CA1266502A - Permanent magnet field dc machine - Google Patents
Permanent magnet field dc machineInfo
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- CA1266502A CA1266502A CA000532256A CA532256A CA1266502A CA 1266502 A CA1266502 A CA 1266502A CA 000532256 A CA000532256 A CA 000532256A CA 532256 A CA532256 A CA 532256A CA 1266502 A CA1266502 A CA 1266502A
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Abstract
Abstract:
A permanent magnet field DC machine comprises a rotor and a stator. The rotor comprises an armature core, an armature winding, and a commutator. The stator com-prises a yoke, permanent magnets disposed on the inner periphery of the yoke, and magnetic pole pieces inter-posed between the yoke and a portion of each magnetic pole. The magnetic pole pieces is made of a material the permeability of which is greater than that of the permanent magnets. The arrangement enables the machine, when used as a motor, to generate an increased starting torque and to rotate at higher speed under low load, than has been possible with conventional machines of this type.
A permanent magnet field DC machine comprises a rotor and a stator. The rotor comprises an armature core, an armature winding, and a commutator. The stator com-prises a yoke, permanent magnets disposed on the inner periphery of the yoke, and magnetic pole pieces inter-posed between the yoke and a portion of each magnetic pole. The magnetic pole pieces is made of a material the permeability of which is greater than that of the permanent magnets. The arrangement enables the machine, when used as a motor, to generate an increased starting torque and to rotate at higher speed under low load, than has been possible with conventional machines of this type.
Description
;5~
Permanent ma~net field DC machine This invention relates to a so-called permanent magnet field DC machine, i.e. one employing a field system of permanent magnets.
The amount of magnetic flux relative to the armature current is substantially constant in conventional permanent magnet field DC motors having-a field system constituted by permanent magnets alone. For this reason, a machine of this ~ind displays shunt-winding output characteristics, and is incapable of generating sufficient torque during starting, when a larger current flows therethrough. Another type of permanent magnet field DC
machine, which is designed in consideration of the magneto-motive force due to the armature reaction, is disclosed in Japanese Patent Laid-Open No. 153558/1982 published on September 22, 1982 with the title "Permanent magnet field starter with auxiliary poles". This machine has auxiliary poles made of a magnetic material, such as soft steel, disposed parallel in the peripheral direction with the permanent magnets.
However, according to conventional methods, ~his machine cannot generate a sufficiently large starting torque, and its rotational speed in the non-loaded state is small, because the amount of torque generating at the permanent magnets is large when the machine has no load.
Permanent ma~net field DC machine This invention relates to a so-called permanent magnet field DC machine, i.e. one employing a field system of permanent magnets.
The amount of magnetic flux relative to the armature current is substantially constant in conventional permanent magnet field DC motors having-a field system constituted by permanent magnets alone. For this reason, a machine of this ~ind displays shunt-winding output characteristics, and is incapable of generating sufficient torque during starting, when a larger current flows therethrough. Another type of permanent magnet field DC
machine, which is designed in consideration of the magneto-motive force due to the armature reaction, is disclosed in Japanese Patent Laid-Open No. 153558/1982 published on September 22, 1982 with the title "Permanent magnet field starter with auxiliary poles". This machine has auxiliary poles made of a magnetic material, such as soft steel, disposed parallel in the peripheral direction with the permanent magnets.
However, according to conventional methods, ~his machine cannot generate a sufficiently large starting torque, and its rotational speed in the non-loaded state is small, because the amount of torque generating at the permanent magnets is large when the machine has no load.
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-- 2 ~
For this reason, when a permanent magnet field DC machine is employed as a vehicle starter motor, it acts as a load on the engine of the vehicle after starting the engine and returning to the non-loaded state~ For the purpose of increasing the starting torque, it is necessary to increase the areas of ~he permanent magnets. When rare-earth magnets, such as samarium cobalt magnets or neodymium group magnets, are employ~d as the permanent magnets for obtaining the same magnetic flux as ferrite magnets and thin magnets, the cost of the field poles is increased, since it is necessary to provide these magnets with large areas.
An object of the present invention is to provide a permanent magnet field DC machine that can generate a larger torque under high load, for instance during starting, and can rotate at a higher rotational speed in the non-loaded state.
The present invention provides a permanent magnet field DC machine having magnetic pole pieces made of a magnetic material whose permeability is greater than the reversible permeability of the permanent magnets and whose thickness defined at the magnetizing end is larger than that defined on the demagnetizing side.
In this arrangement, each of the magnetic pole pieces of magnetic material is so formed as to reduce the magnetic gap between the magnetic pole piece and the armature core on the magnetizing side, thereby efficiently utilizing the magnetizing effect of the armature reaction and enabling the field poles to generate great magnetic flux at the time of starting or under high-load when the armature current is large, and to reduce the amount of magnetic flux in the non-loaded state or under small load when the armature current is small.
The present invention can thus ensure that the starting torque of the machine can be increased, as well 5~
as its rotational speed in the non-loaded state.
In the drawings:
FIG. 1 is a radial cross section taken along I-I' of FIG. 2 of a permanent magnet field motor to which one embodiment of the present invention is applied;
FIG. 2 is a partial axial cross section of the motor taken along II-II' of FIG. l;
FIG. 3 is a diagram of the distribution of armature reaction applied to the magnetic field pole shown in FIG.
10 1, FIG . 4 is a magnetic flux distribution diagram of the motor of FIG. 1 during starting;
FIG. 5 is a characteristic diagram showing the amount of magnetic flux of a field pole corresponding to the armature current;
FlG. 6 is a characteristic diagram showing the torque and the rotational speed corresponding to ~he armature current;
FIGs. 7 to 12 show radial cross sections of other embodiments relating to FIG. 1 of the present invention;
FIG. 13 is a modification of FIG. 2;
FIG. 14 is a radial cross section taken along XIV-XIV' of FIG . 15 of a permanent magnet field motor with auxiliary poles in accordance with an embodiment of the present invention;
FIG. 15 is a partial axial cross section of the motor taken along XV-XV' of FIG. 14;
FIG. 16 is a diagram of the distribution of armature reaction applied to the magnetic pole shown in FIG. 14;
FIG. 17 is a magnetic flux distribution diagram of the motor of FIG. 14 during starting;
FIG. 18 is a graph of the amount of magnetic flux of the field pole corresponding to the armature current;
and FIGs. 19 to 25 are radial cross sections of other 5~3~
embodiments rela-ting to FIG. 14 of the present invention.
Referring to FIGs. 1 and 2, a rotor, consisting of a shaft 1, a commutator 2 and an armature consisting of an armature core 3 and a coil 4 wound on the core 3, is supported on end memhers 6a and 6b by bearings 5a and 5b.
The end members 6a and 6b are fixed to a cvlindrical yoke 7. Permanent magnets 8, consisting e.g. of ferrite magnets, and magnetic pole pieces 9 are disposed around the inner periphery of the yoke 7. The thickness of each of these magnets 8 in the radial direction is greatest over a portion thereof defined by an angle ~A on a demagnetizing side 11, and gradually decreases over a portion defined by an angle ~B from the demagnetizing side toward a magnetizing end 10 thereof. The magnets ~ face the armature core 3 with a gap therebetween. A magnetic pole piece 9, made of a magnetic material such as soft sceel which has a high permeability, is disposed between the yoke 7 and the portion of each permanent magnet 8 defined by the angle ~B. The thickness of each of the magnetic pole pieces 9 in the radial direction is greatest at each magnetizing end 10 and gradually decreases towards the corresponding demagnetizing side 11. Therefore, the magnetic gap between each magnetic pole piece 9 and the armature core
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-- 2 ~
For this reason, when a permanent magnet field DC machine is employed as a vehicle starter motor, it acts as a load on the engine of the vehicle after starting the engine and returning to the non-loaded state~ For the purpose of increasing the starting torque, it is necessary to increase the areas of ~he permanent magnets. When rare-earth magnets, such as samarium cobalt magnets or neodymium group magnets, are employ~d as the permanent magnets for obtaining the same magnetic flux as ferrite magnets and thin magnets, the cost of the field poles is increased, since it is necessary to provide these magnets with large areas.
An object of the present invention is to provide a permanent magnet field DC machine that can generate a larger torque under high load, for instance during starting, and can rotate at a higher rotational speed in the non-loaded state.
The present invention provides a permanent magnet field DC machine having magnetic pole pieces made of a magnetic material whose permeability is greater than the reversible permeability of the permanent magnets and whose thickness defined at the magnetizing end is larger than that defined on the demagnetizing side.
In this arrangement, each of the magnetic pole pieces of magnetic material is so formed as to reduce the magnetic gap between the magnetic pole piece and the armature core on the magnetizing side, thereby efficiently utilizing the magnetizing effect of the armature reaction and enabling the field poles to generate great magnetic flux at the time of starting or under high-load when the armature current is large, and to reduce the amount of magnetic flux in the non-loaded state or under small load when the armature current is small.
The present invention can thus ensure that the starting torque of the machine can be increased, as well 5~
as its rotational speed in the non-loaded state.
In the drawings:
FIG. 1 is a radial cross section taken along I-I' of FIG. 2 of a permanent magnet field motor to which one embodiment of the present invention is applied;
FIG. 2 is a partial axial cross section of the motor taken along II-II' of FIG. l;
FIG. 3 is a diagram of the distribution of armature reaction applied to the magnetic field pole shown in FIG.
10 1, FIG . 4 is a magnetic flux distribution diagram of the motor of FIG. 1 during starting;
FIG. 5 is a characteristic diagram showing the amount of magnetic flux of a field pole corresponding to the armature current;
FlG. 6 is a characteristic diagram showing the torque and the rotational speed corresponding to ~he armature current;
FIGs. 7 to 12 show radial cross sections of other embodiments relating to FIG. 1 of the present invention;
FIG. 13 is a modification of FIG. 2;
FIG. 14 is a radial cross section taken along XIV-XIV' of FIG . 15 of a permanent magnet field motor with auxiliary poles in accordance with an embodiment of the present invention;
FIG. 15 is a partial axial cross section of the motor taken along XV-XV' of FIG. 14;
FIG. 16 is a diagram of the distribution of armature reaction applied to the magnetic pole shown in FIG. 14;
FIG. 17 is a magnetic flux distribution diagram of the motor of FIG. 14 during starting;
FIG. 18 is a graph of the amount of magnetic flux of the field pole corresponding to the armature current;
and FIGs. 19 to 25 are radial cross sections of other 5~3~
embodiments rela-ting to FIG. 14 of the present invention.
Referring to FIGs. 1 and 2, a rotor, consisting of a shaft 1, a commutator 2 and an armature consisting of an armature core 3 and a coil 4 wound on the core 3, is supported on end memhers 6a and 6b by bearings 5a and 5b.
The end members 6a and 6b are fixed to a cvlindrical yoke 7. Permanent magnets 8, consisting e.g. of ferrite magnets, and magnetic pole pieces 9 are disposed around the inner periphery of the yoke 7. The thickness of each of these magnets 8 in the radial direction is greatest over a portion thereof defined by an angle ~A on a demagnetizing side 11, and gradually decreases over a portion defined by an angle ~B from the demagnetizing side toward a magnetizing end 10 thereof. The magnets ~ face the armature core 3 with a gap therebetween. A magnetic pole piece 9, made of a magnetic material such as soft sceel which has a high permeability, is disposed between the yoke 7 and the portion of each permanent magnet 8 defined by the angle ~B. The thickness of each of the magnetic pole pieces 9 in the radial direction is greatest at each magnetizing end 10 and gradually decreases towards the corresponding demagnetizing side 11. Therefore, the magnetic gap between each magnetic pole piece 9 and the armature core
3 is smallest at the magnetizing end 10 and increases towards the demagnetizing side.
In the embodiment thus arranged, the magnetomotive force of the armature reaction acts on the field poles when the armature coil is energized. As shown in FIG. 3, the magnetomotive force of the armature reaction acts as a magnetizing force on the left hand side of the center of magnetism 0-0' and as a demagnetizing force on the right hand side, when a current flows through the armature coil in the direction from behind the plane of the figure to the front.
Generally, the demagnetizing force Ha is expressed 12~
by the following formula (1). lt is in proportion to the angLe ~ from the cen-ter of magnetism and in reverse proportion to the thickness t of the magnet in the direction of the magnetization thereof.
H oC ~/t ............................ (1) The demagnetizing force acting on the permanent magnet 8 has a maximum value of Ha. In this embodiment the radial thickness of t is made large so that the magnet can resist this demagnetizing force Ha. The intensity of the field system of the magnet is thereby maintained. A
demagnetizing force Hb also acts Oll a boundary portion 12 between each permanent magnet 8 and the corresponding magnetic pole piece 9, but the magnitude of the demagnet-izing force Hb is approximately 3a, as shown in FIG. 3.
The magnetic pole piece 9 disposed between each permanent magnet 8 and the yoke 7 is made from a magnetic material having a high permeability, as described above, so that it generates a large amount of magnetic flux, because of the magnetiæing effect of the armature reaction when the armature current flows at a higher rate during starting or when under load. This state is shown in the distribution chart of FIG. 4. The magnetic pole piece 9 is formed so that its radial thickness increases from the boundary portion 12 of the demagnetizing side to the magnetizing end 10 thereof, so that the magnetic flux generated by the armature reaction is led to the magnet-izing end 10. In addition, the magnetizing end 10 faces the armature core 3 via a gap, and the magnetic gap is narrow in the vicinity of the magnetizing end 10, so that the amount of the flux 14 is large at the magnet-izing end 10 of the pole piece 9. This arrangement ensures a larger amount 18 of magnetic flux during starting or under load, when the armature current flows at a high level, as expressed by a solid-line curve ~A in FIG. 5. This arrangement is free from short-circuited magnetic flux, since the magnetic gap betweeneach pole piece 9 and the armature core 3 is wide at about the center of magne-tism thereof.
The radial thickness of the permanent magnet 8 is largest at the angle ~A portion and gradually decreases toward the magnetizing end 10 over the angle ~B portion, as described above. Accordingly, the cross sectional area of the permanent magnet 8 is small and the amount of magnetic flux 16 generated from the permanent magnet 8 is reduced, as expressed by the solid-line curve ~M
in FIG. 5, while the amount of magnetic flux 15 generated by a magnetic pole constituted by the permanent magnet alone is as expressed by the broken-line curve ~M'.
However, as expressed by the curve ~ in FIG. 5, the amount o~ magnetic flux 17 of the field pole, which is the sum of ~M and ~A, is small in the substantially non-loaded state when the armature current is small, and is large when the load and hence the armature current is large. When this embodiment is used as an electric motor, it exhibits a larger rotational speed 21 when it is not loaded and the armature current is small, and can output its greatest torque 19 when it is started or is loaded when the armature current is large, as shown in FIG. 6. In FIG. 6, numerals 22 and 20 respectively represent characteristic curves of rotational speed and torque versus armature current in the conventional apparatus.
As described above, the cross sectional area of each permanent magnet 8 is small in this embodiment so that the weight of the permanent magnets can be reduced to a significant extent. ~he magnetic pole piece 9 face the armature core at the magnetizing end thereof, but its radial thickness decreases toward the demagnetizing side so that the magnetic gap is increased, thereby preventing the occurrence of eddy-current losses due _ 7 _ ~ S~
to slot ripples. Therefore, there is no delay of magnetic flux relative to the rise in armature current.
The present invention has been described above with respect to a quadrapole permanent magnet field DC machine, but it is possible for the principle of -the invention to be applied to other multi-pole machines, such as dipole or six-pole machines. The present invention is effective for generators as well as electric motors. Each permanent magnet 8 is formed of a ferrite magnet in the above embodiment, but the material of the permanent magnet 8 is not limited; other kinds of materials, such as samarium cobalt and neodymium magnets, whi~h are rare-earth magnets, iron and boron magnets can be used. The material of each magnetic pole piece 9 can be laminated silicon steel plates or a ferrite core.
FIG. 7 shows an arrangement in which each magnetic pole piece 9 is disposed on the magnetizing side only, relative to the center of magnetism 0-0', whereby the same magnetizing effect of the present invention can be realized. FI~s. 8, 9, and 10 show other arrangements in which each line of the boundary between the magnetic pole piece 9 and the permanent magnet 8 is in the form of a circular arc. These arrangements also exhibit the same effects as that of FIG. 1. FIG. 11 shows still another arrangement in which portions of the magnet 8 and the pole piece 9 having a small thickness are cut off so as to form gaps 13 and 23, thereby preventing damage to the edges of the magnet ~ and the pole piece 9, and facilitating their manufacture. FIG. 12 shows still another arrangement in which edge portions of the magnet 8 and the pole piece 9 that are oppositely located in the peripheral direction are cut off so that a magnetic density distribution in the form of a sine wave is provided in the gap between the field pole and the armature core, thereby reducing noise and vibration of the motor.
1~3~
In the arrangement shown in FIGs. 1 and 2, the pole piece 9 and the magnet 8 have the same axial length, but they can be different in length. Tha-t is, when an axial length ~ of the armature core is assumed, the axial length of the magne~ic pole piece 9 is set to be about 1.2 ~ , as shown in FIG. 13, over which the magnetizing force of the armature reaction is distributed, while the axial length of the permanent magnet 8 is set to be 1.3 ~ to2.~ ~.
It is therby possible to introduce a large amount of magnetic flu~ from the axial end of the permanent magnet 8, which is out of the effective range of the armature reaction, into the armature core, in the loaded state or during starting when the armature current flows at a high level. A larger amount of magnetic flux is thus obtained.
In the above described embodiment of the present invention, the magnetic pole piece whose thic~ness is decreased toward the demagnetizing side is formed at a portion of the permanent magnet so that the magnetizing effect of the armature reaction can be efficiently utilized, thereby obtaining a larger amount of magnetic flux when the current flows at a high level. In addition, the amount of magnetic flux generating from the permanent magnet is reduced, as the area of the permanent magnet is small. Accordingly, a motor having a field pole in accordan~e with the present invention exhibits a direct-winding characteristic whereby the motor can output a larger torque when the current flows at a high level, and can rotate at a high rotational speed in the non-loaded state when the current flows at a low level. Themotor can thereby be reduced in size and manufacturing cost. In addition, it is possible to greatly reduce the cost of the magnets when rare-earth magnets are used whose cost per weight is high, since the weight of the permanent magnet is reduce.
g Another embodiment of permanent magnet field DC
machine according to the present invention will now be described. FIG. 1~ is a radial cross section through a quadrapole permanent magnet field DC machine with auxiliary poles, and FIG. 15 is an axial cross section of the same. As shown in FIGs. 14 and 15, the rotor, consisting of a shaft 1, a commutator 2 and an armature consisting of an armature core 3 and a coil 4 wound on the armature core 3, is supported on end m~mbers 6a and 6b by bearings 5a and 5b. The end members 6a and 6b are fixed to a cylindrical yoke 7. Auxiliary poles 80 fixed to the yoke 7 and having a peripheral angle of 01 are made of a magnetic material, e.g., soft steel, and act to intensify the magnetomotive force of the armature reaction. They face the armature core 3 via a gap.
Magnetic pole pieces 9 with a peripheral angle of ~2 and made of a magnetic material are fixed to the yoke 7 to abut the auxiliary poles 80 in the peripheral direction, and are disposed partially on the demagnetizing side.
Permanent magnets 8 are disposed around the inner per-iphery of the cylindrical yoke 7. Each magnet 8 consists of a magnet 101 ~Fig. 16) having a smaller thickness and disposed under the magnetic pole piece 9 on the side of the gap, and a magnet 102 having a greater thickness disposed on the demagnetizing side toward the end 11 thereof. The directions of magnetization of the magnets 101 and 102 are the same, when these magnets are disposed in the same pole. The radial thickness of the magnet 101 is half that of the magnet 102.
In this arrangement, the magnetomotive force of the armature reaction acts on the field poles when the arm-ature coil is energized. As shown in FIG. 16, the magnetomotive force of the armature reaction acts as a magnetizing force on the left hand side of the center of magnetism 0-0' and as a demagnetizing force on the right ~2~
hand side, when a current flows through the armature coil in the direction from behind the plane of the figure to the front. The demagnetizing force acting on the permanent magnet 8 has a maximum value of lla at the demagnetizing end ll of the magnet 102. The radial thickness t is made large so that the magnet 102 can resist this demagnetizing force Ha.
A demagnetizing force Hb acts on the magnet 101 which is laminated and laid on the magnetic pole piece 9 at the portion 12 on the demagnetizing side. Since the angle 3B from the center of the magnetism of the magnet lOl is about 1/3 of the angle ~A of the magnet 102 and the thickness tl of the former is aboùt a half of that of the latter, the demagnetizing force HB becomes approximately 3 times Ha, as apparent from the formula (l).
FIG. 17 shows the magnetic flux distribution of this embodiment. A large amount of magnetic flux is generated by the magnetizing effect of the armature reaction on each auxiliary pole 80 which is formed of a material of high permeability. Each magnetic pole piece 9 formed of a magnetic ma~erial having high permeability, as that of the auxiliary pole acts to reduce the magnetomotive force consumption of the yoke, because it forms a part of the magnetic flux flow path. The pole piece 9 leads the reaction magnetic flux of the armature reaction to the magnetizing side, thus acting in the same manner as in the case of the auxiliary pole. There is substantially no occurrence of short-circuited magnetic flux due to the armature reaction which does not contribute to the torque generation, since the magnetic gap between the armature core 3 and each pole piece 9 is large. Accordingly, as expressed by the solid line 26 in FIG. 18, a larger amount of magnetic flux is generated at a larger armature current ia2. In this embodiment, the permeance coefficient of the permanent magnet 8 is reduced, because of the reduced ~adial ~hickness of the permanent magnet 101. For this reason, the amount of magnetic flux generated by the permanent magnet 101 is small, compared with the conven-tional arrangements. Therefore, as expressed by the solid line 26 in FIG. 18, the amount of magnetic flux of the field pole is small at a small armature current ial substantially in the non-loaded state, compared with that of the prior art expressed by the broken line 27.
In this embodiment of the present invention, the amount of flux of the magnetic pole is small in the non-loaded state, but it is large in a loaded condition or during starting when the armature current is large, compared with the conventional arrangements. For this reason, the rotational speed in the non-loaded stated is high and a large torque can be obtained in the loaded state or during starting of the machine. When this embodiment is used as a starter motor, it does not act as a load on the engine.
In addition, the volume of each permanent magnet 8 is reduced, since the radial thickness of the magnet 101 is reduced while maintaining the resistance to the demagneti7ing field of the armature reaction, as described above. It is thus possible to realize a permanent magnet that is reduced in weight and cost.
The description has been made with respect to a quadrapole permanent magnet field DC machine, but it is possible for the principle of the invention to be applied to other multipole machines such as dipole or six-pole machines. The present invention is effective for generators as well as electric motors. Each permanent magnet may be integrally formed or composed of two parts.
The material of the permanent magnet is not limited specifically, and it is possible to use magnetic materials such as ferrite magnets, rare-earth magnets involving samarium cobalt, cerium, cobalt, neodymium, iron and s~
boron magnets, and plastic magnets. The auxiliary pole and magnetic pole piece may be integrally formed. With reference to FIG. 16, the values of the angle ~B and the thickness tl of the magnet 101 can be respectively set to be about ~A/3 and t/2 in relation to those of the magnets 102. It is possible to freely select the dimensions of the magnet 101. Theoretically, they should satisfy the relationship: ~A x tl = ~B x t. For instance, 9B may be aA/2 when the thickness tl of the ma~net 101 is assumed to be about t/2. However, in practice, the dimension eA/3 = 9B and tl = t/2, as given above, can be selected (instead of tl - t/3) to achieve an even stronger demagnet-ization force on the magnet.
It is possi~le to arrange that the radial thickness of an auxiliary pole 9' decreases toward the demagnetizing side, as shown in a radial cross section of FIG. 19 This arrangement facilitates the integral formation of the permanent magnets, so as to save cost and labor when assembling the machine. In the arrangement of FIG. 19, the thickness of the magnet is decreased at an end 12 compared with that shown in FIG. 14. The resistance to the demagnetizing force is thereby further improved as well as the magnetizing effect.
FIG. 20 shows in radial cross section of another modified example in which the edge of the demagnetizing end 12 of the auxiliary pole g which abuts on the magnet 102 is cut to form a gap 23. A short circuit of the reaction magnetic flux is thereby more positively prevented, and the leakage flux of the permanent magnet can be reduced.
The same effect in accordance with the present invention can be realized by the arrangement shown in FIG. 21 in which the cross sectional shape of the pole piece 9 is triangular. The same effect as in FIG. 14 is also possible in the arrangement shown in FIG. 22 in ~hich a laminar auxiliary pole 80' is fixed by welding to the underside of a magnetic pole piece 9" which is integrally formed from the magnetizing end portion to the demagnetizing side. The process of fixing the auxiliary pole 80' to the yoke is simplified by this arrangement. It is a matter of course that, as shown in FIG. 23, edge portions of the magnet portions 101 and 102 constituting the permanent magnet 8, which respectively abut on the auxiliary pole 80 and the magnetic pole piece 9 in the peripheral direction, are cut so as to form a gap 130. In the arrangement shown in FIG. 24, the aux-iliary pole 80 and the magnetic pole piece 9 are disposed in the manner shown in FIG. 14, and a permanent magnet 8 is disposed alone at the demagnetiziny end so as to form a substantial space 23 under the magnetic pole piece 9, thereby greatly reducing the weight of the magnet.
This permanent magnet 8 may be in the form of an L or a trapezoid L-shape for the same effect. FIG. 25 shows another arrangement in which the boundary line between the pole piece 9 and the magnet 8 is in the form of a circular arc.
In the embodiment shown in FIGs.14 and 15, the auxiliary pole 80 and the magnetic pole piece 9 have the same axial length as that of the magnetic portions 101 and 102 of the permanent magnet 8, but the former length can be different from the latter. That is, when an axial length ~ of the armature core is assumed, the axial length of each of the auxiliary pole and magnetlc pole piece is set about 1.2 ~ while the axial length of the permanent magnet 9 is set from 1.3 ~ to 2.0 ~ It is thereby possible, during starting, to introduce a large amount of magnetic flux from the axial end of the permanent magnet 8 into the armature core, thus obtaining a larger amount of magnetic flux.
In the above described embodiment of the present ~t~
invention, -the first auxiliary pole and the magnetic pole piece extend from the magnetizing side to a part of the demagne-tizing side, thereby conducting the magnetizing effect of the armature reaction. A larger amount of magnetic flux can be generated during starting or under load when the current flows at a higher level, thus realizing a motor having a larger torque. The thickness of the permanent magnet portion disposed under the magnetic pole piece is reduced, so that the permeance coefficient of the permanent magnet becomes small, and the amount of magnetic flux in the non-loaded state of the motor is reduced. For this reason, the rotational speed of the motor in the non-loaded state can be increased and the reliability of the motor can be improved. In addition, it is possible to reduce the weight of the permanent magnet and hence the cost of the motor, since the volume of the permanent magnet can be reduced.
As is apparent from the above description, the amount of magnetic flux can be increased under high load, for instance at the time of starting, and can be reduced under low load, thus providing a permanent magnet field DC machine capable of outputting a higher torque under high load and capable of rotating at a higher rational speed under low load, namely,a device having preferable output characteristics for vehicle starters.
In the embodiment thus arranged, the magnetomotive force of the armature reaction acts on the field poles when the armature coil is energized. As shown in FIG. 3, the magnetomotive force of the armature reaction acts as a magnetizing force on the left hand side of the center of magnetism 0-0' and as a demagnetizing force on the right hand side, when a current flows through the armature coil in the direction from behind the plane of the figure to the front.
Generally, the demagnetizing force Ha is expressed 12~
by the following formula (1). lt is in proportion to the angLe ~ from the cen-ter of magnetism and in reverse proportion to the thickness t of the magnet in the direction of the magnetization thereof.
H oC ~/t ............................ (1) The demagnetizing force acting on the permanent magnet 8 has a maximum value of Ha. In this embodiment the radial thickness of t is made large so that the magnet can resist this demagnetizing force Ha. The intensity of the field system of the magnet is thereby maintained. A
demagnetizing force Hb also acts Oll a boundary portion 12 between each permanent magnet 8 and the corresponding magnetic pole piece 9, but the magnitude of the demagnet-izing force Hb is approximately 3a, as shown in FIG. 3.
The magnetic pole piece 9 disposed between each permanent magnet 8 and the yoke 7 is made from a magnetic material having a high permeability, as described above, so that it generates a large amount of magnetic flux, because of the magnetiæing effect of the armature reaction when the armature current flows at a higher rate during starting or when under load. This state is shown in the distribution chart of FIG. 4. The magnetic pole piece 9 is formed so that its radial thickness increases from the boundary portion 12 of the demagnetizing side to the magnetizing end 10 thereof, so that the magnetic flux generated by the armature reaction is led to the magnet-izing end 10. In addition, the magnetizing end 10 faces the armature core 3 via a gap, and the magnetic gap is narrow in the vicinity of the magnetizing end 10, so that the amount of the flux 14 is large at the magnet-izing end 10 of the pole piece 9. This arrangement ensures a larger amount 18 of magnetic flux during starting or under load, when the armature current flows at a high level, as expressed by a solid-line curve ~A in FIG. 5. This arrangement is free from short-circuited magnetic flux, since the magnetic gap betweeneach pole piece 9 and the armature core 3 is wide at about the center of magne-tism thereof.
The radial thickness of the permanent magnet 8 is largest at the angle ~A portion and gradually decreases toward the magnetizing end 10 over the angle ~B portion, as described above. Accordingly, the cross sectional area of the permanent magnet 8 is small and the amount of magnetic flux 16 generated from the permanent magnet 8 is reduced, as expressed by the solid-line curve ~M
in FIG. 5, while the amount of magnetic flux 15 generated by a magnetic pole constituted by the permanent magnet alone is as expressed by the broken-line curve ~M'.
However, as expressed by the curve ~ in FIG. 5, the amount o~ magnetic flux 17 of the field pole, which is the sum of ~M and ~A, is small in the substantially non-loaded state when the armature current is small, and is large when the load and hence the armature current is large. When this embodiment is used as an electric motor, it exhibits a larger rotational speed 21 when it is not loaded and the armature current is small, and can output its greatest torque 19 when it is started or is loaded when the armature current is large, as shown in FIG. 6. In FIG. 6, numerals 22 and 20 respectively represent characteristic curves of rotational speed and torque versus armature current in the conventional apparatus.
As described above, the cross sectional area of each permanent magnet 8 is small in this embodiment so that the weight of the permanent magnets can be reduced to a significant extent. ~he magnetic pole piece 9 face the armature core at the magnetizing end thereof, but its radial thickness decreases toward the demagnetizing side so that the magnetic gap is increased, thereby preventing the occurrence of eddy-current losses due _ 7 _ ~ S~
to slot ripples. Therefore, there is no delay of magnetic flux relative to the rise in armature current.
The present invention has been described above with respect to a quadrapole permanent magnet field DC machine, but it is possible for the principle of -the invention to be applied to other multi-pole machines, such as dipole or six-pole machines. The present invention is effective for generators as well as electric motors. Each permanent magnet 8 is formed of a ferrite magnet in the above embodiment, but the material of the permanent magnet 8 is not limited; other kinds of materials, such as samarium cobalt and neodymium magnets, whi~h are rare-earth magnets, iron and boron magnets can be used. The material of each magnetic pole piece 9 can be laminated silicon steel plates or a ferrite core.
FIG. 7 shows an arrangement in which each magnetic pole piece 9 is disposed on the magnetizing side only, relative to the center of magnetism 0-0', whereby the same magnetizing effect of the present invention can be realized. FI~s. 8, 9, and 10 show other arrangements in which each line of the boundary between the magnetic pole piece 9 and the permanent magnet 8 is in the form of a circular arc. These arrangements also exhibit the same effects as that of FIG. 1. FIG. 11 shows still another arrangement in which portions of the magnet 8 and the pole piece 9 having a small thickness are cut off so as to form gaps 13 and 23, thereby preventing damage to the edges of the magnet ~ and the pole piece 9, and facilitating their manufacture. FIG. 12 shows still another arrangement in which edge portions of the magnet 8 and the pole piece 9 that are oppositely located in the peripheral direction are cut off so that a magnetic density distribution in the form of a sine wave is provided in the gap between the field pole and the armature core, thereby reducing noise and vibration of the motor.
1~3~
In the arrangement shown in FIGs. 1 and 2, the pole piece 9 and the magnet 8 have the same axial length, but they can be different in length. Tha-t is, when an axial length ~ of the armature core is assumed, the axial length of the magne~ic pole piece 9 is set to be about 1.2 ~ , as shown in FIG. 13, over which the magnetizing force of the armature reaction is distributed, while the axial length of the permanent magnet 8 is set to be 1.3 ~ to2.~ ~.
It is therby possible to introduce a large amount of magnetic flu~ from the axial end of the permanent magnet 8, which is out of the effective range of the armature reaction, into the armature core, in the loaded state or during starting when the armature current flows at a high level. A larger amount of magnetic flux is thus obtained.
In the above described embodiment of the present invention, the magnetic pole piece whose thic~ness is decreased toward the demagnetizing side is formed at a portion of the permanent magnet so that the magnetizing effect of the armature reaction can be efficiently utilized, thereby obtaining a larger amount of magnetic flux when the current flows at a high level. In addition, the amount of magnetic flux generating from the permanent magnet is reduced, as the area of the permanent magnet is small. Accordingly, a motor having a field pole in accordan~e with the present invention exhibits a direct-winding characteristic whereby the motor can output a larger torque when the current flows at a high level, and can rotate at a high rotational speed in the non-loaded state when the current flows at a low level. Themotor can thereby be reduced in size and manufacturing cost. In addition, it is possible to greatly reduce the cost of the magnets when rare-earth magnets are used whose cost per weight is high, since the weight of the permanent magnet is reduce.
g Another embodiment of permanent magnet field DC
machine according to the present invention will now be described. FIG. 1~ is a radial cross section through a quadrapole permanent magnet field DC machine with auxiliary poles, and FIG. 15 is an axial cross section of the same. As shown in FIGs. 14 and 15, the rotor, consisting of a shaft 1, a commutator 2 and an armature consisting of an armature core 3 and a coil 4 wound on the armature core 3, is supported on end m~mbers 6a and 6b by bearings 5a and 5b. The end members 6a and 6b are fixed to a cylindrical yoke 7. Auxiliary poles 80 fixed to the yoke 7 and having a peripheral angle of 01 are made of a magnetic material, e.g., soft steel, and act to intensify the magnetomotive force of the armature reaction. They face the armature core 3 via a gap.
Magnetic pole pieces 9 with a peripheral angle of ~2 and made of a magnetic material are fixed to the yoke 7 to abut the auxiliary poles 80 in the peripheral direction, and are disposed partially on the demagnetizing side.
Permanent magnets 8 are disposed around the inner per-iphery of the cylindrical yoke 7. Each magnet 8 consists of a magnet 101 ~Fig. 16) having a smaller thickness and disposed under the magnetic pole piece 9 on the side of the gap, and a magnet 102 having a greater thickness disposed on the demagnetizing side toward the end 11 thereof. The directions of magnetization of the magnets 101 and 102 are the same, when these magnets are disposed in the same pole. The radial thickness of the magnet 101 is half that of the magnet 102.
In this arrangement, the magnetomotive force of the armature reaction acts on the field poles when the arm-ature coil is energized. As shown in FIG. 16, the magnetomotive force of the armature reaction acts as a magnetizing force on the left hand side of the center of magnetism 0-0' and as a demagnetizing force on the right ~2~
hand side, when a current flows through the armature coil in the direction from behind the plane of the figure to the front. The demagnetizing force acting on the permanent magnet 8 has a maximum value of lla at the demagnetizing end ll of the magnet 102. The radial thickness t is made large so that the magnet 102 can resist this demagnetizing force Ha.
A demagnetizing force Hb acts on the magnet 101 which is laminated and laid on the magnetic pole piece 9 at the portion 12 on the demagnetizing side. Since the angle 3B from the center of the magnetism of the magnet lOl is about 1/3 of the angle ~A of the magnet 102 and the thickness tl of the former is aboùt a half of that of the latter, the demagnetizing force HB becomes approximately 3 times Ha, as apparent from the formula (l).
FIG. 17 shows the magnetic flux distribution of this embodiment. A large amount of magnetic flux is generated by the magnetizing effect of the armature reaction on each auxiliary pole 80 which is formed of a material of high permeability. Each magnetic pole piece 9 formed of a magnetic ma~erial having high permeability, as that of the auxiliary pole acts to reduce the magnetomotive force consumption of the yoke, because it forms a part of the magnetic flux flow path. The pole piece 9 leads the reaction magnetic flux of the armature reaction to the magnetizing side, thus acting in the same manner as in the case of the auxiliary pole. There is substantially no occurrence of short-circuited magnetic flux due to the armature reaction which does not contribute to the torque generation, since the magnetic gap between the armature core 3 and each pole piece 9 is large. Accordingly, as expressed by the solid line 26 in FIG. 18, a larger amount of magnetic flux is generated at a larger armature current ia2. In this embodiment, the permeance coefficient of the permanent magnet 8 is reduced, because of the reduced ~adial ~hickness of the permanent magnet 101. For this reason, the amount of magnetic flux generated by the permanent magnet 101 is small, compared with the conven-tional arrangements. Therefore, as expressed by the solid line 26 in FIG. 18, the amount of magnetic flux of the field pole is small at a small armature current ial substantially in the non-loaded state, compared with that of the prior art expressed by the broken line 27.
In this embodiment of the present invention, the amount of flux of the magnetic pole is small in the non-loaded state, but it is large in a loaded condition or during starting when the armature current is large, compared with the conventional arrangements. For this reason, the rotational speed in the non-loaded stated is high and a large torque can be obtained in the loaded state or during starting of the machine. When this embodiment is used as a starter motor, it does not act as a load on the engine.
In addition, the volume of each permanent magnet 8 is reduced, since the radial thickness of the magnet 101 is reduced while maintaining the resistance to the demagneti7ing field of the armature reaction, as described above. It is thus possible to realize a permanent magnet that is reduced in weight and cost.
The description has been made with respect to a quadrapole permanent magnet field DC machine, but it is possible for the principle of the invention to be applied to other multipole machines such as dipole or six-pole machines. The present invention is effective for generators as well as electric motors. Each permanent magnet may be integrally formed or composed of two parts.
The material of the permanent magnet is not limited specifically, and it is possible to use magnetic materials such as ferrite magnets, rare-earth magnets involving samarium cobalt, cerium, cobalt, neodymium, iron and s~
boron magnets, and plastic magnets. The auxiliary pole and magnetic pole piece may be integrally formed. With reference to FIG. 16, the values of the angle ~B and the thickness tl of the magnet 101 can be respectively set to be about ~A/3 and t/2 in relation to those of the magnets 102. It is possible to freely select the dimensions of the magnet 101. Theoretically, they should satisfy the relationship: ~A x tl = ~B x t. For instance, 9B may be aA/2 when the thickness tl of the ma~net 101 is assumed to be about t/2. However, in practice, the dimension eA/3 = 9B and tl = t/2, as given above, can be selected (instead of tl - t/3) to achieve an even stronger demagnet-ization force on the magnet.
It is possi~le to arrange that the radial thickness of an auxiliary pole 9' decreases toward the demagnetizing side, as shown in a radial cross section of FIG. 19 This arrangement facilitates the integral formation of the permanent magnets, so as to save cost and labor when assembling the machine. In the arrangement of FIG. 19, the thickness of the magnet is decreased at an end 12 compared with that shown in FIG. 14. The resistance to the demagnetizing force is thereby further improved as well as the magnetizing effect.
FIG. 20 shows in radial cross section of another modified example in which the edge of the demagnetizing end 12 of the auxiliary pole g which abuts on the magnet 102 is cut to form a gap 23. A short circuit of the reaction magnetic flux is thereby more positively prevented, and the leakage flux of the permanent magnet can be reduced.
The same effect in accordance with the present invention can be realized by the arrangement shown in FIG. 21 in which the cross sectional shape of the pole piece 9 is triangular. The same effect as in FIG. 14 is also possible in the arrangement shown in FIG. 22 in ~hich a laminar auxiliary pole 80' is fixed by welding to the underside of a magnetic pole piece 9" which is integrally formed from the magnetizing end portion to the demagnetizing side. The process of fixing the auxiliary pole 80' to the yoke is simplified by this arrangement. It is a matter of course that, as shown in FIG. 23, edge portions of the magnet portions 101 and 102 constituting the permanent magnet 8, which respectively abut on the auxiliary pole 80 and the magnetic pole piece 9 in the peripheral direction, are cut so as to form a gap 130. In the arrangement shown in FIG. 24, the aux-iliary pole 80 and the magnetic pole piece 9 are disposed in the manner shown in FIG. 14, and a permanent magnet 8 is disposed alone at the demagnetiziny end so as to form a substantial space 23 under the magnetic pole piece 9, thereby greatly reducing the weight of the magnet.
This permanent magnet 8 may be in the form of an L or a trapezoid L-shape for the same effect. FIG. 25 shows another arrangement in which the boundary line between the pole piece 9 and the magnet 8 is in the form of a circular arc.
In the embodiment shown in FIGs.14 and 15, the auxiliary pole 80 and the magnetic pole piece 9 have the same axial length as that of the magnetic portions 101 and 102 of the permanent magnet 8, but the former length can be different from the latter. That is, when an axial length ~ of the armature core is assumed, the axial length of each of the auxiliary pole and magnetlc pole piece is set about 1.2 ~ while the axial length of the permanent magnet 9 is set from 1.3 ~ to 2.0 ~ It is thereby possible, during starting, to introduce a large amount of magnetic flux from the axial end of the permanent magnet 8 into the armature core, thus obtaining a larger amount of magnetic flux.
In the above described embodiment of the present ~t~
invention, -the first auxiliary pole and the magnetic pole piece extend from the magnetizing side to a part of the demagne-tizing side, thereby conducting the magnetizing effect of the armature reaction. A larger amount of magnetic flux can be generated during starting or under load when the current flows at a higher level, thus realizing a motor having a larger torque. The thickness of the permanent magnet portion disposed under the magnetic pole piece is reduced, so that the permeance coefficient of the permanent magnet becomes small, and the amount of magnetic flux in the non-loaded state of the motor is reduced. For this reason, the rotational speed of the motor in the non-loaded state can be increased and the reliability of the motor can be improved. In addition, it is possible to reduce the weight of the permanent magnet and hence the cost of the motor, since the volume of the permanent magnet can be reduced.
As is apparent from the above description, the amount of magnetic flux can be increased under high load, for instance at the time of starting, and can be reduced under low load, thus providing a permanent magnet field DC machine capable of outputting a higher torque under high load and capable of rotating at a higher rational speed under low load, namely,a device having preferable output characteristics for vehicle starters.
Claims (10)
1. A permanent magnet field DC machine having a rotor and a stator, said rotor comprising an armature core, an armature winding and a commutator, and said stator compris-ing a yoke and field poles having a center of magnetism including permanent magnets disposed on the inner periphery of said yoke, characterized in further comprising magnetic pole pieces made of a material whose permeability is greater than that of said permanent magnets the magnetic pole pieces being connected to said yoke, being interposed between said yoke and a portion of each of said permanent magnets and being disposed on a magnetizing side of a magnetomotive force of the armature reaction thereof relative to the center of the magnetism of each field pole, and said permanent magnets being connected to said magnetic pole pieces and said yoke facing to said rotor and disposed on both the magnetizing side and a demagnetizing side thereof.
2. A permanent magnet field DC machine according to claim 1, wherein each of said permanent magnets comprises a rare-earth magnet.
3. A permanent magnet field DC machine according to claim 1, wherein each of said magnetic pole pieces is formed so as to face said armature core at the magnetizing side and to gradually decrease in radial thickness from said magnetizing side toward the demagnetizing side and said permanent magnet is formed so as to gradually decrease in radial thickness from a portion located on said demagnetizing side toward the magnetizing side.
4. A permanent magnet field DC machine according to claim 3, wherein the sectional configuration of each of said magnetic pole pieces is substantially triangular and the sectional configuration of said permanent magnet is substantially trapezoidal.
5. A permanent magnet field DC machine having a rotor and a stator, said rotor comprising an armature core, an armature winding, and a commutator, and said stator comprising a yoke and permanent magnets disposed on an inner periphery of said yoke and auxiliary poles made of a magnetic material disposed parallel with said permanent magnets, characterized in that each of said auxiliary poles comprises a first auxiliary pole connected to said yoke having a radial thickness and disposed at a magnetizing side of a magnetomotive force of the armature reaction thereof, and a second auxiliary pole connected to said yoke and the first auxiliary pole and having a smaller radial thickness compared with the thickness of the first auxiliary pole and disposed on the magnetizing side and partially on a demagnetizing side thereof, and said permanent magnets comprising a first magnet portion connected to the first auxiliary pole and the second auxiliary pole and facing to said rotor, and a second magnet portion connected to an end of said second auxiliary pole and said first magnet portion on said inner periphery of said yoke and disposed at said demagnetizing side thereof.
6. A permanent magnet field DC machine according to claim 5, wherein the radial thickness of said second auxiliary pole is set to be constant from said magnetizing side to said demagnetizing side.
7. A permanent magnet field DC machine according to claim 5, wherein the radial thickness of said second auxiliary pole gradually decreases from said magnetizing side to said demagnetizing side.
8. A permanent magnet field DC machine according to claim 5, wherein each of said permanent magnet is formed of a rare-earth magnet.
9. A permanent magnet field DC machine having a rotor and a stator, said rotor comprising an armature core, an armature winding and a commutator, and said stator comprising a yoke and field poles having a center of magnetism including permanent magnets disposed on the inner periphery of said yoke, and magnetic pole pieces made of a material whose permeability is greater than that of said permanent magnets, the magnetic pole pieces being connected to said yoke, being interposed between said yoke and a portion of each of said permanent magnets and being disposed in a range from a magnetizing end of a magneto-motive force of the armature reaction thereof relative to the center of the magnetism of each field pole to a portion of a demagnetizing side thereof, and said permanent magnets being connected to said magnetic pole pieces and said yoke facing to said rotor and disposed on both a magnetizing side and the demagnetizing side thereof.
10. A permanent magnet field DC machine having a rotor and a stator, said rotor having an armature core, an armature winding and a commutator;
said stator comprising a yoke, field poles having a center of magnetization including permanent magnets connected to the inner periphery of said yoke and facing said rotor, and magnetic pole pieces made of a material having a permeabilty which is greater than the permeability of the permanent magnets, said pole pieces being magnetically connected directly to the yoke and there being on opposite sides of the center of the magnetization of each field pole a magnetizing and a demagnetizing magnetomotive force due to armature reaction;
said pole pieces being connected to both the permanent magnets and said yoke, interposed between the yoke and a portion of each of said permanent magnets, and disposed on a magnetizing side of the magnetomotive force due to the armature reaction; and said permanent magnets facing said rotor and disposed on both the magnetizing side and the demagnetizing side of said field poles.
said stator comprising a yoke, field poles having a center of magnetization including permanent magnets connected to the inner periphery of said yoke and facing said rotor, and magnetic pole pieces made of a material having a permeabilty which is greater than the permeability of the permanent magnets, said pole pieces being magnetically connected directly to the yoke and there being on opposite sides of the center of the magnetization of each field pole a magnetizing and a demagnetizing magnetomotive force due to armature reaction;
said pole pieces being connected to both the permanent magnets and said yoke, interposed between the yoke and a portion of each of said permanent magnets, and disposed on a magnetizing side of the magnetomotive force due to the armature reaction; and said permanent magnets facing said rotor and disposed on both the magnetizing side and the demagnetizing side of said field poles.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000532256A CA1266502A (en) | 1986-03-17 | 1987-03-17 | Permanent magnet field dc machine |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61-56824(1986) | 1986-03-17 | ||
| JP61056824A JPH0824420B2 (en) | 1986-03-17 | 1986-03-17 | Permanent magnet field type DC machine |
| CA000532256A CA1266502A (en) | 1986-03-17 | 1987-03-17 | Permanent magnet field dc machine |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1266502A true CA1266502A (en) | 1990-03-06 |
Family
ID=25671267
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000532256A Expired - Lifetime CA1266502A (en) | 1986-03-17 | 1987-03-17 | Permanent magnet field dc machine |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1266502A (en) |
-
1987
- 1987-03-17 CA CA000532256A patent/CA1266502A/en not_active Expired - Lifetime
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