Electric machine

Abstract

An electric machine comprising a stator, a rotor rotatable about an axis relative to the stator, the rotor comprising permanent magnets, at least one short-circuit ring axially displaceable by a distance D between a first position and a second position, the short-circuit ring being further away from the rotor in the first position than in the second position, and an induced magnetic flux of the permanent magnets being reduced when the at least one short-circuit ring is displaced towards the second position, and at least one actuating arrangement actuating the at least one short-circuit ring to displace it from the first position to the second position.

Description

[0001] The application relates to an electrical machine with a stator, a rotor which is rotatable about an axis relative to the stator, the rotor having permanent magnets, at least one short-circuit ring which is axially displaceable by a distance D between a first position and a second position, the short-circuit ring being further away from the rotor in the first position than in the second position and an induced magnetic flux of the permanent magnets being reduced when the at least one short-circuit ring is displaced towards the second position, and at least one actuating arrangement which hydraulically actuates the at least one short-circuit ring and displaces the at least one short-circuit ring from the first position to the second position.

[0002] Permanent magnet electric machines are known for their high torque density and efficiency. The induced back electromotive force of permanent magnet electric machines increases with speed and generally reaches the inverter voltage limit at a base speed. To maintain a constant back electromotive force, it is known to weaken the magnetic flux coupling of the permanent magnets, which can be achieved, for example, by adjusting the relative position of active and / or passive parts of the electric machine.

[0003] US 8 390 232 B2 discloses an electric machine with permanent magnets, in which the rotor or stator has at least one movable iron segment. The magnetic field of the electric machine is weakened when the movable iron segment is moved away from the rotor or stator. When the movable iron segment is in a first position, for example in contact with the rotor or stator, the field strength is high. When the movable iron segment is in a second position in which the movable iron segment is displaced away from the rotor or stator, the field strength is low. The ability to weaken the field strength leads to an increase in the speed ratio at constant power, thus increasing the usefulness of the electric machine for applications where a wide speed range is desired. The electric machine can be used both as a permanent magnet motor and as a generator.

[0004] CN 102170211 B discloses a variable excitation permanent magnet synchronous motor. The variable excitation permanent magnet synchronous motor includes a stator and a rotor mounted on a motor shaft, each of the two sides of the rotor being provided with a set of flux weakening control mechanisms. The flux weakening control mechanism includes soft iron plates arranged on the two sides of the rotor and coaxial with the rotor; a spring is arranged between the rotor and the soft iron plate; and connecting rod counterweight mechanisms are provided for each soft iron plate, respectively.The permanent magnet synchronous motor with variable excitation has the advantage of automatically adjusting the distances between the rotor and the soft iron plates according to the change of the speed, thereby changing the magnetic flux path, which achieves the goal of controlling the reduction of the excitation intensity of the motor with the increase of the speed and further increasing the maximum speed of the motor.

[0005] JP-H-11275787 A describes a high-torque electric motor with a wide constant power range. A rotor is provided with a rotor body, a flux barrier, a permanent magnet embedded in the flux barrier, a slot portion extending from a region between the end portions of adjacent flux barriers to a region near the end surface of the rotor, a magnetic flux passing member disposed in the slot portion, and a spring for moving the magnetic flux passing member provided on the slot portion.The magnetic flux passing element is movable in the slot part, is located in a gap position where no magnetic flux flows to the magnetic flux passing element when the rotor rotates at a low speed, the magnetic flux passing element protrudes from the gap part when the rotor rotates at a high speed, and a magnetic flux short-circuit part is formed at the slot part, thereby achieving a weak field effect and high torque regardless of the high-speed rotation.

[0006] One task may be to provide an electric motor with a less complex adjustment mechanism that is at least as reliable and durable as the state of the art.

[0007] The object is achieved by an electrical machine comprising a stator, a rotor with permanent magnets that can be rotated about an axis relative to the stator, and at least one short-circuit ring that can be axially displaced by a distance D between a first position and a second position, wherein the short-circuit ring is further away from the rotor in the first position than in the second position. The induced magnetic flux of the permanent magnets is reduced when the at least one short-circuit ring is displaced towards the second position. At least one actuating arrangement that hydraulically actuates the at least one short-circuit ring displaces it from the first position to the second position as a function of a rotational speed of the rotor.

[0008] The advantage of the electric motor is that the magnetic field can be weakened, increasing the motor speed at a given voltage after the maximum power of the electric motor has been reached. By weakening the magnetic field, the electric motor can achieve higher speeds and lower torque at maximum power.

[0009] The electric machine can also be referred to as a permanent magnet electric machine or permanent magnet electric motor, which can also be used as a generator. According to one embodiment, two axially displaceable short-circuit rings are provided, one at each axial end of the rotor, wherein the respective first position has an axial distance D from the respective second position. Both short-circuit rings can be hydraulically actuated by a common actuating arrangement. According to a further embodiment, each of the two short-circuit rings is assigned an actuating arrangement for hydraulic actuation. The distance D between the first and second positions can be between one and ten percent of the axial length or diameter of the rotor, and displacing the at least one short-circuit ring from the first to the second position reduces the induced magnetic flux of the permanent magnets by at least five percent.According to a further embodiment, the at least one short-circuit ring extends such that it covers a magnetic section of the rotor in which the permanent magnets are located. The at least one short-circuit ring can be made of a magnetizable material.

[0010] According to a further embodiment, the at least one actuating arrangement rotates together with the rotor about the axis. The actuating arrangement can be rigidly connected to the rotor. The at least one actuating arrangement can thus advantageously be passively controlled by the centrifugal force acting on the rotating actuating arrangement.

[0011] According to a further embodiment, the at least one actuating arrangement comprises at least one cavity and a fluid within the cavity, wherein the cavity is arranged such that the fluid is centrifuged radially outward from the axis by a centrifugal force of the rotating actuating arrangement. At least one piston can be hydraulically connected to a radially outer end of the cavity. A hydraulic force resulting from the centrifugal force acting on the fluid is transmitted via the piston to the short-circuit ring. The piston and the short-circuit ring can be formed as a one-piece component.

[0012] According to a further embodiment, the at least one cavity forms a closed hydraulic system, wherein a volume of the closed hydraulic system is changed by a movement of the piston, wherein the piston can be displaceable in the axial direction. The at least one cavity can have a reservoir arranged at a radially inner end of the at least one cavity. The actuating arrangement can have only one cavity, which is designed as an annular cavity, wherein the piston is an annular piston and the annular cavity and the annular piston are arranged around the axis. The annular cavity and the piston advantageously distribute the centrifugal force acting on the liquid evenly over the circumference of the short-circuit ring.

[0013] According to a further embodiment, at least one spring element is arranged between the rotor and the at least one short-circuit ring. The spring element exerts an axial preload force on the short-circuit ring in the direction of the first position and thus ensures a restoring force that moves the short-circuit ring back to its first position as the rotor speed decreases. The at least one spring element can be designed as an annular spring or as a stack of annular springs for each short-circuit ring. The spring element can also consist of a plurality of spiral springs arranged circumferentially around the axis. The spiral springs can advantageously be arranged in recesses in the rotor or in recesses in the short-circuit ring, so that the short-circuit ring rests against the rotor in the second position.

[0014] According to a further embodiment, a total force acting on the short-circuit ring in the axial direction toward the second position is composed of the hydraulic force of the fluid and a magnetic force exerted by the rotor. This total force exceeds the preload force of the spring element acting on the short-circuit ring in the axial direction toward the first position above a predetermined rotor speed. The predetermined speed can be in a range between 10,000 and 30,000 revolutions per minute.

[0015] Exemplary embodiments and further advantages of the electric machine are explained below with reference to the attached drawings. Fig. 1 shows a first exemplary embodiment of the electric machine in a perspective view; Fig. 2 the embodiment of Fig. 1 in a longitudinal section view; Fig. 3 a detail from Fig. 2 in a first position; Fig. 4 a detail from Fig. 3 in a second position; Fig. 5 shows a second exemplary embodiment of the electric machine; Fig. 6 the embodiment of Fig. 5 in a longitudinal section view; Fig. 7 a detail from Fig. 6 in a first position; Fig. 8 a detail from Fig. 7 in a second position; Fig. 9 a schematic sectional view of a general electrical machine.

[0016] In the Fig. Figure 9 shows a schematic sectional view of a general electrical machine for illustrative purposes. The electrical machine consists of a stator 10 and a rotor 1, which is rotatable relative to the stator 10 about an axis L, wherein the rotor 1 has permanent magnets 11. In this case, eight permanent magnets 11 arranged in pairs in a V-shape are integrated into the rotor 1. Slots 19 are provided in the stator 10 for receiving a winding (not shown). Fig. 1 to 8 is the stator 10 ( Fig. 9) not shown.

[0017] In the Fig. 1 is an embodiment of the electric machine shown in perspective, partly as an exploded view. The electric machine consists of the stator 10 (not shown, see Fig. 9), the rotor 1, which is rotatable relative to the stator 10 about the axis L. The permanent magnets 11 are arranged in V-shaped recesses of the rotor 1. Two short-circuit rings 2 are arranged at two axially spaced ends of the rotor 1, and two actuating assemblies 3 hydraulically actuate the short-circuit rings 2 to displace them in the axial direction along the axis L. Fig. Figure 2 shows the embodiment in a longitudinal section. A detail A is shown in the Fig. 3 or the Fig. 4 shown in different positions. The Fig. 1 to 4 are described together.

[0018] The short-circuit rings 2 are axially displaceable by a distance D, as best shown in the Fig. 3 can be seen, between a first position, which is in the Fig. 3, and a second position shown in the Fig. 4. The short-circuit rings 2 are further away from the rotor 1 in the first position than in the second position.

[0019] The induced magnetic flux of the permanent magnets 11 is reduced when the short-circuit rings 2 are moved to the second position. The actuating assemblies 3 hydraulically actuate the short-circuit rings 2 to move them from the first position to the second position depending on the speed of the rotor 1. The actuating assemblies 3 are passively controlled by centrifugal force, which will be explained in more detail below.

[0020] One of the two actuating arrangements 3 is in the Fig. 1 in an exploded view. The actuating arrangement 3 consists of a first housing part 14 and a second housing part 15, both of which are annular and, when assembled, form an annular cavity 4 between them. A housing sealing ring 17 is provided to seal the cavity 4. The short-circuit ring 2 is connected to an annular piston 5, which interacts with an annular piston chamber 18 formed between the first housing part 14 and the second housing part 15, which is best illustrated in Fig. 4 can be seen. The piston 5 has a groove with a piston sealing ring 16. The piston chamber also has a groove, which is formed on the second housing part 15, with a further piston sealing ring 16. The piston sealing rings 16 seal the cavity 4.

[0021] The actuating assemblies 3 rotate together with the rotor 1 about the axis L. In the illustrated embodiment, the rotor 1 and both the first housing parts 14 and the second housing parts 15 of the actuating assemblies 3 are connected to a drive shaft 12. A liquid, e.g., oil, is located in the cavity 4. Due to the shape of the cavity 4, the liquid is centrifuged radially outward from the axis L by the centrifugal force of the rotating actuating assembly 3. Since the piston 5 is hydraulically connected to a radially outer end of the cavity 4, a hydraulic force of the liquid acts on the piston 5 and on the short-circuit ring 2, which is connected to the piston 5. The cavity 4 forms a closed hydraulic system whose volume is changed by a movement of the axially displaceable piston 5.The rotational force acting on the fluid centrifuges the fluid from a storage container 6, which is arranged at a radially inner end of the at least one cavity 4, in the direction of the radially outer piston chamber 18.

[0022] Between the rotor 1 and each short-circuit ring 2, a spring element 7 is arranged, which exerts an axial prestressing force on the respective short-circuit ring 2 in the direction of the first position. In the illustrated embodiment, the at least one spring element 7 is an annular spring 7a, which can have a smaller outer diameter than the inner diameter of the short-circuit ring 2, so that the short-circuit ring 2 can bear against the rotor 1 in the second position, as shown in Fig. 4 shown.

[0023] In the Fig. Figure 5 shows a second embodiment of the electric machine in a perspective, partially exploded view. The electric machine consists of the stator 10 (not shown, see Fig. 9), the rotor 1, which is rotatable relative to the stator 10 about the axis L. The permanent magnets 11 are arranged in V-shaped recesses of the rotor 1. Two short-circuit rings 2 are arranged at two axially spaced ends of the rotor 1, and two actuating assemblies 3 hydraulically actuate the short-circuit rings 2 for displacement in the axial direction along the axis L. In this respect, the second embodiment is identical to the first described embodiment and will not be described again in detail. Fig. Figure 6 shows the embodiment in a longitudinal section. A detail A is shown in the Fig. 7 or the Fig. 8 shown in different positions. The Fig. 5 to 8 are described together.

[0024] In the second embodiment, the spring element 7 consists of a plurality of spiral springs 7b distributed circumferentially around the axis L, instead of the annular spring 7a. The eight spiral springs 7b are arranged in recesses 8 in the rotor 1 and in recesses 9 in the short-circuit ring 2, as shown in Fig. 7 is best seen so that the short-circuit ring 2 is in the second position, which is Fig. 8, can rest on the rotor 1.

[0025] The short-circuit rings 2 extend in the radial direction and overlap with an outer radial extension of the rotor 1, preferably with a magnetic section of the rotor 1 in which the permanent magnets are located. The short-circuit rings 2 can be made of a magnetizable material. A combined force in the axial direction from the hydraulic force of the fluid and a magnetic force exerted by the rotor 1 on the short-circuit ring 2 exceeds the preload force of the spring element 7 above a predetermined rotational speed of the rotor 1, which, for example, lies in a range between 10,000 and 30,000 revolutions per minute. The distance D from the first position to the second position can be between one and ten percent of an axial length or a diameter of the rotor 1. Moving the at least one short-circuit ring 2 from the first to the second position reduces the induced magnetic flux of the permanent magnets 11 by at least 5%. Reference symbol 1 rotor 2 short-circuit ring 3 Actuating arrangement 4 Cavity 5 pistons 6 storage containers 7 Spring element 7a Annular spring 7b Spiral springs 8 recess 9 Recess 10 Stator 11 permanent magnets 12 Drive shaft 14 First housing 15 Second housing 16 Piston seal ring 17 Housing sealing ring 18 Piston chamber 19 slots QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 8 390 232 B2

[0003] CN 102170211 B

[0004] JP-H-11275787 A

[0005]

Claims

[1] Electrical machine, comprising: a stator (10); a rotor (1) with permanent magnets (11) rotatable about an axis (L) relative to the stator (10); at least one short-circuit ring (2) axially displaceable by a distance D between a first position and a second position, wherein the short-circuit ring (2) is further away from the rotor (1) in the first position than in the second position, and wherein an induced magnetic flux of the permanent magnets (11) is reduced when the at least one short-circuit ring (2) is displaced towards the second position; and at least one actuating arrangement (3) which hydraulically actuates the at least one short-circuit ring (2) and displaces the at least one short-circuit ring (2) from the first position to the second position as a function of a rotational speed of the rotor (1). [2] Electrical machine according to claim 1, characterized bythat the at least one actuating arrangement (3) is passively controlled by centrifugal force. [3] Electrical machine according to one of the preceding claims, characterized by that the at least one actuating arrangement (3) rotates together with the rotor (1) about the axis (L). [4] Electrical machine according to one of the preceding claims, characterized by that the at least one actuating arrangement (3) has at least one cavity (4) and a fluid inside the cavity, wherein the cavity is arranged such that the fluid is centrifuged radially outwards from the axis (L) by a centrifugal force of the rotating actuating arrangement (3). [5] Electrical machine according to claim 4, characterized bythat the actuating arrangement (3) has at least one piston (5) which is hydraulically connected to a radially outer end of the cavity (4) in order to transmit a hydraulic force of the fluid to the short-circuit ring (2), wherein the piston (5) and the short-circuit ring (2) are formed integrally as one part. [6] Electrical machine according to one of the preceding claims 4 or 5, characterized by that the at least one cavity (4) forms a closed hydraulic system, wherein a volume of the closed hydraulic system is changed by a movement of the piston (5), wherein the piston is axially displaceable. [7] Electrical machine according to one of the preceding claims 4 to 6, characterized by that the at least one cavity (4) has a storage container (6) which is arranged at a radially inner end of the at least one cavity (4). [8] Electrical machine according to one of the preceding claims 4 to 7, characterized by that the actuating arrangement has only one cavity (4) which is designed as an annular cavity, and wherein the piston (5) is an annular piston, wherein the annular cavity and the annular piston are arranged around the axis (L). [9] Electrical machine according to one of the preceding claims, characterized by at least one spring element (7) arranged between the rotor (1) and the at least one short-circuit ring (2), wherein the at least one spring element (7) exerts an axial prestressing force on the at least one short-circuit ring (2) in the direction of the first position. [10] Electrical machine according to claim 9, characterized by that the at least one resilient element (7) is an annular wave spring (7a). [11] Electrical machine according to claim 9, characterized bythat the spring element (7) is formed by a plurality of spiral springs (7b) which are arranged distributed in the circumferential direction around the axis (L). [12] Electrical machine according to claim 11, characterized by that the spiral springs (7b) are arranged in recesses (8) in the rotor (1) and / or in recesses (9) in the short-circuit ring (2), so that abutment of the short-circuit ring (2) against the rotor (1) is possible in the second position. [13] Electrical machine according to one of the preceding claims, characterized by that the at least one short-circuit ring (2) covers a magnetic section of the rotor (1). [14] Electrical machine according to one of the preceding claims 9 to 13 and according to claim 5, characterized bythat a total force in the axial direction of the hydraulic force of the fluid and a magnetic force exerted by the rotor (1) on the short-circuit ring (2) exceeds the prestressing force of the spring element (7) at a predetermined speed of the rotor (1), wherein the predetermined speed is preferably in a range between 10,000 and 30,000 revolutions per minute. [15] Electrical machine according to one of the preceding claims, characterized by that two of the short-circuit rings (2) are arranged at two axially spaced ends of the rotor (1) in respective first positions, wherein two of the actuating arrangements (3) are provided for hydraulically actuating the two short-circuit rings (2) from the respective first position to the respective second position.

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