Single-phase electric motor

An electric motor (10) has a stator (20) having a number S of stator poles (21, 22, 23, 24, 25, 26); a rotor (40) having a rotor magnet (40′), which rotor magnet (40′) has a number R of rotor poles (41, 42, 43, 44, 45, 46), R being equal to S, and the rotor (40) or the stator (20), or both, exhibiting a magnetic asymmetry. The asymmetry facilitates startup. The electric motor has a single-phase winding arrangement (30) with first (11), second (12) and third (13) terminals. Current can be made to flow, selectively, from either the first or the second terminal, through certain coils, to the third terminal (13). There is an output stage (50), preferably an H-bridge. The W total coils comprise a plurality of subgroups (TG1, TG2) of coils. A method for current flow through an electric motor utilizes these sub-groups (TG1, TG2) for current flow.

This application is a section 371 of PCT/EP2014/053817 filed 2014 Feb. 27.

FIELD OF THE INVENTION

The invention relates to a single-phase electric motor.

BACKGROUND

In three-phase motors having a stator and a rotor, the ratio between stator poles and rotor poles is always unequal. For example, a three-phase motor having six stator poles that are arranged at a spacing of 60° from one another, and has four rotor poles that are arranged at a spacing of 90° from one another. Each of the three phases here has two mutually oppositely located stator poles associated with it. The result is that, in any rotor position, it is possible to generate a torque via at least two of the three phases, since a magnetically different position of the rotor poles is located opposite each of the three phases. It is thus possible to start the motor with high torque in any rotor position.

With single-phase motors, the number of rotor poles corresponds to the number of stator poles. The consequence of this is that whenever each rotor pole is located opposite exactly one stator pole, no torque can be generated by a flow of current through the winding arrangement. In addition, for example in fans, the rotor preferentially assumes precisely that position when stopped, since it corresponds to the lowest-energy state.

Several methods are already known for enabling starting of such a motor, despite this. DE 8 702 271 U1, corresponding to SCHIMIDER U.S. Pat. No. 5,109,171, describes an electric motor in which soft magnetic iron plates are mounted on the rotor in such a way that in the zero-current-flow state, it assumes a position from which starting is possible. This is also referred to as generating an “auxiliary reluctance torque.”

DE 3 149 766 A1, corresponding to MUELLER U.S. Pat. No. 4,730,136, describes an electric motor in which the stator poles are implemented asymmetrically, so that the spacing between the stator poles and the rotor decreases as viewed in a circumferential direction. The rotor poles of the rotor magnet preferentially assume a position in which they are on average as close as possible to the stator pole. This once again results, in the zero-current-flow state, in a starting position from which the motor can begin to operate.

Millions of such motors are used in CD players and hard drives.

The aforesaid approaches require a motor in which the external torque and the friction that occur are not too great, as is the case e.g. with fans. Otherwise there is no guarantee that the starting position can reliably be assumed. The area of application for these approaches is thus limited.

SUMMARY OF THE INVENTION

An object of the invention is to furnish a novel single-phase motor.

The object is achieved by an electric motor that comprises: a stator having a number S of stator poles, a rotor having a rotor magnet, which rotor magnet has a number R of rotor poles, R being equal to S, and the rotor or the stator or both exhibiting an asymmetry; a single-phase winding arrangement having a first winding terminal and a second winding terminal, current being capable of flowing through a number W of coils of the winding arrangement via the first winding terminal and the second winding terminal; an output stage that is implemented to enable a current between the first winding terminal and the second winding terminal; a first apparatus that is implemented to enable, in interaction with the output stage, a current flow through at least one sub-group of the W coils, the at least one sub-group encompassing more than none of the W coils and fewer than W of the W coils.

The asymmetry is preferably implemented to make possible, at any rotor position of the rotor, the generation of a torque via at least one of the following current-flow processes:

current flow through all W coils, or

current flow through the at least one sub-group of the coils.

Preferably at least two sub-groups are provided.

Preferably the first apparatus comprises a third winding terminal and a switch in order to enable a current between the first winding terminal or the second winding terminal on the one hand, and the third winding terminal on the other hand.

Preferably the number of coils between the first winding terminal and the third winding terminal is not equal to the number of coils between the third winding terminal and the second winding terminal.

Preferably the winding arrangement comprises a plurality of mutually parallel sub-strands, and the first apparatus comprises a switch that is implemented, in the nonconducting state, to prevent a current through a first portion of the sub-strands but not to prevent a current through the remaining sub-strands.

Preferably the rotor exhibits an asymmetry that is generated by the fact that the R rotor poles have, at least in part, an angular extent different from one another.

Preferably the rotor exhibits an asymmetry that is generated by the fact that the angular distance of the magnetic center of one rotor pole from the magnetic center of an adjacent rotor pole is, at least in part, not equal to 360°/R.

Preferably the rotor exhibits an asymmetry that is generated by an asymmetrical magnetization of the rotor magnet.

Preferably the rotor exhibits an asymmetry that is achieved by an asymmetrical arrangement of different materials in the region of the rotor, the different materials having different magnetic properties.

Preferably the stator exhibits an asymmetry that is generated by the fact that the angular distance of the adjacent stator poles is, at least in part, not equal to 360°/S, where preferably S=2.

Preferably the at least one sub-group encompasses at least one of the W coils and at most W−1 coils.

Preferably the output stage comprises a full bridge circuit in order to enable a current flow through the winding arrangement between the first winding terminal and the second winding terminal in both directions.

Preferably the rotor magnet comprises permanent-magnet rotor poles or electromagnetically generated rotor poles; in the case of the electromagnetically generated rotor poles, each rotor pole having, associated with it, a winding through which current flows during operation.

The object is achieved by a method for current flow through an electric motor having a stator having S stator poles, a rotor having R rotor poles, R being equal to S; having a single-phase winding arrangement having a first winding terminal and a second winding terminal, W coils being electrically connected between the first winding terminal and the second winding terminal; having an output stage that is implemented to enable a current between the first winding terminal and the second winding terminal; having a first apparatus that is implemented to enable, in interaction with the output stage, a current flow through at least one sub-group of the W coils, the at least one sub-group encompassing more than none of the W coils and fewer than W of the W coils; which method comprises the following steps:

A) with the electric motor in a first state, the output stage is controlled in such a way that current flows through all W coils via the first winding terminal and the second winding terminal;

B) with the electric motor in a second state, the output stage is controlled in such a way that current flows through only the at least one sub-group of the W coils.

Preferably the rotation speed of the electric motor is sensed, and a switchover occurs from the first state of the electric motor into the second state when the rotation speed of the electric motor is below a predetermined minimum rotation speed.

Preferably a switchover into the second state occurs upon starting of the motor, and then a switchover into the first state occurs.

Preferably in the first state the direction of the current flow between the first winding terminal and the second winding terminal is predetermined as a function of the rotor position of the rotor.

Further details and advantageous refinements of the invention are evident from the exemplifying embodiments, in no way to be understood as a limitation of the invention, that are described below and depicted in the drawings.

DETAILED DESCRIPTION

FIG. 1shows an electric motor10having a stator20and a rotor40. Stator20has a winding arrangement30associated with it, and it has six stator poles21to26. Rotor40has a rotor magnet40′ likewise having six rotor poles41to46that are preferably implemented as permanent-magnet rotor poles41to46.

Winding arrangement30has six coils31to36, connected in series, that are connected or electrically joined in series between a first winding terminal11and a second winding terminal12. Each stator pole21to26has one of coils31to36associated with it; coils31to36are wound in such a way that when current flows, a North pole is followed by a South pole, then a North pole again, etc. alternatingly in the respective adjacent stator poles21to26, since the rotor poles41to46can also respectively change direction. Winding arrangement30begins—proceeding from first winding terminal11—at stator pole21, proceeds therefrom to stator pole24and then to stator poles25,26,22, and23, and from there to second winding terminal12. Current can thus flow through coils31to36via first winding terminal11and second winding terminal12.

A third winding terminal13, which can also be referred to as a “tap,” is provided on winding arrangement30between stator poles24and25.

FIG. 2shows a corresponding circuit diagram for motor10ofFIG. 1. It depicts winding arrangement30having the six coils31to36and having first winding terminal11, second winding terminal12, and third winding terminal13, as well as a control apparatus70and an output stage50for influencing the current through winding arrangement30.

A first lead57(+UB) and a second lead58(GND or reference potential) are provided in order to deliver a supply voltage +UBto output stage50, for example from a DC voltage source71.

A switch51is provided between first lead57and first winding terminal11, and a switch52is provided between first winding terminal11and second lead58.

A switch53is provided between first lead57and second winding terminal12, and a switch54is provided between second winding terminal12and second lead58.

The arrangement having the four switches51,52,53, and54is also referred to as a “full bridge circuit” or “H bridge,” in which winding arrangement30constitutes the bridge arm of the full bridge circuit.

A switch56is provided between third winding terminal13and second lead58.

Lead58is connected via a so-called “base resistor”60to a lead59, and switches52,54,56are correspondingly connected via lead59indirectly to lead58. Resistor60is usually low-impedance, and it can additionally or alternatively be provided in lead57, or can be omitted entirely.

A control apparatus70has five control leads61,62,63,64, and66through which it is connected to the five switches51to54and56in order to render them conductive or non-conductive.

Unless otherwise indicated, switches51,52,53,54,56, and55that are used are preferably controllable switches, more preferably semiconductor switches such as MOSFETs, IGBTs (isolated gate bipolar transistors), or bipolar transistors (seeFIG. 6andFIG. 7). Relays, for example, can also be used for switches55,56.

The upper switches51,53,55are also referred to as “high side” switches, and the lower switches52,54,56as “low side” switches.

Switches51to56preferably each have a freewheeling diode associated with them (seeFIG. 26) in order to prevent a current through the switches in the reverse direction, as can occur e.g. as a result of the induced voltage when switches51to56are non-conductive and rotor40is rotating. Alternatively, a freewheeling diode can also be provided only on switches51,52,53,54, and switch56can be without a freewheeling diode, since the current flow through switch56can be limited to the starting operation so that a large induced voltage does not yet occur.

A rotor position sensor67(e.g. Hall sensor or magnetoresistive [MR] sensor or encoder) is preferably arranged on rotor40, in order to identify the rotor position, and rotor position sensor67is connected via a lead68to control apparatus70.

Control apparatus70is connected via a lead72to lead59in order to measure the potential at base resistor60.

Operation

In normal operation, i.e. when rotor40is rotating and preferably has reached a minimum rotation speed, current flows through winding arrangement30via full bridge circuit51,52,53,54.

This is done, for example, by alternatingly either, in a first state Z1, rendering switches51and54conductive or, in a second state Z2, rendering switches53and52conductive.

In the first state Z1, a current flows from first lead57through switch51, winding terminal11, winding arrangement30, second winding terminal12, switch54, lead59, and base resistor60to second lead58.

In the second state Z2, the current flows from operating voltage57through switch53, second winding terminal12, winding arrangement30, first winding terminal11, switch52, lead59, and base resistor60to ground58.

In the first state Z1and second state Z2, the remaining switches are non-conductive.

Operation switches back and forth between the first state Z1and the second state Z2, depending on the rotor position of rotor40, so as thereby to drive rotor40. The rotor position is sensed via rotor position sensor67. Sensing can also occur, however, in sensorless fashion.

The control procedure described above for normal current flow through output stage50during operation is an example, and one skilled in the art knows of a plurality of control options for output stages, i.e. including, for example, clock-timed application of control to at least some of switches51to54, or block commutation.

Base resistor60serves to measure the current through output stage50so that control apparatus70can detect an overcurrent via lead72.

Control apparatus70controls switches51to53in order to drive, or optionally also to decelerate, motor10. Closed- or open-loop control of rotation speed, power output, etc. is possible here, for example.

Because commutation is effected via switches (here51to54) and not via commutator brushes, the motor is also referred to as a “brushless” or “electronically commutated” motor.

Starting the Motor

When motor10ofFIG. 2starts, it is possible for rotor40to be in an unfavorable rotor position, in which a current flow, through winding arrangement30via switches51,54or53,52, generates very little or no torque.

Via third winding terminal13, it is possible to make switches51and56conductive in a third state Z3, so that a current flows from first lead57through switch51, first winding terminal11, coils31and32, third winding terminal13, switch56, lead59, base resistor60to second lead58. Current thus flows through a first sub-group TG1of coils31to36that encompasses only coils31and32.

It is likewise possible to make switches53and56conductive in a fourth state Z4, so that a current flows from first lead57through switch53, second winding terminal12, coils36,35,34,33, third winding terminal13, switch56, lead59, base resistor60to second lead58. Current thus flows through a second sub-group TG2of coils31to36that encompasses only coils33and36.

In this exemplifying embodiment, no coils are therefore contained in common in sub-groups TG1, TG2, but instead current flows through different coils in each case.

The expression for the magnetic (internal) torque M_i of motor10is
M_i=k_mI(1)
where
k_m=torque constant (also called “flux linkage”)
I=winding current through winding30

For the actual torque or output torque M, the negatively acting frictional torque M_R must also be taken into account.

The expression for the voltage U_i induced in winding arrangement30is
U_i=k_momega=k_m2pin/60  (2)
where
omega=ω=angular speed
n=rotation speed in min−1

When the output stage is blocked or output stage transistors51,52,53,54,56are nonconductive, the voltage U applied to winding terminals11,12(armature voltage) becomes
U=IR+U_i(3)
where
R=resistance of winding arrangement30.

The torque constant k_m is a function of the rotor position phi of rotor40, i.e. k_m=k_m(phi). The voltage constant kE, which is proportional to k_m and is sometimes also referred to as Ke, is often also considered instead of the torque constant k_m.

As is evident from equations (1) and (2), the torque constant k_m creates both the proportionality between the torque M_i and the winding current I and the proportionality between the induced voltage U_i and the angular speed omega. It is therefore possible, for example, to ascertain the torque constant k_m by externally driving rotor40at a constant angular speed omega and simultaneously measuring the induced voltage U_i, and the profile of the resulting curve is proportional or identical to the curve for the magnetic torque M_i.

FIG. 3shows a measurement of the induced voltage M_i over one full revolution of rotor40from phi=0 to 360°.

Curve201shows the induced voltage U_i that is measured between first winding terminal11and second terminal12. It is apparent that curve201has six zero crossings; and if the motor comes to rest in a rotor position at which curve201exhibits a zero crossing, then no torque can be generated by a current flow between first winding terminal11and second winding terminal12.

Curve202shows the induced voltage U_i that is induced between first winding terminal11and third winding terminal13in coils31,32(sub-group TG1). Curve202has a lower amplitude than curve201, since what is added is only the signal from the two coils31,32rather than the signal of all six coils31to36, as in curve201. It is evident that the zero crossings of curve202occur at different rotor positions than the zero crossings of curve201.

Curve203shows the induced voltage U_i that is induced between second winding terminal12and third winding terminal13in coils33to36(sub-group TG2). Curve203has a lower amplitude than curve201and a higher amplitude than curve202, since the signal of the four coils33to36is added. It is evident that the zero crossings of curve203occur at different rotor positions than the zero crossings of curves201and202.

FIG. 4shows a portion ofFIG. 3for the angle range from 0° to approximately 150°.

Curve201, which reproduces the induced voltage U_i between first winding terminal11and second winding terminal12, has a zero crossing at 60°, the angle of 60° being characterized by vertical line210and the zero crossing at 120° being characterized by vertical line215. At points210and215, no torque can be generated by a current flow between winding terminals11and12because the curve for the torque constant k_m corresponds to the curve for the induced voltage U_i, and both of them have a zero crossing.

Curve202, however, has its zero crossing at a point213(at approximately 62°) located after point210, and at point210curve202still has a negative value that is characterized as horizontal line211.

Curve203has its zero crossing before point210, at point214(at approximately 57°), and at point210curve203has already risen into the positive region, the value being characterized by a horizontal line212.

Because curves202,203are different from zero at point210, a torque can be generated there either via coils31,32associated with curve202(sub-group TG1) or via coils33to36associated with curve203(sub-group TG2).

At point215, which corresponds to a rotor position of 120°, curve202has already had a zero crossing at a smaller angle (at point218) and has dropped to a negative value that is characterized by a horizontal line216.

Curve203has its zero crossing just after point215at point219, and curve203is slightly in the positive region at point215.

As is evident, the torque achievable via curves202,203at point215is less than at point210, and a greater torque can be generated by a current flow through coils31,32associated with curve202than via coils33to36associated with curve203.

At the zero crossings213,218of curve202, the other curves201,203are respectively positive and negative, and at the zero crossings214,219of curve203the other curves201,202are respectively positive and negative, i.e. not equal to zero.

The result is that a torque can be generated at any rotor position phi.

Now that the fundamental principle has been presented, details and variants will be discussed below.

Motor Type

The approach presented, with which a torque can be generated at any rotor position, is in principle independent of motor type. Internal-rotor, external-rotor, or disk-armature motors, for example, can be used.

Stator20can comprise a stator core as shown, for example, inFIG. 1, but it can also be configured without a stator core; this is also referred to as an “air-core” winding. The stator core is preferably implemented as a stator stack or stator lamination stack, but other variants are also possible.

The number R of rotor poles41,42preferably corresponds to the number S of stator poles21,22, etc.

Rotor40is preferably a permanent-magnet rotor40having permanent-magnet rotor poles41,42, etc., or a permanent-magnet rotor magnet40′. It is also possible, however, to use, for example, a motor having electromagnetically generated rotor poles41,42, etc., in which e.g. each rotor pole41,42, etc. comprises a winding, depicted inFIG. 28, through which current flows during operation; current flow occurs as a result of a voltage source49, and the winding is wound, for example, around a lamination stack. Voltage source49can be arranged on rotor40but need not obligatorily be arranged in rotor40. In the case of an external arrangement, an electrical connection can be effected e.g. via wiper contacts or other contacts that enable electrical conduction despite the rotational motion of the rotor. Current flows in rotor40preferably in such a way that rotor magnets41,42, etc. always generate a magnetic field in the same direction during operation, so that they can be used like permanent-magnet rotor magnets41,42, etc.

In the exemplifying embodiment ofFIG. 1, stator20has six slots into which the winding arrangement is distributed. This is therefore referred to as a “six-slot” or “six-pole” motor.

Winding Arrangement and Wiring Configuration for Partial Current Flow Through the Coils

FIG. 5toFIG. 7andFIG. 26show a variety of variants for wiring a single-phase, single-strand motor having two poles. The two coils31,32have first winding terminal11and second winding terminal12. First winding terminal11is connected via switch51to first lead57, and via switch52to second lead58. Second winding terminal12is connected via switch53to first lead57and via switch54to second lead58; switches51to54form a full bridge circuit. Third winding terminal13is arranged between coils31,32.

InFIG. 5, third winding terminal13is connected via switch56to second lead58. With the aid of switch56, a current can flow through switch51, coil31(sub-group TG1), and switch56, or a current can flow through switch53, coil32(sub-group TG2), and switch56. The arrangement of switch56leading to lead58has the advantage that corresponding semiconductor switches and driver circuits are often more inexpensive than for switches that are used between first lead57and a winding terminal11,12,13.

InFIG. 6, third winding terminal13is connected via a switch55to first lead57. With the aid of switch55, a current can flow through switch55, coil31(sub-group TG1), and switch52, or a current flows through switch55, coil32(sub-group TG2), and switch54.

InFIG. 7, third winding terminal13is connected both via switch55to operating voltage57and via switch56to ground58. This makes possible a current flow individually through coils31,32in both directions. This can be necessary, for example, when the application permits absolutely no rotation in the wrong direction. In cases in which this is noncritical, however, for example in a fan, the use of two switches55,56on second winding terminal13results in unnecessary additional cost.

FIG. 26corresponds to the circuit ofFIG. 5, winding terminal13being located not exactly between the two coils31,32but rather inside first coil31. With all the exemplifying embodiments it is therefore possible in principle also to arrange winding terminal13inside a coil31,32, and in the present example a current flow between winding terminals11,13allows current to flow through two-thirds of coil31, and a current flow between winding terminals13,12allows current to flow through one-third of coil31and all of coil32. This yields the following possible sub-groups:

FIG. 8shows a single-phase, two-strand winding arrangement for a stator having two stator poles, in which a first strand encompasses coils31,32and a second strand encompasses coils33,34. Each of the strands can be connected in only one direction from lead57(UB) to lead58(GND). A current flow through the strand having coils31,32acts exactly oppositely to a current flow through the strand having coils33,34, as characterized by the black dots next to coils31,32,33,34. Coils31,32have winding terminals11,12, and coils33,34have winding terminals11,12′. Winding terminal12is connected via a switch52to lead58(GND), and winding terminal12′ is connected via a switch54to lead58(GND). The two strands are preferably configured as a bifilar winding, but can also be wound sequentially.

Arranged between coils31,32of the first strand is a third winding terminal13that is connected via a switch56to lead58(GND) in order to enable a current flow to coil31at startup. This yields the following current flow possibilities:

An arrangement of this kind having a larger number S of stator poles is of course also possible, for example where S=4, 6, 8, 10, etc.

FIGS. 9 to 12show (not exhaustively) a variety of variants for wiring a single-phase motor having four poles. The four coils31to34have a first winding terminal11and a second winding terminal12. Winding terminals11and12are connected via a full bridge circuit having switches51,52,53,54between first lead57and second lead58.

InFIG. 10, a winding terminal13A is provided between coils31and32, a winding terminal13B between coils32and33, and a winding terminal13C between coils33and34. Winding terminals13A,13B, and13C are connectable to second lead58via a respective switch56A,56B,56C. The provision of three additional switches56A,56B,56C is more expensive than a variant having only one switch56, but it makes possible the use of a rotor40or rotor magnet40′ having less asymmetry, since specific rotor poles can be more variably influenced via the interconnection pattern. Current flow to the following sub-groups of coils31to36is possible, for example:

At least some of coils31to36are present in several of the sub-groups TG1to TG6.

With this variant it is possible to additionally provide switches55A,55B,55C (not depicted) at winding terminals13A,13B,13C in order to enable an interconnection to first lead57. The result is that coils31to36can be controlled with even more variants, and with a winding arrangement wired in this manner the asymmetry in a single rotor pole is sufficient to allow generation of a torque in any rotor position.

InFIG. 11andFIG. 12, coils31and32are connected in series between winding terminals11,12, and coils33,34are likewise connected in series between winding terminals11,12, so that coils31,32are connected in parallel with coils33,34.

InFIG. 11, third winding terminal13is provided between coils31,32and said terminal is connectable via switch56to second lead58. The result is that at startup, current can flow through one of coils31(sub-group TG1, via switches51,56) or32(sub-group TG2, via switches53,56).

FIG. 12shows another possibility for effecting current flow through only some of coils31to34. A switch69is provided in the sub-strand (arm) having coils33,34between first winding terminal11and coil33, and via this switch69the sub-strand having coils33,34can be cut off from the current flow at startup. It is advantageous for such a variant if at least some of the coils are connected in parallel. A sub-group TG1=(31,32) thus exists. A disadvantage of this approach is that when current is flowing in normal operation via winding terminals11,12, a current constantly flows through switch69. This results in losses, and an expensive switch69having low resistance and/or good cooling may be necessary. But because switch69is not switched in normal operation, it is possible to use, for example, a relay. Switch69can also be arranged between coils33,34, or between coil34and second winding terminal12, or in one of coils33,34. It is furthermore possible to disconnect winding terminal11for the two arms31,32and33,34and to provide a switch51and52for each winding arm, or else, for example in the context of a winding arrangement having three parallel sub-strands, to implement either only one sub-strand or two sub-strands via switch69so they can be shut off. It is also possible to additionally provide a third winding terminal in order to have further possibilities for current flow through sub-groups of the coils.

Generating Asymmetry

With a symmetrical stator20and symmetrical rotor40, no torque can be generated even by current flow through some or through a sub-group of coils21to26, since exactly the same voltage U_i is being induced in each of coils31to36.

An asymmetry must therefore be present either in stator20or in rotor40or in both, so that the voltages induced in the individual coils31,32, etc. in normal operation differ at least in part from one another.

Asymmetry in the Rotor

An asymmetry can be achieved by the fact that the angular extent of at least one of rotor poles41to46differs from the angular extent of at least one other of rotor poles41to46, i.e. that rotor magnet40′ is implemented asymmetrically. InFIG. 1, for example, rotor poles41,44each have an angular extent of 60°, rotor poles42,45an angular extent of 55°, and rotor poles43,46an angular extent of 65°. With this arrangement, the angular distribution of rotor poles41,42,43corresponds to angular distribution44,45,46. The advantage of this is that any half of rotor40has the same number of North-South or South-North poles on each side. This is positive both for the total torque of motor10and for noise emission. It is also positive to select, as inFIG. 1, two oppositely located stator poles21,24for the partial current flow to coils31to36, since these two stator poles21,24and the associated coils31,32“see” the same magnets41and44in magnetic terms, so that the torque resulting upon current flow through coils31,32, in connection with rotor poles41,44, adds up.

InFIG. 13, rotor poles41,43located opposite one another each have an angular extent phi_RM of 85°, and rotor poles42,44each have an angular extent phi_RM of 95°.

InFIG. 14, rotor pole41has an angular extent phi_RM of 90°, rotor poles42,44adjacent thereto have an angular extent phi_RM of 87°, and rotor pole43of rotor magnet40′ has an angular extent phi_RM of 96°. The use of three different angular extents phi_RM_in principle offers more possibilities for generating a torque upon startup than with rotor40ofFIG. 13, and with such a rotor40a torque can be generated in any rotor position, even with a symmetrical stator20, using the simple output stage according toFIG. 9. But because bisecting a rotor40of this kind does not result in the same amount of identically magnetized pole material on each half, this can result in a radial tension, which is undesirable. The differences should therefore be as small as possible.

InFIG. 15, rotor poles41to44of rotor magnet40′ each have the same angular extent phi_RM=80°. In addition, neutral zones41A to44A are respectively provided between rotor poles41and44, and thanks to their asymmetry it is also possible to generate an asymmetry of rotor40or of rotor magnet40′ that allows the motor to start. For this, intermediate regions44A (between rotor poles44and41) and43A (between rotor poles43and44) have an angular extent phi N=10°, intermediate region41A (between rotor poles41,42) has an angular extent phi N=5°, and intermediate region42A (between rotor poles42and43) has an angular extent phi N=15°. The asymmetry becomes evident when viewing the magnetic centers41M to44M of rotor poles41to44. Magnetic centers41M,44M, and43M are each at an angular distance of 90°, or generally 360°/R where R=number of rotor poles, and magnetic center42M is shifted 5° out of the 90-degree pattern. The result is that the angular distance between magnetic center41M and magnetic center42M is 85°, and the angular distance between magnetic centers42M and43M is 95°.

FIG. 16shows a rotor40having four poles41,42,43,44of rotor magnet40′, a neutral region47arranged axially below the poles, and preferably a magnetic track48arranged axially below neutral region47. The pole boundaries between poles41,42,43, and44are each oblique; pole boundaries43Z (between poles43,44) and44Z (between rotor poles44and41) are visible on the peripheral side of rotor magnet40′, and the oblique pole boundary41Z between rotor poles41and42is visible on the inner side of rotor40. With this configuration as well, it is helpful to look at the magnetic center, which is drawn in for rotor pole44, for example, as44M.

The additional magnetic track48, which can be arranged in a variety of ways relative to poles41to44, serves to generate a sensor magnetic field suitable for the rotor position sensors in order to enable good commutation. This is especially important when poles41to44have different angular extents (see description ofFIG. 23).

The asymmetry of rotor40or of rotor magnet40′ can also be generated by using different magnetic materials or by way of an asymmetry in the magnetization of permanent-magnet rotor magnet40′.

Asymmetry in the Stator

An asymmetry of stator20ofFIG. 1can be achieved, for example, by the fact that at least one of poles21to26is arranged with a slight rotation, so that it is at an angular distance from at least one of the other stator poles21to26that is not equal to 60° or to a multiple thereof. Variants are of course possible here as well.

FIG. 17shows a stator20having six stator poles21to26, of which stator poles21and24are implemented with a slight clockwise rotation with respect to stator poles22,23,25,26. The angle between poles21,22and poles24,25is respectively 65°, the angle between poles22,23and poles25,26respectively 60°, and the angle between poles23,24and26,21respectively 55°.

FIG. 18shows an asymmetry in a two-pole stator20. Here the two poles are not arranged exactly at an angular distance phi_s of 180° (360°/S where S=2), but instead, for example, at an angular distance phi_s=175° (or 185°, viewed from the opposite side). The angular offset Delta phi_s with respect to the standard angle 180° is selected to be as small as possible, since it results in somewhat poorer efficiency for motor10. The asymmetry of stator20is especially advantageous with a two-pole motor: with a single-phase two-pole motor, if an asymmetry is provided only in rotor40, there is still a rotor position in which both coils31,32of the two stator poles21,22simultaneously have a zero crossing, namely when the center of each of rotor poles41,42is located exactly opposite one of stator poles21,22.

Advantages Compared with a Single-Phase Motor with Auxiliary Reluctance Torque

With the rotor pole distribution according toFIG. 1(65°, 60°, 55°, 65°, 60°, 55°) it was found that the voltage constant kE is reduced by approximately two percent as compared with a rotor40having symmetrical rotor poles and a symmetrical stator.

This is less of a loss, however, than with a motor having a reluctance notch for generating an auxiliary reluctance torque, i.e. in which the air gap between the stator pole and rotor magnet40′ respectively increases circumferentially in one direction, since the size of the air gap influences the magnetic flux between rotor and stator and thus also the voltage constant kE. The motor according to the present invention can thus supply a higher power output than a corresponding single-phase motor with auxiliary reluctance torque, and the efficiency is better.

The cogging torque of the single-phase motor according to the present invention is considerably reduced as compared with a conventional single-phase motor with auxiliary reluctance torque. This is understandable, since a motor with auxiliary reluctance torque is specifically implemented so that the rotor latches into a rotor position that is suitable for starting. Measurements have indicated a decrease in cogging torque of between 50% and 90% compared with a motor with auxiliary reluctance torque. This has the great advantage that less motor noise is also produced, since a lower cogging torque results in less motor noise.

Single-phase motors whose starting position is defined via an auxiliary reluctance torque require an application in which a large external torque or excessive friction do not occur, i.e. for example a fan application or a motor for a CD player. The single-phase motor according to the present invention makes possible additional applications in which moderate external torques or greater friction can also occur, for example in liquid pumps. The potential utilization range of the motor according to the present invention is thus wider than with a single-phase motor with auxiliary reluctance torque, but narrower than with a three-phase motor.

Advantages Compared with a Three-Phase Motor

The cost advantages of using a single-phase winding arrangement30having a third winding terminal13and a switch56as shown inFIG. 2are compared, by way of example, with a three-phase motor having a full bridge circuit.

A full bridge circuit for a three-phase motor has three high-side switches (switched to operating voltage) and three low-side switches (switched to ground).

The full bridge circuit for the single-phase motor ofFIG. 2, on the other hand, has only two high-side switches51,53and two low-side switches52,54. One low-side switch56for the third winding terminal is additionally provided. The result is thus on the one hand that one switch, and optionally an associated driver module, are eliminated. In addition, the low-side switch56can be a simpler and more economical model with higher internal resistance, since switch56is utilized only when starting, and the power loss or heat generation caused by switch56is therefore noncritical.

In addition, in a motor having rotor position sensors (e.g. Hall sensors), three rotor position sensors are necessary in the three-phase motor, whereas only one is required in the single-phase motor. Sensorless motor control is nevertheless also possible in both cases.

A calculation with several of the Applicant's high-output fans has shown that a very large cost reduction, on the order of 10%, is possible for the drive system (motor and electronics).

A further advantage of the single-phase motor according to the present invention is that in principle, the stator cores and lamination stacks can be the same as those used with a three-phase motor without auxiliary reluctance torque. The same stamping tool can thus be used for both a three-phase and a single-phase stator, e.g. having a number of stator poles S=6, 12, 18, etc.

It is also possible, however, to select exclusively single-phase variants with S=2, 4, 8, etc.

Comparative Measurements with Different Motor Types

Measurements of cogging torque and of the voltage constant kE, which is proportional to k_M, were carried out. The resulting curves for the voltage constant kE refer in each case to the signal of one coil.

The following motor types were investigated:

HeightOutsideofdiameter oflaminationlaminationNameSRstackstackCommentsM2314414 mm54 mmsingle-phase, no auxiliaryreluctance torque, obliqueM2326614 mm54 mmsingle-phase, with auxiliaryreluctance torqueM2336615 mm56 mmsingle-phase, with auxiliaryreluctance torqueM2346414 mm54 mmthree-phase, no auxiliaryreluctance torque
FIG. 19shows the measurement of the voltage constant kE for the M231and M232motors, in each case over one revolution of the rotor covering two rotor poles.

Curve M231A shows the voltage constant kE for an M231motor according to the present invention, which has no auxiliary reluctance torque. Curve M231A is therefore largely symmetrical around an average maximum.

Curve M232A shows the voltage constant kE for a known single-phase motor with auxiliary reluctance torque. It is clearly evident that curve M232A rises in each case from left to right, and reaches its maximum only in the right-hand region.

It was found in this measurement that the area under curve M231A is approximately 3% larger than the area under curve M232A, and this results in slightly higher efficiency.

Curve M231A was measured using a four-slot motor (S=4), and curve M232A using a six-slot motor (S=6). It is presumed that the area under curve M231A would be even larger in percentage terms, relative to the area under curve M232A, if a comparison had been made with a six-slot motor.

FIG. 20shows a measurement of the cogging torque for the M231, M232, and M234motors, in each case over one revolution of the rotor covering two rotor poles.

Curve M232B shows the single-phase M232motor with auxiliary reluctance torque, and the cogging torque is correspondingly very high. Curve M231B shows the cogging torque for the single-phase M232motor according to the present invention (here without auxiliary reluctance torque), and the cogging torque is reduced by 87% compared with curve M232B. The jagged profile of curve M231presumably results from the fact that a different measurement apparatus was used for the measurement.

For comparison, a further curve M234B is plotted which shows the cogging torque of the three-phase M234motor without auxiliary reluctance torque. The result is that with the M231motor according to the present invention, corresponding to curve M231B, a cogging torque can be achieved that is appreciably less than that of an existing single-phase motor with auxiliary reluctance torque, and is comparable to the cogging torque of a three-phase motor. This results in an appreciable reduction in noise compared with the known single-phase motor.

FIG. 21shows a measurement of the voltage constant kE for the M231and M233motors, in each case over one revolution of the rotor covering two rotor poles.

Curve M231A shows the voltage constant kE for an M231motor according to the present invention, which has no auxiliary reluctance torque. Curve M231A is therefore largely symmetrical around an average maximum.

Curve M233A shows the voltage constant kE for the single-phase M233motor with auxiliary reluctance torque, currently used in large numbers by the Applicant.

The M231and M233motors have slightly different outside diameters and a slightly different lamination stack height, but the M233motor has a smaller end winding and thus a comparable axial height for the overall stator, and the two motors M231, M233are therefore usable in the same applications.

It is evident from curve M233A that the stator in question has an auxiliary reluctance torque as a result of an air gap that becomes smaller in the circumferential direction, since curve M233A rises in the upper region and reaches a maximum only on the right-hand side.

It was found with this measurement that the area under curve M231A is approximately 1.6% larger than the area under curve M233A, so that the M231motor according to the present invention has higher efficiency.

FIG. 22shows a measurement of cogging torque for the M231, M233motors. Curve M233B shows the cogging torque of the M233motor, and curve M231B the cogging torque of the M231motor according to the present invention.

The M231motor according to the present invention achieves a reduction in cogging torque of 80.2% with comparable efficiency, and this results in an appreciably quieter motor.

Improving Rotor Position Sensing

FIG. 23shows a measurement of the current through output stage50ofFIG. 2, measured at base resistor60. Signal240A shows the measured current, which is highly irregular; this is attributable to the fact that rotor position sensor67(seeFIG. 2) ascertains the rotor position based on the asymmetrical rotor poles41to46ofFIG. 1. Depending on whether a rotor pole is presently larger than, smaller than, or corresponds to 360°/R, commutation occurs either too early, too late, or correctly, and the result is that the current often reaches its maximum too early or too late. The motor functions, but efficiency is poor.

An additional, symmetrical magnetic track48was therefore provided on rotor40ofFIG. 16, and arranged relative to rotor position sensor67in such a way that the latter can sense the additional magnetic track48.

FIG. 24shows signal241of rotor position sensor67ofFIG. 2; because of the additional, symmetrical magnetic track48, this signal is likewise symmetrical. Motor controller70can effect commutation on the basis of signal241, and the current240B resulting therefrom is appreciably better than the current240A ofFIG. 23. The efficiency of motor10is thereby increased.

Alternatively, it is also possible to optimize the commutation effected by control apparatus70ofFIG. 2by the fact that it measures, for example at a constant speed, the angular extent of the individual poles, which is proportional to the time between pole changes. Control apparatus70can then determine at the present rotation speed, via a timer proceeding from the last pole change, when the next commutation needs to occur.

Overview of Starting Methods

Since a torque can be generated via a current flow through the entire winding arrangement30, or via a current flow through a first sub-group TG1(e.g. coils31,32inFIG. 1) and optionally also further sub-groups TG2(e.g. coils33to36inFIG. 1), etc. of winding arrangement30, it is also possible for the motor to start.

Starting Method 1

A simple variant for starting motor10consists in moving rotor40, by means of a first current flow through first sub-group TG1of winding arrangement30, into a predetermined first rotor position RS1relative to first sub-group TG1of winding arrangement30and, proceeding from that rotor position RS1, starting motor10by means of a second current flow through the entire winding arrangement30or through a second sub-group TG2. When a rotor position sensor67is used (seeFIG. 2), the direction of the second current flow, and optionally also of the first current flow, is defined preferably as a function of the signal of rotor position sensor67.

After a successful start, operation can switch over to the normal single-phase mode.

Starting Method 2

A further variant for starting motor10consists in, as a function of rotor position or as a function of the signal of rotor position sensor67,

firstly effecting a first current flow through the entire winding arrangement30and checking whether the motor has started. If not,

effecting a second current flow through first sub-group TG1of winding arrangement30and checking whether motor10has started,

effecting a third current flow through second sub-group TG2of winding arrangement30and checking whether motor10has started,

effecting a further current flow through the further sub-groups of winding arrangement30and checking whether motor10has started.

A successful start can be detected, for example, by the occurrence of changes in the signal of the rotor position sensor. After a successful start, operation can switch over to the normal single-phase mode.

Both the direction of the first current flow through the entire winding arrangement30and selection of the first sub-group TG1(in the case of multiple possible sub-groups) are preferably defined as a function of the signal of rotor position sensor67(seeFIG. 2).

FIG. 27shows a flow chart for carrying out starting method 2.

The routine begins with step S300, and in S302the variable CHANGE_HALL is set to zero in order to indicate that no change in the rotor position signal has taken place. The state variable STATE_NEW is set to the value STATE_1_2in order to indicate that current flow is to occur through the entire winding arrangement30via the main winding terminals11,12(see, for example,FIG. 1). A state variable STATE_OLD is set to the value STATE_4in order to indicate that the most recent current flow was through sub-group TG2; this need not actually have taken place (initialization of variables). Execution then branches to S304, and in this sub-program a commutation (COMMUT_HALL) is effected via winding terminals11,12, i.e. current flow occurs through the entire winding arrangement.

The motor remains in sub-program S304as long as rotor40is rotating and a regular change in the rotor position signals occurs.

After each commutation of the motor, the elapsed time T_LAST_COMMUT since that commutation is measured; and if that time exceeds a maximum elapsed time T_MAX, current flow occurs through either sub-group TG1or sub-group TG2. For this, the variable STATE_OLD is evaluated, and if it corresponds to the value STATE_4, execution branches to S326. In S326the variable STATE_NEW is set to the value STATE_3and the variable CHANGE_HALL to the value zero. Execution then branches to S328, and a current flow through sub-group TG1occurs in this subroutine, the state being referred to as STATE_3. For the commutation in S328as well, the elapsed time T_LAST_COMMUT since the last commutation is measured, and if a maximum elapsed time T_MAX is exceeded, execution branches to S332. In S332the variable STATE_OLD is set to the value STATE_3in order to indicate that the last state was the state STATE_3. The variable STATE_NEW is set to the value STATE_1_2and the variable CHANGE_HALL is set to zero, in order to indicate that no change in the rotor position signal has taken place. Execution then branches back to S304.

If a change in the rotor position signal (HALL_CHANGE) has, however, taken place in S328before the maximum time T_MAX elapses, execution then branches to S330, where the variable STATE_OLD is set to the value STATE_3, the variable STATE_NEW to the value STATE_1_2, and the variable CHANGE_HALL to the value 1, in order to indicate that a change in the rotor position signal has taken place. Execution then branches to S304.

If, conversely, the variable STATE_OLD has the value STATE_3in S304, then if the maximum elapsed time T_MAX since the last commutation COMMUT_HALL is exceeded, execution branches to S306. In S306the variable STATE_NEW is set to the value STATE_4, and the variable CHANGE_HALL is set to the value zero. Execution then branches to S308. In the S308routine the motor is in the STATE_4state, and a commutation of sub-group TG2occurs (COMMUT_TG2). The elapsed time T_LAST_COMMUT since the last commutation COMMUT_TG2is measured, and if a maximum elapsed time T_MAX is exceeded, execution branches to S312. In S312the variable STATE_OLD is set to the value STATE_4, the variable STATE_NEW to the value STATE_1_2, and the variable CHANGE_HALL to the value zero, and execution branches to S304.

If, on the other hand, a change in the rotor position signal (HALL_CHANGE) has taken place before the maximum time T_MAX has elapsed, execution then branches from S308to S310, where the variable STATE_OLD is set to the value STATE_4, the variable STATE_NEW to the value STATE_1_2, and the variable CHANGE_HALL to the value 1, and execution branches to S304.

At motor startup, or while it is running, a check is made after every commutation as to whether the next change in the rotor position signal occurs within the maximum elapsed time T_MAX; if not, either a changeover to the state STATE_3with commutation of sub-group TG1is carried out, or a changeover to the state STATE_4, in which current flow occurs to sub-group TG2; proceeding from the state STATE_1_2, the state STATE_3or the state STATE_4is always selected alternately. Current flow through sub-group TG1or TG2causes the rotor to move into a position from which starting can occur via the state STATE_1_2.

Many variations are possible; for example, alternatively to the state STATE_1_2, execution can branch to the state STATE_3and then to the state STATE_4, until the rotor is turning and execution branches back to the state STATE_1_2in S304.

Many variants and modifications are of course possible in the context of the present invention.

Instead of a full bridge circuit, for example, it is also possible to use a single bridge circuit that permits a current flow through coil31,32, etc. in only one direction; bifilar winding can also be used, in which each of the coils on a stator pole is associated with one current flow direction, so that for S stator poles, a total of 2*S coils are present. It is also possible for only some of the stator poles to be wound.

An auxiliary reluctance torque can additionally be provided, for example so that a starting position from which starting can occur via a current flow between first winding terminal11and second winding terminal12is reached more often; this auxiliary reluctance torque can be weaker than in the case of a motor that obligatorily relies for starting on a corresponding orientation of the rotor by way of the auxiliary reluctance torque.