WO2019116389A1

WO2019116389A1 - Unitary stator, slit rotor and a switched reluctance device thereof

Info

Publication number: WO2019116389A1
Application number: PCT/IN2018/050832
Authority: WO
Inventors: Gopalaratnam NARAYANAN; Pramod Kumar; Syed SHAHJAHAN AHMAD; Eshan DHAR; Naveenkumar ADAYYA HODLURAMATH
Original assignee: Indian Institute Of Science
Priority date: 2017-12-12
Filing date: 2018-12-12
Publication date: 2019-06-20

Abstract

The present invention provides a stator assembly (300) for a switched reluctance device formed from stack (301) of integrated metallic plates (302) with stator poles (312) and cooling fins (309). The stator assembly (300) includes a unitary stator core that is formed from an integral combination of the metallic plates (302). The present invention also provides a rotor assembly (530a) with a unitary slit torque member (532). The present invention also provides a SRD (650) that is operable at high speeds with the stator (300) and rotor (530a) assemblies with unitary stator core and slit torque member (532). The SRD (650) is also equipped with a position encoder that is suitable for higher speeds of the SRD (650).

Description

UNITARY STATOR, SLIT ROTOR AND A SWITCHED

RELUCTANCE DEVICE THEREOF

Technical Field

The present invention relates to stator and rotor assemblies for a switched reluctance device (SRD) that is operable at higher speeds. The present invention particularly relates to a unitary stator and a slit rotor assemblies. The invention also relates to a switched reluctance device (SRD) that is provided with the unitary stator and the slit rotor assemblies, to operate at higher speeds. Background of the invention

A switched reluctance device (SRD) is a torque producing device, having a stator and a rotor, where only the stator has windings and the rotor is generally formed of ferromagnetic laminations stacked onto a shaft. Further, such rotors also do not contain any electrical conductors or permanent magnets. In such reluctance device, when a current is passed through one of the stator windings, the torque is generated between the rotor and the stator by the tendency of the rotor to align with the excited stator pole. In such devices, the rotor is usually designed for low shaft speed and the rotor is laminated and the shaft is separated from the rotor. In other words, shaft and rotor are different entities, which are assembled together. Such SRDs are considered as unfavourable to function at high shaft speeds and at high shaft temperatures.

In known switched reluctance devices, such as switched reluctance motors (SRMs), it is generally preferred to undertake shaft-position sensing, in order to synchronize the phase excitation pulses to the rotor position. These sensors can constitute a substantial portion of the total system cost and tend to reduce system reliability. In case of an incorporation of an external position sensor, in such motors, an additional arrangement in the form of additional bearings and a coupling are usually resorted to, which are found to be unsuitable for high-speed operations exceeding 20,000 revolutions per minute (rpm).

Besides, the suitable electromagnetic design, SRM motors also require an efficient thermal design, to have an optimal performance of the motors, since suitable cooling system helps to decrease the temperature in the body of SRM and consequently increasing its lifetime. However, in known SRM motors, there is a significant thermal contact resistance between the external cooling fins and the stator yoke, leading to an ineffective cooling of the stator.

The stator generally is made up of silicon steel stampings or punchings with inward projected poles. The number of stator poles is an even number and these poles carry field coils. The field coils of certain poles are connected in series such that their magneto motive forces (MMFs) are additive to constitute phase windings. Each of the phase windings are connected to the terminal of the motor. In such arrangements, the stator punchings are completely assembled together, and permanently held in their assembled or compressed condition, before being pressed into a stator external casings, and this design has at times utilized a sufficiently tight fit, between the outer periphery of the stator punchings or laminations, and the inside of the stator stator external casing, so as to effect a heat-exchange between the stator laminations and the stator external casing. However, such heat-exchange is constrained by the thermal contact resistance between the stator laminations and the stator external casing. Also, such a compress fitting arrangement of the stator stack inside the machine housing (i.e stator external casing) results in mechanical stress on the stator laminations and thereby higher energy losses in the laminations.

A known stator assembly for an SRM device includes a stator core 10 made of stacked laminations and a stator external casing 11. The stator core 10 and the external casing 11 are made of different materials as shown in FIG.1(a) and are assembled together, as shown in FIG.1(b), after they were made separately. The stator external casing 11 has cooling fins 12 in outer periphery. It is known that the heat generated in the stator core 10 flows through the external casing 11 and then dissipated in the cooling fins 12. Since stator core 10 and external casing 11 are two separate structures, there is a significant thermal contact resistance in between these two. The thermal contact resistance depends on how these two structures are joined together. A higher thermal contact resistance results in higher temperature rise, which reduces the operating lifetime of the device. Higher thermal resistance also leads to lower power and torque density of the device. A known method to assemble the stator core 10 and external casing 11 is using shrink fitting as shown in FIG 1(b). In this method the external casing 11 is heated and allowed to expand. The stator core 10 is inserted inside the heated and expanded external casing 11 and then the assembly is allowed to cool. This results in interference fit, and the external casing 11 applies large compressive force on the stator core 10. In alternative method, the stator core 10 may be press-fitted using for example hydraulic press inside the external casing 11. In all cases, there is large compressive force exerted by the external casing 11 on the stator core 10. Large compressive force is required to minimize the thermal contact resistance in between the stator core 10 and the external casing 11. However, as known in the art, large compressive force on the stator core 10 increases the stator iron loss, thereby increasing the heat generated in the stator core 10 and lowering efficiency. Thus, in known stator assembly there is significant thermal contact resistance between stator core and cooling fins, higher temperature rise, lower power and torque density, higher energy losses and lower efficiency. There is extra assembly process of fitting the stator core 10 and the external casing 11 together.

In the known stator assembly, the external casing 11 is made using extrusion process. This aspect limits the possible shapes of the cooling fins 12. As known in the art, the shape and orientation of the cooling fins 12 have a major role in its ability to dissipate heat. The cooling fins 12, due to the adoption of extrusion manufacturing process, are known to have a straight configuration due to the adoption of extrusion manufacturing process, which limits their cooling effectiveness. Thus, inability to realize intricate cooling fin geometry with better heat dissipation capability is another limitation of known stator assembly.

A shaft 13 of a known rotor of a switched reluctance motor (SRM), where the shaft is machined from a single piece of shaft material, such as case hardening alloy steel, is as shown in

FIGs.2(a-c). One end of the shaft may have an arrangement for coupling it to an other shaft. The shaft 13 may also have an arrangement for shaft position and/or speed encoder at one of the ends of the shaft. Usually, a stack 14 made of lamination is provided in the central portion of the shaft. On either end of the lamination carrying part of the shaft, bearings are placed. As shown in FIG.2(b), each lamination in the stack 14 is obtained from thin sheets of ferromagnetic material such as silicon iron and alloys of cobalt and nickel with thin electrical insulating coating on both sides of the thin sheet. The insulating coating is typically made of organic or synthetic material. The laminations are cut from the thin sheet by processes such as die punching, laser cutting, plasma cutting or any other suitable processes. As shown in FIG.2(c), the laminations can be held together to form the stack 14 by various techniques such as welding, gluing, stud rods, cleating, end plates among other techniques. The laminations can also have an interlocking arrangement to hold them together. There can also be a key arrangement to transmit the torque from each of the lamination to the rotor shaft. It is also known that the lamination can be joined together to form a rotor core assembly and then shrink fitted to the shaft. It is also further known that a sleeve, which is made up of material such as carbon fibre or Inconel or steel is mounted on top of the laminations to hold them together. Such rotor structures having lamination stack 14 and shaft 13, which are made of different materials and assembled together are unfavourable for high-speed SRMs due to lower critical speed. Due to dissimilar material, the stack 14 and shaft 13 have differing thermal coefficients of expansion. Hence, if the rotor gets heated, due to energy loss in the rotor or external heat source connected to the shaft such as turbine, the stack 14 and the shaft 13 will tend to have different thermal expansion. As known in the art, this will produce large thermal stress at the contact between lamination stack 14 and the shaft 13. Additional stress on the rotor, is also unsuitable for high speed operation. In high speed rotor, the rotor, in particular the shaft 13 and the lamination stack 14, already have large radial stress due to centrifugal forces.

Hence, any additional stress, such as thermal stress in known rotor assembly is a disadvantage. Further, the insulation coating of the laminates degrade with high temperature. Gluing of laminates together also limits the working temperature of the rotor. Thus known SRM rotor is not preferred for a high speed and a high rotor temperature operation. Objects of the present invention

The primary object of the present invention is to provide a stator assembly for a switched reluctance device, with a unitary stator core that is formed from a stack of metallic plates and a plurality of cooling fins that are integral to the stator core, to dissipate directly, the heat generated by the stator core through the cooling fins, to reduce the heat generation in stator core and to lower the operational temperature of the stator assembly.

An object of the present invention is to provide a rotor assembly for a switched reluctance device, with a unitary torque member having rotor poles with slits that are integrally connected to movable shaft, to achieve a lower iron loss in the rotor, along with a higher mechanical rigidity, higher critical speeds, less deformation, less thermal stress and reliable operation at high shaft temperature.

Another object of the present invention is to provide a switched reluctance device (SRD) that is configured with the stator the rotor assemblies of the present invention, for operating at higher speeds as well as higher rotor temperature. The SRD also incorporates a high speed position sensor, without requirement of additional bearings and coupler, for synchronising the excitation of stator phase windings with rotor position.

Summary of the present invention

The present invention provides a stator assembly for a switched reluctance device formed from stack of integrated metallic plates with stator poles and cooling fins. The stator assembly includes a unitary stator core that is formed from an integral combination of the metallic plates. The stator assembly of the present invention includes an integrated segmented stacks of the metallic plates. The present invention also provides a rotor assembly with a unitary rotor with a slit torque member. The present invention also provides a Switched Reluctance Device (SRD) with a position encoder along with the stator and rotor assemblies that is operable at high speeds.

Brief description of the drawings

FIGs.l(a)-(b) are perspective views of a known stator for a switched reluctance motor.

FIGs.2(a)-(c) are perspective views of a stator of known switched reluctance motor.

FIG.3(a) is a perspective view of a stator assembly, in accordance with an embodiment of the present invention.

FIGs.3(b-e) are perspective views of cooling fins of solitary metallic plates of the stator assembly, with variable fin configurations.

FIG.3(f) is an exploded perspective view of the stator assembly of the present invention.

FIG.3(g) is a partial sectional perspective view of the stator assembly of the present invention.

FIGs.3(h-j) are perspective views of various embodiments of the stator assembly with cooling fins having curvy, herringbone and serrated configurations.

FIG.4(a) is a perspective view of a solitary metallic plate of the stator assembly of the present invention.

FIG.4(b) is a perspective exploded view of the stator assembly with segmented stator poles, in accordance with an embodiment of the present invention.

FIG.4(c) is an exemplary perspective view of a segmented stator pole with an electromagnetic winding.

FIG.4(d) is an exploded perspective view of the stator assembly of the present invention.

FIG.5 is a perspective view of a slit solid rotor assembly, in accordance with an embodiment the present invention. FIG.6(a) is a side sectional view of the slit rotor assembly and FIG.6(b) is a partial detailed view of FIG.6(a).

FIG.7 is a perspective view of an embodiment of the slit rotor assembly, having curved torque member.

FIG.8(a) is a perspective view of an embodiment of the slit rotor assembly, having round and smooth torque member with internal intervening spaces between stator poles.

FIG.8(b) is a perspective view of an embodiment of the slit rotor assembly, having round and smooth torque member, with open intervening spaces between stator poles.

FIG.8(c) is a perspective view of an embodiment of the slit rotor assembly, having round and smooth torque member, with open intervening spaces between stator poles, as shown in FIG.8(b) and the intervening spaces are filled with an insulating material.

FIG.9 is a perspective view of an embodiment of the slit rotor assembly, having a combination of slit and solid torque member.

FIG.lO(a-i) are sectional perspective views of the torque member of the torque assembly, illustrating various slit configurations.

FIG.11(a) is a partial sectional view of an exemplary Switched Reluctance Device (SRD) having the stator and rotor assemblies of the present invention.

FIG.11(b) is a partial sectional view of the exemplary SRD illustrating a detailed view of a position encoder assembly.

FIG.11(c) is cross-sectional view of the exemplary SRD showing the stator assembly with integral cooling fins and the rotor of the present invention. FIG.11(d) is an exploded view of a rotor portion of a position encoder, in accordance with an embodiment of the present invention.

FIGs.l2(a-b) are views illustrating the rotor portion of the position encoder, in accordance with an embodiment of the present invention.

FIG.12(c) is an exemplary sectional view of the SRD illustrating an embodiment of the arrangement of a sensing element of the position encoder.

Description of the invention

Accordingly, the present invention provides a stator assembly for use in a switched reluctance device, such as a switched reluctance motor. The stator assembly 300(a) of the present invention, as shown in FIG.3(a), is formed from a stack 301 of individual or solitary metallic plates 302, where the individual metallic plates 302 are integrated to form a unitary stator core 303.

The preferred embodiments of an individual metallic plate 302, are described by initially referring to FIG.3(b). The reference number 302 is referred to both individual and group of metallic plates, in the specification, as required by the context. The metallic plate 302 is advantageously provided with a preferably circular shape of a desired thickness. The metallic plate 302 is obtained from a metallic thin sheet. The metallic plate 302 in this exemplary aspect is shown with a circular shape and other suitable shapes such as square or rectangular shapes can also be adapted for use. The shape of the metallic plate 302, forming a cluster or group, determines the shape of the unitary stator core 303. The unitary stator core 303, which is formed from the metallic plates 302 with square or rectangular shape can be useful in certain application of a SRD. The thickness of the metallic plate plate 302 has a direct bearing on the stator iron energy losses in the SRD. Lower thickness results in lower eddy current losses, and therefore preferred from efficiency point of view. However, lower thickness also increases the cost of manufacturing of the thin metallic sheets, cost of cutting or punching the metallic plates 302 from the metallic sheets and assembling the metallic plates 302 into the stator stack 301. Accordingly, the preferred thickness of metallic plates 302 for low speed SRD is in the range of 0.65 mm to 0.35 mm. For a high speed SRD, lower thickness in the range of 0.35 mm to 0.1 mm is desirable.

The metallic plate 302 is configured to form an inner portion 304, a central portion 305 and a peripheral portion 306, where these portions 304, 305, 306 are seamlessly arranged to form a single unit.

A plurality of legs 307 are arranged to extend in radially and in inward directions from the inner portion 304 of the metallic plate 302. The legs 307 are configured to support electromagnetic windings. In this exemplary aspect as shown in FIG.3(a), a total number of six legs 307 are shown extending radially inwards from the inner portion 304, to facilitate the formation six stator poles, as hereinafter described. The number of legs 307 can be suitably varied, such as 8, 12 etc., depending on the requirement of number of stator poles for the unitary stator core 303.

Multiple pass-through openings 308 are made in the central portion 305 of the metallic plate 302, which are used to assist in the formation of the stack assembly 300.

Multiple cooling fins 309 are advantageously formed integrally, on the peripheral portion 306 of the metallic plate 302, as shown in FIG.3(b). The cooling fins 309 are formed to project radially outward from the peripheral portion 306. The cooling fins 309 as shown in FIG.3(b) are provided as straight structures that are extending from the outer periphery of the peripheral portion 306 of the metallic plate 302. The other suitable configurations for the cooling fins 309 can be selected from tapered, curved, trapezoidal or wavy configurations, as exemplarily shown in FIGs.3(c)-(e). It is also understood by a skilled person here that a suitable combination of any of these configurations can be also suitably adapted for use.

The metallic plate 302 in the stack 301 is obtained from thin sheets of ferromagnetic material. Such thin sheets of ferromagnetic material include different grades of silicon steel and different alloys of cobalt and nickel. The thin sheets, and therefore the metallic plate 302 also have insulation coatings on both sides, which can be organic or synthetic of different grades, that are suitable for different temperature application. The metallic plate 302 is cut from the thin ferromagnetic sheet using die punching, laser cutting, plasma cutting, electric discharge machining (EDM) or other such sheet metal cutting techniques.

Now, the preferred embodiments of the stack 301 of the metallic plates 302 are described by particularly referrring to FIG.3(f). The stack 301 of the metallic plates 302 is formed by integrating individual metallic plates 302 and connecting them through support members 310, which are permitted in the pass through openings 308. A pair of end flanges 311 is employed on either side of the stack 301, to which the support members 310 are connected, through a lock nut arrangement 313 or any other suitable locking arrangement. The support members 310 can be studs, rods or any other suitable supporting contraptions. The support members 310 can be welded to the end flanges 311 or can be screwed to the end flanges 311. Once the individual metallic plates 301 are stacked together, the legs 307 together form a plurality of radially inward oriented stator poles 312. Alternately, the stack 301 can be formed by welding the metallic plates 302 together either along with the support members 310 and the end flanges 311. The stack 301 can also be formed using stator cleat structures. In this configuration, the metallic plates 302 are clamped at their outer periphery using U- shaped metallic plates. In another configuration, the metallic plates 302 can be interlocked together to form the stack 301. In yet another configuration, the metallic plates 302 can be held by glue like substance, to form the stack 301.

Once the stack 301 is formed from the individual metallic plates 302, the integrated plurality of legs 307 act as stator poles 312. Suitable electromagnetic windings 314 are provided to the stator poles and are powered with a suitable power source to generate a magnetic field and a corresponding torque. In the arrangement of stator poles 312 with electromagnetic windings 314 as particularly shown in FIG.3(g), the windings are held in the space in between the stator poles 312 by using winding retainers 315. The winding retainers 315 can be of any solid electrically insulating material, which can provide a structural integrity and withstand a high temperature in the electromagnetic windings 314. Alternative arrangements to hold the windings 314 in place are also available and one such alternative arrangement is to encapsulate the electromagnetic windings 314 in an epoxy like filler material. Another alternative arrangement can be to hold the electromagnetic windings 314 using insulating materials such as paper or plastic slot insulator. Yet another alternative arrangement is to hold the windings 314 tightly with the stator stack 301, using threads or wires that are made of an insulating material.

The electromagnetic windings 314 produce magnetic field in the stator stack 301, when electrical current is passed through it. Magnetic field or magnetic flux links with the rotor of the SRD through the stator poles 312. An electromagnetic torque is generated on a torque member of a slit rotor, as hereinafter described. The magnitude of the torque at any instant depends on the orientation of the torque member of the slit rotor, with respect to the stator poles 312 at that instant and as well as the current flowing in the electromagnetic windings 314 at the same instant. Plurality of electromagnetic windings 314 are provided on the stator poles 312. Each of these electromagnetic windings 314 generate different torque on the rotor torque member as per their orientation with respect to the rotor torque member. Thus, by controlling the current through the plurality of windings 314 desired magnitude and direction of torque can be produced on the rotor of the SRD. The torque is greatly influenced by the magnitude of magnetic field. The magnetic field is aided and guided by the ferromagnetic material in the stator stack 301. Each individual metallic plate 302 in the stator stack 301 carries magnetic flux lines. The metallic plates 302 are oriented in parallel to the magnetic flux lines.

In a similar way, once the individual metallic plates 302 are stacked together the individual cooling fins 309 form a cluster of plurality of radially outward cooling fins 309 (the cluster of cooling fins are also referred to with part number 309) that are integrally disposed at the peripheral portions of the metallic plates 302. These cooing fins 309 dissipate the heat generated in the stator stack 301 and the electromagnetic windings 314. The heat generated in the electromagnetic windings 314, that is a copper loss, flows through the inner portion 304, the central portion 305 and the peripheral portion 306 of the metallic plates 302, which form the stator stack 301 and finally to the cooling fins 309 that are formed integrally on the peripheral portion 306. The heat generated by the metallic plates 302, that is an iron loss, flows to the integrally formed cooling fins 309 directly. The cluster of plurality of radially outward cooling fins 309 is exposed to ambient conditions and in contact with air or any other suitable coolant medium. Accordingly, the heat is dissipated by convective and radiative heat transfer, from the cooling fins 309 to a coolant medium or into ambient conditions. Alternatively, the coolant can be forced to flow through the cooling fins 309 to obtain a forced cooling system.

Thus, the unitary stator core 303 is formed from the integral combination of metallic plates 302 having a plurality of radially inward oriented stator poles 312 and the plurality of radially outward oriented cooling fins 309. This arrangment of the stator core 303 prevents any possible additional thermal contact resistance between the cooling fins 309 and the stator stack 301. Accordingly, due to the the unitary structure of the stator assembly

300 the heat generated in the windings 314 and the stator stack

301 can readily flow to the cooling fins 309. This arrangement improves cooling efficiency of the machine (SRM), reduces temperature rise and enhances torque and power density. In this exemplary aspect, the cooling fins 309 are formed by cutting or punching of the metallic plates 302 from a thin metallic sheet. Therefore, the intricate fin geometries, as illustrated in FIGs.3(c)- (f), can be formed and these geometries help in improving the cooling efficiency of the cooling fins 309.

In yet another aspect of the present invention, non-limiting exemplary configurations, for the cooling fins 309, of the stator assembly 300(a) are as shown in FIGs.3(h-j), where FIG.3(h) illustrates an arrangment of the cooling fins 309 with a curved configuration. FIG.3(i) illustrates the cooling fins 309 with a herringbone configuration and FIG.3(j) illustrates an arrangement of the cooling fins 309 with a serrated configuration. These exemplary configurations facilitiate an increase the total surface area of the cluster of cooling fins 309 and thereby improving the heat transfer property of the cooling fins 309. In additon, such configurations also assist in improving a coolant flow path around the fins 309, to aid in heat transfer.

Accordingly, the stator assembly 300(a) for a switched reluctance device of the present invention is structured from the plurality of metallic plates 302 including inner portions 304, central portions 305 and peripheral portions 306. The inner portions 304 are defined by the plurality of legs 307, the central portions 305 are defined by the pass-through openings 308 and the peripheral portions 306 are defined by the plurality of radially outward oriented cooling fins 309. The stack 301 of the plurality of metallic plates 302 is formed by integrating the metallic plates 302 through support members 310 that are permitted through the pass-through openings 308 and connected to end flanges 311, where the radially inward oriented legs 307 are integrally disposed to form radially inward oriented stator poles 312. The unitary stator core 303 is formed from the integral combination of the metallic plates 302 with plurality of radially inward oriented stator poles 312 and the plurality of radially outward oriented cooling fins 309.

Hitherto, the preferred embodiments, pertaining to the stator assembly that is formed from multiple metallic plates are to form a unitary stator core are described. Now, yet another aspect of the present invention, the stator assembly 400(a) that is formed from segmented and nested stator poles, which are integrally connected to form a unitary stator core, are described. As shown in FIG.4(a), the metallic plate 402 is advantageously provided with a substantially "T" shape and with a desired thickness. The metallic plate 402 is provided with an inner portion 404, a central portion 405 and a peripheral portion 406. The peripheral portion 406 is advantageously in the shape of circular arc. The central and peripheral portions of the metallic plates are provided with variable dimensions.

A leg 407 is arranged to extend in a radially inward direction from the inner portion 404 of the metallic plate 402. The leg 407 is configured to support an electromagnetic winding. A pass through opening 408 is made in the central portion 405 of the metallic plate 402, which is used to in the formation of the stack assembly 400(a).

Multiple cooling fins 409 are advantageously formed integrally, on the peripheral portion 406 of the metallic plate 402, as shown in FIG.4(a). The cooling fins 409 are formed to project radially outward from the peripheral portion 406. The cooling fins 409 are provided as straight structures that are extending from the peripheral portion 406 of the metallic plate 402. The cooling fins 409 can also be made as structures with configurations, selected from wavy, tapered, curved, herringbone, serrated or trapezoidal configurations. It is also understood here that a suitable combination of any of these configurations can also be suitably adapted for use.

The individual metallic plates 402 are arranged to form segmented stacks 401a, 401b, 401c, 401d, 40 le, 401f, as shown in FIGs.4(b).

The segmented stacks 401a, 401b, 401c, 401d, 401e,

401f, are nested by interlocking the ends of the central 405 and peripheral ends 406 of the adjacent metallic plates 402. As can be particularly seen in FIG.4(b), the adjacent metallic plates 402 are mated where lengthier end 420 of one metallic plate 402 mates with shorter end 421 of the adjacent metallic plates 402, so as to form a nesting of the segmented stacks 401a, 401b, 401c, 401d, 401e, 401f. Accordingly, when a nesting of the segmented stacks 401a, 401b, 401c, 401d, 40le, 401f is performed, the nesting or interlocking zones among the nested segmented stacks 401a, 401b, 401c, 401d, 401e, 401f are preferably maintained offset to each other. The number of segments is preferably maintained same as the number of stator poles. In this arrangement, alternate layers (metallic plates) of stator segment, which fit into the corresponding gap of the next stator segment, form the desired nesting of segments. The adjacent layers (metallic plates) of the segments, join at different points along the stator periphery. This increases the mechanical rigidity of the stator as well reduces vibrations and noise. The nesting arrangement also provides for continuity of magnetic field lines through the metallic plates 402.

In this exemplary aspect as shown in FIG.4(b), a total number of six legs 407 are shown that are extending radially inwards from the central portion 405, from the segmented stacks 401a, 401b, 401c, 401d, 401e, 401f to facilitate the formation of six stator poles 412, as hereinafter described. The total number of legs 407 can be suitably varied, such as 8, 12 etc., depending on the requirement of number of stator poles for the unitary stator core 403.

Once segmented stacks 401a, 401b, 401c, 401d, 401e, 401f are formed, the integrated plurality of legs 407 act as stator poles 412. Suitable electromagnetic windings are provided to the stator poles 412 and are powered accordingly, to generate a magnetic field and a corresponding torque.

[001] An illustration of assembled stator segment 401a with winding is shown in FIG.4(c). In this embodiment of the invention, dense electromagnetic windings 414, which are wound on the stator pole 412 of the stator segment 401a prior to assembly of the unitary stator core 403, are used advantageously to obtain greater utilization of the available space for stator phase winding and thereby increasing the power density of SRD.

[002] In an aspect as shown in FIG.4(d), the six stator segments along with electromagnetic windings 414 are joined together. The nested segmented stacks 401a, 401b, 401c, 401d, 401e, 40 If are also supported by the support members 410, which are permitted in the pass-through openings 408. A pair of end flanges 411 is employed on either side of the stack 401g, to which are the support members 410 are connected. The support members 410 can be studs, rods or any other suitable supporting contraptions. The support members 410 can be welded to the end flanges 411 or can be screwed to the end flanges 411.

Alternately, the nested segmented stacks 401a, 401b, 401c, 401d, 401e, 401f can also be formed by welding the metallic plates 402 together either along with the support members 410 and the end flanges 411 or otherwise.

In a similar way, once the nested and segmented stacks 401a, 401b, 401c, 401d, 401e, 401f are formed and the cooling fins 409 form a cluster of plurality of radially outward cooling fins that are integrally disposed at the peripheral portions of the metallic plates 402.

Therefore, the stator assembly 300a for a switched reluctance device, comprises the plurality of metallic plates 302 with circular profiles, wherein each of the metallic plates 302 is a single piece of metal, including inner 304, central 305 and peripheral portions 306. The inner portions 304 are defined by the plurality of radially inward oriented legs 307, the central portions 305 are disc-shaped with pass-through openings 308 and the peripheral portions 306 are defined by the plurality of radially outward oriented cooling fins 309. The stack 301 of the plurality of the metallic plates 302 is formed by integrating the metallic plates 302 and integrated metallic plates 302 are supported by flanges 311 through the support members 310 that are disposed in the pass-through openings 308, and the radially inward oriented legs 307 of the integrated plates 302 are disposed to form radially inward oriented stator poles 312. The unitary stator core 303 includes the integrated metallic plates 302 with plurality of radially inward oriented stator poles 312 and the plurality of radially outward oriented cooling fins 309.

In yet another aspect of the present invention, the integrated metallic plates 302 are welded to form the stack 301.

In another aspect of the present invention, the plurality of nested stacks 401g including the plurality of segmented stacks 401a, 401b, 401c, 401d, 401e, 401f of the metallic plates 402 with arc-shaped profiles, having inner 404, central 405 and peripheral 406 portions, where the central and the peripheral portions 405, 406 of the metallic plates 402 are with variable lengths. The central and peripheral portions 405, 406 are configured to be interlocked to each other, to form disc-shaped metallic plates 402.

In yet another aspect of the present invention, the cooling fins

409 are configured to be straight, tapered, curved or trapezoidal, herringbone, serrated configurations or a combination thereof.

Now, the preferred embodiments of the rotor assembly 530a of the present invention are described by initially referring to FIG.5. The rotor assembly 530a is the rotating member of a switched reluctance device. The rotor assembly 530a includes a rotatable shaft 531 with terminal ends 535 and 536. These terminal ends are used to connect to a rotor position encoder and driven elements, such as a generator, motor, pump, compressor, pulley etc., that are to be connected to the rotatable shaft 531. A step arrangement is formed on the ends of the rotatable shaft 531 for mounting bushes, bearings etc. A torque member 532 with a unitary structure is integrally formed, preferably in the central portion of the rotatable shaft 531. The rotatable shaft 531 and the torque member 532 are made by any suitable machining of a cylindrical metallic member. The material of the cylindrical metallic member can be a ferromagnetic alloy with high electrical resistivity and suitable as shaft material, for example certain variants of iron- silicon alloys, iron-cobalt alloys and iron-nickel alloys. The torque member 532 is formed to possess a greater diameter than that of the rotatable shaft 531 and is arranged longitudinal to the horizontal axis of the rotatable shaft 531 axis. Therefore, the torque member 532 is thus an extension of the rotatable shaft 531 and is integral to the rotatable shaft member 531.

A plurality of slits 533 are formed on the torque member as shown in FIG.5(a). The slits 533 are formed by any suitable method such as an electrical discharge machining (EDM), laser or etching methods. The slits 533 are provided along a radial plane of the torque member 532. The slits 533 are provided with desired slit pitch, slit width and slit depth profiles, to accommodate airgaps, as shown in FIGs.6(a) and FIG.6(b). The rotor 530a with integrally formed slits 533 in the torque member 532, has the advantage of much lower degradation in performance with increase in shaft temperature than any comparable and known rotor. The slits 533 prevent flow of undesirable eddy currents along the length of the torque member 532 and consequentially reduce iron loss in the rotor torque member 532, reduce temperature rise of the rotor 530a and improve efficiency of the SRD. The dimensions of slit pitch, slit width and slit depth and their profiles can be advantageously arranged to achieve low magnetic loss in the torque member 532, low temperature rise, superior structural integrity and higher critical speeds of the rotor. A plurality of longitudinal intervening spaces 534 are formed along the longitudinal axis of the torque member 532. These longitudinal intervening spaces 534 form radial divisions in the torque member 532, as shown in FIG.5. These radial divisions act as rotor poles 538. Accordingly, in the rotor assembly 530a, there are 4 rotor poles, forming a 4 rotor pole and 6 stator pole switched reluctance device in conjunction with the 6 stator poles of the stator assembly 300a. Therefore, when the rotor assembly 500a is used in conjunction with the stator assembly 300a, in a power mode, functional scenarios of alignment of stator poles 312 or 412 and rotor poles 538 and unalignment of the stator poles 312 or 412 and rotor poles 538 do occur. In the aligned positions, the stator poles 312 or 412 and rotor poles 538 are aligned and face each other and whereas in unaligned positions, the stator poles 312 or 412 face the intervening spaces 534. Such scenarios result in the difference in inductance values of an individual stator winding 314, thereby generating a reluctance torque when the stator winding 314 is suitably excited in synchronism with rotor 530a position that rotates the rotatable shaft 531 of the rotor assembly 530a.

The torque member 532 and the rotatable shaft 531 are integrated to form a single continuous structure and the integrated structure is formed advantageously from a single piece of material, where the material is preferably a ferromagnetic alloy. Therefore, the rotor assembly 530a is a non-laminated structure. The integrated solid structure of the torque member 532 and the rotatable shaft 531 imparts a high mechanical rigidity and higher critical speed to the SRD. A higher critical speed enables stable operation of the SRD at higher shaft speeds. The integrated structure of torque member 532 and rotatable shaft 531 also avoids internal thermally induced stresses in the rotor assembly 530a which is possible otherwise in known rotor with separate shaft and lamination stack. The integral structure prevents deformation due to thermal stress and leads to uniform thermal expansion ensuring smooth operation even at high temperatures.

In yet another exemplary aspect of the present invention, a rotor assembly 530b, with an alternative geometry is as shown in FIG.7. In this exemplary arrangement the profiles of the rotor poles 538 are provided with curved configuration. The sides of the rotor pole 538 towards the intervening space 534 are curved. The curved structure distributes the centrifugal force and the resulting stress on the torque member 532 more evenly than straight structure. Lowering of stress is advantageous at high shaft speed and increases the margin between operating speed and rotor mechanical failure speed. Additionally, it also permits higher diameter of the torque member 532 keeping the stress levels same at the same operating speed. Higher diameter produces higher torque on the torque member 532 and hence higher torque is obtained, and output power of the SRD is increased. Thus, the curved configuration of the rotor poles 538 and the intervening space 534 helps in reducing the centrifugal stress on the rotor assembly 530b thereby facilitating the use of the rotor assembly in high speed SRD.

In yet another exemplary aspect of the present invention, a rotor assembly 530c, with an alternative geometry is as shown in FIG.8. In this exemplary arrangement the torque member 532 is provided with a smooth surface and a round profile. The intervening space 534 is formed by removing material from the two ends of the torque member 532. The rotor poles 538 are therefore joined by thin metallic structure at outer periphery. The smooth surface of the outer periphery of the torque member 532 is advantageous to reduce aerodynamic losses. The air drag offered by the smooth cylindrical rotor torque member 532 is lower than when it has non-smooth projecting rotor poles 538. This reduces overall mechanical loss in the SRD, particularly at high speed where aerodynamic losses can be predominant and improves efficiency of the SRD. The acoustic noise due to air drag of smooth rotor poles 538 is also significantly lower compared to non-smooth variant of rotor pole 538.

In yet another exemplary aspect of the present invention, a rotor assembly 530d, wherein a rotor sleeve 540 is utilized to obtain a smooth and round profile of the torque member 532, is shown in FIG.8(b) . The rotor sleeve 540 can be a metal pipe of materials such as steel or Inconel or alternately composite material such as carbon fibre or glass fibre composite. The sleeve 540 is inserted by means of shrink fitting or press fitting or any other suitable means over the rotor poles 538, to form a smooth and round surface. This advantageously reduces drag and acoustic noise. The sleeve 540 also serves to hold the rotor torque member 532 together in the presence of high centrifugal forces at high speeds. The sleeve 540 can have higher yield strength than the torque member 532, and thereby enable operation with higher centrifugal load at higher shaft speed than otherwise possible.

In yet another exemplary aspect of the present invention, a rotor assembly 530e, with the intervening space 534 and slit 533 filled with a filling material is as shown in FIG.8(c). This also results in smooth and round shape of the torque member 532 thereby reducing aerodynamic loss and acoustic noise. The filler material can be epoxy or polyset resin or urethane moulding. Optionally only the intervening space 534 can be filled, while the slits 533 can remain unfilled.

In yet another exemplary aspect of the present invention, a rotor assembly 530f, with an alternative geometry is as shown in FIG.9. In this exemplary arrangement the torque member 532 is provided with a combination of slit 533 and solid 539 profiles. Part of the torque member along axial direction has slits 533 provided into them. This part of the shaft has lower iron loss, but also lower rigidity. On the other remaining part of the torque member 532, no slits are provided, and referred hereinafter as solid portion 539. The solid portion 539 increases the rigidity and tends to increase the critical speed of the rotor. Thus, the combination of solid and slit portion can be used advantageously to obtain desired trade-off between critical speed and rotor iron loss.

Now the preferred embodiments of the slit profiles of the torque member of the rotor assembly, with varying depth and configurations, are described by referring to FIGs.10(a) to 10(i). The required mechanical and electrical characteristics such as aerodynamic loss, natural frequency of the rotor, iron loss, torque capability of the rotor assembly of the present invention can be suitably varied by providing a suitable slit profile characteristics.

As shown in FIG.10(a), the slits 533b of the torque member can be cut with deeper profiles so as to reduce electromagnetic loss.

The slit profile 533c of the torque member as shown in FIG.10(b), is provided with a shallower profile as compared to the profile as shown in FIG.10(a). The rotor assembly with this slit profile exhibits a higher mechanical strength.

The rotor assembly can also be provided with a combination of deeper and shallow slit profiles 533d for the torque member, as shown in FIG.10(c) and FIG.10(d).

In yet another aspect of the present invention, the torque member of the rotor assembly is provided with a slit profile 533e having a varying depth along the axial direction of the torque member, as shown in FIG.10(e). In a further aspect of the present invention, the width of the slit profile 533f of the torque member is varied with varying depth, so as to form a trapezoidal configuration as shown in FIG.10(f). Accordingly, the slit profile of the torque member, with varying width provide a varying cross section for the magnetic flux resulting in varying electromagnetic performance. Particularly, the rotor iron loss distribution can be suitably varied.

In yet another aspect of the present invention as shown in FIG.10(g), the torque member of the rotor assembly is provided with a slit profile 533g, where the slits are formed perpendicular to the axis of the rotatable shaft.

In a further aspect of the present invention, as shown in FIG.10(h), the torque member of the rotor assembly is provided with a slit profile 533h, where the slits are provided with angular configuration.

In a further aspect of the present invention, as shown in FIG.lO(i), the torque member of the rotor assembly is provided with a slit profile 533i, where the slits are provided with angular configuration, where the slit angle is varied along the axial length of the slit. In this exemplary embodiment the slits are configured to have alternate slit angles.

Therefore, the rotor assembly 530a for a switched reluctance device, comprises the torque member 532 with the unitary structure, which is integrally connected to a rotatable shaft 531. The torque member 532 is defined by rotor poles 538 with slits 533 that are disposed along a radial plane of the rotatable shaft 531. Each of the rotor poles 538 is disposed with radially separated intervening spaces 534.

In yet another aspect of the present invention, the insulating material is disposed in the radially separated intervening spaces 534. In a further aspect of the present invention, the radially separated intervening spaces 534 are disposed inside the torque member.

In yet another aspect of the present invention, the torque member 532 is defined by an integral structure of solid 539 and slit rotor poles 538.

It is also an aspect of the present invention, where the slits of the torque member 532 are with deep profiles 533b, shallow profiles 533c or a combination 533d thereof, along the axial direction of the torque member 532.

In a further aspect of the present invention, the vertical width of the slit profile 533f of the torque member 532 is variable.

In yet another aspect of the present invention, the configuration of the slit profile 533g of the torque member 532, is perpendicular to the axis of the rotatable shaft 531.

In another aspect of the present invention, the slit profile 533h of the torque member 532, is angular with a uniform slit angles, along the axial length of the rotatable shaft 531.

In yet another aspect of the present invention, the slit profile 533i of the torque member 532 is angular with variable slit angles along the axial length of the rotatable shaft 531.

The preferred embodiments of an exemplary switched reluctance device 650, that is incorporated with the stator assembly 600 with stator windings 614 and rotor assembly 630b of the present invention, are described by referring to FIGs.11(a)- (d). The switched reluctance device (SRD) 650, of the present invention, which is exemplarily shown in FIG.11(a), can operate both in generating mode and motoring mode and the shaft can rotate in both clockwise or counter-clockwise direction, which is also known as four-quadrant operation in the art. The SRD 650 is preferably in three phase. However, it is understood here that the SRD 650 may be other than a three phase SRD. Broadly stated, the SRD 650 basically comprises a housing member (not shown in the figures), in which the integrated stator 600 and a rotor 630b assemblies are arranged. The housing member generally includes a cooling fan.

As shown in FIG.11(a), the stator assembly 600, of the present invention is connected to a bearing housing 651, through the end flanges 611 of the stator assembly 600. The end flanges 611 and the bearing housing 651 are joined using bolts 653 arranged in circular fashion around the bearing housing 651 and end flanges 611. In this embodiment, bearings 652 are inserted in the bearing housing 651 and on the side not facing the stator assembly 600. The bearing housing holds the bearings 652 firmly in place, which in turn holds the rotor 630b in place allowing for only rotational motion of the rotor 630b and forming a small airgap 637 in between the stator poles 612 and the rotor poles 638.

One end of the rotatable shaft 636 of the rotor 630b can be connected to another driven shaft using a suitable coupling mechanism such as spline, shrink fit, keyway or other such techniques. In this exemplary embodiment, a spline is used at the shaft end 636 for connecting to another driven shaft. The other end of the shaft 635 is connected to the rotor portion of the encoder assembly 654a.

The rotor rotor portion of encoder assembly 654a includes a non-magnetic spacer 655, which is connected to the rotatable shaft 631 using a bolt 656 centrally placed on the shaft 631. A magnet holder 657 is placed inside the non-magnetic spacer 655 using press-fit, push fit, glue or any other similar means. A position sensing permanent magnet 658 is placed inside the magnet holder 657 using glue, push fit or any other suitable means. The magnet holder 657 is also non-magnetic. The non magnetic nature of the spacer 656 and that of the magnet holder

657 ensure that the magnetic field of the position sensing magnet

658 neither distorts nor is distorted by the magnetic field of the rotor assembly 630b.

The stator portion of the encoder assembly 659a is provided with a sensing element 664 connected to a printed circuit board (PCB) 660 to obtain the orientation of the permanent magnet 658 mounted on the magnet holder 657 and placed centrally on the rotor 630b. The PCB 660 is connected to a PCB flange 661 using a suitable support structure 662 such as studs. The PCB flange 660 in turn is supported by the bearing housing 651 by means of another set of studs 663.

Thus, the SRD assembly 650 includes an integrated rotor position encoder, which comprises a rotor portion 654a and a stator portion 659a, while referring to FIG.11(a). A close-up view of the encoder is shown in FIG.11(b).

The exemplary rotor position encoder has a sensing element 664 that is connected to the bearing housing 651, using supporting structures, and a rotatable magnet element 658 connected to the rotor assembly 630b. The rotor position is obtained by sensing the orientation of the magnet 658 with respect to the sensor 664. The sensing element 664 and the magnet element 658 are both integral part of the SRD, thus external position sensing encoder is not required, and consequently, a pair of bearings and an extra coupler for the external rotor position encoder are also not required, reducing system cost and enabling high speed operation. In known position encoder high speed operation is constrained due to these additional bearings and coupler arrangement. A close-up view of the encoder is shown in FIG.11(b). A cross-sectional view of the SRD 650 showing the stator assembly 600 with integral cooling fins 609 and the rotor 630b is shown in FIG.11(c). The metallic plates of the stator stack 602 with integrated cooling fins 609 are advantageously used to achieve better cooling of the stator assembly 600 which includes the electromagnetic winding 614. A slot insulation 665 is provided in between the metallic plates 602 and the winding 614. The slot insulation 665 protects the winding from being electrically connected to the metallic plate 602. Winding retainers 615 are inserted in between the stator poles 612 to hold the windings 614 in place. The rotor assembly 630b is placed centrally on the stator assembly 600 with a small air gap 637. The rotor 630b is held in place by the bearings 652, which are housed in the bearing housing 651, as indicated earlier.

A detailed and exploded view of the rotor 630b connected to the rotor portion of the position encoder 654a is shown in FIG.11(d). As described earlier, the position sensing permanent magnet 658 is held centrally to the shaft 631, while separating its magnetic field from that of the rotor assembly 630b.

Another configuration of the rotor portion of the position encoder 654b is shown in FIG.12(a)-(b). In this configuration, first the non-magnetic spacer 655 is joined centrally to the shaft 631 using bolt 656. Then the magnet holder 657 is inserted centrally to the non-magnetic spacer 655 and held in place using multiple grub screws 666. The grub screws 666 are placed symmetrically about the axis to minimize rotor unbalance. Then the magnet 658 is inserted centrally into a slot in the magnet holder 657. Another magnet retention plate 667 is connected to the top of the magnet to hold the magnet in place. The retention plate 667 and magnet holder 658 are joined together by welding around the periphery of the retention plate. In this configuration, the grub screws 666 hold the magnet holder 657 securely and prevent it from popping out even at high speeds. Similarly, the magnet retention plate 667 holds the magnet 658 securely in place and prevents it from detachment or any misalignment even at high speeds.

Another configuration of the stator portion of the position encoder 659b is shown in FIG.12(c). In this alternate configuration the encoder PCB 660 is mounted using supporting studs 662 to PCB flange 661. The flange 661 is welded to a threaded rod 668. The threaded rod 668 allows for fine adjustment of axial position of the encoder PCB 660, to take care of final assembly tolerances between the sensing element 664 and the position sensing magnet 658, which is on the rotor portion of the position encoder assembly 654. This fine adjustment ensures proper spacing between sensing element 664 and the sensing magnet 658 required for correct measurement of rotor position. The aforementioned threaded rod 668 is connected to a jack-nut 669. The jack-nut 669 is in turn is connected to encoder cover 670 through steel balls 671 and O-ring 672. Finally, the encoder cover 670 is attached to the bearing housing 651 of the exemplary switched reluctance device 600. The jack nut is compressed against the steel balls 671 and the O-ring 672 by means of a jack- nut retention plate 673, which in turn is held in place by bolt 674. The jack-nut 669 can be rotated with respect to encoder cover 670, due to presence of steel balls 671. This moves the threaded rod 668 axially, without any rotation. In this manner fine adjustment of axial motion of the encoder sensing element 664 is possible. Optionally a protective acrylic cover 675 can be provided. This configuration ensures proper orientation of the sensing element 664 with respect to the sensing magnet 658. Combination of the rotor portion of the position encoder 654b and stator portion of the position encoder 659b enables precise measurement of rotor position with low distortion and good accuracy and linearity even at high rotor speeds.

Therefore, the switched reluctance device (SRD) 650, comprises the stator assembly 600 including the plurality of metallic plates with circular profiles, wherein each of the metallic plates is a single piece of metal, including inner, central and peripheral portions. The inner portions are defined by a plurality of radially inward oriented legs, the central portions are disc-shaped with pass-through openings 608 and the peripheral portions are defined by a plurality of radially outward oriented cooling fins 609. The stack of the plurality metallic plates is formed by integrating the metallic plates and integrated metallic plates are supported by flanges 611 through the support members 610 that are disposed in the pass-through openings 608, and the radially inward oriented legs of the integrated plates are disposed to form radially inward oriented stator poles 612. The unitary stator core includes the integrated metallic plates having a plurality of radially inward oriented stator poles and the plurality of radially outward oriented cooling fins. Whereas the rotor assembly 630b includes the torque member 632 with a unitary structure, which is integrally connected to the rotatable shaft 631. The torque member 632 is defined by rotor poles 638 with slits 633 that are disposed along a radial plane of the rotatable shaft 631. Each of the rotor poles 638 is disposed with radially separated intervening spaces. The position encoder with rotor 654a and stator portions 659a, is connected to the rotatable shaft 631 and the bearing housing 651 with bearings 652.

In yet another aspect of the present invention, the stator assembly 600 of the switched reluctance machine 650 includes a plurality of nested and segmented stacks of the metallic plates with arc-shaped profiles including inner, central and peripheral portions, the central and the peripheral portions of the metallic plates are with variable lengths. The central and peripheral portions are configured to be interlocked to each other, to form disc-shaped metallic plates.

In yet another aspect of the present invention, the stator assembly 600 of the switched reluctance machine 650 includes the integrated metallic plates that are welded to form the stacks

In further aspect of the present invention, the stator assembly 600 of the switched reluctance machine 650, the radially outward oriented cooling fins are configured to be straight, tapered, curved trapezoidal, herringbone, serrated configurations or a combination thereof.

In further aspect of the present invention, the insulating material is disposed in the radially separated intervening spaces of the torque member 632 of the rotor assembly 630b, of the switched reluctance machine 650.

In a further aspect of the present invention, the radially separated intervening spaces are disposed inside the torque member 632 of the rotor assembly 630b, of the switched reluctance machine 650.

In yet another aspect of the present invention, the torque member 632 of the rotor assembly, of the switched reluctance machine 650, is defined by an integral structure of solid and slit rotor poles.

In a further aspect of the present invention, the slits of the torque member 632 are with deep profiles, shallow profiles or a combination thereof, along the axial direction of the torque member 532, of the switched reluctance machine 650. In yet another aspect of the present invention, the vertical width of the slit profile is variable of the torque member 532 of the switched reluctance machine 650.

In a further aspect of the present invention, the configuration of the slit profile of the torque member 532 of the switched reluctance machine 650, is perpendicular to the axis of the rotatable shaft 631.

In still another aspect of the present invention, the slit profile of the torque member 532 of the switched reluctance machine 650, is angular with uniform slit angles, along the axial length of the rotatable shaft 631.

In yet another aspect of the present invention, the slit profile the slit profile of the torque member 532 of the switched reluctance machine 650, is angular with variable slit angles along the axial length of the rotatable shaft 631.

Advantages of the present invention

[003] The SRD of the present invention, where the rotor (slit rotor or combination of solid and slit rotor) and the rotatable shaft are made of a continuous single material, has a higher rotor stiffness as compared to an SRD where shaft and laminated rotor are separately constructed. Accordingly, deformation of the rotatable shaft in the SRD of the present invention is minimal, and the desired critical speed of the rotor is higher.

[004] The slit rotor or the combination of the solid and slit rotor assembly of the present invention while used in SRDs with high critical speed, provide better damping characteristics as compared to a laminated rotor. Further, since the rotatable shaft also carries magnetic flux, rotor dimensions can be smaller for same rated power, thereby reducing bearing loss, windage loss and inertia. [005] An insulation that is provided in between the laminated sheets in laminated rotor (known rotors), limits working temperature of the rotor. The laminates are typically glued or shrunk-fit to the shaft in known laminated SRD rotors. However, glues tend to be unsuitable for high temperature application.

Whereas, the slit rotor or the combination of the solid and slit rotor of the SRD of the present invention, is suitable for higher temperature applications.

[006] The manufacture of the slit rotor or the combination of the solid and slit rotor of the SRD of the present invention is much easier than a laminated rotor.

[007] Iron loss in the slit rotor or the combination of the solid and slit rotor is reckoned higher than the laminated rotor. However, cooling is better in slit rotor or the combination of the solid and slit rotor as thermal resistance between shaft and lamination is avoided. In addition, since the axial heat flow is better in the slit rotor or the combination of the solid and slit rotor, the temperature rise is lower compared to an existing laminated rotor.

[008] The rotor with slits of the SRD of the present invention demonstrates lower losses than the solid rotor, and it is electromagnetically close to laminated rotor, but avoids need of insulating material and shrink fitting/gluing of the lamination to the shaft.

[009] The integrated cooling fins of the stator of the SRD of the present invention, are integral part of the stator lamination, thereby avoiding contact resistance between the stator yoke and the external cooling fins, resulting in improved cooling efficiency. The integrated cooling fins can be adapted for use with variable geometries and in different sizes yielding further improvement. [010] The segmented and nested stator of the SRD of the present invention, has reduced manufacturing cost due to its modularity. In the segmented and nested stator of the present invention coil winding is easier and the available space between the stator poles is utilized better. In view of this arrangement it is possible to have a winding with a denser and trapezoidal configuration leading to higher power density of the SRD.

[Oil] Nested and segmented stator has higher mechanical rigidity and lower acoustic noise as compared to only segmented stator.

[012] In the SRD of the present invention, a position encoder is integrated, thereby avoiding additional bearing and coupling. The shaft extension for the encoder is smaller and provides a correct alignment. The permanent magnet on the shaft is held in position while leaving its magnetic field undistorted. Since, the shaft for the encoder and the rotor is same, there is no slip between encoder shaft and rotor shaft. The position encoder of the SRD is suitable for higher speeds.

Claims

We claim:

1. A stator assembly 300a for a switched reluctance device, comprising :

a plurality of metallic plates 302 with circular profiles, wherein each of the metallic plates 302 is a single piece of metal, including inner 304, central 305 and peripheral portions 306;

the inner portions 304 are defined by a plurality of radially inward oriented legs 307, the central portions 305 are disc-shaped with pass-through openings 308 and the peripheral portions 306 are defined by a plurality of radially outward oriented cooling fins 309;

a stack 301 of the plurality of the metallic plates 302 is formed by integrating the metallic plates 302 and integrated metallic plates 302 are supported by flanges 311 through the support members 310 that are disposed in the pass-through openings 308, and the radially inward oriented legs 307 of the integrated plates 302 are disposed to form radially inward oriented stator poles 312; and

a unitary stator core 303 including the integrated metallic plates 302 with plurality of radially inward oriented stator poles 312 and the plurality of radially outward oriented cooling fins 309.

2. The stator assembly 300 as claimed in claim 1, wherein the integrated metallic plates 302 are welded to form the stack

301.

3. The stator assembly 300 as claimed in claim 1, wherein

- a plurality of nested stacks 401g including a plurality of segmented stacks 401a, 401b, 401c, 401d, 40 le, 401f of the metallic plates 402 with arc-shaped profiles including inner 404, central 405 and peripheral 406 portions, the central and the peripheral portions 405, 406 of the metallic plates 402 are with variable lengths; and the central and peripheral portions 405, 406 are configured to be interlocked to each other, to form disc-shaped metallic plates 402.

4. The stator assembly 300 as claimed in claim 1, wherein the cooling fins 409 are configured to be straight, tapered, curved or trapezoidal, herringbone, serrated configurations or a combination thereof.

5. A rotor assembly 530a for a switched reluctance device, comprising :

a torque member 532 with a unitary structure, is integrally connected to a rotatable shaft 531; the torque member 532 is defined by rotor poles 538 with slits 533 that are disposed along a radial plane of the rotatable shaft 531; and each of the rotor poles 538 is disposed with radially separated intervening spaces 534.

6. The rotor assembly 530a as claimed in claim 5, wherein an insulating material is disposed in the radially separated intervening spaces 534.

7. The rotor assembly 530a as claimed in claim 5, wherein the radially separated intervening spaces 534 are disposed inside the torque member.

8. The rotor assembly 530a as claimed in claim 5, wherein the torque member 532 is defined by an integral structure of solid 539 and slit rotor poles 538.

9. The rotor assembly 530a as claimed in claim 5, wherein the slits of the torque member 532 are with deep profiles 533b, shallow profiles 533c or a combination 533d thereof, along the axial direction of the torque member 532.

10. The rotor assembly 530a as claimed in claim 5, wherein the vertical width of the slit profile 533f of the torque member 532 is variable.

11. The rotor assembly 530a as claimed in claim 5, wherein the configuration of the slit profile 533g of the torque member 532, is perpendicular to the axis of the rotatable shaft 531.

12. The rotor assembly 530a as claimed in claim 5, wherein the slit profile 533h of the torque member 532, is angular with a uniform slit angles, along the axial length of the rotatable shaft 531.

13. The rotor assembly 530a as claimed in claim 5, wherein the slit profile 533i of the torque member 532 is angular with variable slit angles along the axial length of the rotatable shaft

531.

14. A switched reluctance device (SRD) 650, comprising :

a stator assembly 600 including a plurality of metallic plates with circular profiles, wherein each of the metallic plates is a single piece of metal, including inner, central and peripheral portions; the inner portions are defined by a plurality of radially inward oriented legs, the central portions are disc-shaped with pass-through openings 608 and the peripheral portions are defined by a plurality of radially outward oriented cooling fins 609; a stack of the plurality metallic plates is formed by integrating the metallic plates and integrated metallic plates are supported by flanges 611 through the support members 610 that are disposed in the pass-through openings 608, and the radially inward oriented legs of the integrated plates are disposed to form radially inward oriented stator poles 612; and a unitary stator core including the integrated metallic plates with plurality of radially inward oriented stator poles and the plurality of radially outward oriented cooling fins;

a rotor assembly 630b including a torque member 632 with a unitary structure, is integrally connected to a rotatable shaft 631; the torque member 632 is defined by rotor poles 638 with slits 633 that are disposed along a radial plane of the rotatable shaft 631; and each of the rotor poles 638 is disposed with radially separated intervening spaces; and

- a position encoder with rotor 654a and stator portions

659a, is connected to the rotatable shaft 631 and a bearing housing 651 with bearings 652.

15. The switched reluctance machine 650 as claimed in claim 14, wherein the stator assembly 600 includes a plurality of nested and segmented stacks of the metallic plates with arc-shaped profiles including inner, central and peripheral portions, the central and the peripheral portions of the metallic plates are with variable lengths; and the central and peripheral portions are configured to be interlocked to each other, to form disc- shaped metallic plates.

16. The switched reluctance machine 650 as claimed in claim 14, wherein the integrated metallic plates of the stator assembly 600 are welded to form the stacks.

17. The switched reluctance machine 650 as claimed in claim 14, wherein the radially outward oriented cooling fins of the stator assembly 600 are configured to be straight, tapered, curved trapezoidal, herringbone, serrated configurations or a combination thereof.

18. The switched reluctance machine 650 as claimed in claim 14, wherein an insulating material is disposed in the radially separated intervening spaces of the torque member 632 of the rotor assembly 630b.

19. The switched reluctance machine 650 as claimed in claim 14, wherein the radially separated intervening spaces are disposed inside the torque member 632 of the rotor assembly 630b.

20. The switched reluctance machine 650 as claimed in claim 14, wherein the torque member 632 of the rotor assembly is defined by an integral structure of solid and slit rotor poles.

21. The rotor assembly as claimed in claim 14, wherein the slits of the torque member 632 are with deep profiles, shallow profiles or a combination thereof, along the axial direction of the torque member 532.

22. The rotor assembly as claimed in claim 14, wherein the vertical width of the slit profile is variable.

23. The rotor assembly as claimed in claim 14, wherein the configuration of the slit profile is perpendicular to the axis of the rotatable shaft 631.

24. The rotor assembly as claimed in claim 14, wherein the slit profile is angular with uniform slit angles, along the axial length of the rotatable shaft 631.

25. The rotor assembly as claimed in claim 14, wherein the slit profile is angular with variable slit angles along the axial length of the rotatable shaft 631.