Rotating electric machine and electrically driven vehicle

A rotating electric machine allowing a rotor and a stator thereof to assume any of various numbers of poles and any of various numbers of slots and enabling a reduction in vibration and noise is provided. The rotating electric machine according to the present invention includes a stator having a plurality of teeth and a plurality of slots, which is configured so that the shape of the front ends of the teeth and the opening width of the slots are made to change cyclically F times along the circumferential direction (F is a natural number equal to or greater than 2).

TECHNICAL FIELD

The present invention relates to a rotating electric machine and an electrically driven (electric-propulsion) vehicle having installed therein a rotating electric machine.

BACKGROUND ART

The present invention relates to a rotating electric machine used in traveling drive of an electrically driven vehicle such as an HEV or an EV.

Rotating electric machines used in applications such as home appliance products and various types of OA devices have come to be used in recent years in electrically driven vehicles such as hybrid vehicles (HEVs) and electric vehicles (EVs).

The rotating electric machine for an electrically driven vehicle such as an HEV or an EV in particular, must be able to provide large output. At the rotating electric machine for electrically driven vehicle application, which is engaged in operation over a wide rotation-rate range, the excitation frequency of the electromagnetic exciting force changes over a wide range and the natural frequency of vibration inherent to the structure of the rotating electric machine and the excitation frequency match at a specific rotation rate. For this reason, the occurrence of vibration and noise attributable to resonance is inevitable.

At the same time, there is an ongoing pursuit of improvement in the cabin environment with an attendant increase in the need for lessened vibration and noise. This has led to the development of numerous technologies for reducing vibration and noise originating from the rotating electric machine.

The electromagnetic exciting force, which causes vibration and noise originating from the rotating electric machine, works along three directions, i.e., the radial direction, the tangential direction and the axial direction. In order to reduce noise in the audible band, in particular, the amplitudes of harmonics in such electromagnetic exciting forces must be reduced.

The AC rotating electric machine disclosed in PTL 1, at which the number of slots formed in correspondence to a single pole in a given phase is two, openings (01, 02) at the individual slots are formed so that the intervals between centerlines A extending along the radial direction through slot openings formed next to one another are not uniform and a first three-phase stator winding and a second three-phase stator winding are installed at the stator core with a phase difference of 31° through 34° in electrical angle, succeeds in reducing the electromagnetic sound of 12f components of harmonics and as well as the sound of wind. The number of slots that can be formed at a stator core to adopt this invention is limited by a function of the number of phases and the number of poles, and thus, the technology must be further finessed in order for it to be adopted in stator cores with any numbers of slots free of such restrictions.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

The method proposed in the related art, through which noise caused by electromagnetic vibration is reduced by altering the shapes and pitches of the teeth formed on the stator side, does not assure enough flexibility to allow it to be adopted in conjunction with varying numbers of poles and varying numbers of teeth (slots) at the stator that may be formed in different combinations.

Solution to Problem

One aspect of the invention provides a rotating electric machine having a stator with a plurality of teeth and a plurality of slots, characterized in that the shape at front end areas of the teeth and the width of openings formed at the slots cyclically change F times (F is a natural number equal to or greater than 2) along the circumferential direction.

Advantageous Effects of Invention

According to the present invention, the amplitude of harmonics of the electromagnetic exciting force occurring along the tangential direction, which would lead to vibration and noise, can be reduced without having to alter the periodic boundary conditions, and as a result, vibration and noise occurring in the rotating electric machine can be reduced.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a schematic illustration showing the structure of a hybrid type electric vehicle having installed therein rotating electric machines achieved in an embodiment. An engine120, a first rotating electric machine200, a second rotating electric machine202and a battery180are mounted at a vehicle100. When a drive force generated via the rotating electric machines200and202is needed, the battery180provides DC power to a power conversion device (inverter device)600engaged in drive of the rotating electric machines200and202, and the power conversion device600converts the DC power supplied thereto to AC power which is then provided to the rotating electric machines200and202individually. During a regenerative traveling operation, on the other hand, the rotating electric machines200and202generate AC power by using the kinetic energy imparted by the vehicle and provide the AC power thus generated to the power conversion device600. The power conversion device600then converts the AC power to DC power and provides the DC power to the battery180. In addition, although not shown, a battery that provides low-voltage power (e.g., 14 V power) is installed in the vehicle so as to supply constant-voltage DC power to the control circuits to be described below.

Rotational torque generated via the engine120and the rotating electric machines200and202is transmitted to front wheels110via a transmission130and a differential gear unit132. The transmission130is controlled by a transmission control device134, whereas the engine120is controlled by an engine control device124. The battery180is controlled by a battery control device184. The transmission control device134, the engine control device124, the battery control device184, the power conversion device600and an integrated control device170are connected with one another via a communication line174.

The integrated control device170receives, via the communication line174, information originating from the transmission control device134, the engine control device124, the power conversion device600and the battery control device184, indicating the statuses at the individual control devices which are lower-order control devices relative to the integrated control device170. Based upon the information thus received, the integrated control device170generates, through arithmetic operation, a control command for each corresponding control device. The control command generated through the arithmetic operation is then transmitted to the particular control device via the communication line174.

The high-voltage battery180, constituted with secondary battery cells such as lithium ion battery cells or nickel hydride battery cells, is capable of outputting high-voltage DC power in a range of 250 to 600 V or higher. The battery control device184outputs, via the communication line174, information indicating the state of discharge in the battery180and the states of the individual battery cell units constituting the battery180to the integrated control device170.

Upon judging, based upon the information provided by the battery control device184, that the battery180needs to be charged, the integrated control device170issues a power generation operation instruction for the power conversion device600. The primary functions of the integrated control device170further include management of torque output from the engine120and the rotating electric machines200and202, arithmetic processing executed to calculate the overall torque, representing the sum of the torque output from the engine120and the torques output from the rotating electric machines200and202, and to calculate a torque distribution ratio, and transmission of control commands generated based upon the arithmetic processing results to the transmission control device134, the engine control device124and the power conversion device600. Based upon a torque command issued by the integrated control device170, the power conversion device600controls the rotating electric machines200and202so as to output torque or generate power as indicated in the command.

The power conversion device600includes power semiconductors that constitute inverters via which the rotating electric machines200and202are engaged in operation. The power conversion device600controls switching operation of the power semiconductors based upon a command issued by the integrated control device170. As the power semiconductors are engaged in the switching operation as described above, the rotating electric machines200and202are each driven to operate as an electric motor or as a power generator.

When engaging the rotating electric machines200and202in operation as electric motors, DC power provided from the high-voltage battery180is supplied to DC terminals of the inverters in the power conversion device600. The power conversion device600controls the switching operation of the power semiconductors so as to convert the DC power supplied to the inverters to three-phase AC power and provide the three-phase AC power to the rotating electric machines200and202. When engaging the rotating electric machines200and202in operation as generators, the rotors of the rotating electric machines200and202are rotationally driven with a rotational torque applied thereto from the outside and thus, three-phase AC power is generated at the stator windings of the rotating electric machines200and202. The three-phase AC power thus generated is converted to DC power in the power conversion device600and the high-voltage battery180is charged with the DC power supplied thereto.

It is to be noted that the rotating electric machine200and the rotating electric machine202are controlled independently of each other. For instance, when the rotating electric machine200is engaged in operation as an electric motor, the rotating electric machine202may operate as a motor or as a generator, or it may remain in an operation OFF state. This principle obviously applies to the rotating electric machine200as well. The integrated control device170determines a specific mode in which the rotating electric machine200and the rotating electric machine202are to be engaged in operation and issues a command for the power conversion device600accordingly. Based upon this command, the power conversion device600enters a motor operation mode, a generator operation mode or an operation OFF mode.

FIG. 2is a conceptual circuit diagram pertaining to the power conversion device600shown inFIG. 1. The power conversion device600includes a first inverter device for the rotating electric machine200and a second inverter device for the rotating electric machine202. The first inverter device comprises a power module610, a first drive circuit652that controls switching operation of power semiconductors21in the power module610and a current sensor660that detects an electric current at the rotating electric machine200. The drive circuit652is disposed at a drive circuit board650. The second inverter device comprises a power module620, a second drive circuit656that controls switching operation of power semiconductors21in the power module620and a current sensor662that detects an electric current at the rotating electric machine202. The drive circuit656is disposed at a drive circuit board654. A control circuit648disposed at a control circuit board646, a capacitor module630and a transmission/reception circuit644mounted at a connector board642are all shared by the first inverter device and the second inverter device.

The power modules610and620are engaged in operation with drive signals output from the corresponding drive circuits652and656. The power modules610and620each convert the DC power provided from the battery180to three-phase AC power and provide the three-phase AC power resulting from the conversion to a stator winding constituting an armature winding of the corresponding rotating electric machine200or202. In addition, the power modules610and620convert AC power induced at the stator windings of the rotating electric machines200and202to DC power and provide the DC power resulting from the conversion to the high-voltage battery180.

As indicated inFIG. 2, the power modules610and620each include a three-phase bridge circuit constituted with serial circuits each corresponding to one of the three phases electrically connected in parallel between the positive pole side and the negative pole side of the battery180. Each serial circuit includes a power semiconductor21constituting an upper arm and a power semiconductor21constituting a lower arm connected in series. Since the power module610and the power module620adopt circuit structures substantially identical to each other as shown inFIG. 2, the following description focuses on the power module610chosen as a representative example.

The switching power semiconductor elements used in the embodiment are IGBTs (insulated gate bipolar transistors)21. An IGBT21includes three electrodes; a collector electrode, an emitter electrode and a gate electrode. A diode38is electrically connected between the collector electrode and the emitter electrode of the IGBT21. The diode38includes two electrodes; a cathode electrode and an anode electrode, with the cathode electrode electrically connected to the collector electrode of the IGBT21and the anode electrode electrically connected to the emitter electrode of the IGBT21so as to define the direction running from the emitter electrode toward the collector electrode at the IGBT21as a forward direction.

It is to be noted that MOSFETs (metal oxide semiconductor field effect transistors) may be used as the switching power semiconductor elements, instead. A MOSFET includes three electrodes; a drain electrode, a source electrode and a gate electrode. The MOSFET does not require a diode38, such as those shown inFIG. 2, since it includes a parasitic diode with which the direction running from the drain electrode toward the source electrode is defined as the forward direction, present between the source electrode and the drain electrode.

The upper and lower arms in the serial circuit corresponding to a given phase are configured by electrically connecting the source electrode of one IGBT21and the drain electrode of another IGBT21in series. It is to be noted that while the figure shows the upper arm and the lower arm corresponding to a given phase each constituted with a single IGBT, a large current control capacity needs to be assured in the embodiment and thus, a plurality of IGBTs are connected in parallel to constitute an upper arm or a lower arm in the actual power module. However, for purposes of simplification, the following explanation is given by assuming that each arm is constituted with a single power semiconductor.

In the example presented inFIG. 2, the upper arms or the lower arms, each corresponding to one of the three phases, are configured with three IGBTs. The drain electrode of the IGBT21constituting the upper arm in a given phase is electrically connected to the positive pole side of the battery180, whereas the source electrode of the IGBT21constituting the lower arm in a given phase is electrically connected to the negative pole side of the battery180. A middle point between the arms corresponding to each phase (an area where the source electrode of the upper arm-side IGBT and the drain electrode of the lower arm-side IGBT are connected) is electrically connected to the armature winding (stator winding) at the corresponding phase at the corresponding rotating electric machine200or202.

The drive circuits652and656, constituting drive units via which the corresponding inverter devices610and620are controlled, generate drive signals used to drive the IGBTs21based upon a control signal output from the control circuit648. The drive signals generated at the individual drive circuits652and656are respectively output to the gates of the various power semiconductor elements in the corresponding power modules610and620. The drive circuits652and656are each configured as a block constituted with six integrated circuits that generate drive signals to be provided to the gates of the upper and lower arms corresponding to the various phases.

The control circuit648, which controls the inverter devices610and620, is constituted with a microcomputer that generates, through arithmetic operation, a control signal (a control value) based upon which the plurality of switching power semiconductor elements are engaged in operation (turned on/off). A torque command signal (a torque command value) provided from a higher-order control device, sensor outputs from the current sensors660and662, and sensor outputs from rotation sensors mounted at the rotating electric machines200and202are input to the control circuit648. Based upon these signals input thereto, the control circuit648calculates control values and outputs control signals to be used to control the switching timing to the drive circuits652and656.

The transmission/reception circuit644mounted at the connector board642, which electrically connects the power conversion device600with an external control device, is engaged in information exchange with another device via the communication line174shown inFIG. 1. The capacitor module630, constituting a smoothing circuit via which the extent of DC voltage fluctuation occurring as the IGBTs21are engaged in switching operation is reduced, is electrically connected in parallel with DC-side terminals of the first power module610and the second power module620.

FIG. 3is a schematic sectional view of a permanent magnet rotating electric machine10configured as an example of the rotating electric machine according to the present invention. This permanent magnet rotating electric machine10may be used as the rotating electric machine200or the rotating electric machine202in the hybrid vehicle (seeFIG. 1andFIG. 2) described above. It is to be noted that as explained later, the structure of the rotating electric machine according to the present invention may be adopted in a synchronous reluctance motor or an induction motor instead of a permanent magnet rotating electric machine.

The structural features characterizing the present invention, as achieved in embodiments 1 through 4, will be described next in reference toFIG. 3throughFIG. 14. It is to be noted that coils are wound at the teeth of the stator through distributed winding in each of the embodiments described below. This means that the computation results presented inFIGS. 7 through 10andFIGS. 13 and 14have been obtained in conjunction with coils wound through the distributed winding method.

FIG. 3illustrates embodiment 1 of the rotating electric machine according to the present invention. The rotating electric machine shown inFIG. 3represents an example in which the present invention is adopted in a three-phase permanent magnet rotating electric machine with eight poles and 72 slots. Each group of teeth may be made up with m (=9) teeth, with m representing the quotient calculated by dividing the number S (=72) of slots at the stator by the greatest common divisor N (=8) of the number of poles P and the number of stator slots S, or with d (=3) teeth, with d representing a divisor of m. The teeth in a single group include a tooth having a groove formed at the front end thereof and a tooth having no such groove, and the slots in the group include those with varying opening widths.FIG. 4illustrates an example of a shape that may be assumed in grooves formed at the front ends of nine teeth5ato5imaking up a single tooth group50.FIG. 4also illustrates examples of opening widths that may be assumed at nine slots4ato4imaking up a single slot group40. It is to be noted that unless specifically noted, a given tooth or slot will be simply referred to as a tooth5or a slot4. It is also to be noted that reference numeral8indicates a permanent magnet.

FIG. 4shows the nine teeth5athrough5iincluded in one tooth group50, with grooves6cthrough6hformed at the front ends of six teeth5cthrough5hamong the nine teeth. At a stator core1shown inFIG. 3, the arrangement of the nine teeth5athrough5iinFIG. 4are iterated cyclically so that there are eight groups of teeth set along the circumferential direction. It is to be noted thatFIG. 3does not include an illustration of the shapes of the front ends of these teeth. In addition, it does not include an illustration of stator coils wound through the slots4at the stator core1constituting the rotating electric machine10.

Furthermore, a single slot group40is formed with nine slots4athrough4icorresponding to the nine teeth5athrough5imaking up the single tooth group50inFIG. 4. The slot group40includes slot subgroups42each made up with d (=3) slots, with d representing a divisor of m, which is the quotient, obtained by dividing the number of slots S by the greatest common divisor N. The openings at the individual slots are formed so that openings (41a,41d,41g) have equal opening widths, openings (41b,41e,41h) have equal opening widths and openings (41c,41f,41i) have equal opening widths. In addition, slot sub-groups are each made up with the slots4athrough4c, the slots4dthrough4for the slots4gthrough4i. In other words, the m slots in a single slot group40may form sub-groups42, each made up with d (≠m) slots with d representing a divisor of m (seeFIG. 4). Likewise, the m teeth5in a single tooth group50may form sub-groups each made up with d (≠ m) teeth with d representing a divisor of m.

The □ marks inFIG. 7indicate computation results obtained in conjunction with a rotating electric machine (embodiment 1) that includes the stator core1, having the tooth groups50and the slot groups40formed as shown inFIG. 4. It is to be noted thatFIG. 7andFIG. 8also provide computation results obtained in correspondence to other embodiments (embodiments 2 and 3) and the rotating electric machine having a stator core1of the related art, as will be explained later.

FIG. 5illustrates embodiment 2 of the rotating electric machine according to the present invention. A single tooth group51is made up with three stator teeth5jthrough5land a single slot group43is made up with three slots4jthrough4l(with slot openings41jthrough41l). Grooves6(6k,6l) are formed at the front ends of teeth5in the tooth group51, as shown inFIG. 5. In the example presented inFIG. 5, the grooves6kand6lformed at the front ends of the teeth5kand5lhave identical shapes. In addition, the slot openings41jand41khave equal opening widths with the slot opening41lhaving a different opening width in the example presented inFIG. 5. A tooth group50such as that shown inFIG. 3can be formed by disposing the teeth making up the tooth group51and the slot group43(4jthrough4l) corresponding to the tooth group51cyclically along the circumferential direction at the stator core1so that three groups of teeth and slots are set side-by-side along the circumference of the stator core1.

In other words, the stator core1shown inFIG. 3is formed by disposing the teeth5and the slots4corresponding to a single tooth group51shown inFIG. 5cyclically so that a total of 24 groups are formed side-by-side along the circumferential direction in embodiment 2. The computation results corresponding to this structure (embodiment 2) are indicated with ∘ marks inFIG. 7.

FIG. 6illustrates embodiment 3 of the rotating electric machine according to the present invention. A single tooth group51is made up with three teeth5mthrough5oand a single slot group44is made up with three slots4mthrough4o(with slot openings41mthrough41o). Grooves6(6n,6o) are formed at the front ends of the teeth5forming the tooth group51. In the example presented inFIG. 6, the grooves6nand6oformed at the front ends of the teeth5nand5ohave identical shapes. These grooves are formed in a shape identical to that of the grooves6(6kand6l) inFIG. 5. However, the example presented inFIG. 6is distinguishable from that inFIG. 5in that the middle slot among the three slots has an opening width different from the opening width of the other slots. Namely, the slot openings41mand41ohave equal opening widths and the slot opening41nhas an opening width different from the opening width of the other two slot openings.

In the example presented inFIG. 5, the slot openings41jand41khave equal opening widths and the slot opening41lhas a different opening width. In the example presented inFIG. 6, the slot openings41mand41ohave equal opening widths and the slot opening41nhas a different opening width. In other words, the structure shown inFIG. 5(embodiment 2) and the structure shown inFIG. 6(embodiment 3) are distinguishable from each other in that the position of the slot opening having an opening width different from that of the other slot openings in the slot group43is different from the position of the slot opening having an opening width different from that of the other slot openings in the slot group44. This means that the pattern with which the shapes of the tooth grooves at the individual teeth forming a given tooth group change and the pattern with which the opening widths at the slot openings in the slot group corresponding to the tooth group change inFIG. 5are different from those shown inFIG. 6. This may otherwise be described as follows. Namely, the tooth groove shape change pattern and the slot opening width change pattern inFIG. 6are offset relative to those shown inFIG. 5. It is to be noted that the patterns in the structure shown inFIG. 6, allowing the tooth groove shapes and the slot opening widths to achieve symmetry relative to a radial line passing through the center of the middle slot4nat the central position in the slot group44can be formed by inverse laminating the laminated steel material used to configure the stator core1.

In embodiment 3, the stator core1shown inFIG. 3is formed by forming the teeth5and the slots4arranged in a tooth group51shown inFIG. 6cyclically, so that a total of 24 groups are disposed side-by-side along the circumferential direction. The computation results corresponding to this structure (embodiment 3) are indicated with ⋄ marks inFIG. 7.

The periodic boundary conditions of the geometric configuration achieved as a combination with a rotor core2and the magnets8in the related art, in which all the teeth5and all the slots4have uniform shapes, is defined by the value ⅛. According to the present invention, tooth grooves at the individual teeth in each tooth group are not formed uniformly and/or the opening widths at the openings in each slot group are not all equal. However, by iterating a tooth group50or51and a slot group40,43or44, formed as in any of embodiments 1 through 3, along the entire circumference of the stator core1, the amplitudes of the electromagnetic force harmonics can be adjusted without having to alter the periodic boundary conditions of the geometric configuration achieved as the combination with the rotor core2and the magnets8from the periodic boundary conditions defined by the value ⅛ in the related art.

In embodiments 1 through 3, the reluctance in the air gap (the space between the inner circumference of the stator core1and the outer circumference of the rotor core2) can be varied by forming grooves at the front ends of teeth5and altering the opening width at the slot openings41. As the reluctance is altered, the amplitudes or the phases of the magnetic flux harmonics change, which, in turn, results in a change in the amplitudes of the electromagnetic force harmonics.

(Effect of Electromagnetic Exciting Force Harmonic Reduction Achieved in the Rotating Electric Machine According to the Present Invention)

FIG. 7presents results obtained through analysis, indicating the electromagnetic force harmonic amplitudes of the 0th-order in space along the tangential direction at rotating electric machines having stator cores1with the teeth and the slots thereof formed as in embodiments 1 through 3 and in the related art. InFIG. 7, the electromagnetic force harmonic amplitudes are rendered dimensionless in reference to the rotation 72nd-order harmonic amplitude in the related art. Pertaining to the related art,FIG. 7indicates that among the electromagnetic force harmonics of the tangential direction space 0th-order, the electromagnetic force harmonic component of the rotation 72nd-order achieves the largest amplitude and that when the excitation frequency of the electromagnetic harmonic of rotation 72nd-order and the natural frequency of the rotating electric machine excited by this exciting force match, significant vibration and noise occur.

FIG. 8represents a dB representation of the tangential direction space 0th-order harmonic amplitude of the rotation 72nd-order prepared in view of the above findings.FIG. 8indicates that the electromagnetic force harmonic amplitude is reduced relative to the related art by 3.6 dB in embodiment 1 by 4.7 dB in embodiment 2 and by 3.8 dB in embodiment 3. This means that through embodiments 1 through 3, vibration and noise caused by the electromagnetic force harmonic of the tangential direction space 0th-order with the rotation 72nd-order can be reduced relative to the vibration and noise occurring in the related art.

FIG. 9presents computation results obtained with regard to levels of acoustic power generated from rotating electric machines, one equipped with a stator core1having teeth and slots formed as in embodiment 2 and another equipped with a stator core1having teeth and slots formed as in the related art, by inputting an electromagnetic force harmonic of the tangential direction space 0th-order with the rotation 72nd-order. InFIG. 9, the acoustic power levels are rendered dimensionless in reference to the acoustic power level maximum value in the related art.FIG. 9indicates that the acoustic power level peak manifesting in the vicinity of 2000 rpm is lowered relative to the acoustic power level peak in the related art.

At the same time, asFIG. 7indicates, the amplitude of the rotation 24th-order harmonic is greater than that of the rotation 72nd-order in embodiment 2.FIG. 10presents computation results obtained for the levels of acoustic power generated from the rotating electric machines in embodiment 2 and the related art, prepared in few of this point.FIG. 10indicates that the acoustic power level corresponding to the rotation 24th-order peaks in a range equal to or above 5000 rpm and that the acoustic power level peak value is greater than the peak value corresponding to the rotation 72nd-order in the related art by approximately 10 dB.

The extent to which noise from other sound sources such as wind noise and road noise contribute to the overall noise in the vehicle increases as the speed of the vehicle increases. In addition, the noise tolerance value determined based upon the relationship among speed, noise and human perception also goes up at higher speed. Furthermore, when the rotating electric machine is installed in an HEV, the engine is started up as the rotation rate goes up and thus, it is natural to assume that noise from the engine is greater than the electromagnetic noise generated in the rotating electric machine over a range equal to and above 5000 rpm. For these reasons, the acoustic power level of the rotation 24th-order electromagnetic noise exceeding that of the rotation 72nd-order acoustic power level by 10 dB or so is deemed acceptable.

The present invention may be adopted in the three-phase permanent magnet rotating electric machine shown inFIG. 11with the number of poles P at 8, the number of slots S at 48 and the greatest common divisor N at 8. The present invention in this application example will be compared with the related art. For purposes of simplification, all the teeth inFIG. 11are indicated by reference numeral5. Specific reference numerals are also assigned to a stator core (1), a rotor core (2) and magnets (8) in the stator and the rotor configuring the rotating electric machine.

In embodiment 4, a single tooth group50is made up with m teeth5and m slots4, with m calculated to be 6 by dividing the number of slots S by the greatest common divisor N (=8) and grooves6q,6r,6tand6uare formed at the front ends of four teeth5(5q,5r,5t,5u) among these teeth5(5pthrough5u) with the openings (41pthrough41u) at the slots4having varying opening widths, as illustrated inFIG. 12.

The stator core1shown inFIG. 11is formed by cyclically iterating the group50made up with the teeth5and the slots4arranged as shown inFIG. 12, so that a total of 8 groups are set along the circumferential direction at the stator core1. Computation results obtained for a rotating electric machine having this stator core1(embodiment 4) are indicated by □ marks inFIG. 13, whereas computation results for a rotating electric machine having the stator core1in the related art are indicated with ♦ marks inFIG. 13.

In embodiment 4, the tooth group50and a slot group45corresponding to the tooth group50, formed as shown inFIG. 12, are iterated over the entire circumference of the stator core1shown inFIG. 11and, as a result, the amplitudes of the electromagnetic force harmonics can be adjusted as in embodiments 1 through 3 without having to alter the periodic boundary conditions of the geometric configuration achieved as a combination with the rotor core2and the magnets8from the periodic boundary conditions defined by the value ⅛ in the related art.

In embodiment 4, as well, the reluctance in the air gap (the space between the inner circumference of the stator core1and the outer circumference of the rotor core2) can be varied by forming grooves at the front ends of teeth5and altering the opening width at the slot openings, as in embodiments 1 through 3. As the reluctance is altered, the amplitudes or the phases of the magnetic flux harmonics change, which, in turn, results in a change in the amplitudes of the electromagnetic force harmonics.

FIG. 13presents results obtained through analysis, indicating the electromagnetic force harmonic amplitudes of the 0th-order in space along the tangential direction at rotating electric machines having stator cores1with the teeth and the slots thereof formed as in embodiment 4 and in the related art. InFIG. 13, the electromagnetic force harmonic amplitudes are rendered dimensionless in reference to the rotation 48th-order harmonic amplitude in the related art.FIG. 13indicates that the rotation 48th-order harmonic amplitude can be reduced through embodiment 4 relative to that in the related art. In addition, smaller harmonic amplitudes are achieved for other harmonics through embodiment 4 relative to the rotation 48th-order harmonic amplitude in the related art, indicating that an overall reduction in vibration and noise is achieved.

FIG. 14presents computation results obtained with regard to levels of acoustic power generated from rotating electric machines, one equipped with a stator core1having teeth and slots formed as in embodiment 4 and another equipped with a stator core1having teeth and slots formed as in the related art, by inputting an electromagnetic force harmonic of the rotation 48th-order. InFIG. 14, the acoustic power levels are rendered dimensionless in reference to the acoustic power level maximum value in the related art.FIG. 14indicates that the acoustic power level peak manifesting in the vicinity of 3000 rpm is lowered relative to the acoustic power level peak in the related art.

Embodiments 1 through 4 described above may be summarized as follows. According to the present invention, the shape of the tooth front end area and the slot opening width are cyclically altered F times (F is a natural number equal to or greater than 2) along the circumferential direction and, as a result, the amplitudes of harmonics of the electromagnetic exciting force occurring along the tangential direction, which are bound to adversely affect vibration and noise conditions, can be reduced without having to change the periodic boundary conditions. Though not mentioned earlier, it has been learned that the structure of the rotating electric machine according to the present invention may be adopted in an 8-pole/12-slot rotating electric machine or an 8-pole/10-slot rotating electric machine, as well.

As explained above, according to the present invention, the tangential direction space 0th-order electromagnetic force harmonic amplitudes, which are bound to affect the vibration and noise conditions, can be reduced and thus, vibration and noise can be reduced.

In addition, even in a rotating electric machine having a combination of the number of poles and the number of slots not conforming to the stipulations set forth in PTL 1 (the number of slots corresponding to n poles and s phases be 2n×s), the tangential direction electromagnetic force harmonic amplitudes can be reduced by adopting the present invention to ultimately result in a reduction in vibration and noise.

It is to be noted that the embodiments described above simply represent examples and the present invention is in no way limited to these examples as long as the features characterizing the present invention remain intact. Any other mode conceivable by persons skilled in the art within the technical range of the present invention should, therefore, be considered to be within the scope of the present invention.

The present invention is particularly noteworthy in that it may be adopted in various types of rotating electric machines, each equipped with a stator made up with tooth groups having a specific combination of different stator tooth front end shapes and slot opening widths, as has been described in reference to embodiments 1 through 4. This means that the present invention is not limited to applications in rotating electric machines with the number of phases, the number of poles and the number of slots set as in the embodiments described above. It is to be noted that while the embodiments have been described by assuming that coils are wound at the individual stator teeth through a distributed winding method, the present invention may instead be adopted in conjunction with coils wound through concentrated winding or in conjunction with specific dispersal winding methods such as that described in Japanese Laid Open Patent Publication No. 2009-247196.

REFERENCE SIGNS LIST