Patent Description:
The statements here only provide background information related to this application, and do not necessarily constitute prior art. In recent years, due to the energy-saving trend of the electrical equipment such as air-conditioning units, high-efficiency brushless DC motors have been used to replace induction motors to drive blowers, pumps, gears, and other loads. These brushless DC motors are generally driven by inverters, which adopt a pulse width modulation (hereinafter referred to as PWM) method as a driving method. When using the PWM driving method, a common mode voltage is always generated because that the neutral point potential of the winding is not zero. In the case of high frequency, a voltage between the inner ring and outer ring of the bearing (bearing capacitor branch) is generated by the common mode voltage via a loop, which is formed by the coupling capacitors generated between various structural parts of the motor, including the stator, the rotor, the permanent magnet, the bearing bracket, and the bearing capacitors. This voltage between the inner ring and the outer ring of the bearing caused by the common mode voltage is called shaft voltage. The shaft voltage contains the high-frequency components of the high-speed switching action of the semiconductor during PWM driving. If the shaft voltage reaches the insulation breakdown voltage of the lubricating oil film inside the bearing, the current will be generated due to discharge, resulting in local erosion between the inner surface and the balls of the bearing, that is, electric corrosion (also called electric erosion) occurring inside the bearing. When the electric corrosion is aggravated, wave-shaped abrasion will occur inside the bearing, such as the inner ring, outer ring or balls of the bearing, causing abnormal noise and decrease in the service lift of the bearing. <CIT> relates generally to a fixing structure for an anti-corrosion conductive sheet suitable for a small motor. <CIT> relates generally to a plastic motor which reduces bearing electric corrosion. <CIT> relates generally to a motor in which an occurrence of electric erosion is suppressed. <CIT> relates generally to a motor which provides the long-term effectiveness of the electrical connection between the two bearing supports.

An object of embodiments of the present application is to provide a brushless motor to solve the problem in the related arts that excessively high shaft voltage of the brushless motor causes electric erosion of the bearing.

Invention is defined by the independent claim <NUM>. Aspects (i.e. examples or embodiments) of the invention are set out in the dependent claims. In order to achieve the object, the following technical solutions are adopted by the present application:.

A brushless motor is provided. The brushless motor comprises: a casing having an insulating property; a stator fixed within the casing; and a rotor rotatably arranged within the stator. The stator comprises a stator core and a winding wound around the stator core. The rotor comprises a rotor core and a shaft passing through the rotor core. Two bearings are sleeved on the shaft at positions corresponding to two ends of the rotor core, respectively, and two bearing brackets are installed at two ends of the casing for fixing the two bearings. The brushless motor further comprises: a conductive sheet, configured for adjusting a capacitive reactance between the stator core and each of the two bearing brackets. The conductive sheet is spaced apart from the stator core at an outer circumferential side of the stator core, and the conductive sheet is insulated from the stator core. The conductive sheet and the stator core each at least partially has an area overlapping with each other when seen from a radial direction of the stator core. The conductive sheet is in electrical connection with at least one of the two bearing brackets.

Another object of the present application is to provide an electrical equipment, including the brushless motor as described in the above.

The above one or more technical solutions in embodiments of the present application have at least one of the following technical effects:.

In the brushless motor of the present application, the conductive sheet is attached to the outer circumferential surface of the casing, so that the conductive sheet and the stator core each has an area overlapping with each other when seen from the radial direction, forming a coupling capacitor between the stator core and the conductive sheet; moreover, the bearing brackets are located at ends of the casing, the adjusting of the equivalent capacitance between the stator core and the bearing bracket can be achieved, the potential between the outer ring and the inner ring of the bearing is therefore balanced, and the.

shaft voltage is reduced, thereby preventing the bearing from electric erosion.

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings that need to be used in the description of the embodiments or the exemplary art will be briefly described hereinbelow.

<FIG> disclose embodiments of the present invention. <FIG> represents standard measurement equipment used for shaft voltage detection. <FIG> represents measurements taken from comparative example not covered by the present invention (no conductive sheets are present). <FIG> are waveforms measured on the motors according to the embodiments of the present invention.

In the drawings, the following reference numerals are adopted:
<NUM>: Brushless motor; <NUM>: Casing; <NUM>: Positioning groove; <NUM>: Stator; <NUM>: Stator core; <NUM>: Winding; <NUM>: Rotor; <NUM>: Shaft; <NUM>: Rotor core; <NUM>: Bearing; <NUM>: Bearing bracket; <NUM>: First bracket; <NUM>: Second bracket; <NUM>: Conductive sheet; <NUM>: Conductive arm; <NUM>: Conductive piece; <NUM>: Dielectric layer; <NUM>: Oscilloscope; and <NUM>: Differential probe.

In order to make the purposes, technical solutions, and advantages of the present application clearer and more understandable, the present application will be further described in detail hereinafter with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are only intended to illustrate but not to limit the scope of the present invention, which is defined by the appended claims.

All embodiments in the paragraphs below belong to the present invention.

It should be noted that when an element is described as "fixed" or "arranged" on/at another element, it means that the element can be directly or indirectly fixed or arranged on/at another element. When an element is described as "connected" to/with another element, it means that the element can be directly or indirectly connected to/with another element. Moreover, terms like "first" and "second" are only used for the purpose of description, and will in no way be interpreted as indication or hint of relative importance or implicitly indicate the number of the referred technical features. Thus, the features prefixed by "first" and "second" will explicitly or implicitly represent that one or more of the referred technical features are included. In the description of the present application, "multiple"/ "a plurality of" refers to the number of two or more than two, unless otherwise clearly and specifically defined. The meaning of "several" is one or more than one, unless otherwise specifically defined. It should be understood that terms "center", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicating orientation or positional relationship are based on the orientation or the positional relationship shown in the drawings, and are merely for facilitating and simplifying the description of the present application, rather than indicating or implying that a device or component must have a particular orientation, or be configured or operated in a particular orientation, and thus should not be construed as limiting the application. In the present application, unless otherwise specifically stipulated and defined, terms like "install", "connect", "couple", "fix" should be construed broadly, for example, they may indicate a fixed connection, a detachable connection, or an integral as a whole; may be a mechanical connection, or an electrical connection; may be in direct connection, or indirect connection via an intermediate, and may also reflect internal communication of two elements or interactions between two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to specific conditions.

A brushless motor <NUM> provided by the present application is described hereinbelow with reference to <FIG>. The brushless motor <NUM> comprises: a casing <NUM>, a stator <NUM>, a rotor <NUM>, two bearings <NUM>, and two bearing brackets <NUM>. Both the stator <NUM> and the rotor <NUM> are installed in the casing <NUM>, and the stator <NUM> is configured to drive the rotor <NUM> to rotate. The two bearings <NUM> are installed at the rotor <NUM> to support the rotor <NUM>. The two bearing brackets <NUM> support the two bearings <NUM>, respectively, thereby supporting the rotor <NUM>. In the meanwhile, the two bearing brackets <NUM> are installed at two ends of the casing <NUM>, respectively, so as to support the rotor <NUM> within the casing <NUM> and enabling the rotor <NUM> to flexibly rotate. The use of the bearing brackets <NUM> to support the bearings <NUM> can achieve more stable supporting of the bearings <NUM>, thereby ensuring excellent rotation of the bearings <NUM>.

The casing <NUM> has insulating property, and plays the main role of support and protection. The casing <NUM> can be injection-molded using a resin material, which can facilitate processing and manufacture, and can have good insulation effect. In addition, the casing <NUM> can also dissipate heat. It can be understood that in order to improve the heat dissipation efficiency, some heat dissipation fins can be arranged on the casing <NUM>.

The stator <NUM> comprises a stator core <NUM> and a winding <NUM>. The winding <NUM> is wound on the stator core <NUM>. When a current passes through the winding <NUM>, a magnetic field is generated, and the magnetic field is reinforced and guided by the stator core <NUM>. The stator core <NUM> is formed by stacking a plurality of the silicon steel sheets to reduce eddy currents. The stator core <NUM> generally comprises a plurality of tooth-like structures, and the winding <NUM> is wound on the respective teeth. These tooth-like structures are enclosed to for a circular shape, which enables the rotor to be arranged within the stator <NUM> and to be driven to rotate.

The rotor <NUM> comprises: a shaft <NUM> and a rotor core <NUM>. The shaft <NUM> passes through a center of the rotor core <NUM>, such that the rotor core <NUM> can be supported by the shaft <NUM>; and the rotor core <NUM> is placed in the stator <NUM>. Therefore, when the winding <NUM> is energized, an alternating magnetic field is generated on the stator core <NUM> to drive the rotor core <NUM> to rotate and in turn drive the shaft <NUM> to rotate. In addition, the rotor core <NUM> may be a combined structure of the rotor core <NUM> and magnets, or may be formed by punching the silicon steel sheets into a cage-like shape by a punching machine, and stacking punched silicon steel sheets, casting with aluminum for processing.

Both the two bearings <NUM> are sleeved outside the shaft <NUM>, and are located at the two ends of the rotor core <NUM>, respectively. Since the weight of the rotor <NUM> is mostly concentrated at the position of the rotor core <NUM>, the center of gravity of the rotor <NUM> is also at the position corresponding to the rotor core <NUM>. Such arrangement of the two bearings <NUM> at the two ends of the rotor core <NUM> respectively can better support the shaft <NUM>, and in turn support the rotor core <NUM>, which makes the rotor core <NUM> and the shaft <NUM> more stably rotate. The arrangement of the two bearings <NUM> for supporting the shaft <NUM> enables the rotation of the shaft <NUM> more flexibly.

Two bearings <NUM> are arranged within the two bearing brackets <NUM>, respectively, such that the two bearings <NUM> and in turn the rotor <NUM> are supported by corresponding bearing brackets <NUM>. The two bearing brackets <NUM> are respectively installed at two ends of the casing <NUM> to support the rotor <NUM> in the casing <NUM> and enable the rotor <NUM> to rotate flexibly in the casing <NUM>. Moreover, the stator core <NUM> is insulated from the respective bearing brackets <NUM>. The use of the two bearing brackets <NUM> can support the bearings <NUM> more stably, ensure the smooth rotation between the outer ring and the inner ring of each bearing <NUM>, and can reduce vibration, avoid the bearings <NUM> from creeping. The outer rings of the bearings <NUM> are in electrical connection to the bearing brackets <NUM>, respectively. The "electrical connection" means the ability to conduct electricity, but is not limited to that the current always passing through the outer ring of the bearing <NUM> and the corresponding bearing bracket <NUM>. For example, the "electrical connection" may refer to a contact state between a metal bearing bracket and a metal outer ring of the corresponding bearing.

As shown in <FIG>, in an embodiment, the stator <NUM> and the casing <NUM> are plastic packaged into an integrated structure, so that the stator <NUM> is firmly and stably fixed in the casing <NUM>. The casing <NUM> can be manufactured to have a relatively small size, thereby reducing the volume and the weight of the manufactured brushless motor <NUM>. For example, when the casing <NUM> is made by injection molding, the stator <NUM> can be placed in a mold, so that when the casing <NUM> is injection molded, the casing <NUM> and the stator <NUM> form an integrated structure. It can be understood that, in some other embodiments, the casing <NUM> can also be made separately, and the stator <NUM> can be fixed in the casing <NUM>.

As shown in <FIG>, in an embodiment, the two bearing brackets <NUM> are composed of a first bracket <NUM> and the second bracket <NUM>. The first bracket <NUM> and the second bracket <NUM> are located at the two ends of the casing <NUM>, respectively. The first bracket <NUM> is used as an end cover of the casing <NUM>, and the second bracket <NUM> and the casing <NUM> are molded into an integral structure, that is, when the casing <NUM> is injection molded, the second bracket <NUM> can be placed in the mold, such that the second bracket <NUM> and the casing <NUM> can be injection molded as a whole during the injection molding of the casing <NUM>. In this way, the second bracket <NUM> is firmly fixed in the casing <NUM>, which facilitates the processing and manufacture and reduces the weight and the cost. The use of the first bracket <NUM> as the end cover of the casing <NUM> enables the whole end cover to be made of a metal, or only a part of the end cover that supports the bearing <NUM> to be made of the metal, thereby preventing the bearing <NUM> from creeping and ensuring stable rotation of the bearing <NUM>. The second bracket <NUM> may be a part only supporting the corresponding bearing <NUM>, so that the second bracket <NUM> and the casing <NUM> can be easily molded into an integral structure during injection molding.

As shown in <FIG>, in an embodiment, both the two ends of the casing <NUM> may be designed to be open structures, and both the two bearing brackets <NUM> may be used as two end covers. Such that a fan and other structures can be installed in one end of the casing <NUM> to better dissipate heat. It can be understood that such a structure has more practical significance for motors that require output at both ends of the shaft <NUM>. In addition, the configuration of two ends of the casing <NUM> as the open structures and the two bearing brackets <NUM> as end covers may increase the strength of the whole brushless motor <NUM> via the bearing bracket <NUM>. In addition, the bearing bracket <NUM> can also be used for heat dissipation, in order to improve heat dissipation efficiency.

As shown in <FIG>, in an embodiment, the brushless motor <NUM> further comprises: a conductive sheet <NUM>, configured for adjusting a capacitive reactance between the stator core <NUM> and each of the two bearing brackets <NUM>. The conductive sheet <NUM> is attached to the outer circumferential surface <NUM> of the casing <NUM>. The conductive sheet <NUM> and the stator core <NUM> each at least partially has an area overlapping with each other when seen from the radial direction, so as to form a capacitor between the conductive sheet <NUM> and the stator core <NUM>. The conductive sheet <NUM> is connected to at least one of the two bearing brackets, which is equivalent to connecting a coupling capacitor in parallel to the original capacitor formed between each of the bearing brackets and the stator core. By changing the size of the conductive sheet <NUM>, the area of the conductive sheet <NUM> aligned to the stator core <NUM> can be adjusted, such that the capacitive reactance between the stator core <NUM> and each bearing bracket <NUM> can be adjusted, that is, the capacitive reactance between the stator core and the outer ring of each bearing can be adjusted. In this way, an equivalent capacitance between the stator core <NUM> and the inner ring of each bearing <NUM> is approximate to or equal to an equivalent capacitance between the stator core <NUM> and the outer ring of each bearing <NUM>, that is, the equivalent capacitance between the stator core <NUM> and the inner ring of each bearing <NUM> and the equivalent capacitance between the stator core <NUM> and the outer ring of each bearing <NUM> are balanced, in turn, the potential between the outer ring of each bearing <NUM> and the inner ring of each bearing <NUM> are balanced, such that the potential of the outer ring of each bearing <NUM> and the potential of the inner ring of each bearing <NUM> are similar, a potential difference between the outer ring of each bearing <NUM> and the inner ring of each bearing <NUM> are reduced, thereby decreasing a shaft voltage and avoid the bearing <NUM> from electric erosion.

In some other embodiments, the conductive sheet <NUM> can be arranged within the casing <NUM>, in which case the distance between the conductive sheet <NUM> and the stator core <NUM> is reduced. That is, it is only required that the conductive sheet <NUM> is spaced apart from the stator core <NUM> at an outer circumferential side of the stator core <NUM>, and the conductive sheet <NUM> is insulated from the stator core <NUM>.

Furthermore, in the above embodiment, the two bearing brackets <NUM> are in electrical connection, so that the potentials of the two bearing brackets <NUM> are kept consistent, and the potentials of the outer rings of the two the bearing <NUM> are kept consistent. In the above embodiment, the first bracket <NUM> and the second bracket <NUM> are electrically connected, so that the first bracket <NUM> and the second bracket <NUM> have the same potential. In this way, the capacitive reactance between the stator core <NUM> and each of the two bearing brackets <NUM> can be adjusted synchronously by the conductive sheet <NUM>, which adjustment is more convenient. In some other embodiments, in case that the structures of the two bearing brackets <NUM> are different, the potential differences between the inner rings and the outer rings of the two bearings <NUM> are also different, and the conductive sheet <NUM> can be electrically connected to only one of the bearing brackets <NUM>, so that only the capacitive reactance between said one of the bearing brackets <NUM> and the stator core <NUM> is adjusted.

Furthermore, in the above embodiment, the conductive piece <NUM> may be arranged within the casing <NUM> to electrically connect the two bearing brackets <NUM>. It can be understood that the conductive piece <NUM> can also be attached from the outside of the casing <NUM> to electrically connect the two bearing brackets <NUM>. Specifically, the conductive piece <NUM> may be an elongated metal sheet, a metal wire, a conductive tape, or the like.

Furthermore, in the above embodiment, a circumferential side <NUM> of the first bracket <NUM> extends to an outer circumferential surface <NUM> of the casing <NUM>. The conductive sheet <NUM> is attached to the circumferential side <NUM> of the first bracket <NUM>. In this way, the electricity of the first bracket <NUM> and the second bracket <NUM> is introduced to the conductive sheet <NUM>, and as a capacitor is formed between the conductive sheet <NUM> and the stator core <NUM>, each of the two bearing brackets <NUM> and the stator core <NUM> form capacitive connection. By adjusting the size of the conductive sheet <NUM>, the equivalent capacitance between the stator core <NUM> and each of the bearing brackets <NUM> is adjusted, thereby reducing the potential difference between the inner ring and outer ring of the respective bearings <NUM>, so as to reduce the shaft voltage and avoid the bearings <NUM> from electric erosion.

Furthermore, in the above embodiment, one conductive sheet <NUM> is arranged on the casing <NUM>. By adjusting the size of the conductive sheet <NUM>, the capacitance is adjusted. The use of one conductive sheet <NUM> is convenient for installation.

Furthermore, in the above embodiment, the conductive sheet <NUM> is spaced apart from the stator core <NUM>, and a distance between the conductive sheet <NUM> and the outer circumferential surface of the stator core <NUM> is smaller than or equal to <NUM>. Since the casing <NUM> has insulating property, the distance between the conductive sheet <NUM> and the outer circumferential surface of the stator core <NUM> is arranged to be smaller than or equal to <NUM>, such that sufficient capacitance can be reached between the conductive sheet <NUM> and the stator core <NUM>, meanwhile, the area of the conductive sheet <NUM> can be reduced, which is convenient for the installation and use of the conductive sheet <NUM>. When the distance between the conductive sheet <NUM> and the outer circumferential surface of the stator core <NUM> is too large, a relatively small capacitance between the conductive sheet <NUM> and the stator core <NUM> is resulted, and if a large enough coupling capacitance is to be obtained, the area needs to be increased.

In some embodiments, an accommodation groove can be defined in the outer circumferential surface <NUM> of the casing <NUM> to install the conductive sheet <NUM>, thereby reducing the distance between the conductive sheet <NUM> and the stator core <NUM>. It can be understood that the arrangement of the accommodation groove can also function in positioning the conductive sheet <NUM>. It can also be understood that when the size of the conductive sheet <NUM> is adjusted, a partial area of the conductive sheet <NUM> can also be extended beyond the accommodation groove. That is, the outer circumferential surface <NUM> of the casing <NUM> defines therein an accommodation groove, and the conductive sheet <NUM> is at least partially accommodated in the accommodation groove.

According to the invention an outer circumferential area of the stator core <NUM>, that is, an area of the outer circumferential surface of the stator core <NUM> is defined as S, the area of each of the conductive sheet <NUM> and the stator core <NUM> overlapping with each other when seen from the radial direction of the stator core <NUM> is defined as S1, and S1 ≥ S/N, where N is a number of teeth of the stator. Based on a large number of experiments of the applicant, it is found that the area of each of the conductive sheet <NUM> and the stator core <NUM> overlapping with each other when seen from the radial direction of the stator core <NUM>, the area of the outer circumferential surface of the stator core <NUM>, and the teeth number N of the stator core <NUM> satisfy S1 ≥ S/N. In case that S1 is less than S/N, it is found in the experiments that the conductive sheet <NUM> cannot significantly adjust the capacitance between the stator core <NUM> and the bearing brackets <NUM>, and the shaft voltage only drops slightly, which cannot meet the requirements.

Furthermore, in the above embodiment, N ≥ <NUM>, the area of each of the conductive sheet <NUM> and the stator core <NUM> aligned to each other in the radial direction of the stator core <NUM> is no smaller than <NUM>/<NUM> of the outer circumferential area of the stator core <NUM>. Designing N to be greater than or equal to <NUM> can enable the stator <NUM> of the brushless motor <NUM> to better drive the rotor <NUM> to rotate, facilitating more precise adjustment. It can be understood that, in some embodiments, N can also be designed to be less than <NUM>, such as the number of teeth of the stator core <NUM> is <NUM>, <NUM>, <NUM>, or the like. The width of the conductive sheet <NUM> extending in the circumferential direction of the stator <NUM> is not less than <NUM>/<NUM> of the circumference of the outer circumferential surface of the stator core <NUM>, which can achieve a significant reduction in the shaft voltage.

As shown in <FIG>, in an embodiment, the capacitance between the conductive sheet <NUM> and the stator core <NUM> is <NUM>-<NUM> PF, which ensures good adjustment of the capacitance between each of the bearing brackets <NUM> and the stator core <NUM> and in turn a good adjustment of the potential difference between the inner ring and the outer ring of each bearing <NUM>. In case that the capacitance between the conductive sheet <NUM> and the stator core <NUM> is less than <NUM> PF, the effect of adjusting the potential difference between the inner ring and the outer ring of each bearing <NUM> is poor. When the capacitance between the conductive sheet <NUM> and the stator core <NUM> is greater than <NUM> PF, the potential reverse difference between the inner ring and the outer ring of each bearing <NUM> is greater, that is, the potential difference between the inner ring and the outer ring of each bearing <NUM> is still greater.

As shown in <FIG>, in an embodiment, one side of the conductive sheet <NUM> is an adhesive side having a conductive property, so that the conductive sheet <NUM> can be easily adhered on the outer circumferential surface <NUM> of the casing <NUM>, which is convenient to use. The other side of the conductive sheet <NUM> is an insulating side having an insulating property, which can reduce the influence of external devices on the conductive sheet <NUM> and make the conductive sheet <NUM> more stable to adjust the capacitive reactance between the stator core <NUM> and each of the two bearing brackets <NUM>.

As shown in <FIG>, one side of the conductive sheet <NUM> away from the casing <NUM> is printed with a logo, thus, the conductive sheet <NUM> may also use as a brand name of the brushless motor <NUM>.

As shown in <FIG>, in an embodiment, the conductive sheet <NUM> is a conductive paper, thereby being convenient to be attached to the casing <NUM> as well as to be cut to adjust the size thereof. It should be understood that in some embodiments, the conductive sheet <NUM> is a metal foil, for example, a copper foil, an aluminum foil, and the like may be adopted.

It can be understood that in some other embodiments, the conductive sheet <NUM> may also be a conductive coating. The conductive coating is applied on the outer circumferential surface <NUM> of the casing <NUM> to form the conductive sheet <NUM>, thereby ensuring that the conductive sheet <NUM> is firmly fixed on the casing <NUM>. The conductive coating can be made of a conductive glue, a conductive paste, and other materials. Furthermore, the conductive coating can be applied on the casing <NUM> by spraying, coating, or printing, which facilitates the arrangement of the conductive coating.

Furthermore, as shown in <FIG>, in order to better describe the effect of the use of the conductive sheet <NUM> in the brushless motor <NUM> in this embodiment to reduce the shaft voltage, the following comparison experiment was further performed:.

In specific examples, a piece of aluminum foil having a glue on the surface is used as the conductive sheet <NUM>, and is adhered to the outer circumferential surface of the casing <NUM>; and an edge of one side of the conductive sheet <NUM> is adhered to the circumferential side <NUM> of the first bracket <NUM>, such that the conductive sheet <NUM> and the first bracket <NUM> are directly connected in a conducting state. During specific implementations, for each motor of different schemes, the conductive sheet <NUM> having different areas can be adhered to the outer circumferential surface of the casing <NUM> in advance, by testing the variation of the shaft voltage, the area and corresponding adhering position of the conductive sheet <NUM> in the case of relatively low shaft voltage are acquired, thus the technical scheme for improving the shaft voltage of the corresponding motor is obtained, which can be applied to mass production. Comparison of the test results of the shaft voltage of the same brushless motor <NUM> using different conductive sheets and without using the conductive sheet <NUM> is listed in Table <NUM>. It can be seen from the results that by adjusting the conductive sheet <NUM>, the shaft voltage significantly changes and exhibits excellent regularity, and thus the shaft voltage can be effectively controlled. The distance between the conductive sheet <NUM> and the outer circumferential side of the stator core <NUM> is <NUM>.

The above Table <NUM> adopts the shaft voltage measurement method shown in <FIG>. A DC stabilized power supply was utilized to supply power to the brushless motor <NUM>. The stator of the brushless motor <NUM> used in the experiment had <NUM> teeth, and the measurement was carried out under the same working conditions, that is, a power supply voltage Vm of the wind was DC <NUM> V, the control voltage Vcc of driving current of the motor was controlled to be DC <NUM> V, and the rotational speed of the motor was set to <NUM> rpm by adjusting a speed adjusting voltage Vsp. The shaft voltage was measured using a digital the oscilloscope <NUM> and a differential probe <NUM>. The two ends of the differential probe <NUM> were respectively connected to the shaft <NUM> and the corresponding bearing bracket <NUM> of the brushless motor <NUM> via a metal wire. During the test, in order to prevent the wave of the shaft voltage from being unstable due to the discontinuous of the grease lubrication of the bearing <NUM> which is caused by the accidental disturbance during the operation of the brushless motor <NUM> and other factors, the brushless motor <NUM> utilized in the experiment was equipped with ceramic ball bearings <NUM>. The first to fifth conductive sheets had the same gap of <NUM> from the stator core <NUM> in the radial direction of the motor, but were different from each other in the area aligned to the stator core. In particular, the area of each of the first conductive sheet and the stator core <NUM> overlapping with each other when seen from the radial direction of the stator core <NUM> was <NUM>/<NUM> of the outer circumferential area of the stator core <NUM>. The area of each of the second conductive sheet and the stator core <NUM> overlapping with each other when seen from the radial direction of the stator core <NUM> was <NUM>/<NUM> of the outer circumferential area of the stator core <NUM>. The area of each of the third conductive sheet and the stator core <NUM> overlapping with each other when seen from the radial direction of the stator core <NUM> was <NUM>/<NUM> of the outer circumferential area of the stator core <NUM>. The area of each of the fourth conductive sheet and the stator core <NUM> overlapping with each other when seen from the radial direction of the stator core <NUM> was <NUM>/<NUM> of the outer circumferential area of the stator core <NUM>. The area of each of the fifth conductive sheet and the stator core <NUM> overlapping with each other when seen from the radial direction of the stator core <NUM> was <NUM>/<NUM> of the outer circumferential area of the stator core <NUM>.

<FIG> is a measured waveform of the shaft voltage when no conductive sheet is adopted in the corresponding brushless motor in the comparative example. not covered by the scope of the present invention. In the figure, "Main: <NUM>" refers to that the time base is <NUM>, and P-P(C1) refers to the shaft voltage, a scan speed as indicated in a horizontal axis in the figure is <NUM>/div, a voltage sensitivity as indicated in a vertical axis is <NUM> V/div, and the waveform illustrates the variation of the shaft voltage over time. The shaft voltage of the brushless motor measured from the waveform is <NUM> V.

<FIG> is a measured waveform of the shaft voltage when the first conductive sheet is adopted in the brushless motor. In the figure, "Main: <NUM>" refers to that the time base is <NUM>, and P-P(C1) refers to the shaft voltage, a scan speed as indicated in a horizontal axis in the figure is <NUM>/div, a voltage sensitivity as indicated in a vertical axis is <NUM> V/div, and the waveform illustrates the variation of the shaft voltage over time. The shaft voltage of the brushless motor measured from the waveform is <NUM> V.

<FIG> is a measured waveform of the shaft voltage when the second conductive sheet is adopted in the brushless motor. In the figure, "Main: <NUM>" refers to that the time base is <NUM>, and P-P(C1) refers to the shaft voltage, a scan speed as indicated in a horizontal axis in the figure is <NUM>/div, a voltage sensitivity as indicated in a vertical axis is <NUM> V/div, and the waveform illustrates the variation of the shaft voltage over time. The shaft voltage of the brushless motor measured from the waveform is <NUM> V.

<FIG> is a measured waveform of the shaft voltage when the third conductive sheet is adopted in the brushless motor. In the figure, "Main: <NUM>" refers to that the time base is <NUM>, and P-P(C1) refers to the shaft voltage, a scan speed as indicated in a horizontal axis in the figure is <NUM>/div, a voltage sensitivity as indicated in a vertical axis is <NUM> V/div, and the waveform illustrates the variation of the shaft voltage over time. The shaft voltage of the brushless motor measured from the waveform is <NUM> V.

<FIG> is a measured waveform of the shaft voltage when the fourth conductive sheet is adopted in the brushless motor. In the figure, "Main: <NUM>" refers to that the time base is <NUM>, and P-P(C1) refers to the shaft voltage, a scan speed as indicated in a horizontal axis in the figure is <NUM>/div, a voltage sensitivity as indicated in a vertical axis is <NUM> V/div, and the waveform illustrates the variation of the shaft voltage over time. The shaft voltage of the brushless motor measured from the waveform is <NUM> V.

<FIG> is a measured waveform of the shaft voltage when the fifth conductive sheet is adopted in the brushless motor. In the figure, "Main: <NUM>" refers to that the time base is <NUM>, and P-P(C1) refers to the shaft voltage, a scan speed as indicated in a horizontal axis in the figure is <NUM>/div, a voltage sensitivity as indicated in a vertical axis is <NUM> V/div, and the waveform illustrates the variation of the shaft voltage over time. The shaft voltage of the brushless motor measured from the waveform is <NUM> V.

As shown in <FIG>, in an embodiment, a plurality of conductive sheets <NUM> can be arranged on the casing, and each of the plurality of conductive sheets <NUM> is in electrical connection with the bearing brackets <NUM>. The arrangement of the plurality of conductive sheets <NUM> can better adjust the sizes of the conductive sheets <NUM>, so as to adjust the area of each of the conductive sheet <NUM> and the stator core <NUM> overlapping with each other when seen from the radial direction, and in turn adjust the capacitive reactance between each conductive sheet <NUM> and the stator core <NUM>, the adjusting of which is convenient.

Furthermore, in the above embodiment, all the plurality of conductive sheets <NUM> can be in electrical connection with the two bearing brackets <NUM>, which is convenient to adjust the equivalent capacitance between the stator core <NUM> and each of the two bearing brackets <NUM>, and in turn to adjust the potential difference between the inner ring and the outer ring of each bearing <NUM>, thereby decreasing the shaft voltage. It can be understood that, in an embodiment, the casing <NUM> can be provided with only one conductive sheet <NUM>, and both the bearing brackets <NUM> are in electrical connection with the one conductive sheet <NUM>, such that the capacitive reactance between the stator core <NUM> and each of the two bearing brackets <NUM> can be adjusted by the one conductive sheet <NUM>.

Furthermore, in the above embodiment, the electrical connection of the conductive sheet <NUM> with the two bearing brackets <NUM> can be achieved as follows: a conductive piece <NUM> can be arranged within the casing <NUM> for electrically connecting the two bearing brackets <NUM>, and the conductive sheet <NUM> is electrically connected to one of the bearing brackets <NUM>, such that the conductive sheet <NUM> is electrically connected with the two bearing brackets <NUM>.

Furthermore, in the above embodiment, the circumferential side <NUM> of one of the two bearing brackets <NUM> extends to the outer circumferential surface <NUM> of the casing <NUM>. During the arrangement of the conductive sheet <NUM>, the conductive sheet <NUM> can be directly attached to the circumferential side <NUM> of the one of the bearing brackets <NUM>, such that the conductive sheet <NUM> is electrically connected to the one of the bearing brackets <NUM>, and to the other one of the bearing brackets <NUM> via the conductive piece <NUM> arranged within the casing <NUM>. Specifically, the two bearing brackets <NUM> are composed of the first bracket <NUM> and the second bracket <NUM>, the first bracket <NUM> and the second bracket <NUM> are connected via the conductive piece <NUM>, and the circumferential side <NUM> of the first bracket <NUM> extends to the outer circumferential surface <NUM> of the casing <NUM>. When the conductive sheet <NUM> is installed, the conductive sheet <NUM> is attached to circumferential side of the first bracket <NUM>.

It should be understood that, in some embodiments, the conductive piece <NUM> can also be arranged within the casing <NUM> to electrically connect the two bearing brackets <NUM>, the conductive sheet <NUM> is attached to the outer circumferential surface <NUM> of the casing <NUM>, a conductive arm <NUM> is arranged on the outer circumferential surface <NUM> of the casing <NUM>, and the conductive arm <NUM> is electrically connected to one or both of the two bearing brackets <NUM>.

As shown in <FIG>, in an embodiment, the conductive arm <NUM> may be provided on the casing <NUM> to connect the two bearing brackets <NUM>, and a part of the conductive arm <NUM> exposes out of the outer circumferential surface <NUM> of the casing <NUM>. Therefore, during the installation of the conductive sheet <NUM>, the conductive sheet <NUM> can be attached to the conductive arm <NUM>, so as to electrically connect the conductive sheet <NUM> with the two bearing brackets <NUM>. Specifically, the conductive arm <NUM> may be made of a metal strip, a metal wire, or a metal tape. It can be understood that, in some embodiments, the conductive arm <NUM> may also be a structure such as the conductive coating.

Furthermore, in the above embodiment, the conductive arm <NUM> may be electrically connected to the corresponding bearing bracket <NUM> by bonding, riveting, abutting, welding, and the like.

Furthermore, in the above embodiment, the casing <NUM> defines therein a positioning groove <NUM>, and the conductive arm <NUM> is accommodated in the positioning groove <NUM>, which is convenient for the installation and fixation of the conductive arm <NUM>.

It can be understood that, in the above embodiment, in order to ensure good electrical connection between the two bearing brackets <NUM>, the conductive piece <NUM> can be extended into the casing <NUM> to connect the two bearing brackets <NUM>.

As shown in <FIG>, in an embodiment, in case that the circumferential side <NUM> of one of the bearing brackets <NUM> extends to the outer circumferential surface <NUM> of the casing <NUM>, during arrangement of the conductive sheet <NUM>, the conductive sheet <NUM> can be directly attached to the circumferential side <NUM> of the bearing bracket <NUM>, and the other one of the bearing brackets <NUM> is electrically connected to the conductive sheet <NUM> via a conductive arm <NUM>, such that the two bearing brackets <NUM> are electrically connected and the conductive sheet <NUM> is able to simultaneously adjust the equivalent capacitance between the stator core <NUM> and each of the two bearing brackets <NUM>. Such a structure is particularly suitable for situations where the two bearing brackets <NUM> have different diameters. For example, when the two bearing brackets <NUM> are composed of the first bracket <NUM> and the second bracket <NUM>, the circumferential side <NUM> of the first bracket <NUM> extends to the outer circumferential surface <NUM> of the casing <NUM>, and the second bracket <NUM> can be a part only supporting the corresponding bearing <NUM> and form an integral structure with the casing <NUM> by injection molding, in such case, during the arrangement of the conductive sheet <NUM>, the conductive sheet <NUM> can be attached to the circumferential side <NUM> of the first bracket <NUM>, and the second bracket <NUM> can be connected to the conductive sheet <NUM> via the conductive arm <NUM>.

It can be understood that, in some embodiments, if the casing <NUM> is in a structure having two open ends and the two bearing brackets <NUM> are both used as end covers to cover the two ends of the casing <NUM>, and the circumferential side <NUM> of each bearing bracket <NUM> extends to the circumferential <NUM> of the outer surface of the casing <NUM>, in such case, the conductive sheet <NUM> can also be attached to the circumferential side <NUM> of one of the two bearing brackets <NUM>, and the other one of the two bearing brackets <NUM> is connected to the conductive sheet <NUM> via the conductive arm <NUM>.

As shown in <FIG>, in an embodiment, if the casing <NUM> is in a structure having two open ends and the two bearing brackets <NUM> are both used as end covers to cover the two ends of the casing <NUM>, and the circumferential side <NUM> of each bearing bracket <NUM> extends to the circumferential <NUM> of the outer surface of the casing <NUM>, in such case, the conductive sheet <NUM> is attached to the circumferential sides <NUM> of both the two bearing brackets <NUM>, such that the two bearing brackets <NUM> are electrically connected via the conductive sheet <NUM>, and the capacitive reactance between the stator core <NUM> and each of the two bearing brackets <NUM> can be directly adjusted by the conductive sheet <NUM>.

As shown in <FIG>, in the above embodiment, the conductive arm <NUM> is a separate metal sheet arranged at the casing <NUM>, which facilitates the installation and fixation thereof and ensures good strength of the conductive arm <NUM>. Furthermore, the conductive arm <NUM> is arranged within the casing <NUM>, and only a part of the conductive arm <NUM> which is located on the outer circumferential side of the casing <NUM> protrudes on the outer circumferential surface, so as to be attached to the conductive sheet <NUM>. Such a structure can better protect the conductive arm <NUM>.

As shown in <FIG>, in some embodiments, the conductive arm <NUM> may also be a part of the conductive sheet <NUM>, that is, the conductive arm <NUM> extends from one side of the conductive sheet <NUM>, that is, the conductive arm <NUM> and the conductive sheet <NUM> form an integral structure, and the conductive arm <NUM> is formed by extending a lateral side of the conductive sheet <NUM>, so that the arrangement of the conductive sheet <NUM> is more convenient and the two bearing brackets <NUM> can be electrically connected.

As shown in <FIG>, in an embodiment, when the two bearing brackets <NUM> each has an inner diameter smaller than an outer diameter of the casing <NUM>, the two bearing brackets <NUM> each can be in electrical connection with the conductive sheet <NUM> via the conductive arm <NUM>. It can be understood that, a conductive piece <NUM> can also be arranged within the casing <NUM> to electrically connect the two bearing brackets <NUM>, and one of the two bearing brackets <NUM> is electrically connected to the conductive sheet <NUM> via the conductive arm <NUM>. In some other embodiments, conductive arms <NUM> connected to the two bearing brackets <NUM> may be respectively provided, and the respective two conductive arms <NUM> are electrically connected to the conductive sheet <NUM>.

As shown in <FIG>, in an embodiment, a plurality of conductive sheets <NUM> may also be arranged on the casing <NUM>, and the two bearing brackets <NUM> are electrically connected to different conductive sheets <NUM>, respectively. In this way, the capacitive reactance between each of the respective bearing brackets <NUM> and the stator core <NUM> can be adjusted separately through the conductive sheets <NUM>.

The brushless motor <NUM> according to embodiments of the present application can effectively balance the electric potential between the inner ring and the outer ring of each bearing <NUM>, reduce the voltage between the inner ring and the outer ring of each bearing <NUM>, and avoid electric erosion between the inner ring and the outer ring of each bearing <NUM>, thereby ensuring excellent and smooth operation of the brushless motor <NUM>, reducing the noise and the vibration, and prolonging the service life. The brushless motor <NUM> according to embodiments of the present application can be applied to electrical appliances such as air conditioners, washing machines, microwave ovens, refrigerators, and the like.

Furthermore, an embodiment of the present application further provides an electrical equipment, which includes the brushless motor <NUM> as described in any of the above embodiments. The use of the brushless motor <NUM> in the electrical equipment can ensure a good service life of the brushless motor <NUM>.

Claim 1:
A brushless motor (<NUM>), comprising:
a casing (<NUM>) having an insulating property;
a stator (<NUM>) fixed within the casing (<NUM>), the stator (<NUM>) comprising a stator core (<NUM>) and a winding (<NUM>) wound around teeth of the stator core (<NUM>); and
a rotor (<NUM>) rotatably arranged within the stator (<NUM>), the rotor (<NUM>) comprising a rotor core (<NUM>) and a shaft (<NUM>) passing through the rotor core (<NUM>), wherein two bearings (<NUM>) are sleeved on the shaft (<NUM>) at positions corresponding to two ends of the rotor core (<NUM>), respectively, and two bearing brackets (<NUM>) are installed at two ends of the casing (<NUM>) for fixing the two bearings (<NUM>);
wherein
the brushless motor (<NUM>) further comprises: a conductive sheet (<NUM>), configured for adjusting a capacitive reactance between the stator core (<NUM>) and each of the two bearing brackets (<NUM>);
the conductive sheet (<NUM>) is spaced apart from the stator core (<NUM>) at an outer circumferential side of the stator core (<NUM>), and the conductive sheet (<NUM>) is insulated from the stator core (<NUM>);
the conductive sheet (<NUM>) and the stator core (<NUM>) each at least partially has an area overlapping with each other when seen from a radial direction of the stator core (<NUM>); and
the conductive sheet (<NUM>) is in electrical connection with at least one of the two bearing brackets (<NUM>);
characterised in that an outer circumferential area of the stator core (<NUM>) is defined as S, the area of each of the conductive sheet (<NUM>) and the stator core (<NUM>) overlapping with each other when seen from the radial direction of the stator core (<NUM>) is defined as S1, and S1 ≥ S/N, wherein N is a number of the teeth of the stator (<NUM>).