Force measurement sensor for a crankset
A crankset assembly to be mounted on a bicycle includes at least one right-hand bearing for mounting a crankset shaft and a force sensor positioned around the outer ring of the bearing. The force sensor includes a peripheral portion, a central portion, and a top frame connecting a top section of the peripheral portion to a top portion of the central portion. The frame is positioned at a diameter oriented along an axis (Y′). The axis (Y′) makes an angle (φ) of between 10° and 30° with the vertical axis (Y) and the top frame is positioned behind the vertical axis (Y).
1. A crankset assembly configured to be mounted on a bicycle, said assembly comprising:
at least one right-hand bearing for mounting a crankset spindle and a single force sensor placed around an outer ring of said bearing, said force sensor comprising a peripheral portion, a central portion and a top frame linking a top section of the peripheral portion to a top portion of the central portion, said top frame being placed on a diameter oriented on an axis (Y′),
wherein the axis (Y′) forms an angle (φ) of between 10° and 30° with a vertical axis (Y) in a counter clockwise direction when seen from a right side of the bicycle so that the top frame is oriented towards a rear side of the bicycle with respect to the vertical axis (Y).
2. The assembly as claimed in claim 1 , wherein the angle (φ) is between 20° and 25°.
3. The assembly as claimed in claim 1 , wherein the sensor is equipped with a single measuring channel.
4. The assembly as claimed in claim 1 , wherein four strain gauges are placed on the top frame, said four strain gauges being mounted in Wheatstone bridge configuration in order to supply a signal to the single measuring channel.
5. The assembly as claimed in claim 1 , wherein said central portion comprises a seat configured to receive an outer ring of a bearing in order to mount a shaft rotating about an axis.
6. The assembly as claimed in claim 1 , wherein the top frame comprises a web plate bracketed by two arms that are substantially parallel to one another such that said top section of the peripheral portion, said top portion of the central portion, and the two arms form a parallelogram.
7. The assembly as claimed in claim 6 , wherein a thickness of the web plate, on an axis (Z), is less than 50% of a thickness of the arms.
8. The assembly as claimed in claim 6 , wherein the web plate is in contact with the two arms, with the top section, and with the top portion.
9. The assembly as claimed in claim 6 , wherein the web plate, the two arms, the top section, and the top portion form part of one and a same piece produced in a single material.
10. The assembly as claimed in claim 6 , wherein the web plate is planar and is oriented on a radial plane, at right angles to an axis (Z).
11. The assembly as claimed in claim 6 , wherein, on an axis (Z), the web plate occupies a central position with respect to the arms.
12. The assembly as claimed in claim 1 , wherein a bottom frame, which is substantially identical to the top frame, links the peripheral portion to the central portion, and the top frame and the bottom frame are diametrically opposed.
13. The assembly as claimed in claim 1 , wherein a bottom frame, which is substantially identical to the top frame, links the peripheral portion to the central portion, and the top frame and the bottom frame are diametrically opposed along the axis (Y′).
14. A method for controlling an electric assist motor for a bicycle, comprising:
equipping said bicycle with the crankset assembly as claimed in claim 1 , wherein a signal S generated by the force sensor corresponds to the component, on an axis (X′, X′), that is at right angles to (Y′) and to (Z), of the action R right being exerted on the right-hand bearing, the component being denoted: R Rx′ Total, and
wherein the part of the component R Rx′ Total, which is generated by a cyclist, R Rx′ Cyclist, is equal to:
R RX′ Cyclist=R RX′ Total−K 1 *K 2 *I
in which, I is the current consumed by the assist motor; K 1 is a constancy of torque of the assist motor and K 2 is a factor dependent on a number of teeth of a chain ring meshing with a transmission chain, and wherein the current supplied to the electric assist motor is determined according to an action of the cyclist R Rx′ Cyclist deduced from the signal S.