JP2005289123A - Automobile low flat pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automobile low flat pneumatic tire which prevents the damage of a tire due to pinch cut, and improves high-speed traveling durability. <P>SOLUTION: The flat pneumatic tire is assembled in a rim and filled with normal inner pressure. A rim flange has a rim flange surface Fr extending from a bead base line to an inflection point v, and a flange curved surface Fc having a center on a tire axial direction line passing through the inflection point v and contacting with the rim flange surface Fr at the inflection point v. A bead surface has a center on the tire axial direction line passing through the tire maximum width position. A side wall reference arc Cs with a side reference radius Rs passing through the tire maximum width position contacts with the flange curved surface Fc in a range of a bead arc contacting surface till a terminate point Pe exceeding a flange reference contacting point Ps contacting wtih the flange curved surface Fc. The height Hv of the inflection point v is made to be 7.5 to 10.0 mm, the flange radius Rf is made to be 8.5 to 11.0 mm. Height Hg is made to 17.0 to 20.5 mm, and an opening angle θis made to be 45° to 80°. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a low-flat pneumatic tire for automobiles that prevents tire damage due to pinch cuts and has improved high-speed running durability performance.

  With the increase in performance of passenger cars, the flattening of tires for automobiles is progressing, and low-flattening tires for automobiles with a flatness ratio of 50% or less are often used.

  However, in such a low-flat pneumatic tire for automobiles, the height in the radial direction of the sidewall portion is small, so when riding on a protrusion such as a curb or sinking into a large recess such as a pothole The tire is also greatly deformed and the tire outer surface such as the sidewall is sandwiched between the road surface and the rim flange and receives a strong impact, the cord inside the tire is cut, or the sidewall structure is changed, due to the internal pressure A part of the side wall portion swells like a bubble, and so-called pinch cuts such as penetration sometimes occur easily. This pinch cut may also lead to a tire burst.

  The shape of the rim flange is not uniform depending on the conforming standard, and the allowable range of the design is not small. Therefore, the tire bead portion usually needs to be adapted to a rim on the market. For this reason, the bead portion of the tire can be properly fitted to a rim on the market, and in order to prevent the occurrence of air leakage, vibration, etc., the contact between the rim flange upper portion and the tire is usually set as small as possible. Yes. For this reason, when a shocking excessive load is applied and the tire is deformed, it has been found that the bead portion easily deforms beyond the normal assumption and the rim sandwiches the tire to cause the pinch cut.

  On the other hand, as shown in FIG. 8, the tire has a side outer surface with a large contact range with the curved portion a of the rim flange and with an outer bulge portion b that is smoothly connected to the flange arc outer surface of the tire in contact with the curved portion. Has been proposed (for example, Patent Document 1).

JP-A-6-72108

  However, the proposed tire is a pneumatic tire for construction vehicles that travels on rough terrain such as an excavator loader and a dump truck, and this tire has a foreign object at the interface between the outer surface of the bead portion and the inner surface of the rim flange. Is intended to prevent so-called rim chaefing, and the technical field is different from a low flat pneumatic tire for automobiles, and the outer bulging portion b is illustrated as having an arcuate surface, and It is a requirement to smoothly connect to the contact area. Therefore, as the outer bulging portion b comes into contact with the curved portion of the rim flange as the tire deforms during deformation, the thickness of the bead at the contact portion increases, and as a result, smooth contact of pressure equalization tends to be hindered and the tire is lifted up. Rim deviation may occur, and even if it is a technique suitable for a pneumatic tire for construction vehicles, it is not an idea that can be applied to a low-flat pneumatic tire for automobiles intended to prevent pinch cuts.

  An object of the present invention is to provide a low-flat pneumatic tire for automobiles that can prevent tire damage due to pinch cuts.

The invention according to claim 1 is a low flat pneumatic tire for an automobile having a tire outer surface including a tread surface, sidewall surfaces at both ends thereof, and a bead surface, and a rim assembled to the rim and filled with a normal internal pressure. And
The rim has a center on a tire axial direction line passing through the inflection point v, and a rim flange surface Fr extending linearly outward from the bead base line Lb to the inflection point v having the inflection point height Hv. A flange F having a flange curved surface Fc with a flange radius Rf in contact with the rim flange surface Fr at the inflection point v;
The bead surface has a center on a tire axial line Xm passing through the tire maximum width position Wm, and a side wall reference arc Cs having a side reference radius Rs passing through the tire maximum width position Wm is the flange curved surface Fc. In contact with the flange curved surface Fc in the range of the bead arc contact surface Tf to the end point Pe beyond the flange reference contact Ps in contact with
The inflection point height Hv is 7.5 mm or more and 10.0 mm or less, the flange radius Rf is 8.5 mm or more and 11.0 mm or less, and the total flange height Hg of the inflection point height Hv and the flange radius Rf. (= (Hv + Rf)) is 17.0 mm or more and 20.5 mm or less, and the opening angle θ of the bead arc contact surface Tr to the terminal point Pe is 45 ° or more and 80 ° or less.

  In the invention according to claim 2, the bead surface is a curved surface parallel to the sidewall reference arc Cs or a substantially parallel straight line from the end point Pe to the flange total height Hg radially outward. The invention according to claim 3 is provided with a raised area having a projecting surface extending to an additional point Pa having an additional point height Ha added with 0 to 5 mm. The invention according to claim 3, wherein the bead surface is disposed radially outward of the additional point Pa. The recess radius extending from the side wall reference arc Cs is 0.3 mm to 2.0 mm and extending in the circumferential direction, and the recess radius Re is 2.0 mm to 5.0 mm. It is said.

  According to a fourth aspect of the present invention, the tire outer surface protrudes outward from the sidewall reference arc Cs on the radially outer side of the recess, and a protrusion length Lt along the sidewall surface is 2.0 mm or more. In the invention according to claim 5, the rib extending in the circumferential direction of 0 mm or less is formed, and the tire outer surface is parallel to the sidewall reference plane between the terminal point Pe and the additional point height Ha. It is a raised area extending in a curved surface or a substantially parallel straight line, and the side correction radius 0.80 to 0.95 times the side reference radius Rs between the additional point height Ha and the tire maximum width position Wm. The modified sidewall surface using Rr and the joint arc Cj continuous from the lower end to the raised region, and the invention according to claim 6 is characterized in that the tire outer surface includes the end point Pe and the front end Pe. Between the tire maximum width position Wm, a corrected sidewall surface having a side correction radius Rr that is 0.80 to 0.95 times the side reference radius Rs of the sidewall reference surface, its lower end, and the end point Pe. Each is characterized by being formed by a joining arc Cj.

  In the invention according to claim 1, the opening angle θ of the bead arc contact surface Tr in which the bead surface is in contact with the curved surface of the rim is 45 ° or more and 80 ° or less, and conventional low flat pneumatic tires for automobiles are 15 to 30. Because it is greatly extended compared to ゜, even in the case of a large deformation that causes a pinch cut, the tire will come into contact with the flange curved surface Fc of a large area in advance, reducing the stress concentration. , Pinch cuts such as cord breakage and tire structure damage can be prevented. Further, by setting the angle to 80 ° or less, it is possible to prevent the rim assembly from being deteriorated in the low-flat pneumatic tire for automobiles and to prevent the rim from excessively protruding outward in the tire axial direction.

  Furthermore, the inflection point height Hv is 7.5 mm or more and 10.0 mm or less, the flange radius Rf is 8.5 mm or more and 11.0 mm or less, and the total flange height of the inflection point height Hv and the flange radius Rf. The height Hg (= (Hv + Rf)) is not less than 17.0 mm and not more than 20.5 mm. When the rim is assembled with the bead surface of the low flat pneumatic tire for automobiles, the contact with the rim flange surface Fr and the flange curved surface Fc is not It is set without becoming excessive, making the rim assembly good and helping to prevent the occurrence of pinch cuts.

  Further, as in the invention according to claim 2, there is a protrusion having a projecting surface extending from the end point Pe of the bead arc contact surface Tf to the additional point Pa of the additional point height Ha obtained by adding 0 to 5 mm to the flange total height Ha. By providing the area, the bending stress is increased during tire deformation to withstand the deformation, and the support rigidity of the bead surface at the time of large deformation that causes pinch cut is increased, the shock is reduced, and the stress at the time of large deformation In addition to achieving dispersion and setting the distance from the terminal point Pe to the additional point Pa to 0 to 5 mm as described above, it is possible to prevent an excessive increase in rigidity and moderate stress dispersion in the raised region. Further, since the raised region is formed by a curved surface parallel to the sidewall reference arc Cs or a substantially parallel straight line and there is no increase in thickness, it is possible to prevent rim displacement without raising the bead portion during deformation.

  Further, by providing the recess as in the invention according to claim 3, the contact pressure in the vicinity of the terminal point Pe at the time of large deformation can be released. In addition, when it forms in the circumferential direction, the contact pressure which arises in the end point Pe vicinity of the flange curved surface Fc can be released, and pinch cut is suppressed. If the punching radius Re is smaller than 2.0 mm, the pinch cut has a certain effect, but the surface distortion during normal use increases, and the possibility of cracking due to local deformation increases. Further, when the depth De is smaller than 0.3 mm, there is no effect, and when it exceeds 2 mm, stress concentration tends to occur, preferably about 0.5 to 1 mm.

  Further, the ribs in the circumferential direction of the invention according to claim 4 are not intended for stress dispersion, can prevent the internal components from being disturbed in the tire vulcanization process, and facilitate the control of the rubber gauge of the recess.

  Further, as in the invention according to claim 5, the sidewall surface is an arc surface having a side correction radius Rr that is 0.80 to 0.95 times the side reference radius Rs between the raised region and the tire maximum width position Wm. This facilitates control of the rubber gauge such as the raised region in the tire vulcanization process.

  By adopting the configuration of the invention of claim 6, the configuration of the outer surface of the tire can be simplified without using raised regions, ribs, and the like, and can be suitably used particularly for a low-flat pneumatic tire for automobiles having a small tire size.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in FIGS. 1 and 2, a low-flat pneumatic tire for automobile (hereinafter sometimes simply referred to as a tire) 1 includes a tire outer surface 5 including a tread surface 2, a sidewall surface 3, and a bead surface 4. The rim is assembled to a rim 6 (hereinafter simply referred to as a rim) 6 having a flange F having a rim flange surface Fr and a flange curved surface Fc, and is filled with a normal internal pressure. The bead arc contact surface Tf is in contact with the flange curved surface Fc and the bead arc contact surface Tf has an opening angle θ of 45 ° or more and 80 ° or less to the end point Pe.

  The rim 6 means a normal rim that is defined for each tire in the standard system including the standard on which the tire is based. For example, a standard rim for JATMA, “Design Rim” for TRA, Or, for ETRTO, “Measuring Rim”. In addition, the normal internal pressure is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA, and the table "TIRE LOAD LIMITS AT VARIOUS COLD" is TRA. The maximum value described in “INFLATION PRESSURES”, “INFLATION PRESSURE” in the case of ETRTO, is 180 KPa in the case of a passenger car such as the low flat pneumatic tire for automobiles of the present invention.

  As is well known, the rim 6 raises flanges F on both sides of a seat portion having a bead seat surface 9, and the rim flange surface Fr is a tire at the intersection of the bead seat surface 9 and the rim flange surface Fr. A straight line extends radially outward from the bead base line Lb passing in the axial direction to the inflection point v having the inflection point height Hv. The flange curved surface Fc has a center radius Rfo on a tire axial line passing through the inflection point v and on the outer side in the tire axial direction of the rim, and a flange radius Rf in contact with the rim flange surface Fr at the inflection point v. Have

  The inflection point height Hv, the flange radius Rf, and the flange total height Ha (= (Hv + Rf)) of the inflection point height Hv and the flange radius Rf are set on the basis of the selection of the regular rim. doing. The inflection point height Hv is in the range of 7.5 mm to 10.0 mm. If it is less than 7.5 mm, the contact pressure between the tire and the rim flange becomes excessive, which tends to cause poor meshing. Conversely, if it exceeds 10.0 mm, the support rigidity of the bead portion is lowered and it is difficult to obtain the effect.

  The flange radius Rf is in the range of 8.5 mm to 11.0 mm. If the distance is less than 8.5 mm, the contact between the tire and the rim flange becomes local, which tends to cause poor meshing. Conversely, if it exceeds 11.0 mm, the support rigidity of the bead portion becomes low, and the effect is difficult to obtain.

  Further, the total flange height Ha (= (Hv + Rf)) of the inflection point height Hv and the flange radius Rf is set in a range of 17.0 mm or more and 20.5 mm or less. If it is less than 17.0 mm, the contact between the tire and the rim flange becomes local, which tends to cause poor meshing. On the other hand, if it exceeds 20.5 mm, the support rigidity of the bead portion is lowered, and it is difficult to obtain the effect.

  Further, the flange radius Rf in contact with the rim flange surface Fr is set to about 9.0 to 11.0 mm, and the flange curved surface Fc sandwiches from the inflection point v to the edge Pc of the flange curved surface Fc. The edge opening angle θc is set to about 110 to 135 °.

  These rim shapes define the tire outer surface 5 including the shape of the bead surface 4 in a region where the tire 1 is in contact with the rim 6 in a state where the tire is assembled with rims and filled with normal internal pressure, and the rim shape is set. Therefore, as described above, the rim 1 and the low-flat pneumatic tire 1 for an automobile are selected so that the contact is appropriate and not excessive based on the regulation of the regular rim.

  The tire 1 includes a bead bottom surface 14 of the tire T seated on the rim seat surface 9 and a bead outer surface 15 in contact with the rim flange surface Fr at the bead portion. The rim flange curved surface Fc has a sidewall reference arc Cs having a center Rso on a tire axial direction line Xm passing through the tire maximum width position Wm and having a side reference radius Rs passing through the tire maximum width position Wm. The flange curved surface Fc is contacted. When the point where the sidewall reference arc Cs contacts the rim flange curved surface Fc is defined as the flange reference contact Ps, the bead surface 4 contacts the flange curved surface Fc in a range up to the end point Pe exceeding the flange reference contact Ps. Yes.

  The range between the inflection point v and the terminal point Pe is called a bead arc contact surface Tr, and the opening angle θ of the bead arc contact surface Tr is 45 ° or more and 80 ° or less. The lower limit is more preferably 50 ° or more, and the upper limit is more preferably less than 70 °. In this way, the opening angle θ is a wide angle, and the flange curved surface Fc is extended and formed outward in the tire axial direction, so that the input at the time of impact such as riding on the road curb while running is alleviated by spreading and pinching cut Occurrence can be prevented. If the angle is less than 45 °, the area of the flange curved surface Fc is insufficient, which may cause a pinch cut with respect to impact input. Conversely, if the angle exceeds 80 °, the rim assembly property deteriorates, and the tire 1 and the rim 6 There is a possibility of poor fitting.

  Further, in the present embodiment, the bead surface 4 (in this specification, the bead surface 4 including a region in contact with the flange curved surface Fc when a load is applied and a region 5 mm above the radial direction) is referred to from the terminal point Pe. The additional point height Ha obtained by adding 0 to 5 mm to the flange total height Hg outwardly in the radial direction with a curved surface parallel to the sidewall reference arc Cs or a substantially parallel straight line (in this embodiment, a straight line). The protrusion area 17a extends to the additional point Pa.

  The raised region 17 is connected from the additional point Pa of the projecting surface 17a to the tire outer surface 5 using a joint surface 17b having a curvature radius R17b of about 1.0 to 4.0 mm, and in this embodiment, the additional point Pa. And the tire maximum width position Wm, the tire outer surface 5 is formed by the reference sidewall surface Tr. The joint surface 17b is preferably in contact with the tire outer surface 5 smoothly.

  When the raised region 17 is deformed, the projecting surface 17a is in contact with the flange curved surface Fc to protect the bead portion and disperse the stress, thereby preventing damage such as pinch cut. In the above-mentioned 0 to 5 mm which is the difference between the additional point height Ha of the additional point Pa and the total flange height Hg, if it is smaller than 0, the raised region 7 becomes too small and the rigidity is insufficient. If the difference exceeds 5 mm, the rigidity becomes excessive and an effective stress dispersion effect cannot be obtained. Preferably it is 2-4 mm.

  Further, in the raised region 7, the raised height t1, which is the minimum distance from the sidewall reference plane Cs, is determined by the side reference radius Rs and the difference between the added point height Ha and the flange total height Hg. The thickness is about 1.5 to 5.0 mm. The lower limit is more preferably 2.0 mm or more, and the upper limit is more preferably 4.0 mm or less.

  Thus, in the case of including a raised region having a protruding surface extending from the end point Pe of the bead arc contact surface Tf to the additional point Pa of the additional point height Ha obtained by adding 0 to 5 mm to the flange total height Ha. The support rigidity of the bead surface at the time of large deformation that generates a pinch cut in which the contact pressure increases as the upper part of the flange increases, stress distribution at the time of large deformation is achieved, and the radial direction between the terminal point Pe and the additional point Pa By setting the height difference to 0 to 5 mm, an excessive increase in rigidity in the raised region is prevented, and a stress dispersion effect is achieved. Further, since the raised region is formed by a curved surface parallel to the sidewall reference arc Cs or a substantially parallel straight line and there is no increase in thickness, it is possible to prevent rim displacement without raising the bead portion during deformation.

  Furthermore, FIG. 3 shows the case where the recessed part 20 extended in the circumferential direction is formed in the said bead surface 4 on the radial direction outer side of the said addition point Pa. FIG. The recess 20 disperses the stress by releasing the contact pressure with the rim 6 generated at the time of impact generated during traveling, thereby preventing the occurrence of pinch cuts. Also in this embodiment, the sidewall surface 3 is formed by the sidewall reference arc Cs.

  The recess 20 has a recess radius Re of 2.0 mm or more and 5.0 mm or less, and a recess depth De from the sidewall reference arc Cs of 0.3 mm to 2.0 mm or less. The part length L20 is formed to be about 3 to 8 mm, and the joint surface 17b of the raised region 17 is continuously formed from the additional point Pa with the punch radius Re. In addition, the recessed part 20 can also be formed as a recessed groove | channel which was not a simple circular arc shape, and the bottom face was flat.

  The bore radius Re is preferably 3.0 mm or more for the lower limit and more preferably 4.5 mm or less for the upper limit. If it is less than 2.0 mm, the surface distortion of the tire outer surface 5 during normal running may be excessive, which may cause cracks. Conversely, if it exceeds 5.0 mm, it is difficult to obtain a stress dispersion effect.

  Further, the bore depth De is preferably 0.5 mm or more for the lower limit and more preferably 2.0 mm or less for the upper limit. If it is less than 0.3 mm, the effect of releasing the contact pressure cannot be obtained. Conversely, if it exceeds 2.0 mm, a problem of stress concentration occurs.

  FIG. 4 shows that the outer surface 5 of the tire protrudes outward from the side wall reference arc Cs on the radially outer side of the recess 20, and ribs 22 are formed in the circumferential direction to prevent internal components in the vulcanization process from being disturbed. Example of the present invention is shown. The rib 22 has a protruding surface 22a formed of a curved surface substantially parallel to the sidewall reference arc Cs or a substantially parallel plane, and the protruding height t2 of the protruding surface 22a from the sidewall reference arc Cs is: In this embodiment, the height is set equal to the raised height t1 of the raised area 17. In addition, protrusion height t2 is about 1.0-5.0 mm, and can be made larger or smaller than the protrusion height t1.

  Further, the protrusion length Lt of the protruding surface 22a along the protruding surface 22a is set to 2.0 mm or more and 5.0 mm or less. The lower limit is more preferably 2.5 mm or more, and the upper limit is more preferably 4.0 mm or less. If it is less than 2.0 mm, it is inferior in the effect which suppresses disturbance to an internal component in the said vulcanization process, and conversely exceeding 5.0 mm is unnecessary in the normal case.

  Further, the joint surface 22b below the lower end of the protruding surface 22a can continue the punch radius Re of the recess 20, and the joint surface 22c above the upper end is formed in the same manner as the joint surface 17b of the raised region 17. be able to. Various shapes can be selected for the upper and lower joint surfaces 22b and 22c.

  FIG. 5 shows another aspect in which the protruding height t3 of the protruding surface 22a of the rib 22 from the side wall reference arc Cs is, for example, about 10 to 15 mm, which is significantly larger than the case of FIG. Yes. Such a rib 22 can function as a protector that prevents damage to the bead portion due to contact with the road shoulder surface.

  FIG. 6 shows that the bead surface 4 includes the raised region 17 between the terminal point Pe and the additional point height Ha, and between the additional point height Ha and the maximum tire width position Wm. An embodiment is shown in which a modified sidewall surface Cr using the side modified radius Rr and a joint arc Cj connected from the lower end to the additional point Pa of the raised region 17 are shown.

  The side correction radius Rr is 0.80 to 0.95 times the side reference radius Rs of the sidewall reference arc Cs, and is centered on the center Rro on the tire axial direction line Xm passing through the tire maximum width position Wm. To do. Thus, by forming the tire outer surface 5 radially outside the raised region 7 with the modified sidewall surface soot Tr having a smaller diameter than the sidewall reference arc Cs, the raised region 7 can be used in the vulcanization process of tire manufacture. It becomes easy to arrange the necessary rubber gauge.

  If the side correction radius Rr is less than 0.80 times the side reference radius Rs, the rigidity of the raised region 17 becomes too low. Conversely, if the side correction radius Rr exceeds 0.95 times, the effect of providing Rr is not obtained.

  The joint arc Cj is in contact with the modified sidewall surface Cj and extends radially inward to the additional point Pa of the raised region 7, and the joint arc radius Rcj is, for example, in the range of about 2.0 to 5.0 mm. Is preferred.

  In the embodiment illustrated in FIG. 7, the tire outer surface 5 including the bead surface 4 has a modified sidewall surface Cr having a side modified radius Rr between the terminal point Pe and the maximum tire width position Wm. The case where it is formed by a joint arc Cj connecting the lower end and the end point Pe is illustrated. As described above, the modified sidewall surface Cr is formed with a side modified radius Rr that is 0.80 to 0.95 times the side reference radius Rs. By configuring in this way, a raised region 17 having a triangular cross section with the end point Pe as an apex can be formed, and this raised region 17 also helps control the rubber gauge in the tire vulcanization process.

  As in the embodiment shown in FIG. 6, the joint arc Cj is in contact with the modified sidewall surface Ce and extends radially inward to the additional point Pa of the raised region 7, and the joint arc radius Rcj is, for example, A range of about 2.0 to 5.0 mm is preferable.

  A tire with a tire size of 205 / 55R16 was prototyped according to the specifications shown in Table 1, and assembled to the rim (16 x 6.5J) with regular internal pressure, and mounted on all wheels of a vehicle (domestic 2000cc). A 10 cm high curb ride test was conducted. The test method was repeated at the speed gradually increased from the low speed to repeat the above-mentioned passing test. The test was terminated when a clear cut was generated in the bead portion or an air leak occurred, and the speed at the end time was measured. It shows. The higher the end speed, the better the performance.

1 is a tire meridian cross-sectional view illustrating an embodiment of the present invention. It is a diagram which expands and shows the shape of the principal part. It is a diagram which illustrates embodiment which provides a crevice. 1 is an enlarged diagram illustrating an embodiment having ribs. FIG. FIG. 6 is an enlarged diagram illustrating another embodiment comprising a rib. FIG. 6 is an enlarged diagram illustrating an embodiment having a modified sidewall surface. FIG. 6 is an enlarged diagram illustrating still another embodiment having a modified sidewall surface. It is sectional drawing which shows a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Low flat pneumatic tire for motor vehicles 2 Tread surface 3 Side wall surface 4 Bead surface 5 Tire outer surface 6 Rim 17 Raised area 17a Projection surface 17b Joint surface 20 Concave portion 22 Rib 22a Projection surface Cj Joint arc Cs Side wall reference arc De F Flange Fc Rim curved surface Fr Rim flange surface Ha Additional point height Hg Flange total height Hv Inflection point height Lt Projection height Pa Additional point Pe End point Ps Flange reference contact Rr Side correction radius Rs Side reference radius Tf Flange contact surface Tr Modified sidewall surface v Inflection point Wm Tire maximum width position

Claims (6)

A low-flat pneumatic tire for automobiles having a tire outer surface composed of a tread surface, sidewall surfaces at both ends and a bead surface, and a rim assembled to the rim and filled with normal internal pressure, the rim being a bead baseline A rim flange surface Fr extending linearly outward from Lb to an inflection point v having an inflection point height Hv, and a center on a tire axial direction line passing through the inflection point v, and the rim at the inflection point v A flange F having a flange curved surface Fc with a flange radius Rf in contact with the flange surface Fr;
The bead surface has a center on a tire axial line Xm passing through the tire maximum width position Wm, and a side wall reference arc Cs having a side reference radius Rs passing through the tire maximum width position Wm is the flange curved surface Fc. In contact with the flange curved surface Fc in the range of the bead arc contact surface Tf to the end point Pe beyond the flange reference contact Ps in contact with
The inflection point height Hv is 7.5 mm or more and 10.0 mm or less, the flange radius Rf is 8.5 mm or more and 11.0 mm or less, and the total flange height Hg of the inflection point height Hv and the flange radius Rf. (= (Hv + Rf)) is 17.0 mm or more and 20.5 mm or less, and the opening angle θ of the bead arc contact surface Tr to the terminal point Pe is 45 ° or more and 80 ° or less. Low flat pneumatic tire for use.   The bead surface is an additional point obtained by adding 0 to 5 mm to the total height Hg of the flange radially outward from a curved surface parallel to the sidewall reference arc Cs or a substantially parallel straight line from the end point Pe. 2. A low flat pneumatic tire for an automobile according to claim 1, further comprising a raised region having a projecting surface extending to an additional point Pa having a height Ha.   The bead surface has an outside radius Re of 2.0 mm or more and 5.0 mm or less and an outside depth De from the side wall reference arc Cs of 0.3 mm to 2.0 mm on the radially outer side of the additional point Pa. 3. The low flat pneumatic tire for automobiles according to claim 2, wherein a recess extending in the circumferential direction is formed.   The outer surface of the tire has a rib that protrudes outward from the sidewall reference arc Cs on the radially outer side of the recess and extends in the circumferential direction with a projection length Lt along the sidewall surface of 2.0 mm or more and 5.0 mm or less. The low flat pneumatic tire for automobiles according to claim 3, which is formed.   The tire outer surface is a raised area extending between the terminal point Pe and the additional point height Ha along a curved surface parallel to the sidewall reference surface or a substantially parallel straight line, and an additional point height. Between Ha and the tire maximum width position Wm, a modified sidewall surface using a side modified radius Rr 0.80 to 0.95 times the side reference radius Rs, and a joint arc Cj continuous from the lower end to the raised region The low flat pneumatic tire for automobiles according to claim 1, wherein   The tire outer surface has a corrected sidewall having a side correction radius Rr that is 0.80 to 0.95 times the side reference radius Rs of the sidewall reference surface between the terminal point Pe and the maximum tire width position Wm. The low flat pneumatic tire for automobiles according to claim 1, wherein the low flat pneumatic tire for automobiles is formed by a surface, a joint arc Cj connecting the lower end and the end point Pe.

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