Patent Description:
Electric motors typically include a ferromagnetic body and electricity-carrying conductors. The ferromagnetic body may also be electrically conductive and therefore must be electrically insulated from the electricity-carrying conductors. An insulator made from paper or plastic is typically is used.

The present invention provides, in one aspect, a stator according to claim <NUM>.

The present invention provides, in another aspect, an electric motor according to claim <NUM>.

The present invention provides, in another aspect, a power tool according to claim <NUM>.

<CIT> relates to providing a uniform distribution of magnetic flux. <CIT> relates additional short circuited windings in electrical machines to compensate unbalanced magnetic pull effects. <CIT> relates to an enhanced electromagnetic radiation transmission device by providing electrically conductive laminations. <CIT> relates to an arrangement for cooling the poles of a salient pole machine. <CIT> relates to a brushless motor assembly power tool.

With reference to <FIG>, which does not show the inventive wire, a power tool <NUM> includes a housing <NUM> and an electric motor <NUM> positioned within the housing <NUM>. In some embodiments, the housing <NUM> is formed as two mating clamshell housings. The electric motor <NUM> includes a stator <NUM> and a rotor <NUM>. In the illustrated embodiment, the rotor <NUM> is positioned within the stator <NUM> and is rotatable with respect to the stator <NUM>. In other embodiments, the stator <NUM> is positioned within the rotor <NUM> (i.e., an outer-rotor motor design). In other embodiments, the electric motor <NUM> is a linear motor with the rotor configured to translate along the stator. In some embodiments, the electric motor <NUM> is a brushless DC motor. In some embodiments, the electric motor <NUM> is configured as a generator.

With continued reference to <FIG>, the rotor <NUM> includes a rotor main body <NUM> and a shaft <NUM>. In the illustrated embodiment, the rotor main body <NUM> is formed by a plurality of rotor laminations <NUM> stacked together to form a lamination stack. In other embodiments, the rotor main body <NUM> is a unitary piece of material. In the illustrated embodiment, the rotor main body <NUM> is ferromagnetic and includes magnet slots <NUM> in which to receive permanent magnets <NUM>. In other embodiments, the rotor main body <NUM> includes a slot that receives a winding.

The stator <NUM> includes a stator main body <NUM>. In the illustrated embodiment, the stator main body <NUM> is formed by a plurality of laminations <NUM> stacked together to form a lamination stack. In other embodiments, the stator main body <NUM> may be a unitary piece of material. In the illustrated embodiment, the stator main body <NUM> is ferromagnetic. An outer circumferential surface <NUM> of the stator <NUM> is at least partially supported by a plurality of supports <NUM> on the housing <NUM> that extend radially inward.

The stator main body <NUM> defines a plurality of slots <NUM> at least partially formed by stator teeth <NUM> extending radially inward from an outer ring <NUM> towards the shaft <NUM>. Stator windings <NUM> are wound around the stator teeth <NUM> and are at least partially positioned within the slots <NUM>. The stator windings <NUM> are electrically coupled to a power supply and are selectively energized during operation of the electric motor <NUM>. In some embodiments, the power supply includes a battery pack or a standard AC electrical outlet connected to a power cord. An inverter may be positioned between the power supply and the stator windings <NUM> and may be utilized to control electrical energization of the stator windings <NUM>. Each stator winding <NUM> is formed from a magnet wire having an electrically conductive core and an electrically insulative film. The individual coils or turns of the stator windings <NUM> may be bonded together by an adhesive, an epoxy, a thermal plastic, or other suitable bonding material.

With continued reference to <FIG>, an insulator <NUM> is positioned within the slots <NUM> formed in the stator main body <NUM>. The insulator <NUM> is positioned between the stator windings <NUM> and the stator main body <NUM>. The insulator <NUM> prevents the stator windings <NUM> from physically contacting the stator main body <NUM>. Contact between the stator windings <NUM> and the stator main body <NUM> can create a short circuit and cause electric motor failure. The insulator <NUM> is an electrical insulator. The insulator <NUM> illustrated in <FIG> is a slot liner made from paper or plastic. Although the insulator <NUM> is adequate to electrically insulate the stator windings <NUM>, the insulator <NUM> is also a thermal insulator that traps unwanted heat within the stator windings <NUM>. In other words, the insulator <NUM> acts as a thermal barrier that prevents the conduction of accumulated heat in the stator windings <NUM> to the stator main body <NUM>, therefore preventing effective cooling of the stator windings <NUM>.

With reference to <FIG>, a prior art arrangement is illustrated of the stator winding <NUM> and the insulator <NUM> positioned within the slot <NUM> of the stator main body <NUM>. The stator winding <NUM> forms a plurality of coils wrapped around the stator tooth <NUM>. The insulator <NUM> is a unitary piece of electrically insulating material. In the illustrated embodiment, the insulator <NUM> is positioned along an outermost extent of the slot <NUM> and is positioned between the winding <NUM> and the main body <NUM>. As the stator winding <NUM> is electrically energized, the stator winding <NUM> generates heat. In addition to electrically insulating the stator windings <NUM> from the stator main body <NUM>, the insulator <NUM> acts as a thermal insulator and prevents heat from transferring from the stator winding <NUM> to the stator main body <NUM> where the heat can be more effectively dissipated. An excess of heat within the stator winding <NUM> can result in reduced motor performance or failure.

With reference to <FIG>, a wire <NUM> and the winding <NUM> are positioned within the slot <NUM> of the main body <NUM>. The wire <NUM> is positioned between the winding <NUM> and the main body <NUM>. In particular, the wire <NUM> is positioned between the winding <NUM> and the stator teeth <NUM>, and between the winding <NUM> and the outer ring <NUM>. In other words, the wire <NUM> physically separates the winding <NUM> from the main body <NUM>. The wire <NUM> is electrically isolated from the winding <NUM>. In other words, the winding <NUM> is electrically coupled to the power supply, but the wire <NUM> is not electrically coupled to the power supply. In the illustrated embodiment, the wire <NUM> is a magnet wire. With reference to <FIG>, the wire <NUM> includes an electrically conductive core <NUM> (e.g., copper) and an electrically insulative film <NUM>. In some embodiments, the insulative film <NUM> is a polymer. In other embodiments, the insulative film <NUM> is an enamel. In the illustrated embodiment, the wire <NUM> is round. In other embodiments, the wire <NUM> may be rectangular, square, or any suitable shape. No slot liner paper or unitary plastic insulator (like the insulator <NUM>) is used in the arrangement of <FIG>.

With reference to <FIG>, the winding <NUM> is formed from magnet wire having a first cross-sectional area <NUM>, and the wire <NUM> is also formed from magnet wire having a second cross-sectional area <NUM>. In the illustrated embodiment, the second cross-sectional area <NUM> is smaller than the first cross-sectional area <NUM>. In other embodiments, the second cross-sectional area <NUM> is larger than the first cross-sectional area <NUM>. In other embodiments, the second cross-sectional area <NUM> is approximately the same as the first cross-sectional area <NUM> (i.e., the same sized magnet wire is used for the winding <NUM> and the wire <NUM>). The wire <NUM> is positioned along the outermost extent of the slot <NUM>. The insulative film <NUM> of the wire <NUM> directly contacts the winding <NUM>. The insulative film <NUM> of the wire <NUM> includes a first portion <NUM> contacting the winding <NUM> and a second portion <NUM> contacting the main body <NUM>. The first portion <NUM> is positioned radially opposite the second portion <NUM>. In some embodiments, the second portion <NUM> of the film <NUM> is removed. The second portion <NUM> may be removed, for example, during installation of the wire <NUM> into the slot <NUM>. The removal of the second portion <NUM> may occur due to the second portion <NUM>, for example, scratching or rubbing against the main body <NUM> during installation of the wire <NUM> within the slot <NUM>. In some embodiments, the electrically conductive core <NUM> of the wire <NUM> directly contacts the main body <NUM>. The core <NUM> of the wire <NUM> is a good thermal conductor and has a thermal conductivity that is higher than an insulator, such as insulator <NUM>.

The wire <NUM> may be referred to as a sacrificial winding because the wire <NUM> does not carry electricity from the power supply. Typically, the amount of current-carrying wire within the slot <NUM> is maximized in order to increase power density. However, the wire <NUM> in the illustrated embodiment is wound around each stator tooth <NUM> as a sacrificial first and separate winding of motor magnet wire that is positioned directly against the laminations <NUM> of the main body <NUM>. The main stator winding <NUM> is then wound over the top of the wire <NUM>. The wire <NUM> is utilized as an electrical insulator (i.e., a material with a large electrical resistance) and a thermal conductor instead of being used to carry electricity from the power supply. The wire <NUM> conducts heat away from the winding <NUM>, which results in better performance from the electric motor <NUM>, while simultaneously electrically insulating the winding <NUM> from the main body <NUM>.

With reference to <FIG>, a combination of the insulator <NUM> (e.g., a portion thereof) and the wire <NUM> is used to electrically isolate different portions of the winding <NUM> from the main body <NUM>. In the illustrated embodiment, the insulator <NUM> is positioned along a radially outward surface <NUM> of the slot <NUM> and the wire <NUM> is positioned along a radially inward surface <NUM> and a side surface <NUM> of the slot <NUM>. The side surface <NUM> extend in a radial direction between the radially inward surface <NUM> and the radially outward surface <NUM>. The combination of the insulator <NUM> and the wire <NUM> may be determined by manufacturing capabilities. For example, positioning wire <NUM> along the radially outward surface <NUM> of the slot <NUM> may require advanced fixtures to properly hold the wire <NUM> in place. Therefore, the combination of the insulator <NUM> positioned along the radially outward surface <NUM> with the wire <NUM> positioned along the radially inward surface <NUM> and side surface <NUM> is a cost-effective combination and arrangement that does not require advanced manufacturing fixtures. In other embodiments, any combination of the insulator <NUM> and the wire <NUM> may be provided and positioned within the slot <NUM>. In some embodiments, the relative positioning of the insulator <NUM> and the wire <NUM> may be utilized to conduct heat from the winding <NUM> in a desired direction (i.e., the direction toward the wire <NUM>) while preventing heat from conducting in an undesired direction (i.e., the direction toward the insulator <NUM>).

Although in the illustrated embodiment the wire <NUM> is positioned within the stator <NUM>, in other embodiments, the wire <NUM> may be positioned within the rotor <NUM> or other suitable portions of the electric motor <NUM> to provide electrical insulation and thermal conductivity. As mentioned above, the rotor <NUM> may include a winding positioned within a slot of a rotor main body <NUM>. In some embodiments, the wire <NUM> is positioned between the winding and the rotor main body <NUM>. In other words, the wire <NUM> may be included in either or both the stator <NUM> and the rotor <NUM>.

Claim 1:
A stator (<NUM>) comprising:
a main body (<NUM>) with a slot (<NUM>) defined therein;
a winding positioned within the slot (<NUM>); and
a wire (<NUM>) not electrically coupled to a power supply and positioned within the slot (<NUM>), the wire (<NUM>) positioned between the winding (<NUM>) and the main body (<NUM>) to physically separate the winding (<NUM>) from the main body (<NUM>), and the wire (<NUM>) conducting heat away from the winding (<NUM>) while simultaneously electrically insulating the winding (<NUM>) from the main body (<NUM>).