Brush assembly

A brush assembly including a housing having a first opening, a second opening, and an interior space defined between the first opening and the second opening. The brush assembly further includes a removable cover at least partially received within the interior space and covering the first opening, and a brush at least partially received within the interior space and extending from the second opening. The brush is operable to move between an extended position and a retracted position. More of the brush is received within the interior space in the retracted position than in the extended position. The brush assembly further includes a contact received within a mounting aperture formed in the removable cover. The contact is electrically connected to the brush. The brush assembly also includes a spring coupled to the removable cover. The spring biases the brush into the extended position.

BACKGROUND

The present invention relates to a brush assembly for sliding electrical contacts such as those used in, for example, electric motors, and more specifically a brush assembly for use in a grounding circuit.

Induced and static charges on motor shafts commonly cause failures due to current flowing through the bearings and other components. With reference toFIG. 1, a prior art brush assembly10for a grounding circuit is mounted to an axial drive end14of an electric motor18by fasteners22. The brush assembly10includes a brass housing26and a brush30that is biased by a spring34to extend from the brass housing26. The brush30is biased to remain in contact with a rotating shaft38of the electric motor18. A contact42electrically connects the brush30to the brass housing26, and the brass housing26is electrically connected to the axial end14of the motor18by the fasteners22. As such, an electrical connection is formed between the shaft38and the axial end14of the motor18, which is commonly electrical ground.

SUMMARY

In one aspect, the invention provides a brush assembly including a housing having a first opening, a second opening, and an interior space defined between the first opening and the second opening. The brush assembly further includes a removable cover at least partially received within the interior space and covering the first opening, and a brush at least partially received within the interior space and extending from the second opening. The brush is operable to move between an extended position and a retracted position. More of the brush is received within the interior space in the retracted position than in the extended position. The brush assembly further includes a contact received within a mounting aperture formed in the removable cover. The contact is electrically connected to the brush. The brush assembly also includes a spring coupled to the removable cover. The spring biases the brush into the extended position.

In another aspect, the invention provides a brush assembly including a housing having a first opening, a second opening, and an interior space defined between the first opening and the second opening. The housing includes an adjustable mount. The brush assembly also includes a removable cover at least partially received within the interior space and covering the first opening; and a brush at least partially received within the interior space and extending from the second opening. The brush is operable to move between an extended position and a retracted position, wherein more of the brush is received within the interior space in the retracted position than in the extended position. The brush is formed from a silver graphite composition. The brush assembly further includes a contact received within a mounting aperture formed in the removable cover. The contact is electrically connected to the brush. The brush assembly also includes a constant-force spring coupled to the removable cover, the spring biasing the brush into the extended position. A grounding circuit is formed between the brush and the contact and the grounding circuit is insulated by the holder and the removable cover.

DETAILED DESCRIPTION

With reference toFIGS. 2-5, a brush assembly110according to one embodiment of the invention includes a housing114, a removable cover118, and a brush122. The housing114includes a first opening126(FIG. 4), a second opening130(FIG. 5), and an interior space134defined between the first opening126and the second opening130. The removable cover118is at least partially received within the interior space134and the removable cover118covers the first opening126. The removable cover118includes a stem portion138that is received within a cover track142formed in the housing114. The removable cover118also includes a lip146and the removable cover118is secured to the housing114with a releasable press-fit engagement between the lip146and the housing114. More specifically, in the illustrated embodiment, the lip146includes a protrusion150that is received within a groove154formed in the housing114. The protrusion150received within the groove154secures the removable cover118to the housing114, but is easily overcome (i.e., separated) by a user attempting to remove the removable cover118from the housing114. When the removable cover118is removed from the housing114, the interior space134of the housing114is exposed.

With references toFIGS. 2-5, the brush122is at least partially received within the interior space134and extending from the second opening130. The brush122is operable to move between an extended position (FIG. 2) and a retracted position (FIG. 3). More of the brush122is received within the interior space134when the brush122is in the refracted position than when the brush122is in the extended position. The brush122is formed from silver graphite. In some embodiments, the brush122is 50% silver and 50% graphite by weight. The silver content in the brush122provides low contact resistance for electrical grounding, and the graphite content in the brush122provides low friction for extended life. The housing114further includes a brush track158in which the brush122is slidably received. In other words, the brush122slides along the brush track158as the brush122moves between the extended and retracted positions.

With reference toFIGS. 4 and 5, the brush assembly110further includes a spring162biasing the brush122into the extended position (FIG. 2). The spring162is coupled to the removable cover118. In the illustrated embodiment, the spring162is a constant-force spring and is coupled to the stem portion138of the removable cover118. In the illustrated embodiment, the spring162directly contacts a rear surface166of the brush122, and the rear surface166is curved to correspond to the spring162coil. As the brush122retracts further into the housing114, the brush122causes the spring162to partially unfurl along a spring track170formed in the stem portion138. The spring162provides a biasing force on the brush122that is optimized for low contact resistance and long life.

When the removable cover118is secured to the housing114, the spring162is encapsulated within the housing114, and removing the removable cover118provides access to the spring162. In other words, when the removable cover118is on the housing114, the spring162is protected from exterior debris and environmental damage, but once the removable cover118is removed a user has access to the spring162for inspection, maintenance, and replacement purposes. In addition, once the removable cover118is removed, a user may similarly inspect the brush122for wearing or replace the brush122completely. As such, the removable cover118improves the serviceability of the brush assembly110, while protecting internal components from environmental hazards.

With continued reference toFIGS. 4 and 5, the brush assembly110further includes a contact174received within a mounting aperture178formed in the removable cover118. The contact174is electrically connected to the brush122via a wire182, and the contact174is ultimately connected to an external ground (e.g., a motor chassis or frame). The housing114further includes a contact track186that receives the contact174and the wire182. As such, the electrical connection (e.g., the wire182) between the contact174and the brush122is protected within the housing114, but the removable cover118can be removed in order to provide access to the electrical connection. The housing114and removable cover118are made from an insulating material (e.g., a phenolic resin). As such, a grounding circuit is formed between the brush122and the contact174, but the portions of the contact174, the brush122, and the wire182contained by the housing114and the removable cover118within the grounding circuit are insulated.

Moreover, the combination of the housing114and the removable cover118seal the brush122, the spring162, and the wire182from contaminants and particulate that could disturb the function of these parts. While at the same time, the removable cover118provides the user access to the brush122, the spring162, and the wire182should they need to be inspected, replaced, maintained, or otherwise accessed. Therefore, the removable cover118provides a multi-purpose functional advantage over the prior art.

With reference toFIGS. 2-5, the brush assembly110further includes an adjustable mount. In the illustrated embodiment, the adjustable mount is formed on the housing114as slots190. The slots190are configured to receive a fastener (not shown) within the slot190for securing the housing114to, for example, an axial end of a motor. The fasteners can move within the slots190to provide adjustable mounting prior to fully tightening the fasteners. Being able to adjustably mount the brush assembly110is important for correctly orientating and positioning the brush122relative to a motor shaft, for example. With reference toFIG. 6, an alternative adjustable mount is illustrated as a reclosable fastener194. More specifically, a first portion198of the reclosable fastener194is secured to the housing114with an adhesive and a second, corresponding portion202of the reclosable fastener194is secured to the area in which the brush assembly110is desired with an adhesive. The reclosable fastener194is, for example, Dual Lock™ commercially available from 3M™.