Airless tire
An airless tire includes a tread ring, a hub positioned on radially inner side of the ring, and a spoke structure including polymer material and connecting the ring and hub, the structure including spoke pieces arrayed in circumferential direction. Each spoke piece has a tread connecting portion, a hub connecting portion, and a spoke curved portion between the tread and hub connecting portions, each spoke piece has straight radial length LSb of at least 1.05 times straight radial length LSa and curved radial length LLb of at least 1.03 times LSb when positioned at 0° on coordinate around the tire axis where a perpendicular line extending vertically upward from the tire axis is set 0°, LSb is measured along the base line under base-load condition, LSa is measured along the base line under no-load condition, and LLb is measured along a curve of each spoke piece under the base-load condition.
1. An airless tire, comprising:
a tread ring having a cylindrical form;
a hub positioned on a radially inner side of the tread ring and configured to be fixed to an axle; and
a spoke structure comprising a polymer material and connecting the tread ring and the hub, the spoke structure comprising a plurality of spoke pieces arrayed in a circumferential direction,
wherein each of the spoke pieces comprises a tread connecting portion connected to an inner circumferential surface of the tread ring, a hub connecting portion connected to an outer circumferential surface of the hub, and a spoke curved portion formed between the tread connecting portion and the hub connecting portion such that the tread connecting portion and the hub connecting portion are positioned on a base line extending radially from a tire axis and the spoke curved portion has a first curved portion extending in a curve veering off from the base line in the circumferential direction and a second curved portion extending in a curve veering off from the base line in an opposite circumferential direction to set the first and second curved portions in a line symmetry at the base line, each of spoke pieces comprises a first portion and a second portion such that the first portion extends from the hub connection portion to the tread connection portion and includes the first curved portion and that the second portion extends from the hub connection portion to the tread connection portion and includes the second curved portion, and each of the spoke pieces has a straight radial length LSb of at least 1.05 times a straight radial length LSa and a curved radial length LLb of at least 1.03 times the straight length LSb when positioned at 0° on a coordinate around the tire axis where a perpendicular line extending vertically upward from the tire axis is set as 0° on the coordinate, the straight radial length LSb is measured from the hub connection portion to the tread connection portion along the base line under a base-load condition which is 60% of a normal load exerted on the airless tire where the normal load corresponds to a normal load on a pneumatic tire with a tire size corresponding to the airless tire, the straight radial length LSa is measured from the hub connection portion to the tread connection portion along the base line under a no-load condition, and the curved radial length LLb is measured from the hub connection portion to the tread connection portion along a curve of each of the spoke pieces under the base-load condition.
2. The airless tire according to claim 1 , wherein when each of the spoke pieces is at 0° on the coordinate, each of the spoke pieces has the curved radial length LLb of no greater than 1.005 times a curved radial length LLa, where the curved radial length LLa is measured along a carve of each of the spoke pieces under the no-load condition.
3. The airless tire according to claim 1 , wherein each of the spoke pieces has the straight radial length LSb of at least 1.07 times the straight radial length LSa and the curved radial length LLb of at least 1.05 times the straight length LSb when positioned at 0° on the coordinate around the tire axis.
4. The airless tire according to claim 1 , wherein the spoke structure has a joint portion formed such that the joint portion is connecting the first curved portion of one spoke piece and the second curved portion of another spoke piece positioned adjacent to the one spoke piece in the circumferential direction.
5. The airless tire according to claim 4 , wherein the first and second curved portions of a spoke piece has a complex elastic modulus E* 1 which is set at least 1.5 times a complex elastic modulus E * 2 of the joint portion.
6. The airless tire according to claim 4 , wherein each of the first and second curved portions of a spoke piece has a thickness which is set at least 1.5 times a thickness of the joint portion.
7. The airless tire according to claim 1 , wherein each of the spoke pieces comprises a spoke outer base extending along the base line between the tread connecting portion and a radially outer edge of the spoke curved portion, and a spoke inner base extending along the base line between the hub connecting portion and a radially inner edge of the spoke curved portion.
8. The airless tire according to claim 1 , wherein each of the spoke pieces has a radially outer edge of the spoke curved portion which is set as the tread connecting portion and a radially inner edge of the spoke curved portion which is set as the hub connecting portion.
9. The airless tire according to claim 4 , wherein when each of the spoke pieces is at 0° on the coordinate, each of the spoke pieces has the curved radial length LLb of no greater than 1.005 times a curved radial length LLa, where the curved radial length LLa is measured along a curve of each of the spoke pieces under the no-load condition.
10. The airless tire according to claim 3 , wherein the spoke structure has a joint portion formed such that the joint portion is connecting the first curved portion of one spoke piece and the second curved portion of another spoke piece positioned adjacent to the one spoke piece in the circumferential direction.
11. The airless tire according to claim 9 , wherein the first and second curved portions of a spoke piece has a complex elastic modulus E* 1 which is set at least 1.5 times a complex elastic modulus E * 2 of the joint portion.
12. The airless tire according to claim 9 , wherein each of the first and second curved portions of a spoke piece has a thickness which is set at least 1.5 times a thickness of the joint portion.
13. The airless tire according to claim 2 , wherein each of the spoke pieces comprises a spoke outer base extending along the base line between the tread connecting portion and a radially outer edge of the spoke curved portion, and a spoke inner base extending along the base line between the hub connecting portion and a radially inner edge of the spoke curved portion.
14. The airless tire according to claim 2 , wherein each of the spoke pieces has a radially outer edge of the spoke curved portion which is set as the tread connecting portion and a radially inner edge of the spoke curved portion which is set as the hub connecting portion.
15. The airless tire according to claim 3 , wherein each of the spoke pieces comprises a spoke outer base extending along the base line between the tread connecting portion and a radially outer edge of the spoke curved portion, and a spoke inner base extending along the base line between the hub connecting portion and a radially inner edge of the spoke curved portion.
16. The airless tire according to claim 3 , wherein each of the spoke pieces has a radially outer edge of the spoke curved portion which is set as the tread connecting portion and a radially inner edge of the spoke curved portion which is set as the hub connecting portion.
17. The airless tire according to claim 4 , wherein each of the spoke pieces comprises a spoke outer base extending along the base line between the tread connecting portion and a radially outer edge of the spoke curved portion, and a spoke inner base extending along the base line between the hub connecting portion and a radially inner edge of the spoke curved portion.
18. The airless tire according to claim 4 , wherein each of the spoke pieces has a radially outer edge of the spoke curved portion which is set as the tread connecting portion and a radially inner edge of the spoke curved portion which is set as the hub connecting portion.
19. The airless tire according to claim 9 , wherein each of the spoke pieces comprises a spoke outer base extending along the base line between the tread connecting portion and a radially outer edge of the spoke curved portion, and a spoke inner base extending along the base line between the hub connecting portion and a radially inner edge of the spoke curved portion.
20. The airless tire according to claim 9 , wherein each of the spoke pieces has a radially outer edge of the spoke curved portion which is set as the tread connecting portion and a radially inner edge of the spoke curved portion which is set as the hub connecting portion.