pneumatic tires

Abstract

To provide a pneumatic tire configured so as to suppress deterioration in uniformity caused by attachment of stud pins.SOLUTION: A tread 3 includes: a plurality of main grooves 11 extending continuously along a tire circumferential direction: and lateral grooves 12 extending across shoulder main grooves 11s positioned at outermost sides in a tire axial direction of the plurality of main grooves 11 to partition the tread 3 into a plurality of belt-like sections in an extending range of the grooves. The tread 3 is divided into shoulder areas SA closer to outsides in the tire axial direction than the shoulder main grooves 11s and a center area CA closer to inside in the tire axial direction than the shoulder main grooves 11s. In at least either of a pair of tread half parts partitioned by a tire equator TC, belt-like sections including attachment holes 10 formed in the shoulder areas SA and belt-like sections including the attachment holes 10 formed in the center area CA are arranged alternately along the tire circumferential direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0005] ,

[0001] The present disclosure relates to a pneumatic tire having mounting holes for attaching stud pins formed in a tread.

Background Art

[0002] A pneumatic tire with stud pins attached to the tread is also called a stud tire or a spike tire and is mainly used for driving on icy and snowy roads. Since stud pins are generally made of a metal material, attaching a large number of stud pins may deteriorate the uniformity of the tire. Therefore, although it is desirable to adopt a structure considering this point, no specific configuration suitable for this has been proposed.

[0003] In Patent Document 1, a region partitioned between a pair of tire meridians arranged such that the interval on the tire equator line is 0.8% of the tire circumference is defined as a strip region, and when a plurality of strip regions are arranged over the entire tire circumference by shifting them one by one along the tire circumferential direction, the plurality of strip regions include a concentrated region where four or more stud pins are present and a scattered region where three or fewer stud pins are present, and a stud tire has been proposed in which such concentrated regions intermittently exist along the tire circumferential direction. However, intermittently having such concentrated regions is considered to cause deterioration of the uniformity of the tire.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present disclosure is to provide a pneumatic tire capable of suppressing deterioration of uniformity associated with the attachment of stud pins. [Means for solving the problem]

[0006] The pneumatic tire of the present disclosure comprises a tread having mounting holes for attaching stud pins, the tread including a plurality of main grooves extending continuously along the circumferential direction of the tire, and transverse grooves extending across a shoulder main groove located on the outermost side in the axial direction of the plurality of main grooves, and dividing the tread into a plurality of strip-shaped regions within the extent of the extension, the tread being divided into a shoulder region on the outer side in the axial direction of the tire and a center region on the inner side in the axial direction of the tire, and in at least one of a pair of tread halves separated by the tire equator, the strip-shaped regions including the mounting holes formed in the shoulder region and the strip-shaped regions including the mounting holes formed in the center region are alternately arranged along the circumferential direction of the tire. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic cross-sectional view of the tire meridian showing the pneumatic tire of this embodiment. [Figure 2] Plan view of the tread of the pneumatic tire of this embodiment [Figure 3] Enlarged view of the main part in Figure 2 [Figure 4] Diagram showing a modified example regarding the arrangement of mounting holes. [Figure 5] Diagram illustrating the relative positions of mounting holes. [Figure 6] Enlarged view of the main part in Figure 2 [Modes for carrying out the invention]

[0008] One embodiment of this disclosure will be described with reference to the drawings.

[0009] As shown in Figure 1, the pneumatic tire T of this embodiment (hereinafter sometimes simply referred to as "tire T") comprises a pair of bead portions 1, sidewalls 2 extending radially outward from each of the bead portions 1, and treads 3 connected to the radially outer ends of each of the sidewalls 2. The tire T further comprises a carcass 4 provided between the pair of bead portions 1, a belt 5 laminated on the radially outer side of the carcass 4, and an inner liner 6 disposed on the inner surface of the tire.

[0010] Here, the tire radial direction is the direction along the diameter of tire T, and corresponds to the vertical direction in Figure 1. In Figure 1, the upper side is the outer side in the tire radial direction, and the lower side is the inner side in the tire radial direction. The tire axial direction is the direction parallel to the rotation axis of tire T, and corresponds to the left-right direction in Figure 1. The side approaching the tire equator TC is the inner side in the tire axial direction, and the side moving away from the tire equator TC is the outer side in the tire axial direction. The tire equator TC is located at the center of tire T in the tire axial direction and is an imaginary line perpendicular to the tire rotation axis in a plan view. The tire circumferential direction is the direction around the rotation axis of tire T.

[0011] An annular bead core 1a is embedded in the bead portion 1. The bead core 1a is formed by covering a converging body such as steel wire with rubber. A bead filler 1b is positioned on the radially outer side of the bead core 1a. The bead filler 1b is formed of triangular-shaped rubber extending radially outward from the bead core 1a. Rim strip rubber 7, which forms the outer surface of the bead portion 1, is provided on the axially outer side of the bead core 1a and bead filler 1b.

[0012] The carcass 4 extends in a toroidal shape across a pair of bead portions 1. The carcass 4 is wound from the inside to the outside in the tire axial direction, sandwiching the bead core 1a and the bead filler 1b. The carcass 4 is formed from carcass plies formed by covering carcass cords with rubber. The carcass cords are aligned in a direction intersecting the tire circumferential direction (for example, in a direction at an angle of 75 to 90 degrees with respect to the tire circumferential direction). Sidewall rubber 8, which forms the outer surface of the sidewall 2, is provided on the tire axial outer side of the carcass 4.

[0013] The belt 5 is formed by multiple belt plies 5a and 5b that are laminated together. Each belt ply 5a and 5b is formed by covering belt cords with rubber, which are aligned in a direction inclined with respect to the circumferential direction of the tire. The belt plies 5a and 5b are laminated so that the belt cords intersect each other in opposite directions. On the radially outer side of the belt 5, there is tread rubber 9 which forms the outer surface of the tread 3. The inner liner 6 is made of a rubber with excellent air-shielding properties, such as butyl rubber. The inner liner 6 maintains the internal pressure of the tire T.

[0014] The tread 3 has mounting holes 10 for attaching stud pins. The tire T is configured as a stud tire (also called a spiked tire) by attaching stud pins (not shown) to each of the mounting holes 10. Generally, stud pins are made of cylindrical metal members. The shape, material, and size of the stud pins to be attached to the tire T are not particularly limited. In this embodiment, the mounting holes 10 have a flask-shaped cross-section, but are not limited to this.

[0015] The outer circumferential surface of the tread 3 has a tread pattern as shown in Figure 2. In this embodiment, a tread pattern is employed that is symmetrical with respect to the tire equator TC and has a phase shift in the circumferential direction of the tire. Tire T is a directional tire in which the direction of tire rotation is specified. Arrow RD indicates the direction of tire rotation when moving forward. The forward direction of rotation RD1 is also called the push-off side, and the rearward direction of rotation RD2 is also called the push-off side. Tire T is not limited to such a directional pattern and may have a non-directional pattern. For example, a tread pattern formed symmetrically with a center point on the tire equator TC may also be used.

[0016] The tread 3 includes a plurality of main grooves 11 that extend continuously along the circumferential direction of the tire. The groove width W11 of the main grooves 11 on the outer surface of the tread 3 is, for example, 10 mm or more. Of the plurality of main grooves 11, the one located on the outermost side in the axial direction of the tire is called the shoulder main groove 11s. In this embodiment, the tread 3 includes two main grooves 11, which correspond to the shoulder main grooves 11s. However, the tread 3 may include three or more main grooves. The tread 3 is divided into a shoulder region SA on the outer side in the axial direction of the tire and a center region CA on the inner side in the axial direction of the tire, based on the groove width center of the shoulder main groove 11s.

[0017] A pair of shoulder main grooves 11s are positioned to straddle the tire equator TC. The distance D11 from the center of the groove width of the shoulder main groove 11s to the tire equator TC is, for example, 52-62% of the contact patch width HW. The contact patch width HW is the axial distance of the tire from the tire equator TC to the contact edge TE. The contact edge TE is the outermost position in the axial direction of the contact surface when a tire T mounted on a regular rim, filled with the regular internal pressure, is placed perpendicular to a flat road surface and a regular load is applied. The contact width TW is the axial distance of the tire between the pair of contact edges TE, and half of this contact width TW is the contact patch width HW.

[0018] The regular rim is the "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, or the "Measuring Rim" in the ETRTO standard. The regular internal pressure is the "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "INFLATION PRESSURE" in the ETRTO standard. The regular load is the load defined for each tire in the standard system including the standard on which the tire is based. For JATMA, it is the maximum load capacity; for TRA, it is the maximum value described in the above table; for ETRTO, it is "LOAD CAPACITY". However, when the tire is for a passenger car, the load shall be 88% of the above load.

[0019] As shown in FIGS. 2 and 3, the tread 3 extends across the shoulder main groove 11s and includes a transverse groove 12 that divides the tread 3 into a plurality of strip-shaped regions BA in its extending range. The groove width W12 of the transverse groove 12 at the connection point with the main groove 11 is, for example, 5 mm or more. A plurality of transverse grooves 12 are formed at intervals in the tire circumferential direction. The transverse groove 12 extends from one end located in the center region CA toward the outside in the tire axial direction and reaches the grounding end TE across the shoulder main groove 11s. The transverse groove 12 extends obliquely with respect to the tire axial direction. As a whole, the transverse groove 12 is gently curved in a direction convex toward the kicking-out side (rearward in the rotational direction RD).

[0020] FIG. 3 is an enlarged view of the main part of FIG. 2, schematically showing a strip-shaped area BA partitioned by the transverse groove 12. Such a strip-shaped area BA is included in each of a pair of tread halves divided by the tire equator TC. In FIG. 3, however, the strip-shaped area BA included in one of them (the tread half located on the right side in FIG. 2) is shown. As described above, the transverse groove 12 divides the tread 3 into a plurality of strip-shaped areas BA in its extending range. The strip-shaped area BA extends in a strip shape from the center area CA to the shoulder area SA. The strip-shaped area BA is curved along the transverse groove 12. Each of the strip-shaped areas BA includes one shoulder block 13 and one block-shaped land portion 14, which will be described later.

[0021] The strip-shaped area BA includes a strip-shaped area BAs including the mounting hole 10 formed in the shoulder area SA and a strip-shaped area BAc including the mounting hole 10 formed in the center area CA. The strip-shaped area BAs does not include the mounting hole 10 formed in the center area CA, and the strip-shaped area BAc does not include the mounting hole 10 formed in the shoulder area SA. In this tire T, in at least one of a pair of tread halves divided by the tire equator TC, the strip-shaped area BAs including the mounting hole 10 formed in the shoulder area SA and the strip-shaped area BAc including the mounting hole 10 formed in the center area CA are alternately arranged along the tire circumferential direction.

[0022] According to such a configuration, it is possible to prevent the uneven distribution of the mounting holes 10 in the tread 3 and suppress the deterioration of uniformity associated with the attachment of the stud pins. In particular, since the deterioration of uniformity as the tire shape in the tire circumferential direction can be suppressed, the deterioration of fuel consumption performance (rolling resistance) and noise performance can be well suppressed. Further, since the stud pins are evenly arranged in the tread 3, the scraping effect of the stud pins on the ice and snow road is enhanced. In the present embodiment, the alternate arrangement of the strip-shaped area BAs and the strip-shaped area BAc as described above is applied to each of the pair of tread halves, and the improvement effect described above is excellent.

[0023] Figure 3 shows an example where strip-shaped areas BAs and BAc are arranged alternately, one at a time, but this is not the only example. For example, as shown in Figure 4, multiple strip-shaped areas BAs may be arranged between strip-shaped areas BAC in the circumferential direction of the tire. Conversely, multiple strip-shaped areas BAC may be arranged between strip-shaped areas BAs in the circumferential direction of the tire. In that case, it is preferable that the number of consecutively arranged strip-shaped areas BAs or strip-shaped areas BAC is 3 or less. That is, it is preferable that strip-shaped areas BAs and BAc are arranged alternately in groups of 1 to 3.

[0024] The strip-shaped area BA may include a strip-shaped area in which mounting holes 10 are formed in both the shoulder area SA and the center area CA, or a strip-shaped area in which mounting holes 10 are not formed in both the shoulder area SA and the center area CA. However, in the tread half, the number of such strip-shaped areas is preferably less than 30% of the total number of strip-shaped areas BA around the entire circumference of the tire, and more preferably less than 20%. That is, in the tread half, it is preferable that 70% or more of the total number of strip-shaped areas BA around the entire circumference of the tire are occupied by strip-shaped areas BAs and strip-shaped areas BAc.

[0025] The number of mounting holes 10 formed in the shoulder region SA is preferably greater than the number of mounting holes 10 formed in the center region CA. This enhances the scratching effect in the shoulder region SA, which is under high load during cornering, thereby improving handling stability. This relationship only needs to be satisfied when at least one (preferably both) half of the tread is viewed along the entire circumference of the tire. In the tread half, the difference between the number of mounting holes 10 formed in the shoulder region SA and the number of mounting holes 10 formed in the center region CA is preferably 3 or more, and more preferably 5 or more.

[0026] As shown in Figure 5, in this embodiment, a mounting hole 10 formed in the shoulder region SA (more precisely, the center of the mounting hole 10) is positioned in a section S in the tire circumferential direction, sandwiched between the midpoint CP (center point) of the mounting holes 10 formed in the center region CA and the mounting hole 10 adjacent to the kick-out side (rear RD2 in the rotational direction) of the midpoint CP. With this configuration, the scratching effect when driving on icy or snowy roads can be enhanced, and the grip force can be improved.

[0027] In the shoulder region SA, multiple shoulder blocks 13, separated by lateral grooves 12, are arranged in the circumferential direction of the tire. This creates an edge effect from the block edges of the shoulder blocks 13, improving driving performance on icy and snowy roads. In the shoulder region SA, shoulder blocks 13 with mounting holes 10 and shoulder blocks 13 without mounting holes 10 are alternately arranged in the circumferential direction of the tire. These are arranged one by one alternately, but they may be arranged in groups of 1 to 3 alternately. From the viewpoint of suppressing deterioration of uniformity, it is preferable that the number of mounting holes 10 formed in a single shoulder block 13 is one or less.

[0028] In the center region CA, multiple block-shaped land sections 14, separated by lateral grooves 12, are arranged in the circumferential direction of the tire. This creates an edge effect from the block edges of the block-shaped land sections 14, improving driving performance on icy and snowy roads. In the center region CA, block-shaped land sections 14 with mounting holes 10 and block-shaped land sections 14 without mounting holes 10 are alternately arranged in the circumferential direction of the tire. These are arranged one at a time in alternation, but they may also be arranged one to three at a time in alternation. From the viewpoint of suppressing deterioration of uniformity, it is preferable that the number of mounting holes 10 formed in one block-shaped land section 14 is one or less.

[0029] As shown in Figure 2, within the center region CA, the area corresponding to 28% of the contact width TW centered on the tire equator TC is designated as the equatorial region RA, and the area between the equatorial region RA and the shoulder main groove 11s is designated as the equatorial adjacent region NA. The equatorial region RA is provided with ribs 15 that extend continuously in the circumferential direction of the tire. This ensures a contact surface in the equatorial region RA, where high loads are applied during braking on icy or snowy roads, thereby improving grip. Instead of ribs 15, the equatorial region RA may be provided with rows of blocks arranged in a sequence.

[0030] The mounting holes 10 formed in the center region CA are located in the equatorial adjacent region NA, avoiding the equatorial region RA. By not placing the stud pins in the equatorial region RA, it is advantageous to ensure a contact surface in the equatorial region RA, where high loads are applied during braking on icy or snowy roads. Furthermore, from the viewpoint of ensuring a contact surface in the equatorial region RA, it is preferable that the main groove is not provided in the equatorial region RA.

[0031] Multiple sipes 16 are formed on the shoulder block 13, block-shaped land portion 14, and rib 15, respectively. The sipes 16 are formed by cuts with a width of 1.0 mm or less. The sipes 16 may be two-dimensional sipes whose shape does not change along the depth direction, or three-dimensional sipes which include a portion whose shape changes along the depth direction. Each shoulder block 13 has sipes 16 that extend along the tire axis direction. Multiple sipes 16 are formed, extending substantially parallel to the lateral groove 12 that divides the shoulder block 13, and spaced apart in the thickness direction. The shoulder block 13 may also have sipes that extend parallel to the tire circumferential direction or sipes that extend at an angle.

[0032] When the shoulder blocks 13 are arranged at a variable pitch in the circumferential direction of the tire, that is, when the pitch length (circumferential length of the tire) of the pitch element which is the basis for repeating the pattern design is varied in various ways, it is preferable that the number of sipes 16 on the shoulder block 13 with the minimum circumferential length is smaller than the number of sipes 16 on the shoulder block 13 with the maximum circumferential length. With this configuration, the difference in contact area per unit area of ​​the shoulder block 13 due to the difference in pitch is reduced, which is advantageous in suppressing uneven wear on a block-by-block basis.

[0033] The center region CA is provided with a land area comprising a centrally located rib 15 and an arrangement of block-shaped land areas 14 located on both sides thereof. In the center region CA, lateral grooves 12 extending in a substantially straight line and lateral grooves 12 bent in an L-shape are alternately arranged in the circumferential direction of the tire, and these divide the block-shaped land areas 14. In the equatorial region NA, block-shaped land areas 14 containing sipes 16 inclined in the same direction as the lateral grooves 12 that divide the block-shaped land areas 14, and block-shaped land areas 14 containing sipes 16 inclined in the opposite direction are alternately arranged in the circumferential direction of the tire. The rib 15 has sipes 16 that extend substantially parallel to the tire axis direction.

[0034] Figure 6 is an enlarged view of the main part of Figure 2, showing the land area located in the center region CA. As shown in Figure 6, the mounting holes 10 formed in the equatorial adjacent region NA on one side of the tire axial direction and the mounting holes 10 formed in the equatorial adjacent region NA on the other side of the tire axial direction are arranged in a staggered pattern along the circumferential direction of the tire. This prevents uneven distribution of the mounting holes 10 in the center region CA of the tread 3, effectively suppressing the deterioration of uniformity associated with the installation of stud pins.

[0035] The central points CP of the mounting holes 10 formed in the equatorial region NA on one side of the tire axial direction and the central points CP of the mounting holes 10 formed in the equatorial region NA on the other side of the tire axial direction are offset from each other in the circumferential direction of the tire, such that the line connecting them sequentially along the circumferential direction of the tire forms a wave-like (zigzag) shape.

[0036] Furthermore, as shown in Figure 2, mounting holes 10 formed in the equatorial adjacent region NA and mounting holes 10 formed in the adjacent shoulder region SA across the shoulder main groove 11s from the equatorial adjacent region NA are arranged in a staggered pattern along the circumferential direction of the tire. In this embodiment, such a staggered arrangement of mounting holes 10 is applied to each of the pair of tread halves, resulting in excellent improvement effects as described above.

[0037] The pneumatic tire T of this embodiment is equivalent to a normal stud tire (however, before stud pins are attached to the mounting holes 10) except for the arrangement of the mounting holes 10 as described above, and any conventionally known materials, shapes, structures, etc., can be used. The pneumatic tire T may also be one in which stud pins are attached to the mounting holes 10 of the tread 3.

[0038] [1] As described above, the pneumatic tire T of this embodiment includes a tread 3 with mounting holes 10 for attaching stud pins. The tread 3 includes a plurality of main grooves 11 that extend continuously along the circumferential direction of the tire, and a transverse groove 12 that extends across the shoulder main groove 11s located on the outermost side in the axial direction of the tire, and divides the tread 3 into a plurality of strip-shaped regions BA within its extended range. The tread 3 is divided into a shoulder region SA on the outer side in the axial direction of the tire, and a center region CA on the inner side in the axial direction of the tire, with respect to the groove width center of the shoulder main groove 11s. In at least one of the pair of tread halves separated by the tire equator TC, strip-shaped regions BAs including mounting holes 10 formed in the shoulder region SA and strip-shaped regions BAc including mounting holes 10 formed in the center region CA are alternately arranged along the circumferential direction of the tire. This makes it possible to suppress deterioration of uniformity associated with the attachment of stud pins.

[0039] [2] In the pneumatic tire T described in [1] above, it is preferable that the number of mounting holes 10 formed in the shoulder region SA is greater than the number of mounting holes 10 formed in the center region CA. This enhances the scratching effect in the shoulder region SA, which is under high load during cornering, thereby improving handling stability.

[0040] [3] In the pneumatic tire T described in [1] or [2] above, it is preferable that the tire rotation direction is specified and that the mounting holes 10 formed in the shoulder region SA are located in a section S in the circumferential direction of the tire, sandwiched between the central point CP of the spacing of mounting holes 10 formed in the center region CA and the mounting hole 10 adjacent to the kicking side of the central point CP. With this configuration, the scratching effect when driving on icy or snowy roads can be enhanced, and the grip force can be improved.

[0041] [4] In any one of the above [1] to [3] pneumatic tire T, when the area within the center region CA that is 28% of the contact width TW centered on the tire equator TC is defined as the equatorial region RA, and the area between the equatorial region RA and the shoulder main groove 11s is defined as the equatorial adjacent region NA, it is preferable that the equatorial region RA is provided with a rib 15 that extends continuously in the circumferential direction of the tire, or a row of blocks arranged in a plurality of blocks. With this configuration, it is possible to secure the contact surface of the equatorial region RA, which is subjected to a high load during braking on icy or snowy roads, and to improve grip.

[0042] [5] In any one of the above [1] to [4] pneumatic tire T, it is preferable that the mounting hole 10 formed in the center region CA is located in the region adjacent to the equator NA, avoiding the region directly below the equator RA. This configuration is advantageous in securing the contact surface in the region directly below the equator RA, where a high load acts during braking on icy or snowy roads.

[0043] While embodiments of this disclosure have been described with reference to the drawings, it should be understood that the specific configurations are not limited to these embodiments. The scope of this disclosure is defined not only by the above-described embodiments but also by the claims, and further includes all modifications within the meaning and scope equivalent to the claims.

[0044] The pneumatic tire of this disclosure is not limited in any way to the embodiments described above, nor is it limited to the effects described above. The pneumatic tire of this disclosure can be modified in various ways without departing from its essence. [Explanation of symbols]

[0045] 1. Bead section 2 sidewalls 3 tread 10 mounting holes 11 Main groove 11s Shoulder main groove 12 Yokomizo 13 Shoulder Block 14 Block-shaped land area 15 Ribs 16 sipes

Claims

1. It has a tread with mounting holes formed for attaching stud pins, The tread includes a plurality of main grooves that extend continuously along the circumferential direction of the tire, and a transverse groove that extends across the shoulder main groove located on the outermost side in the axial direction of the tire, and divides the tread into a plurality of strip-shaped areas within its extended range. The tread is divided into a shoulder region on the outer side of the tire axial direction and a center region on the inner side of the tire axial direction, with reference to the center of the groove width of the shoulder main groove. In at least one of a pair of tread halves separated by the tire equator, the strip-shaped area including the mounting hole formed in the shoulder region and the strip-shaped area including the mounting hole formed in the center region are arranged alternately one by one along the circumferential direction of the tire. Of the aforementioned center region, the region representing 28% of the contact width centered on the tire equator is defined as the region directly below the equator, and the region between the region directly below the equator and the shoulder main groove is defined as the region adjacent to the equator. The mounting holes formed in the equatorial region on one side of the tire axial direction and the mounting holes formed in the equatorial region on the other side of the tire axial direction are arranged in a staggered pattern along the circumferential direction of the tire. A pneumatic tire in which, in each of the pair of tread halves, the mounting holes formed in the equatorial region and the mounting holes formed in the shoulder region adjacent to the equatorial region, with the shoulder main groove in between, are arranged in a staggered pattern along the circumferential direction of the tire.

2. The tire rotation direction is specified. The pneumatic tire according to claim 1, wherein the mounting holes formed in the shoulder region are arranged in a section in the tire circumferential direction sandwiched between the central point of the spacing of the mounting holes formed in the center region and the mounting hole adjacent to the kicking side of the central point of the spacing.

3. The pneumatic tire according to claim 1 or 2, wherein the region directly below the equator is provided with ribs extending continuously in the circumferential direction of the tire, or rows of blocks arranged in a plurality of blocks.

4. The pneumatic tire according to claim 3, wherein the mounting hole formed in the center region is located in the region adjacent to the equator, avoiding the region directly below the equator.

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