DC motor with commutator

Abstract

To provide a DC motor with a commutator capable of sufficiently control conduct and radiate an electromagnetic noise generated, for example, between a carbon brush and the commutator to an outside.SOLUTION: A DC motor 10 includes an electric noise prevention element connected with a commutator 19. Commutator 19 constitutes a recessed element storage space with extending strip parts of plural commutator segments, an insulating cylinder part 24 and an outer end face of the commutator 19. In the element storage space, any one of plural electrodes of the electric noise prevention element and any one of the extending strip parts are integrally joined respectively by a fusion zone using solder welding. The commutator 19, a carbon brush 22, a brush holder 21 and the electric noise prevention element are arranged inside an end cap 20. A coating layer formed by a conductive material for preventing conduction noises and radiation noises is provided on the entirety of an outer peripheral surface of the end cap 20.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a small DC motor with a commutator for use in electric actuators in automobiles and the like, and more particularly to a DC motor with a commutator that is inexpensive and capable of reducing electrical noise that adversely affects communication equipment. [Background technology]

[0002] Compared to other motors such as brushless motors, DC motors with small commutators are inexpensive and have excellent rotational characteristics as control motors, such as large torque, linear rotational characteristics in response to changes in applied voltage, and linearity of output torque in response to input current. However, because of the presence of carbon brushes and a commutator as mechanical contacts, there is a drawback in that spark discharge occurs between the carbon brushes and the commutator during commutation, and electromagnetic noise is also conducted and radiated.

[0003] Patent Document 1 discloses an invention in which a conductive layer is provided to cover the outer circumferential surface of a gear housing that constitutes a part of a motor case, and the conductive coating layer blocks the radiation noise emitted from a rotating electric machine, thereby reducing the amount of radiation noise. It describes that the coating layer is formed by electroless plating, for example, a plating layer having a multi-layer structure of copper and nickel. Furthermore, Patent Document 2 discloses an invention in which, in a motor device in which a choke coil or a noise killer capacitor is connected to the brush holder as a means of improving EMC performance, the emission of electromagnetic waves is prevented by partially covering the brush housing and terminal housing, which are sources of noise, from the outside with a single metal piece.

[0004] Furthermore, Patent Document 3 discloses an invention in which the surface of a reducer housing made of synthetic resin is plated with a conductive metal to shield the brush holder and control circuit, which serve as power supply means and are sources of electromagnetic noise, with the conductive metal. With this configuration, electromagnetic noise generated in the brush holder and control circuit is shielded. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2001-352706 A [Patent Document 2] JP 2018-121420 A [Patent Document 3] JP 2017-28839 A Summary of the Invention [Problem to be solved by the invention]

[0006] Moreover, with the recent spread of wireless devices using high frequencies above 1 GHz, there is a demand to fully secure appropriate electromagnetic compatibility (EMC) requirements and to suppress external radiation of high-frequency electromagnetic noise. The EMC circuits installed to suppress this electromagnetic noise become new sources of electromagnetic noise. As a result, the frequency of the electromagnetic noise generated by DC motors equipped with commutators spans a wide range, from low frequencies to high frequencies exceeding 1 GHz. However, as electric motors become smaller, the size of the capacitor that can be mounted on the surface of the end cap is limited, so a capacitor alone to eliminate spark discharges that occur between the carbon brushes and the commutator is insufficient to counter conducted and radiated noise in the low frequency band below 30 MHz.

[0007] In particular, in the limited space of an automobile, there is a natural limit to the degree of freedom in installing each piece of equipment, and it is not easy to ensure a sufficient distance between the motor and the sensors and antennas that serve as the receiving parts of the communications equipment. Therefore, it is desirable to have a lower level of conducted and radiated noise generated by electric motors, and as there are increasing opportunities to install receiving parts such as antennas near motors used in automobile electric actuators, there is a demand for compact motors that generate less conducted and radiated noise.

[0008] According to the invention disclosed in Patent Document 1, the entire outer surface of the gear housing of the rotating electrical machine is simply covered with a coating layer. Although this type of configuration can block electromagnetic noise to a certain extent, it is difficult to block all frequency bands, and is not sufficient to ensure electromagnetic compatibility (EMC) requirements. The invention disclosed in Patent Document 2 also applies a plating treatment with a conductive metal to the entire surface of the reducer housing. Although this configuration can block electromagnetic noise to a certain extent, it is difficult to block all frequency bands, and it is not sufficient to ensure the requirements for electromagnetic compatibility (EMC). Furthermore, plating the surface of the reducer housing with a conductive metal requires a large amount of conductive material to form the conductive metal, which increases manufacturing costs.

[0009] According to the invention disclosed in Patent Document 3, a single metal piece partially covers the brush housing and the terminal housing, which are noise sources, from the outside, to prevent the emission of electromagnetic waves. Although the electromagnetic noise can be blocked in the part covered by the metal piece, electromagnetic noise leaks from the gap between the metal piece and the brush housing and the gap between the metal piece and the terminal housing. In order to eliminate the gap between the metal piece and the noise source as much as possible, the invention of Patent Document 3 bends the metal piece in a complex manner. However, since the noise source is covered by an integrated metal piece with a complex shape, the size of the brush housing and the terminal housing becomes large. Furthermore, there is a problem that the efficiency of taking the number of metal pieces from the original sheet of thin metal plate is low, and the number of processes for bending in a complex manner is also increased, which increases the manufacturing cost of the metal piece.

[0010] The present invention is devised to solve such problems of the conventional technology, and has an object to provide a small, inexpensive DC motor with a commutator that can sufficiently suppress the external conduction and radiation of a wide range of electromagnetic noise, from low frequencies to high frequencies exceeding 1 GHz, which is generated simultaneously with the spark discharge that occurs between the carbon brushes and the commutator. [Means for solving the problem]

[0011] The DC motor with a commutator of the present invention is A rotating shaft rotatably supported within a motor case; An end cap made of a non-conductive resin and fixed to the motor case; a commutator fixed to the rotating shaft, the commutator having a plurality of commutator segments connected to an armature winding; A carbon brush that is in sliding contact with the commutator; A brush holder held by the end cap; a DC motor having an electrical noise suppression element connected to the commutator, The commutator is a cylindrical insulating tubular portion made of an insulating material and having an inner end surface and an outer end surface; a plurality of commutator segments made of a conductive material and fixed to an outer periphery of the insulating cylindrical portion in a spaced relationship; Each of the commutator segments has a connection portion with an armature winding at a position corresponding to an outer circumferential side of the inner end surface of the insulating cylindrical portion, Each of the commutator segments is integrally provided with an extension strip portion at a position corresponding to an outer circumferential side of the outer end surface, the extension strip portion extending outward from the outer end surface in the same direction as the rotation axis and having a width shorter than a circumferential length of the commutator segment, the extension strip portions of the plurality of commutator segments, the insulating cylindrical portion, and the outer end surface of the commutator form a recessed element accommodating space, The electrical noise prevention element has a plurality of electrodes, In the element accommodating space, any one of the plurality of electrodes of the electric noise prevention element and any one of the extension strip portions are integrally connected to each other by a fusion zone formed by solder welding, the commutator, the carbon brushes, the brush holder, and the electrical noise prevention element are disposed inside the end cap; The end cap is characterized in that a coating layer for preventing conducted and radiated noise, which is made of a conductive material, is provided on the entire outer peripheral surface of the end cap.

[0012] According to the present invention, an electrical noise prevention element is connected inside an element housing space provided on the end face of the commutator, which is the source of electromagnetic noise, and further, a coating layer for preventing conducted and radiated noise, formed of a conductive material, is provided on the outer peripheral surface of the end cap close to the source of the electromagnetic noise, thereby blocking radiated noise and reducing the amount of radiated noise. [Brief description of the drawings]

[0013] [Figure 1] 1 is a longitudinal sectional view of a DC motor with a commutator having a coating layer for preventing conducted and radiated noise according to a first embodiment of the present invention. [Diagram 2] 2 is a perspective view showing the relationship between a commutator and a ring-shaped varistor serving as an electrical noise prevention element in the DC motor of FIG. 1. FIG. [Diagram 3] 3 is a vertical sectional view of the commutator with ring-shaped varistor shown in FIG. 2. [Figure 4] 3 is a front view of the end cap showing the internal configuration of the end cap in which the electrical noise prevention element is incorporated in the first embodiment; FIG. [Diagram 5] 2 is a circuit diagram showing the electrical connection relationship between an armature winding, a commutator with a ring-shaped varistor, and an EMC circuit in the first embodiment. FIG. [Figure 6A] 2 is a perspective view showing the inner and outer circumferential surfaces of an end cap having an electromagnetic shield layer in the first embodiment. FIG. [Figure 6B] FIG. 2 is a perspective view showing the appearance of an end cap having an electromagnetic shielding layer in the first embodiment. [Figure 7] 5A to 5C are diagrams illustrating the effect of reducing electromagnetic noise according to the first embodiment. [Figure 8] 4 is a longitudinal sectional view of a DC motor with a commutator having a covering layer for preventing conducted and radiated noise according to a second embodiment of the present invention. FIG. [Figure 9] 9 is a perspective view showing the relationship between a commutator and a ring capacitor serving as an electrical noise prevention element in the DC motor of FIG. 8. FIG. [Figure 10A]FIG. 11 is a front view of a commutator with a ring capacitor in the second embodiment. [Figure 10B] FIG. 11 is a circuit diagram showing the electrical connection relationship between an armature winding and a commutator with a ring capacitor in a second embodiment. [Figure 11] FIG. 11 is a perspective view showing the appearance of an end cap having an electromagnetic shielding layer in a second embodiment. [Figure 12] 13 is an exploded longitudinal sectional view showing a commutator-equipped DC motor according to a third embodiment of the present invention, in which the outer peripheral surface of the end cap and the inner peripheral surface of the encoder cap are provided with a conductive coating layer. FIG. [Figure 13] 13 is an enlarged vertical sectional view of an end cap and a rotary encoder portion of the DC motor shown in FIG. 12. [Figure 14] FIG. 11 is a circuit diagram showing the electrical connection relationship between an armature winding, a commutator with a ring-shaped varistor, and a rotary encoder in a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of a commutator-equipped DC motor having a coating layer for preventing conducted and radiated noise according to the present invention will be described with reference to the drawings. EXAMPLES

[0015] A first embodiment of the present invention will now be described in detail with reference to an embodiment of a DC motor having a commutator with a ring-shaped varistor as an electrical noise prevention element. 1 is a vertical cross-sectional view of a DC motor with a commutator having a coating layer for preventing conducted and radiated noise according to a first embodiment of the present invention. The motor case 11 of the DC motor 10 is a cup-shaped case made of metal such as iron, with one end open. An end plate 13 is fixed to the open side of the motor case 11, and a cup-shaped end cap 20 made of insulating resin is fixed to the inside of the end plate 13. A magnet 12 constituting the stator of the DC motor is fixed to the motor case 11. An armature winding 17 and a laminated core 18 constituting the rotor of the DC motor are integrally formed with a rotating shaft 16, and this rotating shaft is rotatably supported by the motor case 11 and end plates 13 via bearings 14, 15. The laminated core 18 is polarized in the circumferential direction into multiple poles, and an armature winding 17 is wound around each core, with the ends connected to a commutator 19.

[0016] The DC motor 10 further includes a pair of carbon brushes 22 in sliding contact with a commutator 19 fixed to the rotating shaft 16, and a brush holder 21 held by an end cap 20. Power supply terminals connected to the carbon brushes 22 via pigtails 23a are provided near the radially outer edges of the end caps 20, and these terminals have terminals 23 extending outside the end plates 13. A ring-shaped varistor 25 is fixed integrally to the commutator 19, forming a commutator with a ring-shaped varistor.

[0017] Electromagnetic shield layers 202, 204 are provided on the outer and inner peripheral surfaces of the cup-shaped end cap 20 as coating layers for preventing conducted and radiated noise. The coating layer may be, for example, a copper-nickel multi-layer structure formed by electroless nickel plating on electroless copper plating, or an electrolytic nickel plating may be applied on electrolytic copper plating.

[0018] The end cap 20 is made of a non-conductive material such as synthetic resin (e.g., PPS or PA containing 40% glass fiber), and an electromagnetic wave coating layer made of conductive metal is formed on the surface of the end cap. During the processing stage of the electromagnetic wave coating layer, the power terminal section, the carbon brush sliding section, the carbon brush spring, etc. are appropriately masked, and the electromagnetic wave coating layer is formed on the surface of the end cap without impairing the non-conductive function.

[0019] The end cap has a conductive coating layer on its outer surface that is fitted into an opening at one end of a cylindrical metal frame that also serves as an earthing function, i.e., the motor case 11. In this way, by covering the outer or inner and outer peripheral surfaces of the end cap, which constitutes part of the motor case, with a conductive layer, substantially the entire outer peripheral surface of the motor case, together with the cylindrical metal frame, is covered with a conductor. In this way, the electromagnetic shield layers 202, 204 are formed from multiple metal layers made of different materials, and therefore the characteristics of each material can be used to better suppress the radiation of electromagnetic noise to the outside.

[0020] Fig. 2 is a perspective view showing the relationship between a commutator and a ring-shaped varistor serving as an electric noise prevention element in the DC motor of Fig. 1. Also, Fig. 3 is a vertical sectional view of the commutator with ring-shaped varistor shown in Fig. 2. The commutator 19 has a plurality of copper commutator segments 190 (five in this embodiment) fixed to the outer periphery of a resin insulating cylindrical portion 24. An axially extending extension strip portion 191 is provided at one end of each commutator segment 190, and a recessed element accommodating space 28 for accommodating the ring-shaped varistor 25 is formed inside these extension strip portions 191. An armature winding connecting piece 192 is provided at the other end of each commutator segment 190. An inter-segment gap 193 is provided between each commutator segment.

[0021] The ring-shaped varistor 25 comprises a ring-shaped varistor body and a number of band-shaped copper electrodes 251 provided at equal intervals on the outer peripheral surface of the ring of the varistor body. The varistor body is made of a semiconductor ceramic with non-linear resistance characteristics. Each copper electrode 251 is provided on the outer peripheral surface of the varistor body in correspondence with a commutator segment 190, and there are five copper electrodes in this embodiment. In the element accommodating space 28, any one of the copper electrodes 251 of the ring-shaped varistor 25 and any one of the extension strip portions 191 are integrally joined to each other via a fusion zone 300 formed by solder welding. The ring-shaped varistor used in this embodiment is made of ceramic with high mechanical strength due to adjustment of the crystal grains. Compared to a ring-shaped varistor attached to the armature coil side, the radius size is about half, making it smaller, and therefore more resistant to vibrations caused by the rotation of the motor.

[0022] In this embodiment, the end face of the insulating cylindrical portion 24 opposite the armature winding side is defined as the outer end face 241, and the end face on the armature winding side is defined as the inner end face 242. In other words, the element accommodating space 28 provided on the outer end face of the commutator 19 is a space surrounded by the outer end face 241 of the insulating cylindrical portion 24 and the extension strip portions 191 of each commutator segment 190.

[0023] In this embodiment, the width of the extended strip portion 191 is narrowed relative to the circumferential width of the commutator segment 190, thereby increasing the gap of the element accommodating space 28 and making it a space that is widely open to the outside. As an example, when the diameter of the commutator 19 is 5 mm and there are five commutator segments, the circumferential width of each commutator segment is 4 mm, whereas the circumferential width of the extended strip portion 191 is 0.9 mm. In this case, the circumferential width of each extended strip portion 191 is approximately 1 / 4 of the circumferential width of each commutator segment 190. The circumferential width of the extended strip portion 191 also varies depending on the diameter of the commutator 19 and the number of commutator segments. However, in practice, there is a limit to the diameter of a ring-shaped varistor that can withstand relatively high-speed rotation, and therefore there is also an upper limit to the diameter of the commutator 19 of the motor. Therefore, in practice, it is desirable that the sum of the circumferential widths of the extension strips 191 be 1 / 3 to 1 / 5 of the circumferential length of the outer periphery of the commutator 19. The axial length L of the extension strip is about 1.0 mm to 1.2 mm, and the radial thickness of the extension strip is about 0.4 mm to 0.6 mm. In this way, since the circumferential width of the extension strip portion 191 is considerably smaller than the circumferential width of the commutator segment 190 and the axial length L is also short, the element accommodating space 28 has a large gap and is a space that is widely open to the outside.

[0024] According to this embodiment, the ring-shaped varistor 25 is fixed to the multiple extension strips 191, so that the gap between each extension strip is in direct contact with the external air layer. That is, the ring-shaped varistor itself is not sealed in the space inside the commutator segments of the commutator, nor is it integrated with resin. Also, by exposing one side of the ring-shaped varistor, i.e., the side that does not face the outer end face 241 of the insulating cylindrical part 24, the heat dissipation is improved. Therefore, the ring-shaped varistor 25 of this embodiment has excellent cooling characteristics when the temperature rises. Therefore, even if repeated deformation of the members occurs due to the difference in the thermal expansion coefficient of the multiple members caused by the temperature change due to spark discharge caused by the commutation of the current when the motor is driven, the heat dissipation characteristics of the electric noise prevention element are not impaired, and the electric noise prevention element can be prevented from being destroyed. In addition, since the ring-shaped varistor 25 is supported by a plurality of extended strip portions of the commutator segments, it is also resistant to forces acting in the radial direction (centrifugal direction).

[0025] 4 is a front view of the end cap 20 in the first embodiment. Inside the cup-shaped end cap 20, choke coils 272 (L1, L2), capacitors 274 (C1, C2), resistors, etc. constituting the EMC circuit 27 are provided on a substrate. Electromagnetic shield layers 202, 204 are provided on the entire outer and inner surfaces of the cup-shaped end cap 20 as coating layers for preventing conducted and radiated noise, so as to double-surround the EMC circuit 27. In addition, the earth wire 2740 of the capacitor 274 is in contact with the electromagnetic shield layer 202 in the earth wire groove 2740C on the outer peripheral surface side of the end cap 20.

[0026] 5 is a diagram showing an example of the configuration of an EMC circuit 27 in one embodiment of the present invention. This EMC circuit 27 is a circuit in which elements such as choke coils 272 (L1, L2), capacitors 274 (C1, C2), and PTC (Positive Temperature Coefficient Thermal-Resistor), which constitute an IC filter circuit, are mounted on a substrate. The EMC circuit 27 connected between the terminals of the motor functions as a common mode noise countermeasure and a differential mode noise countermeasure. When the motor output increases, the current flow increases, and noise during commutation increases, so it is necessary to extend the life of the sliding surfaces of the carbon brushes and commutator and suppress the generation of electrical noise. In this embodiment, a ring-shaped varistor 25 is mounted as an electrical noise prevention element. The charge to be discharged is accumulated in the ring-shaped varistor 25, so spark discharge and electrical noise are reduced. That is, the IC filter circuit (EMC circuit) plays a role in absorbing the electromagnetic waves generated between the carbon brushes and the commutator during commutation, and a filtering effect is observed in the low frequency band. On the other hand, the ring-shaped varistor works to suppress electrical noise in a wide frequency band by consuming the Joule heat generated by the surge generated between the carbon brushes and the commutator during commutation with the varistor.

[0027] Furthermore, according to this embodiment, the element accommodating space 28, i.e., the ring-shaped recess, is provided in the back side space of the carbon brush sliding portion, so that the ring-shaped varistor is not exposed outside in the radial direction of the commutator, and the dimensions of the commutator, particularly the radial dimension, are not increased, and it is possible to prevent the motor body from becoming larger. In other words, the element accommodating space can be configured without increasing the radial size of the motor body, and the mass balance of the motor armature becomes uniform.

[0028] Fig. 6A is a perspective view showing the inner and outer circumferential surfaces of an end cap having an electromagnetic shield layer in the first embodiment, and Fig. 6B is a perspective view showing the appearance of the end cap having an electromagnetic shield layer in the first embodiment. According to the embodiment of the present invention, the entire outer and inner surfaces of the cup-shaped end cap 20, which houses the ring-shaped varistor and EMC circuit 27 as an electrical noise prevention element, are each provided with electromagnetic shielding layers 202, 204. The plating of the earth wire groove 2740C in which the earth terminal 2740 of the capacitor 274 is held is performed simultaneously with plating of the electromagnetic shielding layers 202, 204. By providing plating layers on both sides with non-conductive resin in between, the electric field and magnetic field components that pass through the plating layer on the inner surface are absorbed and reflected by the plating layer provided on the outside. This provides a higher electromagnetic wave shielding effect.

[0029] In DC motors with commutators, non-conductive resin is generally used for the end caps that hold the carbon brushes fixed to the opening ends of the cylindrical metal frame. Therefore, the end cap itself generally has a lower shielding effect against electromagnetic waves than conductive metals, and when providing electromagnetic shielding, it is necessary to connect the earth terminal 2740 of the capacitor 274, which is used to remove the electromagnetic noise generated at the same time as the spark discharge, to the metal motor case 11.

[0030] According to an embodiment of the present invention, an electrical noise prevention element is connected in an element housing space provided on the end face of a commutator, which is a source of electromagnetic noise, and further, a coating layer for preventing conducted and radiated noise, formed of a conductive material, is provided on the outer peripheral surface of an end cap close to the source of electromagnetic noise, thereby blocking radiated noise and reducing the amount of radiated noise. That is, according to this embodiment, the earth terminal 2740 of the capacitor for removing spark discharge occurring between the carbon brush and the commutator is held in the earth wire groove 2740C provided on the outer circumferential surface of the end cap, and is fitted into an opening at one end of the motor case 11 which also serves as a conductive coating layer and an earth function. The earth terminal 2740 of the capacitor 274 is sandwiched between the conductive coating layer and the metal motor case 11, thereby completing the earth function and reliably shorting out the conductive noise generated by the spark discharge occurring between the carbon brush and the commutator of the small electric motor.

[0031] Next, the effect of reducing electromagnetic noise according to the first embodiment will be described with reference to FIG. In a DC motor with a commutator, the commutator 19 and carbon brushes 22 are the main noise sources, and when spark discharge occurs between the commutator and the carbon brushes during commutation, electromagnetic noise is conducted and radiated. This noise source generates differential mode noise between the power supply lines, and the noise source is connected in series with the power supply line, causing a noise current (conducted noise: Cn1) of 108 MH or less to flow in the same direction as the power supply current. In addition, noise current leaking from the brushes and commutator, which are noise sources, through stray capacitance, etc. as common mode noise is generated between the power supply and the reference ground (earth) as radiated noise (Rn1, Rn2) of 30 MHz to 2500 MHz. Furthermore, radiation noise (Rn3) of 30 MHz to 2500 MHz is generated from the EMC circuit 27, and further, radiation noise (Rn4) is generated between the wiring behind the EMC circuit 27 and the reference ground (earth). Also, conductive noise (Cn2) of 108 MHz or less that could not be suppressed by the CL filter circuit leaks to the ECU (Electronic Control Unit) 400 side of the automobile.

[0032] The EMC circuit 27 is provided with a capacitor (for low frequency band) as a countermeasure against noise in relatively low frequency bands such as the AM band, and a capacitor (for high frequency band) and a choke coil (inductance) of the EMC circuit 27 as a countermeasure against noise in relatively high frequency bands such as the FM band. Furthermore, the ring-shaped varistor 25 has a surge absorbing effect and is effective in suppressing noise from low to high frequency bands. By using the EMC circuit 27 and the ring-shaped varistor 25 together and providing end caps with electromagnetic shielding, an excellent noise suppression effect can be obtained for each of the conductive noises Cn1 and Cn2 and the radiated noises Rn1 to Rn4.

[0033] In particular, since the ring-shaped varistor 25 is provided in the element accommodating space 28 inside the commutator end close to the noise source, it is possible to efficiently absorb spark discharges and electromagnetic radiation between the commutator and brushes, which are noise sources, and to reduce the radiated noise emitted into the air from the commutator, brushes, brush holders, etc. Furthermore, since the ring-shaped varistor 25 is provided in close proximity to the noise source, the noise suppression effect is great and the ring-shaped varistor itself can be made small. Although the ring-shaped varistor itself is also a source of radiated noise, the secondary radiated noise from the ring-shaped varistor is reduced because the ring-shaped varistor can be made small. Furthermore, since the ring-shaped varistor 25 is provided in the element accommodating space inside the commutator end close to the noise source, the noise level flowing into the EMC circuit 27 is also low, and the capacitances of the L, C, and R components of the EMC circuit 27 can be small. Also, the L, C, and R sizes can be selected from small components. In this way, the capacitance of the EMC circuit 27 can be reduced, so that secondary radiation noise generated from the EMC circuit itself is reduced. In this way, the secondary radiation noise from the ring-shaped varistor and the secondary radiation noise generated from the EMC circuit itself can be reduced, thereby lowering the radiation noise level inside the end cap. Therefore, according to the first embodiment, the end cap with the electromagnetic shield can reliably block electromagnetic radiation, and prevent electromagnetic noise from being emitted to the outside.

[0034] Furthermore, the reduction in the capacity of the EMC circuit 27 leads to a reduction in the size of the circuit board, and makes it possible to reduce the size of the motor.

[0035] Furthermore, in this embodiment, the inner circumferential surface of the end cap, which is closer to the source of electromagnetic noise generated by the commutator and carbon brushes, is also plated, so that the noise radiated without flowing into the connector can be blocked by the inner circumferential surface of the end cap. In other words, by providing a conductive coating layer for preventing conducted and radiated noise on the inner circumferential surface of the end cap, which holds the carbon brushes, it becomes possible to block radiated noise closer to the noise source and minimize the spread of noise. This allows the area of ​​plating with conductive material to be reduced, which reduces material costs.

[0036] The small electric motor according to this embodiment, which generates little conducted and radiated noise, has little effect on the communication devices mounted on the automobile and is suitable as a small electric motor to be placed near the receiving unit, thereby making it possible to prevent malfunctions of the communication devices caused by conducted and radiated noise. EXAMPLES

[0037] Next, a second embodiment of the present invention, that is, a DC motor, will be described. Fig. 8 is a vertical cross-sectional view of a DC motor with a commutator having a coating layer for preventing conducted and radiated noise according to a second embodiment of the present invention. Fig. 9 is a diagram showing the relationship between a commutator 19 and a ring capacitor 26 serving as an electric noise prevention element. The second embodiment differs from the first embodiment in that a ring capacitor 26 is provided in the element accommodating space 28 inside the commutator end of the DC motor 10, and that an electromagnetic shielding layer 202 is provided on the entire outer circumferential surface of the cup-shaped end cap 20, with no electromagnetic shielding layer provided on the inner circumferential surface.

[0038] That is, the ring capacitor 26 has an annular substrate, for example, an annular printed circuit board 260, and a plurality of capacitors 262, six in this embodiment, mounted at equal intervals on one surface of the substrate, here the front surface (inner surface). The annular printed circuit board 260 is, for example, a glass fiber cloth impregnated with epoxy resin and subjected to a heat curing treatment to form a plate. That is, it is an FR (Flame Retardant). A copper foil pattern is formed on the back surface (outer surface) of the annular printed circuit board, as described later. Furthermore, on the outer peripheral surface 263 of the annular printed circuit board 260, at a position corresponding to the extension strip portion 191 of each commutator segment 190, there is a recessed outer peripheral portion where the outer peripheral surface 263 is recessed radially inward, and a first electrode 264 of each capacitor 262 is exposed here. The insulating cylindrical portion 24 has a cylindrical main body portion 240 to which each commutator segment 190 is fixed, and a hollow hole 243 for fixing this main body portion 240 to the rotating shaft 16 . The first electrode 264 of each capacitor is connected to one of the extended strip portions 191 of the corresponding commutator segment 190 via a fusion zone 300 formed by solder welding. Since the first electrode 264 is provided exposed in a recessed outer periphery of the outer periphery 263 of the annular printed circuit board 260, the connection position between the extended strip portion 191 and the first electrode 264 is maintained in a stable position, and the outer diameter of the extended strip portion 191 can be made the same as the outer diameter of the commutator segment 190. In addition, the recessed outer periphery of the outer periphery 263 functions as a positioning point during solder welding.

[0039] In this embodiment, the end face of the insulating cylindrical portion 24 opposite the armature winding side is defined as an outer end face 241, and the end face on the armature winding side is defined as an inner end face 242. On the side of the outer end face 241 of the commutator 19, there is an annular recess surrounded by this outer end face 241 and the extended strip portions 191 of each commutator segment 190, i.e., an element accommodating space 28. Within this element accommodating space 28, one ring capacitor 26 is fixed.

[0040] FIG. 10A is a front view of a commutator with a ring capacitor in the second embodiment, and FIG. 10B is a circuit diagram showing the electrical connection relationship between the armature windings and the commutator with a ring capacitor. Each copper foil pattern 29 is a pattern resembling a sector in which one ring is divided into six parts, and is provided corresponding to each capacitor. The first electrodes 264 of the capacitors 262 are connected to the commutator segments 190 of the commutator 19 by solder welding. The second electrodes 265 of the capacitors 262 are connected to the corresponding copper foil patterns 29. 11 is a perspective view showing the appearance of the end cap 20 in the second embodiment. An electromagnetic shield layer 202 is provided only on the outer peripheral surface of the end cap 20.

[0041] According to an embodiment of the present invention, an electrical noise prevention element is connected in an element housing space provided on the end face of a commutator, which is a source of electromagnetic noise, and further, an electromagnetic shield layer 202 for preventing conducted and radiated noise, which is made of a conductive material, is provided on the outer peripheral surface of an end cap close to the source of electromagnetic noise, thereby blocking radiated noise and reducing the amount of radiated noise. In other words, the ring capacitor 26 serves to suppress electrical noise in a frequency band according to the frequency characteristics of the capacitor by dissipating the Joule heat generated by a surge that occurs between the carbon brushes and the commutator during commutation. Moreover, the electromagnetic shield layer 202 applied to the entire outer periphery of the end cap is effective in reducing common mode noise.

[0042] In this embodiment, the secondary radiation noise from the ring capacitor and the secondary radiation noise generated by the EMC circuit itself can be reduced, so the radiation noise level inside the end cap can be lowered. Therefore, the end cap with an electromagnetic shield can reliably block electromagnetic radiation and prevent electromagnetic noise from being emitted to the outside. EXAMPLES

[0043] Next, a DC motor according to a third embodiment of the present invention will be described. Fig. 12 is an exploded vertical cross-sectional view of a commutator-equipped DC motor 10, in which the outer circumferential surfaces of the end caps and the inner circumferential surface of the encoder cap are provided with conductive coating layers. The basic structure of this DC motor 10 is the same as that shown in Fig. 1. A ring-shaped varistor 25 is fixed integrally to the commutator 19 fixed to the rotating shaft 16, forming a commutator with a ring-shaped varistor. Fig. 13 is an enlarged vertical cross-sectional view of the end cap and rotary encoder of the DC motor 10 shown in Fig. 12. Fig. 14 is a circuit diagram showing the electrical connection relationship between the armature winding, the commutator with ring-shaped varistor, and the rotary encoder in the third embodiment. In the third embodiment, a rotary encoder is further provided on the outside of the end cap of the commutator-equipped DC motor 10. That is, the right end of the rotating shaft 16 is supported by a bearing provided in the end cap 20, and a disk-shaped magnet 512 having a pair of N and S poles is fixed to the end surface of the rotating shaft 16. An encoder board 510 is fixed inside an encoder cap 500 that covers the end cap 20. On the encoder board 510, at a position facing the magnet 512, a signal processing circuit 514 is provided that converts an analog signal that changes with the rotation of the magnet 512 detected by the magnetoresistance element 516 into a digital signal and outputs the digital signal. An encoder signal generating circuit 530 that processes the signal from the magnetoresistance element 516 to generate, for example, incremental information on the rotation angle and rotation direction of the rotating shaft 16 is provided on the outside of the encoder cap 500. This encoder signal generating circuit 530 may be provided on the encoder board 510.

[0044] A conductive electromagnetic wave coating layer is formed on an inner peripheral surface 522 of the encoder cap 500. Furthermore, electromagnetic shield layers 202 and 204 are formed on the outer peripheral surface and inner peripheral surface of the end cap 20, respectively. Furthermore, a ground terminal 2740d provided on the outer peripheral surface of the end cap 20 is configured to come into contact with the inner peripheral surface 522 of the encoder cap 500. An EMC circuit 27 (not shown) as shown in the previous embodiment is provided inside the encoder cap 500.

[0045] Since the ring-shaped varistor is provided in the space inside the commutator end, it can absorb a large amount of spark discharge and electromagnetic radiation between the commutator and the brushes, and since the ring-shaped varistor is compact, radiation to the outside from these is reduced. Furthermore, by providing conductive coating layers 202, 204 on the outer and inner peripheral surfaces of the end caps and providing an EMC circuit 27, electromagnetic noise generated from the carbon brushes is blocked. Furthermore, by covering the outer peripheral surface 205 of the end cap and the inner peripheral surface of the encoder cap 500 with a conductive coating layer, electromagnetic noise generated from the surface of the encoder board 510 installed outside the end cap is also blocked. Furthermore, the contact between the earth terminal 2740d in the EMC circuit and the conductive coating layer on the inner peripheral surface 522 of the encoder cap 500 enhances the earth function. This further improves the CL filter function incorporated in the EMC circuit 27, and the effect of reducing common mode noise is recognized. EXAMPLES

[0046] A composite magnetic material formed by dispersing and mixing metal magnetic powder in resin and forming it into a sheet may be attached to the outer peripheral surface of the end cap 20 on which the electromagnetic coating shown in Example 1 or Example 2 is formed. This makes it possible to effectively suppress recent high-frequency noise exceeding 1 GHz using electrical noise prevention elements such as varistors, resistors, and thick-film integrated circuits. In addition, the frequency band of the actually generated radiation noise can be measured, and then the corresponding frequency band of the electromagnetic wave absorbing sheet can be selected. In addition, whether the electromagnetic shielding layer is provided on the outer peripheral surface or on the inner and outer peripheral surfaces of the end cap, and whether the electrical noise prevention element fixed within the element accommodating space is a ring-shaped varistor or a ring capacitor may be adopted in any appropriate combination depending on the application. [Explanation of symbols]

[0047] 10 DC motor 11 Motor case 16 Rotation Axis 17 Armature Winding 19 Commutator 190 Commutator Segment 191 Extension strip section 20 End Cap 22 Carbon Brush 24 Insulating cylindrical part 241 Outer end face 25 Ring-shaped varistor 26 Ring Condenser 27 EMC circuit 274 Capacitor 2740C Earth Wire Groove 28 Element housing space 202 Electromagnetic Shielding Layer 204 Electromagnetic Shielding Layer 300 Welded joint by solder welding 500 Encoder cap.

Claims

1. A metal motor case having an opening at one end and also serving as an earthing function; a rotating shaft rotatably supported within the motor case; An end cap made of a non-conductive resin and fixed to the motor case; a commutator fixed to the rotating shaft, the commutator having a plurality of commutator segments connected to an armature winding; A carbon brush that is in sliding contact with the commutator; A brush holder held by the end cap; an electrical noise suppression element connected to the commutator; A DC motor having an EMC circuit connected between terminals, The commutator is a cylindrical insulating tubular portion made of an insulating material and having an inner end surface and an outer end surface; the plurality of commutator segments are made of a conductive material and fixed to an outer periphery of the insulating cylindrical portion at a distance from each other, Each of the commutator segments has a connection portion with the armature winding at a position corresponding to an outer circumferential side of the inner end surface of the insulating cylindrical portion, Each of the commutator segments is integrally provided with an extension strip portion at a position corresponding to an outer circumferential side of the outer end surface, the extension strip portion extending outward from the outer end surface in the same direction as the rotation axis and having a width shorter than a circumferential length of the commutator segment, the extension strip portions of the plurality of commutator segments, the insulating cylindrical portion, and the outer end surface of the commutator form a recessed element accommodating space, The electrical noise prevention element has a plurality of electrodes, In the element accommodating space, any one of the plurality of electrodes of the electric noise prevention element and any one of the extension strip portions are integrally connected to each other by a fusion zone formed by solder welding, a coating layer formed of a conductive material for preventing conducted and radiated noise is provided on the entire outer and inner peripheral surfaces of the end cap; the commutator, the carbon brushes, the brush holder, the electrical noise prevention element, and the EMC circuit are disposed inside the end cap; the coating layer on the outer circumferential surface of the end cap is fitted into the opening of the motor case, A small DC motor, characterized in that an earth terminal of a capacitor of the EMC circuit is sandwiched and fixed between the coating layer provided on the outer peripheral surface of the end cap and the opening of the motor case.

2. 2. The DC motor according to claim 1, a coating layer formed on the outer peripheral surface and the inner peripheral surface of the end cap, the coating layer being an electromagnetic shielding layer formed of a plating layer having a multi-layer structure of copper and nickel.

3. 3. The DC motor according to claim 1, 2. A small DC motor, wherein the electrical noise prevention element is a ring-shaped varistor or a ring capacitor.

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