Motor control device for electric automobile

A magnetic force estimating unit (38) for estimating the magnetic force of a permanent magnet of a rotor of a motor (6), a determining unit (39), and a demagnetization responsive timing changing unit (40) are provided in an inverter device (22) or an electric control unit (21). The magnetic force estimating unit (38) performs a determination of the magnetic force with a predetermined rule from detection signals of at least two of the motor rotation number, motor voltage and motor current. The determining unit (39) determines whether or not a demagnetization occurs. In response to the result of determination by the determining unit (39), the demagnetization responsive timing changing unit (40) changes the timing, at which the maximum electric current relative to the phase of the rotor is fed, so that with respect the motor drive by the inverter device the reluctance torque of the motor may be increased.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of PCT/JP2012/079453 filed Nov. 14, 2012 and claims foreign priority benefit of Japanese Patent Application No. 2011-252223 filed Nov. 18, 2011 in the Japanese Intellectual Property Office, the contents of which are incorporated herein by reference.

This application is based on and claims Convention priority to Japanese patent application No. 2011-252223, filed Nov. 18, 2011, the entire disclosure of which is herein incorporated by reference as a part of this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrically driven vehicle such as, for example, a battery operated automobile or a fuel cell powered automobile utilizing a combination of fuel and battery and, more particularly, to a motor control device for the electric automobile of a type utilizing an interior permanent magnet synchronous motor.

2. Description of Related Art

In an electric automobile, reduction in performance and failure of a motor used to drive the automobile significantly affect the roadability and the safety. In particular, with an electric automobile drive device of a battery drive type, an embedded permanent magnet synchronous motor (also referred to as an IPM type DC brushless motor) utilizing a neodymium magnet and having a high efficiency performance has been utilized in order to increase the cruising distance with a limited available battery capacity. Also, in the field of an in-wheel motor device, the system has hitherto been suggested in which for the purpose of securement of the reliability, the temperature of, for example, a motor is measured to monitor the excessive load and the electric drive current for the motor is limited or the motor rotation number (motor number of revolutions or motor speed) is reduced in dependence on the measured temperature (such as disclosed in, for example, the patent documents 1 to 3 listed below).[Patent Document 1] JP Laid-open Patent Publication No. 2006-258289[Patent Document 2] JP Laid-open Patent Publication No. 2004-328819[Patent Document 3] JP Laid-open Patent Publication No. 2008-168790

In the motor used for the electric automobile, particularly the motor of a type utilizing the neodymium permanent magnet, the permanent magnet has a low heat resistance temperature and, therefore, if the ambient temperature exceeds the heat resistance temperature, the irreversible demagnetization occurs. Accordingly, the motor driving capability abruptly decreases and, depending on the circumstances, the automobile will become unable to control. Although as described above, in the in-wheel motor device, the motor temperature is measured to monitor the excessive load and, if required, the drive is limited, the control relying on the result of measurement of the motor temperature is incapable of taking any countermeasure against the reduction in performance brought about by the demagnetization of the permanent magnet used in the motor.

In view of the foregoing, the present invention has for its primary object to provide a motor control device for an electric automobile, which device is capable of suppressing a reduction of the motor driving force in the event of the occurrence of demagnetization in a permanent magnet used in a motor.

Another important object of the present invention is to provide the electric automobile of the type referred to above, which can run by its own bootstraps, i.e., by its resources, to the nearest place where the maintenance servicing is available, with the reduction in motor driving force being prevented, in the event of the occurrence of demagnetization in a permanent magnet used in a motor.

The summary of the present invention will be hereinafter described with the aid of reference numerals shown in the accompanying drawings and used for facilitating a better understanding of preferred embodiments of the present invention.

SUMMARY OF THE INVENTION

The motor control device20herein disclosed in accordance with the present invention is a motor control device20for an electric automobile of a type equipped with a motor drive control unit33configured to perform a control appropriate to a magnetic pole position of a motor rotor75relative to an embedded permanent magnet synchronous motor, which is a motor6used to drive a vehicle wheel2. This motor control device20includes a plurality of sensors35,36and37configured to detect at least two of the motor rotation number, motor voltage and motor current of the motor6respectively, a magnetic force estimating unit38configured to estimate the magnetic force of a permanent magnet80, used in the motor rotor75of the motor6, from detection signals indicative of at least two of the motor rotation number, the motor voltage and the motor current of the motor6in accordance with a predetermined rule, a determining unit39configured to determine whether or not the magnetic force estimated by the magnetic force estimating unit38is within a predetermined permissible range which is determined as a range in which no demagnetization occur, and a demagnetization responsive timing change unit40configured to render the motor drive control unit33to change the timing, at which the maximum electric current relative to a phase of the motor rotor75is fed, in order to enable the reluctance torque of the motor6to increase in the event that the determining unit39determines the magnetic force to be out of the predetermined permissible range.

In the synchronous motor, an alternating current is fed through the stator coil78to form a revolving magnetic field to drive the motor rotor75. In this case, in the embedded permanent magnet synchronous motor, a magnet torque, which is caused by the interaction between a permanent magnet80on a rotor side and a stator73m, and a reluctance torque, which is attributable to an attraction force developed between a core element79on the rotor side and the stator73m, are generated and the rotation takes place by the effect of those two types of torque. The magnet torque referred to above is proportional to the electric current and attains the maximum value when the phase θ between the revolving magnetic field and the rotor permanent magnet80is zero. On the other hand, the reluctance torque referred to above is proportional to the square of the electric current and attains the maximum value when the phase θ referred to above is 45°. Because of that, the embedded permanent magnet synchronous motor referred to above is generally driven under a current condition under which the sum of those two torques is maximized.

In the event that demagnetization occurs in the permanent magnet60on the rotor side as a result of, for example, an excessive increase of the temperature of the motor6, the magnet torque decreases or attains a zero value. However, in the embedded permanent magnet synchronous motor, even though the demagnetization occurs in the permanent magnet80, the motor can be driven by the reluctance torque to a certain extent.

Accordingly, the magnetic force of the permanent magnet80of the motor rotor75is estimated by the magnetic force estimating unit38and whether or not the estimated magnetic force is within the predetermined permissible range is determined by the determining unit39. In the event that the determining unit39determines the estimated magnetic force to be out of the predetermined permissible range, that is, determines the occurrence of demagnetization, the timing at which the maximum electric current relative to the phase of the motor rotor75is fed is changed by the demagnetization responsive timing changing unit40so that the reluctance torque may be increased. Thus, by changing the timing, at which the maximum electric current relative to the phase of the motor rotor75is fed, so that the reluctance torque may be increased, in the event of the occurrence of demagnetization, a reduction of the driving force of the motor6is reduced to allow the electric automobile to be moved by its own bootstraps to, for example, a repair shop or roadside.

Estimation of the magnetic force and determination of the demagnetization can be performed in the following manner. With the motor6of a type utilizing a permanent magnet such as, for example, the embedded permanent magnet synchronous motor, an electromotive force is generated in the stator coil78as a result of rotation of the permanent magnet80of the motor rotor75and this electromotive force so generated increases with the magnetic force (that is, the magnetic flux density) of the permanent magnet80. Because of that, when the motor rotation number and the motor voltage are compared with each other, the magnetic force of the permanent magnet is readily estimated. The electromotive force referred to above affects also the motor current and accordingly, when the motor rotation number and the motor voltage are compared with each other, the magnetic force of the permanent magnet is readily estimated. The relationship between the electromotive force referred to above and the magnetic force of the permanent magnet appears in the relationship between the waveform of the motor voltage and the waveform of the motor current, and the magnetic force of the permanent magnet is also estimated from the comparison thereof. The magnetic force estimating unit38estimates the magnetic force of the permanent magnet80of the rotor75of the motor6from detection signals indicative of at least two of the motor current, the motor voltage and the motor rotation number in accordance with the predetermined rule by providing the suitable rule, which defines the relationships of the motor rotation number, the motor voltage and the motor current referred hereinabove. The output of the magnetic force of the permanent magnet80so estimated may not be a unit descriptive of the magnetic force such as, for example, the magnetic flux density and may be, for example, a value or the like descriptive of which one of suitably defined stage of magnetic forces it belongs.

The determining unit39determined whether or not a demagnetization of the motor rotor occurs by comparing the magnetic force estimated by the magnetic force estimating unit38, with the predetermined permissible range. While the demagnetization may occur as a result of heats of the permanent magnet80, and/or cracking or the like in the permanent magnet80, such demagnetization is determined by comparing the magnetic force estimated by the magnetic force estimating unit38with the predetermined permissive range. The predetermined permissive range referred to above may be suitably provided in accordance with the specification of the motor and others and further with, for example, a range that can be regarded as a normal range of the magnetic force, or a range stipulated in consideration with the safety factor.

In an embodiment of the present invention, the use may be made of a demagnetization responsive motor drive limiting unit43configured to limit a motor drive output from the motor drive control unit33in the event that the determining unit determines the magnetic force to be out of the predetermined permissible range. This limit of the drive may be, for example, a process of lowering the output of the electric current value or the torque that will become a drive command, or a process of halting the outputting.

In another embodiment of the present invention, the motor control device20may include an ECU21, which is an electric control unit configured to integrally control the electric automobile as a whole, and an inverter device22including a power circuit unit28, which includes an inverter31to convert a direct current power of a battery into an alternating current power used to drive the motor, and a motor control unit29configured to control at least the power circuit unit28in accordance with a control of the electric control unit21, and the magnetic force estimating unit38, the determining unit39and the demagnetization responsive timing changing unit40are provided in the inverter device22. With respect to the demagnetization responsive motor drive limiting unit43, it may be provided in the inverter device22. While the electric control unit21and the inverter device22are generally provided in the electric automobile, the provision of the magnetic force estimating unit38, the determining unit39and the demagnetization responsive timing changing unit40in the inverter device22at a position rather close to the motor6is effective to simplify the wiring system and does hence lead to a quick control. Also, the load of the electric control unit21which is getting complicated as it is sophisticated into a high functional equipment can be relieved.

Where the determining unit39and others referred hereinabove are provided in the inverter device22, the inverter device22may be provided with an abnormality annunciating unit44configured to output information indicative of the occurrence of demagnetization to the electric control unit22in the event that the determining unit determines39the magnetic force to be out of the predetermined permissible range. The electric control unit21is a means to perform a control of the automobile as a whole and, where controls as drive limiting and other are carried out by means of the inverter device22and others, a proper integrated control can be performed over the entire automobile in response to the information indicative of the occurrence of the abnormality.

Where the motor control device20is comprised of the electric control unit21and the inverter device22referred hereinabove, the magnetic force estimating unit38and the determining unit39may be provided in the electric control unit21. In this case, the structure of the inverter device22can be simplified.

Also, an abnormality display unit42configured to display and to annunciate the occurrence of an abnormality to a display device27in a driver's seat in the event that the determining unit39determines the occurrence of demagnetizationmay be provided in the electric control unit21. With the presence of the abnormality being displayed in the display device27in the driver's seat, the driver can take a proper and fast treatment such as, for example, halt or slow movement of the automobile or running to the repair shop.

By applying a limit to the drive output from the motor6when lowering of the magnetic force is indicated by the determining unit39, for example, by conducting a process of lowering the output of or halting the motor6while a high temperature condition is caused by the motor drive, a further increase of the high temperature beyond the current temperature is avoided to permit a further deterioration of the magnet of the motor6to be avoided beforehand. By way of example, where the motor6referred to above is an embedded permanent magnet synchronous motor of the type utilizing the neodymium permanent magnet, the heat resistance temperature of the permanent magnet80is low or when the ambient temperature exceeds that temperature, an irreversible demagnetization results in and, therefore, the motor driving performance deteriorates abruptly and, in the worst case, there may happen a risk that the automobile fails to run. However, if a treatment of output lowering or halt of the motor6is taken and the further deterioration of the permanent magnet80is prevented beforehand, the driving failure of the motor6can be avoided and the automobile is permitted to run to the repair shop or any other place where a remedy can be taken. It is to be noted that a predetermined permissible range of the determining unit39may differ between the predetermined permissible range, which is applicable where the demagnetization responsive timing changing unit40is allowed to function, and the predetermined permissible range which is applicable where the demagnetization responsive motor drive limiting unit43is allowed to function.

In a further embodiment of the present invention, the motor may be a motor used to individually drive vehicle wheels of the electric automobile. Where the vehicle wheels2are driven by the individual motor6respectively, it is necessary to balance driving torques of left and right driving wheels relative to each other. Even when running takes place in taking an emergency measure against the demagnetization, to obtain a torque balance between the left and right is desired. For this reason, effect of suppressing the reduction of the motor driving force, which is afforded by the provision of the demagnetization responsive timing changing unit40in accordance with the present invention can become more effective.

The motor6referred to above may form a part of an in-wheel motor drive device8of a type having a part or the whole thereof disposed inside a vehicle wheel2and made up of the motor6, a wheel support bearing assembly4and a reduction gear7. In the in-wheel motor drive device8, as a result of compactization contemplated, the motor6is employed in the form of a motor having a high speed rotating specification. If the motor6rotates in a high speed, the eddy current loss is considerable and the heat emission resulting from the eddy current loss become high. For this reason, the permanent magnet80of the motor6is easy to have a high temperature and, because of this high temperature, the demagnetization is apt to occur in the permanent magnet80. Accordingly, effects mentioned above brought about by the use of the demagnetization responsive timing changing unit40employed in the practice of the present invention can be further effective.

In a further embodiment of the present invention, the use may be made of a reduction gear7configured to reduce the speed of rotation of the motor6, which reduction7is of a type having a high speed reducing ratio of 4 or higher. Also, the use may be made of a reduction gear7to reduce the speed of rotation of the motor6, which reduction7is in the form of a cycloid reduction gear. With the cycloid reduction gear, a high speed reducing ratio can be obtained. Where the speed reducing ratio is increased, the motor6is used of a type compact in size and capable of undergoing a high speed rotation, then heat emission resulting from the eddy current loss becomes high. For this reason, the effects brought about by the provision of the demagnetization responsive timing changing unit40according to the present invention can become further effective.

The electric automobile of the present invention is that equipped with the motor control device20for the electric automobile as discussed above. For this reason, the advantage that in the event of occurrence of the demagnetization of the permanent magnet80of the motor6the reduction of the motor driving force can be suppressed by the motor control device20referred to above can be effectively exerted and, in the event of the occurrence of demagnetization, the running by its own bootstraps to the position where a repair is available can take place.

DESCRIPTION OF PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described in detail with particular reference toFIGS. 1 to 7. The electric automobile shown particularly inFIG. 1is a four wheeled vehicle including an automobile body structure1, in which left and right rear wheels2are rendered to be driving wheels and left and right front wheels3are rendered to be steerable driven wheels. The vehicle wheels2and3, which are rendered to be the driving and driven wheels, respectively, have tires mounted thereon and are rotatably supported by the automobile body structure1in any known manner through respective wheel support bearing assemblies4and5. InFIG. 1, the wheel support bearing assemblies4and5are each designated by “H/B” which stands for an abbreviation of a hub bearing. The left and right vehicle wheels2and2, which serve as the driving wheels, is driven by respective motors6and6that drive independently from each other. The rotation of the motor6is transmitted to the driving vehicle wheel2through a reduction gear7and a wheel support bearing assembly4. The motor6, the reduction gear7and the wheel support bearing assembly4altogether form an in-wheel motor drive device8which is a single assembled component, and the in-wheel motor drive device8is in part or whole disposed inside the vehicle wheel2. The in-wheel motor drive device8is also referred to as an in-wheel motor unit. The motor6may be of a type capable of driving the vehicle wheel2directly, i.e., without the reduction gear7. The driving and driven vehicle wheels2and3are provided with respective brakes9and10of, for example, a type of an electrically operated type.

The vehicle wheels3and3, which will be the left and right front steerable wheels, respectively, can be steered by means of a common rudder mechanism11and can be steered, i.e., swung leftwards or rightwards, by a steering mechanism12. The rudder mechanism11is a mechanism for changing the angle of left and right knuckle arms11b, which hold respective wheel support bearing assemblies5when a tie rod11ais moved leftwards or rightwards, and includes an electrically powered steering (EPS) motor13, which is driven in response to a command from the steering mechanism12to move the tie rod11aleftwards or rightwards through a rotary motion to linear motion converting mechanism (not shown). The steering angle is detected by a steering angle sensor15and an output of this steering angle sensor15is outputted to an electric control unit (ECU)21, information therefrom is utilized in acceleration/deceleration commands and others for the left and right vehicle wheels.

As shown inFIG. 3, the in-wheel motor drive device8is of a structure in which the reduction gear7is interposed between the wheel support bearing assembly4and the motor6and a wheel hub of the vehicle wheel2(shown inFIG. 2), which is the driving wheel supported by the wheel support bearing assembly4, and a rotation output shaft74of the motor6(shown inFIG. 3) are coaxially connected with each other. The reduction gear7is preferably of a type having a speed reducing ratio of 1/6 or more. This reduction gear7is in the form of a cycloidal reduction gear and is of a structure in which a rotation input shaft82coaxially connected with the rotation output shaft74of the motor6is formed with eccentric portions82aand82band, on the other hand, curved plates84aand84bare mounted in the respective eccentric portions82aand82bthrough a bearing assembly85so that eccentric motions of the curved plates84aand84bcam be transmitted as a rotary motion to the wheel support bearing assembly4. It is to be noted that hereinafter in this specification, terms “outboard” and “inboard” represent one side of the in-wheel motor drive device8away from the center of the width of the vehicle body and the other side of the in-wheel motor drive device8close to the center of the width of the vehicle body, respectively, when assembled in the vehicle body.

The wheel support bearing assembly4includes an outer member51having an inner periphery formed with a plurality of rows of rolling surfaces53, an inner member52having an outer periphery formed with rolling surfaces54held in face to face relation with each rolling surfaces53, and a plurality of rows of rolling elements55interposed between the rolling surfaces53in the outer member51and the rolling surfaces54in the inner member52. The inner member52serves a hub mounting the driving wheel. This wheel support bearing assembly4is rendered to be a plurality of rows of angular contact ball bearing and the rolling elements55used therein are in the form of balls that are retained by a retainer56used for each row. The rolling surfaces53and54have an arc sectional shape respectively and those rolling surfaces53and54have contact angles that is held in back-to-back relation to each other. A bearing space delimited between the outer member51and the inner member52has one end on the outboard side sealed by a sealing member57.

The outer member51is a stationary side raceway ring, and is rendered to be of one piece construction including a flange51aconnected with a housing83bon the outboard side of the reduction gear7. The flange51areferred to above is provided with a bolt insertion hole64defined at a plurality of circumferential locations thereof. Also, the housing83bis provided with an internally threaded bolt screwing hole94defined at a location corresponding thereof. Accordingly, when mounting bolts65inserted through the respective bolt insertion holes64are screwed to the corresponding bolt screwing holes94, the outer member51can be fitted to the housing83b.

The inner member52is a rotatable side raceway ring, and includes an outboard side member59, having a wheel mounting hub flange59a, and an inboard side member60integrated with the outboard side member59by means of fastening area where the outboard side is engaged with an inner periphery of the outboard side member59. The rows of the rolling surfaces54referred to previously are formed in these outboard side members59and inboard side member60, respectively. The inboard side member60has a center portion formed with a through bore61defined therein. The hub flange59aintegral with the inner member52has a press fitting hole67defined at a plurality of circumferential locations thereof for receiving a corresponding hub bolt66. In the vicinity of a root portion of the hub flange59ain the outboard side member59, a cylindrical pilot portion63for guiding the driving wheel and a brake component (not shown) protrude towards the outboard side. The pilot portion63has an inner periphery provided with a cap68for closing the end on the outboard side of the through bore61.

The motor6referred to previously is an embedded permanent magnet synchronous motor (that is, IPM motor) of a radial gap type in which a radial gap is defined between a motor stator73, which is fixed to a cylindrical motor housing72, and a motor rotor75, fitted to a rotation output shaft74. The rotation output shaft74is supported in a cantilevered fashion by a cylindrical portion of the housing83aon the inboard side of the reduction gear7through two bearings76.

FIG. 4illustrates a cross sectional view of the motor (which is taken along the line IV-IV inFIG. 3). The motor rotor75of the motor6is made up of a core portion79, comprised of a soft magnetic material such as, for example, a laminated silicon steel plate, and a permanent magnet80built in the core portion79. The permanent magnet80is of a structure in which neighboring two permanent magnets are arranged in a V sectioned shape on the same circumference within the rotor core portion79so as to face with each other. The permanent magnet80is employed in the form of a neodymium magnet. The stator73is comprised of a core portion77made of a soft magnetic material, and a coil78. The core portion77has its outer peripheral surface which is a ring shape having a circular sectional shape, and a plurality of teeth77aeach protruding towards an inner diametric side, are formed in an inner peripheral surface of the core portion77in a row along the circumferential direction thereof. The coil78is wound around each of the teeth77awhich forms a projecting pole of the stator core portion77.

As shown inFIG. 3, the motor6is provided with an angle sensor36for detecting the relative rotation angle between the motor stator73and the motor rotor75. This angle sensor36includes an angle sensor main body70for detecting and outputting a signal indicative of the relative rotation angle between the motor stator73and the motor rotor75and an angle calculation circuit71for calculating the angle from a signal outputted from the angle sensor main body70. The angle sensor main body70is made up of a to-be-detected portion70a, provided in an outer peripheral surface of the rotation output shaft74, and a detecting portion70bprovided in the motor housing72in the vicinity of the to-be-detected portion70aand disposed so as to face the to-be-detected portion70ain a direction, for example, radially thereof.

It is, however, to be noted that the to-be-detected portion70aand the detecting portion70bmay be disposed in the vicinity of each other so as to confront each other in a direction axially thereof and that the angle sensor36may be employed in the form of a resolver.

The motor6being of the structure described above is so designed that, in order to maximize the efficiency thereof, the timing of application of each phase of each wave of an alternating current supplied to the coil78of the motor stator73is controlled by a motor drive control unit33(shown inFIG. 2) of a motor control unit29on the basis of the relative rotation angle between the motor stator73and the motor rotor75, which is detected by the angle sensor36. It is to be noted that a wiring for a motor current of the in-wheel motor drive device8and wirings for various sensor systems and command systems are collectively accomplished by a connector99provided in the motor housing72and others.

The reduction gear7is in the form of the cycloid reduction gear as hereinbefore described and is of a structure in which, as shown inFIG. 5, two curved plates84aand84b, each having such a outer shape as to represents a gentle wavy trochoidal curve, are mounted on respective eccentric portions82aand82bof the rotation input shaft82through associated bearings85. A plurality of outer pins86for guiding respective eccentric motions of those curved plates84aand84bon an outer peripheral side are provided in the housing83bso as to traverse the latter and a plurality of inner pins88fitted to the inboard side member60of the inner member2are engaged having been inserted into respective round throughholes89defined within the each curved plate84aand84b. The rotation input shaft82is splined to the rotation output shaft74of the motor6and is accordingly rotatable together with such rotation output shaft74. It is to be noted that the rotation input shaft82is supported by the housing83aon the inboard side and an inner diametric surface of the inboard side member60of the inner member52through two spaced bearings90.

When the rotation output shaft74of the motor6rotates, the curved plates84aand84bmounted on the rotation input shaft82rotatable together with such rotation output shaft74undergo the respective eccentric motions. The eccentric motions of those curved plates84aand84bare transmitted to the inner member52as a rotary motion by means of the engagement between the inner pins88and the throughholes89. The rotation of the inner member52so effected in the manner described above takes place at a speed reduced relative to the rotation of the rotary output shaft74accordingly. By way of example, the speed reducing ratio of 1/10 or high can be obtained with a single stage cycloid reduction gear.

The two curved plates84aand84bare mounted on the respective eccentric portions82aand82bof the rotation input shaft82in a 180° phase displaced relation to each other so that the respective eccentric motions can be counterbalanced with each other and, so that fluctuations caused by the eccentric motions of the curved plates84aand84bcan be counterbalanced with each other, two counter weights91are mounted on the both side of the each eccentric portion82a,82bmade eccentric in a fashion radially offset relative to the direction of eccentricity of the each eccentric portion82aand82b.

As shown on an enlarged scale inFIG. 6, each of the outer pins86and each of the inner pins88have respective bearings92and93mounted thereon and outer rings92aand93aof those bearings92and93are held in rolling contact with the outer peripheries of the each curved plate84aand84band an inner periphery of the associated throughholes89. Accordingly, while the contact resistance between each of the outer pins86and the outer periphery of any one of the curved plates84aand84band the contact resistance between each of the inner pins88and the inner periphery of any one of the throughholes98are reduced, the respective eccentric motions of the curved plates84aand84bcan be smoothly transmitted as a rotary motion to the inner member52.

Referring toFIG. 3, the wheel support bearing assembly4employed in the in-wheel motor drive device8is fixed to the automobile body structure at an outer peripheral portion of the housing72of the motor6or the housing83bof the reduction gear7through an automobile suspension system (not shown) of a knuckle and others.

The control system will now be described in detail with particular reference toFIG. 1. The electric control unit21for performing a control of the automobile in its entirety, an inverter device22for controlling the driving motor6in accordance with a command of the electric control unit21, and a brake controller23are mounted on the automobile body structure1. In particular, the electric control unit21and the inverter device22cooperate with each other to form the motor control device20. The electric control unit21is comprised of a computer, a program executed by the computer, and various electronic circuits and others.

The electric control unit21, when classified functionally, can be divided into a drive control unit21aand a general control unit21b. The drive control unit21agenerates an acceleration/deceleration command, which is to be applied to the driving motors6and6in the left and right wheels, from an acceleration command outputted by an accelerator operating unit16, a deceleration command outputted by a brake operating unit17and a turn command outputted by the steering angle sensor15and outputs this command to the inverter device22. In addition, the drive control unit21amay however have a function of correcting the acceleration/deceleration command, outputted therefrom, with the use of information on the tire number of revolutions, which is obtained from a rotation sensor24provided in each of the wheel support bearing assemblies4and5in the vehicle wheels2and3and information of various vehicle mounted sensors. The accelerator operating unit16is comprised of an accelerator pedal and a sensor16acapable of detecting the pedaling amount of the accelerator pedal and then outputting the acceleration command referred to previously. The brake operating unit17is comprised of a brake pedal and a sensor17acapable of detecting the pedaling amount of the brake pedal and then outputting the deceleration command referred to previously.

The general control unit21bof the electric control unit21has, for example, a function of outputting the deceleration command, outputted by the brake operating unit17to the brake controller23, a function of controlling various auxiliary equipment systems25, a function of processing an input command from an operating panel26in a console, and a function of causing a display device27to make displays. The display device27is of a type capable of displaying images, such as, for example, a liquid crystal display device. The auxiliary equipment systems25referred to above includes, for example, an air conditioner, lights, wipers, a global positioning system (GPS), air bags and so on and are shown collectively in one block here.

The brake controller23is a means for applying a braking command to any one of the brakes9and10of the front and rear vehicle wheels2and3according to the braking command outputted from the electric control unit21, which includes, in addition to a command generated in response to the deceleration command outputted by the brake operating unit17, a command generated by means for improving the safety factor peculiar to the electric control unit21. The brake controller23additionally have an anti-lock brake system. This brake controller23is comprised of an electronic circuit and a microcomputer or the like.

The inverter device22is comprised of a power circuit unit28provided for each of the motors6and a motor control unit29for controlling these power circuit units28. It is, however, to be noted that the motor control unit29may provided in common to each power circuit unit28or separately to each other, but even when it is provided in common to each power circuit unit28mentioned above, each power circuit unit28may be rendered to be independently controllable so that, for example, the each motor torque may differ. The motor control unit29has a function of outputting each information (hereinafter referred to as “IWM system information) on various detection values, control values and others associated with the in-wheel motor8, which is possessed by the motor control unit29, to the electric control unit.

FIG. 2illustrates a block diagram showing a conceptual construction of the inverter device22. The power circuit unit28is comprised of an inverter31for converting a direct current power of a battery19into a three phase alternating current power, which is used in driving the motor6, and a PWM driver32for controlling the inverter31. The inverter31is made up of a plurality of semiconductor switching elements (not shown) and the PWM driver32performs a pulse width modulation of an inputted current command to apply an ON-OFF command to each of the semiconductor switching elements referred to above.

The motor control unit29is comprised of a computer, a program, which is executed by the computer, and electronic circuits and has the motor drive control unit33as its underlying control unit. The motor drive control unit33is a means in response to the acceleration/deceleration command such as, for example, a torque command or the like applied from the electric control unit, which is a host control means, to convert thereof into the electric current command, and then to apply the electric current command to the PWM driver32of the power circuit unit28. The motor drive control unit33performs an electric current feedback control when a motor current value to be fed from the inverter31to the motor6is applied from an electric current detecting unit35. Also, the motor drive control unit33performs a control such as, for example, a vector control appropriate to the magnetic pole position when the angle of rotation of the rotor of the motor6is applied from the angle sensor36.

In the embodiment now under discussion, the motor control unit29of the structure discussed hereinabove is provided with a magnetic force estimating unit38to be referred hereinafter, a determining unit39, a demagnetization responsive timing changing unit40, a demagnetization responsive motor drive limiting unit43, and an abnormality annunciating unit41, and the electric control unit21is provided with an abnormality display unit42. It is to be noted that the magnetic force estimating unit38, the determining unit39, the demagnetization responsive timing changing unit40and the demagnetization responsive motor drive limiting unit43may be provided in the electric control unit21.

The magnetic force estimating unit38is a means to estimate the magnetic force of the permanent magnet of the rotor of the motor6in accordance with a predetermined rule from at least two among detection signal outputs from the angle sensor36for detecting the angle of rotation of the motor revolution number of the motor6, an electric current sensor35for detecting the motor current, and a voltage sensor37for detecting a motor voltage, that is, from detection signals indicative of at least two of the motor rotation number, the motor current and the motor voltage.

In the synchronous motor6, an electromotive force is generated in the stator coil78as a result of rotation of the permanent magnet of the rotor and this electromotive force so generated increases with the increase of the magnetic force of the permanent magnet80, that is, the increase of the magnetic flux density thereof. Because that, when the motor rotation number and the motor voltage are compared with each other, the magnetic force of the permanent magnet is readily obtained. Since the electromotive force referred to above affects also the motor current, the comparison with the motor rotation number and the motor current makes the magnetic force of the permanent magnet readily. The magnetic force of the permanent magnet also appears in the relationship between the waveform of the motor voltage and the waveform of the motor current and, by the comparison thereof, the magnetic force of the permanent magnet is obtained.

The magnetic force estimating unit38referred to above estimates the magnetic force of the permanent magnet70of the motor rotor75in the motor6in accordance with the predetermined rule from the detection signals indicative of at least two of the motor current, the motor voltage and the motor rotation number by providing an appropriate rule which defines the relationship between the motor rotation number, the motor voltage and the motor current referred to above. An output of the magnetic force of the permanent magnet80so estimated may not necessarily be a unit indicative of the magnetic force such as, for example, the magnetic flux density or the like and may be a value or the like which is indicative of, for example, which one of appropriately determined stages of magnetic forces it belongs. It is to be noted that the magnetic force estimating unit38may be of a type capable of estimating the magnetic force by performing, when the magnetic force of the permanent magnet80is to be estimated, a comparison between the motor rotation number and the motor voltage, a comparison between the motor rotation number and the motor current, and a compassion between the waveform of the motor voltage and the waveform of the motor current.

The determining unit39is a means to compare the magnetic force, which has been estimated by the magnetic force estimating unit38, with the predetermined permissible range and then to determine whether or not it is a demagnetization of the motor rotor75. The predetermined permissible range is recommended to set up in reference to, for example, the specification or the like of the motor6. This predetermined permissible range may be set up as a range of, for example, one threshold value or more. The magnetic force estimating unit38may be of a type capable of providing a two-value output of demagnetization or not demagnetization and, also, capable of providing an output of determination in the form of a stepwise or continuous value descriptive of the extent of the demagnetization when it is determined as the demagnetization.

The demagnetization responsive timing changing unit40is a means to change the timing, at which the maximum current relative to the phase of the motor rotor75is fed so as to increase the reluctance torque of the motor6, in the event that the determining unit39determines the magnetic force to be out of the predetermined permissible range. The change of the timing at which the maximum current is supplied may be of a type so as to change the phase without changing, for example, an electric current waveform (sine wave or others), or so as to change the timing thereof by changing the electric current waveform. It is to be noted that, where the determining unit39is capable of determining the extent of demagnetization, the demagnetization responsive timing changing unit40may be of a type capable of changing the extent of change of the timing, at which the maximum current is supplied relative to the phase of the motor rotor75, in dependence on the extent of demagnetization outputted from the determining unit39.

The demagnetization responsive motor drive limiting unit43is a means to apply a limit to the output from the inverter device22in the event that the determining unit39determines the magnetic force to be out of the predetermined permissible range. The limit of the output of the inverter device22by the demagnetization responsive motor drive limiting unit43may be, for example, a process of lowering the output of the electric current value or the torque, which will become a drive command which will be an output of the PWM driver32or the motor drive control unit33, or a process of stopping the output. Also, it may be a process of interrupting the output of the inverter31. It is to be noted that in the case of a drive halt, it is preferred that the motor6is rotatable.

The abnormality annunciating unit41referred to above is a means to output an abnormality occurrence information to the electric control unit21in the event that the magnetic force determined by the magnetic force determining unit38is determined to be demagnetization by the determining unit39. The abnormality display unit42provided in the electric control unit21is a means to output information indicative of the occurrence of an abnormality or to cause the display device27in a driver's seat to provide a display annunciating the occurrence of an abnormality in response to the abnormality occurrence information outputted from the abnormality annunciating unit41. Where the determining unit39is provided in the electric control unit21, in response to a result of determination, which indicates that the demagnetization is determined by the determining unit39, the display to annunciate the occurrence of the abnormality is effectuated. The display to the display device27may be rendered to be a display in the form of characters and/or symbols, for example a display in the form of icons.

The demagnetization responsive operation according to the magnetic force estimation and its estimation result by the present structure mentioned above will be described next. The magnetic force estimating unit38estimates, at all times, the magnetic force of the permanent magnet80of the motor rotor75of the motor6in accordance with the predetermined rule from the respective outputs of the various sensors35,36and37(the outputs of two of those sensors). The determining unit39monitors this result of estimation, compare the magnetic force estimated by the magnetic force estimating unit38with the predetermined permissible range, and determined the occurrence of demagnetization in the event that the magnetic force departs from the predetermined permissible range. It is to be noted that, in the event of out of the predetermined permissible range, the extent of demagnetization may be determined, too.

Where the determining unit39determines the occurrence of demagnetization, the demagnetization responsive timing changing unit40applies to the motor drive control unit33a command to change the timing, at which the maximum current relative to the phase of the rotor75is fed, so that the reluctance torque of the motor6may increase. This change of the timing will be hereinafter discussed.

With the synchronous motor, the alternating current is supplied to the stator coil78to generate a revolving magnetic field to thereby drive the rotor75. In such case, in the embedded permanent magnet synchronous motor, the magnet torque and the reluctance torque are developed and rotation takes place under the two type of torques. The magnet torque is a torque generated as a result of the interaction between the permanent magnet80on the rotor75side and the stator73m. On the other hand, the reluctance torque is a torque resulting from the magnetic force of attraction F (shown inFIG. 7) developed between the core portion79on the rotor75side and the stator73m.

Referring toFIG. 8, the magnet torque Tm is proportional to the electric current, and becomes, as shown inFIG. 8, maximum when the phase θ between the revolving magnetic field and the rotor permanent magnet80is zero. On the other hand, the reluctance torque Tr is proportional to the square of the electric current and becomes maximum when the phase θ is 45°. Because of that, in the embedded permanent magnet synchronous motor employed in the practice of this embodiment of the present invention, at normal time it is driven under a current application condition in which the sum of those torques Tm and Tr (i.e., Tm+Tr) becomes maximum. For example, assuming that the sum of those torques Tm+Tr becomes maximum at the phase θ (for example, 40°), the control by the motor drive control unit33shown inFIG. 2takes place in order that the maximum electric current is flows at this phase θ=θe (40°). In other words, the electric current control is performed so that the position at which the amplitude of the alternating current such as, for example, a sine waveform attains the maximum value may be that phase θ mentioned above.

FIG. 9illustrates a rotor rotation position at which the phase θ become a zero degree.FIG. 10illustrates a rotor rotation position at which the phase θ becomes 40 degree. It is to be noted thatFIGS. 9 and 10are diagrams to show facing the stator73and the rotor75are viewed as developed in plane.

If the determining unit39determines the occurrence of demagnetization when the control of the current phase is so performed as to render the sum of the torques Tm+Tr to be maximal at the normal time as hereinabove described, the demagnetization responsive timing changing unit40changes the timing (the phase θ), at which the maximum current is supplied, so that the reluctance torque Tr may increase. This change in timing is a change so made as to bring the reluctance torque Tr close to the phase θ at which it becomes maximum and, for example, it is assumed that the phase of 40° at the normal time is advanced only a degree of Δθ (=5°) to 45°. It is, however, to be noted that the change may not necessarily be so made as to render that the reluctance torque Tr to become maximum and may be so made as to render the reluctance torque Tr to increase.

As described above, in the event of the determination of the occurrence of demagnetization, so that the reluctance torque of the motor6may increase, the timing at which the maximum current relative to the phase of the rotor75is supplied is changed. By this reason, it functions as a reluctance motor and any reduction in motor driving force can be suppressed as possible as it can while the influence of the demagnetization is suppressed. Because of that, in the event of the occurrence of the demagnetization, with respect to the movement of the automobile to the place, such as, for example, a repair shop, or where a repair is available, it is possible to allow the automobile to run by its own bootstraps.

Also, when the determining unit39determines the occurrence of demagnetization, the demagnetization responsive motor drive limiting unit43applies a limitation such as, for example, a reduction of the driving current, to an output of the inverter device22. Accordingly, when, for example, the motor6is held in a high temperature condition, an increase of the temperature beyond the current temperature is avoided by taking a treatment to reduce the output of the motor6and, therefore, more possible deterioration of the magnet of the motor6can be avoided beforehand. If the motor6is an embedded permanent magnet synchronous motor of a type utilizing a neodymium permanent magnet, as a result that the heat resistance temperature of the permanent magnet80is low and result that the ambient temperature thereof exceed such heat resistance temperature, the magnet will result in an irreversible demagnetization, so that the motor driving capability is abruptly decreased and, in the worst case it may happen, the automobile will become incapable of being driven. However, if a treatment to inhibit or stop the output of the motor6will be taken place and if the permanent magnet80is beforehand prevented from further deteriorating, the drive incapability of the motor6can be avoided and the automobile can be driven to the place such as a repair shop, where the repair is available. It is to be noted that the predetermined permissible range of the determining unit39used when the timing is changed by the demagnetization responsive timing changing unit40and that used when the drive limitation is applied by the demagnetization responsive motor drive limiting unit43may be different from each other so that the determination output can be carried out based on one of the predetermined permissible ranges whichever appropriate.

In the event that the determining unit39determines the occurrence of demagnetization, the abnormality annunciating unit41furthermore annunciates the occurrence of an abnormality to the electric control unit21. By this annunciation of the abnormality, a proper integrated control of the automobile as a whole by the electric control unit21can take place. Also, as a result of the annunciation of the abnormality, the abnormality display unit42of the electric control unit21causes the display device27in the driver's seat to provide an indication of the abnormality. For this reason, in the event that the roadability of the electric automobile is not good, the driver can be acknowledged that the cause thereof lies in the demagnetization and, therefore, a proper treatment can be more quickly taken.

In the practice of this embodiment of the present invention, in view of the fact that the motor6forms the in-wheel motor drive device8and compactization can therefore be achieved, a high speed rotating specification is employed for the motor6and, for the reduction gear7, the cycloid reduction gear is employed which can provide a high speed reducing ratio of 4 or higher (specifically, a high speed reducing ratio of 10 or higher). When the motor6rotates at a high speed, the eddy current loss is large and heat emission resulting from the eddy current loss become considerable. Accordingly, the permanent magnet80of the motor6is apt to involve a high temperature and, hence, the demagnetization of the permanent magnet is apt to occur under the high temperature. Because of those, effects brought about by the use of the magnetic force estimating unit38, the determining unit39and the demagnetization responsive timing changing unit40, and so on, can become more effective in this embodiment.

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