Electronically commutated electric motor

Abstract

The present invention relates to an electronically commutated electric motor (10), comprising: - a static motor stator (12) having a ferromagnetic stator body (14) and at least one stator coil (16); - a rotatable and permanently magnetized motor rotor (18); - a static magnetic field sensor (38) for detecting the rotor magnetic field and providing a corresponding trigger signal; and - motor electronics (36) for supplying power to at least one of the stator coils (16) based on the trigger signal, - wherein the motor rotor (18) is provided with two axially adjacent axial rotor portions. (22, 24), namely: # the drive rotor portion (22) arranged within the axial range (A) of the stator body (14), and # the sensor rotor portion (24) disposed at the axial end (26) of the motor rotor (18) facing the magnetic field sensor, # wherein the drive rotor portion (22) and the sensor rotor portion (24) have different circumferential magnetization modes from each other, and - wherein the magnetic field sensor (38) is a latching magnetic field sensor (38) positioned adjacent to the sensor rotor portion (24). For a wide range of rotor speeds, especially for low rotor speeds, the motor rotor (18) with two axial rotor portions (22, 24) provides energy-efficient and reliable drive of the motor rotor (18) through the motor stator (12).

Description

Technical Field

[0001] This invention relates to an electronically commutated electric motor, and more preferably to an electric motor for a motor vehicle auxiliary unit. Background Technology

[0002] An electronically commutated electric motor comprises: a static motor stator with a ferromagnetic stator body and at least one stator coil, and a permanently magnetized motor rotor rotatable relative to the motor stator about a rotation axis. The motor rotor is alternately magnetized in the circumferential direction, such that the rotating motor rotor generates an alternating magnetic field at the static circumferential position. The electric motor includes a static magnetic field sensor that detects the alternating rotor magnetic field and provides a corresponding trigger signal. The electric motor also includes motor electronics that supply power to the stator coils, wherein the drive current is commutated based on the trigger signal provided by the magnetic field sensor. As a result, the alternately magnetized motor rotor is driven by the alternating stator magnetic field generated by the electromagnetic motor stator. For example, such an electronically commutated electric motor is disclosed in EP 2 450 575 A1, in which the electric motor drives the pump impeller of a fluid pump in a motor vehicle.

[0003] However, especially at low rotor speeds, the rotor of this electronically commutated electric motor "oscillates," meaning it alternately moves back and forth at small angles without rotating. This oscillation effect occurs if the rotor's rotational speed is slow enough that the stator magnetic field polarization is reversed before the rotor passes a critical rotational position. The result is that the stator magnetic field polarity reversal causes the rotor to rotate backward instead of forward. If, during this backward rotation, the interface between the two oppositely magnetized rotor sectors passes a magnetic field sensor, the sensor triggers the motor electronics to commutate the drive current, causing the stator magnetic field polarity to reverse again. As a result, the rotor moves back and forth slightly, during which the interface between the two oppositely magnetized rotor sectors moves back and forth in front of the magnetic field sensor, causing the magnetic polarity detected by the sensor to continuously alternate, resulting in continuous commutation of the stator drive current.

[0004] Because the motor electronics continuously energize the motor stator, a significant amount of energy is consumed during the rotor's oscillation. However, all this energy is wasted during the oscillation because the rotor is not rotating. Furthermore, without additional sensor components, the motor electronics cannot detect the rotor's oscillation, as they cannot distinguish the trigger signal generated by an oscillating rotor from that generated by a normally rotating rotor. Therefore, the electric motor may become "stuck" in an oscillating state, thus preventing reliable rotor operation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an energy-saving electronically commutated electric motor that allows reliable driving of the motor rotor over a wide range of rotor speeds, especially at low rotor speeds.

[0006] This technical problem is solved by an electronically commutated electric motor having the features of claim 1.

[0007] The electronically commutated electric motor according to the present invention is provided with a static motor stator, which includes a ferromagnetic stator body and at least one stator coil. The stator body may be a solid monolithic ferromagnetic stator body, or alternatively, a laminated stator body composed of stacked ferromagnetic metal sheets.

[0008] The electronically commutated electric motor according to the present invention further comprises a permanently magnetized motor rotor that is rotatable relative to the motor stator about a rotation axis. The motor rotor is alternately magnetized circumferentially, such that the rotating motor rotor generates an alternating magnetic field at a static circumferential position. The motor rotor can be implemented as a single permanently magnetized rotor body, but it can also be preferably configured as a ferromagnetic rotor body with separate permanent magnets.

[0009] The electronically commutated electric motor according to the invention also includes a static magnetic field sensor. The magnetic field sensor is located in a static circumferential position and detects the alternating magnetic field generated by the rotating motor rotor. The magnetic field sensor provides a trigger signal corresponding to the detected magnetic field, wherein the trigger signal is particularly dependent on the magnetic polarity of the detected magnetic field. The magnetic field sensor can be, for example, a low-cost Hall sensor with an integrated evaluation unit. According to the invention, the magnetic field sensor is a latching type magnetic field sensor, i.e., the magnetic field sensor provides a generally digital trigger signal, wherein the trigger signal level switches only when the polarization of the detected magnetic field reverses. Specifically, if the detected magnetic field has a first polarization whose amplitude exceeds a first threshold level, the trigger signal switches to a first trigger signal level, and if the detected magnetic field has an opposite second polarization whose amplitude exceeds a second threshold level, the trigger signal switches to a second trigger signal level.

[0010] The electronically commutated electric motor according to the invention further includes motor electronics for supplying power to at least one stator coil of the motor stator based on a trigger signal provided by a magnetic field sensor. Specifically, the motor electronics supply the stator coil with a generally alternating drive current, wherein the drive current is commutated based on the trigger signal. The motor electronics typically include several power semiconductors for commutating the drive current.

[0011] According to the present invention, the motor rotor comprises two axially adjacent axial rotor portions: a drive rotor portion and a sensor rotor portion. The drive rotor portion is arranged within the axial range of the motor stator, while the sensor rotor portion is located at the axial end of the motor rotor facing the magnetic field sensor. The drive rotor portion and the sensor rotor portion have different circumferential magnetization modes, i.e., the order, position, and / or range of the magnetic north pole, magnetic south pole, and non-magnetic intermediate region along the circumference of the motor rotor differ between the two rotor portions. Hereinafter, the term "non-magnetic" refers to a magnetization level below the detection threshold level of the magnetic field sensor.

[0012] Because the drive rotor section is arranged within the axial range of the motor stator, the circumferential magnetization of the drive rotor section interacts with the stator magnetic field generated by the electromagnetic motor stator to drive the motor rotor. Conversely, an alternating magnetic field generated by the circumferential magnetization mode of the sensor rotor section is detected by a static magnetic field sensor positioned adjacent to the sensor rotor section. As a result, the trigger signal provided to the motor electronics to commutate the drive current is determined substantially by the circumferential magnetization mode of the sensor rotor section, and not, or at least not significantly, by the circumferential magnetization mode of the drive rotor section. Consequently, the drive rotor section can be equipped with a drive magnetization mode that allows for energy-efficient driving of the motor rotor, while the sensor rotor section can be independently designed with different sensor magnetization modes, which ensure reliable drive of the motor rotor and, in particular, avoid motor rotor wobbling. Consequently, the electronically commutated electric motor according to the invention allows for energy-efficient and reliable drive of the motor rotor.

[0013] In a preferred embodiment of the invention, the drive rotor portion of the motor rotor radially surrounds the motor stator, i.e., the electric motor has an outer rotor. The outer rotor can simply and reliably consist of two axially adjacent but magnetically independent axial rotor portions.

[0014] Preferably, the drive rotor section has permanent magnetic drive ring sectors that are alternately magnetized along the rotor circumference, while the sensor rotor section has permanent magnetic sensor ring sectors that are alternately magnetized along the rotor circumference, and also includes non-magnetic sensor ring sectors located between the permanent magnetic sensor ring sectors in the circumferential direction. If the motor rotor moves back and forth at a small angle, the non-magnetic sensor ring sectors between the permanent magnetic sensor ring sectors avoid continuous polarization reversal at the static circumferential position. As a result, the non-magnetic sensor ring sectors avoid continuous switching of trigger signals, thus reliably preventing motor rotor oscillation.

[0015] In a preferred embodiment of the invention, the circumferential range of each permanent magnetic drive ring sector of the drive rotor portion substantially corresponds to the circumferential range of the sensor sector pair of the sensor rotor portion, wherein the sensor sector pair consists of one permanent magnetic sensor ring sector and one non-magnetic sensor ring sector. As a result, the number of permanent magnetic drive ring sectors is equal to the number of permanent magnetic sensor ring sectors. More preferably, the circumferential starting position of each permanent magnetic sensor ring sector, i.e., the circumferential position of the edge of the ring sector pointing in the direction of rotation of the motor rotor, is substantially equal to the circumferential starting position of the corresponding permanent magnetic drive ring sector. As a result, at the defined static circumferential position, the polarization of the sensor magnetic field always reverses simultaneously with the polarization of the drive magnetic field. As a result, the trigger signal provided by the magnetic field sensor is synchronized with the alternating frequency of the magnetic field of the rotating motor rotor. This allows for reliable and energy-efficient driving of the motor rotor without requiring complex compensation logic.

[0016] Preferably, the circumferential range of the non-magnetic sensor ring sector is larger than that of the permanent magnet sensor ring sector, resulting in a relatively large circumferential distance between the permanent magnet sensor ring sectors. As a result, the motor rotor can move at relatively large angles without altering the polarization of the magnetic field detected by the magnetic field sensor. This reliably avoids motor rotor oscillation, and consequently provides energy-efficient and reliable drive for the motor rotor.

[0017] In a preferred embodiment of the invention, the motor rotor with two axially adjacent rotor sections is a monolithic unit, preferably having a homogeneous material composition. The entire rotor body is magnetized in a separate process, with the drive rotor section and the sensor rotor section having different circumferential magnetization patterns. This provides a compact and robust motor rotor without requiring the assembly of any individual rotor sections.

[0018] Alternatively, the drive rotor section and the sensor rotor section are defined by separate rotor bodies fixed together. The separate rotor bodies can be magnetized individually, allowing for different circumferential magnetization modes to be provided to the separate rotor bodies in a simple manner. The separate rotor bodies can be fixed together, for example, by adhesive bonding.

[0019] In a preferred embodiment of the invention, the non-magnetic sensor ring sector is provided by an axial rotor recess. This allows for a simple and reliable implementation of the non-magnetic sensor ring sector.

[0020] Preferably, the magnetic field sensor and sensor rotor section of the motor rotor are configured such that for each magnetic rotor stationary position—that is, the rotor position to which the motor rotor moves when not driven—a permanent magnet sensor ring sector is located within the detection range of the magnetic field sensor. This ensures reliable and effective starting of the motor rotor rotation.

[0021] In a preferred embodiment of the invention, the magnetic field sensor is arranged radially inside and adjacent to the sensor rotor portion. This provides reliable detection of the sensor's magnetic field, and as a result, allows for efficient driving of the motor rotor. Attached Figure Description

[0022] Embodiments of the present invention are described with reference to the accompanying drawings, wherein...

[0023] Figure 1 A detailed longitudinal section view of an electronically commutated electric motor according to the present invention is shown, wherein the electric motor is part of a motor vehicle pump.

[0024] Figure 2 Show Figure 1 The cross-section of the drive rotor section of the electric motor, and

[0025] Figure 3 Show Figure 1 The cross-section of the sensor rotor section of the electric motor. Detailed Implementation

[0026] Figure 1 A vehicle fluid pump 8 with an electronically commutated electric motor 10 according to the invention is shown. The vehicle fluid pump 8 may be, for example, a coolant pump for a vehicle coolant system.

[0027] The electric motor 10 has a static motor stator 12, which includes stacked stator bodies 14 and a plurality of stator coils 16. The electric motor 10 also has a can-shaped motor rotor 18 that radially surrounds the motor stator 12 and is rotatable relative to the motor stator 12 about a rotation axis R. Therefore, in this embodiment of the invention, the electric motor 10 is a so-called external rotor motor.

[0028] The motor rotor 18 is rotatably connected to the pump impeller 20, which in this embodiment of the invention is integrally formed with the motor rotor 18. The motor rotor 18 has two axially adjacent axial rotor portions: a drive rotor portion 22 and a sensor rotor portion 24. The drive rotor portion 22 is axially located within the axial range A of the motor stator 12, while the sensor rotor portion 24 is located at the axially distal end 26 of the pump impeller of the motor rotor 18. In this embodiment of the invention, the motor rotor 18 is a monolithic body made of homogeneous material. Alternatively, the motor rotor 18 may comprise separate rotor bodies fixed together, wherein the drive rotor portion 22 and the sensor rotor portion 24 are defined by separate rotor bodies. In this case, the sensor rotor portion 24 is preferably a separate rotor body, which is attached, for example, to the lateral end surface 27 of the drive rotor portion 22 by adhesive bonding.

[0029] like Figure 2As shown, the drive rotor portion 22 is provided with permanent magnetic drive ring sectors 28. The permanent magnetic drive ring sectors 28 are alternately magnetized along the circumference of the drive rotor portion 22. The magnetic north pole is marked with the letter N, and the magnetic south pole with the letter S. The permanent magnetic drive ring sectors 28 substantially cover the entire circumference of the drive rotor portion 22. However, due to the manufacturing process, inconspicuous non-magnetic regions may exist between the permanent magnetic drive ring sectors 28. Because the drive rotor portion 22 is axially located within the axial range A of the motor stator 12, the permanent magnetic drive ring sectors 28 interact with the magnetic field generated by the electromagnetic motor stator 12 to drive the motor rotor 18.

[0030] like Figure 3 As shown, the sensor rotor portion 24 is provided with permanent magnetic sensor ring sectors 30 and non-magnetic sensor ring sectors 32, wherein the non-magnetic sensor ring sectors 32 are located circumferentially between the permanent magnetic sensor ring sectors 30. In this embodiment of the invention, the non-magnetic sensor ring sectors 32 are implemented by an axial recess within the sensor rotor portion 24. Alternatively, the non-magnetic sensor ring sectors 32 may be provided by a solid material, wherein the magnetization level of the material is lower than the detection threshold level of the magnetic field sensor 38. Because the sensor rotor portion 24 is axially located outside the axial range of the motor stator 12, the non-magnetic sensor ring sectors 32 do not significantly affect the drive of the motor rotor 18 caused by the motor stator 12.

[0031] The drive rotor portion 22 and the sensor rotor portion 24 are configured such that the circumferential range of each permanent magnetic drive ring sector 28 of the drive rotor portion 22 corresponds to the circumferential range of a pair of sensor sectors 34, wherein the pair of sensor sectors 34 includes a permanent magnetic sensor ring sector 30 and a non-magnetic sensor ring sector 32. The magnetic polarization of each permanent magnetic drive ring sector 28 is equal to the magnetic polarization of the corresponding permanent magnetic sensor ring sector 30. The circumferential starting position of each permanent magnetic drive ring sector 28 is equal to the circumferential starting position of the corresponding permanent magnetic sensor ring sector 30.

[0032] The electric motor 10 also includes motor electronics 36 and a magnetic field sensor 38. Motor electronics 36 is electrically connected to the stator coil 16 to supply drive current to the stator coil. Motor electronics 36 commutates the drive current based on a trigger signal provided by the magnetic field sensor 38.

[0033] The magnetic field sensor 38 is a latching Hall effect sensor and is arranged radially inside and adjacent to the sensor rotor portion 24. Therefore, the magnetic field sensor 38 detects the sensor magnetic field generated by the permanent magnetic sensor ring sector 30 of the sensor rotor portion 24. The magnetic field sensor 38 provides a substantially digital trigger signal, wherein the trigger signal has a first signal level if a magnetic north pole (N) is detected, and a second trigger level if a magnetic south pole (S) is detected. As a result, the trigger signal can only be switched for transitions from the non-magnetic sensor ring sector 32 to the permanent magnetic sensor ring sector 30, and not for any transitions from the permanent magnetic sensor ring sector 30 to the non-magnetic sensor ring sector 32. Therefore, if the motor rotor 18 moves slightly back and forth, the trigger signal can only switch once, and cannot switch continuously between two trigger signal levels. This avoids oscillation of the motor rotor 18, thus allowing reliable drive of the motor rotor 18. The magnetic field sensor 38 and the sensor rotor section 24 are arranged such that for each magnetic rotor stationary position of the motor rotor 18, there is a permanent magnet sensor ring sector 30 within the detection range of the magnetic field sensor 38.

[0034] List of reference numerals

[0035] 8. Fluid pumps

[0036] 10 Electric motors

[0037] 12 Motor stator

[0038] 14 Stator body

[0039] 14 Stator body

[0040] 16 stator coils

[0041] 18 Motor rotor

[0042] 20 Pump impeller

[0043] 22 Drive rotor section

[0044] 24 Sensor Rotor Section

[0045] 26 Axial motor rotor end

[0046] 27. End face of the drive rotor section

[0047] 28 Permanent Magnet Driven Ring Sector

[0048] 30 Permanent Magnet Sensor Ring Sector

[0049] 32 Non-magnetic sensor ring sector

[0050] 34 sensor sector pairs

[0051] 36 Motor Electronic Components

[0052] 38 Magnetic field sensor

[0053] Axial range

[0054] N magnetic north pole

[0055] R Rotation axis

[0056] S magnetic south pole

Claims

1. An electronically commutated electric motor (10), comprising: - A static motor stator (12) with a ferromagnetic stator body (14) and at least one stator coil (16). - A motor rotor (18) that is capable of rotation and is permanently magnetized. - A static magnetic field sensor (38) for detecting the rotor magnetic field and providing a corresponding trigger signal, and - Motor electronics (36) for supplying power to at least one of the stator coils (16) based on a trigger signal. -The motor rotor (18) is provided with two axially adjacent axial rotor portions (22, 24), namely: • The drive rotor portion (22) arranged within the axial range (A) of the stator body (14), and • A sensor rotor portion (24) is disposed at the axial end (26) of the motor rotor (18) facing the magnetic field sensor. •The drive rotor section (22) and the sensor rotor section (24) are provided with different circumferential magnetization modes. •The drive rotor section (22) is provided with a permanent magnetic drive ring sector (28) that is alternately magnetized (N, S) along the rotor circumference. •The sensor rotor part (24) is provided with a permanent magnetic sensor ring sector (30) that is alternately magnetized (N, S) along the circumferential direction of the rotor and a non-magnetic sensor ring sector (32) located between the permanent magnetic sensor ring sector (30) in the circumferential direction. • In this context, the circumferential range of each permanent magnetic drive ring sector (28) of the drive rotor section (22) corresponds to the circumferential range of the sensor sector pair (34) of the sensor rotor section, wherein the sensor sector pair (34) includes a permanent magnetic sensor ring sector (30) and a non-magnetic sensor ring sector (32), and - Wherein, the magnetic field sensor (38) is a latching magnetic field sensor (38) positioned adjacent to the sensor rotor portion (24), and -The circumferential starting position of each permanent magnet drive ring sector (28) is approximately equal to the circumferential starting position of the corresponding permanent magnet sensor ring sector (30).

2. The electronically commutated electric motor (10) of claim 1, wherein, The drive rotor portion (22) of the motor rotor (18) radially surrounds the motor stator (12).

3. The electronically commutated electric motor (10) of claim 1, wherein, The circumferential range of the non-magnetic sensor ring sector (32) is greater than the circumferential range of the permanent magnetic sensor ring sector (30).

4. The electronically commutated electric motor (10) according to claim 1, wherein, The motor rotor (18) is a single block.

5. The electronically commutated electric motor (10) according to claim 1, wherein, The drive rotor section (22) and the sensor rotor section (24) are defined by separate rotor bodies fixed together.

6. The electronically commutated electric motor (10) according to claim 1, wherein, The non-magnetic sensor ring sector (32) is provided by the axial rotor recess.

7. The electronically commutated electric motor (10) according to claim 1, wherein, The magnetic field sensor (38) and the sensor rotor portion (24) of the motor rotor (18) are configured such that for each magnetic rotor stationary position, a permanent magnet sensor ring sector (30) is located within the detection range of the magnetic field sensor (38).

8. The electronically commutated electric motor (10) according to claim 1, wherein, The magnetic field sensor (38) is arranged radially inside the sensor rotor portion (24) and is radially adjacent to the sensor rotor portion (24).

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