The present disclosure relates generally to the field of electric motors which employ commutators and brushes and, more particularly, to electric motor brush arm assemblies that transfer electric current directly to and from commutators.
Electric motors typically include brushes, electrical leads and a rotor that includes an armature and commutator assembly. The armature is an electromagnet that is made by coiling conducting wires around two or more poles of a metal core, and is fixed to the rotor for rotation. The ends of the armature's conducting wires are fused to the commutator assembly, which generally includes at least one pair of metal plates that are fixed to the rotor and directly opposed to one another. The commutator provides electrical connections between the conducting wires of the armature and the stationary brushes.
Brushes are provided to interact in contact with the rotating commutator. Brushes induce rotation of the motor rotor by transferring current from a power source to the commutator assembly, thereby completing an electric circuit between the armature and the power source, and developing a magnetic field that creates torque on the rotor, which causes the rotor to rotate about its axis. Brushes are fabricated from conductive material, typically carbon or copper-containing powder mixtures, and are electrically linked to a power source by a wire or other form of electrical connection.
Because brushes are designed to remain in contact with the rotating plates of a commutator assembly during operation, they are subject to wear and degradation due to debris, friction, heat and other potentially adverse operating conditions. As brushes wear, arcing, sparking and other harmful effects may occur as the brush face crosses from one commutator plate to another; these effects and others can have a deleterious impact on motor operation. Therefore, in order to maintain proper operation of the motor, brushes must be periodically replaced to assure adequate conduction between the power source and the commutator, and to prevent damage to the commutator.
The present disclosure provides improved brush assemblies, featuring a longer brush life based on geometric advancements over the prior art and enhanced methods for signaling the need for brush replacement. The improved brush assembly's features also enable the assemblies to be easily installed into an electric motor, either during original construction of the motor or as replacements in the field.
The present disclosure provides a brush arm assembly that generally delivers a longer brush life and can be installed into electric motors more quickly and easily than standard brush assemblies of the prior art. Indeed, the present invention features several inventive advancements over the prior art which may be practiced alone or in combination, as described herein.
In the field of electric motor design, extending brush life can be accomplished by extending brush lengths. One aspect of the present disclosure is an improved brush assembly geometry that provides for a longer usable brush length. According to the present disclosure, the brush assembly includes an arc-shaped brush and a pivot arm, with the mounting end of the arc-shaped brush bound or otherwise mounted with respect to one end of the pivot arm. The brush generally resembles a long rectangular solid that is curved in the longitudinal direction, and that defines a substantially rectangular cross-sectional area.
The end of the pivot arm that is not bound to the arc-shaped brush typically includes and/or defines a female cylindrical slot for mating with a male shaft that is prefabricated in (or otherwise mounted with respect to) the motor housing, parallel (or substantially parallel) to the rotor's axis. When the disclosed brush assembly is installed into an electric motor, the pivot arm slot is slidably positioned onto the shaft in the motor housing, enabling the brush assembly to pivot about the shaft on a plane that is perpendicular (or substantially perpendicular) to the rotor's axis of rotation. A biasing spring force impels the brush assembly to pivot inward toward the rotor in the longitudinal direction of the brush, and maintains the operating end of the arc-shaped brush in contact with the rotating faces of the commutator.
The arc shape of the disclosed brush improves upon straight-shaped brushes of the prior art in at least three respects. First, the arc shape optimizes brush position on the rotating commutator by maintaining a substantially perpendicular relationship between the brush and the commutator throughout the brush's useful life, thereby ensuring that the surface area of the brush face at its operating end, and the brush's conductive performance, remain approximately constant. Similar brush assemblies with pivot arms in the prior art that feature straight-shaped brushes tend to wear unevenly, such that the brush face surface area changes dramatically throughout brush life. If the brush is not promptly replaced, this effect tends to lead to inefficient motor operation, arcing or sparking, or other harmful effects that can potentially damage the motor.
Additionally, while other brush assemblies in the prior art known as brush boxes or brush holder cartridges maintain a roughly constant surface area in contact with a rotating commutator, the disclosed arc-shaped brush is superior to conventional brush boxes in that it is not subject to grinding and/or friction between the brush and the box or cartridge. The arc-shaped brush of the present disclosure maintains a substantially normal, constant connection with the commutator without the necessity of a box or any framing mechanism. Still further, because electric motor housings are traditionally cylindrically shaped, a brush that features an arced geometry in a circumferential direction around the rotor axis advantageously enables a longer brush length to be stored within the motor housing than a standard straight brush.
Another aspect of the present disclosure is an improved device for sensing the need for brush replacement. More particularly, the present disclosure features an apparatus for halting motor operation, as appropriate, through structural inclusion of a spring-bound interrupter device/mechanism that includes a plunger element that is movably maintained within a deployment hole prefabricated into the arc-shaped brush itself, in the longitudinal direction. An exemplary version of the interrupter device/mechanism of the present disclosure features a non-conductive plunger at its tip; when the arc-shaped brush wears to a predetermined length, the deployment hole is exposed and a biasing spring force will push the plunger element of the interrupter device through the deployment hole and into contact with the rotating faces of the commutator. If biasing spring force on the plunger element exceeds the biasing spring force maintaining the brush face in contact with the commutator, the interrupter device/mechanism pushes the brush face away from the commutator, thereby opening the circuit connecting the power source to the armature. This effect eliminates the magnetic field and, therefore, the torque on the rotor, which automatically stops the motor's rotation.
Unlike other methods for halting motor operation in the prior art, the spring providing the biasing force to the plunger element of the disclosed interrupter device/mechanism is not embedded within the brush itself. Rather, in the present disclosure, the spring that provides the biasing force to the plunger element is maintained physically exterior to the brush, and interacts with the brush through a retaining hole near its mounting end. This structural arrangement reduces the amount of brush length occupied by the interrupter device/mechanism, as compared to embedded interrupter devices in the prior art, and permits more of the brush length to be utilized in motor operation.
Another aspect of the present disclosure is that both the biasing spring force associated with the interrupter device/mechanism and the biasing spring force that maintains the brush operating end in contact with the commutator advantageously originate from a single spring, which is made an integral part of the brush assembly. Because the single spring provides both biasing spring forces and is integral to the brush assembly itself, the brush assembly can be installed into the motor housing more quickly and easily than brush assemblies with pivot arms of the prior art, such as those which necessarily operate using two or more biasing springs.
An additional aspect of the present disclosure relates to the manner in which a physical linkage is established with the electric motor housing. Unlike other brush assemblies featuring pivot arms in the prior art which are durably mounted to their motor housings using caps and screws or other more permanent mounting apparatuses, the disclosed pivot arm includes a cylindrical slot that is configured and dimensioned to mate with a shaft that is fabricated within (or otherwise mounted with respect to) the motor housing. To complete installation, the brush assembly is then pivoted about the shaft until a portion of the pivot arm, referred to herein as a shelf, is situated beneath a hold-down tab that is also fabricated within (or otherwise mounted with respect to) the motor assembly. Once the brush assembly is appropriately positioned with its shelf beneath the hold-down tab, an end of the single spring is physically connected to the motor housing, and the brush assembly is electrically connected to the power supply.
Any form of connection known in the prior art may be used to link the spring with the motor housing and the brush assembly with the power supply, so long as a physical connection is established between the single spring and the motor housing, and an electrical connection is established between the brush and the power source. Preferred connections are established quickly, easily and reliably. Once installed, the disclosed brush assembly is able to pivot about the shaft but is advantageously longitudinally locked in position along the shaft, without the use of standard binding devices, such as caps and screws.
The single spring, shelf and integral cylindrical slot of the present disclosure enable the brush assembly to be installed into electric motors in a few brief steps, neither of which requires the use of any tools. These features simplify the construction of electric motors, which can be assembled in their entirety prior to installing the brush assemblies of the present disclosure. Additionally, the brush assemblies of the present disclosure can be replaced more quickly, easily and reliably than brushes or brush assemblies of the prior art, enabling electric motors to remain in service for longer and more efficient durations.
Further areas of applicability of the present disclosure will become apparent from the drawings and detailed description provided herein. It should be understood that the detailed description and specific examples indicate preferred embodiments of the present disclosure and are intended for illustrative purposes only, but do not limit the scope of the present invention.
The subject matter of the present disclosure will become more fully understood from the detailed description and accompanying drawings, wherein:
The following descriptions of exemplary embodiment(s) of the present disclosure are merely illustrative in nature, and are in no way intended to limit the present disclosure, its application and/or its uses.
Referring to
An example of the geometrically improved arc-shaped brush 10 is also shown in
The pivot arm 12 shown in
With reference to
Benefits of the arc shape of brush 10 are demonstrated with reference to
The consistent brush face surface area maintained by the arc-shaped brush 10 of the present disclosure, as shown in
An exemplary interrupter device is shown in
In exemplary embodiments of the present disclosure, the interrupter device 24 includes a non-conductive tip that is attached to or otherwise in physical communication with the single spring, as is described above. However, the present disclosure is not limited to brush assemblies that include interrupter devices with non-conductive tips. Indeed, the present disclosure extends to and encompasses other devices that are effective to halt a motor's rotation, as will be apparent to persons skilled in the art. Accordingly, the description of an exemplary interrupter device as set forth herein is for illustration purposes only, and is not limiting with respect to the scope of the present disclosure.
With reference to
According to the present disclosure, the biasing spring force applied to the interrupter device must be sufficient to press the brush face away from the rotating commutator. Therefore, this biasing force must exceed the biasing spring force maintaining the brush face in contact with the commutator. While the present invention is not limited to any particular excess biasing spring force on the interrupter device, or any ratio between the two biasing spring forces, the biasing spring force on the interrupter device in the preferred embodiment is approximately twice the biasing spring force that maintains the pivot arm in contact with the rotating commutator.
The installation of a brush assembly of the present disclosure into a motor housing is depicted in
During installation, the brush assembly 50 is positioned such that the male shaft 28 of the motor housing is aligned for insertion into the brush assembly's female cylindrical slot (not shown in
Next, the brush assembly 50 is placed into the operating position by pivoting the pivot arm 12 about the shaft 28, until the face of the brush 10 is placed into contact with the commutator 30, and the shelf 18 is situated beneath the hold-down tab 26. The end 16a of the single spring 16 is then physically connected to the motor housing, and the wire 14 is electrically connected to the power supply in the motor housing.
Although the present disclosure has been described with reference to exemplary embodiments thereof the disclosed designs, assemblies and methods may be embodied and/or implemented in alternative ways without departing from the spirit or scope hereof. Accordingly, the present disclosure expressly encompasses alternative embodiments and implementations that would be readily apparent from those skilled in the art based on the description provided herein.