JP2014195395A - DC motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC motor capable of satisfying a desired motor service life using an appropriate varistor.SOLUTION: The DC motor includes a varistor for suppressing generation of sparks between a brush and a commutator. The varistor has an Evalue of 13-18.4 V and an electrostatic capacitance, at 1 MHz measurement between adjacent electrodes, of not less than 7.5 nF×N (N=(n/n), where nis the number of commutator segments provided in the DC motor and the number of electrodes of the varistor is n). The brush is a metal brush. The DC motor is configured so that a stalling current Is is at least 2 A.

Description

  The present invention relates to a DC motor.

  Conventionally, DC motors have been used as drive sources for various devices and products. For example, it is employed in office appliances such as printers and copiers, various home appliances such as electric shavers, and various electric parts for automobiles (such as steering lock).

  A DC motor having a brush is slidably contacted with a rotating commutator to switch the direction of the rotor while passing a current through a winding of the rotor. In such a motor, sparks are generated by a high voltage induced by the intermittent connection of the commutator during rotation, which causes wear of the brush / commutator and generation of noise. Therefore, a DC motor equipped with a varistor is known to suppress these phenomena.

A varistor used for a DC motor is generally selected on the basis of a voltage at which a current of 10 mA flows through the varistor (hereinafter referred to as “E ₁₀ value” as appropriate). For example, when the driving voltage is the motor of _{12V, E 10} value is varistor 13~16.5V are used.

As a motor using such a varistor, and a commutator and ceramic varistor a plate Baneburashi, small DC motors E ₁₀ value of ceramic varistors is to be equal to or less than 3 times 1.5 times the driving voltage of the motor (See Patent Document 1).

JP 11-285220 A

Incidentally, the present inventors have studied intensively, in the DC motor using a varistor of the same kind of E ₁₀ value is included in the desired range, the purpose of use of the motor, a large variation occurs in the life of the motor I found. Therefore, the selection using only conventional E ₁₀ value it may be difficult to appropriately selecting the desired varistor.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a DC motor that satisfies a desired motor life using an appropriate varistor.

In order to solve the above problems, a DC motor according to an aspect of the present invention includes a varistor that suppresses the generation of a spark between a brush and a commutator. Varistor _{is E 10} value is 13~18.4V, _{n 1} the number of commutator pieces capacitance at 1MHz measurement between adjacent electrodes is provided in the 7.5nF × N (the DC motor, varistor electrodes When the number is n ₂ , N = (n ₁ / n ₂ )) or more. Here, the electrodes of the varistor to be measured may be between any adjacent electrodes.

  According to this aspect, spark wear between the brush and the commutator is reduced, and the life of the motor is improved.

  The DC motor may be configured assuming use in forward rotation operation and reverse rotation operation. Here, “use in forward rotation operation and reverse rotation operation” includes not only the operation of being able to rotate in both directions but also the case where a configuration according to the application is made. For example, this is a case where the position of the slit of the brush or commutator piece is not set to a position where it is positively advanced or retarded (so-called neutral position).

Another aspect of the present invention is also a DC motor. This DC motor includes a varistor that suppresses the generation of sparks between the brush and the commutator. The varistor has a capacitance of 7.5 nF × N when measuring 1 MHz between adjacent electrodes (N = (n when the number of commutator pieces provided in the DC motor is n ₁ and the number of electrodes of the varistor is n _{2). 1} / n ₂ )) or more. The DC motor is configured assuming use in forward rotation and reverse rotation. Here, the electrodes of the varistor to be measured may be between any adjacent electrodes.

  According to this aspect, spark wear between the brush and the commutator is reduced, and the life of the motor is improved.

  The stationary current Is may be configured to be 2 A or more. In applications where high input is assumed in this way, the effect of reducing spark wear is further increased.

  The brush may be a metal brush. As for the commutator, the sliding part with a brush may be comprised with the silver containing metal. The varistor may be a disk-shaped ceramic varistor.

  It should be noted that any combination of the above-described constituent elements and a representation of the present invention converted between a method, an apparatus, a system, etc. are also effective as an aspect of the present invention.

  According to the present invention, an appropriate varistor can be selected regardless of the intended use of the motor. Thereby, the spark wear between the brush and the commutator is reduced, and the life of the motor can be improved.

It is a partially broken sectional view of the DC motor according to the present embodiment. It is the schematic diagram which expanded the sliding part vicinity of a brush and a commutator. It is a schematic diagram for demonstrating the contact state of the brush and commutator which looked at the rotor from the axial direction of the shaft. FIG. 4 (a) is a diagram schematically showing spark wear generated between the brush and the commutator, FIG. 4 (b) is a diagram schematically showing a wear point of the brush, and FIG. 4 (c) is a diagram. It is the figure which showed typically the wear location of the commutator. FIG. 5A is an enlarged view of a worn part of the brush in the contact region between the brush and the commutator in FIG. 4A, and FIG. 5B is a contact region between the brush and the commutator in FIG. It is an enlarged view of the wear part of a commutator. It is a figure which shows the relationship between the abrasion depth of a negative brush at the time of a wear test of DC motor, and the electrostatic capacitance of a varistor. It is a figure which shows the relationship between the abrasion depth of a commutator at the time of a wear test of DC motor, and the electrostatic capacitance of a varistor. It is a figure which shows the relationship between the abrasion depth of a negative brush at the time of carrying out the abrasion test supposing use with an electric shaver, and the electrostatic capacitance of a varistor. It is a figure which shows the relationship between the abrasion depth of a commutator, and the electrostatic capacitance of a varistor at the time of carrying out the abrasion test supposing use with an electric shaver. It is a schematic diagram which shows the state which the positional relationship of a brush and a commutator is an advance angle position. It is a figure which shows the relationship between the wear depth of a negative brush, and the electrostatic capacitance of a varistor at the time of carrying out the wear test of six DC motors from which stationary current Is differs. It is a figure which shows the relationship between the abrasion depth of a commutator, and the electrostatic capacitance of a varistor at the time of carrying out the abrasion test of six DC motors from which stationary current Is differs. FIG. 13A is a partially broken sectional view of a DC motor according to a modification of the present embodiment, and FIG. 13B is an enlarged view of an R region in FIG. It is a figure which shows the result of having performed the predetermined life test about the motor using the varistor from which electrostatic capacitance differs. FIG. 15 is a schematic diagram illustrating a state where the positional relationship between the brush and the commutator is a neutral position. It is a figure which shows an example of the circuit structure of the DC motor shown in FIG. FIG. 17A is a top view of a disk varistor having three electrodes, and FIG. 17B is a top view of a disk varistor having six electrodes. It is a figure which shows an example of the circuit structure of the DC motor shown in FIG. It is a figure which shows the modification of the circuit structure of the DC motor shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. Moreover, the structure described below is an illustration and does not limit the scope of the present invention at all.

(DC motor)
FIG. 1 is a partially broken sectional view of a DC motor according to the present embodiment. FIG. 2 is an enlarged schematic view of the vicinity of the sliding portion between the brush and the commutator. A DC motor 10 shown in FIG. 1 is a two-pole three-groove motor, and one or a plurality of magnets 14 are arranged on the inner wall of a cylindrical housing 12. The magnet 14 is arranged so that the magnetic poles (N pole and S pole) are located inside, and the N pole and the S pole are alternately arranged along the circumferential direction of the inner wall of the housing 12.

  A rotor 16 is disposed at the center of the housing 12. The rotor 16 includes a shaft 18, a core 20, a winding 22, a commutator (commutator) 24, and a varistor 26. The shaft 18 is a rotating shaft that supports the rotor 16 via bearings 28a and 28b. The shaft 18 also functions as an output shaft.

  The core 20 is formed by laminating a plurality of steel plates, and the shaft 18 is fixed in a state where the shaft 18 passes through the core 20. The winding 22 is wound around the groove 20a of the core 20, and generates a magnetic force when a current flows.

  The commutator 24 is fixed to the shaft 18 similarly to the core 20. The commutator 24 is a contact that allows a current passed through the contacting brush 30 to flow through the winding 22 at an appropriate timing. The brush 30 is, for example, a fork-shaped metal brush whose main component is a noble metal or the like. Further, a damper (arranged on the back side of the paper: not shown) is attached to the flexible portion of the brush 30. The brush may be a carbon brush. On the other hand, as for the commutator 24, the sliding part with the brush 30 is comprised with the silver containing metal, for example.

  The brush 30 is fixed to the brush holder 34 while being connected to a brush base 32 serving as a terminal. The brush holder 34 is mounted in the housing 12. Then, the opening of the housing 12 is covered with the end bell 36.

  The varistor 26 is disposed between the core 20 and the commutator 24, and is an element that suppresses the generation of sparks between the commutator 24 and the brush 30 and reduces spark wear. As the varistor 26, for example, a disk-shaped ceramic varistor is used.

  FIG. 3 is a schematic diagram for explaining a contact state between the brush and the commutator when the rotor is viewed from the axial direction of the shaft. As shown in FIG. 3, the commutator 24 includes three commutator pieces 24a, 24b, and 24c. In FIG. 3, one brush 30a of the pair of brushes 30 is in contact with one commutator piece 24a, and the other brush 30b is in contact with the other one commutator piece 24b. Then, when the commutator 24 rotates, the commutator pieces that come into contact with the brushes 30a and 30b are switched, and rectification is performed.

  Next, spark wear between the brush and the commutator will be described. FIG. 4 (a) is a diagram schematically showing spark wear generated between the brush and the commutator, FIG. 4 (b) is a diagram schematically showing a wear point of the brush, and FIG. 4 (c) is a diagram. It is the figure which showed typically the wear location of the commutator.

  As shown in FIG. 4A, in the contact portion 38 between the commutator 24 and the brush 30, a spark is generated when one commutator piece that has been in contact with the brush 30 is separated by the rotation of the rotor. There is. As a result, as shown in FIG. 4B, the contact portion 40 of the brush 30b is worn. In addition, as shown in FIG. 4C, wear also occurs in a partial region 42 of the outer region of the commutator 24. As a result of intensive studies by the present inventors, it has been found that such wear can be improved by using a varistor 26 having appropriate characteristics.

  First, the definition of the wear depth will be described. 5A is an enlarged view of a worn portion of the brush 30b in the contact area between the brush 30b and the commutator 24 in FIG. 4A, and FIG. 5B is a diagram of the brush 30b and the commutator 24 in FIG. 4A. It is an enlarged view of the wear part of the commutator 24 in a contact area | region.

  The wear depth d1 shown in FIG. 5A is a value in a region where the wear caused by the occurrence of a spark or the like is deepest in the sliding portion of the brush 30b. The wear depth d2 shown in FIG. 5 (b) is the value of the deepest region in the sliding portion of the commutator piece 24b where wear caused by the occurrence of a spark or the like is the deepest in the radial direction of the commutator.

  The present inventors have found that the wear depth d1 of the brush 30b and the wear depth d2 of the commutator 24 greatly depend on the motor configuration and the characteristics of the varistor. Hereinafter, an appropriate varistor configuration and motor configuration will be described based on the test results.

  FIG. 14 is a diagram showing a result of a predetermined life test performed on a motor using varistors having different capacitances. Group L varistors have a capacitance of 2.5 to 3.4 nF when measuring 1 MHz between any adjacent electrodes, and Group H varistors are used when measuring 1 MHz between any adjacent electrodes. Capacitance is 7.5 to 8.5 nF. The measurement voltage of the capacitance was 1 Vrms. Further, a general LCR meter was used for the measurement. The life test was conducted in a mode that assumed the operation of the steering lock, which is one of the electrical components of the automobile.

  The test condition is that each varistor is attached to a DC motor, and the voltage is set to 13 V at normal temperature and the load is energized. The load was about 180 g · cm. The energization conditions were such that the motor was rotated in one direction and 0.2 s energization and 7.3 s stop (when stopped, with short brake) were continuously performed up to 38000 cycles (mode 1). If the wear of the brush or commutator exceeds the allowable amount before reaching 38000 cycles in mode 1, the number of cycles up to that time becomes the lifetime.

  When the intermittent rotation operation in one direction of the motor reaches 38000 cycles, the energization condition is changed so that the motor rotates in the other direction. Specifically, it is energized in a load state with a voltage of 14 V at room temperature. The load was about 21 g · cm. The energization conditions at this time were such that the motor was rotated in the other direction, and energization for 0.3 s and 2.7 s stop (when stopped, with short brake) were continuously performed up to 38000 cycles (mode 2). If the wear of the brush or commutator exceeds the allowable amount before reaching 38000 cycles in mode 2, the number of cycles up to that including the number of cycles in mode 1 becomes the lifetime.

  Then, while repeating mode 1 and mode 2 alternately, a life test was performed until the wear of the brush and the commutator exceeded an allowable amount. As a result, as shown in FIG. 14, in a motor using a varistor of group L (capacitance is 2.5 to 3.4 nF) having a relatively low capacitance at 1 MHz measurement (number of samples N = 3). The number of cycles was 33000 cycles, 33000 cycles, and 26000 cycles. On the other hand, in a motor using a varistor of group H (capacitance is 7.5 to 8.5 nF) having a relatively high electrostatic capacity at 1 MHz measurement, the number of cycles is 152,000 cycles, 221,000 cycles, 165000. From these results, it is expected that the difference in the electrostatic capacity of the varistor at the time of 1 MHz greatly affects the life of the motor (the wear life of the brush and the commutator).

  In the motor used in this life test, the position of the commutator is set to be neutral (a position that is neither an advance angle nor a retard angle). FIG. 15 is a schematic diagram illustrating a state where the positional relationship between the brush and the commutator is a neutral position. As shown in FIG. 15, the rotor 16 is configured such that the phase of the slit 24 d of the commutator 24 and the magnetic pole of the core 20 are the same in the rotational direction. That is, the DC motor including such a rotor is configured assuming use in forward rotation operation and reverse rotation operation.

(Abrasion test 1)
FIG. 6 is a diagram showing the relationship between the wear depth of the negative brush and the capacitance of the varistor when a DC motor is subjected to a wear test. FIG. 7 is a diagram showing the relationship between the wear depth of the commutator and the capacitance of the varistor when a DC motor is subjected to a wear test. The DC motor used for the test has, for example, a configuration shown in FIG. 13 to be described later, and is used for driving a vehicle electrical component (for example, a steering lock mechanism), and has a stationary current Is of about 2.6A. Here, the stationary current Is is a current value when the rotation of the motor is stopped by increasing the load of the rotating motor.

The abrasion test was performed under the following conditions. _{First, E 10} value was prepared varistor of 13~18.4V. And the electrostatic capacitance between the arbitrary adjacent electrodes of each varistor was measured at 1 MHz, and it divided into seven groups (AG) according to the electrostatic capacitance. Group A has a capacitance of 2.5 to 3.4 nF (when omitted at 1 MHz, hereinafter omitted), Group B has a capacitance of 4.2 to 4.8 nF, and Group C has a static capacitance. Capacitance between 5.1 and 5.5 nF, Group D with capacitance between 5.6 and 6.1 nF, Group E with capacitance between 6.6 and 7.0 nF, Group F Capacitance is 7.5 to 8.0 nF, and Group G has a capacitance of 8.0 to 8.5 nF. The measurement voltage of the capacitance was 1 Vrms. Further, a general LCR meter was used for the measurement. The number of samples N in each group is 3.

  Then, each varistor is mounted on a DC motor, and the voltage is set to 13 V at normal temperature and energized in a loaded state. The load was about 180 g · cm. The energization conditions were such that the motor was rotated in one direction and 0.2s energization and 7.3s stop (when stopped, with short brake) were performed 20000 cycles. The current at the time of load at that time is about 1.9A. Then, the negative brush 30b and the commutator 24 were taken out from each motor, the wear depths d1 and d2 were measured, and the range and average value were calculated for each group.

  As shown in FIG. 6, the wear depth d1 of the negative brush is very large in the case of a DC motor using a varistor of group A to group E (capacitance is 7 nF or less), and is about 75 μm. On the other hand, in the DC motor using the varistors of groups F and G (capacitance is 7.5 nF or more) whose capacitance exceeds 7 nF, the wear depth d1 of the negative brush is very small, It is about 20-25 micrometers.

  Further, as shown in FIG. 7, the wear depth d2 of the commutator is very large in the case of a DC motor using a varistor of group A to group E (capacitance is 7 nF or less), and is about 70 to 80 μm. . On the other hand, in the DC motor using the varistors of groups F and G (capacitance is 7.5 nF or more) whose capacitance exceeds 7 nF, the wear depth d2 of the commutator is very small. ˜40 μm.

  As described above, there is a case where the degree of wear of the brush and the commutator is greatly different even though the varistor having the constant E10 value is used. That is, it can be seen that the wear of the brush and the commutator does not depend much on the E10 value alone.

That _{is E 10} value is 13～18.4V, the capacitance is greater than 7.0NF (more preferably at least 7.5NF) The DC motor using a varistor, spark wear of the commutator 24 and the negative brushes 30b Since it is reduced to about 1/2 to 1/3, the life of the motor is improved.

(Abrasion test 2)
Next, the case of the abrasion test 2 which is a test condition different from the abrasion test 1 will be described. FIG. 8 is a diagram showing the relationship between the wear depth of the negative brush and the capacitance of the varistor when the DC motor is subjected to a wear test assuming use with an electric shaver. FIG. 9 is a diagram showing the relationship between the wear depth of the commutator and the capacitance of the varistor when a wear test is performed assuming that the DC motor is used in an electric shaver. The DC motor used for the test has, for example, the configuration shown in FIG. 1, and the stationary current Is is about 7A.

  In the motor used here, the position of the commutator is set as an advance angle. FIG. 10 is a schematic diagram showing a state in which the positional relationship between the brush and the commutator is an advance position. As shown in FIG. 10, the rotor 16 is configured such that the slit 24 d of the commutator 24 is at a position advanced by an angle θ with respect to the phase of the magnetic pole of the core 20 in the rotational direction. That is, the DC motor provided with such a rotor is configured assuming use in one direction.

The abrasion test was performed under the following conditions. _{First, E 10} value was prepared varistor of about 1.5~3.5V. And the electrostatic capacitance between the arbitrary adjacent electrodes of each varistor was measured at 1 MHz, and it divided into four groups (A'-D ') according to the electrostatic capacitance. Group A ′ has a capacitance of about 25 nF, Group B ′ has a capacitance of about 17 nF, Group C ′ has a capacitance of about 11 nF, and Group D ′ has a capacitance of about 6 nF. Is. Group E ′ is a case where there is no varistor. The measurement voltage of the capacitance was 1 Vrms. Further, a general LCR meter was used for the measurement. The number of samples N in each group is 3.

  Then, each varistor (group A ′ to D ′) is mounted on a DC motor, and the voltage is set to 1.1 V at room temperature and energized in a load state. The load was about 13 g. The energization conditions were such that the motor was rotated in one direction, and energized for 120 s and stopped for 2 s (when stopped, no short brake) for 2200 cycles. The current at the time of load at that time is about 1.9A. Then, the negative brush 30b and the commutator 24 were taken out from each motor, the wear depths d1 and d2 were measured, and the range and average value were calculated for each group.

  As shown in FIG. 8, the negative brush wear depth d1 is the DC motor using a varistor of group D ′ (capacitance of about 6 nF) or a varistor is not used (group E ′). In this case, it is large and about 30 μm. On the other hand, in a DC motor using a varistor of groups A ′ to C ′ (capacitance is 7.5 nF or more, more preferably 11 nF or more) whose electrostatic capacity exceeds 6 nF, negative brush wear The depth d1 is small and is about 20 μm.

  Further, as shown in FIG. 9, the wear depth d2 of the commutator is very large in the case of a DC motor that does not use a varistor (group E ′), and exceeds 100 μm. On the other hand, in the DC motor using the varistors of groups A ′ to D ′ (capacitance is 6 nF or more) whose electrostatic capacity exceeds 6 nF, the wear depth d2 of the commutator is very small, 20 μm. Degree.

_{That, E 10} value is 1.5～3.5V, capacitance greater than 6.0NF (more preferably at least 7.5NF) a DC motor using varistor, forward operation or reverse operation Even if it is configured to be used only in any one of the rotation directions, since the spark wear of the commutator 24 and the brush 30 is reduced, the life of the motor is improved.

(Abrasion test 3)
Next, a wear test was performed on six types of DC motors having different stationary currents Is using varistors having different capacitances. FIG. 11 is a diagram showing the relationship between the wear depth of the negative brush and the capacitance of the varistor when six DC motors having different stationary currents Is are subjected to wear tests. FIG. 12 is a diagram illustrating the relationship between the wear depth of the commutator and the capacitance of the varistor when six DC motors having different quiescent currents Is are subjected to a wear test. The DC motor used for the test has, for example, a configuration shown in FIG. 13 to be described later, and is used for driving a vehicle electrical component (for example, a steering lock mechanism).

  The motor M1 has a stationary current Is of 1.5A, the motor M2 has a stationary current Is of 1.8A, the motor M3 has a stationary current Is of 2A, the motor M4 has a stationary current Is of 2.2A, and the motor M5 has stopped. The dynamic current Is is 2.4A, and the motor M6 has a stationary current Is of 3A. For each motor, group L (capacitance 2.5 to 3.5 nF) and group H (capacitance 7.5 nF to 8.3 nF) having different capacitances when measuring 1 MHz between any adjacent electrodes A wear test was conducted using a varistor. The measurement voltage of the capacitance was 1 Vrms. Further, a general LCR meter was used for the measurement. The number N of motor samples using the varistors of each group is 3.

  The abrasion test was performed under the following conditions. First, a varistor having an E10 value of 13 to 18.4 V is prepared, each varistor is mounted on a DC motor, and a voltage is set to 13 V at room temperature and energized in a loaded state. The energization conditions were such that the motor was rotated in one direction, and energized for 0.2 s and stopped for 7.3 s (when stopped, with a short brake) for 10,000 cycles. In this case, the load current is about 0.6A. Then, the negative brush 30b and the commutator 24 were taken out from each motor, the wear depths d1 and d2 were measured, and the range and average value were calculated for each group.

  As shown in FIG. 11, the wear depth d1 of the negative brush is determined by using either a group L or a group H varistor in the motor M1 (Is = 1.5A) or the motor M2 (Is = 1.8A). However, there was no significant difference in wear depth. On the other hand, in the motor M3 to the motor M6 (Is = 2A to 3A), the wear depth is reduced when the group H varistor is used rather than the group L. In particular, in the motor M6 (Is = 3A), the wear depth decreases more significantly when the group H varistor is used than when the group L is used.

  Further, as shown in FIG. 12, the wear depth d2 of the commutator is a varistor of either group L or group H in the motor M1 (Is = 1.5A) or the motor M2 (Is = 1.8A). However, there was no significant difference in wear depth. On the other hand, in the motor M3 to the motor M6 (Is = 2A to 3A), the wear depth is reduced when the group H varistor is used rather than the group L. In particular, in the motor M6 (Is = 3A), the wear depth decreases more significantly when the group H varistor is used than when the group L is used.

  Thus, like a DC motor configured such that the stationary current Is exceeds 1.5 A, more preferably, a DC motor configured so that the stationary current Is is 2.0 A or more, In applications where high input is assumed, the effect of reducing spark wear is further enhanced by using a varistor having a capacitance of 7.5 nF or more when measuring 1 MHz between any adjacent electrodes.

  As described above, in the case of a DC motor configured such that the stationary current Is is 2 A or more and a metal brush is used, the wear does not depend only on the E10 value, and 1 MHz between any adjacent electrodes. It turns out that it depends on the electrostatic capacitance (7.5 nF or more) at the time of measurement.

  Next, a modified example of the DC motor will be described. FIG. 13A is a partially broken sectional view of a DC motor according to a modification of the present embodiment, and FIG. 13B is an enlarged view of an R region in FIG.

  The DC motor 110 shown in FIGS. 13A and 13B is greatly different from the DC motor 10 shown in FIG. 1 in that it is a 4-pole 6-groove motor. The DC motor 110 has one or more magnets 114 arranged on the inner wall of a cylindrical housing 112. The magnet 114 is arranged so that the magnetic poles (N pole and S pole) are located inside, and the N pole and the S pole are alternately arranged along the circumferential direction of the inner wall of the housing 112.

  A rotor 116 is disposed at the center of the housing 112. The rotor 116 includes a shaft 118, a core 120, a winding 122, a commutator (commutator) 124, and a varistor 126. The shaft 118 is a rotating shaft that supports the rotor 116 via bearings 128a and 128b. The shaft 118 also functions as an output shaft.

  The core 120 is formed by laminating a plurality of steel plates, and the shaft 118 is fixed in a state where the shaft 118 passes through the core 120. The winding 122 is wound around the groove 120a of the core 120, and generates a magnetic force when a current flows.

  The commutator 124 is fixed to the shaft 118 similarly to the core 120. The commutator 124 is a contact that allows a current supplied through the contacting brush 130 to flow through the winding 122 at an appropriate timing. The brush 130 is, for example, a fork-shaped metal brush whose main component is a noble metal. A damper 131 is attached to the flexible part of the brush 130. The brush may be a carbon brush. On the other hand, in the commutator 124, for example, a sliding portion with the brush 130 is made of a silver-containing metal.

  The brush 130 is fixed to the brush holder 134 while being connected to a brush base 132 serving as a terminal. The brush holder 134 is mounted in the housing 112. Then, the opening of the housing 112 is covered with the end bell 136.

  The varistor 126 is disposed between the core 120 and the commutator 124, and is an element that suppresses the generation of sparks between the commutator 124 and the brush 130 and reduces spark wear. For the varistor 126, for example, a disk-shaped ceramic varistor is used.

Next, the relationship between the number of electrodes of the varistor and the number of commutator pieces and a suitable capacitance of the varistor will be described. For example, in the DC motor 10 shown in FIG. 1, the number of commutator pieces n ₁ is 3, and the number of electrode varistors n ₂ is 3. FIG. 16 is a diagram illustrating an example of a circuit configuration of the DC motor 10 illustrated in FIG. 1. FIG. 17A is a top view of a disk varistor having three electrodes, and FIG. 17B is a top view of a disk varistor having six electrodes.

  FIG. 16 illustrates a case where the three-pole disk varistor shown in FIG. The disk varistor according to the present embodiment is mainly composed of strontium titanate, for example. Since strontium titanate has a high dielectric constant, it is used as a capacitor varistor.

In the commutator 24, a part of each commutator piece 24a, 24b, 24c and each electrode 26a, 26b, 26c of the varistor 26 are connected. Each electrode is formed in an arc shape with a gap therebetween. Further, the other part of the commutator 24 and the winding 22 are connected. More specifically, the winding 22a is connected between the commutator piece 24a and the commutator piece 24b, and the winding 22b is connected between the commutator piece 24b and the commutator piece 24c, and the commutator piece 24c and the commutator piece. A winding 22c is connected to 24a. The varistor 26 shown in FIG. 17A has an outer diameter of about 10 to 11 mm and an inner diameter of about 6 to 7 mm. The area per electrode of the varistor 26 is about 12.6 mm ² .

  FIG. 18 is a diagram illustrating an example of a circuit configuration of the DC motor 110 illustrated in FIG. 13. FIG. 18 illustrates a case where the 6-pole disc varistor shown in FIG. 17B is used.

  The commutator 124 includes arc-shaped commutator pieces 124a, 124b, 124c, 124d, 124e, and 124f obtained by dividing a cylinder into six in the rotation direction. The winding 122 includes six windings 122a, 122b, 122c, 122d, 122e, and 122f wound around the six teeth of the core 120. The varistor 126 includes six arc-shaped electrodes 126a, 126b, 126c, 126d, 126e, and 126f that are provided with a gap therebetween.

In the commutator 124, a part of each commutator piece 124a, 124b, 124c, 124d, 124e, 124f and each electrode 126a, 126b, 126c, 126d, 126e, 126f of the varistor 126 are connected. Further, the other part of the commutator 124 and the winding 22 are connected. More specifically, the windings 122a and 122d are connected between the commutator piece 124a and the commutator piece 124e, and the windings 122b and 122e are connected between the commutator piece 124b and the commutator piece 124f. Windings 122c and 122f are connected between 124c and the commutator piece 124d. Note that the varistor 126 shown in FIG. 17B has an outer diameter of about 8.6 mm ± 0.2 mm and an inner diameter of about 4.9 mm ± 0.1 mm. The area per electrode of the varistor 126 is about 6.3 mm ² . In order to increase the capacitance of the varistor, the area per electrode may be increased, but the varistor becomes larger. Therefore, preferably, the area per electrode of the varistor 126 is 6.3 mm ² or less.

As shown in FIGS. 16 and 18, the number _{n 1} and the number of electrodes of the varistor _{n 2} and the same commutator pieces _{(N = (n 1 / n} 2) = 1) when the DC motor, as described above, the varistor The capacitance at the time of 1 MHz measurement between any adjacent electrodes is preferably greater than 7.0 nF (more preferably 7.5 nF or more).

Next, a case where the number of commutator pieces n ₁ (six pieces) and the number of electrodes varistors n ₂ (three poles) are different will be described. FIG. 19 is a diagram showing a modification of the circuit configuration of the DC motor 110 shown in FIG. The circuit is the same as that shown in FIG. 18 except that the varistor has three poles.

Thus, in the case of a DC motor in which the number n ₁ of the commutator pieces is an integral multiple of the number n ₂ of varistor electrodes (N = (n ₁ / n ₂ ) = 2), the varistor is 1 MHz between any adjacent electrodes. The capacitance at the time of measurement is preferably larger than 7.0 nF × N (more preferably 7.5 nF × N or more).

  As described above, the present invention has been described with reference to the above-described embodiment. However, the present invention is not limited to the above-described embodiment, and the present invention can be appropriately combined or replaced with the configuration of the embodiment. It is included in the present invention. Further, based on the knowledge of those skilled in the art, it is possible to appropriately change the combination and processing order in each embodiment and to add various modifications such as various design changes to the embodiment. Added embodiments may be included in the scope of the present invention.

  10 DC motor, 12 housing, 14 magnet, 16 rotor, 18 shaft, 20 core, 20a groove, 22 winding, 24 commutator, 26 varistor, 30 brush, 38, 40 contact part, 110 DC motor, 112 housing, 114 magnet 116 rotor, 118 shaft, 120 core, 120a groove, 122 windings, 124 commutator, 126 varistor, 130 brush.

Claims (5)

A DC motor having a varistor that suppresses the occurrence of sparks between the brush and the commutator,
The varistor _is an _{E 10} value is 13~18.4V, _{n 1} the number of commutator pieces capacitance at 1MHz measurement between adjacent electrodes is provided in the 7.5nF × N (the DC motor, the varistor N = (n ₁ / n ₂ )) or more, where n ₂ is the number of electrodes of
The brush is a metal brush,
A DC motor characterized in that the stationary current Is of the DC motor is configured to be 2 A or more.   2. The DC motor according to claim 1, wherein the DC motor is configured to be used in forward rotation operation and reverse rotation operation. A DC motor having a varistor that suppresses the occurrence of sparks between the brush and the commutator,
The varistor has a capacitance of 7.5 nF × N when measuring 1 MHz between adjacent electrodes (when the number of commutator pieces included in the DC motor is n ₁ and the number of electrodes of the varistor is n ₂ , N = _(n 1 _{/ n} 2)) or more,
The brush is a metal brush,
The DC motor stationary current Is is configured to be 2 A or more,
A DC motor configured to be used in a forward rotation operation and a reverse rotation operation.   The DC motor according to any one of claims 1 to 3, wherein the commutator includes a silver-containing metal at a sliding portion with the brush.   The DC motor according to any one of claims 1 to 4, wherein the varistor is a disk-shaped ceramic varistor.

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