Method and device for operating an internal combustion engine with exhaust gas driven supercharging with electric support

Abstract

The invention relates to a method for operating an internal combustion engine having an exhaust gas driven supercharger with an electric support drive, having the following steps: - providing an operating point specification of the internal combustion engine; - ascertaining a maximum permissible regeneration power from the operating point specification in a regeneration mode of the electric support drive; - limiting the regeneration power to the maximum permissible regeneration power in the regeneration mode.

Description

TECHNICAL FIELD

[0001] The present application relates to a supercharged internal combustion engine with an exhaust-gas-driven supercharger having an electric support and, in particular, to a method for regenerating electric energy by means of an electric support drive of the supercharger in an electric power generation mode. BACKGROUND

[0002] Supercharged internal combustion engines generally have an exhaust-gas-driven supercharger, a so-called exhaust-gas turbocharger, which sucks in and compresses ambient air using the exhaust-gas enthalpy of the combustion exhaust gas and supplies it to the internal combustion engine at a higher supercharging pressure relative to the ambient pressure for delivery to the combustion chambers of the cylinders.

[0003] The supercharging pressure or compression power that can be provided depends to a large extent on the air mass flow of the flow path compressor and the provided exhaust-gas enthalpy of the combustion exhaust gas. The provided exhaust-gas enthalpy determines the compression power provided for compressing the sucked-in fresh air and is predetermined by the operating point of the internal combustion engine. Furthermore, the compressor is limited by standards for component protection and by so-called compressor maps, which provide the operating conditions of the compressor, wherein vibrations and flow separations occur on the compressor wheel blades.

[0004] In order to increase the power of such an exhaust-gas-driven supercharger, the exhaust-gas-driven supercharger can be provided with an electric support drive, a so-called ETA (Electric Turbo Assist), in order to achieve a compression by delivering electric power, which cannot be achieved by using only the exhaust-gas enthalpy. The electric support drive acts on the shaft between the compressor and the turbine of the supercharger in order to additionally accelerate the compressor of the supercharger by providing an additional electrically generated drive torque. This is described, for example, in document DE 10 2016 222 928 A1.

[0005] It is furthermore known that electric energy can also be regenerated by means of the electric support drive by converting the mechanical energy obtained from the exhaust-gas enthalpy. The electric power that can be regenerated is related to the operating point of the internal combustion engine. In principle, the higher the load range and the rotational speed of the internal combustion engine, the higher the electric energy that can be regenerated, since the exhaust-gas enthalpy is correspondingly increased. In the transition range for component protection at high motor loads and high rotational speeds, however, the high electric power that can be regenerated can lead to excessively high exhaust gas temperatures, at which the exhaust-gas-driven supercharger is not allowed to be operated for reasons of component protection or requires an increased mixture enrichment. SUMMARY

[0006] According to the application, a method for operating an internal combustion engine having an exhaust gas driven supercharging device with an electrically supported drive is provided according to claim 1, and a device and a motor system are provided according to the dependent claims.

[0007] Further design proposals are explained in the dependent claims.

[0008] According to a first aspect, a method for operating an internal combustion engine having an exhaust gas driven supercharging device with an electrically supported drive is provided, having the following steps:

[0009] - providing an operating point specification of the internal combustion engine;

[0010] - determining a maximum permissible regenerative power from the operating point specification in a regenerative operation of the electrically supported drive; and

[0011] - limiting the regenerative power to the maximum permissible regenerative power in the regenerative operation.

[0012] The operation of the exhaust gas driven supercharging device is generally directly coupled to the operating point of the internal combustion engine. The more exhaust gas enthalpy is available, the greater the mechanical power that can be tapped and the greater the available compression power and the regenerable electric power. However, the operation of the supercharging device is limited in order to protect components, in particular the turbine blades of the exhaust gas turbine, in order to limit the temperature and the rotational speed of the exhaust gas turbine. Generally, measures for limiting the temperature of the exhaust gas turbine involve a limitation of the exhaust gas temperature, which is generally achieved by enriching the air-fuel mixture in the internal combustion engine with an additional injection of fuel (operation with a fuel excess beyond the stoichiometric air / fuel ratio).

[0013] In connection with a high regenerative power, i.e. in connection with the conversion of a large proportion of the exhaust gas enthalpy into electrical energy generated by the support drive of the supercharging device, an undesired increase in the enrichment range can occur. The method described above therefore provides that the regenerative power is maximized, but at the same time limited to the maximum permissible regenerative power in accordance with the operating point of the internal combustion engine when there is a risk that the exhaust gas temperature will be further increased at higher regenerative power and thus possibly reach or exceed the maximum permissible exhaust gas temperature.

[0014] In principle, it applies to exhaust gas driven supercharging devices with an electrically supported drive that there is a nearly linear relationship between fuel consumption and available regenerative power in the regenerative operation when the energy of the regeneration is fed to the drive of the motor vehicle. Alternatively, the electrical energy of the regeneration can also be fed to the on-board electrical system, which in turn leads to a de-loading of the internal combustion engine and thus to a lower fuel consumption. It is therefore always advantageous with regard to fuel consumption to regenerate the maximum possible electrical power and to add the regenerative power to the drive energy or to the on-board electrical system as long as the internal combustion engine is in a suitable power range.

[0015] Especially in the case of high load ranges, in which the load torque and the motor rotational speed are high, the potential for regenerating electric power by means of the electric support drive is theoretically large due to the high enthalpy of the combustion exhaust gases. In the operating range, the combustion exhaust gases, however, have a high exhaust gas temperature, which usually exceeds the limit values permissible for components in the exhaust gas turbine of the exhaust gas system, for example, the supercharger. In order to reduce the exhaust gas temperature, a protective function provides measures in which the exhaust gas temperature is limited by means of enrichment of the air-fuel mixture. The enrichment requirement, however, leads to higher consumption and more emissions.

[0016] Furthermore, a higher exhaust gas back pressure is formed upon closing the wastegate or the supercharger regulator, which leads to higher gas exchange losses and more residual gas in the cylinder. A higher tendency to knock results therefrom, which leads to a later combustion situation, whereby the exhaust gas temperature likewise rises. In the transition range for enrichment at high motor power and at exhaust gas temperatures which have not yet reached the temperature threshold of the exhaust gas turbine, electric power can always still be regenerated by means of the electric support drive. For this reason, it is provided that the maximum regenerative power of the electric support drive is determined as a value depending on the operating point, which is below the maximum regenerable power, but still converts a share of the available exhaust gas enthalpy which does not lead to a further increase in the exhaust gas temperature.

[0017] This can be carried out, for example, by means of a pre-control in relation to a characteristic curve. Alternatively or additionally, it can be provided that the adjustment of the exhaust gas temperature is carried out, for example, on the basis of a measurement of the exhaust gas temperature by means of an exhaust gas temperature sensor.

[0018] Furthermore, the operating point specification can be preset by means of the rotational speed and / or the load torque of the internal combustion engine.

[0019] According to an embodiment, the maximum permissible regenerative power can be determined depending on the operating point specification by means of a preset limiting function, wherein a limiting function is preset, as a result of which, in the regenerative operation with the maximum permissible regenerative power, the exhaust gas temperature of the combustion exhaust gases is not further increased, or the exhaust gas temperature of the combustion exhaust gases is not increased beyond the temperature limit preset for the exhaust gas turbine or other components of the exhaust gas system on the basis of the regenerative operation.

[0020] It can be provided that the maximum permissible regenerative power is loaded by means of a correction variable, which is derived from at least one subsequent variable (ignition time point, ambient temperature and oil temperature or cooling water temperature) by means of a further characteristic curve.

[0021] According to an embodiment, the maximum permissible regeneration power can be corrected on the basis of a regulation of the exhaust gas temperature, wherein the regeneration power correction is known as a regulation variable, wherein the regulation is based on a regulation deviation, which is derived from a pre-set maximum permissible exhaust gas temperature, which corresponds to a temperature limit for components of the exhaust system of the internal combustion engine, and the actual exhaust gas temperature.

[0022] Furthermore, a regenerative operation of the supercharging device can be employed when a greater amount of exhaust gas enthalpy is available compared to the exhaust gas enthalpy required for compression in the compressor of the supercharging device.

[0023] According to another aspect, a device for operating an internal combustion engine having an exhaust gas driven supercharging device with an electric support drive is provided, wherein the device is configured to

[0024] - provide an operating point specification, which specifies an operating point of the internal combustion engine;

[0025] - know a maximum permissible regeneration power in a regenerative operation of the electric support drive from the operating point specification;

[0026] - limit the regeneration power to the maximum permissible regeneration power in the regenerative operation. BRIEF DESCRIPTION OF DRAWINGS

[0027] Embodiments are subsequently explained in detail with the aid of the drawings. Therein:

[0028] Figure 1 A schematic diagram of a motor system having an exhaust gas driven supercharging device with an electric support drive is shown;

[0029] Figure 2 A flow chart for illustrating a method for operating an internal combustion engine is shown; and

[0030] Figure 3 Characteristic curves with respect to operating states of an internal combustion engine are shown, in which operating states a limitation of the regeneration power is provided in accordance with the method according to the application. DETAILED DESCRIPTION

[0031] Figure 1 A motor system 1 is shown, which has an internal combustion engine 2, which has a number of cylinders 3. In the present embodiment, four cylinders 3 are exemplarily provided.

[0032] In a manner known per se, ambient air is conveyed to the internal combustion engine 2 by means of an air conveying system 4. Combustion exhaust gases are conducted from the cylinders 3 by means of an exhaust system 5. The air conveying system 4 is connected to the cylinders 3 of the internal combustion engine 2 in a manner known per se by means of intake valves (not shown). The combustion exhaust gases are discharged into the exhaust system 5 by means of corresponding exhaust valves (not shown) in a manner known per se.

[0033] A supercharging device 6 can be provided, which has an exhaust gas turbine 61 in the exhaust gas system 5 and a supercharger compressor 62 in the air delivery system 4. The exhaust gas turbine 61 is mechanically coupled to the supercharger compressor 62, for example by a shaft 64, so that the exhaust gas enthalpy converted into mechanical energy in the exhaust gas turbine 61 is used for compressing ambient air taken from the surroundings in the supercharger compressor 62. The amount or proportion of exhaust gas enthalpy converted into mechanical energy can be variably adjusted by means of a supercharger regulator 63 arranged on or in the exhaust gas turbine 61.

[0034] The supercharger regulator 63 can be configured in a manner known per se as a VTG regulator (VTG: variable turbine geometry), wastegate regulator or the like.

[0035] It can be provided that the compression by the supercharger compressor 62 is supported by means of a support drive 65 in the supercharging device 6 as an electric drive. The support drive 65 can introduce additional mechanical energy by mechanical coupling to the supercharger shaft 64 of the exhaust gas turbine 61 and to the supercharger compressor 62, so that the supercharger compressor 62 can also be operated independently of the mechanical energy provided by the exhaust gas turbine 61.

[0036] Downstream of the compressor 62, a charge air cooler 7 can be provided. Downstream of the charge air cooler 7, there is a charge air section 41 of the air delivery system 4, in which the charge air is provided at a charge pressure.

[0037] The charge air section 41 can be limited downstream by means of a throttle valve 9. Between the throttle valve 9 and the intake valves of the cylinders 3 of the internal combustion engine 2, there is a suction pipe section 42 of the air delivery system 4. In an alternative embodiment, the charge air cooler 7 can also be arranged downstream of the throttle valve 9.

[0038] Between the section of the exhaust gas system 5 located between the exhaust valves of the cylinders 3 of the internal combustion engine 2 and the exhaust gas turbine 61, an exhaust gas recirculation line 10 can be led into the suction pipe section 42. An exhaust gas recirculation valve 11 (AGR valve) can be arranged in the exhaust gas recirculation line 10, so that the level of the recirculated exhaust gas mass flow can be adjusted.

[0039] Furthermore, an exhaust gas cooler 12 can be arranged in the exhaust gas recirculation line 10, in order to reduce the temperature of the recirculated exhaust gas. Instead of exhaust gas recirculation by means of the exhaust gas recirculation line 10, it is also possible to achieve exhaust gas recirculation by means of variable valve drives for the intake valves and the exhaust valves. Exhaust gas recirculation is achieved here by opening the intake valves while the exhaust valves are still open, so that fresh air compressed upstream of the exhaust gas turbine 61 by the higher pressure in the suction pipe section 42 relative to the pressure in the exhaust gas system 5 flows over into the exhaust system through the cylinders 3 (scavenging).

[0040] Generally, in the normal operation of the internal combustion engine 2, the exhaust gas back pressure in the exhaust gas system 5 is greater than the suction pipe pressure in the suction pipe section 42 of the air supply system 4. The pressure drop is generally used to guide the exhaust gas from the exhaust side of the internal combustion engine 2 to the intake side of the internal combustion engine in a controlled manner.

[0041] A control unit 15 is provided, which operates the internal combustion engine 2 in a manner known per se by setting actuators, such as the throttle valve 9, the supercharger regulator 63, the exhaust gas recirculation valve 11, the fuel injection valve for presetting the amount of fuel (not shown) for injection, etc., depending on the current operating state of the internal combustion engine 2 and depending on a preset, such as a driver desired torque.

[0042] The method for operating the motor system is then described in detail according to the flowchart of Figure 2 In principle, it is meaningful from an efficiency point of view to convert the maximum available exhaust gas enthalpy into supercharging of the internal combustion engine 2 and, if necessary, to convert it into regenerative electrical energy by means of an electrically driven support drive. However, based on component protection (by means of which, inter alia, the exhaust gas temperature must be limited to a maximum exhaust gas temperature), it is not permissible to convert the exhaust gas enthalpy completely into regenerative energy in the high load range. The higher exhaust gas back pressure caused by the regeneration leads to a further increase in the exhaust gas temperature based on an intervention in the operation of the internal combustion engine 2, so that in a predetermined operating range of high loads, the regeneration is no longer permissible, or in the regenerative operation, the permissible regenerative power is limited to 0.

[0043] The subsequent method provides that, in the transition range between the operating point with complete conversion of the available exhaust gas enthalpy into supercharging of the fresh air and the regenerative electrical energy and the operating point of high loads, in which the regenerative electrical energy is not permissible, the operation of the internal combustion engine 2 is influenced by presetting a maximum regenerative power.

[0044] To this end, in step S1, an operating point of the internal combustion engine 2 is provided, which can be determined by a load torque and a rotational speed of the internal combustion engine.

[0045] In step S2, the maximum permissible regenerative power is determined by means of the operating point of the internal combustion engine 2. This can be done by means of an appropriate preset limit model, in particular based on a look-up table, etc.

[0046] The limit model can be selected so that, between the operating range in which the exhaust gas enthalpy can be used completely for regenerating electrical power and the operating range in which, based on component protection, the regenerative electrical power is not permissible or completely prohibited, only a part of the maximum available regenerable power is tapped. This is done by limiting the maximum permissible regenerative power generated.

[0047] Thereby, the exhaust gas temperature is prevented from further increasing in the direction of the maximum permissible exhaust gas temperature or is limited to the maximum permissible exhaust gas temperature. The maximum regeneration power is determined in particular such that, in the relevant operating point and in a steady-state motor system, a further increase in the exhaust gas temperature beyond the temperature permissible for the exhaust gas turbine 61 does not occur.

[0048] In step S3, the maximum permissible regeneration power can optionally be loaded with a correction variable, which is derived from at least one subsequent variable (ignition time point, ambient temperature, oil temperature and cooling water temperature) according to a further characteristic curve.

[0049] Furthermore, in step S4, a correction of the maximum regeneration power can also be carried out on the basis of a regulation of the exhaust gas temperature. The above-mentioned limitation of the regeneration power serves for a pre-control.

[0050] The regulation intervention for regulating the exhaust gas temperature corresponds to a regeneration power correction as a regulation variable, with which the regeneration power known in step S2 or S3 is loaded. The regulation is based on a regulation deviation, which is derived from a preset maximum permissible exhaust gas temperature, which corresponds to a temperature limit for components of the exhaust gas system 5, and an actual exhaust gas temperature, which can be measured or modelled. The regulation can be designed as a P, PI, PID or PD regulation. In this way, the maximum exhaust gas temperature can be further adjusted.

[0051] In step S5, the retrieved regeneration power is thus limited to the maximum permissible regeneration power in the electric support drive.

[0052] In Figure 3 A characteristic curve with respect to the operating point of the internal combustion engine 2 is shown schematically in Fig. 1. The characteristic curve shows, depending on the operating point of the internal combustion engine 2, operating ranges in which there is no regeneration (operating range A), maximum regeneration (operating range B), suppressed regeneration (operating range C) and limited regeneration (operating range D) from the point of view of the conversion of exhaust gas enthalpy.

[0053] In the operating range A, no regeneration is carried out, since, based on the low exhaust gas enthalpy and based on the small exhaust gas mass flow, the regeneration potential can only be insufficient. The operation of the motor system 1 in the operating range B, which is characterized by operating points with higher loads, enables the maximum regeneration of the available exhaust gas enthalpy, while in the case of operation in the operating range C, the regeneration is suppressed, since the internal combustion engine 2 is operated in a rich operating mode, i.e. combustion takes place with fuel excess, in order to limit the exhaust gas temperature to the preset maximum permissible exhaust gas temperature for component protection.

[0054] In the operating range D in the load point between the operating range B and the operating range C, a transition is provided according to the above-described method, in which the excess exhaust gas enthalpy is not completely converted into regenerative power, but only a part is converted into regenerative power. This enables, on the one hand, the exhaust gas temperature not to exceed the permissible temperature limit values for the components in the exhaust gas system, in particular the exhaust gas turbine 61, which would subsequently require enrichment, and, on the other hand, the available exhaust gas enthalpy to be used to regenerate electrical power.

Claims

1. Method for operating an internal combustion engine (2) with an exhaust gas driven supercharger (6) with an electric support drive (65), with the following steps: - providing an operating point specification which specifies an operating point of the internal combustion engine (2); - specifying the operating point specification by means of a rotational speed and / or a load torque of the internal combustion engine (2); - ascertaining (S2) a maximum permissible regenerative power in a regenerative operation of the electric support drive (65) in accordance with the operating point specification; - limiting (S5) the regenerative power to the maximum permissible regenerative power in the regenerative operation, wherein the maximum permissible regenerative power is corrected on the basis of a regulated exhaust gas temperature, wherein the regenerative power correction is ascertained as a regulating variable, wherein the regulating is based on a regulating deviation which is derived from a pre-specified maximum permissible exhaust gas temperature and an actual exhaust gas temperature, the maximum permissible exhaust gas temperature corresponding to a temperature limit for components of an exhaust system (5) of the internal combustion engine (2). - providing (S1) an operating point specification which specifies an operating point of the internal combustion engine (2), wherein The maximum permissible regenerative power is determined by a pre-specified limiting function in accordance with the operating point specification, wherein the limiting function is pre-specified such that, in the regenerative operation with the maximum permissible regenerative power, the exhaust gas temperature of the combustion exhaust gas is not further increased or is not increased beyond a pre-specified temperature limit for components of the exhaust system (5) on the basis of the regenerative operation. The maximum permissible regenerative power is loaded by a correction variable which is derived from at least one of an ignition time point, an ambient temperature, an oil temperature and a cooling water temperature by means of a further characteristic curve. The regenerative operation of the supercharger (6) is employed when a greater amount of exhaust gas enthalpy is available compared to the exhaust gas enthalpy required for compression in the compressor of the supercharger (6).

5. Device for operating an internal combustion engine (2) with an exhaust gas driven supercharger (6) with an electric support drive (65), wherein the device is configured for: - providing an operating point specification which specifies an operating point of the internal combustion engine (2); - specifying the operating point specification by means of a rotational speed and / or a load torque of the internal combustion engine (2); - ascertaining a maximum permissible regenerative power in a regenerative operation of the electric support drive (65) in accordance with the operating point specification; - limiting the regenerative power to the maximum permissible regenerative power in the regenerative operation, wherein the maximum permissible regenerative power is corrected on the basis of a regulated exhaust gas temperature, wherein the regenerative power correction is ascertained as a regulating variable, wherein the regulating is based on a regulating deviation which is derived from a pre-specified maximum permissible exhaust gas temperature and an actual exhaust gas temperature, the maximum permissible exhaust gas temperature corresponding to a temperature limit for components of an exhaust system (5) of the internal combustion engine (2).

2. The method of claim 1, wherein, 6. Computer program product with program code means, the computer program product having a computer program which is set up to carry out the method according to one of claims 1 to 4 when the computer program is executed on a computing unit.

3. The method of claim 1 or 2, wherein, 7. Machine-readable storage medium with a computer program stored on the storage medium for carrying out the method according to one of claims 1 to 4.

4. The method of claim 1 or 2, wherein, ​ ​ ​ - the maximum allowed regenerative power is determined from the operating point specification in the regenerative operation of the electric support drive (65), wherein ​ ​ ​ ​ ​

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