electric machine

Abstract

A motor (100) is disclosed having a noise damping member (402) and a rotor (204) having a slit on an outer surface (204AA). This arrangement helps to reduce noise from the motor (100) caused by the stator (205) and the rotor (204).

Description

TECHNICAL FIELD

[0001] The present subject matter relates generally to an electric machine of a vehicle. More particularly, but not exclusively, the present subject matter relates to noise damping of an electric machine of a vehicle. BACKGROUND

[0002] Typically, a vehicle has an electric machine coupled to an engine. When the engine is running, the electric machine generates electrical energy from mechanical energy for charging the battery and running other electrical systems. The electric machine mainly comprises two components: a stator and a rotor. The rotor is the rotating part while the stator is the stationary part. The rotor is connected to the shaft while the stator is housed in the crankcase. The rotor is also fitted with a fan that rotates with the rotor. The rotor contains a plurality of magnets and the stator contains laminations with slots and windings. The laminations in the stator are usually made of ferromagnetic material. When the electric machine is running, the rotor rotates with the shaft. BRIEF DESCRIPTION OF DRAWINGS

[0003] In all the drawings, like reference numerals are used to refer to like features and components.

[0004] Figure 1 A cross-sectional view of a conventional electric machine is shown exemplarily, in accordance with one or more embodiments.

[0005] Figure 2 A perspective view of an electric machine is shown exemplarily, in accordance with one or more embodiments.

[0006] Figure 3 A perspective view of a rotor is shown exemplarily, in accordance with one or more embodiments.

[0007] Figure 4 An exploded view of an electric machine is shown exemplarily, in accordance with one or more embodiments.

[0008] Figure 5 A perspective view of a noise damping component is shown exemplarily, in accordance with one or more embodiments.

[0009] Figure 6 A side view of an electric machine is shown exemplarily, in accordance with one or more embodiments.

[0010] Figures 7-10 Statistical data of noise damping under various conditions is shown exemplarily, in accordance with one or more embodiments.

[0011] Figure 11 A method flow diagram for suppressing noise is shown exemplarily, in accordance with one or more embodiments. DETAILED DESCRIPTION

[0012] An electric machine of a vehicle, which includes a stator and a rotor, is mainly composed of two materials, the stator is made of ferromagnetic material and the rotor has a plurality of magnets. The rotor along with the shaft rotates in the stator produces a fluctuating magnetic field, such that the electric machine can operate as a motor or generator as per the requirement. Further, the rotor and the stator undergoes continuous vibrations when the generator operates. Further, with the advancement in technology, the demand for electric power has increased, which requires larger electric machines, which means larger size of the stator and the rotor. The fluctuating magnetic field in the stator and the vibrations of the rotor produces a humming noise.

[0013] It is conventionally believed to mount the stator on a metal plate to suppress the noise. However, such a method of preventing the stator from vibrating increases the weight of the vehicle and also includes the complexity of mounting the stator on a metal plate, which increases the size of the engine in the width direction of the vehicle.

[0014] In another prior art of the conventional electric machine, the air flow is restricted by placing shields on the sides of the stator, thereby restricting the vibrations of the air molecules. However, this system increases the number of child parts and increases the overall weight of the vehicle.

[0015] In yet another prior art of the conventional electric machine, the stator is fitted with a piezoelectric actuator to prevent the deformation caused by the fluctuating magnetic field on the stator and the vibrations of the rotor. However, this method increases the cost and requires additional power and control devices to control the piezoelectric material.

[0016] It is also believed in the prior art that to control the humming noise from the rotor vibrations, the resonant frequency of the rotor has been changed. However, the change in the resonant frequency is effective only in the case where the operating frequency is fixed. But the engine of the vehicle can operate in a wide range of frequencies. Therefore, this method of changing the resonant frequency can not always be effective. Further, there are various rotor mounting mechanisms on the engine to prevent vibrations. However, this method involves complex mounting mechanisms and high cost.

[0017] Since the rotor has a plurality of magnets and the stator is made of ferromagnetic material, the stator undergoes a magnetic field fluctuation during the rotation of the rotor along with the shaft. This fluctuating magnetic field exerts a magnetostrictive force on the stator. The magnetostrictive force changes the shape and size of the stator, i.e. the stator undergoes torsional and bending modes, due to which the stator body deforms. The torsional and bending modes can also be generated by the vibrations produced by the engine or the magnetic interaction between the stator and the rotor. The torsional and bending modes cause vibrations in the stator and other supporting structural members, which in turn excite the nearby air molecules and produce noise or a low-pitched humming sound. This noise affects the sound quality of the vehicle and gives an unpleasant experience to the user.

[0018] Further, vibrations from the engine and its associated components are transmitted to the rotor due to magnetic interaction between the stator and the rotor, thus the outer surface of the rotor deforms perpendicular to the axis of the rotor. The deformed outer surface excites the nearby air molecules, which further increases the hum noise generated by the stator. Further, there is a challenge of limited space, which restricts any configuration modification that can effectively reduce the hum noise generated by the deformation of the stator and the rotor.

[0019] Therefore, there is a need for effectively reducing the hum from the electric machine by a system which is simple, easy to manufacture, cost effective, space saving, light in weight, compliant with the existing system configuration and is capable of effectively overcoming all other challenges and the drawbacks of the prior art.

[0020] It is an object of the present invention to provide an electric machine which is simple, easy to manufacture, cost effective, space saving, light in weight and does not require major changes in the existing system configuration to reduce the hum noise from the electric machine. The claimed subject matter is applicable to any type of vehicle with required variations and without departing from the scope of the present invention.

[0021] According to an aspect of the present invention, the disclosed electric machine comprises a stator fixedly attached to a housing member, a rotor rotatably attached to a shaft member. The shaft member is held by the housing member. The stator comprises a plurality of teeth and one or more windings wound on the plurality of teeth. The rotor comprises a plurality of magnets arranged circumferentially along an inner periphery of the rotor. The plurality of magnets are arranged to abut the plurality of teeth of the stator. A noise dampening member is arranged circumferentially around the shaft, wherein the noise dampening member is sandwiched between the stator and the housing member.

[0022] According to yet another aspect of the present invention, the electric machine comprises a stator fixedly attached to a housing member, a rotor rotatably attached to a shaft member, the shaft member is held by the housing member. The stator comprises a plurality of teeth and one or more windings wound on the plurality of teeth. The rotor comprises an outer surface comprising an outer cylindrical member and an inner cylindrical member. A plurality of magnets are arranged circumferentially along an inner periphery of the outer cylindrical member of the rotor. The plurality of magnets are arranged to abut the plurality of teeth of the stator and the inner cylindrical member is mounted on the shaft member. The outer surface comprises one or more openings arranged radially along the outer surface.

[0023] According to yet another aspect of the present invention, the outer surface of the rotor comprises one or more first sets of openings radially disposed between the one or more openings.

[0024] According to another aspect of the present invention, the outer surface of the rotor comprises one or more second sets of openings radially disposed between the one or more first sets of openings. The second sets of openings are capable of mounting a fan.

[0025] According to another aspect of the present application, the noise dampening member includes a plurality of openings.

[0026] According to another aspect of the present application, the noise dampening member includes one or more protrusions.

[0027] According to another aspect of the present application, the one or more protrusions are capable of extending in a gap formed between the plurality of teeth of the stator.

[0028] According to another aspect of the present application, the noise dampening member includes one or more stepped surfaces for allowing wire extending out of the one or more windings to pass through.

[0029] According to yet another aspect of the present application, an electric machine disclosed herein includes a stator fixedly attached to a housing member, a rotor rotatably attached to a shaft member. The shaft member is held by the housing member. The stator includes a plurality of teeth and one or more windings wound on the plurality of teeth. The rotor includes an outer surface comprising an outer cylindrical member and an inner cylindrical member, and a plurality of magnets are arranged circumferentially along an inner periphery of the outer cylindrical member of the rotor. The plurality of magnets are arranged adjacent to the plurality of teeth of the stator, and the inner cylindrical member is mounted on the shaft member, wherein the outer surface includes one or more openings arranged radially along the outer surface. A noise dampening member is arranged circumferentially around the shaft, wherein the noise dampening member is sandwiched between the stator and the housing member.

[0030] The present application provides an electric machine which is simple, easy to manufacture, economical, space saving, light in weight, and does not require major changes to existing system configurations to reduce the hum noise from the generator.

[0031] The subject matter is further described in the following claims by reference to the appended drawings. It should be noted that the description and drawings merely illustrate the principles of the subject matter. Although specific arrangements were described in this document, other arrangements can be designed by those skilled in the art which will encompass the principles of the subject matter. Furthermore, all statements as to the arrangements, principles and examples given herein are meant to encompass equivalents for the present subject matter.

[0032] Figure 1An exploded perspective view of an existing total assembly of an electric motor is shown exemplarily, which comprises a stator (102) and a rotor (103) coupled with a power source, such as a battery or an engine. More specifically, the stator (102) is attached with a housing member (101) of the engine through fasteners, while a shaft member holds the rotor (103). The stator (102) has a plurality of teeth, which further comprises a plurality of windings wound around them. The windings are made of ferromagnetic material. The inner periphery of the rotor (103) has a plurality of magnets arranged inside them. The plurality of magnets and the plurality of teeth of the stator (102) abut each other. When the engine starts running, the vibrations from the engine are transmitted to the rotor (103). The vibrations of the rotor (103) cause out-of-plane deformation of the outer surface (204AA) of the rotor (103) perpendicular to the axis of the rotor (103). The deformed outer surface (204AA) starts vibrating, which further excites the nearby air molecules, whereby the vibrations of the rotor (103) produce a continuous humming noise. The amplitude of the noise is directly proportional to the number of air molecules excited.

[0033] Figure 2 An exploded perspective view of an electric motor is shown exemplarily, in accordance with an embodiment of the present application. The present application discloses an electric motor (200) having two main parts, namely a stator (102) and a rotor (103) with slits (201, 202, 203). The stator (205) has a plurality of teeth, which further comprises a plurality of windings wound around them. The rotor (204) is attached with the shaft of the engine. The outer surface (204AA) of the rotor (204) has a plurality of slits (201, 202, 203) consisting of one or more openings (201) and a first set of openings (202) and a second set of openings (203). The rotor (204) with slits (201, 202, 203) is hereinafter referred to as a slitted rotor (204).

[0034] Figure 3A perspective view of a slotted rotor (204) is shown in accordance with the present application. The rotor (204) comprises an outer cylindrical member (301), an inner cylindrical member (302). The inner circumference (304) of the outer cylindrical member (301) is configured with a plurality of magnets (not shown) arranged such that the plurality of magnets and the plurality of teeth of the stator (205) abut each other. The inner cylindrical member (302) is mounted on a shaft member. The outer surface (204AA) is configured with a plurality of slots consisting of one or more openings (201) and one or more first set of openings (202) and one or more second set of openings (203). The one or more openings (201) are configured circumferentially along the outer surface (204AA) of the rotor (204). The first set of openings (202) are disposed circumferentially between the one or more openings (201) while the second set of openings (203) are disposed circumferentially at a lower radial distance than the radial distance of the first set of openings (202). The second set of openings (203) are capable of holding the fan. By providing the openings (201) and the first set of openings (202) on the outer surface (204AA) of the rotor (204), the total surface area of the rotor (204) is reduced. More specifically, by reducing the surface area of the rotor (204), the vibrations of the rotor (204) due to various reasons not limited to the magnetic interaction between the stator (205) and the rotor (204) such as vibrations transmitted through the engine operation and other associated components are reduced due to the overall area of vibration being reduced. Fewer air molecules in the vicinity are excited by a small surface area compared to a large surface area. Therefore, the rotor (204) of smaller surface area will produce less humming noise than a conventional rotor. By reducing the surface area of the rotor (204), there is no change in the resonant frequency and hence the configuration can work at all engine frequencies. Further, the slots on the outer surface (204AA) of the rotor (204) are configured in such a specific pattern that the openings (201) and the first set of openings (202) allow a larger amount of air to pass through, thereby allowing lower temperatures to be maintained for the stator (205). The present configuration does not require any additional changes in the installation, additional cost or weight to reduce the humming noise due to deformation of the rotor (204). The slotted rotor provides the advantage of both mechanical integrity and a smaller surface area to produce noise. The features to reduce the surface area of the outer surface (204AA) are not limited to the openings (201) and the first set of openings (202) or the second set of openings (203).

[0035] Figure 4An exploded perspective view of an electric motor according to an embodiment of the present application is shown by way of example. The electric motor (200) comprises a stator (205), a rotor (204) having openings (201), a first set of openings (202) and a second set of openings (203). A fan (401) is arranged on the second set of openings (203) of the outer surface (204AA) of the rotor (204) and a noise damping member (402) is axially arranged between the housing member (206) and the stator (205). As mentioned above, in a conventional electric motor, when the rotor (204) rotates along with the shaft (403), the stator (205) is subjected to magnetostriction forces due to the fluctuating magnetic field as the rotor (204) contains a plurality of magnets and the teeth of the stator (205) are made of ferromagnetic material. Due to the magnetostriction forces and vibrations of the engine and its associated components, the stator (205) experiences torsional and bending modes. This results in deformation on the surface of the stator (205) which leads to vibrations of the stator (205) and other supporting structural members. The vibrations further excite the air molecules in the vicinity and produce noise and contribute to the hum produced by the rotor (204) vibrations. The present application axially sandwiches the noise damping member (402) between the stator (205) and the housing member (206). The noise damping member (402) is circumferentially arranged around the shaft member (403). The noise damping member (402) provides a constant elastic tension on the surface of the stator (205) and is slightly elastically compressed when the stator (205) is abutantly mounted, thereby restricting the stator (205) from deforming or vibrating due to any kind of force or vibration. More particularly, the noise damping member (402) sandwiches the outer edge of the stator (205) where the stator (205) is prone to high vibrations and deformation. Thus, the amplitude of the noise produced by the vibrations or deformation of the stator (205) is significantly reduced. The noise damping member can be placed between the stator (205) and any fixed surface such as a metal plate or a crankcase. The noise damping member (402) is such that it has a negligible weight which can be suitably fitted between the available space of the housing member (101) and the stator (205) and thus does not add any significant change to the vehicle configuration and weight. Further, the noise damping member (402) simply sandwiches the stator (205) with the existing mounting fasteners used to mount the stator to the housing member (101) and thus does not require any additional mounting mechanism and hence does not add to the manufacturing cost. The present application does not require an increase in the size or space between the housing (101) and the stator (205).

[0036] Figure 5A perspective view of the noise dampening member (402) is shown exemplarily. The noise dampening member (402) is configured with one or more circumferential protrusions (501) and one or more circumferential stepped surfaces (502) on the side surface. The protrusions (501) are capable of extending in the gaps formed between the plurality of teeth of the stator (205) and thereby engaging with the plurality of teeth of the stator (205). The stepped surfaces (502) allow the wires of the windings extending out of the teeth of the stator (205) to pass through. The noise dampening member (402) further comprises a plurality of openings or holes (not shown). These openings allow passage of sufficient amount of air to maintain the temperature of the engine. The noise dampening member (402) can be made of any material having wear resistance, specific gravity, tear resistance, such as rubber.

[0037] Figure 6 A side cut section view of the motor (100) assembly along with the mounting member and the drive shaft member (e.g. crankshaft) is shown exemplarily in accordance with an embodiment of the present application. The stepped surfaces (502) of the noise dampening member (402) as shown allow the wires (601) to pass laterally from the teeth of the stator (205) and be wired. Figure 5 The fan (401) mounted on top of the rotor (204), the rotor (204) having the openings (201) and the first set of openings (202) and the noise dampening member (402) having the openings, protrusions (501) and stepped surfaces (502) together help in significantly reducing the hum noise and also help in reducing the temperature of the engine.

[0038] Figures 7-8 Statistics of the test results of various conditions of the motor (100) under acceleration and deceleration conditions are shown. The statistical results are plotted with respect to the noise (dB) and the engine revolutions per minute (RPM). Figure 7 It can be seen from the It can be seen from the

[0039] It can be seen from the Figure 8 It can be seen from the

[0040] Figures 9-10 Graphical differences in the noise levels under acceleration and deceleration conditions are shown respectively. It can be seen from the Figure 9It can be inferred that, at the time of acceleration of the vehicle, the noise level is maximum (901) in the conventional configuration. In the fan (401) and the rotor (204) with the slotted configuration, the noise level is moderate (902), whereas the noise level is minimum (903) when the noise dampening member (402) and the rotor (204) with the fan (401) are configured in the motor (100). Figure 10 It can be inferred that, at the time of deceleration of the vehicle, the noise level is maximum (901). In the fan (401) and the rotor (204) with the slotted configuration, the noise level is moderate (902), whereas the noise level is minimum (903) when the noise dampening member (402) and the rotor (204) with the fan (401) are configured in the motor (100).

[0041] Figure 11 A flow chart showing the method of reducing noise from the motor (100) is shown. When the engine starts running, if the noise is from the motor (100), then the method shown in accordance with the present application significantly reduces the noise. The method involves the following steps (1101-1105): forming a plurality of openings (201) on the outer surface (204AA) of the rotor (204); forming a first set of openings (202) on the outer surface (204AA) of the rotor (204); and forming a second set of openings (203) on the outer surface (204AA). To maximize the reduction of noise, a noise dampening member (402) is introduced between the stator (205) and the fixed surface (1105) (e.g. housing member (101)).

[0042] Many other modifications and changes can be incorporated without departing from the scope of the present application.

[0043] List of reference signs

[0044] 100: Motor

[0045] 101: Housing member according to prior art

[0046] 102: Stator according to prior art

[0047] 103: Rotor according to prior art

[0048] 104: Outer surface

[0049] 200: Motor according to the present application

[0050] 201: Opening

[0051] 202: First set of openings

[0052] 203: Second set of openings

[0053] 204: Rotor according to the invention

[0054] 204AA: Outer surface of the rotor

[0055] 205: Stator according to the invention

[0056] 206: Housing member according to the invention

[0057] 301: Outer cylindrical member

[0058] 302: Inner cylindrical member

[0059] 303: Inner circumference

[0060] 401: Fan

[0061] 402: Noise dampening member

[0062] 403: Shaft member

[0063] 501: Protrusion

[0064] 502: Stepped surface

[0065] 601: Wire

[0066] 901-903: Lines of the graph

[0067] 1101-1105- Method flow chart.

Claims

1. An electric machine (100), the electric machine (100) comprising: A stator (205) fixedly attached to a housing member (101), a rotor (204) rotatably attached to a shaft member (403), and a noise dampening member (402) arranged circumferentially around the shaft member (403), the shaft member (403) held by the housing member (101), the stator (205) comprising a plurality of teeth and one or more windings wound on the plurality of teeth, the rotor (204) comprising a plurality of magnets arranged circumferentially along an inner circumference (303) of the rotor (204), the plurality of magnets arranged to abut the plurality of teeth of the stator (205), wherein the noise dampening member (402) is sandwiched between the stator (205) and the housing member (101), wherein the noise dampening member (402) comprises: one or more circumferential protrusions (501) engageable with a gap of a tooth of the stator (205); and one or more circumferential stepped surfaces (502) for allowing routing of wire (601) of one or more windings of a tooth of the stator (205) extending out of the stator (205).

2. An electric machine (100), the electric machine (100) comprising: A stator (205) fixedly attached to a housing member (101), a rotor (204) rotatably attached to a shaft member (403), a plurality of magnets, and a noise dampening member (402) arranged circumferentially around the shaft member (403), the shaft member (403) held by the housing member (101), the stator (205) comprising a plurality of teeth and one or more windings wound on the plurality of teeth, the rotor (204) comprising an outer surface (204AA) comprising an outer cylindrical member (301) and an inner cylindrical member (302), the plurality of magnets arranged circumferentially along an inner circumference (303) of the outer cylindrical member (301) of the rotor (204), the plurality of magnets arranged to abut the plurality of teeth of the stator (205), and the inner cylindrical member (302) mounted on the shaft member (403), wherein the outer surface (204AA) comprises one or more openings (201) arranged circumferentially along the outer surface (204AA), wherein the noise dampening member (402) comprises: one or more circumferential protrusions (501) engageable with a gap of a tooth of the stator (205); and one or more circumferential stepped surfaces (502) for allowing routing of wire (601) of one or more windings of a tooth of the stator (205) extending out of the stator (205).

3. The electric machine (100) of claim 2, wherein the outer surface (204AA) of the rotor (204) comprises one or more first sets of openings (202) disposed circumferentially between the one or more openings (201).

4. The electric machine (100) as claimed in claim 2, wherein the outer surface (204AA) of the rotor (204) comprises one or more second set of openings (203) disposed circumferentially at a lower radial distance than the radial distance of the one or more first set of openings (202), wherein the second set of openings (203) are capable of mounting a fan (401).

5. The electric machine (100) as claimed in claim 1, wherein the noise dampening member (402) comprises a plurality of openings.

6. The electric machine (100) as claimed in claim 1, wherein the noise dampening member (402) is a resilient member.

7. An electric machine (100), the electric machine (100) comprising: a stator (205) fixedly attached to a housing member (101), a rotor (204) rotatably attached to a shaft member (403) held by the housing member (101), a plurality of magnets, and a noise dampening member (402) disposed circumferentially around the shaft member (403), the stator (205) comprising a plurality of teeth and one or more windings wound on the plurality of teeth, the rotor (204) comprising an outer surface (204AA) comprising an outer cylindrical member (301) and an inner cylindrical member (302), the plurality of magnets disposed circumferentially along an inner circumference (303) of the outer cylindrical member (301) of the rotor (204), the plurality of magnets disposed to abut the plurality of teeth of the stator (205), and the inner cylindrical member (302) mounted on the shaft member (403), wherein the outer surface (204AA) comprises one or more openings (201) disposed circumferentially along the outer surface (204AA), wherein the noise dampening member (402) is resiliently sandwiched between the stator (205) and the housing member (101), wherein the noise dampening member (402) comprises: one or more circumferential protrusions (501) capable of engaging the gap of the teeth of the stator (205); and one or more circumferential stepped surfaces (502) for allowing routing of wire (601) of the one or more windings of the teeth of the stator (205) extending out.

8. A noise dampening member (402) comprising: one or more circumferential protrusions (501) capable of engaging the gap of the teeth of a stator (205); and one or more circumferential stepped surfaces (502) for allowing routing of wire (601) of the one or more windings of the teeth of the stator (205) extending out.

9. A method of dampening noise in an electric machine (100), the method comprising the steps of: forming a plurality of openings (201) on a rotor (204); forming a first set of openings (202) on the rotor (204); forming a second set of openings (203) on the rotor (204); and disposing a noise dampening member (402) between a stator (205) and any fixed surface, wherein the noise damping member (402) comprises one or more circumferential protrusions (501) capable of engaging with the gap of the teeth of the stator (205); and one or more circumferential stepped surfaces (502) for allowing routing of wire (601) of one or more windings extending out of the teeth of the stator (205).

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