Transmission device for bicycle

A transmission device for a bicycle, including:

• a housing, configured to be disposed on the bicycle;
• a mandrel, rotatably disposed on the housing and extending along an axial direction, each of two axially opposite ends of the mandrel being configured to be assembled with a crank of the bicycle;
• an assembling member, configured to be assembled with a sprocket of the bicycle, the assembling member having a driving gear co-movably disposed thereon;
• a transmission assembly, rotatably disposed on the housing and engaged with the driving gear;
• a derailleur assembly, including a first derailleur gear and a second derailleur gear which are rotatable relative to the housing, the first derailleur gear and the second derailleur gear being respectively engaged with the transmission assembly;
• a clutch assembly, including a clutch member which is co-movably assembled with the mandrel and movable between a first position and a second position along the axial direction;
• wherein when the clutch member is in the first position, the clutch member is engaged with the first derailleur gear and disengaged from the second derailleur gear, and the mandrel drives the first derailleur gear, the transmission assembly and the driving gear to rotate;
• when the clutch member is in the second position, the clutch member is engaged with the second derailleur gear and disengaged from the first derailleur gear, the mandrel drives the second derailleur gear, the transmission assembly and the driving gear to rotate;
• wherein the clutch member is non-rotatably sleeved to the mandrel and movable between the first position and the second position in the axial direction relative to the mandrel, and the first derailleur gear and the second derailleur gear are rotatably sleeved to the mandrel and located at two opposite sides of the clutch member.