Brush wear indicator

In a brush wear indicator for a direct current machine having a rotating armature and commutator, a yoke surrounding said commutator, a plurality of brush holders on said yoke, positive- and negative-polarity carbon brush means mounted in said brush holders for translatory movement relative to said commutator, said positive- and negative-polarity brush means each having a contact face spring-pressed against said commutator, said positive- and negative-polarity brush means being connectable respectively to positive and negative lines of an external power circuit, the invention comprising:

• a. each said carbon brush means having an elongated groove formed in one side thereof, said groove having opposed sides and a bottom, said groove having a terminating end spaced from the end of said brush means away from said contact face, said groove extending from said terminating end towards said contact face,
• b. an electrically conductive probe for each brush means, each probe being mounted in fixed relation to said yoke and said brush holders and having an end portion extending into said groove of the brush means associated therewith, said end portion of said probe being spaced from the sides and bottom of said groove during translatory movement of said brush means but engageable with said terminating end of said groove,
• c. an electrically energizable signal device,
• d. means responsive to engagement of the terminating end of the groove of one of said brush means with the probe associated therewith for energizing said signal device from said power circuit.