JP2019043238A - Pneumatic radial tire - Google Patents

Abstract

To provide a pneumatic radial tire that does good to improve turning performance of a four-wheel vehicle.SOLUTION: A pneumatic radial tire 1 for a passenger vehicle includes a carcass 6, a belt layer 7 and a tread part 2 having a tread pattern in which a direction of mounting to a vehicle is specified formed. A circumferential land part 15 of the tread part 2 includes an inner shoulder land part 16, an outer shoulder land part 17 and at least one middle land part 18. In the middle land part 18 are provided a plurality of middle lug grooves 20 which extend from an edge 18i of an inner tread end Ti side toward an outer tread end To and terminates in the middle land part 18, and a plurality of middle sipes 21 that completely cross the middle land part 18.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic radial tire for a passenger car, and more particularly, to a pneumatic radial tire useful for improving the turning performance of a four-wheeled vehicle.

  FIG. 12 shows time-series changes in turning operation of a general four-wheeled vehicle having a steering mechanism on the front wheels. First, as in state A, when the steering wheel is operated by the driver while traveling straight ahead, a slip angle is given to the tire b of the front wheel, and the tire b of the front wheel may be called cornering force (hereinafter referred to as "CF") ) (State B). Here, the "slip angle" is an angle between the traveling direction of the vehicle body c and the tire b. Further, “cornering force” is a component of force acting laterally with respect to the traveling direction among the frictional force generated on the ground contact surface of the tire b when the four-wheeled vehicle a turns, and in particular, the slip angle is 1 degree. The cornering force at the time may be called cornering power.

  The cornering force generated by the front wheel tire b brings about a pivoting movement of the vehicle body c with yaw. Since this turning motion gives a slip angle to the tire b of the rear wheel, the tire b of the rear wheel also generates a cornering force (state C). When the moment based on the cornering force of the front wheel tire b and the moment based on the cornering force of the rear wheel tire b substantially balance around the center of gravity CG of the vehicle (state D), the vehicle body c is A steady state in which the yaw acceleration moves substantially at zero and obliquely moves (hereinafter, such a traveling state may be referred to as a “revolution traveling state”).

  The inventors are aware that it is important to shift the vehicle body to the revolving state as soon as possible after turning and steering in order to improve the turning performance of the four-wheeled vehicle. Repeated research.

Generally, when a tire is mounted on a vehicle, the cornering power generated by the tire is referred to as equivalent cornering power (hereinafter "equivalent CP"). The equivalent CP has a relationship of the following formula (1) with the cornering power (hereinafter referred to as “stand-up CP”) of the tire unit measured in the bench test and the like.
Equivalent CP = bench CP × CP amplification factor ... (1)
The equivalent CP is the cornering power including the effects of so-called roll steer, compliance steer, etc., and is the cornering power when assuming that the roll characteristics and the suspension characteristics of the vehicle are taken into the tire. These characteristics are represented by CP amplification factor.

  FIG. 13 is a graph showing the relationship between the stand CP of a general pneumatic radial tire and the load acting thereon. Generally, it is found that after the CP rises up with the increase of load and reaches a peak, it gradually decreases. The graph also shows the approximate load area of a tire mounted on a FF four wheel vehicle during turning. First, in the FF four-wheeled vehicle, the front tire tends to be loaded more than the rear wheel tire. In addition, in each of the front wheel and the rear wheel, a larger load tends to act on the tire on the outside of the turning than in the tire on the inside of the turning. Therefore, a relatively large difference occurs between the front wheel tire and the rear wheel tire with respect to the average bench CP values Ff and Fr generated at the time of turning.

  Assuming that the above load distribution to each tire is premised, during the turning operation of the vehicle, the equivalent CP of the front wheel tire is relatively lowered in order to shift to the revolving state as soon as possible to improve the turning performance. On the other hand, it is considered effective to relatively increase the equivalent CP of the rear wheel tire, that is, to make both equivalent CPs close to each other or improve them so as to approach early.

  The inventors focused on self aligning torque (hereinafter sometimes referred to simply as “SAT”), which has not been paid much attention so far, in order to relatively lower the equivalent CP of the front wheel tire.

  Here, we will briefly describe SAT. FIG. 14 shows a contact surface of the tire b turning at a slip angle α with respect to the traveling direction Z, as viewed from the road surface side. As shown in FIG. 14, the tread rubber of the contact surface P is elastically deformed to generate CF in the lateral direction. If the point of action G of the CF (corresponding to the centroid of the hatched contact surface) is behind the contact center point Pc of the tire, the tire has a small slip angle α around the contact center point Pc. SAT, which is a moment in the direction of movement, works. That is, SAT works in a direction to reduce the slip angle around the tire contact center point Pc. The distance NT along the traveling direction Z between the ground contact point Pc and the action point G of the CF is defined as a pneumatic trail.

  Also, as a result of various experiments by the inventors, it has been found that the CP amplification factor of the above-mentioned formula (1) is approximately proportional to the reciprocal of SAT. For this reason, a tire with a large SAT results in relatively lowering the equivalent CP.

  On the other hand, since the rear wheel has no steering mechanism and is not affected by SAT, the equivalent CP can be increased by raising the stand CP as a tire.

  As is apparent from the above, in a four-wheeled vehicle, in particular an FF four-wheeled vehicle in which a large load is applied to the front wheels, a large SAT can be used as a tire to quickly shift to a revolving state during turning. Characteristics that generate the

  The inventors further studied the relationship between SAT and the tread pattern of the tire and found that it is effective to improve the middle land portion to enhance SAT.

JP, 2012-017011, A JP, 2009-162482, A

  The present invention has been made in view of the above problems, and has as its main object to provide a pneumatic radial tire which is useful for improving the turning performance of a four-wheeled vehicle.

  According to the present invention, a carcass having a radial structure, a belt layer consisting of at least two belt plies disposed on the outside of the carcass, and a tread portion having a tread pattern in which the direction of mounting on a vehicle is specified A pneumatic radial tire for a passenger car including: the tread portion having an outer tread end and an inner tread end located respectively at the outer side of the vehicle and at the inner side of the vehicle when the vehicle is mounted; The tread portion is divided into a plurality of circumferential land portions by a plurality of main grooves continuously extending in the tire circumferential direction, and the circumferential land portions are the innermost side. An inner shoulder land portion on the tread end side, an outer shoulder land portion on the outermost tread end side, and the inner shoulder land portion and the outer shoulder A plurality of middle land portions disposed between the second land portion and the plurality of middle land portions extending from the edge on the inner tread end side to the outer tread end side and interrupting in the middle land portion A middle lug groove and a plurality of middle sipes completely crossing the middle land portion are provided.

  In the pneumatic radial tire according to the present invention, it is preferable that the axial length of the middle lug groove be 30% to 80% of the axial width of the middle land portion.

  In the pneumatic radial tire according to the present invention, preferably, the middle lug groove includes a first middle lug groove and a second middle lug groove having a length in the tire axial direction larger than that of the first middle lug groove.

  In the pneumatic radial tire according to the present invention, a length of the first middle lug groove in the tire axial direction is 30% to 50% of a tire axial width of the middle land portion, and a tire shaft of the second middle lug groove The length of the direction is preferably 50% to 80% of the axial width of the middle land portion.

  In the pneumatic radial tire according to the present invention, the middle lug groove includes a first portion disposed on the inner tread end side, a second portion disposed on the outer tread end side with respect to the first portion, and It is desirable to include a tapered portion in which the first portion and the second portion are joined and the groove depth gradually decreases from the first portion to the second portion.

  In the pneumatic radial tire according to the present invention, the groove depth of the second portion is preferably 50% or less of the groove depth of the first portion.

  In the pneumatic radial tire according to the present invention, the middle land portion includes an inner middle land portion on the inner tread end side and an outer middle land portion on the outer tread end side with respect to the inner middle land portion. desirable.

  In the pneumatic radial tire according to the present invention, the middle lug groove includes a plurality of inner middle lug grooves provided in the inner middle land portion and a plurality of outer middle lug grooves provided in the outer middle land portion, The ratio (a1 / b1) of the axial length a1 of the inner middle lug groove to the axial width b1 of the inner middle land portion is the axial length a2 of the outer middle lug groove and the outer middle land It is desirable to be larger than the ratio (a2 / b2) to the tire axial direction width b2 of the part.

  In the pneumatic radial tire according to the present invention, the groove depth of the inner middle lug groove is preferably larger than the groove depth of the outer middle lug groove.

  In the pneumatic radial tire according to the present invention, the groove width of the inner middle lug groove is preferably larger than the groove width of the outer middle lug groove.

  In the pneumatic radial tire according to the present invention, the total axial axial length of all the outer middle lug grooves provided in the outer middle land portion is the tire of all the inner middle lug grooves provided in the inner middle land portion. Preferably 70% to 90% of the total axial length.

  In the pneumatic radial tire according to the present invention, the middle sipe is a first sipe portion disposed on the inner tread end side, a second sipe portion disposed on the outer tread end side with respect to the first sipe portion, and It is preferable that the first sipe portion and the second sipe portion be joined together and a tapered portion whose depth gradually decreases from the first sipe portion toward the second sipe portion.

  In the pneumatic radial tire according to the present invention, the depth of the second sipe portion is preferably 50% or less of the depth of the first sipe portion.

The pneumatic radial tire according to the present invention preferably satisfies the following formula (1) under the following running conditions.
Mounting rim: Normal rim tire internal pressure: Load applied to normal internal pressure tire: 70% of normal load
Speed: 10 km / h
Slip angle: 0.7 degree Camber angle:-(minus) 1.0 degree
SAT ≧ 0.18 × L × CF (1)
Here, “SAT” is self aligning torque (N · m), “L” is a maximum contact length (m) of the tread circumferential direction of the tread portion, and “CF” is a cornering force (N).

  In the pneumatic radial tire according to the present invention, the arrangement of the middle lug grooves relatively reduces the rigidity of the middle land portion on the inner tread end side, so that the SAT can be enhanced. Therefore, the four-wheeled vehicle equipped with the pneumatic radial tire according to the present invention on four wheels can be rapidly shifted to the revolving state during turning and can provide excellent turning performance.

1 is a cross-sectional view of an embodiment of a pneumatic radial tire according to the present invention. It is an expanded view of the tread part of the tire of FIG. It is a top view of the middle land part of this embodiment. It is an explanatory view showing SAT which acts on a front wheel tire when a vehicle is turning left. (A) And (b) is explanatory drawing of the measuring method of the rigidity of a land part. (A) is the BB sectional drawing of FIG. 3, (b) is the CC sectional view shown in FIG. It is an enlarged view of the middle land part of FIG. It is an enlarged view of the inside shoulder land part of FIG. It is the DD sectional view taken on the line of FIG. It is an enlarged view of the outer side shoulder land part of FIG. It is the EE sectional view taken on the line of FIG. It is an explanatory view showing turning operation of a four-wheeled passenger car. It is a graph which shows the relationship between stand CP of a common pneumatic radial tire, and the load which acts on it. It is an explanatory view showing the contact surface of the tire of the front wheel at the time of turning of the vehicle.

Hereinafter, an embodiment of the present invention will be described based on the drawings.
FIG. 1 is a cross-sectional view including a tire rotation axis of a pneumatic radial tire 1 (hereinafter sometimes simply referred to as “tire”) of the present embodiment. FIG. 2 is a development view of the tread portion 2 of the tire 1 of FIG. FIG. 1 corresponds to a cross-sectional view taken along line A-A of FIG. The tire 1 of the present embodiment is configured as a pneumatic radial tire for a passenger car. The tire 1 of the present embodiment is suitable for use in a passenger car in which the vertical load acting on the front wheels is larger than the vertical load acting on the rear wheels in a stationary state, and is particularly suitably used for a passenger car of the FF.

  As shown in FIG. 1, the tire 1 of the present embodiment includes a carcass 6 of a radial structure and a belt layer 7.

  The carcass 6 passes from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4. The carcass 6 is formed of, for example, one carcass ply 6A. The carcass ply 6A is made of, for example, a carcass cord made of organic fibers arranged at an angle of 75 to 90 degrees with respect to the circumferential direction of the tire.

  The belt layer 7 is composed of at least two belt plies 7A and 7B. The belt plies 7A, 7B are made of, for example, steel cords arranged at an angle of 10 to 45 degrees with respect to the tire circumferential direction. The belt ply 7A is made of, for example, a steel cord inclined in the opposite direction to the steel cord of the adjacent belt ply 7B. On the outside of the belt layer 7, a further reinforcing layer such as a band layer may be arranged.

  As shown in FIG. 2, the tread portion 2 is formed with a tread pattern in which the direction of attachment to the vehicle is designated. The tread pattern of the tread portion 2 is formed asymmetrically with respect to the tire equator C. The direction of attachment of the tire 1 to the vehicle is displayed, for example, in the side wall portion 3 or the like by characters or symbols.

  The tread portion 2 has an outer tread end To and an inner tread end Ti. The outer tread end To is located outside the vehicle (right side in FIG. 2) when the vehicle is mounted. The inner tread end Ti is located inside the vehicle (left side in FIG. 2) when the vehicle is mounted.

  Each tread end To, Ti is a contact position on the outermost side in the tire axial direction when a normal load is applied to the tire 1 in a normal state and the tire is grounded on a plane at a camber angle of 0 °. The normal state is a state in which the tire is rim-assembled on a normal rim, filled with a normal internal pressure, and unloaded. In the present specification, unless otherwise noted, the dimensions and the like of each part of the tire are values measured in the normal state. In the normal state, the axial axial distance between the outer tread end To and the inner tread end Ti is defined as the tread width TW.

  In the standard system including the standard to which the tire is based, the "regular rim" is the rim which the standard defines for each tire, and if it is JATMA, "standard rim", if it is TRA, "design rim" or ETRTO. For example, "Measuring Rim".

  The “normal internal pressure” is the air pressure specified by each standard in the standard system including the standard on which the tire is based, and in the case of JATMA, the “maximum air pressure”; in the case of TRA, the table “TIRE LOAD LIMITS AT The maximum value described in VARIOUS COLD INFlation PRESSURES, and in the case of ETRTO, it is “INFLATION PRESSURE”.

  "Normal load" is the load defined by each standard in the standard system including the standard on which the tire is based, and if it is JATMA, "maximum load capacity", if it is TRA, the table "TIRE LOAD LIMITS At the time of ETRTO, it is "LOAD CAPACITY".

  The tread portion 2 of the present embodiment is divided into a plurality of circumferential land portions 15 by a plurality of main grooves 10 extending continuously in the tire circumferential direction. The main groove 10 includes an inner shoulder main groove 11 and an outer shoulder main groove 12. The main groove 10 of the present embodiment further includes a crown main groove 13.

  The inner shoulder main groove 11 is provided, for example, on the innermost tread end Ti side among the plurality of main grooves 10. The inner shoulder main groove 11 is provided on the inner tread end Ti side with respect to the tire equator C.

  The outer shoulder main groove 12 is provided, for example, on the outermost tread end To side among the plurality of main grooves 10. The outer shoulder main groove 12 is provided closer to the outer tread end To than the tire equator C.

  The crown main groove 13 is provided between the inner shoulder main groove 11 and the outer shoulder main groove 12. For example, one crown main groove 13 is provided on the tire equator C. In another aspect, one crown main groove 13 may be provided on each side of the tire equator C in the tire axial direction, for example.

  In the present embodiment, the main groove 10 extends linearly, for example, along the tire circumferential direction. In another aspect, the main groove 10 may extend in a wavy or zigzag manner, for example. The groove width of the main groove (the groove width W1 of the inner shoulder main groove 11, the groove width W2 of the outer shoulder main groove 12, and the groove width W3 of the crown main groove 13) can be arbitrarily determined according to conventional practice. In order to provide sufficient drainage performance while maintaining the pattern rigidity of the tread portion 2, for example, about 2.5% to 5.0% of the tread width TW is desirable for each of the groove widths W1, W2 and W3. The depth of each of the main grooves 11 to 13 is preferably, for example, about 5 to 10 mm in the case of a radial tire for a passenger car.

  In the tread portion 2 of the present embodiment, an inner shoulder land portion 16 on the innermost tread end Ti side, an outer shoulder land portion 17 on the outermost tread end To side, and a circumferential land portion 15 are arranged between them. And at least one middle land portion 18 is included. The inner shoulder land portion 16 includes an inner tread end Ti in the present embodiment. The outer shoulder land portion 17 includes an outer tread end To in the present embodiment.

  FIG. 3 is a development view of an embodiment of the middle land portion 18. As shown in FIG. 3, the middle land portion 18 has an edge 18 d on the inner tread end Ti side extending in the tire circumferential direction and an edge 18 e on the outer tread end To side extending in the tire circumferential direction.

  The middle land portion 18 is provided with a plurality of middle lug grooves 20 extending from the edge 18 d on the inner tread end Ti side to the outer tread end To side and interrupting in the middle land portion 18.

  In the present invention, the middle land portion 18 is provided with the above-mentioned middle lug groove 20, which is one of the features.

  As described above, it is effective to generate a large SAT in order to improve the turning performance by shifting the vehicle to the revolving state as soon as possible during turning of the four-wheeled vehicle. The inventors have analyzed the pressure distribution on the contact surface during turning of the tire in detail, and find that improving the configuration of the middle land portion 18 of the tread portion 2 is effective in enhancing the SAT. Obtained. Hereinafter, as shown in FIG. 4, this point will be described by taking the case where the vehicle is turning left as an example.

  In the front tire having a slip angle with respect to the traveling direction, the circumferential land portion 15 is deformed counterclockwise due to the friction between the road surface and the tread surface. When the slip angle becomes substantially constant, each deformed circumferential land portion 15 tries to return to the original state, and generates a reaction force, that is, SAT, clockwise as shown by the arrow in the figure. In order to increase the SAT, that is, the clockwise torque around the contact center point Pc of the tread portion 2, the contact area of the outer shoulder land portion 17 of the turning outer tire (right tire) having a high contribution to the SAT It is effective to generate a large driving direction force in the rear region X1 of. In order to generate such force, it is important to increase the tire circumferential rigidity of the outer shoulder land portion 17.

  On the other hand, with regard to the inner shoulder land portion 16, in order to enhance the SAT, a large braking direction is obtained in the front region X2 of the contact region of the inner shoulder land portion 16 of the turning outer tire (right tire) having a high contribution to SAT. It is effective to generate force. In order to generate such a force in the braking direction, the inner shoulder land portion 16 lowers the rigidity in the circumferential direction of the tire contrary to the outer shoulder land portion 17 and has a ground contact ability to flexibly follow the road surface. It is effective to improve.

  As shown in FIG. 3, for the middle land portion 18, a large SAT can be obtained by relatively reducing the rigidity on the inner tread end Ti side. That is, by making the rigidity on the inner tread end Ti side of the middle land portion 18 relatively small, the clockwise deformation around the contact center point Pc on the inner tread end Ti side of the middle land portion 18 becomes large. Therefore, it is possible to increase the SAT by increasing the soft followability to the road surface. Further, by setting the rigidity of the middle land portion 18 on the outer tread end side to be relatively large, the reduction of the force to return from the above deformation is suppressed, so that the force in the driving direction is increased. It can be kept high. In this specification, the inner tread end Ti side of the middle land portion 18 in the tire axial direction is referred to as the inner half portion 18i, and the outer tread end is in the tire axial direction center position of the middle land 18 Let the To side be the outer half 18o.

  Therefore, as in the present invention, the tire 1 having a plurality of middle lug grooves 20 extending from the edge 18 d on the inner tread end Ti side to the outer tread end To side and interrupting in the middle land portion 18 is an inner half of the middle land portion 18. The rigidity of the portion 18i is relatively reduced. Moreover, in the tire 1 of the present invention, the rigidity of the outer half portion 18 o of the middle land portion 18 is relatively increased. Thereby, the tire 1 of the present invention can obtain a large SAT. For this reason, the four-wheeled vehicle equipped with the tire 1 of the present invention on four wheels can quickly shift to the revolving state during turning, providing excellent turning performance and improving wet performance.

  Furthermore, the outer diameter of the pneumatic radial tire 1 gradually decreases toward the axial outer side at the shoulder land portion. For this reason, in the tire on the turning outside of the front wheel, the outer shoulder land portion 17 generates a camber thrust which is a force opposite to the cornering force of the tire. The inner shoulder land portion 16 generates a camber thrust in the same direction as the cornering force of the tire. The outer shoulder land portion 17 is desirably configured to be larger than the inner shoulder land portion 16 with respect to tire axial rigidity. Thus, the outer shoulder land portion 17 generates a camber thrust greater than that of the inner shoulder land portion 16. Accordingly, the camber thrust generated by the outer shoulder land portion 17 helps to reduce the cornering force of the front wheel tire, and thus the vehicle in cornering can be more rapidly transferred to the revolving state.

  In the preferred embodiment, the outer shoulder land portion 17 is 1.05 to 1.40 times as stiff as the inner shoulder land portion 16 with respect to the circumferential rigidity of the tire in order to prevent occurrence of uneven wear while generating a larger SAT. It is desirable to have the ratio σ 1. Similarly, regarding the tire axial rigidity, the outer shoulder land portion 17 desirably has a rigidity ratio σ2 of 1.05 to 1.40 times that of the inner shoulder land portion 16.

  The tire circumferential rigidity and the tire axial rigidity of the land portions 16 and 17 are indicated by the force required to generate a unit deformation amount in each direction. Specific measurement methods include the following. In FIG. 5A, the inner shoulder land portion 16 is shown as an example of the land portion. As shown in FIG. 5A, the inner shoulder land portion 16 to be measured is cut out from the tire 1 with a tire circumferential direction length of two or more pitches. At this time, the land portion test strip TP is a surface PS1 parallel to the tread surface of the tread portion 2 through the groove bottom 10b of the main groove 10 and a surface PS2 extending along the tire radial direction through the inner tread end Ti. It is cut out (shown in FIG. 5 (b)). Next, the ground contact surface of the land portion test piece TP is pressed against a flat test surface, for example, with a normal load to maintain the ground contact state. Next, the test surface is moved with a force F in the tire circumferential direction Y or the tire axial direction X, and the displacement of the land portion in each direction X or Y is measured. Then, the force F is divided by the amount of displacement of the land portion test piece TP in each direction to obtain the land portion rigidity in each of the directions Y and X.

In a preferred embodiment, it is desirable that the tire 1 satisfy the following formula (1) under the following traveling conditions in, for example, a bench test (for example, a test using a flat belt type tire tester). .
Mounting rim: Normal rim Tire internal pressure: Normal internal pressure Load applied to the tire: 70% of the normal load
Speed: 10 km / h
Slip angle: 0.7 degree Camber angle:-(minus) 1.0 degree
SAT ≧ 0.18 × L × CF (1)
Here, “SAT” is the self aligning torque (N · m), “L” is the maximum contact length (m) of the tread portion 2 in the tire circumferential direction, and “CF” is the cornering force (N). Also, "minus" of the camber angle means an inclination such that the upper part of the tire is directed to the center of the vehicle.

  The above measurement conditions are based on the condition of the front wheels in a turning state (lateral acceleration of about 0.2 G) which tends to occur frequently in four-wheeled vehicles. The inventors mount various sensors on a four-wheeled vehicle, measure the condition (load, camber angle, slip angle, and angle) of the tire in the above-mentioned turning state, and approximate it by bench test As a thing, the above-mentioned running condition was obtained. Therefore, the tire 1 satisfying the above equation (1) can generate SAT reliably and sufficiently large in a normal turning state. That is, it is possible to more rapidly shift the vehicle on which it is turning to the revolving state.

  The tire 1 of the present invention can be easily realized by improving the tread pattern of the tread portion 2 on the premise of the above-described basic radial structure. In the following, several embodiments of such tread patterns are described.

[Middle land section composition]
As shown in FIG. 3, in the middle land portion 18 of the present embodiment, middle lug grooves 20 and middle sipes 21 are provided. In the present specification, “sipe” is defined as a slit having a width of 0.8 mm or less, and is distinguished from a “groove” having a width larger than this.

  The middle lug groove 20 extends, for example, without being connected to another groove. The middle lug groove 20 extends at a small angle θ1 with respect to the tire axial direction. The angle θ1 of the middle lug groove 20 is desirably, for example, 0 to 10 degrees. In the present embodiment, the angle θ1 linearly extends along the tire axial direction (angle θ1 = 0 degrees). Such a middle lug groove 20 sufficiently maintains the axial rigidity of the middle land portion 18 and can provide a large equivalent CP, especially when the tire 1 is mounted on the rear wheel of the vehicle. Further, even when the vehicle starts turning and lateral force is applied, the lateral force applied to the middle land portion 18 is not dispersed in the tire circumferential direction, so that the decrease in CF is suppressed.

  The middle lug groove 20 preferably has a length L1 in the tire axial direction of 30% to 80% of the axial width Wm of the middle land portion 18. The groove width W4 of the middle lug groove 20 is preferably, for example, 10% to 40% of the tire axial direction width Wm of the middle land portion 18. In the present embodiment, the groove width W4 is fixed, but may be changed. When the length L1 and the groove width W4 of the middle lug groove 20 are defined, the rigidity of the outer half 18o and the rigidity of the inner half 18i can be set as preferable ranges, and good wet performance can be provided.

  The middle lug groove 20 is configured to include a first middle lug groove 20 a and a second middle lug groove 20 b whose length in the tire axial direction is larger than that of the first middle lug groove 20 a. The second middle lug groove 20 b enhances the wet performance, and the first middle lug groove 20 a suppresses an excessive decrease in the rigidity of the middle land portion 18. In the present embodiment, the first middle lug grooves 20a and the second middle lug grooves 20b are alternately provided in the tire circumferential direction. In addition, the middle lug groove 20 is not limited to such an aspect, For example, the length of a tire axial direction may be formed in the same aspect.

  In order to exert the above-mentioned effect effectively, it is desirable that the axial length L1a of the first middle lug groove 20a be 30% to 50% of the axial width Wm of the middle land portion 18. The axial length L1b of the second middle lug groove 20b is preferably 50% to 80% of the axial width Wm of the middle land portion 18.

  FIG. 6A shows a cross-sectional view of the middle lug groove 20 of FIG. 3 taken along the line B-B. As shown in FIG. 6A, the middle lug groove 20 is formed to include a first portion 20A, a second portion 20B, and a tapered portion 20C. The first portion 20A of the present embodiment is disposed on the inner tread end Ti side. The second portion 20B of the present embodiment is disposed closer to the outer tread end To than the first portion 20A. In the tapered portion 20C of the present embodiment, the groove depth gradually decreases from the first portion 20A to the second portion 20B. Such a middle lug groove 20 can provide a favorable wet performance while being able to make the rigidity of the outer half 18 o and the rigidity of the inner half 18 i more effectively fall within a preferable range. In addition, the tapered portion 20C suppresses an excessive decrease in the rigidity of the middle land portion 18.

  The groove depth d2 of the second portion 20B is desirably 50% or less of the groove depth d1 of the first portion 20A. Thereby, the above-mentioned effect is exhibited effectively. If the depth d2 of the second portion 20B is excessively small, there is a possibility that the wet performance can not be enhanced. Therefore, the depth d2 of the second portion 20B is desirably 20% or more of the groove depth d1 of the first portion 20A. The groove depth d1 of the first portion 20A is desirably about 20% to 90% of the groove depth d of the inner shoulder main groove 11.

  Furthermore, in order to exhibit the above-mentioned effect effectively, 20 to 50% of tire axial direction width Wm of middle land part 18 is desirable for length La of the axial direction of the 1st portion 20A, for example. The axial length Lb of the second portion 20B is preferably, for example, 20 to 40% of the tire axial width Wm of the middle land portion 18.

  As shown in FIG. 3, the middle sipes 21 are full open types that completely cross the middle land portion 18 in the present embodiment. Since such middle sipes 21 have a large edge effect, the water film between the road surface and the tread surface of the middle land portion 18 is removed to improve the wet performance.

  The middle sipes 21 extend in a straight line in the present embodiment, but may, for example, extend in a wavy or zigzag manner. The sipe 21 is disposed at an angle θ2 of 10 degrees or less with respect to the tire axial direction. As a result, even when the vehicle starts turning and lateral force is applied, lateral force applied to the middle land portion 18 is not dispersed in the tire circumferential direction, thereby suppressing a decrease in CF. In the sipe 21 of the present embodiment, θ2 is disposed at 0 degrees.

  FIG.6 (b) is CC sectional view taken on the line of FIG. As shown in FIG. 6B, the middle sipe 21 is formed to include a first sipe portion 21A, a second sipe portion 21B, and a tapered portion 21C. The first sipe portion 21A is disposed on the inner tread end Ti side. The second sipe portion 21B is disposed closer to the outer side tread end To than the first sipe portion 21A. The tapered portion 21C joins the first sipe portion 21A and the second sipe portion 21B, and the depth gradually decreases from the first sipe portion 21A toward the second sipe portion 21B. Such middle sipe 21 can make the rigidity of the outer half 18o and the rigidity of the inner half 18i more effectively in the preferable range. In addition, the tapered portion 21C suppresses an excessive decrease in the rigidity of the middle land portion 18.

  In the present embodiment, the first sipe portion 21A is continuous with the edge 18d on the inner tread end Ti side. In the present embodiment, the second sipe portion 21B is continuous with the edge 18e on the outer tread end To side.

  The depth d4 of the second sipe portion 21B is desirably 50% or less of the depth d3 of the first sipe portion 21A. Thereby, the above-mentioned effect is exhibited effectively. If the depth d4 of the second sipe portion 21B is excessively small, the edge effect may be reduced, and the wet performance may not be enhanced. Therefore, the depth d4 of the second sipe portion 21B is preferably 20% or more of the depth d3 of the first sipe portion 21A. The depth d3 of the first sipe portion 21A is desirably about 20% to 90% of the groove depth d of the inner shoulder main groove 11.

  Furthermore, in order to exert the above-mentioned effect effectively, as for length Lc of the tire axial direction of the 1st Sipe part 21A, 20 to 60% of tire axial direction width Wm of middle land part 18 is desirable, for example. The axial length Ld of the second sipe portion 21B is preferably, for example, 40 to 80% of the axial width Wm of the middle land portion 18.

  In the preferred embodiment, with respect to the circumferential rigidity of the tire, the outer half 18o of the middle land 18 is 1.05-1. It is desirable to have a stiffness ratio σ 3 of 50 times. Similarly, with regard to tire axial rigidity, it is desirable that the outer half 18 o of the middle land 18 have a rigidity ratio σ 4 that is 1.05 to 1.20 times that of the inner half 18 i.

  The tire circumferential rigidity and tire axial rigidity of the outer half portion 18o and the inner half portion 18i of the middle land portion 18 are measured by cutting out the land portions from the tread portion 2 as described above.

  The middle land portion 18 includes, for example, middle rib-shaped portions 22A between the main groove 10 and each middle lug groove 20, and middle block pieces 22B divided between the middle lug grooves 20 adjacent in the tire circumferential direction. The middle rib-shaped portion 22A is, for example, not provided with a groove, and extends continuously in the tire circumferential direction. Such middle rib-shaped portion 22A can increase the rigidity of the outer tread end To of the middle land portion 18 and thus enhance SAT. The middle block piece 22B is divided between the middle lug grooves 20 adjacent in the tire circumferential direction.

  7 is an enlarged view of the middle land portion 18 of the tread portion 2 of FIG. As shown in FIG. 7, the middle land portion 18 of the present embodiment includes an inner middle land portion 18A on the inner tread end Ti side and an outer middle land portion 18B on the outer tread end To side. The inner middle land portion 18 </ b> A of this embodiment is divided between the crown main groove 13 and the inner shoulder main groove 11. The outer middle land portion 18 </ b> B of the present embodiment is divided between the crown main groove 13 and the outer shoulder main groove 12. In this embodiment, the inner middle land portion 18A and the outer middle land portion 18B respectively have axial axial widths b1 and b2 of 0.10 to 0.20 times the tread width TW. In the present embodiment, b1> b2 but b1 = b2.

  As a result of various experiments of the inventors shown in FIG. 4, the tire circumferential rigidity and the tire axial rigidity of the outer middle land portion 18B also have a large contribution to SAT, and they should be higher than the inner middle land portion 18A. So, it was found that SAT was increased by almost the same mechanism as above.

  In the preferred embodiment, the outer middle land portion 18B has a rigidity ratio σ5 of 1.05 to 1.40 times that of the inner middle land portion 18A with respect to the tire circumferential rigidity in order to enhance the wet performance while generating a larger SAT. It is desirable to have. Similarly, with regard to tire axial stiffness, it is desirable that the outer middle land portion 18B have a rigidity ratio σ6 that is 1.05 to 1.40 times that of the inner middle land portion 18A. Hereinafter, differences in the configuration of specific patterns that can realize the above-described difference in rigidity will be described.

  The middle lug grooves 20 include a plurality of inner middle lug grooves 23 provided in the inner middle land portion 18A and a plurality of outer middle lug grooves 24 provided in the outer middle land portion 18B.

In the present embodiment, the length ratio of the inner middle lug grooves 23 (a1 / b1) is to much larger than the length ratio of the outer middle lug grooves 24 (a2 / b2), the axially stiffness of the outer middle land portion 18B Of the inner middle land portion 18A in the tire axial direction. This makes it possible to improve the turning performance and the ride comfort in a well-balanced manner. More preferably, (a1 / b1) / (a2 / b2) is 1.1 to 1.4.

  The “length ratio (a1 / b1) of the inner middle lug groove 23” is a ratio of the axial length a1 of the inner middle lug groove 23 to the tire axial width b1 of the inner middle land portion 18A. The "length ratio (a2 / b2) of the outer middle lug groove 24" is a ratio of the axial length a2 of the outer middle lug groove 24 to the tire axial width b2 of the outer middle land portion 18B. Further, as in the present embodiment, when the middle lug groove 20 is configured by the first middle lug groove 20a and the second middle lug groove 20b having different lengths, the ratio is the first middle lug groove 20a and the second middle lug groove. Calculated as the average of the length of 20b.

  It is desirable that the groove depth (not shown) of the inner middle lug groove 23 be larger than the groove depth (not shown) of the outer middle lug groove 24. The groove width Wa of the inner middle lug groove 23 is preferably larger than the groove width Wb of the outer middle lug groove 24. The total axial axial length of all the outer middle lug grooves 24 of the outer middle land portion 18B is 70% to 90% of the total axial axial length of all the inner middle lug grooves 23 of the inner middle land portion 18A. Is desirable. The groove depth is the maximum groove depth.

  The groove depth of the outer middle lug groove 24 is preferably about 20% to 95% of the groove depth of the inner middle lug groove 23 in order to more effectively exert the above-described action. The groove width Wb of the outer middle lug groove 24 is desirably about 80% to 95% of the groove width Wa of the inner middle lug groove 23.

  The area S2 of the cross section along the groove center line of the outer middle lug groove 24 is preferably smaller than the area S1 of the cross section along the groove center line of the inner middle lug groove 23. The area S2 is preferably, for example, 0.80 to 0.95 times the area S1.

  The number N1 of the outer middle lug grooves 24 (total number) is the same as the number N2 of the inner middle lug grooves 23 in the present embodiment. As a result, the difference in rigidity between the outer middle land portion 18B and the inner middle land portion 18A is suppressed from becoming excessively large, so that the above-described action is effectively exhibited. The number N1 of the outer middle lug grooves 24 is preferably, for example, in the range of 65 to 85.

  The middle block piece 22B includes an inner middle block piece 25A disposed in the inner middle land portion 18A and an outer middle block piece 25B disposed in the outer middle land portion 18B. The inner middle block piece 25A has a tire circumferential length Mbi. The outer middle block piece 25B has a tire circumferential length Mbo. In a desirable mode, it is desirable that the tire circumferential direction length Mbo of the outer middle block piece 25B be larger than the tire circumferential direction length Mbi of the inner middle block piece 25A. In a particularly preferred embodiment, the ratio Mbi / Mbo of the tire circumferential length between the inner middle block piece 25A and the outer middle block piece 25B is preferably in the range of 0.7 to 0.9. Thereby, the rigidity balance between the inner middle land portion 18A and the outer middle land portion 18B is further enhanced.

  The inner middle land portion 18A desirably has a land ratio of 75% to 85%, for example. Such an inner middle land portion 18A can improve the wet performance and the steering stability in a well-balanced manner. In the present specification, the “land ratio” is the ratio of the total ground area Sb of the actual land portion to the total area Sa of the virtual ground plane in which all the grooves provided in the target land portion are filled (Sb / Sa Defined as).

  The outer middle land portion 18B desirably has a land ratio greater than, for example, the inner middle land portion 18A. The land ratio of the outer middle land portion 18B is preferably, for example, in the range of 1.05 to 1.10 times the land ratio of the inner middle land portion 18A. This allows more SAT to be generated.

[Configuration of inner shoulder land portion]
An enlarged view of the inner shoulder land portion 16 is shown in FIG. As shown in FIG. 8, the inner shoulder land portion 16 is formed between the inner tread end Ti and the inner shoulder main groove 11. The inner shoulder land portion 16 has, for example, an axial width Ws of 0.25 to 0.35 times the tread width TW.

  The inner shoulder land portion 16 is provided with a plurality of inner shoulder lug grooves 27 extending inward in the tire axial direction from the inner tread end Ti. The inner shoulder lug groove 27 can drain to the inner tread end Ti, which helps to enhance the wet performance.

  The inner shoulder lug groove 27 is interrupted, for example, in the inner shoulder land portion 16 without being continuous with other grooves. The inner shoulder lug groove 27 of the present embodiment is, for example, inclined at an angle θ3 of 10 to 45 degrees with respect to the tire axial direction. In addition, it is desirable that the inner shoulder lug grooves 27 extend in a straight line so as to be inclined at a constant angle with respect to the tire axial direction, for example.

  The axial length L2 of the inner shoulder lug groove 27 is preferably, for example, 0.70 to 0.85 times the axial width Ws of the inner shoulder land portion 16 in the tire axial direction. The groove width W5 of the inner shoulder lug groove 27 is preferably 0.70 to 0.85 times the groove width W1 of the inner shoulder main groove 11, for example. Further, in order to secure the wet performance, the groove width W5 of the inner shoulder lug groove 27 is desirably 2 mm or more. When the length L1 and the groove width W5 of the inner shoulder lug groove 27 are defined, good wet performance is provided while reducing the tire circumferential rigidity and the tire axial rigidity of the inner shoulder land portion 16 in a more preferable range. be able to.

  FIG. 9 is a cross-sectional view taken along the line D-D in FIG. As shown in FIG. 9, in the inner shoulder lug groove 27, for example, in the region between the inner tread end Ti and the inner shoulder main groove 11, the groove depth gradually decreases toward the inner shoulder main groove 11. There is. Thereby, the water in the groove is smoothly discharged to the inner tread end Ti. In a particularly preferred embodiment, the depth d5 at the inner end of the inner shoulder lug groove 27 is preferably 40% to 60% of the depth d6 at the inner tread end Ti of the inner shoulder lug groove 27. The depth d5 of the inner end is measured from the inner end of the inner shoulder lug groove 27 at a position where 25% of the length L2 in the axial direction of the tire is L3 outside the axial direction of the tire. I assume.

  As shown in FIG. 8, the inner shoulder lug groove 27 of the present embodiment extends, for example, with a constant groove width. However, the present invention is not limited to such an embodiment. In another embodiment of the present invention, for example, the inner shoulder lug groove 27 may have a groove width gradually decreasing inward in the tire axial direction. Such inner shoulder lug grooves 27 serve to adjust the rigidity of the inner shoulder land portion 16 to a preferred range.

  In order to reduce the tire circumferential rigidity and the tire axial rigidity of the inboard shoulder land portion 16 to a preferable range, the number N3 of the inboard shoulder lug grooves 27 (total number) is, for example, in the range of 65 to 85. desirable.

  The inner shoulder land portion 16 is formed of an inner shoulder rib-shaped portion 28 between the inner shoulder main groove 11 and each inner shoulder lug groove 27 and a plurality of inner portions divided between the inner shoulder lug grooves 27 adjacent in the tire circumferential direction. The shoulder block piece 29 is included.

  The inner shoulder rib-shaped portion 28 is not provided with a groove, for example, and extends continuously in the tire circumferential direction. Such an inner shoulder rib-like portion 28 enhances the tire circumferential rigidity in the tire axial direction inner region of the inner shoulder land portion 16 and thus helps to obtain a large equivalent CP. The axial width W6 of the inner shoulder rib portion 28 is preferably, for example, 0.15 to 0.30 times the width Ws of the inner shoulder land portion 16.

  The inner shoulder block piece 29 has a tire circumferential length Sbi. The tire circumferential direction length Sbi of the inner shoulder block piece 29 of the present embodiment is preferably, for example, 0.9% to 1.2% of the one tire circumferential length of the inner shoulder land portion 16. In a more desirable aspect, the inner shoulder block piece 29 extends obliquely in the tire axial direction with a constant tire circumferential length Sbi.

  The inner shoulder land portion 16 desirably has a land ratio of, for example, 75% to 85%.

[Configuration of outer shoulder land portion]
An enlarged view of the outer shoulder land portion 17 is shown in FIG. As shown in FIG. 10, the outer shoulder land portion 17 is formed between the outer tread end To and the outer shoulder main groove 12. The outer shoulder land portion 17 has, for example, an axial width Wt of 0.25 to 0.35 times the tread width TW. As a desirable aspect, the outer shoulder land portion 17 of the present embodiment is configured to have the same width as the inner shoulder land portion 16 (shown in FIG. 8).

  The outer side shoulder land portion 17 is provided with, for example, a plurality of outer side shoulder lug grooves 30. Each outer shoulder lug groove 30 extends, for example, inward in the axial direction of the tire from the outer tread end To, and is interrupted in the outer shoulder land portion 17. In the preferred embodiment, the outer shoulder lug grooves 30 are interrupted within the outer shoulder lands 17 without communicating with other grooves. In the present embodiment, each outer shoulder lug groove 30 has the same shape, but is not limited to such an aspect.

  The outer shoulder lug grooves 30 extend, for example, at an angle θ 4 (not shown) smaller than the inner shoulder lug grooves 27 (shown in FIG. 8, hereinafter the same) with respect to the tire axial direction. The angle θ4 is desirably, for example, 0 to 10 degrees, and in the present embodiment, the outer shoulder lug groove 30 linearly extends along the tire axial direction, and the angle θ4 is equal to 0 degrees. The outer shoulder lug groove 30 can, among other things, make the tire axial rigidity of the outer shoulder land portion 17 more effective than the inner shoulder land portion 16 and thus increase the SAT.

  The axial length L4 of the outer shoulder lug grooves 30 is preferably smaller than the axial length L2 of the inner shoulder lug grooves 27. For example, the length L4 of the outer shoulder lug groove 30 is preferably 0.90 to 0.98 times the length L4 of the inner shoulder lug groove 27. Such an outer shoulder lug groove 30 can also relatively increase the tire circumferential rigidity of the outer shoulder land portion 17 and thus enhance the SAT.

  The groove width W7 of the outer shoulder lug groove 30 is desirably 0.1 to 0.4 times the groove width W2 of the outer shoulder main groove 12, for example. In the present embodiment, the groove width W7 is constant. However, the present invention is not limited to such an embodiment. In another embodiment of the present invention, for example, the outer shoulder lug groove 30 may have a groove width gradually decreasing inward in the tire axial direction. Such outer shoulder lug grooves 30 maintain the rigidity of the outer shoulder lands 17 and help to further increase the SAT.

  The EE sectional view taken on the line of FIG. 10 is shown by FIG. As shown in FIG. 11, the outer shoulder lug groove 30 has a groove depth gradually decreasing from the outer tread end To toward the inner side in the tire axial direction, for example. Such outer shoulder lug grooves 30 may improve wet performance. The depth d7 at the inner end of the outer shoulder lug groove 30 is desirably 40% to 60% of the depth d8 at the outer tread end To of the outer shoulder lug groove 30. The depth d7 of the inner end is measured from the inner end of the outer shoulder lug groove 30 at a position at which 25% of the axial length L4 of the axial direction L4 is separated to the outer side in the tire axial direction. I assume.

  From the same viewpoint, it is desirable that the area S4 of the cross section along the groove center line of the outer shoulder lug groove 30 be smaller than the area S3 of the cross section along the groove center line of the inner shoulder lug groove 27. The area S4 of the outer shoulder lug groove 30 is preferably, for example, 0.85 to 0.95 times the area S3 of the inner shoulder lug groove 27.

  As shown in FIG. 10, it is desirable that the number (total number) N4 of the outer shoulder lug grooves 30 provided in the outer shoulder land portion 17 be smaller than the number N3 of the inner shoulder lug grooves 27, for example.

  In particular, the number N4 of the outer shoulder lug grooves 30 is preferably in the range of 55 to 75, and preferably in the range of 0.5 to 0.9 times the number N3 of the inner shoulder lug grooves 27. By providing a difference between the numbers N3 and N4 of the inner side shoulder lug grooves 27 and the outer side shoulder lug grooves 30, the tire circumferential rigidity and the tire axial direction rigidity of the outer shoulder land portion 17 are relative to the inner shoulder land portion 16 Can be enhanced.

  The outer shoulder land portion 17 is, for example, a plurality of outer shoulder rib-like portions 33 between the outer shoulder main groove 12 and the outer shoulder lug grooves 30 and a plurality of outer shoulder lug grooves 30 adjacent to each other in the tire circumferential direction. And an outer shoulder block piece 34.

  The outer shoulder rib-shaped portion 33 is not provided with a groove, for example, and extends continuously in the tire circumferential direction. Such an outer shoulder rib-like portion 33 can effectively enhance the tire circumferential rigidity of the outer shoulder land portion 17.

  The axial width W8 of the outer shoulder rib-shaped portion 33 is preferably 0.20 to 0.30 times the axial width W7 of the outer shoulder land portion 17, for example. As a result, the rigidity of the outer shoulder land portion 17 can be appropriately maintained, and as a result, high SAT can be generated.

  The outer shoulder block piece 34 has a tire circumferential length Sbo. In the present embodiment, the tire circumferential length Sbo of the outer shoulder block pieces 34 is formed larger than the tire circumferential length Sbi of the inner shoulder block pieces 29. In a preferred embodiment, the tire circumferential length ratio (Sbi / Sbo) of the inner shoulder block piece 29 to the outer shoulder block piece 34 is, for example, in the range of 0.5 to 0.8. This gives a high SAT and thus an excellent turning performance.

  From the same point of view, it is desirable that the outer shoulder land portion 17 have, for example, a land ratio greater than that of the inner shoulder land portion 16. The land ratio of the outer shoulder land portion 17 is desirably, for example, in the range of 1.05 to 1.10 times the land ratio of the inner shoulder land portion 16.

  As mentioned above, although the tire of one embodiment of the present invention was explained in detail, the present invention can be changed and carried out in various modes, without being limited to the above-mentioned specific embodiment.

A tire of size 205 / 55R16 having the basic pattern of FIG. 2 was prototyped based on the specifications of Table 1. Various tests were conducted on each test tire. The ratio of the length of the middle lug groove to the axial width of the middle land portion is the same in both the inner middle land portion and the outer middle land portion. The ratio of the first middle lug groove to the second middle lug groove is the same for both the inner middle lug groove and the outer middle lug groove.
Groove depth d1 / d of first part: 50%
Depth of first sipe part d3 / d: 50%

[Table test]
Using the flat belt type tire testing machine, the SAT and the maximum contact length L and CF in the tire circumferential direction of the tread portion are measured under the following conditions, and whether each test tire satisfies the following equation (1) It was investigated.
Mounting rim: 16 × 6.5 JJ
Tire internal pressure: 200kPa
Speed: 10 km / h
Slip angle: 0.7 degree Camber angle: -1.0 degree Tire load: 70% of normal load
SAT ≧ 0.18 × L × CF (1)

<Swirl performance>
A test tire is attached to four wheels of a FF passenger car with a displacement of 2000 cc, and it is made to turn from high speed (100 to 120 km / h) to low speed (40 to 80 km / h) on dry road with one driver. The turning performance of the vehicle was evaluated by the driver's sense. A result is a score which sets comparative example 1 to 100. The larger the value is, the faster the vehicle has shifted to the revolving state during turning.
The results of the test are shown in Table 1.

  As a result of the test, it was confirmed that the tire of the example exhibited excellent turning performance while maintaining the wet performance.

DESCRIPTION OF SYMBOLS 1 pneumatic radial tire 2 tread portion 6 carcass 7 belt layer 15 circumferential land portion 16 inner shoulder land portion 17 outer shoulder land portion 18 middle land portion 18i middle land edge 20 middle lug groove 21 middle sipe Ti inner tread end To outer tread end

Claims (14)

For a passenger car including a carcass of radial structure, a belt layer consisting of at least two belt plies disposed outside the carcass, and a tread portion on which a tread pattern having a designated direction of mounting on a vehicle is formed A pneumatic radial tire,
The tread portion has an outer tread end and an inner tread end located on the outer side and the inner side of the vehicle, respectively, when the vehicle is mounted.
The tread pattern is formed asymmetrically with respect to the tire equator,
The tread portion is divided into a plurality of circumferential land portions by a plurality of main grooves continuously extending in the tire circumferential direction,
The circumferential land portion is an inner shoulder land portion on the innermost tread end side, an outer shoulder land portion on the outermost tread end side, and at least at least disposed between the inner shoulder land portion and the outer shoulder land portion. Including one middle land section,
In the middle land portion, a plurality of middle lug grooves extending from the edge on the inner tread end side to the outer tread end side and interrupting in the middle land portion and a plurality of middle sipes completely crossing the middle land portion are included. Pneumatic radial tire provided.   The pneumatic radial tire according to claim 1, wherein the axial length of the middle lug groove is 30% to 80% of the axial width of the middle land portion.   The pneumatic radial tire according to claim 1 or 2, wherein the middle lug groove includes a first middle lug groove and a second middle lug groove having a length in the tire axial direction larger than that of the first middle lug groove. The axial length of the first middle lug groove is 30% to 50% of the axial width of the middle land portion, and
The pneumatic radial tire according to claim 3, wherein a length in an axial direction of the second middle lug groove is 50% to 80% of an axial width of the middle land portion.   The middle lug groove includes a first portion disposed on the inner tread end side, a second portion disposed on the outer tread end side relative to the first portion, and the first portion and the second portion. The pneumatic radial tire according to any one of claims 1 to 4, further comprising a tapered portion in which the groove depth gradually decreases from the first portion to the second portion.   The pneumatic radial tire according to claim 5, wherein the groove depth of the second portion is 50% or less of the groove depth of the first portion.   The air according to any one of claims 1 to 6, wherein the middle land portion includes an inner middle land portion on the inner tread end side and an outer middle land portion on the outer tread end side with respect to the inner middle land portion. Enter radial tire. The middle lug groove includes a plurality of inner middle lug grooves provided in the inner middle land portion and a plurality of outer middle lug grooves provided in the outer middle land portion.
The ratio (a1 / b1) between the axial length a1 of the inner middle lug groove and the tire axial width b1 of the inner middle land portion is the axial length a2 of the outer middle lug groove and the outer middle groove The pneumatic radial tire according to claim 7, which is larger than a ratio (a2 / b2) of the land portion to the axial axial width b2.   The pneumatic radial tire according to claim 8, wherein a groove depth of the inner middle lug groove is larger than a groove depth of the outer middle lug groove.   The pneumatic radial tire according to claim 8 or 9, wherein the groove width of the inner middle lug groove is larger than the groove width of the outer middle lug groove.   The total axial axial length of all the outer middle lug grooves provided in the outer middle land portion is 70% of the total axial axial length of all the inner middle lug grooves provided in the inner middle land portion. The pneumatic radial tire according to any one of claims 8 to 10, which is% to 90%.   The middle sipe includes a first sipe portion disposed on the inner tread end side, a second sipe portion disposed on the outer tread end side with respect to the first sipe portion, and the first sipe portion and the second sipe portion. The pneumatic radial tire according to any one of claims 1 to 11, further comprising a tapered portion joined to the sipe portion and having a gradually decreasing depth from the first sipe portion to the second sipe portion.   The pneumatic radial tire according to claim 12, wherein the depth of the second sipe portion is 50% or less of the depth of the first sipe portion. The pneumatic radial tire according to any one of claims 1 to 13, wherein the following formula (1) is satisfied under the following traveling conditions.
Mounting rim: Normal rim Tire internal pressure: Normal internal pressure Load applied to the tire: 70% of the normal load
Speed: 10 km / h
Slip angle: 0.7 degree Camber angle:-(minus) 1.0 degree
SAT ≧ 0.18 × L × CF (1)
Here, “SAT” is self aligning torque (N · m), “L” is a maximum contact length (m) of the tread circumferential direction of the tread portion, and “CF” is a cornering force (N).