Method for deceleration of an electrically driven vehicle

Abstract

The invention relates to a method for deceleration of an electrically driven vehicle (10) having an electric drive train (12), which comprises at least one electric machine (14), an inverter (20), a high-voltage traction battery (46), at least one on-board electrical system (24), an eddy-current brake (34, 36) and / or friction brakes (38), as well as at least one clutch (42), and the following method steps are carried out individually or in combination with one another: a) feeding braking energy during deceleration of the electrically driven vehicle (10) into the electric drive train (12) thereof with the exception of the high-voltage traction battery (46), such that b) an active short-circuit of the three phases of the electric machine (14) is generated by means of the inverter (20) and the braking energy is absorbed in the ohmic resistance of the windings; and / or c) at high rotation speeds of the electric machine (14), the braking energy is fed into an eddy current brake (34, 36) and / or friction brake (38), and / or d) when a maximum torque of the electric machine (14) is reached in the event of active short-circuit (AKS), braking energy is fed into at least one slip-affected clutch (42) in the electric drive train (12).

Description

[0001] Description

[0002] title

[0003] The invention relates to a method for braking an electrically powered vehicle having an electric drive train comprising at least one electric motor, an inverter, a high-voltage traction battery, at least one electrical system, an eddy-current brake, and / or friction brakes. Furthermore, the invention relates to the use of the method in an electrically powered vehicle.

[0004] State of the art

[0005] DE 10 2012 200 932 A1 relates to a device and a method for controlling an electric machine arranged in a vehicle. The electric machine generates a torque acting on driven vehicle wheels. The electric machine has a phase path that can be connected to an energy storage unit via a controllable inverter. The inverter has a bridge circuit, wherein the phase path is assigned to two switch paths and can be connected to the energy storage unit in such a way that the phase path current direction is reversible. Furthermore, a first detection unit for detecting a charging capacity state of the energy storage unit and a second detection unit for detecting a vehicle operating state characterized by a wheel braking torque are provided.Depending on the charging capacity state and the vehicle operating state, the inverter is controlled such that, when the vehicle operating state is present, the electric motor generates a braking torque acting on a driven wheel based on the phase path current. As long as the charging capacity state differs from a predefined state, it is controlled with a first control pattern and the energy storage unit is charged by the phase path current. As soon as the charging capacity state corresponds to the predefined state, it is controlled with a second control pattern and the energy storage unit is not charged by the phase path current. DE 10 2016 010 740 A1 relates to the operation of a drive train by means of a brief active short circuit. The electric drive train includes an electrical energy storage device, a converter, and an electric machine for driving a motor vehicle.An electrical connection between the converter and the electrical energy storage device is broken, an active short circuit is initiated by short-circuiting a winding of the electrical machine, and a current flow associated with the winding is determined. To prevent the occurrence of both high voltages and high currents in the electrical machine and / or converter when a disconnecting element is opened, the active short circuit of the winding is interrupted when the current flow associated with it passes through zero.

[0006] To ensure that an entire system of an electrically powered vehicle functions flawlessly, at least one high-voltage traction battery, a battery management system, for example, a 12-V electrical system, a high-voltage electrical system, and communication components, the electric vehicle is generally braked using the electric motor. However, if the overall system outlined above is faulty, the electric motor cannot be used to brake, meaning that in this case, the friction brakes on the vehicle absorb all of the braking energy generated. This can also occur in fault-free situations, for example, if the temperature of the high-voltage battery is extremely low, the battery is already overcharged, or too hot, i.e.has a temperature that is too high, or charging of the battery as part of regenerative braking is not currently permitted due to self-diagnosis by the battery management system, to name just a few scenarios. In such situations, the high-voltage traction battery cannot absorb the charging current that would arise when the electric vehicle brakes and be fed into the high-voltage traction battery, or there is currently no reliable information for release in the inverter or the power electronics in the electric drive train of the electrically powered vehicle. As a result, braking with the electric drive cannot be carried out in every driving situation and the friction brakes mounted on the electrically powered vehicle must still be designed so that they can absorb the entire braking energy in the worst-case scenario. Description of the invention.

[0007] According to the invention, a method for braking an electrically driven vehicle is proposed, wherein the electrically driven vehicle has an electric drive train comprising at least one electric machine, an inverter, a high-voltage traction battery, at least one on-board electrical system, an eddy current brake and / or friction brakes, with the following method steps, individually or in combination with one another: a) feeding braking energy when braking the electrically driven vehicle into its electric drive train with the exception of the high-voltage traction battery, such thatthat b) an active short circuit of the three phases of the electrical machine is generated by means of the inverter and the braking energy is absorbed in the ohmic resistance of the windings and / or c) at high speeds of the electrical machine, the braking energy is fed into an eddy current brake and / or friction brake and / or d) when a torque maximum of the electrical machine is reached with an active short circuit (AKS), braking energy is fed into at least one slip-prone clutch in the electric drive train.

[0008] The solution proposed by the invention advantageously ensures that the braking energy generated during deceleration of the electric vehicle, which would be fed into the high-voltage traction battery during recuperation, can now be absorbed by the components of the electric drive train and the inverter. The absorption of braking energy can be facilitated by the relatively high thermal mass of the components installed in the electric drive train and the fact that at least one of the components installed there is often water-cooled.

[0009] In an advantageous development of the method proposed according to the invention, according to method step b), the active short circuit of the three phases on the electrical machine is carried out permanently until the electrically driven vehicle comes to a standstill or a clocking or partial switching of the active short circuit is carried out according to method step b) in such a way that power loss is generated at switching elements.

[0010] In a further advantageous embodiment of the method proposed according to the invention, according to method step b) at the operating point of the electric machine, a maximum torque of approximately 50% of a nominal torque is achieved.

[0011] In a further advantageous embodiment of the method proposed according to the invention, the braking torque of the electric machine is further increased according to method step c) by generating the energy required to drive the eddy current brake in the generator mode of the electric machine. Therefore, no additional separate circuit components or additional components are required to increase the braking energy dissipation; the braking energy can be absorbed solely by the components already installed in the electric drive train.

[0012] In the method proposed by the invention, the eddy-current brake is coupled to the electric motor and driven at its speed. Because the eddy-current brake is driven at the motor speed of the electric motor and not at the wheel speed or the speed of a cardan shaft, the eddy-current brake can be designed very compactly and space-savingly. Furthermore, an eddy-current brake is characterized by its relatively low weight.

[0013] In an advantageous development of the method proposed according to the invention, when the short circuit is active according to method step b), the electric machine has a speed at which the maximum torque is present. A clutch can absorb a speed difference.

[0014] In an advantageous development of the method proposed by the invention, a portion of the braking energy is converted by the slip occurring at the said differential speed. Here, too, the clutch can be used as a passive component that converts braking energy, which is already arranged in the drive train of the electric motor. In an advantageous development of the method proposed by the invention, the driver's braking request can be transmitted to the inverter directly via a control unit (Vehicle Control Unit = VCU) or via a driver assistance system such as the ESP system, in such a way that a portion of the braking energy attributable to the friction brakes of the electrically powered vehicle is calculated beforehand.

[0015] Advantageously, the method proposed by the invention can be used to indicate to the driver of the electrically powered vehicle the number of braking applications performed by the electric drive train or the high-voltage traction battery using a temperature model. This can generate an additional safety aspect, which is particularly beneficial for inexperienced drivers and can make a significant contribution to the control of an electrically powered vehicle.

[0016] In an advantageous embodiment of the method proposed according to the invention, if braking operations are not available, the speed of the electrically driven vehicle can be limited and / or the vehicle can be parked in a controlled manner after braking has been carried out.

[0017] Furthermore, the invention relates to the use of the method in an electrically powered vehicle.

[0018] Advantages of the invention

[0019] The method proposed according to the invention allows the components of the electric drive train of an electrically powered vehicle to be used to absorb braking energy, since their thermal mass is relatively high and components in the electric drive train of an electrically powered vehicle can be cooled by a cooling medium. The solution proposed according to the invention takes into account the fact that recuperation energy generated during braking operations of an electrically powered vehicle can no longer be introduced into the high-voltage traction battery if the high-voltage traction battery is already fully charged, if its temperature is too high, or if self-diagnosis routines are running, thereby significantly increasing overall driving safety.By means of the method proposed according to the invention, other components incorporated in the electric drive train of an electrically powered vehicle can be used to convert the braking energy occurring during braking.

[0020] In the case of the windings of the electric motor, their ohmic resistance is used to convert the braking energy. Furthermore, switching components, such as those on the inverter, where power losses occur, can be used. Finally, the use of the eddy-current brake can further increase the braking torque of the electric motor in generator mode. It should not go unmentioned that the solution proposed by the invention also allows a slip-prone clutch provided in the drive train to convert braking energy. One design variant of a slip-prone clutch is, for example, a "Twinster" clutch.

[0021] The solution proposed according to the invention makes it possible to brake safely using only the components of an electric drive train and the inverter contained therein, even if the high-voltage traction battery or other components are faulty or are in a state in which the absorption of recuperation energy, i.e. braking energy, generated during braking is not possible. The solution proposed according to the invention ensures, on the one hand, a reliable availability of braking, and on the other hand, the classic braking system with disc or drum brakes on the driven axles of a vehicle can be made smaller and thus more cost-effective and, above all, lighter. Ideally, the conventional mechanical brake can be omitted entirely on the driven axle, i.e. the axle driven by the electric motor.

[0022] The solution proposed by the invention further takes into account the fact that if normal communication between the electric axle, battery management, and brakes fails, electric braking is still possible. This means, firstly, that there is no reliable information about whether the high-voltage or traction battery can accept charging current, and secondly, there is no reliable information about whether braking should be applied at all. This would come from the braking system, which always dictates how much braking should be applied with the friction brake and how much electrically.

[0023] The solution proposed by the invention ensures that braking occurs in such a way that no charging current is transferred to the high-voltage or traction battery and, in particular, that all possibilities are utilized, in particular the active short circuit. Furthermore, an additional signal path can be laid from the brake pedal or from the module for braking request detection to the electric axle, so that it can brake even if the normal communication with the braking system is faulty. According to the solution proposed by the invention, electrical braking is possible even if the usual communication between power electronics (inverter) and a braking system or between the inverter is faulty. Conventional methods no longer use electrical braking, but rely on the braking system alone to handle the driving situation, without any communication with the inverter.

[0024] Short description of the drawings

[0025] The invention is described in more detail below with reference to the drawings.

[0026] They show:

[0027] Figure 1 an electrically powered vehicle,

[0028] Figure 2 Braking torque curves of an electrical machine, an eddy current brake and an electrical machine in generator mode and

[0029] Figure 3 is a perspective, partially sectioned view of an electric axle module with drive shafts, a transmission, a slip clutch, and an electric motor, which are housed in a common housing. Embodiments of the invention

[0030] In the following description of the embodiments of the invention, identical or similar elements are designated by the same reference numerals, whereby a repeated description of these elements is omitted in individual cases. The figures only schematically illustrate the subject matter of the invention.

[0031] Figure 1 shows an electrically powered vehicle 10 having an electric drive train 12 and the components arranged therein.

[0032] The electrically powered vehicle 10 according to the schematic representation in Figure 1 has an electric drive train 12 comprising at least one electric machine 14. The at least one electric machine 14 is housed in a common housing 16, which also serves to accommodate a transmission 18. An inverter 20 is assigned to the electric machine 14, wherein the inverter 20 is also referred to as power electronics. The electric drive train 12 or the electrically powered vehicle 10 is controlled via a control unit 22 (Vehicle Control Unit = VCU). In the exemplary embodiment of the electrically powered vehicle 10 according to Figure 1, the control unit 22 is housed in the front part of the vehicle 10, assigned to a front axle 26.In addition to the front axle 26, the electric drive train 12 also includes a rear axle 28, which is represented by a first drive shaft 30 and a second drive shaft 32, which are driven by the at least one electric machine 14.

[0033] In addition, the electric drive train 12 has a central brake 34, which is preferably designed as an eddy current brake 36. The rear axle 28, driven by the at least one electric machine 14 in the exemplary embodiment according to Figure 1, does not include friction brakes 38, as are arranged on the wheels of the front axle 26 in the illustration according to Figure 1. The friction brakes 38 are also controlled via the control unit 22 of the electrically powered vehicle 10. Furthermore, a charging connection 40 is provided on the electrically powered vehicle 10, which can be located on a longitudinal side or in the area of ​​the trunk or a front cover of the electrically powered vehicle 10. The electric machine 14 or its transmission 18 is assigned a clutch 42, which can, for example, replace a conventional differential gear.The clutch 42 is shown as a slip clutch and comprises meshing plate parts and can be designed, for example, as a “twinster” clutch 44.

[0034] At least one high-voltage traction battery 46 is located in the floor of the electrically powered vehicle 10, shown in plan view in Figure 1. The electrically powered vehicle 10 also includes at least one electrical system 24, which may, for example, be a high-voltage electrical system. Furthermore, the electrically powered vehicle 10 includes another battery 48, for example, operating at a voltage level of 12 V, which may optionally represent another electrical system of the electrically powered vehicle 10.

[0035] If the electrically powered vehicle 10 shown in Figure 1 is traveling with a fully charged high-voltage traction battery 46, or if the high-voltage traction battery 46 has a very high temperature, or if the high-voltage traction battery 46 is in self-diagnosis mode, it cannot absorb the braking energy that is regenerated during braking in the electric machine 14 operating in generator mode during a braking operation or even during an emergency braking operation. According to the invention, in this case, the electric drive train 12 or the components present therein absorb the braking energy.This ensures, on the one hand, a reliable availability of braking operations with the electric drive train 12, and on the other hand, a conventional braking system on the drive axle in the present example according to Figure 1, for example on the rear axle 28, can be designed to be smaller, lighter in weight, and thus more cost-effective, or even eliminated entirely. Since, in the scenario described above, the braking energy is no longer permitted to flow towards the high-voltage traction battery 46, the braking energy must be absorbed solely by the components of the electric drive train 12. The thermal mass of the components present in the electric drive train 12 is relatively high, and generally at least one of the components installed in the electric drive train 12 is provided with external cooling, for example water cooling.

[0036] If braking occurs in the scenario described above, a logic circuit is activated in the inverter 20 such that the three phases of the electric machine 14 are short-circuited. As a result, the braking energy is absorbed by the ohmic resistance of the windings of the electric machine 14 without having to resort to other high-voltage components within the electric drive train 12. The short circuit can be an active short circuit that is continuously performed until the electrically powered vehicle 10 has come to a complete stop, which occurs within a few seconds. Alternatively, the active short circuit can be performed in a cyclical manner or as part of a partial circuit, resulting in power loss at the switching elements 90 installed in the electric drive train 12.With such a control system, a maximum torque of typically 50% of the nominal torque can be achieved at the operating point of the electric machine 14 with an active short circuit.

[0037] Such absorption of braking energy in the electric drive train 12 can be achieved solely by the operating strategy illustrated in method step b), where an active short circuit of the three phases of the electric machine 14 is generated by means of the inverter 20 and the braking energy is absorbed in the ohmic resistance of the windings of the electric machine 14.

[0038] If the braking torque applied by the electric machine 14 in generator mode is insufficient, which is generally the case at very high speeds, the braking torque can also be provided by the central brake 34, as shown in the illustration of the electrically powered vehicle 10 by the eddy current brake 36. An eddy current brake 36 or a friction brake 38 is advantageously used. In particular, the operating characteristics of an eddy current brake 36 are ideal for supporting the setting of the braking torque in the electric drive train 12 of an electrically powered vehicle 10. An important feature of the eddy current brake 36 is that it does not rotate at the wheel speed or at the speed of a cardan or drive shaft, but at the engine speed, i.e., the speed of the electric machine 14.As a result, the eddy current brake 36 integrated in the electric drive train 12 and acting as a central brake 34 can be designed very compactly and thus with low weight and cost-effectively.

[0039] Due to the fact that the eddy current brake 36 consumes energy during operation, the braking torque of the electric machine 14 can be increased by obtaining the energy required to operate the eddy current brake 36 from the electric machine 14 when it is operated in generator mode.

[0040] Figure 2 shows the torque curves of the electric machine 14 and the eddy current brake 36 in standard or booster mode.

[0041] In the illustration according to Figure 2, a speed curve 52 of the electric machine 14 is plotted. The braking torque requirement 50 is shown in the illustration according to Figure 2 only in a negative range from 0 Nm to -250 Nm. The illustrated speed curve 52 of the electric machine 14 extends from speed 0 min' 1 up to 14000 rpm 1 .

[0042] From the comparison of the graphs shown in Figure 2, it can be seen that in this example a braking torque request 50 is requested corresponding to a deceleration torque 54. In this case, the electric machine 14 sets to a speed of approximately 2000 min 1according to the plateau 58 shown in Figure 2, a large part of the braking torque, whereas the eddy current brake 36 is still almost ineffective at relatively low speeds of the electric machine 14. The braking torque provided by the eddy current brake 36 runs according to the torque curves 62 for the eddy current brake 36 or according to a

[0043] Amplification mode 64 for the torque curve 62 of the eddy current brake 36. The latter amplification mode 64 represents an amplification of the torque curve 62, which is standardly located at the

[0044] Eddy current brake 36 is set. From the illustration in Figure 2, it can be seen that the proportion of braking torque generated by the eddy current brake 36 increases with increasing speeds, whereas after passing through the plateau 58, the torque curve 56 for the electric machine 14 experiences a torque weakening 60 with increasing speeds. The higher the speed of the electric machine 14, the greater the weakening 60 of the braking torque component provided by it. Reference numeral 66 designates a torque curve of an electromechanical parking brake. This can be optionally installed in the vehicle 10 and brakes at low speeds, particularly in the range in which the eddy current brake 36 is unable to provide any torque.

[0045] In the solution proposed by the invention, the braking energy is not only converted according to method steps b) and c), but according to feature c) of the independent method claim, when a torque maximum is reached during an active short circuit (AKS), braking energy is fed into at least one slip clutch 42 in the electric drive train 12. This allows a "serial brake" to be implemented. Since a pronounced torque maximum occurs between the phases of the electric machine 14 when an active short circuit is induced, this can be exploited to set the corresponding differential speed for a slip clutch 42 installed in the electric drive train 12. As a result, part of the braking power is absorbed by the slip that occurs within the clutch 42.Instead of a conventional differential, for example, a “Twinster” clutch 44 indicated in Figure 3 can be used, which is essentially represented by clutch plates 72, divided into a stationary plate group 74 and a rotating plate group 76.

[0046] In this context, Figure 3 shows a perspective view of an electric axle module in which the electric motor 14 and the associated transmission 18, the inverter 20, and the slip clutch 42 are accommodated in the common housing 16. On both sides of the common housing 16, shown in a partial perspective view in Figure 3, the two drive shafts 30, 32 extend to the wheels (not shown in Figure 3) of the driven axle formed by the drive shafts 30, 32. The slip clutch 42 is integrated into the transmission 18; here, it is designed as a "Twinster" clutch 44, which assumes the function of a differential that is omitted here. The drive shafts 30, 32 are encapsulated by sleeves 84; the common housing 16 comprises a transmission housing section 80 and electrical connections 82.The common housing 16 is also assigned the inverter 20, which is located, for example, below or above the common housing 16.

[0047] In the perspective view shown in Figure 3, the slip clutch 42 comprises the clutch plates 72, of which a stationary plate group 74 is located on the rotating components, i.e., on the axle parts driven by the electric machine 14, whereas a rotating plate group 76 is located within the clutch housing of the slip clutch 42. The clutch 42 shown schematically in Figure 3 replaces a conventional differential gear.

[0048] According to the solution proposed by the invention, a possibility for braking an electrically powered vehicle 10 is provided which utilizes the components of the electric drive train 12 of the electrically powered vehicle 10 to absorb the braking energy. The braking energy can be distributed according to several strategies, wherein first, an active short circuit of the three phases of the electric machine 14 is generated by means of the inverter 20, and the braking energy is absorbed by the ohmic resistance of the windings. This allows a relatively high proportion of the braking energy to be absorbed. Taking into account the high speeds of the electric machine 14, according to a further aspect of the solution proposed by the invention, the braking energy that can no longer be absorbed in the charged high-voltage traction battery 46 is fed into an eddy current brake 34, 36 and / or friction brakes 38, where it is essentially converted into heat.

[0049] Finally, a slip-prone clutch 42 housed in the electric drive train 12 of the electrically powered vehicle 10 can dissipate braking energy through slip and also convert it into heat. Thus, in the described exceptional scenario of a high-voltage traction battery 46 not ready to absorb braking energy, either because it is fully charged, because its temperature is too high, or because it is in self-diagnosis mode, it is ensured that the braking energy can be converted in the components with relatively high thermal mass in the electric drive train 12. The inverter 20 receives the braking request either from the control unit 22 or from the ESP system. Typically, the proportion provided by the friction brakes 38, which, as shown in Figure 1, are located on the front axle 26 of the electrically powered vehicle 10, is already determined.Alternatively, the inverter 20 can also directly read the braking request via a brake pedal 92 itself. This has the advantage that the inverter 20 can initiate braking operations even if communication with other components in the electric drive train 12 is faulty. Overbraking is then prevented even without driving dynamics information from the ESP system by monitoring the deceleration via the engine speed. In the above scenario, regenerative braking is not possible, so the braking energy or braking torque is converted by the aforementioned components according to method steps b), c), and d). The braking torque is distributed between the active short circuit and, if present, the braking elements, in particular the eddy current brake 36 acting as the central brake 34. In the case of an active short circuit, the control is modulated according to the braking request and the energy distribution.For example, a complete short circuit or, as indicated in process step b), a clocking or partial switching can be carried out.

[0050] A further aspect of the solution proposed by the invention is that the availability of braking operations via the electric drive train 12 can be determined using a temperature model. The speed of the electrically powered vehicle 10 can be limited, or if sufficient braking operations are no longer available, the electrically powered vehicle 10 can be safely shut down after a controlled braking operation. However, the active short-circuit phases are typically designed such that continuous operation is still possible.

[0051] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, numerous modifications are possible within the scope of the claims, which are within the scope of one skilled in the art.

Claims

Claims 1 . Method for braking an electrically powered vehicle (10) with an electric drive train (12) comprising at least one electric machine (14), an inverter (20), a high-voltage traction battery (46), at least one on-board electrical system (24), an eddy current brake (34, 36) and / or friction brakes (38), with the following method steps, individually or in combination with one another: a) feeding braking energy when braking the electrically driven vehicle (10) into its electric drive train (12) with the exception of the high-voltage traction battery (46), such that b) an active short circuit of the three phases of the electric machine (14) is generated by means of the inverter (20) and the braking energy is absorbed in the ohmic resistance of the windings and / or c) at high speeds of the electric machine (14), the braking energy is fed into an eddy current brake (34,36) and / or friction brakes (38) and / or d) when a maximum torque of the electric machine (10) is reached during an active short circuit (AKS), braking energy is fed into at least one slip-prone clutch (42) in the electric drive train (12).

2. Method according to claim 1, characterized in that according to method step b) the active short circuit of the three phases on the electrical machine (14) is carried out permanently until the electrically driven vehicle (10) comes to a standstill or a timing or partial switching of the active short circuit is carried out according to method step b) in such a way that power loss is generated at switching elements.

3. Method according to claims 1 and 2, characterized in that according to method step b) with an active short circuit (AKS) at the operating point of the electrical machine (14) a maximum torque of approximately 50% of a nominal torque is achieved.

4. Method according to claims 1 to 3, characterized in that according to method step c) the braking torque of the electric machine (14) is increased again by obtaining the energy required for driving the eddy current brake (34, 36) in the generator mode of the electric machine (14).

5. Method according to claims 1 to 4, characterized in that the eddy current brake (34, 36) is coupled to the electric machine (14) and is driven at its speed.

6. Method according to claims 1 to 5, characterized in that in the case of a torque maximum occurring in accordance with method step b) during an active short circuit, at least one clutch (42) installed in the electric drive train (12) absorbs the speed difference corresponding to the torque maximum.

7. Method according to claim 6, characterized in that part of the braking energy is converted by the slip occurring at the differential speed.

8. Method according to claims 1 to 7, characterized in that the braking request is transmitted to the inverter (20) either via a control unit 22 (VCU) or by a driver assistance system, in particular by an ESP system, in such a way that a portion of the braking energy attributable to the friction brakes (38) is already deducted.

9. Method according to claims 1 to 8, characterized in that by means of a temperature model, the availability of braking by means of the electric drive train (12) or the high-voltage traction battery (46) is indicated to the driver of the electrically driven vehicle (10).

10. The method according to claim 9, characterized in that if braking operations are not available, the speed of the electrically driven vehicle (10) is limited and / or the vehicle (10) is parked in a controlled manner after braking has been carried out.

11. Use of the method according to one of claims 1 to 10 in an electrically powered vehicle (10).

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