AU2004202040B2

AU2004202040B2 - Pneumatic Tire

Info

Publication number: AU2004202040B2
Application number: AU2004202040A
Authority: AU
Inventors: Toshiharu Tanikawa
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 2003-05-16
Filing date: 2004-05-13
Publication date: 2009-02-26
Anticipated expiration: 2024-05-13
Also published as: JP4098668B2; GB2401588A; GB0410555D0; AU2004202040A1; GB2401588B; DE102004024162A1; JP2004338628A

Description

S&F Ref: 676535

AUSTRALIA

PATENTS ACT 1990 COMPLETE

SPECIFICATION

FOR A STANDARD

PATENT

Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Sumitomo Rubber Industries, Ltd., of 6-9, Wakinohamacho 3-chome Chuo-ku, Kobe-shi, Hyogo-ken, Japan Toshiharu Tanikawa Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Pneumatic Tire The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c

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SPNEUMATIC TIRE The present invention relates to a pneumatic re capa- O ble of exhibiting high dry grip performance and wear resistance when racing, such as for circuit racing and for gymkhana races while sufficiently securing excellent we- grip performance (hydroplaning resistance) when running on a general road.

For high performance tires produced not only for running on a general road but also for racing, such as for circuit racing and for gymkhana races, use is widely made of an S-shape pattern produced mainly for the sake of enhancing the dry grip performance as shown in Fig. 7(A) and of a V-shaped pattern produced mainly for the sake of enhancing both wet grip performance and dry grip performance as shown in Fig.

7(B) (see Figs. 2 and 8 of Japanese Patent Application Laidopen No. 2000-127715).

In the S-shaped pattern, since pattern rigidity with respect to the lateral acceleration (lateral G) is high, although the dry grip performance (especially lateral grip performance) is excellent, there is a tendency for wear to proceed quickly in a portion P1 where an angle 9 between a tread groove a and a circumferential direction of the tire becomes small. The majority of the tread groove has a large angle 0 of 35° or more, and the hydroplaning resistance is inferior.

In the V-shaped pattern, the wet grip performance is excellent, but when a vehicle races on a road or surface having a high friction coefficient p, such as a race course at high lateral acceleration (lateral the lateral rigidity in an outer tread half located at an outer side of the vehi- D 2

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cle is not high, and it is difficult to shorten the running time or lap time even if the composition of tread rubber and the structure of the tire are changed. There is a problem that in the tread groove disposed in the outer tread half, a portion P2 where the angle 0 becomes 350 or smaller is worn fast.

It is an object of the present invention to provide a pneumatic tire capable of appropriately enhancing the pattern rigidity while securing an excellent dewatering effect, and capable of further enhancing dry grip performance, wet grip performance and wear resistance In order to achieve the above object there is provided, in accordance with the present invention, a pneumatic tire having an asymmetric pattern in which tread patterns on opposite sides of the tire with respect to a tire equator are different from each other, wherein a tread surface is divided in a virtual manner by the tire equator into an inner tread half and an outer tread half a groove area ratio Li of the tread pattern in the inner tread half is set greater than a groove area ratio Lo of the tread pattern in the outer tread half by 0.05 or greater (Li-Lo 0.05), with a groove area ratio L of the tread pattern of the entire tread surface lying in a range of 0.15 to 0.35, the inner tread half includes a straight circumferential main groove which continuously extends in a circumferential direction of the tire and which is disposed in a region Y away from the tire equator by a distance corresponding to to 55% of a tread half width from the tire equator an inner end of the tread, an inclination angle a of each groove 3 Swall surface of the circumferential main groove with fespect S to a normal toward the tread surface being 30 to the outer tread half is not provided with a circumferential groove which continuously extends in the circumferential direction of the tire, but is provided with a plurality Sof outwardly inclined lateral main grooves, each having a lateral groove main portion which extends from an inner end on the tire equator toward an outer end of the tread and having an inclination angle 3 of 35° or greater formed between the lateral groove main portion and the circumferential direction of the tire, and each of the outwardly inclined lateral main grooves includes an inner communication portion which is connected to an inner end of the lateral groove main portion and which is in communication with the circumferential main groove beyond the tire equator and/or an outer communication portion which is connected to an outer end of the lateral groove main portion and which is in communication with the outer tread end, the inclination angle P at the communication position of the communication portion being in the range from 75 to The present invention will now be described in more detail with reference to the accompanying drawings in which: Fig. 1 is a sectional view of an embodiment of a pneumatic tire of the present invention; Fig. 2 is a development of a tread pattern of the tire; Fig. 3 is a lateral sectional view of a circumferential main groove;

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Figs. 4(A) and are diagrams for explaining an inclination angle of a groove wall surface of the circumferential main groove; Fig. 5 is a diagram showing one example of a tread for a pneumatic tire not in accordance with the present teaching, the tread having a circumferential groove which is to be eliminated from an outer tread half; Fig. 6 is a development showing another embodiment of a tread pattern used in the invention; and Figs. 7(A) and are developments showing one example of a tread pattern of a conventional tire.

An embodiment of the present invention will be explained with reference to the drawings. Fig. 1 shows a meridional cross section of a pneumatic tire according to the present invention. Fig. 2 shows a tread pattern of the pneumatic tire and the arrow shows the direction in which the tire turns.

In Fig. i, the pneumatic tire 1 is a high performance tire produced for both running on a general road and running on a race track such as for circuit racing and for gymkhanas.

The pneumatic tire 1 includes a carcass 6 of a radial structure. The carcass 6 extends under the tread portion 2 and at both sides of the tire to respective bead cores S of bead portions 4 through respective sidewall portions 3.

A belt layer 7 is provided radially outward of the carcass 6 and radially inward of the tread portion 2. A tire aspect ratio H/W, which is a ratio of the height H of a tire cross section and the tire width W, is set to 50% or lower 40%) by hoop effect. With this configuration, tire U C :.igidity is enhanced, the tread width TW is increased, and :igh speed performance and steering stability are enhanced.

Here, the "tread width TW" is a distance of the tire in Its axial direction between the lateral limits of the tread, ri i.e. the tread ends El and Here, a point of intersec- C tion of a phantom line which is obtained by extending an outline of the tread surface 2S outwardly in the axial direction Ci of the tire and a phantom line obtained by extending an outline of a buttress surface 3S outwardly in a radial direction of the tire is defined as The "tread end E" is a point where a line in the radial direction of the tire passing through this intersection point J intersects with the tire surface.

In the pneumatic tire 1 of this invention, when the tread surface 2S is divided in a virtual manner from a tire equator C into an inner tread half Si located at an inner side of a vehicle when the tire is mounted to the vehicle and an outer tread half So located at an outer side of the vehicle. A tread pattern of the inner tread half Si and a tread pattern of the outer tread half So are different from each other and are asymmetric with respect to each other.

More specifically, as shown in Fig. 2, the inner tread half Si includes one circumferential main groove 10 which extends continuously in a circumferential direction of the tire and thus forms a straight line in a flat development of the tread surface as shown in Fig. 2. In other words, the circumferential groove 10 lies in a plane parallel to an equatorial plane of the tire. The circumferential main groove 10 is formed in a region Y separated from the tire equator C by a distance corresponding to 20 to 55% of a tread half width TW/2 (1/2 of the tread width TW) CI 6 The circumferential main groove 10 is a straight groove having high dewatering effect, and its groove width GWO is 14 mm or wider, and preferably 18 mm. It can e.g. be a maximum of about 25 mm wide. A center lihe of the groove is located in the region Y. That is, a distance LO between the groove center line and the tire equator C is 20 to 55% of the tread C-I half width TW/2.

If the circumferential main groove 10 is disposed further towards the outer side of the vehicle from the region Y, pattern rigidity in the outer tread half So can not sufficiently be secured, and it becomes difficult to satisfy the requirement for high dry grip performance and wear resistance at a high level which is required in the case of racing. If the circumferential main groove 10 is disposed further toward the inner side of the vehicle than the region Y, the wet grip performance required when running on a general road can not sufficiently be secured.

It can be seen from Fig. 2 that the inner tread half includes first inner laterally extending grooves 11A communicating with said main circumferential groove 10 and second inner laterally extending grooves liB extending from the inner tread end Ei in the direction towards said equator C. The first inner laterally extending grooves 11A and the second inner laterally extending grooves 11B are inclined to the tread running direction of the tire, by an angle yl less than over at least a major portion of their lengths.

For securing the dry grip performance and wear resistance, in a groove cross section which is perpendicular to the groove center line of the circumferential main groove as shown in Fig. 3, it is preferable that the groove wall Q surface c is inclined at an inclination angle c as great as 30 to 50° witi, respect to a normal of the. groove side edge with respect co the tread surface 2S. A large lateral force is applied to the outer side of the vehicle as compared with the inner side of the vehicle especially when the vehicle turns. Therefore, it is preferable that an inclination angle cto of a groove wall surface go located towards an outer side of the tire is greater (ao ai) than an inclination angle ai of a groove wall surface gi located towards an inner side of the tire within the above-described angle range. If the inclination angle c is less than 300, the rigidity in the vicinity of the groove side edge is insufficient, deviated wear such as orbit wear is caused and the wear resistance deteriorates. If the inclination angle cx exceeds 50°, the groove volume is reduced and the dewatering effect deteriorates.

When the groove wall surface g is curved into a convex circular shape as shown in Fig. an inclination angle cx of a tangent at each position of the curved surface is in a range of 30 to 500. When the groove wall surface g is a bent surface having a plurality of surfaces or facets as shown in Fig. an inclination angle a of each surface or facet is in a range of 30 to 50°. When the inclination angle ai and the inclination angle ao are compared with each other, if the groove wall surface g is the curved surface, the comparison is made using an average value of a maximum value and a minimum value of the inclination angle a of the tangent, and if the groove wall surface g is the bent surface, the comparison is made using an average value of the inclination angles a of the surfaces.

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ToThe inner tread half Si can be provided with an inner inclined lateral main groove 11 between the circumferential main groove 10 and the inner tread end Ei. The inner inclined lateral main groove 11 of this example includes a first inner inclined lateral main groove 11A whose inner end is in commnunication with the circumferential main groove and whose outer end is spaced from the inner tread end Ei by a distance L1 in the axial direction of the tire.

Especially in this example, the inner inclined lateral main groove 11 includes, in addition to the first inner inclined lateral main groove 11A, a second inner inclined lateral main groove liB whose outer end is in communication with the inner tread end Ei and inner end is away from the circumferential main groove 10 by a distance L2 in the axial direction of the tire. It is preferable that the first and second inner inclined lateral main grooves 11A and 11B are disposed alternately in the circumferential direction in terms of uniformity.

The distances L1 and L2 are preferably 7% to 14% of the tread width TW. If the distances are less than the rigidity is lowered and there is a tendency for the dry grip performance and the wear resistance to deteriorate. If the distances exceed 14%, there is a tendency for the wet grip performance to reduce. To secure the wet grip performance, it is preferable that the first and second inner inclined lateral main grooves 11A and 11B are superposed on each other in the circumferential direction of the tire to form a superposed or overlapping portion 12 (overlap in the axial direction) It is preferable that the inclination angle y formed between the inner inclined lateral main groove 11 and the

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circumferentLal direction is 350 or greater. It is especially preferable that an inclination angle yl formed between the circumferential main groove 10 and the inner groove end at O their communication position is 75 to 90°. With this configuration, it is possible to suppress the excessive reduc- Stion in rigidity and deterioration of wear resistance at the communication position.

C Since greater lateral force is applied to the outer tread half So when the vehicle turns, higher lateral rigidity is required. For this purpose, as shown in Fig. 2, the outer tread half So is not provided with a circumferential groove continuously extending in the circumferential direction of the tire, and is formed with an outwardly inclined lateral main groove 20 inclined with respect to the circumferential direction of the tire.

The above expression that "the outer tread half So is not provided with a circumferential groove continuously extending in the circumferential direction of the tire" means that all circumferential grooves which may reduce the pattern lateral rigidity are eliminated. For example, grooves which should be eliminated are a main groove having a width of 3 mm or wider provided mainly for the sake of dewatering, a thin groove having a width of 1.0 to 3 mm provided mainly for the sake of optimizing the dewatering and pattern rigidity, and a siping having a width of less than 1.0 mm provided mainly for the sake of optimizing the patter rigidity and securing the edge effect. As briefly shown in Fig. 5, connection grooves which sequentially connect the outwardly inclined lateral main grooves 20 and 20 to each other and which are adjacent to each other in the circumferential direction of the tire

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Scn also be regarded as one zigzag circumferential groove and such grooves should also be eliminated.

The outwardly inclined lateral main groove 20 (Fig. includes at least a lateral groove main portion 21 (Fig. 2) which has an inclination angle f of 35' or greater with respect to the circumferential direction of the tire and which extends from an inner end 21Ei on the tire equator C toward an outer tread end Eo. For alternate lateral grooves 20B the lateral groove main portions 21 are continuously provided with an inner communication portion 22i which extends from a position corresponding to the inner end 21Ei to the circumferential main groove 10 and which is in communication with the circumferential main groove 10 beyond the tire equator C.

Every second lateral groove 20A has a main portion 21 which starts at a position corresponding to 21Ei and has an outer communication portion 220 which extends to an outer end 21Eo of the lateral groove main portion 21 and which is in communication with the outer tread end Eo.

Thus, in this example, the outwardly inclined lateral main groove 20 includes first outwardly inclined lateral main grooves 20A whose outer communication portions 220 are connected to the lateral groove main portions 21, and second outwardly inclined lateral main grooves 20B whose inner communication portions 22i are connected to the lateral groove main portions 21. It is preferable that the first and second outwardly inclined lateral main grooves 20A and 20B are alternately disposed in terms of uniformity. If necessary, an edge-projecting portion 24 (shown with a chain-dotted line in Fig. 2) can extend from the inner end 21Ei of the lateral groove main portion 21 of groove 20A beyond the tire equator C and can be separated from the circumferential main groove

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10 by a distance L3 in the axial direction of the tire. Such an extension 21. can be provided as part of the first outwardl, inclined la-eral main groove Here, in the outwardly inclined lateral main groove it is necessary that the inclination angle 3 is 35° or greater. If the angle is less than 350, the lateral rigidity of the pattern with respect to the lateral force at the time of turning of the vehicle is insufficient. As a result, the dry grip performance (especially lateral grip performance) during racing becomes insufficient, running time can not be enhanced, and the wear resistance in the vicinity of the groove side edge of the outwardly inclined lateral main groove deteriorates.

There is a tendency that in the outwardly inclined lateral main groove 20, the rigidity of the communication position between the outer tread end Eo and the circumferential main groove 10 is reduced, and that the wear resistance deteriorates. Thus, it is important that the inclination angle P0 at the communication position of the communication portions 22i and 22o is set in a range of 75 to 90° and the reduction in rigidity is suppressed.

When the outwardly inclined lateral main grooves 11 and are curved, the inclination angles P and y are indicated by the inclination angle of the local tangent to the main grooves.

In the second outwardly inclined lateral main groove 203, it is preferable that a distance L4 between its outer end and outer tread end Eo is 10 to 20% of the tread width TW. If the distance L4 is less than 10%, the rigidity is reduced and there is a tendency for the dry grip performance 12

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Q and the w.ar resist3nce to reduce. If the distance L4 exceeds 20% on the contrary, there is a tendency to reduce the wet grip performance. If the first outwardly inclined lateral main groove 20A is provided. with the edge-projecting portion 24, it is preferable that the distance L3 between the edge-projecting portion 24 and the circumferential main groog ve 10 is 12% or more of the tread width TW in order to secure C the dry grip performance and wear resistance.

Next, in the pneumatic tire 1 of the present invention, a groove area ratio L of the tread pattern in the entire tread surface 2S is in a range of 0.15 to 0.35. A groove area ratio Lo of the tread pattern in the outer tread half So is set smaller than a groove area ratio Li of the tread pattern in the inner tread half Si by 0.05 or smaller (Li-Lo 0.05) so that the pattern rigidity is enhanced and greater lateral grip can be obtained in the outer tread half So. The groove area ratio means a ratio of an opening area of the tread groove which occupies the tread surface to the total area of the tread surface.

If the groove area ratio L is less than 0.15, it is difficult to secure the necessary wet grip performance. If the groove area ratio L is greater than 0.35 and if a difference Li-Lo of the groove area ratios is less than 0.05, it becomes difficult to satisfy the high dry grip performance and wear resistance required for racing. It is preferable that the difference Li-Lo of the groove area ratios is 0.12 or less in terms of the wet grip performance.

The inner and outwardly inclined lateral main grooves 11 and 20 are dewatering main grooves having widths GW1 and GW2 of 3 rmm or more. The upper limit values of the groove widths GWO, GW1 and GW", and forming pitches of the inner and outwardly inc.lined lateral main grooves 11 and 20 are appropriately set in accordance with the groove area ratio L, and the difference Li-Lo of the groove area ratios.

Next, with reference to Fig. 1, in order to largely en- C1 hance the turning performance while sufficiently utilizing r C the excellent lateral grip performance, a ratio Hi-Ho of a Sradial distance Hi of the inner tread end Ei from the tire equator point CO and a radial distance Ho of the outer tread end Eo from the tire equator point CO is 1.02 to 1.20, and the pneumatic tire 1 of the present invention has an asymmetric tread outline shape.

When a vehicle turns, in a tire thereof closer to the turning center, a ground-contact center of the tire is on the side of the inner tread half Si. In a tire of the vehicle on the opposite side from the former tire closer to the turning center, a ground-contact center of the tire is on the side of the outer tread half So. At that time, if the ratio Hi/Ho is 1.02 to 1.20, an actual rotating radius of the tire closer to the turning center, an actual rotating radius on the side of the inner tread half Si can be smaller than an actual rotating radius of the tire opposite from the turning center, an actual rotating radius of the outer tread half So, and the vehicle can turn smoothly. If the ratio Hi/Ho is less than 1.02, the above effect can not be exhibited, and if the ratio exceeds 1.20, there are tendencies for the straight running performance to deteriorate, for the ground-contact pressure distribution to become uneven, and for the wear resistance to deteriorate.

Fig. 6 shows another embodiment of the tread pattern.

In Fig. 6, an inner inclined lateral main groove 11 comprising only the first inner inclined lateral main groove 11A is 2 disposed in the inner tread half Si, and an outwardly inclined lateral main groove 20 comprising only the first outwardly inclined lateral main groove 20A is disposed in the outer tread half So.

Although the preferred embodiment has been described in detail, the tire of the present invention can be employed as O a tire for a general passenger car, and the invention is not limited to the illustrated embodiment, and the invention can be variously modified and carried out.

Examples Pneumatic tires (255/40ZR17) having the structure shown in Fig. 1 and having tread patterns shown in Figs. 2, 6 and 7 were prototyped in accordance with specifications shown in Table 1, the wet grip performance and running time in a gymkhana race of the prototyped tires were measured, and results thereof are shown in Table 1. Specifications not shown in Table 1 are substantially the same.

Wet grip performance (straight hydroplaning resistance): -6 The prototyped tires were mounted to all wheels of a passenger car (2600 cc) having rims (9Jxl7) and internal pressure (230 kPa), the vehicle was allowed to accelerate on a straight road (depth of water was 10 mm), and the acceleration limit speed was measured. Results of the measurement are shown with indices in which a comparative example 1 is 100. The higher the numeric value, the more excellent the result is.

Wet grip performance (lateral hydroplaning resistance):

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The same vehicle was allowed to run on an asphalt road surface having a puddle (depth of water was 5 mm and length was 20 the speed was increased in stages, the lateral acceleration (lateral G) was measured, and average lateral G of a front wheel at the speed of 50 to 80 km/h was calculated.

The average lateral G is indicated with indices in which the S comparative example 1 is 100. The higher the numeric value, the more excellent the result is.

Table 1 Tread pattern Groove area ratio L Groove area ratio Li Groove area ratio Lo Circumferential main groove Groove width GWO (mm) Distance LO (mm) Inclination angle of groove wall surface (ai, ao) Inner inclined lateral main groove Groove width GW1 (mm) Inclination angle y (minimum value) (0) Inclination angle yl Distance L1 (mm) Distance L2 (mm) Outer inclined lateral main groove Groove width GW2 (mm) Inclination angle P (minimum value) (0) Inclination angle p1 (0) Distance L3 (mm) Distance L4 (mm) Straight hydroplaning resistance Lateral hydroplaning resistance Running time Comparative Example 1 Fig.- 7 0.22 0.22 0.22 No groove groove Example 1 Fig. 6 0.22 0.24 0.20 Straight 18 45 (45, 45) Groove 14 55 55 34 Groove 13 50 90 36 102 103 1'01"05 Example 2 Fig.! 2 0.22 0.26 0. 18 Straight 18 (45, Groolve 14 34 19 Groove 13 36 36 105 105 1' 00"84 No groove 100 100 1'01"42 It is thus confirmed that, for the present examples of the tire of the invention (Examples 1 and both the 'wet grip performance and dry grip performance is enhanced.

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Effect of the Invention Since the present invention has the above-described structure, it is possible to appropriately enhance the pat- 0 tern rigidity while securing excellent dewatering effect, and the dry grip performance, hydroplaning resistance, and wear I resistance can be enhanced.

Claims

1. A pneumatic tire having an asymmetric pattern in which tread patterns on opposite sides of the tire with re- spect to a tire equator are different from each other, whe- rein a tread surface is divided in a virtual manner by the tire equator into an inner tread half and an outer tread half. a groove area ratio Li of the tread pattern in the in- ner tread half is set greater than a groove area ratio Lo of the tread pattern in the outer tread half by 0.05 or greater (Li-Lo 0.05), and a groove area ratio L of the tread pat- tern of the entire tread surface is in a range of 0.15 to 0.35, the inner tread half includes a straight circumferen- tial main groove which continuously extends in a circumferen- tial direction of the tire and which is disposed in a region Y away from the tire equator by a distance corresponding to to 55% of a tread half width from the tire equator to an inner end of the tread, an inclination angle a of each groove wall surface of the circumferential main groove with respect to a normal toward the tread surface being 30 to the outer tread half is not provided with a circumfer- ential groove which continuously extends in the circumferen- tial direction of the tire, but is provided with a plurality of outwardly inclined lateral main grooves, each having a lateral groove main portion which extends from an inner end on the tire equator toward an outer end of the tread end and having an inclination angle P of 35° or greater formed be- tween the literal groove main porj:ion and the circumferential direction of the tire, and each Df the outwardly inclined lateral main grooves in- O eludes an inner communication portion which is connected to an inner end of the lateral groove main portion and which is in communication with the circumferential main groove beyond the tire ecuator and/or an outer communication portion which is connected to an outer end of the lateral groove main por- tion and which is in communication with the outer tread end, the inclination angle 3 at the communication position of the communication portion being 75 to

2. The pneumatic tire according to claim 1, wherein the outwardly inclined lateral main grooves comprise only a first outwardly inclined lateral main groove in which an outer communication portion is connected to the lateral groove main portion.

3. The pneumatic tire according to claim 1, wherein the outwardly inclined lateral main grooves includes first outwardly inclined lateral main grooves in which an outer communication portion is connected to the lateral groove main portion, and second outwardly inclined lateral main grooves in which the inner communication portion is connected to the lateral groove main portion.

4. The pneumatic tire according to claim 3, wherein the outwardly inclined lateral main grooves comprise alter- nately disposed first outwardly inclined lateral main grooves and second outwardly inclined lateral main grooves.

U Tne pneumatic tire according to any one of claims 1 to 4, wherein in the treaci surface, a ratio Hi/Ho of a dis- tance Hi measured in a radial direction from the inner tread end to the tire equator and a distance Ho measured in a ra- dial direction from the outer tread end to the tire equator C C-I is 1.02 to 1.20. i

6. A tire in accordance with any one of the preceding claims, wherein said main circumferential groove has a width in the range from 14 mm to 25 mm.

7. A tire in accordance with any one of the preceding claims, wherein the inner tread half includes first inner laterally extending grooves communicating with said main cir- cumferential groove and second inner laterally extending grooves extending from said inner tread end in the direction towards said equator.

8. A tire in accordance with claim 7, wherein said first inner laterally extending grooves and said second inner laterally extending grooves are inclined to the tread running direction, i.e. to a circumferential direction of the tire, by an angle less than 900 over at least a major portion of their lengths.

9. A pneumatic tire substantially as described herein with reference to and as illustrated in the accompanying dra- wings of Figs. 1 to 4 and Fig. 6.