Patent Application
20160294235
The present invention relates to a permanent magnet type motor equipped with a rotor having a permanent magnet that does not contain a heavy rare earth element such as dysprosium (Dy), terbium (Tb), or the like.
The structure of a permanent magnet type motor has been created in the past; and as a permanent magnet of a rotor, a sintered magnet different in distribution of a heavy rare earth element such as Dy or the like is disclosed in Patent Document 1 and Patent Document 2. Patent Document 1 is the sintered magnet having structure in which areas different in a rate of content of the heavy rare earth element such as Dy or the like are integrally coupled. Furthermore, Patent Document 2 is structure having a distribution in a rate of content in the sintered magnet by diffusing Dy.
Patent Document 1: Japanese Unexamined Patent Publication No. S62-37907
Like a motor in which magnets are arranged on an outer circumference surface portion of the rotor, magnetic coercive force is increased to be difficult to be demagnetized by forming a portion having a high rate of content of Dy on both end portions of the magnet that are easy to be demagnetized; however, a problem exists in that the heavy rare earth element that is rarer than neodymium is added and accordingly a magnet cost increases.
The present invention has been made to solve the foregoing problem, and an object of the present invention is to obtain a permanent magnet type motor in which the amount of usage of a magnet effective for torque is found out in a magnet in which a heavy rare earth element such as Dy that improves magnet coercive force is not added and thereby being capable of achieving a reduction in motor cost and avoiding a risk of cost fluctuations of the heavy rare earth element such as Dy.
According to the present invention, there is provided a permanent magnet type motor including: a stator composed of armature windings and a stator core having a slot that incorporates each of the armature windings; and a rotor composed of a rotor core provided on the inner circumferential side of the stator via an air gap and configured by laminating electromagnetic steel sheets, a plurality of permanent magnets fixed at intervals on a circumferential surface portion of the rotor core, and a shaft that passes through along a center axis line of the rotor core, wherein when the number of poles of the permanent magnets is set to P and the number of the slots is set to N, the relationship of P:N=2n:12n is established, where n is an integer equal to or more than 2; an air gap length between the inner circumference of the stator core and the outer circumference of the permanent magnets is less than or equal to 1.0 mm; the permanent magnet does not contain a heavy rare earth element and is embedded in the rotor core except for a curve portion of an outer circumference portion; and a circumferential center thickness of the permanent magnet is 2.4 to 4.2 mm.
The permanent magnet type motor according to the present invention can avoid from rapidly decreasing torque due to demagnetization of the magnet when a circumferential center thickness of the permanent magnet is equal to or more than 2.4 mm, even when the heavy rare earth element such as Dy that improves magnet coercive force is not contained. Furthermore, the permanent magnet that does not contain the heavy rare earth element becomes thicker in magnet thickness than a conventional magnet that contains the heavy rare earth element and accordingly it is difficult to increase torque for the amount of usage of the magnet at a constant air gap length; however, the torque can be increased by effectively utilizing the amount of usage of the magnet at a thickness of less than or equal to 4.2 mm. Therefore, the heavy rare earth element that is high cost is not used and thus the permanent magnet type motor capable of achieving a reduction in motor cost and avoiding a risk of cost fluctuations can be obtained.
Objects, features, aspects, and advantageous effects other than the above mention of the present invention will become more apparent from the following detailed description of the present invention which refers to the accompanying drawings.
Hereinafter, respective embodiments of a permanent magnet type motor of the present invention will be described with reference to drawings. Incidentally, the same reference numerals as those shown in the respective drawings represent the same or corresponding elements.
On the other hand, automobile information such as vehicle speed is converted to an electrical signal and is transmitted to the ECU 4 via a second connector 5. The ECU 4 calculates necessary assist torque from the automobile information such as the torque of the steering and the vehicle speed and supplies a current to the motor 6 through an inverter. The motor 6 is arranged in a direction parallel to a moving direction shown by an arrow A of a rack shaft in a housing 7. Furthermore, power source supply to the ECU 4 is performed from a battery or an alternator via a power source connector 8. Torque generated by the motor 6 is decelerated by a gear box 9 in which a belt (not shown in the drawing) and a ball screw (not shown in the drawing) are incorporated and generates propulsive force that moves the rack shaft (not shown in the drawing) placed inside the housing 7 in the direction of the arrow A to assist steering force of the driver.
This allows a tie-rod 10 to move and thus tires can be turned to circle the vehicle. As a result of being assisted by the torque of the motor 6, the driver can circle the vehicle with less steering force. Incidentally, a rack boot 11 is provided so that a foreign substance does not enter into the electric power steering apparatus. Furthermore, the motor 6 and the ECU 4 are integrated to constitute an electric drive apparatus 100.
A pulley 20 is press-fitted at one end portion of the shaft 19, that is, on the output axis side; and the pulley 20 is operable to transfer driving force to the belt of the electric power steering apparatus. A permanent magnet for a sensor 21 is provided on the other end portion of the shaft 19. A rotor core 22 is press-fitted onto the shaft 19 and a permanent magnet 23 is fixed to the rotor core 22. A first connector 3 that receives a signal from the torque sensor 2, a second connector 5 that receives the automobile information such as the vehicle speed, and the power source connector 8 for the power source supply are attached to the ECU 4.
The ECU 4 includes the inverter circuit that drives the motor 6; and the inverter circuit has a switching element 24 such as a metal oxide semiconductor field effect transistor (MOS-FET). As the switching element 24, there is conceivable, for example, a configuration in which a bare chip is mounted on a direct bonded copper (DBC) substrate and a configuration in which a bare chip is molded with resin to form a module. Current that drives the motor 6 flows in the switching element 24, thereby generating heat. Consequently, the switching element 24 is structured to dissipate the heat by being brought into contact with a heat sink 25 via adhesive, an insulation sheet, or the like. The inverter circuit includes a smoothing capacitor, a coil for eliminating noise, a power source relay, busbars that electrically connect those components, and the like, in addition to the switching element 24; however, such components are omitted in
The busbars are integrally formed with resin to form an intermediate member 26. Furthermore, a control substrate 27 is provided next to the intermediate member 26. The control substrate 27 sends a control signal to the switching element 24 that adequately drives the motor 6 on the basis of the information received from the first connector 3 and the second connector 5. The control signal is transmitted by a connection member 28 that electrically connects between the control substrate 27 and the switching element 24. The connection member 28 is fixed by wire-bonding, press-fitting, soldering, or the like. The inverter circuit and the control substrate 27 are covered by a case 29. The case 29 may be made of resin, may also be made of metal such as aluminum, or may also be made of one in which resin and metal such as aluminum are combined. The control substrate 27 is arranged so as to be along a plane perpendicular to the shaft 19 of the motor 6.
A sensor portion 30 is arranged on the motor 6 side of the heat sink 25. The sensor portion 30 has a magnetic sensor 31, a substrate 32, the connection member 28, and a supporting member 33; and the substrate 32 mounted with the magnetic sensor 31 is fixed to the heat sink 25 by screws (not shown in the drawing). The magnetic sensor 31 is arranged at a position coaxially with and corresponding to the permanent magnet for the sensor 21. The magnetic sensor 31 detects a magnetic field generated by the permanent magnet for the sensor 21 and detects a rotational angle of a rotor 34 of the motor 6 by knowing the direction of the magnetic field, the rotor 34 being composed of the rotor core 22 and the permanent magnet 23. The ECU 4 supplies an adequate drive current to the motor 6 according to the rotational angle.
Further, the connection member 28 is supported by the supporting member 33 and electrically connects the substrate 32 of the sensor portion 30 and the control substrate 27. This connection may be made by press-fitting or soldering. Incidentally, the connection member 28 needs to pass through the heat sink 25 and the intermediate member 26; and thus, a hole portion (not shown in the drawing) through which the connection member 28 passes is formed in the heat sink 25 and the intermediate member 26. Further, although not shown in the drawing, the intermediate member 26 is configured such that a guide capable of positioning the connection member 28 is provided.
In
As for the ECU 4, the first inverter 42 and the second inverter 43 are depicted and other configuration is omitted. A three phase current is supplied from the inverters 42,43 to two armature windings 40,41, respectively. A direct current (DC) power source is supplied from a power source 44 such as a battery to the ECU 4 to which power source relays 45,46 are connected via a coil for eliminating noise 68.
A first capacitor 47 and a second capacitor 48 are smoothing capacitors. In
Further, one shunt resistor is connected to the ground (GND) side for each of the lower three MOS-FETs (the second MOS-FET 50, the fourth MOS-FET 52, and the sixth MOS-FET 54), the shunt resistors being regarded as a first shunt 55, a second shunt 56, and a third shunt 57, respectively. These shunts 55 to 57 are used for detecting current values. Incidentally, three shunts 55 to 57 are exemplified; however two shunts or one shunt may also be permissible because current detection can be made and such a configuration may also be permissible. As shown in
The second inverter 43 is also a similar configuration. In the second inverter 43, the first MOS-FET 61 and the second MOS-FET 62 are connected in series; the third MOS-FET 63 and the fourth MOS-FET 64 are connected in series; and the fifth MOS-FET 65 and the sixth MOS-FET 66 are connected in series. Further, these three sets of the MOS-FETs (61,62; 63,64; and 65,66) are connected in parallel. Further, one shunt resistor is connected to the GND side for each of the lower three MOS-FETs (the second MOS-FET 62, the fourth MOS-FET 64, and the sixth MOS-FET 66), the shunt resistors being regarded as a first shunt 58, a second shunt 59, and a third shunt 60, respectively. These shunts 58 to 60 are used for detecting current values.
As shown in
Two first and second inverters 42,43 perform switching by signals sent from a control circuit to the MOS-FETs 49 to 54 and 61 to 66 according to rotational angles detected by a rotation angle sensor 67 (corresponding to the magnetic sensor 31 of
A total of forty-eight teeth 72 are provided; and therefore, the number of the slots 73 is also forty-eight. Four coils of the armature winding 40 or 41 are incorporated in each one of the slots 73. The first armature winding 40 is composed of three phases of the U1-phase, the V1-phase, and the W1-phase; and the second armature winding 41 is composed of three phases of the U2-phase, the V2-phase, and the W2-phase. As shown in
In this regard, however, the first armature winding 40 is arranged so that the U1 winding of the first slot 73 and the U1 winding of the seventh slot 73 are opposite to each other in the direction of currents; and the second armature winding 41 is also similarly arranged. More specifically, it is configured to be a distributed winding which is wound from the first slot 73 to the seventh slot 73. Then, the armature windings 40,41 straddle a total of six teeth 72. This corresponds to an electrical angle of 180 degrees and a short pitch winding coefficient becomes 1. Thus, a magnetic flux generated by the permanent magnets 23 can be effectively used, the motor 6 with a small size and high torque can be obtained, and the amount of the permanent magnets 23 can be reduced; and therefore, an effect exists in that a reduction in cost can be achieved as compared to a motor with a small winding coefficient.
The rotor 34 equipped with the permanent magnets 23 on a circumferential surface portion of the rotor core 22 is provided on the inner circumferential side of the stator 70. Eight permanent magnets 23 are circumferentially disposed at intervals to provide an 8-pole configuration. Polarities of the adjacent permanent magnets 23 are opposite to each other. Further, protrusions 74 are provided on the rotor core 22. An air gap 75 which is for reducing leakage flux is formed between the protrusion 74 and the permanent magnet 23. An effect exists in that the protrusion 74 reduces an air gap length of the motor 6 and inductance increases. This increases a salient-pole ratio; and thus an effect exists in that reluctance torque is easily generated and torque during high speed rotation can be improved.
It is effective to reduce the air gap length between the inner diameter of the stator core and the protrusion 74 as much as possible and to increase the protrusion 74; and therefore, an air gap length between the inner diameter of the stator core and each of circumferential both end portions of the permanent magnet 23 increases as compared to the air gap length between the inner diameter of the stator core and the protrusion 74. It is effective to set the height to be opposite to a protrusion of magnet positioning in a normal surface permanent magnet type motor and to provide the protrusions 74 over an axial direction because the volume of the protrusion can be increased. More specifically, except for curve portions of an outer circumference portion of the permanent magnet 23, a configuration is made such that the lateral sides of the permanent magnet 23 are also surrounded by the protrusions 74 and the permanent magnet 23 is embedded in the rotor core 22.
Hole portions 76 are formed in the rotor core 22 at equally spaced intervals along the circumferential direction. A reduction in weight and a reduction in inertia can be achieved by providing the hole portions 76. The rotor core 22 is configured by laminating electromagnetic steel sheets or the like and the electromagnetic steel sheets are coupled to each other by caulking portions 77. The shaft 19 passes through a center axis line of the rotor core 22. Referring to
When roundness of the inner circumference surface of the stator 70, deflection of the rotor 34, the metallic cylinder for magnet scattering prevention are taken into account, the air gap length of the motor 6 needs about 0.6 mm. Further, the processing dimension of the magnet is about ±0.05 mm; and thus, the air gap length is set to 0.65 mm. Furthermore, the torque ratio is a ratio when a magnet center thickness of 3.0 mm, which is the maximum in gradient of the following torque increase rate, is set to 100%. The torque rapidly decreases due to demagnetization when the magnet center thickness is less than or equal to 2.4 mm. Since the torque decreases in the case of less than or equal to 2.4 mm, a driver has to put forth large steering force; and thus such a magnet center thickness is not suitable as a motor use area.
A torque increase rate α is defined by α={T(t+Δt)−T(t)}/{T(t)−T(t−Δt)} from a torque T(t) at a certain magnet center thickness t, a torque T(t+Δt) in the case of increasing the thickness by at, and a torque T(t−Δt) in the case of decreasing the thickness by Δt. More specifically, α is an index that represents a torque gradient before and after the magnet center thickness; and when the torque rapidly decreases at a substantially constant gradient and/or when the torque hardly changes at a substantially constant gradient, α becomes a substantially constant value.
In the case of the former, that is, from
From the above, in order to sufficiently assist steering of the driver by the motor, t needs to be t≧2.4 mm; and in order to suppress motor cost by suppressing an increase of the amount of usage of the magnet, it is obvious that t≧4.2 mm is appropriate. The motor is suitable for applying to a motor with an outer diameter of 80 to 100 mmφ and an output of 400 to 900 W. Since a motor for an electric power steering apparatus (EPS) is attached to a steering gear, the motor comes into contact with the steering gear if the outer diameter is large; and thus, the size of the outer diameter is naturally limited.
Particularly, in the electric power steering apparatus for a vehicle, torque per unit of magnet weight is increased by taking into account the processing accuracy of the magnet, by setting the air gap length to the range of 0.6±0.05 mm, and by setting the magnet center thickness to near 3.0 mm that is a large change in the torque increase rate; and therefore, there can be achieved a small and lightweight motor effective for improvement in fuel consumption. Incidentally, in this embodiment, the description has been made on the case of a double three phase motor with 8 poles and 48 slots; however, it goes without saying that similar effects can be obtained even in the case of a single three phase motor with 2n poles and 12n slots (n is an integer equal to or more than 2).
In Embodiment 2, when a magnet center thickness is set to t and a circumferential length of a magnet (magnet width) is set to Wm, the relationship of t/Wm≧0.2 is held (t and Wm are shown in
In Embodiment 3, when a thickness of circumferential both end portions of a permanent magnet (both end portions of the magnet) is set to We and a height of a protrusion 74 is set to Wc, the relationship of 1.8 mm≦We<Wc is held. Incidentally, the protrusion height We is a height from the lower end of the protrusion 74 to the outer circumference surface of the protrusion (see
In the processing of the sintered magnet, the crack and/or the chip at a corner portion is prevented by providing the corner R. In a hog-backed-shaped magnet like
Particularly, in an electric power steering apparatus for a vehicle, steering feeling is improved by reducing the rotational pulsation and a motor that achieves comfortable driving can be provided by reducing noise and vibration. Furthermore, when the magnet is cracked and/or chipped in manufacturing processes such as magnet attachment, magnetization, and assembly, and the crack and/or the chip is remained in the motor, a rotor is locked to cause a danger. Particularly, the magnet after magnetization has magnetic force; and accordingly, it is difficult to remove the crack and/or the chip. However, the crack and/or the chip is difficult to occur by the configuration of 1.8 mm≦We and a removing process in the manufacturing processes can also be simplified.
Incidentally, the present invention can freely combine the respective embodiments and appropriately modify and/or omit the respective embodiments, within the scope of the present invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/061920 | 4/29/2014 | WO | 00 |
