JP4602879B2 - Rectifier for small motor - Google Patents

Description

  The present invention relates to a commutator for a small motor that includes a commutator fixed on a motor rotor shaft and a pair of brushes that are in sliding contact with the commutator.

  FIG. 7 is a longitudinal sectional view partially showing a commutator portion of a rotor of a normal small motor in a cross section. The motor rotor is configured by integrally assembling a rotor magnetic pole constituted by a laminated core (not shown) and a winding (not shown) and a commutator on a shaft. The commutator piece of the commutator is fixed to the outer peripheral surface of the resin commutator core via a fixture (washer). Disc varistors are provided for spark elimination. The commutator device includes a commutator and a brush that is in sliding contact with the commutator. The brushes are configured as a pair so as to be connected to the positive side and the negative side of the power source, respectively. The pair of illustrated brushes is a commutator piece having two elongated flat plates integrally joined on the base side. As a set, it is configured by being provided respectively at the top and bottom in the figure. A winding end (not shown) is connected to the bent end (winding connection end) of the commutator piece.

  After the motor rotor thus configured is inserted from the opening of the metal case (not shown), an end cap (only a part of which is shown) is fitted so as to close the opening of the metal case. The In this state, the rotor shaft is rotatably supported by a bearing (not shown) provided on the bottom of the metal case and a bearing provided on the end cap. At this time, the brush is disposed so as to abut on the commutator piece. The electric current supplied from the external power source through the brush and the commutator piece flows in the winding wound around the rotor magnetic pole, thereby allowing the motor to rotate.

Such a small motor is also used for a low voltage, low speed rotation and discontinuous operation such as a pick motor for driving a pickup of a CD player or a DVD player. However, the problem is that the contact resistance between the commutator and the brush slidingly contacting it becomes unstable as the elapsed time of use increases. Conventionally, for example, a silver-copper alloy containing copper is used for the commutator material, and silver palladium is used for the brush material. However, since the copper and palladium are easily oxidized, the brush is used. The material tends to oxidize and become wear powder. In addition, the organic matter in the air is carbonized by the spark caused by the sliding of the brush and the commutator, and becomes an insulator. When the brush rides on the wear powder or the insulating material, the contact becomes unstable. When the contact resistance becomes unstable, the motor starting voltage (applied voltage necessary for starting the motor) increases. When this starting voltage rises above a predetermined value of applied voltage, there arises a problem that the motor is stopped and cannot be started.
Japanese Patent No. 28895793

  The present invention solves such problems, maintains the contact resistance between the commutator and the brush stably even after long-time use, prevents excessive increase of the motor starting voltage, It is intended to enable stable use in applications that operate discontinuously at low speed.

  The commutator for a small motor according to the present invention includes a commutator fixed on the motor rotor shaft and a pair of brushes that are in sliding contact with the commutator. The material constituting the sliding portion of either the commutator or the brush is formed by dispersing tungsten carbide (WC) particles in a silver (Ag) matrix.

The tungsten carbide (WC) particles, Ru dispersed in a range of 2.3~20wt%. The material formed by dispersing tungsten carbide (WC) particles in this silver (Ag) matrix can be used as a brush material, and the sliding member quality of the commutator can be made of gold (Au).

  Each of the pair of brushes can be constituted by a plurality of inverted V-shaped brush portions or a combination of a V-shaped brush portion and an inverted V-shaped brush portion.

  According to the present invention, a material formed by dispersing tungsten carbide (WC) particles in a silver (Ag) matrix is used for the commutator or the sliding portion of the brush, so that the gap between the commutator and the brush is increased. Maintain stable contact resistance after a long period of use to prevent excessive increase in motor starting voltage, especially in applications that operate discontinuously at low voltage and low speed. it can.

  Further, by using gold as the material that is difficult to oxidize as the counterpart material, it is possible to further stabilize the contact resistance because it does not oxidize even if abrasion powder occurs.

  Furthermore, by setting the cross-sectional shape of the brush to an inverted V shape or V shape, it is possible to make sliding contact with the commutator in a line shape, thereby increasing the contact pressure and further stabilizing the contact resistance.

  In the present invention, WC (tungsten carbide) particles are dispersed and used in an Ag (silver) matrix as a material composition of either the commutator material (commutator piece material) or the brush material. The WC particles dispersed in the Ag matrix have electrical conductivity, and even if wear powder is caught, the start voltage can be prevented from rising by energizing between the commutator and the brush by the WC particles. The dispersion ratio is desirably the remaining Ag with respect to 2.3 to 20% by weight of WC, as shown in the examples in detail.

  Au (gold), AuAg (gold-silver) alloy, AgCu (silver-copper) alloy, and Ag (silver) are used as the other material (brush or commutator) used in combination with such a commutator or brush. By using Au, AuAg alloy, AgCu alloy, or Ag, oxidation can be suppressed. In particular, since Au is difficult to oxidize, even if wear powder is generated, oxidation of the wear powder is suppressed. The contact resistance between the brushes can be stabilized.

  FIG. 1 is a diagram for conceptually explaining the action of WC particles dispersed in an Ag matrix constituting a sintered brush, in which (A) shows the initial state of the brush, and (B) shows the state after long time use. Is shown. A material formed by dispersing WC particles in Ag powder in a predetermined ratio and then sintering can be used for both a brush and a commutator, but the figure shows a case where the material is used for a brush. ing. As shown in FIG. 1A, since the commutator is not worn in the initial state, the commutator surface and the brush surface can be in good contact with each other. On the other hand, after a long period of use, the commutator and the brush are worn, and the wear powder enters between the contact portions of the commutator and the brush, and the brush rides on the wear powder. Although the resistance is destabilized, in the illustrated material, only Ag is mainly worn, and hard WC particles are hardly worn. Therefore, as shown in FIG. 1B, the WC particles protrude on the brush surface. For this reason, even if it wears in the wear powder and enters between the brush and the commutator piece, the wear powder enters the gap generated between the protruding WC particles and the commutator piece, and the brush and the commutation piece. Energization between the children can be performed stably via the WC particles protruding on the surface. This can prevent an increase in starting voltage.

  A small motor having a brush or commutator piece formed of the above-described material was prepared. This material is rolled on a base material (copper or copper alloy spring material is used for brushes, or copper or copper alloy is used for commutator pieces) as usual. Formed (clad). And it tested using such a small motor, and the starting voltage and the contact resistance were measured. 2 and 3 are diagrams illustrating such a small motor structure, in which (A) is a view partially showing the rotor structure in cross-section, and (B) is only a brush portion in contact with the commutator. It is a perspective conceptual diagram which takes out and shows. The motor structure shown in FIGS. 2 and 3 is illustrated as the same as the conventional small motor described with reference to FIG. 7 except for the brush shape. Therefore, a detailed description of the configuration and operation other than the brush shape is omitted.

  The brush shown in FIG. 2 has three brush portions having a reverse V-shaped cross section arranged in the axial direction, whereas the brush in FIG. 3 has two brush portions having a V-shaped cross section and a reverse V-shaped side by side. The only difference is. Here, both the V-shaped brush and the inverted V-shaped brush are common in that an elongated flat plate having a relatively narrow width and a long length is bent into a V shape on both sides with a folding center at the center. However, the contact mode with respect to the commutator piece is different. In the V-shaped brush, the folding line at the center of the width is in sliding contact with the commutator piece, whereas the reverse V-shaped brush is in sliding contact with both sides in the width direction. As shown in the figure, the brush is composed of three brush portions (FIG. 2) or two brush portions (FIG. 3). Although these three or two brush portions are not shown in the drawing, they are used by being integrally coupled electrically and structurally on the base end side.

  The brush shape illustrated in FIG. 7 as a prior art is an elongated flat plate, and is in sliding contact with the commutator over the entire surface, whereas the brush illustrated in FIG. 2 or FIG. It is possible to increase the contact pressure by sliding contact in a line shape. The reverse V shape is in sliding contact with the commutator on two lines on both sides, whereas the V shape is different in that it is in sliding contact with one central line. Contact. As shown in FIG. 3, in the upper and lower sides in the figure, one side is formed into a V shape and the other is formed into an inverted V shape so that the line that is in sliding contact with the commutator is entirely aligned with the shaft of the cylindrical commutator. It becomes possible to shift in the direction. That is, the contact tracks do not overlap. This can reduce commutator wear. Alternatively, as shown in FIG. 2, the contact resistance can be further stabilized even when wear powder is caught by increasing the contact line by increasing the number of contact lines to three, and securing a current-carrying portion. In this case, further, it is possible to reduce the wear of the commutator by attaching the lower brush in the axial direction to the upper brush in the drawing.

(Measuring method)
The measurement was performed after 150 hours of operation. The starting voltage was measured by using the small motor prepared as described above as the measuring motor, gradually increasing the applied voltage, and recording the voltage at which the motor started rotating as the starting voltage.

  The contact resistance was measured with a measurement circuit as shown in FIG. As shown, the measurement motor is driven by an external drive motor that is controlled to rotate at 1 rpm. Then, a 0.2V DC power source is connected to the measuring motor through a 1Ω resistor, and the current flowing through the measuring motor is recorded as a voltage across the 1Ω resistor by a recorder. Thereby, the contact resistance during one rotation of the measuring motor can be continuously measured and recorded. The partial increase (instability) of the contact resistance during one revolution of the measuring motor is recorded as a decrease in the measuring voltage.

(Measurement result)
FIG. 5 is a table summarizing the measurement results. Since all of the exemplified measuring motors are manufactured assuming that a voltage of 1V is applied and used, a motor whose starting voltage exceeds 1V means that starting is impossible. All the examples are the results of tests using four motors, and the starting voltage and contact resistance columns in the table show the worst results. Example 1 shows the example in which the amount of dispersed WC particles is the smallest in the examples (2.3 wt%) and is used for a commutator, but both the starting voltage and the contact resistance are good. The brush shape “V / reverse V” indicates the brush shape described with reference to FIG. 3, and “three-reverse V” indicates the brush shape described with reference to FIG. .

  Examples 2 to 11 show the results of measuring the same brush shape (three reverse V) by changing the WC dispersion ratio and commutator component composition, but both the starting voltage and the contact resistance are good. In particular, Examples 9-11 show the best contact resistance, but these use gold (100 wt%) for the commutator. Example 12 has the same conditions as Example 10 except that the brush shape is “V / reverse V”, and shows good results. However, the contact resistance is more stable than Example 10. It turns out that the nature is inferior.

  The comparative example shown in FIG. 6 shows bad results for both the starting voltage and the contact resistance. Comparative Example 1 is an example in which the WC dispersion ratio is 2 wt%. Comparative Examples 2 and 3 are examples of a silver-copper alloy as the commutator component composition and silver palladium as the brush component composition.

  As in Example 4 and Example 11, good results were shown even when 20 wt% WC was dispersed. However, a material in which WC was further dispersed was pasted on a base material and rolled. Since cracks occurred during the process, the processing was practically difficult. Therefore, the dispersion amount of WC is desirably 2.3 to 20 wt%.

It is a figure which illustrates notionally the effect | action by the WC particle disperse | distributed in Ag matrix which comprises a sintered brush, (A) shows a brush initial state, (B) shows a state after long-time use. It is a figure which illustrates the small motor structure which arranged three brush parts of the cross-section reverse V shape, (A) is a figure which shows a rotor structure in a cross section, (B) is only the brush part which contacts a commutator. It is a perspective view which takes out and shows. It is a figure which illustrates the small motor structure which juxtaposed two brush parts of the cross-section V shape and reverse V shape, (A) is a figure which shows a rotor structure in a cross section, (B) is a contact with a commutator It is a perspective view which takes out and shows only the brush part to perform. It is a figure which shows the measurement circuit of contact resistance. It is the table | surface which put together the measurement result. It is a table | surface which shows the comparative example which has shown the bad result in both starting voltage and contact resistance. It is a longitudinal cross-sectional view which shows the commutator part of the rotor of the conventional small motor partially in cross section.

Claims (4)

In a small motor rectifier comprising a commutator fixed on a motor rotor shaft and a pair of brushes in sliding contact with the commutator,
The commutator or the material constituting the sliding portion of the brush is formed by dispersing tungsten carbide (WC) particles in a silver (Ag) matrix,
A rectifier for a small motor in which the tungsten carbide (WC) particles are dispersed in a range of 2.3 to 20 wt% . 2. The rectifier for a small motor according to claim 1, wherein the material constituting the sliding portion is a sintered material obtained by dispersing and sintering tungsten carbide (WC) particles in silver (Ag) powder . 2. The sliding member of the commutator is made of gold (Au) using the material formed by dispersing tungsten carbide (WC) particles in a silver (Ag) matrix as a brush material. Rectifier for small motors. 2. The small-sized brush according to claim 1, wherein each of the pair of brushes includes a plurality of inverted V-shaped brush portions or a combination of a V-shaped brush portion and an inverted V-shaped brush portion. Motor rectifier.

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