Motor brush and method for producing same

Abstract

A motor brush according to the present invention comprises copper, tin, and graphite, wherein the motor brush in a state of being immersed in oil makes contact with a slip ring of a motor so that a drive current for the motor is passed through the sliding surface between the motor brush and the slip ring. A slit is provided in the sliding surface, which is the bottom surface of the brush and is in contact with the slip ring. The slit, when viewed in the rotation direction of the slip ring, has an inlet for oil in the front surface of the brush and an outlet for oil in the rear surface or a side surface of the brush. Oil that is to enter the bottom surface of the brush when the slip ring rotates is led to the slit from the inlet, and is then discharged through the outlet. The material of a sliding part of the brush contains, in terms of the mass ratio, 70-90 mass% of the copper, 5-15 mass% of the tin, and 3-20 mass% of the graphite. Thus, it is possible to obtain a brush that can drive a motor in a state of being immersed in oil. In particular, it is possible to prevent oil entering between the brush and the slip ring at the sliding surface from hindering the passage of electricity, and to reduce a voltage drop in the sliding surface between the brush and the slip ring. Moreover, it is possible to suppress wear of the brush due to sparks.　

Description

Motor Brush and Method for Manufacturing the Same

[0001] This invention relates to a motor brush and a method for manufacturing the same, and particularly to an EESM (wound field synchronous motor) and a method for manufacturing the same. This invention particularly relates to a motor brush used by being immersed in oil and a method for manufacturing the same.

[0002] As the drive motor of an electric vehicle, alternating current (AC) is the mainstream, and among them, there is a wound field synchronous motor (EESM) in which a field coil is provided in the rotor instead of a permanent magnet. The EESM energizes a direct current adjusted by a converter to the field winding wound around the rotor, and the current supply is performed through a brush and a slip ring. The EESM is used in electric vehicles and hybrid vehicles, and is equipped with a slip ring and a brush for supplying current to the field winding. Since the battery mounted for the running of an electric vehicle requires a high voltage, it is 300V to 800V, and the brush for the EESM is required to have a quality that can be driven with high output.

[0003] To drive the EESM stably, cooling is required, and particularly when miniaturizing, oil cooling is often adopted. In an EESM with an oil cooling specification, the cooling oil circulates through holes for the oil passage, etc. At this time, if the brush is contaminated with oil components, problems such as abnormal wear will occur, so the sliding contact area between the slip ring and the brush needs to be isolated with an oil seal or the like. On the other hand, there is a method of using a brush and a slip ring that can be used under oil without using the oil seal, and using them in a state where the sliding surface between the slip ring and the brush is immersed in oil.

[0004] The applicant has proposed an earth brush provided with a slit for discharging oil on the sliding surface (Patent Document 1: WO2022 / 024682A). However, the brush of Patent Document 1 is for discharging an earth current, and in order to change the earth brush to a brush with a high voltage and high output specification such as for the EESM, it is necessary to increase the conductivity of the brush.

[0005] WO2022 / 024682A

[0006] The earth brush described in Patent Document 1 and conventional conductive brushes used in internal combustion engine vehicles and rotating electric machines are generally manufactured by press-molding a powder material, which is a mixture of carbon such as graphite and metal powder such as copper, with a resin binder and additives, and then firing it. In this case, if the copper content of the brush is increased compared to the conventional brush in order to improve conductivity, the powder material will adhere to the die used for press molding, making it difficult to remove from the mold. Therefore, a material that has low resistance and does not easily adhere to the die is required. In addition, although the slits are formed by cutting in Patent Document 1, cutting a brush with a high metal content causes the blade to wear out in a short time. Therefore, a method for efficiently creating slits in the brush is required.

[0007] Furthermore, when using brushes immersed in oil, applying a current suitable for driving the motor to the brushes resulted in the insulating oil hindering current flow between the brush and the sliding surface of the slip ring, causing intense sparks, increased voltage drop across the brushes, and unstable current (see Figures 9 and 10).

[0008] The object of this invention is to provide a motor brush that can drive high-voltage, high-output motors such as EESMs while immersed in oil, and a method for manufacturing the same. The object of this invention is to provide a brush that has low resistance due to its high copper content, liquid-phase sintering is possible by melting the tin during sintering of the brush by containing an appropriate amount of tin, and can be removed from the die after pressing due to containing an appropriate amount of graphite, and a method for manufacturing the same. Furthermore, the object of this invention is to provide a manufacturing method that allows slits to be easily provided in the brush. Here, sintering refers to the phenomenon of obtaining a strong sintered body by firing a molded body containing metal powder at a temperature lower than the melting point of the main metal contained. On the other hand, the aforementioned Patent Document 1 and many conventional brushes are obtained by firing a molded body containing inorganic materials such as metal powder and graphite and an organic resin binder, which is different from the sintering of the present invention.

[0009] The motor brush of this invention contains copper, tin, and graphite, and when immersed in oil, it contacts the slip ring of the motor to conduct the motor's drive current between the sliding surfaces of the brush and the slip ring. The brush has a slit on the bottom surface of the brush, which is the sliding surface with respect to the slip ring. The slit has an oil inlet on the front of the brush when viewed from the direction of rotation of the slip ring, and an oil outlet on the rear or side of the brush. The slit guides oil that tries to enter the bottom surface of the brush due to the rotation of the slip ring from the inlet to the slit and discharges it from the outlet. Furthermore, the material of the sliding part of the brush is characterized in that the mass ratio of copper, tin, and graphite is 70 mass% to 90 mass%, tin is 5 mass% to 15 mass%, and graphite is 3 mass% to 20 mass%.

[0010] The present invention provides a method for manufacturing a motor brush, which contains copper, tin, and graphite, and is immersed in oil. By contacting the motor's slip ring, the brush transmits the motor's drive current between the sliding surfaces of the brush and the slip ring. The manufactured motor brush has a slit on its bottom surface, which is the sliding surface with the slip ring. The slit has an oil inlet on the front of the brush when viewed from the direction of rotation of the slip ring, and an oil outlet on the rear or side of the brush. The slit is configured to guide oil attempting to enter the bottom surface of the brush due to the rotation of the slip ring from the inlet to the slit and discharge it from the outlet.

[0011] In the manufacturing method of this invention, a lower punch and an upper punch that can move up and down are arranged above and below a die having a cavity, and a projection corresponding to the shape of the slit is provided on the bottom surface of the upper punch or the top surface of the lower punch. A powder material in which the mass ratio of copper, tin, and graphite is 70 mass% to 90 mass%, tin 5 mass% to 15 mass%, and graphite 3 mass% to 20 mass%, is put into the cavity as the material for the sliding part of the brush, and the lower punch is raised and the upper punch is lowered at the same time to press the powder material to form a precursor for the brush and to form a slit with the projection, and then the upper punch is raised to a position away from the die and the upper end of the lower punch is raised to at least the top surface of the die to remove the precursor for the brush from the cavity, and then the precursor for the brush is sintered in a non-oxidizing atmosphere.

[0012] The sliding part refers to the portion of the brush that is intended to slide against the slip ring. As shown in the example, in a single-layer brush, the sliding part is the portion of the brush excluding accessories such as lead wires. In a multi-layer brush, which has a base portion that is not intended to slide against the slip ring in addition to the sliding part at the tip, the base portion is not included in the sliding part.

[0013] Preferably, the material of the sliding part of the motor brush consists only of copper, tin, and graphite, and does not contain a resin binder. In this case, by not including a resin binder and increasing the copper concentration, high conductivity is ensured, and liquid-phase sintering with tin is performed in the sintering process after pressing, thereby eliminating the need for a resin binder.

[0014] Preferably, the motor brushes are configured to slide against the slip rings of the EESM (winding field synchronous motor). This invention allows the EESM to be driven at high power.

[0015] This invention provides a brush that can drive a motor while immersed in oil. In particular, the oil that enters between the sliding surfaces of the brush and the slip ring does not obstruct the conduction of electricity, and the voltage drop between the sliding surfaces of the brush and the slip ring can be reduced. Furthermore, by reducing the voltage drop, wear of the brush due to spark generation can be suppressed.

[0016] This invention enhances the conductivity of the brush by using copper and enables liquid-phase sintering by using tin. As a result, a low-resistance brush with a high metal content is obtained. Brushes with a high metal content tend to cause the powder material to adhere to the die cavity during pressing, making demolition after pressing difficult. Therefore, an appropriate amount of graphite is added to facilitate demolition.

[0017] In this manufacturing method, the punch protrusions are transferred to the brush precursor during press molding, and slits can be formed on the bottom surface of the brush precursor. Furthermore, by adding an appropriate amount of graphite, the brush can be removed from the die. In addition, sufficient strength can be imparted to the brush by liquid-phase sintering with tin, and the resistivity of the brush can be reduced by increasing the copper content, allowing the EESM to be driven at high output.

[0018] Perspective view showing the motor brush and slip ring of the embodiment Plan view of the sliding surface of the first embodiment Plan view of the sliding surface of the second embodiment Plan view of the sliding surface of the third embodiment Plan view of the sliding surface of the fourth embodiment A diagram showing the pressing process of the brush of the embodiment, where (a) shows the state when powder is filled, (b) shows the state when pressurization is complete, and (c) shows the state when the mold is removed. Side view of the upper punch used in Figure 6 Schematic diagram of the EESM with the brush of the embodiment mounted Characteristic diagram showing the voltage drop of the brush with a constant current of 5A in the first embodiment Characteristic diagram showing the voltage drop of the brush with a constant current of 5A in the comparative example

[0019] The following shows an optimal embodiment for carrying out the present invention. The present invention is not limited to the embodiments, but is defined based on the claims and can be modified by adding matters known to those skilled in the art to the embodiments.

[0020] Figures 1 to 10 show the structure, manufacturing method, and characteristics of motor brushes 2, 22, 32, and 42 of the embodiment. Figure 1 shows the motor brush 2 of the first embodiment in use. The brush 2 is immersed in oil and slides on the slip ring 4, supplying power to the slip ring 4. The rotation direction of the slip ring 4 is indicated by an arrow. The brush 2 is approximately rectangular in shape, with 5 being the front surface of the brush 2 along the rotation direction of the slip ring, 6 being the rear surface, and 7 being the side surface. There is a slit 8 on the bottom surface of the brush 2, with an inlet 9 on the front surface 5 and an outlet 10 on the rear surface 6. The brush 2 also has outlets 11 on the sides 7, 7.

[0021] The oil in which the brush 2 and slip ring 4 are immersed enters the slit 8 from the inlet 9 and exits from the outlets 10 and 11. As a result, the formation of an oil film between the bottom surface of the brush 2 and the sliding surface of the slip ring 4 is suppressed, and even if an oil film is formed, fluctuations in the thickness of the film can be suppressed. For these reasons, electrical connection between the brush 2 and the slip ring 4 can be ensured. The oil enters the slit 8 (inlet 9) from the front in the direction of rotation and is discharged from, for example, the outlets 10 and 11. If an oil film that hinders electrical conduction forms between the bottom surface of the brush 2 and the sliding surface of the slip ring 4, the oil will be discharged from, for example, the outlet 11 due to the movement of the brush 2 relative to the slip ring 4.

[0022] 12 is the lead wire of the brush 2, which is fixed to the top surface of the brush 2, for example. Instead of the lead wire 12, a conductive terminal plate (not shown) or the like may be brought into contact with the brush 2. The white arrow 15 indicates the forward direction of rotation, and 16 indicates the backward direction. The brush holder and the spring that presses the brush 2 against the slip ring are not explained.

[0023] Figures 3, 4, and 5 show brushes 22, 32, and 42 of other embodiments, which are equipped with slits 24, 34, and 44, and have inlets 25, 35, and 45 and outlets 26, 36, and 47. Brush 42 in Figure 5 is not as desirable as brushes 2, 22, and 32 in Figures 2 to 4 because some of the oil in the slit 44 may not be discharged from the outlet 47 and may enter the rear side of brush 12.

[0024] The depths of the slits 8, 24, 34, and 44 are determined such that they remain open for the entire service life of the brushes 2, 22, 32, and 42, and are preferably between 0.5 mm and 10 mm. If the slit depth is less than 0.5 mm, oil discharge will be insufficient, hindering the electrical connection between the slip ring and the brush. If it exceeds 10 mm, shape defects may occur due to insufficient filling of the cavity during press molding, and demolding after pressing will become difficult.

[0025] Figure 6 schematically shows the pressing of brush 2, and brushes 22, 32, and 42 are pressed in the same manner. 50 is a die, in which the lower punch 51 rises from below and the upper punch 52 descends from above, pressing the powder material 56 inside the die 50 with a predetermined pressure. There is a projection 54 at the tip of the upper punch 52, and the shape of the projection 54 corresponds to the slit 8. Since the brush pressing is performed symmetrically from top to bottom, the projection 54 may also be provided on the lower punch 51. Figure 7 shows a side view of the projection 54, which has a projection 54a in the longitudinal direction and a projection 54b in the short-side direction.

[0026] In Figure 6(a), the powder material is filled into the cavity of the die 50, and then the lower punch 51 and the upper punch 52 move together, applying pressure to the powder material 56 symmetrically from above and below. Figure 6(b) shows the state in which the punches 51 and 52 have advanced. After this, the upper punch 52 is retracted, and the upper end of the lower punch 51 is raised to a height above the top surface 53 of the die 50, thereby removing the brush 2 before sintering from the cavity of the die 50. In this invention, carbon is included in the powder material of the brush, which is done by taking advantage of the low friction of carbon to enable the brushes 2, 22, 32, and 42 to be removed from the die 50.

[0027] The lead wires may be supplied into the powder material 56 from the lower punch 51. Alternatively, holes may be made in the top surface of the brush after pressing, etc., to secure the lead wires.

[0028] Figure 8 schematically shows an EESM (winding field synchronous motor) 60 with brushes 2 mounted. EESMs are used for driving electric vehicles, etc., and have pairs of brushes 2, 2 in contact with slip rings 4, 4. The slip rings 4 are attached to a drive shaft 62, and a rotor 64 is provided integrally with the shaft 62, with a stator 66 surrounding it. 68 is the housing of the motor 60.

[0029] Motor brushes 2, 22, 32, and 42 were manufactured by mixing electrolytic copper powder, tin powder, and graphite powder in predetermined proportions, and then press-molding the brushes 2, 22, 32, and 42 at 150 MPa as shown in Figure 6. After press molding, the brushes 2, 22, 32, and 42 were sintered, for example, in a nitrogen atmosphere at 800°C, and the lead wires 12 were fixed in place. The sintering temperature and pressing pressure are arbitrary.

[0030] The materials of brushes 2, 22, 32, and 42 preferably do not contain resin binders such as phenolic resin. They may also contain solid lubricants such as molybdenum disulfide and tungsten disulfide, and abrasive materials such as silica and alumina. However, in this invention, the oil between the sliding surfaces of the brush and the slip ring acts as a lubricant, so solid lubricants are not required. Also, since the wear mechanism is different from that of brushes used in air, abrasive materials are not required. The brush material preferably consists only of copper, tin, and carbon.

[0031] Table 1 shows the powder material of brush 2 for both the examples and comparative examples. The composition is expressed in mass%, and resistance indicates the resistivity along the direction of pressure during pressing. In the examples, the total content of copper and tin was high, causing the compressed powder material (precursor of the brush) in the die 50 to adhere to the die 50, making demolition difficult. By including graphite, the adhesion of the powder material to the die 50 was weakened, making demolition possible. On the other hand, increasing the graphite concentration increased the resistivity of the brush, preventing it from meeting the basic performance requirements for an EESM brush.

[0032] The brush in Example C (3 mass% graphite) could be demolded after pressing, but the brush in Comparative Example B (2 mass% graphite) was difficult to demold after pressing and was often damaged when removed from die 50. No problems occurred during demolding with 6 mass% graphite in Example A, and no problems occurred during demolding with 20 mass% graphite in Example B, but the brush had a high resistivity. Comparative Example A had too much graphite (26 mass%) and the brush had too high a resistivity. For these reasons, the graphite concentration should be between 3 mass% and 20 mass%, preferably between 3 mass% and 20 mass%. Preferably, the remainder is copper and tin. The mass ratio of copper to tin should be 95:5 or less, preferably 80:20 or more.

[0033] The strength of the brush improved as the graphite concentration decreased and the copper and tin concentrations increased. However, even in Comparative Example A, where the graphite concentration was excessive, a practical brush strength was obtained. The mechanism by which the brush strength is developed is thought to be liquid-phase sintering, where tin melts during sintering.

[0034]

[0035] The voltage drop across the brushes (Figures 9 and 10) was measured for brush 2 (Example 1) using the powder material of Example A, and for a comparative example brush using the same powder material but without the slit 8.

[0036] In contrast, when the EESM was driven with a constant DC current of 5A, the brush in Example 1 showed stable voltage drop of 0.1V or less across the brush, demonstrating performance suitable for use with the EESM. The motor's drive voltage fluctuated around 600V, and the rotational speed was 5000rpm. In the comparative example, intense sparking occurred, and the test was stopped.

[0037] Figure 9 shows the voltage drop in Example 1, where the voltage drop was small and no vibration was observed. Figure 10 shows the voltage drop in the Comparative Example, where the voltage drop was large and vibrated violently. This indicates that in the Comparative Example, oil entered between the sliding surfaces of the brush and the slip ring, causing unstable current flow between the brush and the slip ring sliding surfaces, resulting in an increased voltage drop and vibration in the voltage drop. It is also believed that this caused violent sparks to be generated.

[0038] ​In this embodiment, a brush capable of driving a motor while immersed in oil is obtained. In particular, the oil that penetrates between the sliding surfaces of the brush and the slip ring does not obstruct the electrical current, thereby reducing brush wear and minimizing the voltage drop between the sliding surface of the brush and the sliding surface of the slip ring.

[0039] In this embodiment, a slit can be formed on the bottom surface of the brush during press molding. Furthermore, by adding an appropriate amount of graphite, the brush can be removed from the die. In addition, by liquid-phase sintering the brush with tin, sufficient strength can be provided, and by increasing the copper content, the resistivity of the brush can be reduced, allowing the EESM to be driven at high output.

[0040] 2 Motor brushes 4 Slip rings 5 ​​Front 6 Rear 7 Side 8 Slits 9 Inlet 10, 11 Outlet 12 Lead wires 15 Front 16 Rear 22, 32, 42 Motor brushes 24, 34, 44 Slits 25, 35, 45 Inlet 26, 36, 47 Outlet 50 Die 51 Lower punch 52 Upper punch 53 Top surface 54 Projection 56 Powder material 60 EESM 62 Shaft 64 Rotor 66 Stator 68 Housing

Claims

1. A motor brush containing copper, tin, and graphite, which, when immersed in oil, contacts the slip ring of a motor to conduct the motor's drive current between the sliding surfaces of the brush and the slip ring, wherein the bottom surface of the brush, which is the sliding surface with respect to the slip ring, is provided with a slit, and the slit has an oil inlet on the front of the brush when viewed from the direction of rotation of the slip ring, and an oil outlet on the rear or side of the brush, so that oil attempting to enter the bottom surface of the brush due to the rotation of the slip ring is guided from the inlet to the slit and discharged from the outlet, and furthermore, the material of the sliding part of the brush is such that the mass ratio of copper, tin, and graphite is 70 mass% or more and 90 mass% or less for copper, 5 mass% or more and 15 mass% or less for tin, and 3 mass% or more and 20 mass% or less for graphite, characterized in that 2. The motor brush according to claim 1, characterized in that the material of the sliding part of the motor brush consists only of copper, tin, and graphite, and does not contain a resin binder.

3. A motor brush according to claim 1 or 2, characterized in that it is configured to slide with the slip ring of an EESM (winding field synchronous motor).

4. A method for manufacturing a motor brush containing copper, tin, and graphite, which, when immersed in oil, comes into contact with the slip ring of a motor, thereby conducting the motor's drive current between the sliding surfaces of the brush and the slip ring, wherein the motor brush has a slit on the sliding surface with the slip ring, which is the bottom surface of the brush, and the slit has an oil inlet on the front surface of the brush when viewed from the direction of rotation of the slip ring, and an oil outlet on the rear surface or side surface of the brush, and is configured to guide oil that tries to enter the bottom surface of the brush due to the rotation of the slip ring from the inlet to the slit and discharge it from the outlet, and a lower punch and an upper punch that can move up and down are arranged above and below a die having a cavity, and a projection corresponding to the shape of the slit is provided on the bottom surface of the upper punch or the top surface of the lower punch, A method for manufacturing a motor brush, comprising: introducing a powder material into the cavity, in which the mass ratio of copper, tin, and graphite is 70 mass% to 90 mass%, tin 5 mass% to 15 mass%, and graphite 3 mass% to 20 mass%, as the material for the sliding part of the brush; pressing the powder material to form a brush precursor by raising the lower punch and simultaneously lowering the upper punch, and forming a slit with the projections; then raising the upper punch to a position away from the die and raising the upper end of the lower punch to at least the top surface of the die, thereby removing the brush precursor from the cavity; and then sintering the brush precursor in a non-oxidizing atmosphere.

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