Motor and electric pump

Abstract

Motor in which a drive current supplied to a winding (12) is controlled according to a rotational position of a rotor (20) which is detected on the basis of a waveform of an induced voltage between phases (U, V, W), wherein the motor has: a stand (10) with 3 × n teeth (11a), wherein the teeth (11a) are arranged in a circumferential direction and extend inwards in a radial direction, and grooves are formed between adjacent teeth (11a) in the circumferential direction; windings (12) which are assigned to three phases (U, V, W) such that each tooth (11a) is wound with one of the windings which is assigned to one of the three phases (U, V, W), and a rotor (20) with a rotor core (22) arranged in the radial direction inwards from the stator (10), a number n of magnets (23) arranged in the circumferential direction of the rotor core (22), and a number n of salient poles (22b) arranged in the rotor core (22), wherein the magnets (23) function as one of the magnetic poles, the salient poles (22b) function as the other of the magnetic poles (23), and Each salient pole (22b) is spaced apart in the circumferential direction by a gap (K) from the respective adjacent magnets (23), wherein an angular distance between adjacent magnets (23) essentially corresponds to the angular distance between the teeth (11a) which are wound with the turns (12), which are assigned to the same phase of the three phases (U, V, W), when the magnets (23) are opposite the teeth (11a), which are assigned to one of the three phases (U, V, W), each of the limb poles (22b) is opposite a circumferential midpoint between adjacent teeth (11a) that are assigned to the other two of the three phases (U, V, W), n is a natural number, the magnets (23) and the gap (K) are arranged in the radial direction from an outer contour of the rotor core (22) inwards, and an electric angle between two ends of each magnet (23) is set such that it is smaller than an electric angle between two ends of each salient pole (22b), each of the magnets (23) has a circumferential width that is less than or equal to a circumferential width at a distal end of each of the teeth (11a), and if the electric angle between two ends of each magnet (23) is represented by A and the electric angle between two ends of each salient pole (22b) is represented by B, the two electric angles are set such that 0.92 ≤ A / (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 ) ≤ 1.08 is fulfilled.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a motor and an electric pump using a consequent pole type rotor.

[0002] Japanese Patent Laid-Open No. JP 2010-263763 A describes a motor using a so-called consequent-pole type rotor. The motor has a stator with twelve slots and a rotor with eight magnetic poles. The rotor has a rotor core with four salient poles and four magnets (neodymium magnets) embedded in the rotor core in the circumferential direction of the rotor core. The four magnets function as one of the magnetic poles. The four salient poles are arranged between adjacent ones of the four magnets and each function as the other magnetic pole. A motor using such a consequent-pole type rotor, or a drive device for an electric pump or the like using such a motor, achieves higher output with a smaller and lighter structure and reduces costs.

[0003] Another type of motor uses a sensorless drive method. The motor controls the drive current supplied to a stator based on an induced voltage waveform, that is, a control signal with the induced voltage waveform, without using a rotation sensor. However, in a motor using a consequent-pole type rotor, in which magnets are embedded in the rotor core, a stable induced voltage cannot be obtained when the rotor starts rotating. This means that a certain period of time is required for the induced voltage to stabilize. Thus, time is required before execution of control based on the induced voltage can begin.

[0004] Furthermore, the induced voltage waveform of a motor using a consequent-pole type rotor is uneven compared to a conventional motor that has no salient poles and has eight magnets constituting eight magnetic poles. Therefore, it is difficult to apply the sensorless control method to a motor using a consequent-pole type rotor.

[0005] Specifically, for a normal motor, the distortion factor is 1.3% with respect to a sine wave and is low in the induced voltage waveform for each phase. This allows for a satisfactory application of the sensorless control method. In contrast, Fig. 6 shows the waveform of the induced voltage for each phase (U, V, and W phases) of a motor using a consequent-pole type rotor, in which the electrical angle between the two ends of one magnetic pole (magnetic pole of the magnet) and the other magnetic pole (magnetic pole of the salient pole) is the same (e.g., 27° as a mechanical angle). In such a motor, as shown in Fig. 6, the distortion factor with respect to a sine wave is 21.1%. Furthermore, in a star-connected motor using a similar consequent-pole type rotor, the waveform of the induced voltage between terminals (UV, VW, and WU) becomes uneven, as shown in Fig. 7. In a delta-connected motor using a similar consequent-pole type rotor, the waveform of the induced voltage between terminals (UV, VW and WU) becomes uneven, as shown in Fig. 8. It is assumed that the waveforms are as shown in the Fig. 7 and Fig. 8 become uneven because the magnetic poles of the salient poles do not produce a strong magnetic flux like the magnetic poles of magnets.

[0006] Furthermore, for example, the waveforms of the Fig. 6 to 8, the peaks deviate from normal positions. More precisely, the peak interval is approximately 110°, where it should be 90°. Furthermore, the waveform is asymmetrical with respect to each peak. It is difficult to use an induced voltage with such an uneven waveform as a control signal. Therefore, it is difficult to apply the sensorless control method to control a consequent-pole type rotor.

[0007] Further prior art is cited in US 5 682 073 A, JP H04- 71 342 A and JP 2005- 269 840 A. SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide a motor and an electric pump that enable the satisfactory application of a sensorless drive method. One aspect of the present invention is a motor in which the drive current supplied to a winding is controlled according to a rotational position of a rotor detected based on a waveform of an induced voltage between phases. The motor includes a stator and a rotor. The stator has 3xn teeth and windings for three phases sequentially wound around the teeth. The teeth are arranged in a circumferential direction and extend inward in a radial direction, and grooves are formed between each adjacent tooth in the circumferential direction.The rotor has a rotor core arranged inward in the radial direction from the stator, an n number of magnets arranged in the circumferential direction of the rotor core, and an n number of salient poles arranged in the rotor core. The magnets function as one of the magnetic poles, the salient poles function as the other magnetic pole, and each salient pole is spaced from the adjacent magnets in the circumferential direction by a gap. Here, n is a natural number. The magnets and the gap are arranged inward in the radial direction from an outer contour of the rotor core. An electrical angle between two ends of each magnet is set to be smaller than an electrical angle between two ends of each salient pole.

[0009] A further embodiment of the present invention is an electric pump comprising the motor of the first embodiment, a housing for accommodating the motor, and an impeller rotating in the housing as a unit with the rotor.

[0010] Further aspects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, which illustrate the basic ideas of the invention by way of example. BRIEF DESCRIPTION OF THE DRAWING

[0011] A fuller understanding of the invention, together with its objects and advantages, may be obtained by reference to the following description of the presently preferred embodiments taken in conjunction with the accompanying drawings, in which: Fig. 1A is a plan view of an engine according to an embodiment of the present invention; Fig. 1B is a partially enlarged plan view of a rotor of Fig. 1A; Fig. 2 a circuit diagram of a control device for the motor of Fig. 1A; Fig. 3 is a graphical representation of the relationship between the electrical angle between the two ends of one magnetic pole and the electrical angle between the two ends of the other magnetic pole in a motor with a uniform waveform; Fig. 4 a diagram of the electrical angle and the waveform of the induced voltage for the motor of Fig. 1A; Fig. 5 a diagram of the electrical angle and the waveform of the induced voltage for the motor of Fig. 1A; Fig. Figure 6 is a diagram of the electrical angle and induced voltage waveform for a prior art motor; Fig. Figure 7 is an electrical angle and induced voltage waveform diagram for a prior art motor; Fig. Figure 8 is a diagram of the electrical angle and the waveform of the induced voltage for a prior art motor; and Fig. 9 is a schematic cross-sectional view of an electric pump using the motor of Fig. 1A used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An embodiment of the present invention will now be described with reference to the Fig. 1 to 5 described.

[0013] With reference to Fig. 1A, an inner rotor type brushless motor M includes a stator 10. The stator 10 includes a stator core 11 and windings 12. The stator core 11 has twelve teeth 11a arranged in the circumferential direction of the stator 10. The windings 12 for three phases (U, V, and W phases) are wound sequentially around the teeth 11a. Thus, the stator 10 is a twelve-slot stator.

[0014] The motor M further comprises a rotor 20 arranged on the inside of the stator 10. As shown in the Fig. 1A and Fig. As shown in Figure 1B, the rotor 20 includes a rotating shaft 21 and an annular rotor core 22 mounted on the rotating shaft 21. The rotor core 22 has a peripheral portion near an outer peripheral surface. The peripheral portion has four magnet receiving holes 22a arranged at 90° intervals in the circumferential direction. Four N-pole magnets 23 are respectively arranged in the four magnet receiving holes 22a.

[0015] The circumferential portion of the rotor core 22 further includes a plurality of salient poles 22b. Each salient pole 22b is spaced apart from the magnets adjacent in the circumferential direction by a gap K. Each gap K forms part of a magnet receiving opening 22a. The two gaps K arranged on opposite sides of each salient pole 22b have the same (fixed) area. More specifically, the two gaps K on opposite sides of each magnet 23 have a symmetrical shape in the circumferential direction. That is, the two gaps K are mirror-symmetrical with respect to a line extending in the radial direction through the center of the magnet 23. Each gap K is formed such that its cross-sectional area in the axial direction is constant over the entire gap K. The magnets 23 and the gaps K are arranged inward in the radial direction from the outer contour (outer circumference) of the rotor core 22.The term “arranged inward in the radial direction from the outer contour of the rotor core 22” refers to a state of being arranged inward in the radial direction from an outermost position of the rotor core 22 in the radial direction.

[0016] The centers of the magnets 23 and the salient poles 22b are arranged alternately at equal angular intervals of 45°. Thus, the rotor 20 is a so-called consequent-pole type rotor with eight magnetic poles: the magnets 23, each acting as an N pole serving as one of the magnetic poles, and the salient poles 22b, each acting as an S pole serving as the other of the magnetic poles.

[0017] With reference to Fig. 1B, the rotor 20 of the present embodiment is configured such that the electrical angle (A) between the two ends of one of the magnetic poles (the magnetic pole of each magnet 23) is smaller than the electrical angle (B) between the two ends of the other of the magnetic poles (magnetic pole of each salient pole 22b).

[0018] If the electrical angle between the two ends of one of the magnetic poles (the magnetic pole of each magnet 23) is represented by A and the electrical angle between the two ends of the other of the magnetic poles (magnetic pole of each salient pole 22b) is represented by B, the rotor 20 is set to be A = (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 ) ±8 % is met.

[0019] More specifically, A is set as 108° (mechanical angle of 27°), and B is set as 132° (mechanical angle of 33°).

[0020] In other words, A is set so that (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 ) × 0.92 ≤ A ≤ (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 ) × 1.08 is met.

[0021] That is, the rotor 20 of the present embodiment is set so that 0.92 ≤ A / (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 ) ≤ 1.08 is met.

[0022] The above equations are based on data obtained from experimental results. In detail, an approximate equation is derived from a curve X of Fig. 3, which is obtained by subtracting angles when the waveform is as shown in the Fig. 4 and Fig. 5. A width (±8%) is then added to the approximate equation. The width (±8%) is a value at which the waveform is uniform (waveform equal to or better than) relative to the waveform of an induced voltage for a normal motor—that is, a motor without salient poles in which all magnetic poles are formed by all magnets—when added to the approximate equation.

[0023] If A = 6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 is satisfied, ie when the electrical angles A and B in the curve X of Fig. 3, then the waveform is as shown in the Fig. 4 and Fig. 5. When the electrical angles A and B are within the range of ±8%, the waveform is uniform relative to the waveform of an induced voltage in a normal motor. More precisely, the waveform is the same as or better than the waveform of the induced voltage in a normal motor. That is, in the range between the dotted lines in Fig. 3, the distortion factor is 1.3% with respect to a sine wave of the induced voltage of a motor which has no salient poles and in which all magnetic poles are formed by means of all magnets. Fig. 4 shows that the waveform of the induced voltage of each phase (U, V and W phase) of the motor shown in curve X of Fig. 3 is included, to A = 6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 is set. In Fig. 4 the distortion factor is 0.9% based on the sine wave of the normal motor. Fig. Figure 5 shows the waveform of the induced voltage between terminals (UV, VW and WU) of the motor (star and delta connection), which is shown in curve X of Fig. 3 and set to A = 6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 is set.

[0024] As in Fig. As shown in Figure 2, terminals 12u, 12v, and 12w of the windings 12 in the motor M are connected to a control device 51, and the drive current supplied to the windings 12 of the stator 10 is controlled based on the waveform of the induced voltage as a control signal. In this way, the motor M employs a sensorless drive method. In detail and with reference to Fig. 2, the control device 51 of the present embodiment includes a rotational position detection circuit 52 connected to the terminals 12u, 12v, and 12w of the windings 12. The rotational position detection circuit 52 detects the induced voltage induced to the winding 12 for each phase, generates a rotational position pulse signal corresponding to the rotational position of the rotor 20 based on the waveform of the induced voltage between the phases, and outputs the rotational position pulse signal to a microcomputer 53. The microcomputer 53 generates a commutation signal based on the received rotational position pulse signal and outputs the commutation signal to an inverter circuit 55 via a driver circuit 54. Switching control is performed on switching elements 55a to 55f by the commutation signal received from the inverter circuit 55.In addition, the inverter circuit 55 performs a commutation operation which sequentially supplies the winding 12 of each phase with drive current.

[0025] The operation of motor M is now described.

[0026] When the rotor 20 starts to rotate, an induced voltage corresponding to the rotation is generated. With reference to Fig. 5, the control device 51 generates a rotational position pulse signal based on the waveform of the induced voltage between terminals (UV, VW, and WU) as a control signal, using the waveform of the induced voltage starting from 0 V. A commutation signal is generated based on the rotational position pulse signal, and the drive current supplied to the windings 12 is switched. The induced voltage generated in this state is not uneven. Therefore, the rotor 20 undergoes satisfactory rotation control.

[0027] The above embodiment has the advantages described below. (1) The number of teeth 11a is three times greater than the number of magnets 23. Thus, the magnets 23 always face the teeth 11a for the same one of the three phases (U, V, or W phase). In addition, the electrical angle between one of the magnetic poles (magnets 23) is smaller than the electrical angle between the two ends of the other magnetic poles (salient poles 22b). Thus, even if the magnets 23 and the gaps K are arranged inward from the outer contour of the rotor core 22, the attractive force of the magnets 23 acting on the teeth 11a is concentrated within a small area. This easily stops the rotor in a state where the magnets 23 and the teeth 11a face each other, and increases the probability of starting rotation from the same position.Thus, a stable induced voltage is obtained within a short period of time, and the time until control using the induced voltage starts can be shortened on average. (2) The electrical angle A between the two ends of one of the magnetic poles (the magnetic poles of the magnets 23) and the electrical angle B between the two ends of the other of the magnetic poles (the magnetic poles of the salient poles 22b) are set so that A = (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2) ±8% is satisfied. Therefore, experimental results stabilize the induced voltage waveform. More specifically, with the experimental result, the induced voltage waveform of the motor M using the consequent-pole type rotor 20 is uniform with respect to the induced voltage waveform of a motor that does not have the salient poles 22b and forms all magnetic poles using all magnets. That is, the waveform is the same as or better than the induced voltage waveform of the ordinary motor. As a result, with the motor M using the consequent-pole type rotor 20, the sensorless drive method can be satisfactorily used, that is, with a speed characteristic similar to that of an ordinary motor.

[0028] It will be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. In particular, it should be understood that the present invention may be embodied in the following forms.

[0029] Although not specifically mentioned in the foregoing description, the motor M of the above embodiment can be used as any driving device. For example, the motor M as shown in Fig.9 can be applied to an electric pump 61 that uses a motor. In detail, the electric pump 61 is provided with a housing 65 including a motor housing 62, a pump housing 63, and an end housing 64. The motor housing 62 is cylindrical and has a closed bottom. The pump housing 63 is fixed to the open end of the motor housing 62 and has a suction port 63a and a discharge port 63b. The end housing 64 is fixed to the outer side of the bottom of the motor housing 62. The electric pump 61 includes the stator 10, the rotor 20, a shaft 66, and an impeller 67. The stator 10 is held in a cylindrical portion 62a of the motor housing 62. The shaft 66 is fixed to the inner side of the bottom of the motor housing 62. The rotor 20 is rotatably supported by the shaft 66. The impeller 67 rotates as a unit with the rotor 20.Furthermore, the electric pump 61 includes a control circuit substrate 68 constituting the control device 51 of the above embodiment, which is housed in a receiving compartment surrounded by the outer surface of the bottom of the motor housing 62 and the end housing 64. The electric pump 61 can satisfactorily employ the sensorless drive method, and the electric pump 61 can be miniaturized.

[0030] In the above embodiment, the motor M has the twelve-slot stator 10 with the twelve teeth 11a and the eight-magnetic pole rotor 20 with the four magnets 23. The structure of the motor M can be changed as long as the stator has 3xn (where n is a natural number) slots with 3xn teeth and the rotor has 2xn magnetic poles with n magnets.

[0031] For example, the motor M may have an eighteen-slot stator with eighteen teeth and a twelve-pole rotor with six magnets. In this case, it is also preferable that A = (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 ) ±8% is met.

[0032] The above embodiment is set to be A = (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B 2 + 1.14 × 10 2 ) ±8%. Instead, for example, A = (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 ) ±4% must be met.

[0033] This achieves an even more stable waveform for the induced voltage and allows the application of the sensorless drive method in a more satisfactory manner, thereby increasing the efficiency.

[0034] Furthermore, A = (6.10 × 10 -3 × B 2- 8.69 × 10 -1 × B + 1.14 × 10 2 ) ±8% may not be satisfied, and the electrical angle (A) between the two ends of one of the magnetic poles (the magnetic poles of the magnets 23) may be smaller than the electrical angle (B) between the two ends of the other of the magnetic poles (the magnetic poles of the salient poles 22b). This also achieves the advantage (1) of the above embodiment.

[0035] The present examples and embodiments should be considered as illustrative and not restrictive, and the invention should not be limited to the details given above, but may be modified within the scope and equivalence of the appended claims.

Claims

[1] A motor in which a drive current supplied to a winding (12) is controlled according to a rotational position of a rotor (20) detected based on a waveform of an induced voltage between phases (U, V, W), the motor comprising: a stator (10) with 3 × n teeth (11a), wherein the teeth (11a) are arranged in a circumferential direction and extend inwardly in a radial direction, and grooves are formed between respective adjacent teeth (11a) in the circumferential direction; Windings (12) associated with three phases (U, V, W) such that each tooth (11a) is wound with one of the windings associated with one of the three phases (U, V, W), and a rotor (20) having a rotor core (22) arranged inwardly in the radial direction from the stator (10), a number n of magnets (23) arranged in the circumferential direction of the rotor core (22), and a number n of salient poles (22b) arranged in the rotor core (22), wherein the magnets (23) function as one of the magnetic poles, the salient poles (22b) function as the other of the magnetic poles (23), and each salient pole (22b) is spaced in the circumferential direction by a gap (K) from the respectively adjacent magnets (23), wherein an angular distance between adjacent magnets (23) substantially corresponds to the angular distance between the teeth (11a) wound with the windings (12), which are assigned to the same phase of the three phases (U, V, W), when the magnets (23) are opposite the teeth (11a), which are assigned to one of the three phases (U, V, W), each of the salient poles (22b) is opposite a circumferential center between adjacent teeth (11a) which are assigned to the other two of the three phases (U, V, W), n is a natural number, the magnets (23) and the gap (K) are arranged in the radial direction from an outer contour of the rotor core (22) inwards, and an electrical angle between two ends of each magnet (23) is set to be smaller than an electrical angle between two ends of each salient pole (22b), each of the magnets (23) has a circumferential width that is less than or equal to a circumferential width at a distal end of each of the teeth (11a), and when the electrical angle between two ends of each magnet (23) is represented by A and the electrical angle between two ends of each salient pole (22b) is represented by B, the two electrical angles are set so that 0.92 ≤ A / (6.10 × 10 -3 × B 2 - 8.69 × 10 -1 × B + 1.14 × 10 2 ) ≤ 1.08 is met. [2] Engine according to claim 1, characterized by , that the number of grooves is twelve, the total number of magnetic poles is eight, a mechanical angle between the two ends of each magnet (23) is set to 27°, and a mechanical angle between the two ends of each salient pole (22b) is set to 33°. [3] Electric pump, characterized by : the engine according to claim 1 or 2; a housing (65) for accommodating the motor; and an impeller (67) rotating in the housing (65) as a unit with the rotor (20).

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