Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-04-30
2002-03-26
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S049540, C310S045000, C310S179000, C310S254100, C029S596000
Reexamination Certificate
active
06362544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of electromagnetic device design and manufacturing.
2. Description of the Prior Art
An electromagnetic device, such as an electric motor or an electric generator, contains two electromagnetic components: a stationary component known as a “stator,” and a rotating component known as a “rotor.” In the most common embodiment, the rotor and the stator are cylindrical in shape. The cylindrical rotor is installed inside the hollow, cylindrical stator in such a way that when the rotor rotates, the outer surface of the rotor is proximate to, but does not touch, the inner surface of the stator. The space between the outer surface of the rotor and the inner surface of the stator is known as the “air gap”.
It is known in the art that a stator and a rotor each may be manufactured from a core made from a magnetic material, around which or within which insulated electrical conductors known as “windings” are installed. The rotor core and stator core together form the magnetic “flux path” for the electromagnetic device.
A typical stator of a design known in the art is comprised of a hollow, cylindrical core, the inner surface of which contains slots which extend the full length of the core parallel to the axial direction of the core. The portions of the stator core between the slots are known as the “teeth.” The measurement made by adding the width of one slot measured at the base of the slot to the width of one adjacent tooth is known as the “slot pitch”.
The prior art stator windings are inserted in the slots in the core, usually by a manual means. After the stator windings are installed into the stator core, the stator may be finished by filling the remaining volume of the stator slots and coating the external surface of the stator with a non-reactive, non-conducting material such as, for example, varnish or epoxy. The non-reactive, non-conducting material serves to protect the stator from corrosion, and to prevent the stator windings from moving within the stator slots during use. Such movement, if permitted, could damage the electrical insulation on the stator windings, and/or could alter the electromagnetic characteristics of the stator.
It is well known in the art to manufacture a stator core from sheet steel. Steel laminations are punched from the sheet steel. The punched steel laminations include slots, alignment holes, and other assembly features. The punched steel laminations are stacked so that the inner surface of the core, the outer surface of the core, the slots, and the alignment holes are aligned. The stacked steel laminations then are secured together by methods known in the art including, for example, welding or riveting.
The method of manufacturing a stator core from sheet steel laminations possesses several disadvantages. The process of punching the steel laminations from the sheet steel creates scrap steel pieces, which often cannot be used productively by the manufacturer. In addition to the cost of the wasted sheet steel pieces, often the manufacturer must incur additional expense involved with the disposal of the wasted sheet steel pieces. Finally, the process of producing the finished stator core from the raw sheet steel is a multiple step process requiring expensive material handling to be performed during and/or between each process step.
U.S. Pat. No. 4,947,065 to Ward et al. disclosed another method for manufacturing a stator core using iron powder particles coated with a thermoplastic material. The method disclosed in U.S. Pat. No. 4,947,065 addresses the disadvantages present in the prior art method of manufacturing a stator core from sheet steel laminations. Scrap is eliminated by the use of a premeasured amount of thermoplastic coated iron particles. The stator core is formed by heating the premeasured amount of the thermoplastic coated iron particles to a predetermined temperature, placing the heated particles into a heated mold that is shaped to produce a stator core of the desired shape, activating a means for compacting the heated particles within the heated mold, thereby compacting the heated particles within the heated mold for a predetermined time at a predetermined pressure. Material handling is reduced because the raw thermoplastic coated iron particle material is manufactured into a finished stator in fewer process steps. The stator core of Ward et al. does not overcome all disadvantages of a prior art stator core made with steel laminations. To fabricate a finished stator from a stator core according to the disclosure of Ward et al., the stator windings must be installed into the slots by a manual means after the stator core is formed, as was required in the stator core made with steel lamination.
Stator windings are conventionally produced from an insulated electrical conductor of types known in the art including, for example, insulated single strand copper wire. The insulated electrical conductor is conventionally formed by methods known in the art into substantially cylindrical winding configurations which will fit within the slots in the stator core, and which will produce the desired electrical effect when the windings are placed in a moving magnetic field, or the desired magnetic effect when the windings are energized with an electric current. The windings are inserted into slots in the stator to maximize the electromagnetic coupling between the windings and the flux path, and to minimize the air gap between the rotor and stator. The portion of the windings which is aligned parallel to the axial direction of the core is conventionally known as the “active portion”of the windings. The portions of the windings which resides outside the stator core at each axial end of the stator core, and which function to conduct electricity from the active portion of the windings which resides in a first slot to the active portion of the windings which resides in a second slot, are conventionally known as the “end turns”.
Electric motors and generators operate on the principle of magnetic flux cutting. Electric motors and generators have a source of magnetic flux, such as an electromagnet or a permanent magnet, and a set of windings that intercept the flux. The flux path is always ferromagnetic. The flux is cut when rotation of the rotor occurs. The desired torque and power set the rotor dimension, while the stator dimensions are driven by both the rotor dimension and by the flux return requirements. An important rotor dimension is the “rotor active volume”. If “r” is the rotor radius and “
1
” is the rotor active length, then the rotor active volume “X” is calculated as “X=(&pgr;r
2
1)”.
A vehicular alternator is an example of electromagnet based electric generator. In a vehicular alternator, the magnetic flux is generated with a multi-pole electromagnet in the rotor. It is desired in the art to maximize the average magnetic flux density, or the “magnetic loading”, of the air gap. The magnetic loading may be limited by magnetic saturation of the stator core. A disadvantage present in prior art stator design using internally slotted stator cores, is that the slots reduce the internal surface area of the stator adjacent to the rotating rotor, thereby reducing the ability for magnetic flux to flow between the stator and the rotor. Due to the reduced internal surface area, the stator core teeth reach magnetic saturation more readily than would a stator core without internal slots. When the stator core teeth saturate, the magnetic flux density in the air gap is limited to the ratio of the tooth width to slot pitch multiplied by the saturation flux density of the stator material. For a typical vehicular alternator stator material the saturation flux density is about 1.5T, and the tooth width to slot pitch ratio is about ½, making the magnetic loading about 0.75T.
Reducing the slot width and increasing the tooth width increases the magnetic loading by increasing the internal surface area of the stator adjacent to the rotating rotor. However, because the slot must
Cho Chahee Peter
Johnston Ralph
Martin Ronald A.
Delco Remy International, Inc.
Miller Ice
Mullins Burton S.
Taylor Jay G.
Walsh Thomas A.
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