Title of Invention

METHOD OF ACCURATELY ASSEMBLING A 3-PHASE BRUSHLESS DC MOTOR

Abstract

A method of accurately assembling a 3-phase brushless DC motor (1)comprising making a stator assembly(2)by winding conductors of a first phase in a stator slot (4)referenced with and indicator(18)provided on the stator core(3)followed by winding conductors of a second phase in a stator slot located at 120º electrical angle with respect to the stator slot referenced with the indicator in the anticlockwise direction and winding conductors of a third phase in a stator slot located at 240º electrical angle with respect to the stator slot referenced with the indicator in the anticlockwise direction The stator assembly is pressed in a motor housing (6) provided with an indicator (19) externally after aligning the indicators provided on the stator core and motor housing. A rotor assembly (7) is made by locating a plurality of pairs of main magnets(8) on a rotor core(9) mounted on a rotor shaft (10) provided with an indicator(20) which is aligned with the center line separating the N and S poles of one pair of main magnets, The top end shield (13) has three mounting holes (23a,24a,25a)formed therein one of which is aligned with the indicator on the motor housing. A PCB(11)of a controller has three mounting holes (23b,24b,25b)formed therein which correspond to the mounting holes in the top end shield and is fitted with three hall sensors (Sa, Sb and Sc). One hall sensor corresponding to the first phase windings of the stator assembly is mounted on the PCB in alignment with the mounting hole aligned with the indicator on the motor housing. A second and a third hall sensors corresponding to the second phase windings and third phase windings of the stator assembly are mounted on the PCB at 120º and 124º electrical angle with respect to the hall sensor corresponding to the first phase windings in the anti clockwise direction. The encoder is mounted on the rotor shaft with the center line separating the N and S poles of one pair of auxiliary magnets aligned with the indicator on the rotor shaft.

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) As amended by the Patents (Amendment) Act, 2005 & The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2005 COMPLETE SPECIFICATION (See section 10 and rule 13) TITLE OF THE INVENTION Method of accurately assembling a 3-phase brushless DC motor APPLICANTS Name : CROMPTON GREAVES LIMITED Nationality : Indian Company Address : CG House, Dr Annie Besant Road, Prabhadevi, Mumbai 400025, Maharashtra, India PREAMBLE TO THE DESCRIPTION The following specification particularly describes the nature of this invention and the manner in which it is to be performed : FIELD OF INVENTION This invention relates to a method of accurately assembling a 3-phase brushless DC motor. This invention also relates to a 3-phase brushless DC motor assembled by the above method. BACKGROUND OF INVENTION A 3-phase brushless DC motor comprises a stator assembly comprising phase windings wound in the stator core slots and located in a motor housing. It also comprises a rotor assembly comprising a plurality of pairs of main magnets located on a rotor core mounted on a rotor shaft. The rotor assembly is located within the stator assembly and rotatably held in a top end shield and a bottom end shield fixed to the top and bottom ends of the motor housing. It also comprises a controller including a PCB and hall sensors for sensing the rotor position relative to the phase windings. Further it comprises an encoder mounted on the rotor shaft externally of the top end shield. The encoder comprises a plurality of pairs of auxiliary magnets corresponding to the main magnets and located on a disc. In order to ensure smooth rotation and functioning of the motor it is essential that the phase windings are energized at correct time intervals and sequence. For this the hall sensors and the phase windings and the auxiliary magnets and the main magnets are to be accurately aligned and positioned. 2 A 3-phase brushless DC motor is assembled by making a stator assembly by winding conductors in the stator slots provided in a stator core to form phase windings and pressing the stator assembly in a motor housing . A rotor assembly made by locating a plurality of pairs of main magnets on a rotor core mounted on a rotor shaft, is located in the motor housing within the stator assembly. A top end shield and a bottom end shield are fixed to the respective sides of the motor housing and the rotor shaft is rotatably held in the end shields. PCB of the controller with hall sensors mounted thereon is fixed on the top end shield. An encoder comprising a disc having a plurality of pairs of auxiliary magnets corresponding to the main magnets and located thereon is mounted on the rotor shaft externally of the top end shield. The hall sensors are to be aligned with the phase windings before they are fixed on the PCB. Similarly the auxiliary magnets are also to be aligned with the main magnets before the encoder is mounted on the rotor shaft. Alignment of the hall sensors with the phase windings and auxiliary magnets with the main magnets is done by trial and error. This is cumbersome, time consuming and requires skilled persons. The trial and error method increases assembly time of the motor and reduces productivity. There is also overall cost increase. OBJECTS OF INVENTION An object of the invention is to provide a method of accurately assembling a 3-phase brushless DC motor, which reduces assembly time, renders the assembly easy and convenient to carry out and increases productivity. 3 Another object of the invention is to provide a method of accurately assembling a 3-phase brushless DC motor, which does not require skilled persons. Another object of the invention is to provide a method of accurately assembling a 3-phase brushless DC motor, which gives overall cost benefit. Another object of the invention is to provide a 3-phase a brushless DC motor assembled by the above method. DETAILED DESCRIPTION OF INVENTION According to the invention there is provided a method of accurately assembling a 3-phase brushless DC motor comprising making a stator assembly by winding conductors of a first phase in a stator slot referenced with an indicator provided on the stator core followed by winding conductors of a second phase in a stator slot located at 120° electrical angle with respect to the stator slot referenced with the indicator in the anticlockwise direction and winding conductors of a third phase in a stator slot located at 240° electrical angle with respect to the stator slot referenced with the indicator in the anticlockwise direction; pressing the stator assembly in a motor housing provided with an indicator externally after aligning the indicators provided on the stator core and motor housing; making a rotor assembly by locating a plurality of pairs of main magnets on a rotor core mounted on a rotor shaft provided with an indicator which is aligned with the center line separating the N and S poles of one pair of main 4 magnets; locating the rotor assembly within the stator assembly already located in the motor housing; mounting a top end shield and a bottom end shield to the respective ends of the motor housing with the rotor shaft being rotatably held in the top and bottom end shields; the top end shield having formed with three mounting holes one of which is aligned with the indicator on the motor housing; a PCB of a controller having formed with three mounting holes corresponding to the mounting holes in the top end shield and fitted with three hall sensors, one hall sensor corresponding to the first phase windings of the stator assembly being mounted on the PCB in alignment with the mounting hole aligned with the indicator on the motor housing, a second hall sensor corresponding to the second phase windings of the stator assembly being mounted on the PCB at 120° electrical angle with respect to the hall sensor corresponding to the first phase windings in the anti clockwise direction and a third hall sensor corresponding to the third phase windings of the stator assembly being mounted on the PCB at 240° electrical angle with respect to the hall sensor corresponding to the first phase windings in the anticlockwise direction and mounting an encoder on the rotor shaft externally of the top end shield, the encoder comprising a disc having a plurality of pairs of auxiliary magnets corresponding to the main magnets located thereon, the encoder being mounted on the rotor shaft with the center line separating the N and S poles of one pair of auxiliary magnets aligned with the indicator on the rotor shaft. It is to be clearly understood that the indicators on the stator and motor housing are essentially for giving references for aligning the phase windings with respect to the hall sensors accurately during assembly of the motor. Similarly the indicator on the motor shaft is essentially for a reference to 5 align the N and S poles of the main magnets with respect to the N and S poles of the auxiliary magnets. The indicators can be any indicating means such as marks, symbols, projections, notches or arrows which will serve the purpose. Typically the indicator on the stator comprises an aperture, the indicator on the motor housing comprises a projection and the indicator on the rotor shaft comprises a notch. According to the invention there is also provided a 3-phase brushless DC motor comprising indicators provided as references on the stator core, motor housing and rotor shaft and mounting holes in the top end shield and PCB and hall sensors fixed on the PCB as described above and assembled by the method as described above. This application has been divided out of our patent application No 1050/MUM/2000 filed on 21st November 2000. The following is a detailed description of the invention with reference to the accompanying drawings, in which: Fig 1 is an exploded view of a 3-phase brushless DC motor without the rotor assembly and encoder according to an embodiment of the invention; 6 Fig 2 is diagrammatic representation of the top end view of the motor of Fig 1 without the top end shield aligned with a view of the top end shield and a view of the PCB of the controller thereof; and Fig 3 is isometric view of the rotor assembly and encoder of the motor of Fig l. The 3-phase brushless DC motor 1 as illustrated in Fig 1 of the accompanying drawings comprises a stator assembly 2 comprising a stator core 3 provided with stator slots 4 and phase windings 5R, 5Y and 5B wound in the stator slots. The motor also includes motor housing 6 and a rotor assembly 7 comprising a plurality of pairs of main magnets 8 located on a rotor core 9 which is mounted on a rotor shaft 10 (Fig 3). 11 is a PCB of a controller of the motor including three hall sensors marked Sa, Sb and Sc. 13 and 14 are the top end shield and bottom end shield of the motor. 15 is an encoder comprising a plurality of pairs of auxiliary magnets 16 located on a disc 17 mounted on the rotor shaft externally of the top end shield (Fig 3). Other details of the motor have not been illustrated in the drawings as such are not concerned with the invention. The motor is assembled as follows: The stator assembly is made by winding conductors of the R phase in a stator slot 4 in the stator core to form phase windings 5R corresponding to R phase of the motor. The stator core in which phase windings corresponding to phase R are wound is referenced by an indicator comprising an aperture 18 provided on the stator core. This is followed by winding conductors in a stator slot 4 located at 120° electrical angle with respect to the stator 7 slot 4 referenced with aperture 18 in the anticlockwise direction to form phase windings 5Y corresponding to phase Y and further winding conductors in a stator slot 4 located at 240° electrical angle with respect to the stator 4 referenced with the aperture 18 in the anticlockwise direction to form phase windings 5R corresponding to phase R. The stator assembly is pressed in the motor housing provided with a projection 19 externally after aligning the aperture 18 provided on the stator core and the projection 19 on the motor housing. The rotor assembly is made by locating pairs of main magnets on the rotor core mounted on the rotor shaft which is provided with a notch 20. The center line separating the N and S poles of one pair of main magnets is aligned with the notch 20 (Fig 3). The rotor assembly is located within the stator assembly already located in the motor housing. The top end shield and bottom end shield are mounted to the top and bottom ends of the motor housing, respectively with the rotor shaft rotatably held in the end shields using bearings (not shown). The top end shield is formed with three mounting holes 23a, 24a and 25a (Fig 2). The mounting hole 23a is aligned with the projection 19 on the motor housing (Fig 2). The PCB 11 is provided with three mounting holes 23b, 24b and 25b corresponding to the mounting holes 23a, 24a and 25a in the top end shield and fitted with the three hall sensors Sa, Sb and Sc such that hall sensor Sa corresponding to the R phase windings is mounted on the PCB in alignment with the mounting hole 23b aligned with the projection 19 on the motor housing (Fig 2). Hall sensor Sb corresponding to the Y phase windings of the stator assembly is mounted on the PCB at 120° electrical angle with respect to the hall sensor Sa in the anticlockwise direction and hall sensor Sc corresponding to the B phase windings of the stator assembly is mounted on the PCB at 240° electrical angle with respect to the hall sensor Sa in the 8 anticlockwise direction (Fig 2). The encoder comprising a plurality of pairs of auxiliary magnets is mounted on the rotor shaft after aligning the center line separating the N and S poles of one pair of auxiliary magnet with the notch 20 on the rotor shaft (Fig 3). Mountings flanges on the bottom end shield are marked 26 (Fig 2). According to the invention, the references provided by the indicators make the assembly easy, simple and convenient to be carried out besides reducing the assembly time. The hall sensors are accurately aligned with respect to the phase windings of the motor during assembly of the motor itself ie hall sensors Sa, Sb and Sc are aligned with phase windings R, Y and B, respectively. The auxiliary magnets are also accurately aligned with the main magnets during assembly of the motor itself. It eliminates the trial and error method for alignment of the hall sensors with the phase windings and alignment of the main magnets with the auxiliary magnets. The assembly can be carried out even by unskilled persons. Due to reduced assembly time, productivity is increased. There is also overall cost benefit. 9 We claim: . A method of accurately assembling a 3-phase brushless DC motor comprising making a stator assembly by winding conductors of a first phase in a stator slot referenced with an indicator provided on the stator core followed by winding conductors of a second phase in a stator slot located at 120° electrical angle with respect to the stator slot referenced with the indicator in the anticlockwise direction and winding conductors of a third phase in a stator slot located at 240° electrical angle with respect to the stator slot referenced with the indicator in the anticlockwise direction; pressing the stator assembly in a motor housing provided with an indicator externally after aligning the indicators provided on the stator core and motor housing; making a rotor assembly by locating a plurality of pairs of main magnets on a rotor core mounted on a rotor shaft provided with an indicator which is aligned with the center line separating the N and S poles of one pair of main magnets; locating the rotor assembly within the stator assembly already located in the motor housing; mounting a top end shield and a bottom end shield to the respective ends of the motor housing with the rotor shaft being rotatably held in the top and bottom end shields; the top end shield having formed with three mounting holes one of which is aligned with the indicator on the motor housing; a PCB of a controller having formed with three mounting holes corresponding to the mounting holes in the top end shield and fitted with three hall sensors, one hall sensor corresponding to the first phase windings of the stator assembly being mounted on the PCB in alignment with the mounting hole aligned 10 with the indicator on the motor housing, a second hall sensor corresponding to the second phase windings of the stator assembly being mounted on the PCB at 120° electrical angle with respect to the hall sensor corresponding to the first phase windings in the anti clockwise direction and a third hall sensor corresponding to the third phase windings of the stator assembly being mounted on the PCB at 240° electrical angle with respect to the hall sensor corresponding to the first phase windings in the anticlockwise direction and mounting an encoder on the rotor shaft externally of the top end shield, the encoder comprising a disc having a plurality of pairs of auxiliary magnets corresponding to the main magnets located thereon, the encoder being mounted on the rotor shaft with the center line separating the N and S poles of one pair of auxiliary magnets aligned with the indicator on the rotor shaft. 2. A method of accurately assembling a 3-phase brushless DC motor as claimed in claim 1, wherein the indicator on the stator comprises an aperture, the indicator on the motor housing comprises a projection and the indicator on the rotor shaft comprises a notch. 3. A 3-phase brushless DC motor comprising indicators provided as references on the stator core, motor housing and rotor shaft and mounting holes in the top end shield and PCB and hall sensors fixed 11 on the PCB as claimed in claim 1 and assembled by the method as claimed in claim 1. Dated this 29th day of September 2005 (Jose M A) of Khaitan & Co Agent for the Applicants 12 ABSTRACT A method of accurately assembling a 3-phase brushless DC motor (1) comprising making a stator assembly (2) by winding conductors of a first phase in a stator slot (4) referenced with an indicator (18) provided on the stator core (3) followed by winding conductors of a second phase in a stator slot located at 120° electrical angle with respect to the stator slot referenced with the indicator in the anticlockwise direction and winding conductors of a third phase in a stator slot located at 240° electrical angle with respect to the stator slot referenced with the indicator in the anticlockwise direction. The stator assembly is pressed in a motor housing (6) provided with an indicator (19) externally after aligning the indicators provided on the stator core and motor housing. A rotor assembly (7) is made by locating a plurality of pairs of main magnets (8) on a rotor core (9) mounted on a rotor shaft (10) provided with an indicator (20) which is aligned with the center line separating the N and S poles of one pair of main magnets. The top end shield (13) has three mounting holes (23a, 24a and 25a) formed therein one of which is aligned with the indicator on the motor housing. A PCB (11) of a controller has three mounting holes (23b, 24b and 25b) formed therein which correspond to the mounting holes in the top end shield and is fitted with three hall sensors (Sa, Sb and Sc). One hall sensor corresponding to the first phase windings of the stator assembly is mounted on the PCB in alignment with the mounting hole aligned with the indicator on the motor housing. A second and a third hall sensors corresponding to the second phase windings and third phase windings of the stator assembly are mounted on the PCB at 120° and 240° electrical angle with respect to the hall sensor corresponding to the first phase windings in the anti clockwise direction. The encoder is mounted on the rotor shaft with the center line separating the N and S poles of one pair of auxiliary magnets aligned with the indicator on the rotor shaft (Figs 2 and 3).

Documents:

1227-mum-2005-abstract(29-8-2008).doc

1227-mum-2005-abstract(29-8-2008).pdf

1227-mum-2005-abstract.doc

1227-mum-2005-abstract.pdf

1227-MUM-2005-CANCELLED PAGES(29-8-2008).pdf

1227-MUM-2005-CLAIMS(29-8-2008).pdf

1227-mum-2005-claims(granted)-(29-8-2008).doc

1227-mum-2005-claims(granted)-(29-8-2008).pdf

1227-mum-2005-claims.doc

1227-mum-2005-claims.pdf

1227-MUM-2005-CORRESPONDENCE(29-8-2008).pdf

1227-mum-2005-correspondence(ipo)-(11-8-2008).pdf

1227-mum-2005-correspondence-received-ver-191005.pdf

1227-mum-2005-correspondence-received.pdf

1227-mum-2005-description (complete).pdf

1227-MUM-2005-DESCRIPTION(COMPLETE)-(29-8-2008).pdf

1227-MUM-2005-DRAWING(29-8-2008).pdf

1227-mum-2005-drawings.pdf

1227-MUM-2005-FORM 1(30-9-2005).pdf

1227-mum-2005-form 18(19-10-2008).pdf

1227-mum-2005-form 2(29-8-2008).pdf

1227-mum-2005-form 2(granted)-(29-8-2008).doc

1227-mum-2005-form 2(granted)-(29-8-2008).pdf

1227-MUM-2005-FORM 2(TITLE PAGE)-(29-8-2008).pdf

1227-mum-2005-form 26(12-1-2004).pdf

1227-MUM-2005-FORM 3(29-8-2008).pdf

1227-mum-2005-form 3(29-9-2008).pdf

1227-mum-2005-form-1.pdf

1227-mum-2005-form-18.pdf

1227-mum-2005-form-2.doc

1227-mum-2005-form-2.pdf

1227-mum-2005-form-26.pdf

1227-mum-2005-form-3.pdf

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