Front chainring assembly
A chainring assembly includes a chainring carrier adapted to be coupled to a crank arm. The chainring carrier is rotatable about a rotation axis and includes an outer periphery having carrier threads. A chainring structure includes an inner periphery having chainring threads and an outer periphery comprising a plurality of teeth. The inner periphery of the chainring structure is threadably engaged with the outer periphery of the chainring carrier. In one embodiment, a power meter device includes a body having a torque input section and a torque output section, with the torque output section including an outer periphery having threads adapted to be coupled to a chainring structure.
1 . A front chainring assembly comprising:
a power meter device comprising:
a body comprising a torque input section and a torque output section, the body configured to transmit power between the torque input section and the torque output section, the torque input section adapted to be coupled to a crank arm, wherein the body is rotatable about a rotation axis, the torque output section comprising an outer periphery comprising power meter threads and an axial stop surface; and
a plurality of circumferentially spaced strain measurement devices spaced radially outwardly from the rotation axis and coupled to the body, the plurality of strain measurement devices configured to provide a signal indicative of a strain detected in the body; and
circuitry interpreting the signal and determining a corresponding power transmitted between the torque input section and the torque output section; and
a chainring structure comprising an inner periphery comprising chainring threads and an outer periphery comprising a plurality of teeth and a axial face, wherein the inner periphery of the chainring structure is threadably engaged with the outer periphery of the torque output section, wherein the axial face comprises a plurality of circumferentially spaced axial projections separated by circumferentially spaced recesses, and wherein the chainring structure is rotatable relative to the body between a disengaged position and an engaged position, wherein the circumferentially spaced axial projections engage the stop surface when the chainring structure is the engaged position and wherein the plurality of strain measurement devices are radially aligned with the recesses when the chainring structure is in the engaged position.
2 . The front chainring assembly of claim 1 , wherein the torque output section comprises an annular flange extending radially outwardly adjacent the power meter threads on the outer periphery of the torque output section, wherein the annular flange defines the stop surface.
3 . The front chainring assembly of claim 1 , wherein at least some of the power meter threads comprise a blunt thread start and at least some of the chainring threads comprise a blunt thread start.
4 . The front chainring assembly of claim 1 , wherein the body comprises an annular cavity disposed radially between the torque input section and the torque output section, wherein the plurality of strain measurement devices are attached to a base surface of the annular cavity.
5 . The front chainring assembly of claim 1 , wherein the body comprises a plurality of circumferentially spaced openings positioned between the plurality of strain measurement devices, wherein the plurality of openings are radially aligned with the plurality of axial projections when the chainring structure is in the engaged position.
6 . The front chainring assembly of claim 5 wherein at least some of the plurality of openings are circumferentially elongated.
7 . The front chainring assembly of claim 5 wherein the plurality of openings comprises five openings and the plurality of axial projections comprises five axial projections.
8 . The front chainring assembly of claim 1 wherein the chainring structure comprises an outboard side and an inboard side, wherein the axial face is formed on the outboard side.
9 . A front chainring assembly comprising:
a chainring carrier adapted to be coupled to a crank arm, wherein the chainring carrier is rotatable about a rotation axis, and wherein the chainring carrier comprises:
an inboard side defining an axial stop surface;
an outboard side;
an outer periphery comprising carrier threads;
a plurality of circumferentially spaced strain measurement devices spaced radially outwardly from the rotation axis; and
a plurality of circumferentially spaced openings positioned between the plurality of strain measurement devices; and
a chainring structure comprising:
an inboard side;
an outboard side comprising an axial face, wherein the axial face comprises a plurality of circumferentially spaced axial projections separated by circumferentially spaced recesses;
an inner periphery comprising chainring threads, wherein the inner periphery of the chainring structure is threadably engaged with the outer periphery of the chainring carrier; and
an outer periphery comprising a plurality of teeth;
wherein the chainring structure is rotatable relative to the chainring carrier between a disengaged position and an engaged position, wherein the circumferentially spaced axial projections engage the stop surface when the chainring structure is the engaged position, wherein the plurality of openings are radially aligned with the plurality of axial projections when the chainring structure is in the engaged position and wherein the plurality of strain measurement devices are radially aligned with the plurality of recesses when the chainring structure is in the engaged position.
10 . The front chainring assembly of claim 9 , wherein the chainring carrier comprises an annular flange extending radially outwardly adjacent the carrier threads on the outer periphery of the chainring carrier, wherein the annular flange defines the stop surface.
11 . The front chainring assembly of claim 9 , wherein at least some of the carrier threads comprise a blunt thread start and at least some of the chainring threads comprise a blunt thread start.