Abstract:
A rotary electrical machine, comprising a stator ( 100 ) having at least one armature winding ( 140 ) mounted in slots which define stator poles, and a rotor ( 200 ) mounted for rotation inside the stator, the rotor having at its outer periphery magnetic poles comprising, firstly, North-South magnets ( 210 N- 210 S), and secondly, magnetic reluctance pieces ( 215-215 ′), wherein the North-South magnets of two consecutive n, n+1 poles are grouped side by side, and in that the magnetic reluctance pieces of two consecutive n+1, n+2 poles are also side by side.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general terms to rotary electrical machines, and in particular to a synchronous rotary machine having a permanent magnet rotor, such as an alternator or alternator-starter for a motor vehicle. 
     2. Description of Related Art 
     It is already known in the state of the art to provide rotary machines in which the rotor has a set of permanent magnets, which are for example arranged on the surface or inset a certain distance below the surface of the rotor, so as to define an appropriate pattern of South and North poles. 
     Because the excitation of such a machine is imposed permanently by the rotor magnets, it is necessary to provide, in the case of an alternator, arrangements for adjusting the electrical power delivered by the machine to output load: in this connection, power output is currently linked to loads in which consumption varies over time. 
     In the case of motor vehicle alternators, the load connected to the armature of the alternator can, in this context, vary greatly, and may even be zero or substantially zero while the inductive rotor of the alternator is in motion. 
     In order to adjust the electrical power delivered by the rotary machine, one known solution consists in interposing magnetic defluxing parts between the magnets of the rotor in order to channel part of the magnetic flux flowing between the rotor and the stator. This defluxing flux does not contribute to the generation of current by the windings of the stator armature. The intensity of this flux adjusts itself as a function of the load imposed on the armature output. 
     One known defluxing solution is accordingly illustrated in FIG. 1, in which a rotor  20  comprises magnets  22 S which define South poles, and magnets  22 N defining North poles, arranged alternately. This known solution consists in interposing between each pair of adjacent magnets a magnetic defluxing piece  25 , these pieces being adapted to cooperate with the poles of the stator in order to produce defluxing. 
     Also illustrated, in FIG. 2 in a developed form, is the diagrammatic behaviour of this rotor in cooperation with a stator  10  having teeth  16  delimited by slots  14  which contain armature windings  18 , with an induced flux F 1  created by the magnets and an inverse defluxing flux FD. It will be noted in this Figure that the induced flux and the defluxing flux are poorly individualised. It has been found that this partial superimposition on each others induced fluxes and the defluxing fluxes flowing in opposite directions, limits the defluxing capacity of the machine, and therefore the range of possible excitations of the machine. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to enable rotary machines to be made which deliver electrical energy that is optimised as a function of the load connected to the armature of the machine. 
     In order to achieve this object, the invention proposes a rotary electrical machine, comprising a stator having at least one armature winding located in slots defining stator poles, and a rotor mounted for rotation inside the stator, the rotor having at its outer periphery magnetic poles comprising, firstly, North-South magnets, and secondly, magnetic reluctance pieces, wherein the North-South magnets of two consecutive poles n, n+1 are grouped side by side, and in that the magnetic reluctance pieces of two consecutive poles n+1, n+2 are also side by side. 
     In order to achieve the said object, the invention also proposes a rotary electrical machine, comprising a stator having a single armature winding located in slots defining stator poles, and a rotor mounted for rotation inside the stator, the rotor having at its outer periphery magnetic poles comprising, firstly, North-South magnets, and secondly, magnetic reluctance pieces, wherein the North-South magnets of two consecutive poles n, n+1 are grouped side by side, and in that the magnetic reluctance pieces of two consecutive poles n+1, n+2 are also side by side. 
     Thanks to the invention, high quality defluxing is obtained in the machine, because the flux induced by the magnets on the one hand, and the defluxing flux on the other hand, are individualised better than in the known versions. It has also been found that this arrangement has the advantage that it leads to a reduction in variations of torque during operation of the machine. 
     Preferred but not limiting aspects of the rotary machine according to the invention are as follows: 
     the stator includes an excitation winding which is fixed around the stator, the stator having two magnetic parts separated by a non-magnetic region in line with the excitation winding on the inner side of the latter, 
     a magnetic member is arranged, surrounding the said magnetic parts of the stator and in contact with them, in such a way as to enable the said magnetic path to be closed in the stator, the said magnetic member having a slot for receiving the excitation winding, 
     the axial width of the non-magnetic region is substantially greater than the width of the airgap separating the rotor from the stator, 
     the magnets of the rotor are disposed asymmetrically with respect to the centre plane transverse to the axis (X) of rotation of the rotor which is situated in line with the excitation winding, 
     the magnets of the rotor occupy a space the width of which, in a direction tangential to the rotor, varies with displacement in a direction parallel to the axis (X) of rotation of the rotor, 
     the said at least one global excitation winding is connected to a variable electrical power supply such that the magnetic flux generated by the said global excitation winding is able to reinforce the fluxes induced between the rotor and the stator, 
     means are provided for reversing the sign of the power supply of the global excitation winding, in such a way that the magnetic flux generated by the global excitation winding reduces the fluxes induced in the stator, 
     the rotor has, in its tangential direction, a distribution of polar parts with a permanent magnet or magnets, the or each magnet defining two poles the polarity of which is imposed by a magnet or magnets, and polar reluctance parts each defining two poles having free polarities, 
     the magnets are magnets with essentially radial flux, 
     the magnets are ferrite magnets, 
     the magnets are rare earth magnets, 
     the magnets are ferrite and rare earth magnets, 
     the rotary electrical machine consists of a motor vehicle alternator-starter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Further aspects, objects and advantages of the present invention will appear more clearly on a reading of the following detailed description of various embodiments of the latter given by way of non-limiting example and with reference to the attached drawings, in which, besides FIGS. 1 and 2 which have already been described: 
     FIG. 3 is a diagrammatic half view in axial cross section of a first embodiment of a machine in accordance with the invention, showing the general principle of operation of the invention which makes use of a so-called “global” excitation winding, 
     FIG. 4 is a diagrammatic view of part of a rotary machine in accordance with the invention, 
     FIG. 5 is a developed view, in plan, of a first embodiment of a rotor adapted for use in a machine according to the invention, 
     FIG. 6 is a perspective view of the rotor corresponding to the developed view in FIG. 5, 
     FIG. 7 is a developed view, in plan, of a second embodiment of a rotor adapted for use in a machine according to the invention, 
     FIG. 8 is a perspective view of the rotor corresponding to the developed view in FIG. 7, 
     FIG. 9 is a perspective view of a third embodiment of a rotor designed for use in a machine according to the invention, 
     FIGS. 10 a  and  10   b  are two diagrammatic views showing part of a machine according to the invention making use of the rotor of FIG. 9, 
     FIG. 11 is a detail view of a rotor arm in a machine according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The rotor structure may be of a known kind for a rotor such as that shown in FIGS. 1 and 2, making use of North and South poles arranged alternately and defined by permanent magnets which are separated by magnetic defluxing pieces. As will be seen later on in this text, the structure of the rotor may also be adapted in a specific way so as further to increase the defluxing capacities of the machine. 
     The stator  100  consists mainly of four elements: 
     a stator carcass consisting of a stack  100  of generally annular stator laminations and surrounding the rotor. As will be seen later herein, the laminations may be of conventional geometry and may include on their inner periphery a set of slots similar to the slots  14  in FIG. 2, which are delimited by stator poles. The stator poles do not constitute an uninterrupted stack in the axial direction parallel to the axis X. Instead, the laminations are divided into two packs  110   a  and  110   b , which are adjacent to the two respective axial ends of the machine, thereby defining a non-magnetic central space  115  which is open into the airgap. The space  115  can be left free (that is to say full of air), or it may consist of any known non-magnetic material, 
     the stator is surrounded in the radial direction by a second annular magnetic carcass  120  which is a flux return member and with which the stator laminations are in contact. The carcass  120  includes on its inner periphery, and in a middle region considered axially, an annular cavity  125  which is in communication with the space  115 , 
     a so-called “global” excitation winding  130 , which is supplied from a voltage source of variable sign and amplitude, and which is located within the cavity  125 , 
     and polyphase armature windings  140  which are wound on the stator poles. The windings  140  (the chignons of which are shown diagrammatically beyond the laminations which they surround) are conventional. 
     It will be understood that, when the excitation winding  130  is energised, it sets Lip in the region of the rotor, via the carcasses  120  and  110 , a magnetic flux FD′ which returns into the stator from one side with respect to the middle axial region, and leaves it on the other side. This flux is superimposed on the other fluxes that result from the interaction between the rotor and the stator. 
     In this connection it is important to observe that the width in the axial direction of the space  115 , denoted L, is substantially greater than the thickness e of the airgap. This arrangement guarantees that the flux FD′ generated by the excitation winding does not follow a path closed within the stator by passing directly between the packs of laminations  110   a  and  110   b , the flux being forced to pass through the rotor. 
     Thus, the excitation winding  130  generates a flux FD′ of substantially toroidal geometry between the stator and the rotor, and this flux is then able, especially with those examples of rotors which are described later herein, to modify the excitation of the machine in a way that is adjustable in accordance with the sign and amplitude of the power supply to the excitation winding. 
     In the case of a motor vehicle alternator, it is possible to design the rotor and stator in such a way as to produce, in the absence of the flux FD′ generated by the global excitation winding  130 , electrical energy which is less than that produced at full load. 
     The electrical energy delivered by the alternator is then adapted by adjusting the supply to the global excitation winding  130 : this winding can thus be supplied with a voltage of a first sign in such a way as to reinforce the intensity of the aggregate flux in the armature when there is an increase in load. 
     Conversely, the winding  130  may be supplied with a voltage of opposite sign, so as to reduce the intensity of the aggregate flux in the armature when the load is decreased; to this end, the winding  130  and its power supply are designed as a function of the desired range of outputs. 
     The control means for this global excitation may make use of either a single switching transistor in the case of power supply of constant sign designed simply to reinforce the fluxes induced between the rotor and the stator, or an H bridge with four transistors in the case where it is desired to be able to reverse the sign of the supply to the global excitation winding  130 . 
     With reference now to FIG. 4, this shows diagrammatically a rotary machine in accordance with the invention with its stator  100  enclosing a global excitation winding  130 , the armature windings  140  not being shown in this Figure. The rotor  210  of this machine has at its periphery two pairs of magnets  210 N,  210 S, arranged alternately with two pairs of magnetic pieces  215  and  215 ′. 
     It is of course possible to provide a rotor with any number whatever of pairs of magnets arranged alternately with magnetic pieces. 
     With a rotor of this kind of structure, and in particular because of the side by side grouping of the permanent magnets corresponding to two successive poles n and n+1, and the grouping of the magnetic pieces corresponding to two successive poles n+1 and n+2, it is possible to obtain high quality defluxing of the machine because the induced fluxes, in the magnets on the one hand and defluxing pieces on the other hand, are individualised better than in the known embodiment in FIGS. 1 and 2. It has also been found that this arrangement has the advantage that it reduces variations in torque during operation of the machine. 
     Thus, with a high defluxing capacity it is possible to use the winding  130  solely in order to reinforce the flux, so that the winding can be supplied by a uni-directional current, which avoids the need to make use of an expensive H bridge. 
     With reference now to FIGS. 5 and 6, these show a first actual embodiment of a rotor which enables the global excitation winding  130  to be used for the purpose of modifying the excitation. 
     The rotor  220  accordingly has triangular magnets with radial flux. More precisely, a North magnet  220 N has the general form of a right angled triangle, a major side of which is parallel to the axis of rotation, with a minor side of the triangle flush with one axial end of the rotor, so as to define a pole. This North magnet  220 N is adjacent, on its major side, to the major side of a South magnet  220 S which is oriented in head-to-toe relationship and which defines, through its minor side, a pole at the opposite end. Magnetic reluctance pieces  225 ,  225 ′ extend along the magnets from their hypotenuses. 
     Preferably, the magnets made in the general form of right angled triangles, in particular, reduce the magnetic noise of the rotary electrical machine. 
     Here again any number whatsoever of pairs of magnets  220 N,  220 S can be provided, arranged alternately with a corresponding number of pairs of magnetic pieces. 
     As to FIGS. 7 and 8, these show the application of the present invention to the case of a rotor  230  with arms, in a second preferred embodiment of the rotor. 
     Such a rotor comprises, in the manner known per se, a first member  231  having a first set of generally triangular arms  2310  and a second member  232  having a second set of generally triangular arms  2320 , these arms being interleaved with each other. 
     In this case, each arm  2310  in the first set has, in a given tangential direction (from left to right in FIG.  7 ), a magnetic reluctance piece  235  followed by a magnet  230 N defining a North pole, while each arm  2320  in the second set has, in the same direction, a magnet  230 S defining a South pole, followed by a magnetic reluctance piece  235 ′. Accordingly, we have here a structure of magnets and magnetic reluctance pieces similar to that in FIG.  4 . 
     FIG. 9 shows an embodiment of the present invention with a rotor  240 , having arms, in a third preferred embodiment of the rotor. 
     The rotor  240  includes, in the manner known per se, a first member  241  which is provided with a certain number of generally triangular arms  2410 , and a second portion  242  which is provided with a certain number of generally triangular arms  2420 , the arms  2410 ,  2420  being interleaved with each other. 
     In this case, there are provided, in the circumferential direction of the rotor, two reluctance arms and two magnet arms having surface or inset magnets  240 S and  240 N, so as to impose respective North and South polarities on it, and so on. 
     FIGS. 10 a  and  10   b  are, respectively, a half view in axial cross section of a machine in accordance with the invention which includes the rotor  240  having arms, which is described with reference to FIG. 9, and a developed view of part of that rotor, with a magnetic core  2450  coupling the pole pieces  241  and  242  together. These pole pieces can equally be of the half-core type. 
     It will be understood that the flux FD′ created by the winding  130  reinforces (or reduces, according to its size) the total flux in the armature. In FIG. 10 b , the flux FD′ enters and leaves the rotor mainly through the poles of the reluctance arms, thereby avoiding the magnet poles due to the fact that the mean airgap equivalent to a path that would pass through the magnets is larger (it includes twice the thickness of a magnet). 
     Thus, in order to reinforce the total flux, the South magnet pole  2410  and North magnet pole  2420  will be followed in the configuration of FIG. 10 b  by a South reluctance pole  2430  and a North reluctance pole  2440 , which corresponds to a regular South-North-South-North distribution of poles in a given direction of the excitation current. 
     In order to reduce the total flux in the armature, the sign of the current with which the winding  130  is supplied will be reversed, so as to give, in a configuration not shown in the drawings, a North reluctance pole  2430  and a South reluctance pole  2440 , which corresponds to a South-North-North-South pole distribution. If the inverse current is such that the magnet poles have the same flux in absolute value as the flux of the reluctance poles, the total flux is zero, as is usable power. 
     The invention may also be employed in various rotary machines in which the rotor has to include magnetised or magnetic paths which do not extend strictly parallel to the axis of rotation of the rotor of the machine. 
     FIG. 11 shows one embodiment of the arms of the rotor  240  in the case where the latter carries surface magnets, the said surface magnets being then inserted within the arms. 
     It is thus possible to form the general profile of the side walls  241  of the arms  2400  by moulding, with the definitive form of the arms being made by machining the inside of the said side faces  2401  in such a way as to form returns  2402  which hold the magnets in place. As will have been understood, a stator of conventional type (not shown) which does not include global excitation means ( 130 ) could also be used in combination with a rotor, such as the rotors described in FIGS. 3 to  10   b , having no global excitation means. 
     The present invention is of course in no way limited to the embodiments described and shown, but the person in this technical field will be able to apply to it any variations or modifications in accordance with its spirit. 
     It is thus possible according to the invention to provide a plurality of excitation windings such as the winding  130 , distributed in a plurality of slots in the carcass  120 , and the return flux paths between the stator and the rotor (which correspond in FIG. 3 to the two peripheral axial zones in which the respective packs of laminations  110   a  and  110   b  are close to the rotor) must then flank all of the excitation windings. 
     In addition, depending on the defluxing capacity desired, the proportion between the sectors with magnet poles and the sectors with reluctance poles provided on the rotor can be adjusted, and it is for example possible to provide a sector with two magnet poles, namely a North and South pole, an identical second sector with South and North magnet poles, a sector with two reluctance poles, and then once again two sectors each having two magnet poles, etc. In all cases, the preferred embodiments of rotor described above are clearly not limiting. 
     In general terms, depending on the defluxing capacity desired, the relative sizes of the magnets and magnetic reluctance pieces may be chosen at will.