JPH0612674B2 - Electric brush - Google Patents

Description

The present invention relates to an electric brush for a rotating electric machine.

(Prior art and its problems) The conventional method for improving the rectifying performance of an electric brush used for a DC machine and an AC commutator machine, which are difficult to rectify, is to install an electric brush between two adjacent commutator pieces. In order to reduce the short-circuit current flowing through the brush material, increase the specific resistance of the brush material, and to improve the sliding contact of the electric brush on the commutator, lower the elastic modulus of the brush material to reduce the viscosity coefficient and specific resistance. Was to raise. However, with respect to recent advances in electric machines, it has become impossible to catch up with such methods alone, so that composite brushes, that is, layered brushes and split brushes have come into practical use inside and outside.

In the armature coil of the rotating electric machine, a counter electromotive force (reactance voltage) that prevents a change in the current flowing through the coil during rectification is generated due to the self-inductance (Lc) of the coil, and this reactance voltage Er is expressed by the formula Er = Lc × There is a relationship of di / dt (i is a short-circuit current, t is a time during which the electric brush moves the commutator). The moving time increases as the thickness of the electric brush increases, and the reactance voltage is inversely proportional to the thickness of the electric brush. However, even if the thickness of the electric brush is increased in order to reduce the reactance voltage, the contact area between the electric brush and the commutator increases, and the short-circuit current i increases. On the other hand, when the thickness of the electric brush is reduced, the reactance voltage Er increases and the short-circuit current i also increases because Lc is constant from the above equation. When this reactance voltage becomes large, the change in the current to be rectified is delayed, which causes a large spark when the electric brush leaves the commutator piece, which deteriorates rectification.

Therefore, it is difficult to properly determine the thickness of the electric brush and maintain a good rectifying function. Therefore, in order to improve the rectifying function by increasing the resistance of the short-circuit current path, the electric brush is divided into a plurality of parts. Shi. A segmented brush in which the segmented pieces are allowed to move to some extent, the segmented pieces are adhered with, for example, a synthetic resin to insulate the segmented pieces from each other and to reduce the thickness of the entire electric brush, that is, to increase the reactance voltage. There is a laminated brush with high resistance in the short-circuit current path. However, these electric brushes are expensive because they are difficult to process and require a lot of processing man-hours. Applications include large-scale DC machines such as motors for steel rolling mills and train main motors. Used only for motors for automobile starters,
It is not used for small electric brushes such as blower motors, wiper motors, electric tool motors, household cleaner motors, etc., but the current single electric brush is used. In addition, a layered brush has been proposed in which raw material powders having different properties, for example, different electric resistivity when molded and fired are laminated and molded in layers and fired. FIGS. 5 and 6 show examples of the layered brush, in which 1 is a high electric resistance raw material powder, 2 is a low electric resistance raw material powder, 3 is a lead wire, and arrow 4 is the rotation direction of the rotor. However, this conventional layered brush has the disadvantage that the shrinkage rate of each raw material powder at the time of firing is different, so that stress is generated at the boundary portion of the layer and delamination from the boundary portion or cracks occur in the layer. However, since the layers are stacked, the boundary between the layers is not linear as shown in the figure, and the rectification improving effect is not as expected.

(Object of the Invention) An object of the present invention is to improve the above-mentioned drawbacks of the layered brush and to provide an electric brush having a good rectifying action.

(Structure of the Invention) The present invention relates to an electric brush in which the thickness of the electric brush is the rotation direction of the rotating electric machine, and a layer of a carbon fiber sheet impregnated with resin having a high electric resistance and an electric brush having a low electric resistance in the thickness direction The present invention relates to an electric brush formed by alternately laminating layers of raw material powder and firing the layers.

The carbon fiber sheet impregnated with resin in the present invention is an alternative to the high electric resistance raw material powder of FIG.
It is preferable to impregnate a varnish of a thermosetting resin such as a phenol resin, a furan resin, or an epoxy resin into a sheet or a stack of a plurality of sheets. The raw material powder for electrobrush to form a layer with low electric resistance is metal powder such as electrolytic copper powder, mixed powder with metal powder and graphite powder, graphite powder is kneaded with phenol resin varnish as binder or tar pitch, and then pulverized. It is the molding powder of the electro-brush material.

The electric brush of the present invention is, for example, (A) a resin-impregnated carbon fiber sheet is laid on the bottom of the die by an ordinary press for integral molding, and raw material powder for the electric brush is poured on the carbon fiber sheet to integrally mold the lead wire, (B). After the resin-impregnated carbon fiber sheet is laid on the bottom of the die, the electric brush raw material powder and then the resin-impregnated carbon fiber sheet are laminated one or more times, and then the lead wire is embedded in the die for molding. Then, for example, it is fired at 700 ° C., and an electric brush having the carbon fiber sheet 6 adhered to the lower surface in the thickness direction as shown in FIG. 2, the carbon fiber sheet 6 as shown in FIG. Obtain an electric brush etc. that is in close contact with the middle part.

(Operation) In the electric brush obtained as described above, the resin in the carbon fiber sheet binds the carbon fiber having a relatively high electric resistance, and the carbon fiber sheet and the electric brush raw material powder compact are fired. It strengthens the adhesion with layers with low resistance and reduces the short-circuit current when it is mounted on a rotating electrical machine.

(Example) Next, an example will be described.

Carbon fiber cloth (Nippon Kynol, trade name N501)
Phenolic resin varnish (Hitachi Kasei VP-11
N) vacuum impregnated and air dried, then 2 hours at 40 ° C, 1 hour at 65 ° C
A resin-impregnated carbon fiber sheet (hereinafter referred to as an impregnated sheet) was dried for an hour and cut into 11 × 16 mm sheets.
One piece was prepared (two of them were punched out with a hole 7 into which a lead wire is inserted as shown in FIG. 3). 70% by weight of electrolytic copper powder (manufactured by Fukuda Metal Foil Powder Co., Ltd., product name CE-8) as raw material powder for electric brush
And scaly graphite (Nippon Graphite Industry Co., Ltd., trade name CB-100)
A 30% by weight mixed powder was prepared.

A die having a cross section of 11 × 16 mm and upper and lower punches is attached to the mechanical press, and as shown in FIG. 4, a sheet 5 having no holes is formed on the lower punch 10 surrounded by the die 9 and the lower punch 10. , The electric brush raw material powder 8, the perforated sheet 5 ′, the electric brush raw material powder 8, and the perforated sheet 5 ′ are stacked in this order, and then the lead wire 3 is passed through the hole 7 from the upper punch to move up and down. The punch was lowered and raised to perform integral molding at a pressure of 4 ton / cm ² . The molded product is baked at 700 ° C in a nitrogen gas atmosphere and has a thickness of 7 mm ×
An electric brush having a width of 11 mm and a length of 16 mm was obtained.

As a comparative example, only the electric brush raw material powder was molded and fired under the same conditions to obtain an electric brush having the same size.

The electric brushes obtained in Examples and Comparative Examples were incorporated into a 12V, 1KW automotive starter, and a starter motor start cycle test was conducted under conditions of 1.5 seconds ON and 8.5 seconds OFF, and rectified sparks at that time were observed. The wear of the electric brush was measured.

As a result, when rectifying sparks are judged according to the standard defined in JEC-54, it is 4 to 5 when the electric brush of the embodiment is used.
No. 5 and No. 6 using the electric brush of the comparative example, the electric brush wear amount is also small as shown in FIG.
The example electrobrushes are shown to have excellent rectification.

(Effects of the Invention) According to the present invention, the delamination and cracking unlike the conventional layered brush does not occur, and the short-circuit current can be reduced without changing the thickness of the electric brush. It can be applied to small electric motors for automobiles and home appliances.

[Brief description of drawings]

1 and 2 are sectional views showing an example of the electric brush of the present invention,
3 and 4 are front views of a resin-impregnated carbon fiber sheet of an electric brush according to an embodiment of the present invention and cross-sectional views for explaining a forming method, and FIGS. 5 and 6 are cross-sectional views of a conventional stratified brush. , FIG. 7 is a sectional view showing the number of times the starter is started and the amount of wear of the electric brush. Explanation of symbols 1 ... Raw powder of high electric resistance 2 ... Raw powder of low electric resistance 3 ... Lead wire, 4 ... Rotating direction of rotor 5, 5 '... Sheet, 6 ... Carbon fiber sheet 7 ... Hole, 8 ... Electro brush raw material Flour 9 ... Soybean, 10 ... Lower punch 11 ... Upper punch

Front page continuation (72) Inventor Hiroaki Kawamura 3-3-1 Ayukawa-cho, Hitachi City, Ibaraki Hitachi Chemical Co., Ltd. Sakuragawa Plant (72) Inventor Fukumi Akatsu 3-3-1 Ayukawa-cho, Hitachi City, Ibaraki Hitachi Chemical Co., Ltd. Sakuragawa Plant (56) References Japanese Patent Laid-Open No. 56-24777 (JP, A) Japanese Patent Publication No. 56-54673 (JP, B2)

Claims (1)

[Claims] 1. An electric brush in which the thickness of the electric brush is the direction of rotation of a rotating electric machine, a layer of a carbon fiber sheet impregnated with resin having high electric resistance and a layer of raw material powder of electric brush having low electric resistance in the thickness direction. An electric brush made by alternately forming and firing.