Abstract:
In a peripheral length adjusting apparatus and a peripheral length adjusting method for an endless metallic ring, an endless metallic ring is wound on plural rollers, and an interval between the plural rollers is enlarged such that the endless metallic ring is stretched while the plural rollers are rotated, whereby the endless metallic ring is plastically deformed and a peripheral length of the endless metallic ring is adjusted to a target peripheral length. In the peripheral length adjusting apparatus and the peripheral length adjusting method, the peripheral length of the endless metallic ring before adjustment is measured, and the peripheral length of the endless metallic ring is adjusted to the target peripheral length by enlarging the interval between the rollers based on the measured peripheral length such that the peripheral length of the endless metallic ring at the time of adjustment is longer than the target peripheral length by a contraction amount due to elastic deformation of the endless metallic ring after adjustment.

Description:
INCORPORATION BY REFERENCE  
         [0001]    The disclosure of Japanese Patent Application No. 2003-034616 filed on Feb. 13, 2003, including the specification, drawings and abstract is incorporated herein by reference in its entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to an endless metallic belt formed by annularly arranging multiple plate-shaped elements that face each other, and passing an endless metallic ring through the elements so as to annularly join the elements. More particularly, the invention relates to a peripheral length adjusting apparatus and a peripheral length adjusting method which improves an accuracy of a peripheral length of an endless metallic ring.  
           [0004]    2. Description of the Related Art  
           [0005]    There is a vehicle including a continuously variable transmission (hereinafter, referred to as “CVT”) which continuously adjusts a speed ratio according to a running state of the vehicle. The CVT can efficiently transmit an engine output, and contributes to improving fuel efficiency and running performance. In one of CVTs that are put into practical use, a metallic belt and a pair of pulley are used, and an effective radius of each pulley is changed by a hydraulic pressure such that the speed ratio is continuously changed. In this CVT, an endless metallic belt is wounded on an input side pulley fitted to an input shaft and an output side pulley fitted to an output shaft. Each of the input side pulley and the output side pulley includes a pair of sheaves in which a groove width can be continuously changed. By changing the groove width of each of the input side pulley and the output side pulley, a belt-winding radius with respect to each of the input side pulley and the output side pulley is changed. Thus, a ratio between the rotational speed of the input shaft and the rotational speed of the output shaft, that is, the speed ratio can be continuously changed.  
           [0006]    Conventionally, a metallic ring which is used for such an endless metallic belt is produced in the following manner. First, both ends of a thin plate of super-strong steel such as maraging steel are bonded by welding such that a ring-shaped drum is formed. Then, the drum is cut at a predetermined width, and is rolled out, whereby a metallic ring with a predetermined thickness is obtained. The metallic ring with the predetermined thickness obtained by rolling is subjected to solution heat treatment, and then peripheral length adjusting processing, whereby the peripheral length of the metallic ring is adjusted to a desired peripheral length. Further, the metallic ring is subjected to aging treatment and nitriding treatment, whereby hardness of the metallic ring is increased. Plural metallic rings with peripheral lengths which are slightly different from each other are laminated to be used for the endless metallic belt. Accordingly, the peripheral length adjusting processing is extremely important for laminating plural metallic rings to be used for the endless metallic belt.  
           [0007]    Japanese Patent Laid-Open Publication No. 11-290971 discloses a peripheral length adjusting apparatus which performs peripheral length adjusting processing. The apparatus includes a drive roller and a driven roller on which a metallic ring is wound, and a correction roller which is provided between the drive roller and the driven roller.  
           [0008]    In the peripheral length adjusting apparatus disclosed in Japanese Patent Laid-Open Publication No. 11-290971, the metallic ring is wound on the drive roller, the driven roller, and the correction roller. First, the driven roller is displaced such that the metallic ring is tensed. Then, while the drive roller is rotated, a displacement amount of the driven roller is measured by a displacement sensor with the metallic ring being tensed. An actual peripheral length of the metallic ring is calculated based on a center distance between the drive roller and the driven roller. Based on a difference between the actual peripheral length thus obtained and a desired peripheral length, a displacement amount of the correction roller, which is required for adjusting the peripheral length of the metallic ring to the desired peripheral length, is calculated. By applying urging force to the correction roller so as to move the correction roller by the calculated displacement amount, the metallic ring is plastically deformed. When the actual displacement amount of the correction roller matches the calculated displacement amount, application of the urging force to the correction roller is cancelled. The actual peripheral length of the metallic ring after the adjusting processing is calculated based on the center distance between the drive roller and the driven roller while the metallic ring is tensed by the driven roller. A difference between the actual peripheral length after the adjusting processing and the desired peripheral length is obtained. When the actual peripheral length matches the desired peripheral length, the operation is finished.  
           [0009]    According to such a peripheral length adjusting method, an operation of applying the urging force to the correction roller needs to be repeated plural times until the actual peripheral length of the metallic ring is adjusted to the desired peripheral length, which is troublesome. Japanese Patent Laid-Open Publication No. 2001-105050 discloses a peripheral length correction method for a metallic ring which can adjust a peripheral length of a metallic ring to a desired peripheral length easily and reliably.  
           [0010]    The peripheral length correction method disclosed in Japanese Patent Laid-Open Publication No. 2001-105050 includes the steps of winding a metallic ring on a drive roller and a driven roller which can be relatively displaced in a displacement direction so as to be away from each other, and a correction roller which is provided between the drive roller and the driven roller, and which can be displaced in a direction orthogonal to the displacement direction of the drive roller and the driven roller; maintaining the drive roller and the driven roller at a predetermined interval, and displacing the correction roller by a predetermined displacement amount with respect to a reference value of the peripheral length of the metallic ring in the direction which is orthogonal to the displacement direction of the drive roller and the driven roller and in which the metallic ring is stretched; obtaining an actual peripheral length of the metallic ring which is wounded on the drive roller, the driven roller, and the correction roller, while the drive roller and the driven roller are relatively displaced in the displacement direction so as to be away from each other by predetermined force, and the metallic ring is tensed by the drive roller and the driven roller; comparing the actual peripheral length of the metallic ring and the reference value of the peripheral length of the metallic ring so as to obtain a difference therebetween; and correcting the displacement amount of the correction roller according to the difference between the actual peripheral length of the metallic ring and the reference value.  
           [0011]    According to the peripheral length correction method disclosed in Japanese Patent Laid-Open Publication No. 2001-105050, the drive roller and the driven roller on which the metallic ring is wounded are maintained at the predetermined interval, and the correction roller which is provided between the drive roller and the driven roller is displaced in the direction which is orthogonal to the displacement direction of the drive roller and the driven roller, and in which the metallic ring is stretched, whereby the metallic ring is plastically deformed, and the peripheral length is adjusted. Basically, the correction roller is displaced by the predetermined displacement amount with respect to the reference value of the peripheral length of the metallic ring. As the reference value, for example, a value which is set, for design and process management, as the peripheral length of the metallic ring after the rolling processing and the solution heat treatment is employed. The actual peripheral length of the metallic ring is obtained while the drive roller and the driven roller are relatively displaced in the displacement direction so as to be away from each other by predetermined force, and the metallic ring is tensed by the drive roller and the driven roller. Then, the difference between the actual peripheral length and the reference value is obtained, and the displacement amount of the correction roller is adjusted according to the difference. Therefore, the displacement amount of the correction roller with respect to the actual peripheral length can be obtained based on the reference value. Accordingly, the peripheral length of the metallic ring can be adjusted to the desired peripheral length easily and reliably by performing the operation of displacing the correction roller only once, and the yield can be enhanced.  
           [0012]    After the endless metallic ring whose peripheral length is thus adjusted is removed from the drive roller and the driven roller, the peripheral length of the endless metallic ring is contracted due to elastic deformation, as compared with when the peripheral length is adjusted. It is possible to enlarge the interval between the rollers for adjusting the peripheral length considering such a contraction amount of the peripheral length (hereinafter, referred to as “spring back amount”). However, the spring back amount varies according to the peripheral length of the endless metallic ring before adjustment. Since the peripheral length of the endless metallic ring before adjustment has a deviation, the accuracy of the peripheral length of the endless metallic ring deteriorates.  
         SUMMARY OF THE INVENTION  
         [0013]    In view of the above, it is an object of the invention to provide a peripheral length adjusting apparatus and a peripheral length adjusting method which improves an accuracy of a peripheral length of an endless metallic ring.  
           [0014]    An aspect of the invention relates to a peripheral length adjusting apparatus for an endless metallic ring in which an endless metallic ring is wound on plural rollers, and an interval between the plural rollers is enlarged such that the endless metallic ring is stretched while the plural rollers are rotated, whereby the endless metallic ring is plastically deformed and a peripheral length of the endless metallic ring is adjusted to a target peripheral length. The peripheral length adjusting apparatus includes a peripheral length measuring device which measures the peripheral length of the endless metallic ring before the peripheral length is adjusted; and an adjusting device which adjusts the peripheral length of the endless metallic ring to the target peripheral length by enlarging the interval between the rollers based on the measured peripheral length such that the peripheral length of the endless metallic ring when the peripheral length is adjusted is longer than the target peripheral length by a contraction amount due to elastic deformation of the endless metallic ring after the peripheral length is adjusted.  
           [0015]    In the aforementioned peripheral length adjusting apparatus for an endless metallic ring, the adjusting device adjusts the peripheral length of the endless metallic ring to the target peripheral length by enlarging the interval between the rollers. At this time, the adjusting device enlarges the interval between the rollers based on the peripheral length before adjustment such that the peripheral length of the endless metallic ring when the peripheral length is adjusted is longer than the target peripheral length by the contraction amount due to elastic deformation of the endless metallic ring after adjustment. Thus, since the peripheral length is adjusted considering the contraction amount due to elastic deformation based on the peripheral length before adjustment, an accuracy of the peripheral length of the endless metallic ring does not deteriorate even when the peripheral length of the endless metallic ring before adjustment has a deviation. Accordingly, it is possible to provide the peripheral length adjusting apparatus which improves the accuracy of the peripheral length of the endless metallic ring.  
           [0016]    Another aspect of the invention relates to a peripheral length adjusting method for an endless metallic ring in which an endless metallic ring is wound on plural rollers, and an interval between the plural rollers is enlarged such that the endless metallic ring is stretched while the plural rollers are rotated, whereby the endless metallic ring is plastically deformed and a peripheral length of the endless metallic ring is adjusted to a target peripheral length. The peripheral length adjusting method includes the steps of: measuring the peripheral length of the endless metallic ring before the peripheral length is adjusted; and adjusting the peripheral length of the endless metallic ring to the target peripheral length by enlarging the interval between the rollers based on the measured peripheral length such that the peripheral length of the endless metallic ring when the peripheral length is adjusted is longer than the target peripheral length by a contraction amount due to elastic deformation of the endless metallic ring after the peripheral length is adjusted.  
           [0017]    In the aforementioned peripheral length adjusting method, since the peripheral length is adjusted considering the contraction amount due to elastic deformation based on the peripheral length before adjustment, an accuracy of the peripheral length of the endless metallic ring does not deteriorate even when the peripheral length of the endless metallic ring before adjustment has a deviation. Accordingly, it is possible to improve the accuracy of the peripheral length of the endless metallic ring. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    The above mentioned embodiment and other embodiments, objects, features, advantages, technical and industrial significance of this invention will be better understood by reading the following detailed description of the exemplary embodiments of the invention, when considered in connection with the accompanying drawings, in which:  
         [0019]    [0019]FIG. 1 is a sectional view showing a CVT using an endless metallic belt whose peripheral length is adjusted by a peripheral length adjusting apparatus according to an embodiment of the invention;  
         [0020]    [0020]FIG. 2 is a partial perspective view describing the endless metallic belt;  
         [0021]    [0021]FIG. 3 is a perspective view showing an entire configuration of the endless metallic belt;  
         [0022]    [0022]FIG. 4 is a front view of an element;  
         [0023]    [0023]FIG. 5 is a side view of the element;  
         [0024]    [0024]FIG. 6 is a schematic view showing a peripheral length adjusting apparatus according to the embodiment of the invention;  
         [0025]    [0025]FIG. 7 is a graph showing a relationship between a volume of a hoop before a peripheral length thereof is adjusted and a spring back rate;  
         [0026]    [0026]FIG. 8 is a graph showing a relationship between a temperature of a hoop when the peripheral length thereof is adjusted and the spring back rate; and  
         [0027]    [0027]FIG. 9 is a flowchart showing a procedure of control for deciding the peripheral length at the time of adjustment, which is performed in the peripheral length adjusting apparatus according to the embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    In the following description and the accompanying drawings, the present invention will be described in more detail in terms of exemplary embodiments.  
         [0029]    Hereinafter, the embodiment of the invention will be described with reference to the accompanying drawings. In the following description, like components are denoted by like reference numerals. Names and functions thereof are the same. Therefore, detailed description thereof will not be repeated.  
         [0030]    First, an endless metallic belt and a CVT using the endless metallic belt will be described. The endless metallic belt is formed by annularly arranging multiple elements that face each other in a plate thickness direction, and passing a hoop as an endless metallic ring through each of right and left saddle portions of the elements so as to annularly combine the elements.  
         [0031]    Referring to FIG. 1, a CVT  100  using an endless metallic belt will be described. The endless metallic belt is formed using the hoop whose peripheral length is adjusted by a peripheral length adjusting apparatus according to the embodiment of the invention. In the CVT  100 , an endless metallic belt  106  is wound on an input side pulley  220  fitted to an input shaft  200  and an output side pulley  320  fitted to an output shaft  300 .  
         [0032]    Each of the input side pulley  220  and the output side pulley  320  includes a pair of sheaves  108  in which a groove width can be continuously changed. The groove width of each of the input side pulley  220  and the output side pulley  320  is changed using a hydraulic pressure circuit that is controlled according to a running state of a vehicle, whereby each of the belt-winding radii of the endless metallic belt  106  with respect to the input side pulley  220  and the output side pulley  320  is changed. Thus, the ratio between the rotational speed of the input shaft  200  and the rotational speed of the output shaft  300 , that is the speed ratio can be continuously changed.  
         [0033]    Referring to FIG. 2, the endless metallic belt  106  will be described. The endless metallic belt  106  is formed by annularly arranging multiple elements  102  that face each other in a plate thickness direction, and passing a hoop  104  as an endless metallic ring through each of right and left saddle portions of the elements so as to annularly join the elements  102 , as shown in FIG. 3.  
         [0034]    An example of a shape of the element  102  is shown in FIG. 4 and FIG. 5. Both side surfaces of the element  102  in the width direction are referred to as sheave-contacting friction surfaces  112 . The sheave-contacting friction surfaces  112  are tapered surfaces, and contact and match tapered sheave surfaces  110  of the sheaves  108 . A neck portion  116  extending upward is provided in a center portion in the width direction of a base body portion  114  including the sheave-contacting friction surfaces  112 . The neck portion  116  is continuous to a top portion  118  extending in a lateral direction. Slits  126  are formed between the top portion  118  extending in the lateral direction and the base body portion  114 . Each hoop  104  is passed through each of the two slits  126  on the right and left sides. A surface of the base body portion  114  which each hoop  104  contacts is referred to as a saddle surface  120 .  
         [0035]    The height of the saddle surfaces  120  is expressed as a dimension from a pitch line P which transverses the base body portion  114 . The width of the element  102  is expressed as a dimension on the pitch line P. A convex portion  122  is formed on one of both surfaces of the element  102  at a position above the neck portion  116 . Also, a dimple  123  is formed on the other of both surfaces of the element  102  at the position above the neck portion  116 . Thus, the convex portion  122  and the dimple  123  of the elements  102  which are adjacent to each other are fitted to each other. The surface of the element  102  including the convex portion  122  is regarded as a front surface of the element  102 . The surface of the element  102  including the dimple  123  is regarded as a rear surface of the element  102 .  
         [0036]    As shown in FIG. 4, each saddle surface  120  has a curved convex shape. Each hoop  104  contacts each saddle surface  120  along the curved shape.  
         [0037]    The endless metallic belt  106  is sandwiched between the pair of sheaves  108 . Since the sheave surfaces  110  and the sheave-contacting friction surfaces  112  are tapered surfaces, a load is applied to each element  102  toward the outside in the radial direction due to pressing force of the sheaves  108 . However, since the elements  102  are joined by the hoop  104 , movement of the elements  102  toward the outside in the radial direction is restricted by tension of the hoop  104 . As a result, due to shearing force of an oil between the sheave surfaces  110  and the sheave-contacting friction surfaces  112 , frictional force is generated. Thus, torque is transmitted between the sheaves  108  and the endless metallic belt  106 .  
         [0038]    More particularly, the hoop  104  includes 9 to 12 hoops which are laminated, and joins the elements  102 , as shown in FIG. 2 and FIG. 4 (however, it is shown that the hoop  104  includes 3 hoops instead of 9 to 12 hoops in FIG. 2 and FIG. 4). In this case, as the hoop  104  is arranged as a lower layer, the peripheral length thereof is shorter. As the hoop  104  is arranged as a higher layer, the peripheral length thereof is longer.  
         [0039]    Thus, the endless metallic belt  106  is configured using the hoop  104  which includes 9 to 12 hoops  104 . The peripheral length of each of the laminated hoops  104  is fine-adjusted. In a process of producing the hoop  104 , a thin plate of steel material such as maraging steel is formed into a drum shape by welding. Then, in order to uniformize the composition of the welded portion, solution heat treatment is performed on the plate. As the solution heat treatment, for example, heat treatment is performed in a vacuum furnace for a predetermined time at a predetermined temperature. The thin plate of steel material having the drum shape is cut into hoops each of which has a predetermined width, and the peripheral length and the thickness of each hoop is made uniform. Then, in order to remove processing residual stress, solution heat treatment is performed on the hoops. Subsequently, the peripheral length of each hoop  104  is fine-adjusted. In the process of this fine-adjustment, the peripheral length adjusting apparatus according to the embodiment of the invention is used.  
         [0040]    [0040]FIG. 6 is a schematic side view showing a peripheral length adjusting apparatus  1000  according to the embodiment of the invention. The peripheral length adjusting apparatus  1000  includes a first roller  1010  and a second roller  1020  on which a hoop  104  is wound, a drive mechanism  1012  for the first roller, a drive mechanism  1022  for the second roller, a moving mechanism  1040  for the second roller, a detecting portion  1030  which detects a moving amount of the second roller  1020 , and a temperature sensor  1050  which measures the temperature of the hoop  104  at the time of adjustment. The first roller  1010  is rotated by the drive mechanism  1012  and the second roller  1020  is rotated by the drive mechanism  1022 . The moving mechanism  1040  moves the second roller  1020  in a horizontal direction such that the interval between the second roller  1020  and the first roller  1010  is changed. The detecting portion  1030  detects the moving amount of the second roller  1020 .  
         [0041]    The peripheral length adjusting apparatus  1000  is controlled by a control portion (not shown). The control portion receives the moving amount of the second roller  1020  from the detecting portion  1030 , and the temperature of the hoop  104  from the temperature sensor  1050 . Also, the control portion receives the volume of the hoop  104  before adjustment of the peripheral length, and the peripheral length of the hoop  104  after adjustment.  
         [0042]    The control portion controls the moving mechanism  1040  for the second roller  1020  such that the interval between the relative positions of the first roller  1010  and the second roller  1020  becomes equal to a predetermined value. While the first roller  1010  and the second roller are in this state, the hoop  104  is wound on the first roller  1010  and the second roller  1020 . The control portion controls the rotation of the first roller  1010  and the rotation of the second roller  1020 . In addition, the control portion changes the interval between the first roller  1010  and the second roller  1020 . The control portion moves the second roller  1020  to a target position while rotating the first roller  1010  and the second roller  1020 . Thus, predetermined stretching force (F) is applied to the hoop  104 , which makes it possible to adjust the peripheral length of the hoop  104  to a target peripheral length. At this time, a speed at which the second roller  1020  is moved is set to a speed at which a load (load in a plastic zone) that causes plastic deformation can be applied to the hoop  104 .  
         [0043]    Then, the second roller  1020  is moved to a position such that the peripheral length of the hoop  104  is adjusted to a peripheral length which is longer than the target peripheral length by a contraction amount. Movement of the second roller  1020  is stopped at this position, and thus the process of stretching the hoop  104  is completed. In this process, a rate of the contraction amount may be considered instead of the contraction amount. The contraction amount signifies a length obtained by subtracting a peripheral length L( 3 ) of the hoop  104  which is measured after the hoop  104  is removed from the peripheral length adjusting apparatus  1000  from a peripheral length L( 2 ) of the hoop  104  at the time of adjustment by the peripheral length adjusting apparatus  1000 . The rate of the contraction amount signifies a value obtained by dividing the contraction amount by a peripheral length L( 1 ) of the hoop  104  before adjustment. Hereinafter, the contraction amount will be referred to as “spring back amount”, and the rate of the contraction amount will be referred to as “spring back rate”. The spring back rate is denoted by a reference character α.  
         [0044]    The spring back rate α varies according to the volume of the hoop  104  before adjustment, and the temperature of the hoop  104  at the time of adjustment. The control portion stores the change in the spring back rate α in a memory. FIG. 7 is a graph showing a relationship between the volume of the hoop  104  before adjustment and the spring back rate α. FIG. 8 is a graph showing a relationship between the temperature of the hoop  104  at the time of adjustment and the spring back rate α. As shown in FIG. 7, the control portion can calculate the spring back rate α based on the volume of the hoop  104  before adjustment. As shown in FIG. 8, the control portion can calculate the spring back rate α based on the temperature of the hoop  104  at the time of adjustment. The relationship between the volume of the hoop  104  and the spring back rate α shown in FIG. 7, and the relationship between the temperature of the hoop  104  and the spring back rate α shown in FIG. 8 are exemplary, and the invention is not limited to the relationships shown in FIG. 7 and FIG. 8.  
         [0045]    Referring to FIG. 9, description will be made of a control structure of a program for deciding the peripheral length when the peripheral length of the hoop  104  is adjusted, which is performed by the control portion in the peripheral length adjusting apparatus  1000  according to the embodiment of the invention.  
         [0046]    In step  100 , the control portion reads out, from the memory, the peripheral length L( 1 ) of the hoop  104  before adjustment. The peripheral length L( 1 ) of the hoop  104  before adjustment is stored in the memory in advance. In step S 110 , the control portion reads out, from the memory, an aiming peripheral length L( 4 ) of the hoop  104  which is the target peripheral length after adjustment by the peripheral length adjusting apparatus  1000 . In step S 120 , the control portion reads out, from the memory, the spring back rate α corresponding to the hoop  104  subjected to the peripheral length adjusting processing. The spring back rates a according to types of metal of the hoop  104  and the like are stored in the memory in advance.  
         [0047]    In step S 130 , the control portion makes a determination as to whether the spring back rate α needs to be corrected based on the volume of the hoop  104 , that is, a volume correction needs to be performed. This determination is made based on information input to the control portion. If the volume correction of the spring back rate α needs to be performed (i.e., YES in step S 130 ), the process proceeds to step S 140 . If not (i.e., NO in step S 130 ), the process proceeds to step S 160 .  
         [0048]    In step S 140 , the control portion calculates the volume of the hoop  104  before adjustment. The volume of the hoop  104  may be calculated based on the weight of the hoop  104  before adjustment and the density of the metal constituting the hoop  104 , or based on the width, the thickness, and the peripheral length of the hoop  104  before adjustment. In step S 150 , the control portion corrects the spring back rate α based on the volume calculated in step S 140 . At this time, the map shown in FIG. 7 is used.  
         [0049]    In step S 160 , the control portion makes a determination as to whether the spring back rate α needs to be corrected based on the temperature of the hoop  104 , that is, a temperature correction needs to be performed. This determination is made based on information input to the control portion. If the temperature correction of the spring back rate α needs to be performed (i.e., YES in step S 160 ), the process proceeds to step S 170 . If not (i.e., NO in step S 160 ), the process proceeds to step S 190 .  
         [0050]    In step S 170 , the control portion detects the temperature of the hoop  104  at the time of adjustment based on the information input from the temperature sensor  1050 . In step S 180 , the control portion corrects the spring back rate α based on the temperature detected in step S 170 . At this time, the map shown in FIG. 8 is used.  
         [0051]    In step S 190 , the control portion calculates the peripheral length L( 2 ) at the time of adjustment, using an equation L( 4 )+α×L ( 1 ). In step S 200 , the control portion expands the interval between the first roller  1010  and the second roller  1020  based on the peripheral length L( 2 ) at the time of adjustment, which was calculated in step S 190 . More particularly, the moving amount of the second roller  1020  is obtained using the interval between the first roller  1010  and the second roller  1020  which is calculated based on the peripheral length L( 2 ) at the time of adjustment. Then, the moving mechanism  1040  for the second roller is controlled such that a difference between the moving amount of the second roller  1020  which is detected by the detecting portion  1030  and the obtained moving amount becomes 0. Thus, the interval between the first roller  1010  and the second roller  1020  is adjusted.  
         [0052]    Description will be made of the operation of the peripheral length adjusting apparatus according to the embodiment of the invention, which is based on the structure and the flowchart described above.  
         [0053]    With regard to one hoop  104  subjected to the peripheral length adjusting processing, an operator measures the peripheral length L( 1 ) before adjustment, and makes the memory store the peripheral length L( 1 ). Also, the operator makes the memory store the aiming peripheral length L( 4 ) which is the target peripheral length of the hoop  104  after adjustment. Further, the operator makes the memory store the spring back rate α of the hoop  104 .  
         [0054]    Then, with regard to the hoop  104  subjected to the peripheral length adjusting processing, the peripheral length L( 1 ) before adjustment, the aiming peripheral length L( 4 ), and the spring back rate α of the hoop  104  are read out from the memory (steps S 100 , S 110 , S 120 ). If the volume correction needs to be performed (i.e., YES in step S 130 ), the volume of the hoop  104  before adjustment is calculated (S 140 ). The spring back rate α is corrected based on the calculated volume using the map shown in FIG. 7 (S 150 ). If the temperature correction needs to be performed (i.e., YES in step S 160 ), the temperature of the hoop  104  at the time of adjustment is detected (S 170 ), and the spring back rate α is corrected based on the detected temperature using the map shown in FIG. 8 (S 180 ).  
         [0055]    Based on the peripheral length L( 1 ) before adjustment, the aiming peripheral length L( 4 ), and the corrected spring back rate α, the peripheral length L( 2 ) at the time of adjustment is calculated using the equation L( 4 )+α×L ( 1 ) (S 190 ). Based on the calculated peripheral length L( 2 ) at the time of adjustment, the control portion controls the moving mechanism  1040  for the second roller so as to adjust the interval between the first roller  1010  and the second roller  1020  (S 200 ).  
         [0056]    As described above, in the peripheral length adjusting apparatus for an endless metallic ring according to the embodiment of the invention, the peripheral length at the time of adjustment is calculated considering the spring back amount. The spring back amount varies according to the peripheral length of the metallic ring before adjustment. Since the peripheral length at the time of adjustment is calculated based on the peripheral length before adjustment, the target peripheral length, and the spring back rate, the accuracy of the peripheral length of the endless metallic belt does not deteriorate even when the peripheral length of the endless metallic ring before adjustment has a deviation. The spring back rate varies according to the volume of the hoop before adjustment, and the temperature of the hoop at the time of adjustment as well. Since the spring back rate is corrected considering the volume of the hoop before adjustment and the temperature of the hoop at the time of adjustment, the peripheral length of the hoop can be adjusted without being influenced by variation in the volume of the hoop before adjustment or a change in the temperature of the hoop at the time of adjustment.  
         [0057]    The spring back rate may have a deviation due to a deviation of composition of the endless metallic ring resulting from a deviation of processing in a preparation process. In this case, with regard to approximately  10  endless metallic rings in each production lot, the peripheral length L( 3 ) after adjustment may be measured, and the interval between the first roller  1010  and the second roller  1020  which is calculated based on the peripheral length L ( 2 ) at the time of adjustment may be corrected such that a difference between the measured peripheral length L( 3 ) and the aiming peripheral length L( 4 ) becomes 0. More particularly, a correction value for the spring back rate α, which is set such that the difference between the average of the measured peripheral lengths L( 3 ) and the aiming peripheral length L( 4 ) becomes 0, may be calculated, and the spring back rate α may be corrected using the correction value. Alternatively, a correction value for the interval between the first roller  1010  and the second roller  1020  may be calculated, and the interval may be corrected using the correction value. When the interval between the first roller  1010  and the second roller  1020  at the time of adjustment is corrected, the peripheral length of the endless metallic ring can be adjusted to the target peripheral length with high accuracy even when the spring back rate has a deviation due to a deviation of composition of the endless metallic ring resulting from a deviation of processing in a preparation process.  
         [0058]    While the invention has been described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the exemplary embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.