhaust gas discharge tract 7 arise due to the successively staggered ejection strokes of the cylinder 3 during operation of the internal combustion engine 2 , in each of which combustion exhaust gas into the exhaust gas discharge tract 7 is ejected. By a suitable system model can now be the pressure distribution of the combustion exhaust gas in the exhaust gas discharge tract 7 depending on the speed of the internal combustion engine 2 be modeled based on the emergence of standing waves, so that the exhaust back pressure on the exhaust valve 6 at the time of the intake stroke of a corresponding cylinder 3 can be determined.

In step S2, depending on the determined exhaust back pressure on the exhaust valve 6 a corresponding cylinder 3 determines the amount of combustion exhaust gas after the exhaust stroke in the cylinder in question 3 remained. This results in step S3 for each of the cylinders 3 a maximum air charge. The maximum air charge indicates what amount of air in a subsequent intake stroke in the cylinder 3 can be maximally sucked, especially if the respective inlet valves 5 have a maximum opening period.

In step S4, the maximum air charge of that cylinder 3 determined as reference air filling, the associated maximum air charge due to the largest amount of in the cylinder 3 remaining combustion exhaust gas (depending on the exhaust back pressure during the exhaust stroke) is minimal.

Accordingly, the valve timing of the intake valve is now in step S5 5 of the next cylinder entering the combustion cycle 3 adjusted so that a suction of fresh air in the direction of the reference air filling is reduced. In particular, the valve timing of the intake valve 5 of the next cylinder entering the combustion cycle 3 be adjusted so that the amount of fresh air is sucked, which is needed to reach the reference air filling.

Generally, according to the timing of the four-stroke operation of the internal combustion engine 2 the valve timing of the intake valves 5 the cylinder 3 adapted to each other so that in a stationary operation of the internal combustion engine 2 in the cylinders 3 intake of air for all cylinders 3 becomes equal. This is basically possible by the intake valves 5 those cylinders 3 , on their exhaust valves 6 during a exhaust stroke, there is a higher exhaust back pressure, so controlled that during a subsequent intake stroke, it will provide a longer valve opening time for the intake valves 5 and vice versa. In this way it is achieved that, despite the increased amount of combustion exhaust gas in the cylinder 3 the same amount of air in the combustion chamber of the cylinder 3 gets as in the cylinders 3 , for the previously a reduced exhaust back pressure at their exhaust valves 6 was determined. Alternatively, as described above, the valve opening times of those intake valves 5 be reduced in the intake stroke, which had a lower exhaust back pressure during the last exhaust stroke.

The above method may after each exhaust stroke for each of the cylinders 3 be executed cyclically.

In this way it is achieved that the moment contribution of the individual cylinders 3 is matched to each other, so that an improved smoothness of the internal combustion engine is achieved.

Although the above procedure provides, by modeling, the amount of air charge for each cylinder 3 , based on a previously modeled or provided exhaust back pressure, and a corresponding valve opening time of the intake valves 5 can also be provided in simplified embodiments, only the firing interval of the individual successive reaching into the combustion cycle cylinder 3 for controlling the valve opening times of the intake valves 5 to take into account. In particular, when changing the firing intervals between cylinders 3 a cylinder bank 11 and between cylinders 3 different cylinder banks 11 the valve timing, in particular the opening time of the respective intake valve, regardless of the rotational speed of the internal combustion engine 2 be applied with an offset. This makes it possible to adapt the air fillings without great computational effort for the modeling of the exhaust gas back pressure at the individual cylinders 3 or to realize a resulting air filling.

Claims (11)

Method for operating an internal combustion engine ( 2 ) with several cylinders ( 3 ) in a four-stroke operation, each of the cylinders ( 3 ) Fresh air via at least one inlet valve ( 5 ) is supplied in an intake stroke and combustion exhaust gas from each of the cylinders ( 3 ) via at least one outlet valve ( 6 ) is ejected in an exhaust stroke, comprising the following steps: - providing (S1) an exhaust gas back pressure indication for each of the cylinders ( 3 ), wherein the exhaust back pressure indication an exhaust back pressure for the relevant cylinder ( 3 ) during the exhaust stroke; Adjusting (S5) at least one valve timing of the intake valve ( 5 ), in particular a valve opening time and / or a valve closing time, for each of the cylinders ( 3 ) based on the exhaust backpressure indications of each of the cylinders ( 3 ). The method of claim 1, wherein the exhaust back pressure indications each have a firing interval of the relevant cylinder ( 3 ) to the previously entering the combustion cycle cylinder ( 3 ) or correspond to this. The method of claim 1 or 2, wherein the exhaust gas backpressure information using an exhaust tract model from an operating state of the internal combustion engine ( 2 ). Method according to one of claims 1 to 3, wherein a maximum air charge for each of the cylinders based on the exhaust gas backpressure information of the respective cylinder ( 3 ), wherein the valve timing of the intake valve ( 5 ), which is in the intake stroke, depending on the maximum air charges of all cylinders ( 3 ), in particular depending on the smallest of the maximum air fillings of all cylinders ( 3 ) is set. The method of claim 4, wherein the valve timing of the intake valves ( 5 ) of those cylinders ( 3 ), on their exhaust valves ( 6 ) is a higher exhaust back pressure than the exhaust back pressure on the cylinder during an exhaust stroke ( 3 ) with the smallest maximum air charge, are controlled so that their opening times are extended during a subsequent intake stroke. The method of claim 4, wherein the valve timing of the intake valves ( 5 ) of those cylinders ( 3 ), on their exhaust valves ( 6 ) during a exhaust stroke is a lower exhaust back pressure than the exhaust back pressure on the cylinder ( 3 ) with the largest maximum air charge, are controlled so that their opening times are shortened during a subsequent intake stroke. Device, in particular control device, which is designed to carry out the method according to one of Claims 1 to 6. Engine system ( 1 ) with an internal combustion engine ( 2 ) and with a device according to claim 7. Engine system according to claim 8, wherein the internal combustion engine ( 2 ) has a plurality of cylinder banks, which are arranged in particular in cross-plane construction. Computer program adapted to perform all the steps of a method according to any one of claims 1 to 6 when executed on a data processing device. Machine-readable storage medium on which a computer program according to claim 10 is stored.

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