Earth brush unit

Abstract

In this earth brush unit, an earth brush to which a base part of a lead wire is attached is housed in a housing comprising a box-shaped resin part and a plate-shaped metal part, and the tip of the lead wire is fixed to the metal part. The earth brush is housed in a brush housing hole of the resin part and energized by a spring. The metal part includes a bottom plate at the bottom of the resin part and a pair of attachment plates extending from the bottom to both sides of the resin part, and the attachment plates are arranged from the center to the tip portion of the resin part at positions along the direction from the base end to the tip of the resin part. The tip of the lead wire is attached to the metal part at a position closer to the base end of the resin part than the pair of attachment plates. The high-frequency impedance of the earth brush unit is reduced.

Description

Earth Brush Unit

[0001] The present invention relates to an earth brush unit comprising an earth brush and a housing for earthing the drive shaft of an electric vehicle to the vehicle body, for example, to reduce high-frequency noise.

[0002] It is known that electric vehicles equipped with motors as a driving source for the vehicle's running can experience distorted car radio audio due to electromagnetic noise generated by the inverter that controls the motor. Car navigation systems, TVs, drive recorders, and other receiving devices installed in the vehicle's cabin, as well as other electrical equipment, are also affected by electromagnetic noise. For this reason, reducing electromagnetic noise has become increasingly important in recent years. Furthermore, in vehicles that use inverters to control generators, the bearings on the generator's drive shaft can be subject to electrolytic corrosion due to electromagnetic noise.

[0003] The applicant has proposed an earth brush made primarily of silver and carbonaceous materials that reduces electromagnetic noise emitted from the drive shaft of an electric vehicle by earthing the drive shaft, etc. (Patent Document 1: JP7250337B). When in use, this earth brush is housed in a housing and comes into sliding contact with the drive shaft.

[0004] The housing that houses the earth brush is also called a brush holder. In Patent Document 2 (JP2020-202608A), the earth brush is housed in a brush holder and biased toward the drive shaft of the motor by a spring. The earth brush is then devised to prevent it from jumping out of the brush holder when assembled to the drive shaft. In Patent Document 3 (JP2011-135720A), a spring biases the earth brush toward the drive shaft, electrically connecting the earth brush to the housing. Furthermore, in Patent Document 3, the earth brush prevents electrolytic corrosion of the drive shaft, etc.

[0005] JP7250337BTC2020-202608AJP2011-135720A

[0006] The applicant prototyped a housing 4' shown in Figure 6 as the housing for the earth brush of Patent Document 1. The housing 4' consists of a resin portion 5 and a plate-shaped metal portion 6'. An earth brush 12 is housed in a brush housing hole in the resin portion 5, and a spring 14 brings the earth brush 12 into sliding contact with the drive shaft 30. A lead wire 16 is attached to the side of the earth brush 12, which is then attached to the back plate 8 of the metal portion 6'. The drive shaft 30 is then earthed from the back plate 8 via the mounting plates 7', 7' and mounting holes 10', 10' of the metal portion 6'. However, this housing 4' did not provide sufficient electromagnetic noise reduction.

[0007] The inventors then modified the metal part 6 as shown in Figure 1, so that the earth current that reached the rear panel 8 would flow in the opposite direction to the lead wire 16, and would flow from the metal plate 7 located at the center of the housing to the mounting hole 10. This reduced the high-frequency impedance of the earth brush unit (Figure 5, Table 1). In other words, by allowing the earth current to flow in the opposite direction to the lead wire 16 at the bottom of the resin part 5, the high-frequency impedance was reduced.

[0008] An object of the present invention is to reduce the high frequency impedance of an earth brush unit by improving the structure of the housing of the earth brush unit.

[0009] In this earth brush unit, an earth brush with a base portion of a lead wire attached thereto is housed in a housing consisting of a box-shaped resin part and a plate-shaped metal part, and the tip of the lead wire is fixed to the metal part. The base portion of the earth brush is housed in a brush housing hole that extends from the base end of the resin part to the tip and is open at the tip, and a spring in the hole urges the earth brush outward from the brush housing hole. The metal part includes a bottom plate at the bottom of the resin part and a pair of mounting plates that extend from the bottom to both sides of the resin part in a direction perpendicular to the direction from the base end of the resin part to the tip. The pair of mounting plates are positioned from the center to the tip of the resin part in the direction from the base end to the tip, and the tip of the lead wire is attached to the metal part at a position closer to the base end of the resin part than the pair of mounting plates.

[0010] Preferably, the metal part has a back plate at the base end of the resin part, and for ease of installation, the tips of the lead wires are attached to the back plate.

[0011] Preferably, in addition to the brush housing hole, the resin part is provided with a lead wire housing hole parallel to the brush housing hole to prevent interference between the spring and the lead wire. A slit is then provided between the brush housing hole and the lead wire housing hole, and the lead wire is guided from the earth brush to the lead wire housing hole, with the tip of the lead wire attached to the back panel.

[0012] Preferably, the average gap (spacing) between the lead wire and the bottom plate is 0.5 mm or more and 10 mm or less. The shorter the gap, the lower the high-frequency impedance of the earth brush unit (see Figure 5 and Table 1). The average gap is preferably 1 mm or more and 10 mm or less, and particularly preferably 1 mm or more and 5 mm or less. For example, shortening the average gap from 8 mm to 2 mm reduces the high-frequency impedance by, for example, 2 / 3 or less.

[0013] The earth brush is preferably a silver-carbon brush containing silver and carbon, which has low impedance and low contact resistance with the drive shaft.

[0014] In this invention, the direction of the earth current is opposite between the lead wire and the bottom plate of the metal part, so the magnetic flux caused by the earth current cancels out between the lead wire and the bottom plate. This reduces the high-frequency impedance of the earth brush unit, making it easier for the earth current to flow and reducing high-frequency noise generated from the drive shaft, etc. In this specification, high frequency refers broadly to frequencies between 3 and 100 MHz, and narrowly to frequencies between 3 and 30 MHz.

[0015] A cross-sectional view of the earth brush unit of the embodiment. A cross-sectional view of the earth brush unit of the embodiment, showing the state in which the earth brush has worn down and become shorter. A cross-sectional view of the earth brush unit of the embodiment taken along the III-III direction in Figure 2. A view showing the mounting state of the earth brush unit of the embodiment. A characteristic diagram showing high-frequency impedance in the embodiment and a comparative example in which the position of the mounting plate of the housing is changed. A cross-sectional view of the earth brush unit of the comparative example.

[0016] The best mode for carrying out the present invention will be described below. The present invention is not limited to the mode, but is defined by the claims, and can be modified by adding matters known to those skilled in the art to the mode.

[0017] Figures 1 to 5 show an earth brush unit 2 according to an embodiment. The housing 4 is formed by insert-molding a box-shaped resin section 5 so that the rear panel 8 is integrated with a bent, plate-like metal section 6. The metal section 6 comprises a bottom plate 9 at the bottom of the resin section 5, a pair of mounting plates 7 extending from the bottom plate 9 to both sides of the resin section 5, and a rear panel 8 located at the base of the resin section 5 and bent from the bottom plate 9. The mounting plates 7 are attached to the exterior, for example, using mounting holes 10. The mounting plates 7 are provided from the center to the tip of the resin section 5 along a direction connecting the base (lower part in Figures 1 and 2) and the tip (upper part in Figures 1 and 2) of the resin section 5. "Provided from the center to the tip" means that the mounting plates may be provided at the center, the tip, or both the center and the tip.

[0018] The earth brush 12 is preferably made of silver-carbon material, with silver being 30% by mass or more and 90% by mass or less, and carbon being 70% by mass or less and 10% by mass or more, when the total mass of silver and carbon is 100% by mass.

[0019] The resin portion 5 is insulating and is made of, for example, polyphenylene sulfide, but polyethylene, polypropylene, polystyrene, AS resin, ABS resin, phenolic resin, urea resin, melamine resin, etc. may also be used. The resin portion 5 has a brush housing hole 13 and a lead wire housing hole 17 that extend from its base to its tip, and the tip is open. The brush housing hole 13 houses an earth brush 12. The base of the earth brush 12 is biased toward the tip by a spring 14, such as a spring coil, so that the tip of the brush 12 slides against the drive shaft 30 of an electric vehicle or the like. Note that in this specification, the term "electric vehicle" includes hybrid cars. In addition to reducing high-frequency noise, the earth brush unit 2 can also be used to prevent electrolytic corrosion of the drive shaft of an inverter-controlled generator in an internal combustion engine vehicle.

[0020] For example, the base of the lead wire 16 is attached to the side of the brush 12, and the lead wire 16 enters the lead wire accommodating hole 17 through a slit 18 connecting the brush accommodating hole 13 and the lead wire accommodating hole 17, and its tip is soldered to the back plate 8 of the metal part 6, for example, by solder 20.

[0021] The earth brush 12 wears and shortens with use, and Fig. 1 shows the initial state, with the lead wire 16 having play and repeatedly bending or curving. Fig. 2 shows the state after further wear, with the lead wire 16 having less play and approaching a straight state.

[0022] As shown in FIG. 3 , the bottom plate 9 extends from the rear plate 8 toward the tip of the housing 4 along the bottom surface of the resin portion 5, and the upper surface of the bottom plate 9 is covered with the resin portion 5, insulating the bottom plate 9 from the lead wires 16. The gap g between the bottom plate 9 and the lead wires 16 is, for example, 0.5 mm to 10 mm, preferably 1 mm to 10 mm, and particularly preferably 1 mm to 5 mm. In this embodiment, the initial dimensions of the earth brush 12 are, for example, 5 mm x 5 mm x 15 mm, and the resin portion 5 is, for example, 11 mm x 17 mm x 30 mm. The brush receiving hole 13 is, for example, 5.2 mm x 5.2 mm x 28 mm. The lead wire receiving hole 17 has a diameter of 3 mm and a length of 28 mm.

[0023] 4 shows the installation state of the earth brush unit 2. The drive shaft 30 is supported by, for example, a bearing 32, and one end protrudes from the casing 34. The earth brush unit 2 is fixed to the casing 34 with fasteners 35 and 36, and the drive shaft 30 is earthed to the casing 34 in the order of the earth brush 12, lead wire, back plate, bottom plate 9, mounting plate, and fasteners 35 and 36.

[0024] The impedance between the drive shaft 30 and the casing 34 was measured for Examples 1 and 2 (average gap values ​​of 2 mm and 8 mm) and the comparative example (structure shown in Figure 6). The results are shown in Figure 5 and Table 1. In Examples 1 and 2, the impedance at frequencies between 3 and 50 MHz was, for example, 70% or less of that of the comparative example. Furthermore, reducing the gap g from 8 mm to 2 mm reduced the impedance to approximately two-thirds. This indicates that the magnetic flux caused by the current flowing through the lead wire 16 and the magnetic flux caused by the current flowing through the bottom plate 9 cancel each other out. Based on this principle, electromagnetic noise generated by the drive shaft and other components can be reduced. In other words, the condition for reducing high-frequency impedance is the existence of an area where the earth current flows in opposite directions between the lead wire 16 and the bottom plate 9. The resulting effect is that the high-frequency impedance of the earth brush unit 2 can be reduced compared to the comparative example. Reducing the high-frequency impedance of the earth brush unit 2 increases the earth current flowing toward the vehicle body, reducing electromagnetic noise, especially high-frequency noise, emitted from the drive shaft and other components.

[0025] 2.1 2.1 2.1 2.1 * The average gap g between the lead wire and the metal part 6 was 2 mm in Example 1 and 8 mm in Example 2. * The housing 4' in Figure 6 was used in the comparative example.

[0026] 2 Earth brush unit 4 Housing 5 Resin part 6 Metal part 7, 7' Mounting plate 8 Back plate 9 Bottom plate 10, 10' Mounting hole 12 Earth brush 13 Brush accommodating hole 14 Spring 16 Lead wire 17 Lead wire accommodating hole 18 Slit 20 Solder 30 Drive shaft 32 Bearing 34 Casing 35, 36 Fastener g Gap

Claims

1. An earth brush unit in which an earth brush with a base portion of a lead wire attached thereto is contained in a housing consisting of a box-shaped resin part and a plate-shaped metal part, and the tip of the lead wire is fixed to the metal part, wherein the base portion of the earth brush is contained in a brush housing hole that faces from the base end of the resin part to the tip and is open at the tip, and a spring in the hole urges the earth brush toward the outside of the brush housing hole, the metal part comprises a bottom plate at the bottom of the resin part and a pair of mounting plates that extend from the bottom to both sides of the resin part along a direction perpendicular to the direction from the base end of the resin part to the tip, the pair of mounting plates are positioned from the center of the resin part to the tip, in a direction facing from the base end of the resin part to the tip, and the tip of the lead wire is attached to the metal part at a position closer to the base end of the resin part than the pair of mounting plates.

2. The earth brush unit of claim 1, wherein the metal part has a back plate at the base end of the resin part, and the tip of the lead wire is attached to the back plate.

3. An earth brush unit according to claim 2, characterized in that the resin part has, in addition to the brush housing hole, a lead wire housing hole parallel to the brush housing hole, a slit connecting the brush housing hole and the lead wire housing hole is provided in the resin part, and the lead wire is housed in the lead wire housing hole and has its tip attached to the back panel.

4. The earth brush unit of claim 3, wherein the average gap between said lead wires and said bottom plate is 0.5 mm or more and 10 mm or less.

5. The earth brush unit according to claim 4, wherein the earth brush is a silver-carbon brush containing silver and carbon.

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