Measuring and testing – Tire – tread or roadway
Reexamination Certificate
1999-05-03
2001-04-10
McCall, Eric S. (Department: 2855)
Measuring and testing
Tire, tread or roadway
C073S008000
Reexamination Certificate
active
06212947
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for estimating a tire wear life, and more particularly, to a method for estimating a tire wear life which enables accurately estimating the tire wear life in actual use.
DESCRIPTION OF THE RELATED ART
Heretofore, the wear life of a tire used for vehicles has been estimated from the condition of wear (the degree of wear or the amount of wear) after a vehicle on which the tire whose wear life is to be estimated is mounted is actually driven for a specific distance.
However, this method has a drawback in that the test is quite time-consuming because the distance to be driven by the vehicle for the test must be great in order to get an accurate measurement of the amount of wear of the tire required for a highly precise estimation.
To overcome the above drawback, in the technology disclosed in Japanese Patent Application Publication (hereinafter, referred to as JP-B) 1-56374, at least two pairs of test tires are mounted on a vehicle used for the test and are driven on roads in a manner such that the rotation speeds of the tires are different between the pairs by a desired extent so that the wear of the tire due to the driving force and the braking force can be evaluated simultaneously.
As the method for estimating the amount of wear of a tire, a method using values obtained by a test with an actual vehicle in which both an input load applied to the tire and a dynamic alignment are taken into consideration is reported in “Estimation Method of Tire Treadwear on a Vehicle” (SAE TECHNICAL PAPER SERIES 910168).
As the formula for estimating the amount of wear of a tire, Schallamach's formula of the amount of wear has been known. In accordance with this theoretical formula, the amount of wear M of a tire per unit distance of driving is considered to be proportional to the friction energy and can be expressed by the following formula (1):
M=&ggr;&rgr;F
2
/C
(1)
In formula (1), &ggr; represents the degree of wear of a tire, &rgr; represents resilience, F represents an external force applied to the tire and C represents the rigidity of the tire against a force in the longitudinal direction or in the transverse direction. When the rigidity C is more specifically expressed by the rigidity in the longitudinal direction (in the direction of driving) Cd and the rigidity in the direction of braking Cb and the rigidity in the transverse direction Cs, Schallamach's formula of the amount of wear is expressed by the following formula (2):
M=&ggr;&rgr;F
2
/(
Cd+Cb+Cs
)=&ggr;&rgr;(
Fx+
2
/Cd+Fx−
2
/Cb+Fy
2
/Cs
) (2)
In the above formula, Fx+ represents a force in the forward direction generated by the driving force, Fx− represents a force in the backward direction generated by braking force and Fy represents an input force in the transverse direction.
However, the technology described in the specification of JP-B 1-56374 has a drawback in that at least one actual road test must be conducted for a long time and thus it still takes a long time to estimate the tire wear life, although the time required for the test can be decreased in comparison with the time required for methods of estimation using only one pair of tires in one run of the road test.
In the method reported in “Estimation Method of Tire Treadwear on a Vehicle”, the amount of wear is estimated on the basis of a test using an actual vehicle and the effect of the vehicle and the effect of the tire on the amount of wear cannot be examined separately. Therefore, this method has a drawback in that the accuracy of the estimation of the amount of wear is poor when a tire is mounted on a vehicle which is different from the vehicle used in the test or when a tire is used in an area whose environment is different from the environment of the test.
In the method reported in “Estimation Method of Tire Treadwear on a Vehicle”, the amount of wear of a tire is estimated by taking a force in the transverse direction, a force in the longitudinal direction, a force in the vertical direction and a camber angle into consideration. In Schallamach's formula of the amount of wear, rigidities in the direction of driving, in the direction of braking and in the transverse direction alone are taken into consideration. However, accurately estimating the wear life of a tire mounted on a vehicle in actual use is difficult when the factors taken into consideration are limited to these parameters.
When driving a vehicle in actual use, there are more diverse factors affecting the wear of a tire such as; the properties of the rubber of the tire tread portion, tire tread patterns and structures and input forces experienced by a tire in the actual use of the tire (during driving under the conditions of the actual use of the vehicle). Therefore, in the actual driving condition of a vehicle which is affected by so many diverse factors, it is obviously difficult to accurately estimate the wear of a tire using Schallamach's formula of the amount of wear in which only rigidities in the direction of driving, in the direction of braking and in the transverse direction are considered.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above problems and has an object to provide a method for estimating the tire wear life which enables accurate estimation of the tire wear life in a short time.
To achieve the above object, the method for estimating a tire wear life of the present invention has the following aspects.
In the first aspect of the present invention, a friction energy of the tire Ewf in free rolling, a friction energy of the tire Ewa in a state in which the tire is provided with a toe angle, a friction energy of the tire Ews in a state in which a side force is applied to the tire, a friction energy of the tire Ewd in a state in which a driving force is applied to the tire and a friction energy of the tire Ewb in a state in which a braking force is applied to the tire are obtained. A wear resistance index G
1
of rubber of a tire tread portion is also obtained. A friction energy Ew expressed as the total of the friction energies Ewf, Ewa, Ews, Ewb and Ewd is obtained and the tire wear life is estimated on the basis of a product of the wear resistance index G
1
and a reciprocal of the friction energy Ew (1/Ew), i.e., G
1
×(1/Ew).
In other words, the friction energy Ew is calculated as the sum of the above friction energies as follows:
Ew=Ewf+Ewa+Ews+Ewb+Ewd
An expected value TI of the tire wear life is calculated in accordance with the following formula:
T
1
=
G
1
×(1/
Ew
)×(
NSD−
1.6)
In accordance with the first aspect of the present invention, the friction energy Ewf and the friction energy Ewa are used as the factors for estimating the tire wear life in addition to the friction energy Ews, the friction energy Ewd and the friction energy Ewb. Therefore, the tire wear life can be estimated more accurately in comparison with the estimation of the tire wear life in accordance with conventional methods.
In the second aspect of the present invention, the friction energy Ew is calculated by taking data of a vehicle to which the tire for the estimation is fitted into consideration. The data of the vehicle comprises: a toe angle, a camber angle and a load per one tire under a static condition of the vehicle; and changes in the toe angle, the camber angle and the load per one tire due to change in the condition of the vehicle from the static condition to a dynamic condition (or the toe angle, the camber angle and the load per one tire under the dynamic condition of the vehicle). The static condition means the condition of the vehicle while the vehicle is stopped and the dynamic condition means the condition of the vehicle while the vehicle is driven.
In accordance with the above aspect, the tire wear life can be estimated more accurately in comparison with the estimation in which the above data of the vehicle are not taken in
Haraguchi Tetsunori
Katoh Kohshi
Kobayashi Hiroshi
Mouri Hiroshi
Sasaka Naohiro
Bridgestone Corporation
McCall Eric S.
Oliff & Berridg,e PLC
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