Title of Invention

SENSORLESS SWITCHED RELUCTANCE ELECTRIC MACHINE WITH SEGMENTED STATOR

Abstract

A sensorless switched reluctance electric machine (12) comprising: A stator (114) having a plurality of circumferentially-spaced stator segment assemblies (113) that comprise a stator segment core (120) and winding wire (124) that is precisely wound around individual ones of said stator segment core (120) to provide substantially uniform inductance and resistance characteristics, wherein said windings define a slot fill that is greater than 65%; a rotor (116) defining a plurality of rotor poles (156), wherein said rotor tends to rotate relative to said stator to maximize the inductance of an energized winding; characterized in that a sensorless drive circuit (10) that derives rotor position based on parameters that vary with at least one of said substantially uniform inductance and resistance characteristics of said stator segment assemblies and that energizes said winding wire around said stator segment assemblies to control operation of said switched reluctance machine based on said derived position of said rotor.

Full Text

FIELD OF THE INVENTION [0001] This invention relates to electric machines and, more particularly to sensorless switched reluctance electric machines including segmented staters. BACKGROUND OF THE INVENTION [0002] Reluctance electric machines, such as motors and generators, typically include a stator that is mounted inside a machine housing and a rotor that is supported for rotation relative to the stator. Reluctance electric machines produce torque as a result of the rotor tending to rotate to a position that minimizes the reluctance (or maximizes the inductance) of the magnetic circuit The reluctance is minimized (and the inductance is maximized) when the salient rotor poles are aligned with the energized salient stator poles. A drive circuit generates a set of stator winding currents that are output to the stator pole windings and that create a magnetic field. The rotor rotates in response to the magnetic field. In synchronous reluctance electric machines, the windings are energized at a controlled frequency. In switched reluctance electric machines, the drive circuit and/or transducers detect the angular position of the rotor. The drive circuit energizes the stator windings as a function of the sensed rotor position. The design and operation of switched reluctance electric machines is known in the art and is discussed in T.J.E. Miller, "Switched Reluctance Motors and Their Control", Magna Physics Publishing and Clarendon Press, Oxford, 1993, which is hereby incorporated by reference. [0003] Conventional switched reluctance electric machines generally include a stator with a sold stator core or a laminated stator. The laminated stator includes a plurality of circular stator plates that are punched from a magnetically conducting material. The stator includes pairs of diametrically opposed stator poles that project radially inward. The rotor also includes pairs of diametrically opposed rotor poles. Windings or coils are typically disposed about the stator poles. The windings that are wound around any two diametrically opposed stator poles are connected in series or in parallel to define a machine phase or a phase coil. [0004] By passing current through the phase coil, magnetic fields are established about the stator poles and torque is produced as the energized phase ooil attracts a pair of rotor poles into alignment. The current in the phase coils to generated in a predetermined sequence to create the magnetic field that produce continuos rotating torque on the to the phase coil is known as the active stage. At a predermined point, either as the rotor poles become aligned with the stator poles or el sons point prior thereto, the current in the phase coil is commulated to prevent braking torque from acting on the rotor poles. Ones the commutation point is reached, the oorrent is switched to another phase col. During the inactive stage, the current is slowed to classipate from the phase coil. [0005] In order to maintain torque on the rotor, it is important to maintain the Proper relationship between the possition of the rotor and the active stage of each machine phase.If the active is initialed and/or commmulated early or too late with respect to the position of the rotor, the torque on to rotor will vary and/or fee machine will not operate at optimum efficiency. [0006] The drive circuits of conventtonai switched reluctants electric machine control the current in the phase cob. The drive circuits maintain the proper relationship between the active stage of the machine phases and the position of the rotor by continously sensing rotor position. There are two distinct appreance for detecting the angular position of the rotor, In a "sansar" approach, an external physical sensor senses the angular position of the rotor. For example, a rotor position transducer (RPT) with a half effect sensor or an optical sensor physically sense the angular position of the rotor. In a "sensorless"approach,electronics that are associated with the drive circut derive the angular rotor position without an externed physical sensor. [0007] Them are many problems that are associated won switched relutance electric machines that employ the sensed approach. The RPT typically includes a sensor board with one or mors sensors and a shuttre that is coupled to and rotates with the shaft of the rotor. The shutter includes a plurality of shutter teeth that pass through optical sensors as the rotor rotates- Becauae the angular rotor position is critical to proper operation, sophisticated alignment ensure that the sensor board of the RPT is properly positioned with respect to the housing and the stator. Missalignment of the sensor board la (mown to degrade the performance of the electric machine. Unfortunately, utilization of these complex alignment techniques increases the manufacturing costs for switched reluctance eiectric machines equipped wtth RPTs. [0008] The RPTs also increase the overall size of the switched reluctance electric machine, which can adversely impact machine and product packaging requirements. The coats of the RPTs often place switched reluctance electric machines at a competitive disadvantage in applications that are suitable for open loop induction motors that do not require RPTs. Another drawback with RPTs Invokes field servicing of the switched reluctance electric machines. Specifically wear elements, such as me bearings, that are located within the enclosed rotor housing may need to be repaired or replaced To reach the wear oiornsnts. an end shield must be removed from the housing. Because alignment of the sensor board is critical, replacement of the end shield often requires the use of complex realignment techniques.When the aliognment techniques are improperly performed by the technician. the sensor board is misaligned and the motor's performence is adversely impacted. [0008] Various methods for dkepensty with the RPT have been proposed. several of these are reviewed in "Seneorless Methods for Determining the Rotor Position of Switched Reluctance Motors" by W F %Ray and IH Al Bahadly, published in the proceeding of The European Power Electronics Conferance, Brighton,UK, 13-16 Sep 1993. VbL 6, pp 7-13, hereby incorporated by reference. Many of these methods propoeed for toe rotor position estimation use the measurement of phase flux-inkage (i.e. the integral of applied voltage with respect to time) and current in one or more phasee. Position is calculated using knowledge of the variation in inductance of Ihe machine as a function of angle and currant The storage of this data Involves the use of a large memory array and/or additional system overheads for interpolation of data between stored points. [0010] In U. S. Patent Nos. 6.777,416 to Kolomeitsev, 6,011,368 to Katoatol et at, and 6.107.772 to Uu et at, which are Incorporated by reference, a drive circuit measures the dee time of current in a ststor wincing between two predetermined current levels. The drive circuit calculates the inductance of the phase col from the current dee time. The drive oka* estimates toe angular position of the rotor from the inductaanc of the phase coil.The drive circuit adjusts the active stage of the phase art based on the rotor position. OS. Pat Noc 5,962,117 to Taylor et at. and 5383.485 to MeWhom, which are incorporated by reference, likewise monitor current in unenergtod windings to determine the inductance of the phase coil and toe position of the rotor. In U.S. Pat No. 4.772,839 to MacMinn, which is incorporated by reference, a drive circuit simultaneously measures changes in the currant in two unwonted phases. The drive circuit derives rotor position estimates for each phase and combines the rotor position estimates into a combined (0011] Some methods make use of this data at low speeds where "choping"current control is the dominant control strategy for varying the developed torque. These methods usually employ diagnontic. productive phases (i.e. those phases which are not energized directly from the power supply at a particular moment). A method suited to low-speed operation to proposed by N M Mvungr and J M tephenson in 'Accurate Sensorless Rotor Position Detection in a S R Motor", published in Proceeding of the European Power Eectronics Conference, Frenze. Itely. 1991, Vol. 1, pp 390-393, which is hereby incorporated by reference. [0012] In U.S. Pat No. 4,959,596 to MacMinn, at al., which is incorporated by reference, a drive circuit employs a phase inductanee sensing technique to indirectly estimate rotor position. Voltage sensing pulses are output to an unexcited phase. The voltage sensing pulses cause a change in phase current that inversely proportional to the instantanneous phase inductance. Cornmutation time is determined by comprising the change in phase current to a threshold current U.S. Patent No. 5V589.518 to Vilunic which is incorporated by reference, also discloses a drive circuit that employs diagnostic pulses. [0013] Other methods employ the 'singls-pulse" mode of energization at higher speeds. The current and inductance waveforms, over a phase inductance period, are morror ikages of the monitoring waveforms.These methods monitor me operating voltages and currants of an active phase without interfering with normal operation. A typical higher speed method to desribed in OS. Patent No. 5,173,650 to Hedlund,which is hereby incorporated by referance . [0014] Both the chopping and single-pulse modes described above are normally used whan the converter apptfee a feed value of supply voltage to the phase windings. A further control strategy is the pulse width modulated (PWM) mods, where one or more switches are switched rapidly to effectively produce a supply vottage that is proportional to the duty cycle of me PWM waveform. This allows the use of single-pulse current waveforms at much lower speeds than would be possible on the full supply voltage. The current waveform is made up of a large number of segments, carrespondng to the current carried by the switches and diodes respectfully. [0015] Having to store a two-dimensional array of machine data in order to operate without a position sensor is an obvious disadvantage. Alternative methods have been proposed, which avoid the need for the majority of angularly referenced information and instead store data at one angle only. One such method described in U.S. Patent No. 5,467,025 to Ray which is hereby incorporated by reference. This method senses the phase flux-linkage and currents a predefined angle by adjusting the diagnostic point via the calculated deviation away from a desired point Two one- dimentional tables are stored in the preferred embodiment, one of flux-linkage versus current at a referenced rotor angle and another of the deferential of flux- Iinkage with respect to rotor angle versus current By monitoring phase voltage and current, the deviation away from a predicted angle can be assessed, with the aid of the look-up tables. and system operation can be adjusted accordingly. However, such methods, although reducing the amount of information which has to be stored, still have to detect or compute the flux-limkage at a specific rotor angle and may be sensitive to repeatability or manufacturing tolerances to the machine. t [0016] A similar approach is disclosed in U.S. Patent No. 5,793,179 to Watkins, hereby incorported by reference, where the arrival of the rotor at the peak of the inductance profile is predicted and the system is then put into a freewheeling mode, during which the gradient of the current is measured. While this method works well in the absence of noise, it is not robust enough to disregard false readings produced by noise. Though the current waveform may be relatively immune to induced noise, a drive that uses a PWM voltage supply generates a noisy current waveform. The method disclosed by Watkins '179 also must be used with a converter circuit that is capable of freewheeling. [0017] Other attempts to overcome these deficiencies are described in"A New Rotor Position Estimation Method for Swsched ReJuctarwe Motors using PWM Voltage Control", by Gallegos-Lopez. G. Kjaer, PC & Miller, TJE, in Proc EPE'97. 7th European Cont on Power Electronics and Applications, 8-10 Sept 1997, Trondheim, Norway, Vol. 3, pp 580-585, hereby incorporated by reference. This method continuously samples the current waveform and attempts to detect the change in gradient that is produced by the start of pole overlap and the consequent sudden rise in inductance of the phase. The basic method described by Gallegoe-Lopez el al involves detecting the point of pole overlap for monitoring (or pole separation for generating) by detecting the point where the rate of change of the current waveform, with respect to time, is zero. The detector includes a differentiator, a oomparator and a single shot multivibrator. The differentiator differentiates the current signal so that at the point of zero di/dt the differentiator output is zero. The comparator detects this zero output and tips state. The system does not require either stored magnetization data or an interval of freewhilling. The system does current feedback and does not work ratably in the presence of noise. Improvements to this system include samping and storage of over several intervals and interpolation to reduce the effects of false detection caused by noise. [0018] When seining the angular rotor position using the sensoriess approach, variations in the electrical characteristics of the individual stator pole windings can adversely impact the ability of the sensoriess drive circurts to correctly derive the angular position of the rotor. Most of the sensoriess approaches measure the resistance and/or inductance of the windings. If the resistance and/or inductance varies from one stator winning to derive the angular position of the rotor. This problem is made worse if the windings on the stator poles creep or move over time. When this occurs, the cross section of the stator winnings changes, which changes the inductance and resistance of the stator pole winding. [0019] There are several conventional methods for on the stator of a swiched reluctance electric machine. The wincing wire can be initially wound and transferred onto the stator poles. Transfer winding tends to leave excess winding wire or loops around axial ends of the stator poles. Transfer winding can typically utilize approximately 60-65% of available stator slot area. Needle wincing employs a needs that winds the wire directly on the stator poles. The needle, however, takes up some of the stator slot area, which reduces slot fill to approximately 50%. The positioning of winding wire on the stator poles using these methods varies from one stator pole to the next Winding creep and other assembly variations also impact the inductance and resistance of the winning wire over time, which makes it difficult to accurately perform "sensortess" control due to the non- conformity of the salient stator poles. (0020] While the design of switched reluctance electric machines is relatively mature, there are several areas requiring improvement Specifically, it is desirable to improve the uniformity of the electrical characteristics of the stator of switched reluctance electric machines. It is also desirable to eliminate the need for RPTs in switched reluctance electric machines to decrease the cost and to improve both durability and serviceability. SUMMARY OF THE INVENTION [0021] A sensorises swithed reluctance electric machine according to the invention includes a rotor and a segmented stator having a plurality of stator segment assamblles. The stator segment assmbies define salient stator poles and inter-poler stator slots. Each of the stator segment assemblles includes winding wire that is wound around the stator segment core. The rotor defines a plurality of rotor poles. The rotor tends to rotate relative to the stator to a ratational position that maxizes the inductance of an energized winding. A sensorless drive circuit derives rotor position and energizes the warning wire around the stator segment aasembles based on the derived position of the rotor. [0022] According to other features of the invention, the atator segment core includes a plurality of stator passe. Each stator plate has an outer rim section and a tooth-shaped pole seofon. The stator segment assembles includs an end cap assembly that includes a pair of end caps that are secured to opposes ends of the stator segment core. A pair of retainer plates connect the end caps on opposite sides of the stator segment core. The end cap assembly defines an annular rention channel within which the winding wire is wound. The retention channel faciliates improved precision in the winding process and tends to reduce winding creep during use. [0023] By proving a segmented stator with the end cap assembly in the switched reluctance electric machine, the present invention improves the torque density of the switched reluctance electric machine. As a result, the torque output of the swashed reluctance electric machine can be increased and/or the dimensions of the switched reluctanoa atactic machine can be reduced tor a given torque output In addition, the satator segment assemblies can be manufactured with a greater electrical uniformity. The inductance and resistance of fhe individual stator segments and the stator are also more uniform. Ssneoriess techniques can be used more effecetively when the inductance and resistance characteristics of the atator are more uniform. Sensorless rotor posion sensing techniques lower the manufacturing costs of the switched reluctance electric machine when compared to sensed rotor position techniques and improve reliability and serviceability in the field. [0024] Other objects, features and advantages will be apparent from the specification, the claims and the drawings. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS [0025] FIG. 1 is a functional block diagram of a sensorless drive circuit and a switched reluctance machine; [0026] FIG. 2 is a functional block diagram of a first exemplary sensorless drive circuit and the switched reluctance eleclric machine; [0027] FIG. 3A is a functional block diagram of a second exemplary sensorless circuit and the switched reluctance electiric machne; [0028] FIG.3B illustrates current and inductance as a function of rotor and satator pole position: [0028] FIG.4A is a functional block diagram of a third exemplary sensories drive circuit and to switched reluctance electric machine; [0030] FIG. 4B illustrates the inductance of phase coils of the switched reluctance machine as a function of rotor position; [0031] FIG. 5 is a functional block diagram drive circuit and the switched reluctance electric machine; [0032] FIG.6 illustrates a segmented slater and a rotor for the switched [0033] FIG.7A illustrates a stator plate; [0034] FIG.7Bidentifies tooth width, projection width and stator pole arc on the stator plate of FIG3.7A; [0035] FIG.8 is a perspective view of a stator segment assembly associated with the stator; [0036] FIG. 9 illustrates the sensoriess drive circuit and a circuit board for connecting the sensorless drive circuit to terminals of the stator segment assembles; [0037] FIG. 10A shows the stator segment assembly with wire windings and insulation removed to better illustrate a stack of stator plates and the end cap assembly; [0036] FIG.10E is a plan view of the end cap assembly shown in FIG. 10A; [0030] FIG. 10C is an end view of the end cap assembly shown in FIG3.10B; [0040] FIG. 11A is similar to FIG. 10A except that an alternate end cap assembly is shown; [0041] FK3.11B shows a plan view of the alternate end cap assembly of FIG. 11 A; and [0042] FIG. 11C illustrates an end view of the alternate end cap assembly shown in FIG. 11B. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0043] The following delailed description embodiments provides preferred exemplary embodiments only and is not intended to limt the scope, applicability or configuration of the present invention. Rather, the detailed description of the preferred exemplary embodiments will provide those sidlled in the art with an enabling description for implemnting the preferred exemplary embodiments of the persent invention. It will be understood that various changes may be mde in the function and f arrrranment of the elements without departing from the spirit and scope of the invention as set forth in the [0044] The stator of the switched reluctance etectric machine accoroing to the present invention has highly uniform electrical characteristics. The segmented stator and the end cap asseblyaccording to the invention allow more precise winding of the stator poles and retention of the winding during use.As a result of the more uniform electrical characteristics, sensorless measurement techniques for deriving rotor position can be employed more successfully. The sensorless switched reluctance machine can be manufactured at a lower cost with improved reliaability and serviceability. [0045] referring now to FIG.1, a sensorless drive circiut 10 is connected to a switched reluctance electric machine 12. The sensorless drive circuit 10 derives the position of the rotor in a sensorless manner, In other words, tha sensorless drive circuit 10 lacks a physical sensor such as the RPT. The sensorless drive circuit 10 includes an application specific integarted circuit (ASIC), a controller, a processor, memory (such as read only memory (ROM), random access memory (RAM), flash memory, etc.), hardwired circuitry, and/or combination thereof. [0046] Referring now to FIG. 2, a sensoless drive circuit 10-1 includes a commutating circuit 14, a lookup table 16, a current sensor 18, and a flux sensor 20. The sensorless drive circuit 10-1 senses the phase frux-linkage and current at a predefined angle using the current sensor 18 and the flux eensor 20. Two one- dimensional tables are stored in the lookup table 16. By monitoring phase voltage and current, the deviation away from a pricted angle can be assweed with the and of the lookup table and system operation can be adjusted accordingly. [0047] Referring now to FIGs. 3A and 3B, a sensorless drive circuit 10-2 includes a commulating circuit 22, a current sensor 24, a slope calculating drouft 26, and a stope storage circuit 2a As can be seen to RG. 38, aa the rotor pole approaches the stator pole with an energized stator winding..CUrrent increases to a maximum value that occurs when the leading edge of the rotor tooth is aligned with the trailing edge of the stator pole. By monitoring the slope of the current as it transitions from a positive value to zero to a negative value, the position of the rotor pole can be identified. [0048] reffering now to FIG. 4A, a sensorless drive circuit 10-3 includes an inductance measuring circuit 30, a rotor position determining circuit 32, and a commulating circuit 34. As can be seen in FIG.4B,the inductance of the machine with its phase cols varies front a minimum to a maximum value as a function of angular rotor position. The senaodess drive circuit 10-3 employs this property when deriving the position of the rotor. The Inductance of the machine with its phase cols varies in approximatly Iinear fashion between the maximum and minimum idcuctance values. Using the relationship set forth in FIG.4B,the rotor position to determine angular position of the rotor and employs the rotor position to determine the commulating timing of the phase coils. [0040] The inductance measuring circuit 30 measures the inductance of one or more unenergized phase coils. The rotor position determining circuit 32 derives the angular position of the rotor based on the inductance measurement and outouts rotor position signal to the commuting circuit 34. The commulatating circuit 34 calculates the optimum commulation angle to deenergize one or more coils and to energize one or more other phase cols based in part on the derived rotor position signal [0050] Referring now to HG. 5, a sensorless drive circuit 10-4 for the sensoriess switched reluctance electric machine 12 includes a putse generator 52, a sensing circuit 54, a rotor position estimating The rotor position eatlrnafing drcuit 56 triggers the pulse generator 52 to output diagnostic pulses to one or more phase cote of the sensorless switched reluctance electric machine 12. The sensing circuit 54 senses changes in the phase cument of the phase coil and outputs a phase current change signal to the rotor position estimating circuit 58. The rotor position estimating circuit 56 derives the angular rotor position from the sensed phase current change signal and outputs a rotor position signal to the commulating circuit 58. The commulating circuit 58 determines the optimum angle to de-energize one or more phase coils and to energize one or more other phase coils. [0051] As can be appreciated by skilled artisans, other sensoriess drive circuits may be employed. For example, the specific sensoriess drive circuits set forth in the U.S. Patents that are identified above may be employed. The switched reluctance electric machine ,that is a set forth in moredetail below, is particularly suitable for sensorless operation due to its uniform electrical characteristics. [0062] Referring now to the remaining drawings, the sensorless switched reluctance machine 12 is shown to include a housing 112, a segmented stator 114 mounted in the housing 112, and a rotor 118 supported for rotation rotative to the segmnted stator 114.In accordance with the present invention,the segmented 114 includes a plurality of stator segment asset rites 118 that can be individually assembled and subsequently combined with additional stator segment assemblies to provide the segmanted stator 114. As wilt be detailed, each stator segment assembly 118 includes a stator segment core 120, an end cap assembly 122, and winding wire 124 that is wound around the stator segment core 120 and the end cap assembly 122. The end cap assembly 122 insulates the ends of the stator segment core 120 and provides retention for additional turns of the winding wire 124. [0063] Preferring prirmarlly to FIGs. 6, 7A and 78, the stator aegment core 120 iicludae a sold core or a slack of individual stator plates 126. Each stator ptate 126 includes an outer rim section 128 and a tooth-ehapedpoto section 130. An outer edge surface 132 of the outer rim section 128 is shaped for mounting to a/i imer wafl surface 134 of the housing 112. Each outer rim section 128 has a tongue projection 136 formed on one edge surface 138 and a groove 140 on Is opposes edge surface 142. This tongue and groove arrangement helps align the stator segment helps align the during manufacturing. Because the stator segment assemblies are press fit or hot dropped into the housing, the tongue and groove arrangement can be omitted. Each pole section 130 of the stator plates 126 has an arcuate inner edge surface 144 and a pair of circumferencially-xtending projections 146. [0054] As previously mentioned, the stator segment core 120 to defined by a plurality of stator plates 126 that are stacked together. The stator plates 126 are die cut from thin sheets of magnetically conductive material. During the die cutting operation, a first pair of ate 150 are cut into the outer rim section 120 end a second pair of slits 152 are cut into toe pole section 130 and central portions between the slits are deformed. The ate 150 are transverse in alignment relative to the ete 152. The stator plates 126 that form the stator segment core 120 are stacked and press fit This operation results in the stator plates 126 being releasably interconnected to define the stator segment core 120. [0055] The rotor 116 is shown to include a circular rim section 154 and a plurality of tooth-shaped pole sections 156 that project radially from toe rim section 154. A circular bore 158 is formed in the rotor 116 and may include keyways 160. A rotor shaft (not shown) is received by the circular bore 156 of the rotor 116. In the particular embodiment shown, the rotor 116 has eight equaly-spaced rotor pole sections 156 and the segmented stator 114 has twelve eaually-spaced pole sections 130. other rotor pole and stator pole combinations one also contemplated. In addition, each rotor pole section 156 has an arcuate outer edge surface 162 that defines an at gap 163 with respect to its arcuate Inner edge surface 144 on the pole sections 130 of the stator segment core 120. 0056]referrong to FIG.7B,tooth width W1, projection with W2, and stator pole arc Bs are shown. As a result of segmenting the stator, the designer of the switched reluctance electric machine has gerater flexibility in designing the dimensions of the stator segment assembles. The slot opening dimension between radially Inner ends of the stator teeth restricts the projection width W2 when needle and transfer wiving method are employed This restriction is eliminated when the segmented stator assemblies are employed because the stator teeth can be wound individually before being assembled Into the stator. [0057] The tooth width W1 determmines the magnetic flux denaity in the stator tooth and how much area is available for winding wire in the inter-polar stator slot. The designer of the switched reluctnce electric machine can select the tooth witdh W1 so that it is sufficient to accomodate the maximum anticipated magnetic flux in the stator poles, but is not wider than necessary. By optimizing the tooth width W1, the slot area is increased, which slows additional winding wire. By increasing the current carrying capacity of the windings without causing overheating, the torque density of the switched reluctance electric machine can be improved. The design of the stator plates also depends on other factors such as the type of steel that is selected,the axial length of the stator stack, the opening speed, the overall size of the motor, and the desired magnetic flux density in the stator teeth. [0068] Referring to FIG. 8, the stator segment assembly 118 is shown fully assembled to include the stator segment core 120, the end cap assembly 122 and the winding wire 124. The end cap assembly 122 is made from magnetically peomeable material and includes a first end cap 164A, a second end cap 164B and a pair of elongated winding retainer section 166A and 166B. The first end cap 164A is located at one end of the stator segment core 120 and the second end cap 1648 to located at the opposite end of the stator segment core 120. The winding retainer sections 166A and 166B interconnect the first and second end caps 164A and 164B and are located adjacent to the projections 146 near the racially inner end of the pole sections 130 of the stator segment core 120. Preferably, the end cape 164A and 1848 are similar in configuration. Likewise, it is preferable that the retainer sections 166A and 166B are similar in configuration. Snap-in connections are contamplated for connecting the opposite ends of each retainer section 166A and 166B to the end caps 164A and 164B. Additionally, it is contamplated that adhesives are used for bonding the end caps 164A and 1648 to the opposite ends of the stator segment core 120 and the retainer sections to aides of the stator segment core 120. The end caps 164A and 164B and the retainer sections 166A and 166B can also be molded as an integral end cap assembly 122, Since the first end cap 164A is similar to the second end cap 164B, the following description of the components will use reference numerals with an "A" suffix for the first end cap 164A and the reference numerals for similar components of the second end cap 164B will be identical with a"B" suffix. [0059] Terminals 170 and 172 are shown in FIGs. 8 and 10A to be mounted in slots 174 and 176 (FIG. 10C) formed in an end surface 178A of the first end cap 164A. One end of the winding wire of 124 is connecred to the first terminal 170 while an opposite end of the waving wire 124 is connected to the second terminal 172. Insulating malarial 177 is shown to be positioned to cover winding wire 124 on both lateral sides of stator oore 120, The insulating meterial 177 is also positioned (but not shown) between the stator segment core 120 and the winding wire 124. [0060] Referring to FIG. 9, the sensorless drive circuit 10 is shown connected vie connecting wires 162,184 and 186 tom a printed circuit board 188. The printed circus board 186 is circular and has a plurality of radially outwardly projecting terminal pads 190. Each terminal pad 190 has conductive terminal slots 192 and 194 arranged to accept installation of the terminals 170 and 172 for each stator segment assembly 118. [0061] To more dearly illustrate the structure of the end cap assembly 122, FIG. 10A shows the stator segment assembly 118 prior to the winding wire 124 being wound thereon. The first end cap 164A incfudee an outer section 196A and an inner section 200A interconnected by a hub section 202A. all defining a common faoe surface 204A. The face surfece 204A abuts and is boridsd to an axial end surface 206 of the stator segment oore 120. Similarty, the face surface 2048 of second end cap 164B abuts and is bonded to an end surface 208 of the stator segment core 120. When the first end cap 164A is secured to the stator segment oore 120, its outer section 198A extends sightly radially inward with respect to the outer rim section 128 and is parallel to the outer rim section 128. The hub section 202A is signed with pole section 130 and the inner section 200A is aligned with and extends laterally beyond the inner edge surface 144 and the projections 146. A similar alignment is provided when the second end cap 164B is secured to the opposte end surface 206 of the stator segment core 120. Moreoverr, the width of the sections 202A and 202B is less than or equal to the width of the pole sections 130 of the stator segment core 120. The opposte ends of the retainer sections 166A and 1668 are connected to the face surfaces 204A and 2048 of the end caps 164A and 1648. respectively, adjacent to their inner sections 200A and 200B. As such, the end cap assembly 122 defines a continuous annular channel within which the winding wire 124 can be precisely installed and maintained. [0062] FIG.10B shows the innner section 200A of the first endcap 164Aand the inner section 2008 of the second end cap 184B to be rectangular to shape. It is contemplated, however, that other configurations (i.e. semi-circular, square, tapered, etc) could be used. As a further option, the retainer sections 166A and 168B could be provided as a cantilevered section that is irtegrally fomed win the end caps 164A or 1648 and adapted for connection to the inner section of the opposite end cap. To reduce the weight of the end cap assembly 122 or to make the molding process easier, lateral axial grooves 210 and a central axial groove 212 can be formed on the outer section of the end cape 164A and 164B. Likewise, a cavity 214 can also be formed to provide additional weight reduction or to make the molding process easier. [0063] Referring now to FIG3s. 11A, 11B and 11C, an alternative cap assembly 222 is shown for connection to the stator segment core 120 and supporting the winding wire 124. Reference numerals from FlGs. 10A, 10B and IOC will be used where appropriate to identify similar elements. Specifically, the first end cap 224A is generally simitar to the first end cap 164A. The alternative end cap assembly 222 includes an additional pari of retainer of retainer sections. An outer retainer section 226A extends axially from the common face surface 204A adjacent to the outer section 196A for connection to the outer section 196B of the second endcap 224a An outer retainer section 226B likewise extends axially from its common face surface 204B for connection to common face surface 204A of first end cap 224A. The outer retainer sections 226A and 2268 provide additional support for the end cap assembly 122. The outer retainer sections 226A and 2268 fill the arcuate inner edge 230 of the outer rim section 128. As a result, a substantially right angle projection to pote section 130 is formed. The outer retainer sections allow more precise control of the winding and minizes damage that may be caused by a sharp edge defined by inner edge 230 and the edge surface 138 and 142. The outer rattier section 226A and 2268 have a tepered profile to male with the profile of inner arcuate wall surfaces 230 (FIG.7A) of the outer rim secfion 128. [0064] As can be appreciated from the foregeing, the sensorless switched reluctancs machine according to the invention has improved torqus density due to the segmented stator and the pradisely wound stotor segment assmeblies. The stator segment assemblies in the electric machine can be produced with a greater electrical uniformity and with lower varitions in inductance and resistance, As a result, sensorless rotor position sensing techniques can be employed more effectively, which dramatically lowers the manufacturing costs and improves rliability and serviceability in the field. Because the manufacturing tolerance of the stator segments have been improved, less costly sensorless drive circuit can be employed and/or more accurate control can be achieved. In addtion, the end cap assemblies acording to the invention prevent winding creep and further hato improve the electrical uniformity of the stator segment assemblies during use. [0065] Those sidlled in the art can now appeciate from the foregoing description that the broad teachinge of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particaular examples thereof, the true eoope of the invention should not be so limited since other modafication will becoms apparent to the sidlled practitioner upon a study of the drawings, the specification and the following claims. We Claim:- 1. A sensorless switched reluctance electric machine (12) comprising: A stator (114) having a plurality of circumferentially-spaced stator segment assemblies (113) that comprise a stator segment core (120) and winding wire (124) that is precisely wound around individual ones of said stator segment core (120) to provide substantially uniform inductance and resistance characteristics, wherein said windings define a slot fill that is greater than 65%; a rotor (116) defining a plurality of rotor poles (156), wherein said rotor tends to rotate relative to said stator to maximize the inductance of an energized winding; characterized in that a sensorless drive circuit (10) that derives rotor position based on parameters that vary with at least one of said substantially uniform inductance and resistance characteristics of said stator segment assemblies and that energizes said winding wire around said stator segment assemblies to control operation of said switched reluctance machine based on said derived position of said rotor. 2. The sensorless switched reluctance electric machine as claimed in claim 1 wherein said sensorless drive circuit has a flux sensor (20) that senses inductance of said winding wire of one of said stator segment assemblies wherein said sensorless drive circuit derives said rotor position from said sensed inductance. 3. The sensorless switched reluctance electric machine as claimed in claim 1 wherein said sensorless drive circuit includes a diagnostic pulse generator (52) that generates a diagnostic pulse that is output to said winding wire of one of said stator segment assemblies, wherein said sensorless drive circuit derives said rotor position based on a sensed change in phase current due to said diagnostic pulse. 4. The sensorless switched reluctance electric machine as claimed in claim 1 wherein said sensorless drive circuit determines rotor position by monitoring a slope of a current waveform related to current flowing in said energized winding and by identifying when said slope is zero. 5. The sesorless switched reluctance electric machine as claimed in claim 1 wherein said sensorless drive circuit monitors current and flux and employs a look up table to determine said derived position of said rotor. 6. The sensorless switched reluctance electric machine as claimed in claim 1 wherein said stator segment core has stator plates with an outer rim section and a tooth section that extends radially inwardly from a center portion of said outer rim section. 7. The sensorless switched reluctance electric machine as claimed in claim 6 further comprising: an insulation layer located between said winding wire and said stator segment core. 8. The sensorless switched reluctance electric machine as claimed in claim 1 comprising: projections extending from opposite sides of a radially inner end of said tooth section. 9. The sensorless switched reluctance electric machine as claimed in claim 8 comprising: first and second end caps connected to opposite axial ends of said stator segment core; and first and second end cap retainer sections that extend adjacent to said projections and that connect said first and second end caps, wherein said first and second end caps and said first and second end cap retainer sections define an annular retention channel that reduces movement of said winding wire during use and wherein said first and second end caps and said first and second end cap retainer sections are not located between said winding wire and axial said surfaces of said tooth section. 10. The sensorless switched reluctance electric machine as claimed in claim 6 wherein said stator plates of said stator segment core have redial and lateral slits and first and second central portions that are deformed to hold said stack of stator plates together. 11. A sensorless switched reluctance electric machine (12) comprising: a stator(114); a rotor(116); a machine housing(112); a plurality of circumferentially-spaced stator segment assemblies (118) that are arranged around an inner surface of said machine housing; said stator segment assemblies defining a salient stator pole (130) that extends in a radially inward direction; said stator segment assemblies having a stator segment core (120) and winding wire (124) that is precisely wound around individual ones of said stator segment core to provide substantially uniform inductance and resistance characteristics, wherein said windings define a slot fill that is greater than 65%; and a sensorless drive circuit (10) that is connected to said winding wire, that derives rotor position based on parameters that vary with at least one of said substantially uniform inductance and resistance characteristics of said stator segment assemblies and that energizes said winding wire around said stator segment assemblies to control operation of said switched reluctance machine based on said derived position of said rotor. 12. The sensorless switched reluctance electric machine as claimed in claim 11 wherein said sensorless drive circuit has a flux sensor (120) that senses inductances of one of said stator segment assemblies, wherein said sensorless drive circuit derives said rotor position based on said sensed inductance. 13. The sensorless switched reluctance electric machine as claimed in claim 11 wherein said sensorless drive circuit has a diagnostic pulse generator (52) that generates diagnostic pulses that are output to one of said stator segment assemblies, wherein said sensorless drive circuit senses changes in phase resulting from said diagnostic pulse and derives said rotor position therefore. 14. The sensorless switched reluctance electric machine as claimed in claim 11 wherein said sensorless drive circuit determines rotor position by monitoring a shape of a current waveform related to current flowing in said energized winding and by identifying when said slope is zero. 15. The sensorless switched reluctance electric machine as claimed in claim 11 wherein said sensorless drive circuit monitors current and flux and employs a look up table to determine said derived position of said rotor. 16. The sensorless switched reluctance electric machine as claimed in claim 11 wherein said stator segment core has stator plates with a radially outer rim section and a tooth section that extends radially inwardly from said radially outer rim section. 17. The sensorless switched reluctance electric machine as claimed in claim 16 comprising: an insulation layer located between said winding wire and said stator segment core. 18. The sensorless switched reluctance electric machine as claimed in claim 16 comprising : projections extending from opposite sides of a radially inner end of said tooth section. 19. The sensorless switched reluctance electric machine as claimed in claim 18 comprising: first and second end caps connected to opposite axial ends of said stator segment core; and first and second end cap retainer sections that extend adjacent to said projections and that connect inner ends of said first and second end caps, wherein said first and second end caps and said first and second axial end cap retainer sections define an annual retention channel that reduces movement of said winding wire during use and wherein said first and second end caps and said first and second end cap retainer sections are not located between said winding wire and axial side surfaces of said tooth section. 20. The sensorless switched reductance electric machine as claimed in claim 16 wherein said stator plates of said stator segment core has radial and first and second central portions that are deformed to hold said stator segment core together. Dated this 10th day of SEPTEMBER 2003. A sensorless switched reluctance electric machine (12) comprising: A stator (114) having a plurality of circumferentially-spaced stator segment assemblies (113) that comprise a stator segment core (120) and winding wire (124) that is precisely wound around individual ones of said stator segment core (120) to provide substantially uniform inductance and resistance characteristics, wherein said windings define a slot fill that is greater than 65%; a rotor (116) defining a plurality of rotor poles (156), wherein said rotor tends to rotate relative to said stator to maximize the inductance of an energized winding; characterized in that a sensorless drive circuit (10) that derives rotor position based on parameters that vary with at least one of said substantially uniform inductance and resistance characteristics of said stator segment assemblies and that energizes said winding wire around said stator segment assemblies to control operation of said switched reluctance machine based on said derived position of said rotor.

Documents:

1152-kolnp-2003-correspondence.pdf

1152-KOLNP-2003-FORM 27.pdf

1152-kolnp-2003-form-18.pdf

1152-kolnp-2003-granted-abstract.pdf

1152-kolnp-2003-granted-claims.pdf

1152-kolnp-2003-granted-correspondence.pdf

1152-kolnp-2003-granted-description (complete).pdf

1152-kolnp-2003-granted-drawings.pdf

1152-kolnp-2003-granted-examination report.pdf

1152-kolnp-2003-granted-form 1.pdf

1152-kolnp-2003-granted-form 2.pdf

1152-kolnp-2003-granted-form 3.pdf

1152-kolnp-2003-granted-form 5.pdf

1152-kolnp-2003-granted-others.pdf

1152-kolnp-2003-granted-pa.pdf

1152-kolnp-2003-granted-reply to examination report.pdf

1152-kolnp-2003-granted-specification.pdf