Gear assembly

A planetary gear assembly comprising:

• primary planetary gear means and secondary planetary gear means, one of said primary planetary gear means and said secondary planetary gear means comprising a planetary gear set and the other of said primary planetary gear means and said secondary planetary gear means comprising a plurality of co-axial planetary gear sets;
• selection means for selecting one of the plurality of co-axial planetary gear sets;
• a rotatable housing which is mounted for rotation around the planetary gear sets, wherein a rotational input drives the primary planetary gear means, an output from the primary planetary gear means being transmitted to the rotatable housing, an output from the rotatable housing driving the secondary planetary gear means and an output from the secondary planetary gear means being transmitted to a rotational output means;
• and
• gear engagement means associated with each of said plurality of co-axial gear sets, the gear engagement means and the plurality of planetary gear sets being arranged for relative translation movement in a direction which is substantially parallel to the axis of the plurality of the planetary gear sets, and the arrangement of the planetary gear assembly being such that, in use, the relative translation movement brings a selected one of the plurality of planetary gear sets into engagement with a respective one of the gear engagement means, and said respective one of the gear engagement means acts at least in part as a rotational transmission means between said primary gear set and said secondary gear set.

A planetary gear assembly comprising:

• primary planetary gear means and secondary planetary gear means, one of said primary planetary gear means and said secondary planetary gear means comprising a planetary gear set and the other of said primary planetary gear means and said secondary planetary gear means comprising a plurality of co-axial planetary gear sets;
• selection means for selecting one of the plurality of co-axial planetary gear sets;
• a rotatable housing which is mounted for rotation around the planetary gear sets, wherein a rotational input drives the primary planetary gear means, an output from the primary planetary gear means being transmitted to the rotatable housing, an output from the rotatable housing driving the secondary planetary gear means and an output from the secondary planetary gear means being transmitted to a rotational output means;
• gear engagement means associated with each of said plurality of co-axial gear sets, the gear engagement means and the plurality of planetary gear sets being arranged for relative translation movement in a direction which is substantially parallel to the axis of the plurality of the planetary gear sets, and the arrangement of the planetary gear assembly being such that, in use, the relative translation movement brings a selected one of the plurality of planetary gear sets into engagement with a respective one of the gear engagement means, and said respective one of the gear engagement means acts at least in part as a rotational transmission means between said primary gear set and said secondary gear set;
• and
• caming means which is operative to cause the relative translational movement of said planetary gear set and said respective gear engagement means;
• wherein the assembly comprises a rack and pinion arrangement, and in use, suitable movement of the rack effects rotation of the pinion which causes the relative translational movement of said planetary gear set and said respective gear engagement means.

A planetary gear assembly comprising:

• a primary planetary gear assembly and a secondary planetary gear assembly, the gear assemblies each comprising a plurality of co-axial planetary gear sets;
• a selection device for selecting a co-axial planetary gear set in the primary planetary gear assembly and a co-axial planetary gear set in the secondary planetary gear assembly;
• and
• a rotatable housing for housing the gear assemblies and mounted for rotation around the gear assemblies, wherein the housing is rigidly attached to first and second portions of the selection device such that when the selected co-axial planetary gear set in the primary planetary gear assembly is driven by a rotational input, the first portion of the selection device engaging the primary planetary gear assembly drives the selected co-axial planetary gear set in the secondary planetary gear assembly via the housing and the second portion of the selection device engaging the secondary gear assembly and an output of the selected secondary planetary gear assembly is transmitted to a rotational output means.