Micromotor for automobile and method for improving performance of micromotor

Abstract

The embodiment of the invention discloses a method for improving performance. The method comprises the following steps of raw material mixing, plasma treatment, secondary mixing, compression molding, sintering treatment, inner hole finishing, cleaning and oil soaking treatment. According to the powder metallurgy bearing treated through the method for improving the performance, under the condition that other parts and assembly conditions are the same, the resonance proportion of a micromotor at the low temperature of minus 40 DEG C can be reduced to 5% and below from original 50% and above, and the low-temperature resonance problem is effectively reduced; in addition, the noise of the micromotor can be effectively reduced, and the sound pressure within the measuring distance of 1 meter is further lowered to 48dB and below from the original 52dB and below. By the adoption of the technical scheme, the reliability of the automobile micromotor can be obviously improved, and the new requirement of the intelligent development trend of the new energy automobile industry for the reliability of the matched micromotor is met.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of new energy vehicles, and particularly to a method for improving performance. Background Art

[0002] Traditional powder metallurgy oil-impregnated bearings can be processed into spherical bearings with the function of self-aligning in position, so they can be used in combination with ball bearings, which is the most commonly used bearing combination design for automotive micro-motors. Among them, the ball bearing is generally placed at the torque output end to bear the radial load; the powder metallurgy bearing is generally placed at the non-torque output end to provide rotational alignment and radial load. However, the powder metallurgy bearing also has some disadvantages. The powder metallurgy bearing mainly relies on its own capillary pores to store and release lubricating oil, and the release of the lubricating oil is mainly driven by the combined action of thermal expansion and pump suction. During the start-up stage of the micro-motor, the dry friction between the rotating shaft and the powder metallurgy bearing will generate heat on the friction surface, which will cause the overall temperature of the powder metallurgy bearing to rise. The expansion coefficient of liquid lubricating oil is generally on the order of 10 -4 order of magnitude, while the expansion coefficient of the powder metallurgy bearing is generally on the order of 10 -5 -10 -4 order of magnitude. Therefore, the lubricating oil will expand due to heat and overflow. In addition, due to the rotation of the metal shaft, a certain negative pressure will also be generated in the friction surface area of the powder metallurgy bearing, which will accelerate the overflow of the lubricating oil in the capillary pores.

[0003] Therefore, the overflow of the lubricating oil depends on the frictional heat and rotation between the motor rotating shaft and the powder metallurgy bearing. In principle, it results in obvious dry friction at the moment of starting the motor. The dry friction between the rotating shaft and the powder metallurgy bearing at the moment of starting the micro-motor will bring an instantaneous "impact source" to the motor. When the frequency of the "impact source" is close to that of the rotor or stator of the motor, the whole motor will generate severe "resonance". In particular, at low temperatures, the viscosity of the lubricating oil rises rapidly, and the period required for the lubricating oil to overflow from the powder metallurgy bearing will be longer, and the frequency of the "resonance" generated by the motor will be higher. This is the industry pain point of "low-temperature resonance" existing in the motor industry. The "resonance" generated by the micro-motor will cause the rotor rotation to be unstable. On the one hand, it will cause the contact between the carbon brush and the commutator to be unstable, resulting in abnormal electric sparks and electro-corrosion, seriously affecting the life of the motor; on the other hand, the unstable rotor drives the rotating shaft to generate high-frequency mechanical hard impacts on the powder metallurgy bearing, causing rapid wear of the powder metallurgy bearing, which also seriously reduces the life and reliability of the motor.

[0004] Currently, with the development trend of intelligentization such as autonomous driving and automatic parking of automobiles, the reliability requirements for each supporting functional module are getting higher and higher. Therefore, solving the "resonance" risk of automotive micro-motors is of great significance for promoting the future application of motor products in intelligent vehicles. Summary of the Invention

[0005] In order to solve the deficiencies of the above technologies, the present invention provides a method for improving performance, which includes the following steps:

[0006] S1: Prepare raw materials; the raw materials include metal powder and expanded graphite powder;

[0007] S2: Primary mixing; Pour the metal powder and expanded graphite powder into a V-type mixer for mixing. The rotation speed of the V-type mixer is 30-40 revolutions per minute, and the mixing time is 55-65 minutes to obtain mixed powder;

[0008] S3: Low-energy plasma treatment; Pour the mixed powder into a graphite container, and place the graphite container filled with the mixed powder into the cavity of a plasma processor; Then, connect the two electrode heads of the plasma processor to the graphite container respectively; Next, use a vacuum pump to pump the vacuum degree in the cavity of the plasma processor to 30 Pa or below, and supplement the mixed gas into the cavity; After the flow rate of the mixed gas is stable, turn on the plasma discharge device to ionize the mixed gas and generate plasma; The active plasma continuously physically bombards the powder surface, cleaning and activating the powder surface for 5-10 minutes;

[0009] S4: High-energy plasma treatment; Bombard the powder surface with plasma of higher energy for 20-30 minutes; After reaching the set time, obtain activated powder;

[0010] S5: Secondary mixing; Take out the activated powder and put it into a V-type mixer for secondary mixing. The rotation speed is 30-40 revolutions per minute, and the mixing time is 10-15 minutes to further mix the powder evenly;

[0011] S6: Pressing and sintering; Press and form the powder after secondary mixing; Then sinter the formed blank. Provide a reducing atmosphere of N2:H2 = 1:1 throughout the sintering process. After sintering, a powder metallurgy bearing is obtained;

[0012] S7: Inner hole finishing; Carry out inner hole finishing treatment on the powder metallurgy bearing to ensure that the accuracy of the inner hole diameter of the bearing reaches a tolerance range of ±0.003 mm;

[0013] S8: Cleaning; Pour the finished powder metallurgy bearing into carbon tetrachloride solvent and start auxiliary ultrasonic cleaning for 10 minutes. Take out the parts and drain them, and repeat the cleaning 2-3 times, and then heat and dry them. The drying conditions are 55-65 °C and keep warm for 30 minutes to ensure that the cleaning agent in the capillary pores is completely vaporized to complete the cleaning process;

[0014] S9: Oil immersion; subject the cleaned powder metallurgy bearing to oil immersion treatment to obtain an oil-impregnated powder metallurgy bearing after the treatment is completed.

[0015] Preferably, in step S1, the metal powder includes electrolytic copper powder, tin powder and atomized iron powder. Among them, the weight ratio of electrolytic copper powder, tin powder, atomized iron powder and expanded graphite powder is 80:10:5:5; the purity of the electrolytic copper powder is ≥99.5%, the particle size is 45 - 75μm, and the loose bulk density is 1.5 - 1.9g / cm 3 ; the purity of the tin powder is ≥99%, the particle size is 35 - 55μm, and the loose bulk density is 2.5 - 3.5g / cm 3 ; the purity of the atomized iron powder is ≥98.5%, the particle size is 35 - 55μm, and the loose bulk density is 0.8 - 1.2g / cm 3 ; the purity of the expanded graphite powder is ≥99.8%, the particle size is 1 - 10μm, and the specific surface area is ≥25m 2 / g.

[0016] Preferably, in step S3, the graphite container includes a hollow cavity, an upper sealing head and a lower sealing head. The upper sealing head is provided with an upper limiting boss, and the lower sealing head is provided with a lower limiting boss; the upper limiting boss and the lower limiting boss are respectively arranged in cooperation with the hollow cavity; the hollow cavity, the upper sealing head and the lower sealing head satisfy the following conditions: when the mixed powder is filled, the diameter-height ratio of the mixed powder in the hollow cavity is ≥1.

[0017] Preferably, in step S3, the mixed gas is composed of Ar and O2; in this step, the Ar and O2 mixed gas is supplemented into the cavity, where the Ar gas flow rate is 60sccm and the O2 flow rate is 10sccm; after the gas flow rate is stable, turn on the plasma discharge device with a frequency of 13.5MHz and an output voltage of 4V, and the powder current density is 0.5 - 1A / cm 2 .

[0018] Preferably, in step S4, the Ar gas flow rate is increased to 100sccm, the O2 flow rate is 20sccm, the output voltage is 4V, and the output power of the pulse current generator is increased to 5 - 6A / cm 2 , and bombard the powder surface with a higher-energy plasma.

[0019] Preferably, in step S6, the interval time between preparing the activated powder and the powder pressing and forming treatment process is less than 24 hours, and the formed green body must enter the sintering process within 48 hours; during the powder pressing and forming treatment process, the forming pressure is 100 - 150MPa and the pressure holding time is 1 - 1.5 seconds.

[0020] Preferably, in step S6, the sintering equipment used for sintering treatment is a continuous tunnel kiln. The temperature of the highest sintering temperature zone in the continuous tunnel kiln is 750 - 800 °C, and the travel of the highest sintering temperature zone is not less than 1.5 hours.

[0021] Preferably, in step S7, the inner hole finishing process of the powder metallurgy bearing is as follows: use a finishing mandrel with a tolerance of ±0.001 mm. Press the shaping mandrel into the bearing inner hole and keep it for 1 second, then pull out the mandrel to complete the shaping process. The finishing mandrel is a silicon nitride mandrel or a silicon carbide mandrel with a low coefficient of thermal expansion, good wear resistance, and self-lubricating characteristics. The head of the finishing mandrel has a 45° chamfer to ensure the introduction during through-hole shaping.

[0022] Preferably, the oil soaking treatment in step S9 includes the following steps:

[0023] S9-1: Spread the powder metallurgy bearing on the steel plate, and control the stacking thickness of the parts within 3 times the height or diameter of the bearing.

[0024] S9-2: Place the steel plate into the plasma processing machine cavity, turn on the vacuum pump, evacuate the vacuum degree in the cavity to 30 Pa, then fill in the Ar / O2 mixed gas. The Ar gas flow rate is 60 sccm, and the O2 flow rate is 10 sccm. Use the high-frequency alternating electromagnetic field generated by the microwave source in the cavity with the steel plate to ionize the Ar / O2 gas to generate plasma. The frequency is 13.5 MHz, and the current density is 0.5 - 1 A / cm2. The active plasma continuously physically bombards the surface of the porous powder metallurgy bearing, and after 20 minutes of continuous activation, take it out.

[0025] S9-3: Quickly transfer the powder metallurgy bearing after plasma treatment into the oil soaking device, pour in the required lubricating oil, evacuate the oil soaking device until the vacuum degree is below -80 KPa, and maintain it for 0.5 - 1 hour to ensure that the lubricating oil can completely enter the capillary pores of the porous powder metallurgy bearing.

[0026] A micro-motor for an automobile, the micro-motor for the automobile is assembled with an oil-impregnated powder metallurgy bearing.

[0027] As can be seen from the above technical solutions, the embodiments of the present invention have the following advantages: For the powder metallurgy bearings processed by the performance improvement method of the present invention, under the condition that other parts and assembly conditions are the same, the proportion of the micro-motor resonating at -40°C can be reduced from the original 50% or more to 5% or less, effectively reducing the occurrence of low-temperature resonance problems. In addition, it can effectively reduce the noise of the micro-motor, and the sound pressure at a measurement distance of 1 meter can be further reduced from the original 52 dB or less to 48 dB or less. By adopting the technical solution of the present invention, the reliability of automotive micro-motors can be significantly improved, meeting the new requirements for the reliability of supporting micro-motors in the intelligent development trend of the new energy vehicle industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 It is a flowchart of the method for improving the performance of the present invention;

[0030] Figure 2 It is a schematic structural diagram of the graphite container adopted by the method for improving the performance of the present invention;

[0031] Among them, the markings in the figure are shown as follows:

[0032] 1 - hollow cavity, 2 - upper sealing head, 21 - upper limiting boss, 3 - lower sealing head, 31 - lower limiting boss. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The embodiments of the present invention provide a method for improving performance, which is used to prepare powder metallurgy bearings. By using this powder metallurgy bearing, under the condition that other parts and assembly conditions are the same, the occurrence of low-temperature resonance problems can be effectively reduced, and the noise of the micro-motor can be effectively reduced. By adopting the technical solution of the present invention, the reliability of automotive micro-motors can be significantly improved, meeting the new requirements for the reliability of supporting micro-motors in the intelligent development trend of the new energy vehicle industry.

[0034] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0035] Please refer to Figure 1 , the present invention provides a method for improving performance. The present invention provides a method for improving performance, and the method comprises the following steps:

[0036] S1: Prepare raw materials; the raw materials include metal powder and expanded graphite powder;

[0037] S2: Primary mixing; pour the metal powder and expanded graphite powder into a V-type mixer for mixing. The rotation speed of the V-type mixer is 30 - 40 revolutions per minute, and the mixing time is 55 - 65 minutes to obtain mixed powder;

[0038] S3: Low-energy plasma treatment; pour the mixed powder into a graphite container, and place the graphite container filled with the mixed powder into the cavity of a plasma processor; then, connect the two electrode heads of the plasma processor to the graphite container respectively; next, use a vacuum pump to pump the vacuum degree in the cavity of the plasma processor to 30 Pa or below, and supplement the mixed gas into the cavity; after the flow rate of the mixed gas is stable, turn on the plasma discharge device to ionize the mixed gas and generate plasma; the active plasma continuously physically bombards the powder surface to clean and activate the powder surface for 5 - 10 minutes;

[0039] In this step, physically bombarding the powder surface with active plasma can effectively remove pollutants such as impurities and oxides on the powder surface and clean the powder surface.

[0040] S4: High-energy plasma treatment; bombard the powder surface with plasma of higher energy for 20 - 30 minutes; after reaching the set time, obtain activated powder;

[0041] In steps S4 and S5, the two plasma treatments adopt a plasma treatment process with gradient energy. In step S4, low-energy plasma is used to clean foreign matters on the surfaces of expanded graphite and metal powder and generate active groups on the powder surface. Then, in step S5, the plasma energy is further increased to stimulate a large amount of heat released from the activated surfaces between the expanded graphite powder and the metal powder, promoting the migration of a small amount of metal ions to the surface of graphite particles to form a certain transition metalized thin film layer, and this metalized thin film layer can significantly improve the interfacial bonding strength between graphite and metal during subsequent sintering.

[0042] S5: Secondary mixing; take out the activated powder and put it into a V-type mixer for secondary mixing. The rotation speed is 30 - 40 revolutions per minute, and the mixing time is 10 - 15 minutes to further mix the powder evenly;

[0043] The V-type mixer is used twice in step S2 and step S5. The unique structure of the V-type mixer enables the material to produce good convection and diffusion effects during the mixing process. The rotation speed of 30 to 40 rpm and the appropriate mixing time can ensure that the metal powder and the expanded graphite powder are fully and evenly mixed, avoiding the situation of uneven local components, and laying the foundation for subsequent processing and product quality. First, a mixing is performed to initially evenly distribute the two powders, and then a secondary mixing is performed after plasma treatment. The expanded graphite and metal powders after plasma treatment have more active functional groups such as hydroxyl, carboxyl, and carbonyl on the surface, and have higher surface energy, so the activity and compatibility between the powders are significantly improved. Therefore, the treated powder can be mixed for a second time to further improve the uniformity of powder mixing, enhance the consistency of powder metallurgy bearings, and make the performance of the final product more stable.

[0044] S6: pressing and sintering; pressing and molding the secondary mixed powder; then sintering the pressed green body, providing a reducing atmosphere of N2:H2=1:1 during the whole sintering process, and obtaining a powder metallurgy bearing after sintering;

[0045] S7: Inner hole finishing: The inner hole of the powder metallurgy bearing is finished to ensure that the accuracy of the inner hole diameter of the bearing is within the tolerance range of ±0.003mm;

[0046] S8: cleaning; pour the finished powder metallurgy bearing into carbon tetrachloride solvent and start auxiliary ultrasonic cleaning for 10 minutes, take out the parts, drain and repeat the cleaning 2 to 3 times, and then heat and dry them. The drying condition is 55 to 65°C and keep warm for 30 minutes to ensure that the cleaning agent in the pores is completely gasified, and the cleaning process is completed;

[0047] In this step, the powder metallurgy bearing needs to be cleaned after shaping, and the cleaning agent is carbon tetrachloride organic solvent. Specifically, pour the powder metallurgy bearing into the carbon tetrachloride solvent and start the auxiliary ultrasonic cleaning for 10 minutes, then take out the parts and drain them, repeat the cleaning 2-3 times and then heat and dry them. The drying condition is 60±5℃ and keep warm for 30 minutes to ensure that the cleaning agent in the pores is completely vaporized and the cleaning is completed.

[0048] S9: soaking in oil; soaking the cleaned powder metallurgy bearing in oil to obtain an oil-containing powder metallurgy bearing.

[0049] In view of the shortcomings of the powder metallurgy bearing products currently used in micromotors, the present invention adopts a systematic innovative technical solution, including plasma pretreatment and secondary mixing of powders, the use of expanded graphite to replace traditional flake graphite in the additive formula, and plasma activation treatment of powder metallurgy parts before oil soaking.

[0050] First, the improvement of the formula and process; in the formula components, expanded graphite is used instead of flake graphite used in the traditional process, which can make full use of the characteristics of expanded graphite with larger interlayer spacing, looser structure, and lower interlayer peeling energy. As a result, the graphite layer can be transferred to the friction surface more quickly, rapidly reducing the friction coefficient of the friction surface.

[0051] Secondly, aiming at the problems of chemical inertness brought by strong covalent bonds in the graphite layer and affecting the interfacial bonding strength between it and metal components, a special treatment process of multi-stage surface treatment of the mixed powder of expanded graphite and metal powder raw materials is carried out by using plasma with gradually increasing energy. In the plasma treatment process with gradient energy, first, low-energy plasma is used to clean foreign substances on the surface of expanded graphite and metal powder and generate active groups on the powder surface. Then, by further increasing the plasma energy, a large amount of heat will be released by activating the surface between the expanded graphite powder and the metal powder, promoting the migration of a small amount of metal ions to the surface of graphite particles to form a certain transition metalized thin film layer, which can significantly improve the interfacial bonding strength between graphite and metal during later sintering.

[0052] By improving the interfacial bonding strength between metal particles and between expanded graphite and metal particles through plasma treatment of the powder, the particle migration ability between metal particles can be significantly increased, and the sintering bonding strength between metal particles can be enhanced. In addition, it can effectively solve the limitation of the rapid decline of mechanical strength caused by adding graphite powder in the traditional process. Furthermore, it can improve the mutual restraint between the strength, wear resistance of powder metallurgy bearings and the improvement of the friction coefficient by adding graphite. On the basis of ensuring the mechanical strength of powder metallurgy bearings, the upper limit of the addition ratio of traditional flake graphite can be increased from 3% to 5% or even higher for expanded graphite. The high increase ratio of expanded graphite, on the one hand, can make full use of the characteristics of the fluffy layered structure of the expanded graphite layer, and can form a graphite solid lubricating layer on the friction surface between the rotating shaft and the sliding powder metallurgy bearing more quickly, reducing the time period for forming the solid lubricating film; on the other hand, by using a higher addition of expanded graphite, a more complete and firm solid lubricating film can be formed on the friction surface. The sliding friction coefficient between the rotating shaft and the powder metallurgy bearing is significantly reduced from the original 0.08 - 0.1 to between 0.05 - 0.08, which can significantly improve the dry friction coefficient before lubricating oil overflows and reduce the "impact energy" caused by friction at the moment of motor startup.

[0053] The advantages of the present invention in preparing powder metallurgy oil-impregnated bearings by using the plasma treatment method are as follows:

[0054] (1) Using plasma to treat the powder can significantly increase the particle migration ability between metal particles, thereby enhancing the sintering bonding strength between metal particles. At the same time, plasma treatment of the powder can improve the interfacial bonding strength between metal particles and between expanded graphite and metal particles.

[0055] (2) The mechanical strength reduction caused by adding graphite powder can be effectively solved by plasma treating the powder, thereby improving the mutual restraint limitation among the strength, wear resistance of the powder metallurgy bearing and the improvement of the friction coefficient by adding graphite, and increasing the addition ratio of traditional flake graphite from 3% to 5% or even higher for expanded graphite.

[0056] (3) The expanded graphite and metal powder after plasma treatment have more active functional groups such as hydroxyl, carboxyl, and carbonyl groups on the surface, with a higher surface energy. Therefore, the activity and compatibility between the powders are significantly improved. At the same time, the sintering temperature can be reduced by 10 - 50 °C, saving energy consumption and reducing the production and manufacturing cost of the powder metallurgy bearing.

[0057] Preferably, in step S1, the metal powder includes electrolytic copper powder, tin powder, and atomized iron powder. Among them, the weight ratio of electrolytic copper powder, tin powder, atomized iron powder, and expanded graphite powder is 80:10:5:5; the purity of the electrolytic copper powder ≥ 99.5%, the particle size is 45 - 75 μm, and the loose bulk density is 1.5 - 1.9 g / cm 3 ; the purity of the tin powder ≥ 99%, the particle size is 35 - 55 μm, and the loose bulk density is 2.5 - 3.5 g / cm 3 ; the purity of the atomized iron powder ≥ 98.5%, the particle size is 35 - 55 μm, and the loose bulk density is 0.8 - 1.2 g / cm 3 ; the purity of the expanded graphite powder ≥ 99.8%, the particle size is 1 - 10 μm, and the specific surface area ≥ 25 m 2 / g.

[0058] In this step, the weight ratio of electrolytic copper powder, tin powder, atomized iron powder, and expanded graphite powder is 80:10:5:5. With such a proportion, the electrolytic copper powder is the main component. Utilizing the good electrical conductivity, thermal conductivity, ductility, and corrosion resistance of copper, it provides good basic properties for the bearing, enabling the bearing to work stably in various electrical and mechanical environments. The addition of an appropriate amount of tin powder can form an alloy with copper, improving the strength, hardness, and wear resistance of the alloy. At the same time, tin can also improve the anti-seizure performance of the bearing, reducing the possibility of seizure during the operation of the bearing. The addition of atomized iron powder can improve the strength and toughness of the bearing, enhance the load-bearing capacity of the bearing, enabling the bearing to withstand greater loads and impact forces, and meeting some application scenarios with higher requirements for mechanical properties.

[0059] Preferably, in step S3, the graphite container includes a hollow cavity, an upper sealing head, and a lower sealing head. The upper sealing head is provided with an upper limiting boss, and the lower sealing head is provided with a lower limiting boss. The upper limiting boss and the lower limiting boss are respectively arranged in cooperation with the hollow cavity. The hollow cavity, the upper sealing head, and the lower sealing head satisfy the following condition: when the mixed powder is filled, the diameter-to-height ratio of the mixed powder in the hollow cavity ≥ 1.

[0060] Please refer to Figure 2 , Figure 1 which is a schematic structural diagram of a graphite container. In this step, the powder that has been mixed according to the formula is poured into the graphite container with a hollow cavity 1 structure. The powder includes raw materials such as graphite and metal powder. The graphite container is composed of a hollow cavity 1, an upper sealing head 2, and a lower sealing head 3. Among them, the upper sealing head 2 is provided with an upper limiting boss 21, and the lower sealing head 3 is provided with a lower limiting boss 31. The upper limiting boss 21 and the lower limiting boss 31 are respectively clamped with the hollow cavity 1, so that after the upper and lower sealing heads 3 are inserted and reach the limiting position, no additional pressure is applied to the filled powder to prevent agglomeration during the powder treatment process.

[0061] Preferably, in step S3, the mixed gas is composed of Ar and O2. In this step, the Ar and O2 mixed gas is supplemented into the cavity. The Ar gas flow rate is 60 sccm, and the O2 flow rate is 10 sccm. After the gas flow rate is stable, turn on the plasma discharge device with a frequency of 13.5 MHz and an output voltage of 4V. The current density passing through the powder is 0.5 - 1 A / cm 2 . Place the graphite container filled with powder into the plasma processing machine cavity, and press the electrode head of the plasma device on the upper and lower graphite sealing heads. Turn on the vacuum pump, evacuate the vacuum degree in the cavity to 30 Pa or below, and then fill in the Ar / O2 mixed gas with an Ar gas flow rate of 60 sccm and an O2 flow rate of 10 sccm. Turn on the plasma discharge device with a frequency of 13.5 MHz, which is commonly used in commercial products, an output voltage of 4V, and a current density passing through the powder of 0.5 - 1 A / cm 2 , and use the microwave source in the graphite cavity to oscillate by the electrode to generate a high-frequency alternating electromagnetic field, ionize the Ar / O2 gas, generate plasma, and the active plasma continuously physically bombards the powder surface to clean and activate the powder surface for 5 - 10 minutes.

[0062] Preferably, in step S4, the Ar gas flow rate is increased to 100 sccm, the O2 flow rate is 20 sccm, the output voltage is 4V, and the output power of the pulse current generator is increased to 5 - 6 A / cm 2, bombard the surface of the powder with a higher-energy plasma. In this step, adjust the Ar gas flow rate to 100 sccm, the O2 flow rate to 20 sccm, maintain the output voltage at 4 V, and adjust the output power of the pulsed current generator to 5 - 6 A / cm2 to bombard the surface of the powder with a higher-energy plasma for 20 - 30 minutes. The surface energy of the graphite and metal powder rapidly increases, and a small amount of metal ions migrate to the surface of the graphite particles, forming a certain transition metalized thin film layer.

[0063] Preferably, in step S6, the interval time between preparing the activated powder and the powder pressing and forming process is less than 24 hours, and the formed green body must enter the sintering process within 48 hours; during the powder pressing and forming process, the forming pressure is 100 - 150 MPa, and the pressure holding time is 1 - 1.5 seconds. In this step, take out the powder that has undergone plasma special treatment and secondary mixing, and perform a pressing and forming process according to the conventional powder metallurgy method, with a forming pressure of 100 - 150 MPa and a pressure holding time of 1 - 1.5 seconds. At the same time, to ensure the activity of the surface groups of the powder, all powders must enter the pressing and forming process within 24 hours, and the formed green body must enter the sintering process within 48 hours.

[0064] Preferably, in step S6, the sintering equipment used for the sintering treatment is a continuous tunnel kiln. The temperature of the highest sintering temperature zone of the continuous tunnel kiln is 750 - 800 °C, and the travel of the highest sintering temperature zone is not less than 1.5 hours. The formed green body enters the sintering treatment. The sintering equipment preferably uses a continuous tunnel kiln. The temperature of the highest sintering temperature zone of the tunnel kiln is between 750 - 850 °C, and the time required for the travel of the highest sintering temperature zone is about 1 - 1.5 hours to ensure sufficient alloying between the powders, such as Cu - Sn powders, in-situ generating a tin bronze alloy with high hardness and good wear resistance, and generating capillary pores with a volume ratio of 17 - 23% using the volume change during alloying. At the same time, based on the activation effect of the plasma pretreatment on the powder, the bonding strength between the metal powders in the powder metallurgy bearing and between the metal and graphite powders is significantly improved. After adding 5% by weight of graphite powder, the crushing strength and wear resistance of the powder metallurgy bearing can be close to those of pure metal (without adding graphite) without plasma pretreatment; provide a reducing atmosphere of N2:H2 = 1:1 throughout the sintering process.

[0065] Preferably, in step S7, the process of finishing the inner hole of the powder metallurgy bearing is as follows: use a finishing mandrel with a tolerance of ±0.001 mm. After pressing the shaping mandrel into the bearing inner hole, hold it for 1 second and then pull out the mandrel to complete the shaping process. The finishing mandrel is a silicon nitride mandrel or a silicon carbide mandrel with a low coefficient of thermal expansion, good wear resistance, and self-lubricating characteristics. The head of the finishing mandrel has a 45° chamfer to ensure the introduction during through-hole shaping. For the powder metallurgy bearing product after sintering, due to multiple effects such as density densification and volume change during high-temperature sintering, inner hole finishing treatment is required to ensure that the diameter accuracy of the bearing inner hole reaches a tolerance range of ±0.003 mm, so as to ensure the tolerance fit between the powder metallurgy bearing and the rotating shaft branch and meet the vibration and noise requirements of the micro-motor. Specifically, use materials such as silicon nitride or silicon carbide with a low coefficient of thermal expansion, good wear resistance, and certain self-lubricating characteristics to process a finishing mandrel with a tolerance of ±0.001 mm. The head of the mandrel has a 45° chamfer to ensure the introduction during through-hole shaping. After pressing the shaping mandrel into the bearing inner hole, hold it for 1 second and then pull out the mandrel to complete the shaping process.

[0066] Preferably, the oil soaking treatment in step S9 includes the following steps:

[0067] S9-1: Spread out the powder metallurgy bearings on the steel plate, and control the stacking thickness of the parts within 3 times the height or diameter of the bearing;

[0068] S9-2: Place the steel plate into the plasma treatment machine cavity, turn on the vacuum pump, evacuate the vacuum in the cavity to 30 Pa, and then fill it with an Ar / O2 mixed gas. The Ar gas flow rate is 60 sccm, and the O2 flow rate is 10 sccm. Use the high-frequency alternating electromagnetic field generated by the microwave source in the cavity where the steel plate is placed to ionize the Ar / O2 gas to generate plasma. The frequency is 13.5 MHz, and the current density is 0.5 - 1 A / cm2. The active plasma continuously physically bombards the surface of the porous powder metallurgy bearing, and after continuous activation for 20 minutes, take it out;

[0069] S9-3: Quickly transfer the powder metallurgy bearing after plasma treatment into the oil soaking device, pour in the required lubricating oil, evacuate the oil soaking device until the vacuum degree is below -80 KPa, and maintain it for 0.5 - 1 hour to ensure that the lubricating oil can completely enter the capillary pores of the porous powder metallurgy bearing.

[0070] Before the final oil immersion, it is necessary to pretreat the porous powder metallurgy bearing with low-energy plasma again, which can improve the surface energy of the capillary pores and the bearing surface inside the bearing, reduce the wetting angle between the lubricating oil and the bearing. This can not only increase the oil filling rate of the lubricating oil in the capillary pores and reduce the thermal expansion overflow period of the lubricating oil during the starting stage of the micro-motor, but also form a certain lubricating oil film on the inner hole surface of the bearing. All of these can effectively reduce the dry friction impact energy at the moment of motor startup and reduce the risk of "low-temperature resonance" of the micro-motor, meeting the new requirements brought by the intelligent development of new energy vehicles.

[0071] The following elaborates on the method for improving the performance of the present invention through embodiments:

[0072] (1) Powder treatment.

[0073] Prepare raw materials, including electrolytic copper powder, tin powder, atomized iron powder, and expanded graphite powder. Among them, copper powder mainly forms a dispersed alloyed bronze reinforcement phase with tin and is formed by plastic deformation; iron powder improves the bearing capacity of the bearing; expanded graphite powder reduces the friction coefficient of the bearing. The weight ratio of each component is: copper powder: tin powder: atomized iron powder: graphite powder = 80:10:5:5;

[0074] The specifications of electrolytic copper powder are: purity ≥ 99.5%, particle size 45 - 75μm, loose bulk density 1.5 - 1.9 g / cm3;

[0075] The specifications of tin powder are: purity ≥ 99%, particle size 35 - 55μm, loose bulk density 2.5 - 3.5 g / cm3;

[0076] The specifications of atomized iron powder are: purity ≥ 98.5%, particle size 35 - 55μm, loose bulk density 0.8 - 1.2 g / cm3;

[0077] The specifications of expanded graphite powder are: purity ≥ 99.8%, particle size 1 - 10μm, specific surface area ≥ 25 m2 / g.

[0078] Then, pour the raw materials that have been weighed according to the ratio into a V-type mixer for the first mixing, with a rotation speed of 30 - 40 revolutions per minute and a mixing time of 55 - 65 minutes. Pour the mixed powder into a graphite container with a hollow cavity structure, place the graphite container filled with powder into the cavity of the plasma processing machine, and press the electrode head of the plasma equipment on the upper and lower graphite sealing heads to complete the powder loading process.

[0079] Turn on the vacuum pump and evacuate the vacuum degree in the cavity to 30 Pa or below, and then fill it with Ar / O2 mixed gas. The Ar gas flow rate is 60 sccm, and the O2 flow rate is 10 sccm. After the gas flow rate is stable, turn on the plasma discharge device with a frequency of 13.5 MHz commonly used in commercial products, an output voltage of 4 V, and a powder current density of 0.5 - 1 A / cm2. Use the electrode to generate a high-frequency alternating electromagnetic field by oscillating the microwave source in the graphite cavity, ionize the Ar / O2 gas to generate plasma, and the active plasma continuously physically bombards the powder surface to clean and activate the powder surface for 5 - 10 minutes to complete the preliminary cleaning and activation process of the powder.

[0080] Adjust the Ar gas flow rate to 100 sccm and the O2 flow rate to 20 sccm, maintain the output voltage at 4 V, and adjust the output power of the pulse current generator to 5 - 6 A / cm2 to bombard the powder surface with a higher-energy plasma for 20 - 30 minutes. The surface energy of the expanded graphite and the metal powder rapidly increases, and a small amount of metal ions partially migrate to the surface of the graphite particles to form a certain transition metalized thin film layer to complete the deep activation and interfacial alloying process of the powder.

[0081] Take out the processed powder and put it into a V-type mixer for secondary mixing at a rotation speed of 30 - 40 revolutions per minute for 10 - 15 minutes to further mix the powder evenly. After pouring out the powder, the powder treatment process is completed.

[0082] (2) Subsequent production

[0083] Press and form the powder that has been specially treated by plasma and secondary mixed according to the conventional powder metallurgy method. The forming pressure is 100 - 150 MPa, and the pressure is maintained for 1 - 1.5 seconds. At the same time, to ensure the activity of the surface groups of the powder, all powders must enter the pressing and forming process within 24 hours, and the formed billet must enter the sintering process within 48 hours.

[0084] The formed billet enters the sintering treatment. The sintering equipment preferably uses a continuous tunnel kiln. The temperature in the highest sintering temperature zone of the tunnel kiln is between 750 - 800 °C, and the time required for the highest sintering temperature zone to travel is about 1.5 hours to ensure the full alloying between the Cu - Sn powders; a reducing atmosphere of N2:H2 = 1:1 is provided throughout the sintering process.

[0085] After the sintering of the powder metallurgy bearing product, it enters the inner hole finishing process to ensure that the diameter accuracy of the bearing inner hole reaches the tolerance range of ±0.003 mm, so as to ensure the tolerance fit between the powder metallurgy bearing and the rotating shaft branch and meet the vibration and noise requirements of the micro-motor. Specifically, a finishing mandrel with a low coefficient of thermal expansion, good wear resistance and certain self-lubricating characteristics, such as silicon nitride or silicon carbide, is processed to a tolerance of ±0.001 mm. The head of the mandrel has a 45° chamfer to ensure the introduction during through-hole shaping. After the shaping mandrel is pressed into the bearing inner hole and kept for 1 second, the mandrel is pulled out to complete the shaping process.

[0086] Pour the powder metallurgy bearing into carbon tetrachloride solvent and start auxiliary ultrasonic cleaning for 10 minutes. Then take out the parts and drain them. Repeat the cleaning 2-3 times and then carry out heating and drying. The drying condition is 60±5 °C and keep warm for 30 minutes to ensure that the cleaning agent in the capillary pores is completely vaporized to complete the cleaning.

[0087] The cleaned powder metallurgy bearing is subjected to oil immersion treatment to obtain an oil-impregnated powder metallurgy bearing to be assembled on the micro-motor. Among them, before oil immersion, the powder metallurgy bearing needs to be subjected to plasma pretreatment again. The specific treatment process is as follows: (1) Spread the porous powder metallurgy bearing on the steel plate, and the stacking thickness of the parts is controlled within 3 times the height or diameter of the bearing to ensure the effect of plasma surface activation. Put the steel plate into the plasma processor cavity, turn on the vacuum pump, evacuate the vacuum in the cavity to 30 Pa, and then fill in the Ar / O2 mixed gas. The Ar gas flow rate is 60 sccm, and the O2 flow rate is 10 sccm. Use the high-frequency alternating electromagnetic field generated by the oscillation of the bearing steel plate and the microwave source in the cavity to ionize the Ar / O2 gas to generate plasma. The frequency is 13.5 MHz selected for commercial plasma products, and the current density is 0.5-1 A / cm2. The active plasma continuously physically bombards the surface of the porous powder metallurgy bearing. After continuous activation for 20 minutes, take it out and carry out oil immersion within 24 hours; (2) Quickly transfer the powder metallurgy bearing after plasma pretreatment to the oil immersion device, pour in the required lubricating oil, evacuate the oil immersion device until the vacuum degree is below -80 KPa, and keep it for 0.5-1 hour to ensure that the lubricating oil can completely enter the capillary pores of the porous powder metallurgy bearing. Take out the powder metallurgy bearing and drain it to complete the process of vacuum oil immersion to obtain the immersed powder metallurgy bearing for subsequent motor assembly.

[0088] A micro-motor for an automobile, wherein the micro-motor for an automobile is assembled with an oil-impregnated powder metallurgy bearing.

[0089] As can be seen from the above technical solutions, the embodiments of the present invention have the following advantages: For the powder metallurgical bearings processed by the performance improvement method of the present invention, under the condition that other parts and assembly conditions are the same, the resonance ratio of the micromotor at -40°C can be reduced from the original 50% or more to 5% or less, effectively reducing the occurrence of low-temperature resonance problems; in addition, the noise of the micromotor can be effectively reduced, and the sound pressure at a measurement distance of 1 meter can be further reduced from the original 52 dB or less to 48 dB or less. By adopting the technical solution of the present invention, the reliability of automotive micromotors can be significantly improved, meeting the new requirements for the reliability of supporting micromotors in the intelligent development trend of the new energy vehicle industry.

[0090] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for improving performance, characterized in that The method comprises the following steps: S1: Prepare raw materials; the raw materials include metal powder and expanded graphite powder; S2: initial mixing; pouring the metal powder and the expanded graphite powder into a V-type mixer for mixing, the speed of the V-type mixer is 30 to 40 rpm, and the mixing time is 55 to 65 minutes to obtain a mixed powder; S3: Low-energy plasma treatment; pour the mixed powder into a graphite container, and place the graphite container filled with the mixed powder into the cavity of the plasma treatment machine; then, connect the two poles of the plasma treatment machine to the graphite container respectively; then, use a vacuum pump to evacuate the vacuum degree in the cavity of the plasma treatment machine to 30Pa or below, and add the mixed gas into the cavity; after the mixed gas flow rate is stable, turn on the plasma discharge device to ionize the mixed gas and generate plasma; the active plasma continuously physically bombards the powder surface to clean and activate the powder surface for 5 to 10 minutes; S4: High-energy plasma treatment: bombard the powder surface with higher-energy plasma for 20 to 30 minutes; after reaching the set time, activated powder is obtained; S5: secondary mixing; taking out the activated powder and putting it into a V-type mixer for secondary mixing at a speed of 30 to 40 rpm for 10 to 15 minutes to further mix the powder evenly; S6: pressing and sintering; pressing and molding the secondary mixed powder; then sintering the pressed green body, providing a reducing atmosphere of N2:H2=1:1 during the whole sintering process, and obtaining a powder metallurgy bearing after sintering; S7: Inner hole finishing: The inner hole of the powder metallurgy bearing is finished to ensure that the accuracy of the inner hole diameter of the bearing is within the tolerance range of ±0.003mm; S8: cleaning; pour the finished powder metallurgy bearing into carbon tetrachloride solvent and start auxiliary ultrasonic cleaning for 10 minutes, take out the parts, drain and repeat the cleaning 2 to 3 times, and then heat and dry them. The drying condition is 55 to 65°C and keep warm for 30 minutes to ensure that the cleaning agent in the pores is completely gasified, and the cleaning process is completed; S9: soaking in oil; soaking the cleaned powder metallurgy bearing in oil to obtain an oil-containing powder metallurgy bearing.

2. The method for improving performance according to claim 1, characterized in that: In step S1, the metal powder includes electrolytic copper powder, tin powder and atomized iron powder, wherein the weight ratio of electrolytic copper powder, tin powder, atomized iron powder and expanded graphite powder is 80:10:5:5; the purity of the electrolytic copper powder is ≥99.5%, the particle size is 45-75μm, and the bulk density is 1.5-1.9g / cm 3 The purity of the tin powder is ≥99%, the particle size is 35-55μm, and the bulk density is 2.5-3.5g / cm 3 The purity of the atomized iron powder is ≥98.5%, the particle size is 35-55μm, and the bulk density is 0.8-1.2g / cm 3 The purity of the expanded graphite powder is ≥99.8%, the particle size is 1-10μm, and the specific surface area is ≥25m 2 / g.

3. The method for improving performance according to claim 1, characterized in that: In step S3, the graphite container includes a hollow cavity (1), an upper sealing head (2) and a lower sealing head (3); the upper sealing head is provided with an upper limit boss (21), and the lower sealing head is provided with a lower limit boss (31); the upper limit boss and the lower limit boss are respectively arranged in coordination with the hollow cavity; the hollow cavity, the upper sealing head and the lower sealing head meet the following conditions: when the mixed powder is filled, the diameter-to-height ratio of the mixed powder in the hollow cavity is ≥1.

4. The method for improving performance according to claim 1, characterized in that: In step S3, the mixed gas is composed of Ar and O2; in this step, the mixed gas of Ar and O2 is added into the chamber, wherein the Ar gas flow rate is 60sccm and the O2 flow rate is 10sccm; after the gas flow rate is stable, the plasma discharge equipment is turned on, the frequency is 13.5MHz, the output voltage is 4V, and the current density through the powder is 0.5-1A / cm 2 .

5. The method for improving performance according to claim 4, characterized in that: In step S4, the Ar gas flow rate is increased to 100 sccm, the O2 flow rate is 20 sccm, the output voltage is 4 V, and the output power of the pulse current generator is increased to 5-6 A / cm 2 , bombarding the powder surface with higher energy plasma.

6. The method for improving performance according to claim 1, characterized in that: In step S6, the interval time between the preparation of activated powder and the powder pressing and molding process is less than 24 hours, and the pressed body must enter the sintering process within 48 hours; during the powder pressing and molding process, the molding pressure is 100-150 MPa, and the holding time is 1-1.5 seconds.

7. The method for improving performance according to claim 6, characterized in that: In step S6, the sintering equipment used for the sintering process is a continuous tunnel kiln, the temperature of the highest sintering temperature zone of the continuous tunnel kiln is 750-800°C, and the sintering time in the highest temperature zone is not less than 1.5 hours.

8. The method for improving performance according to claim 1, characterized in that: In step S7, the inner hole finishing process of the powder metallurgy bearing is as follows: a finishing mandrel with a tolerance of ±0.001mm is used, the shaping mandrel is pressed into the inner hole of the bearing, and then the shaping mandrel is pulled out after being held for 1 second to complete the shaping process; the finishing mandrel is a silicon nitride mandrel or a silicon carbide mandrel with a low thermal expansion coefficient, good wear resistance, and self-lubricating properties; the head of the finishing mandrel has a 45° chamfer to ensure the introduction during through-hole shaping.

9. The method for improving performance according to claim 1, characterized in that: The oil soaking process in step S9 includes the following steps: S9-1: Spread the powder metallurgy bearing on the steel plate, and control the stacking thickness of the parts within 3 times the height or diameter of the bearing; S9-2: Place the steel plate in the plasma treatment chamber, start the vacuum pump, draw the vacuum degree in the chamber to 30Pa, and then fill it with Ar / O2 mixed gas, with an Ar gas flow rate of 60sccm and an O2 flow rate of 10sccm. Use the high-frequency alternating electromagnetic field generated by the oscillation of the bearing steel plate and the microwave source in the chamber to ionize the Ar / O2 gas to generate plasma with a frequency of 13.5MHz and a current density of 0.5-1A / cm2. The active plasma continuously physically bombards the surface of the porous powder metallurgy bearing, and takes it out after continuous activation for 20 minutes; S9-3: Quickly transfer the plasma-treated powder metallurgy bearing to the oil bubble device, pour in the required lubricating oil, evacuate the oil bubble device to a vacuum degree below -80KPa, and maintain it for 0.5 to 1 hour to ensure that the lubricating oil can completely enter the pores of the porous powder metallurgy bearing.

10. A micromotor for automobile, characterized in that: The automotive micromotor is equipped with an oil-containing powder metallurgy bearing obtained by the method according to any one of claims 1 to 9.

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