Emergency braking device for electric machine with brake medium

Abstract

The invention relates to an electromechanical unit (1) for a motor vehicle comprising: - an electric machine (2) for driving a vehicle component, wherein the electric machine (2) has a stator (3) with currentable stator windings for exciting a stator magnetic field and a rotor (4) rotatably mounted relative to the stator (3) with a magnetic field-exciting component for exciting a rotor magnetic field, wherein an air gap (8) is formed between the rotor (4) and the stator (3), and - an emergency braking device (10) for braking the rotating rotor (4) in the event of a fault, wherein the emergency braking device (10) is designed to introduce a medium (12) into the air gap (8) in the event of a fault to increase the air gap friction braking the rotor (4).

Description

The invention relates to an electric motor unit for a motor vehicle. The electric motor unit comprises an electric machine for driving a vehicle component of the motor vehicle, wherein the electric machine has a stator with currentable stator windings for exciting a stator magnetic field and a rotor rotatably mounted relative to the stator with a magnetic field-exciting component for exciting a rotor magnetic field. An air gap is formed between the rotor and the stator. The electric motor unit also includes an emergency braking device for braking the rotating rotor in the event of a fault. The invention further relates to a motor vehicle. The focus here is on electromechanical units with electric machines for motor vehicles. Such electromechanical units can be, for example, electric drive units for electrified motor vehicles, such as electric vehicles, hybrid vehicles, or fuel cell vehicles, and may include electric machines in the form of traction machines for driving the vehicle's wheels. The electromechanical units may also include electric machines in the form of electric motors for compressors, for example, in the form of an air compressor for fuel cell vehicles. In the event of a fault or critical incident, such as an accident or crash involving a vehicle, it is essential that the electric motor be braked or switched off as quickly as possible. This prevents the electric motor from continuing to generate electrical voltages after the critical incident, which could endanger people or safety-related systems. Specifically, the feed-in of electrical energy into the vehicle's electrical system, for example, a high-voltage and / or low-voltage system, must be prevented. A known method for braking electric motors involves creating an active short circuit (ACS). This is achieved by short-circuiting the connecting leads of the electric motor.However, the time it takes for the electric machine to decelerate during an active short circuit can be very long compared to the timescales during an accident, and may exceed the shutdown speeds required in such an event. Furthermore, the AKS requires a reliable power supply. Additionally, the components necessary for the AKS, such as the power supply and connecting cables, require mechanical crash protection to prevent them from being destroyed before the short circuit is initiated in the event of an accident. From DE 10 2017 222 005 A1, an electric motor with a stator, a rotor and a mechanical braking device is known, which includes a mechanical and / or pyrotechnic braking unit. This is designed to brake the rotor in order to prevent voltage generation by the electric motor after a critical event involving the motor vehicle. The object of the present invention is to provide an alternative solution to the prior art for braking a rotor of an electric machine of a motor vehicle in the event of a fault. This problem is solved according to the invention by an electric motor unit and a motor vehicle with the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the figures. An electromechanical unit according to the invention for a motor vehicle comprises an electric machine for driving a vehicle component of the motor vehicle. The electric machine has a stator with currentable stator windings for exciting a stator magnetic field and a rotor rotatably mounted relative to the stator with a magnetic field-exciting component for exciting a rotor magnetic field, wherein an air gap is formed between the rotor and the stator. Furthermore, the electromechanical unit has an emergency braking device for braking the rotating rotor in the event of a fault. The emergency braking device is designed to introduce a medium into the air gap in the event of a fault to increase the air gap friction that brakes the rotor. The invention also includes a motor vehicle with at least one electric motor unit. The motor vehicle is, in particular, an electrified motor vehicle and has the at least one electric motor unit as a drive unit. Here, the electric motor is designed as a traction motor for driving a vehicle component in the form of the vehicle's wheels, which is supplied with electrical energy by a traction battery, in particular a high-voltage energy storage device, of the motor vehicle. Alternatively, the vehicle component can be designed as a compressor, for example for a fuel cell vehicle, which is driven by the electric motor. The electric machine comprises a stator and a rotor. The stator has a stator body, for example, a stator lamination stack, with slots in which current-carrying electrical conductors are arranged. These electrical conductors form the stator windings for exciting the stator magnetic field or magnetic flux. The rotor has a rotor body, for example, a rotor lamination stack, which carries the magnetic field-generating component for exciting the rotor magnetic field or magnetic flux. The electric machine can be a separately excited electric machine in which the magnetic field-generating component has current-carrying rotor windings. Preferably, the electric machine is a permanent magnet electric machine in which the magnetic field-generating component has a permanent magnet arrangement with at least one permanent magnet per rotor pole. The stator and rotor are mounted at a distance from each other, forming an air gap. This air gap carries an air-gap field created by the superposition of the magnetic fields of the stator and rotor. The air gap has an annular cross-section. In the case of an external rotor machine, the rotor surrounds the stator, so that the air gap is formed between an outer surface of the stator laminations and an inner surface of the rotor laminations. In the case of an internal rotor machine, the stator surrounds the rotor, so that the air gap is formed between an outer surface of the rotor laminations and an inner surface of the stator laminations. The rotor also has a rotor shaft, which is fixedly connected to the rotor body and mechanically coupled to a vehicle component to be driven, such as the vehicle's wheels. The rotor can be coupled to the vehicle component directly or indirectly, for example, via a transmission. In the case of indirect coupling, the transmission is coupled to the rotor shaft on the input side and to at least one wheel on the output side, for example, via a vehicle axle. Through the mechanical coupling between the electric machine and the vehicle component, the rotation of the rotor is converted into movement of the vehicle component. In a critical event, such as a vehicle accident, the rotor may continue to be driven via the mechanical coupling, for example, by the vehicle's wheels continuing to rotate unintentionally.Particularly in the case of a permanent magnet electric machine, the rotating rotor can induce a voltage in the stator windings, which is undesirably fed back into the vehicle's electrical system. To brake the rotor as quickly as possible in such a fault, for example in less than 50 ms, and in particular in no more than 15 ms, the electric motor unit has an emergency braking device. In the event of a fault, the emergency braking device introduces a medium, which is in particular a highly viscous fluid and / or a foaming agent, into the air gap. This abruptly increases the air gap friction and mechanically blocks the rotation of the rotor. This also blocks the movement of the vehicle component mechanically coupled to the rotor, for example, the rotation of the vehicle's wheels, thus bringing the vehicle to a safe state. The gearbox may also be designed to have a predetermined breaking point, which, when the rotor is braked by the medium, is designed to yield and interrupt the mechanical coupling between the electric motor and the wheels via the gearbox.The wheels are set into a freewheel state by the yielding of the predetermined breaking point, which is not critical for the electric motor, and can continue to rotate without further driving the rotor. This also ensures a safe state for the vehicle. In one embodiment of the invention, the emergency braking device comprises a cartridge in which the medium is located away from the fault location and which, in the event of a fault, is designed to introduce the medium into the air gap and release it. The cartridge has a controllable opening mechanism that is activated in the event of a fault, allowing the medium to escape from the cartridge. For example, the opening mechanism can have a predetermined breaking point or a tear seam that is subjected to a controllable mechanical load to open the cartridge. For example, the emergency braking system has a control unit designed to receive a fault signal and then activate the cartridge to open. This control unit can be integrated into the vehicle's airbag control unit, which can deploy the vehicle's airbags to protect the occupants in the event of a critical incident. The control unit is designed to detect the critical incident using sensor data from a vehicle-side sensor unit and to activate the emergency braking unit to decelerate the rotor. The sensor unit might include, for example, acceleration sensors to detect a collision and yaw rate sensors to detect a rollover. The control unit then activates the cartridge's opening mechanism, releasing the fluid into the air gap. The electromechanical unit may be provided with a housing in which the electric motor is arranged, and the emergency braking device is designed to flood the interior of the housing, and thus the air gap, at least partially with the medium. For example, the cartridge containing the medium may also be arranged in the interior and introduce the medium into the interior after the opening mechanism is actuated. The embodiments and advantages presented with reference to the electromechanical unit according to the invention apply accordingly to the motor vehicle according to the invention. Further features of the invention will become apparent from the claims, the figures, and the description of the figures. 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 in the figures alone, are usable not only in the combinations specified, but also in other combinations or individually. The invention will now be explained in more detail with reference to a preferred embodiment and the drawing. Figure 1 shows a schematic representation of an electromechanical unit for a motor vehicle in the absence of a fault; and Figure 2 shows a schematic representation of the electromechanical unit in the event of a fault. In the figures, identical and functionally equivalent elements are provided with the same reference symbols. Fig. 1 shows a longitudinal section of an electric motor unit 1 for a motor vehicle, which is designed in particular as a drive unit for an electrically powered motor vehicle. The electric motor unit 1 comprises an electric machine 2 with a stator 3 and a rotor 4 mounted to rotate with respect to the stator 3. Here, the stator 3 surrounds the rotor 4 and has a stator lamination stack 5 and stator windings (not shown). The rotor 4 has a rotor lamination stack 6, a rotor shaft 7 non-rotatably connected to the rotor lamination stack 6, and a magnetic field-exciting component (not shown). The magnetic field-exciting component consists in particular of permanent magnets, so that the electric machine is designed as a permanent magnet synchronous machine (PMSM). The rotor shaft 7 is mechanically coupled to a vehicle component, for example, the wheels of the motor vehicle, for torque transmission.An air gap 8 is formed between the rotor 4 and the stator 3. The electromechanical unit 1 also has a housing 9 in which the electric machine 2 is arranged. The rotor shaft 7 passes through housing covers of the housing 9. To brake the rotor 4 in the event of a fault, the electromechanical unit 1 also has an emergency braking device 10. The emergency braking device 10 comprises a cartridge 11 or sleeve arranged in the housing 9, which is filled with a medium 12. The medium 12 is, for example, a highly viscous fluid. In the event of a fault, the emergency braking device 10, as shown in Fig. 2, is designed to direct the medium 12 into the air gap 8, thereby abruptly increasing the air gap friction and bringing the rotor 4, which continues to rotate due to the fault, to a standstill. For example, a control unit of the emergency braking device 10 (not shown here) is designed to open the cartridge 11 in order to direct the medium 12 into the interior 13 of the housing 9 and thus into the air gap 8.For example, the cartridge 11 can be under high pressure and opened, for example by puncturing it at a predetermined breaking point, so that the medium 12 is suddenly distributed in the interior 13 and thus in the air gap. The medium 12 can also be an expandable, curable medium, for example a PU foam, which flows into the air gap 8 and cures there. QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature DE 10 2017 222 005 A1

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Claims

An electromechanical unit (1) for a motor vehicle comprising: - an electric machine (2) for driving a vehicle component, wherein the electric machine (2) has a stator (3) with current-carrying stator windings for exciting a stator magnetic field and a rotor (4) rotatably mounted relative to the stator (3) with a magnetic field-exciting component for exciting a rotor magnetic field, wherein an air gap (8) is formed between the rotor (4) and the stator (3), and - an emergency braking device (10) for braking the rotating rotor (4) in the event of a fault, characterized in that the emergency braking device (10) is designed to introduce a medium (12) into the air gap (8) in the event of a fault to increase air gap friction braking the rotor (4). Electromotive unit (1) according to claim 1, characterized in that the electric machine (2) is designed as an at least partially permanently excited electric machine and the magnetic field-generating component has a permanent magnet arrangement. Electromotive unit (1) according to claim 1 or 2, characterized in that the electromotive unit (1) has a housing (9) in the interior (13) of which the electric machine (2) is arranged, wherein the emergency braking device (10) is designed to flood the interior (13) of the housing (9) and thus the air gap (8) at least partially with the medium (12). Electromotive unit (1) according to one of the preceding claims, characterized in that the emergency braking device (10) has a cartridge (11) in which the medium (12) is arranged away from the fault situation and which, in the event of a fault, is designed to introduce the medium (12) into the air gap (8) in order to release the medium (12). Electromotive unit (1) according to claim 4, characterized in that the emergency braking device (10) has a control unit which is designed to receive a fault-related signal and then to control the cartridge (11) to open. Electromotive unit (1) according to one of the preceding claims, characterized in that the medium (12) comprises a highly viscous fluid. Electromotive unit (1) according to one of the preceding claims, characterized in that the medium (12) comprises a foaming agent. Electromotive unit (1) according to one of the preceding claims, characterized in that the electromotive unit (1) is an electric drive unit which has a gearbox which is coupled on the drive side to a rotor shaft (7) of the rotor (4) and can be coupled on the output side to wheels of the motor vehicle, wherein the gearbox has a predetermined breaking point on the output side which is designed to give way by braking the rotor (4) by means of the medium (12) and to interrupt the mechanical coupling formed via the gearbox between the electric machine (2) and the wheels. motor vehicle comprising at least one electromechanical unit (1) according to one of the preceding claims.

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