Methods and systems for evaluating tire properties
A method is provided for evaluating a tire. The method includes impacting the tire with a force; measuring motion information; extracting the resonant frequencies from the measured motion information; and calculating stiffness characteristics of the tire from the resonant frequencies.
1. A method for evaluating a tire, the method comprising the steps of:
impacting the tire with a force;
measuring motion information;
extracting the resonant frequencies from the measured motion information; and
calculating stiffness characteristics of the tire from the resonant frequencies, wherein the calculating step includes calculating the stiffness characteristics in a lateral direction, a radial direction, and a tangential direction.
2. The method of claim 1 , further comprising the step of determining undamped resonant frequencies from the motion information.
3. The method of claim 2 , further comprising the step of calculating damping.
4. The method of claim 1 , wherein the calculating step includes calculating the stiffness characteristics at a plurality of tire pressures.
5. The method of claim 4 , wherein the calculating step further includes calculating pneumatic and nonpneumatic contributions to the stiffness characteristics.
6. The method of claim 1 , wherein the calculating step includes calculating stiffness coefficients for at least one of bending, first shear, second shear, and radial stiffness.
7. The method of claim 1 , wherein the calculating step includes calculating a first stiffness coefficient for bending, a second stiffness coefficient for a first shear, a third stiffness coefficient for a second shear, and a fourth stiffness coefficient for radial stiffness.
8. The method of claim 1 , wherein the calculating step includes calculating the stiffness characteristics with a regression fit model of the resonant frequencies.
9. The method of claim 1 , wherein the calculating step includes calculating the stiffness characteristics according to the following equation:
ρ
·
[
2
π
]
2
·
f
0
n
2
·
[
1
+
1
n
2
]
=
Coef
1
R
4
·
[
n
2
-
1
]
2
+
Coef
2
R
2
·
[
n
-
1
n
]
2
+
Coef
3
·
1
n
2
+
Coef
4
wherein
f 0n =temporal frequencies, f 0 , of the undamped modes, n, where n=1, 2, 3, . . . N
n=mode number
N=total number of modes
ρ=density per unit circumference, M/(2πR), kg/m
R=radius of tire, m
Coef 1 =the stiffness coefficient associated with bending
Coef 2 =the stiffness coefficient associated with first shear
Coef3=the stiffness coefficient associated with second shear
Coef 4 =the stiffness coefficient associated with radial displacement.
10. The method of claim 1 , further comprising correlating the stiffness characteristics to at least one of a laboratory-measured and driving responses.
11. The method of claim 10 , wherein the correlating step includes calculating an influence coefficient that relates at least one of the stiffness and damping characteristics to the at least one of a laboratory-measured and driving responses.
12. A system for evaluating a tire, comprising:
a force device configured to strike the tire;
an accelerometer coupled to the tire and configured to gather vibration information from the tire; and
a post processor coupled to the accelerometer and configured to receive the vibration information from the accelerometer, the post processor further configured to
extract resonant frequencies from the vibration information, and
calculate at least one of a stiffness characteristic of the tire from the motion information at a plurality of tire pressures.
13. The system of claim 12 , wherein the post processor is further configured to determine undamped resonant frequencies from the motion information.
14. The system of claim 12 , wherein the post processor is further configured to calculate pneumatic and nonpneumatic contributions to the stiffness characteristics.
15. The system of claim 12 , wherein the post processor is further configured to calculate the stiffness characteristics including stiffness coefficients for at least one of bending, first shear, second shear, and radial stiffness.
16. The system of claim 12 , wherein the post processor is further configured to calculate stiffness characteristics according to the following equation:
ρ
·
[
2
π
]
2
·
f
0
n
2
·
[
1
+
1
n
2
]
=
Coef
1
R
4
·
[
n
2
-
1
]
2
+
Coef
2
R
2
·
[
n
-
1
n
]
2
+
Coef
3
·
1
n
2
+
Coef
4
wherein
f 0n =temporal frequencies, f 0 , of the undamped modes, n, where n=1, 2, 3, . . . N
n=mode number
N=total number of modes
ρ=density per unit circumference, M/(2πR), kg/m
R=radius of tire, m
Coef 1 =the stiffness coefficient associated with bending
Coef 2 =the stiffness coefficient associated with first shear
Coef3=the stiffness coefficient associated with second shear
Coef 4 =the stiffness coefficient associated with radial displacement.
17. The system of claim 13 , wherein the post processor is further configured to correlate the stiffness characteristics to at least one of a laboratory measured and driving responses.
18. The system of claim 10 , wherein the post processor is further configured to calculate an influence coefficient that relates at least one of the stiffness and damping characteristics to at least one of the laboratory measured and driving responses.
19. A method for evaluating a tire, the method comprising the steps of:
impacting the tire with a force;
measuring motion information;
extracting the resonant frequencies from the measured motion information;
determining undamped resonant frequencies from the motion data;
calculating stiffness characteristics of the tire from the undamped resonant frequencies, the stiffness characteristics including pneumatic and nonpneumatic contributions for crown bending, crown shear, sidewall shear, and sidewall radial stiffness, the calculating step including calculating the stiffness characteristics according to the following equation:
ρ
·
[
2
π
]
2
·
f
0
n
2
·
[
1
+
1
n
2
]
=
Coef
1
R
4
·
[
n
2
-
1
]
2
+
Coef
2
R
2
·
[
n
-
1
n
]
2
+
Coef
3
·
1
n
2
+
Coef
4
wherein
f 0n =temporal frequencies, f 0 , of the undamped modes, n, where n=1, 2, 3, . . . N
n=mode number
N=total number of modes
ρ=density per unit circumference, M/(2πR), kg/m
R=radius of tire, m
Coef 1 =the stiffness coefficient associated with bending
Coef 2 =the stiffness coefficient associated with first shear
Coef3=the stiffness coefficient associated with second shear
Coef 4 =the stiffness coefficient associated with radial displacement; and
correlating the stiffness characteristics to a driving response.