Patent Publication Number: US-4924129-A

Title: Electrical brushgear

Description:
BACKGROUND TO THE INVENTION 
     This invention relates to electrical brushgear for dynamo-electric machines and particularly to a brush assembly intended for use in a machine wherein the brushes bear axially on commutator segments. 
     The main object of the invention is to provide an improved assembly in which the brush is removable either axially or radially with respect to the axis of the rotor. 
     SUMMARY OF THE INVENTION 
     According to the invention electrical brushgear comprises a brush, a frame supporting the brush against movement in directions corresponding to directions towards a motor axis and peripherally of the motor, and adapted to allow movement of the brush in a first direction away from the motor axis and in a second direction orthogonal to the first direction and axially of the motor, and a clip releasably securable to said frame and adapted to bear on the brush to prevent the said movement away from the axis, the clip including a spring biassing means for engagement with a rear portion of the brush. 
     According to another aspect, the invention provides brushgear comprising a trapezoidally-sectioned carbon brush, which has a transverse section in the form of a wedge, a frame which supports the brush on three side faces corresponding to the equilateral sides and end of the wedge, and a clip which is releasably securable to the frame and is adapted to support the brush on the fourth side face, the brush being relatively movable lengthwise relative to the frame and clip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an end view of one embodiment of an assembly according to the invention; 
     FIG. 2 is a side view of part of the assembly; 
     FIG. 3 is a view of a frame member forming part of the assembly; and FIGS. 4, 5 and 6 are top, end and side views of a clip forming part of the assembly. 
    
    
     DETAILED DESCRIPTION 
     The Figures illustrate an assembly 1 by means of which a carbon brush 2 is supported in position relative to the commutator ring of a d.c. motor. In this embodiment the brush is positioned so as to bear on an end face of the commutator. The brush 2 is generally of trapezoid shape, having a section like a truncated wedge and the two radial side faces 3 and 4 are mutually inclined, being in radial planes which intersect at the axis 5 of the machine. The shape provides even wear over the front surface 6 of the brush. 
     The brush is supported in a frame 7 (shown by itself in FIG. 3) composed of two generally triangular section members 8 and 9 joined by a channel member 10. This member accommodates the bottom of the brush, which fits slidably into the channel 11 in the member 10. The trangular section members each slidably engage and support one each of the sidefaces 3 and 4 of the brush, having mutually tapered wall portions 12 and 13 for this purpose. The frame has at its corners circular recesses 14 which extend throughout the depth of the frame and can each receive a respective supporting pin. 
     The brush has, extending from its rear face, a braided cable 15 leading to a terminal fitting plate 16. 
     The frame supports the brush on three sides and allows the brush to be inserted or removed both axially and radially. The fourth side of the brush is supported by a removable clip 17 which is adapted to provide restraint of the brush in the radial direction, by bearing on the top side of the brush, and to provide a spring-bias in the axial direction, to urge the brush into contact with the commutator segments. 
     The clip 17 (also shown in FIGS. 4, 5 and 6) may be formed from sheet metal and comprises a central channel portion 18 including two downwardly protruding ridges 19 which bear on the top side of the brush. The central portion 18 fits in a channel defined by shoulders 20 on the triangular frame parts. On each side of the central portion the clip has an outer arm 21 in each of which is formed a hook 22. Each hook can engage the rim of a respective aperture 23 in the frame in such manner as to prevent movement of the clip towards the commutator, i.e. in the direction of the arrow in FIG. 3. The clip has an upturned rear lug 24 constituting a handle. 
     Between the two ridges is mounted a coil 25 of spring strip, anchored at its outer end to the clip. The coil bears on the brush&#39;s rear face 26, which is preferably inclined to provide a ramp for the spring. The spring may be a coil spring of ribbon steel sold under the trademark TENSATOR spring, the purpose of which is to exert constant pressure on the electrical brush. 
     Removal of the clip requires only a slight rearward movement to disengage the hooks; and then an outward lifting movement; the brush may then be removed in a radial or an axial direction. Insertion of a new brush is the reverse process. 
     The duality of insertion or removal movement of the brush provides in general greater freedom in the arrangement of the machine and greater convenience in maintenance of the machine.