- 1 PNEUMATIC TIRE TECHNICAL FIELD [0001] The present invention relates to a pneumatic tire and, in particular, intends to 5 propose a technology for achieving highly improved drainage property and traction performance in a well-coordinated manner. RELATED ART [0002] In general, in order to improve the drainage property, conventional pneumatic 10 tire employs a tread pattern defined by combining a circumferential groove extending along a tread circumferential direction in the vicinity of a tire equatorial plane with plural acutely angled grooves (so-called high angle grooves) extending obliquely with respect to the tread circumferential direction at a relatively small angle, as described, for example, in Patent Document 1. 15 [0003] However, in such a tire, blocks defined by the circumferential groove and the acutely angled grooves have a narrow, elongated shape. Therefore, the rigidity of the blocks reduces, and there is a room for further improvement in terms of the traction performance (driving performance). [0004] In order to improve the traction performance, it is a general practice to employ a 20 tread pattern defined by combining a circumferential groove extending along the tread circumferential direction in the vicinity of the tire equatorial plane with plural obtusely angled grooves (so-called low angled groove) extending obliquely with respect to the tread circumferential direction at a relatively large angle, as described, for example, in Patent Document 2. However, in such a tire, there is a room for further improvement in 25 terms of the drainage property. [0005] As described above, with the conventional pneumatic tires, it has been considered to be difficult to simultaneously achieve both of the drainage property and the traction performance of the tire at a high level. 30 (Patent Documents) [0006] Patent Document 1: Japanese Patent Application Laid-open No. 2005-231430 Patent Document 2: Japanese Patent Application Laid-open No. 2001-026205 5243577_1 (GHMatters) P92598.AU -2 DISCLOSURE OF THE INVENTION (Problems to be Solved by the Invention) [0007] An advantage of the present invention is to provide a pneumatic tire that achieves both of the drainage property and the traction performance at a high level. 5 (Means for Solving the Problems) [0008] A pneumatic tire according to the present invention comprises, in a ground contact surface of a tread portion: a first circumferential groove positioned in the vicinity of a tire equatorial plane and extending along a tread circumferential direction; and, a 10 second circumferential groove disposed between the first circumferential groove and a tread end and extending along the tread circumferential direction, thereby defining a land portion between the first and the second circumferential grooves, said land portion being provided with plural combined grooves having a zigzag-shape, for sectioning the land portion into plural blocks, wherein said combined grooves includes: 15 - a first groove portion extending obliquely with respect to the tread circumferential direction from the first circumferential groove at a first angle, one end of the first groove portion being open to the first circumferential groove and the other end of the first groove portion terminating within said land portion; - a second groove portion extending obliquely with respect to the tread 20 circumferential direction in the same direction as the first groove portion at a second angle, one end of the second groove portion being positioned within said land portion, and the other end of the second groove portion being open to the second circumferential groove; and - a third groove portion extending obliquely with respect to the tread 25 circumferential direction at a third angle and communicating with the other end of the first groove portion and the one end of the second groove portion, wherein the first and second angles are smaller than the third angle. The circumferential grooves and groove portions of the tread portion in the vicinity of the tire equatorial plane may be mirrored on an opposing side of the tire equatorial plane. 30 The vicinity of the tire equatorial plane may include a position situated within 35% of a tread width on both sides of the tire equatorial plane and as measured therefrom. [0009] According to the present invention, it is only necessary that the circumferential grooves each have a shape extending along the tread circumferential direction, and in addition to a straight shape, the circumferential grooves may extend as main grooves 35 having a zigzag shape, wavy shape, curved shape, cranked shape or other shapes. 5243577_1 (GHMatters) P92598.AU -3 [0010] Each of the angles was measured in a state where the tire is assembled with a rim specified in industrial standards effective in regions where the tire is manufactured or used, and is inflated at the maximum pneumatic pressure, these industrial standards being specified, for example, in "JATMA (The Japan Automobile Tyre Manufacturers 5 Association) YEAR BOOK" in Japan, "ETRTO (The European Tyre and Rim Technical Organisation) Standards Manual" in Europe, and "TRA (The Tire and Rim Association Inc.) Year Book" in the United States. [0011] In the tire as described above, it is more preferable that the angle and the second angle are in the range of 150 to 450 with respect to the tread circumferential 10 direction, and the third angle is in the range of 450 to 90' with respect to the tread circumferential direction. [0012] Further, it is preferable that at least one of the first angle and the second angle is different to the third angle by more than or equal to 15'. [0013] Yet further, it is preferable that a distance between a position of the other end of 15 the first groove portion and a groove wall of the second circumferential groove in the tread width direction is in the range of 10 to 30% of the width of the second land portion. [0014] Yet further, it is preferable that a chamfered portion sloping toward a groove bottom of the first groove portion is provided on an upper end portion of a side wall of the block facing a groove wall on the tire equatorial plane side of the first groove portion. 20 Yet further, it is preferable that a chamfered portion sloping toward a groove bottom of the second groove portion is provided on an upper end portion of the side wall of the block facing a groove wall on the tread end side of the second groove portion. [0015] The chamfers may have a flat-like shape or a curved-surface-like shape. [0016] Yet further, it is preferable that a groove depth of the third groove portion from 25 the tread ground contact surface is formed so as to be shallower than an average groove depth of the first groove portion and the second groove portion measured from the tread ground contact surface. [0017] Yet further, it is preferable that there is provided a sipe that is opened to the first groove portion and the second groove portion adjacent to each other in the tread 30 circumferential direction of the land portion. [0017a] In an alternative embodiment, there is provided a pneumatic tire having a tread portion in contact with ground, the tread portion comprising: a first circumferential groove positioned in the vicinity of a tire equatorial plane and extending in a tread circumferential direction; and a second circumferential groove disposed between the 35 first circumferential groove and a tread end of the tire, the second circumferential groove 5243577_1 (GHMatters) P92598.AU -4 extending in the tread circumferential direction, wherein a land portion is defined between the first and the second circumferential grooves, said land portion being provided with a plurality of grooves having a zigzag-shape, thereby sectioning the land portion into a plurality of blocks, wherein said plurality of grooves comprises: a first groove portion 5 extending across the tread portion obliquely to the first circumferential groove at a first angle, a first end of the first groove portion being open to the first circumferential groove and a second end of the first groove portion terminating within said land portion; a second groove portion extending across the tread portion obliquely in the same direction as the first groove portion at a second angle, a first end of the second groove portion being 10 positioned within said land portion, and a second end of the second groove portion being open to the second circumferential groove; and a third groove portion extending obliquely across the tread portion at a third angle and connecting the second end of the first groove portion with the first end of the second groove portion, wherein the first and second angles are smaller than the third angle. At least one of the first angle and the second 15 angle may be at least 150 smaller than the third angle. The first and second angles may be substantially the same. (Effects of the Invention) [0018] According to the pneumatic tire of the present invention, the land portion is 20 provided with so-called plural combined grooves having a zigzag shape and includes: a first groove portion extending obliquely with respect to the tread circumferential direction from the first circumferential groove at a relatively small angle, one end of the first groove portion being open to the first circumferential groove and the other end of the first groove portion terminating within the land portion; a second groove portion extending 25 obliquely with respect to the tread circumferential direction in the direction same as the first groove portion at a relatively small angle, one end of the second groove portion being positioned within the land portion, and the other end of the second groove portion being open to the second circumferential groove; and, a third groove portion extending obliquely with respect to the tread circumferential direction at a relatively large angle and 30 communicating the other end of the first groove portion and the one end of the second groove portion. With this configuration, it is possible to improve the drainage property with the first groove portion and the second groove portion having a low angle with respect to the tread circumferential direction, and, in addition to the drainage property, improve the traction performance with the third groove portion having a high angle with 35 respect to the tread circumferential direction, whereby it is possible to simultaneously 5243577_1 (GHMatters) P92598.AU -5 achieve both of the drainage property and the traction performance with one type of the second land portion. BRIEF DESCRIPTION OF THE DRAWINGS 5 [0019] FIG. 1(a) is a partial development view of a tread pattern illustrating an embodiment of a pneumatic tire according to the present invention; and FIGS. 1(b) to 1(e) are enlarged sectional views taken, respectively, along the lines B-B, C-C, D-D and E-E of FIG. 1(a). [0020] FIG. 2(a) is a partial development view of a tread pattern illustrating one 10 example of conventional pneumatic tire, and FIG. 2(b) is a partial development view of a tread pattern illustrating another example of conventional pneumatic tire. BEST MODE FOR CARRYING OUT THE INVENTION [0021] Hereinbelow, a pneumatic tire according to the present invention will be 15 described in detail with reference to the drawings. Since a structure for reinforcing the inside of the tire is similar to that of a general radial tire or bias tire, illustration in the drawing thereof is omitted. [0022] Reference numeral 1 in the drawing represents an entire ground contact surface of a tread portion. On the ground contact surface 1 of the tread portion, two first 20 circumferential grooves 2 located on both sides of a tire equatorial plane and extending along a tread circumferential direction are provided at positions within 35%, in the drawing, at positions of 30% of a tread width measured from the tire equatorial plane, and second circumferential grooves 3 extending along the tread circumferential direction are provided between respective tread ends so as to be adjacent to side portions of the 25 respective first circumferential grooves 2. [0023] It should be noted that, although, in the drawing, two first main grooves are disposed in the vicinity of the tire equatorial plane, it may be possible to dispose one first circumferential groove at the tire equatorial plane. [0024] A first land portion 4 is formed between two circumferential grooves adjacent 30 to each other, in the drawing, between the two first circumferential grooves 2; a second land portion 5 (the "land portion" in claim 1) is formed between the first circumferential groove 2 and the second circumferential groove 3; and a third land portion 6 is formed between the second circumferential groove 3 and a side edge of the tread. [0025] The first land portion 4 is a rib-like land portion extending in the tread 35 circumferential direction, in which no groove is provided in the drawing. With the rib 5243577_1 (GHMatters) P92598.AU -6 like land portion, the rigidity of the tire increases in the vicinity of the tire equatorial plane, whereby it is possible to improve the steering stability. [0026] In the pneumatic tire, the second land portion 5 has a first groove portion 7a extending obliquely with respect to the tread circumferential direction from the first 5 circumferential groove 2 at a high angle, preferably, in the range of 15 to 450 and terminating within the second land portion 5; a second groove portion 7b extending obliquely with respect to the tread circumferential direction in the same direction as the first groove portion 7a from the second circumferential groove 3 at a high angle, preferably, in the range of 15 to 45'and terminating within the second land portion 5; and, 10 a third groove portion 7c communicating with the first groove portion 7a and the second groove portion 7b and extending obliquely with respect to the tread circumferential direction at a low angle, preferable, in the range of 0 to 45'. With theses grooves, a zigzag groove 7 having a zigzag shape is formed. A plurality of the zigzag grooves 7 forms a plurality of second blocks 8. 15 [0027] In the second block 8, it is preferable that a second sipe 9 in the drawing is provided at a high angle, preferably, in the range of -45' to +45' with respect to the tread width direction and at an angle in the range of -75' to +75' with respect to a line normal to the first groove portion 7a or the second groove portion 7b, the second sipe 9 being opened to the first groove portion 7a of the zigzag groove 7 and the second groove 20 portion 7b of the zigzag groove 7 adjacent to the first groove portion 7a in the tread circumferential direction. [0028] With the second sipe 9, the second land portion 5 can easily deform, whereby deterioration of the steering stability and partial wear resistance due to excess twisting of the second land portion 5 can be reduced when the tire is rotating and a handle is steered. 25 [0029] Groove widths of the first circumferential groove 2 and the second circumferential groove 3 may be set in the range of 5 to 15 mm; groove depths of the first circumferential groove 2 and the second circumferential groove 3 may be set in the range of 5 to 15 mm; a groove width of the zigzag groove 7 may be set in the range of I to 15 mm; and, a groove depth of the zigzag groove 7 may be set in the range of 3 to 10 mm. 30 [0030] In the vicinity of the center of the second block 8, a first chamfered portion 10 gradually decreasing toward a groove bottom of the first groove portion 7a, for example, in a planar state is provided on an upper end of a side wall of the second block 8 facing a groove wall on the tire equatorial plane side of the first groove portion 7a, in the drawing, at a corner portion formed by the first groove portion 7a and the third groove portion 7c; a 35 second chamfered portion 11 gradually decreasing toward a groove bottom of the second 5243577_1 (GHMatters) P92598.AU -7 groove portion 7b, for example, in a planar state is provided on an upper end of a side wall of the second block 8 facing a groove wall on the tread end side of the second groove portion 7b, in the drawing, at a corner portion formed by the second groove portion 7b and the third groove portion 7c; the first chamfered portion 10 extends, for example, 5 along the first groove portion 7a; and the second chamfered portion 11 extends along the second groove portion 7b. [0031] Further, in the second block 8, a third chamfered portion 12 gradually decreasing, for example, in an arcuate manner is provided at a corner portion formed by the first circumferential groove 2 and the first groove portion 7a of the zigzag groove 7, 10 and a fourth chamfered portion 13 gradually decreasing, for example, in an arcuate manner is provided at a corner portion formed by the second circumferential groove 3 and the second groove portion 7b of the zigzag groove 7. With this configuration at the corner portions adjacent to the high-angled first groove portion 7a and second groove portion 7b, an excellent drainage property can be obtained, but partial wear is likely to 15 occur. In this respect, by making the extending length of the third chamfered portion 12 longer than that of the fourth chamfered portion 13 to improve the rigidity of the land portion, it is possible to achieve both reduction in the partial wear and improvement in the drainage property. [0032] Since the zigzag groove 7 is opened to the first circumferential groove 2 and the 20 second circumferential groove 3, water can be smoothly discharged mainly from the first circumferential groove 2 to the second circumferential groove 3 at the time when the tire is rotated, by the synergistic effect of specifying the rotational direction of the tire. [0033] In the third land portion 6, plural third blocks 15 are formed by lateral grooves 14 that traverse the third land portion 6, extend obliquely in the tread width direction, is 25 opened to the second circumferential groove 3 and the side edge of the tread, and have a groove width increasing from the second circumferential groove 3 toward the side edge of the tread in a funnel-like form. [0034] Further, a third sipe 16 opened to the second circumferential groove 3 and the side edge of the tread is provided in the vicinity of the center of the third block 15 in the 30 tread circumferential direction. [0035] Further, in the third block 15, a fifth chamfered portion 17 gradually decreasing, for example, in a planar state is provided at a corner portion formed by the second circumferential groove 3 and the lateral groove 14. [0036] In the tire as described above, more preferably, an inclination angle a of the 35 first groove portion 7a and the second groove portion 7b of the zigzag groove 7 with 5243577_1 (GHMatters) P92598.AU -8 respect to the tread circumferential direction is set in a range of 150 to 450, so that it is possible to effectively improve the drainage property especially in the tread circumferential direction. [0037] If the angle a exceeds 450, a difference in angel from the third groove portion 5 7c is insufficient to form the zigzag groove 7, whereby it is difficult to effectively achieve both of the drainage property and the traction performance. On the other hand, if the angle a is less than 150, the block shape of the second block 8 is undesirably long and narrow, whereby the rigidity of the block tends to be lower. [0038] Preferably, the inclination angle 0 of the third groove portion 7c with respect to 10 the tread circumferential direction is set in the range of 450 to 900, so that it is possible to increase the gripping force with the ground surface and in particular, effectively improve the traction performance. [0039] If the angle exceeds 900, the distance between the first groove portion 7a and the second groove portion 7b disposed in the second land portion 5 is undesirably long, 15 possibly deteriorating the drainage property. On the other hand, if the angle is less than 450, the acutely angled shape of the blocks adjacent to portions where the third groove portion 7c communicates with the first groove portion 7a and the third groove portion 7c communicates with the second groove portion 7b is undesirable long and narrow, whereby the rigidity of the blocks tends to be lower. 20 [0040] More preferably, a difference between the inclination angle a of the first groove portion 7a and the second groove portion 7b and the inclination angle 0 of the third groove portion 7c is set to be 150 or more. [0041] With this configuration, it is possible to suppress the decrease in rigidity of the blocks adjacent to the vicinity of the portions where the third groove portion 7c 25 communicates with the first groove portion 7a, and the third groove portion 7c communicates with the second groove portion 7b. [0042] More preferably, a distance t in the tread width direction between the second circumferential groove 3 and the outmost position of the first groove portion 7a of the zigzag groove 7 in the tread width direction is set in the range of 10 to 30% of the land 30 width of the second land portion, so that it is possible to improve the drainage property even if the first groove portion 7a of the zigzag groove 7 is not opened directly from the first circumferential groove 2 to the second circumferential groove 3. [0043] With the first chamfered portion 10 and the second chamfered portion 11 being provided in the second block, it is possible to effectively discharge the water without 35 trapping a stone into the groove, even if the stone enters the long extending zigzag groove 5243577_1 (GHMatters) P92598.AU -9 7, whereby it is possible to improve the stone-trapping resistance. [0044] The groove depth of the third groove portion 7c measured from the ground contact surface of the tread is shallower than the average groove depth of the first groove portion 7a and the second groove portion 7b measured from the ground contact surface of 5 the tread, and is preferably in the range of 2 to 4 mm or is preferably in the range of 30 to 50% of the groove depth of the first groove portion 7a and the second groove portion 7b measured from the ground contact surface of the tread. With this configuration, uneven force is applied to the block portion extending over the first groove portion 7a and the second groove portion 7b having the acute angle in the zigzag groove 7, and the first 10 groove portion 7a and the second groove portion 7b approach to each other especially when the slip angle occurs to the tire, whereby it is possible to reduce an adverse effect on the drainage. EXAMPLE 15 [0045] Next, sample tires were prepared, including Example tires 1 and 2, which are pneumatic tires having a size of PSR 215/45R17 and a tread pattern as illustrated in FIG. 1, Comparative tire 1 having a tread pattern in which acute-angle grooves 27 are provided to the second land portion as illustrated in FIG. 2(a), and Comparative tire 2 having a tread pattern in which obtuse-angle grooves 37 are provided to the second land portion as 20 illustrated in FIG. 2(b). Table 1 shows inclination angles of the grooves with respect to the tire circumferential direction, distances t in the tire-tread width direction, extending lengths of the chamfered portions, and depths of the third groove. [0046] It should be noted that the other configurations of Comparative Examples 1 and 2 are set so as to accord with Example tires. 25 5243577_1 (GHMatters) P92598.AU - 10 [0047] [Table 1] Example tire 1 Example tire 2 Comparative Comparative Example tire 1 Example tire 2 Inclination angle cc () 15 15 15 65 Inclination angle $3(0) 60 60 - Distance t in tread width 176 176 - direction (mm) Extending length of first 32 32 - chamfered portion (mm) Extending length of second 34 34 - chamfered portion (mm) Extending length of third 19 19 chamfered portion (mm) Extending length of fourth 6 6 chamfered portion (mm) Extending length of fifth 8 8 chamfered portion (mm) Groove depth of first groove 6.2 6.2 portion (mm) Groove depth of second groove 6.2 3.1 portion (mm) Groove depth of third groove 6.2 6.2 portion (mm) [0048] For the prepared tires described above, evaluation was made on the drainage 5 property, the traction performance, and the stone-trapping resistance. [0049] (Drainage property) Each of Example tires, and Comparative tires 1 and 2 was assembled with a rim having a size of 17 inches and 8J and inflated at a tire pneumatic pressure of 220 kPa, and then, was mounted to a vehicle that carries two people. For each of the tires, braking 10 distance at the time of full braking from an initial speed of 30 km/h was measured on a ground surface made of a steel plate with a water depth of 2 mm, and, on the basis of the measured braking distance, the drainage property of each of the tires was evaluated. The 5243577_1 (GHMatters) P92598.AU - 11 evaluation results are shown in Table 2. [0050] It should be noted that figures in Table 2 are index values obtained by setting the value of Comparative Example tire Ito be 100. The larger index values represent the better drainage property. 5 [0051] (Traction performance) Each of Example tires, and Comparative tires 1 and 2 was assembled with a rim having a size of 17 inches and 8J and inflated at a tire pneumatic pressure of 220 kPa, and then, was mounted to a vehicle that carries two people. For each of the tires, a feeling evaluation was made by a test driver at the time of traveling on an asphalt test course 10 under various traveling modes, and, on the basis of the feeling evaluation, the traction performance of each of the tires was evaluated. The evaluation results are shown in Table 2. [0052] It should be noted that figures in Table 2 are index values obtained by setting the value of Comparative Example tire Ito be 100. The larger index values represent 15 the better traction performance. [0053] (Stone-trapping resistance) Each of Example tires, and Comparative tires 1 and 2 was assembled with a rim having a size of 17 inches and 8J and inflated at a tire pneumatic pressure of 220 kPa, and then, was mounted to a vehicle that carries two people. After the vehicle traveled 10000 20 km at a speed of 0 to 100 km/hour, the number of stones trapped in the second land portion was counted for each of the tires to be an index, and evaluation thereof was made. The evaluation results are shown in Table 2. [0054] It should be noted that figures in Table 2 are index values obtained by setting the value of Comparative Example tire Ito be 100. The smaller index values represent 25 the smaller stone-trapping rate, and the better stone-trapping resistance. [0055] [Table 2] Example tire 1 Example tire 2 Comparative Comparative Example tire 1 Example tire 2 Drainage property 100 100 100 80 Traction performance 120 125 100 120 Stone-trapping resistance 120 125 100 100 5243577_1 (GHMatters) P92598.AU - 12 [0056] According to Table 2, Example tires exhibit the excellent traction performance and stone-trapping resistance as compared with Comparative Example tire 1. Further, although only one end of the high-angled groove portion of the zigzag groove is opened to the circumferential groove, Example tires can obtain the drainage property 5 similar to Comparative Example tire 1. Further, although the traction performance is similar between Example tires and Comparative Example tire 2, Example tires exhibit the excellent stone-trapping resistance and drainage property as compared with Comparative Example 2. (Reference Numerals) 10 [0057] 1, 21 Ground contact surface of tread portion 2, 22 First circumferential groove 3, 23 Second circumferential groove 4 First land portion 5 Second land portion 15 6 Third land portion 7 Zigzag groove 7a First groove portion 7b Second groove portion 7c Third groove portion 20 8, 28 Second block 9 Second sipe 10 First chamfered portion 11 Second chamfered portion 12 Third chamfered portion 25 13 Fourth chamfered portion 14 Lateral groove 15 Third block 16 Third sipe 17 Fifth chamfered portion 30 27 Acute-angle groove 37 Obtuse-angle groove [0058] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 35 [0059] In the claims which follow and in the preceding description of the invention, 5243577_1 (GHMatters) P92598.AU - 13 except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the 5 invention. 5243577_1 (GHMatters) P92598.AU