GB883950A - Improvements in or relating to brush holders - Google Patents

Abstract

883,950. Brushgear for dynamo-electric machines. LAING, N., and LUDIN, L. Dec. 23, 1957 [Dec. 24, 1956], No. 39249/56. Class 35. A brush holder for use with an electrical commutator machine comprises, in the Figs. 1 and 2 embodiment, a body 30 for supporting in juxtaposition for engagement with a commutator not shown a first brush 4 and at least one replacement brush 5 for subsequent commutator engagement after the first brush 4 has been consumed to a predetermined residual length, spring-loaded pressure levers 7, 8 urging respective brushes towards the commutator and pivoted about a common axis 9 at least the first lever 7 having a cam 18, and a retaining pawl 19 or detent which holds the replacement brush 5 out of engagement with the commutator until the pawl is released by the cam 18 when the first brush reaches its residual length. The pressure lever springs 11, 15 are tensioned between lugs 12, 13, 16 so positioned that as the brushes progressively wear the lengths of the moment arms 26, 27 increase at a greater rate than the decrease in tension due to shortening of the springs, thereby resulting in steadily increasing brush pressure during the brush life and widely varying natural frequency of vibration. In another embodiment, Figs. 3, 5, 10, arcuate brushes 28, 29 are fixed to radial pressure levers one of which is shown at 34 and are inclined to the common axis of the solid and hollow shafts 31, 32 with which the respective levers are fast so that during their life the brushes present faces which move axially along the commutator. Secured to the shaft 31 of the first brush 28 is a cam 52 which when the brush reaches its residual length raises a slide member 45 whose hook portion 50 releases the lever 35, not shown, of the replacement brush 29. Spiral springs 37, 43 convey through arms 41 a steadily increasing brush pressure, and brush chatter is minimized by the provision of a spring 54 or a resilient damping member.