Patent Publication Number: US-2005139303-A1

Title: Low internal pressure pneumatic tire

Description:
This application claims priority on Patent Application No. 2003-428756 filed in Japan on Dec. 25, 2003.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a structure of a pneumatic tire of a low internal pressure type. The pneumatic tire of this type is employed for a buggy running over a rough road such as an uneven ground and other ATVs (All Terrain Vehicles).  
      2. Description of the Related Art  
      In general, a tire to be employed for a vehicle is to have a traction performance and a sliding performance. The traction performance realizes a high straight running stability for a vehicle. The sliding performance implies a cornering response performance during steering. The sliding performance realizes a high cornering stability for a vehicle. For example, a tire to be employed for an ATV is to have an excellent traction performance and sliding performance for a rough road such as an uneven ground. Usually, the tire for the ATV is a pneumatic tire of a low internal pressure type. In the tire of this type, the tread portion of the tire is provided with a plurality of blocks in an erecting state along a tread surface.  
      In the tire for the ATV, conventionally, the external shape of the block, the way of an array, the depth of a groove formed between the blocks and the like are set corresponding to the specification of the tire. The combination of these elements causes the traction performance and the sliding performance to be consistent with each other. Consequently, the expected object of the tire for the ATV can be achieved. Japanese Laid-Open Patent Publications Nos. 2002-362113 and Hei 1-148606 have described the foregoing.  
      In recent years, the output of an engine to be mounted on an ATV has been increased and the weight of the ATV has also been increased. For this reason, the tire for the ATV has been demanded to maintain a high traction performance and sliding performance at a high load.  
      In the case in which the performance of the tire for the ATV is to be maintained by a conventional method, however, the following problem arises. As a result, an expected performance cannot be achieved. More specifically, in the case in which the external shape of a block is large, for example, a traction performance is enhanced and a control performance is deteriorated. On the other hand, in the case in which the external shape of the block is small, a sliding performance is enhanced and the traction performance is deteriorated. In the case in which the external shape of the block is small and the depth of a groove formed between the blocks is great, both the traction performance and the sliding performance tend to be enhanced and the weight of the tire is increased. The increase in the weight of the tire deteriorates a ride comfort, and furthermore, lowers a running performance (a straight running stability, a cornering stability and the like).  
     SUMMARY OF THE INVENTION  
      The present invention has been made in such a background. It is an object of the present invention to provide a low internal pressure pneumatic tire which suppresses a deterioration in a running performance and enhances a traction performance and a sliding performance.  
      The low internal pressure pneumatic tire according to the present invention is used for running over an uneven ground. A plurality of blocks is provided on a tread. Each of the blocks is formed to be protruded outward in the radial direction of the tire. Each of the blocks is formed to take a solid shape specified by a long side dimension W, a short side dimension L and a high side dimension H. The outer peripheral surface of each block forms a tread surface. The outer peripheral surface of each block is provided with a recess specified by a long side dimension WR, a short side dimension LR and a deep side dimension HR.  
      The dimensions have the following relationship: 
 
 WR/W= 0.33 to 0.87, 
 
 LR/L= 0.2 to 0.8, and 
 
 HR/H= 0.15 to 0.85. 
 
      A ratio of a block volume BT to a recess volume RT is set to be RT/BT=0.08 to 0.25.  
      Thus, the relative size of the recess with the block is set. When the low internal pressure pneumatic tire rolls over a road surface, consequently, each block is deformed properly so that a grip force is generated. The grip force enhances a traction performance and a sliding performance. In addition, an increase in the weight of the low internal pressure pneumatic tire is suppressed so that a running performance can be prevented from being deteriorated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an enlarged front view showing the main part of a tire according to an embodiment of the present invention,  
       FIG. 2  is an enlarged view showing the tread of the tire according to the embodiment of the present invention,  
       FIG. 3  is a sectional view taken along III-III in  FIG. 2 , and  
       FIG. 4  is a sectional view taken along IV-IV in  FIG. 2 .  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention will be described below in detail based on a preferred embodiment with reference to the drawings.  
      As shown in  FIG. 1 , a low internal pressure pneumatic tire (hereinafter referred to as a “tire”)  10  according to the embodiment of the present invention is used for running over an uneven ground and is employed for an ATV or the like, for example. The tire  10  has a well-known internal structure and is manufactured by a well-known method. The tire  10  has a carcass constituting a frame, a reinforcing layer for reinforcing the carcass, and a tread  11  formed to cover the reinforcing layer. The tire  10  according to the present embodiment features the structure of the tread  11 . Since the tread  11  has the following structure, the tire  10  exhibits an excellent traction performance and sliding performance. In  FIG. 1 , a transverse direction is set to be an axial direction and a direction of an equator plane E is set to be a radial direction.  
      The tread  11  is formed symmetrically about the equator plane E. The tread  11  is provided with a plurality of blocks  12  to  15  in a circumferential direction. Each of the blocks  12  to  15  is continuously formed symmetrically about the equator plane E and regularly. Each of the blocks  12  to  15  is formed to take a solid shape. The block  12  is formed like a rectangular parallelepiped and the blocks  13  to  15  have sections formed like polygonal columns. Indeed, the shapes of the blocks  12  to  15  are not restricted thereto but can be designed and changed properly corresponding to the specification of the tire.  
      As shown in  FIGS. 3 and 4 , the block  12  has a long side dimension W set to be 25 mm to 35 mm, a short side dimension L set to be 15 mm to 25 mm and a high side dimension H set to be 10 mm to 15 mm. The high side dimension H represents a distance from a tread surface  25  to an upper surface  19  of the block  12 . Each of the dimensions W, L and H can be designed and changed properly corresponding to the specification of the tire.  
      The block  12  includes a recess  21  having an opening  20 . The opening  20  is provided on the upper surface  19  of the block  12 . The recess  21  has a long side dimension WR set to be 10 mm to 20 mm, a short side dimension LR set to be 2 mm to 4 mm and a deep side dimension HR set to be 2 mm to 4 mm. The deep side dimension HR represents a distance from an internal bottom surface  26  of the recess  21  to the upper surface  19  of the block  12 . The recess  21  is formed with an internal wall surface taking an almost U shape as shown in  FIG. 4 . It is a matter of course that the shape of the internal wall surface of the recess  21  is not restricted thereto.  
      The block  13  is formed to be almost wedge-shaped as shown in  FIGS. 1 and 2 . The block  13  has a long side dimension W set to be 24 mm to 34 mm, a short side dimension L set to be 10 mm to 20 mm and a high side dimension (H) set to be 12 mm to 17 mm. The high side dimension (H) is not shown in these drawings and represents a distance from the tread surface  25  to the upper surface of the block  13  in the same manner as in the block  12 . Referring to the block  13 , similarly, each of the dimensions W, L and H can be designed and changed properly corresponding to the specification of the tire.  
      The block  13  also includes a recess  24  having an opening. The recess  24  has a long side dimension WR set to be 20 mm to 30 mm, a short side dimension LR set to be 2 mm to 3 mm and a deep side dimension (HR) set to be 1 mm to 2 mm. The deep side dimension (HR) is not shown in these drawings and represents a distance from the internal bottom surface of the recess  24  to the upper surface of the block  13  in the same manner as in the block  12 . The recess  24  is formed with an internal wall surface taking an almost U shape in the same manner as the recess  21 . However, the shape of the internal wall surface of the recess  24  is not restricted thereto.  
      The block  14  has a section formed like a polygonal column as shown in  FIGS. 1 and 2 . The block  14  has a long side dimension W set to be 30 mm to 40 mm, a short side dimension L set to be 15 mm to 25 mm and a high side dimension (H) set to be 12 mm to 17 mm. The high side dimension (H) is not shown in these drawings and represents a distance from the tread surface  25  to the upper surface of the block  14  in the same manner as in the block  12 . The long side dimension W of the block  14  is shown in  FIG. 2 . More specifically, in the case in which the presence of a virtual rectangle surrounding the block  14  is assumed, the length of the long side of the virtual rectangle is equal to the long side dimension W. In the virtual rectangle, the upper and lower sides of the block  14  make a pair of opposed sides. On the other hand, the short side dimension L of the block  14  is equal to the length of the short side of the virtual rectangle. Referring to the block  14 , similarly, each of the dimensions W, L and H can be designed and changed properly corresponding to the specification of the tire.  
      The block  14  also includes a recess  27  having an opening. The opening is provided on the upper surface of the block  14 . The recess  27  has a long side dimension WR set to be 10 mm to 20 mm, a short side dimension LR set to be 1 mm to 2 mm and a deep side dimension (HR) set to be 1 mm to 2 mm. The deep side dimension (HR) is not shown in these drawings and represents a distance from the internal bottom surface of the recess  27  to the upper surface of the block  14  in the same manner as in the block  12 . The recess  27  is formed with an internal wall surface taking an almost U shape in the same manner as the recess  21 . However, the shape of the internal wall surface of the recess  27  is not restricted thereto.  
      The block  15  has a section formed like a polygonal column as shown in  FIGS. 1 and 2 . The block  15  has a long side dimension W set to be 30 mm to 40 mm, a short side dimension L set to be 15 mm to 25 mm and a high side dimension (H) set to be 10 mm to 15 mm. The high side dimension (H) is not shown in these drawings and represents a distance from the tread surface  25  to the upper surface of the block  15  in the same manner as in the block  12 . The long side dimension W and the short side dimension L of the block  15  are defined in the same manner as those of the block  14 . More specifically, in the case in which the presence of a virtual rectangle surrounding the block  15  is assumed, the length of the long side of the virtual rectangle is equal to the long side dimension W. In the virtual rectangle, the upper and lower sides of the block  15  make a pair of opposed sides. On the other hand, the short side dimension L of the block  15  is equal to the length of the short side of the virtual rectangle. Referring to the block  15 , similarly, each of the dimensions W, L and H can be designed and changed properly corresponding to the specification of the tire.  
      The block  15  also includes a recess  28  having an opening. The opening is provided on the upper surface of the block  15 . The recess  28  has a long side dimension WR set to be 10 mm to 20 mm, a short side dimension LR set to be 1 mm to 2 mm and a deep side dimension (HR) set to be 1 mm to 2 mm. The deep side dimension (HR) is not shown in these drawings and represents a distance from the internal bottom surface of the recess  28  to the upper surface of the block  15  in the same manner as in the block  12 . The recess  28  is formed with an internal wall surface taking an almost U shape in the same manner as the recess  21 . However, the shape of the internal wall surface of the recess  28  is not restricted thereto.  
      A shoulder portion  16  of the tire  10  is also provided with blocks  17  and  18 . The blocks  17  and  18  are provided continuously in a circumferential direction. The blocks  17  and  18  are provided alternately. The block  17  has a recess  29  and the block  18  has a recess  30 .  
      Referring to each of the blocks  12  to  15 , the long side dimension W, the short side dimension L, the high side dimension H, the long side dimension WR, the short side dimension LR and the deep side dimension HR have the following relationship. More specifically, there are set 
 
 WR/W= 0.33 to 0.87, 
 
 LR/L= 0.2 to 0.8, and 
 
 HR/H= 0.15 to 0.85. 
 
 There are preferably set 
 
 WR/W≧ 0.40 , WR/W≦ 0.70, 
 
 LR/L≧ 0.30 , LR/L≦ 0.60, and 
 
 HR/H≧ 0.20 , HR/H≦ 0.70. 
 
 There are more preferably set 
 
 WR/W≧ 0.40 , WR/W≦ 0.60, 
 
 LR/L≧ 0.30 , LR/L≦ 0.50, and 
 
 HR/H≧ 0.20 , HR/H≦ 0.60. 
 
      Referring to each of the blocks  12  to  15 , furthermore, the ratio of a block volume BT to a recess volume RT is set to be 
 
 RT/BT= 0.08 to 0.25. 
 
 The ratio is preferably set to be 
 
 RT/BT≧ 0.10 , RT/BT≦ 0.20. 
 
 The ratio is more preferably set to be 
 
 RT/BT≧ 0.10 , RT/BT≦ 0.17. 
 
     EXAMPLES  
      The effects of the present invention will be apparent below by way of examples. The present invention should not be construed to be restricted based on the description of the examples.  
      Table 1 shows a result obtained by executing a comparison test for a conventional tire (comparative examples 1 to 5) for the handling stability of a tire according to each of examples 1 to 7 of the present invention.  
      The specification of the tire according to each of the examples and the comparative examples is a low internal pressure tire (AT22 10-10 KT857) for off-road use which is attached to a four-wheel buggy. The tire according to each of the examples and the comparative examples comprises a plurality of blocks. Each of the blocks is provided on a tread so as to be protruded outward in a radial direction. Each of the blocks includes a recess.  
     Example 1  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 640 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.67, a dimension ratio LR/L is set to be 0.4, a dimension ratio HR/H is set to be 0.62, and a volume ratio RT/BT is set to be 0.16.  
     Example 2  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 400 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.67, a dimension ratio LR/L is set to be 0.4, a dimension ratio HR/H is set to be 0.38, and a volume ratio RT/BT is set to be 0.10.  
     Example 3  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 320 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.33, a dimension ratio LR/L is set to be 0.4, a dimension ratio HR/H is set to be 0.62, and a volume ratio RT/BT is set to be 0.08.  
     Example 4  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 960 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.67, a dimension ratio LR/L is set to be 0.6, a dimension ratio HR/H is set to be 0.62, and a volume ratio RT/BT is set to be 0.25.  
     Example 5  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 416 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.87, a dimension ratio LR/L is set to be 0.8, a dimension ratio HR/H is set to be 0.15, and a volume ratio RT/BT is set to be 0.11.  
     Example 6  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 572 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.87, a dimension ratio LR/L is set to be 0.2, a dimension ratio HR/H is set to be 0.85, and a volume ratio RT/BT is set to be 0.15.  
     Example 7  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 400 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.33, a dimension ratio LR/L is set to be 0.8, a dimension ratio HR/H is set to be 0.38, and a volume ratio RT/BT is set to be 0.10.  
     Comparative Example 1  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 160 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.67, a dimension ratio LR/L is set to be 0.4, a dimension ratio HR/H is set to be 0.15, and a volume ratio RT/BT is set to be 0.04.  
     Comparative Example 2  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 1280 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.67, a dimension ratio LR/L is set to be 0.8, a dimension ratio HR/H is set to be 0.62, and a volume ratio RT/BT is set to be 0.33.  
     Comparative Example 3  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 2288 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.87, a dimension ratio LR/L is set to be 0.8, a dimension ratio HR/H is set to be 0.85, and a volume ratio RT/BT is set to be 0.59.  
     Comparative Example 4  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 260 mm 3 . Moreover, a dimension ratio WR/W is set to be 0.87, a dimension ratio LR/L is set to be 0.2, a dimension ratio HR/H is set to be 0.38, and a volume ratio RT/BT is set to be 0.07.  
     Comparative Example 5  
      A block has a long side dimension W of 30 mm, a short side dimension L of 10 mm, a high side dimension H of 13 mm, a block volume BT of 3900 mm 3 , and a recess volume RT of 50 mm. Moreover, a dimension ratio WR/W is set to be 0.17, a dimension ratio LR/L is set to be 0.2, a dimension ratio HR/H is set to be 0.38, and a volume ratio RT/BT is set to be 0.01.  
      The comparison test is carried out in the following procedure. More specifically, the tire according to each of the examples and the comparative examples is attached to a four-wheel buggy. A test driver synthetically judges a traction performance, a control performance and a ride comfort in the running of the four-wheel buggy and decides them to be excellent or bad.  
                                                                   TABLE 1                                           Com-       Com-           Com-       Com-       Com-                   parative       parative           parative       parative       parative           Exam-   Exam-   Exam-   Exam-   Exam-   Exam-   Exam-   Exam-   Exam-   Exam-   Exam-   Exam-           ple 1   ple 2   ple 1   ple 3   ple 2   ple 4   ple 5   ple 3   ple 6   ple 4   ple 7   ple 5                                                                                        Long side   30   30   30   30   30   30   30   30   30   30   30   30       dimension       W (mm)       Short side   10   10   10   10   10   10   10   10   10   10   10   10       dimension       L (mm)       High side   13   13   13   13   13   13   13   13   13   13   13   13       dimension       H (mm)       Block   3900   3900   3900   3900   3900   3900   3900   3900   3900   3900   3900   3900       volume       BT       Recess   640   400   160   320   1280   960   416   2288   572   260   400   50       volume       RT       WR/W   0.67   0.67   0.67   0.33   0.67   0.67   0.87   0.87   0.87   0.87   0.33   0.17       LR/L   0.4   0.4   0.4   0.4   0.8   0.6   0.8   0.8   0.2   0.2   0.8   0.2       HR/H   0.62   0.38   0.15   0.62   0.62   0.62   0.15   0.85   0.85   0.38   0.38   0.38       RT/BT   0.16   0.10   0.04   0.08   0.33   0.25   0.11   0.59   0.15   0.07   0.10   0.01       Evaluation   Excel-   Excel-   Bad   Excel-   Bad   Excel-   Excel-   Bad   Excel-   Bad   Excel-   Bad       of handling   lent   lent       lent       lent   lent       lent       lent       stability                  
 
      As shown in the Table, when a dimension ratio WR/W=0.33 to 0.87, a dimension ratio LR/L=0.2 to 0.8, a dimension ratio HR/H=0.15 to 0.85 and a volume ratio RT/BT=0.08 to 0.25 are satisfied for each of the blocks, the handling stability is excellent. The reason is that the relative size of the recess with the block is set within the range described above. More specifically, each of the blocks is properly deformed and the proper deformation generates a grip force. As a result, a traction performance and a sliding performance can be enhanced.