DE102019217554A1 - Method for operating an electrically assisted exhaust gas turbocharger - Google Patents

Abstract

The invention relates to a method for operating an electrically assisted exhaust gas turbocharger (30) of a vehicle (1) with exhaust gas turbocharging, the vehicle (1) being driven by at least one electric drive (22, 23) and by an internal combustion engine (10), the the following steps are carried out:
- Operating the exhaust gas turbocharger (30) in a first operating state in which recuperation by the exhaust gas turbocharger (30) is limited by at least one operating criterion, the operating criterion being specific at least for an efficiency of the exhaust gas turbocharger and / or the internal combustion engine (10),
- Monitoring at least one operating parameter of the vehicle (1) to detect a critical state for the electric drive (22, 23),
- Operating the exhaust gas turbocharger (30) in a second operating state when the critical state is detected, the limitation of the recuperation by the operating criterion being lifted in the second operating state.

Description

The present invention relates to a method for operating an electrically assisted exhaust gas turbocharger of a vehicle with exhaust gas turbocharging.

Exhaust gas turbochargers are known from the prior art, in which part of the energy of the engine exhaust gas in motor vehicles can be reused by means of an exhaust gas turbine. In addition, it is known that the behavior of the exhaust gas turbocharger can be improved by means of an electric machine. This technology is also known as an electrically assisted exhaust gas turbocharger (eATL or E-Turbo for short). The auxiliary drive used for support can be connected to the shaft of the turbocharger to support the compressor, and also provide power for driving the compressor. The electric motor used here as an auxiliary drive can also be used to recuperate exhaust gas energy. However, the gas exchange of the engine can deteriorate during recuperation - there is a higher exhaust gas back pressure. Therefore, the recuperation is used taking into account the engine map, and the exhaust gas energy is only converted into electrical energy in those areas of the engine map in which the engine parameters do not change significantly as a result. In other words, the recuperation is limited in such a way that a high level of efficiency of the engine is always guaranteed.

From the DE 10 2013 106 643 A1 and DE 10 2014 221 331 A1 processes are also known in which energy is recovered from the exhaust gas by an exhaust gas turbine. Here, too, the recovered energy is maximized with the proviso that the operating point with the highest efficiency of the motor is set.

It is also known that in HEV drives, that is to say in hybrid electric vehicles, the specification of the high-voltage battery limits the electrical performance. For example, a low state of charge (SoC) and an impermissible operating temperature of the high-voltage battery (HV battery) can result in a hybrid driving mode being severely restricted or even not available. This can be particularly problematic in vehicles that use electric all-wheel drive. For example, one of the axles, such as the front axle, can be driven via the main drive unit and the other of the axles, such as the rear axle, can be driven via an electric drive. Restricting or losing the hybrid driving mode can then lead to the loss of all-wheel drive capability.

In principle, it can be advantageous in the situations described to use energy recovery via the exhaust gas turbine. However, the problem with conventional solutions for energy recovery from the exhaust gas is that the recovered energy may not be sufficient in some situations to maintain operationally relevant functions of the vehicle.

It is therefore an object of the present invention to at least partially remedy the disadvantages described above. In particular, it is the object of the present invention to propose an improved operation of the exhaust gas turbocharger.

The above object is achieved by a method with the features of claim 1. Further features and details of the invention emerge from the respective subclaims, the description and the drawings.

The object is achieved in particular by a method for operating at least one, in particular electrically assisted, exhaust gas turbocharger of a vehicle. The vehicle can be driven by an internal combustion engine - and in particular also by at least one electric drive. The exhaust gas turbocharger is hereinafter referred to as ATL for short and the electrically assisted exhaust gas turbocharger is also referred to for short as eATL.

Since the exhaust gas turbocharger is provided in the vehicle, exhaust gas turbocharging is provided in the vehicle by the exhaust gas turbocharger, which can serve to increase the engine output or the efficiency of the internal combustion engine. In other words, the exhaust gas turbocharger can be used primarily to improve the efficiency of the internal combustion engine. Accordingly, it can be provided as a first method step of the method according to the invention that the exhaust gas turbocharger is operated in a first operating state, with recuperation by the exhaust gas turbocharger being limited by at least one operating criterion in the first operating state. In the first operating state, the exhaust gas turbocharger can thus preferably be operated in such a way that the efficiency is optimized in accordance with the operating criterion. In other words, it is an efficiency-optimized operation of the exhaust gas turbocharger in the first operating state. The operating criterion is thus specific at least for an efficiency of the exhaust gas turbocharger and / or the internal combustion engine. The recuperation is carried out here, but only to a limited extent.

In a second method step, at least one operating parameter of the vehicle can be monitored to detect a critical one State for the electric drive. At least one possible operating parameter that is relevant for the electric drive can be a state of charge and / or a temperature of a traction battery for the electric drive. Thus, the monitoring z. B. can be carried out by a battery management system, which uses appropriate sensors (and / or measuring devices) on the traction battery.

Then, according to a third method step, the exhaust gas turbocharger can be operated in a second operating state, in particular when the critical state is detected. In the second operating state, the limitation of the recuperation by the operating criterion can be lifted. In other words, in the second operating state, the operating criterion of the first operating state is no longer primarily important. Instead, in the second operating state - in contrast to the first operating state - the exhaust gas turbocharger can be operated primarily for recuperation. For example, the efficiency is therefore only taken into account in a secondary manner or no longer in the operation of the second operating state.

By means of a method according to the invention, the advantage can be achieved that in certain situations, e.g. B. with limited capacity of the traction battery, the operability of the electric drive can be guaranteed. Another advantage can be achieved if the vehicle has an at least partially electrically operated all-wheel drive. The method according to the invention can then ensure a significant all-wheel drive capability even in a critical state.

The process steps of a process according to the invention can be carried out one after the other or in any order. Individual and / or all steps can also be carried out repeatedly. The method steps can be carried out at least partially by vehicle electronics, in particular by at least one control device and / or battery management system and / or the like.

Specifically, in the solution according to the invention, it can be provided that the operating point of the internal combustion engine (in particular in the function of a main drive unit of the vehicle) is selected in the second operating state in such a way that the turbine output of the eATL is at its maximum (i.e. maximum while adhering to the stability criteria of the internal combustion engine combustion process). With this maximum turbine power, the eATL can recuperate a maximum electrical power which can be used directly for the operation of electrical consumers and / or directly for the electrical drive and preferably for driving an electrical axle of the vehicle. In this way, for example, in a vehicle with electric all-wheel drive, the advantage can be achieved that a significant all-wheel capability is ensured even with limited capacity of the traction battery. It can therefore be a deliberate setting of an operating point that is not optimal from the point of view of efficiency and / or other operating criteria such as the vehicle's CO2 emissions, in which the operating strategy is optimized for maximum recuperation of exhaust gas energy to drive the electric axle. Another advantage here is the availability of electrical power to operate the electric axle regardless of the performance of the traction battery. The additional energy generated can reduce the size of the cost-intensive traction battery, since the electrical energy is recuperated and can be used to drive the electric axle.

It is also advantageous if the vehicle is designed as a motor vehicle, in particular a trackless land motor vehicle. So the vehicle can z. B. be designed as a hybrid vehicle comprising an internal combustion engine and an electric machine for traction. The vehicle can preferably be designed with a high-voltage electrical system and / or at least one electric motor (in particular as the electric drive of the vehicle). The vehicle can have a rechargeable traction battery, in particular a high-voltage battery, for operating the electric motor or the electric drive. The vehicle can also be designed as a fuel cell vehicle. The vehicle can also be a passenger vehicle or a truck. In addition, the vehicle can have all-wheel drive. The all-wheel drive is in particular an electric all-wheel drive, in which a loss of the hybrid driving mode can lead to a loss of the all-wheel drive capability. The traction battery can preferably be designed as a high-voltage battery of the vehicle, which is designed to be rechargeable. The traction battery can be used to drive the vehicle, i.e. for the electric drive.

It may be possible for one of the axles of the vehicle, such as the front axle, to be driven via the main drive unit and the other of the axles, such as the rear axle, to be driven via an electric drive, in particular an electric motor. In this context, one can also speak of an electric all-wheel drive. The electrically driven axle can also be driven independently of the main drive unit, and thus as an independent electric axle.

The first operating state can advantageously designate normal operation, which is mainly used when the vehicle is in operation. Correspondingly, the second operating state can be an exceptional operation.

In the first operating state, it can be provided in accordance with the operating criterion that the effects of recuperation by the eATL on the engine operation of the vehicle are kept as small as possible. Correspondingly, during recuperation by an electric machine of the eATL, the load on the internal combustion engine (i.e. internal combustion engine or ICE for short) of the vehicle can remain essentially constant. A maximum possible recuperation can be predefined depending on the operating point of the ICE. This maximum recuperation can, for example, have been determined beforehand on the engine test bench and, for example, can be specified in the form of a characteristic map. The pressure in front of the turbine of the eATL can increase during recuperation, whereby a limit for the maximum pressure can be used in the first operating state. The recuperation can then be limited on the basis of this limit, the limit being able to be selected as a function of the operating point. In order to carry out the recuperation in an energy-efficient manner, a variable turbine geometry (VTG) of the eATL can be set. The use of recuperation and / or the setting of the VTG can take place in the first operating state in such a way that the efficiency and operating behavior of the exhaust gas turbocharger and the ICE are improved. In other words, in the first operating state or in normal operation, there is an efficiency-optimized operation of the eATL and an efficiency-optimized recuperation. The VTG, i.e. the variable geometry of the turbine, can also be set in an efficiency-optimized manner and / or the electric machine of the eATL can be used as a switchable generator to absorb excess power provided by the turbine. If more power is made available on the shaft of the eATL than intended due to the efficiency-optimized operation of the turbine, the power made available on the shaft can be reduced by means of the power consumed by the electric machine as a generator.

It is possible to switch to the second operating state when the critical state is detected, for example a charge state of the traction battery falls below a limit value or the temperature of the traction battery falls below a further limit value. By changing to the second operating state, the first operating state is exited. In this way, recuperation can be released and activated. Another prerequisite for activating recuperation in accordance with the operating criterion can be dispensed with. Specifically, with regard to compliance with limits for an efficiency-optimized operation, it can remain unchecked that a permissible operating point of the ICE is present, whereby stability criteria for the combustion are of course still adhered to.

For example, it can be provided that the efficiency is reduced in the second operating state in order to increase the electrical power recuperated by the exhaust gas turbocharger for operating the electrical drive. This has the advantage that recuperation can be maximized if the deterioration in efficiency is accepted.

It can furthermore be possible for a turbine output of the exhaust gas turbocharger to be increased in the second operating state, as a result of which the efficiency of the internal combustion engine is reduced and the recuperation is increased. Thus, increasing the turbine power is proposed as a specific measure in order to obtain a maximum of electrical power for operating the electrical drive of the vehicle through recuperation, regardless of the degree of efficiency.

Advantageously, within the scope of the invention it can be provided that the exhaust gas turbocharger is designed with a variable turbine geometry (VTG), in particular in order to be able to adjust the turbine power. Specifically, it can be provided that the turbine of the exhaust gas turbocharger, that is to say the exhaust gas turbine, has the VTG. This allows further adaptation to the respective operating point of the ICE by adjusting the turbine geometry and in particular the effective turbine cross-section. If necessary, a speed-dependent or load-dependent regulation of the turbine geometry can take place to a certain extent. In the inlet area of the turbine, guide vanes can be arranged to influence the direction of flow. In contrast to the rotating blades of the rotating impeller, the guide blades cannot rotate with the shaft of the turbine. If the turbine has a fixed, unchangeable geometry, the guide vanes - if they exist - are not only stationary but also completely immovable in the inlet area, i.e. H. rigidly fixed. If, on the other hand, a turbine with VTG is used, the guide vanes are stationary, but not completely immobile, but rotatable around their axis, so that the flow to the rotor blades can be influenced.

The ICE can have the at least one exhaust gas turbocharger, in particular eATL, for charging. In addition to the turbocharger, this charged ICE can also have an intake system for supplying charge air and an exhaust gas discharge system for discharging the Have exhaust gas. The turbocharger can have a turbine arranged in the exhaust gas discharge system and a compressor arranged in the intake system. The turbine and the compressor can be arranged on the same rotatable shaft of the ATL. The turbine of the ATL can have a variable turbine geometry. Furthermore, an auxiliary drive that can be at least drive-connected to the shaft of the at least one turbocharger can be provided, which is used to support the compressor and can additionally provide power for driving the compressor and output it to the compressor. The auxiliary drive and the variable geometry of the turbine can be controlled as a function of one another. It is possible in the first operating state for the variable geometry of the turbine to be set in an efficiency-optimized manner, with the auxiliary drive being used as a connectable auxiliary drive to satisfy a requested additional power requirement. An electric machine can be used as an auxiliary drive. It may also be possible that the electric machine drive-connected to the shaft is operated as a generator and takes power from the turbine, whereby the power provided by the turbine for driving the compressor is reduced and the boost pressure is lowered downstream of the compressor. It is also possible that the power consumed by the generator is stored as electrical energy in a traction battery, that is to say that recuperation is provided by the electric machine.

It is also optionally conceivable that the monitored operating parameter is specific for a charge state of a traction battery of the vehicle in order to detect a low charge state for the detection of the critical state. In particular, if the state of charge falls below a limit value, this can be detected as the critical state. To this comes z. B. the voltage measurement on the traction battery by means of a battery management system in question.

Another advantage can be achieved within the scope of the invention if the monitored operating parameter is specific for an operating temperature of a traction battery of the vehicle in order to detect at least one critical operating temperature for the detection of the critical state. The supply of energy by the traction battery can be restricted, especially at low temperatures. Here, the second operating state can maintain the functionality of the electric drive.

Furthermore, it is optionally possible within the scope of the invention for the vehicle to be designed as a hybrid electric motor vehicle, the critical state being specific to the fact that a hybrid driving mode of the vehicle is restricted or prevented. Specifically, this can be the case when the traction battery of the vehicle is not able to provide sufficient energy to operate the electric drive. The change from the first to the second operating state can then serve to maintain the hybrid driving mode.

In addition, it is conceivable within the scope of the invention that the vehicle has an all-wheel drive in which the front or rear axle, in particular only, is driven by the electric drive. In other words, one of the axles of the vehicle can be designed as an electric axle. It is thus provided that this axis can only be driven electrically, and thus the drive of this axis is dependent on a sufficient supply of electrical energy. In the first operating mode, the energy can be provided predominantly by a traction battery, and in the second operating mode predominantly through recuperation of the eATL.

Furthermore, it is conceivable that, in the second operating state, the recuperation is limited only by a stability criterion which is specific to the internal combustion engine's internal combustion engine. In other words, it can be provided that only the stability of the ICE is taken into account in the second operating state. For example, the recuperation is only deactivated in the second operating state when the stability of the combustion process is endangered, e.g. B. a limit value for the load of the ICE is exceeded.

Another advantage within the scope of the invention can be achieved if, in the first operating state, the activation of the recuperation is dependent on an operating point of the internal combustion engine, and in particular the recuperation is activated on the basis of a predefined map in order to carry out the recuperation in an efficiency-optimized manner, with the efficiency-optimized activation in the second Operating state is canceled. For example, in normal operation, recuperation of the eATL can be activated according to the map when a scavenging gradient (i.e. a difference between intake manifold pressure and exhaust gas back pressure) is positive. Efficiency-optimized operation can thus take place, which, however, can be canceled in the second operating state.

The limitation of the recuperation by the operating criterion can take place accordingly at least in that the activation of the recuperation is dependent on an operating point of the internal combustion engine and / or the recuperation is activated on the basis of a predefined characteristic map. The operating criterion is therefore specific to the efficiency of the exhaust gas turbocharger and / or the internal combustion engine. The map can, for example, indicate For which operating point of the ICE recuperation is released.

• 1 bis 8 schematische Darstellungen von Fahrzeugen mit ATL, welche durch ein erfindungsgemäßes Verfahren betreibbar ist,
• 9 eine schematische Darstellung zur Visualisierung von Verfahrensschritten eines erfindungsgemäßen Verfahrens.

Further advantages, features and details of the invention emerge from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can be essential to the invention individually or in any combination. Show it:

• 1 to 8th schematic representations of vehicles with ATL, which can be operated by a method according to the invention,
• 9 a schematic representation for the visualization of method steps of a method according to the invention.

In the following figures, the same reference numerals are used for the same technical features from different exemplary embodiments.

In 1 is a vehicle 1 shown which an internal combustion engine 10 and an electric motor 22nd to provide an electric drive for the front axle. In addition, an electric four-wheel drive is provided in which the rear axle 23 is driven purely electrically. The rear axle 23 of the vehicle 1 thus has an electric axle drive 23 on.

With this extended topology, there is the possibility of using an e-machine 22nd to generate electrical energy and for propulsion on the rear axle 23 to use ("electric cardan shaft"). The drive train components involved (e.g. power / efficiency of the ICE at the current operating point, fuel supply, continuous output of the electric machine) limit the process 22nd or the belt-driven starter generator 11 ) the possibilities of the system. When the energy for the electric final drive 23 continues to come from the fuel, however, heavy losses are caused by the repeated energy conversion. In order to better utilize the chemically bound energy in the fuel and to increase the overall efficiency, the electrically assisted exhaust gas turbocharger 30th (eATL) contribute to the drive train. This eATL 30th can be designed to generate electrical energy from the lost energy in the exhaust gas via generator operation and to make this available to the drive system.

In the 1 VKM shown 10 generates mechanical energy and waste heat. Via the electrically assisted ATL 30th energy is recuperated from the exhaust gas and can be used to drive the electric axle 23 be used. This is especially possible and useful if by the traction battery 21 insufficient energy to operate the electric axis 23 can be made available. It may be possible that regardless of the eATL 30th continue to use the electric motor 22nd mechanical energy is recovered.

In 2 is a configuration according to 1 shown, but 48 volt components are used in the electric drive. The eATL 30th can be designed as a 48 volt eATL. The electrical power is correspondingly lower. There is also a belt starter generator 11 shown, which can also be used for recuperation.

In 3 and 4th Another configuration is shown in which an electric motor 22nd to drive the front axle is dispensed with. The VKM 10 generates mechanical energy to drive the front axle and the eATL generates it from the waste heat in the exhaust gas 30th additional electrical energy to drive the electric rear axle 23 and / or charging the traction battery 21 . It can also be a DC / DC converter 24 provided if a 48 volt eATL 30th is used (s. 4th ).

In the 5 and 6th a configuration is shown in which the VKM 10 mechanical energy generated for the drive of the VA. In addition, an electric motor (EM) 22nd to provide a hybrid drive for the vehicle 1 intended. The eATL 30th electrical energy is also recuperated from the exhaust gas, which is used to drive the electric motor 22nd for the vehicle 1 and / or for the RSG 11 and / or to charge the traction battery 21 can be used.

The 7th and 8th show a combination of all components considered so far (VKM 10 , RSG 11 , EM 22nd , electric axis 23 and eATL 30th ). In this way, various operating states of the overall system can be represented, which are justified under the respective point of view (e.g. optimal overall efficiency, maximum mechanical propulsion energy, maximum electrical energy generation). Basically, the VKM generates 10 The eATL generates mechanical energy and the ICE waste heat 30th electrical power.

In 9 is a method for operating an electrically assisted exhaust gas turbocharger 30th of a vehicle 1 visualized with exhaust gas turbocharging. According to the above explanations, the vehicle can 1 by at least one electric drive 22nd , 23 and by an internal combustion engine 10 is driven. The electric drive 22nd , 23 can e.g. B. a purely electric driven axle 23 include, and / or a Electric motor 22nd to provide a hybrid drive for at least the front axle.

According to a first process step 101 the exhaust gas turbocharger is operated 30th in a first operating state in which recuperation by the exhaust gas turbocharger 30th is limited by at least one operating criterion, the operating criterion at least for an efficiency of the exhaust gas turbocharger and / or the internal combustion engine 10 is specific. In other words, the operating criterion can contain the condition that the efficiency of the ICE is optimized. According to a second process step 102 at least one operating parameter of the vehicle is monitored 1 for the detection of a critical condition for the electric drive 22nd , 23 . A third method step then takes place 103 an operation of the exhaust gas turbocharger 30th in a second operating state when the critical state is detected, the limitation of the recuperation by the operating criterion being lifted in the second operating state.

The above explanation of the embodiments describes the present invention exclusively in the context of examples. Of course, individual features of the embodiments can be freely combined with one another, provided that they are technically sensible, without departing from the scope of the present invention.

List of reference symbols

1

vehicle

10

Internal combustion engine, internal combustion engine, ICE

11

Belt starter generator, RSG

21

Traction battery

22nd

Electric motor

23

electric rear axle, electric final drive

24

DC-DC converter

30th

Exhaust gas turbocharger

101

first procedural step

102

second procedural step

103

third process step

22.23

electric drive

QUOTES INCLUDED IN THE DESCRIPTION

This list of the 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.

Patent literature cited

• DE 102013106643 A1 [0003]
• DE 102014221331 A1 [0003]

Claims (10)

Method for operating an electrically assisted exhaust gas turbocharger (30) of a vehicle (1) with exhaust gas turbocharging, the vehicle (1) being driven by at least one electric drive (22, 23) and by an internal combustion engine (10), the following steps being carried out : - Operating the exhaust gas turbocharger (30) in a first operating state in which recuperation by the exhaust gas turbocharger (30) is limited by at least one operating criterion, the operating criterion being specific at least for an efficiency of the exhaust gas turbocharger and / or the internal combustion engine (10), - Monitoring at least one operating parameter of the vehicle (1) to detect a critical state for the electric drive (22, 23), - Operating the exhaust gas turbocharger (30) in a second operating state when the critical state is detected, the limitation of the recuperation by the operating criterion being lifted in the second operating state. Procedure according to Claim 1 , characterized in that in the second operating state the efficiency is reduced in order to increase an electrical power recuperated by the exhaust gas turbocharger (30) for operating the electrical drive (22, 23). Procedure according to Claim 1 or 2 , characterized in that a turbine output of the exhaust gas turbocharger (30) is increased in the second operating state, whereby the efficiency is reduced and the recuperation is increased. Method according to one of the preceding claims, characterized in that the exhaust gas turbocharger (30) is designed with a variable turbine geometry. Method according to one of the preceding claims, characterized in that the monitored operating parameter is specific for a state of charge of a traction battery (21) of the vehicle (1) in order to detect a low state of charge to detect the critical state. Method according to one of the preceding claims, characterized in that the monitored operating parameter is specific for an operating temperature of a traction battery (21) of the vehicle (1) in order to detect at least one critical operating temperature for the detection of the critical state. Method according to one of the preceding claims, characterized in that the vehicle (1) is designed as a hybrid electric vehicle, the critical state being specific to the fact that a hybrid driving mode of the vehicle (1) is restricted or prevented. Method according to one of the preceding claims, characterized in that the vehicle (1) has an all-wheel drive in which the front or rear axle, in particular only, is driven by the electric drive (22, 23). Method according to one of the preceding claims, characterized in that, in the second operating state, the recuperation is limited only by a stability criterion which is specific for the internal combustion engine (10). Method according to one of the preceding claims, characterized in that in the first operating state the activation of the recuperation is dependent on an operating point of the internal combustion engine (10), and in particular the recuperation is activated on the basis of a predefined characteristic map in order to carry out the recuperation in an efficiency-optimized manner, the efficiency-optimized activation is canceled in the second operating state.

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