JPS6247351B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a current collecting brush made of metal-coated carbon fiber. A large number of metal-coated carbon fibers of a suitable length are bundled by coating the surfaces of carbon fibers with a micro diameter (approximately 7 μm) with aluminum, copper, silver, etc. or their alloys using the ion plating method, and the proximal end portions are bundled together. The fiber bundle is heat-pressed together with a conductive metal plate stacked on top of the conductive metal plate to solid-phase diffusion bond them together, and the tip of the fiber bundle is made into a parting part where the fibers are separated into brush-like shapes, and the tip of this parting part is The current collection brush used as the current collection sliding contact surface generally has an appropriate current flow when each metal-coated carbon fiber in the splitting section maintains appropriate flexibility and is in sliding contact with the slip ring or commutator. , shows good sliding properties under peripheral speed and brush pressure. 1 and 2 show the schematic structure of the current collecting brush, and in FIG. 1, a metal coating of carbon fibers and a solid-phase diffusion layer are formed above and below the base end 2 of a bundle 1 of metal-coated carbon fibers. Metal plates 3 and 4 that can be bonded are placed together and solid-phase diffusion bonded together using heat and pressure.
4 is formed in the shape of a knife edge with a suitable slope, and the fibers are diffusion bonded to each other and integrated with high density from the base end 2, the density gradually decreases along the slope to form a splitting part. 5, each fiber is separated into a brush-like shape in the separating section 5, and the distal end surface of the separating section 5 is used as a sliding surface 6 that slides in the direction of the arrow. Further, in FIG. 2, a metal plate 7 is inserted between the fiber bundles 1, and the proximal end portion 2 and the metal plate 7 are integrally diffusion bonded. The lead wire 8 may be connected to the metal plates 3, 4 by any suitable known means, or may be simultaneously diffusion bonded into the proximal end 2 or into the metal plates 3, 4 during diffusion bonding. The sliding contact surface 6 is used by sufficiently sliding on the slip ring or commutator so that it slides uniformly, and by supporting the base end 2 on a brush holder and applying an appropriate contact pressure to the sliding contact surface 6 by a spring. . In the brush having the above structure, the degree of density of the metal-coated carbon fibers in the separating section 5 has a large effect on the brush sliding characteristics. For example, if the degree of density is too high, the fibers in the separating section 5 will bind each other and the flexibility will decrease, resulting in chattering in the recipient as well as in conventional solid brushes, or the tips of each fiber may Due to improper contact with the sliding contact surface, the current concentrates on some carbon fibers, increasing the contact voltage drop, and as a result, the coating metal melts, causing galling or sparks on the other sliding contact surface. etc., making it unfit for actual use. On the other hand, if the density is too small, each carbon fiber will become red hot due to excessive current, and the coating metal will melt or the carbon fibers will be burnt out. Therefore, there is an appropriate range for the density. In the present invention, this density is expressed as a percentage of the weight distribution density of the metal-coated carbon fibers in the sliding surface 6 and the cross-sectional weight density in a state where there is no space between the fibers, and this is expressed as the filling rate. It is defined as Next, test results of the metal-coated carbon fiber brush will be explained. Table 1 shows the specifications of each type of brush A to G used in the test.

[Table] The results of testing the above types of brushes are as follows. (1) Type A and B brushes, which have a high degree of ease of movement of each fiber and a high filling rate, have no flexibility in the separating section 5 and behave like solid brushes.
Difficult to rub together and not suitable for continuous use. The movement of the C-type brush is a little stiff because the fibers in the separating section 5 bind each other, but since the fibers are not fixed to each other, they can be bent by the sliding contact pressure, and the sliding speed is 15.
It was observed that the sliding contact surface 6 became optically sensitive after about 30 minutes, and was able to make good sliding contact with the slip ring. Therefore, from this point of view, it is appropriate to set the upper limit of the filling rate to about 40%. However, even with a C-type brush with a filling rate of 39%, if the contact voltage drop exceeds a certain value, the fibers will partially stick to each other on the sliding surface 6, so it is necessary to limit the contact voltage drop. It was also observed that the C-type brush sometimes caused chattering. Therefore, we created prototype brushes of the D, E, EM, and F types that were even more flexible, but the D type had the same number of fibers as the C type, but the thickness of the coated metal was halved, and the E type was the same as the C type. The number of fibers is adjusted with the same coating thickness,
In addition, type F has a coating thickness of 1 μm, and the number of fibers is adjusted so that the total cross-sectional area of aluminum coated is the same as type E. The EM type is almost the same as the E type except that it uses carbon fiber with a high modulus of elasticity. All of these D to F type brushes had flexible parting portions 5, and showed a very smooth sliding contact state, compared to the C type brush which sometimes caused chattering. However, even with type D to F brushes, when the contact voltage drop exceeded a certain level, a phenomenon was observed in which the aluminum coating at the tip of the brush melted and the fibers partially stuck to each other. (2) Contact voltage drop The contact voltage drop tends to increase over time due to oxidation of the slip ring surface, and if this exceeds a certain value, the above-mentioned bonding between fibers will occur. When conducting tests using silver plating as a noble metal layer, it was found that even with a low brush load, large currents could be passed with a low contact voltage drop. Figure 3 a and b are
Each E on a silver-plated brass slip ring.
The actual measured value of the contact voltage drop when a type brush (positive electrode side) and an F type brush (negative electrode side) are combined is shown, and the measurement point numbers in the figure indicate the measurement order. Each measurement point was measured after energizing for at least 1.5 hours, and although there were some exceptions, it was generally observed that the later in the order the contact voltage drop for the same current decreased. Particularly in the latter case, stable reproducibility was obtained. This is thought to be because the brush has become accustomed to the slip ring. The curve in the figure shows the minimum voltage drop characteristic, and the current density is a value calculated based on the area of the brush sliding contact surface in the actual sliding contact state. FIG. 4 shows the positive and negative contact voltage drop characteristics of a G-type brush for a slip ring similar to FIG. 3. In this case as well, a considerably large current density can be obtained, but the flexibility of the separating section 5 is comparable to that of the C-type brush. (3) Generation of sparks Tests have shown that the generation of sparks is related to the phenomenon of partial sticking between fiber tips due to an increase in contact voltage drop.The results of this study will be explained below. First, when the brush tip was brought into contact with and separated from a copper piece under constant DC voltage to see how sparks were generated, the limit voltage for spark generation was 0.5V. In addition, the measured specific resistance value (6×10 ^-6
The resistance of one fiber is calculated from Ωcm) and is 6.3Ωcm. Therefore, the fiber current when a spark occurs is
0.5V/6.3Ωcm=0.08A. On the other hand, when the single fibers were observed under a microscope while being energized, it was found that the fibers became red hot at about 0.1 A and were burned out at higher currents. This limiting current is approximated to the current when a spark occurs (0.08A). From this, it is inferred that the sparks in the aluminum-coated carbon fiber brush are caused by the fibers being burned away by the current exceeding the limit current. As mentioned above, the phenomenon of partial fixation of the fibers at the tip of the brush when the contact voltage drop exceeds a certain value is thought to occur because the current concentrates on the fibers through which the current flows particularly easily when the brush is in sliding contact. It is necessary to keep the current to a certain limit to prevent sparks and to prevent the fiber tips from sticking partially, and metal-coated carbon fiber brushes can maintain the maximum current of conventional solid brushes at a relatively small contact voltage drop of about 0.1V. It can be seen that it is possible to collect current at a much higher current density than the current density (25 A/ ^cm2 ). As is clear from the above test results, the current of each fiber must be set within a range that does not cause red heat, and therefore the minimum number of fibers that make up the brush is determined by the current capacity of each fiber. , if we express the filling rate instead of the number of fibers, the filling rate is 5.
% or more; if it is less than this, there is a risk that the fibers will be burned out. The present invention has the above-mentioned configuration, and in the current collecting brush made of metal-coated carbon fibers, the filling rate of the fibers is preferably selected in the range of 5 to 40%. higher than current density
At a current density of 30 A/cm ² or more, it has the effect of exhibiting good sliding characteristics against the mating sliding surface.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing different structures of current collecting brushes made of metal-coated carbon fiber according to the present invention, and FIGS. 3a and 3b are E-type and F-type brushes, respectively.
FIG. 4 is a diagram showing the contact voltage drop of the G-type brush. 2...Proximal end portion, 5...Dividing portion, 6...Sliding contact surface.

Claims (1)

[Claims] 1. A current collecting brush in which a large number of metal-coated carbon fibers are bundled and their base ends are solid phase diffusion bonded to each other, and the tip of the brush-like branching part at the tip slides into a slip ring or a commutator, and the surface is coated with a noble metal. A current collecting brush made of metal-coated carbon fibers, which is brought into sliding contact with a slip ring or commutator on which a coating layer is formed, and whose filling rate on the brush sliding contact surface of the fibers is 5 to 40%.