Abstract:
The invention relates to an electrical machine, especially an alternator ( 10 ) comprising a stator winding ( 11 ) with a total of seven phase conductors (P 1  to P 7 ) which are interconnected in series at the same electrical angle (a). The aim of the invention is to dampen magnet noise and to increase machine performance. For this purpose, at least every other electrically subsequent phase conductor (P) is skipped when the phase conductors (P 1  to P 7 ) are connected in series.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The invention described and claimed hereinbelow is also described in German Patent Application DE 10 2005 061 892.8 filed on Dec. 23, 2006. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an electrical machine, in particular to an alternator with a multiple-phase stator winding. 
     With alternators for motor vehicles, electrical machines are primarily used that include a claw-pole rotor excited by direct current, in order to adequately supply the DC electrical system of the particular motor vehicle even while the engine is idling. In addition to numerous other requirements on the alternator, it is also necessary to dampen the magnetic noise of the alternator, which is noticeable—and disturbing—in the lower rotational speed range of the machine in particular. To suppress the magnetic noises, it is known to distribute the individual phase windings on the three-phase stator winding of the alternator in such a manner that they are placed partially in the slots of the adjacent phase winding. This measure results in reduced alternator output and increased losses, however. Due to the ripple of the direct current that is output, it is also possible for oscillatory noises to occur in the wiring harnesses of the motor vehicle at certain engine speeds. 
     It is also known to equip the alternator with a six-phase system, in order to double the frequency of the rectification and, therefore, to reduce the ripple of the direct current, which is supplied via a rectifier assembly to a storage battery of the motor vehicle electrical system. It is known from EP 0454 039 B1 ( FIG. 6 ) to design the stator winding of an alternator using two winding systems, each of which includes three phase windings that are interconnected to form a star connection. The phase windings are offset electrically by 120° in the star connection. The two winding systems are electrically offset from each other by approximately 30°. The magnetic noises of the machine that are produced are not adequately damped, however, particularly in the lower rotational speed range. A further disadvantage is the fact that machines of this type still have a large voltage and torque ripple, which applies in particular for high-output machines when operated either in the alternator mode or the engine mode. Finally, it is known from DE 102 09 054 A1 to use a seven-phase stator winding in order to dampen the magnetic noises and to reduce the current ripple of a motor vehicle alternator, and to connect its seven phase conductors—which lie side-by-side in the slots of a stator core—in a star connection, or to connect them in series to form a heptagon. Even though these designs have a lower current ripple and less magnetic noise than do seven-phase systems, they are still inadequately damped in the lower rotational speed range. In addition, the upward slope of the performance characteristic of the machine is insufficient, since, in motor vehicles, the power requirement in the vehicle electrical system is often high in the idling range of the internal combustion engine. 
     SUMMARY OF THE INVENTION 
     The object of the present invention, therefore, is to increase the damping of the magnetic noise and improve the electrical output in the lower rotational speed range of the electrical machine. 
     The inventive electrical machine has the advantage that, with the new type of connection of a seven-phase stator winding compared with the known designs, improved electromagnetic utilization is attained, which results in reduced voltage and torque ripple, a higher performance characteristic, and a further suppression of magnetic noises, particularly in the lower rotational speed range of the machine. A further advantage is that, with high-output alternators in particular, the reduced voltage and torque ripple also results in lower mechanical loads on the machine. 
     To simplify manufacture to the greatest extent possible, and to equalize the load on the machine, it is advantageous that all seven phase conductors are of equal size, they are composed of at least one coil, and they are interconnected at an electrical angle α that is between 180°/7≈25.7° and 180°*4/7≈102.9°. With four-pole or multiple-pole machines, it is also advantageous for the manufacture of the stator winding when the individual phase conductors are composed of several coils, which are preferably connected in series. With a stator core with an equidistant distribution of teeth around the circumference of the working air gap of the machine, optimal damping of the magnetic noises and the voltage and torque ripple is attained when the phase conductors are interconnected at an electrical angle α of 180°/7*3°≈77.3°. With an uneven distribution of teeth, the optimum of the electrical angle α—which must be determined on an individual basis—is between 60° and 100°. Particularly good damping is attained when, if the seven phase conductors are connected in series, one electrically subsequent phase conductor is jumped over in every case, with the phase conductors preferably being connected in series in the phase sequence P 1 -P 3 -P 5 -P 7 -P 2 -P 4 -P 6 . It is also possible to jump over two electrically subsequent phase conductors in each case. 
     When the present invention is used in alternators for motor vehicles, a particularly advantageous design of the stator winding results when the connections between the phase conductors are guided outwardly to a converter, in particular to a rectifier assembly with seven rectifier bridges. The phase conductors are advantageously interconnected at one of the two winding overhangs of the machine such that, of the connections between the phase conductors, only one connection in each case is guided to one of the seven rectifier bridges. 
     With electrical machines, the stator windings of which may be manufactured using a winding wire, it is advantageous when the coils of each phase winding are wound with the winding wire. It may also be advantageous when the phase windings are also wound with a winding wire, in order to create the series connection in a cost-favorable manner. 
     With regard for the use of the electrical machine as an alternator in a 14V vehicle electrical system in motor vehicles, particularly good noise damping is attained when the number of phase conductors or coils in the stator slots is greater than five and smaller than 10, and is preferably eight. 
     With regard for noise damping, it has also proven advantageous when the phase conductors are placed in the slots of the stator core with a slot fill factor that is greater than 50%. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details of the present invention are explained in greater detail below, as an example, with reference to the attached drawing. 
         FIG. 1  shows a longitudinal sectional view through an alternator for motor vehicles with a claw-pole rotor, 
         FIG. 2  shows the wiring diagram of an alternator with an inventive stator winding and rectifier assembly, 
         FIG. 2A  illustrates the series conductive nature of the path of the seven phase conductors of the multi-phase stator winding; 
         FIG. 3  shows the rotational speed vs. noise characteristics of various alternators, and 
         FIG. 4  shows the rotational speed vs. output characteristics of generators, by comparison, 
         FIG. 5  shows a winding scheme of an inventive stator wave winding, 
         FIG. 6  shows a further winding scheme with a stator loop winding, and 
         FIG. 7  shows a section of a stator core of the electrical machine shown in  FIG. 2 , with an inventive stator winding. 
         FIG. 8  shows a further variant of the connection of the seven-phase stator winding. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a sectional view through an electrical machine, which is designed as an alternator  10  for motor vehicles. It includes, e.g., a two-piece housing  33 , which is composed of a first end shield  33 . 1  and a second end shield  33 . 2 . End shield  33 . 1  and end shield  33 . 2  enclose a stator  36  that includes an annular stator core  18 , in whose inwardly open and axially extending slots  35  a stator winding  11   a  is placed. Annular stator  36  surrounds—via its radially inwardly oriented surface—a rotor  12 , which is excited electromagnetically and is designed as a claw-pole rotor. Rotor  12  is also composed of two claw-pole plates  42  and  43 , on the outer circumference of which axially extending claw-pole fingers  44  and  45  are located. Claw-pole plates  42  and  43  are located in rotor  12  such that their axially extending claw-pole fingers  44 ,  45  alternate with each other as north and south poles around the circumference of rotor  12 . This results in magnetically required claw-pole intermediate spaces between oppositely-magnetized claw-pole fingers  44  and  45 , which extend at a slight diagonal relative to the machine axis, given that claw-pole fingers  44  and  46  taper toward their free ends. For simplicity, their extension is referred to as axial in the description of the present invention, below. Rotor  12  is rotatably supported in particular end shields  33 . 1  and  33 . 2  via n shaft  47  and a roller bearing  48  located on each side of the rotor. Rotor  12  has two axial end faces, on each of which a fan  50  is mounted. Fan  50  is composed essentially of a plate-shaped or disk-shaped section, out of which fan blades extend in a known manner. Fans  50  serve to make air exchange possible—via openings  60  in end shields  33 . 1  and  33 . 2 —between the outside and the interior of electrical machine  10 . To this end, openings  60  are provided on the axial ends of end shields  33 . 1  and  33 . 2 , via which cooling air is drawn into the interior of electrical machine  10  by fan  50 . This cooling air is accelerated radially outwardly via the rotation of fans  50 , so that it may pass through winding overhangs  65 —which are permeable to cooling air—on the drive side, and through winding overhangs  66  on the electronics side (the side with the slip ring, brushes, or rectifier). The winding overhangs are cooled via this effect. After the cooling air passes through the winding overhangs, or after it has flowed around these winding overhangs, it follows a path radially outwardly through not-shown openings between segments, which are indicated. A protection cap  67 , which protects various components from environmental influences, is shown at the right in  FIG. 1 . Protective cap  67  covers, e.g., a slip-ring assembly  69 , which supplies an excitation winding  13  with excitation current. A heat sink  73 , which acts as a positive heat sink in this case, is located around slip-ring assembly  69 . End shield  33 . 2  serves as the negative heat sink. A connecting plate  76  is located between end shield  33 . 2  and heat sink  73 , which connects negative diodes  78  installed in end shield  33 . 2  and positive diodes—which are not shown in this illustration—of a rectifier  15  in heat sink  73  with each other, in the form of a bridge circuit. 
       FIG. 2  shows a schematic depiction of an inventive electrical machine in the form of an alternator  10  for supplying power to the electrical system of motor vehicles. Alternators of this type, which include a multi-phase stator winding  11 , are typically equipped with an electrically excited claw-pole rotor  12 , the excitation winding  13  of which is supplied with power via a controller  14  from the direct-current output of a rectifier unit  15 , and which is installed along with controller  14  on the not-shown rear end shield of the alternator, and is fixedly connected therewith. Depending on the number and connection of phase conductors of stator winding  11 , when the alternator is operated, a direct current that is pulsating to a greater or lesser extent is provided at the output of rectifier assembly  15  to the not-shown vehicle electrical system, in which positive and negative terminals  16  of rectifier assembly  16  are connected directly with a storage battery in the vehicle. 
     Fan noises are induced—as the rotational speed increases—by the fans that are typically used with machines of this type. Depending on the type and connection of stator winding  11 , and in interaction with claw-pole rotor  12 , these fan noises are superposed with magnetic noises created by the stator winding. These magnetic noises occur in the lower speed range in particular, so they are perceived as particularly disturbing. 
     To dampen the magnetic noises of the electrical machine to the greatest extent possible, and to reduce their voltage and torque ripple, stator winding  11  of alternator  10  is provided with a total of seven phase conductors P 1  through P 7 . All seven phase conductors are identical in terms of their number of coils and windings, and they are connected with each other at the same electrical angle α. In the exemplary embodiment shown in  FIG. 2 , phase conductors P 1  through P 7  are connected in series such that, in the series connection, one electrically subsequent phase conductor is jumped over in each case. As shown in  FIG. 2 , the result is that phase conductors P 1  through P 7  are connected in series in phase sequence P 1 -P 3 -P 5 -P 7 -P 2 -P 4 -P 6 . In this manner, all phase conductors P 1  through P 7  are interconnected at an electrical angle α of 180/7*3°≈77.1°. With alternators that have different tooth distributions on their stator cores, it is therefore not possible to interconnect the seven phase conductors with the same electrical angle α. To attain good damping of magnetic noises and ripples in this case as well, it is necessary to interconnect phase conductors P 1  through P 7  in the aforementioned phase sequence at an electrical angle α, which is in the range between 60° and 100°. 
     An electrical machine, in particular an alternator for a motor vehicle, is therefore provided that includes a rotor  12  and claw-pole fingers  44 ,  45  that extend in the axial direction and alternate between the north and south pole around the circumference of rotor  12 , a stator  36 , which includes a stator core  18  with a stator winding  11  located in slots  35  of stator core  18 , stator  36  being located opposite to rotor  12 . Stator  36  and rotor  12  are supported by two end shields  33 , with an annular coil-shaped excitation winding  13  attached to rotor  12 . Stator winding  11  includes seven phase windings P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , which are connected in series at an electrical angle α that is at least nearly uniform. With the series connection of phase conductors P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , at least one adjacent phase conductor P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7  is jumped over in each case. The connection or series connection of phase conductors P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7  is designed such that the electrically active winding path of stator winding  11  and, therefore, the seven phase conductors P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , is closed after two revolutions. 
       FIG. 2A  depicts multi-phase stator winding  11  separately, surrounded by a virtual conductor  11 V (virtual conductor  11 V is for exemplary purposes and is not actually found in the electrical machine) formed as two interconnected loops in a seris interconnection. The two loops of virtual conductor  11 V include nodes (Node 1 , Node 2 , Node 3 , Node 4 , Node 5 , Node 6 , and Node 7 ), between which are representative parts of the conductor loop formed out of phase conductors(P 1  through P 7 ), which is closed after two revolutions. That is, the part related to phase conductor P 1  is between Node 4 , and Node 1 , the part related to phase conductor P 3  is between Node 1  and Node 2 , the part related to phase conductor P 5  is between Node 2  and Node 3 , the part related to phase conductor P 7  is between Node 3  and Node 7 , the part related to phase conductor P 2  is between Node 7  and Node 5 , the part related to phase conductor P 4  is between Node 5  and Node 6 , and the part related to phase conductor P 6  is between Node 6  and Node 4 , as shown. 
     In addition, an alternator  10  is provided, with which stator winding  11  includes winding overhangs  65 ,  66 , which may be cooled by an approximately radial flow of cool air created by fans  50  installed on at least one axial end of a claw-pole plate  42 ,  43 . 
     As shown in  FIG. 2 , the connections between phase conductors P 1  through P 7  are each guided to one of seven rectifier bridges B 1  through B 7  of rectifier assembly  15 . Rectifier bridges B 1  through B 7  are connected to a two-path rectifier assembly  15  in a known manner using two diodes in each case. The connection of phase conductors P 1  through P 7  is advantageously located on the rear winding overhang of the machine, in whose region rectifier assembly  15  is also located, in a known manner. It is provided that, of the connections between phase conductors P 1  through P 7 , only one connection  1   a  through  7   a  is guided to one of the seven rectifier bridges B 1  through B 7  in each case. 
       FIG. 3  shows a comparison of the noise characteristic—which is a function of rotational speed and is produced by the alternator shown in FIG.  2 —with the noise characteristics of known alternators of the same size. Noise characteristic a of an alternator with a known three-phase stator winding is shown in upper graph n 1 . It shows a significant increase in noise in the lower rotational speed range between 1500 and 4000 rpms, which is due to the magnetic noises of the alternator and which are superposed on the fan noise. When the rotor excitation of the alternator is switched off, what is left are the noises that are generated solely by the fan of the machine, as indicated as dashed characteristic a′. The noise level—which is a function of rotational speed—of an alternator with a known, seven-phase stator winding connected in a heptagon shape is plotted as characteristic b in middle graph n 2 . In this case as well, a noise level that is less than characteristic a but that is still elevated is also noticeable in the lower rotational speed range between 1500 and 4000 rpms compared with the pure fan noise plotted as characteristic b′. This noise level is still perceived to be disturbing. Finally, with an alternator with a seven-phase stator winding that is connected as shown in  FIG. 2 , the magnetically-induced noise level is now also damped in the lower rotational speed range—as indicated by characteristic c in graph n 3 —to the extent that it is acoustically practically imperceptible compared with the fan noise indicated by characteristic c′. 
     The performance characteristics of the alternators are plotted against rotational speed in a diagram in  FIG. 4 . Dashed characteristic A shows the course of power output by an alternator with a known three-phase stator winding, the nominal output of which is 100%, and which is attained at a rotational speed n of 6000 rpms. Characteristic B, which is plotted as a dashed-dotted line, shows the power output of an alternator whose stator winding is composed in a known manner of seven phases connected in a heptagon shape. Solid-line characteristic C shows the rotational speed-dependent output of an inventive alternator with a seven-phase stator winding that is connected as shown in  FIG. 2 . 
     The comparison of these characteristics reveals that the alternator designed according to the present invention—per its characteristic C—attains its nominal output at approximately 5000 rpms and, in the lower rotational speed range in particular, may output much more power than the known designs represented by characteristics A and B. At a no-load speed n 0  of 1800 rpms, the output could therefore be raised from approximately 51% per characteristic A and B to 66% per characteristic C. 
       FIG. 5  shows a schematic depiction of a winding scheme of a seven-phase stator winding  11   a , in which the seven phase conductors P 1  through P 7  are placed—in the form of a wave winding—in the slots of a not-shown stator core. In the present example, the machine has a two-poled rotor  12   a . As indicated with a dashed line on the right-hand side in  FIG. 4 , each phase conductor P 1  through P 7  is inserted in several waves into slots N 1  through N 14 , thereby resulting in a coil composed of one or more windings for each phase conductor P 1  through P 7 . The starts of phase conductors P 1  through P 7  are labeled as  1   a  through  7   a , and the ends are labeled as  1   e  through  7   e . The winding step of wave winding  11   a  involves seven slots. Ends  1   e  through  7   e  of winding conductors P 1  through P 7  form the connections with the coil start of the subsequent phase conductor in the series. Since, with the series connection of phase conductors P 1  through P 7 , the electrically subsequent coil phase is jumped over in this case as well in order to dampen the magnetic noise and ripple in an optimal manner, the coil phases are connected in series in this case just as they are in the exemplary embodiment shown in  FIG. 2 . End  1   e  of first phase winding P 1  is connected with winding start  3   a  of phase conductor P 3 , whose end  3   e  is connected with start  5   a  of phase conductor P 5 , whose end  5   e  is connected with start  7   a  of phase conductor P 7 , whose end  7   e  is connected with start  2   a  of phase conductor P 2 , whose end  2   e  is connected with start  4   a  of phase conductor P 4 , whose end  4   e  is connected with start  6   a  of phase conductor P 6 , whose end if connected with start  1   a  of first phase conductor P 1 . All seven connections are located on the same side, at rear winding overhang of stator winding  11   a , with starts  1   a  through  7   a  of phase conductors P 1  through P 7  being guided outwardly for connection with a rectifier assembly  15  with seven rectifier bridges—as shown in FIG.  2 —of the machine. 
       FIG. 6  shows, as a further exemplary embodiment, the winding scheme of a seven-phase stator winding in the form of a loop winding, which is also inserted in 14 slots, N 1  through N 14 , of a stator core, for a two-poled rotor as shown in  FIG. 5 . In this case, phase conductors P 1  through P 7  are formed of two series-connected coils S 1  through S 14  with a winding step that includes seven slots. For coil phase P 1 , for example, first coil S 1  is placed with, e.g., four windings, in slots N 1  and N 8 . Coil start  1   a  is guided out for connection with a rectifier assembly  15  at the rear winding overhang. Subsequently and without interruption, second coil S 2  is placed with four windings in slots N 8  and N 1 , and its end  1   e  is also guided out to rectifier assembly  15 . In the same manner, coils S 3  and S 4  of second phase conductor P 2  are inserted, with four windings each, in the stator slots, with coil S 3  located in slots N 3  and N 10 , and coil S 4  located in slots N 10  and N 3 . In this case as well, start  2   a  of coil phase P 2  and its end  2   e  are guided out at rear winding overhang to rectifier assembly  15 . This scheme repeats in the same manner for subsequent phase conductors P 3  through P 7 . The seven phase conductors are connected in the phase sequence illustrated in  FIG. 2  using appropriate, not-shown connecting posts inside rectifier assembly  15 . Advantageously, the two series-connected coils S of each phase winding P are wound with a winding wire  17 . Likewise, all seven phase conductors P may be wound with a winding wire  17  in order to attain the desired series connection, in which case—as shown in FIG.  4 —ends  1   e  through  7   e  of phase windings P 1  through P 7  are placed—as connections with particular start  3   a  through  2   a  of the second phase winding P ahead—on the winding overhang of the machine located on the rectifier side. 
       FIG. 7  shows a section of a stator core  18  of alternator  10  in  FIG. 1  with seven-phase stator winding  11 . Phase conductors P 1 , P 5 , P 2 , P 6  are accommodated in adjacent slots N 1 , N 2 , N 3 , N 4  with eight conductors L in each case. As shown in  FIG. 6 , phase conductors P may be made of two series-connected coils, each with four conductors L, or they may be made of a wave winding with eight waves, as shown in  FIG. 5 . With regard for damping the magnetic noise, it has also proven advantageous when phase conductors P are placed in slots N of stator core  18  with a slot fill factor Nf that is greater than 50%, as shown in the embodiment depicted in  FIG. 7 . 
       FIG. 8  shows a further possible connection configuration of seven-phase stator winding  11  in which, with individual phase conductors P 1  through P 7  connected in series, two subsequent phase conductors P are jumped over in each case. In this manner, phase conductors P are connected in series in phase sequence P 1 -P 4 -P 7 -P 3 -P 6 -P 2 -P 5  via connections  1   e  through  7   e . In this case as well, starts  1   a  through  7   a  of coil phases P 1  through P 7  are guided out on the end face for connection with a rectifier assembly  15  as shown in  FIG. 2 . With the connection configuration, phase conductors P 1  through P 7  are connected in series at an electrical angle α of 180/7°≈25.7°. This variant may be less optimal than the embodiment depicted in  FIG. 2  in terms of noise and performance. 
     Due to the various possibilities for connecting seven-phase stator winding  11  in series, and due to different tooth distributions, an electrical angle α in the range between 50° and 90° results for series-connected phase conductors P. 
     The present invention is not limited to the exemplary embodiments shown and described in  FIGS. 1 through 8 . It is entirely possible, for example, when the present invention is used in alternators for motor vehicles with a vehicle electrical supply voltage of 14 V, to select the number of conductors Z in slots N of stator core  18  to be greater than 5 and less than 10, provided this is advantageous in terms of optimizing the machine output. A preferred application of the present invention results with alternators for motor vehicles with 4-pole to 18-pole claw-pole rotors and a controlled excitation current. Instead of a phase conductor of the stator winding that has been wound with a winding wire, it may be more advantageous for high-performance electrical machines to place pre-manufactured conductor rods in the slots of the stator core and to interconnect them at the winding overhang using a known technique. In addition, the individual coils of phase conductors P may be connected in series or in parallel. Instead of a thick winding wire, it is also possible to wind two or more parallel winding wires to form phase conductors.