Method and apparatus for operating an internal combustion engine with electrically assisted exhaust gas driven supercharging - Patents.com

Abstract

To protect, from high-temperature exhaust gas, an exhaust gas drive type supercharging mechanism that is electrically assisted and regenerates electric energy by operating itself as a power generator.SOLUTION: The method comprises the steps of: providing an operating point notification for an internal combustion engine, which can be determined by the load torque and speed of the internal combustion engine; determining maximum permissible regenerative output during regenerative operation of an electrical assist drive part, depending on the operating point notification; and limiting the regenerative output to the maximum permissible regenerative output during the regenerative operation.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a supercharged internal combustion engine with an electrically assisted exhaust-gas-driven supercharging mechanism and in particular to a method for recovering electrical energy by operating an electrical auxiliary drive for the supercharging mechanism as a generator. [Background technology]

[0002] A turbocharged internal combustion engine typically has an exhaust gas-driven turbocharging mechanism, a so-called exhaust gas turbocharger, which utilizes the exhaust gas enthalpy of the combustion exhaust gas to intake, compress, and provide ambient air to the internal combustion engine at a boost pressure increased above ambient pressure for supplying into the combustion chamber of the cylinder.

[0003] The available boost pressure or compressor performance is determined primarily by the air mass flow through the compressor and the available exhaust gas enthalpy of the combustion exhaust gases, which determines the available compression performance for compressing the intake fresh air and is set by the operating point of the internal combustion engine. The compressor is additionally limited by the criteria for component protection and by the so-called compressor surge, which is a compressor operating state where vibrations and stalls at the compressor blades occur.

[0004] In order to increase the dynamics of such exhaust-gas-driven turbochargers, they can be equipped with an electric auxiliary drive, the so-called ETA (Electric Turbo Assist), in order to provide an electrical power output and thereby achieve a compression that cannot be achieved solely by utilizing the exhaust gas enthalpy. The electric auxiliary drive is attached to the shaft between the compressor and the turbine of the turbocharger in order to provide an electrically generated additional drive torque and thus additionally accelerate the compressor of the turbocharger. This is described, for example, in DE 10 2016 222 928 A1.

[0005] It is further known that electrical auxiliary drives can be used to recover electrical energy by conversion of mechanical energy obtained from exhaust gas enthalpy. The electrical power that can be recovered depends on the operating point of the internal combustion engine. Basically, the higher the load range and speed of the internal combustion engine, the higher the electrical energy that can be recovered, since the exhaust gas enthalpy increases accordingly. However, in the transition range to component protection at high engine loads and speeds, the high recovered energy power can lead to exhaust gas temperatures that are too high, at which point operation of the exhaust gas-driven supercharging is not permitted for reasons of component protection or increased mixture enrichment is required. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] DE 102016222928 A1 Summary of the Invention [Means for solving the problem]

[0007] According to the invention there is provided a method for operating an internal combustion engine with exhaust-gas driven supercharging with electrical auxiliary according to claim 1 as well as an apparatus and an engine system according to the other independent claims.

[0008] Further aspects are set out in the dependent claims. According to a first aspect, a method for operating an internal combustion engine equipped with an exhaust-gas-driven supercharging mechanism equipped with an electric auxiliary drive is provided, the method comprising the following steps: - providing an operating point notification of the internal combustion engine; - determining a maximum permitted regenerative power during regenerative operation of the electric auxiliary drive as a function of the operating point signal; - limiting the regenerative power output to a maximum allowed regenerative power output during regenerative operation.

[0009] The operation of an exhaust-gas-driven turbocharger is generally directly linked to the operating point of the internal combustion engine. The more exhaust gas enthalpy is provided, the higher the mechanical power that can be extracted and the higher the compression performance and electrical power that can be recovered. However, the operation of the turbocharger is subject to restrictions to protect the components, in particular the turbine blades of the exhaust gas turbine, which limits the temperature and the speed of the exhaust gas turbine. Measures to limit the temperature of the exhaust gas turbine are usually related to the limiting of the exhaust gas temperature, which is usually achieved by enrichment of the air-fuel mixture in the internal combustion engine with additional injected fuel (operation with a fuel surplus above the stoichiometric air-fuel ratio).

[0010] 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 that the auxiliary drive of the turbocharging system generates as a generator, an undesirable expansion of the enrichment range can occur. The above-described method therefore maximizes the regenerative power, but at the same time limits it to the maximum permissible regenerative power depending on the operating point of the internal combustion engine, if there is a risk that at a relatively high regenerative power the exhaust gas temperature will increase further and thus the maximum permissible exhaust gas temperature may be reached or exceeded.

[0011] If during regenerative operation the regenerated energy is fed to the drive of the vehicle, it can be said in principle that for exhaust-gas-driven supercharging with an electric auxiliary drive there is an approximately linear relationship between fuel consumption and the regenerative power that can be provided. Alternatively, the regenerated electrical energy can also be fed to the on-board network, which also reduces the load on the internal combustion engine and thus results in lower fuel consumption. Thus, while the internal combustion engine is in the medium power range, regenerating the maximum possible electrical power and adding this regenerative power to the drive energy or to the on-board network is always favorably related to fuel consumption.

[0012] Due to the high exhaust gas enthalpy of the flue gases, especially in the high load range with high load torque and engine speed, there is a theoretically high potential for the recuperation of electrical power by the electric auxiliary drive. However, in this operating range, the flue gases have high exhaust gas temperatures, which generally exceed the permissible limit values ​​for components in the exhaust gas system, such as the exhaust gas turbine of the turbocharger. To reduce the exhaust gas temperature, a protective function takes measures to limit the exhaust gas temperature by enriching the air-fuel mixture. However, the demand for enrichment leads to higher consumption and higher emissions.

[0013] Furthermore, closing the wastegate or the turbocharger adjustment results in a relatively high exhaust gas backpressure, which leads to relatively high gas exchange losses and a relatively high amount of residual gas in the cylinder. This results in a relatively high knock tendency, which in turn leads to a relatively late combustion position, which also increases the exhaust gas temperature. In the transition range to enrichment, when the engine power is high and the exhaust gas temperature has not yet reached the temperature threshold of the exhaust gas turbine, electrical power can still be regenerated by the electric auxiliary drive. For this reason, the maximum regeneration power of the electric auxiliary drive is defined as a value that, depending on the operating point, is lower than the maximum regenerative power, but converts the proportion of the available exhaust gas enthalpy that does not further increase the exhaust gas temperature.

[0014] This can be done, for example, by means of a pre-control which is correlated to a characteristic map. Alternatively or additionally, the exhaust gas temperature can be controlled, for example, on the basis of a measurement of the exhaust gas temperature by means of an exhaust gas temperature sensor.

[0015] Furthermore, the operating point notification may be set by the engine speed and / or the load torque. According to one embodiment, the maximum permissible regenerative power can be determined depending on the operating point notification by a set limiting function, which is set so that during regenerative operation at the maximum permissible regenerative power, no further increase in the exhaust gas temperature of the combustion exhaust gas occurs based on the regenerative operation, or no increase in the exhaust gas temperature of the combustion exhaust gas occurs beyond a temperature limit set for the exhaust gas turbine or other components of the exhaust gas system.

[0016] It can be provided that the maximum permissible regenerative power is influenced by a correction quantity, which is known on the basis of further characteristic maps resulting from at least one of the following quantities: ignition timing, ambient temperature, and oil or coolant temperature.

[0017] According to one embodiment, the maximum permissible regenerative power can be corrected based on the control of the exhaust gas temperature, in which case the regenerative power correction is determined as the manipulated variable, and the control is based on the control deviation determined from the maximum permissible exhaust gas temperature set corresponding to the temperature limits for the components of the exhaust gas system of the internal combustion engine and the actual exhaust gas temperature.

[0018] Furthermore, regenerative operation of the turbocharging mechanism can be performed if a larger amount of exhaust gas enthalpy is provided than is necessary for compression in the compressor of the turbocharging mechanism. According to a further aspect, there is provided an apparatus for operating an internal combustion engine with an exhaust-gas driven supercharging mechanism with an electric auxiliary drive, the apparatus comprising: - To provide an operating point notification that indicates the operating point of the internal combustion engine. - depending on the operating point notification, to determine the maximum permitted regenerative power during regenerative operation of the electrical auxiliary drive, - configured to limit the regenerative power to the maximum permitted regenerative power during regenerative operation.

[0019] Hereinafter, the embodiments will be described in more detail with reference to the accompanying drawings. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram of an engine system equipped with an exhaust gas-driven supercharging mechanism equipped with an electric auxiliary drive. [Diagram 2] FIG. 2 is a flow chart for specifically explaining a method of operating the internal combustion engine. [Diagram 3] 4 shows a characteristic map for the operating state of an internal combustion engine with a limitation of the regenerative power according to the method according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 1 shows an engine system 1 having an internal combustion engine 2 with several cylinders 3. In this exemplary embodiment, four cylinders 3 are provided by way of example. The internal combustion engine 2 is supplied with ambient air via an air supply system 4 in a manner known per se. The combustion exhaust gases are led off from the cylinders 3 via an exhaust gas system 5. The air supply system 4 is connected in a manner known per se with the cylinders 3 of the internal combustion engine 2 via inlet valves (not shown). The combustion exhaust gases are discharged in a manner known per se into the exhaust gas system 5 via corresponding outlet valves (not shown).

[0022] A supercharging arrangement 6 may be provided having an exhaust gas turbine 61 in the exhaust gas system 5 and a supercharger compressor 62 in the air supply system 4. The exhaust gas turbine 61 is mechanically coupled to the supercharger compressor 62, for example via a shaft 64, so that the exhaust gas enthalpy converted to mechanical energy in the exhaust gas turbine 61 is used in the supercharger compressor 62 to compress ambient air taken from the surroundings. The amount or proportion of the exhaust gas enthalpy converted to mechanical energy may be variably adjusted by a supercharger regulator 63 arranged adjacent to or in the exhaust gas turbine 61.

[0023] The supercharger regulator 63 may be formed in a manner known per se as a VTG regulator (Variable Turbine Geometry), a wastegate regulator or the like.

[0024] An auxiliary drive 65 (as an electric drive) in the turbocharging mechanism 6 can be used to assist the compression by the turbocharger compressor 62. The auxiliary drive 65 can provide additional mechanical energy to the exhaust gas turbine 61 and the turbocharger compressor 62 via a mechanical connection with the turbocharger shaft 64, so that the turbocharger compressor 62 can operate without relying on the mechanical energy provided by the exhaust gas turbine 61.

[0025] Downstream of the compressor 62 a charge air cooler 7 may be provided. Downstream of the charge air cooler 7 there is a charge air section 41 of the air supply system 4, in which charge air is provided at charge pressure.

[0026] The supercharged air section 41 can be limited downstream by a throttle valve 9. Between the throttle valve 9 and the inlet valve of the cylinder 3 of the internal combustion engine 2 there is an intake pipe section 42 of the air supply system 4. In an alternative embodiment, a supercharged air cooler 7 can also be arranged downstream of the throttle valve 9.

[0027] Between the section of the exhaust gas system 5 that lies between the outlet valve of the cylinder 3 of the internal combustion engine 2 and the exhaust gas turbine 61, an exhaust gas recirculation conduit 10 can be routed through the intake pipe section 42. In the exhaust gas recirculation conduit 10, an exhaust gas recirculation valve 11 (AGR valve) can be arranged so that the magnitude of the recirculated exhaust gas mass flow can be adjusted.

[0028] An exhaust gas cooler 12 can further be arranged in the exhaust gas recirculation line 10 in order to reduce the temperature of the recirculated exhaust gases. Instead of the exhaust gas recirculation realized by the exhaust gas recirculation line 10, this can also be realized by a variable valve train for the inlet and outlet valves. In this case, exhaust gas recirculation occurs by opening the inlet valve while the outlet valve is still open, so that the higher pressure in the intake pipe section 42 with respect to the pressure in the exhaust gas system 5 causes fresh air, which has been pressurized upstream of the exhaust gas turbine 61, to spill over into the exhaust gas system through the cylinder 3 (scavenging).

[0029] During normal operation of the internal combustion engine 2, the exhaust gas backpressure in the exhaust gas system 5 is often greater than the intake pipe pressure in the intake pipe section 42 of the air supply system 4. This pressure difference is normally utilized for controlled exhaust gas recirculation from the outlet side to the inlet side of the internal combustion engine 2.

[0030] A control unit 15 is provided which operates the internal combustion engine 2 in accordance with the current operating state of the internal combustion engine 2 and in accordance with a setting, e.g. the torque desired by the driver, by adjusting, in a manner known per se, adjusters such as the throttle valve 9, the turbocharger adjuster 63, the exhaust gas recirculation valve 11, a fuel injection valve for setting the amount of fuel injected (not shown), and the like.

[0031] The operation of the engine system is explained in more detail below on the basis of the flow diagram in FIG. 2. Basically, from the viewpoint of efficiency, it makes sense to convert the maximum available exhaust gas enthalpy into regenerative energy for the supercharging of the internal combustion engine 2 and possibly for the regeneration of electrical energy via the electric auxiliary drive. However, due to component protection, which must, among other things, limit the exhaust gas temperature to a maximum exhaust gas temperature, in the high load range, it is not permissible to convert all of the exhaust gas enthalpy into regenerative energy. The relatively high exhaust gas backpressure caused by the regeneration further increases the exhaust gas temperature due to interference with the operation of the internal combustion engine 2, so that in a predefined high load operating range, regeneration is no longer permissible or the permissible regenerative power during regenerative operation is limited to zero.

[0032] The following method aims to influence the operation of the internal combustion engine 2 by setting a maximum regenerative output within the transition range between an operating point where all of the provided exhaust gas enthalpy is converted into fresh air charging and electrical energy regeneration, and a high load operating point where electrical energy regeneration is not permitted.

[0033] For this purpose, in step S1, an operating point of the internal combustion engine 2 is provided, which can be determined by the load torque and the rotational speed of the internal combustion engine. In step S2, the maximum permissible regenerative power is determined based on the operating point of the internal combustion engine 2. This can be done by means of a suitable set limiting model, in particular on the basis of a look-up table or the like.

[0034] This limitation model can be selected in such a way that between the operating range in which the entire exhaust gas enthalpy is utilized for the regeneration of electrical power and the operating range in which the regeneration of electrical power is not permitted due to component protection, i.e. is completely switched off, only a portion of the maximum available and regenerative power is drawn off, which is consequently achieved by a limitation to the maximum permitted regeneration power.

[0035] This prevents or limits a further increase in the exhaust gas temperature in the direction of the maximum permissible exhaust gas temperature. In particular, the maximum regeneration power is defined in such a way that in the case of a steady-state engine system at the operating point in question, the exhaust gas temperature does not increase further above the temperature tolerated by the exhaust gas turbine 61.

[0036] In step S3, optionally, the maximum permissible regenerative power can be influenced by a correction amount, which is determined on the basis of further characteristic maps resulting from at least one of the following quantities: ignition timing, ambient temperature, and oil and coolant temperatures.

[0037] Furthermore, in step S4, a correction of the maximum regenerative power based on the control of the exhaust gas temperature can also be carried out, in which case the above-mentioned limit of the regenerative power is used for pre-control. The control intervention of the exhaust gas temperature control corresponds to a regenerative power correction as a manipulated variable, by which the regenerative power determined in step S2 or S3 is acted upon. This control is based on the control deviation that is found between the maximum permissible exhaust gas temperature, which is set according to the temperature limits for the components of the exhaust gas system 5, and the actual exhaust gas temperature, which can be measured or modeled. This control can be designed as a P control, a PI control, a PID control or a PD control. In this way, the maximum exhaust gas temperature can be further adapted.

[0038] Thus, in step S5, the regenerated power drawn off in the electric auxiliary drive is limited to the maximum permitted regenerative power. 3, characteristic maps are shown diagrammatically for operating points of the internal combustion engine 2. The characteristic maps show operating ranges in which, depending on the operating point of the internal combustion engine 2, there is no regeneration from the conversion of exhaust gas enthalpy (operating range A), maximum regeneration (operating range B), no regeneration (operating range C), and limited regeneration (operating range D).

[0039] In the operating range A, due to the low exhaust gas enthalpy and the low exhaust gas mass flow rate, only an insufficient regeneration potential is possible, so no regeneration is carried out. Operation of the engine system 1 in the operating range B, which is characterized by a higher load operating point, allows a maximum regeneration of the available exhaust gas enthalpy, whereas in the case of operation in the operating range C, the internal combustion engine 2 is operated in enriched operation, i.e. the combustion takes place with a fuel surplus, so that in order to limit the exhaust gas temperature to a set maximum permissible exhaust gas temperature for component protection, regeneration is inhibited.

[0040] In the operating range D at a load point between the operating ranges B and C, a transition is provided in the manner described above, in which not all of the excess exhaust gas enthalpy is converted into regenerative power, but only a part of it. This makes it possible, on the one hand, to ensure that the exhaust gas temperature does not exceed the permissible temperature limit values ​​for the components in the exhaust gas system, in particular the exhaust gas turbine 61 (enrichment may then be necessary), and, on the other hand, to make use of the provided exhaust gas enthalpy for the regeneration of electrical power.

Claims

1. A method for operating an internal combustion engine (2) equipped with an exhaust-gas-driven turbocharging mechanism (6) equipped with an electric auxiliary drive (65), comprising the steps of: - providing an operating point notification (S1) informing of an operating point of said internal combustion engine (2); determining (S2) a maximum permissible regenerative power during regenerative operation of the electric auxiliary drive (65) as a function of said operating point notification; - limiting (S5) the regenerative power to the maximum permitted regenerative power during the regenerative operation; In a method of operation having the steps of: the maximum permitted regenerative power is determined by a set limiting function depending on the operating point notification, the limiting function being set in such a way that, during a regenerative operation at the maximum permitted regenerative power, a further increase in the exhaust gas temperature of the flue gas due to the regenerative operation does not occur or the increase in the exhaust gas temperature of the flue gas does not occur beyond a temperature limit set for a component of an exhaust gas system (5); The operating point notification is set according to a rotation speed and / or a load torque of the internal combustion engine (2). method.

2. A method as described in claim 1, wherein the maximum permissible regenerative power is corrected based on control of the exhaust gas temperature, in which case the regenerative power correction is determined as an operating variable, and in which the control is based on a control deviation determined from a maximum permissible exhaust gas temperature set corresponding to temperature limits for components of the exhaust gas system (5) of the internal combustion engine (2) and an actual exhaust gas temperature.

3. 3. The method according to claim 1, further comprising the step of: acting on the maximum permitted regenerative power by means of a correction quantity, the correction quantity being determined on the basis of further characteristic maps resulting from at least one of the following quantities: ignition timing, ambient temperature and oil or coolant temperature.

4. 4. The method according to claim 1, wherein the regenerative operation of the exhaust gas-driven turbocharging mechanism (6) is performed when a larger amount of exhaust gas enthalpy is provided than is required for compression in a compressor of the exhaust gas-driven turbocharging mechanism (6).

5. A device for the operation of an internal combustion engine (2) with an exhaust-gas-driven supercharging system (6) with an electric auxiliary drive (65), said device comprising: - providing an operating point notification for indicating an operating point of the internal combustion engine (2); - determining a maximum permissible regenerative power during regenerative operation of the electric auxiliary drive (65) in dependence on said operating point notification, - limiting the regenerative power to the maximum permitted regenerative power during the regenerative operation; In the apparatus, the maximum permitted regenerative power is determined by a set limiting function depending on the operating point notification, the limiting function being set in such a way that, during a regenerative operation at the maximum permitted regenerative power, a further increase in the exhaust gas temperature of the flue gas due to the regenerative operation does not occur or the increase in the exhaust gas temperature of the flue gas does not occur beyond a temperature limit set for a component of an exhaust gas system (5); The operating point notification is set according to a rotation speed and / or a load torque of the internal combustion engine (2). Device.

6. A computer program for carrying out the method according to any one of claims 1 to 4.

7. A memory medium having the computer program described in claim 6 recorded thereon.

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