Electric drive for a compressor for a fuel cell system of a vehicle, in particular a utility vehicle, compressor, fuel cell system, and vehicle

Abstract

The invention relates to an electric drive (110) for a compressor (100) for a fuel cell system (205) of a vehicle (200a), in particular a utility vehicle (200b), wherein the electric drive (110) has a stator (120) and a rotor (130) having a holding device (135) made of electrically conductive material (136) and an excitation device (138), held by the holding device (135), for interacting with the stator (120), the electric drive (110) is designed as a synchronous machine (111), and the electric drive (110) is configured to generate an opposing field (G) in the holding device (135) that brings about a braking torque (M) in order to brake the electric drive (110).

Description

[0001] Electric drive for a compressor for a fuel cell system of a vehicle, in particular a commercial vehicle, compressor, fuel cell system, vehicle

[0002] The disclosure relates to an electric drive for a compressor for a fuel cell system of a vehicle, in particular a commercial vehicle. The disclosure also relates to a compressor for a fuel cell system of a vehicle, in particular a commercial vehicle, comprising an electric drive, a fuel cell system for a vehicle, in particular a commercial vehicle, comprising a fuel cell arrangement and a compressor, wherein the compressor is configured to supply the fuel cell arrangement with supply air, and a vehicle, in particular a commercial vehicle, comprising a fuel cell system.

[0003] Fuel cell systems are well known. Fuel cells are galvanic cells that can be used to convert chemical energy into electrical energy. The electrical energy is generated from the so-called fuel cell reaction, a chemical reaction between a continuously supplied fuel, such as hydrogen, and an oxidizing agent, usually oxygen. To increase energy generation, several fuel cells can be combined in a fuel cell array or fuel cell stack.

[0004] In fuel cell systems, a compressor (also called a compressor) is used to draw in air, compress it, and feed it to a fuel cell inlet on the cathode side of the fuel cell to carry out the fuel cell reaction. The compressed mixture of substances flows through the fuel cell assembly. The mixture of substances remaining after the fuel cell reaction exits the fuel cell assembly as a gaseous fluid stream from a fuel cell outlet on the cathode side.

[0005] Known compressors comprise a bearing unit with an air bearing and a rotor with a shaft, with the shaft being non-rotatably connected to the rotor. The shaft is rotatably mounted in an opening in the air bearing. During compressor operation, the shaft rotates at a high speed, for example, in excess of 100,000 revolutions per minute. Bearings lubricated with grease, for example, are therefore unsuitable for this type of compressor due to the high speed.

[0006] An air bearing for a bearing unit of a compressor for a fuel cell system is known, for example, from document DE 10 2018 213 700 A1. The air bearing disclosed therein has an outer ring surrounding a central opening for receiving a shaft. A spring foil with a spring stiffness and a top foil are arranged in the opening, with the spring foil being arranged between the outer ring and the top foil.

[0007] Air bearings are plain bearings in which the bearing surfaces of two bearing partners are separated by a thin film of air. So-called aerodynamic air bearings create this air film themselves by the bearing surfaces of the bearing partners moving against each other – in this case, due to the rotation of the shaft in the opening of the air bearing – and generating excess pressure. The air in the resulting gap between the bearing partners compresses as the shaft rotates, builds up, and forms an air cushion. While this eliminates the need for an additional compressed air supply, the bearing partners do not come into contact with each other below a characteristic relative speed, which in this case is a shaft rotation speed of approximately 15,000 revolutions per minute.Before this rotational speed, also known as the lift-off speed in the case of air bearings, is reached, particularly before and during the start-up phase of the compressor and after the lift-off speed has been exceeded when the compressor is braking, the two bearing partners rub against each other, resulting in severe abrasion and wear. This in turn means that the air bearings often have to be replaced several times over the service life of a compressor. During the braking phase, the speed should therefore be reduced to zero as quickly as possible after the lift-off speed has been exceeded in order to reduce wear. A synchronous machine with permanent magnets is typically used as the electric drive for such a compressor. Such electric drives typically have a comparatively low moment of inertia of the rotor, which is beneficial for operation at the comparatively high speeds.It is known that a rotor of such a synchronous machine has essentially cylindrical and / or partially cylindrical magnets arranged in a metallic sleeve. The sleeve serves mechanical purposes, particularly to stiffen the rotor, particularly to increase its stability at comparatively high speeds. Furthermore, synchronous machines typically have simpler power electronics than induction machines.

[0008] There are various practical and technical limitations when braking the rotor or the electric drive. Typically, the vehicle, the fuel cell system, and / or other components of such compressors require that the compressor not be operated generatively, thus preventing energy from being fed back into the compressor. Furthermore, braking the compressor with a synchronous machine by short-circuiting the phases can only be effectively achieved at comparatively low speeds of, for example, approximately 3,000 revolutions per minute or less, i.e., below the takeoff speed, since otherwise only a low braking torque is generated and / or the compressor's power electronics are subjected to comparatively high currents or energy.

[0009] Against the background of this prior art, one object of the present disclosure is to provide an electric drive for a compressor of a fuel cell system of a vehicle, in particular a commercial vehicle, which is suitable for enriching the prior art and improving at least the above-mentioned aspects of the prior art. In particular, the object of the disclosure is to provide wear-reducing braking at speeds optionally above and in particular below the take-off speed of an electric drive for a compressor of a fuel cell system of a vehicle, in particular a commercial vehicle. This object is achieved by the features of the independent claims. The subclaims contain further developments of the disclosure.

[0010] According to one aspect of the disclosure, the object is achieved by an electric drive for a compressor for a fuel cell system of a vehicle, in particular a commercial vehicle, wherein the electric drive has a stator and a rotor with a holding device made of electrically conductive material and an excitation device held by the holding device for interacting with the stator, the electric drive is designed as a synchronous machine, and the electric drive is designed to generate a counter field in the holding device that causes a braking torque in order to brake the electric drive.

[0011] It was discovered that the holding device can be used to generate the opposing field. Analogous to the principle of an eddy-current brake, this can generate a braking torque that slows the rotor or the electric drive, thus reducing the speed. For this purpose, the braking torque or opposing field can be generated analogously to the electromagnetic field when braking a three-phase asynchronous motor or a three-phase induction motor.

[0012] It was therefore recognized that even with an electric drive designed as a synchronous machine, braking can be achieved in the same way as with a three-phase asynchronous machine. The holding device made of the electrically conductive material can take on the function of a cage of a squirrel-cage rotor of a three-phase asynchronous machine: the electrically conductive material makes it possible to generate the opposing field in the holding device.

[0013] This allows the rotor and electric drive to be effectively braked over a wide speed range, even below the takeoff speed. This reduces rotor running at a speed below the takeoff speed and the associated wear. The process can also be combined with other braking methods, for example, the braking described above at comparatively low speeds below the takeoff speed, in order to apply the most effective braking method depending on the speed range.

[0014] Optionally, the opposing field is generated by an electromagnetic field generated by the stator, rotating against the direction of rotation of the rotor, and / or a direct field. It has been recognized that there are various ways to generate the opposing field and thus achieve the braking torque. A direct field, i.e., a temporally constant electromagnetic field, can be particularly effective. An electromagnetic field rotating against the direction of rotation of the rotor can achieve a better braking effect.

[0015] Optionally, the electric drive is configured to detect the rotor's speed and generate the opposing field depending on the speed. It has been recognized that braking can depend on the speed. Depending on the speed, the opposing field can be generated in such a way as to produce a suitable braking torque.

[0016] Optionally, the holding device is a cylindrical sleeve. The cylindrical sleeve can effectively hold the excitation device, and the opposing field can be generated effectively and optionally over a large area within the sleeve to achieve a suitable braking torque. It was recognized that the rotor typically has an excitation device with an at least partially circular contour, which can be effectively integrated into the cylindrical geometry of the sleeve.

[0017] Optionally, the holding device is made of a nickel-based alloy and / or contains chromium. Such holding devices can be stronger than steel, allowing for a comparatively thin or thin-walled sleeve. This can reduce the rotor's moment of inertia. Furthermore, such sleeves are particularly temperature- and corrosion-resistant. At the same time, nickel-based alloys and / or alloys containing chromium have such magnetic and electrical properties that they can generate the opposing field and thus produce a suitable braking torque. Optionally, the excitation device comprises a permanent magnet. Optionally, the permanent magnet is a cylindrical permanent magnet or a so-called bar magnet. This eliminates the need for electrical current to the excitation device. The excitation device is maintenance-free and can be installed efficiently.

[0018] According to one aspect of the disclosure, a compressor for a fuel cell system of a vehicle, in particular a commercial vehicle, is provided, comprising an electric drive described above. Optionally, the electric drive has one or more of the features described as optional and / or advantageous in order to achieve an associated technical effect.

[0019] According to one aspect of the disclosure, a fuel cell system for a vehicle, in particular a commercial vehicle, comprising a fuel cell assembly and a compressor described above is provided, wherein the compressor is configured to supply the fuel cell assembly with supply air. Optionally, the compressor and / or its electric drive comprises one or more of the features described as optional and / or advantageous in order to achieve an associated technical effect.

[0020] According to one aspect of the disclosure, a vehicle, in particular a commercial vehicle, comprising a fuel cell system as described above is provided. Optionally, the fuel cell system, its compressor, and / or its electric drive have one or more of the features described as optional and / or advantageous in order to achieve an associated technical effect.

[0021] In the following, one embodiment is described with reference to the figures.

[0022] Fig. 1 schematically shows a vehicle, in particular a commercial vehicle, according to one aspect of the disclosure; and

[0023] Figure 2 schematically shows a vehicle, in particular a commercial vehicle, according to one aspect of the disclosure. Figure 1 shows a schematic representation of a vehicle 200a, in particular a commercial vehicle 200b, according to one embodiment of the disclosure.

[0024] The vehicle 200a, in particular the commercial vehicle 200b, is referred to below as the vehicle 200a, 200b. The vehicle 200a, 200b is, for example, a land vehicle or a watercraft.

[0025] The vehicle 200a, 200b has a fuel cell system 205, an energy storage device 260, and an electric main drive 250. The fuel cell system 205 is configured to provide electrical energy 65 to the energy storage device 260. The energy storage device 260 is, for example, a rechargeable energy storage device 260 and serves as a buffer battery for buffering electrical energy 65. The energy storage device 260 is connected to the electric main drive 250 to supply the electric main drive 250 with electrical energy 65 so that the electric main drive 250 can drive the vehicle 200a, 200b.

[0026] The fuel cell system 205 comprises a compressor 100, a fuel cell stack 206, and optionally an expander 270. The compressor 100 is configured to supply an air flow 240 to the cathode side of the fuel cell stack 206. For this purpose, the compressor 100 is configured to be supplied with electrical energy 65 in order to draw in air, compress it, and supply it to the fuel cell stack 206 as supply air 240. The expander 270 is configured to be supplied with exhaust air 245 from the fuel cell stack 206 in order to convert energy from the exhaust air 245 into electrical energy 65.

[0027] The compressor 100 comprises an electric drive 110 configured to drive the compressor 100. This allows the compressor 100 or a fan wheel of the compressor 100 to be set in rotation in order to provide the supply air 240. For this purpose, the electric drive 110 can be supplied with electrical energy 65. The electric drive 110 is configured as a synchronous machine 111. The electric drive 110 comprises a stator 120 and a rotor 130. The stator 120 is configured to generate a rotating field, and the rotor 130 is configured to rotate synchronously with the rotating field.

[0028] The stator 120 is the stationary part of the electric drive 110 and can optionally form an outer frame. The stator 120 is configured to generate the rotating field to set the rotor 130 in motion. For this purpose, the stator 120 has coils that can be supplied with an alternating current. These coils generate the rotating field, i.e., a rotating magnetic field that drives the rotor 130.

[0029] To generate the rotating field, the electric drive 110 has a control unit 112 with power electronics (not shown). The control unit 112 and the stator 120 or its coils are electrically connected to each other so that the stator 120 or its coils can be supplied with electrical current to generate the rotating field.

[0030] The rotor 130 is the rotatable part of the electric drive 110 and is typically arranged radially within the stator 120 with respect to a rotation axis. Thus, the rotor 130 can be arranged in the rotating field generated by the stator 120 and is caused to rotate by this rotating field in a rotation direction R defined by the rotation axis.

[0031] The rotor 130 can rotate at a speed N. The control unit 112 is configured to detect, or detect, specify, and / or determine the speed N. In the synchronous machine 111, the speed N results from the rotating field, i.e., from the application of electrical current to the stator 120. The control unit 112 thus implicitly specifies the speed N and can thus detect the speed N. Alternatively or additionally, the compressor 110 has a tachometer (not shown) that is communicatively connected to the control unit 112 and can detect the speed N and transmit it to the control unit 112. To ensure that the rotor 130 can rotate with as little friction as possible even at comparatively high speeds N, the compressor 100 has an air bearing 131. The air bearing 131 creates a mechanical separation between the rotor 130 and the rotationally fixed components of the compressor 100, particularly during rotation of the rotor 130, due to an air film.The air bearing 131 thus ensures low friction, particularly at comparatively high speeds N, and thus low wear.

[0032] The rotor 130 has a holding device 135 made of electrically conductive material 136. The electrically conductive material 136 enables a counter-field G (see schematic arrows with a dotted line) to be generated in the holding device 135. The counter-field G is generated by an electromagnetic field EF generated by the stator 120 and rotating counter to the direction of rotation R of the rotor 130 (see schematic arrows with a dot-dashed line). In other words, the electric drive 110 or the control unit 112 is configured to apply electric current to the stator 120 such that the stator 120 generates the electromagnetic field EF rotating counter to the direction of rotation R of the rotor 130. The stator 120 generates the electromagnetic field EF by applying electric current to the stator 120.The electromagnetic field EF induces an electric current in the holding device 135, which current in turn generates the opposing field G. The electric drive 110 is designed to induce the opposing field G as a function of the rotational speed N. The electromagnetic field EF rotating against the direction of rotation R of the rotor 130 thus generates the opposing field G in the holding device 135. This creates a braking torque M. The electric drive 110 is therefore designed to generate an opposing field G in the holding device 135, which causes the braking torque M, in order to brake the electric drive 110.

[0033] The holding device 135 is a cylindrical sleeve 137. The cylindrical sleeve 137 has at least partially a cylindrical surface facing the stator 120, in which the opposing field G can be effectively generated. The holding device 135 is made of a nickel-based alloy 136' and contains chromium 136". The rotor 130 has an excitation device 138 held by the holding device 135 for interacting with the stator 120. The excitation device 138 is configured to generate a magnetic field for rotating the rotor 130 that is synchronized with the rotating magnetic field of the stator. The excitation device 138 is thus configured to generate a magnetic field that interacts with the rotating magnetic field of the stator 120 and thus generates a torque that drives the rotor 130. The excitation device 138 is designed as a permanent magnet 139.The permanent magnet 139 generates a constant magnetic field that is stable during operation of the electric drive 110 because the arrangement of the permanent magnets 139 is rotationally fixed to the rotor 130. The permanent magnetic field of the rotor 130 interacts with the rotating magnetic field of the stator 120, thus generating a torque that sets the rotor 130 in motion and / or synchronizes the rotor 130 with the synchronous speed of the stator 120. Alternatively or additionally, the rotor 130 can have excitation windings that can be energized by an electric current.

[0034] Figure 2 shows a schematic representation of a vehicle 200a, in particular a commercial vehicle 200b, according to an embodiment of the disclosure. Figure 2 is described with reference to Figure 1, describing the differences between Figures 1 and 2.

[0035] According to Figure 2, the opposing field G is generated by a DC field GF generated by the stator 120 (see schematic arrows with dot-dashed lines). In other words, the electric drive 110 or the control unit 112 is configured to apply electric current to the stator 120 such that the stator 120 generates the DC field GF, for example, by applying a temporally constant DC current to the phases of the stator 120. This creates a temporally constant magnetic field as a DC field GF. The DC field GF generates the opposing field G in the holding device 135. The stator 120 generates the DC field GF by applying electric current to the stator 120. The DC field GF induces an electric current in the holding device 135, which current in turn generates the opposing field G. This creates a braking torque M.The electric drive 110 is thus designed to generate a counter field G in the holding device 135, which produces the braking torque M, in order to brake the electric drive 110.

[0036] The electric drive 110 is configured to generate the opposing field G as a function of the rotational speed N. The electromagnetic field EF rotating against the direction of rotation R of the rotor 130 according to Figure 1 and the constant field GF according to Figure 2 can also be combined. For example, the constant field GF can be applied in a first speed regime, and the electromagnetic field EF rotating against the direction of rotation R of the rotor 130 can be applied in a second speed regime different from the first speed regime.

[0037] Reference symbol (part of the description):

[0038] 65 electrical energy 100 compressor 110 electric drive 111 synchronous machine 112 control unit 120 stator 130 rotor 131 air bearing

[0039] 135 Holding device 136 Electrically conductive material 136' Nickel-based alloy 136“ Chrome 137 Sleeve 138 Excitation device 139 Permanent magnet

[0040] 200a Vehicle 200b Commercial vehicle 205 Fuel cell system 206 Fuel cell assembly 240 Supply air 245 Exhaust air 250 Electric main drive 260 Energy storage device

[0041] 270 expanders

[0042] EF electromagnetic field G opposing field GF direct field

[0043] M Braking torque N Speed

[0044] R Rotation direction

Claims

Patent claims:

1. Electric drive (110) for a compressor (100) for a fuel cell system (205) of a vehicle (200a), in particular a commercial vehicle (200b), wherein - the electric drive (110) has a stator (120) and a rotor (130) with a holding device (135) made of electrically conductive material (136) and an excitation device (138) held by the holding device (135) for interacting with the stator (120), - the electric drive (110) is designed as a synchronous machine (111), and - the electric drive (110) is designed to generate a counter field (G) in the holding device (135) which causes a braking torque (M) in order to brake the electric drive (110).

2. Electric drive (110) according to claim 1, wherein the opposing field (G) is generated by an electromagnetic field (EF) and / or a direct field (GF) generated by the stator (120) and rotating against a direction of rotation (R) of the rotor (130).

3. Electric drive (110) according to claim 1 or 2, wherein the electric drive (110) is configured to detect a rotational speed (N) of the rotor (130) and to generate the opposing field (G) as a function of the rotational speed (N).

4. Electric drive (110) according to one of the preceding claims, wherein the holding device (135) is a cylindrical sleeve (137).

5. Electric drive (110) according to one of the preceding claims, wherein the holding device (135) is made of a nickel-based alloy (136') and / or comprises chromium (136").

6. Electric drive (110) according to one of the preceding claims, wherein the excitation device (138) comprises a permanent magnet (139).

7. Compressor (100) for a fuel cell system (205) of a vehicle (200a), in particular a commercial vehicle (200b), comprising an electric drive (110) according to one of the preceding claims.

8. Fuel cell system (205) for a vehicle (200a), in particular a commercial vehicle (200b), comprising a fuel cell arrangement (206) and a compressor (100) according to claim 7, wherein the compressor (100) is configured to supply the fuel cell arrangement (206) with supply air (240).

9. Vehicle (200a), in particular commercial vehicle (200b), comprising a fuel cell system (205) according to claim 8.

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