| 摘要 |
The electrically operated drum brake (10) comprises an electric motor assembly (80, 180) disposed between opposing ends (62, 72) of two brake shoes (12, 14), the electric motor assembly (80, 180) replacing both the hydraulic wheel cylinder and the parking brake strut and lever. The electric motor assembly (80, 100) comprises a housing (82, 182) having an interior opening (84, 184) in which is disposed an electric motor (86, 186). The electric motor (86) drives a planetary gear assembly (91) which operates a screw mechanism (102) that engages an end (72) of an adjacent brake shoe (14), the housing (82) engaging the other brake shoe (12). An alternative embodiment includes an electric motor (186) which drives a bearing drive member (198), the bearing drive member (198) having a bearing track (200) which receives a plurality of bearing balls (205). The bearing balls (205) engage a fixed bearing track (187) on the housing ( 182) and also a curved surface (202) on a rotatable bearing member (201). The rotatable bearing member (201) engages a screw mechanism (204) so that when rotation of the bearing balls (205) causes rotation of the rotatable bearing member (201), the screw mechanism (204) is displaced against a brake shoe (14) and, by reaction, the housing (182) is displaced against the other brake shoe (12).
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