pneumatic tires

Abstract

To provide a pneumatic tire that can strike a balance between uneven wear-resistant performance and wet brake performance.SOLUTION: A pneumatic tire includes: a carcass layer 13 constituting a skeleton of a tire; and a belt layer 14 arranged in an outer periphery of the carcass layer 13. The tire has 5.0% or less peripheral fluctuation rate of an actual ground-contact area image when a load rate is set to 70% load capacity according to a pneumatic pressure which is defined according to a predetermined standard.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] A known technology for improving uneven wear resistance in pneumatic tires is disclosed in Patent Document 1. In Patent Document 1, adjacent blocks sandwiching a main groove are shifted from each other in the tire circumferential direction so that the rate of variation in the total contact length at the contact leading edge is 25% or less over one circumference of the tire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-255216 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 does not take wet braking performance into consideration, and there is room for improvement in achieving both uneven wear resistance and wet braking performance in pneumatic tires.

[0005] The present invention has been made in view of the above, and an object of the present invention is to provide a pneumatic tire that can achieve both uneven wear resistance and wet braking performance. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, a pneumatic tire according to one aspect of the present invention comprises a carcass layer constituting a framework of the tire, a belt layer disposed on an outer periphery of the carcass layer, and a tread portion provided on the outer side of the belt layer, wherein the tread portion comprises at least two circumferential grooves extending in the tire circumferential direction, shoulder land portions extending in the tire circumferential direction and including tire ground contact edges, and auxiliary grooves which extend in the tire width direction without crossing the tire equatorial plane and do not extend to the outer side of the shoulder land portions in the tire width direction, excluding the circumferential groove portions, and the auxiliary grooves are inclined with respect to the tire circumferential direction over their entire lengths, the sub-groove is arranged to intersect with the circumferential main groove, the sub-groove has a short portion on the outer side in the tire width direction and a long portion on the inner side in the tire width direction with the circumferential main groove as a boundary, the groove center line of the short portion and the groove center line of the long portion are on the same straight line, and the inclination direction of the sub-groove with respect to the tire circumferential direction is the same on both sides of the circumferential main groove that intersects with the sub-groove, When the load rate is set to 70% of the load capacity by air pressure specified in a specified standard and the road plate is moved while the tire is pressed against the road plate, the circumferential variation rate of the actual contact area image is 5.0% or less.

[0007] If the length along the tire circumferential direction passing through the center of the total contact area obtained from the tire contact shape is defined as the central contact length, and the length along the tire width direction passing through the center of the total contact area is defined as the central contact width, it is preferable that the circumferential variation rate of the central contact length is equal to or greater than the circumferential variation rate of the central contact width.

[0008] The circumferential variation rate of the central contact length and the circumferential variation rate of the central contact width are preferably defined by the following formulas. Circumferential variation rate of center contact length≦-3.3×A+8.0 Circumferential variation rate of center contact width≦-1.9×A+3.9 Load factor A = (measured load) / (load capacity by air pressure specified in the standard)

[0009] before It is preferable that the auxiliary grooves, each having a groove width of 2 mm or less, are provided at predetermined intervals in the tire circumferential direction in land portions adjacent to the circumferential groove.

[0010] When a groove extending in the tire width direction and extending outward in the tire width direction of the shoulder land portion is defined as a shoulder lug groove, the width of the shoulder lug groove is preferably 2 mm or less.

[0011] It is preferable that the auxiliary grooves and the shoulder lug grooves are arranged alternately in the tire circumferential direction.

[0012] The sub-groove preferably extends across the circumferential groove, and the angle of the extending direction of the sub-groove with respect to the tire width direction is preferably 0 degrees or more and 45 degrees or less.

[0013] The tread portion preferably has a tread pattern that is repeated at a predetermined pitch, and the pitch ratio of the predetermined pitch is preferably 1.38, 1.19, or 1.00.

[0014] The circumferential variation rate of the actual contact area image is preferably defined by the following formula: Circumferential fluctuation rate of actual contact area image ≦-3.4×A+7.38 Load factor A = (measured load) / (load capacity by air pressure specified in the standard) [Effects of the Invention]

[0015] The pneumatic tire according to the present invention can achieve both uneven wear resistance and wet braking performance. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing a tread portion of the pneumatic tire shown in FIG. [Figure 3] FIG. 3 is a diagram showing the circumferential average and circumferential variation rate of the actual contact area image of a tire. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of a tire contact patch shape analysis device used to analyze the tire contact patch shape. [Figure 5] FIG. 5 is a block diagram showing the functions of the tire contact patch shape analysis device shown in FIG. [Figure 6] FIG. 6 is a flow chart showing an example of the operation of the tire contact shape analysis device. [Figure 7] FIG. 7 is a flowchart showing an example of the calculation process in FIG. [Figure 8] FIG. 8 is a diagram showing an example of a specific arrangement of the camera and the illumination lamp when acquiring a ground surface image. [Figure 9] FIG. 9 is a diagram showing an example of a specific arrangement of the camera and the illumination lamp when acquiring a ground surface image. [Figure 10] FIG. 10 is a diagram showing an example of a specific arrangement of the camera and the illumination lamp when acquiring a ground surface image. [Figure 11] FIG. 11 is a view of the side surface of the tire as viewed from the direction of the rotation axis. [Figure 12] FIG. 12 is a view of the tire viewed from below the lower surface side of the road plate. [Figure 13] FIG. 13 is a view of the side of the tire viewed from a direction perpendicular to the rotation axis. [Figure 14] FIG. 14 is a view of the side surface of the tire as viewed from the direction of the rotation axis. [Figure 15] FIG. 15 is a view of the tire viewed from below the lower surface side of the road plate. [Figure 16] FIG. 16 is a view of the side of the tire viewed from a direction perpendicular to the rotation axis. [Figure 17] FIG. 17 is a diagram showing an example of an image obtained by photographing. [Figure 18] FIG. 18 is a diagram illustrating an example of GCA. [Figure 19] FIG. 19 is an explanatory diagram of the expansion process. [Figure 20] FIG. 20 is an explanatory diagram of the contraction process. [Figure 21] FIG. 21 is a diagram illustrating an example of the GCA. [Figure 22] FIG. 22 is a diagram showing another example of a tread portion of a pneumatic tire. [Figure 23] FIG. 23 is a diagram showing another example of a tread portion of a pneumatic tire. [Figure 24] FIG. 24 is a diagram showing examples of ACA circumferential variation rates for various tires. [Figure 25] FIG. 25 is a table showing the tires that were the subject of the analysis. [Figure 26] FIG. 26 is a diagram showing examples of the circumferential variation rate of the center contact length for various tires. [Figure 27] FIG. 27 is a diagram showing examples of the circumferential variation rate of the center contact width for various tires. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description of each embodiment, components that are the same as or equivalent to those in other embodiments will be given the same reference numerals, and their description will be simplified or omitted. The present invention is not limited to each embodiment. Furthermore, the components of each embodiment include those that are easily replaceable by those skilled in the art, or those that are substantially the same. Note that the configurations described below can be combined as appropriate. Furthermore, the configurations can be omitted, replaced, or modified within the scope of the gist of the invention.

[0018] Fig. 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. Fig. 1 shows a cross-sectional view of one side region in the tire radial direction. Fig. 1 also shows a radial tire for passenger cars as an example of a pneumatic tire 1 (hereinafter referred to as tire 1 as appropriate). Fig. 2 is a plan view showing a tread portion 3 of the pneumatic tire 1 shown in Fig. 1.

[0019] In the following description, a meridian section of a tire refers to a section obtained by cutting the tire along a plane including the tire's rotation axis (not shown). The tire radial direction refers to a direction perpendicular to the rotation axis (not shown) of the tire 1, the tire radially inner side refers to the side toward the rotation axis in the tire radial direction, and the tire radially outer side refers to the side away from the rotation axis in the tire radial direction. The tire circumferential direction refers to a direction around the rotation axis as the central axis. The tire width direction refers to a direction parallel to the rotation axis, the tire widthwise inner side refers to the side toward the tire equatorial plane (tire equatorial line) CL in the tire width direction, and the tire widthwise outer side refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane perpendicular to the rotation axis of the tire 1 and passing through the center of the tire width of the tire 1. The tire equator line refers to a line on the tire equatorial plane CL that runs along the tire circumferential direction of the tire 1. In this embodiment, the tire equator line is given the same symbol "CL" as the tire equatorial plane.

[0020] In Figure 1, points T and T are ground contact edges. The ground contact edges refer to the outermost ends in the tire width direction of the area where the tread portion 3 of the tire 1 comes into contact with the road surface when the tire 1 is mounted on a specified rim, inflated to a specified internal pressure, and subjected to 70% of a specified load. The ground contact edges are continuous in the tire circumferential direction.

[0021] Here, the specified rim is the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. The specified internal pressure is the "maximum air pressure" specified by JATMA, the maximum value listed in the "tire load limits at various cold inflation pressures" specified by TRA, or the "inflation pressures" specified by ETRTO. For example, the specified internal pressure is 250 kPa.

[0022] The pneumatic tire 1 has an annular structure centered on the tire rotation axis, and includes a pair of bead cores 110, 110, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber 2, a pair of sidewall rubbers 160, 160, and a pair of rim cushion rubbers 17, 17. An inner liner 150 is formed along the carcass layer 13 on the inside of the carcass layer 13, or on the inner side of the carcass layer 13 in the pneumatic tire 1.

[0023] The pair of bead cores 110, 110 are annular members formed by bundling multiple bead wires and form the cores of the left and right bead portions 10. The pair of bead fillers 12, 12 are arranged on the outer periphery of the pair of bead cores 110, 110 in the tire radial direction, respectively, to form the bead portion 10.

[0024] The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass plies stacked together, and is toroidally laid between the left and right bead cores 110, 110 to form the tire framework. Both ends of the carcass layer 13 are wrapped back and secured to the outside in the tire width direction so as to enclose the bead cores 110 and the bead fillers 12. The carcass ply of the carcass layer 13 is formed by covering multiple carcass cords made of steel or organic fiber material (e.g., aramid, nylon, polyester, rayon, etc.) with coating rubber and rolling them.

[0025] The belt layer 14 is formed by laminating a pair of cross belts 141, 142 and a belt cover 143, and is disposed so as to be wound around the outer periphery of the carcass layer 13. The pair of cross belts 141, 142 are formed by covering a plurality of belt cords made of steel or organic fiber material with coating rubber and rolling them, and have a cord angle of 15 degrees or more and 55 degrees or less in absolute value. The pair of cross belts 141, 142 have cord angles (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of opposite signs to each other, and are layered so that the belt cords' longitudinal directions cross each other (so-called cross-ply structure).

[0026] The belt cover 143 is configured by covering a belt cover cord made of steel or organic fiber material with coating rubber, and has a cord angle of 0 degrees or more and 10 degrees or less in absolute value. The belt cover 143 is, for example, a strip material configured by covering one or more belt cover cords with coating rubber, and is configured by winding this strip material spirally around the outer circumferential surfaces of the cross belts 141 and 142 multiple times in the tire circumferential direction. The belt cover 143 is disposed to cover the entire area of the cross belts 141 and 142.

[0027] The tread rubber 2 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form the tire tread portion 3. A pair of sidewall rubbers 160, 160 are disposed on the outer sides of the carcass layer 13 in the tire width direction to form left and right sidewall portions 6. A pair of rim cushion rubbers 17, 17 are disposed on the inner sides of the left and right bead cores 110, 110 and the turned-up portions of the carcass layer 13 in the tire radial direction to form the contact surfaces of the left and right bead portions 10 with the rim flanges.

[0028] [Tread pattern] As shown in Fig. 2, a plurality of circumferential main grooves 20 are provided in the tread portion 3. In this example, two circumferential main grooves 20 are provided in the tread portion 3. The pneumatic tire 1 of this example has in the tread portion 3 two circumferential main grooves 20 extending in the tire circumferential direction, a center land portion 31 and shoulder land portions 33 partitioned into three rows by the two circumferential main grooves 20, and a plurality of sub-grooves 41.

[0029] The center land portion 31 is a land portion between two circumferential main grooves 20. The center land portion 31 includes the tire equatorial plane CL. The center land portion 31 extends continuously in the tire circumferential direction. The shoulder land portions 33 are land portions on the outer side of the circumferential main grooves 20. A land portion located within a range of ¼ of the contact width of the tread portion 3 from the outer side in the tire width direction can also be called a shoulder land portion 33. The shoulder land portion 33 extends continuously in the tire circumferential direction.

[0030] The circumferential main groove 20 is a circumferential groove having a wear indicator that indicates the end of wear, and generally has a groove width of 5.0 mm or more and a groove depth of 7.5 mm or more.

[0031] The secondary grooves 41 are provided in the center land portion 31 and the shoulder land portions 33 adjacent to the circumferential main groove 20. The secondary grooves 41 extend in the tire width direction, penetrating the circumferential main groove 20. One end of each secondary groove 41 terminates in the center land portion 31. The other end of each secondary groove 41 terminates in the shoulder land portion 33. The secondary grooves 41 are provided at predetermined intervals in the tire circumferential direction. In this example, the secondary grooves 41 do not intersect with each other. In this example, the secondary grooves 41 are provided parallel to each other. In this example, each secondary groove 41 has a long portion 41a provided in the center land portion 31 and a short portion 41b provided in the shoulder land portion 33.

[0032] In Fig. 2, the symbol T denotes a tire ground contact edge. The tire ground contact edge T refers to the edge in the tire width direction of the portion of the tread portion 3 that comes into contact with the ground when the tire 1 is mounted on a standard rim, inflated to a standard internal pressure, placed vertically on a flat surface, and under a load condition with a standard load applied.

[0033] The groove width is measured as the maximum distance between the left and right groove walls at the groove opening when the tire 1 is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. In a configuration in which the land portion has a notch or chamfered portion at the edge, the groove width is measured based on the intersection of the tread surface and an extension of the groove wall in a cross-sectional view normal to the groove length direction. In addition, in a configuration in which the groove extends in a zigzag or wavy pattern around the tire circumferentially, the groove width is measured based on the center line of the amplitude of the groove wall.

[0034] The groove depth is measured as the maximum distance from the tread surface to the groove bottom when the tire 1 is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. If the groove has partial unevenness or sipes at the groove bottom, the groove depth is measured excluding these.

[0035] A "regulatory rim" is a rim that is specified for each tire 1 in the standard system that includes the standard on which tire 1 is based, and is a standard rim for JATMA, a "Design Rim" for TRA, and a "Measuring Rim" for ETRTO. However, if tire 1 is an original equipment tire, the original wheel on which tire 1 is mounted should be used.

[0036] "Specified internal pressure" refers to the air pressure specified for each tire 1 in the standard system that includes the standard on which tire 1 is based, and is the maximum air pressure in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and "INFLATION PRESSURE" in the case of ETRTO. However, if tire 1 is an original equipment tire, the air pressure shall be the one indicated on the vehicle.

[0037] "Specified load" refers to the load specified for each tire 1 in the standard system including the standard on which tire 1 is based, and is the maximum load capacity in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and "LOAD CAPACITY" in the case of ETRTO. However, if tire 1 is for a passenger car, it shall be a load equivalent to 88% of the above load. If tire 1 is a tire fitted to an original equipment vehicle, it shall be the wheel load calculated by dividing the front and rear axle loads listed on the vehicle inspection certificate by the number of tires.

[0038] 2, the ratio of the pitch PT of the tread pattern of the tread portion 3, i.e., the pitch ratio, is, for example, 1.38, 1.19, or 1.00. That is, the pitch PT is set to 1.19, with the minimum value being 1.00, or 1.38, which is the maximum value. By adopting this pitch ratio, uneven wear resistance and wet braking performance are further improved.

[0039] [ACA average and fluctuation rate] FIG. 3 is a diagram showing the circumferential average and circumferential variation rate of the actual contact area image (hereinafter referred to as ACA) of the tire 1. As shown in FIG. 3, the ACA varies depending on the rotation angle of the tire 1. The ACA is the total area of the blocks in the tread that are in contact with the road surface. The total ground contact area image (hereinafter referred to as GCA), which will be described later, is the total area enclosed by the outer ring line when the grooves are filled in the ACA.

[0040] The horizontal axis of Fig. 3 is the tire circumferential position [deg], and the vertical axis of Fig. 3 is the ACA [cm 2 In Figure 3, when the load rate is set to 70% of the load capacity by air pressure specified in the specified standard, it is preferable that the ACA circumferential variation rate be 5.0% or less. This improves resistance to uneven wear, i.e., heel-and-toe wear, polygonal wear (wear with corners at a certain rate around the tire circumference), and wet braking performance.

[0041] In FIG. 3, the dashed line SS1 represents the circumferential average Vave of the ACA. The circumferential average Vave is the arithmetic average of the contact characteristics in all regions at positions on the tire circumference. The reciprocating arrow SS2 represents the circumferential fluctuation rate Vfluc of the ACA. The circumferential fluctuation rate Vfluc is the ratio of the difference between the maximum value Vmax and the minimum value Vmin to the circumferential average Vave. In other words, the circumferential fluctuation rate Vfluc can be calculated using the following formula (1). Vfluc=(Vmax-Vmin) / Vave×100…(1)

[0042] Here, the maximum value Vmax is the maximum value of the contact characteristic (here, ACA) in the entire region on the tire circumference, and the minimum value Vmin is the minimum value of the contact characteristic (here, ACA) in the entire region on the tire circumference.

[0043] The tire size of tire 1 was 195 / 65R15 91Q, and the ACA average Vave and the circumferential fluctuation rate Vfluc were measured under the conditions of an air pressure of 230 kPa and a load of 4.5 kN. As a result, the ACA average Vave was 138.1 cm 2], and the circumferential fluctuation rate of ACA Vfluc=4.3[%] was obtained. In other words, the circumferential fluctuation rate of ACA of tire 1 is 5.0% or less.

[0044] The load rate is calculated by JATMA's load capacity by air pressure (600 [kg] x gravitational acceleration 9.8 [m / s 2 ]) was set to 70.1%. The measurements were performed in two parts, and after the first measurement was completed, the tire 1 was rotated half a circumference, and the starting position was set as the second measurement. Note that Figure 3 shows the measurement results for half a circumference of the tire, as the position on the tire circumference was changed from 0 [deg] to 180 [deg] in one measurement. It is preferable to obtain the ACA circumferential variation for the entire circumference of the tire.

[0045] [Tire contact shape analysis device] Hereinafter, a description will be given of a tire contact patch shape analysis device for measuring the circumferential variation rate of the ACA of the tire 1. Fig. 4 is a configuration diagram that schematically shows the tire contact patch shape analysis device 100 used to analyze the contact patch shape of the tire 1. Fig. 5 is a block diagram showing the functions of the tire contact patch shape analysis device 100 shown in Fig. 4. In these figures, Fig. 4 schematically shows the overall configuration of the tire contact patch shape analysis device 100, and Fig. 5 shows the main functions of the tire contact patch shape analysis device 100.

[0046] The tire contact patch analysis device 100 is applied to a system that acquires an image of the contact patch 61 of a tire 1 and analyzes the contact patch 61. The tire contact patch analysis device 100 includes a tire testing machine 200 and a tire contact patch analysis device 201.

[0047] The tire testing machine 200 is a device that imparts test conditions to a tire 1 that is the object of analysis. In the configuration of FIG. 4, the tire testing machine 200 has a support device 300, a drive device 5, and a road surface plate 11. The support device 300 is a device that rotatably supports the tire 1, and has a rim 400 on which the tire 1 is mounted. The drive device 5 is a device that imparts driving force to the tire 1 and the road surface plate 11. The drive device 5 is composed of a motor 60 that drives the tire 1 and the road surface plate 11, and a motor control device 7 that controls the motor 60.

[0048] The driving device 5 includes gears (not shown) and horizontally drives the road surface plate 11. The driving device 5 drives the road surface plate 11 so that it moves relative to the tire 1 that is the analysis target.

[0049] In this tire testing machine 200, a support device 300 supports a tire 1 mounted on a rim 400, and the tire 1 is pressed against an upper surface 11U, which is one main surface of a road surface plate 11, to apply a load to the tire 1. In this example, the load is applied by fixing the distance between the road surface plate 11 and the rotation axis of the tire 1.

[0050] The road surface plate 11 reproduces a flat road surface. When the tire 1 is pressed against the road surface plate 11, the contact surface 61 deforms in the same way as when the tire 1 is running on a flat road surface. By driving the road surface plate 11 horizontally, the rolling state of the tire 1 when the vehicle is running is reproduced with the surface of the road surface plate 11 as the road surface, and the dynamic contact characteristics can be analyzed.

[0051] It is preferable that the moving speed of the road surface plate 11 is as slow as possible to ensure measurement accuracy. If the moving speed of the road surface plate 11 is made high, it is necessary to shorten the exposure time to prevent image blurring when photographing the tire contact surface. This results in an insufficient amount of light from the lighting, reducing the difference in brightness between the contact area and the non-contact area, making it difficult to ensure accuracy in the circumferential fluctuation rate of the ACA. For these reasons, it is preferable that the moving speed of the road surface plate 11 is made low.

[0052] The support device 300 can also displace the rim 400 to adjust the positional relationship between the tire 1 and the road plate 11, thereby applying a slip angle or tilt angle to the tire 1. The drive device 5 can drive the motor 60 via the motor control device 7 to rotate the rim 400 by a predetermined angle. The support device 300 and drive device 5 can also change test conditions by adjusting the load, rotational speed, slip angle, tilt angle, etc. The predetermined angle is the angle in the tire rotation direction around the tire rotation axis. For example, by using a stepping motor as the motor 60, the rim 400, i.e., the tire 1, can be rotated by an angle corresponding to the number of pulses applied to the motor 60. For example, the tire 1 can be rotated by an angle of 1 degree or less. When the ACA is obtained every degree around the tire circumference, for example, if the tire size is 195, the ACA can be obtained at intervals of approximately 6 mm.

[0053] The road surface plate 11 is a light-transmitting plate that has the property of transmitting light. The road surface plate 11 does not need to transmit 100% of light, as long as it has a light transmittance that allows the surface of the tire 1 to be photographed through the road surface plate 11. The road surface plate 11 is, for example, a flat plate made of acrylic resin or a flat plate made of glass. The contact state between the tire 1 and the flat plate is photographed and analyzed, making it possible to analyze a more realistic ground contact state of the tire 1. By moving the road surface plate 11 by driving the driving device 5, which is the road surface driving unit, it is possible to obtain the ground contact characteristics of the tire 1 for each measurement angle when the tire 1 is in contact with the main surface of the road surface plate 11. Note that there are no specifications specified for the road surface plate 11, such as the thickness of the plate or the angle of refraction.

[0054] The tire testing machine 200 also has a camera 15, which is an imaging unit that images the tire 1, and an illumination lamp 16, which is a light source. The camera 15 is configured, for example, by a CCD (Charge Coupled Device) camera. The camera 15 is fixed to the tire testing machine 200. The camera 15 images the tire 1 through the road surface plate 11, thereby imaging the contact surface 61 of the tire 1 pressed against the road surface plate 11. More specifically, the camera 15 is disposed on the lower surface 11D side, which is the other main surface of the road surface plate 11, with its optical axis oriented perpendicular to the lower surface 11D side, and images the tire 1 from the lower surface 11D side through the road surface plate 11. In this way, the camera 15 images the tire 1, including at least the contact surface 61, and generates digital image data of the tire 1, including the contact surface 61.

[0055] The lighting lamp 16 is a lamp that illuminates the shooting range of the camera 15, and is configured, for example, by a halogen lamp. The lighting lamp 16 emits light onto the contact surface 61 of the tire 1 that is pressed against the road surface plate 11. The lighting lamp 16 emits light from the lower surface 11D side of the road surface plate 11 through the road surface plate 11, or from between the upper surface 11U side of the road surface plate 11 and the tire 1. The multiple lighting lamps 16 are each arranged at positions other than the position where the road surface plate 11 moves. Note that even if the road surface plate 11 moves, the positions of the tire rotation axis, the camera 15, and the lighting lamps 16 remain fixed throughout.

[0056] The number of these lighting lamps 16 may vary depending on the test conditions in the tire testing machine 200. For example, when the load when pressing the tire 1 against the road surface plate 11 is small, the contact area is narrow, so the number of lighting lamps 16 may be relatively small, and they may be arranged in two locations diagonally with respect to the direction of movement of the road surface plate 11. On the other hand, when the load when pressing the tire 1 against the road surface plate 11 is large, the contact area is wide, so it is necessary to irradiate light onto the contact surface 61 from more directions. Therefore, in this case, the lighting lamps 16 are arranged in four or more locations surrounding the contact surface 61. Furthermore, these lighting lamps 16 may be of a constant lighting type or a flashing lighting type.

[0057] The tire contact patch analysis device 201 is, for example, a PC (Personal Computer) installed with a predetermined analysis program, and processes images of the tire 1 input from the camera 15 to analyze the contact patch 61 of the tire 1. The process of analyzing the contact patch 61 of the tire 1 includes a process of calculating the contact patch 61 based on the captured images of the tire 1. The tire contact patch analysis device 201 has a processing device 23 that performs arithmetic processing such as analysis of the contact patch 61 and stores data, an input unit 21 that an operator uses to input data to the tire contact patch analysis device 201, and a display unit 22 that displays analysis results and various information. The input unit 21 uses a pointing device such as a keyboard or a mouse, and the display unit 22 uses a display device such as a liquid crystal display. The input unit 21 and the display unit 22 are electrically connected to the processing device 23, which allows the operator to perform input operations on the input unit 21 while viewing the display unit 22. Furthermore, the camera 15 is connected to a processing device 23 of the tire contact patch analysis device 201 , which enables the tire contact patch analysis device 201 to acquire images taken by the camera 15 .

[0058] The processing device 23 of the tire contact patch analysis device 201 is configured to include a processing unit 23a having a CPU (Central Processing Unit) or the like, and a storage unit 35 such as a RAM (Random Access Memory). The processing unit 23a and the storage unit 35 configured in this manner may be provided in the same housing, or in different housings, or multiple storage units 35 may be provided in both forms.

[0059] The processing unit 23a included in the processing device 23 functionally includes a road surface driving unit 231, a ground contact characteristic acquisition unit 232, a ground contact characteristic variation calculation unit 233, and a storage unit 35. The road surface driving unit 231 controls the driving device 5 to rotate the tire 1.

[0060] The ground contact characteristic acquisition unit 232 acquires a photographed image of the contact surface 61 of the tire 1 taken by the camera 15. The photographed image is a digital image of the contact surface 61 of the tire 1 taken by the camera 15. The ground contact characteristics that can be acquired by the ground contact characteristic acquisition unit 232 are characteristics that can be acquired based on the image of the contact surface 61 of the tire 1, and are, for example, the ACA, GCA, contact length, contact width, and rectangularity.

[0061] The ground contact characteristic variation calculation unit 233 calculates the circumferential variation rate of the ground contact area. The ground contact characteristic variation calculation unit 233 in this example has an on-circumferential average value calculation unit 233a and an on-circumferential variation rate calculation unit 233b. The on-circumferential average value calculation unit 233a calculates the average value of the ground contact characteristics. The on-circumferential variation rate calculation unit 233b calculates the variation rate of the ground contact characteristics.

[0062] The memory unit 35 pre-stores an analysis program used by the tire contact patch analysis device 201. When acquiring the contact characteristics of the contact patch 61 of the tire 1, the processing unit 23a calls up the program stored in the memory unit 35 and executes operations in accordance with the program, thereby performing each function.

[0063] The tire contact patch shape analysis device 100 according to this embodiment has the above-described configuration. The operation of the tire contact patch shape analysis device 100 will be described below. When analyzing the contact patch 61 of the tire 1 using the tire contact patch shape analysis device 100, the tire 1 is mounted on the support device 300 of the tire testing machine 200, and the road surface plate 11 is moved while the tire 1 is pressed against it. As a result, the tire 1 is rotated, and the contact patch 61 is photographed by the camera 15 at every predetermined rotation angle (every measurement angle). At this time, the tire 1 is photographed with light irradiated from multiple directions by multiple illumination lamps 16. This allows the camera 15 to photograph the tire 1 with a difference in brightness between the contact patch 61 and portions other than the contact patch 61. The photographed images are acquired by the tire contact patch analysis device 201, which then analyzes the contact patch 61 based on the acquired images.

[0064] [Lighting conditions for shooting] When acquiring an image of the contact area of the ground contact surface 61 of the tire 1, it is preferable to arrange the lighting lamps 16 on the upper surface 11U side of the road surface plate 11 so as to surround the contact area 61. When acquiring an image of the contact area of the ground contact surface 61 of the tire 1, it is preferable to acquire the image by irradiating the tire 1 with light from the lighting lamps 16 arranged on the upper surface 11U side so as to surround the contact area. An example of the arrangement of the lighting lamps 16 will be described later.

[0065] [Operation of tire contact shape analysis device] FIG. 6 is a flow diagram showing an example of the operation of the tire contact patch shape analysis device 100. When analyzing a tire 1, the tire contact patch shape analysis device 100 irradiates light from the illumination lamp 16 onto the tire 1 pressed against the road surface plate 11 when an operation is performed on the input unit 21 (step S0). Next, the tire contact patch shape analysis device 100 starts driving the motor 60 using the motor control device 7 (step S1). While continuing to drive the motor 60 (step S2), the tire contact patch shape analysis device 100 determines whether the rotation angle of the tire 1 has reached a measurement angle (step S3). The measurement angle is the angle at which contact patch shape data is acquired. If the rotation angle of the tire 1 has not reached the measurement angle, the tire contact patch shape analysis device 100 continues driving the motor 60 (step S3, No → S2).

[0066] When the rotation angle of the tire 1 reaches the measurement angle, the tire contact contour analysis device 100 photographs the tire 1 with the camera 15 and acquires contact characteristic data (step S3, Yes → S4). Furthermore, the tire contact contour analysis device 100 stores the acquired data in the storage unit 35 (step S5).

[0067] The tire contact patch shape analyzing device 100 determines whether or not acquisition of all data has been completed (step S6). If acquisition of all data has not been completed, the tire contact patch shape analyzing device 100 continues driving the motor 60 (step S6, No → S2).

[0068] When all data acquisition has been completed, the tire contact shape analysis device 100 performs a process of calculating the circumferential average value and the circumferential variation rate (step S6, Yes → S7). The tire contact shape analysis device 100 outputs the calculation results of the circumferential average value and the circumferential variation rate to the display unit 22 or the like (step S8). Thereafter, the tire contact shape analysis device 100 stops driving the motor 60 (step S9), and the process ends. Through the above process, contact characteristic data on a dry road surface can be acquired.

[0069] Fig. 7 is a flowchart showing an example of the calculation process (step S7) in Fig. 6. Fig. 7 is a flowchart showing the content of the process for calculating the average of the ground contact characteristics on the circumference and the rate of variation of the ground contact characteristics on the circumference.

[0070] In Figure 7, the tire contact patch shape analysis device 100 calculates the circumferential average value Vave of the contact patch characteristics (step S7a). Next, the tire contact patch shape analysis device 100 calculates the circumferential variation rate Vfluc of the contact patch characteristics (step S7b). The circumferential variation rate Vfluc is the ratio of the difference between the maximum and minimum values (Vmax-Vmin) to the circumferential average value Vave, and can be calculated using the above-mentioned formula (1). If the value of the circumferential variation rate Vfluc of the ACA is small, there is a possibility that uneven wear resistance will be improved.

[0071] [Sub-groove width and inclination angle] Referring again to Figure 2, the sub-groove 41 extends in the tire width direction. The groove width of the sub-groove 41 is preferably 2 mm or less. This reduces circumferential variations in the ACA and the center contact width. Note that if the groove width of the sub-groove 41 exceeds 2 mm, the contact area decreases and uneven wear resistance deteriorates, which is undesirable.

[0072] One end of the sub-groove 41 terminates within the center land portion 31, and the other end of the sub-groove 41 terminates within the shoulder land portion 33. The sub-groove 41 extends outward in the tire width direction from the center land portion 31, straddles the circumferential main groove 20, and extends to the shoulder land portion 33. In other words, the sub-groove 41 extends in the tire width direction, penetrating the circumferential main groove 20.

[0073] The inclination angle α of the extension direction of the sub-groove 41 with respect to the tire width direction is preferably 0 degrees or more and 45 degrees or less. If the inclination angle α is in this range, water discharge efficiency is further improved, and wet braking performance is further improved. If the inclination angle of the sub-groove 41 with respect to the tire width direction exceeds 45 degrees, water discharge efficiency decreases, and wet braking performance decreases, so this is not preferable. Note that if the sub-groove 41 is not linear, the inclination angle α of the sub-groove 41 is the inclination of the straight line connecting both ends of the groove center line.

[0074] [Examples of specific layouts and photographed images] Next, specific examples of the arrangement of the camera 15 and the illuminating lamps 16 will be described. Figs. 8 to 10 are diagrams showing specific examples of the arrangement of the camera 15 and the illuminating lamps 16 when acquiring a ground contact patch image. Below, a case where the illuminating lamps 16 include lamps 161 to 168 will be described. Fig. 8 is a diagram showing the arrangement of each lamp as viewed from a direction along the rotation axis of the tire 1. Fig. 9 is a diagram showing the arrangement of each lamp as viewed from the upper surface 11U side of the road surface plate 11, which is a transparent plate. Fig. 10 is a diagram showing the arrangement of each lamp as viewed from a direction perpendicular to the rotation axis of the tire 1. In the following description, the direction along the rotation axis of the tire 1 is called the tire width direction, and the direction perpendicular to the rotation axis is called the tire circumferential direction.

[0075] [Lighting installed on the top side of the road board] 8 to 10 are diagrams showing examples of the arrangement of lamps 161, 162, 163, and 164 provided on the upper surface 11U side of the road surface plate 11. Fig. 8 is a diagram showing the side of the tire 1 as viewed from the rotation axis direction. Fig. 9 is a diagram showing the tire 1 as viewed from above the upper surface 11U side of the road surface plate 11. Fig. 10 is a diagram showing the side of the tire 1 as viewed from a direction perpendicular to the rotation axis.

[0076] 8 to 10, a tire 1 is in contact with the upper surface 11U of the road plate 11. A camera 15 is provided on the lower surface 11D side of the road plate 11. The camera 15 is positioned so that its optical axis 151 is located on the normal to the center point of the contact patch of the tire 1. By positioning the optical axis 151 of the camera 15 so that it passes through the center point of the contact patch, the contact patch can be photographed from the normal direction of the center point of the contact patch. This ensures stable analysis accuracy. The closer to the edge of the captured image, the greater the influence of lens aberration, causing fluctuations in spatial resolution and unstable analysis accuracy. By positioning the camera 15 in this way, the influence of lens aberration can be minimized.

[0077] 8 to 10, lamps 161, 162, 163, and 164 are arranged on the upper surface 11U side of the road surface plate 11. The lamps 161, 162, 163, and 164 are arranged at positions spaced apart from the tire 1 in the tire travel direction and the tire width direction. The lamps 161 and 162 and the lamps 163 and 164 are arranged on different sides of the tire 1. In this way, the lamps 161 to 164 are arranged to surround the contact patch of the tire 1. If the lamps do not illuminate the contact patch of the tire 1 on all four sides, it becomes difficult to define the outline of the contact shape, which may reduce analysis accuracy. In contrast, by arranging the lamps 161 to 164 to surround the contact patch of the tire 1 and irradiating light on all four sides of the contact patch, the outline of the contact shape can be made clearer, thereby improving analysis accuracy.

[0078] 8 and 10, H1 to H4 represent the distances from the center of the light-emitting surface of each lamp 161 to 164 to the upper surface 11U of the road surface plate 11. In FIG. 8, θ1 to θ4 represent the inclination angles of each lamp 161 to 164, i.e., the angles between the light irradiation direction and the upper surface 11U of the road surface plate 11. In FIG. 9, D1 to D4 represent the distances in the tire traveling direction from the center of the light-emitting surface of each lamp 161 to 164 to the center of the tire 1. In FIG. 9, A1 to A4 represent the distances in the tire width direction from the center of the light-emitting surface of each lamp 161 to 164 to the tire center.

[0079] In this example, the distances and angles for each of the lamps 161 to 164 were set as follows: distance H1 = 85 mm, distance H2 = 120 mm, distance H3 = 130 mm, distance H4 = 125 mm, distance D1 = 1050 mm, distance D2 = 1020 mm, distance D3 = 980 mm, distance D4 = 1150 mm, distance A1 = 390 mm, distance A2 = 320 mm, distance A3 = 380 mm, distance A4 = 340 mm, angle θ1 = 4.9 [deg], angle θ2 = 5.3 [deg], angle θ3 = 5.3 [deg], angle θ4 = 5.8 [deg].

[0080] [Lighting installed on the underside of the road board] 11 to 16 are diagrams showing examples of the arrangement of lamps 165, 166, 167, and 168 provided on the lower surface 11D side of the road surface plate 11. As shown in Figs. 11 to 16, it is preferable to provide lamps 165, 166, 167, and 168 on the lower surface 11D side of the road surface plate 11.

[0081] Fig. 11 is a view of the side of the tire 1 from the direction of the rotation axis. Fig. 12 is a view of the tire 1 from below the lower surface 11D side of the road plate 11. Fig. 13 is a view of the side of the tire 1 from a direction perpendicular to the rotation axis.

[0082] 11 to 13, lamps 165 and 166 are arranged on the lower surface 11D side of the road plate 11. The lamps 165 and 166 are arranged at positions spaced apart in the tire width direction from the tire 1. The lamps 165 and 166 are provided on different sides of the tire 1.

[0083] 11 and 12, it is preferable that lamps 165 and 166 have a length in the tire traveling direction and irradiate light in a direction parallel to the tire width direction, thereby improving measurement accuracy.

[0084] 12 and 13, H5 and H6 are the distances from the center of the light-emitting surface of each lamp 165, 166 to the underside 11D of the road plate 11. In Fig. 13, θ5 and θ6 are the inclination angles of each lamp 165, 166, i.e., the angles of the light irradiation direction with respect to the underside 11D of the road plate 11. In Fig. 12, D5 and D6 are the distances in the tire width direction from the center of the light-emitting surface of each lamp 165, 166 to the center of the tire 1.

[0085] In this example, the distances and angles for the lamps 165 and 166 were set as follows: H5=87 mm, H6=82 mm, D5=D6=130 mm, θ5=11.7 [deg], and θ6=18.0 [deg].

[0086] Fig. 14 is a view of the side of the tire 1 seen from the direction of the rotation axis. Fig. 15 is a view of the tire 1 seen from below the lower surface 11D side of the road plate 11. Fig. 16 is a view of the side of the tire 1 seen from a direction perpendicular to the rotation axis.

[0087] 14 to 16, ramps 167 and 168 are arranged on the underside 11D of the road plate 11. The ramps 167 and 168 are arranged at positions spaced apart from the tire 1 in the tire traveling direction. The ramps 167 and 168 are provided on different sides of the tire 1.

[0088] 14 and 15, it is preferable that lamps 167 and 168 have a length in the tire width direction and irradiate light in a direction parallel to the tire traveling direction, thereby improving measurement accuracy.

[0089] In Fig. 14, H7 and H8 are the distances from the center of the light-emitting surface of each lamp 167 and 168 to the underside 11D of the road plate 11. In Fig. 14, θ7 and θ8 are the inclination angles of each lamp 167 and 168, i.e., the angles of the light irradiation direction with respect to the underside 11D of the road plate 11. In Fig. 15, D7 and D8 are the distances in the tire traveling direction from the center of the light-emitting surface of each lamp 167 and 168 to the center of the tire 1.

[0090] In this example, the distances and angles for the lamps 167 and 168 were set as follows: H7=92 mm, H8=94 mm, D7=D8=400 mm, and θ7=θ8=2.1 degrees.

[0091] Under the above conditions, images of the contact patch of the tire 1 can be obtained by continuously photographing the contact patch of the tire 1. The contact patch of the tire 1 is preferably photographed every 3 degrees of the rotation angle of the tire 1, and more preferably every 1 degree. By photographing at intervals of this angle or less, the circumferential variation rate of the ACA can be obtained with high accuracy. In other words, the measurement angle is preferably 3 degrees or less, and more preferably 1 degree.

[0092] FIG. 17 is a diagram showing an example of an image obtained by photographing. FIG. 17 shows an example of a general image, not the tread pattern of the tread portion 3 shown in FIG. 2. The image shown in FIG. 17 is an ACA. The ACA is the total area of the blocks in contact with the road surface. Based on the ACA shown in FIG. 17, for example, the GCA shown in FIG. 18 can be obtained.

[0093] The GCA is the total area enclosed by the outer ring line of the ACA when the grooves are filled. Figure 18 is a diagram showing an example of the GCA. For the ACA shown in Figure 17, for example, the GCA shown in Figure 18 can be obtained by performing the expansion process 80 times and the contraction process 80 times in that order.

[0094] FIG. 19 is an explanatory diagram of the dilation process. FIG. 20 is an explanatory diagram of the erosion process. As shown in FIG. 19, the dilation process is a process in which, if there is even one black pixel around a pixel of interest, the pixel of interest is replaced with a black pixel. That is, the dilation process is a process in which a white pixel is set as a center pixel, and if there is even one black pixel among the eight surrounding pixels (one pixel each in the upper left, upper, upper right, right, lower right, lower, lower left, and left closest to the center pixel), the center pixel is replaced with a black pixel. Conversely, the erosion process is a process in which, for example, when the pixel of interest is a black pixel, if there is even one white pixel around the pixel of interest, as shown in FIG. 20. That is, the erosion process is a process in which a black pixel is set as a center pixel, and if there is even one white pixel among the eight surrounding pixels (one pixel each in the upper left, upper, upper right, right, lower right, lower, lower left, and left closest to the center pixel), the center pixel is replaced with a white pixel.

[0095] [Center contact width, center contact length, etc.] Next, the center contact width and center contact length will be explained. FIG. 21 is a diagram showing an example of a GCA. In FIG. 21, the maximum contact length Wr is the maximum length of the GCA in the tire forward direction. The position at half of the maximum contact length Wr, i.e., Wr / 2, is the center position Wrc of the length in the tire forward direction. The center position Wrc of the length in the tire forward direction is the center position of one side in the tire circumferential direction of the smallest rectangle KK that surrounds the GCA. The length of the GCA in the tire width direction at the center position Wrc of the length of the GCA in the tire forward direction is the center contact width Wc. The center contact width Wc is the widthwise length of the GCA at the center position in the tire circumferential direction.

[0096] In addition, in Figure 21, the maximum contact patch width Wm is the maximum length of the GCA in the tire width direction. The position at half of the maximum contact patch width Wm, i.e., Wm / 2, is the center position Wmc in the tire width direction. The center position Wmc in the tire width direction is the center position of one side in the tire width direction of the smallest rectangle KK that surrounds the GCA. The length of the GCA in the tire forward direction at the center position Wmc of the GCA's length in the tire width direction is the center contact patch length Wrr. The center contact patch length Wrr is the circumferential length of the GCA at the center position in the tire width direction.

[0097] [Another example of the tread] Fig. 22 is a diagram showing another example of the tread portion of a pneumatic tire. In Fig. 22, the tread portion 3a has a configuration in which shoulder lug grooves 42 are added to the tread portion 3 of Fig. 2. The shoulder lug grooves 42 are provided in the shoulder land portions 33. The shoulder lug grooves 42 are grooves that extend in the tire width direction. One end of the shoulder lug grooves 42 terminates within the shoulder land portions 33. The ratio of the pitch PT of the tread pattern of the tread portion 3a, i.e., the pitch ratio, is, for example, 1.38, 1.19, or 1.00.

[0098] The shoulder lug grooves 42 are provided at predetermined intervals in the tire circumferential direction. The secondary grooves 41 and the shoulder lug grooves 42 are provided alternately in the tire circumferential direction. That is, in the shoulder land portion 33, one shoulder lug groove 42 is provided between two adjacent secondary grooves 41 in the tire circumferential direction. Also, in the shoulder land portion 33, one secondary groove 41 is provided between two adjacent shoulder lug grooves 42 in the tire circumferential direction. Because the secondary grooves 41 and the shoulder lug grooves 42 are provided alternately in the tread portion 3a, the circumferential variation rate of the ACA can be reduced more than in the tread portion 3 of FIG. 2.

[0099] The groove width of the shoulder lug grooves 42 is preferably 2 mm or less. If the groove width of the shoulder lug grooves 42 exceeds 2 mm, the impact of the shoulder lug grooves 42 on the ACA increases. As a result, the circumferential variation rate of the ACA increases, and uneven wear resistance and wet braking performance decrease.

[0100] FIG. 23 is a diagram showing another example of a tread portion of a pneumatic tire. As shown in FIG. 23, the tread portion 3b has a circumferential main groove 20 and a circumferential groove 43. The tread portion 3b does not have secondary grooves or lug grooves. In the tread portion 3b, the circumferential grooves 43 are provided in each of the center land portion 31 and the shoulder land portion 33. The circumferential grooves 43 extend in the tire circumferential direction by a predetermined length. The circumferential grooves 43 are not continuous in the tire circumferential direction, but are provided intermittently in the tire circumferential direction.

[0101] Even when the tire 1 has the tread portion 3b shown in Fig. 23, it is preferable that the circumferential variation rate of the ACA is 5.0% or less when the load rate is 70% of the load capacity by air pressure specified in a predetermined standard, as explained with reference to Fig. 3. This improves resistance to uneven wear, i.e., heel-and-toe wear and polygonal wear (wear with corners at a certain rate in the circumferential direction of the tire).

[0102] [ACA, center contact width, and center contact length variability around the circumference] Here, it is preferable that the circumferential variation rate of the center contact width Wc is equal to or less than the circumferential variation rate of the center contact length Wrr. The influence of the contact width direction on uneven wear resistance and wet braking performance is large. By suppressing the circumferential variation of the center contact width, uneven wear resistance and wet braking performance are improved.

[0103] If the circumferential variation rate of the center contact width Wc is greater than the circumferential variation rate of the center contact length Wrr, wet braking performance will be reduced, which is undesirable. For example, the tread portion 3b in Figure 23 described above has a circumferential variation rate of the center contact width Wc that is greater than the circumferential variation rate of the center contact length Wrr, which is undesirable from the perspective of improving wet braking performance.

[0104] Incidentally, it is also possible to specify the circumferential variation rates of the maximum contact width Wm instead of the center contact width Wc and the maximum contact length Wr instead of the center contact length Wrr. That is, the circumferential variation rate of the maximum contact width Wm can be set to a value equal to or less than the circumferential variation rate of the maximum contact length Wr. However, if specified in this way, tires with good uneven wear resistance and wet braking performance will coexist with tires with poor wet braking performance (e.g., Figure 23), making it impossible to narrow down the tires with good performance. For this reason, it is not appropriate to specify tire 1 based on the circumferential variation rates of the maximum contact width Wm and the maximum contact length Wr.

[0105] It is preferable that the circumferential variation rate of the ACA of the tire 1 satisfies the following formula (2). ACA fluctuation rate ≦-3.4×A+7.38…(2) In formula (2), "A" is the load factor. The load factor A is the ratio of the measured load to the load capacity by air pressure specified in the standard. The same applies to formulas (3) and (4) described below.

[0106] FIG. 24 is a diagram showing examples of ACA circumferential variation rates for various tires. The numerous points shown in FIG. 24 represent the results of an analysis citing static contact shape data at different circumferential positions for various tires measured at Yokohama Rubber Co., Ltd.'s testing equipment. The same applies to FIGS. 26 and 27, which will be described later. The line SS3 in FIG. 24 is a line corresponding to the ACA circumferential variation rate = -3.4 × A + 7.38. Tires whose ACA circumferential variation rate is equal to or less than the line SS3 in FIG. 24 are tires that satisfy formula (2).

[0107] By ensuring that the circumferential variation rate of the ACA of tire 1 satisfies equation (2), it is possible to improve resistance to uneven wear (heel-and-toe wear and polygonal wear) and wet braking performance. As the load load factor A increases, uneven wear occurs even if the circumferential variation rate of the ACA is small. The slope of line SS3 is preferably negative -3.4. The intercept is automatically determined so that the circumferential variation rate of the ACA is 5.0% or less when the load capacity by air pressure specified in the specified standard is 70%.

[0108] Figure 25 is a table showing the tires analyzed. For each tire size, Figure 25 shows the product code, pattern, rim size, air pressure [kPa], load [kN], and the number of circumferential locations analyzed. Note that all camber angles were set to zero.

[0109] 26 is a diagram showing examples of the circumferential variation rate of the center contact length for various tires. For tire 1, it is preferable that the circumferential variation rate of the center contact length satisfies the following formula (3). Circumferential variation rate of center contact length ≦-3.3×A+8.0…(3)

[0110] The straight line SS4 in Figure 26 corresponds to the circumferential variation rate of the center contact length = -3.3 x A + 8.0. The slope is preferably negative -3.3. Tires whose circumferential variation rate of the center contact length is equal to or less than the line SS4 in Figure 26 satisfy formula (3).

[0111] 27 is a diagram showing examples of the circumferential variation rate of the central contact width for various tires. For tire 1, it is preferable that the circumferential variation rate of the central contact width satisfies the following formula (4). Circumferential variation rate of center contact width ≦-1.9×A+3.9…(4)

[0112] The straight line SS5 in Figure 27 corresponds to the circumferential variation rate of the center contact width = -1.9 x A + 3.9. The slope is preferably negative -1.9. A tire whose circumferential variation rate of the center contact width is equal to or less than the line SS5 in Figure 27 satisfies formula (4).

[0113] By satisfying formulas (3) and (4), it is possible to further improve uneven wear resistance. However, as the load factor A increases, uneven wear occurs even if the circumferential variation rates of the center contact length and center contact width are small.

[0114] [Example] In this example, performance tests were conducted on uneven wear resistance and wet braking performance for several types of tires under different conditions (see Table 1). In this performance test, new test tires were mounted on specified wheels and mounted on a test vehicle (sedan) with an engine displacement of 3L, and the air pressure was set to 250 kPa.

[0115] To evaluate uneven wear resistance, a laser displacement meter was used to obtain a profile of the tire's tread after the tire was mounted on a test vehicle and driven 10,000 km. This profile was then compared with the profile of the tread of a new tire. The difference in the tire's radial length in the tread was measured as the amount of wear, and the average amount of wear across the entire tread was calculated. The average amount of wear was calculated by dividing the average amount of wear in the conventional example by the average amount of wear in the example and multiplying the result by 100 to obtain an index. The higher the index value, the better the uneven wear resistance.

[0116] For wet braking performance, the braking distance was measured at a speed of 100 km / h on a wet road surface with 1 mm of water depth. The braking distance of the conventional example was set as the standard (100), and the braking distance of the conventional example was divided by the braking distance of the example, and the result multiplied by 100 was used as an index. The higher the index value, the better the wet braking performance.

[0117] All of the tires of Examples 1 to 7 in Table 1 have sub-grooves with a groove width of 2 mm or less in the tread portion. The conventional tire in Table 1 has sub-grooves with a groove width of 2.5 mm in the tread portion.

[0118] As shown in the test results in Table 1, it is clear that the tires of each example are excellent in uneven wear resistance and wet braking performance.

[0119] [Table 1] [Explanation of symbols]

[0120] 1 pneumatic tire 2 Tread rubber 3 Tread section 5. Drive unit 6 Sidewall 7 Motor control device 10 Bead section 11 Road board 12 Bead filler 13 Carcass layer 14 Belt Layer 15 Camera 16. Lighting lamps 17 Rim cushion rubber 20 Circumferential main groove 21 Input section 22 Display section 23 Processing equipment 23a Processing section 31 Center Land Section 33 Shoulder land area 35 Storage section 41 minor groove 42 Shoulder lug groove 43 Circumferential groove 60 motor 61 Ground plane 100 Tire contact shape analysis device 110 bead core 141, 142 Cross Belt 143 Belt cover 150 inner liner 160 Sidewall rubber 200 Tire Testing Machine 201 Tire contact surface analysis device 231 Road surface drive unit 232 Ground characteristics acquisition section 233 Grounding characteristic fluctuation calculation unit 233a Circumferential average calculation section 233b Circumferential fluctuation rate calculation section 300 Support device CL Tire equatorial plane

Claims

1. A carcass layer constituting the skeleton of a tire, a belt layer disposed on the outer periphery of the carcass layer, and a tread portion provided outside the belt layer, wherein the tread portion includes at least two circumferential grooves extending in the tire circumferential direction, a shoulder land portion extending in the tire circumferential direction and including a tire ground contact end, and a sub-groove that extends in the tire width direction without crossing the tire equatorial plane and does not extend outside the tire width direction of the shoulder land portion, excluding the circumferential groove portion, and the sub-groove is inclined with respect to the tire circumferential direction over its entire length, the sub-groove is arranged to intersect the circumferential main groove, the sub-groove has a short portion on the outer side in the tire width direction and a long portion on the inner side in the tire width direction with the circumferential main groove as a boundary, the groove center line of the short portion and the groove center line of the long portion are on the same straight line, the inclination direction of the sub-groove with respect to the tire circumferential direction is the same on both sides of the circumferential main groove where the sub-groove intersects, an inflated tire, wherein the load load factor is 70% of the load capacity by air pressure determined according to a predetermined standard, and when the road surface plate is moved with the tire pressed against the road surface plate, the circumferential fluctuation rate of the actual ground contact area image is 5.0% or less.

2. When defining the length along the tire circumferential direction passing through the center of the total ground contact area obtained from the tire ground contact shape as the center ground contact length, and the length along the tire width direction passing through the center of the total ground contact area as the center ground contact width, the inflated tire according to claim 1, wherein the circumferential fluctuation rate of the center ground contact length is greater than or equal to the circumferential fluctuation rate of the center ground contact width.

3. The inflated tire according to claim 2, wherein the circumferential fluctuation rate of the center ground contact length and the circumferential fluctuation rate of the center ground contact width are defined by the following formulas. Circumferential fluctuation rate of center ground contact length ≦ -3.3×A + 8.0 Circumferential fluctuation rate of center ground contact width ≦ -1.9×A + 3.9 Load load factor A = (measured load) / (load capacity by air pressure determined according to the standard)

4. The inflated tire according to any one of claims 1 to 3, wherein the sub-groove with a groove width of 2 mm or less is provided at a predetermined interval in the tire circumferential direction on the land portion adjacent to the circumferential groove.

5. When defining a groove that extends in the tire width direction and extends outside the tire width direction of the shoulder land portion as a shoulder lug groove, the inflated tire according to claim 4, wherein the width of the shoulder lug groove is 2 mm or less.

6. The pneumatic tire according to claim 5, wherein the sub-grooves and the shoulder lug grooves are alternately arranged in the tire circumferential direction.

7. The sub-grooves extend across the circumferential groove, The pneumatic tire according to any one of claims 1 to 6, wherein an angle of the extending direction of the sub-grooves with respect to the tire width direction is 0 [deg] or more and 45 [deg] or less.

8. The tread portion has a tread pattern that repeats at a predetermined pitch, and the pitch ratio of the predetermined pitch is 1.38, 1.19, 1.

00. The pneumatic tire according to any one of claims 4 to 7.

9. The pneumatic tire according to any one of claims 1 to 8, wherein a circumferential fluctuation rate of the actual contact area image is defined by the following formula. Circumferential fluctuation rate of actual contact area image ≦ -3.4 × A + 7.38 Load load ratio A = (measured load) / (load capacity according to air pressure determined by the standard)

Images