Rotary electric machine with air gaps configured to cancel torque pulsations

A rotary electric machine includes a stator having stator windings; and a rotor rotatably disposed in the stator, said rotor having a rotor core provided with a plurality of magnets and a plurality of magnetic auxiliary salient poles formed between poles of the magnets. In this rotary electric machine: a magnetic air gap is provided in an axial direction of the rotor in a position shifted in a circumferential direction from a q axis passing through a center of the magnetic auxiliary salient pole within the magnetic auxiliary salient pole; and an amount of shifting the magnetic air gap from the q axis in the circumferential direction differs according to a position of the magnetic air gap in the axial direction so as to cancel torque pulsation in energization caused due to the magnetic air gap.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotary electric machine, and an electric vehicle including the same.

2. Description of the Related Art

Drive motors used for electric vehicles or hybrid vehicles are required to output large power. Thus, permanent magnet type motors using a sintered magnet made of rare earth material for holding large energy is generally used. An embedded magnet type motor among the permanent magnet type motors is used as the drive motor which can satisfy requirements, including low-speed and large-torque output, and a wide range of rotation speeds.

Torque pulsation of the motor causes noise or vibration. In particular, the torque pulsation on the low-speed side of the electric vehicle disadvantageously deteriorates ride quality. In a conventional motor, a permanent magnet is generally skewed so as to reduce cogging torque. Instead of skewing the permanent magnet, JP-A-2005-176424 has proposed that a rotary electric machine is provided with slots on the outer peripheral side of the embedded magnet or the outer peripheral surface of a pole piece so as to reduce the cogging torque such that the slot is formed to be shifted in the direction of rotation as viewed from the direction of a rotation axis.

The occurrence of torque pulsation in a rotary electric machine is caused by the cogging torque due to a magnetic circuit for allowing a magnetic flux generated from a permanent magnet provided in a rotor to pass through a stator and then to return to the rotor again, and by a rotating magnetic flux generated by a current of the stator. The above-mentioned JP-A-176424/2005 relates to a technique for reducing the cogging torque as mentioned above.

The invention is directed to reduction of the pulsation due to the rotating magnetic flux generated by the stator current as mentioned above.

When the method disclosed in the above-mentioned JP-A-176424/2005 is intended to be used for reducing torque pulsation due to the stator current, which is to be solved by the invention, the appropriate reduction of the cogging torque becomes very difficult. That is, the method disclosed in JP-A-176424/2005 is designed to reduce the cogging torque. When the concept of this method is intended to be further applied so as to reduce the torque pulsation due to the stator current, the inherent cogging torque cannot be appropriately reduced.

General techniques proposed for reducing torque pulsation have the same influence on both of the cogging torque and the torque pulsation due to the stator current. As a result, in order to reduce both torque pulsations, it is necessary to handle the rotary electric machine taking into consideration the influence on both. This makes it difficult to easily solve both pulsations.

The inventors have thought that the entire torque pulsation can be more easily reduced and adjusted if the torque pulsation due to the stator current can be reduced by a structure or way which has little influence on the cogging torque. For example, when the cogging torque can be reduced and additionally the torque pulsation due to the stator current can also be reduced, the entire torque pulsation can be easily reduced.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a technique which can reduce the torque pulsation due to the stator current by a way or structure which has little influence on the cogging toque.

In order to achieve the object described above, according to a first aspect of the present invention, there is provided a rotary electric machine including: a stator having stator windings; and a rotor rotatably disposed in the stator, said rotor having a rotor core provided with a plurality of magnets and a plurality of magnetic auxiliary salient poles formed between poles of the magnets, wherein a magnetic air gap is provided in an axial direction of the rotor in a position shifted in a circumferential direction from a q axis passing through a center of the magnetic auxiliary salient pole within the magnetic auxiliary salient pole, and wherein an amount of shifting the magnetic air gap from the q axis in the circumferential direction differs according to a position of the magnetic air gap in the axial direction so as to cancel torque pulsation in energization caused due to the magnetic air gap.

It is preferable that circumferential positions of the magnets in the rotor core are constant regardless of the axial positions of the magnets.

Further, it is preferable that the rotor core is divided into a plurality of division cores provided in the axial direction, each of said division cores having the magnet, the magnet auxiliary salient pole, and the magnetic air gap, and that the circumferential positions of the magnets in the division cores are constant regardless of the axial positions of the magnets.

Further, it is preferable that the rotary electric machine further includes a plurality of core groups, said core group including division cores having the magnetic air gaps located substantially in the same respective circumferential positions, and that the total thicknesses in the axial direction of the respective core groups are substantially the same.

Further, it is preferable that the rotary electric machine further includes two core groups with the magnetic air gaps located in different respective circumferential positions, and that phases of torque pulsations generated by the respective two core groups are shifted by 15 degrees or 30 degrees in terms of electrical angle.

Further, it is preferable that the rotary electric machine further includes first, second, and third core groups with the magnetic air gaps located in different respective circumferential positions, and that phases of torque pulsations respectively generated by the first, second, and third core groups are shifted by 10 degrees or 20 degrees in terms of electrical angle between the first core group and the second core group, and between the second core group and the third core group, respectively.

Further, it is preferable that the magnetic air gap is a concave portion formed at the surface of the rotor core, or a hole formed in the rotary core.

Further, it is preferable that a circumferential angle of the concave portion is set equal to or less than one half a peripheral length of an auxiliary salient pole.

Further, it is preferable that the hole serving as the magnetic air gap is integrally formed with a hole having the magnet provided therein.

Further, it is preferable that the plurality of magnets each of whose magnetization directions is a radial direction of the rotor core are arranged in the circumferential direction such that the magnetization directions are alternately reversed.

Further, it is preferable that the respective magnets constitute a magnet group including a plurality of magnets whose magnetization directions are substantially equal.

Further, it is preferable that the magnetic auxiliary salient poles are provided with a plurality of the magnet air gaps.

Further, it is preferable that the rotor core is formed by laminating electromagnetic steel plates, each plate having a hole or a cutout formed therein for forming the magnetic air gap.

Further, it is preferable that the two types of magnetic air gaps located in different circumferential positions are formed in the rotor core by laminating one steel plate on another steel plate turned upside down.

According to a second aspect of the present invention, there is provided an electric vehicle including: the rotary electric machine according to the first aspect; a battery for supplying a direct-current power; and a converter for converting the direct-current power of the battery into an alternating-current power, and supplying the alternating-current power to the rotary electric machine, wherein the electric vehicle is traveled by a drive force of the rotary electric machine.

According to the configuration of the present invention, the torque pulsation caused in relation to the stator current supplied to a stator winding can be reduced by the way or structure which has little influence on the cogging torque.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following embodiments can solve not only the problems associated with the above-mentioned object of the invention, but also other problems. Now, the representative problems to be solved by the embodiments, some of which are the same as those associated with the object of the invention, and a basic structure in relation to the solving of the problems will be described below.

(Good Torque Properties as Drive Rotary Electric Machine for Vehicle)

A rotary electric machine for driving a vehicle is required to output high torque in a start state of rotation or in a low-speed rotation region. Further, the torque output is also required even in a high-speed rotation region of the rotary electric machine. For example, the torque output is apparently necessary at 6000 rpm or more. The torque output is required at 10000 rpm or more. The electric motor which can be used at 12000 rpm makes the driving of the vehicle more preferable.

When the torque output in the low speed rotation region including the rotation start state is intended to be generated by magnet torque of a permanent magnet, the amount of use of the magnet becomes large. Further, an induced voltage induced based on the magnetic flux generated by the permanent magnet in the high-speed rotation region becomes high, which makes it difficult to supply the power to the rotary electric machine and thus needs a very high power supply voltage. That is, it is difficult to greatly increase the power supply voltage. This makes it difficult to obtain the torque output in a relatively high-speed rotation region, for example, at 6000 rpm or more.

In the embodiment to be described later, when the axis of the permanent magnet is set as the d axis, a magnetic resistance in the q-axis direction is made small, which generates large reluctance torque. The required torque consists of both magnet torque and reluctance torque, so that the ratio of the magnet torque to the required torque can be small. For example, when about 30 to 50% or more, or about 55% of the required torque can be the reluctance torque, the magnet torque can be reduced by a degree corresponding to the ratio, which can decrease the amount of permanent magnet material. Thus, the induced voltage by the permanent magnet in the high speed rotation can be decreased, which facilitates supply of the power from an inverter even in the high speed rotation, and can generate rotary torque even in the high speed rotation. The rotary electric machines of the following embodiments have a structure which can effectively generate the reluctance torque, and thus can output the rotary torque even in the above high-speed rotation region as well as the large rotary torque in the low-speed rotation region.

The rotation region capable of driving a vehicle is widened, whereby, for example, a hybrid vehicle having a narrow rotation region owned by an engine can be driven well, which leads to improvement of the fuel efficiency of the vehicle. Further, the decrease in amount of permanent magnet material can reduce no-load loss of the rotary electric machine, leading to improvement of efficiency of traveling of the vehicle.

The drive rotary electric machine for a vehicle is desired to have its volume downsized in addition to having the above torque properties. In this embodiment, the number of magnetic poles of the rotor is equal to or more than eight, which is advantageous in downsizing and high output. Since the number of the magnetic poles of the rotor is equal to or more than eight, a magnetic circuit generated in the stator tends to be formed near a portion of a stator core near the rotor. Thus, the length of the stator core in the radial direction thereof can be reduced. This decreases the length of the stator in the radial direction, that is, the dimension in the radial direction through the center axis of a section perpendicular to a rotary shaft.

The reduction of torque pulsation has been described in the above-mentioned paragraphs of the effect of the invention and the problems to be solved by the invention. The reduction of torque pulsation performed by the following embodiments will be described specifically below. The embodiments to be described later can respectively reduce the cogging torque and the torque pulsation due to the stator current.

(1) Reduction of Cogging Torque

In a structure having a permanent magnet embedded in a rotary core, a magnetic flux density in the direction of rotation of a gap between a rotor and a stator tends to drastically change at an end of the permanent magnet in the rotation direction (which can also be described as “an end in the circumferential direction”), which may cause cogging torque. In the following embodiments, a magnetic air gap257is provided at an end of the permanent magnet corresponding to an end of a rotor magnetic pole (field pole) formed by the permanent magnet. The magnetic air gap257can reduce a drastic change in magnetic flux density of a gap between the above rotor and stator in the rotation direction. The magnetic air gap257can have an effect of decreasing the cogging torque.

(2) Reduction of Pulsation Due to Stator Current

In the following embodiments, a magnetic air gap258is formed in an auxiliary magnetic pole (auxiliary salient pole259) for forming a magnetic circuit on the q axis. The positions of the magnetic air gaps258are changed in the rotation direction as viewed along the direction of a rotary shaft. Such an arrangement can reduce the pulsation due to the stator current.

(3) Reduction of Pulsation Due to Stator Current by Structure Having Little Influence on Cogging Torque

The conventional technique of reducing the torque pulsation has influences on both the cogging torque and the pulsation due to the stator current. When the cogging torque is intended to be reduced, the effect of reducing the pulsation due to the stator current becomes insufficient, or too sufficient. Thus, it is necessary to find out such conditions that can reduce both torque pulsations by repeating experiments. That is, even when an optimal condition for reducing the pulsation due to the stator current is found out, the condition is not always preferable for reduction of the cogging torque, and may be undesired one in many cases. Thus, it is very difficult to find a condition that can reduce both torque pulsations. Even if the preferable condition is found out, the condition tends to change depending on various factors. Every time a new rotary electric machine is designed, the experiment needs to be repeated. The solving means described in the above paragraph (2) has very little influence on the cogging torque. When a condition for reduction of the pulsation due to the stator current is adjusted, the adjustment cannot deteriorate the state of the cogging torque. This reduces the torque pulsation very easily.

(Improvement of Efficiency of Rotary Electric Machine)

In the embodiment to be described below, the length of a magnetic bridge can be increased, which can reduce a leakage magnetic flux of the permanent magnet, leading to improvement of the efficiency of the rotary electric motor. The magnetic bridges can, be formed along the magnetic air gaps257or slots282provided on both ends of the field pole, thereby preventing the concentration of stress, resulting in a decreased sectional area of the magnetic flux, which leads to improvement of the efficiency.

The external appearance of the rotary electric machine in an embodiment to be described later can be produced by punching using a silicon steel plate. Thus, the embodiment has excellent productivity. A core301has the shape symmetric with respect to that of the core302as will be described later. One silicon steel plate subjected to punching can be turned upside down to be used as the other core. As a result, the number of types of cores to be produced can be decreased to improve the productivity.

In the embodiments to be described, magnets introduced into the rotary electric machine along the axial direction of the rotor are disposed without being shifted in the circumferential direction, or are hardly displaced in the circumferential direction, which facilitates a magnetization work, thereby improving productivity. As will be described later, the permanent magnet may be magnetized, and then embedded in the rotor core. Alternatively, the permanent magnet may be inserted into the rotary core before being magnetized, and then magnetized by applying a strong magnetic field to the magnet. The latter does not interrupt an insertion work of the magnets because of an attraction force of the magnets in insertion of the magnets, and can suppress adhesion of contaminant or the like, thereby further improving the productivity. In employing such a magnetization method, when the magnet is axially divided into parts shifted from each other in the circumferential direction, each magnet part divided may be separately magnetized so as to improve magnetization properties. In the embodiment described later, the magnet is not divided in the axial direction, or the number of division of the magnet is small, which can reduce the number of repeating of the magnetization work, thereby improving the productivity. In the case of magnetizing a magnet extending in the axial direction at one time, nonuniform magnetization hardly occurs due to an influence, such as a difference in distance up to a magnetization device, and can improve the magnet properties and productivity as compared to the case in which the magnet is axially divided to be shifted from each other in the circumferential direction.

Now, preferred embodiments for implementing the invention will be described below with reference to the accompanying drawings. The rotary electric machine of the invention can respectively reduce the cogging torque in non-energization and the torque pulsation in energization, thereby achieving reduction in size, cost, and torque pulsation as will be described later. Thus, for example, the rotary electric machine is suitable for use as a motor for traveling an electric vehicle. The rotary electric machine of the invention can provide an electric vehicle having low vibration, low noise, and good ride quality. The rotary electric machine of the invention can be applied to a pure electric vehicle which is run only by the rotary electric machine, and a hybrid electric vehicle driven by both the engine and the rotary electric machine. Now, the hybrid electric vehicle will be described as one example.

FIRST EMBODIMENT

FIG. 1is a diagram showing a schematic construction of a hybrid electric vehicle equipped with the rotary electric machine according to one embodiment of the invention. A vehicle100is equipped with an engine120, a first rotary electric machine200, a second rotary electric machine202, and a battery180. The battery180supplies direct-current power to a power converter (inverter)600for driving the rotary electric machines200and202when driving forces for the machines200and202are necessary. The power converter600converts the direct-current power into alternating-current power, and respectively supplies the converted alternating-current power to the rotary electric machines200and202. In regeneration traveling, the rotary electric machines200and202generate alternating-current power based on kinetic energy of the vehicle to supply the power to the power converter600. The power converter600converts the alternating-current power into direct-current power to supply the direct-current power to the battery810. A battery (not shown) for supplying low-voltage power (for example, 14 volt power) is mounted on the vehicle, and thus the direct-current power of a constant voltage is supplied to a control circuit to be described later.

The rotary torques of the engine120and the rotary electric machines200and202are transferred to front wheels110via a transmission130, and a differential gear132. The transmission130is controlled by a transmission controller134, and the engine120is controlled by an engine controller124. The battery180is controlled by a battery controller184. The transmission controller134, the engine controller124, the battery controller184, the power converter600, and an integrated controller170are connected to one another via a communication line174.

The integrated controller170receives information about states of respective low-level controllers with respect to the integrated controller170, that is, the transmission controller134, the engine controller124, the power converter600, and the battery controller184, from these controllers via the communication line174. The integrated controller170computes a control command of each controller based on such information. The control command computed is transmitted to the corresponding controller via the communication line174.

The battery180having a high voltage is constructed of a secondary battery, such as a lithium ion battery or a nickel hydride battery, and outputs a direct-current power of high voltage of 250 to 600 volts or more. The battery controller184outputs information about a discharge state of the battery118and a state of each unit cell constituting the battery18to the integrated controller170via the communication line174.

The integrated controller170gives an instruction of a power generating operation to the power converter600when the charging of the battery180is determined to be necessary based on the information from the battery controller184. The integrated controller170mainly manages output torques of the engine120and the rotary electric machines200and202, computes a total torque of the output torque of the engine120and the output torques of the rotary electric machines200and202, or a torque distribution ratio between these torques, and transmits control commands to the transmission controller134, the engine controller124, and the power converter600based on the result of the computation. The power converter600controls the rotary electric machines200and202so as to provide the torque output or generated power based on a torque command from the integrated controller170according to the command.

The power converter600is provided with a power semiconductor constituting an inverter so as to drive the rotary electric machines200and202. The power converter600controls a switching operation of the power semiconductor based on the command from the integrated controller170. Such a switching operation of the power semiconductor causes the rotary electric machines200and202to be driven as an electric motor or a generator.

When the rotary electric machines200and202are operated as an electric motor, the direct-current power from the high-voltage battery is supplied to a direct-current terminal of the inverter of the power converter600. The power converter600controls the switching operation of the power semiconductor to convert the supplied direct-current power into a three-phase alternating-current power, and then to supply the alternating-current power to the rotary electric machines200and202. On the other hand, when the rotary electric machines200and202are operated as the generator, the rotors of the rotary electric machines200and202are rotatably driven by rotary torque added from the outside, whereby the three-phase alternating-current power is generated in stator windings of the rotary electric machines200and202. The generated three-phase alternating-current power is converted into direct-current power by the power converter600, and the direct-current power is supplied to the high-voltage battery180, so that the battery is charged.

The rotary electric machine200and the rotary electric machine202are independently controlled. For example, when the rotary electric machine200is operated as the electric motor, the rotary electric machine202can be operated as the electric motor, and also as the generator, and further can be stopped. It is apparent that the opposite is also true. The integrated controller170determines in which mode each of the rotary electric machines200and202is operated, and gives a command to the power converter600. Based on the command, the power converter600is in an operating mode of the electric motor, or in an operating mode of the generator, or in a stopped mode of operation.

FIG. 2schematically shows a circuit diagram of the power converter600shown inFIG. 1. The power converter600is provided with a first inverter for the rotary electric machine200and a second inverter for the rotary electric machine202. The first inverter includes a power module610, a first drive circuit652for controlling a switching operation of each power semiconductor21of the power module610, and a current sensor660for detecting a current of the rotary electric machine200. The drive circuit652is provided in a drive circuit substrate650. On the other hand, the second inverter includes a power module620, a second drive circuit656for controlling a switching operation of each power semiconductor21of the power module620, and a current sensor662for detecting a current of the rotary electric machine202. The drive circuit656is provided in a drive circuit substrate654. The control circuit648provided in a control circuit substrate646, a condenser module630, and a transmitting and receiving circuit644mounted on a connector substrate642are commonly shared between the first inverter and the second inverter.

The power modules610and620are operated according to drive signals output from the respective drive circuits652and656. The power modules610and620respectively convert direct-current power supplied from the battery180into three-phase alternating-current power, and supply the power to the stator windings, which are armature windings of the respective rotary electric machines200and202. The power modules610and620converts alternating-current power induced in the stator windings of the rotary electric machines200and202into direct current, and supplies the direct current to the high-voltage battery180.

The power modules610and620include three-phase bridge circuits as shown inFIG. 2, and series circuits corresponding to the three-phase circuits are electrically connected in parallel between a positive electrode and a negative electrode of the battery180. Each series circuit includes a power semiconductor21constituting an upper arm and a power semiconductor21constituting a lower arm. These power semiconductors21are connected in series to each other. The power module610and the power module620have substantially the same circuit configuration as shown inFIG. 2. Here, the power module610will be described below as a representative.

In this embodiment, an insulated gate bipolar transistor (IGBT)21is used as a power semiconductor element for switching. The IGBT21includes three electrodes, namely, a collector electrode, an emitter electrode, and a gate electrode. A diode38is electrically connected to between the collector electrode and the emitter electrode of the IGBT21. The diode38includes two electrodes, namely, a cathode electrode and an anode electrode. The cathode electrode is electrically connected to the collector electrode of the IGBT21and the anode electrode is electrically connected to the emitter electrode of the IGBT21such that a direction from the emitter electrode to the collector electrode of the IGBT21is the forward direction.

A metal-oxide semiconductor field-effect transistor (MOSFET) may be used as a power semiconductor element for switching. The MOSFET has three electrodes, namely, a drain electrode, a source electrode, and a gate electrode. The MOSFET has a parasitic diode between the source electrode and the drain electrode such that the direction from the drain electrode to the source electrode is the forward direction, and thus does not need to have the diode38shown inFIG. 2.

The arm of each phase is constructed by electrically connecting the source electrode of the IGBT21to the drain electrode of the IGBT21in series. Although only one IGBT of each of the upper and lower arms of the respective phases is shown in this embodiment, a plurality of IGBTs are electrically connected in fact in parallel because a current capacity to be controlled is large. For simplification, one power semiconductor will be described below.

In an example shown inFIG. 2, each of the upper and lower arms of the respective phases is constructed of three IGBTs. The drain electrode of the IGBT21of each upper arm of each phase is electrically connected to the positive electrode of the battery180, and the source electrode of the IGBT21of each lower arm of each phase is electrically connected to the negative electrode of the battery180. An intermediate point of each arm of the phase (a connection portion between the source electrode of the IGBT on the upper arm side and the drain electrode of the IGBT on the lower arm side) is electrically connected to an armature winding (stator winding) of the corresponding phase of each of the rotary electric machines200and202.

Drive circuits652and656constitutes drive units for controlling the respective inverters610and620, and generate drive signals for driving the IBGTs21based on a control, signal output from the control circuit648. The drive signals generated by the drive circuits652and656are respectively output to the gates of the respective power semiconductor elements of the power modules610and620. Each of the drive circuits652and656is provided with six integrated circuits for generating the drive signal to be supplied to the gate of each of the upper and lower arms of each phase. The six integrated circuits are constructed as one block.

A control circuit648constitutes a controller for each of the inverters610and620. The control circuit648is constructed of a microcomputer for computing a control signal (control value) for operating (turning on and off) the power semiconductor elements for switching. The control circuit648receives inputs of a torque command signal (torque command value) from a high-level controller, sensor outputs from the electric current sensors660and662, and sensor outputs from the rotary sensors mounted on the rotary electric machines200and202. The control circuit648computes the control value based on the input signals, and outputs control signals for controlling switching timing of the drive circuits652and656.

The transmitting and receiving circuit644mounted on the connector substrate642is to electrically connect the power converter600to the external controller, and transmits and receives information with another device via the communication line174shown inFIG. 1. The condenser module630constitutes a smoothing circuit for suppressing variations in direct-current voltage generated by the switching operation of the IGBT21. The condenser630is electrically connected in parallel to terminals on the direct-current side of the first and second power modules610and620.

FIG. 3is a sectional view of the rotary electric machine200or202shown inFIG. 1. The rotary electric motor200has substantially the same structure as that of the rotary electric motor202. Now, the structure of the rotary electric machine200will be described below as the representative. The structure to be described later does not need to be used in both rotary electric machines200and202, and thus may be used in at least one of them.

A stator230is held in the housing212, and includes a stator core232and stator windings238. A rotor250is rotatably held via an air gap222inside the stator core232. The rotor250includes a rotor core252and a permanent magnet254. The rotor core252is fixed to a shaft218. The housing212has a pair of end brackets214with bearings216provided therein, and the shaft218is rotatably held by the bearings216. The stator core232is made by laminating a number of magnetic steel plates, for example, silicon steel plates, each having a thickness of 0.2 to 0.35 millimeters. The lamination of thin steel plates can suppress the occurrence of eddy current, thus reducing iron loss. The reduction of iron loss is very important to a rotary electric machine used in the high-speed rotation region, such as that of this embodiment.

FIG. 4is a diagram showing an external appearance of the stator230. The stator windings238provided in the stator230are formed by distributed winding of coils233. A magnetic field formed by the stator windings238distributed and wound has the magnetic flux distribution substantially in the shape of a sine wave. Thus, the rotary electric machine employing the distributed winding stator230easily obtains the reluctance torque, and is appropriated for obtaining a motor property for an electric vehicle or the like. In this embodiment, the stator including the distributed winding type stator windings will be mainly described as an example. Although a concentrated winding type state winding has a slightly worse electric property, it can be used.

As shown inFIG. 3, the shaft218is provided with a rotor position sensor224for detecting the position of a pole of the rotor250, and a rotation speed sensor226for detecting the rotation speed of the rotor250. Outputs from the sensors224and226are taken into the control circuit648shown inFIG. 2. The control circuit648outputs a control signal to the drive circuit653based on the output taken. The drive circuit653outputs the drive signal based on the control signal to the power module610. The power module610performs the switching operation based on the control signal, and converts the direct-current power supplied from the battery180into the three-phase alternating-current power. The three-phase alternating-current power is supplied to the stator windings238shown inFIGS. 3 and 4, so that a rotating magnetic field is generated in the stator230. The frequency of the three-phase alternating current is controlled based on the detection value of the rotation speed sensor226. The phase corresponding to the rotor250of the three-phase alternating current is controlled based on the detection value of the rotor position sensor224.

FIG. 5Ais a perspective view showing the rotor core252of the rotor250. The rotor core252consists of three cores301,302, and301as shown inFIG. 5B. The length H2of the core302in the axial direction is set about twice as long as the length H1of the core301in the axial direction.FIG. 6shows sections of the stator230and the rotor250, in whichFIG. 6Ais a sectional view taken along the line A-A passing through the part of the core301(seeFIG. 3), andFIG. 6Bis a sectional view taken along the line B-B passing through the part of the core302(seeFIG. 3).FIG. 6omits the illustration of the housing212, the shaft218, and the stator winding238. The rotor core252is made by laminating a number of magnetic steel plates, for example, silicon steel plates, each having a thickness of 0.2 to 0.35 millimeters, like the above-mentioned stator core. The lamination of thin steel plates can suppress the occurrence of eddy current, thus reducing iron loss. The reduction of iron loss is very important to the rotary electric machine used in the high-speed rotation region, like this embodiment.

A number of slots24and teeth236are evenly arranged along the entire periphery of the stator core232on the inner peripheral side thereof, and the coil233is wound as shown inFIG. 4. In this embodiment, the number of slots is 72, but may be any other one. InFIG. 6, all slots and teeth are not designated by reference numerals, and only parts of the teeth and slots are indicated as the representatives by the respective reference numerals. A slot insulator (not shown) is provided in the slot24, and a plurality of phase windings of u to w phases constituting the stator windings238are mounted on the slots24. As mentioned above, this embodiment employs the distributed winding as the way to wind the stator windings238.

The term “distributed winding” as used herein means a winding system in which the phase windings are wound around the stator core232such that each phase winding is accommodated in two of the slots24spaced apart from each other via other slots. In this embodiment, the distributed winding is used as the winding system, and thus the control can be performed by using weak field magnet control and reluctance torque in a wide range of the number of revolutions, including not only a low rotation speed, but also a high rotation speed. As mentioned above, the reluctance torque is used to enable reduction of the magnet torque due to the magnetic flux generated by the magnet, which can decrease the amount of permanent magnet material. As a result, the amount of magnetic flux generated from the magnet is decreased, so that the induced voltage generated in the stator winding together with the rotation becomes small. When the induced voltage generated in the stator winding238is large, a difference between a voltage applied from the power converter600to the rotary electric machine200or202and the induced voltage becomes small, which makes it difficult to supply the alternating current from the power converter600. In this embodiment, the use of the reluctance torque can reduce the induced voltage generated in the stator winding238, so that the alternating current can be supplied from the power converter600to the stator winding238even in the high-speed rotation region, thereby enabling generation of rotary torque at the rotary electric machine.

Each of the cores301and302of the rotor core252has holes310into each of which a magnet having a magnetic section shown inFIG. 6, that is, a substantially rectangular or fan-shaped section at a surface perpendicular to the rotation axis is inserted. The holes310are formed at even intervals along the entire periphery of the rotor as shown inFIG. 5. The permanent magnet254is embedded in each hole310, and fixed thereto by an adhesive or the like. The width of the hole310in the circumferential direction is set larger than that of the permanent magnet254in the circumferential direction, and the magnetic air gaps257are formed on both sides of the permanent magnet254. The magnetic air gap257may have the adhesive embedded therein, or may be integrally fixed together with the permanent magnet254by resin, or may be a hollow air gap. The permanent magnet254acts as a field pole of the rotor250. In this embodiment, one permanent magnet forms one magnetic pole, but a plurality of magnets may form one magnetic pole. The permanent magnets may be arranged in the direction of rotation, or may be superimposed on each other in the radial direction. The permanent magnets need to generate the magnetic flux having the same polarity in units of magnetic pole, and are required to be magnetized in the same direction in relation to the opposed stator. The increase in number of magnets for each magnetic pole can increase the total amount of magnetic fluxes thereby to increase the magnet torque.

The magnetization direction of the permanent magnet254is the radial direction. The magnetization direction is reversed every field pole. That is, the stator side surface of a permanent magnet254ais the N pole, and the axis side surface thereof is the S pole. The stator side surface of an adjacent permanent magnet254bis the S pole, and the axis side surface thereof is the N pole. These permanent magnets254aand254bare alternately arranged in the circumferential direction. In this embodiment, twelve permanent magnets254are arranged at even intervals, and the rotor250has twelve poles.

The permanent magnet254may embed the rotor core252after magnification. Alternatively, the permanent magnet254may be inserted into the rotor core252before magnification, and then may be magnified by applying a strong magnetic field. The permanent magnetic254after magnetization becomes a strong magnet. When the magnet is magnetized before the permanent magnet254is fixed to the rotor250, a strong attraction force is generated between the permanent magnet254and the rotor core252in fixing the permanent magnet254, and then acts to interrupt the work. The strong attraction force may cause contaminants, such as iron powder, to adhere to the permanent magnet254. Thus, the permanent magnet254is inserted into the hole310of the rotor core252, and magnified after being fixed, which improves the productivity of the rotary electric machine.

The permanent magnet254can be made of a neodymium-based sintered magnet, a samarium-based sintered magnet, a ferrite magnet, a neodymium-based bonded magnet, or the like. In particular, the neodymium-based permanent magnetic has a strong magnetic force, and thus is suitable in use for the rotary electric machine for driving the vehicle which generates high torque. The residual reflux density of the permanent magnet254is desirably about 0.4 to 1.3 T.

FIG. 7Ais an enlarged view of the vicinity of the permanent magnet254bwhose section is shown inFIG. 6A. The core301of the stator core252is provided with slots for forming magnetic air gaps258aon the surface of the rotor250, in addition to the magnetic air gaps257formed on both sides of the permanent magnet254. The magnetic air gap257is provided for reducing the cogging torque, and the magnetic air gap258ais provided for reducing the torque pulsation in energization. The magnetic air gap258ais arranged shifted rightward with respect to the q axis serving as the center axis between the magnets.

FIG. 7Bis an enlarged view showing the vicinity of the permanent magnet254bwhose section is shown inFIG. 6B. A core302shown inFIG. 7Bhas magnetic air gaps258bformed, instead of the magnetic air gaps258a. The magnetic air gap258bis arranged shifted leftward with respect to the q axis. As shown inFIGS. 6 and 7, the core301and the core302have the same sectional shape except for the positions of the magnetic air gaps258aand258b.

The magnetic air gaps258aand258bhave the symmetric positions and shapes to each other with respect to the q axis. That is, the thin silicon steel plate (electromagnetic steel plate) constituting the core301is turned upside down to be laminated on another steel plate, thereby to form the core302. This can reduce a manufacturing cost because a mold costs less. The positions of the holes310of each of the cores301and302in the circumferential direction are aligned with each other without misalignment. As a result, each permanent magnet254fitted in each hole310integrally penetrates each of the cores301and302without being separated in the axial direction. It is apparent that permanent magnets254divided into may be provided so as to be laminated in the axial direction of the holes310.

When the rotating magnetic field is generated in the stator230by the three-phase alternating current, the rotating magnetic field acts on the permanent magnets254aand254bof the rotor250to generate the magnet torque. The reluctance torque in addition to the magnet torque also acts on the rotor250.

FIG. 8is a diagram for explaining the reluctance torque. Generally, the axis on which the magnetic flux passes through the center of the magnet is referred to as a “d axis”, and the axis on which the magnetic flux flows from between poles of one magnet to between poles of another magnet is referred to as a “q axis”. At this time, a core portion between field poles is referred to as an “auxiliary salient pole259”. Since the magnetic permeability of the permanent magnet254provided in the rotor250is substantially the same as that of air, a d-axis portion is magnetically concave, and a q-axis portion is magnetically convex as viewed from the stator side. Thus, a core of the q-axis portion is referred to as a salient pole. The reluctance torque is generated by a difference of permeability of magnetic flux between the d axis and the q axis, that is, a salient pole ratio.

As mentioned above, the rotary electric machine of this embodiment is a rotary electric machine using both magnet torque and reluctance torque of the auxiliary salient pole. Torque pulsations from the magnet torque and the reluctance torque are respectively generated. The torque pulsation includes a pulsation component generated in non-energization and a pulsation component generated in energization. The pulsation component generated in non-energization is generally called as cogging torque. Most of the conventionally methods for reducing the torque pulsation as described in the related art takes into consideration only the cogging torque. However, in use of the rotary electric machine under load, the torque pulsation of a mixture of the cogging torque and the pulsation component in energization is actually generated.

Most of the methods for reducing such torque pulsation of the rotary electric machine take into consideration only the reduction of the cogging torque, and hardly consider the torque pulsation generated in energization. Noise of the rotary electric machine occurs under no load, but under load in many cases. That is, in order to reduce noise of the rotary electric machine, it is important to reduce the torque pulsation under load. Only measures against the cogging torque are not sufficient.

Now, a method for reducing torque pulsation in this embodiment will be described below.

First, the magnet torque will be described.FIG. 9is a sectional view of a simulation result of distribution of magnetic flux, taken along the line A-A, when no current passes through the stator winding338, that is, of magnetic flux provided by the permanent magnet254. In non-energization, the magnetic flux of the permanent magnetic254short-circuits the end of the magnet. Thus, the magnetic flux generated by the permanent magnet254hardly passes through the auxiliary salient pole259for allowing the magnetic flux on the q axis to pass therethrough. It is found that the magnetic flux also hardly passes through the magnetic air gap258aprovided slightly shifted from the magnetic air gap257of the end of the magnet. The magnetic flux passing through the stator232leads to the teeth236through the core on the stator side of the permanent magnet254.

The same distribution of magnetic flux as that on the sectional view taken along the line A-A is also obtained on a sectional view taken along the line B-B. The magnetic flux never passes through the auxiliary salient pole259for allowing the magnetic flux on the q axis to pass therethrough, and hardly passes through the part of the magnetic air gap258b. Thus, the magnetic air gaps258aand258bhave little influence on the magnetic flux associated with the cogging torque in non-energization. As a result, the magnetic air gaps258aand258bhave little influence on the cogging torque.

FIG. 10Ashows a waveform of cogging torque actually measured, andFIG. 10Bshows a waveform of induced voltage generated on the stator side when the rotor250rotates. The lateral axis indicates a rotation angle of the rotor in terms of electrical angle.

The line L11indicates the rotor without the magnetic air gap258, the line L12indicates the rotor provided with the magnetic air gap258a, and the line L13indicates the rotor provided with the magnetic air gap258b. As can be seen from the result shown inFIG. 10B, the presence or absence of the magnetic air gaps258aand258bhardly have influence on the cogging torque.

The induced voltage is a voltage generated by causing the magnetic flux of the magnet of the rotating rotor250to intersect the stator windings238. However, as shown inFIG. 10B, the waveform of the induced voltage has a sine wave shape without being influenced by the presence or absence of the magnetic air gaps258aand258b. The induced voltage reflects the magnetic flux of the magnet shown inFIG. 9. The fact that the induced voltage hardly changes means that the magnetic air gaps258aand258bhardly have any influence on the magnetic flux of the magnet.

Now, influences of the magnetic air gaps258aand258bon the reluctance torque will be described below.FIGS. 11 and 12show magnetic fluxes in energization.FIG. 11is a sectional view taken along the line A-A, andFIG. 12is a sectional view taken along the line B-B. The rotary electric machine of this embodiment is a motor having 6 slots per one pole. The coils233of the stator windings238provided in the slots24of the stator core232are divided into two layers in the direction of depth of the slot. When a slot adjacent to the coil233disposed on the bottom side of the corresponding slot is countered as the first slot, each coil233is inserted into another slot on the rotor side of the sixth slot24across first to fifth slots, which is fractional pitch winding. The fractional pitch winding can reduce higher harmonic of a magnetomotive force of the stator, and has a short coil end and a little copper loss. Such winding for reduction of the higher harmonic can lessen the sixth torque pulsation specific to the three-phase motor, so that only the twelfth pulsation component remains.

As can be seen fromFIGS. 11 and 12, many magnetic fluxes pass through the q axis, and the magnetic air gaps258aand258ballow many magnetic fluxes to flow therethrough. This is because the current of the stator230makes magnetic fluxes on the q axis. Thus, the magnetic air gaps258aand258blocated at the auxiliary salient poles exert a magnetic influence in energization.

FIG. 13shows the level of torque pulsation calculated per unit axial length. The line L21indicates the case where the magnetic air gap258is not formed, the line L22indicates the case where the magnetic air gap258ais formed, and the line L23indicates the case where the magnetic air gap258bis formed. The line L24indicates the torque pulsation in this embodiment employing the rotor250with the rotor core252shown inFIG. 5. As mentioned above, in the rotary electric machine of this embodiment, a twelfth component of torque pulsation, that is, a component having 30 degrees as one cycle in terms of electrical angle is predominant. As can be seen fromFIG. 13, the twelfth component is predominant, and the sixth component hardly exists.

The case of forming the magnetic air gap258a, and the case of forming the magnetic air gap258bare found to cause the waveform of the torque pulsation to change with respect to the torque pulsation obtained when not forming the magnetic air gap258. This means that the magnetic flux in energization is influenced by the magnetic air gaps258aand258b. The waveform in forming the magnetic air gap258ahas a phase substantially opposite to that of a waveform in forming the magnetic air gap258b. As shown inFIG. 5, the ratio of the axial length of the core301to that of the core302, which constitute the rotor250, is set to about 1:2, so that the total torque pulsation L24received by the entire rotor is an average of the torque pulsations indicated by the lines L22and L23. The total torque pulsation L24is found to be small with respect to the case in which the magnetic air gap258is not provided.

In this way, in this embodiment, the provision of the above magnetic air gaps258aand258bcan reduce the torque pulsation in energization. In order to obtain such an effect, the width angle (the angle in the circumferential direction) of the slot forming the magnetic air gap258is preferably set equal to or less than half an angle of the auxiliary salient pole in the circumferential direction.

The formation of the magnetic air gaps has the advantage of not decreasing the torque as compared to the case in which no magnetic air gap is provided. Conventionally, a structure with skew for reducing torque pulsation results in a decrease in torque by the skew. This makes it difficult to downsize the conventional rotary electric machine structure. However, this embodiment can reduce only the torque pulsation of the reluctance torque, separately from the cogging torque, which has the advantage that the torque itself is not reduced. This is because the toque pulsation in the rotor without slots has the predominant twelfth component, and because the fractional pitch winding of the stator windings is implemented.

As mentioned above, the formation of the magnetic air gaps258aand258bdoes not have any influence on the cogging torque in non-energization. Thus, the conventional method for reducing the cogging torque can be applied to reduce the cogging torque, separately from the reduction of the torque pulsation in energization. In this embodiment, the following arrangement can also reduce cogging torque.

FIGS. 14 and 15are diagrams for explaining the method for reducing the cogging torque.FIG. 14is a sectional view of parts of the rotor250and the stator core232. InFIG. 14, τp is a polar pitch of the permanent magnet254, and τm is a width angle of the permanent magnet254. Further, τg is an angle formed by combination of the permanent magnet254and the magnet air gaps257provided on both sides thereof, that is, a width angle of the hole310as shown inFIG. 5. Thus, the cogging torque can be reduced by adjusting the angle ratio of .τm/τp, and the angle ratio of τg/τp. In this embodiment, the ratio of τm/τp is hereinafter referred to as a magnet pole arc degree, and the ratio of τg/τp as a magnet hole pole arc degree.

FIG. 15is a diagram showing the relationship between the ratio of magnet pole arc degree τm/τp and the cogging torque. The result shown inFIG. 15is obtained in the case of τm=.τg. InFIG. 15, the longitudinal axis indicates an amplitude of cogging torque, and the lateral axis indicates a rotation angle of the rotor250in terms of electrical angle. The level of the amplitude of pulsation changes depending on the ratio of τm/τp. For τm=τg, when the τm/τp is selected to be about 0.75, the cogging torque can be reduced. The tendency that the magnetic air gap258shown inFIG. 10does not change the cogging torque can also be applied to any case where the ratio of the magnet width to the pole pitch, that is, τm/τp takes any value as shown inFIG. 15, in the same way. Thus, under the above-mentioned conditions, the shape of the rotor250is set to that shown inFIG. 5or6, which can reduce both the dogging torque and torque pulsation in energization.

In an example shown inFIG. 14, the following is set: τm/τp=0.55, and τg/τp=0.7. In this case, these values are optimal for simultaneously reducing the cogging torque in non-energization and the torque pulsation in energization. In this example, the magnet has a fan-like shape. When the magnet has a rectangular shape, such values are slightly changed, which is apparently within the same scope of the invention.

(Effective Use of Reluctance Torque)

In the example shown inFIG. 15, the relation of τm=.τp is satisfied as described above. In order to effectively use the reluctance torque, which is an effect of the auxiliary salient pole259, the magnet hole pole arc degree τg/τp may be preferably set to about 0.5 to 0.9, and more preferably to about 0.7 to 0.8.

FIG. 16shows a calculation example of the maximum torque obtained by changing the magnet pole arc degree τm/τp and the magnet hole pole arc degree τg/τp. The lateral axis indicates the magnet hole pole arc degree τg/τp.FIG. 16shows that the magnet hole pole arc degree τg/τp of 0.7 corresponds to the ratio of the auxiliary salient pole259to a pitch between poles of 0.3. The magnet width τm cannot be larger than an opening angle τg of the magnet hole, leading to τg≧τm. As the τm is increased, the width of the permanent magnet254is increased, thereby increasing the torque. On the other hand, when the τm is constant, the τg is an optimal value. When the ratio of τg/τp is about 0.7 to 0.8, the maximum torque becomes largest. This is because the size of the auxiliary salient pole259can take an appropriate value, and because the reluctance torque becomes small when the value of τg is much larger or smaller than the appropriate value. When the value of τm is larger than 0.75, τm=τg is desirable so as to make the auxiliary salient pole259as large as possible.

In this way, when τg/τp is about 0.7 to 0.8, the reluctance torque can be used most efficiently, which can make the permanent magnet254small. In use of a rare-earth sintered magnet as the permanent magnet254, the magnet is required to be used most efficiently in terms of amount because the sintered magnet is very expensive as compared to other materials. Since the permanent magnet254is small, the induced voltage due to the magnetic flux of the permanent magnet254can be lessened, so that the rotary electric machine can be rotated at higher speed. Thus, the electric vehicle uses the rotary electric machine using the reluctance torque like this embodiment as a rotary electric machine for driving the electric vehicle, thereby to obtain preferable properties.

[Explanation about Shift of Magnetic Air Gaps258]

In the above description about the embodiments, the magnetic air gaps258are arranged in two different positions. That is, provision of the magnetic air gaps258aand258bin different positions reduces the torque pulsation in energization. Now, the way to shift the magnetic air gap258for reducing the torque pulsation will be described below.

A structure with a magnet skewed is conventionally known as means for reducing the torque pulsation. The inventors have found through studies that this concept of skew can be applied to the shift of the magnetic air gaps258. First, the skew of the magnet will be described below.FIGS. 17A and 17Bare perspective views for explaining the concept of the rotor250with skew, in whichFIG. 17Ashows the case in which the rotor250is divided into two parts in the axial direction, andFIG. 17Bshows the case in which the rotor250is divided into three parts in the axial direction.FIG. 17is a schematic diagram showing an example in which the permanent magnet254is provided on the surface of the rotor. The same can go for a rotor in which a permanent magnet is embedded. InFIG. 17, the reference numeral θ indicates an angle of skew. In the example shown inFIG. 17B, the center core is skewed by the angle θ with respect to the cores on both ends.

Among various methods for skewing, four kinds of methods for skewing by laminating the cores as shown inFIG. 17will be described below with reference toFIG. 18. In any one of cases shown inFIGS. 18A to 18D, a rotor core252is divided into eight cores having the same thickness in the axial direction. As shown inFIGS. 18A to 18C, when the skewing operation is performed in two stages, the skew angle θ is normally set to be 15 degrees or 30 degrees in terms of electrical angle. When setting a mechanical skew angle θ, a phase shift needs to be performed based on the electrical angle corresponding to the skew angle θ. In the following, the skew in terms of electrical angle will be described below.

The reason for setting the skew angle θ to 15 degrees or 30 degrees in terms of the electrical angle is that the three-phase motor normally includes sixth and twelfth torque pulsations for an electric frequency, and that the reduction of the torque pulsation needs skewing by such an angle. For example, when the sixth torque pulsation is a primary component of torque pulsation having a cycle of 60 degrees in terms of the electrical angle, a half cycle of the torque pulsation corresponds to 30 degrees in terms of electrical angle. Thus, when the skew angle θ of the core corresponds to the electrical angle of 30 degrees in skewing the divided cores, the primary components of the torque pulsations in the cycle of 60 degrees, which pulsations are generated in two respective cores shifted from each other, have reverse phases to each other, and act to cancel the respective pulsations to each other. As a result, the total torque pulsation is reduced.

Thus, the cores into which the rotor250is divided are shifted by 30 degrees in terms of the electrical angle as mentioned above, which can reduce the primary component of the torque pulsation. Likewise, in the case of the third component, since one cycle corresponds to 20 degrees in terms of electrical angle, 30 degrees in terms of electrical angle corresponds to one and half cycle. Further, likewise, in the case of the fifth component, 30 degrees in terms of electrical angle corresponds to two and half cycles. Thus, like the first component, the torque pulsations are substantially cancelled each other, so that the total torque pulsation is reduced. Also, the same goes for a seventh or more odd-numbered component, and the cores are skewed by 30 degrees in terms of electrical angle, which can reduce the odd-numbered component of the torque pulsation.

However, when the cores are shifted by 30 degrees in terms of electrical angle, even-numbered components, such as secondary, fourth, and the like, of the torque pulsation generated from the cores have the identical cycle to each other to increase the amplitude of the total torque pulsation. Thus, when the secondary component of the torque pulsation is smaller than the primary component thereof, shifting of the cores by 30 degrees in terms of electrical angle has an effect of reducing the torque pulsation. Conversely, when the primary component of the torque pulsation is smaller, and the secondary component thereof is larger than the primary component, shifting of the cores by 15 degrees in terms of electrical angle is very effective for reduction of the torque pulsation. For example, in the case of the secondary component, 60 degrees in terms of electrical angle corresponds to two cycles. Thus, the shifting of the cores by 15 degrees in terms of electrical angle corresponds to a phase shift of 0.5 cycle, so that the torque pulsations cancel each other.

In the examples shown inFIGS. 18A to 18C, the skew is performed in two stages, and in the example shown inFIG. 18D, the skew is performed in three stages. The permanent magnet254may not be divided in the axial direction in a block not skewed, or may be divided into a plurality of parts. In the example shown inFIG. 18D, a shift angle between the adjacent cores is set to 10 degrees or 20 degrees in terms of electrical angle. When the primary component is the sixth torque pulsation, that is, torque pulsation in a cycle of 60 degrees in terms of electrical angle, the shifting of the cores by 10 degrees or 20 degrees in terms of electrical angle allows the primary component to be shifted by one sixth of a cycle or one third of a cycle. In the skew method of shifting by one third of a cycle, a 3n-th component of the torque pulsation remains, but other components disappear. This method lessens the torque pulsation as compared to the above-mentioned general method using the reverse phases.

In the examples shown inFIGS. 18A to 18C, an excitation force is applied in the axial direction in driving the motor. In the method shown inFIG. 18D, the excitation force is not generated axially. Thus, no vibration is applied to the external part of the rotary electric machine, which makes the rotary electric machine silent. Also, in this case, when the primary component of the torque pulsation is small and the secondary component thereof is predominant, skewing may preferably be performed by 10 degrees, and not 20 degrees. In any one of cases shown inFIGS. 18A to 18D, the total axial thickness of the cores with the same shift angle is equal regardless of the shift angle. As long as the total axial thickness of the cores with the same shift angle is constant regardless of the shift angle, the method for shifting cores is not limited to the methods shown inFIGS. 18A to 18D, and may be any combination of methods for shifting cores.

In the above description, the stator core, that is, the permanent magnet254is skewed thereby to reduce the sixth toque pulsation of the three-phase motor, for simplification. The inventors considered that the pulsation due to the rotating magnetic flux made by the stator current using the magnetic air gaps258can be handled by introducing the above-mentioned concept of the means for skewing with skew by the magnet (seeFIG. 18).

For example, the inventors have found through studies that the combination of the above-mentioned cores301and302shown inFIG. 5can be basically applied to the case shown inFIG. 18A. That is, as shown inFIG. 13, the cycle and amplitude of torque pulsation generated in the cores301and302with the magnetic air gaps258aand258bformed therein may be actually examined, and the positions of the cores301and302may be found in such a manner that the torque pulsations due to the respective cores have reverse phases from each other, or are shifted from each other by one third of a cycle. Then, the cores301and302may be disposed such that the total torque pulsation is reduced.

Furthermore, the conventional stage skew for axially dividing the magnet and the simulated skew for shifting the magnetic air gaps258provided in the auxiliary salient pole259may be used together. For example, the primary component of the torque pulsation in a cycle of 60 degrees is electrically cancelled by shifting the permanent magnets254from each other by 30 degrees in terms of electrical angle, and the secondary component of the torque pulsation in a cycle of 30 degrees is cancelled by the simulated skew of the magnetic air gaps258.

In the above-mentioned embodiment, the skew structure for shifting in stages as shown inFIG. 18is employed so as to prepare only one type of mold for forming the rotor core252using a silicon steel plate. Alternatively, as shown inFIGS. 19A and 19B, a skew structure may be taken so as to have the continuously shifted magnetic air gap258. In the figure, the case of 60 degrees is to reduce the odd-numbered component of the torque pulsation, while the case of 30 degrees is to reduce the even-numbered component of the pulsation. In any case, the magnetic air gap258is shifted so as to continuously change the cycle of the pulsation from zero to one cycle.

FIG. 20shows the case where this embodiment is applied to a surface magnet type rotor. A method for fixing the magnets254(254a,254b) to the rotor core252may include fixing with an adhesive. Another method may include holding a tape on the surface of a rotor by winding the tape on the rotor surface. An auxiliary salient pole259is provided between the permanent magnets254, and a slot is formed as a magnetic air gap258ain a position shifted from the center of the auxiliary salient pole259(on the q axis).FIG. 20shows a section of the rotor taken along the line A-A. In the section taken along the line B-B, a magnetic air gap (slot)258bis formed in a position symmetric to the magnetic air gap258a, like the above-mentioned embodiment.

In the example shown inFIG. 20, the slot is provided in the auxiliary salient pole, but the auxiliary salient pole itself may be bilaterally asymmetric. The sectional shape of the permanent magnet254is an arc shape on the stator core side, but may be linear. Conventionally, such a surface magnet type motor reduces the torque pulsation by means of a curvature radius of the permanent magnet254on the outer peripheral side. Provision of the magnetic air gaps258of this embodiment in such a motor structure can reduce higher level torque pulsation.

FIG. 21shows the concentrated winding of stator windings238shown as the example inFIG. 20. Torque pulsation in this embodiment depends on the shape of the rotor250. Thus, even the concentrated winding system, which is different from the above-mentioned winding system on the stator side, can reduce the torque pulsation, like the case described above.

The above-mentioned rotary electric machine of this embodiment has the following operation and effects.

(1) The magnetic air gaps258aand258bare provided in the auxiliary salient poles259. The magnetic air gaps258aand258bare arranged to be shifted from each other such that the torque pulsations caused by the gaps258aand258bin energization cancel each other as shown inFIG. 13. As a result, the torque pulsation of the rotary electric machine can be reduced in energization. In particular, the rotary electric machine of this embodiment that can reduce the torque pulsation in energization can be used as a motor for traveling an electric vehicle or the like to reduce vibration and noise in low-speed acceleration, which can provide the electric vehicle with good ride quality and high level of silence.
(2) As shown inFIG. 9, in non-energization, the magnetic air gap258has little influence on the magnetic flux. Thus, measures for reducing the cogging torque due to the magnetic flux of the permanent magnet254, and measures for reducing the torque pulsation in energization can be independently taken. As a result, both optimization of the magnet torque and reduction of the torque pulsation in energization can be achieved so as to lessen the cogging torque and increase the torque in energization. Conventionally, the magnet is constructed so as to maximize the torque, and thereafter the skew or the like is provided so as to lessen the cogging torque, which results in reduced torque (magnet torque). However, this embodiment can avoid reduction of torque caused due to reduction of the torque pulsation.
(3) As mentioned above, since reduction of the magnet torque together with the reduction of torque pulsation can be prevented, the magnet can be made as small as possible, which can achieve reduction in size and cost of the rotary electric machine.
(4) Since the positions of the magnetic air gaps258aand258bprovided in the auxiliary salient poles259are shifted from each other to reduce the torque pulsation in energization, the permanent magnet254does not need to be axially divided into a plurality of parts and magnetized while being skewed, unlike the conventional skew structure. A rare-earth magnet, typified by a neodymium-based magnet, for example, is used for the permanent magnet254, and is subjected to grinding to be shaped. Thus, the accuracy for preventing a manufacturing error is enhanced, which directly leads to an increase in cost. Thus, according to this embodiment which does not need dividing the magnet in the axial direction, the cost of the rotary electric motor can be reduced. Thus, the accumulation of tolerances of the magnets does not increase variations in properties of the rotary electric machines, and does not deteriorate yield ratios of the machines. In this way, this embodiment can achieve improvement of productivity of the rotary electric machine, and also reduction in manufacturing cost.
(5) A leakage of magnetic flux of the field pole can be reduced by the magnetic air gap257to improve the efficiency of the rotary electric machine. As mentioned above, the magnetic air gap257has an effect of reducing the cogging torque. Further, the magnetic air gap257has another effect of reducing the leakage of magnetic flux from the permanent magnet. Now, the effect will be described usingFIG. 9. The permanent magnets254sand254bhas an N/S pole on the stator230side, and a reverse S/N pole on the center side of the rotor. A magnetic circuit for short-circuiting of a portion between the poles of the permanent magnet254via the auxiliary salient pole259can be generated. The short-circuited magnetic flux does not contribute to the magnet torque, leading to reduction in efficiency of the rotary electric machine. Provision of the magnetic air gap257can form a narrow and long magnetic passage (magnetic bridge) between the magnetic air gap257and the outer periphery of the rotor along the direction of rotation (in the peripheral direction). As shown inFIG. 9, the provision of the magnetic air gap257can form the magnetic bridge, thereby reducing leakage magnetic fluxes. The sectional area of the magnetic circuit of the magnetic bridge is small, and thus the magnetic circuit is brought into a magnetic saturation state, whereby the amount of magnetic reflux passing through the magnetic bridge can be reduced thereby to improve the efficiency of the rotary electric machine. The amount of magnetic reflux passing through the magnetic bridge can be decreased, which makes the influence of the magnetic air gap258on the cogging torque very small. The magnetic air gap257can have various shapes, and further can have a shape with a curved line. This shape is formed so as to avoid concentration of mechanical stress, whereby the mechanical stress is only slightly concentrated, so that the sectional area of the shape can be made small to reduce the leakage magnetic flux.

SECOND EMBODIMENT

FIGS. 22 to 24are diagrams for explaining the second embodiment of the invention.

FIG. 22Ais a sectional view of the rotor250corresponding to the section taken along the line A-A shown inFIG. 6A, andFIG. 22Bis a sectional view of the rotor250corresponding to the section taken along the line B-B shown inFIG. 6B. That is, also in the second embodiment, the rotor core252is constructed of three cores as shown inFIG. 5.FIG. 22Ashows the section of the core301, and theFIG. 22Bshows the section of the core302. In the above example shown inFIG. 6, the magnetic air gaps258are formed as the slot on the surface of the rotor core252. In the second embodiment, the air gaps258are formed inside the rotor core252.

The sectional shape of the permanent magnets245(254a,254b) is rectangular, and the magnetic air gap258is provided so as to be in contact with one side of the field pole made by the permanent magnets245(254a,254b). InFIG. 22A, a magnetic air gap258ais provided so as to be in contact with one side of the permanent magnet254in the circumferential direction. InFIG. 22B, a magnetic air gap258bis provided so as to be in contact with the other side of the permanent magnet254in the circumferential direction. Also in this case, the permanent magnet254is located at the center on the d axis. The magnetic air gap258ais disposed shifted toward the permanent magnet254awith respect to the center (q axis) of the auxiliary salient pole259, and the magnetic air gap258bis disposed shifted toward the permanent magnet254bwith respect to the q axis.

Also, in the second embodiment, different torque pulsations are generated in the core301and in the core302. These pulsations act to cancel each other, thereby enabling reduction of the total torque pulsation. Like the first embodiment, the magnetic air gap258is formed in the auxiliary salient pole259, which has little influence on the cogging torque. That is, the magnetic air gap258is provided to suppress the influence of the cogging torque on reduction of the pulsation, and thus can reduce the torque pulsation in energization substantially separately from the cogging torque pulsation. The use of the permanent magnet254having a rectangular section can reduce a processing cost of magnets.

The example shown inFIG. 23is a modified one of the rotor250shown inFIG. 22.

In the example shown inFIG. 22, one of the sides of the permanent magnet254is in contact with the rotor core252, and the other of the sides thereof is in contact with the magnetic air gap258. Thus, the other side of the permanent magnet in contact with the magnetic air gap258allows the short-circuited portion of the magnet magnetic flux to be shifted toward the magnetic air gap258, so that the center of the magnet is shifted from the center of the magnetic flux of the magnet. In the example shown inFIG. 23, a bridge260constructed of the stator core252is provided between the permanent magnet254and the magnetic air gap258. In this way, the magnetic flux is also short-circuited by the bridge260on the magnetic air gap side, thus allowing the magnetic flux to leak in the same manner as that on the other side of the permanent magnet254. Thus, routes for short-circuiting the magnetic fluxes on both sides of the permanent magnet254are the same to each other, and thus can more reduce the influences of the magnetic air gap258on the cogging torque and induced voltage.

FIG. 24is a diagram of another example of the second embodiment, showing a plurality of permanent magnets245provided on the respective poles of the rotor250. The rotor250and the entire rotary electric machine including the stator and the sensor have the same structures and also the same basic operations and effects as those described above, except for the permanent magnets254aand254bconstituting the respective field poles, or the magnetic air gap257for reducing the cogging torque or leakage magnetic flux, or the magnetic air gap258bfor reducing pulsation due to the rotating magnetic field made by a stator current. In the example shown inFIG. 24, the permanent magnets for forming field poles are constructed of a plurality of permanent magnets254(two magnets in this embodiment) disposed in a V shape. The sectional view shown inFIG. 23corresponds to the sectional view taken along the line B-B shown inFIG. 6B. A pair of permanent magnets254aand a pair of permanent magnets254bcorrespond to the permanent magnets254aand254bshown inFIG. 6B. A core portion between a magnetic pole made by each of the permanent magnets254aarranged in the V shape and a magnetic pole made by each of the adjacent permanent magnets254barranged in the V shape serves as the auxiliary salient pole259, and the q axis is located at the center of the auxiliary salient pole259.

Magnetic air gaps257for treating cogging torque are respectively provided on both ends in the circumferential direction of the permanent magnet254having a rectangular section, like the rotor250shown inFIG. 6. Also, in the rotor250shown inFIG. 24, the magnetic air gap258bis provided in the rotor core252, and is arranged shifted toward one side (left side) in the rotation direction (circumferential direction) with respect to the q axis provided at the center of the auxiliary salient pole259. The effect of suppressing the torque pulsation by the magnetic air gap258bbecomes higher as the magnetic air gap258bis located closer to the surface of the rotor core252. The rotor core is disposed in the magnetic air gap258bto be shifted toward one side (left side) in the rotation direction with respect to the q axis provided at the center of the auxiliary salient pole259. A rotor core (not shown) is disposed in the magnetic air gap258ato be shifted toward the other side (right side) in the rotation direction with respect to the q axis provided at the center of the auxiliary salient pole259. These rotor cores are arranged along the rotation axis as explained inFIGS. 18 and 19. Thus, the pulsations generated in the rotor cores are cancelled each other, which can reduce the total pulsation.

In the example shown inFIG. 24, the auxiliary salient pole259is widened, so that the reluctance torque can be used more effectively. A magnet hole for accommodating therein the permanent magnet254is formed to make the bridge260narrow such that the magnetic flux of the permanent magnet254does not run around and enter the core. Although the magnetic air gap258bis provided in the rotor core252, a concave portion (slot) may be provided as the magnetic air gap258bon the surface of the rotor core252, like the first embodiment. The structure having the section as shown in the sectional view taken along the line A-A is the same as the section shown in the sectional view taken along the line B-B inFIG. 24, except that the magnetic air gap258ais provided in a position symmetric to the q axis. Thus, as mentioned above, the description and illustration thereof will be omitted.

In other example, the V shaped magnet structure includes doubly superimposed magnets. The magnetic air gaps258are arranged shifted in the auxiliary salient pole259with respect to the q axis to reduce the torque pulsation. This effect does not apparently change regardless of the arrangement of the permanent magnets254. InFIG. 24, a magnetic air gap258ais provided adjacent to the magnetic air gap257. A slot like the first embodiment may be provided, or the magnetic air gap257and the magnet air gap258amay be integrated.

THIRD EMBODIMENT

FIG. 25shows a rotor250according to a third embodiment.FIG. 25Ais a sectional view corresponding to the sectional view taken along the line A-A shown inFIG. 6A, andFIG. 25Bis a sectional view corresponding to the sectional view taken along the line B-B shown inFIG. 6B. In the example shown inFIG. 25, two kinds of magnetic air gaps per one pole are provided. That is, a pair of magnetic air gaps251are also provided in the core on the outer peripheral side of the magnet, in addition to the magnetic air gaps258in the auxiliary salient pole259. The magnetic air gaps251are symmetrically provided with respect to the d axis passing through the center of the permanent magnet. The magnetic air gaps251may be provided asymmetrically. The magnetic air gap251is mainly provided for reducing the cogging torque, and thus is disposed in the core on the outer peripheral side of the magnet through which the magnet flux passes. Such an arrangement can respectively reduce the primary and secondary torque pulsations, and also the cogging torque and the torque pulsation in energization.

The rotor250having slots formed as the magnetic air gap258on the surface of the rotor core252can be cooled through the slots. As shown inFIG. 26, the rotary electric machine200is sealed in the housing234, in which oil403for cooling is charged so as to slightly cover the rotor250. The oil403circulates by a pump402for cooling and is cooled by a radiator401. The rotor250has slots257which allow the oil to penetrate the core302located at the axial center shown inFIG. 5. With the slant slots (magnetic air gaps258) shown inFIG. 24, the rotation of the rotor250allows the oil to enter the rotor thereby to cool the axial center of the rotor250. A neodymium-based magnet has a low heatproof temperature of about 200° C., and thus demagnetized at high temperatures, which is a problem from the viewpoint of downsizing. Thus, the provision of such a cooling route is effective for downsizing the motor for the hybrid vehicle or the electric vehicle. Two or more types of magnetic air gaps258may be formed in the auxiliary salient pole259. This can enhance flexibility of reduction of torque pulsation, and further can reduce the torque pulsation in more detail.

As mentioned above, in the embedded magnet type rotary electric machine of this embodiment using reluctance torque generated by the auxiliary salient pole259, the cores with the magnetic air gaps258are laminated in the direction of lamination in respective positions shifted from the q axis which is the center of the auxiliary salient pole259to constitute the rotor. The rotary electric machine can reduce the torque pulsation in energization separately from the reduction of pulsation of the cogging torque. As a result, such a rotary electric machine is applied to the motor for traveling the electric vehicle or hybrid vehicle, thus resulting in less vibration and noise in low-speed acceleration, thereby improving the ride quality and the level of silence.

FOURTH EMBODIMENT

A fourth embodiment of the invention will be described below usingFIGS. 27 to 32.FIG. 27is a partial diagram of the outer appearance of a rotor core252. The rotary electric machine includes a core301having the rotor core252and a magnetic air gap (cutout)258formed on one side thereof in the rotation direction with respect to the center of the auxiliary salient pole259, and a core302having a magnetic air gap (cutout)258formed on the other end in the rotation direction with respect to the center of the auxiliary salient pole259. As described inFIG. 5, the length of the core302in the direction of the rotor is about twice as long as that of the core301. The rotary electric machine structure is not limited thereto, and the shape and combination of the cores may be modified as explained with reference toFIGS. 17 to 19. Permanent magnets254aand254binserted into the cores301and302have substantially the same shape in the substantially same rotation position. An integrated permanent magnet254may be inserted. Alternatively, a permanent magnet may be divided regardless of the cores301and302. The hole for insertion of the permanent magnet254and the magnetic air gap257in the core301have substantially the same respective shapes and rotation positions as those of the hole and the magnetic air gap257in the core302. These holes and air gaps are continuously formed in the direction of rotation axis.

In this embodiment, each field pole has one permanent magnet254. Alternatively, as shown inFIG. 24, each field pole may have a plurality of permanent magnets254. An auxiliary salient pole259is provided between the adjacent field poles, and the above-mentioned magnetic air gap257, the magnetic bridge272, and the slot282are further provided between the auxiliary salient pole259and an area between the field poles. A stator side core of each permanent magnet254serves as a magnet pole piece262. The magnetic flux generated from the permanent magnet254ais guided from the magnetic pole piece262formed on the stator side of the permanent magnet254ato the stator, and then guided from the stator to the permanent magnet254bvia the magnet pole piece262formed on the stator side of the permanent254b. The above-mentioned permanent magnet254aand the permanent magnet254bare magnified to reverse polarities as described above.

Each magnetic bridge272provided between each field pole and the auxiliary salient pole259serves to lessen the magnetic fluxes which leak from the magnetic pole piece262to the auxiliary salient pole259, or serves to lessen the magnetic fluxes which leak from the magnetic pole pieces262to the magnetic pole on the side opposite (on the rotation axis side) to each permanent magnet254. That is, when each magnetic bridge272is magnetically saturated, a magnetic resistance becomes very large, and the magnet reflux passing is restricted. Further, in this embodiment, the slot282is provided to make the magnetic bridge272long, and to have a spring property, thereby preventing concentration of stress due to a centrifugal force. The slot282has such a shape with a wide bottom284and with a curved surface similar to an arc shape as to prevent concentration of the stress.

FIGS. 28 and 29, andFIGS. 30 to 32show parts of sections perpendicular to the stator and the rotation axis of the rotor.FIGS. 30 to 32slightly differ fromFIGS. 28 and 29in the shape of the magnetic air gap257, the magnetic bridge272, and the slot282, but have the same basic concept as that ofFIGS. 28 and 29.FIGS. 28,30, and32show the structure of the rotor core used in the core301, andFIGS. 29 and 31show the structure of the rotor core used in the core302. The basic structures ofFIGS. 28 to 32are those such as described above with reference toFIG. 27. In these drawings, the magnetic air gaps257are respectively provided on the auxiliary salient pole259of the permanent magnet254. The magnet air gap257extends in the rotation direction of the rotor to form the magnetic bridge272between the magnetic air gap257and the surface of the rotor. The magnetic bridge272leads to the magnetic pole piece262via the air gap. The magnetic air gap257extends in the rotation direction along the outer periphery of the rotor250thereby to relieve a drastic change in magnetic flux density in the rotation direction (circumferential direction) caused by the air gap between the rotor230and the rotor250, thus reducing the cogging torque.

The slot282is formed on the auxiliary salient pole259side of the magnetic bridge272, and the magnetic bridge272directed in the radial direction is formed between the magnetic air gap257and the slot282. In these embodiments, the outer peripheral side of the magnetic bridge272directed in the radial direction is directed in the direction of the line L2with respect to the normal line L1extending radially through the rotation axis. The length of the magnetic air gap257in the radial direction is shorter than that of the permanent magnet254in the radial direction. The magnet bridge272has its direction changed along the shape of the magnetic air gap257on the auxiliary salient pole259side, and is directed in the direction of the line L3. The line L2is directed from the permanent magnet254to the auxiliary salient pole259as the line L2approaches the center of the rotor. That is, the line L2is directed such that a distance from the line L1becomes wider in the rotation direction as the line L2approaches the center of the rotor. The line L3is directed from the auxiliary salient polar259to the permanent magnet254as the line L3approaches the center of the rotor. That is, the line L3is directed such that a distance from the line L1becomes narrower in the rotation direction as the line L3approaches the center of the rotor. Thus, the magnetic bridge272changes from the direction of the line L2to the direction of the line L3which is directed opposed to the rotation direction with respect to the line L1.

The magnetic bridge272has such a shape to prevent the centrifugal force with respect to the mass of the permanent magnet254and the magnetic polar piece262from being concentrated on a part of the bridge272, and thus has resistance to high-speed rotation. Conversely, the magnetic sectional area of the magnetic bridge272can be made small, which can reduce the leak magnetic flux, thereby improving the magnetic properties. The bottom284of the slot282is formed deeply in the rotation axis direction with respect to the magnetic air gap257, and expands along the circumferential direction (rotation direction), facilitating the change from the direction of the line L2of the magnetic bridge272to the direction of the line L3. Further, the concentration of stress on the slot bottom284can be prevented.

As shown inFIGS. 28 and 29, the magnetic air gap258has a relatively small cutout, but as shown inFIGS. 30 to 32, the gap258has a relatively large cutout.FIG. 28toFIG. 32precisely illustrate the sizes of the rotor, the stator, and the slot, and the relationship between the sizes of other components. The ratio .θa/θm of an angle θa in the rotation direction of the auxiliary salient pole259sandwiched between the slots282to an angle θm in the rotation direction of the permanent magnet254is about 0.5 (θa/θm≅0.5). The ratio θc/θm of an angle θc in the rotation direction of the magnetic air gap (cutout)258to the angle θm is about 0.5 (θc/θm≅0.5). This relationship is one of examples.

The condition of θa/θm is desirably more than 0.25 and less than 0.75 (0.75>θa/θm>0.25). It is desirable that θc is larger than the opening on the rotor side of each slot of the stator, and that θc/θm is smaller than 0.7 (0.7>θc/θm). Further, the condition of θc/θm that is less than 0.5 is optimal. The depth of the magnetic air gap258in the radial direction is equal to or less than a half of the width of the permanent magnet254in the radial direction.

The embodiments shown inFIGS. 27 to 32have the operations and effects exhibited by the above-mentioned embodiments. That is, the magnetic air gap258formed on the outer periphery of the auxiliary salient pole259on the stator side can reduce the pulsation caused due to the rotating magnetic field generating stator current. The slot282is formed between the magnetic air gap258and the permanent magnet254to reduce the amount of magnetic flux passing through the magnetic air gap258and generated by the permanent magnet254to a very small level, whereby the shape of the magnetic air gap258has very little influence on the cogging torque. In this embodiment, the magnetic air gaps257in addition to the slots282exist, whereby the shape of the magnetic air gap258has very little influence on the cogging torque. This can reduce pulsation due to the stator current by the above-mentioned solving means which has a very little influence on the cogging torque.

The magnetic air gap257provided on the auxiliary salient pole259side of each field magnetic pole of the rotor250further has an effect of reducing the cogging torque.

The bridge272is formed along the magnetic air gap257. The shape of the magnetic air gap257on the auxiliary salient pole259side can be made by a combination of curved lines, or by a combination of a curved line and a straight line. The shape of the magnetic bridge272on the magnetic air gap257side can be made into a curved shape, thereby preventing the concentration of stress. The magnetic bridge272is formed between the magnet air gap257and the slot282, thereby enabling prevention of the concentration of stress. This can form the magnetic bridge272having such a shape to endure a large centrifugal force generated in the permanent magnet254and the magnet pole piece262in high-speed rotation.

In each of the above-mentioned embodiments, the motor for driving the vehicle has been described. The invention is optimally applied to the rotary electric machine for driving the vehicle, but is not limited thereto. The invention can be applied to various types of motors. Further, the invention can also be applied to various types of rotary electric machines, including a generator, such as an alternator, in addition to the motor. The invention is not limited to the embodiments described herein without departing from the features of the invention.