Method for operating an internal combustion engine, control unit for an internal combustion engine, and internal combustion engine

Abstract

The invention relates to a method for operating an internal combustion engine (1), which has a compressor (5) arranged in an air path (3) for compressing ambient air of the internal combustion engine (1) flowing along the air path (3), a turbine (9) arranged in an exhaust gas path (7) and drivingly connected to the compressor (5), and an electric motor (11), wherein the electric motor (11) is drivingly connected to the compressor (5), wherein at least one operating parameter is detected that is characteristic of a density of the ambient air of the internal combustion engine (1), and wherein the electric motor (11) is controlled as a function of the at least one operating parameter.

Description

[0001] DESCRIPTION

[0002] Method for operating an internal combustion engine, control device for an internal combustion engine and internal combustion engine

[0003] The invention relates to a method for operating an internal combustion engine, a control unit for an internal combustion engine and an internal combustion engine.

[0004] In internal combustion engines, particularly gas engines, an exhaust gas turbocharger typically uses a turbine that is undersized relative to the engine's rated power to provide a boost pressure control reserve at low air density—particularly due to high ambient temperatures or an engine operating location at a geodetically high altitude—for the purpose of regulating the engine speed and delivering the required power. However, this results in excessive boost pressure at a majority of operating points, and in particular for over 90% of operating time. This pressure must be regulated by a pressure control device, such as a throttle valve. This adversely reduces the engine's efficiency.The provision of boost pressure control reserve could be achieved without the disadvantageous reduction in efficiency using a variable turbine geometry, but such turbines are highly complex, expensive, and mechanically prone to failure. Therefore, especially in gas engines used for power generation, such turbines with variable turbine geometry are hardly economically viable due to the very long maintenance intervals typically associated with these engines.

[0005] The invention is based on the object of providing a method for operating an internal combustion engine, a control unit for an internal combustion engine, and an internal combustion engine, wherein the aforementioned disadvantages are at least reduced, preferably not occurring at all. This object is achieved by providing the present technical teaching, in particular the teaching of the independent claims and the preferred embodiments disclosed in the dependent claims and the description.

[0006] The object is achieved in particular by providing a method for operating an internal combustion engine, wherein an internal combustion engine is operated which has a compressor arranged in an air path for compressing ambient air of the internal combustion engine flowing along the air path—in particular, air drawn in from the environment of the internal combustion engine—a turbine arranged in an exhaust path, which is drive-connected to the compressor, and an electric motor. The electric motor is drive-connected to the compressor. At least one operating parameter is detected which is characteristic of a density of the ambient air—in particular in the environment—of the internal combustion engine, and the electric motor is controlled as a function of the at least one operating parameter.Advantageously, the required boost pressure can be provided even at low air density by controlling the electric motor, by driving the compressor in addition to the turbine. The electric motor thus provides a boost pressure reserve that can be called upon as needed and therefore in a targeted manner. At operating points where this is not required, however, the additional drive from the electric motor can be omitted, at least by not controlling the electric motor, and in particular by not controlling it. Since the turbine does not have to provide the drive power required at peak times on its own, it can be dimensioned larger, which advantageously results in a higher overall efficiency of the internal combustion engine.In particular, the excessive boost pressure that occurs at many operating points in conventional designs is eliminated, and therefore does not need to be regulated by the pressure control device. At the same time, the exhaust backpressure is reduced. In particular, there is no need to undersize the turbine relative to the rated power of the internal combustion engine. In particular, the internal combustion engine operated within the framework of the process can simultaneously exhibit high dynamics with boost pressure control reserve and high efficiency.

[0007] The power of the internal combustion engine is controlled, in particular, by means of the pressure control element arranged in the air path. The pressure control element is designed, in particular, as a throttle valve. Within the scope of the method, the internal combustion engine is operated, in particular, with a fuel gas. In particular, the internal combustion engine is designed as a gas engine. In particular, the fuel gas can be introduced into the air path upstream of the compressor. An ambient air-fuel gas mixture then flows in the air path to the compressor and is compressed by the compressor. Alternatively or additionally, it is possible for the fuel gas to be introduced directly into a combustion chamber of the internal combustion engine.

[0008] In the context of the present technical teaching, a fuel gas is understood to mean, in particular, a combustible gas or gas mixture that is gaseous at room temperature and ambient pressure, in particular at 25 °C and 1013 mbar. In particular, natural gas, in particular liquefied natural gas (LNG), in particular with a variable hydrogen content, or hydrogen, is used as the fuel gas.

[0009] According to a further development of the invention, the electric motor is controlled to drive the compressor when the at least one operating parameter indicates that the density of the ambient air is less than a predetermined limiting density. This advantageously allows targeted control of the electric motor to provide the required boost pressure. Controlling the electric motor to drive the compressor means, in particular, that the electric motor is controlled as a motor. In its capacity as an electric machine, it is also possible to control the electric motor as a generator at other operating points, i.e., to operate it as a generator.

[0010] According to a further development of the invention, it is provided that the electric motor is at least not controlled by a motor, in particular not, if the at least one operating parameter allows the conclusion that the density of the ambient air corresponds at least to the predetermined limit density. Advantageously, the efficiency of the internal combustion engine is therefore particularly high, in particular because under conditions in which no additional drive of the compressor by the electric motor is required, no energy is provided for the compressor. According to a further development of the invention, it is provided that a drive power of the electric motor is selected depending on the at least one operating parameter. Advantageously, the drive power required to provide the required boost pressure can thus be provided in a targeted manner. In particular, no additional energy is consumed, which has a beneficial effect on the efficiency of the internal combustion engine.

[0011] According to a development of the invention, at least one parameter is recorded as the at least one operating parameter, wherein the at least one parameter is selected from a group consisting of: an actual power of the internal combustion engine, in particular in comparison to a target power of the internal combustion engine; an actual torque of the internal combustion engine, in particular in comparison to a target torque of the internal combustion engine; an ambient temperature of the internal combustion engine, and an ambient pressure of the internal combustion engine. In one embodiment, a combination of at least two, in particular more than two, of the parameters mentioned here is used as the at least one operating parameter. In particular, the operating parameters mentioned here are suitable for inferring the density of the ambient air.

[0012] It is possible for the ambient pressure or the ambient temperature to be measured directly. However, it is also possible for at least one of these values ​​to be determined indirectly, in particular based on at least one other parameter or measured value from which the corresponding value can be inferred. For example, at least one pressure and / or temperature value can be measured along the air path, from which the ambient pressure and / or the ambient temperature can be inferred—for example, based on a flow model.

[0013] In particular, if the actual power of the internal combustion engine is lower than the target power, this can be interpreted as an indication that the required boost pressure is not being achieved due to a low density of the ambient air. The same applies if the actual torque of the internal combustion engine is lower than the target torque. The ambient temperature, like the ambient pressure, is a direct indicator of air density. If the various parameters are combined, the density of the ambient air can be determined with greater accuracy, or the various parameters can be used for mutual plausibility checks. According to a further development of the invention, the drive power of the electric motor is selected as a function of a control deviation of the power of the internal combustion engine.In this way in particular, drive power can advantageously be allocated to the electric motor in a targeted and demand-based manner to provide the required boost pressure. In particular, the electric motor is controlled in a motor-like manner in the event of a negative control deviation, i.e. when the actual power is less than the target power of the internal combustion engine. In particular, the electric motor is at least not controlled in a motor-like manner in the event of a positive control deviation, i.e. when the actual power is greater than the target power of the internal combustion engine. However, in one embodiment it is possible for the electric motor to be controlled in a generator-like manner - i.e. operated as a generator - when the actual power is greater than the target power of the internal combustion engine, in particular in order to increase the efficiency of the internal combustion engine or the electrical efficiency or the total electrical power of a genset, and / or to brake the compressor.Alternatively or additionally, the electric motor is at least not controlled by a motor, especially not when the actual power exactly corresponds to the target power.

[0014] In the context of the present technical teaching, a control deviation is understood in particular as a deviation of an actual value from an assigned target value.

[0015] Alternatively or additionally, it is provided that the drive power of the electric motor is selected depending on a control deviation of the torque of the internal combustion engine. In this way, too, drive power can be allocated to the electric motor in a targeted and needs-based manner to provide the required boost pressure. In particular, the electric motor is activated in the event of a negative control deviation, i.e. when the actual torque is less than the target torque of the internal combustion engine. In particular, the electric motor is at least not activated as a motor, in particular not activated, in the event of a positive control deviation, i.e. when the actual torque is greater than the target torque of the internal combustion engine. Even in this case, however, operation of the electric motor as a generator is possible - as described above. Alternatively or additionally, the electric motor is not activated if the actual torque exactly corresponds to the target torque.According to a further development of the invention, the drive power of the electric motor is selected depending on the ambient pressure and temperature of the internal combustion engine. In particular, the combination of ambient pressure and temperature allows a precise determination of the ambient air density.

[0016] In one embodiment, the drive power of the electric motor is read from a characteristic map as a function of the ambient pressure and the ambient temperature of the internal combustion engine. In particular, the characteristic map contains values ​​for the drive power of the electric motor as a function of the ambient pressure and the ambient temperature. This represents a particularly simple and low-computational-intensive embodiment of the method.

[0017] According to a further development of the invention, it is provided that the electric motor is only controlled by a motor if at least one additional condition is also met, wherein the at least one additional condition is in particular selected from a group consisting of: a load parameter of the internal combustion engine indicates a high instantaneous load, and a instantaneous compressor speed of the compressor is lower than a maximum compressor speed of the compressor. Advantageously, in this way in particular, the electric motor is only controlled by a motor if there is actually a need for the boost pressure control reserve and / or if it is still possible at all - in particular safely - to continue driving the compressor.

[0018] In the context of the present technical teaching, a high load is understood in particular to mean a load that is greater than a predetermined load limit. The predetermined load limit can in turn depend on at least one further parameter, which in turn can be characteristic of the density of the ambient air. In particular, the predetermined load limit can be greater at a higher ambient air density than at a lower ambient air density, and vice versa. However, the load limit can additionally or alternatively also depend on other conditions such as aging or wear of the turbine or compressor, the degree of contamination of an air filter, and optionally other parameters that influence the boost pressure.In particular, a parameter selected from a group consisting of: an opening position of the pressure control element, in particular the throttle valve, a rotational speed of the internal combustion engine, and a torque of the internal combustion engine is used as the load parameter. In one embodiment, the electric motor is only controlled—motorically—if the at least one additional condition is met, namely that the pressure control element is fully open, in particular that the throttle valve arranged in the air path is fully open.

[0019] If the compressor has already reached its maximum speed, it may be detrimental to drive it beyond this speed. This could lead to damage or even destruction of the compressor.

[0020] In one embodiment, the electric motor is only controlled - motor-wise - if both of the above-mentioned additional conditions are met - cumulatively.

[0021] The object is also achieved by providing a control unit for an internal combustion engine that is configured to carry out a method according to the invention or a method according to one or more of the previously described embodiments. In connection with the control unit, the advantages already explained above in connection with the method arise, in particular.

[0022] The object is also achieved by providing an internal combustion engine, wherein the internal combustion engine has a compressor arranged in an air path of the internal combustion engine, which compressor is configured to compress ambient air flowing along the air path, a turbine operatively connected to the compressor drive and arranged in an exhaust gas path, an electric motor operatively connected to the compressor drive, and a control unit, wherein the control unit is operatively connected to the electric motor and configured to determine at least one operating parameter that is characteristic of a density of the ambient air of the internal combustion engine. The control unit is also configured to control the electric motor depending on the at least one operating parameter. In particular, the internal combustion engine has a control unit according to the invention or a control unit according to one or more of the previously described embodiments.In connection with the internal combustion engine, the advantages that have already been described in connection with the method or the control unit arise in particular.

[0023] The internal combustion engine has in particular a pressure control element arranged in the air path, in particular a throttle valve.

[0024] In one embodiment, the internal combustion engine is an internal combustion engine powered by a fuel gas, in particular a gas engine. In particular, in one embodiment, the internal combustion engine is drive-connected to an electric machine operable as a generator. The invention also encompasses an internal combustion engine arrangement comprising an internal combustion engine according to the invention or an internal combustion engine according to one or more of the embodiments described here and below, as well as an electric machine operable as a generator and drive-connected to the internal combustion engine. The internal combustion engine arrangement is, in particular, a generator set or genset.

[0025] In one embodiment, the control unit is operatively connected to at least one parameter sensor and configured to detect the at least one operating parameter using the parameter sensor. Alternatively or additionally, the control unit is configured to determine, in particular calculate, the at least one operating parameter—in particular from other operating parameters or measured values. Alternatively or additionally, the control unit is configured to obtain, in particular calculate, the at least one operating parameter based on a mathematical or physical model of the internal combustion engine. Alternatively or additionally, the at least one operating parameter is known in the control unit.

[0026] According to a further development of the invention, the internal combustion engine has at least one parameter sensor that is operatively connected to the control unit and configured to detect the at least one operating parameter. The at least one parameter sensor is selected, in particular, from a group consisting of: a speed sensor, a torque sensor, a pressure sensor, and a temperature sensor. According to a further development of the invention, the turbine is larger than a turbine of an internal combustion engine whose control unit is not configured to control an electric motor depending on the at least one operating parameter, or which does not have such an electric motor, in particular by 5% to 10% larger.In particular, the turbine is larger than the turbine of an internal combustion engine with the same rated power, whose control unit is not configured to control the electric motor depending on the at least one operating parameter, or which does not have such an electric motor. In particular, the advantages already described above are achieved in this way.

[0027] The invention is explained in more detail below with reference to the drawings, which show:

[0028] Figure 1 is a schematic representation of an embodiment of an internal combustion engine;

[0029] Figure 2 is a schematic representation of embodiments of a method for operating the internal combustion engine according to Figure 1, and

[0030] Figure 3 is a schematic representation of the operation of the internal combustion engine according to Figure 1 and the method according to Figure 2.

[0031] Fig. 1 shows a schematic representation of an embodiment of an internal combustion engine 1.

[0032] The internal combustion engine 1 has an air path 3 and a compressor 5 arranged therein, wherein the compressor 5 is configured to compress ambient air flowing along the air path 3 and drawn in from an environment 6 of the internal combustion engine 1. In an exhaust path 7, the internal combustion engine 1 has a turbine 9 that is drive-connected to the compressor 5. The internal combustion engine 1 also has an electric motor 11 that is drive-connected to the compressor 5, and a control unit 13 that is drive-connected to the electric motor 11—in particular via a converter (not shown here). The control unit 13 is also configured to determine at least one operating parameter that is characteristic of a density of the ambient air of the internal combustion engine 1, in particular its density in the environment 6. The control unit 13 is further configured to control the electric motor 11 depending on the at least one operating parameter.The internal combustion engine 1 has, in particular, a pressure control element 15 arranged in the air path 3, which is preferably designed as a throttle valve 17. The pressure control element 15 is, in particular, operatively connected to the control unit 13 and can be controlled by the control unit, in particular to provide power control or torque control of the internal combustion engine 1. In the exemplary embodiment shown here, a charge air cooler 19 is also arranged in the air path 3.

[0033] In particular, the internal combustion engine 1 has at least one parameter sensor 20, which is operatively connected to the control unit 13 and configured to detect the at least one operating parameter. In the exemplary embodiment illustrated here, the at least one parameter sensor 20 is, in particular, a pressure sensor and / or a temperature sensor.

[0034] The internal combustion engine 1 is operated in particular with a fuel gas, in particular it is designed as a gas engine.

[0035] Turbine 9 is, in particular, designed to be larger than a turbine of an internal combustion engine with the same rated power, but whose control unit is not configured to control an electric motor depending on the at least one operating parameter, or which does not have such an electric motor. In particular, turbine 9 is 5% to 10% larger.

[0036] Fig. 2 shows a schematic representation of embodiments of a method for operating the internal combustion engine 1 according to Figure 1.

[0037] Identical and functionally identical elements are provided with the same reference symbols in all figures, so that reference is made to the preceding description in each case.

[0038] In a), a first embodiment of the method is shown, in which the at least one operating parameter is an actual power P ist of the internal combustion engine 1. From the actual power Pi S t, a target power P soii is subtracted, resulting in a power control deviation ep which is input to a computing element 23. The computing element 23 calculates, depending on the power control deviation ep, a control variable 25, here in particular a drive power PA, for the electric motor 11, with which in particular a converter 27 electrically connected to the electric motor 11 is controlled. Preferably, at least one additional condition Z is also input to the computing element 23. In this case, in particular, the control variable 25 is set to zero, i.e. the electric motor 11 is not controlled if the at least one additional condition Z is not met. In a preferred embodiment, the computing element 23 is a PID controller. Preferably, the control variable 25 is also set to zero if the power control deviation ep is zero or positive.

[0039] In another embodiment, the control variable 25 can be calculated as a function of a torque control deviation of the torque of the internal combustion engine 1, otherwise completely analogous to the representation shown here for the power.

[0040] In particular, the control variable 25 is only calculated, or a non-zero, particularly positive value is assigned to the control variable 25, if the power control deviation ep or the torque control deviation eu is negative, a required target power P so ii or a required target torque is not currently being achieved.

[0041] The at least one additional condition Z is in particular selected from a group consisting of: a load parameter of the internal combustion engine 1 indicates a high instantaneous load, and a current compressor speed of the compressor 5 is less than a maximum compressor speed. As the load parameter, in particular, a parameter is used that is selected from a group consisting of: an opening position of the pressure control element 15, in particular the throttle valve 17, a speed n of the internal combustion engine 1, and a torque of the internal combustion engine 1.

[0042] In particular, the electric motor 11 is only controlled if the at least one additional condition Z is met, namely that the pressure control element 15 is fully open, in particular that the throttle valve 17 arranged in the air path 3 is fully open.

[0043] In particular, the electric motor 11 is only controlled if both of the above-mentioned additional conditions Z are fulfilled - cumulatively.

[0044] In b), a second embodiment of the method is shown, in which an ambient pressure p and an ambient temperature T of the internal combustion engine 1 are used as the at least one operating parameter. In particular, the control variable 25 for the electric motor 11, here again the drive power PA, is read from a characteristic map 29 as a function of the ambient pressure p and the ambient temperature T of the internal combustion engine 1. By means of a logic element 31, the control variable 25 is only forwarded to the electric motor 11, in particular to the converter 27, if the at least one additional condition Z is met.

[0045] Fig. 3 shows a schematic representation of the functioning of the internal combustion engine 1 according to Figure 1 and the method according to Figure 2.

[0046] In particular, it is shown schematically here at which operating points of the internal combustion engine 1 the electric motor 11 is controlled, that is to say in particular driven or supplied with drive power PA.

[0047] As already explained above, the criterion used as at least one additional condition is whether a load parameter of the internal combustion engine 1 indicates a high instantaneous load. The load parameter used can in particular be the torque M or the speed n of the internal combustion engine 1, but in particular also a combination of torque M and speed n. A high load is understood in particular to mean a load that is greater than a predetermined load limit value. The predetermined load limit value can in turn depend on at least one further parameter, which in turn can be characteristic of the density of the ambient air. In particular, the predetermined load limit value can be greater when the ambient air density is higher than when the ambient air density is lower, and vice versa.

[0048] Figure 3 shows an operating state diagram of the internal combustion engine 1, which is spanned by the speed n plotted on the abscissa and the torque M of the internal combustion engine 1 plotted on the ordinate. Also shown are three limit curves Gl, G2 and G3, which are used as load limit curves in the sense of the load limit value. Above a currently valid limit curve of the limit curves Gl, G2, G3, the additional condition that the load parameter indicates a high instantaneous load is met, whereas below the currently valid limit curve Gl, G2, G3, this additional condition is not met. The electric motor 11 is therefore only driven if the operating state of the internal combustion engine 1 is above the currently valid limit curve Gl, G2, G3. If the operating state lies exactly on the currently valid limit curve Gl, G2, G3, the electric motor 11 can either be driven or not, depending on the design of the method.Which limit curve Gl, G2, G3 is currently used as the valid limit curve Gl, G2, G3 depends on the density of the ambient air, in particular on the ambient temperature and / or the ambient pressure. For example, at low ambient temperatures, the first limit curve Gl can be used as the valid limit curve, while at medium ambient temperatures the second limit curve G2 is used as the valid limit curve, and at high ambient temperatures the third limit curve G3 is used as the valid limit curve. The lower the density of the ambient air - or in the specifically described case, the higher the ambient temperature - the wider the range in the operating state diagram within which the electric motor 11 is controlled - motor-wise.

[0049] Which of the limit curves Gl, G2, G3 is used as the currently valid limit curve can additionally or alternatively depend on at least one other condition such as aging or wear of the turbine or compressor, degree of contamination of an air filter, and optionally other parameters that influence the boost pressure.

[0050] The target speed n also shown in the diagram so ii refers to the specified speed at which the internal combustion engine 1 is operated when it drives an electric synchronous machine in parallel operation with the mains.

Claims

CLAIMS 1. A method for operating an internal combustion engine (1) comprising a compressor (5) arranged in an air path (3) for compressing ambient air of the internal combustion engine (1) flowing along the air path (3), a turbine (9) arranged in an exhaust gas path (7) and drivingly connected to the compressor (5), and an electric motor (11), wherein the electric motor (11) is drivingly connected to the compressor (5), wherein - at least one operating parameter is detected which is characteristic of a density of the ambient air of the internal combustion engine (1), and wherein the electric motor (11) is controlled as a function of the at least one operating parameter.

2. The method according to claim 1, wherein the electric motor (11) is controlled to drive the compressor (5) when the at least one operating parameter indicates that the density of the ambient air is less than a predetermined limit density.

3. Method according to claim 2, wherein the electric motor (11) is at least not motor-controlled if the at least one operating parameter indicates that the density of the ambient air corresponds at least to the predetermined limit density.

4. Method according to one of the preceding claims, wherein a drive power of the electric motor (11) is selected as a function of the at least one operating parameter.

5. Method according to one of the preceding claims, wherein at least one parameter, in particular a combination of parameters, is detected as the at least one operating parameter, wherein the at least one parameter is selected from a group consisting of: an actual power of the internal combustion engine (1), in particular in comparison to a target power of the internal combustion engine (1); an actual torque of the internal combustion engine (1), in particular in comparison to a target torque of the internal combustion engine (1); an ambient temperature of the internal combustion engine (1), and an ambient pressure of the internal combustion engine (1).

6. Method according to one of the preceding claims, wherein a drive power of the electric motor (11) is selected as a function of a control deviation of a power or a torque of the internal combustion engine (1).

7. Method according to one of the preceding claims, wherein a drive power of the electric motor (11) is selected as a function of an ambient pressure and an ambient temperature of the internal combustion engine (1), in particular read from a characteristic map.

8. Method according to one of the preceding claims, wherein the electric motor (11) is only controlled if at least one additional condition is additionally fulfilled, wherein the at least one additional condition is in particular selected from a group consisting of: A load parameter of the internal combustion engine (1) indicates a high instantaneous load, and a momentary compressor speed of the compressor (5) is less than a maximum Compressor speed of the compressor (5).

9. Control unit (13) for an internal combustion engine (1), configured to carry out a method according to one of claims 1 to 8.

10. Internal combustion engine (1), with a compressor (5) arranged in an air path (3) of the internal combustion engine (1), which is designed to compress ambient air flowing along the air path (3), a turbine (9) which is drive-connected to the compressor (5) and arranged in an exhaust gas path (7), an electric motor (11) which is drive-connected to the compressor (5), and with a control unit (13) which is operatively connected to the electric motor (11) and is designed to determine at least one operating parameter which is characteristic of a density of the ambient air of the internal combustion engine (1), wherein the control unit (13) is also designed to control the electric motor (11) depending on the at least one operating parameter.

11. The internal combustion engine (1) according to claim 10, wherein the internal combustion engine (1) further comprises at least one parameter sensor (20) operatively connected to the control unit (13) and configured to detect the at least one operating parameter.

12. The internal combustion engine (1) according to one of claims 10 or 11, wherein the turbine (9) is larger than a turbine of an internal combustion engine (1) whose control unit (13) is not configured to control an electric motor (11) as a function of the at least one operating parameter, or which does not comprise such an electric motor (11), in particular by 5% to 10% larger.

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