Non-pneumatic wheel
A non-pneumatic wheel having spokes that are constructed such that collectively the plurality of spokes exhibit a fractional radial stiffness value within a range of 1 N/mm/deg to 10 N/mm/deg and a non-linearity of less than 20% when deflected under normal loading conditions.
1. A non-pneumatic wheel defining an axis of rotation and defining an axial direction, a radial direction, and a circumferential direction, the non-pneumatic wheel comprising:
an outer band, an outer surface of the outer band having a ground contacting surface; wherein the outer band forms a contact patch under a normal loading condition;
a hub; and
a plurality of spokes;
wherein the non-pneumatic wheel provides an average contact pressure equal to a value in the range of 2 to 4 bar;
wherein each spoke is constructed such that collectively the plurality of spokes exhibit a fractional radial stiffness value within a range of 1 N/mm/deg to 10 N/mm/deg and a non-linearity of less than 20% when deflected under normal loading conditions.
2. The non-pneumatic wheel of claim 1 wherein the average contact pressure is calculated by a total load exerted on the wheel by a vehicle measured in a static state on a flat surface divided by an area within the outer perimeter of the contact patch.
3. The non-pneumatic wheel of claim 1 wherein each spoke has a stiffness and wherein the fractional stiffness is calculated by adding together the stiffness of each spoke and dividing by 360 degrees, where the stiffness of each spoke is calculated by measuring a first force F 1 exerted when the spoke is displaced a first displacement D 1 equal to that when it is at the center of the contact patch under normal loading conditions, measuring a second force F 2 exerted when the spoke is displaced a second displacement D 2 equal to that when it is in position at 180 degrees from the center of the contact patch under normal loading conditions, wherein the stiffness of each spoke is equal to (F 1 −F 2 )/(D 1 −D 2 ) for each spoke.
4. The non-pneumatic wheel of claim 3 wherein the nonlinearity is calculated by plotting a force exerted by each spoke against a displacement of each spoke over a plurality of displacement values from the first displacement D 1 to the second displacement D 2 , plotting a first line between the first displacement, second force value coordinate (D 1 , F 1 ) and the second displacement, second force value coordinate (D 2 , F 2 ) and measuring the maximum deviation of force (DF max ) from the first line for any given value along the force ordinate, the nonlinearity represented as a percentage, the ratio of (DF max /(F1−F2)).
5. The non-pneumatic wheel of claim 1 where each spoke forms a generally radial line between a connection point of the spoke with the hub and a connection point of the spoke with the outer band.
6. The non-pneumatic wheel of claim 1 wherein the plurality of spokes each possess a v-shaped geometry.
7. The non-pneumatic wheel of claim 6 wherein each of the plurality of spokes nest with an adjacent spoke.
8. The non-pneumatic wheel of claim 6 wherein each of the plurality of spokes nest with the adjacent spoke such that a nose of the spoke extends past a vertical line drawn between a connection point of the adjacent spoke with the hub and a connection point of the adjacent spoke with the outer band.
9. The non-pneumatic wheel of claim 1 wherein the normal loading condition is 80% of a maximum loading condition.
10. The non-pneumatic wheel of claim 1 wherein the normal loading condition is a maximum loading condition.
11. The non-pneumatic wheel of claim 1 wherein the spokes are in pre-compression when the wheel is in an unloaded state.
12. The non-pneumatic wheel of claim 1 wherein the spokes are in pre-tension when the wheel is in an unloaded state.
13. The non-pneumatic wheel of claim 1 wherein the spokes are in a neutral state when the wheel is in an unloaded state.
14. The non-pneumatic wheel of claim 1 wherein the fractional radial stiffness value is within a range of 2 N/mm/deg to 6 N/mm/deg.
15. The non-pneumatic wheel of claim 1 wherein the fractional radial stiffness value is within a range of 3 N/mm/deg to 3.66 N/mm/deg.
16. A non-pneumatic wheel defining an axis of rotation and defining an axial direction, a radial direction, and a circumferential direction, the non-pneumatic wheel comprising:
an outer band, an outer surface of the outer band having a ground contacting surface; wherein the outer band forms a contact patch under a normal loading condition;
a hub; and
a plurality of spokes;
wherein the non-pneumatic wheel provides an average contact pressure equal to a value in the range of 2 to 4 bar, the average contact pressure calculated by a total load exerted on the wheel by a vehicle measured in a static state on a flat surface divided by an area within the outer perimeter of the contact patch;
wherein each spoke is constructed such that collectively the plurality of spokes exhibit a fractional radial stiffness value within a range of 1 N/mm/deg to 10 N/mm/deg, wherein each spoke has a stiffness and the fractional stiffness is calculated by adding together the stiffness of each spoke and dividing by 360 degrees, where the stiffness of each spoke is calculated by measuring a first force F 1 exerted when the spoke is displaced a first displacement D 1 equal to that when it is at the center of the contact patch under normal loading conditions, measuring a second force F 2 exerted when the spoke is displaced a second displacement D 2 equal to that when it is in position at 180 degrees from the center of the contact patch under normal loading conditions, wherein the stiffness of each spoke is equal to (F 1 −F 2 )/(D 1 −D 2 ) for each spoke;
wherein each spoke is constructed such that the plurality of spokes exhibit a non-linearity of less than 20% when deflected under normal loading conditions, the nonlinearity calculated by plotting a force exerted by each spoke against a displacement of each spoke over a plurality of displacement values from the first displacement D 1 to the second displacement D 2 , plotting a first line between the first displacement, second force value coordinate (D 1 , F 1 ) and the second displacement, second force value coordinate (D 2 , F 2 ) and measuring the maximum deviation of force (DF max ) from the first line for any given value along the force ordinate, the nonlinearity represented as a percentage, the ratio of (DF max /(F1−F2)).