JP2002171724A - Electric noise reducing method for commutator motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electric noise of a high-level impulse, which is especially generated when an arc becomes extinct, from among those caused by arcs generated between a brush and a commutator segment 4. SOLUTION: At least on one side surface of those along the direction of rotation of each commutator segment 4, layers 2, 3 of zinc or an alloy of zinc are formed.

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 of the commutator motor.

[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. In particular, high-level impulse electric noise is generated when the arc is extinguished.

[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. We know it will be higher.

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 electric 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 DC 20 V, the current when the contacts are closed is 1 A, and the load inductance is 0.8.
5 mH, the contact opening speed was 0.1 m / s, and the surrounding atmosphere was air. The load inductance corresponds to the inductance of the armature. The voltage between the contacts is measured as an arc voltage with an oscilloscope. The center frequency of the electric noise measuring instrument is 30 MHz and the bandwidth is 100 k.
The output detected as Hz was measured as electrical noise 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 represents the gap length of the contacts converted at a breaking speed of 0.1 m / s, and the position 0 represents the position where the arc is ignited when the contacts are broken.

As shown in FIG. 1, electric noise is continuously generated during the arc generation period. In particular, when the arc is extinguished, that is, when the voltage suddenly rises, impulsive electric noise having a level exceeding 80 dBμV is generated. You can see that. Further, as shown in FIG. 2, the time differential value dV / dt of the arc voltage at the time of arc extinction exceeds 3 V / μs.

FIG. 3 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, at a noise generation time ratio of 0.1, electric noise of 67.7 dBμV or more occupies. Table 1: Electrical noise thresholds for major noise generation rates

The high level impulsive electrical noise generated when the arc is extinguished contributes to the threshold of the electrical noise having a noise generation time ratio of 0.01 or less. From Table 1, the threshold value of the electrical noise for the noise generation time rate 0.01 is 8
9.2 dBμV.

[0010]

As described above, the threshold of the electric noise is 89.2 dBμV with respect to the noise generation time rate of 0.01 due to the high level of the impulse electric noise generated at the time of arc extinction. When converted to a dBpW value, it is 72.2 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, the limit value is exceeded by about 17.2 dB, and a filter for reducing electric noise having an attenuation effect of 17.2 dB or more must be installed.

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art and to reduce high-level impulse-type electrical noise generated when an arc is extinguished.

[0012]

SUMMARY OF THE INVENTION The object of the present invention is to provide an impulse electric noise near the arc extinguishing due to a rapid change in the arc voltage. Focusing on the fact that the impulse electric noise can be reduced by reducing the absolute value of the above, this can be achieved by providing a layer of zinc or an alloy containing zinc on at least one of the side surfaces along the rotational direction of the commutator piece.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing one embodiment. FIG. 10 schematically shows the commutator 1 of the present invention, in which zinc or an alloy containing zinc is formed 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. 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 and 3, the arc generated as described above when each commutator piece 4 separates from the brush is formed by the metal vapor of copper (Cu) and zinc (Zn) from the commutator piece 4. Formed by The melting point of zinc is 419.58.
The boiling point is 903 ° C., the melting point of copper is 1084.5 ° C. and the boiling point is 2580 ° C. Zinc has a lower melting and boiling point than copper. Therefore, the metal vapor density of zinc (Zn) increases, and the arc is easily maintained, so that the arc lengthens. Then, the arc voltage gradually increases. Therefore, the arc voltage near the arc extinction is increased and dV / dt is reduced as compared with the case of using only copper. As a result, high-level impulsive electrical 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 made of an alloy of zinc and copper (mixing ratio: copper 60 wt%, zinc 4
0 Wt%), and the other contact was formed of graphite. FIG.
5 and 6 show the measurement results.

In FIG. 4, as in FIG. 1, electric noise is continuously generated during the arc generation period. But,
From FIG. 5, dV / dt in the vicinity of the arc disappearance is the same as that in FIG.
Accordingly, the peak value of the noise level generated near the arc extinction becomes lower by 15 dB or more when the contact is formed of an alloy of zinc and copper than when the contact is formed of copper.

FIG. 6 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 threshold values of the electrical noise for all the noise occurrence time rates are lower than those in FIG. The threshold value of the electrical noise for the noise generation time rate 0.01 is 6
4.8 dBμV, which is 24.4 dB lower.
Also, when converted to a dBpW value, it is 47.8 dBpW, which is below the limit value of the Electrical Appliance and Material Control Law. Table 2: Threshold values of electrical noise with respect to main noise occurrence time rates

FIGS. 7, 8 and 9 show the measurement results when copper having zinc adhered to the surface was formed as one contact and the other contact was made of graphite under the above measurement conditions. Also in FIG. 7, electric noise is continuously generated during the arc generation period as in FIGS. However, by attaching zinc to copper, dV / dt near the arc extinction becomes smaller than that in FIG. 2 as shown in FIG. 8 as in FIG. 5, and the peak value of the noise generated near the arc extinction becomes About 3
0 dB lower.

From FIG. 9 and Table 3, the threshold values of the electrical noise for all the noise occurrence time rates are lower than those in FIG. The threshold value of the electrical noise with respect to the noise generation time rate 0.01 is 59.5 dBμV, and the reduction amount of the threshold value is 29.7 dB, which is 5.3 dB lower than that in FIG. Also, when converted to a dBpW value, it is 42.5 dBpW, which is below the limit value of the Electrical Appliance and Material Control Law. Table 3: Noise thresholds for major noise occurrence time rates

From the above, when one of the contacts is made of graphite, the other contact is made of an alloy of zinc and copper or copper having zinc adhered to the surface, so that the contact particularly occurs when the arc is extinguished. It can be seen that high level impulse electrical noise can be reduced. Therefore, commutator piece 4
It can be understood that this electrical noise can be reduced if is formed of zinc or an alloy of zinc and copper.

However, making the entire commutator piece 4 zinc or such an alloy is disadvantageous from the viewpoint of the temperature rise of the commutator piece 4. That is, it is clear that the resistance value of zinc is about 3.5 times higher than the resistance value of copper, and the temperature tends to rise more easily than in the case of the commutator piece 4 formed of conventional copper.

Therefore, as shown in FIG. 10, the present invention uses a zinc 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. 10) to suppress a rise in temperature and to reduce high-level impulse-type electrical noise generated when the arc is extinguished. The reason why zinc or alloy layers 2 and 3 are provided on both sides of the side surface is because a commutator motor is assumed to be a reversible motor that can rotate in the reverse direction. What is necessary is just to provide a zinc or alloy layer only on the side surface. In other words, if the clockwise rotation is performed in FIG. 10, the zinc or alloy layer 3 on the front side in the rotation direction can be omitted.

According to the above embodiment, since the zinc 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 zinc or alloy layers 2, 3 are present. Therefore, the effect of reducing electric noise can be maintained until the commutator piece 4 is completely worn.

Further, the layers 2 and 3 may be formed of a layer containing an element having a melting point of 700 ° C. or less. By doing so, the arc generated between the commutator piece and the brush becomes longer, and accordingly, the arc voltage at the time of arc extinction becomes higher, and high-level impulsive electrical noise generated at the time of arc extinction can be reduced.

[0025]

As described above, according to the present invention, high-level impulse electric noise generated when the arc between the commutator piece and the brush is extinguished while suppressing the temperature rise of the commutator piece. Can be reduced until it is completely worn.

[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 a time differential value dV / dt of the arc voltage of FIG.

FIG. 3 is an explanatory graph showing an amplitude probability distribution (APD) of electrical noise when a contact is opened 100 times.

FIG. 4 is an explanatory graph showing a relationship between an arc voltage and electrical noise when a contact is opened according to the present invention.

FIG. 5 is an explanatory graph showing a time differential value dV / dt of the arc voltage in FIG. 4;

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

8 is an explanatory graph showing a time differential value dV / dt of the arc voltage in FIG.

FIG. 9 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. 10 is a schematic view showing an embodiment of a commutator according to the present invention.

[Explanation of symbols]

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

Claims (4)

[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 zinc or an alloy containing zinc is provided on at least one of the side surfaces along the rotation direction of the commutator piece, and has a melting point higher than that of copper.
The low boiling point zinc increases the metal vapor density to maintain the arc, lengthens the arc between the commutator strip and the brush,
A method for reducing electric noise of a commutator motor, characterized in that an impulse electric noise generated when an arc is extinguished is reduced by increasing an arc voltage. 2. The thickness of a layer of zinc or an alloy containing zinc provided on a side surface of the commutator piece is set to be 1 / (thickness) of the width of the commutator piece.
3. The method for reducing electric noise of a commutator motor according to claim 1, wherein the number is 3 or less. 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. A layer containing an element having a melting point of 700 [° C.] or less is provided on at least one of the side surfaces along the rotation direction of the commutator piece, the metal vapor density for maintaining the arc is increased, and the commutator piece and the brush An electric noise reduction method for a commutator motor, characterized in that an arc is lengthened and an arc voltage is increased to reduce impulsive electric noise generated when the arc is extinguished. 4. The method according to claim 1, wherein a thickness of a layer provided on a side surface of the commutator piece and containing an element having a melting point of 700 ° C. or less is equal to or less than １ ／ of a width of the commutator piece. Item 3. An electric noise reduction method for a commutator motor according to Item 3.