| 摘要 |
A hammer mechanism (200,200') for a power tool comprises a housing (203), a chuck spindle (201) journalled for rotation in the housing and having axial freedom of movement in the housing, a rotary ratchet (204) fixed on the spindle, the ratchet having teeth (207) facing a rear end of the housing, a fixed ratchet (205) rotationally fixed in the housing but having axial freedom of movement in the housing, the fixed ratchet surrounding the spindle and having teeth (207) facing the teeth of the rotary ratchet, and a spring (213) between the fixed ratchet and housing resiliently biasing the fixed ratchet towards the rotary ratchet. A first cam (208,209) between the fixed and rotary ratchets has two positions. In a first position, the ratchets can engage one another, whereby reciprocal motion is imparted on the spindle on rotation thereof. In a second position the ratchets are prevented from inter-engagement. A second cam (224) between the fixed ratchet and housing have two positions. In a first position, the fixed ratchet is axially locked and in a second position the fixed ratchet is permitted rearward movement against the spring.
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