FR2467504A1 - DIRECT CURRENT MOTOR HAVING SWITCH DEVICE FOR FACILITATING STARTING - Google Patents

Abstract

The present invention relates to a DC motor comprising a stator 1 which produces a magnetic flux having a distribution of its density consisting of a fundamental component and an auxiliary component and a rotor 3 comprising two magnetic rings, the first of the rings having poles arranged in an even angular pitch around a shaft 4 and the second having a number of poles which is an even multiple of the poles of the first magnet, the point of the distribution of the flux density of the second magnet being at a different position from that of the tips of the auxiliary component when a pole of the magnets is in a position corresponding to the tips of the flux density distribution of the fundamental component of the stator, as a result of which the motor can start even from dead points of the rotor thanks to a torque produced by the magnetic forces exerted between the second magnet of the rotor and the auxiliary component of the stator. (CF DRAWING IN BOPI)

Description

The present invention relates to a motor with

  and especially an easy-start DC motor with switching devices

instead of an ordinary collector.

  Most conventional DC motors with switching devices are provided with a plurality of stator windings and a rotor having the same number of permanent magnet poles which are arranged at the same angular pitch as the poles of permanent magnets. stator windings. The windings of the stator and the poles of the permanent magnets of the rotor are arranged with angular steps

  equal around the axis of the engine. In a current driver

  conventional tinu of this type, if the rotor is in a place where the poles of its permanent magnets are opposite the poles of the stator and that the polarity of the poles facing each other is the same, the magnet of the rotor will be likely

  pushed back in one or the other of the two directions of rotation. This-

  during, if the poles opposite are exactly opposite,

  the equilibrium of magnetic powers of repulsion renders im-

  possible starting of the rotor. If the polarities of the opposing poles are opposite, each magnet of the rotor is attracted by the stator. Therefore, there are two kinds of dead spots in a conventional DC motor. The first

  is an unstable dead center and the second a stable dead point.

  2. If the rotor is in these two dead spots, the engine

  can not start even if it is powered by electricity.

  In order to solve the problem of dead spots, a special rotor motor has been proposed in U.S. Patent No. 3,299,335 to Wessels et al. The rotor of this engine of the prior art consists of magnetic parts and non-magnetic parts which are placed on the circumference of the rotor, the latter being

  placed between successive pairs of metal parts poles

  netic. With such a structure, this engine can start

  whatever the angular position of the rotor.

  However, in this conventional DC motor

  that, the rotor consists of several parts, and two

  different kinds of materials, that is, the parts

  and the non-magnetic parts are related to each other. Therefore, the motor has the disadvantage of being difficult to manufacture since arc-shaped components of different nature must be joined to form a ring having a precise balance in rotation, and to have a rotor that can be rotated. to break as a result of the effects of the centrifugal force. The present invention provides a DC motor which has no dead point, and can start whatever the position of the rotor. The rotor of the DC motor of the present invention may be made of a uniform material about its angular position, after which the rotor can be manufactured very easily and

  is sustainable. In the case where a magnetic detector is used

  to detect the rotation of the rotor, one of the magnets of the

  rotor can be used per se to apply a magnetic flux

alternative to this detector.

  The present invention will be well understood during the

  following description made in conjunction with the drawings

  joints in which Fig. 1 is a schematic plan view of a basic structure of a DC motor according to the present invention; 3. Figures 2 (a) to 2 (f) are curves showing the distribution of the flux density of a DC motor as a function of the angular position about the axis

rotor;

  Fig. 3 is a plan view of a first embodiment of the present invention; Fig. 4 is a perspective view of the magnetic rings of the rotor of a second embodiment of the present invention; Fig. 5 is a plan view of the stator of the second embodiment of the present invention; FIG. 6 is a sectional elevational view of the

  second embodiment of the present invention.

tion; and

  Figures 7 (a), 7 (b) and 7 (c) are

  showing the distributions of the flow density of the engine

  of the second embodiment of the present invention according to

  angular position about the axis of the rotor.

  In Figure 1 of the drawings, a stator 1 of shape

  cylindrical comprises two main poles 2a and 2b diagonally

  opposed to each other, that is to say placed at 1800 from each other with respect to the axis of the rotor, and two field coils 2a 'and

  2b 'are wound around the main poles 2a and 2b,

  tively. A rotor 3 is fixed directly or indirectly

  to a shaft 4 in the stator 1. The rotor 3 comprises two

  permanent elements 5 and 6 which are connected coaxially or fixed

  4. The permanent magnet 5 has two main poles.

  (north and south poles) diagonally opposite, that is,

  located at 1800 from each other in relation to the axis, as

  this is shown in FIG. 1. The permanent magnet 6

  takes four auxiliary poles placed in a cross, in a way

  such that the opposite poles are located at 90 one of the

  relative to the axis, and each pole of the permanent magnet is placed between the poles of the permanent magnet 6, with respect to the angular position about the axis of the rotor 3.

  The surface of the permanent magnet 5 shown in FIG.

  lower than that of the permanent magnet 6, and consequently 4.

  the magnetic force exerted by the first magnet is greater than

  than the second. The field coils 2a ', 2b' are

  alternatively fed and cut according to rotation

  rotor 3 by means of a rotor position detector, comprising, for example, a Hall effect device. The

  The switching currents of field coils 2a 'and 2b' are

  chrones with a polarity change of the magnetic flux of the

  main poles 2a and 2b due to the magnet 5. In order to

  kill this timing of switching, the device at iO Hall effect is placed in a place directly across

of the magnet 5.

  When the field coil 2a 'is excited, a magnetic flux is induced in the stator 1, and the distribution of the flux density as a function of the angular position of

  the shaft 4 of the stator 1 is represented in FIG. 2a. The posi-

  angle given on the abscissa of Figures 2a to 2f correspond to

  the angular position shown in FIG.

  2a, the distribution of the flux density of the stator l has a shape such that it can be divided into two components, one of them being a fundamental component represented in FIG. 2b and the other an auxiliary component represented

  in Figure 2c; At the 0 o position is the center of the

  the principal 2a, the fundamental component and the auxiliary component have their peak value in the distribution of the flux density and the auxiliary component in the form of a harmonic of rank 2 of the fundamental component. the

  instants ix \ diques in Figures 1 and 2, the main pole 2a (an-

  e = 0O) is excited to constitute a north pole and the other main pole 2b a south pole. On the other hand, in the rotor 3 of FIG. 1, the permanent magnets 5 and 6 have a flux density distribution which is represented in FIG.

  Figures 2 (d) and 2 (e) respectively. That is to say that the

  partition of the flux of the permanent magnet 5 is substantially the same as that of the fundamental component of the stator 1, and that of the permanent magnet 6 is substantially the same as

  that of the auxiliary component, but the phase of the

  of the flux density of the permanent magnet 6 is de-

5.

  450 compared to that of the auxilia-

  as shown in Figures 2 (c) and 2 (e).

  Under these circumstances, the permanent magnet 5 of the rotor 3 is in the unstable neutral position, since the balance of the magnetic repulsion force acting between the permanent magnet 5 and the stator 1 is maintained as shown in FIGS. 2 (b), 2 (c) and 2 (d). However, a force

  magnet between the permanent magnet 6 and the

  tor 1, ie the magnetic force exerted between

  the permanent magnet 6 and the auxiliary component of the

  the flow density, causes the rotation of the rotor 3 in the clockwise direction shown by the arrow A of FIG. 1. During the rotation of the rotor 3, a torque having the direction of clockwise is produced between the permanent magnet 5 and the fundamental component of the distribution of the flux density, and the rotor 3 continues to rotate. When the rotor rotates to 1800 and reaches the point

  stable death, where the permanent magnet 5 is attracted by the

  tor 1 to be maintained, the excitation of the coil of

  field 2a 'is stopped and the field coil 2b' is then ex-

  cited. The distribution of the flux density of the exciter stator 1

  by the field coil 2b 'then takes the form of

  Figure 2 (f). At that moment, by switching the former

  citation, an unstable dead break occurs again between the main pale 2b excited then to give a north pole and the pole N of the permanent magnet 5. However, the rotor 3 continues to turn in the same direction (direction of the needles

  of a watch) as a result of the magnetic force exerted

  be the permanent magnet 6 and the stator 1 and the inertia force

  tie. Thus, after staggered unsteady passage, a clockwise torque is produced between the permanent magnet 5 and the fundamental component of the flux density distribution in the same way as in the previous case. . Therefore, the engine continues to

turn.

EXAMPLE 1

  FIG. 3 shows a two-pole internal rotor type direct-current motor 6. according to the present invention. In Figure 3, the stator 11 comprises two main poles 21a and 21b diametrically opposed and two additional poles 21c and 21d which are each arranged between the main poles 21a and 21b. The additional poles 21c and 21d serve to produce an auxiliary component of

  the distribution of the flux density of the stator 11.

  field bins 21a 'and 21b' are wrapped around the necks of the main poles 21a and 21b. One end of the two field coils 21a 'and 21b' is connected to transistors

  Trl and Tr2, respectively, and the other end

  mity of the coils to a source of DC voltage. The rotor

  31 of this embodiment of the present invention is -

  identical to that of FIG. 2. A detection means, for example, a Hall effect HD device is placed in front of the additional pole 21c in order to detect the rotation of the rotor 31. The rotation signals produced by the HD device synchronized with the variation of the magnetic flux of the permanent magnet 5 are applied to a switching circuit 71 which comprises, for example, a toggle circuit and controls the switching transistors Tr1 and Tr2, alternately, so that they become conductive. Thanks to such a structure, the current flowing in the field coils is switched by transistors Tr1 and Tr2 in synchronism with

the rotation of the motor 31.

EXAMPLE 2

  Figures 4, 5 and 6 represent a way of

  of a DC motor of the external rotor type

  according to the present invention. In this embodiment, the outer-type rotor 32 has a cylindrical shape having a hole, that is, a short-length tube or ring as shown in FIG. 4. The rotor 32 of this embodiment consists of a first ring-shaped permanent magnet 52 having four blades and a second ring-shaped permanent magnet 62 having eight auxiliary poles. The north and south vanes of the permanent magnets 52 and 62 are alternately disposed on the periphery, and one of the two faces of each pole of the permanent magnet 62

  is applied against the poles of the permanent magnet 52

  this is shown in Figure 4. The permanent magnets 52 and 62 have the same inner and outer diameters and the same thickness. However, the height "a" of the magnet

  manent 52 is greater than the height "b" of the magnet

  manent 62, so that the magnetic force of the magnet 52

  is greater than that of the magnet 62. The two magnets

  Ring-shaped hinges 52 and 62 are coaxially connected to each other about the axis of the rotor 32. The stator 12 of this embodiment has four main poles 22a, 22b, 22c and 22d, and four additional poles 22e, 22f,

  22g and 22h, which are each placed between the previous poles

  teeth. The additional poles 22e to 22h serve to produce the auxiliary component of the distribution of the flux density. Field coils 22a 'and 22e', which are wound

  at the respective main poles 22a and 22c, are connected

  in series between a DC voltage source E and a switching transistor Tr3. Field coils 22b 'and 22d' which are wound on the respective main poles

  22b and 22d are connected in series between a source of voltage

  continuous voltage E and a switching transistor Tr4. A

  HD Hall effect device for detecting rotation

  The rotor 32 is held close to the additional pole 22f and applies the detected signals to a switching circuit.

  72. Circuit 72 includes, for example, a flip-flop and

  In this case, the alternating state of the switching transistors Tr3 and Tr4 depends on the rotation of the rotor 32. As shown in FIG. 6, the stator 12 is fixed on a base 13 of a motor casing. The rotor 32

  is arranged around the stator 12 and fixed to a flas-

  33 of a lid 34. The lid 34 is held in place

  on the base 13 by a shaft 42 mounted in a roller

14.

  In this embodiment, the distribution of the flux density of the stator 12 at the moment when the field coils 22a 'and 22c' are excited is represented in FIG. 8.

  7 (a). As this figure shows, the shape of the distribution

  flow density is similar to that of the. figure

  2 (a), but has a frequency double that of the first

  ple. As in the first example, the distribution of the flux density of the stator 12 can be divided into two components.

  which is a fundamental component and a component

  auxiliary health. The distribution of the density of the flow of

  permanent magnets 52 and 62 of the rotor 32 is likewise

  than that of Figures 2 (d) and 2 (e), but with frequent

  this double. Therefore, the motor of this embodiment can start regardless of the angular position of the rotor

  as previously described.

  In the embodiments described above, the auxiliary component of the distribution of the stator flux density is a second order harmonic wave of the fundamental component. However, the auxiliary component can be any harmonic wave of even rank of

the fundamental component.

  The DC motor of the present invention

  It does not have dead spots as is the case with conventional engines, and therefore can start for any angular position of its rotor. In addition, the rotor

  of the present invention comprises only two magnetic rings.

  ticks that have very good resistance to centrifugal force, and the motor is easy to manufacture and is very

  Moreover, in the case where a provision is made

  Hall effect as a means of detecting rotation,

  it is not necessary to use other magnets for

  to create an alternative magnetic flux for the device

  Hall effect to allow synchronization with the rotation

rotor.

  The present invention is not limited to the examples

  which has just been described, it is necessary to

  which may be subject to variations and modifications

to the man of the art.

9.

Claims (4)

  1 - DC motor comprising a rotor with permanent magnets and a stator comprising at least two   excitation coils o a direct current applied to the coils   The excitation nodes are switched alternately according to the angular position of the rotor, characterized in that: - the stator has a predetermined number of main poles to be excited by the excitation coils   and produces a magnetic flux having a distribution, as a function of   the angular position of the stator axis, which   takes a fundamental component of a distribution of   wave-shaped flux density and an auxiliary component of a distribution of the flux density of an even-numbered harmonic wave of the shaped flux density distribution   the harmonic wave having a peak for the same posi-   angular extent that a peak of the wave of the fundamental component   damentale, the rotor comprises a first magnet and a second magnet, the first magnet having the same number of poles as the main poles, the first magnet having a first flux distribution with respect to the angular positions of the magnet;   the axis of the rotor, this first flow distribution having   the same form as that of the fundamental component of   the, and the second magnet having the even number of poles of   auxiliary rotor and having a second distribution of densi-   the flow distribution relative to the angular position of the rotor axis, this second flux distribution being substantially of the same shape as the distribution of the flow density of the auxiliary component, but a wavelength of the second   flux density distribution being shifted by a predetermined angle   determined with respect to a wave point of the auxiliary component, the first and second magnets being arranged coaxially on the axis of the rotor; 2 - DC motor according to the claim   1, characterized in that the auxiliary component of the   of the stator flux density is a harmo-   rank 2 of the fundamental component.   10. 3 - DC motor according to the claim   1, characterized in that the first magnet has a magnetic force   higher than the second magnet.   4 - DC motor according to the claim   1, characterized in that the first and second magnets of the rotor are permanent magnets.   - DC motor according to claim   1, characterized in that the stator comprises additional poles   between the main poles, respectively.   6 - DC motor according to claim 1, characterized in that the first and second magnets are related to each other.   7 - DC motor according to the claim   1, characterized in that a switching circuit is connected   in series with the excitation coils, and in that this switching circuit comprises means for detecting the variation of the magnetic flux of the first magnet of the rotor, so as to cause switching.