Electric motor with explosion inhibiting material

Abstract

An electric motor has a motor enclosure defining an enclosed volume and includes therein an annular stator and a cylindrical rotor separate by an air gap. The enclosed volume further includes a drive end compartment and a non-drive end compartment at axially opposite ends of the motor enclosure that are fluidly connected by the air gap. To dissipate a traveling flame front caused by an ignition in one of the drive and non-drive ends and axially pro- propagating toward the other, the electric motor includes a flame arresting porous material located in the air gap. The flame arresting porous material can be structurally formed as a cylindrical porous lining affixed to one or both of the annular stator and the cylindrical rotor.

Description

771187 (P240378 W001)ELECTRIC MOTOR WITH EXPLOSION INHIBITING MATERIALFIELD

[0001] The present disclosure relates to electrical machines. In particular, the present disclosure relates to an electric motor designed to operate in an explosive atmosphere.BACKGROUND

[0002] Electrical machines, specifically electric motors, may be designed to specifically operate in an explosive atmosphere. For example, electric motors may need to operate in environments that are particularly susceptible to combustion or explosion such as in the presence of flammable gasses, oil and fossil fuels, or combustible dust particles. The electric motors may be designated as “flameproof’ or “explosion proof’ to indicate their operability in such explosive atmospheres. “Flameproof’ motors typically refer to the ability of the motor to withstand the explosion pressure in case of internal ignition and to prevent the transmission of a flame or sparks that start inside the motor enclosure from reaching the exterior environment.

[0003] International standards have been developed to rate and designate electric motors as “flameproof’ and manufacturers are required to test their motors against the standards to designate the motors as being in compliance. An example of a standard is IEC 60079-1 that sets forth the standards for electrical equipment operating in explosive atmospheres. One of the tests involves measuring the internal pressure of the motor enclosure in the event of an internal explosion or ignition of gasses. The internal pressure is a result of the rapid forceful expansion of the internal gasses contained in the motor enclosure.SUMMARY

[0004] A first aspect of the present disclosure provides an electric machine such as an electric motor including a motor enclosure defining an enclosed volume and a motor axis extending there through. The interior volume may also include an axially opposed drive end compartment and a non-drive end compartment axially spaced apart from each other. The electric motor also includes an annular stator fixed to the enclosure frame axially between the drive end and the non-drive end and defining a rotor bore and a cylindrical rotor rotatably disposed in the rotor bore and separated from the stator by an air gap. To reduce or limit the internal pressure caused by a spark or ignition, a porous material comprising a plurality of771187 (P240378 W001) interconnected voids having an open cell structure is used to line surfaces of the rotor and stator that form the air gap between the drive end and the non-drive end compartments.

[0005] A second aspect of the present disclosure provides a method that includes installing a flame arresting porous material having an open cell structure located between an annular stator and a cylindrical rotor accommodated in an enclosed volume of a motor enclosure. In accordance with the method, a combustible gas may be ignited in a first end compartment of the enclosed volume, thereby increasing pressure within the first end compartment and creating a propagating frame front. In accordance with the method, thermal energy and heat from the flame front traveling in the air gap is absorbed into and dissipated by the flame arresting porous material that may line the air gap.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The subject matter of the present disclosure will be described in even greater detail below based on the exemplary figures. The features and advantages of various embodiments will become apparent by reading the following detailed description with reference to the attached drawings, which illustrate the following:

[0007] Figure 1 is a schematic cross-section of an electric motor in accordance with the disclosure that shows the arrangement of the internal motor components accommodated in a motor enclosure that separates the enclosed volume from the ambient environment.

[0008] Figure 2 is a possible example comparing the internal pressures of the electric motor measured at the drive end and the non-drive end with and without the flame arresting porous material.

[0009] Figure 3 is a detailed view of the air gap between the interfacing stator and rotor including a flame arresting porous material located therein to delay propagation of an internal explosion or flame.

[0010] Figure 4 is an isometric view of a porous lining manufactured from a flame arresting porous material that can be used to line the surfaces of the annular stator and cylindrical rotor forming the air gap.

[0011] Figure 5 is an isometric view of the porous lining configured as a porous rotor sleeve that is adapted to be fixedly attached to the exterior of the cylindrical rotor.

[0012] Figure 6 is an isometric view of the porous lining configured as a porous stator insert or bushing internally inserted and fixedly attached to the interior of the annular stator.771187 (P240378 W001)

[0013] Figure 7 is a cross-sectional view of the annular stator including the porous material configured as porous wedges located in the stator slots in accordance with the disclosure.DETAILED DESCRIPTION

[0014] Examples of the present application will now be described more fully hereinafter with reference to the accompanying figures, wherein whenever possible like reference numbers will refer to like elements. The application may be exemplified in different forms and should not be construed as limited to the examples set forth herein; rather, these examples are provided so that the application will satisfy applicable legal requirements. Where possible, any terms expressed in the singular form herein are meant to also include the plural form and vice versa, unless explicitly stated otherwise. Also, as used herein, the term “a” and / or “an” shall mean “one or more” even though the phrase “one or more” is also used herein. Furthermore, when it is said herein that something is “based on” something else, it may be based on one or more other things as well. In other words, unless expressly indicated otherwise, as used herein “based on” means “based at least in part on” or “based at least partially on”.

[0015] Referring to FIG. 1, there is a sectional view of an electric machine 100, for example, an electrical motor, which converts electrical power to rotational mechanical power and torque for certain speeds of rotation. The rotational torque is applied through a rotating drive shaft 102 that protrudes from a housing or a motor enclosure 104 of the motor and which is aligned with and defines a motor axis 106. The motor enclosure 104 or motor frame forms the supporting structure defining an enclosed interior 108 inside of which are accommodated and housed the internal components of the electric motor 100 that interact to rotate the motor shaft 102. The motor enclosure 104 can correspond to industry standardized motor frame sizes that reference the physical dimensions and characteristics of the electric motor 100.

[0016] By way of example, industry standards include the Nation Electrical Manufacturers Association (NEMA) enclosure standards or the International Electrotechnical Commission (IEC) standards. These standards may define the type of enclosure for the electric motor 100 including the types of protection against ingress of dust or water, the type of cooling or heat removal such as air convection or fan cooled, and its suitability for different operating environments and hazards. For example, the standards may designate a motor enclosure as an opened drip proof (ODP) enclosure that may include vents to the ambient environment or a totally enclosed fan cooled (TEFC) enclosure that is enclosed to the environment to prevent dirt or water from entering and is cooled by an external fan. The771187 (P240378 W001) standards may also relate to frame size or frame configuration of the motor enclosure that can specify the configuration and dimensions for various mounting structures such the mounting feet at the base of the motor enclosure. Standardization of these aspects facilitates compatibility of the electrical motors 102 in different industrial settings.

[0017] To couple to an external load, the motor shaft 102 can protrude from a first axial end of the enclosure frame 104 referred to as the drive end 110. The opposite second axial end can be referred to as the non-drive end 112 at which the motor shaft 102 terminates. Structurally, the drive end 110 can be associated with a first end shield 114 and the non-drive end can be associated with a second end shield 116. The axially opposed first and second end shields 114, 116 define the axial length of the enclosure frame 104 and function as the structural support for the motor shaft 106. The motor enclosure 104 also includes a frame sleeve 118 that extends between the first and second end shields 114, 116 and is structurally configured as an open tube concentric about the motor axis 106 and surrounding the enclosed interior 108. The first and second end shields 114, 116 can be attached to the frame sleeve 118 by fasteners, welding, or other similar attachment techniques.

[0018] To cause the motor shaft 102 to rotate with respect to the rotational axis 108, the electric motor 102 can include an annular stator 120 and an electromagnetically interacting cylindrical rotor 122 accommodated in the enclosed interior 108 defined by the motor frame 104. The annular stator 120 can be a stationary annular structure that is fixedly mounted to the interior of the frame sleeve 118 and is concentric about the rotational axis 102 and the cylindrically shaped rotor 122. In an AC induction motor, the annular stator 120 may be made of a plurality of windings or coils which are conductive, and which can receive electricity from an external source. The cylindrical rotor 122 can be formed on and radially disposed about the motor shaft 102 such that, in operation, the rotor assembly rotates with the motor shaft. The cylindrical rotor 122 can be made of a corresponding set of electromagnetically reactive coils, and or bars, and or magnets, and or laminations and a combination thereof; radially attached to the motor shaft 102.

[0019] When alternating current is supplied to the coils of the annular stator 120, it generates a rotating magnetic field. The rotor 122 interacts with the rotating magnetic field or flux from the annular stator 120 causing the rotor to follow the primary field and generate rotary motion and torque. The rotational forces applied to the cylindrical rotor 122 thus cause rotation of the motor shaft 102 with respect to the motor enclosure 104 and results in transmission of torque. In addition to the foregoing description of an alternating current motor,771187 (P240378 W001) aspects of the disclosure may also be applicable to electric motors operating according to other principles and techniques, such as direct current motors.

[0020] To allow the moveable cylindrical rotor 122 supported on the motor shaft 102 to rotate with respect to the annular stator 120 fixed to the motor enclosure 104, the structures are physically separated by an air gap 124. The air gap 124 may be annular in shape conforming with its location between the annular stator 120 and the cylindrical rotor 122. The annular stator 120 defines the outer diameter of the air gap 124 and the cylindrical rotor 122 defines the inner diameter. Axially, the length of the air gap 124 is coextensive with the axial interface between the annular stator 122 and the cylindrical rotor 122.

[0021] Dimensionally, the annular air gap 124 should be large enough to prevent contact between the rotating cylindrical rotor 122 and the annular stator 120. The air gap 124 also circulates airflow within the enclosed volume 108 by allowing airflow between the electromagnetically interacting components, thereby cooling the electric motor 100. Conversely, the annular dimension of the air gap 124 is desirably small enough to increase the electromagnetic interaction between the annular stator 120 and the cylindrical rotor 122.

[0022] To enable relative rotation of the motor shaft 102 and the motor enclosure 104, the motor shaft 102 can be supported at the drive end 110 and the non-drive end 112 by bearings 125 fitted into corresponding bearing apertures disposed in the first and second end shields 114, 116. The bearings 125 can be seated into the bearing apertures and enable the motor shaft 102 to rotatably connect with and protrude through the first and second end shields 114, 116.

[0023] The electromagnetic interaction of the annular stator 120 and the cylindrical rotor 122, and the rotation of the bearings 125 supporting the motor shaft 102, may generate thermal energy or heat within the enclosed interior 108 of the motor enclosure 104. To circulate air within the motor enclosure 104 and dissipate heat, portions of the enclosed volume 108 can remain unoccupied thereby creating one or more compartmentalized volumes. For example, axially located between the first end shield 114 and the forward axial face of the annular stator 120 can be a drive end compartment 126 associated with the drive end 110 of the motor enclosure 104. Similarly, a non-drive end compartment 128 can be located axially between the rear face of the annular stator 120 and the second end shield 116 of the non-drive end 112.

[0024] The drive end compartment 126 and the non-drive end compartments 128 are empty spaces that are axially separated, i.e., compartmentalized, from each other by the physical presence of the annular stator 120 and the cylindrical rotor 122. The drive end and the non- drive end compartments 126, 128 are fluidly connected by the air gap 124 which extends axially771187 (P240378 W001) between the compartments. It will be appreciated that the air gap 124 forms a continuous open annulus axially extending between the drive end and the non-drive end compartments 126, 128.

[0025] The motor enclosure 104 can include or be associated with additional structures that assist motor operation. For example, to further cool the electric motor 100 during operation, a fan 130 can be attached to the motor shaft 102 protruding from the second end shield 116 at the non-drive end 112. The fan 130 is thus located exteriorly of the enclosed interior 108 and can be enclosed by a fan cover 132 that is axially attached to the second end shield 116. The fan 130 can be arranged to direct an airflow axially over the exterior of the motor enclosure 104 to remove heat by convection.

[0026] To interface with an external power source, the motor enclosure 104 can include a terminal box 134, which may be situated on top of the electric motor 100 and attached to the frame sleeve 118. The terminal box 134 can include electrical connections and devices for regulating and conducting electrical power to the coil windings associated with the annular stator 120. The terminal box 134 can be an assembled shell or box that can be opened for periodic rewiring of the electrical connections.

[0027] The design and functionality of the motor enclosure 104 can be designated in accordance with various industry standards. For example, the motor enclosure 104 can be designated as an explosion proof motor designed for operation in an explosive atmosphere in which there may be a presence of flammable or combustible materials, particularly gasses, vapors, or airborne particles. A flameproof enclosure is constructed to withstand an explosion of a gas, vapor or dust that may occur within the enclosure. Should an explosion occur within the enclosed interior 108, the motor enclosure 104 should prevent the ignition or explosion of the gas or vapors that may surround the electric motor 100.

[0028] Alternatively, the motor enclosure 104 may be designated as “flameproof.” A flameproof motor enclosure 104 is also designed for operation within an explosive environment in which flammable gasses may be present and is configured to prevent a spark or flame from transmitting from the enclosed interior 108 to the ambient environment surrounding the motor enclosure 104.

[0029] Explosion proof and flame proof enclosures must be tested in accordance with agreed industry standards, for example IEC 60079- 1 , for manufacturers to designate the electric motors as such. A typical test for designating motor enclosures as flameproof involves initiating combustion or an internal explosion within the enclosed interior 108 and measuring the pressure increase contained by the motor enclosure 104. Combustions and explosions are characterized by a rapid expansion of gasses accompanying the release of energy. The increase771187 (P240378 W001) in pressure in the enclosed interior 108 corresponds to the ability of the motor enclosure 104 to contain an explosion. By way of example, for an electric motor to be designated as “flame proof,” the motor enclosure 104 should withstand four to five times the maximum explosion pressure of a combustible gas that serves as a reference.

[0030] Ignition may begin at a particular point within the enclosed interior 108 and can move or expand outwardly therefrom. Ignition can be caused by an electrical spark from the windings and coils associated with the annular stator 120, or may be caused as a result of internal friction and / or self-heating of the gasses generating heat in excess of the combustion temperature. During certification testing, for example, ignition of the gasses contained in the in enclosed interior 108 can be caused by a sparkplug. Once ignition occurs, the combustion may propagate through the motor enclosure 104 as a traveling flame that spreads through the enclosed interior 108. The flame front separates the burnt gasses that have combusted and the unbumt gasses located away from the point of ignition.

[0031] The expanding flame front also creates pressure wave that compresses the unbumt gasses located forwardly of it. Compression of the unbumt gasses ahead of the flame front corresponds to an increase in the local pressure and the fluid turbulence of those unbumt gasses. Further, when the flame front reaches the unbumt gasses, the combustion may be greatly accelerated due to the increase pressure and turbulence, resulting in a more energetic explosion and a resulting higher peak pressure. This phenomena may be referred to as pressure-piling. The geometry of the enclosed interior 108 including the drive end 110 and the non-drive end 112 fluidly connected by the air gap 124 enhances the occurrence of press piling. The combustion and explosive pressures are therefore more energetic as the flame front moves from one compartment to another, for example, through the air gap 124 of the motor enclosure 104.

[0032] In an possible example, referring to FIG. 2, there is illustrated a chart 140 that shows pressure on the Y-axis 142, for example in bars, in comparison with time on the X axis 144, for example in milliseconds. To generate the pressure curves shown in FIG. 2, an explosion test could be conducted on a flameproof motor and the internal pressure measured using a plurality of appropriately located pressure sensors. By way of example, the test may be conducted using 8% ethylene C2H4 gas mixture in the enclosed volume 108. The ignition may occur in the drive end compartment 126 and is indicated in the first pressure curve 146. The first pressure curve 146 shows a quick pressure rise that then slows to a first peak pressure 148 at time X.

[0033] In the example wherein the enclosed volume 108 includes the drive end compartment 126 where ignition occurs, the pressure-piling effect may result in a more771187 (P240378 W001) energetic explosion and higher peak pressures in the non-drive end compartment 128. The pressure wave created by the combustion in the drive end compartment 126 increases the pressure and the turbulence of the unbumt gasses in the non-drive end compartment 128, which are fluidly connected by the air gap 124 between the annular stator 120 and the cylindrical rotor 122. Accordingly, when the flame front reaches the non-drive compartment 128 via the air gap 124, the compressed and turbulent gasses combust and explode much more rapidly and energetically. It should be noted that ignition may start in the non-drive end 128 and proceed to the drive end compartment 126.

[0034] With continued reference to FIG. 2, the pressure-piling effect is indicated by the second pressure curve 150. The second pressure curve 150 initiates later in time than the first pressure curve 146 reflecting the travel time of the flame front from the drive end compartment 126 to the non-drive end compartment 128 and the delayed ignition therein. However, due to the pressure-piling effect and the pre-compression of the unbumt gasses in the non-drive end compartment 128, the peak pressure of the resulting explosion is significantly higher, as indicated at the second peak pressure 152. Again, ignition may occur in either of the drive end and non-drive end compartments 126, 128 and the first and second pressure curves 146, 150 may be associated accordingly. The chart in FIG. 2 is illustrative and prophetic only, and certain of the curves therein are not indicative or based on experimental data.

[0035] In accordance with the disclosure, the electric motor 100 is structurally configured to include a flame arresting material to reduce the pressure-piling effect in the non-drive end compartment 128. The flame arresting porous material is adapted to quench or oppose the travel of a flame front or the combustion gasses within the enclosed volume 108 of the motor enclosure 104. The flame arresting porous material may absorb and dissipate the thermal energy or heat associated with the burning gasses and combustion, thus preventing or delaying the combustion of unbumed gasses within the non-drive end compartment 128 and reducing the velocity of the flame front traveling through the air gap 124 and correspondingly reducing the pressure increases within the motor enclosure 104

[0036] For example, referring to FIG. 2, the chart includes a third pressure curve 154 that indicates the fluid pressure as measured in the non-drive end compartment 128 with the addition of the flame arresting and pressure dampening material. The third pressure curve 154 is prophetic and indicative of a possible response to the inclusion of the flame arresting porous material, and may have a different shape and curve than as shown. Specifically, the third pressure curve 154 indicates a lower third peak pressure 156 than the second peak pressure 152 of the second pressure curve 150 that results from the pressure -piling effect. The explosion in771187 (P240378 W001) the non-drive compartment 128, as indicated by the third pressure curve 154, is less powerful compared with the second pressure curve 150.

[0037] Referring to FIG. 3, to incorporate the flame arresting configuration that reduces the pressure -piling effect and lowers the peak pressures in the enclosed volume 108, the electric motor 100 can include a flame arresting porous material 160 that can be used to line the air gap 124 between the annular stator 120 and the cylindrical rotor 122. The porous material 160 is characterized by the presence of voids 162 such as opened or empty spaces within a supporting material comprised of substantive matter 164. For example, the voids 162 function as empty volumes present and dispersed within the substantive matter 164 that provides the structure defining and shaping the voids.

[0038] The porous materials 160 are also characterized as having a ratio of high surface area to volume ratio due to the voids 162 dispersed in the substantive matter 164. Surface area may refer to the exposed areas of the porous material 160 that interface with fluids or gasses, which may be increased significantly due to the presence of the voids 162. In an example, the porous material 160 may be an open celled structure in which the voids 162 are continuously interconnected to define elaborate, elongated passageways so that a fluid can travel through the entire structure via the tortuous passageways.

[0039] The porous material 160 provides a flame quenching effect that reduces or delays the second peak pressure 152 of the second pressure curve 150 associated with the non-drive end compartment 128. For example, the porosity of the flame arresting porous material 160 can absorb heat from the combusting gasses and may provide localized quenching of the advancing flame front. The high surface area of the porous material 160 allows for absorption of heat from combustion and thus cooling down the burning internally contained gasses and eventually extinguishing the deflagration flame inside the motor enclosure 104. By absorbing heat and lowering the thermal energy in the enclosed volume 108, the flame arresting porous material may prevent or delay combustion of the remaining unbumed gasses, thus slowing the velocity of a traveling flame front and possibly quenching or extinguishing the internal explosion. In cases where the deflagration flame transitions to a detonation, the flame arresting porous material 160 can also act as a shock attenuating structure that absorbs shock waves and energy from the detonation.

[0040] The pressure flame arresting porous material 160 can line the airgap 124 that fluidly interconnects the drive end compartment 126 and the non-drive end compartment 128 such that the flame front and the pressure wave is required to traverse the flame arresting porous material. The flame arresting porous material 160 can be physically located between the annular stator771187 (P240378 W001)120 and the cylindrical rotor 122 and can axially extend parallel to the motor axis 106 to be coextensive with the overlapping axial regions of the structures.

[0041] The flame arresting porous material 160 is therefore fluidly exposed to the air gap 124, and a flame front traveling therein or combustion occurring therein must thermally interact with the flame arresting porous material. The increased surface area associated with the porous material 160 enables a greater degree and rate of thermal interaction and transfer of thermal energy between the porous material 160 and the combusting gasses. Hence, the significant surface area provided by the porous material 160 can absorb heat and reduce the thermal energy within the air gap 124, thereby impeding and delaying ignition of unbumed gasses, and possibly quenching or extinguishing the flame or explosion.

[0042] The flame arresting and flame quenching characteristics of the porous material 160 thus hinders the propagation of a flame front as it travels through the air gap 124 from the drive end compartment 126 to the non-drive end compartment 128 (or vice versa depending on where ignition begins). For example, by absorbing heat and reducing the thermal energy of the burning gasses as they propagate through the air gap 124 slows or delays the ignition of the trapped gasses, or possibly extinguishes the combustion, preventing the rapid combustion and pressure rise in the non-drive end compartment 128.

[0043] Physically, the flame arresting porous material 160 can be structurally configured as a cylindrical porous lining 170 that is pre-constructed for inclusion into the electric motor 100 during assembly. Referring to FIG. 4, the cylindrical porous lining 170 can be a cylindrical annulus having an annular thickness 172 defined by outer diameter 174 and an inner diameter 176 dimensioned to correspond with the airgap 124. The annular thickness 172 can range from 2 mm to 10 mm. The cylindrical porous lining 170 can be manufactured as an extruded tube that is cut into the desired axially length 178 with a saw. The axial length 178 can correspond to the overlapping axial interface between the annular stator 120 and the cylindrical rotor 122.

[0044] In another example, the cylindrical porous lining 170 can be formed by a sintering process in which a granular source material is compacted into the annular or tubular shape of the lining. The granular source material can be a non-ferromagnetic material such as a ceramic. Pressure and / or heat is applied to the compacted granular material formed to the specific shape causing the material to bond or join together into a solid rigid mass. An advantage of using a sintering process to create the cylindrical porous lining 170 is that porosity of the finished part can be controlled through the application of heat and pressure.

[0045] As another example of manufacturing, the porous material 160 can be sputtered onto a surface to form the cylindrical porous lining 170. In a sputtering process, a source771187 (P240378 W001) materially may be energized to dislocate microscopic particles that are deposited onto a surface to create a solid layer of a desired thickness. The source material may be a suitable type of nonferromagnetic material and the sputtering process can facilitate the creation of voids 162 within the substantive matter 164 described above.

[0046] A variety of different porous materials can be selected for the flame arresting porous lining 170. To avoid disturbing the magnetic flux path between the annular stator 120 and the cylindrical rotor 122, the porous material used for the flame arresting cylindrical porous lining 170 may be non-ferromagnetic and unresponsive to magnetic influences. Examples of suitable porous non-ferromagnetic materials include metal foam (stainless steel, etc.), ceramic foam, non-ferromagnetic or non-magnetic foam, metal wool (such as stainless-steel wool), and aluminum silicate wool. Metal wools may be made for meshed metal filaments held together. Ceramics and plastics may also be used as the flame arresting porous material.

[0047] In another configuration wherein the flame arresting porous material is provided as a cylindrical porous lining 170, for example, placed adjacent to the surfaces of the cylindrical rotor and / or the annular stator, the porous material may be ferromagnetic and resistive. The inclusion of ferromagnetic materials on the surfaces of the rotor may not adversely affect the electromagnetic interaction and the percentage of ferromagnetic material can be controlled to alter the resistance that may induce eddy currents. Ferromagnetic material may also be used as a liner on the inner surface of the annular stator.

[0048] The porosity ofthe material, i.e., the volume ratio of voids 162 to substantive matter 164, may for example be at least 25%. Porous materials 160 with porosity of 85%-90% can be more effective in slowing the progress of the flame front through the air gap 124 and dampening the peak pressure resulting in the non-drive end compartment 128. The highly porous materials 160 having an open cell structure provide beneficial pressure dampening characteristics while continuing to enable internal air circulating within the interior volume 108 for cooling of the annular stator 120 and cylindrical rotor 122.

[0049] To facilitate assembly, referring to the example in FIG. 5, the cylindrical porous lining 170 can be configured as a tubular porous rotor sleeve 180 that may be fixed to the rotor 122. For example, the inner lining diameter 176 can be dimensioned to create a sliding fit or an interference fit with the exterior rotor surface 182, which may also be generally cylindrical. The rotor 122 can be forcibly inserted into the tubular porous sleeve 180 to be fixed in contact with the exterior rotor surface 182. The porous sleeve 180 is therefore fixed in rotation with the rotor 122. Further, the outer lining diameter 174 can be dimensioned to provide a clearance771187 (P240378 W001) with respect to the annular stator 120 to allow for unobstructed rotation of the cylindrical rotor 122.

[0050] Referring to the example in FIG. 6, the cylindrical porous lining 170 can be configured as a tubular porous stator insert 190 or bushing that may be fixedly inserted into the annular stator 120. The porous stator insert 190 can be configured to have the same cylindrically annular shape as the cylindrical porous lining 170 with the outer lining diameter 174 dimensioned to form an interference fit with the inner stator surface 192. The porous stator insert 190 can be press fit into the hollow core of the annular stator 120 and is statically fixed to the structure. To enable relative rotation of the cylindrical rotor 122, the inner lining diameter 176 can be dimensioned to provide a clearance with respect to the exterior rotor surface.

[0051] To further facilitate assembly, in an example, the annular stator 120 can include first and second axial end rings 194, 196 that are located at axially opposite ends of the stator. The axial end rings 194, 196 may have inner dimeters that are smaller than the inner lining diameter 176 to constrain the axial location of the porous stator insert 190 with respect to the annular stator 120. The axial end rings 194, 196 can be press fit or threaded onto the axial ends of the stator structure.

[0052] Referring to FIG. 3, in an exemplary configuration, the electric motor 100 may include both the porous rotor sleeve 180 affixed to the exterior of the cylindrical rotor 122 and the porous stator insert 190 fixed to the annular stator 120. To enable relative rotation the porous rotor sleeve 180 and the porous stator insert 190 may remain spaced apart and separated by the air gap 124 between the annular stator 180 and the cylindrical rotor 190.

[0053] In a possible configuration for an electric motor 100 illustrated in FIG. 7, the annular stator 200 may be characterized has having a plurality of stator slots 202 that are disposed radially into the inner stator surface 204. The stator slots 202 are aligned parallel to the motor axis 106 and extend radially into the structural laminations that make up the annular stator 200 such that the stator slots are radially directed toward the rotor when inserted. The stator slots 202 can be angularly spaced about the circumference of the inner stator surface 204 so as to define a plurality of circumferential stator teeth 206 that are radially oriented toward the motor axis 106.

[0054] The stator slots 202 can accommodate the conductive windings 210 that may be formed as copper conductive wires continuously wound to form coils about the protruding stator teeth 206. The conductive windings 210 are typically located deep into the recesses created by the stator slots 202 and fill the stator slots thereby building the coils radially inward toward the inner stator surface 204. However, the conductive windings 210 may not be located771187 (P240378 W001) flush with the inner stator surface 202 such that a slot gap 212 exists that includes the unoccupied space of the stator slots 202.

[0055] In the example of annular stator 200 having a plurality of slot gaps 212, the flame arresting porous material 160 can be included as porous slot wedges 214 that can be fit within in the slot gaps. The porous slot wedges 214 can function to impede the travel of the flame front and the pressure wave through the otherwise unoccupied slot gaps 212 that extend axially across the inner stator surface 202 and hold the conductive windings 210 within the stator slot 200. The porosity of the porous slot wedges 214 also increase the surface area the combusting gasses may interact with, thereby absorbing thermal energy from the adjoining air gap and impeding, delaying, or quenching the traveling flame front. The porous slot wedges 214 can be made of any of the exemplary non-ferromagnetic porous materials. The presence of ferromagnetic material in the slot 212 may alter the flux and change the motor performance. As shown in FIG. 7, the slot wedges 214 can conform in shape to the shape of the slot gaps 212 that may be irregularly shaped to facilitate accommodating the conductive windings 212 therein.

[0056] In an example, the porous slot wedges 214 can be included as an integral structural part of the porous stator insert 216 previously described herein. For example, the plurality of porous slot wedges 214 can projected radially outward from the outer circumference of the tubular porous stator insert 216 and can be angularly spaced apart to confirm in angular location with the plurality of stator slots 208. Accordingly, when the porous stator insert 216 is inserted into the annular stator 120 during assembly, the angularly spaced plurality of porous slot wedges 214 can be aligned and make a sliding fit within the correspondingly located plurality of slot gaps 212. Further, the sliding fit between the porous slot wedges 214 and the slot gaps 212 can function to secure the porous stator insert 216 within the annular stator 200.

[0057] To manufacture the integral form of the plurality of porous stator wedges 214 joined to the outer circumference of the porous stator insert 216, the porous material can be extruded through a complex shaped die. In another example, the porous slot wedges 214 can be made separate from the porous stator insert 216 and installed individually into the slot gaps 212 prior to inserting and installing the porous stator insert into the hollow core of the annular stator 200. In another example in which the porous material is made from a non-metallic foam or metal wool, the porous slot wedges 214 can be pressed into the slot gaps 212 prior to inserting the porous stator insert 216.

[0058] Referring to FIGS. 1, 2 and 3, the functionality of the flame arresting porous material 160 can be appreciated. An internal explosion may occur due to an ignition in the771187 (P240378 W001) enclosed volume 108 that may originate in one of the drive end compartment 126 or non-drive end compartment 128. The internal explosion is characterized by the combustion and rapid expansion of any combustible gasses in the internal volume 108. For example, the explosion may originate at an initial ignition point and result in an outward expanding flame front that consumes or bums the combustible gasses as it expands. The initial explosion and expansion is represented by the first pressure curve 146 showing in FIG. 2, which is further characterized by an increase in the internal pressure to the first peak pressure 148 at time X.

[0059] The increasing pressure also creates a pressure wave that propagates through the interior volume 108 and that may compress the combustible gasses upstream or forward of the outwardly expanding flame front. Because the drive end compartment 126 and the non-drive end compartment 128 are fluidly connected by the air gap 124, the pressure wave and the fame front must propagate through and axially traverse the air gap. Absent the flame arresting porous material 160, the flame front may exit the air gap 124 at the non-drive end 124 at a higher temperature and speed causing the pressure-piling effect and resulting in a more rapid and powerful explosion in the non-drive end compartment 128. The pressure-piling effect is represented by the second pressure curve 152 in FIG. 2, which may be characterized by a second peak pressure 152, possibly exceeding the first peak pressure 148. The pressure-piling effect may accelerate the increase in pressure in the non-drive end compartment 128 as the combustible gasses in the drive end compartment continue to combust and expand.

[0060] The advantage of incorporating the porous material 160 in the air gap 124 fluidly connecting the drive end and the non-drive end compartments 126, 128 is the reduction or dissipation of the traveling flame front. For example, as the traveling flame front propagates through the flame arresting porous material 160, the significant surface area associated with the interconnected voids 162 is available to absorb heat and thermal energy from combusting gasses. The rate and velocity at which the traveling flame front can propagate from the drive end compartment 126 to the non-drive end compartment 128 is reduced and the flame front is possibly quenched and extinguished before reaching the non-drive end compartment. Hence, the pressure in the non-drive end compartment 128 increases at a slower rate as indicated by the third pressure curve 156 and to a lower third peak pressure 156. The flame arresting porous material 160 and the heat absorbing capabilities due to the increased surface area associated with the interconnected voids 162 regulates and limits the pressure increase in the non-drive end compartment 128.

[0061] By reducing the possible internal pressures caused by an internal explosion and the pressure-piling effect, the ability of the motor enclosure 104 to comply with various explosion771187 (P240378 W001) proof and / or flameproof certifications such as the IEC 60079-1 standard is increased. The motor enclosure can be manufactured by a less robust assembly process and may save materials and costs. These and other possible advantages of the disclosure should be apparent from the foregoing description and accompanying drawings.

[0062] While subject matter of the present disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Any statement made herein characterizing the invention is also to be considered illustrative or exemplary and not restrictive as the invention is defined by the claims. It will be understood that changes and modifications may be made, by those of ordinary skill in the art, within the scope of the following claims, which may include any combination of features from different embodiments described above.

[0063] The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and / or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.

Claims

771187 (P240378 W001)CLAIMSWhat is claimed is:

1. An electric motor comprising: a motor enclosure defining an enclosed volume extending along an motor axis between a drive end and a non-drive end; an annular stator fixed to the motor enclosure and defining a rotor bore; a cylindrical rotor rotatably located in the rotor bore and separated from the stator by an air gap; and a flame arresting porous material comprising a plurality of interconnected voids having an open cell structure fixedly attached to one or more of the annular stator and cylinder rotor to be fluid exposed to the air gap and thermally interact with a traveling flame front therein.

2. The electric motor of claim 1, wherein the flame arresting porous material is integrally structured as a cylindrical porous lining.

3. The electric motor of claim 2, wherein the cylindrical porous lining is a porous rotor sleeve fixedly attached to an exterior rotor surface.

4. The electric motor of claim 2, wherein the cylindrical porous lining is a porous stator insert fixedly attached to an inner stator surface.

5. The electric motor of claim 1, wherein the flame arresting porous material has a porosity density of at least 25%.

6. The electric motor of claim 1, wherein the flame arresting porous material is a ferromagnetic material.

7. The electric motor of claim 1, wherein the flame arresting porous material reduces the velocity of the traveling flame front in the air gap.

8. The electric motor of claim 1, wherein the annular stator includes a plurality of stator slots are arranged parallel to the motor axis and the flame arresting porous material is provided as a plurality of porous stator wedges each located in the corresponding plurality of stator slots.771187 (P240378 W001)9. The electric motor of claim 8, wherein the plurality of porous stator wedges radially project from a circumference of a cylindrical porous lining of the flame arresting porous material.

10. The electric motor of claim 8, wherein the plurality of porous stator wedges are of a non-ferromagnetic material.

11. A method of configuring an electric motor comprising: fixedly attaching a flame arresting porous material having an open cell structure to one or more of an annular stator and a cylindrical rotor located in an enclosed volume defined by a motor enclosure such that the flame arresting porous material is fluidly exposed to an air gap between the annular stator and the cylindrical rotor; igniting a combustible gas in a first end compartment of the enclosed volume thereby increasing pressure within the first end compartment and creating a traveling flame front; and dissipating the traveling flame front passing through the air gap toward the second end compartment by thermal interaction with the flame arresting porous material.

12. The method of claim 11, wherein the step of installing the flame arresting porous material includes fixing a pre-constructed and integrally structured cylindrical porous lining to one of an inner stator surface of the annular stator and an exterior rotor surface of the cylindrical rotor.

13. The method of claim 12, wherein the flame arresting porous material is a ferromagnetic material.

14. The method of claim 11, wherein the flame arresting porous material has a porosity density of at least 25%.

15. The method of claim 11, wherein the flame arresting porous material absorbs thermal energy from the traveling flame front.

16. The method of claim 11, wherein the flame arresting porous material reduces the velocity of the traveling flame front in the air gap.

17. The method of claim 11, wherein the step of installing the flame arresting porous material is preceded by a process of extruding and cutting a cylindrical porous lining.771187 (P240378 W001)18. The method of claim 10, wherein the step of installing the flame arresting porous material is preceded by a process of sintering a cylindrical porous lining.

19. The method of claim 10, wherein the step of installing the flame arresting porous material includes fixing a porous slot wedge into a slot gap radially formed in the annular stator.

20. The method of claim 10, wherein the porous slot wedge projects radially from a circumferential surface of a cylindrical porous lining.

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