Measuring and testing – Tire – tread or roadway
Reexamination Certificate
1999-05-06
2001-08-07
Oen, William (Department: 2855)
Measuring and testing
Tire, tread or roadway
Reexamination Certificate
active
06269690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. 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 estimating the tire wear lie or the degree of wear of rubber in actual use.
2. 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 mounting the tire whose wear life is to be estimated is actually driven for a specific distance (as for the definition of the word “wear life”, refer to page 13 of the specification).
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 to a vehicle used for the test and are driven on roads in a manner such that the rotation speeds of the two tires are different between the pairs by a desired extent so that the wear of the tire due to the driving force and due to the braking force can be evaluated simultaneously.
As the formula for estimating the amount of wear of a tire, Schallamach's formula of the amount of wear is 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 the transverse direction thereof When the rigidity C is expressed move specifically by the rigidity in the longitudinal direction, (in the driving direction) 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 a driving force, Fx− represents a force in the backwards direction generated by a 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.
Moreover, Schallamach's formula of the amount of wear has a drawback in that, although the formula takes rigidities in the direction of driving, in the direction of braking and in the transverse direction into consideration, accurate estimation of tire wear life of a tire mounted to a vehicle in actual use is still difficult when 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 by the customers (during driving in the conditions of actual road 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 objective of providing 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, in the first aspect of the method for estimating the tire wear life of the present invention, a friction energy of the tire Ewf in free rolling, a friction energy of the tire Ewa when the tire is mounted with a toe angle, a friction energy of the tire Ews under application of a side force to the tire, a friction energy of the tire Ewd under application of a driving force to the tire and a friction energy of the tire Ewb under application of a braking force to the tire are obtained. In addition, a friction energy ew of a rubber sample made of the same material as the material used in the tire tread portion under a severity substantially the same as the severity in the actual use of the tire and a wear depth W per given driving distance are also obtained.
The tire wear life is estimated on the basis of a value including a product of a rubber index Gi and a reciprocal of a friction energy Ew (1/Ew), i.e., Gi/Ew. The rubber index Gi is a value obtained by dividing the friction energy ew by the wear depth W, i.e., ew/W. The friction energy Ew is expressed by the following formula:
Ew=Ewf+Ewa+Ews+Ewb+Ewd
In accordance with the first aspect of the present invention, the friction energy of the tire Ewf in free rolling and the friction energy of the tire Ewa when the tire is mounted with a toe angle are used as the factors for estimating the tire wear life in addition to the friction energy of the tire Ews under application of a side force (force in the transverse direction) to the tire, the friction energy of the tire Ewd under application of a driving force to the tire and the friction energy of the tire Ewb under application of a braking force to the tire. Therefore, the tire wear life can be estimated more accurately in comparison with the estimation of the tire wear life in accordance with the Schallamach's formula of the amount of wear in which rigidity in the direction of driving, in the direction of braking and in the transverse direction alone are taken into consideration.
In this aspect, the rubber index Gi is measured under a severity which is approximately the same as the severity in the actual use of the tire and used for estimation of the tire wear life. Therefore, the tire wear life can be estimated more accurately in comparison with the estimation using the friction resistance index obtained by the conventional Lambourn abrasion tester specified in Japanese Industrial Standard K 6264.
In the second aspect of the present invention, it is preferable that the value including the product Gi/Ew is a value selected from the product Gi/Ew or a value obtained by multiplying the product Gi/Ew by a remaining groove depth remaining before the groove depth reaches the limit for disposal of the tire.
As the remaining groove depth remaining before the groove depth reaches the limit for disposal of the tire, it is preferable that a value obtained by subtracting the value which is considered to be the limit for disposal of the tire, for example 1.6 (mm), from the groove depth NSD is used.
In the third aspect of the present invention, using an input force in a transverse direction Fy, a force in a forward direction Fx+ generated by the driving force, a force in a backward direction Fx− generated by the braking force, undetermined coefficients S, D and B and exponents ns, nd and nb, the friction energy Ews, the friction energy Ewd and the friction energy Ewb are expressed by the following formulae:
Ews=S×Fy
ns
Ewd=D×Fx+
nd
Ewb=B×FX−
nb
The
Haraguchi Tetsunori
Katoh Kohshi
Kobayashi Hiroshi
Mouri Hiroshi
Sasaka Naohiro
Bridgestone Corporation
Oen William
Oliff & Berridg,e PLC
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