DE102023123306A1 - Internal combustion engine - Google Patents

Abstract

The invention relates to an internal combustion engine (1) with internal combustion and spark ignition, with an exhaust manifold (2) integrated in the cylinder head and with an exhaust gas turbocharger (4), which is connected to an electric machine (12). High efficiency can be achieved by providing thermal insulation in the integrated exhaust manifold (2). The invention also relates to a drive system for a motor vehicle with such an internal combustion engine (1) and a method for controlling such a drive system.

Description

The invention relates to an internal combustion engine with spark ignition with an exhaust manifold integrated in the cylinder head and with an exhaust gas turbocharger which is connected to an electrical machine.

It has long been known that the efficiency and performance of internal combustion engines can be improved by charging with an exhaust gas turbocharger. When designing such exhaust gas turbochargers, there is typically a conflict of objectives between high efficiency and high performance on the one hand and fast response behavior on the other. One way to improve both aspects is to use a so-called E-Turbo. An electric machine is provided that drives the exhaust gas turbocharger when necessary if there is not enough power available at the turbine. Conversely, at higher speeds, an electrical machine can be operated as a generator to generate electricity to charge a battery.

From the DE 10 2016 115 125 A or the DE 20 2015 101 924 U Such charged internal combustion engines with an electric turbo are known. It is also known to integrate the exhaust manifold in the cylinder head, which makes it possible to arrange the exhaust gas turbocharger in the immediate vicinity of the cylinder head. However, a well-known advantage of the integrated exhaust manifold is to cool the exhaust gases as they flow through the cooled cylinder head and thus ensure compliance with specified temperature limits in the exhaust gas turbine.

The present invention is based on an internal combustion engine of the type described above. Such internal combustion engines have a very good response, but are still perceived as having room for improvement in terms of their efficiency. In particular, it is difficult to generate a sufficient amount of electrical energy in an entire driving cycle to compensate for consumption during engine operation.

An exhaust manifold integrated into the cylinder head means that the exhaust ports of several cylinders open directly into the inlet area of a turbocharger, in particular without the interposition of a separate collector component.

The object of the present invention is to avoid these disadvantages and to provide an internal combustion engine which has high efficiency and whose electric machine simultaneously generates at least as much electrical power as it consumes over a typical driving cycle. The internal combustion engine should be particularly suitable for hybrid drives and have a simple and inexpensive structure. A further object of the present invention is to provide a drive system for a motor vehicle with high efficiency. In addition, a further task is to provide a method for operating an internal combustion engine with which an e-turbo can be used optimally.

According to the invention, thermal insulation is provided in the integrated exhaust manifold. In this way, it is possible to achieve a higher energy yield on the turbine of the exhaust gas turbocharger due to the higher temperatures of the exhaust gas in wide areas of the map, without impermissibly detrimentally loading the engine's charge cycle.

At the same time, the integrated exhaust manifold makes it possible to keep the flow paths of the exhaust gas very short, which is advantageous both for heat loss and for the response behavior of the turbocharger and thus of the internal combustion engine.

It is known per se to provide thermal insulation on an exhaust manifold in order to increase the temperature on the exhaust gas turbocharger. Such a solution is used, for example, in the DE 10 2016 213 386 A described. However, the insulation is provided on an external exhaust manifold and is designed to be switchable in a complex manner.

In the present invention, however, the cooling of the exhaust gases by the cooling medium in the cylinder head is deliberately greatly reduced, but at the same time overheating of the exhaust gas turbine is avoided by various temperature-reducing measures of the engine control and regulation. A typical reduction in the heat release to the coolant that is otherwise usual with an integrated exhaust manifold is in a range between 20% and 50%.

One such temperature-reducing measure is a lowered full load line, which means that the effective mean pressure is limited to a lower limit depending on the engine speed compared to a theoretically possible value. Although this reduces the maximum performance of the internal combustion engine, it is particularly tolerable in so-called dedicated hybrid engines.

Another very effective measure is a particularly high compression ratio in connection with an alternative combustion process. In the context of the present invention, the Miller cycle and the Atkinson cycle are particularly suitable. In the Miller cycle, the intake valve is closed in the intake stroke before bottom dead center is reached, so that the amount of charge air is limited. This allows the internal combustion engine to be operated with a very high geometric compression ratio that is fully effective as an expansion ratio, without reaching the knock limit during mixture compression. In the Atkinson cycle, the intake valve is only closed after bottom dead center, causing some of the cylinder charge to flow back into the intake tract, which ultimately has a similar effect. The extraordinarily high expansion in the combustion and work cycle is reflected in a comparatively low final or. Exhaust gas temperature.

A further measure in this context is external exhaust gas recirculation, which is preferably designed as a low-pressure exhaust gas recirculation.

These measures are preferably combined and coordinated with one another. For example, the amount of recirculated exhaust gas can be taken into account when adjusting the valve. The cylinder filling can be easily adjusted, particularly with the Miller cycle and the Atkinson cycle.

Overall, in the context of the present invention, the provision of a relatively large exhaust gas turbocharger has proven successful, since a compressor efficiency of more than 70% to approximately 75% can be achieved in this way.

In a first preferred embodiment variant of the present invention, the thermal insulation is designed as an insulating coating. Such a coating can be made, for example, from a suitable ceramic material. The layer can be sprayed on, applied as an enamel or slip layer, or introduced as a prefabricated shell structure before or after the casting process, for example in the form of prepregs.

An alternative embodiment variant proposes that the thermal insulation is designed as an insulating insert. An air gap extending most of the length of the insert isolates the exhaust gas from the cooled cylinder head. An insulating insert can also be provided in only part of the manifold channels, even if this limits the effect achieved.

The invention also relates to a drive system for a motor vehicle with an internal combustion engine of the type described above and at least one further electrical machine that drives the motor vehicle alternatively or in addition to the internal combustion engine. It is therefore a motor vehicle with a hybrid drive in which the internal combustion engine can be operated in a consumption-optimal range in most operating points or can be switched off completely. In particular, the hybrid concept makes it possible to achieve a reduced full-load characteristic curve of the internal combustion engine, which in turn is beneficial for maximizing the compression ratio in an efficient manner. In this way, the consumption advantages achieved during charging can actually be realized and at the same time thermal overstressing of the exhaust gas turbocharger can be avoided.

In addition, the invention also relates to a method for controlling a drive system described above with an internal combustion engine, in which the power of the electric machine is determined primarily based on a difference between a target turbocharger speed and an actual turbocharger speed.

In this context, primary means that there can also be other influencing factors for the performance of the electrical machine, such as the state of charge of the battery, and that of course boundary conditions must be met, such as the maximum permissible power of the electrical machine. The power of the electric machine here is understood to mean both the drive power in the case of engine operation and the braking power in the case of generator operation.

It has been shown that such a control concept is particularly well suited to operating highly efficient hybrid machines with electric turbochargers. The respective turbocharger target speed is preferably determined from a map primarily as a function of the speed of the internal combustion engine and the target boost pressure. Here, too, there may be other factors in addition to the map mentioned, particularly in the long-term range, for example to avoid long-term operation of the electrical machine at high power.

It is also advantageous if a VTG position is determined from a map primarily as a function of the speed of the internal combustion engine and the target boost pressure. However, the VTG position can also be used to carry out longer-term corrections in order to improve the charge/discharge balance of the battery, for example through the generator To keep the operation of the electrified exhaust gas turbocharger in balance.

Due to the special design of the drive system, it is possible in particular to achieve an optimization of the overall efficiency by taking the state of charge of the hybrid battery into account when controlling the exhaust gas turbocharger. For example, if the current state of charge is above a certain limit value, then an increased torque request can be made primarily via the additional electric machine of the hybrid drive and it is not necessary to accelerate the exhaust gas turbocharger electrically. When the charge level is low, however, torque can be built up quickly by appropriately controlling the electric machine of the exhaust gas turbocharger.

In addition, it is also advantageous if the charge state of an electric battery that supplies the electric machine is taken into account when controlling the electric machine.

In one embodiment variant of the method according to the invention it is provided that the turbine of the exhaust gas turbocharger is constantly operated with the full flow of the exhaust gas. This means that no control organs are required for the exhaust-side loading of the turbine and the output control of the exhaust gas turbocharger is solely the responsibility of the electric machine of the exhaust gas turbocharger, which operates as a motor and generator, which reduces the effort.

Alternatively, it can be provided that the power of the turbine of the exhaust gas turbocharger is controlled via a VTG system or via a wastegate. The control is carried out via maps and not via a closed control loop, i.e. a specific position of the wastegate or the guide vanes of the VTG mechanism is assigned to each operating point via the maps. This means that increased flexibility in the design of the components and a much easier coordination of the control can be achieved, since in this way only the power of the electric machine of the exhaust gas turbocharger is regulated and two parallel control loops are not provided that have to be coordinated together.

It is also advantageous if exhaust gas recirculation (EGR) is provided, which is preferably designed as a low-pressure exhaust gas recirculation. The EGR quantity is also determined using maps, particularly taking temperature and pressure into account. The pressure is measured before and after the EGR valve. Together with the flow characteristics of the EGR valve, the EGR quantity can be adjusted to the target EGR quantity.

When using exhaust gas recirculation, the boost pressure requirement increases. In particular, the wastegate or the VTG mechanism is adjusted in such a way that the additional boost pressure requirement of the EGR is taken into account by closing the wastegate or closing the VTG adjustment mechanism. The timing is adjusted so that the cylinder filling is adapted to the EGR requirements. With EGR, a later intake closure is selected in the case of a Miller cycle, and an earlier one in an Atkinson cycle. A correction of the desired generator or motor operation of the electric machine of the exhaust gas turbocharger can also be carried out in this way.

In order to compensate for long-term changes in the behavior of the exhaust gas turbocharger or other components, an adaptive control of the electric machine can be carried out by measuring at least one variable from a group that includes the speed of the exhaust gas turbocharger, the boost pressure, the charge air temperature and the current on the electric machine as well as the Charge state of a battery in the drive train includes hybrid battery. Existing control deviations over a longer period of time are recorded and control parameters are adjusted if necessary.

• • 1 ein Diagramm, in dem die einzelnen Komponenten eines erfindungsgemäßen Antriebssystems dargestellt sind;
• • 2 und 3 Kennfelder, die den Betrieb der Brennkraftmaschine samt Abgasturbolader erklären; und
• • 4 ein Diagramm, das das Regelungsverhalten erklärt.

The present invention is explained in more detail below using the exemplary embodiments shown in the figures. The figures show:

• • 1 a diagram in which the individual components of a drive system according to the invention are shown;
• • 2 and 3 Maps that explain the operation of the internal combustion engine including the exhaust gas turbocharger; and
• • 4 a diagram that explains the control behavior.

1 shows a drive system for a hybrid motor vehicle with an internal combustion engine 1 with an exhaust manifold 2 integrated in the cylinder head, which is connected to an exhaust gas turbocharger 4 via an exhaust pipe 3. The internal combustion engine 1 is connected to a further electrical machine 6 via a transmission 5 in order to alternatively or jointly deliver torque to a drive shaft 7. The present invention can basically be applied to all types of hybrid drive, not only parallel hybrids as shown, but also, for example, to serial hybrids.

The further electrical machine 6 is supplied via a hybrid battery 8 and charges it in generator operation.

The exhaust gas turbocharger 4 has a compressor 9, which takes in air via an intercooler 10 compressed to the internal combustion engine 1. A turbine 11 is connected to the integrated exhaust manifold 2 via the exhaust pipe 3. The exhaust pipe 3 is designed to be as short as possible and can also be omitted if the turbine is mounted directly on the cylinder head. An electrical machine 12 is also arranged on the shaft of the compressor 9 and turbine 11, which either drives the exhaust gas turbocharger 4 or generates electricity as a generator.

An EGR cooler 13 and an EGR valve 14 arranged downstream thereof make it possible to feed exhaust gas from an exhaust line 15 downstream of the turbine 11 into an intake line 16 upstream of the compressor 9.

The electric machine 12 is powered by an electric battery 17. This can be a 12 V or 48 V on-board battery, but it is also possible to combine the functions of the electric battery 17 and the hybrid battery 8 in a single battery.

In 2 The speed of the internal combustion engine 1 is plotted in rpm on the horizontal axis and the effective mean pressure in bar is plotted on the vertical axis. An upper boundary line 20 represents the maximum load depending on the speed that is possible due to the design of the internal combustion engine 1. As a dedicated hybrid machine, however, the load is more limited, namely to an area that is limited upwards by a further boundary line 21 (arrow 22). This further boundary line 21 also represents approximately the upper limit of the range with the best efficiency.

The speed of the internal combustion engine 1, which is designed as a dedicated hybrid machine, is also limited to approximately 5000 rpm (line 25) compared to the technically possible speed of 6000 rpm (line 24).

By regulating the hybrid drive, an attempt is made to avoid operating points below the range with the best efficiency if possible (range 26, arrow 30).

In 3 is the diagram of 2 with the operating ranges of the exhaust gas turbocharger 4 shown. The operating points in which the electric machine 12 drives the exhaust gas turbocharger 4 are located in the lower speed range (area 27). At higher speeds, the electrical machine 12 works in generator mode (range 28). The border between areas 27 and 28 is marked 29. In area 32, which is bounded at the top by line 31, the exhaust gas turbocharger 4 is not active.

In 4 the behavior of various measured variables in a transient driving state is shown over time t. The starting point is an increase in the torque requirement by pressing the accelerator pedal, which can be seen from the slope of curve 36, which indicates the accelerator pedal position selected by the driver.

As a result, the load ultimately increases, i.e. the effective mean pressure (curve 37), while the speeds of the further electrical machine 6 (actual turbocharger speed, curve 38) and the speed of the internal combustion engine 1 (curve 39) change little.

In more detail, as a result of the increased torque requirement, the turbocharger setpoint speed (curve 40) initially increases, and the actual turbocharger speed (curve 41) is then tracked by the control system. This in turn is caused by an increase in the power of the electrical machine (curve 42).

It can also be seen from the diagram that the target charging pressure (curve 43) increases more strongly or earlier than the actual charging pressure (curve 44), which is taken into account by a correction factor (curve 45) that is used when calculating the required power of the electrical machine ( 12) is included.

A further VTG correction value, which is indicated by curve 46, is intended to keep the power of the electric machine within a desired corridor, which is determined from the maximum power for engine or .Generator operation and the state of charge of the battery. At the in 4 In the situation shown, there is no correction of the VTG position.

The present invention makes it possible to produce hybrid drives with particularly high overall efficiency.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102016115125 A [0003]
• DE 202015101924 U [0003]
• DE 102016213386 A [0009]

Claims (15)

Internal combustion engine (1) with internal combustion and spark ignition with an exhaust manifold (2) integrated in the cylinder head and with an exhaust gas turbocharger (4) which is connected to an electric machine (12), characterized in that there is thermal insulation in the integrated exhaust manifold (2). is provided. Internal combustion engine (1). Claim 1 , characterized in that the thermal insulation is designed as an insulating coating. Internal combustion engine (1). Claim 1 , characterized in that the thermal insulation is designed as an insulating insert. Internal combustion engine (1) according to one of the Claims 1 until 3 , characterized in that the internal combustion engine (1) has a high geometric compression ratio, which is preferably greater than 13 and particularly preferably between 14 and 16. Internal combustion engine (1). Claim 4 , characterized in that the internal combustion engine (1) has a valve control that is designed for a Miller or Atkinson cycle. Drive system for a motor vehicle with an internal combustion engine (1) according to one of Claims 1 until 5 and at least one further electrical machine (6) which drives the motor vehicle alternatively or in addition to the internal combustion engine (1). Method for controlling an internal combustion engine according to one of the Claims 1 until 5 , characterized in that the performance of the electric machine (12) is determined primarily based on a difference between a target turbocharger speed and an actual turbocharger speed. Procedure according to Claim 7 , characterized in that the turbocharger target speed is determined from a map primarily as a function of the speed of the internal combustion engine (1) and the target boost pressure. Procedure according to one of the Claims 7 or 8th , characterized in that a VTG position is determined from a map primarily as a function of the speed of the internal combustion engine (1) and the target boost pressure. Procedure according to one of the Claims 7 until 9 , characterized in that the internal combustion engine (1) is operated according to a Miller cycle. Procedure according to one of the Claims 7 until 10 , characterized in that the internal combustion engine (1) is operated according to an Atkinson cycle. Procedure according to one of the Claims 7 until 11 , characterized in that the turbine (11) of the exhaust gas turbocharger (4) is constantly operated with the full flow of exhaust gas. Procedure according to one of the Claims 7 until 12 , characterized in that an exhaust gas recirculation is provided, which is preferably designed as a low-pressure exhaust gas recirculation. Procedure according to one of the Claims 7 until 13 , characterized in that an adaptive control of the electric machine (12) is carried out by measuring at least one variable from a group which includes the speed of the exhaust gas turbocharger (4), the boost pressure, the charge air temperature and the current on the electric machine (12) as well includes the state of charge of a hybrid battery (8). Procedure according to one of the Claims 7 until 14 , characterized in that when controlling the electrical machine (12), the charge state of an electrical battery (17) which supplies the electrical machine (12) is taken into account.

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