Method and apparatus for operating an electric drive device

Abstract

Method for operating an electric drive device (1) for a motor vehicle during towing, in which a drive electric motor (2) is directly coupled to a drive axle (3); with a high-voltage electrical system (4) for operating the drive electric motor (2); with a parking locking device (5) by means of which the drive axle (3) can be locked in the parked position; with a short-circuiting device (7) by which the drive electric motor (2) can be short-circuited; with a cooling device (6) for cooling the drive electric motor (2) and the short-circuiting device (7);- characterized in that- the short-circuiting device (7) comprises a temperature sensor (8) for detecting its operating temperature, wherein- when the parking lock device (5) is actuated for the purpose of unlocking it, it is checked whether the high-voltage electrical system (4) is in proper working order and, in this case, the parking lock device (5) is unlocked and the short-circuiting device (7) is activated, wherein the activated short-circuiting device (7) short-circuits windings of the drive electric motor (2) to create an active short circuit; and- furthermore, the temperature sensor (8) is continuously monitored and the short-circuiting device (7) is deactivated if the temperature sensor (8) detects an impermissibly high temperature, wherein the deactivated short-circuiting device (7) leaves the windings of the drive electric motor (2) open.;

Description

The invention relates to a method and a device for operating an electric drive unit for a motor vehicle during towing, as well as an electric drive unit, wherein a drive electric motor is directly coupled to the drive axle, with a high-voltage electrical system for operating the drive electric motor, with a parking lock device by means of which the drive axle can be locked in the parked position, with a short-circuiting device by which the drive electric motor can be short-circuited, and with a cooling device for cooling the drive electric motor and the short-circuiting device. The invention further relates to a device for carrying out this method and an electric drive unit. US 2010 / 0030412 A1 relates to an electrically powered vehicle comprising an AC electric motor-generator with a rotor to which a magnet is attached and which is configured to alternately transmit rotational power to / from a wheel; an inverter device comprising a plurality of power semiconductor switching elements configured to convert a DC voltage from a power source into a drive voltage for the AC electric motor-generator; a control unit for controlling the inverter device; a shift position selection unit for selecting one of several shift positions, including at least one park position, according to an operation by a driver; and a parking locking mechanism that is activated when the park position is selected.and a power source position selection unit for selecting one of several power source positions that determine a group of devices among those fitted to the vehicle to be energized, according to an actuation by the driver; wherein the several power source positions comprise a first power source position that allows control of the power semiconductor switching element by the control unit and a second power source position that does not allow such control; wherein the electrically powered vehicle further comprises an overlap state avoidance unit for avoiding a state in which the selection of the second power source position and the selection of a switching position in which the parking lock mechanism is inactive overlap when a short-circuit fault of one of the several power semiconductor switching elements has been detected. DE 10 2008 004 300 A1 relates to a motor vehicle comprising an electric machine coupled to at least one drive wheel and capable of being operated at least as a generator, an electrical energy storage device coupled to the electric machine via an electrical coupling unit, and a control unit by which the electric machine is controlled depending on predetermined operating parameters. According to the invention, detection means for recognizing whether the motor vehicle is being towed are further provided, and the control unit is designed such that, in the event of a towing operation, the electric machine is operated in such a way that, during the duration of the towing operation, the vehicle's electrical system and / or the electrical energy storage device are at least temporarily supplied with energy. US 5,619,107 A relates to a device for controlling an electric motor for an electric vehicle, which discharges a smoothing capacitor connected to the input terminals of an inverter according to the state of the electric vehicle. The device comprises a motor drive unit, the smoothing capacitor connected in parallel to the motor drive unit, a switching unit that operates in conjunction with an operator switch, a discharge unit for discharging the smoothing capacitor, a train detection unit, and a discharge limiting unit. The system opens the switching unit to interrupt the output from the battery and discharge the smoothing capacitor when the switching unit is open, but limits the discharge while the electric vehicle is being towed or pulled. US 4,952,856 A relates to a method and apparatus for monitoring the temperature of a resistor in a resistance torque controller. The heating and cooling rates for the resistor are determined, and a predicted resistor temperature is automatically calculated at the beginning of each time interval from successive time intervals by subtracting the product of the resistor's cooling rate and the time interval from the previous temperature prediction and adding the product of the resistor's heating rate and the time interval. A control signal is generated when the predicted resistor temperature for a given time interval meets a threshold temperature. US 7,262,571 B2 relates to a brake module. The brake module comprises a brake load, an input terminal, an output terminal, and control logic. The input terminal is configured to receive a motor drive signal. The control logic is configured to receive a motor enable signal, couple the output terminal to the input terminal in response to the motor enable signal being set, couple the output terminal to the brake load in response to the motor enable signal being reset, and prevent the output terminal from being coupled to the input terminal when the brake module temperature exceeds a predetermined shutdown setpoint. A method for controlling a motor includes coupling a drive line carrying a motor drive signal to a motor line of the motor in response to a motor enable signal. The motor line is coupled to a brake load in response to the motor enable signal being cleared.The coupling of the drive line with the motor line is prevented if the temperature of the brake load exceeds a predetermined deactivation setpoint. US 7 012 392 B2 relates to a multi-stage dynamic braking resistor network comprising a plurality of dynamic braking resistors for dissipating regenerative energy fed into a system bus; a plurality of switches for connecting the dynamic braking resistors to or disconnecting them from the system bus; and a control circuit for controlling the switches so that the dynamic braking resistors are connected to or disconnected from the system bus based on a predetermined voltage threshold of the system bus and based on a predetermined rotation pattern. EP 1 965 489 A1 relates to a control device. The control device converts a torque command value of an AC motor into a current command for the AC motor and uses current control with feedback via a PI controller to match the actual current value to the current command. Furthermore, based on the converted current command, the control device sets a target flow rate for the coolant flowing through a coolant channel, generates a signal to drive a water pump to circulate the coolant at the set target flow rate, and transmits the signal to the water pump. The speed of the water pump is limited according to a signal from the control device so that the coolant circulates through the coolant channel at the flow rate corresponding to the target flow rate. EP 2 189 321 A1 relates to a traction-driven AC motor. The AC motor is connected to the electrical storage system via at least one inverter for converting direct current to alternating current. If the inverter is bidirectional, it comprises at least one primary input or output connected to the electrical storage system and at least one secondary input or output connected to the traction-driven AC motor. When using non-reversible inverters, the input of the primary inverter is connected to the electrical storage system and the output of the primary inverter is connected to the traction-driven AC motor, while the input of the secondary inverter is connected to the traction-driven AC motor and the output of the secondary inverter is connected to the electrical storage system.Another advantage of this type of connection is the integration of at least one diagnostic element, which can optionally be installed in at least one inverter. If the diagnostic element is not integrated into the inverter, the primary input is connected to the electrical storage device and the secondary input to at least one inverter. The diagnostic element also includes an output connected to a display and / or recording device. A further advantage is the integration of at least one device on the electrical storage device for cooling the traction-driven AC motor and / or at least one inverter. In electric vehicles, the drive motor is typically connected directly to the vehicle's drive axle without a clutch. If such a vehicle needs to be towed, whether due to a failure of the low-voltage electrical system, a depleted high-voltage energy storage system in the drive motor, or some other defect, the drive motor will inevitably rotate during the towing process. This results in a generator-generated voltage, particularly when using permanent magnet electric motors, which is typically higher than 60V and therefore subject to relevant high-voltage safety regulations. This means that this operating condition must be designed to be safe. During normal operation, various tests are performed, such as an insulation test, which in turn requires a logic circuit that presupposes a low-voltage electrical system. However, when towing, it is not guaranteed that the low-voltage electrical system (usually a 12V DC system) will be available, because, for example, the reason for the necessary towing operation could be a defective or discharged 12V battery. To circumvent this problem, the drive motor includes a short-circuiting device in which the motor's windings are short-circuited via a power stage of the drive motor's inverter. This is referred to as an "active short circuit." This ensures that no impermissibly high voltages occur in the system, even if high-voltage safety is not guaranteed. The problem, however, is that the short circuit causes high currents to flow in the windings of the drive motor and the inverter's output stage, generating significant power losses. These losses must be dissipated, normally via a water circuit with a pump driven by the low-voltage electrical system. If the low-voltage electrical system fails, the same applies to the water circuit, which can cause the drive motor windings and the inverter's output stage to heat up rapidly and significantly. The inverter's output stage, in particular, can be thermally destroyed very quickly if its maximum permissible temperature is exceeded. Based on this, the invention aims to avoid the aforementioned disadvantages and to provide a method and a device or a drive unit that enables the towing of a motor vehicle with an electric drive and a drive unit directly coupled to the drive axle, regardless of the availability of the low-voltage electrical system. The invention is defined by the features of the independent claims. Advantageous further developments and embodiments are the subject of the dependent claims. Further features, applications, and advantages of the invention will become apparent from the following description and the explanation of exemplary embodiments of the invention illustrated in the figures. The method according to the invention is characterized in that the short-circuiting device comprises a temperature sensor for detecting the operating temperature, wherein, when the parking lock device is actuated for the purpose of unlocking it, it is checked whether the high-voltage electrical system is in proper condition and, in this case, the parking lock device is unlocked and the short-circuiting device is activated, wherein the activated short-circuiting device short-circuits windings of the drive electric motor to produce an active short circuit, wherein the temperature sensor is continuously monitored and the short-circuiting device is deactivated if the temperature sensor detects an impermissibly high temperature, wherein the deactivated short-circuiting device leaves the windings of the drive electric motor open. When the vehicle is parked, the parking lock engages, initially preventing towing as the drive axle cannot rotate. To enable towing, the parking lock must be released to restore limited drivability. Before the parking lock is released, a safety check of the high-voltage electrical system is performed to ensure it is functioning correctly. The parking lock is only released if this check is passed, meaning the high-voltage electrical system meets the high-voltage safety regulations. In this case, the short-circuit protection device is activated, short-circuiting the windings of the drive motor, resulting in an active short circuit (ACS). Alternatively, the active short circuit may already be activated, for example, as the default state of the parked vehicle.If the high-voltage safety test is failed, the parking lock remains engaged and towing of the vehicle is not possible. If the towing process begins, the windings and the output stage can heat up due to the activated short circuit, provided the electric motor cooling system is not functioning for any reason, such as a failure of the low-voltage electrical system. If the low-voltage electrical system has already failed, the towing process cannot be carried out because the high-voltage safety test cannot be performed and the parking lock cannot be released. A more critical scenario is if the low-voltage battery fails during the towing process, for example, due to hazard warning lights being activated. The temperature increase is detected by the temperature sensor, which is located at the most temperature-critical point, usually the semiconductor output stage. If the detected temperature exceeds a maximum permissible value, the short-circuit device is deactivated, thus stopping the current flow and halting the heating process.Simultaneously, the voltage across the now-open windings of the drive motor increases and can exceed 60V. However, since the high-voltage safety was checked initially when the parking lock was released, this is now permissible. The invention makes it possible, after the initial testing of high-voltage safety using the low-voltage electrical system, to tow a aforementioned electric vehicle safely without significant additional construction effort, regardless of the later availability of the low-voltage electrical system. According to the invention, a device for carrying out the method described above is proposed, comprising the aforementioned temperature sensor, an associated control unit, and a final stage for controlling the short-circuit device, which is implemented exclusively using electronic components, as well as a power supply unit connected to the high-voltage vehicle electrical system. This means that only electronic components such as semiconductor elements, resistors, capacitors, NTCs, signal amplifiers, or permanently programmed components such as PLAs are used, but not microprocessors controlled by software. In particular, the circuit is completely independent of the circuits for operating the vehicle, especially the drive system.This ensures that under all circumstances, especially in the event of an accident or other safety-relevant incidents, a safe operating state can always be achieved without the intervention of processors. The problem is further solved by an electric drive device for a motor vehicle for carrying out the above-described method with a drive electric motor directly connected to a drive axle, which includes a temperature sensor for detecting the operating temperature of the short-circuiting device and a shutdown device for switching off or deactivating the short-circuiting device when the temperature sensor detects an impermissibly high temperature, wherein the activated short-circuiting device short-circuits windings of the drive electric motor to create an active short circuit, and the deactivated short-circuiting device leaves the windings of the drive electric motor open. According to an advantageous embodiment of the invention, the electric drive unit comprises a delay unit that only switches off the short-circuiting device after a certain delay. This delay time is preferably in the range of 500 ms to 2000 ms. The delayed activation ensures that, for example, in the event of a crash, the short-circuiting device is switched off, which is expedient for complying with relevant safety regulations for crash situations. Further advantages, features, and details will become apparent from the following description, in which an exemplary embodiment is described in detail with reference to the drawings. The features described and / or illustrated, either individually or in any meaningful combination, constitute the subject matter of the invention, optionally also independently of the claims, and may in particular also be the subject of one or more separate applications. Identical, similar, and / or functionally equivalent parts are designated with the same reference numerals. Figure 1 shows a schematic block diagram of a drive unit, Figure 2 shows a circuit diagram of part of the control unit as a component of the drive unit according to Figure 1, and Figure 3 shows a representation of signal waveforms. Figure 1 schematically depicts a drive unit 1 for propelling an electrically powered vehicle. This unit comprises a drive motor 2 connected to a drive axle 3. A high-voltage battery 4 supplies the drive motor 2 with the energy required for propulsion. A parking lock 5 can be coupled to the drive axle 3 to lock it in place. The drive motor 2 also has an electric motor cooling unit 6 for cooling the windings of the drive motor 2, which is operated by a low-voltage electrical system (not shown). Furthermore, a short-circuiting device 7 is provided, by means of which the windings of the drive motor 2 can be short-circuited. The short-circuiting device 7 has a temperature sensor 8, by means of which the critical temperature in the short-circuiting device 7 can be measured. A control unit 9 receives the signal from the temperature sensor 8 and a readiness signal 10 from a vehicle control unit, indicating limited readiness to drive, in order to release the parking lock 5. The control unit 9 then performs a high-voltage safety test in the high-voltage electrical system 4, and only if the test is passed is a signal sent to the parking lock 5 to unlock it. Furthermore, the control unit 9 determines that the temperature of the short-circuiting device 7, as measured by the temperature sensor 8, is within the permissible range, so that this device is activated, thus short-circuiting the windings of the drive electric motor 2. Figure 2 shows a circuit 12, which is part of the control device 9 shown in Figure 1. On the left is a power supply 11 for the circuit 12, which is explained in more detail below. A 5V and a 15V operating voltage are generated from the HV+ and HV- terminals of the high-voltage energy storage device via series resistors 14 and Zener diodes 16. These supply voltages provide the necessary voltages independently of the low-voltage electrical system. The 5V voltage is used for the logic elements and the 15V voltage for the output stage. Circuit 12 includes a temperature sensor 8, in this case an NTC. Alternatively, with a different circuit design, another type of sensor, e.g., a PTC, can be used. The voltage defined by the temperature sensor 8 and a resistor 20 at the positive input of a comparator 22 is compared with a reference voltage 24 applied to the negative input of the comparator 22. The output of the comparator 22 drives a first gate 26, whose second input 28 receives a signal from the vehicle control unit indicating that the active short circuit should be activated. This input 28 is additionally fed to a monovibrator unit 30, which, for a predetermined period of approximately 500 ms to 2000 ms after a "high" (Hi) signal occurs at the input, displays a "Hi" signal at its output and then falls back to "low" (Lo). The outputs of the first gate 26 and the monovibrator unit 30 feed a second gate 32, whose output drives a power stage 34, which in turn drives a converter (not shown) that can short-circuit the windings of the drive electric motor. Under normal conditions, i.e., at normal temperatures, the temperature sensor 8 exhibits a high resistance, so the voltage at the positive input of the comparator 22 is higher than the reference voltage 24, resulting in the output of the comparator 22 being high (Hi). As soon as the temperature of the temperature sensor 8 rises above a limit value defined by the reference voltage 24 (which is the maximum permissible temperature in the short-circuit device), the output of the comparator 22 switches to low (Lo). If a high signal is present at input 28 and the output of the comparator 22 also exhibits a high signal due to an increased measured temperature, the output signal of the AND gate 26 is also high. The high signal then present at input 28 is passed through the monovibrator unit 30, with a time delay, together with the output of the AND gate 26, to the OR gate 32, which in this case drives the output stage 34. Figure 3 shows in more detail the voltage waveforms when an excessive temperature occurs at the temperature sensor 8. The uppermost signal waveform corresponds to the signal at input 28, the second-highest signal waveform to the output of the comparator 22, the third-highest signal waveform to the output of the monovibrator unit 30, and the lowest signal waveform to the output of the final stage 34. At time T1, a high signal (Hi) is applied to input 28 by the vehicle control unit when the user attempts to release the parking lock and the high-voltage safety test has been successfully completed, in order to activate the short-circuit protection device. Since the vehicle is stationary at this time and the temperature sensor 8 consequently detects a low temperature, the output signal of comparator 22 is high. As the monovibrator unit 30 has been started, its output signal also goes high at this time, and consequently, the output of the power stage 34 also goes high, activating the short-circuit protection device. At time T2, the temperature measured by temperature sensor 8 exceeds the threshold, causing the output of comparator 22 to drop to low (Lo). In this example, the delay time of the monovibrator unit 30 has not yet elapsed, so the OR gate 32 remains high. At time T3, the delay time of the monovibrator unit 30 ends, so its output drops to low (Lo), and consequently, the output of the OR gate 32 also drops to low (Lo). Accordingly, the short-circuit device switches off again, no more current flows through the drive motor, and it cools down. At time T4, the short-circuit device has cooled down sufficiently to fall below the limit temperature and the output of comparator 22 goes back to high, which simultaneously also causes the output of OR gate 32 to go back to high and the short-circuit device to be reactivated.

Claims

Method for operating an electric drive device (1) for a motor vehicle during towing, in which a drive electric motor (2) is directly coupled to a drive axle (3); with a high-voltage electrical system (4) for operating the drive electric motor (2); with a parking locking device (5) by means of which the drive axle (3) can be locked in the parked position; with a short-circuiting device (7) by which the drive electric motor (2) can be short-circuited; with a cooling device (6) for cooling the drive electric motor (2) and the short-circuiting device (7);- characterized in that- the short-circuiting device (7) comprises a temperature sensor (8) for detecting its operating temperature, wherein- when the parking lock device (5) is actuated for the purpose of unlocking it, it is checked whether the high-voltage electrical system (4) is in proper working order and, in this case, the parking lock device (5) is unlocked and the short-circuiting device (7) is activated, wherein the activated short-circuiting device (7) short-circuits windings of the drive electric motor (2) to create an active short circuit; and- furthermore, the temperature sensor (8) is continuously monitored and the short-circuiting device (7) is deactivated if the temperature sensor (8) detects an impermissibly high temperature, wherein the deactivated short-circuiting device (7) leaves the windings of the drive electric motor (2) open.; Device for carrying out the method according to claim 1, characterized in that it comprises the temperature sensor (8), a control device (9) associated therewith, and a final stage (34) for controlling the short-circuit device (7), which is implemented exclusively by means of electronic components, as well as a power supply device (11) which is connected to the high-voltage vehicle electrical system (4). Electric drive device for a motor vehicle for carrying out the method according to claim 1, comprising a drive electric motor (2) directly connected to a drive axle (3), a parking locking device (5) by means of which the drive axle (3) can be locked in the parked position, a short-circuiting device (7) by which the drive electric motor (2) can be short-circuited, a high-voltage testing device for checking the high-voltage safety of the drive electric motor (2), a cooling device (6) for cooling the drive electric motor (2) and the short-circuiting device (7), characterized by a temperature sensor (8) for detecting the operating temperature of the short-circuiting device (7).and- a shutdown device (12) for deactivating the short-circuiting device (7) when the temperature sensor (8) detects an impermissibly high temperature, wherein- the activated short-circuiting device (7) short-circuits windings of the drive electric motor (2) to create an active short circuit, and- the deactivated short-circuiting device (7) leaves the windings of the drive electric motor (2) open.; Electric drive device according to claim 3, characterized in that it comprises a delay unit (30) which performs a shutdown of the short-circuit device (7) only after a delay. Electric drive device according to claim 4, characterized in that the delay unit (30) has a delay time of 500 ms to 2000 ms.

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