Method of fitting pneumatic tires

Abstract: Tires (T) each having a tread pattern comprising sub-grooves (2) diagonally disposed in the same direction are fitted on the left- and right-hand sides of an automobile such that imaginary lines extending respectively from the sub-grooves (2) of the left- and right-hand tires of the same axles intersect each other on the front side of the automobile for the dry road running, while the imaginary lines intersect each other on the rear side of the automobile for the wet road running.

Description: The present invention relates to a method according to the preamble of the claim. Recently, demands for tires having higher performance and wider variety still continues to increase due to the expansion of expressway network to a full extent and due to the continuous improvement of the performance of passenger vehicles. For instance, all-season tires in which the inferiority of the wet running performance to the dry running one is small, tires employing a special belt material in order to improve riding comfort have been proposed. It is known that the dry running performance, i.e., the dry running driving stability and the wet running performance, i.e., the wet running driving stability are in opposite relationship with each other, and that if one of these two performances is improved, the other performance lowers. Due to this fact, it is still impossible to provide a tire that can equally satisfy the above required performances. The inventors of the present invention made various studies on how to equally improve the above two performances, and found that it is when an automobile is run on a corner that the dry running and wet running driving stabilities are most evaluated, coming to make the present invention. Namely, when studying the functions of tires, the inventors did not consider a tire only, but intended to study and find the best functions exhibited while fitted to an automobile. In other words, the inventors intended to equally satisfy the above two performances by improving to a maximum extent a function of a tire that is considered most important in a certain condition. The method according to the preamble of the claim is known from EP-A-0 321384. This document discloses tires having a tread pattern comprising blocks defined by a plurality of annular straight grooves formed within a ground-contacting width of a tread surface of the tire, extending over a whole circumference of the tire, and a plurality of sub-grooves extending in the width direction of the tire and intersecting said straight grooves, arranged at a same inclination relative to the tire circumferential direction. An object of the invention is to improve the wet running performance with the same set of tires which is known from the above-mentioned document. This object is solved by the features of the claim. Each of four tires for performing the method according to the present invention has a tread pattern formed in the tread surface thereof by defining blocks by a plurality of annular straight grooves extending circumferentially in the tread surface of the tire within the ground-contacting width thereof around the tire and disposing also a plurality of sub-grooves intersecting obliquely those straight grooves extending parallely in the widthwise direction of the tire and has words "WET" and "DRY" with arrows thereunder marked on side walls on the serial side indicating the rotational directions of the tire. The method of fitting the tires described above is characterized in that the directions indicated by the arrows under the "WET" and "DRY" are determined such that when the four tires are fitted to an automobile, imaginary lines extending respectively from the sub-grooves of the left- and right-hand side tires confronting each other in the widthwise direction of the automobile when viewed from thereabove intersect each other on the front side of the vehicle for the dry road running, while imaginary lines extending respectively from the sub-grooves of the left- and right-hand side tires intersect each other on the rear side of the automobile for the wet road running. Fig. 1 is a cross-sectional explanatory view, showing a half of an example of pneumatic tires according to the present invention that is cut in the direction of a meridian; Figs. 2 and 3 are explanatory views, showing an example of the tread patterns of the pneumatic tire according to the present invention; Figs. 4 and 5 are explanatory views, showing arrangements of the pneumatic tires according to the present invention when the tires are fitted to an automobile, respectively; Fig. 6 is an explanatory view, showing an example of conventional tread patterns; Fig. 7 is an explanatory view, showing an arrangement of conventional tires when they are fitted to an automobile; and Figs. 8 and 9 are explanatory perspective views of pneumatic tires according to the present invention. A pneumatic tire which can be used for the method according to the present invention is for example a pneumatic radial tire as shown in Fig. 1. A carcass layer 2 is mounted on a pair of left and right bead cores 1, 1, and in a tread 3 two annular belt layers 4, 4 are disposed circumferentially around the tire in such a manner as to surround the outer circumference of the carcass layer 2. Organic fibers such as of nylon and polyester are used as a material for the carcass layer 2, and highly strong and rigid cords such as steel cords, Aramid cords (aromatic polyamide fiber cords) or the like are used as cords for the belt layer 4. A belt cover layer (not shown) comprising nylon cords may be disposed on the outside of the outer belt layer 4 with a view to improving the high-speed running performance. The angle at which cords are disposed in this belt cover layer is substantially 0° (parallel) with respect to the circumferential direction of the tire. In a pneumatic tire used for the method according to the present invention, a tread pattern is formed by defining blocks by a plurality of annular straight grooves circumferentially extending around the tire in the surface of the tread 3, i.e., a tread surface 5 of the tire within the ground-contacting width (within the range from one of the shoulder portions to the other shoulder portion) thereof, and by disposing also a plurality of sub-grooves obliquely intersecting those straight grooves in the tread surface 5 of the tire in the widthwise direction thereof. Figs. 2 and 3 show, respectively, examples of the tread pattern of tires actually fitted to an automobile when viewed from above. In these figures, the reference numeral 1 denotes annular straight grooves provided in the circumferential direction EE′ of the tire, the reference numeral 2 sub-grooves provided in the widthwise direction of the tire, and the reference numeral 3 denotes blocks defined by these grooves. In Fig. 2, the sub-grooves 2 are disposed in such a manner as to direct obliquely to the left with respect to the direction M in which the automobile moves, while in Fig. 3 the sub-grooves 2 are disposed in such a manner as to incline also diagonally but to the left with respect to the direction M in which the automobile moves. The tread pattern shown in Fig. 2 is hereinafter referred to as tread pattern A, while the tread pattern shown in Fig. 3 is hereinafter referred to as tread pattern B. It is preferable that the direction in which cords are disposed in a belt layer closest to the tread surface 5 of the tire (outer belt layer 4) is inclined to the same direction in which the sub-grooves 2 are disposed with respect to the circumferential direction of the tire. This is because in a case where the sub-grooves and the cords of the outer belt layer 4 are declined in the same direction, the cords assist the sub-grooves 2 with rigidity and also serve to enhance the rigidity of the sub-grooves 2, improving the edge effect of the sub-grooves 2 to the road surface when running. (1) According to the method of the present invention, as shown in Fig. 4, tires having the above-mentioned tread patterns A and B are fitted to an automobile such that imaginary lines ℓ, ℓ' extending respectively from the sub-grooves 2 of the left-and right-hand tires confronting each other intersect each other on the front side of the vehicle for the dry running when viewed from above the automobile. In other words, a pair of the sub-grooves 2 of the left and right tires on the same axles form an inverted "V" of the alphabet when viewed from above the automobile. Since sub-grooves 2 are arranged such that they seem to form an inverted "V" when viewed from above the automobile, the sub-grooves 2 come to contact with the road surface such that they form a "V". When the automobile runs a corner, the direction of the sub-grooves 2 of the tires on the outer side of the curve with respect to the direction of the running of the automobile, namely, the tires on the left-hand side of the vehicle when it makes a right turn on a corner or the tires on the right-hand side of the vehicle when it makes a left turn on the corner becomes substantially parallel or close to the parallel angle (0°) with respect to the direction in which the automobile moves, whereby the rigidity of road contacting-surface of the tire with respect to the same direction is greatly enhanced. Since this makes it possible to increase the cornering force produced by the tires which are on the outer side of the curve and which receive the greatest load when the automobile runs a corner, it is possible to improve the dry running performance. (2) Further, according to the method of the present invention, as shown in Fig. 5, tires having the above-mentioned tread patterns A and B are fitted to an automobile such that imaginary lines ℓ, ℓ' extending respectively from the sub-grooves 2 of the left- and right-hand side tires confronting each other in the widthwise direction of the automobile when viewed from thereabove intersect each other on the rear side of the automobile during the wet running. In other words, the sub-grooves 2 of the left and right tires on the same axles form a "V" of the alphabet when viewed from above the automobile. Since the sub-grooves 2 seem to form a "V" of the alphabet when viewed from above the automobile, the sub-grooves 2 come to contact with the road surface such that they form an inverted "V". Therefore, this allows water to be smoothly drained towards the inside of the automobile via the sub-grooves 2 of the tires which are on the outer side of the automobile when it runs a corner. Namely, when the automobile makes a right turn, the sub-grooves 2 of the tires fitted on the left-hand side of the automobile improve the drainage of water towards the inside of the automobile (direction towards the right-hand side of the automobile), while when the automobile makes a left turn, the sub-grooves 2 of the tires fitted on the right-hand side of the automobile improve the drainage of water towards the inside of the automobile (direction towards the left-hand side of the automobile). Further, since a plurality of annular straight grooves are also provided in the tread surfaces of the tires in the circumferential direction thereof, the tires exhibit far better draining capability. Therefore, it is possible to improve the wet running performance. Moreover, the pneumatic tires T for performing the method according to the present invention, as shown in Figs. 8 and 9, may be marked on the sidewall portion thereof with words "WET" and "DRY" and arrows thereunder indicating the rotational directions of the tire T so as to facilitate fitting the tire to the automobile. Namely, the tire T is marked with the words and arrows on the sidewall surfaces on the outer side (generally called a serial side) of the automobile when the tires are fitted to the automobile. When the tires are marked as described above, the tires can be easily fitted to the automobile for dry running so that as shown in Fig. 9, the direction of the "DRY" arrow may be the same as the direction M in which the automobile moves, and that the sidewall so marked may be on the outer side of the automobile. Similarly, for wet running, the tires can be easily fitted to the automobile so that the direction of the "WET" arrows may be the same as the direction M, as shown in Fig. 8, in which the automobile runs and that the sidewall so marked may be on the outer side of the vehicle. For reference, Fig. 7 shows one example of a conventional tread pattern of a tire which is fitted to an automobile when viewed from above an automobile. In Fig. 7, wave-shaped sub-grooves 2 (neutral pattern) are formed in the widthwise direction of the tire, and these sub-grooves 2 are not arranged such that they are tilted downwardly towards the left- or right-hand side with respect to the direction M in which the automobile moves. The tread pattern shown in Fig. 6 is hereinafter referred to as tread pattern C. Tires having this tread pattern C are fitted to the vehicle as shown in Fig. 7. Thus, conventionally tires having neutral patterns are used so that the difference in the cornering force between a left turn and a right turn is made as small as possible. In other words, it has been preferable that every tire shows the same performance in any conditions. Due to this, it has not been possible to equally improve the dry running performance and the wet running performance as in the case of the present invention. An example will be shown below. Example: Tires 1 to 5 having a tire size of 205/60 R 15 89H, shown in Table 1, were fitted to automobiles in accordance with arrangements shown in Table 2 (Automobiles I to V), and the dry running performance and the wet running performance were tested. Test results are shown in the form of index in Table 2. Method of Evaluating Dry Running Performance: Two professinal test drivers carried out ordinary driving stability feeling tests. The test results are shown in the form of indes, taking the results of Automobile V as 100 (greater indexes show better results). Method of Evaluating Wet Running Performance: The automobiles were driven on a circular course with a radius of 100 m having a certain wet area with a water depth of 5 mm. The speeds of the automobiles were gradually increased and lateral accelerations in the wet area were measured. The results are shown in the form of index, taking the results of Automobile V as 100 (greater indexes show better results). Tire 1 Tire 2 Tire 3 Tire 4 Tire 5 Tread Pattern B B A A C Carcass Layer Material 1000 d/2 polyester, 2 layers same as Tire 1 same as Tire 1 same as Tire 1 same as Tire 1 Cord Angle 90° to Circumferetial Direction same as Tire 1 same as Tire 1 same as Tire 1 same as Tire 1 Belt Layers First Belt Layer (Inner) Material 1x5 (0.25) Steel Cord 40 E same as Tire 1 same as Tire 1 same as Tire 1 same as Tire 1 Cord Angle 20° to Circumferential Direction (down to the right same as Tire 1 (down to the left) same as Tire 1 (down to the left) same as Tire 1 (down to the right) same as Tire 1 (down to the right) Second Belt Layer (Outer) Material 1x5 (0.25) Steel Cord 40 E same as Tire 1 same as Tire 1 same as Tire 1 same as Tire 1 Cord Angle 20° to Circumferential Direction (down to the left) same as Tire 1 (down to the right) same as Tire 1 (down to the right) same as Tire 1 (down to the left) same as Tire 1 (down to the left) Automobiles I II III IV V Arrangement of Tires on Automobiles Tire 3 on left side and Tire 1 on right side, Tire 1 on left side and Tire 3 on right side, Tire 4 on left side and Tire 2 on right side, Tire 2 on left side and Tire 4 on right side, Tire 5 on both left side and right side, relative to moving direction of automobile (Fig. 4) (Fig. 5) (Fig. 4) (Fig. 5) (Fig. 6) Dry Running Performance 105 95 106 101 100 Wet Running Performance 102 106 103 107 100 As will be seen from the above Table 2, Automobiles I and III are superior to Automobile V in regard to the dry running performance and that Automobiles II and IV are superior to Automobile V in regard to the wet running performance. As described above, according to the present invention, since imaginary lines extending respectively from the sub-grooves of the left- and right-hand side tires of the same axle are made to intersect each other on the front side of the automobile for the dry road running, while those imaginary lines are made to intersect each other on the rear side of the automobile for the wet road running, not only the dry running performance but also the wet running performance can be sufficiently improved. In particular, the present invention is suitable for fitting pneumatic radial tires.

Claims: A method of fitting pneumatic tires, wherein in fitting on the left- and right-hand sides of an automobile, tires having a tread pattern comprising blocks defined by a plurality of annular straight grooves formed within a ground-contacting width of a tread surface of the tire, extending over a whole circumference of the tire, and a plurality of sub-grooves extending in the width direction of the tire and intersecting said straight grooves, arranged at a same inclination relative to the tire circumferential direction, are fitted such that imaginary lines extending respectively from said sub-grooves of the left- and right-hand side tires confronting each other in the widthwise direction of said automobile when viewed from thereabove intersect each other on the front side of said automobile, characterized in that said tires are fitted such that said imaginary lines intersect each other on the rear side of the automobile for wet road running.

Inventors: MORIKAWA TUNEO, TOMIOKA KIYOSHI, WATANABE SUSUMU, MORIKAWA, TUNEO, TOMIOKA, KIYOSHI, WATANABE, SUSUMU
Applicants: YOKOHAMA RUBBER CO LTD, THE YOKOHAMA RUBBER CO., LTD.
Application year: 1990
Main classification: B60C19
IPC codes: B60C19, B60C5, B62D61, B60C13, B60C11