DE102020001600A1 - Method for operating a drive train of a motor vehicle, in particular a motor vehicle - Google Patents

Abstract

The invention relates to a method for operating an energy store for storing electrical energy, at least one electric traction machine that can be supplied with the electrical energy stored in the energy store, and a drive train of a motor vehicle having a transmission, in which a gear change in the transmission via which the motor vehicle is electrically drivable by means of the traction machine, is carried out, the gear change being carried out as a function of a current electrical voltage of the energy store.

Description

The invention relates to a method for operating a drive train of a motor vehicle, in particular a motor vehicle, according to the preamble of patent claim 1.

the DE 10 2005 022 926 B3 discloses a drive unit for a motor vehicle, with an electric drive motor and a change gearbox with at least two gear stages. Furthermore, the DE 10 2014 119 115 A1 a vehicle with a powertrain known to be inferred.

The object of the present invention is to create a method for operating a drive train of a motor vehicle, so that operation that is particularly efficient can be implemented.

This object is achieved by a method with the features of claim 1. Advantageous configurations with expedient developments of the invention are specified in the remaining claims.

The invention relates to a method for operating a drive train of a motor vehicle, which can preferably be designed as a motor vehicle, in particular as a utility vehicle. In particular, the method is carried out while the motor vehicle is driving, which motor vehicle drives or is driven while driving along a floor or along a roadway. In the case of the method, the motor vehicle has at least one energy store for storing electrical energy or electrical current, wherein the energy store can be, for example, a battery, in particular a high-voltage battery (HV battery). The energy store is also referred to as an electrical store, it being possible for the energy store in particular to be a lithium-ion battery. In the method, the motor vehicle also has at least one electrical machine, which is also referred to as an electrical traction machine or simply also as a traction machine and can be or is supplied with the electrical energy stored in the energy store or with the electrical current stored in the energy store. In other words, the method can provide that the traction machine is supplied with the electrical energy stored in the energy store. By supplying the traction machine with the electrical energy stored in the energy store, the traction machine can be or is operated as an electric motor by means of which the motor vehicle can be or is driven, in particular while the motor vehicle is in motion. The electrical machine is referred to as a traction machine or as an electrical traction machine, since the motor vehicle can be or is driven electrically by means of the electrical machine, in particular purely electrically. Since for this purpose the electrical machine can be or is supplied with electrical energy stored in the energy store, the energy store is also referred to as a traction store or traction battery. In order to be able to realize particularly high electrical powers for driving the motor vehicle, in particular purely electrically, it is preferably provided that the energy store and the traction machine are designed as high-voltage components. This means in particular that the respective high-voltage component (HV component) has an electrical voltage, in particular an electrical operating or nominal voltage, which is preferably at least 48 volts. The electrical voltage, in particular the electrical operating or nominal voltage, is preferably greater than 50 volts, in particular greater than 60 volts. It has been shown to be particularly advantageous if the electrical voltage, in particular the electrical operating or nominal voltage, is several 100 volts in order to be able to provide or implement particularly large electrical powers for, in particular purely electrical, driving of the motor vehicle. The motor vehicle is thus designed, for example, as a hybrid vehicle or as an electric vehicle, in particular as a battery-electric vehicle (BEV).

In the case of the method, the drive train also has a transmission via which the motor vehicle can be or is driven electrically in the method by means of the traction machine, in particular purely. In the method, a gear change is carried out in the transmission. This means that the transmission has at least or precisely two gear steps, also referred to simply as gears, which can each be inserted and disengaged, that is, interchangeable. In particular, the gears or the gear steps differ from one another with regard to their respective gear ratios via which the motor vehicle can be or is driven by means of the electric machine. Thus, for example, a first of the gears has a first ratio and a second of the gears has a second ratio, the second ratio being less than the first ratio, for example. Thus, for example, a gear change is to be understood as meaning that a shift is made from first gear to second gear or from second gear to first gear. When one or the shift from first gear to second gear is the first gear that is initially engaged and thus activated is disengaged, and the second gear that is initially disengaged or deactivated is engaged, that is to say activated. When changing gear from second gear to first gear, the first engaged or activated second gear is disengaged and thus deactivated, and the initially disengaged or deactivated gear is engaged, that is to say activated. A gear change from the first gear to the second gear is also referred to as an upshift or an upshift, with a gear change from the second gear to the first gear also being referred to as a downshift, downshift, downshift or downshift. The respective gear ratio of the respective gear is also referred to as i and results, for example, from: $$\text{i}=\frac{n_{\mathrm{A.}ntrieb}}{n_{\mathrm{A.}btrieb}}$$

Here, n _drive denotes an input speed of the transmission, with n _output denoting an output speed of the transmission. The input speed is, for example, a speed of an input shaft of the transmission, via the input shaft of which torques that can be provided by the electric machine for driving the motor vehicle can be introduced into the transmission. The output speed is, for example, a speed of an output shaft of the transmission, via the output shaft of which the transmission provides drive torques for driving the motor vehicle. The respective drive torque that the transmission provides via its output shaft results, for example, from the respective torque that is introduced into the transmission via the input shaft, the drive torque from the respective torque, also referred to as input torque, which is introduced into the transmission via the input shaft is related to the respective gear ratio of the respective activated gear, for example as follows: $${\text{M.}}_{\text{Downforce}}=\text{i}\cdot {\text{M.}}_{\text{drive}}$$

Here, M _output denotes the drive torque that is provided by the transmission via its output shaft, and M _Antneb denotes the respective torque (input torque), which is provided, for example, by an electrical machine and is introduced into the transmission via the input shaft.

In order to be able to realize particularly efficient or efficient operation of the drive train and thus of the motor vehicle as a whole, the method according to the invention provides that the gear change is carried out as a function of a current electrical voltage of the energy store. The current electrical voltage is to be understood in particular as an electrical voltage, in particular an electrical operating or nominal voltage, which is currently, that is to say currently, made available by the energy store. The current electrical voltage of the energy store is applied, for example, to an electrical energy supply system of the drive train and is thus an electrical voltage applied to the electrical energy supply system or an electrical voltage applied to the electrical energy supply system results from the current electrical voltage of the energy store. It is thus provided in the method according to the invention that the gear change is carried out as a function of the current voltage applied to the electrical energy supply system. The feature that the gear change is carried out as a function of the current electrical voltage of the energy store is to be understood in particular that, for example actively and / or by means of an electronic computing device of the drive train, the current electrical voltage of the energy store or at least one of the current electrical Voltage value characterizing the voltage of the energy store is determined, in particular detected or retrieved, the gear change being carried out as a function of the determined, current electrical voltage of the energy store or as a function of the determined voltage value. The invention is based in particular on the following findings: In partially and fully electrified vehicles, the current electrical voltage of the energy storage device, also referred to as battery voltage, can be due to the discharge of the energy storage device, the discharge of which occurs, for example, when the energy stored in the energy storage device Electrical energy is supplied to the electrical machine in order to operate the electrical machine, in particular in the motor mode, or change, that is to say can decrease, increase or fluctuate, due to the charge of the energy store. The energy store can be charged, for example, through what is known as a recuperation feed. As part of the recuperation feed, recuperation takes place, in the context of which the electrical machine is operated in a generator mode and thus as a generator. By means of the generator, kinetic energy of the motor vehicle is converted into electrical energy, which is provided by the generator and, for example, fed into the energy store, that is to say is stored in the energy store. Furthermore, it can be too a charge of the energy store in the context of or through what is known as a fuel cell feed, in the context of which, for example, a fuel cell provides electrical energy that is stored in the energy store. Changing the electrical voltage of the energy store has effects on the operating points of the traction machine, since if the electrical voltage of the energy store is lower, for example, the aforementioned electrical energy supply system, in particular an inverter of the energy supply system, via whose inverter the traction machine can be supplied with the electrical energy stored in the energy store or is supplied, can no longer provide a desired stator voltage, which is why the traction machine already goes into what is known as field weakening at a lower speed. As a result, the efficiency curves of the traction machine shift in the field weakening range while driving. With a higher electrical voltage, the best possible efficiency range is possible in a wider speed range, while with a lower electrical voltage of the energy storage device, the best possible efficiency range is located in a narrower speed range.

Conventionally, a shift strategy, also referred to simply as a strategy, according to which gear changes are carried out in the transmission, has so far only been dependent on torque and speed. The gear change usually relates to a fixed electrical voltage of the energy store or the current electrical voltage of the energy store and in particular its change is not taken into account, so that the gear change is usually always the same regardless of the current electrical voltage of the energy store, i.e., for example, always in or at the same switching point.

In contrast, it is now provided according to the invention that the shift point, also referred to as the shift time, at or at which the gear change is carried out, is shifted, that is, varied or changed, as a function of the current electrical voltage of the energy store. The switching point is defined in particular by a, in particular current, driving speed of the motor vehicle and by a requested torque to be provided by the traction machine to drive the motor vehicle, the torque to be provided by the traction machine, for example, by the aforementioned electronic computing device or by the driver of the motor vehicle in particular is requested by pressing an accelerator pedal. This is to be understood in particular that the gear change is carried out at the shift point and thus when the torque defining the shift point is requested and the motor vehicle is the driving speed defining the shift point at which the motor vehicle is driven, in particular on the aforementioned lane, having. It is usually provided that this switching point is rigid or fixed regardless of the current electrical voltage of the energy store. In contrast to this, it is now provided according to the invention that the switching point is changed, that is to say shifted, as a function of the current electrical voltage of the energy store. For example, the shift point is part of a characteristic curve, also referred to as a shift line, or part of a characteristic map, the shift line or characteristic map, for example, comprising several shift points at which respective gear changes of the transmission or in the transmission are carried out. In order, for example, to change the switching point or the switching line or the characteristic map as a function of the current electrical voltage of the energy store, in particular to shift it, a factor is used, for example, with which the switching point or the switching line or the characteristic map is multiplied, for example, the factor for example, is varied as a function of the current electrical voltage of the energy store. In other words, the factor influences the switching point or the characteristic curve or the characteristic field. This factor is or, if necessary, takes into account fluctuating electrical voltages of the energy store, in particular while driving.

In order to achieve a particularly efficient and thus low-energy operation of the drive train and thus of the motor vehicle as a whole, it is provided in an advantageous embodiment of the invention that the gear change is carried out as a function of one or, in particular, the current driving speed of the motor vehicle, which, in particular during the aforementioned trip, drives or is driven at the current driving speed, in particular along the aforementioned lane.

It has also been shown to be advantageous if the gear change is carried out as a function of a torque or, in particular, the current, requested torque to be provided by the electric machine for driving the motor vehicle. In this way, a particularly advantageous and, in particular, particularly efficient operation can be ensured.

It has been shown to be particularly advantageous if the implementation of the gear change dependent on the current electrical voltage of the energy store includes that the or at least one switching point, in or at which the gear change is carried out at a predetermined driving speed of the motor vehicle, is requested to a higher one Torque is shifted when the electrical voltage of the energy storage device decreases. In other words, if the current electrical voltage of the energy store has, for example, a first voltage value, the at least one switching point is defined, for example, by the specified driving speed and by a first torque to be provided by the electrical machine for driving the motor vehicle, so that, for example, when the current electrical voltage of the energy store has the first voltage value, then the gear change is carried out in the transmission when the motor vehicle is at the specified driving speed and the first torque is requested. If, however, the current electrical voltage of the energy store has a second voltage value that is lower than the first voltage value, so that the electrical voltage of the energy store has, for example, been lower, then the or the same gear change is carried out when the motor vehicle has the, in particular the same, predetermined driving speed and a second torque, which is greater than the first torque and is to be provided by the electric machine, is requested for driving the motor vehicle. As a result, when the electrical voltage of the energy store decreases, an operation that is favorable in terms of efficiency can be maintained or, in comparison with conventional solutions, an operation that is more favorable in terms of efficiency can be implemented.

Another embodiment is characterized in that performing the gear change as a function of the current electrical voltage of the energy store includes at least one switching point at or at which the gear change is carried out at a requested torque to be provided by the electric machine to drive the motor vehicle , is shifted towards a higher driving speed of the motor vehicle when the electrical voltage of the energy storage device increases. In other words, if, for example, the current electrical voltage of the energy store has a third voltage value, the gear change is carried out when the torque defining the shift point for the third voltage value is requested and the motor vehicle has or reaches a first driving speed at which the motor vehicle, in particular along the aforementioned roadway, drives or is driven. However, if the current electrical voltage of the energy store has a fourth voltage value that is greater than the third voltage value, so that the electrical operating voltage of the energy store has increased, then the gear change, in particular the same, is carried out when the same, the switching point for the third voltage value and for the torque defining the fourth voltage value is requested and the motor vehicle has a second driving speed which is greater than the first driving speed and at which the motor vehicle is driving or being driven, in particular along the aforementioned roadway. In this way it can be ensured, for example, that the electrical machine (traction machine) is operated at least almost always with a particularly high efficiency, i.e. a particularly advantageous efficiency range, despite any change in the current electrical voltage of the energy store, so that a particularly efficient operation of the drive train and thus the motor vehicle as a whole can be guaranteed.

Overall, it can be seen that it is preferably provided according to the invention that the switching point, also referred to as the gear change time, is carried out later at least in some operating points when the battery voltage increases or is higher. In contrast, when the battery voltage is low, the gear change time is set earlier, at least in some operating points.

The gear change or the execution of the gear change is to be understood in particular to mean that the gear change is carried out, for example, by means of the aforementioned electronic computing device and by means of an actuator device, in particular automatically. Here, for example, the electronic computing device controls the actuator device so that shift elements are moved by means of the actuator device in such a way that the first gear is disengaged and the second gear is engaged or the second gear is disengaged and the first gear is engaged as part of the gear change. The electronic computing device is designed, for example, to regulate and / or control the transmission, in particular the drive train, and can comprise at least or precisely one control device or a plurality of control devices which can exchange data with one another via a bus system, for example. The shift point is a point for triggering the gear change, also known as gear shift. This is to be understood in particular as meaning that when the drive train is in one characterized by the switching point Operating status comes, the gear change is triggered, that is, carried out. As already described above, the switching point is defined, for example, by or the driving speed of the motor vehicle, which is traveling at the driving speed, and the switching point is defined by the or a torque that is requested and is to be provided by the electric machine in order to use the torque to drive the motor vehicle. For example, the requested torque to be provided by the electrical machine is the aforementioned respective input torque. The switching point is varied or shifted as a function of the current electrical voltage of the energy store in particular such that, for example, while maintaining the driving speed defining the switching point, the torque defining the switching point is changed as a function of the current electrical voltage of the energy store, and / or that, for example, below Maintaining the torque defining the switching point in time, the driving speed of the motor vehicle defining the switching point in time is changed or varied. This can ensure that the traction machine is operated at least almost always in a particularly good efficiency range and thus with a particularly high efficiency.

It is conceivable that for first current electrical voltages of the energy store, the first electrical voltages being greater or smaller than a mean and / or predetermined or predeterminable electrical voltage of the energy store, a shift of the switching point or switching points at a vehicle speed or at a respective vehicle speed to higher, requested torques takes place.

Alternatively or additionally, provision is made, for example, that for second current electrical voltages of the energy store, the second electrical voltages being smaller or larger than the mean or predetermined or predeterminable electrical voltage of the energy store, a shift of the switching point or the switching points at the vehicle speed or takes place at the respective vehicle speed towards lower torques.

Another embodiment is characterized in that the gear change includes shifting from one of the gears of the transmission to one of the gears of the transmission, which is higher than the one gear, and another of the gears. One gear of the transmission is, for example, the aforementioned first gear, with the other gear of the transmission, for example, being the aforementioned second gear. Thus, for example, the other gear has a lower gear ratio than the one gear.

It has also been shown to be particularly advantageous if the gear change includes shifting from the other gear to one gear. The gear change can thus include an upshift and / or a downshift of the transmission.

In order to avoid excessive shifting of the transmission, what is known as a hysteresis is preferably provided, which is also referred to as a shift hysteresis. Different shift times are preferably provided at which upshifts are made, that is, from first gear to second gear or from one gear to the other gear or downshifting, that is, from the other gear to one gear.

Thus, it is preferably provided that in or at a first shift point from one gear to the other gear and at a second shift point from the other gear to one gear, the first shift point being determined by a first driving speed of the motor vehicle and by a first requested torque to be provided by the electric machine for driving the motor vehicle is defined.

It has been shown to be particularly advantageous if the second switching point is defined by a second driving speed of the motor vehicle that is lower than the first driving speed and by the first requested torque to be provided by the electric machine for driving the motor vehicle. Thus, for example, if the requested torque to be provided by the electric machine remains at least essentially constant, while, for example, the driving speed of the motor vehicle fluctuates, then undesired, excessively frequent switching back and forth due to the hysteresis can be avoided.

Alternatively or additionally, it is preferably provided that the second switching point is defined by the first driving speed of the motor vehicle and a second torque to be provided by the electric machine, which is greater than the first torque, for driving the motor vehicle. In this way, too, a circuit hysteresis can be generated, as a result of which a particularly efficient and efficient operation can be represented.

Further advantages, features and details of the invention emerge from the following description of a preferred embodiment and with reference to the drawing. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively specified combination, but also in other combinations or alone, without the scope of the Invention to leave.

• 1 zwei Schaubilder mit Wirkungsgrad- und Drehmomentkennlinien einer als Traktionsmaschine ausgebildeten elektrischen Maschine für unterschiedliche elektrische Spannungen eines Energiespeichers, mittels welchem die elektrische Maschine mit in dem Energiespeicher gespeicherter elektrischen Energie versorgbar ist;
• 2 ein Diagramm zum Veranschaulichen eines erfindungsgemäßen Verfahrens zum Betreiben eines Antriebsstrangs eines Kraftfahrzeugs;
• 3 ein weiteres Diagramm zum Veranschaulichen des Verfahrens; und
• 4 ein weiteres Diagramm zum Veranschaulichen des Verfahrens.

The drawing shows in:

• 1 two diagrams with efficiency and torque characteristics of an electrical machine designed as a traction machine for different electrical voltages of an energy store, by means of which the electrical machine can be supplied with electrical energy stored in the energy store;
• 2 a diagram to illustrate a method according to the invention for operating a drive train of a motor vehicle;
• 3 a further diagram to illustrate the method; and
• 4th another diagram to illustrate the process.

Identical or functionally identical elements are provided with the same reference symbols in the figures.

A method for operating a drive train of a motor vehicle is described below with reference to the figure. The motor vehicle is preferably a motor vehicle, in particular a utility vehicle. The motor vehicle has at least one electrical machine by means of which the motor vehicle can be or is driven electrically, in particular purely electrically. The electric machine is therefore also referred to as a traction machine or electric traction machine. The motor vehicle also has an energy store in or by means of which electrical energy or electrical current is to be stored or is stored. For example, the method is carried out while the motor vehicle is driving, which is driving or is being driven along a roadway while driving and is driven electrically, in particular purely, by means of the electrical machine. In order to drive the motor vehicle electrically, in particular purely, by means of the traction machine, the electric machine is operated in a motor mode and thus as an electric motor. For this purpose, the electrical machine is supplied with electrical energy stored in the energy store. The energy store is therefore also referred to as a traction store or traction battery, in particular when the energy store is designed as a battery, in particular as a high-voltage battery. The motor vehicle has, for example, an electrical energy supply system via which the electrical machine can be or is supplied with the electrical energy stored in the energy store. For this purpose, the energy store provides an electrical voltage, in particular an electrical operating or nominal voltage, which is then applied to the energy supply system, in particular so that the energy store provides the electrical energy stored in it via the energy supply system to the traction machine. In other words, the traction machine is supplied with the electrical energy stored in the energy store via the energy supply system. For this purpose, the in particular current electrical voltage provided by the energy store is applied to the energy supply system. The electrical voltage, which is provided by the energy store and applied to the energy supply system, can fluctuate, i.e. vary, in particular while driving, so that the electrical voltage provided by the energy store and applied to the energy supply system is a current electrical voltage, which is currently is provided by the energy store.

The motor vehicle also has a transmission, via which the motor vehicle can be electrically driven or is electrically driven by the traction machine, in particular purely. This can in particular be understood to mean that the motor vehicle has at least two vehicle wheels, via which the motor vehicle is supported in the vertical direction of the vehicle downwards on the aforementioned roadway, while the motor vehicle is traveling along the roadway. The vehicle wheels roll on the roadway. In this case, the vehicle wheels are or will be electrically drivable or driven by the electric machine, in particular pure, via the transmission.

The gearbox is, for example, a change gearbox. The transmission includes, for example, at least or precisely two shiftable or changeable gears, which can thus be engaged and disengaged. In the following, one of the gears is also referred to as first gear, while another of the gears is also referred to as second gear. The gears, which are also referred to as gear steps, differ from one another with regard to their respective gear ratios, in particular in such a way that the first gear has a first gear ratio and the second gear has a second gear ratio that is lower than the first gear ratio. As will be explained in more detail below, the method involves at least one gear change in the transmission or in the Transmission carried out. The gear change is to be understood in particular to mean that, for example, the first gear that is initially engaged is disengaged and the second gear that is initially disengaged is engaged. This is also known as an upshift or an upshift. Furthermore, the gear change can include disengaging the second gear initially engaged and engaging the first gear initially disengaged, which is also referred to as downshifting or downshifting. 1 now shows a first diagram 10 , on its abscissa 12th a speed of the electrical machine is plotted. On the ordinate 14th of the diagram 10 a torque is plotted which can be provided or is provided by the electrical machine in order, for example, to drive the motor vehicle by means of the torque provided by the electrical machine. Below that on the abscissa 12th The applied speed of the electric machine is to be understood as follows: The electric machine has, for example, a stator and a rotor which, in particular in motor mode, can be or is driven by the stator and thereby rotatable about an axis of rotation relative to the stator is rotated. In particular, the graph is 10 an efficiency map in which efficiencies with which the electrical machine can be operated are shown. The graph 10 indicates the degrees of efficiency with which the electrical machine (traction machine) can be operated when the current electrical voltage of the energy store has a first value, also referred to as the first voltage value.

Furthermore shows 1 a second diagram 16 , which is a second efficiency map of the same electrical machine. The graph 16 basically corresponds to the diagram 10 but with the difference that the diagram 16 Indicates efficiencies with which the electrical machine can be operated when the current electrical voltage of the energy store has a voltage value that is greater than the first voltage value. Thus the diagram shows 10 a first operating range, also referred to as the first efficiency range 18th , in which the electrical machine can be operated with a high degree of efficiency and thus with a particularly low level of efficiency. In contrast, the diagram shows 16 a second operating range, also known as the second efficiency range 20th , in which the electrical machine can be operated with high levels of efficiency and thus with low efficiency. Using the diagrams 10 and 16 it can be seen that the operating area 20th wider than the operating range 18th is. In other words, the operating range extends 20th over a wider or larger speed range. So it's over 1 It can be seen that the same electrical machine can be operated at higher electrical voltages of the energy store in a broader operating range with high degrees of efficiency than at lower electrical voltages of the energy store.

In order to be able to implement a particularly efficient operation of the drive train, the method provides that the gear change, that is to say the upshift and / or the downshift, is carried out as a function of the current electrical voltage of the energy store. 2 shows a diagram on its abscissa 22nd a driving speed, also referred to simply as speed, for example in units of kilometers per hour, is plotted, the motor vehicle traveling at the driving speed along the roadway. On the ordinate 24 of the in 2 A torque is plotted in the diagram shown. A course illustrates this 26th the greatest possible torque that can be provided by the transmission, in particular via its output shaft, when the first gear is engaged and the second gear is disengaged. Accordingly, for example, illustrates a course 28 the greatest possible torque that can be provided by the transmission, in particular via its output shaft, when the second gear is engaged and the first gear is disengaged. In addition, the in 2 shown diagram of efficiency curves 30th registered. The efficiency curves 30th illustrate degrees of efficiency with which the electric machine can be operated with the first gear engaged or the second gear engaged, with each efficiency profile 30th illustrates constant efficiency. A first of the efficiency curves shows, for example, an efficiency of 0.95 when first or second gear is engaged. A second of the efficiency curves 30th illustrates, for example, an efficiency of 0.94 when first or second gear is engaged. A third of the efficiency gradients 30th illustrates, for example, an efficiency of 0.92 when first or second gear is engaged, and a fourth of the efficiency curves 30th illustrates, for example, an efficiency of 0.9 when first or second gear is engaged.

In addition, the in 2 The diagram shown is a first switching characteristic 32 entered, according to which one or the upshift from first gear to second gear can be carried out. In the in 2 In addition, a second shift characteristic curve is plotted in the diagram shown, according to which, for example, a or downshifting from second gear to first gear can be carried out. Under the switching characteristics 32 and 34 the following can be understood in particular: Will For example, the driver of the motor vehicle requests an at least substantially constant torque to be provided by the traction machine to drive the motor vehicle while first gear is engaged, then an upshift is made, that is, shifted from first gear to second gear when used on the in 2 The diagram shown the driving speed the shift characteristic 32 reached or exceeded. Exceeding is also to be understood as reaching, since the driving speed determines the shift characteristic 32 can only exceed the fact that the driving speed initially the shift characteristic 32 achieved. If, for example, with the same and at least substantially constant torque requested by the driver, the driving speed at which the motor vehicle is traveling along the roadway is, for example, lower again, such that the driving speed exceeds the shift characteristic 34 reaches or falls below, then a downshift is made again, that is, shifted from second gear to first.

Thus includes the respective switching characteristic 32 respectively 34 respective switching points, which are also referred to as switching times or gear change times, the respective switching point being defined by a respective, associated driving speed of the motor vehicle and a respective, associated, requested torque to be provided by the traction machine for driving the motor vehicle. This is explained below with the aid of two switching points 36 and 38 explained, the switching point 36 on the switching characteristic 32 and the switching point 38 on the switching characteristic 34 lies. Thus, the switching point 36 is also referred to as the first switching point, and the switching point 38 is also referred to as the second switching point. The switching point 36 is determined by a first driving speed 40 and by a first requested torque to be provided by the traction machine 42 defined for driving the motor vehicle. The switching point 38 is achieved by a second driving speed which is lower than the first driving speed 44 and by the same, first, requested torque to be provided by the electrical machine 42 defined for driving the motor vehicle. In 2 is also a third switching point 46 shown which on the switching characteristic 34 lies. Is the switching point, for example 38 not provided, the switching point 46 can be viewed as the second switching point. the end 2 it can be seen that the switching point 46 by the same, first driving speed 40 and by a second, requested torque to be provided by the electric machine 48 for driving the motor vehicle is defined, wherein the second torque is greater than the first torque. Based on the switching points 36, 38 and 46 The following can be seen: If, for example, the first gear is engaged while the second gear is disengaged, then a shift is made from the first gear to the second gear at the switching point 36 and in the present case when the motor vehicle reaches the driving speed 40 has or achieved while the torque 42 is requested. In addition, for example, from second gear to first gear at the shift point 38 and in the present case switched when the motor vehicle reaches the driving speed 44 has while the torque 42 is requested. Thus, for example, starting from the switching point 36, the motor vehicle slows down while the torque continues 42 is requested, then a downshift or downshift takes place when the motor vehicle reaches the driving speed 44 achieved.

If, for example, the second gear is initially engaged, then at the shift point 46 and then shifted from second gear to first gear when the torque 48 is requested while the motor vehicle is driving speed 40 having. An upshift from first gear to second gear takes place, for example, at shift point 36 and thus, in the present case, when this is compared to the torque 48 lower torque 42 is requested while the motor vehicle is driving speed 40 having. Overall, it can be seen that the respective gear change is carried out as a function of the vehicle speed and torque. Since the switching points 36 and 38 by the same torque 42 , but due to different driving speeds 40 and 44 or the switching points 36 and 46 by the same driving speed 40 , but due to the different torques 42 and 48 be defined, that is, the switching characteristics 32 and 34 are spaced apart, a so-called, simply also as hysteresis, designated switching hysteresis is created, whereby excessively frequent gear changes can be avoided, for example, when the driving speed of the motor vehicle fluctuates while the same torque is requested.

3 basically shows that in 2 Diagram shown with the abscissa 22nd and the ordinate 24 . In the in 3 The diagram shown are now efficiency lines 50a-c and 52a-c registered. The efficiency lines 50a-c each show the same efficiency of 0.92 of the electrical machine for different electrical voltages of the energy store when first gear is engaged. The efficiency lines show accordingly 52a-c the same efficiency 0.92 of the electrical machine for different electrical voltages of the energy store and when the second gear is engaged. The efficiency line illustrates this 50a the efficiency of 0.92 of the electric machine if the first Gear is engaged and the current electrical voltage of the energy store is 450 volts. The efficiency line 50b shows the efficiency of 0.29 of the electrical machine when first gear is engaged and the current electrical voltage of the energy store is 400 volts. The efficiency line 50c shows the efficiency of 0.92 of the electrical machines when first gear is engaged and the current electrical voltage of the energy store is 325 volts. The efficiency line shows accordingly 52a the efficiency of 0.92 of the electrical machine when the second gear is engaged and the current electrical voltage of the energy store is 450 volts.

The efficiency line 52b illustrates the efficiency of 0.92 of the electrical machine when the second gear is engaged and the current electrical voltage of the energy store is 400 volts. Finally, the efficiency line illustrates 52c the efficiency of 0.92 of the electrical machine when the second gear is engaged and the current electrical voltage of the energy storage is 325 volts. From the efficiency lines 50a-c and 52a-c it is again particularly clear that the electrical machine can be operated at higher electrical voltages of the energy store with an efficiency of, for example 0.92, in a broader speed and torque range than with lower electrical voltages of the energy store. Against this background, it is now provided in the method that the respective gear change is carried out not only as a function of the, in particular current, driving speed of the motor vehicle and as a function of the, in particular current, requested torque to be provided by the electric machine, but rather the Gear changes are also carried out as a function of the current electrical voltage of the energy store. For this purpose, for example, the respective switching point 36, 38 respectively 46 Defined not only by the respective driving speed and the respective requested torque, but also by the current electrical voltage of the energy store. This is over 4th recognizable. 4th shows a diagram with the abscissa 22nd and the ordinate 24 , where in the in 4th The diagram shown shows the switching characteristics 32 and 34 are registered. The shift characteristics 32 and 34 are used, for example, when the current electrical voltage of the energy store is 400 volts, for example, and therefore has a first voltage value or an output value. However, if the current electrical voltage of the energy store has a second voltage value that is greater than the first voltage value, the second voltage value being 450 volts, for example, then instead of the switching characteristic 32 a switching characteristic 32a and instead of the switching characteristic 34 a switching characteristic 34a used. However, if the current electrical voltage of the energy store has a third voltage value which is lower than the first voltage value and thus compared to the second voltage value, which is, for example, 325 volts, then instead of the switching characteristic 32 a switching characteristic 32b and instead of the switching characteristic 34 a switching characteristic 34b used.

This is illustrated below using the example of switching point 36. If, for example, starting from the first voltage value, the current electrical voltage of the energy store increases, for example in such a way that the current electrical voltage of the energy store has the second voltage value, then the switching point 36 is at the same torque 42 towards one versus the driving speed 40 higher driving speed 54 shifted so that instead of the switching point 36 with the same requested torque 42 the switching point 36a is used. If the current electrical voltage of the energy store decreases starting from the first voltage value, so that, for example, the current electrical voltage of the energy store has the third voltage value, then the switching point 36 is at the same or constant torque 42 towards a lower driving speed 56 shifted so that instead of the switching point 36, the switching point 36d is used based on the same requested torque 42 .

The following is also conceivable: If, for example, starting from the first voltage value, the current electrical voltage of the energy store increases so that, for example, the current electrical voltage of the energy store has the second voltage value, then, for example, switching point 36 is set at the same or constant driving speed 40 towards one versus the torque 42 lower torque 58 shifted so that at the same or constant driving speed 40 the switching point 36b is used instead of the switching point 36. However, if, for example, starting from the first voltage value, the current electrical voltage of the energy store decreases so that, for example, the current electrical voltage of the energy store has the third voltage value, at the same or constant driving speed 40 the switching point 36 towards a versus torque 42 higher or greater torque 60 shifted so that then, for example, at the same or constant driving speed 40 instead of switching point 36, switching point 36c is used. Thus, for example, is the respective switching characteristic 32 respectively 34 based on the associated switching characteristics 32a and 32b and 34a and 34b a mean shift curve, so that, for example, at each point of the middle shift line the distance from the respective efficiency line for the first gear is equal to the respective distance from the efficiency line for the first gear equal to the respective distance from the efficiency line for the second gear. In other words, it is provided that the shift characteristics 32 and 34 , 32a and 34a and 32b and 34b are chosen so that the efficiency is the same before the gear change and after the gear change.

• - Wirkungsgraderhöhung des Antriebsstrangs aufgrund der Optimierung einiger Betriebspunkte und somit größere elektrische Reichweite
• - geringere Kühlungsanforderung in den bestimmten Betriebspunkten notwendig, da höherer Wirkungsgrad der elektrischen Maschine bei gleichem Achsmoment beziehungsweise teilweise geringere Kühlleistung des Kühlkreislaufs und mehr elektrische Reichweite
• - Maximaldrehmoment und -leistung des Kraftfahrzeugs kann, wenn die Betriebspunkte im Gangwechselbereich sind, aufgrund geringerer Wärmeentwicklung der elektrischen Maschine länger gefahren werden.

Of course, the method described can be used for all power classes, all voltage levels and also for those multi-speed transmissions that have more than two shiftable gears. Furthermore, the method can be used for any motor vehicle and in particular for any partially or fully electrically operated motor vehicle. In particular, the method results in the following advantages compared to conventional solutions:

• - Increase in efficiency of the drive train due to the optimization of some operating points and thus greater electric range
• - Lower cooling requirements are necessary at the specific operating points, because the electrical machine is more efficient with the same axle torque or, in some cases, the cooling circuit has a lower cooling capacity and greater electrical range
• - Maximum torque and power of the motor vehicle can, if the operating points are in the gear change range, be driven longer due to the lower heat development of the electrical machine.

List of reference symbols

10

graph

12th

abscissa

14th

ordinate

16

graph

18th

Operating area

20th

Operating area

22nd

abscissa

24

ordinate

26th

course

28

course

30th

Efficiency curve

32, 32a, b

Switching characteristic

34, 34a, b

Switching characteristic

36a, d

Switching point

38

Switching point

40

Driving speed

42

Torque

44

Driving speed

46

Switching point

48

Torque

50a-c

Efficiency line

52a-c

Efficiency line

54

Driving speed

56

Driving speed

58

Torque

60

Torque

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 102005022926 B3 [0002]
• DE 102014119115 A1 [0002]

Claims (10)

A method for operating an energy store for storing electrical energy, at least one electric traction machine that can be supplied with the electrical energy stored in the energy store, and a drive train of a motor vehicle having a transmission, in which a gear change in the transmission via which the motor vehicle is electrically powered by means of the traction machine is drivable, is carried out, characterized in that the gear change is carried out as a function of a current electrical voltage of the energy store. Procedure according to Claim 1 , characterized in that the gear change is carried out as a function of a driving speed (40, 44, 54, 56) of the motor vehicle. Procedure according to Claim 1 or 2 , characterized in that the gear change is carried out as a function of a requested torque (42, 48, 58, 60) to be provided by the electric machine. Method according to one of the preceding claims, characterized in that performing the gear change dependent on the current electrical voltage of the energy storage device includes at least one switching point (36) at which the gear change is performed at a predetermined driving speed (40) of the motor vehicle is shifted to a higher requested torque (60) when the electrical voltage of the energy storage device decreases. Method according to one of the preceding claims, characterized in that the implementation of the gear change dependent on the current electrical voltage of the energy store comprises that at least one switching point (36) at which the gear change occurs at a requested torque (42) to be provided by the electric machine. is carried out, is shifted towards a higher driving speed (54) of the motor vehicle when the electrical voltage of the energy store increases. Method according to one of the preceding claims, characterized in that the gear change comprises that a gear of the transmission is switched from one gear of the transmission to another gear of the transmission which is higher than the one gear. Procedure according to Claim 6 , characterized in that the gear change comprises shifting from the other gear to one gear. Procedure according to Claim 7 , characterized in that at a first shift point (36) from one gear to the other gear and at a second shift point (38, 46) different from the first shift point (36) from the other gear to one gear, wherein the first switching point (36) is defined by a first driving speed (40) of the motor vehicle and a first requested torque (42) to be provided by the electric machine. Procedure according to Claim 8 , characterized in that the second switching point (38) is defined by a second driving speed (44) of the motor vehicle that is lower than the first driving speed (40) and the first requested torque (42) to be provided by the electric machine. Procedure according to Claim 8 or 9 , characterized in that the second switching point (46) is defined by the first travel speed (40) and a second torque (48) to be provided by the electric machine, which is greater than the first torque.

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