JP2008162354A - Tire for motorcycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance driving stability at turning by suppressing excessive falling down phenomenon of a tire easily generated at turning. <P>SOLUTION: The tire 1 for the motorcycle is provided with a carcass 6; and a belt layer 7. The carcass 6 comprises carcass plies 6A, 6B, 6C comprising an organic fiber. The belt layer 7 is formed by helically winding a band-like ply in which a steel cord is covered with rubber on an outer side of the carcass at an angle of 5° or less relative to a circumferential direction. An outer surface border line 2a of a tread part 2 includes a crown circular arc Ac extending through a crown area Cr including a tire equator point CP and having a radius of curvature Rc and a shoulder circular arc As extending from a tread edge 2e to a tire equator side and having a radius of curvature Rs. A ratio (Rs/Rc) of a radius of curvature is 0.70 to less than 1.0. A camber ratio obtained by dividing tread height TH, i.e., height from the tread edge 2e to the tire equator point CP by tread half width (TW/2) is 0.60 or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a motorcycle tire, and more particularly, to a technique for improving steering stability during turning by suppressing an excessive tire falling phenomenon that tends to occur during turning.

  In a motorcycle, turning is performed mainly by tilting the vehicle body to give a camber angle to the tire and generating a camber thrust that balances the centrifugal force on the tire. When the turning speed is high or the turning radius is small, a large centripetal force is required, so that a larger camber angle is also given to the tire.

  Here, when the vehicle body is tilted gradually in order to give the camber angle to the tire, the rider can maintain the turning motion with peace of mind if the speed at which the vehicle body tilts (falls down) is constant. However, if the speed at which the vehicle body collapses suddenly increases while the vehicle body is tilted, the balance may be lost and the vehicle may fall over.

More specifically, for example, when a motorcycle is continuously turned at a constant turning radius, it is necessary to gradually increase the camber angle in order to gradually increase the speed. If the increase in the turning speed and the increase in the camber angle are in a proportional relationship, the driver can perform a safe turning operation. However, when the vehicle body falls down abruptly (camber angle increases rapidly), the steering stability at the time of turning significantly deteriorates.
Related technologies include the following.

JP 2002-36812 A

  The present invention has been devised in view of the above problems, and uses a steel cord for the belt layer and optimizes the ratio of the crown arc to the shoulder arc in the outer contour line of the tread portion. Basically, to provide a tire for a motorcycle that can increase the spring constant of the tire based on an increase in the camber angle, thereby suppressing excessive falling of the tire and improving steering stability during turning. Is the main purpose.

  The invention according to claim 1 of the present invention comprises a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer disposed on the outer side in the tire radial direction of the carcass and inside the tread portion. In addition, the carcass includes at least one carcass ply in which carcass cords made of organic fibers are arranged at an angle of 60 to 90 degrees with respect to the tire equator, and the belt layer is made of steel. It is formed by winding a belt-like ply covered with a rubber cord spirally outside the carcass in the tire radial direction at an angle of 5 degrees or less with respect to the tire circumferential direction, and is assembled to a normal rim and filled with a normal internal pressure. In addition, in the normal state of the tire meridian section where there is no load, the outer surface contour line of the tread portion includes the tire equator point. And a shoulder arc with a radius of curvature Rs that extends from the tread edge to the tire equator side, and the ratio of the radius of curvature (Rs / Rc) is 0.70 or more and 1 And the camber ratio obtained by dividing the tread height TH, which is the height in the tire radial direction from the tread edge to the tire equator point, by the tread half width (TW / 2) is 0.60 or less. Features.

  The invention according to claim 2 is the motorcycle tire according to claim 1, wherein the ratio (Rs / Rc) is larger than 0.80 and smaller than 1.0.

  According to a third aspect of the present invention, in the tire meridian cross section, the crown arc extends at least a region of 20% of the tread development width around the tire equator point, and the shoulder arc extends from the tread edge to the tread development width. The motorcycle tire according to claim 1 or 2, wherein the tire extends over a region of 20%.

  In the present invention, a carcass made of at least one carcass ply in which carcass cords made of organic fibers are arranged at an angle of 60 to 90 degrees with respect to the tire equator, and a belt-like ply in which one or a plurality of steel cords are covered with rubber. And a belt layer formed by winding the carcass in a spiral shape at an angle of 5 degrees or less with respect to the tire circumferential direction on the outer side in the tire radial direction of the carcass. The belt layer made of a steel cord can increase the rigidity of the tread portion and suppress excessive deformation of the tread portion when a camber angle is given.

  In the motorcycle tire according to the present invention, in the cross section of the tire meridian in a normal state, the outer surface contour line of the tread portion extends from the crown region including the tire equator point and has a curvature radius Rc, and the tire equator from the tread edge. And a shoulder arc with a radius of curvature Rs, and the ratio of the radius of curvature (Rs / Rc) is set to 0.70 or more and less than 1.0, and the tire from the tread edge to the tire equator point The camber ratio obtained by dividing the tread height TH, which is the height in the radial direction, by the tread half width (TW / 2) is set to 0.60 or less.

  Due to these synergistic effects, the motorcycle tire of the present invention can increase the spring constant as the camber angle increases, and as a result, excessive falling during turning can be prevented and stable turning can be realized.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a tire meridian cross-sectional view including a tire rotating shaft in a normal state of a motorcycle tire 1 of the present embodiment.

  Here, the normal state of the tire is a state in which the tire is assembled on a normal rim (not shown) and filled with a normal internal pressure. In addition, the “regular rim” is a rim determined for each tire in a standard system including a standard on which a tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, For ETRTO, use “Measuring Rim”. The “regular internal pressure” is the air pressure defined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA, and the table “TIRE LOAD” is TRA. Maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO.

  A motorcycle tire 1 according to the present embodiment is suitably mounted on a motorcycle for use in a rear wheel that receives driving force, and includes a tread portion 2 and a pair extending from both ends thereof inward in the tire radial direction. Each of the side wall portions 3 and a bead portion 4 positioned at the inner end of each side wall portion 3, and a carcass 6 made of at least one carcass ply is bridged between the bead portions 4 and 4. At the same time, a belt layer 7 is disposed outside the carcass 6 in the tire radial direction and inside the tread portion 2.

  The tread portion 2 is curved in an arc shape so as to protrude outward in the tire radial direction, and the tread edges 2e and 2e which are the outermost positions in the tire axial direction are the outermost in the tire axial direction. Provided. Accordingly, the tread width TW, which is the distance in the tire axial direction between the tread edges 2e, 2e, forms the maximum tire width.

  The carcass 6 includes at least one carcass cord in which carcass cords are arranged at an angle of 60 to 90 ° with respect to the tire circumferential direction, in this embodiment, three carcass plies 6A, 6B, and 6C. As the carcass cord, an organic fiber cord such as nylon, polyester, or rayon is adopted. Further, as the carcass ply, in the present embodiment, the first carcass ply 6A disposed on the innermost side, the second carcass ply 6B disposed on the outer side in the tire radial direction, and the second carcass ply 6B. And a third carcass ply 6C disposed on the outer side in the tire radial direction.

  Each of the first and second carcass plies 6A and 6B includes a main body portion 6a extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and around the bead core 5 in the tire axial direction. It is comprised as what is called a winding ply including the folding | returning part 6b folded back from the inner side to the outer side. A bead apex 8 made of hard rubber is provided between the main body portion 6a and the folded portion 6b. The bead portion 4 and the side wall portion 3 are formed of a hard rubber extending in a radially outward direction from the bead core 5. Is reinforced. Further, the third carcass ply 6C is a lowering ply composed of only a main body portion 6a extending from the tread portion 2 through the side wall portion 3 and terminating between the first and second carcass plies 6A and 6B. Configured as Such a carcass 6 having a so-called (2-1) structure is preferable in that the rigidity of the sidewall portion 3 and the bead portion 4 is improved in a balanced manner from the tread portion 2 with a small mass.

  The belt layer 7 is composed of at least one belt ply 7A using a steel cord, and in this embodiment, one belt ply 7A. The belt ply 7A is formed by winding a belt-like ply coated with a steel cord in a spiral manner on the outer side in the tire radial direction of the carcass 6 and at an angle of 5 ° or less with respect to the tire circumferential direction.

  As a result of effectively increasing the rigidity of the tread portion 2, the belt layer 7 made of such a steel cord suppresses the shoulder region of the tread portion 2 from being excessively deformed even when a camber angle is given, and thus a spring constant. Can be reliably prevented. On the other hand, when the belt cord is an organic fiber cord, since the rigidity of the tread portion 2 is insufficient, the deformation amount of the tread portion increases as the camber angle increases, and the above-described collapse tends to occur.

  Further, when the angle of the belt cord with respect to the tire circumferential direction is larger than 5 degrees, the tread portion 2 is likely to be largely protruded and deformed during high speed traveling. This greatly deforms the outer surface outline 2a of the tread portion 2, and as a result, there is a possibility that the effect of increasing the spring constant when a camber angle is given cannot be obtained sufficiently.

  In addition, when the belt layer 7 is formed by winding a wide belt ply and splicing both ends thereof, the binding force to the tread portion 2 is insufficient, and in the same way as described above, in the case of high speed running, the tread This is not preferable because large protruding deformation of the portion 2 is likely to occur.

  As the belt-like ply, as shown in FIG. 2 (a), a cord-like belt-like ply P1 in which one steel cord 10 is covered with unvulcanized rubber 11, or as shown in FIG. 2 (b). Any of ribbon-like belt-like plies P2 in which a plurality of steel cords 10 are coated with unvulcanized rubber 11 may be used.

  Further, in the motorcycle tire 1 of the present embodiment, the outer surface contour line 2a of the tread portion 2 in the cross section of the normal tire meridian extends from the crown arc Ac having a radius of curvature Rc extending over the crown region Cr including the tire equator point CP. And a pair of shoulder arcs As extending from the tread edge 2e toward the tire equator C and having a radius of curvature Rs, and the ratio of these radii of curvature (Rs / Rc) is set to 0.70 or more and less than 1.0. The

  Here, when the tread portion 2 is provided with a groove, the outer surface outline 2a of the tread portion 2 is specified in a state in which the groove is filled. The tire equator point CP is an intersection of the tire equator C and the outer surface outline 2 a of the tread portion 2.

  Further, the crown region Cr is a region that is 20% of the developed length of the outer surface outline 2a of the tread portion 2 with the tire equator point CP as the center, and the crown arc Ac is an arc extending through this region. When the radius of curvature of the crown arc Ac changes, the radius of curvature Rc is the radius of an approximate arc having a single radius that is closest to it.

  The shoulder region Sh is a region that is 20% of the developed length of the outer surface outline 2a of the tread portion 2 from the tread edge 2e, and the shoulder arc As is an arc extending from this region. When the radius of curvature of the shoulder arc As changes, the radius of curvature Rs is the radius of an approximate arc having a single radius that it approximates most.

The inventors made various prototypes of tires with the above-described ratio of curvature radii (Rs / Rc) and measured their spring constants with camber angles given using a bench tester. did. In addition, each tire shall have the same structure except the outer surface outline of the tread part 2. The experimental conditions are as follows.
Tire size: 170 / 60ZR17
Rims: 17 x MT5.00
Internal pressure: 290 kPa
Carcass: 3 carcass plies made of rayon cord (2-1 structure)
Belt layer: One piece of steel cord

  FIG. 3 is a graph showing the results. The vertical axis represents the spring constant, and the horizontal axis represents the camber angle. As can be seen from the figure, in the tire 1 having the ratio (Rs / Rc) of 0.60, the spring constant does not substantially change even when the camber angle increases. However, the tires 2 to 4 having the ratio (Rs / Rc) of 0.70 or more and less than 1.0 have the same internal structure as the tire 1, but the spring constant increases as the camber angle increases. It turned out to be bigger. That is, by satisfying the above ratio (Rs / Rc), the radius of curvature Rs of the shoulder arc As is relatively increased, and consequently the effective ground contact area during turning is increased, and the tread package including the belt layer 7 is included. The integral rigidity can be secured. This increases the spring constant as the camber angle increases. As a result of conducting the same test for other tire sizes, substantially the same result was obtained.

  As described above, in the motorcycle tire 1 of the present invention, by setting the ratio (Rs / Rc) to 0.70 or more and less than 1.0, the spring constant of the tire can be increased as the camber angle increases. it can. As a result, during turning of a motorcycle in which a large camber angle is given to the tire during traveling, the tire is prevented from falling excessively, and as a result, traveling stability during turning is greatly improved.

  Further, as is clear from the graph of FIG. 3, in order to more effectively prevent such excessive collapse, the ratio (Rs / Rc) is more preferably greater than 0.75, Preferably 0.81 or more is desirable. On the other hand, when the ratio (Rs / Rc) is 1.0, the stability is deteriorated during straight traveling, and when the camber angle is increased, the tread edge 2e is easily grounded, and the behavior during turning is nonlinear. It becomes. From such a viewpoint, the ratio (Rs / Rc) is preferably 0.99 or less, more preferably 0.95 or less.

  The region between the crown region Cr and the shoulder region Sh may be formed by an arc that smoothly connects the crown arc Ac and the shoulder arc As.

  The ratio (Rc / TW) between the radius of curvature Rc of the crown arc Ac and the tread width TW is preferably 0.67 or more. When the ratio (Rc / TW) is less than 0.67, the crown region Cr is excessively rounded, which may cause deterioration of stability and occurrence of uneven wear during straight traveling. Conversely, when the ratio (Rc / TW) becomes excessively large, the crown region Cr is remarkably flattened, and the steering stability during turning may be deteriorated. From such a viewpoint, the ratio (Rc / TW) is preferably 0.80 or less, more preferably 0.75 or less.

  In the motorcycle tire 1 of the present invention, the camber ratio (2) is obtained by dividing the tread height TH, which is the height in the tire radial direction from the tread edge 2e to the tire equatorial point CP, by the tread half width (TW / 2). -TH / TW) is set to 0.60 or less. The camber ratio represents the degree of flatness of the tread portion 2, and the outer surface outline 2a of the tread portion 2 is flattened as the value decreases. In the present invention, by setting the camber ratio to 0.60 or less, the tread portion 2 is appropriately flattened, and as a result, rigidity when a camber angle is given is ensured.

  When the camber ratio is greater than 0.6, the tread portion 2 is curved, and the spring constant cannot be increased sufficiently when the camber angle is given. On the other hand, if the camber ratio is too small, the outer surface of the tread portion 2 is excessively flattened, which may deteriorate the steering stability during turning. From such a viewpoint, the camber ratio is preferably 0.55 or more, more preferably 0.57 or more.

Test tires (size 170 / 60ZR17) having the structure shown in FIG. 1 were prototyped according to the specifications shown in Table 1, and their stability during straight traveling and the degree of collapse during turning were tested. As the carcass, three carcass plies made of rayon cords were used.
The test method is as follows.

<Stability during straight running>
Test tires were mounted on the rear wheels of large motorcycles under the following conditions, and the stability during low-speed and high-speed straight traveling was comprehensively evaluated by the feeling of a professional driver. A result is a score which sets the comparative example 1 to 100, and it is so favorable that a numerical value is large.
Rims: 17 x MT5.00
Internal pressure: 290 kPa
Test vehicle: displacement 1300cc
Front wheel tire: 120 / 70ZR18
Front wheel rim: 18 x MT3.50
Front wheel internal pressure: 290 kPa

<Falling when turning>
When the vehicle was turned on a circle with a radius of 100 m while gradually increasing the speed, the degree of the vehicle body suddenly falling down and the linear feeling of the camber thrust and camber angle were evaluated by the driver's feeling. A result is a score which sets the comparative example 1 to 100, and it is so favorable that a numerical value is large.

<Tire mass>
The mass per tire was measured. A result is an index | exponent which sets the comparative example 1 to 100, and shows that it is so heavy that a numerical value is large.
Table 1 shows the test results.

  As a result of the test, it was confirmed that the tires of the examples were suppressed from falling during turning. In particular, excellent results were found in Examples where the ratio (Rs / Rc) was 0.81 or more.

1 is a cross-sectional view of a motorcycle tire showing an embodiment of the present invention. (A), (b) is a perspective view which shows embodiment of the strip | belt-shaped ply which forms a belt layer. It is a graph which shows the experimental result of a camber angle and a spring constant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motorcycle tire 2 Tread part 2a Tread outer surface outline 2e Tread edge 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A, 6B, 6C Carcass ply 7 Belt layer Cr Crown area Ac Crown arc Sh Shoulder area As Shoulder Arc CP Tire Equatorial Point TW Tread Width TH Tread Height

Claims (3)

A motorcycle tire comprising a carcass extending from a tread portion through a sidewall portion to a bead core of the bead portion, and a belt layer disposed on the outer side in the tire radial direction of the carcass and inside the tread portion,
The carcass includes at least one carcass ply in which carcass cords made of organic fibers are arranged at an angle of 60 to 90 degrees with respect to the tire equator, and the belt layer includes a belt-like ply in which a steel cord is covered with rubber. It is formed by wrapping in a spiral shape at an angle of 5 degrees or less with respect to the tire circumferential direction on the outer side in the tire radial direction of the carcass,
Moreover, in the tire meridian cross section of the normal state where the rim is assembled to the normal rim and the normal internal pressure is filled, and there is no load,
The outer surface contour line of the tread portion includes a crown arc extending from the crown region including the tire equator point and having a radius of curvature Rc, and a shoulder arc extending from the tread edge to the tire equator side and having a radius of curvature Rs. The ratio (Rs / Rc) is 0.70 or more and less than 1.0,
A tire for a motorcycle, wherein a camber ratio obtained by dividing a tread height TH, which is a height in a tire radial direction from the tread edge to a tire equator point, by a tread half width (TW / 2) is 0.60 or less. .   The motorcycle tire according to claim 1, wherein the ratio (Rs / Rc) is larger than 0.80 and smaller than 1.0. In the tire meridian section, the crown arc extends at least a region of 20% of the tread development width around the tire equator point,
The motorcycle tire according to claim 1 or 2, wherein the shoulder arc extends from the tread edge to an area of 20% of a tread developed width.

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