Patent Description:
This disclosure generally relates to the field of motor technologies, and the invention in particular relates to a motor shaft, a motor, and an electric vehicle.

A motor is mainly formed by a stator, a rotor, a motor housing, a motor shaft, and a bearing. The rotor is mounted on the motor shaft, and the motor shaft is connected to the motor housing through the bearing. The motor shaft and the rotor form a rotor component that is rotatable around a central axis of the motor shaft. The stator and the motor housing form a stator component. During operation of the motor, a magnetic circuit or a phase current between the stator component and the rotor component generates a rotating system flux linkage due to imbalance. When the motor shaft rotates, the flux linkage generates an electric potential difference between the rotor component and the stator component, and a shaft voltage is formed.

A shaft current is generated when the shaft voltage passes through the rotor component, the stator component, the bearing, and the like, to form a closed loop. If the shaft voltage is high, or a lubricating oil film in the bearing is not stable at a moment of motor startup, the shaft voltage discharges and breaks down the lubricating oil film in the bearing to form a path, and the shaft current is generated. High temperature produced by partial discharging of the shaft current can melt the bearing, in other words, electric corrosion is generated. The electric corrosion of the bearing increases noise and vibration during operation of the motor, and likely cause damage to the bearing and lubricant aging, resulting in premature malfunction of the motor.

<CIT> addresses the technical problem of electrical corrosion of motor bearings caused by shaft currents. The solution provided here comprises an insulating structure for the non-extended end of a motor shaft. This structure includes a shaft, a bearing, an end cover, an inner bearing cover, and an outer bearing cover. An insulating coating is applied to the extension surface of the non-extended end of the shaft. This coating is made of several stacked layers of ceramic sheets formed by molten or semi-molten ceramic material impacting the extension surface. The non-shaft extension end of the rotating shaft, coated with the insulating coating, has an interference fit with the bearing, ensuring effective insulation and reliable assembly.

<CIT> also addresses the general technical problem of shaft currents in large and medium-sized motor bearings which can cause damage to the bearings and related components. The solution proposed here involves a shaft current prevention device that includes an insulating layer at the bearing stop on the rotating shaft. This insulating layer is made of a ceramic coating of Al<NUM>O<NUM>-TO<NUM> or Al<NUM>O<NUM> and has a thickness of at least <NUM>. The insulating layer effectively blocks the shaft current, protecting the bearings from damage.

<CIT> addresses the need for an effective insulating structure in assembled rolling bearings. This problem is olved here by providing an assembled rolling bearing that includes an insulating sleeve and an insulating baffle. These components are placed between the bearing and the shaft (or bearing chamber) to provide the necessary insulation. The insulating sleeve is oriented in the transverse direction of the shaft, and the insulating baffle is oriented in the longitudinal direction. This design allows the insulating parts and the bearings to be manufactured separately and then assembled, which improves bearing performance, reduces costs, and enhances supply efficiency. The insulating sleeve and baffle are made with ceramic insulation coatings on a metal body, ensuring effective insulation with an electrical breakdown voltage of 20KV and an insulation resistance of not less than 1000MΩ.

<CIT> also addresses the general technical problem of bearing damage in variable frequency motors due to shaft currents. This problem is here solved by providing a bearing insulation structure that employs a rotating shaft insulation method. This method involves spraying an insulating material, specifically alumina ceramic, on the shaft section where the bearing and end covers are installed. This approach achieves complete insulation between the shaft and the bearing, thereby preventing shaft currents from damaging the bearing. Additionally, insulating gaskets are installed on both end surfaces of the bearing, and an insulating sleeve is placed on the outer ring of the bearing to provide further protection.

The object of the present invention is to provide a motor shaft, a motor, and an electric vehicle that can further reduce a possibility of electric corrosion of a bearing. This object is solved by the attached independent claim and further embodiments and improvements of the invention are listed in the attached dependent claims. Hereinafter, up to the "brief description of the drawings", expressions like ". aspect according to the invention", "according to the invention", or "the present invention", relate to technical teaching of the broadest embodiment as claimed with the independent claims. Expressions like "implementation", "design", "optionally", "preferably", "scenario", "aspect" or similar relate to further embodiments as claimed, and expressions like "example", ". aspect according to an example", "the disclosure describes", or "the disclosure" describe technical teaching which relates to the understanding of the invention or its embodiments, which, however, is not claimed as such.

According to a first aspect according to the invention, the invention provides a motor shaft, including a shaft body and an insulation coating. The shaft body includes a first mounting portion and a second mounting portion that are fastenedly connected. A positioning step surface is disposed at an end that is of the first mounting portion and that is close to the second mounting portion. The first mounting portion is configured to mount a rotor, the second mounting portion is covered with the insulation coating, and the second mounting portion is configured to mount a bearing. A resistivity of the insulation coating is not less than <NUM><NUM> Ω·m.

According to the motor shaft provided in the first aspect of this application, because the second mounting portion is covered with the insulation coating with a resistivity not less than <NUM><NUM> ohm·m (also referred to as Ω·m), a possibility that a shaft current is generated when a shaft voltage discharges and breaks down a lubricating oil film in the bearing to form a path can be effectively reduced. To be specific, the insulation coating can effectively block circulation of the shaft current between the motor shaft and the bearing, so as to reduce a possibility of electric corrosion of the bearing, further reduce a possibility of abnormal operating noise of the motor due to the electrical corrosion of the bearing, and effectively prolong a service life of the motor. The insulation coating has good insulation performance, a simple structure, easy processing, and a low cost. In addition, the positioning step surface is used for locating the bearing when the bearing is sleeved on the second mounting portion, thereby improving convenience of assembling the bearing on the motor shaft.

According to the first aspect according to the invention, in a first implementation of the first aspect according to the invention, in the invention the positioning step surface is covered with the insulation coating. Because the bearing is attached to the positioning step surface when sleeved on the second mounting portion, and the positioning step surface is covered with the insulation coating, all contact surfaces between the shaft body and the bearing are covered with the insulation coating, thereby further reducing a possibility of electric corrosion of the bearing.

According to the first aspect according to the invention or the first implementation of the first aspect according to the invention, in a second implementation of the first aspect according to the invention, in the invention the second mounting portion of the shaft body is further provided with an annular groove extending along a circumferential direction of the second mounting portion, and the groove is located at an end that is of the second mounting portion and that is close to the positioning step surface. The groove is used for improving the precision of size matching between the motor shaft and the bearing. The circumferential direction of the second mounting portion refers to an axial direction around the second mounting portion.

According to the first aspect according to the invention or the first implementation and the second implementation of the first aspect according to the invention, in a third implementation of the first aspect according to the invention, in the invention the groove includes a first connection wall and a second connection wall that are oppositely disposed. The first connection wall is disposed at an end that is of the groove and that is close to the first mounting portion. The insulation coating on the positioning step surface is flush with the first connection wall, and an end surface of an end that is of the insulation coating on the second mounting portion and that is close to the first mounting portion is flush with the second connection wall. In other words, an inner wall of the groove is exposed outside the insulation coating. The groove is a blade clearance groove, which facilitates a cutting tool to perform processing to form a mounting surface (namely, a bearing mounting surface) of the bearing on a peripheral wall of the second mounting portion, and facilitates machining of the motor shaft.

According to the first aspect or the first implementation to the fourth implementation of the first aspect of this application, in a fifth implementation of the first aspect of this application, at least a part of an end surface that is of the second mounting portion and that is away from the first mounting portion is covered with the insulation coating, so as to further increase a coverage area of the insulation coating on the shaft body.

According to the first aspect or the first implementation to the fifth implementation of the first aspect of this application, in a sixth implementation of the first aspect of this application, the first mounting portion includes a mounting section and a shaft shoulder that are fastenedly connected. An outer diameter of the mounting section is greater than an outer diameter of the shaft shoulder, and the outer diameter of the shaft shoulder is greater than an outer diameter of the second mounting portion, to form the positioning step surface. The first mounting portion includes the mounting section and the shaft shoulder, so that the shaft shoulder can increase the strength of the motor shaft and facilitate the mounting of the bearing.

According to the first aspect or the first implementation to the sixth implementation of the first aspect of this application, in a seventh implementation of the first aspect of this application, the mounting section is provided with a rotor mounting groove extending along an axial direction of the mounting section, and is configured to mount the rotor. In this way, convenience of mounting the rotor on the motor shaft is improved.

According to the first aspect or the first implementation to the seventh implementation of the first aspect of this application, in an eighth implementation of the first aspect of this application, a thickness of the insulation coating ranges from <NUM> to <NUM>.

According to the first aspect or the first implementation to the eighth implementation of the first aspect of this application, in a ninth implementation of the first aspect of this application, a minimum insulation resistance of the insulation coating under a <NUM> V direct current voltage is <NUM> MΩ.

According to a second aspect according to the invention, the invention also provides a motor, including the motor shaft, the rotor, the stator, the motor housing, and the bearing according to the first aspect or the first implementation to the sixth implementation of the first aspect. The rotor is fastenedly sleeved on the first mounting portion of the motor shaft, the stator is sleeved on the rotor, and the motor housing is fastenedly sleeved outside the stator. The bearing is sleeved on the second mounting portion of the motor shaft and is fastenedly connected to the motor housing. The bearing abuts against the positioning step surface. The motor shaft is rotatable with the rotor relative to the stator.

According to a third aspect according to the invention, the invention also provides an electric vehicle, including a power supply system and an electric drive assembly. The power supply system is configured to provide electric energy for the electric drive assembly, and the electric drive assembly includes the motor according to the second aspect of this application.

An electric vehicle includes a battery electric vehicle (BEV, Battery Electric Vehicle), a hybrid electric vehicle (HEV, Hybrid Electric Vehicle), and a plug-in hybrid electric vehicle (PHEV, Plug In Hybrid Electric Vehicle).

The BEV includes a motor. An energy source of the motor is a power battery. The power battery of the BEV can be recharged from an external power grid. The power battery of the BEV is actually a unique source of in-vehicle energy for vehicle propulsion.

The HEV includes an internal combustion engine and a motor. An energy source of the engine is fuel, and an energy source of the motor is a power battery. The engine is a main source of energy for vehicle propulsion, and the power battery of the HEV provides supplementary energy for vehicle propulsion (the power battery of the HEV electrically buffers fuel energy and recovers kinetic energy).

The PHEV differs from the HEV in that a power battery of the PHEV has a larger capacity than the power battery of the HEV, and the power battery of the PHEV can be recharged from a power grid. The power battery of the PHEV is a main source of energy for vehicle propulsion until a loss of the power battery of the PHEV reaches a low energy level. In this case, the PHEV operates as the HEV for vehicle propulsion.

The following describes embodiments of this application with reference to the accompanying drawings. In embodiments of this application, a structure of an electric vehicle is described by using a BEV as an example.

Refer to <FIG>. An electric vehicle <NUM> provided in an implementation of this application includes a power supply system <NUM>, an electric drive assembly <NUM>, a vehicle control unit <NUM>, a motor controller <NUM>, a drive wheel <NUM>, and an auxiliary system <NUM>. The power supply system <NUM> includes a power battery <NUM>, a battery management system <NUM>, and a charger <NUM>. The electric drive assembly <NUM> includes a motor <NUM> and a reducer <NUM> mechanically connected to the motor <NUM>. The reducer <NUM> is further mechanically connected to the drive wheel <NUM>, and is configured to transfer power generated by the motor <NUM> to the drive wheel <NUM> to drive the electric vehicle <NUM> to travel.

The vehicle controller (VCU, Vehicle Control Unit) <NUM> is also referred to as a power assembly controller, is a core control component of the entire vehicle, and is equivalent to a brain of the vehicle. After collecting an accelerator pedal signal, a brake pedal signal, and other component signals and making corresponding determining, the VCU controls actions of lower-layer component controllers, to drive the vehicle to normally travel. As a command and management center of the vehicle, main functions of the VCU include drive torque control, brake energy optimization control, vehicle energy management, CAN (Controller Area Network, controller area network) network maintenance and management, fault diagnosis and processing, vehicle status monitoring, and the like. The VCU controls operation of the vehicle. Therefore, performance of the VCU directly determines stability and safety of the vehicle.

The motor controller <NUM> is an integrated circuit that actively works to control the motor <NUM> in the electric drive assembly <NUM> to work based on a specified direction, speed, angle, and response time, and is communicatively connected to the VCU <NUM>. In the electric vehicle <NUM>, the motor controller <NUM> is configured to convert, based on an instruction of a gear, a throttle, a brake, or the like, electric energy stored in the power battery <NUM> into electric energy needed for the motor, to control a traveling status such as startup and operation, a forward/backward speed, or a climbing force of the electric vehicle <NUM>, or help the electric vehicle <NUM> brake and store some brake energy in the power battery <NUM>.

The motor (commonly referred to as a "motor") <NUM> is an electromagnetic apparatus that implements electric energy conversion or transfer based on an electromagnetic induction law, and is electrically connected to the motor controller <NUM> and mechanically connected to the reducer <NUM>. The motor is mainly configured to generate a drive torque as a power source of the drive wheel <NUM>.

The power battery <NUM> is electrically connected to the motor controller <NUM>, and is configured to store and provide electric energy. The power battery <NUM> includes but is not limited to a lead-acid battery, a lithium iron phosphate battery, a nickel-hydrogen battery, a nickel-cadmium battery, and the like. In some embodiments, the power battery <NUM> may alternatively include a supercapacitor.

The battery management system <NUM> is electrically connected to the power battery <NUM>, and is communicatively connected to the VCU <NUM>. The battery management system <NUM> is configured to monitor and estimate statuses of the power battery <NUM> in different working conditions, to improve utilization of the power battery <NUM>, and prevent the power battery <NUM> from being overcharged or over-discharged, thereby prolonging a service life of the power battery <NUM>. Specifically, main functions of the battery management system <NUM> may include real-time battery physical parameter monitoring, battery status estimation, online diagnosis and warning, charging, discharging, and pre-charging control, balancing management and heat management, and the like.

The charger <NUM> is electrically connected to the power battery <NUM>, and is configured to be connected to an external power supply to charge the power battery <NUM>. Specifically, when the electric vehicle <NUM> is connected to an external power supply (such as a charging pile), the charger <NUM> converts an alternating current provided by the external power supply into a direct current, to charge the power battery <NUM>. In addition, the battery management system <NUM> is further connected to the charger <NUM> to monitor a charging process of the power battery <NUM>.

The auxiliary system <NUM> includes a DC/DC converter <NUM>, an auxiliary battery <NUM>, a low-voltage load <NUM>, and a high-voltage load <NUM>. An end of the DC/DC converter <NUM> is connected to the power battery <NUM>, and the other end of the DC/DC converter <NUM> is connected to both the auxiliary battery <NUM> and the low-voltage load <NUM>. The DC/DC converter <NUM> is configured to: after converting a high voltage (such as <NUM> V) output by the power battery <NUM> into a low voltage (such as <NUM> V), charge the auxiliary battery <NUM> and supply power to the low-voltage load <NUM>. In some implementations, the low-voltage load <NUM> includes low-voltage vehicle accessories such as a cooling pump, a fan, a heater, a power steering apparatus, and a brake. Certainly, the auxiliary battery <NUM> may also supply power to the low-voltage load <NUM>. In addition, the power battery <NUM> is further connected to the high-voltage load <NUM> to supply power to the high-voltage load <NUM>. In some implementations, the high-voltage load <NUM> includes a PTC heater, an air conditioning unit, and the like.

It should be noted that electronic modules in the electric vehicle <NUM> may communicate with each other by using one or more vehicle networks. The vehicle network may include a plurality of channels for communication. A channel of the vehicle network may be, for example, a serial bus of a controller area network (Controller Area Network, CAN). One of the channels of the vehicle network may include Ethernet defined by the Institute of Electrical and Electronics Engineers (IEEE) <NUM> standard family. Other channels of the vehicle network may include a discrete connection between modules and may include a power signal from the auxiliary power battery <NUM>. Different signals may be transmitted by using different channels of the vehicle network. For example, a video signal may be transmitted by using a high-speed channel (such as Ethernet), and a control signal may be transmitted by using a CAN or a discrete signal. The vehicle network may include any hardware component and software component assisting in signal and data transmission between modules. The vehicle network is not shown in <FIG>, but it may be implied that the vehicle network may be connected to any electronic module in the electric vehicle <NUM>. For example, the vehicle network may exist in the VCU <NUM> to coordinate operations of the components.

It may be understood that the schematic structure in embodiments of this application constitutes no specific limitation on the electric vehicle <NUM>. In some other embodiments of this application, the electric vehicle <NUM> may include more or fewer components than those shown in the figure, combine some components, split some components, or have different component arrangements. The components shown in the figure may be implemented by hardware, software, or a combination of software and hardware.

Refer to <FIG>. A motor <NUM> includes a motor shaft <NUM>, a rotor <NUM>, a stator <NUM>, a motor housing <NUM>, and a bearing <NUM>. The rotor <NUM> is fastenedly sleeved on the motor shaft <NUM>, and the stator <NUM> is sleeved on the rotor <NUM>. The motor housing <NUM> is fastenedly sleeved on the stator <NUM>, and is configured to accommodate the motor shaft <NUM>, the rotor <NUM>, and the stator <NUM>. The motor shaft <NUM> is rotatable with the rotor <NUM> relative to the stator <NUM>. The bearing <NUM> is sleeved on an end portion of the motor shaft <NUM> and is fastened to the motor housing <NUM>, and is configured to support the motor shaft <NUM>. The bearing <NUM> includes an inner ring <NUM> and an outer ring <NUM> that are rotatable relative to each other. The inner ring <NUM> is fastened to the motor shaft <NUM>, and the outer ring <NUM> is fastened to the motor housing <NUM>.

Refer to <FIG>. The motor shaft <NUM> includes a shaft body <NUM> and an insulation coating <NUM>. The shaft body <NUM> includes a first mounting portion <NUM> and a second mounting portion <NUM> that are fastenedly connected. The second mounting portion <NUM> is located at an end portion of the shaft body <NUM>. A positioning step surface <NUM> is disposed at an end that is of the first mounting portion <NUM> and that is close to the second mounting portion <NUM>. The second mounting portion <NUM> is covered with the insulation coating <NUM>. A resistivity of the insulation coating <NUM> is not less than <NUM><NUM> Ω·m. The rotor <NUM> is fastenedly sleeved on the first mounting portion <NUM>. The inner ring <NUM> of the bearing <NUM> is sleeved on the second mounting portion <NUM> and is in contact with the positioning step surface <NUM>. The positioning step surface <NUM> is configured to contact the bearing <NUM> when the bearing <NUM> is assembled on the second mounting portion <NUM>, so as to limit a position of the inner ring <NUM> of the bearing <NUM>, to facilitate assembly of the bearing <NUM> on the motor shaft <NUM>. It may be understood that a position of the second mounting portion <NUM> on the shaft body <NUM> is not limited in this application. For example, the second mounting portion <NUM> is located in the middle of the shaft body <NUM>.

The motor shaft <NUM> and the rotor <NUM> form a rotor component that is rotatable around a central axis of the motor shaft <NUM>, and the stator <NUM> and the motor housing <NUM> form a stator component. The bearing <NUM> has lubricating oil inside, to improve smoothness of relative rotation between the inner ring <NUM> of the bearing <NUM> and the outer ring <NUM> of the bearing <NUM>.

During operation of the motor, a magnetic circuit or a phase current between the stator and the rotor generates a rotating system flux linkage due to imbalance. When the motor shaft rotates, the flux linkage generates an electric potential difference between the rotor component and the stator component, forming a shaft voltage. A shaft current is generated when the shaft voltage passes through the rotor component, the stator component, the bearing or an auxiliary apparatus, and the like, to form a closed loop. If the shaft voltage is high, or a lubricating oil film in the bearing is not stable at a moment of motor startup, the shaft voltage discharges and breaks down the lubricating oil film in the bearing to form a path, and consequently, the shaft current is generated. Partial discharging of the shaft current produces high temperature that can melt at least part of the bearing, such as the inner ring, the outer ring, or a ball of the bearing, namely, electrical corrosion of the bearing. The electric corrosion of the bearing increases noise and vibration during operation of the motor, and likely cause damage to the bearing and lubricant aging, resulting in premature malfunction of the motor. Operating power of an electric vehicle is usually greater than <NUM> kw, which causes a large shaft voltage generated by the motor, and therefore causes a high risk of the bearing mounted on the shaft body.

In the motor <NUM> provided in this implementation of this application, the second mounting portion <NUM> is covered with the insulation coating <NUM> whose resistivity is not less than <NUM><NUM> ohm·m (also referred to as Ω·m). In other words, the insulation coating <NUM> can withstand a large shaft voltage. This effectively reduces a possibility that the shaft voltage discharges and breaks down the lubricating oil film in the bearing <NUM> to form a path, and further generates the shaft current. The insulation coating <NUM> can effectively block circulation of the shaft current between the motor shaft <NUM> and the bearing <NUM>, so as to reduce a possibility of abnormal operating noise of the motor <NUM> due to electrical corrosion of the bearing <NUM>, and effectively prolong a service life of the motor <NUM>. In addition, the insulation coating <NUM> has good insulation performance, a simple structure, easy processing, and a low cost.

The insulation coating <NUM> is formed by spraying an insulation material on a surface of the shaft body <NUM>. In this implementation, a thickness of the insulation coating <NUM> ranges from <NUM> to <NUM>, and a minimum insulation resistance of the insulation coating <NUM> under a <NUM> V direct current voltage is <NUM> megohms (also referred to as MΩ). The insulation material includes but is not limited to insulation ceramics, Teflon, and other insulation materials and special insulation materials.

In this implementation, an outer diameter of the first mounting portion <NUM> is greater than an outer diameter of the second mounting portion <NUM>, so that the positioning step surface <NUM> is formed at an end portion that is of the first mounting portion <NUM> and that is close to the second mounting portion <NUM>. The positioning step surface <NUM> is covered with the insulation coating <NUM>, so that all contact surfaces between the shaft body <NUM> and the bearing <NUM> are covered with the insulation coating <NUM>, thereby further reducing a possibility of electrical corrosion the bearing <NUM>. It may be understood that the rotor <NUM> may be secured to the first mounting portion <NUM> by using a fastener, an interference fit, or the like.

In this implementation, there are two second mounting portions <NUM>. The two second mounting portions <NUM> are fastenedly connected to two end portions of the first mounting portion <NUM> in a one-to-one correspondence. One second mounting portion <NUM> is connected to an input shaft (not shown in the figure) of the reducer <NUM>, and an output shaft of the reducer <NUM> is connected to the drive wheel <NUM>, so as to transfer power generated by the motor <NUM> to the drive wheel <NUM>.

The second mounting portion <NUM> is further provided with an annular groove <NUM> extending along a circumferential direction of the second mounting portion <NUM>, and the groove <NUM> is located at an end that is of the second mounting portion <NUM> and that is close to the first mounting portion <NUM>. The groove <NUM> is used for improving the precision of size matching between the motor shaft <NUM> and the bearing <NUM>. The inner wall of the groove <NUM> is not covered with the insulation coating <NUM>. To be specific, the inner wall of the groove <NUM> is exposed outside the insulation coating <NUM>. In this implementation, the groove <NUM> is a blade clearance groove, which facilitates a cutting tool to perform processing (for example, grinding) to form a mounting surface (namely, a bearing mounting surface) of the bearing <NUM> on a peripheral wall of the second mounting portion <NUM> and then to be cleared.

The groove <NUM> includes a first connection wall <NUM> and a second connection wall <NUM> that are oppositely disposed, the first connection wall <NUM> is disposed at an end that is of the groove <NUM> and that is close to the first mounting portion <NUM>, the insulation coating <NUM> on the positioning step surface <NUM> is flush with the first connection wall <NUM>, and an end surface of an end that is of the insulation coating <NUM> on the second mounting portion <NUM> and that is close to the first mounting portion <NUM> is flush with the second connection wall <NUM>. It should be noted that in this application, a coverage surface (namely, a spraying range of an insulation material) of the insulation coating <NUM> of the motor shaft <NUM> includes but is not limited to contact surfaces between the motor shaft <NUM> and the bearing <NUM>. For example, refer to <FIG>. At least an edge part of an end surface (namely, an end surface of the shaft body <NUM>) that is of the second mounting portion <NUM> and that is away from the first mounting portion <NUM> is covered with the insulation coating <NUM>, and contrary to the invention the inner wall of the groove <NUM> is covered with the insulation coating <NUM>, so as to increase a coverage area of the insulation coating <NUM> on the shaft body <NUM>. Alternatively, at least a part of an outer surface of the first mounting portion <NUM> may be covered with the insulation coating <NUM>. To be specific, contact surfaces between the motor shaft <NUM> and the rotor <NUM> may also be covered with the insulation coating <NUM>.

It may be understood that a structure of the first mounting portion <NUM> is not limited in this application. For example, in an implementation, refer to <FIG> and <FIG> which are not part of the invention. The shaft body <NUM> includes the first mounting portion <NUM> and the second mounting portion <NUM> that is fastenedly connected to an end portion of the first mounting portion <NUM>. The first mounting portion <NUM> includes a mounting section <NUM> and a shaft shoulder <NUM> that are fastenedly connected. An outer diameter of the mounting section <NUM> is greater than an outer diameter of the shaft shoulder <NUM>, and an outer diameter of the shaft shoulder <NUM> is greater than an outer diameter of the second mounting portion <NUM>, to form the positioning step surface <NUM>. The shaft shoulder <NUM> can increase the strength of the motor shaft and facilitate the mounting of the bearing. The mounting section <NUM> is provided with a rotor mounting groove <NUM> extending along an axial direction of the mounting section <NUM>, and is configured to mount the rotor. In this way, convenience of mounting the rotor on the motor shaft is improved. The groove <NUM> is disposed close to the positioning step surface <NUM>. The second mounting portion <NUM> is covered with the insulation coating <NUM>.

It should be understood that expressions such as "include" and "may include" that may be used in this application indicate existence of the disclosed function, operation, or constituent element, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "include" and/or "have" may be construed as a particular characteristic, quantity, operation, constituent element, or component, or a combination thereof, but cannot be construed as excluding the existence or possible addition of one or more other characteristics, quantities, operations, constituent elements, or components, or combinations thereof.

In addition, in this application, the expression "and/or" includes any and all combinations of words listed in association. For example, the expression "A and/or B" may include A, may include B, or may include both A and B.

In this application, expressions including ordinal numbers such as "first" and "second" may modify elements. However, such elements are not limited by the expressions. For example, the expressions do not limit the order and/or importance of the elements. The expression is used only to distinguish one element from another. For example, first user equipment and second user equipment indicate different user equipment, although both the first user equipment and the second user equipment are user equipment. Similarly, without departing from the scope of this application, a first element may be referred to as a second element, and similarly, a second element may also be referred to as a first element.

When a component "connects" or "is connected" to another component, it should be understood that the component directly connects or is directly connected to the another component, or a further component may alternatively exist between the component and the another component. In addition, when a component "directly connects" or "directly connected" to another component, it should be understood that there is no component between them.

Claim 1:
A motor shaft (<NUM>), comprising a shaft body (<NUM>) and an insulation coating (<NUM>), wherein the shaft body (<NUM>) comprises a first mounting portion (<NUM>) and a second mounting portion (<NUM>) that are fastenedly connected, a positioning step surface (<NUM>) is disposed at an end that is of the first mounting portion (<NUM>) and that is close to the second mounting portion (<NUM>), the first mounting portion (<NUM>) is configured to mount a rotor (<NUM>), the second mounting portion (<NUM>) is covered with the insulation coating (<NUM>), the second mounting portion (<NUM>) is configured to mount a bearing (<NUM>), and a resistivity of the insulation coating (<NUM>) is not less than <NUM><NUM> Ω·m;
wherein the positioning step surface (<NUM>) is covered with the insulation coating (<NUM>);
wherein the second mounting portion (<NUM>) is further provided with an annular groove (<NUM>) extending along a circumferential direction of the second mounting portion (<NUM>), and the groove (<NUM>) is located at an end that is of the second mounting portion (<NUM>) and that is close to the positioning step surface (<NUM>); and
wherein the groove (<NUM>) comprises a first connection wall (<NUM>) and a second connection wall (<NUM>) that are oppositely disposed, the first connection wall (<NUM>) is disposed at an end that is of the groove (<NUM>) and that is close to the first mounting portion (<NUM>), the insulation coating (<NUM>) on the positioning step surface (<NUM>) is flush with the first connection wall (<NUM>), and an end surface of an end that is of the insulation coating (<NUM>) on the second mounting portion (<NUM>) and that is close to the first mounting portion (<NUM>) is flush with the second connection wall (<NUM>).