Method and device for operating a hybrid drive system in a motor vehicle

Abstract

The invention relates to a method for operating a hybrid drive system (1) for a motor vehicle, the motor vehicle having an internal combustion engine (2) and an electric drive, the internal combustion engine having an exhaust-gas-driven supercharging device (24) which is supported by an electric supporting drive (28), the method comprising the following steps: - predicting (S1) the course of a load requirement for a forward driving path; - determining (S2) a predicted course of a target charge state of an electric energy storage device based on the predicted course of the load requirement; - determining (S3, S4) a load distribution and a drive or recuperation power of the electric supporting drive based on the predicted course of the target charge state according to a hybrid operating strategy; - operating (S6, S7) the hybrid drive system according to the determined load distribution and operating the electric supporting drive according to the determined drive or recuperation power.

Description

Technical Field

[0001] The invention relates to a hybrid drive system with an electric drive for a motor vehicle. The invention also relates to an operating strategy for a hybrid drive system with a supercharged internal combustion engine with an exhaust gas-driven supercharging device having an electric auxiliary drive. Background Art

[0002] Hybrid drive systems for motor vehicles usually have an internal combustion engine and an electric drive that cooperate in a suitable manner in order to provide a total drive torque for the motor vehicle. The operating strategy usually specifies the load distribution between the drive units, which usually have the goal of minimizing fuel consumption as much as possible and discharging the electrical energy storage device that supplies energy to the electric drive during the start of the route to be traveled. In addition to the instantaneous vehicle state, a predicted vehicle state is also taken into account for this purpose, which results from observations of the route to be traveled.

[0003] The predicted operating strategy for the hybrid drive system also provides for the kinetic energy of the vehicle to be recovered during coasting or downhill driving and for the electrical energy storage device to be charged accordingly by means of the generator operation of the drive motor.

[0004] In this context, energy management strategies are known which reduce the state of charge of the electric energy storage device before a longer downhill trip in order to increase the charging potential of the electric energy storage device as much as possible for recuperation.

[0005] In this case, the state of charge of the electrical energy storage device is reduced in each case by adjusting the load distribution in favor of the electric drive, so that a larger portion of the drive power is provided by the electric drive before an expected recuperation operation. Summary of the invention

[0006] According to the invention, a method for operating a hybrid drive system having a supercharged internal combustion engine and an electric drive and a hybrid drive system for a motor vehicle are provided.

[0007] Further design solutions are described below.

[0008] According to a further aspect, a method for operating a hybrid drive system for a motor vehicle is provided, the hybrid drive system having an internal combustion engine and an electric drive, the internal combustion engine having an exhaust gas-driven supercharging device supported by an electric auxiliary drive, wherein the auxiliary drive and the electric drive are connected to an electric energy storage device in order to obtain electrical energy from the electric energy storage device or to supply electrical energy to the electric energy storage device by a corresponding recuperation operation, the method comprising the following steps:

[0009] - predicting the trend of load requirements for the upcoming driving path;

[0010] - determining a predicted course of a target state of charge of the electrical energy storage device as a function of the predicted course of the load demand;

[0011] - according to the hybrid operating strategy, the load distribution and the driving or recuperation power of the electric supporting drive are determined according to the predicted trend of the target charge state, the load distribution indicating the load contribution of the internal combustion engine and the electric drive to the total drive torque of the drive system; - the hybrid drive system is operated according to the determined load distribution and the electric supporting drive is operated according to the driving or recuperation power.

[0012] The above-described method is based on the basic idea that during the hybrid operation of the drive system, the charge state of the electric energy storage device is adjusted to a target charge state as a function of the predicted operating state of the motor vehicle. The predicted operating state can be derived, for example, from route information, historical information about the traveled route and other environmental information in a manner known per se and provided as a load requirement of the drive system on the way ahead. Based on the load requirement, a load distribution is derived depending on the operating strategy, which specifies how much load contribution should be provided by the electric drive and how much load contribution should be provided by the internal combustion engine.

[0013] Depending on the predicted course of the load requirement for the forward driving path, it can be specified how much load contribution must be provided by the electric drive according to the current operating state. The load contribution can correspond to a positive load torque or a negative load torque. While the positive load torque of the electric drive includes the conversion of electrical energy from the energy storage device into mechanical drive energy, the negative load torque of the electric drive is provided by a so-called recuperation operation, in which the mechanical kinetic energy of the motor vehicle is converted into electrical energy by the generating operation of the electric drive. The electrical recuperation energy provided in this way can be used to charge the electrical energy storage device.

[0014] Depending on the length or duration of calling up electric power from the electric energy storage device or replenishing the electric energy rate to this electric energy storage device, the state of charge can be close to being completely discharged or fully charged. This may lead in special cases to the situation that when the electric energy storage device is fully charged, it is no longer possible to recover energy for charging the energy storage device. It is also conceivable that a forward section is identified in a predictive operating mode, through which more recuperation energy can be obtained than can be stored in the electric energy storage device due to its high state of charge or small available charging capacity (electric energy receiving capacity). The possibility of recuperating energy is thus at least partially eliminated, and the state of charge cannot be reduced accordingly even by purely electric driving operation up to this forward section. In addition, the braking torque of the motor vehicle caused by recuperation must now be generated by the friction brake, which is therefore worn.

[0015] Therefore, it is provided that the internal combustion engine of the hybrid drive system is equipped with an exhaust gas-driven supercharging device, which additionally has an electric boost drive. The boost drive makes it possible to provide additional boost power for providing charge air at an increased boost pressure while drawing electrical power from the electrical energy accumulator. In addition, the boost drive can charge the electrical energy accumulator by converting waste enthalpy to provide electrical power in generating operation. This makes it possible to use a further degree of freedom when matching the charge state of the electrical energy accumulator to the target charge state predetermined by the predictive operating strategy.

[0016] Thus, for example, a target boost pressure can be provided by increasing the proportion of the boost contribution (increasing the proportion of the boost contribution by increasing the power for the electric auxiliary drive) in order to reduce the state of charge of the electric energy storage device. At the same time, by utilizing the exhaust gas enthalpy, a smaller boost contribution is used to drive the compressor of the supercharging device. The exhaust gas back pressure is thus reduced and the internal combustion engine can be operated more efficiently. Thus, a further possibility is provided, namely, during operating phases in which the driving torque of the hybrid drive system is provided by the load contributions of the electric drive and the internal combustion engine, the state of charge of the electric energy storage device is reduced both by electric operation of the electric drive and by electric operation of the auxiliary drive of the supercharging device.

[0017] Furthermore, the course of the load requirement, in particular in the form of the total drive torque to be provided, can be predicted using the route still to be travelled and map information about the time or route, taking into account in particular speed specifications, downhill or uphill driving lanes and / or weather conditions and / or traffic conditions.

[0018] Provision may be made for the supporting drive to assist in supercharging if it is determined that recuperation energy which cannot be stored due to the charge state of the energy storage device is being provided by the electric drive when a downgrade of the forward driving path is detected.

[0019] Alternatively or additionally, it can be provided that the electric supporting drive and / or the electric drive is activated to receive stored energy when it is confirmed that, when an uphill slope of the forward driving path is detected, a demand for drive energy for the electric drive is determined, which demand cannot be called upon due to the predicted charge state of the energy storage device.

[0020] In particular, when a mixed lubrication operating mode is provided for limiting the exhaust gas temperature, the power input to the support drive can be prioritized over the power input to the electric drive.

[0021] Alternatively or additionally, in particular in the case of a lean-running internal combustion engine, the transmission can be used to control the boost drive during the shifting intervals to support the boost pressure in order to avoid a collapse of the boost pressure provided by the compressor of the boost device.

[0022] It can be provided that, when it is confirmed that, when an uphill slope is identified in the forward driving path, a demand for driving energy for the electric drive is determined (which demand cannot be called upon due to the predicted charge state of the energy accumulator), the supporting drive is controlled to recover electrical energy from the exhaust gas mass flow with the aid of the supporting drive and / or the electric drive is controlled to generate electrical energy.

[0023] Furthermore, at low loads of the internal combustion engine, the electric drive can preferably be used to generate electrical energy, at average loads of the internal combustion engine, the electric drive and the supporting drive are used together to generate electrical energy, and at high loads of the internal combustion engine, the supporting drive is preferably used to recover electrical energy from the exhaust gas.

[0024] According to one embodiment, operation of the electric auxiliary drive according to a determined drive or recuperation power is permitted or prohibited depending on the operating mode of the internal combustion engine and is particularly prohibited in operating modes that provide for mixed lubrication of the internal combustion engine to limit the exhaust gas temperature.

[0025] According to a further aspect, a device is provided for operating a hybrid drive system for a motor vehicle, the hybrid drive system having an internal combustion engine and an electric drive, the internal combustion engine having an exhaust-gas-driven supercharging device which is supported by an electric boost drive, wherein the boost drive and the electric drive are connected to an electric energy storage device in order to obtain electrical energy from the electric energy storage device or to supply electrical energy to the electric energy storage device by a corresponding recuperation operation, wherein the device is designed to:

[0026] - predicting the trend of load requirements for the upcoming driving path;

[0027] - determining a predicted course of a target state of charge of the electrical energy storage device as a function of the predicted course of the load demand;

[0028] - according to the hybrid operating strategy, the load distribution and the driving or recuperation power of the electric supporting drive are determined according to the predicted trend of the target charge state, the load distribution indicating the load contribution of the internal combustion engine and the electric drive to the total drive torque of the drive system; - the hybrid drive system is operated according to the determined load distribution and the electric supporting drive is operated according to the determined driving or recuperation power. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The following is a detailed explanation of the implementation scheme with the help of the accompanying drawings.

[0030] Figure 1 is a schematic diagram of a hybrid drive system with a supercharged internal combustion engine and an electric drive; and

[0031] Figure 2 It is used to illustrate the use of Figure 1 Flowchart of a method for a hybrid drive system. DETAILED DESCRIPTION

[0032] Figure 1 The schematic diagram of a hybrid drive system 1 is shown, which has an internal combustion engine 2 and an electric drive 3, which is mechanically coupled to the internal combustion engine 2, for example, via a common output shaft 5. Thus, load contributions can be provided by the operation of the internal combustion engine 2 and the electric drive 3, which are added to form a total drive torque for driving the motor vehicle. The total drive torque consists of the internal combustion engine torque and the electric drive torque required by the control unit 10 according to an operating strategy. For this purpose, the control unit 10 controls the internal combustion engine 2 and the electric drive 3 in such a way that the corresponding partial drive torque is provided via the output shaft 5. The internal combustion engine 2 and the electric drive 3 are controlled by the control unit 10 in a manner known per se based on the corresponding partial drive torque to be provided.

[0033] The electric drive 3 draws electrical energy from an electrical energy storage device 4 , which can be designed as a rechargeable battery. The electric drive 3 can also be operated in a recuperation mode in order to generate electrical energy and provide this energy for charging the energy storage device 4 .

[0034] The internal combustion engine system 2 comprises an internal combustion engine 21 , into which air is supplied via an air supply system 22 and into which combustion exhaust gases are discharged via an exhaust gas discharge system 23 .

[0035] Furthermore, a supercharging device 24 is provided, which has an exhaust gas turbine 25 driven by exhaust gas in the exhaust gas discharge system 23. A compressor 26 is provided in the air supply system, which is mechanically connected to the exhaust gas turbine 25 via a supercharger shaft 27 in order to use the exhaust gas enthalpy converted in the exhaust gas turbine 25 to drive the compressor 26. The supercharging device 24 can include an electric boost drive 28 in order to provide additional boost power for providing charge air at an increased boost pressure. The electric boost drive 28 is connected to the electric energy storage device 4 in order to draw electrical energy.

[0036] The electric support drive 28 can be connected to the supercharger shaft 27 to directly increase the mechanical power provided for compressing the charge air or to convert the mechanical power provided by the rotation of the supercharger shaft into electrical power. The electric support drive 28 can also be arranged in an auxiliary compressor, which is arranged downstream or upstream of the compressor 26, so as to increase the supercharging power by two-stage supercharging.

[0037] The electric boost drive 28 makes it possible to increase the compression power beyond a certain level that cannot be achieved by a simple conversion of the prepared exhaust gas enthalpy. The electric boost drive 28 draws electrical energy from the energy storage device 4. In addition, the electric boost drive 28 can also be operated in a generator manner in order to convert the existing mechanical power of the supercharger shaft 27, which is caused by the conversion of the prepared exhaust gas enthalpy, into electrical energy for charging the electrical energy storage device 4.

[0038] The control unit 10 is connected to a prediction unit 11 which provides a predicted course of the future load demand of the hybrid drive system 1. The predicted course of the load demand can be provided by route data, driving characteristics data, historical driving data or via a communication connection to a central unit, for example.

[0039] The predicted course of the load demand is converted in a known manner into a course of the target charge state of the electrical energy storage device 4 by means of an operating strategy for the hybrid drive system 1. This then results in a load distribution which describes the partial drive torques to be provided by the internal combustion engine 2 and the electric drive 3.

[0040] exist Figure 2 The following is shown to illustrate the operation Figure 1 Flow chart of a method of a hybrid drive system 1 .

[0041] In step S1, the future course of the load demand is determined in the prediction unit 11 and retrieved from it. The predicted load demand, which is determined based on the route to be traveled and based on the map information about the time or route, is in the form of the total drive torque to be provided. In particular, speed requirements, downhill or uphill driving lanes, weather conditions (wind, rain) and other influences on the load required to propel the motor vehicle (e.g., the load of the motor vehicle) are taken into account.

[0042] In step S2, according to the operating strategy implemented in the control unit 10 and known per se, it is determined in what manner the total drive torque should be provided. For this purpose, the trend of the target charge state of the energy storage device 4 can be determined from the trend of the load requirement on the forward driving path, which shows the share of the load contribution of the electric drive 3 for each road section. The current load distribution is determined accordingly with the instantaneous load requirement, thereby obtaining the size of the internal combustion engine torque and the size of the electric drive torque. The operating strategy used usually stipulates that fuel consumption is minimized, but alternatively or additionally, other optimization goals can also be pursued, such as reducing harmful emissions in urban traffic, etc.

[0043] The course of the state of charge of the electric energy storage device 4 also determines accordingly whether electrical energy should be recuperated or consumed. If the target state of charge of the electric energy storage device 4 can be adjusted by the electric drive 3, operating states are realized when the load demand deviates from the predicted course of the load demand in which it is not entirely possible to recuperate or withdraw electrical energy to reduce the state of charge of the electric energy storage device 4. In particular, at low speeds of the motor vehicle, only a small recuperation or drive power of the electric drive 3 can be called upon. However, if a large change in the target state of charge is required due to the predicted further course of the driving route, it may be necessary to generate additional electrical energy or consume electrical energy in order to adjust the state of charge of the electric energy storage device as quickly as possible.

[0044] For this purpose, provision is made in the operating strategy to take into account the possibility of extracting and recycling electrical energy via the electrical support drive 28 of the supercharging device 24. This creates a degree of freedom in the extraction and recycling of electrical power, which enables a more flexible operation of the motor system 1.

[0045] In step S3, it is checked whether there is an operating situation that requires consumption or recovery of electrical energy by the supporting drive 28 in order to adjust the charge state of the electrical energy storage device 4, for example, when the consumption or recovery of electrical energy by the electric drive 3 is insufficient. For this purpose, the load distribution is determined in a manner known per se from the predicted course of the load demand according to the hybrid operating strategy. From the predicted course of the load distribution thus obtained, the course of the target charge state of the electrical energy storage device 4 is derived, which is to be adjusted or achieved by the input and / or withdrawal of electrical energy. If it is confirmed that there is an operating situation that requires consumption or recovery of electrical energy by the supporting drive 28 in order to adjust the charge state of the electrical energy storage device 4 (option: yes), then the method is continued with step S4, otherwise (option: no) in step S5 the hybrid drive system 1 is operated in a conventional manner according to the hybrid operating strategy and then the method is continued with step S1.

[0046] In step S4 , it is checked whether a consumption of electrical energy is requested via the supporting driver 28 (option: A1 ) or whether an input of electrical energy is requested via the supporting driver 28 (option: A2 ).

[0047] If a request is made to consume electrical energy by the supporting drive 28 (A1), then for this purpose a request can be predefined to reduce the target state of charge of the electrical energy storage device 4 above or below a predefined state of charge threshold value. This can be the case, for example, if, for example, due to a forward downhill route, recuperation energy is available which cannot be completely stored in the energy storage device 4 in a state of charge of the energy storage device 4 which exceeds the state of charge threshold value.

[0048] In the following step S6, the supporting drive 28 is activated as a function of the request to consume electrical energy in order to correspondingly reduce the state of charge of the electrical energy storage device 4. The degree of activation of the supporting drive 28 can be determined as a function of the current state of charge, the target state of charge and the predicted consumption of the electric drive.

[0049] If a higher boost power is provided by the electric boost drive 28, then on the one hand a higher boost pressure is achieved and thus a faster increase in the torque of the internal combustion engine is achieved, and on the other hand the operation of the internal combustion engine 2 becomes more efficient because the exhaust gas back pressure can be reduced. The reduced exhaust gas back pressure is caused by a lower exhaust gas enthalpy extracted from the exhaust gas flow.

[0050] If a request is made to recuperate electrical energy by the supporting drive 28 (A2), the compressor 26 can be driven by the air mass flow into the internal combustion engine 2, so that electrical energy can be generated by the generator operation of the supporting drive 28. This may be the case, for example, when electrical energy is required, which cannot be fully drawn from the energy accumulator 4 in the current state of charge of the energy accumulator 4, for example, due to a forward uphill route. This operating situation can result in the provision of more electrical energy for charging the energy accumulator 4 in combination with downhill driving and the recuperation operation of the electric drive 3.

[0051] In the following step S7, the supporting drive 28 is activated as a function of the request to consume electrical energy in order to correspondingly reduce the state of charge of the electrical energy storage device 4. The degree of activation of the supporting drive 28 can be determined as a function of the current state of charge, the target state of charge and the predicted consumption of the electric drive.

[0052] Overall, the method described above enables a further degree of freedom for adapting the state of charge of electrical energy storage device 4 to a predefined target state of charge.

[0053] Furthermore, at low loads of the internal combustion engine, the electric drive can preferably be used to generate electrical energy, at average loads of the internal combustion engine, the electric drive and the supporting drive are used together to generate electrical energy, and at high loads of the internal combustion engine, the supporting drive is preferably used to recover electrical energy from the exhaust gas.

[0054] According to one embodiment, operation of the electric auxiliary drive according to a determined drive or recuperation power can be permitted or prohibited depending on the operating mode of the internal combustion engine and in particular prohibited in an operating mode for limiting the exhaust gas temperature which provides for mixed lubrication of the internal combustion engine.

[0055] A simple operating strategy can provide that the target state of charge of the energy storage device is reduced before a downhill trip and increased before an uphill trip in order to increase the charge potential for recovering electrical energy. This can avoid a failure to recover or provide electrical drive power because the energy storage device 4 is completely charged or discharged.

Claims

1. A method for operating a hybrid drive system (1) for a motor vehicle, the hybrid drive system having an internal combustion engine (2) and an electric drive, the internal combustion engine having an exhaust-gas-driven supercharger (24) which is supported by an electric boost drive (28), wherein: The supporting drive (28) and the electric drive (3) are connected to an electric energy storage device (4) in order to obtain electric energy from the electric energy storage device or to supply electric energy to the electric energy storage device by a corresponding recuperation operation. The method comprises the following steps: - predicting (S1) the trend of the load requirement for the upcoming driving route; - determining (S2) a predicted course of a target state of charge of the electrical energy storage device as a function of the predicted course of the load demand; - determining ( S3 , S4 ) a load distribution and a drive or recuperation power of the electric support drive according to the predicted course of the target state of charge according to the hybrid operating strategy, the load distribution indicating the load contribution of the internal combustion engine and the electric drive to the total drive torque of the drive system; - operating ( S6 , S7 ) the hybrid drive system in accordance with the determined load distribution and operating the electric supporting drive in accordance with the determined drive or recuperation power, wherein, when it is determined that, when a downhill slope of the forward driving path is detected, recuperation energy which cannot be stored due to the charge state of the energy storage device (4) is provided by the electric drive (3), the electric support drive (28) and the electric drive (3) are activated to receive the stored energy, In this case, when it is confirmed that a demand for drive energy for the electric drive (3) is determined when an uphill slope is identified in the forward driving path, the support drive (28) is controlled to recover electrical energy from the exhaust gas mass flow and the electric drive (3) is controlled to generate electrical energy, wherein the demand for drive energy for the electric drive cannot be called up based on the predicted charge state of the energy storage device (6).

2. The method according to claim 1, wherein: The load demand profile is predicted in the form of the total drive torque to be provided based on the route still to be travelled and based on map information about the time or route, taking into account speed requirements, downhill or uphill driving lanes and / or weather conditions and / or traffic conditions.

3. The method according to claim 1, wherein: When a mixed lubrication operating mode is provided for limiting the exhaust gas temperature, the power input to the auxiliary drive (28) is prioritized over the power input to the electric drive (3).

4. The method according to claim 1, wherein: In a lean-operated internal combustion engine (2), a boost drive (28) is activated by a transmission during a shifting interval to boost the charge in order to avoid a drop in the charge pressure provided by a compressor of the supercharging device.

5. The method according to claim 1, wherein: At low loads of the internal combustion engine (3), the electric drive (2) is used to generate electrical energy, at average loads of the internal combustion engine (2), the electric drive (3) and the supporting drive (28) are used together to generate electrical energy, and at high loads of the internal combustion engine (2), the supporting drive (28) is used to recover electrical energy from the exhaust gas.

6. The method according to any one of claims 1 to 5, wherein: Operation of an electric auxiliary drive (28) according to a determined drive or recuperation power is permitted or prohibited depending on the operating mode of the internal combustion engine (2) and is prohibited in an operating mode for limiting the exhaust gas temperature which provides for mixed lubrication of the operation of the internal combustion engine (2).

7. A device (10) for operating a hybrid drive system (1) for a motor vehicle, the hybrid drive system having an internal combustion engine (2) and an electric drive, the internal combustion engine having a supercharging device (24) driven by exhaust gas and supported by an electric boost drive (28), wherein: The supporting drive (28) and the electric drive (3) are connected to an electric energy storage device (4) in order to obtain electrical energy from the electric energy storage device or to supply electrical energy to the electric energy storage device by a corresponding recuperation operation, wherein the device is designed to: - predicting the trend of load requirements for the upcoming driving path; - determining a predicted course of a target state of charge of the electrical energy storage device as a function of the predicted course of the load demand; - determining a load distribution and a driving or recuperation power of the electric supporting drive according to the predicted course of the target state of charge according to the hybrid operating strategy, the load distribution indicating the load contribution of the internal combustion engine and the electric drive to the total drive torque of the drive system; - operating the hybrid drive system according to the determined load distribution and operating the electric supporting drive according to the determined drive or recuperation power, wherein, when it is determined that, when a downhill slope of the forward driving path is detected, recuperation energy which cannot be stored due to the charge state of the energy storage device (4) is provided by the electric drive (3), the electric support drive (28) and the electric drive (3) are activated to receive the stored energy, In this case, when it is confirmed that a demand for drive energy for the electric drive (3) is determined when an uphill slope is identified in the forward driving path, the support drive (28) is controlled to recover electrical energy from the exhaust gas mass flow and the electric drive (3) is controlled to generate electrical energy, wherein the demand for drive energy for the electric drive cannot be called up based on the predicted charge state of the energy storage device (6). 8 . A computer program product configured to carry out all steps of the method according to claim 1 . 9 . An electronic storage medium on which a computer program is stored, which is designed to carry out all the steps of the method according to claim 1 .

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