Brush of motor for automotive electronics

Abstract

A brush for a motor for electrical equipment in an automobile includes a main brush portion containing carbon and an abrasive having a Vickers hardness higher than or equal to 10 GPa and lower than or equal to 14 GPa. The sliding noise of the brush is reduced in the brush for a motor for electrical equipment in an automobile.

Claims

1. A brush for a motor for electrical equipment in an automobile, the brush comprising: a main brush portion containing carbon and an abrasive having a Vickers hardness higher than or equal to 10 GPa and lower than or equal to 14 GPa; wherein the main brush portion contains a metal at a weight ratio between the carbon and the metal lower than or equal to 90:10 and higher than or equal to 40:60.

2. The brush for a motor for electrical equipment in an automobile according to claim 1, wherein the main brush portion contains the abrasive at a concentration higher than or equal to 0.1 wt % and lower than or equal to 2.0 wt %.

3. The brush for a motor for electrical equipment in an automobile according to claim 1, wherein the abrasive is ZrO.sub.2.

4. The brush for a motor for electrical equipment in an automobile according to claim 3, wherein said ZrO.sub.2 has an average particle diameter less than or equal to 30 μm in a maximum Feret diameter.

5. The brush for a motor for electrical equipment in an automobile according to claim 4, wherein said ZrO.sub.2 particles has an average particle diameter greater than or equal to 5 μm and less than or equal to 20 μm in the maximum Feret diameter.

6. The brush for a motor for electrical equipment in an automobile according to claim 5, wherein the abrasive consists of abrasive particles.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows photographs of a method for measuring a particle diameter of the abrasive included in a brush according to an embodiment.

(2) FIG. 2 is a side view of a brush according to an embodiment.

(3) FIG. 3A is a graph showing the roundness of a commutator after sliding contact with a brush according to Example 1, and FIG. 3B is a graph showing the roundness of a commutator after sliding contact with a brush according to Comparative Example 1.

DETAILED DESCRIPTION

(4) One or more preferred embodiments of the present invention will now be described. The present invention is not limited to these embodiments, but is defined based on the scope of the claims and can be modified by adding matters known by those skilled in the art to the embodiments.

Embodiments

(5) Flake natural graphite with an average particle diameter of 50 μm, an abrasive of, for example, ZrO.sub.2 (with the Vickers hardness of 12.3 Gpa), a solid lubricant, MoS.sub.2 (with an average particle diameter of 2.5 μm and a content of 0.5 wt % in the brush), and a phenol resin binder (equivalent to a carbon content of 5 wt % in the brush) are kneaded by a mixer to be homogeneous, and pulverized into a powder passable through a 32-mesh sieve to form a resin-treated graphite powder. An electrolytic copper powder with an average particle diameter of 30 μm is added to the obtained resin-treated graphite powder, and mixed with a V-shaped mixer until being homogeneous to form a material for the main brush portion. The obtained material for the main brush portion is molded under a pressure of 0.20 MPa, and baked in a predetermined atmosphere to form a brush, including a lead, for a motor for electrical equipment in an automobile. The phenol resin binder is converted into carbon. Thus, brushes containing ZrO.sub.2 that differ in average particle diameter and content are formed, and brushes containing 3Al.sub.2O.sub.3.2SiO.sub.2 (mullite, with the Vickers hardness of 10.8 Gpa) or Si.sub.3N.sub.4 (silicon nitride, with the Vickers hardness of 14.0 Gpa) are formed as examples including a material other than ZrO.sub.2. Brushes of comparative examples contain SiC (with the Vickers hardness of 23.0 Gpa), Al.sub.2O.sub.3 (with the Vickers hardness of 15.2 Gpa), or SiO.sub.2 (with the Vickers hardness of 9.0 Gpa). The composition and the manufacturing conditions, excluding the type of an abrasive, the particle diameter, and the content, are the same for the brushes.

(6) Instead of an electrolytic copper powder, examples of a metal powder include an atomized copper powder, a silver powder, a copper alloy powder such as a brass powder, a tin powder, or a mixture of these powders. The type of metal powder and the average particle diameter may be selected as appropriate. The type of graphite and the average particle diameter may be selected as appropriate. The type and the content of a binder may be selected as appropriate. Instead of a phenol resin, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), or other materials may be used. The total content of graphite and the carbon from the binder is used as the carbon content. Instead of MoS.sub.2, another solid lubricant such as WS.sub.2 may be used. The presence or absence of a solid lubricant and the content, the type, and the average particle diameter of the solid lubricant may be selected as appropriate. The brush may also contain components other than carbon, metal, an abrasive, and a solid lubricant. The average particle diameters of components other than the abrasive are measured in the powder form by the laser light scattering method.

(7) The average particle diameter of the abrasive is measured after a brush is cut, the brush is embedded in a resin, and the resin surface is ground. In the measurement, the surface is observed with a scanning electron microscope (SEM, such as S-300N manufactured by Hitachi High-Tech), and the abrasive particles are observed with an energy dispersion X-ray analyzer (EDX, such as EMAX ENERGY EX-250 manufactured by HORIBA, Ltd.) attached to the SEM to identify the particles of the abrasive. From the SEM image, the maximum distance (maximum Feret diameter) between two parallel lines holding the abrasive particle between them is determined as the particle diameter. The maximum Feret diameters of 100 abrasive particles are measured, and the arithmetic mean of the diameters is used as the average particle diameter of the abrasive. As described above, the maximum Feret diameter is prescribed by JIS Z8827-1:2008.

(8) FIG. 1 shows SEM images and EDX images at two positions captured during measurement of the average particle diameter of ZrO.sub.2 in a brush according to a preferred embodiment (Example 1). The maximum Feret diameter is used, without using laser light scattering or another method that may be inappropriate for measuring the average particle diameter in a brush. In addition to the maximum Feret diameter, for example, the minimum Feret diameter may also be considered for the size of the abrasive particle. However, the function of the abrasive is defined by the maximum Feret diameter rather than, for example, the minimum Feret diameter. In other words, the abrasion function of the abrasive particle having a major axis and a minor axis is more likely to depend on the major axis rather than the minor axis. Thus, the maximum Feret diameter is used as the particle diameter of the abrasive particle. The maximum Feret diameters are 8.35 μm and 8.38 μm in the upper right of FIG. 1 and are 8.84 μm, 6.24 μm, and 9.10 μm in the lower right of FIG. 1.

(9) FIG. 2 shows a brush 2 of a motor for electrical equipment in an automobile. The brush 2 includes a main brush portion 4 and a lead 8 attached to the main brush portion 4. The brush 2 comes in contact with a commutator 10 of the motor at a sliding surface 6. The brush 2 may be a multiple-layered brush such as a double-layered brush or a triple-layered brush. The multiple-layered brush may include at least one layer, or preferably, all the layers according to embodiments of the present invention.

(10) The brushes according to the examples and comparative examples were evaluated as follows. First, the resistivity of each brush was measured. Each brush was subsequently installed in a motor for electrical equipment in an automobile and operated for 200 hours. Thereafter, the motor was operated in a soundproof chamber, and the noise from the motor was measured by a noise meter. Thereafter, the brush and the commutator were removed from the motor, the wear loss of the brush was measured, and the roundness of the outer circumference of the commutator was measured. The conditions for a 200-hour operation, such as the surrounding temperature, the amount of airflow, and the motor operating voltage are the same for all the brushes, and the conditions for measurement with the noise meter are also the same for all the brushes. Tables 1 and 2 show the results. The total amount of graphite and carbon from a binder is used as the amount of carbon, and the content of MoS.sub.2 remains at 0.5 wt %.

(11) TABLE-US-00001 TABLE 1 Example Example Example 2 Example 4 Example Example Example 8 Abrasive 3 Particle 5 6 7 Metal amount: Abrasive diameter: Particle Mullite Metal amount: Example upper amount: slightly diameter: used amount: lower 9 Example limit lower large lower Noise/ upper limit Si.sub.3N.sub.4 1 Wear limit Wear limit wear limit Electric used Preferred loss: Noise: loss: Noise: loss: Noise: resistance: Vickers embodi- slightly slightly slightly slightly slightly slightly slightly hardness: Material/quality ment large large large large large large high 14 GPa Material Metal (Cu) Ratio of wt % 23 23 23 23 23 23 48 15 23 compound Carbon Ratio of wt % 76 74.7 76.3 76 76 76 51 84 76 compound Abrasive ZrO.sub.2 wt % 0.5 1.8 0.2 0.5 0.5 — 0.5 0.5 — Particle μm 9.3 8.5 9.2 22.0 4.5 — 7.8 15.2 — diameter Vickers GPa 12.5 12.5 12.5 12.5 12.5 — 12.5 12.5 — hardness 3Al.sub.2O.sub.3•2SiO.sub.2 wt % — — — — — 0.5 — — — Particle μm — — — — — 28.5 — — — diameter Vickers GPa — — — — — 10.8 — — — hardness Si.sub.3N.sub.4 wt % — — — — — — — — 0.5 Particle μm — — — — — — — — 23.5 diameter Vickers GPa — — — — — — — — 14.0 hardness Total 99.5 99.5 99.5 99.5 99.5 99.5 99.5 99.5 99.5 Quantity Noise dB-A 50 53 58 55 58 56 58 52 58 ≤60 dB Wear loss ≤0.9 mm 0.8 0.85 0.78 0.88 0.6 0.85 0.7 0.8 0.85 Resistivity μΩ .Math. cm 630 630 610 625 620 630 100 1500 650 350-900 Commutator Roundness Good (G) Fair (F) F G F F F G F appearance evaluation

(12) TABLE-US-00002 TABLE 2 Comparative Example 1 Hardness: excessively Comparative high Example 2 Noise: large Hardness: Comparative Wear loss: excessively low Example 3 Material/quality large Noise: large Al.sub.2O.sub.3 Material Metal (Cu) Ratio of wt % 25 25 25 compound Carbon Ratio of wt % 74 74 74 compound Abrasive Content of wt % 0.5 — — SiC Particle μm 10.5 — — diameter Vickers GPa 23.0 — — hardness Content of wt % — 0.5 — SiO.sub.2 Particle μm — 18.5 — diameter Vickers GPa — 8.7 — hardness Content of wt % — — 0.5 Al.sub.2O.sub.3 Particle μm — — 10.6 diameter Vickers GPa — — 15.2 hardness Total 99.5 99.5 99.5 Quantity Noise dB A 70 65 66 ≤60 dB Wear loss ≤0.9 mm 0.95 0.8 0.92 Resistivity μΩ .Math. cm 650 625 630 350-900 Commutator Roundness Poor (P) P P appearance evaluation

(13) Table 3 shows the correlation between the Vickers hardness of the abrasive and the noise level (sliding noise of the brush from the motor) extracted from Tables 1 and 2. The Vickers hardness is in GPa below. As clearly shown in Table 3, the noise level correlates with the Vickers hardness of the abrasive, and the noise level is reduced with the abrasive with the Vickers hardness higher than or equal to 10 and lower than or equal to 14. The best result was obtained for ZrO.sub.2 having the Vickers hardness of 12.5. Aluminum nitride (AlN, with the Vickers hardness of 10.4 Gpa) has a noise level and a wear loss similar to those of 3Al.sub.2O.sub.3.2SiO.sub.2 (mullite, with the Vickers hardness of 10.8 Gpa).

(14) TABLE-US-00003 TABLE 3 Vickers hardness of abrasive, noise level, and wear loss of brush Comparative SiO.sub.2 hardness 65 dB 0.8 mm Example 2 of 8.7 Example 6 3Al.sub.2O.sub.3•2SiO.sub.2 hardness 56 dB 0.85 mm of 10.8 Example 1 ZrO.sub.2 hardness 50 dB 0.8 mm of 12.5 Example 9 Si.sub.3N.sub.4 hardness 58 dB 0.85 mm of 14.0 Comparative A1.sub.2O.sub.3 hardness 66 dB 0.92 mm Example 3 of 15.2 Comparative SiC hardness 70 dB 0.95 mm Example 1 of 23.0

(15) Table 4 shows the correlation between the content of the abrasive (ZrO.sub.2), the average particle diameter, the noise level, and the wear loss extracted from Tables 1 and 2. Table 4 shows the samples having similar average particle diameters. Irrespective of the content of the abrasive, the samples containing ZrO.sub.2 as the abrasive reduced the noise level compared with Comparative Examples 1 to 3 (with the Vickers hardness lower than 10 or higher than 14). The samples containing 0.2 wt %, 0.5 wt %, and 1.8 wt % of ZrO.sub.2 achieved sufficient silence while reducing the wear loss. The sample containing 0.5 wt % of ZrO.sub.2 achieved the highest performance. These results show that the content of the abrasive is preferably higher than or equal to 0.1 wt % and lower than or equal to 2.0 wt %, more preferably, higher than or equal to 0.2 wt % and lower than or equal to 1.8 wt %, and most preferably, higher than or equal to 0.3 wt % and lower than or equal to 1.0 wt %.

(16) TABLE-US-00004 TABLE 4 Content of abrasive (ZrO.sub.2), average particle diameter, noise level, and wear loss Example 3 ZrO.sub.2 0.2 wt % 9.2 μm 58 dB 0.78 mm Example 1 ZrO.sub.2 0.5 wt % 9.3 μm 50 dB 0.8 mm Example 2 ZrO.sub.2 1.8 wt % 8.5 μm 53 dB 0.85 mm

(17) Brushes containing 0.5 wt % of ZrO.sub.2 with different weight ratios between a metal and graphite are extracted from Tables 1 and 2. Table 5 shows the effect of the weight ratio between a metal and graphite on the noise level, the wear loss, and the resistivity. As clearly shown in Table 5, to optimize the noise level and the wear loss, the weight ratio between carbon and a metal is preferably lower than or equal to 90:10 and higher than or equal to 40:60, and particularly preferably, lower than or equal to 85:15 and higher than or equal to 40:60.

(18) TABLE-US-00005 TABLE 5 Weight ratio of carbon/metal, average particle diameter of ZrO.sub.2, noise level, wear loss, and resistivity Example 8 84:15 15.2 μm 52 dB 0.8 mm 1500 μΩ .Math. cm Example 1 76:23  9.3 μm 50 dB 0.8 mm  630 μΩ .Math. cm Example 7 51:48  7.8 μm 58 dB 0.7 mm  100 μΩ .Math. cm

(19) Table 6 shows the correlation between the average particle diameter of ZrO.sub.2, the noise level, and the wear loss of a brush extracted from Tables 1 and 2. All the samples contain 0.5 wt % of ZrO.sub.2. The sample with an average particle diameter of 9.3 μm (Example 1) has the lowest noise level, and the sample with an average particle diameter of 22 μm (Example 4) has an increased noise level and an increased brush wear loss. The sample with an average particle diameter of 4.5 μm (Example 5) has a small wear loss but has a high noise level. Although not particularly limited to these, the average particle diameter of ZrO.sub.2 is preferably less than or equal to 30 μm, and particularly preferably, greater than or equal to 5 μm and less than or equal to 20 μm. Among samples of the abrasive with the Vickers hardness within a range of higher than or equal to 10 and lower than or equal to 14, 3Al.sub.2O.sub.3.2SiO.sub.2 (Example 6, with the Vickers hardness of 10.8) and Si.sub.3N.sub.4 (Example 9, with the Vickers hardness of 14.0) with the same average particle diameter will behave similarly. Thus, the average particle diameter is preferably less than or equal to 30 μm, and particularly preferably greater than or equal to 5 μm and less than or equal to 20 μM.

(20) TABLE-US-00006 TABLE 6 Average particle diameter of ZrO.sub.2, noise level, and wear loss Example 5 4.5 μm 58 dB 0.6 mm Example 1 9.3 μm 50 dB 0.8 mm Example 4 22 μm 55 dB 0.88 mm

(21) When the commutator surface wears unevenly due to sliding contact with the brush, the commutator surface becomes different from a true circle, and the brush noise increases. The roundness of the commutator surface after the 200-hour operation was measured with a roundness and cylindrical-shape measurement device (Roundtest RA-2000) manufactured by Mitutoyo Corporation and analyzed with an analytical software (Roundpak-F2000 Ver. 4) by Mitutoyo Corporation. FIGS. 3A and 3B show the roundness, or a deviation of the commutator surface from a perfect circle in a developed manner FIG. 3A shows the result for Example 1, and FIG. 3B shows the result for Comparative Example 1. The vertical axis represents the deviation from a perfect circle in μm. Downward spikes correspond to undercuts in the commutator and can be neglected. Examples have small deviations from a perfect circle (0.00 on the vertical axis), whereas comparative examples have large deviations. Data with a sharp change from the perfect circle represents the presence of a chip in the commutator surface. The chip mostly results from a spark discharge and indicates uneven wear of the commutator surface. Tables 1 and 2 show the roundness after 200 hours in three levels, good (G), fair (F), and poor (P).

(22) Examples of a motor for electrical equipment in an automobile particularly desired to achieve silence include an automotive interior motor such as a power window motor, a power seat motor, or a blower motor, and a wiper motor installed in an automotive engine room adjacent to the cabin. The brush according to some embodiments of the present invention is suitable for these motors. These motors are installed in or around an automotive cabin. Among these, the brush according to some embodiments of the present invention is particularly suitable for an automotive interior motor installed in an automotive cabin, such as a power window motor, a power seat motor, or a blower motor.

(23) A brush may contain a component other than those described in the examples.

REFERENCE SIGNS LIST

(24) 2 brush for motor for electrical equipment in automobile 4 Main brush portion 6 Sliding surface 8 Lead 10 Commutator