A two-speed power transmission configured for use in a power tool, said power tool comprising a housing;
- an input shaft;
- and an output shaft, wherein said two-speed power transmission comprising:
- a planetary gear
- comprising a sun wheel connected to said input shaft, a ring gear secured in the housing, and a planet wheel carrier;
- a torque responsive gear shift mechanism for directing torque through said planetary gear in a high torque/low speed drive mode or past said planetary gear in a low torque/high speed drive mode, said gear shift mechanism comprising a driving member connected to the sun wheel of said planetary gear, a driven member connected to said output shaft, and a number of coupling elements arranged to intercouple in a first position said driving member and said driven member and to intercouple in a second position said planet wheel carrier and said driven member,
- wherein said driven member comprises a number of axially extending grooves arranged to support said coupling elements for axial displacement of said coupling elements between said first and said second position,
- wherein said driving member comprises:
- an axially acting first cam means for cooperation with said coupling elements in said first position of said coupling elements;
- a first, axially acting spring means configured for biasing said coupling elements toward said first position of said coupling elements, whereby the action of said first spring means counteracts the axial force developed by said first cam means upon said coupling elements, such that said coupling elements are maintained in said first position at torque values below a predetermined level but forced out of said first position by said first cam means at torque values above said predetermined level;
- and
- a second, axially acting cam means provided in said axially extending grooves and arranged to exert an axial shifting force upon said coupling elements toward said second position of said coupling elements against the biasing action of said spring means as said coupling elements have left said first position at torque values above said predetermined level,
- wherein said planet wheel carrier is coupled to a coupling sleeve which provides a radial support for said coupling elements in said second position of said coupling elements only and which is provided with a number of axially extending tracks for cooperation with said coupling elements in said second position of said coupling elements, and
- wherein said driving member comprises a number of recesses, wherein said first axially acting cam element each form part of respectively one of said recesses, and wherein each of said recesses are adapted for receiving and radially supporting one of said coupling elements in said first position of said coupling elements, such that each of said coupling elements are shielded and rotationally decoupled from the coupling sleeve in said high speed/low torque mode.