DE202013104803U1 - Charged spark-ignition internal combustion engine - Google Patents

Abstract

A supercharged spark-ignition internal combustion engine having at least one cylinder head with at least three arranged along the longitudinal axis of the cylinder head cylinders (1, 2, 3, 4), in which - each cylinder (1, 2, 3, 4) has at least one outlet opening, to which a Exhaust pipe (51, 52) for discharging the exhaust gases via Abgasabführsystem connects, the exhaust pipes (51, 52) to form a common exhaust manifold (7) merge to form an exhaust line (6), and - at least one exhaust gas turbocharger is provided, the one in the Comprising at least two cylinders (1, 2, 3, 4) have a different compression ratio εi, wherein the compression ratio εi with the line length .DELTA.li the Abgasabführsystems between the at least one outlet opening of the cylinder (1, 2, 3, 4) and the turbine correlates in such a way that the cylinder (1, 2, 3, 4) having the shorter line length Δli the smaller compression ratio εi.

Description

• – jeder Zylinder mindestens eine Auslassöffnung aufweist, an die sich eine Abgasleitung zum Abführen der Abgase via Abgasabführsystem anschließt, wobei die Abgasleitungen unter Ausbildung eines gemeinsamen Abgaskrümmers zu einer Gesamtabgasleitung zusammenführen, und
• – mindestens ein Abgasturbolader vorgesehen ist, der eine in der Gesamtabgasleitung angeordnete einflutige Turbine umfasst.

The invention relates to a supercharged spark-ignition internal combustion engine having at least one cylinder head with at least three cylinders arranged along the longitudinal axis of the cylinder head, in which

• - Each cylinder has at least one outlet opening, which is followed by an exhaust pipe for discharging the exhaust gases via Abgasabführsystem, wherein the exhaust pipes merge to form a common exhaust manifold to an overall exhaust line, and
• - At least one exhaust gas turbocharger is provided which comprises a arranged in the entire exhaust line single-flow turbine.

An internal combustion engine of the above type is used for example as a drive for a motor vehicle. In the context of the present invention, the term internal combustion engine includes spark ignited gasoline engines, but also spark ignited hybrid internal combustion engines, d. H. Internal combustion engines, which are operated with a hybrid combustion process, or spark-ignited internal combustion engines, which have an electric motor that can be driven in drive with the internal combustion engine, which receives power from the internal combustion engine or additionally delivers power.

Internal combustion engines have a cylinder block and at least one cylinder head, which is used to form the cylinder, d. H. the combustion chambers, are interconnected, including holes in the cylinder head and cylinder block are provided. The cylinder block serves as the upper crankcase half of the receptacle of the piston or the cylinder tube of each cylinder. The upper half of the crankcase formed by the cylinder block is supplemented by the oil pan which can be mounted on the cylinder block and serves as the lower half of the crankcase and which serves to collect and store the engine oil and forms part of the oil circuit. For receiving and supporting a crankshaft at least two bearings are provided in the crankcase. To transmit a torque each piston is pivotally connected to the crankshaft. The crankshaft mounted in the crankcase receives the connecting rod forces and transforms the oscillating stroke movement of the pistons into a rotating rotational movement of the crankshaft.

The cylinder head usually serves to accommodate the valve gear required for the charge cycle. For actuating a valve, on the one hand a valve spring is provided to bias the valve in the direction of valve closing position, and on the other hand, in order to open the valve against the biasing force of this valve spring, a valve actuator. The required actuating mechanism including the valves is referred to as a valvetrain. In the context of the charge exchange, the removal of the combustion gases via the exhaust pipe via the at least one outlet opening and the feeding of the charge air via the intake takes place via the at least one inlet opening of each cylinder. In this case, at least portions of the at least one intake pipe or the at least one exhaust pipe of each cylinder are integrated in the cylinder head.

The exhaust pipes of the at least three cylinders are usually combined and also in the internal combustion engine according to the invention to form a common total exhaust gas line. The combination of exhaust pipes to an overall exhaust line is generally and in the context of the present invention referred to as exhaust manifold.

Downstream of the common exhaust manifold, in the present case, the exhaust gases are supplied to the single-flow turbine of at least one exhaust-gas turbocharger for charging the internal combustion engine and optionally one or more systems for exhaust-gas aftertreatment.

The advantage of an exhaust gas turbocharger, for example compared to a mechanical supercharger, is that there is no mechanical connection to the power transmission between the supercharger and the internal combustion engine. While a mechanical supercharger obtains the energy required for its drive completely from the internal combustion engine and thus reduces the power provided and thus adversely affects the efficiency, the exhaust gas turbocharger uses the exhaust gas energy of the hot exhaust gases.

An exhaust gas turbocharger comprises a compressor arranged in the intake system and a turbine arranged in the exhaust gas discharge system, which are arranged on the same shaft. The hot exhaust gas flow is supplied to the turbine via the entire exhaust gas line and relaxes with the release of energy in this turbine, causing the shaft to rotate. The energy emitted by the exhaust gas flow to the turbine and finally to the shaft is used to drive the compressor, which is also arranged on the shaft. The compressor conveys and compresses the charge air supplied to it, whereby a charge of at least three cylinders is achieved. Optionally, a charge air cooling is provided, with which the compressed charge air is cooled before entering the cylinder.

The charge is used primarily to increase the performance of the internal combustion engine. The air required for the combustion process is compressed, which allows each cylinder per working cycle, a larger air mass can be supplied. Thereby The fuel mass and thus the medium pressure can be increased. The charge is a suitable means to increase the capacity of an internal combustion engine with unchanged displacement or to reduce the displacement at the same power. In any case, the charging leads to an increase in space performance and a lower power mass. At the same vehicle boundary conditions, the load collective can thus be shifted to higher loads in which the specific fuel consumption is lower.

In supercharged internal combustion engines of the type in question, in which the exhaust pipes of a cylinder head are combined to form a common exhaust manifold to a single overall exhaust line and in which the single-flow turbine of an exhaust gas turbocharger is arranged in this total exhaust line, the cylinders have different residual gas components after the charge cycle.

In a cylinder head with four cylinders arranged in series, the inner cylinders have a higher residual gas content after the charge exchange than the two outer cylinders. The 1a and 1b show this phenomenon for a low speed n _mot = 1200min ^-1 (see 1a ) and for a higher speed n _mot = 6000min ^-1 (see 1b ), with the percentage of residual gas in percent [%] of the fresh cylinder charge on the ordinate and the number of cylinders on the abscissa.

The cause of the different residual gas fractions is the dynamic wave processes that take place in the exhaust gas removal system during the charge cycle. The evacuation of the combustion gases from the cylinders of an internal combustion engine as part of the charge exchange is based essentially on two different mechanisms. When, at the beginning of the charge cycle, the exhaust valve opens near bottom dead center, the combustion gases flow at high speed through the exhaust port into the exhaust system due to the high pressure level prevailing in the cylinder at the end of the combustion and the associated high pressure difference between the combustion chamber and the exhaust pipe. This pressure-driven flow process is accompanied by a high pressure peak, which is also referred to as Vorlassstoß and propagates along the exhaust pipe at the speed of sound, whereby the pressure degrades more or less with increasing distance due to friction, d. H. reduced.

In the course of the charge cycle, the pressures in the cylinder and in the exhaust line are the same, so that the combustion gases are primarily not evacuated pressure driven, but are ejected as a result of the stroke of the piston.

The dynamic wave processes or pressure fluctuations in the Abgasabführsystem are the reason why the staggered working cylinder of a multi-cylinder internal combustion engine when changing the charge influence each other, in particular can hinder. A deteriorated torque characteristic or a reduced power supply may be the result.

The pressure waves emanating from a cylinder, not only run through the at least one exhaust pipe of this cylinder, but also along the exhaust pipes of the other cylinder and possibly up to the provided at the end of each pipe outlet. Exhaust gas that has already been ejected or discharged into an exhaust gas line during the charge exchange can therefore again enter the cylinder as a result of the pressure wave that emanates from another cylinder. It proves to be disadvantageous, in particular, if overpressure prevails at the outlet opening of one cylinder towards the end of the charge change or if the pressure wave of another cylinder propagates along the exhaust pipe in the direction of the outlet opening, which counteracts the evacuation of the combustion gases from this cylinder. The combustion gases are significantly pushed out in this phase of the charge change as a result of the stroke of the piston. In some cases, even exhaust gas that originates from one cylinder can get into another cylinder before its outlet closes. It should also be considered in this context that the pressure waves passing through the exhaust gas removal system are reflected and overlap.

The exhaust gas in the cylinder, d. H. the residual gas content remaining in the cylinder has a decisive influence on the knocking behavior of a spark-ignited internal combustion engine, whereby the risk of knocking combustion increases with increasing proportion of exhaust gas. In order to avoid knocking combustion, cylinders with higher residual gas content are ignited later than the other cylinders, d. H. as a cylinder with lower residual gas content, wherein the subsequent combustion of the fuel-air mixture initiated thereby leads to a smaller gas force on the piston and thus to a lower transmitted torque. The different cylinder-related torques lead to torsional vibrations of the crankshaft, which vibrations can propagate into the rest of the internal combustion engine and into the vehicle into it.

Problems when changing the charge of a multi-cylinder internal combustion engine arise especially at low speeds, if during a Valve overlap, in which the exhaust valve is not yet closed when the inlet valve is open, the exhaust gas is to be flushed out of the cylinder at the cost of flushing losses (see also 1a and 1b ).

The mutual influence of the cylinder during the charge cycle could be counteracted by the same length exhaust gas lines of the cylinder at the expense of a complex voluminous Abgasabführsystems or by the exhaust pipes of the individual cylinders are guided separately for a longer distance.

For several reasons, however, it is advantageous to make the exhaust pipes short and to integrate the exhaust manifold as far as possible in the at least one cylinder head, d. H. the merger of the exhaust pipes to make a total exhaust gas as far as possible already in the cylinder head.

This leads to a more compact design of the internal combustion engine and allows a tight packaging of the entire drive unit in the engine compartment. In addition, there are cost advantages in the manufacture and assembly and a weight reduction of the internal combustion engine, in particular in a complete integration of the exhaust manifold in the cylinder head.

Furthermore, the most extensive integration of the connection of the exhaust pipes can advantageously affect the arrangement and operation of an exhaust aftertreatment system, which is provided downstream of the manifold. The path of the hot exhaust gases to the various exhaust aftertreatment systems should be as short as possible so that the exhaust gases are given little time to cool down and the exhaust aftertreatment systems reach their operating temperature or light-off temperature as quickly as possible, in particular after a cold start of the internal combustion engine.

In this connection, efforts are made to minimize the thermal inertia of the section of the exhaust pipes between the exhaust port on the cylinder and exhaust aftertreatment system, which can be achieved by reducing the mass and the length of this section. Leading the way here can be the most extensive integration of the exhaust manifold in the cylinder head.

When charged by means of exhaust gas turbocharger internal combustion engine - such as the internal combustion engine according to the invention - is sought, the turbine as close to the outlet, d. H. close to the outlet openings of the cylinder, to be arranged in order to be able to use the exhaust enthalpy of the hot exhaust gases, which is largely determined by the exhaust pressure and the exhaust gas temperature, optimally and to ensure a rapid response of the turbocharger. Again, the thermal inertia and the volume of the conduit system between the outlet openings of the cylinder and the turbine should be minimized, which in turn is the most extensive integration of the exhaust manifold in the cylinder head is targeted.

Due to the extensive integration of the exhaust manifold in the cylinder head and the shortening of the exhaust pipes generally exacerbated the problem of mutual influence of the cylinder during charge exchange, especially the above-described residual gas problem, which is characterized, inter alia, by different levels of residual gas in the cylinders, the different Require ignition timing and thereby cause different sized torques that lead to torsional vibrations of the crankshaft.

In principle, the mutual influence of the cylinders during the charge exchange could also be prevented by combining the cylinders into groups, whereby the exhaust lines of the cylinders of each cylinder group combine to form an exhaust gas manifold to form an exhaust gas manifold and the total exhaust gas lines are connected to a multi-flow turbine of the type in that in each case an overall exhaust gas line is connected to a flood of the multi-flow turbine.

The cylinder groups would advantageously be configured in such a way that the dynamic wave processes in the exhaust gas lines of the cylinders of a group influence as little as possible adversely. In the case of a cylinder head with four cylinders arranged in series, it is advantageous in this regard to combine two cylinders which have a firing interval of 360 ° CA, in each case into a cylinder group, so that the cylinders of a group have the greatest possible thermodynamic offset. If, for example, the ignition in the cylinders is initiated in accordance with the ignition sequence 1 - 2 - 4 - 3 or in accordance with the ignition sequence 1 - 3 - 4 - 2, it would be advantageous for the outer cylinders to form a first group and the inner cylinders for a second group to get together.

A multi-flow turbine, for example a double-flow turbine in the form of a double-flow turbine or a twin-flow turbine, is significantly more cost-intensive than the single-flow turbine used in the internal combustion engine according to the invention.

Against the background of what has been said, it is the object of the present invention to provide a To provide internal combustion engine according to the preamble of claim 1, which is improved in a cost effective manner with respect to the residual gas problem.

• – jeder Zylinder mindestens eine Auslassöffnung aufweist, an die sich eine Abgasleitung zum Abführen der Abgase via Abgasabführsystem anschließt, wobei die Abgasleitungen unter Ausbildung eines gemeinsamen Abgaskrümmers zu einer Gesamtabgasleitung zusammenführen, und
• – mindestens ein Abgasturbolader vorgesehen ist, der eine in der Gesamtabgasleitung angeordnete einflutige Turbine umfasst,

die dadurch gekennzeichnet ist, dass

• – mindestens zwei Zylinder ein unterschiedliches Verdichtungsverhältnis ε_i aufweisen, wobei das Verdichtungsverhältnis ε_i mit der Leitungslänge ∆l_i des Abgasabführsystems zwischen der mindestens einen Auslassöffnung des Zylinders und der Turbine korreliert, in der Art, dass der Zylinder mit der kürzeren Leitungslänge ∆l_i das kleinere Verdichtungsverhältnis ε_i aufweist.

This object is achieved by a supercharged spark-ignition internal combustion engine having at least one cylinder head with at least three cylinders arranged along the longitudinal axis of the cylinder head, in which

• - Each cylinder has at least one outlet opening, which is followed by an exhaust pipe for discharging the exhaust gases via Abgasabführsystem, wherein the exhaust pipes merge to form a common exhaust manifold to an overall exhaust line, and
• At least one exhaust-gas turbocharger is provided, which comprises a single-flow turbine arranged in the overall exhaust gas line,

which is characterized in that

• - At least two cylinders have a different compression ratio ε _i , the compression ratio ε _i with the line length .DELTA.l _i of Abgasabführsystems between the at least one outlet of the cylinder and the turbine correlated, such that the cylinder with the shorter line length .DELTA.l _i having the smaller compression ratio ε _i .

The cylinders of an internal combustion engine according to the invention are equipped with different compression ratios ε _i , wherein the compression ratio ε _{i is selected} according to the residual gas content remaining in the respective cylinder. According to the invention, namely the cylinders, which have the higher residual gas content due to the shorter distance between the cylinder outlet and turbine after the charge change and are therefore more at risk of knocking combustion, equipped with a lower compression ratio ε _low . The cylinders, in contrast, have a lower residual gas content, because in them the distance between the cylinder outlet and turbine longer fails, are less knock hazards and can therefore be equipped with a higher compression ratio ε _high .

In a cylinder head with four cylinders arranged in series, the inner cylinders due to the shorter exhaust paths after the gas exchange on a higher residual gas content than the two outer cylinders, so that according to the invention, the inner cylinder a lower compression ratio ε _low and the outer cylinder a higher compression ratio ε _high get assigned.

The inventively regarded as relevant distance between the cylinder outlet and the single-flow turbine is referred to herein as the cylinder-related line length .DELTA.l _i of Abgasabführsystems between the at least one outlet of the cylinder and the turbine. The inventive approach according to claim 1 does not directly refer to the actually relevant here residual gas content, but rather on the causally related to the residual gas content constructive or representational feature of the cylinder-related line length .DELTA.l _i . It is assumed that the proportion of residual gas correlates with the cylinder-related line length Δl _i ; though not strictly.

With the internal combustion engine according to the invention is not intended to equalize the residual gas content of the cylinder over all cylinders, ie equalize the cylinder-specific residual gas components. Rather, it is proposed to compensate for the different residual gas fractions by the variation of a structural feature, namely the compression ratio ε _i , or to counteract the effects caused by the different residual gas fractions by different compression ratios ε _i .

Ie. the cylinders of a multi-cylinder internal combustion engine according to the invention have different residual gas fractions due to the manifold and will generally have to be operated with different ignition times t _{ignition, i} . However, similarly large gas forces on the cylinder-associated pistons lead to similarly large cylinder-related torques, so that the torsional vibrations of the crankshaft and associated vibrations are reduced. It should also be considered in this context that the cylinder-specific residual gas content has an influence on the burning rate.

With the internal combustion engine according to the invention, a supercharged spark-ignition internal combustion engine is provided, which is improved in a cost-effective manner with regard to the residual gas problem. Thus, the object underlying the invention is achieved.

The internal combustion engine according to the invention has at least three cylinders. An internal combustion engine usually has to comprise three or more cylinders, so that at least two cylinders have different lengths of exhaust gas to the turbine.

Further advantageous embodiments of the supercharged spark-ignition internal combustion engine are discussed in connection with the subclaims.

Embodiments of the charged spark-ignition internal combustion engine are advantageous, in which the exhaust manifold is symmetrical with respect to a center plane perpendicular to the longitudinal axis of the cylinder head.

The symmetrical design of the manifold, which is customary in practice, leads to the fact that the three or more cylinders arranged along the longitudinal axis of the cylinder head of an internal combustion engine according to the invention have different lengths of exhaust gas pipes as far as the turbine.

As soon as several cylinders along the longitudinal axis of a cylinder head, d. H. in series, there is at least one inboard cylinder positioned in or near the midplane, and at least two outboard cylinders further spaced from the midplane, with the common overall exhaust conduit disposed in the midplane.

Therefore, even in internal combustion engines with three cylinders arranged in series embodiments are advantageous in which the three cylinders form two groups, the two outer cylinders form a first group whose cylinders have a compression ratio ε ₁ and an inner cylinder forms a second group and has a compression ratio ε ₂ with ε ₂ <ε ₁ .

For the reasons mentioned above, in internal combustion engines with four cylinders arranged in series, embodiments are advantageous in which the four cylinders form two groups, the two outer cylinders forming a first group whose cylinders have a compression ratio ε ₁ and the two inner cylinders having a second one Group form and have a compression ratio ε ₂ with ε ₂ <ε ₁ .

• – die zwei außenliegenden Zylinder eine erste Gruppe bilden, deren Zylinder ein Verdichtungsverhältnis ε₁ aufweisen,
• – der eine innenliegende Zylinder eine dritte Gruppe bildet und ein Verdichtungsverhältnis ε₃ aufweist mit ε₃ < ε₁, und
• – die zwei zwischen den außenliegenden Zylindern und dem innenliegenden Zylinder angeordneten Zylinder eine zweite Gruppe bilden, deren Zylinder ein Verdichtungsverhältnis ε₂ aufweisen mit ε₃ < ε₂ < ε₁.

In internal combustion engines with five cylinders arranged in series, embodiments in which the five cylinders form three groups are advantageous in this connection

• The two outer cylinders form a first group whose cylinders have a compression ratio ε ₁ ,
• - An internal cylinder forms a third group and has a compression ratio ε ₃ with ε ₃ <ε ₁ , and
• - The two cylinders arranged between the outer cylinders and the inner cylinder form a second group whose cylinders have a compression ratio ε ₂ with ε ₃ <ε ₂ <ε ₁ .

Embodiments of the supercharged spark-ignition internal combustion engine in which the at least two cylinders with different compression ratio ε _i are distinguished by different cylinder volumes V _i are advantageous, wherein the at least one cylinder of a first group has a compression ratio ε ₁ and a cylinder volume V ₁ and the at least one cylinder a second group has a compression ratio ε ₂ and a cylinder volume V ₂ with ε ₂ <ε ₁ and V ₂ > V ₁ .

In internal combustion engines, in which each cylinder comprises a combustion chamber which is formed by a piston head of a cylinder-associated piston, a cylinder tube and the at least one cylinder head as the combustion chamber roof, embodiments are advantageous, which are characterized in that the different cylinder volumes V _i due geometric differences of the cylinder-related combustion chamber roofs result.

In internal combustion engines, in which each cylinder comprises a combustion chamber which is formed by a piston head of a cylinder-associated piston, a cylinder tube and the cylinder head as the combustion chamber roof, embodiments are also advantageous, which are characterized in that the different cylinder volumes V _i due to geometric Differences in the cylinder-related piston arise.

The cylinder volume V _i and thus the compression ratio ε ₁ to vary by means of different pistons, is a measure that can be retrofitted to already on the market internal combustion engines, in the sense that they can be inexpensively modified to internal combustion engines according to the invention.

In this context, embodiments of the supercharged spark-ignition internal combustion engine in which the geometric differences of the cylinder-associated pistons are differences in the shape of a depression provided in the piston crown are advantageous.

Often, an intended piston recess can not be changed arbitrarily, since the recess primarily serves the charge movement and thus the mixture formation in the combustion chamber.

Therefore, embodiments of the supercharged spark-ignition internal combustion engine in which the geometric differences of the cylinder-associated pistons are differences in the piston height are also advantageous in this connection.

The piston height is determined by the distance between the piston head and the piston pin along the piston longitudinal axis. The piston pin serves the articulated connection of the piston with the connecting rod and is mounted in the piston in a bore, on whose central axis for determining the piston height reference is made.

Also advantageous in this context are embodiments of the supercharged spark-ignition internal combustion engine in which the geometric differences of the cylinder-associated pistons are differences in the piston diameter.

Embodiments of the charged spark-ignition internal combustion engine in which each cylinder is equipped with a spark plug to initiate spark ignition are advantageous. The spark plug is an ignition device for the safe initiation of a spark, which also has the necessary stability and is also inexpensive. Nevertheless, other igniters can be used to initiate spark ignition.

Embodiments of the supercharged spark-ignition internal combustion engine in which each cylinder is equipped with an injection nozzle for the purpose of supplying fuel by means of direct injection are advantageous.

The direct injection is a suitable means for realizing a stratified combustion chamber charge and thus a possibility for dethrottling the gasoline engine or the Otto engine operating method. The direct injection allows within certain limits, a quality control of the gasoline engine, since the fuel-air mixture can lean heavily. The mixture is formed by the direct injection of the fuel into the cylinders or in the cylinders located in the charge air and not by external mixture formation, in which the fuel is introduced into the intake air in the intake air. Nevertheless, embodiments of the internal combustion engine may be advantageous in which for the purpose of a fuel supply, a port injection is provided.

Another way to optimize the combustion process of a gasoline engine, is the use of an at least partially variable valve train. In contrast to conventional valve trains, in which both the stroke of the valves and the control times are not variable, these parameters influencing the combustion process and thus the fuel consumption can be varied more or less by means of variable valve trains. Noticeable fuel savings can be achieved even with only partially variable valve trains. Throttle-free and thus lossless load control is already possible if the closing time of the intake valve and the intake valve lift can be varied. The charge air or mixture mass flowing into the combustion chamber during the intake process is then not controlled by means of a throttle valve, but via the intake valve lift and the opening duration of the intake valve.

Also advantageous are embodiments of the supercharged spark-ignition internal combustion engine, in which at least one at least partially variable valve train is provided.

Embodiments of the supercharged spark-ignition internal combustion engine in which each cylinder has at least two outlet openings are advantageous. During the expulsion of the exhaust gases in the context of the change of charge, it is a primary goal, as quickly as possible to release the largest possible flow cross-sections, to ensure an effective discharge of the exhaust gases, which is why the provision of more than one outlet opening is advantageous.

Embodiments of the supercharged spark-ignition internal combustion engine in which at least two exhaust-gas turbochargers are provided which have turbines of different sizes are advantageous.

In supercharged internal combustion engines with an exhaust gas turbocharger for all cylinders of a cylinder head, as in the internal combustion engine according to the invention, a drop in torque is observed when falling below a certain speed. This torque drop becomes understandable if it is taken into account that the boost pressure ratio depends on the turbine pressure ratio. If, for example, the engine speed is reduced, this leads to a smaller exhaust gas flow and thus to a smaller turbine pressure ratio. As a result, at lower speeds, the boost pressure ratio also decreases, which is equivalent to a torque drop.

The torque characteristic of a supercharged internal combustion engine can be improved by a plurality of turbochargers connected in parallel or in series, optionally in combination with a mechanical supercharger.

The internal combustion engine according to the present embodiment has at least two turbochargers arranged in series. By switching in series of two exhaust gas turbochargers, one of which is an exhaust gas turbocharger as a high pressure stage and an exhaust gas turbocharger as a low pressure stage, the combined compressor map can be widened in an advantageous manner, both towards smaller compressor streams as well as towards larger compressor streams.

In particular, in the exhaust gas turbocharger serving as a high-pressure stage, it is possible to shift the surge limit towards smaller compressor flows, which means that high charge pressure ratios can be achieved even with small compressor flows, which in the lower part-load range Torque characteristic significantly improved. This is achieved by designing the high-pressure turbine for small exhaust gas flows and providing a bypass line, with which increasing exhaust gas flow increasingly exhaust gas is passed to the high-pressure turbine. For this purpose, the bypass line branches off from the exhaust-gas removal system upstream of the high-pressure turbine and flows back into the exhaust-gas removal system downstream of the high-pressure turbine and upstream of the low-pressure turbine, wherein a shut-off element is arranged in the bypass line in order to control the exhaust gas flow conducted past the high-pressure turbine.

Two turbochargers connected in series offer further advantages. The increase in performance through charging can be further increased. Furthermore, the response of such a supercharged internal combustion engine, especially in the partial load range, significantly improved over a comparable internal combustion engine with single-stage supercharging. The reason for this is that the smaller high-pressure stage is less sluggish than a larger exhaust-gas turbocharger used in the context of a single-stage supercharger because the rotor or impeller of a smaller exhaust-gas turbocharger accelerates and decelerates faster.

In the following, the invention is based on the 1a . 1b and on the basis of an embodiment of the supercharged spark-ignition internal combustion engine according to FIG 2 explained in more detail. Hereby shows:

1a in a diagram the percentage of residual gas in the cylinder fresh charge in percent [%] on the ordinate over the number of cylinders on the abscissa for an engine speed n _mot = 1200min ^-1 ,

1b in a diagram, the residual gas content of the fresh cylinder charge in percent [%] on the ordinate on the cylinder number on the abscissa for an engine speed n _mot = 6000min ^-1 , and

2 schematically the cylinder of a first embodiment of the spark-ignited internal combustion engine together with the exhaust manifold.

The 1a and 1b have already been explained in connection with the prior art.

2 schematically shows the four cylinders 1 . 2 . 3 . 4 a spark-ignited four-cylinder in-line engine including exhaust manifold 7 ,

The exhaust pipes 5 ₁ , 5 _{2 of} the four arranged in series, ie along the longitudinal axis of the cylinder head, cylinder 1 . 2 . 3 . 4 lead to the formation of a common exhaust manifold 7 to an entire exhaust line 6 together, with the exhaust manifold 7 is formed symmetrically with respect to a center plane perpendicular to the longitudinal axis of the cylinder head, so that the entire exhaust line 6 lies in this median plane.

The exhaust paths between the respective cylinder outlet and one in the entire exhaust line 6 arranged turbine (not shown) are therefore not for all cylinders 1 . 2 . 3 . 4 uniformly long.

Rather, the exhaust pipes have 5 _{1 of} the two outer cylinders 1 . 4 , which form a first group, a greater line length .DELTA.l ₁ as the exhaust pipes 5 _{2 of} the two inner cylinders 2 . 3 which form a second group and have a shorter line length Δl ₂ . As a result, the inner cylinders 2 . 3 after the charge change a higher residual gas content than the two outer cylinders 1 . 4 ,

The effect caused by the different residual gas components, namely that of cylinder 1 . 4 to cylinder 2 . 3 varying torque is counteracted by different compression ratios ε _i . The two outer cylinders 1 . 4 of the first group receive a compression ratio ε ₁ and the two inner cylinders 2 . 3 the second group has a compression ratio ε ₂ with ε ₂ <ε ₁ .

Ie. the cylinders 2 . 3 with the shorter line length .DELTA.l ₂ are equipped with the lower compression ratio ε ₂ = ε _low and the cylinder 1 . 4 with the longer exhaust pipes 5 ₁ or larger line lengths .DELTA.l ₁ with the higher compression ratio ε ₁ = ε _high . In this respect, the line length Δl _i correlates with the compression ratio ε _i .

At the in 2 shown snapshot are the pistons 1a . 2a of the first and second cylinders 1 . 2 at bottom dead center and the pistons 3a . 4a of the third and fourth cylinders 3 . 4 at top dead center.

The two cylinder groups of in 2 embodiment shown have different cylinder volumes V _i , wherein the outer cylinder 1 . 4 a cylinder volume V ₁ and the inner cylinder 2 . 3 have a cylinder volume V ₂ with V ₂ > V ₁ .

In the present case, the different cylinder volumes V _{i are} due to geometric differences of the cylinder-associated pistons 1a . 2a . 3a . 4a realized by different piston diameter.

LIST OF REFERENCE NUMBERS

1

 first cylinder

1a

 Piston of the first cylinder

2

 second cylinder

2a

 Piston of the second cylinder

3

 third cylinder

3a

 Piston of the third cylinder

4

 fourth cylinder

4a

 Piston of the fourth cylinder

5 ₁

 Exhaust pipe of a cylinder of a first group of cylinders

5 ₂

 Exhaust pipe of a cylinder of a second group of cylinders

6

 Total exhaust pipe

7

 exhaust manifold

_i

 Compression ratio of a cylinder or a group of cylinders

ε ₁

 Compression ratio of a first group of cylinders

ε ₂

 Compression ratio of a second group of cylinders

ε ₃

 Compression ratio of a third group of cylinders

ε _high

 higher compression ratio

_low

 lower compression ratio

Δl _i

 Line length of Abgasabführsystems between an outlet port of a cylinder and the single-flow turbine

° CA

 Degree crank angle

λ

 air ratio

n

 Speed of the internal combustion engine

t _{ignition, i}

 Ignition timing of a cylinder

V _i

 cylinder volume

V ₁

 Cylinder volume of a first group of cylinders

V ₂

 Cylinder volume of a second group of selectable cylinders

Claims (13)

A supercharged spark-ignition internal combustion engine having at least one cylinder head with at least three cylinders arranged along the longitudinal axis of the cylinder head (US Pat. 1 . 2 . 3 . 4 ), in which - each cylinder ( 1 . 2 . 3 . 4 ) has at least one outlet opening, to which an exhaust pipe ( 5 ₁ , 5 ₂ ) for discharging the exhaust gases via Abgasabführsystem connects, the exhaust pipes ( 5 ₁ , 5 ₂ ) while forming a common exhaust manifold ( 7 ) to an overall exhaust gas line ( 6 ), and - at least one exhaust gas turbocharger is provided, one in the overall exhaust gas line ( 6 ) comprising a single-flow turbine, characterized in that - at least two cylinders ( 1 . 2 . 3 . 4 ) have a different compression ratio ε _i , wherein the compression ratio ε _i with the line length .DELTA.l _i of Abgasabführsystems between the at least one outlet opening of the cylinder ( 1 . 2 . 3 . 4 ) and the turbine, in such a way that the cylinder ( 1 . 2 . 3 . 4 ) having the shorter line length Δl _i the smaller compression ratio ε _i . Supercharged spark-ignition internal combustion engine according to claim 1, characterized in that the exhaust manifold ( 7 ) is formed symmetrically with respect to a center plane perpendicular to the longitudinal axis of the cylinder head. Charged spark-ignition internal combustion engine according to claim 2 with three cylinders arranged in series ( 1 . 2 . 3 . 4 ), characterized in that the three cylinders ( 1 . 2 . 3 . 4 ) form two groups, the two outer cylinders ( 1 . 2 . 3 . 4 ) form a first group whose cylinder ( 1 . 2 . 3 . 4 ) have a compression ratio ε ₁ and the one inner cylinder ( 1 . 2 . 3 . 4 ) forms a second group and has a compression ratio ε ₂ with ε ₂ <ε ₁ . Charged spark-ignition internal combustion engine according to claim 2 with four cylinders arranged in series ( 1 . 2 . 3 . 4 ), characterized in that the four cylinders ( 1 . 2 . 3 . 4 ) form two groups, the two outer cylinders ( 1 . 4 ) form a first group whose cylinder ( 1 . 4 ) have a compression ratio ε ₁ and the two inner cylinders ( 2 . 3 ) form a second group and have a compression ratio ε ₂ with ε ₂ <ε ₁ . Charged spark-ignition internal combustion engine according to claim 2 with five cylinders arranged in series ( 1 . 2 . 3 . 4 ), characterized in that the five cylinders ( 1 . 2 . 3 . 4 ) form three groups, wherein - the two outer cylinders ( 1 . 2 . 3 . 4 ) form a first group whose cylinder ( 1 . 2 . 3 . 4 ) have a compression ratio ε ₁ , - an internal cylinder ( 1 . 2 . 3 . 4 ) forms a third group and has a compression ratio ε ₃ with ε ₃ <ε ₁ , and - the two between the outer cylinders ( 1 . 2 . 3 . 4 ) and the inner cylinder ( 1 . 2 . 3 . 4 ) arranged cylinders ( 1 . 2 . 3 . 4 ) form a second group whose cylinder ( 1 . 2 . 3 . 4 ) have a compression ratio ε ₂ with ε ₃ <ε ₂ <ε ₁ . Supercharged spark-ignition internal combustion engine according to one of the preceding claims, characterized in that the at least two cylinders ( 1 . 2 . 3 . 4 ) with different compression ratio ε _i characterized by different cylinder volumes V _i , wherein the at least one cylinder ( 1 . 2 . 3 . 4 ) of a first group has a compression ratio ε ₁ and a cylinder volume V ₁ and the at least one cylinder ( 1 . 2 . 3 . 4 ) of a second group has a compression ratio ε ₂ and a cylinder volume V ₂ with ε ₂ <ε ₁ and V ₂ > V ₁ . A supercharged spark-ignition internal combustion engine according to claim 6, wherein each cylinder ( 1 . 2 . 3 . 4 ) comprises a combustion chamber through a piston head of a cylinder-associated piston ( 1a . 2a . 3a . 4a ), a cylinder tube and the cylinder head is designed as a combustion chamber roof, characterized in that the different cylinder volumes V _i result due to geometric differences of the cylinder-related combustion chamber roofs. A charged spark-ignition internal combustion engine according to claim 6 or 7, wherein each cylinder ( 1 . 2 . 3 . 4 ) comprises a combustion chamber through a piston head of a cylinder-associated piston ( 1a . 2a . 3a . 4a ), a cylinder tube and the cylinder head is designed as a combustion chamber roof, characterized in that the different cylinder volumes V _i due to geometric differences of the cylinder-associated piston ( 1a . 2a . 3a . 4a ). Supercharged spark-ignition internal combustion engine according to claim 8, characterized in that the geometric differences of the cylinder-associated piston ( 1a . 2a . 3a . 4a ) Differences in the shape of a recess provided in the piston crown are. Supercharged spark-ignition internal combustion engine according to claim 8 or 9, characterized in that the geometric differences of the cylinder-associated piston ( 1a . 2a . 3a . 4a ) Are differences in the piston height. Supercharged spark-ignition internal combustion engine according to one of the preceding claims, characterized in that each cylinder ( 1 . 2 . 3 . 4 ) is equipped to initiate a spark ignition with a spark plug. Supercharged spark-ignition internal combustion engine according to one of the preceding claims, characterized in that each cylinder ( 1 . 2 . 3 . 4 ) has at least two outlet openings. Supercharged spark-ignition internal combustion engine according to one of the preceding claims, characterized in that at least two exhaust gas turbochargers are provided which have different sized turbines.

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