JP2001126838A - Method of reducing electrical noise of commutator motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electrical noise due to arc generated between a commutators 4 and brushes, and particularly, electrical noise generated upon the end of the arc. SOLUTION: Graphite layers or alloy layers of graphite with a material having a higher conductivity than graphite 2 and 3 are formed on at least one of the side surfaces along a rotational direction of the commutators 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing electric noise of a commutator motor for reducing electric noise generated by an arc between a commutator piece and a brush.

[0002]

2. Description of the Related Art A commutator coil of an armature winding of a commutator motor repeatedly short-circuits (starts commutation) and opens (completion of commutation). An arc is generated between the child piece and the brush, and electric noise is generated with the arc. Above all, when the arc ends, high-level impulse noise is generated.

[0003] As is well known, the commutator piece may be mainly composed of a highly conductive metal such as copper, or may be formed of a copper alloy containing a trace amount of silver to further improve conductivity. . The main component of the brush is made of graphite.

In the case where the commutator strip and the brush are formed of the above-mentioned materials, the commutator strip and the brush generate electric noise generated by the arc between the commutator strip and the brush on the positive and negative brush sides, respectively. It is known to grow.

In order to measure the arc voltage and the electric noise when the commutator piece is a cathode and the brush is an anode, the short-circuit and opening of the brush and the commutator piece are replaced with the short-circuit and opening of the electrical contact, and the contact is made. We decided to measure the arc voltage and electrical noise when an electrical contact was opened. As measurement conditions,
The open voltage between the contacts, that is, the power supply voltage is 40 V DC, the current when the contacts are closed is 2 A, and the load inductance is 0.8.
5 mH, the opening speed of the contact was 0.1 m / s, and the surrounding atmosphere was air. The load inductance corresponds to the inductance of the armature. The arc voltage measures the voltage between the contacts with an oscilloscope, and the electric noise measures the center frequency of the electric noise measuring instrument at 30 MHz and the bandwidth as 1
Detection was performed at 00 kHz, and the output was measured with an oscilloscope.

FIG. 1 shows an arc voltage and electric noise measured under the above conditions. One contact is the same as the commutator piece.
It was formed of 00% copper and connected to the cathode of the power supply, and the other contact was formed of the same graphite as the brush and connected to the anode of the power supply. The horizontal axis indicates the gap length of the contacts converted at a breaking speed of 0.1 m / s, and the position 0 indicates the position where the arc starts at the time of breaking the contacts.

As shown in FIG. 1, it can be seen that electric noise is continuously generated during the arc generation period, and high-level impulse noise is generated particularly when the arc ends, that is, when the voltage suddenly rises. The rising width of the voltage from the voltage immediately before the arc ends to the open voltage is about 20 V in FIG.

FIG. 2 shows an amplitude probability distribution (APD) of electric noise when an arc is generated 100 times under the above conditions. APD indicates a noise generation time ratio (vertical axis) exceeding a threshold value (horizontal axis) of electric noise during an arc generation period.
Table 1 shows the threshold values of the electrical noise with respect to the main noise occurrence time rates obtained from FIG. For example, the period during which the noise occurrence time ratio is 0.1 is occupied by electrical noise of 66.3 dBμV or more. Table 1: Electrical noise thresholds for major noise generation rates

[0009] The high level impulse noise generated when the arc ends contributes to the threshold value of the electrical noise having a noise generation time rate of 0.01 or less. According to Table 1, when the noise generation time ratio is 0.01, the threshold value of the electric noise is 8
8.8 dBμV.

[0010]

As described above, the threshold value of the electric noise when the noise generation time rate is 0.01 is 88.8 dBμ due to the electric noise when the arc ends.
When this is converted into a dBpW value by V, it is 71.8 dBpW. In the Electrical Appliance and Material Control Law, the limit value of the disturbance power at a frequency of 30 MHz is 55 dBpW. Therefore, 1
The limit value is exceeded by about 6.8 dB, and a filter for reducing electric noise having an attenuation effect of 16.8 dB or more must be installed.

It is an object of the present invention to obviate the above-mentioned disadvantages of the prior art and to reduce electrical noise when the arc is terminated.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention that the impulse noise near the end of the arc is caused by a rapid change in the arc voltage, and that the time change of the arc voltage near the end of the arc, that is, the absolute value of dV / dt. Focusing on reducing the impulse noise, that is, reducing the electrical noise, by reducing the value of, a layer of graphite or an alloy of graphite and a material having higher conductivity than graphite is provided on at least one of the side surfaces along the rotation direction of the commutator piece. Is achieved by

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing one embodiment. FIG. 7 schematically shows a commutator 1 according to the present invention. Graphite or graphite and graphite are provided on both sides of a side surface along a rotation direction of each commutator piece 4 formed of a highly conductive metal such as copper. Layers 2 and 3 of a material having high conductivity, such as an alloy with copper, are provided. As is well known, an insulating material is provided between the commutator pieces 4, but is not shown.

By providing the layers 2, 3, when each commutator piece 4 separates from the brush, an arc is generated as described above. At that time, not only copper (Cu) but also carbon (C) is ionized. The ionization voltage of carbon, which is a constituent element of graphite, is 11.26 (eV), and the ionization voltage of copper is 7.0.
It is larger than 68 (eV). Therefore, in the ionized state,
The arc voltage per unit gap length is larger in the arc formed by carbon ions than in the arc formed by copper ions. That is, the carbon ions act to increase the arc voltage. For this reason, the arc voltage near the end of the arc increases, and the arc voltage gradually increases toward the end of the arc. At the end of the arc, the width of the sharp rise of the arc voltage decreases, and the absolute value of dV / dt decreases. As a result, impulse noise is reduced.

To confirm the above, the contacts were short-circuited and opened, and the arc voltage and electric noise at that time were measured. The measured conditions were the same as above, and one contact was connected to an alloy of graphite and copper (mixing ratio of graphite 50% by weight, copper 50%).
Wt%), and the other contact was made of graphite. 3 and 4 show the measurement results.

In FIG. 3, similarly to FIG. 1, electric noise is continuously generated during the arc generation period, and impulse noise is generated when the arc ends. The sharp voltage rise near the end of the arc is about 10 V, which is smaller than that in FIG. That is, the absolute value of dV / dt is smaller when the contact is formed of an alloy of graphite and copper than when the contact is formed of copper, and the peak value of the noise level generated at this time is also reduced by about 10 dB.

FIG. 4 shows an APD of electric noise when an arc is generated 100 times. Table 2 shows the threshold values of the electrical noise with respect to the main noise occurrence time rates obtained from FIG. The noise occurrence time rate is smaller than that of FIG. 2 and Table 1 at all the electric noise thresholds. The threshold value of the electric noise at the electric noise occurrence time ratio of 0.01 is 72.4.
dBμV, which is 16.4 dB smaller. Also, when converted to a dBpW value, it is 55.4 dBpW,
It is almost the limit value of the Electrical Appliance and Material Control Law. Table 2. Noise thresholds for major noise occurrence rates

FIG. 5 and FIG. 6 show the measurement results when both contacts were made of graphite under the above-mentioned measurement conditions. As shown in FIG. 5, at the end of the arc, the voltage does not rise sharply as in FIGS. 1 and 3, but gradually rises to the open-circuit voltage as compared with FIGS. Therefore, no impulse noise is generated when the arc ends. From FIG. 6 and Table 3, all the electrical noise threshold values are smaller than those in FIG. 2 and Table 1. The threshold value of the electrical noise at an electrical noise generation time rate of 0.01 is 68.8 dBμV, and the reduction amount of the threshold value is 20.0 d.
B is 3.6 dB smaller than that in FIG. Also, when converted to a dBpW value, it is 51.8 dBpW, which is below the limit value of the Electrical Appliance and Material Control Law. Table 3. Noise thresholds for major noise occurrence rates

As described above, when one of the contacts is made of graphite, the other contact is made of graphite or an alloy of graphite and copper, thereby reducing electric noise particularly generated when the arc is terminated. You can see what you can do. Therefore, it can be understood that electric noise can be reduced by forming the commutator piece 4 with graphite or an alloy of graphite and copper.

However, it is disadvantageous from the viewpoint of the temperature rise of the commutator piece 4 that the entire commutator piece 4 is made of graphite or such an alloy. That is, the resistance value of graphite is approximately 1000 times larger than that of copper, and the commutator piece 4 made of conventional copper is not used.
It is obvious that the temperature rises as compared with the temperature rise.

Therefore, as shown in FIG. 7, the present invention employs a graphite or alloy layer 2, 3 having a width of not more than one-third of the commutator piece width along the rotation direction on both sides of the side face along the rotation direction of the commutator piece 4. (L1 / L ≦ １ ／ in FIG. 7) to suppress the temperature rise and reduce the electric noise at the end of the arc. The graphite or alloy layers 2 and 3 are provided on both sides of the side surface because a commutator motor is assumed to be a reversible motor that can rotate in the reverse direction. The graphite or alloy layer may be provided only on the side surface. That is, in FIG. 7, if it rotates clockwise, the graphite or alloy layer 3 on the front side in the rotation direction can be omitted.

According to the above embodiment, since the graphite or alloy layers 2 and 3 are provided on the entire side surface of the commutator piece 4,
Even if the commutator piece 4 is worn, the graphite or alloy layers 2 and 3 are present. Therefore, the effect of reducing electric noise can be maintained until the commutator piece 4 is completely worn.

In the above embodiment, layers 2 and 3 of graphite or an alloy of graphite and a material having a higher conductivity than copper are provided on the side surface of the commutator piece 4. It may be formed of an alloy of a metal and a highly conductive metal such as copper having higher conductivity than carbon. The constituent element of carbonaceous material is carbon, similarly to graphite. Therefore, the same effect as the above embodiment can be expected.

Further, the layers 2 and 3 may be formed of a layer containing an element having an ionization voltage higher than that of copper. By doing so, the voltage of the arc generated between the commutator piece and the brush increases, and impulse noise generated particularly when the arc ends can be reduced.

[0025]

As described above, according to the present invention, the electric noise generated by the arc between the commutator piece and the brush can be reduced until the commutator piece is completely worn while suppressing the temperature rise of the commutator piece. Become like

[Brief description of the drawings]

FIG. 1 is an explanatory graph showing a relationship between an arc voltage and electrical noise when a contact is opened.

FIG. 2 is an explanatory graph showing an amplitude probability distribution (APD) of electrical noise when a contact is opened 100 times.

FIG. 3 is an explanatory graph showing a relationship between an arc voltage and electrical noise at the time of contact opening according to the present invention.

FIG. 4 is an explanatory graph showing an amplitude probability distribution (APD) of electric noise when a contact is opened 100 times according to the present invention.

FIG. 5 is an explanatory graph showing the relationship between arc voltage and electrical noise at the time of contact opening according to the present invention.

FIG. 6 is an explanatory graph showing an amplitude probability distribution (APD) of electric noise when a contact is opened 100 times according to the present invention.

FIG. 7 is a schematic diagram showing one embodiment of a commutator according to the present invention.

[Explanation of symbols]

1 is a commutator, 2 and 3 are graphite or alloy layers, and 4 is a commutator piece.

Claims (6)

[Claims] 1. A commutator motor comprising a brush made of graphite as a main component and a commutator piece made of a highly conductive metal such as copper or an alloy of a highly conductive metal. A layer of graphite or an alloy of graphite and a material having higher conductivity than graphite is provided on at least one of the side surfaces along the rotation direction of the commutator piece, and an arc voltage is increased by increasing an arc voltage between the commutator piece and the brush. A method for reducing electric noise of a commutator motor, characterized in that the electric noise at the time of completion is reduced. 2. The method according to claim 1, wherein the thickness of a layer of graphite or an alloy of graphite and a material having high conductivity provided on a side surface of the commutator piece is set to not more than 1/3 of a width of the commutator piece. The method for reducing electric noise of a commutator motor according to claim 1. 3. A commutator motor including a brush whose main component is made of graphite and a commutator piece whose main component is made of a highly conductive metal such as copper or an alloy of a highly conductive metal. By providing a layer containing carbonaceous material on at least one of the side surfaces along the rotation direction of the commutator piece, and increasing the arc voltage between the commutator piece and the brush, so as to reduce electric noise when the arc ends. A method for reducing electric noise of a commutator motor, characterized in that: 4. The commutator motor according to claim 3, wherein the thickness of the layer containing carbonaceous provided on the side surface of the commutator piece is set to 1/3 or less of the width of the commutator piece. Electrical noise reduction method. 5. A commutator motor comprising a brush whose main component is made of graphite and a commutator piece whose main component is made of a highly conductive metal such as copper or an alloy of a highly conductive metal. A layer containing an element having an ionization voltage higher than that of copper is provided on at least one of the side surfaces along the rotation direction of the commutator piece, and by increasing the arc voltage between the commutator piece and the brush, the electric power at the time when the arc ends is increased. A method for reducing electric noise of a commutator motor, characterized in that noise is reduced. 6. The thickness of a layer provided on a side surface of the commutator piece and containing an element having an ionization voltage higher than that of copper is set to be not more than ３ of the width of the commutator piece. The method for reducing electric noise of a commutator motor according to the above.