Motorcycle with coaxial swingarm pivot and drive sprocket
A motorcycle in which the swingarm pivot is coaxial with the sprocket shaft, and the sprocket is laterally outside the swingarm structures at the swingarm pivot. The swingarm pivot is located in the engine case, such as where the cylinder block meets the crankcase. An optional slipper clutch is located in the crankcase, such as where an upper crankcase half meets a lower crankcase half, and drives the sprocket shaft.
1 . An apparatus comprising:
a motorcycle engine including,
a cylinder block,
a crankcase coupled to the cylinder block,
a crankshaft disposed within the crankcase,
a gearbox coupled to be driven by the crankshaft, and
a sprocket shaft coupled to be driven by the gearbox;
a motorcycle swingarm including,
an elongated body, wheel mounting structure at a rear end of the elongated body for coupling to a wheel, and
pivot mounting structure at a front end of the elongated body coupled to the motorcycle engine at a swingarm pivot which is substantially coaxial with the sprocket shaft; and
a first sprocket coupled to the sprocket shaft outboard of the pivot mounting structure.
2 . The apparatus of claim 1 wherein:
the sprocket shaft exits the motorcycle engine between the cylinder block and the crankcase.
3 . The apparatus of claim 2 further comprising:
a slipper clutch coupling the sprocket shaft to the gearbox.
4 . The apparatus of claim 3 wherein:
the crankcase includes,
an upper crankcase half, and
a lower crankcase half coupled to the upper crankcase half; and
the slipper clutch is coupled to the crankcase between the upper and lower crankcase halves.
5 . The apparatus of claim 4 wherein:
the slipper clutch is coupled to the gearbox by a bevel gear.
6 . The apparatus of claim 1 further comprising:
a second sprocket coupled to the sprocket shaft outboard of the pivot mounting structure at an opposite side of the motorcycle engine from the first sprocket.
7 . The apparatus of claim 1 wherein:
the swingarm is substantially symmetrical about a plane perpendicular to an axis of the sprocket shaft.
8 . A motorcycle comprising:
an engine including,
a cylinder block,
a crankcase coupled to the cylinder block,
a crankshaft coupled to the crankcase,
a gearbox coupled to the crankcase and including a gear train coupled to be driven by the crankshaft,
a sprocket shaft coupled to be driven by the gearbox, and
a first sprocket coupled to the sprocket shaft;
a swingarm coupled to the engine at a swingarm pivot which is substantially coaxial with the sprocket shaft;
wherein the first sprocket is located on the sprocket shaft at a position axially beyond the swingarm.
9 . The motorcycle of claim 8 wherein:
the swingarm pivot comprises bearings which are coupled to the engine.
10 . The motorcycle of claim 9 wherein:
the swingarm pivot bearings are coupled to the engine by a bracket which threads into the engine.
11 . The motorcycle of claim 9 wherein:
the swingarm pivot bearings are coupled to the engine at a location where the cylinder block meets the crankcase, such that a first portion of the swingarm pivot bearings are coupled to the cylinder block and a second portion of the swingarm pivot bearings are coupled to the crankcase.
12 . The motorcycle of claim 8 further comprising:
a slipper clutch which couples the sprocket shaft to the gearbox.
13 . The motorcycle of claim 12 wherein:
the sprocket shaft includes an input gear; and
the slipper clutch includes,
a first gear which couples to the gearbox, and
a second gear which couples to the input gear of the sprocket shaft.
14 . The motorcycle of claim 8 further comprising:
a second sprocket coupled to the sprocket shaft at an end opposite from the first sprocket;
wherein the first and second sprockets are located on the sprocket shaft at respective positions which are axially beyond the swingarm at opposite sides of the engine.