Brushless electric motor

An electric motor has a stator (224) having a bearing tube (238) made of a magnetically transparent material; it also has a rotor (222) having a rotor shaft (234) that is at least partially journaled in the bearing tube (238), and has a ring magnet (250) that is fixedly arranged on the rotor shaft (234) inside the bearing tube (238). Two magnetic-field-dependent analog sensors (248′, 248″) are arranged on a circuit board (246) outside the bearing tube (238), at an angular distance (PHI) from one another, in order to generate rotor position signals as a function of the rotational position of the ring magnet (250). A corresponding device (150) that serves to control the motor is provided, in order to process these rotor position signals into a signal that indicates the absolute rotational position of the rotor (222).

This application is a section 371 of PCT/EP06/06156, filed 27 Jun. 2006 and published 1 Feb. 2007 as WO 2007-12370-A1.

FIELD OF THE INVENTION

The invention relates to an electric motor for sensing a rotor position, and in particular the absolute value of a rotor position.

BACKGROUND

WO 2004/059830 A2 (whose US National Phase became U.S. Pat. No. 7,049,776) discloses a rotor position sensor arrangement for an electric motor having a multi-pole sensor magnet, in which arrangement a rotor position signal is converted into a digital value with a 2-bit resolution. This digital value makes it possible to obtain information from the rotor position signal even within the angle range of one sensor pole (e.g. within region550inFIG. 5below), so that an absolute value for the rotor position can be generated.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to make available a novel arrangement for sensing the rotor position in an electric motor.

According to a first aspect of the invention, this object is achieved by an electric motor having, secured to its rotor shaft, a ring magnet with a sinusoidal flux profile along its circumference, and a rotor position sensors which maps a property of the magnetic flux from the ring magnet to ascertain a absolute value representing the rotor position. This electric motor comprises a stator, a rotor having a rotor shaft and a rotor magnet, a ring magnet arranged nonrotatably on the shaft, and at least one rotor position sensor. The rotor magnet has n pole pairs. The ring magnet is arranged at least partially between the rotor shaft and the at least one rotor position sensor, and it is magnetized in such a way that it has a maximum of n pole pairs, and that a substantially sinusoidal magnetic flux profile occurs at its circumference. The at least one rotor position sensor serves to generate an analog signal that maps a property of the magnetic flux and is suitable for determining an absolute value of the rotor position.

What is thereby obtained is an electric motor having a rotor position arrangement that enables the absolute value of the motor's rotor position to be determined at any point in time.

According to a further aspect, this object is achieved by an electric motor having a ring magnet located at least partially inside a magnetically transparent subregion of the bearing tube which supports the rotor. This electric motor has a stator having a bearing tube, a rotor having a rotor shaft, a ring magnet, and at least one rotor position sensor. The bearing tube is configured from magnetically transparent material, e.g. from die-cast aluminum. The rotor shaft is arranged at least partially in the bearing tube. The ring magnet is arranged nonrotatably on the shaft, and likewise arranged at least partially inside the bearing tube. The at least one rotor position sensor is arranged outside the bearing tube and serves to generate a rotor position signal as a function of the rotational position of the ring magnet. What is thereby obtained is a motor having a rotor position arrangement that enables the absolute value of the motor's rotor position to be determined at any point in time.

DETAILED DESCRIPTION

In the description that follows, the terms “left,” “right,” “upper,” and “lower” refer to the respective Figure of the drawings, and can vary from one Figure to the next as a function of a particular orientation (portrait or landscape) that is selected. Identical or identically functioning parts are labeled with the same reference characters in the various Figures, and usually are described only once.

FIG. 1is a block diagram illustrating the functional principle of an apparatus100for operating an ECM120having a rotor position sensor arrangement according to the present invention. The rotor position sensor arrangement is configured on the one hand to generate rotor position signals and on the other hand to determine absolute values for the rotor position of ECM120from the rotor position signals that have been generated.

According to an embodiment of the present invention, apparatus100encompasses an ECM120having a rotor126that comprises a sensor magnet128, and having a stator124having at least one stator strand. Associated with ECM120is a power stage122for influencing the motor current in the at least one stator strand of stator124.

Apparatus100encompasses a controller130that usefully is configured as a microcontroller, and that is connected to ECM120. Controller130encompasses a commutation controller160(COMMUT) and is connected on the input side to at least one rotor position sensor140that is associated with ECM120. Commutation controller160generates commutation signals for power stage122of ECM120as a function of rotor position signals that are made available by rotor position sensor140.

Controller stage130encompasses a device150(Analyzer) for ascertaining the rotor position, having a normalizing unit156, an averaging unit154, and a processing unit152. Device150constitutes, together with rotor position sensor140and with sensor magnet128, the rotor position sensor arrangement according to the present invention.

Rotor position sensor140is preferably an analog rotor position sensor. The invention is not, however, limited to one specific rotor position sensor type, but instead different kinds of rotor position sensors can be used. For example, analog Hall sensors such as, for example, analog Hall sensors of the A1321 type, AMR Hall sensors, or GMR (giant magnetoresistive) sensors, can be utilized as rotor position sensors. Programmable sensors, e.g. of the Sentron 2SA-10 type, can also be used.

When apparatus100is in operation, an operating voltage is delivered to the at least one stator strand of stator124of ECM120. The currents flowing through the at least one stator strand are controlled, by the commutation signals made available by commutation controller160of power stage122, in such a way that rotor126rotates at a specific rotation speed (ω).

The rotation of rotor126produces a rotation of sensor magnet128at the same rotation speed (ω) at which rotor126is rotating, rotor position signals being generated by rotor position sensor140. These signals are delivered to device150which serves to determine, at each point in time, from the present rotor position signal, an absolute value for the rotational position of rotor126.

According to a preferred embodiment of the invention, the absolute values for the rotor position of rotor126are used by commutation controller160in controller130, upon the generation of suitable commutation signals, to bring about the electromagnetic interaction between rotor126and the at least one strand of stator124that is necessary for rotor126to rotate at the specific rotation speed ω.

The manner in which apparatus100functions for the determination of absolute values for the rotor position of rotor126will be further described below with reference toFIGS. 2 to 9.

FIG. 2is an enlarged longitudinal section through an external-rotor motor200that serves to drive an external component (not depicted), for example a fan wheel. As is evident fromFIG. 2, motor200is arranged in a housing202that comprises a substantially cylindrical housing part204at whose upper end a mounting flange206is mounted by means of at least one screw205.

Motor200has an external rotor222having a rotor cup224, which cup comprises on its inner side a radially magnetized rotor magnet228. Rotor magnet228has n pole pairs, where n=1, 2, . . . .

Rotor cup224is equipped with a base230in which is mounted a lower shaft end232of a rotor shaft234whose upper, exposed shaft end is labeled235. The external component can be driven by the upper, exposed shaft end235. Upper, exposed shaft end235is therefore also referred to hereinafter as the “driving end” of shaft234. Rotor cup224and base230are preferably configured integrally; lower shaft end232can be mounted in base230by Zamak injection. Lower shaft end232can likewise be used for driving. For this, an opening (not depicted) is provided in housing part204in the region of lower shaft end232. An advantage of the sensor arrangement according to the present invention is that, regardless of the type of motor, neither of the shaft ends is occupied by the sensor arrangement.

In the exemplifying embodiment depicted inFIG. 2, rotor shaft234is journaled almost entirely (i.e. with the exception of driving end235) in a magnetically transparent bearing tube238that preferably is configured integrally with mounting flange206. An upper rolling bearing236arranged on the A side of motor200and a lower rolling bearing237arranged on the B side of motor200serve for radial journaling of shaft234. Upper rolling bearing236is pressed into a recess292in mounting flange206, and is retained there by a retaining ring293that is covered by a sealing ring295. Lower rolling bearing237is mounted in a recess294at the lower end of bearing tube238by being pressed in, and the outer ring of said bearing abuts, with upper end240(inFIG. 2) against a compression spring242arranged in bearing tube238.

Internal stator244of motor200is mounted on the outer side of bearing tube238. Internal stator244encompasses a stator carrier282having a stator lamination stack284and a stator winding286. Arranged at the upper end of stator carrier282is a circuit board246that is mounted via a screw299on stator carrier282and serves to support the motor electronics.

Depicted on circuit board246is a terminal connection272that serves for electrical connection of the motor electronics via flexible individual conductors273′,273″,273′″, and273″″ which are bundled into a lead274. Lead274is guided out of housing part204through a seal276.

At least one rotor position sensor248is arranged on circuit board246and thus in the region outside bearing tube238. The sensor serves to generate rotor position signals as a function of the rotational position of a ring magnet250that is arranged nonrotatably on rotor shaft234and is preferably mounted nondetachably thereon.

According toFIG. 2, ring magnet250is arranged at substantially the same height, in the axial direction of rotor shaft234, as rotor position sensor248. Ring magnet250is spaced away from rotor magnet228in the axial direction of shaft234in order to avoid influencing rotor position sensor248when rotor position signals are generated by the stray flux of rotor magnet228. Ring magnet250and rotor magnet228are preferably arranged relative to one another in such a way that each pole transition of ring magnet250corresponds to a pole transition of rotor magnet228.

According to a preferred embodiment of the invention, ring magnet250is magnetized in such a way that it comprises a maximum of n pole pairs, n being (as described above) the number of pole pairs of rotor magnet228. Ring magnet250is preferably magnetized in pole-oriented fashion, i.e. diametrically or sinusoidally, so that a substantially sinusoidal magnetic flux profile occurs at its outer circumference.

The number and arrangement of rotor position sensor or sensors248is coordinated with the number and magnetization of the pole pairs of ring magnet250, to ensure that the rotor position signals for controlling the current flow of stator winding286are unambiguous. When two analog Hall sensors are used, for example, they are preferably arranged at a distance of 90° el. from one another. For the case in which ring magnet250has only one pole pair in this context, the Hall sensors must therefore be arranged at a distance of 90° mech. from one another. For a ring magnet250having two pole pairs, the result is a distance of 45° mech. for the Hall sensors, etc. The distance of rotor position sensor or sensors248from ring magnet250can be more than 10 mm via a relatively large air gap, depending on the magnetization of ring magnet250.

As is evident fromFIG. 2, rotor magnet228terminates at its upper and lower sides flush with the upper and lower sides, respectively, of stator winding286. As a result, however, the stray flux of rotor magnet228can act on the at least one rotor position sensor248and thus falsify the rotor position signal. To prevent the at least one rotor position sensor248from being influenced by the stray flux of rotor magnet228upon generation of the rotor position signals, the height of rotor magnet228can alternatively be shortened in such a way that its upper and lower sides terminate flush with the upper and lower sides, respectively, of stator lamination stack284.

Bearing tube238must be configured so that it enables measurement of the magnetic field generated by sensor magnet250at the location of rotor position sensor248outside the bearing tube. For that purpose, said tube is preferably configured, at least in the region between rotor position sensor248and sensor magnet250, from a magnetically transparent material.

Operation

During the operation of external-rotor motor200, a supply voltage is applied to a power stage associated with motor200(e.g. to power stage122ofFIG. 1) in order to cause current flow in stator winding286. The supply voltage is preferably a substantially constant DC voltage that is generated by a power-supply unit or a battery, and is converted by the electromagnetic interaction between stator winding286and rotor magnet228into rotations of external rotor222, and thus of rotor shaft234and of ring magnet250.

Upon rotation of ring magnet250, the magnetic field acting on rotor position sensor248continuously changes as a function of the magnetic flux profile at the outer circumference of ring magnet250, so that rotor position sensor248generates sinusoidal or cosinusoidal rotor position signals. According to the present invention, absolute values for the rotor position of external rotor222are determined from these rotor position signals.

For determination of the absolute values, the rotor position signals are preferably normalized by period or by means of period averages so that deviations of the rotor position signals from corresponding target values do not cause errors in the calculation of the rotor position angle. This normalization step is carried out by a suitable normalization unit, e.g. normalization unit156ofFIG. 1. The normalized rotor position signals are averaged by a unit for determining an average, e.g. averaging unit154ofFIG. 1, in order to increase measurement accuracy and improve the quality of the resulting signals. The resulting signals are converted by a processing unit, e.g. processing unit152ofFIG. 1, into absolute values for the rotor position angle and e.g. for the rotor position of external rotor222. Suitable conditioning methods for the rotor position signals are described, for example, in WO 2004/059830 A2 (and corresponding U.S. Pat. No. 7,049,776) and therefore need not be further described here.

According to a preferred embodiment of the invention, the absolute values for the rotor position of external rotor222are used to generate commutation signals, e.g. by means of commutation controller160of controller130ofFIG. 1. The commutation signals serve to control the currents flowing through stator winding286. Advantageously, there is no need here for an initialization phase in which rotor222is rotated into a defined starting state in order to assign an initial rotor position to an absolute electrical angle of rotor magnet228that is necessary for commutation. On the contrary, the absolute value of the rotor position is known at every point in time, so that the absolute electrical angle of rotor magnet228that is necessary for commutation is also known at all times. The initialization phase can thus be dispensed with, since the absolute values are drawn upon for generation of the commutation signals.

FIG. 3is a section along line I-I ofFIG. 2, at enlarged scale, through a preferred embodiment of external-rotor motor200having a two-pole ring magnet250. The number n of pole pairs of ring magnet250inFIG. 3is n=1. The two-pole ring magnet250is, as described with reference toFIG. 2, arranged on rotor shaft234, fixed against relative rotation with respect thereto, and at least partially within bearing tube238.

AsFIG. 3clearly shows, circuit board246is mounted on stator carrier282(not visible) with three screws299′,299″,299′″ that are passed through corresponding bores310′,310″,310′″. The motor electronics arranged on the upper side of the circuit board (cf.FIG. 2) encompass, by way of example, terminal connection272and schematically depicted power MOSFETs transistors)320′,320″,320′″.

Two Hall sensors248′,248″, e.g. analog SMD (Surface Mounted Device) Hall sensors, are arranged on the upper side of circuit board246at an angle PHI from one another. Because ring magnet250according toFIG. 3has two poles, this angle PHI is, as described above, 90° el., so that the two Hall sensors are arranged with a distance of 90° mech. from one another.

FIG. 4is a perspective view of an example of a ring magnet400that is suitable, according to a first embodiment of the invention, for implementing ring magnet250ofFIGS. 2 and 3.

As is evident fromFIG. 4, ring magnet400is substantially cylindrical in shape and is magnetized diametrically, i.e. ring magnet400has one magnet-pole pair or two magnet poles: a North pole410(N) and a South pole420(S). The magnetic flux profile between South pole420and North pole410is represented by magnetic field lines430′,430″,430′″, which serve to illustrate a diametrical magnetization.

Be it noted, however, that North pole410and South pole420of ring magnet400form substantially a spherical magnetic field. A substantially sinusoidal flux profile thus results at the outer circumference of ring magnet400. Because the orientation of the magnetic field at the outer circumference of ring magnet400at each magnetic pole permits an unambiguous inference in each case as to the respective rotor position, the generation of suitable rotor position signals by means of the particular rotor position sensors being used, e.g. rotor position sensors248′,248″ ofFIG. 3, is preferably based, when ring magnet400is used as a sensor magnet, on the orientation or direction of the magnetic field. The distance between ring magnet400and rotor position sensors248′,248″ must be selected appropriately in this context.

FIG. 5schematically depicts the magnetic field of a ring magnet500that is suitable, according to a preferred embodiment, for implementing ring magnet250ofFIGS. 2 and 3.

Ring magnet500is configured with four poles and is shown in a top view. It has two magnet-pole pairs, namely two North poles510,520(N) and two South poles530,540(S). Ring magnet500is sinusoidally magnetized according to the present invention, thus resulting in a substantially sinusoidal magnetic flux profile at the outer circumference of ring magnet500. The magnetic flux profile between the individual magnet poles of ring magnet500is indicated by corresponding magnetic field lines. For example, the magnetic flux profile between South pole540and North pole520is illustrated by magnetic field lines550. In terms of a clock face, North pole510is at its maximum at the 12-o'clock position, South pole540at the 3-o'clock position, etc.

When ring magnet500is used as a sensor magnet, the generation of suitable rotor position signals by the respective rotor position sensors being used, e.g. rotor position sensors248′,248″ ofFIG. 3, is preferably based on evaluation of the intensity of the magnetic field. The distance between ring magnet500and rotor position sensors248′,248″ is not critical in this context.

Ring magnet500is preferably substantially cylindrical in shape. Hard ferrite compound 13/22p per DIN 17 410 is suitable, for example, as a magnetic material.

FIG. 6is a top view of a sensor ring magnet arrangement69that can be used in both internal-rotor and external-rotor motors, andFIG. 7is a section through sensor ring magnet arrangement69, sensor ring magnet arrangement69being arranged on a shaft87. Sensor ring magnet arrangement69comprises sensor magnet82having the four sensor poles671,672,673, and674; a metal ring107; and a plastic ring109that connects sensor poles671to674to metal ring107.

Metal ring107sits on shaft87and is nonrotatably connected thereto. Brass is preferably used for metal ring107. Plastic109is introduced, for example by way of an injection-molding process, between metal ring107and sensor magnet82in order to connect them and at the same time to enable compensation for stresses resulting from thermal expansion, which stresses might otherwise cause sensor magnet82to burst.

The outside diameter of sensor magnet82is labeled112and is, for example, 37 mm. The outside diameter is preferably in the range of 15 mm to 50 mm, more preferably in the range of 20 to 40 mm.

The inside diameter of sensor magnet82or the outside diameter of plastic ring109is labeled110. Length110is, for example, 27 mm.

The inside diameter of plastic ring109or the outside diameter of metal ring107is labeled108. Length108is, for example, 20 mm.

The diameter of shaft87is labeled114and is, for example, 8 mm. Preferred values for diameter114of the shaft are in the range of 5 to 15 mm, although larger and smaller diameters are possible depending on the motor size.

The inside diameter of metal ring107is preferably selected so that a good connection with shaft87is created. The use of an inner metal ring107is advantageous because sensor magnet82can be produced in one or more standard sizes, and adaptation of sensor ring magnet69to shaft87can be accomplished by way of a change (favorable in terms of manufacture) in inside diameter114of metal ring107.

The width of magnet material71to74is labeled116, and width116for one sensor magnet is, for example, 7 mm. The width for an exclusively sensor magnet, i.e. one that does not simultaneously serve as a rotor magnet, is preferably in the range of 3 mm to 20 mm, more preferably in the range of 5 mm to 15 mm, and particularly preferably in the range of 6 mm to 12 mm.

The number of sensor poles SP is preferably SP=2, 4, 6, or 8, and particularly preferably SP=2 or 4.

In applications in which sensor ring magnet69is arranged in a corrosive environment, sensor magnet82can additionally be surrounded by a (preferably magnetically nonconductive) corrosion-resistant material. It is possible, for example, to weld the sensor magnet into magnetically nonconductive special steel. With a sensor ring magnet69of this kind, for example, an immersion motor in which the shaft is surrounded by cooling fluid can be implemented.

FIG. 8is an enlarged longitudinal section through an electronically commutated internal-rotor motor20that serves to drive an external component (not depicted), for example a fan wheel. Internal-rotor motor20has a housing22that comprises a cylindrical housing part24, an A-side bell26and a mounting flange29on the A side of motor20, and a B-side bell66and a housing cover17on the B side of motor20.

The lamination stack of an external stator28is arranged in cylindrical housing part24, the winding ends of said stator being indicated at30and32. Stator28has an internal recess34in which a rotor36having a rotor magnet38is arranged on a rotor shaft40whose driving end is labeled42and whose inner shaft end is labeled44. The rotor magnet has n pole pairs, where n=1, 2, . . . . A motor of this kind can also be referred to as a permanently excited synchronous internal-rotor machine.

B-side bell66is mounted in the right, open end of cylindrical housing part24. Said bell has a recess68for a rolling bearing72having an outer ring70and an inner ring74. Inner ring74is mounted on shaft end44. Rotor shaft40has for this purpose an annular collar78with whose right shoulder the shaft abuts against the left side of inner ring74. Abutting against its right side is a molded part80that is pressed toward rotor shaft40by countersunk head81of a retaining member10, said part being approximately annular. Molded part80serves to secure inner ring74on rotor shaft40.

Secure retention of outer ring70is provided by a flat, annular part90that is mounted on its outer periphery, by means of a plurality of screws92(preferably three regularly distributed screws), on B-side bell66, said part abutting with its radially inner part94against outer ring70and pressing the latter to the left. (Recess68is slightly shorter than outer ring70.)

A seal46for rotor shaft40is provided in the usual way in A-side bell26. Also located there is a recess48in which a ring50is mounted. Ring50surrounds an outer ring55of a rolling bearing54. Inner ring60of rolling bearing54is pressed onto rotor shaft40.

A circuit board86, arranged substantially parallel to rotor shaft40, is mounted on A-side bell26. Located on the underside of circuit board86is at least one rotor position sensor84that serves to generate rotor position signals as a function of the rotational position of a ring magnet82. Ring magnet82is in this case fixedly arranged on rotor shaft40between rolling bearing54and driving end42, and is preferably connected nondetachably to shaft40. Ring magnet82is preferably magnetized in such a way that it has a maximum of n pole pairs (n being the number of pole pairs of rotor magnet38) and that a substantially sinusoidal magnetic flux profile occurs at its circumference83.

According toFIG. 8, ring magnet82is arranged, in the axial direction of rotor shaft40, at substantially the same height as the at least one rotor position sensor84. Ring magnet82is preferably spaced away from rotor magnet38with reference to the axial direction of shaft40, in order to prevent rotor position sensor84from being influenced by the stray flux of rotor magnet38upon generation of the rotor position signals. Ring magnet82and rotor magnet38are preferably arranged relative to one another in such a way that each pole transition of ring magnet82corresponds to a pole transition of rotor magnet38.

The arrangement of rotor position sensor or sensors84is coordinated with the number and magnetization of the pole pairs of ring magnet82, to ensure that the rotor position signals for controlling the current flow of stator winding28are unambiguous. When two analog Hall sensors are used, for example, they are preferably arranged at a distance of 90° el. from one another. For the case in which ring magnet82has only one pole pair in this context, the Hall sensors must therefore be arranged at a distance of 90° mech. from one another. For a ring magnet82having two pole pairs, the result is a distance of 45° mech. for the Hall sensors, etc. The distance of rotor position sensor or sensors84from ring magnet82can be more than 10 mm via a relatively large air gap, depending on the magnetization of ring magnet82. The construction and magnetization of ring magnet82are analogous to the embodiments described with reference toFIGS. 4 to 7, and will therefore not be further described here.

The manner of operation of internal-rotor motor20is analogous to the manner of operation of external-rotor motor200ofFIG. 2. Commutation control, as well as the generation of rotor position signals and the determination of absolute values for the rotor position of rotor36of internal-rotor motor20, are likewise accomplished analogously to the operations for external-rotor motor200ofFIG. 2. The manner of operation of internal-rotor motor20, commutation control, and the generation of rotor position signals and the determination of absolute values for internal-rotor motor20will therefore not be further described here.

FIG. 9is a section along line II-II inFIG. 8, at enlarged scale, through a preferred embodiment of internal-rotor motor20having a four-pole ring magnet82. The number n of pole pairs of ring magnet82inFIG. 9is n=2. As described inFIG. 8, four-pole ring magnet82is fixedly arranged on rotor shaft40between driving end42and A-side bell26.

As is clearly evident fromFIG. 9, the upper and lower sides of circuit board86are arranged substantially parallel to the axial orientation of rotor shaft40and are mounted on A-side bell26. Provided on the underside of circuit board86are, for example, two rotor position sensors84′,84″.

Examples of values for individual components of internal-rotor motor20having a four-pole ring magnet82, according to a preferred embodiment, are indicated below:

Distance D (lower side of circuit board 86 to outer10 mmside of ring magnet 82):Distance H (center of sensor 84′ to center of19 mmsensor 84″; sensor type: SMD Hall):Angle PHI (sensor 84′ to sensor 84″):90° el. or 45° mech.Diameter of rotor shaft 40:6 mmDiameter of ring magnet 82:36.6 mm

Many variants and modifications are of course possible within the scope of the present invention.