Abstract:
The toroidal-type continuously variable transmission includes an input disk, an output disk disposed coaxially with the input disk, a trunnion capable of swinging about its pivot shaft portion situated at a torsional relation with respect to the respective center axes of the input and output disks; and a power roller supported on the trunnion and inclinably rollable on and between the input and output disks. The trunnion includes a main body plane portion for holding a displacement shaft supporting the power roller rotatably and a pair of pivot shaft portions respectively formed in the two end portions of the main body plane portion integrally therewith, while two connecting portions respectively between the main body plane portion and the pair of pivot shaft portions are respectively formed so as to include continuous metal flows.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a toroidal-type continuously variable transmission for an automobile and a method for manufacturing a trunnion for use in the present toroidal-type continuously variable transmission. 
     2. Description of the Related Art 
     Conventionally, a toroidal-type continuously variable transmission is known, for example, in Japanese Utility Model Unexamined Publication No. 62-71465 of Showa. That is, as shown in FIGS. 4 and 5, on a shaft  1 , there are rotatably supported an input disk  2  and an output disk  3  through needle shafts  4 . On the back surface side of the input disk  2 , a cam plate  5  is spline engaged with the shaft  1 , a plurality of rollers  6  are interposed between the cam plate  5  and input disk  2 , and there is disposed a pressure mechanism  7  of a loading cam type which is used to press the input disk  2  toward the output disk  3  side. The output disk  3  is engaged with an output gear  9  through a key  8 , so that the output disk  3  and output gear  9  are able to rotate synchronously with each other. 
     Between the input disk  2  and output disk  3 , there is interposed a trunnion  11  which is able to swing about a pivot shaft portion  10  and, in the central portion of the trunnion  11 , there is disposed a displacement shaft  12 . And, on the displacement shaft  12 , there is rotatably supported a power roller  13 . This power roller  13  includes a traction portion in contact with the input disk  2  and output disk  3 , while the power roller  13  is rollably contacted in such a manner that it can incline on and between the input disk  2  and output disk  3 . 
     Also, between the trunnion  11  and power roller  13 , there is disposed a power roller bearing  14 . This power roller bearing  14 , while carrying a load applied to the power roller  13  in its thrust direction, allows the rotation of the power roller  13 . In the power roller bearing  14 , a plurality of balls  15  are held by an annular retainer  17  which is interposed between an annular outer race  16  disposed on the trunnion  11  side and the power roller  13  serving as a rotary part. 
     Further, the trunnion  11  comprises a main body plane portion  18  and the above-mentioned pivot shaft portions  10  respectively formed integrally with the two end portions of the main body plane portion  18 ; and, in the main body plane portion  18 , there is formed a circular hole  19 . In the circular hole  19 , there is disposed a needle bearing  20 , so that the displacement shaft  12  is supported in a freely rotatable manner. Also, the two pivot shaft portions  10  respectively disposed on the two end sides of the trunnion  11  are respectively supported on a support plate  21  in such a manner that they can be swung with respect to the support plate  21 , whereby the inclination angle of the displacement shaft  12  can be freely adjusted by the swing motion of the trunnion  11 . 
     Further, to one end portion of each of the trunnions  11 , there is connected a drive rod  22 ; on the outer peripheral surface of the middle portion of the drive rod  22 , there is disposed a drive piston  23 ; and, a drive cylinder  24  is inserted into the drive piston  23 . 
     According to the above-structured toroidal-type continuously variable transmission, rotation transmitted to the cam plate  5  of the pressure device  7  from a drive source such as an engine is transmitted through the rollers  6  to the input disk  2 . The rotation of the input disk  2  is transmitted through the power roller  13  to the output disk  3 , while the rotation of the output disk  3  is taken out from the output gear  9 . 
     To change a rotation speed ratio between an input side and an output side, a pair of drive pistons  23  may be shifted in the mutually opposite directions. With such shifts of the drive pistons  23 , the trunnions  11  are also respectively shifted in the mutually opposite directions. This changes the direction of the tangential-direction force that acts on the contact portions between the peripheral surfaces  13   a  of the power rollers  13  and the inner peripheral surfaces  2   a ,  3   a  of the input and output disks  2 ,  3 ; and, with such change in the direction of this force, the trunnions  11  are respectively swung in the mutually opposite directions about their associated pivot shaft portions  10  pivotally supported by the support plate  21 . 
     By the way, as shown in FIG. 6, the conventional trunnion  11  is worked by cutting a blank material consisting of a round rod. And, in case the trunnion  11  is experimentally assembled into a toroidal-type continuously variable transmission and a large torque is repeatedly input to the toroidal-type continuously variable transmission, an excessive load is input to the power roller  13 , with the result that an excessive load is repeatedly applied to the trunnion  11  backing up the power roller  13 . 
     On the other hand, since the toroidal-type continuously variable transmission is carried on board a car, the trunnion  11  must also have the necessary and minimum dimension. Therefore, due to the large load repeatedly applied, the center portion of the main body plane portion  18  of the trunnion  11 , while supporting the two ends of the pivot shaft portions  10 , is bent repeatedly. That is, when the displacement is large, there is applied a force of 4t or more when the maximum load of the engine of the car is applied to the trunnion  11  in the maximum deceleration, so that there is applied to the trunnion  11  such a large bending stress as shown by a broken line in FIG.  6 . 
     As a result of this, the connecting portions A between the pivot shaft portions  10  and main body plane portion  18 , in which the stress becomes the highest, is pulled and returned back to their original conditions repeatedly; that is, the bending stress is applied collectively to the connecting portions A, so that the connecting portions A are finally cracked and broken. 
     The reason for this is believed that the conventional trunnion  11  is formed by cutting a round rod and thus, as shown in FIG. 7, metal flows  11   a  at the high-stress portions of the trunnion  11  are cut off. Therefore, the present inventors have conducted another test in which a trunnion  11  is formed by cutting a flat plate instead of the round rod. However, in this test as well, the results are similar to those in the former test. 
     SUMMARY OF THE INVENTION 
     The present invention aims at eliminating the drawbacks found in the conventional toroidal-type continuously variable transmission. Accordingly, it is an object of the invention to provide a toroidal-type continuously variable transmission which can prevent a trunnion against damage even when an excessive load is repeatedly applied thereto to thereby be able to enhance the durability of the trunnion and thus the toroidal-type continuously variable transmission. 
     In attaining the above object, according to the invention, there is provided a toroidal-type continuously variable transmission comprising: an input disk; an output disk disposed coaxially with the input disk; a trunnion capable of swinging about its pivot shaft portion situated at a torsional relation with respect to the respective center axes of the input and output disks; and a power roller supported on the trunnion and inclinably rollable on and between the input and output disks, wherein the trunnion comprises a main body plane portion for holding a displacement shaft supporting the power roller rotatably and a pair of pivot shaft portions respectively formed in the two end portions of the main body plane portion integrally therewith, while two connecting portions respectively between the main body plane portion and the pair of pivot shaft portions are respectively formed so as to include continuous metal flows. Here, “torsional relation” of the pivot shaft portion means a physical relation that the pivot shaft portion is disposed at position along an imaginary plane that is perpendicular to an imaginary line connecting the respective center axes of the input and output disks and distanced from the intersection of the imaginary plane and imaginary line. 
     Also, according to another aspect of the invention, there is provided a method for manufacturing the trunnion, wherein a blank material of the trunnion is disposed in upper and lower forging dies in such a manner that the metal flows of the blank material extend in parallel to the axial direction of the trunnion and, after then, the blank material is pressed in a direction at right angles to the axial direction of the present blank material, thereby producing the trunnion by forging. 
     In the trunnion, generally, an excessive stress is concentrated on the connecting portions between the main body plane portion and two pivot shaft portions. However, according to the present structure, since the metal flows of the blank material are allowed to extend along the configuration of the connecting portions, the metal flows are prevented from being cut in the portion where the stress is concentrated, which not only can enhance the strength of the trunnion but also, even when loads are input repeatedly, can prevent the trunnion from cracking to thereby be able to enhance the durability of the trunnion and thus the toroidal-type continuously variable transmission using such trunnion. 
     Also, in another aspect of the invention, in order that the metal flows of the blank material are allowed to extend along the connecting portions, the trunnion is manufactured by forging. To manufacture the trunnion by forging, at first, the blank material is disposed in the upper and lower forging dies in such a manner that the metal flows of the blank material extend in parallel to the trunnion axis direction and, after then, the blank material is forged in a direction at right angles to the axial direction of the blank material, that is, in the tightening direction of the upper and lower forging dies, so that the metal flows are made to extend along the connecting portions between the trunnion main body plane portion and the trunnion pivot shaft portions, thereby being able to enhance the strength of the connecting portions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A a longitudinal side section view showing a trunnion for use in a toroidal-type continuously variable transmission according to a first embodiment of the invention; 
     FIG. 1B is an enlarged longitudinal side section view showing a connecting portion between a pivot shaft portion and a main body plane portion of the trunnion; 
     FIGS. 2A to  2 D are longitudinal side section views of the trunnion, showing a process for manufacturing the trunnion; 
     FIG. 3 is a graphical representation of the results of a test conducted on the trunnion; 
     FIG. 4 is a longitudinal side section view of a conventional toroidal-type continuously variable transmission; 
     FIG. 5 is a section view taken along the line  5 — 5  shown in FIG. 4; 
     FIG. 6 is a longitudinal side section view of a conventional trunnion; and, 
     FIG. 7 is a longitudinal side section view of a conventional trunnion. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, a description will be given below of the preferred embodiments of the invention with reference to the accompanying drawings. 
     FIGS. 1A to  3  shows a first embodiment of a toroidal-type continuously variable transmission according to the invention and, in more particular, a trunnion employed in the first embodiment. In the present embodiment, a description will be given below of the present trunnion while the same components thereof as those in the conventional trunnion are given the same designations. Now, FIGS. 1A and 1B show a trunnion  11  employed in the present toroidal-type continuously variable transmission. The trunnion  11  comprises a main body plane portion  18  and two pivot shaft portions  10  respectively formed integrally with the two end portions of the main body plane portion  18 , while, in the main body plane portion  18 , there is formed a circular hole  19  which is used to hold a displacement shaft  10  through a needle bearing  20  in a freely rotatable manner. Also, the two pivot shaft portions  10  on the two end portion sides of the trunnion  11  are respectively supported on a support plate  21  in a freely swingable manner, whereby the inclination angle of the displacement shaft  12  can be freely adjusted due to the swing motion of the trunnion  11 . 
     Now, FIGS. 2A to  2 D show a process for manufacturing the trunnion  11 . Specifically, FIG. 2A shows a blank material  31  which consists of a round rod. This blank material  31  is made of chrome molybdenum steel (SCM)  445  having a carbon content of 0.45%; a surface portion hardness of the order of Rockwell C hardness (HRC)  61  and a core portion hardness of the order of HRC  36 , after the blank material  31  is thermally treated into a finished product as the trunnion  11 . Or, in the case of using SCM  435 , the blank material  31  is thermally treated using a carbon content of 0.35% in such a manner that, after completion of the blank material  31  as the trunnion  11 , the pivot shaft portion  10  of the trunnion  11  has a surface portion hardness of the order of HRC  59  and a core portion hardness of the order of HRC  32 . Or, in case of using SCM  45 C, the blank material  31  is thermally treated using a carbon content of 0.45% in such a manner that, after completion of the blank material  31  as the trunnion  11 , the pivot shaft portion  10  of the trunnion  11  has a surface portion hardness of the order of HRC  59  and a core portion hardness of HRC  38 . And, the blank material  31  has a plurality of metal flows  32  in the axial direction thereof. 
     Now, FIG. 2B shows a state in which the blank material  31  is set in a forging die  33 , while the forging die  33  is composed of an upper die portion  34  and a lower die portion  35 . A die split line  36  (see FIG. 2C) is formed in the vicinity of the center line of the pivot shaft portion  10  of the trunnion  11 , while the main body plane portion  18  of the trunnion  11  has steps respectively between its two end portions and center portion in such a manner that it can be divided in the vicinity of its center in the thickness thereof. And, the blank material  31  is disposed in the forging die  33  in such a manner that its metal flows  32  are parallel to the axial direction of the trunnion  11 . 
     Now, FIG. 2C shows a state in which the blank material  31  is held by and between the upper and lower die portions  34  and  35  of the forging die  33  and a forging operation is executed on the blank material  31  so as to press the blank material  31  in a direction at right angles to the axial direction of the blank material  31 . The blank material  31  is produced as a forged blank material  31   a  having a shape following the shapes of the upper and lower die portions  34  and  35  and, burrs  31 b are formed on the end faces of the pivot shaft portions  10 . 
     Now, FIG. 2D shows a state in which the forged blank material  31   a  is taken out of the forging die  33 , while, roughened surfaces  31   c  are left on the outer peripheral surface of the forged blank material  31   a.    
     Next, the burrs  31   b  and roughened surface  31   c  of the forged blank material  31  are cut by milling, and the forged blank material  31   a  is then thermally treated. After then, the forged blank material  31   a  is finish worked by grinding, so that there is completed such trunnion  11  as shown in FIG.  1 A. 
     In the trunnion  11  produced by forging in this manner, the metal flows  32  continue along the connecting portion A between the main body plane portion  18  and pivot shaft portion  10 . When the connecting portion A is enlarged, there can be obtained such a state as shown in FIG.  1 B. 
     That is, since, even when the trunnion  11  is manufactured by forging, it is finished using post-working such as cutting and grinding, it is difficult to leave, as they are, the metal flows  32  formed by forging in the finished trunnion  11 , with the result that, when cutting the connection portion A, the metal flows are actually cut off. 
     Accordingly, from the viewpoint of bending fatigue strength, the present inventors have conducted tests as to whether the sizes of inclination angles θ of the metal flows  32  in the connecting portion A have an influence on the strength of the trunnion. The connecting portion A is an angular portion having a substantially right angle; and, the connecting portion A includes a first surface X substantially parallel to the center S of the trunnion axis and a second surface Y substantially at right angles to the first surface X. In the tests, an inclination angle formed by the first surface X and the metal flow  32   a  that is nearest to the angular portion of the connecting portion A was expressed as θ 1 , an inclination angle formed by the second surface Y and the metal flow  32   a  that is nearest to the angular portion of the connecting portion A was expressed as θ 2 , a larger one of θ 1  and θ 2  was set as a trouble-free allowable angle θmax, and the allowable angle θmax was tested variously. The results of these tests have shown that the allowable angle θmax may be ≦30°, preferably, the allowable angle θmax may be ≦20°. 
     In the tests, there was used a toroidal-type continuously variable transmission of a double cavity type with a toroidal cavity diameter of 130 mm; and, the tests were repeated 1×10 6  times, which corresponds to the target number of times of repetitions of starting of a car, in the input conditions of the maximum deceleration ratio of 2.2 and an input torque of 340 Nm. The results of the tests are as shown in Table 1 and FIG.  3 . Specifically, there were as shown in Table 1 and FIG.  3 . Specifically, there were manufactured trunnions having different metal flow angles and these trunnions were tested each by twice. By the way, in FIG. 3, black round marks show the results of the first test, whereas black triangle marks show the results of the second test. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Angle of metal flow 
                   
               
               
                   
                 to surface of trun- 
               
               
                   
                 nion connecting 
                 Number of times of endurance 
               
               
                   
                 portion θmax 
                 repetitions and results 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Embodiment 1 
                 10° (Forging) 
                 Cut off by 5 × 10 6  and 5 × 10 6   
               
               
                 Embodiment 2 
                 20° (Forging) 
                 Cut off by 5 × 10 6  and 5 × 10 6   
               
               
                 Embodiment 3 
                 30° (Forging) 
                 Crack occurred in angular 
               
               
                   
                   
                 portion in 4.5 × 10 6  and 4.2 × 10 6   
               
               
                 Comparison 
                 40° (Forging) 
                 Crack occurred in angular 
               
               
                 Example 1 
                   
                 portion in 3.9 × 10 5  and 5.1 × 10 5   
               
               
                 Comparison 
                 50° (Forging) 
                 Crack occurred in angular 
               
               
                 Example 2 
                   
                 portion in 8.9 × 10 4  and 7.2 × 10 4   
               
               
                 Comparison 
                 60° (Forging) 
                 Crack occurred in angular 
               
               
                 Example 3 
                   
                 portion in 5.8 × 10 4  and 4.7 × 10 4   
               
               
                 Comparison 
                 90° (Cutting from 
                 Crack occurred in angular 
               
               
                 Example 4 
                 round rod) 
                 portion in 3 × 10 4  and 3.6 × 10 4    
               
               
                   
               
             
          
         
       
     
     As can be seen from comparison examples 1 to 4 respectively shown in Table 1, when θmax is equal to or larger than 40°, cracks occurred early in the angular portion of the connecting portion A. On the other hand, as can be seen from the results of embodiments 1 to 3, when θmax is equal to or smaller than 30°, endurance strength extends greatly. And, when θmax is equal to or smaller than 20°, the endurance strength extends more greatly and, even when the test time passes five times the target time, the trunnion did not break and thus the test was cut off by 5×10 6 . 
     As described above, although an excessive stress is concentrated on the connecting portion A between the main body plane portion  18  and pivot shaft portion  10  of the trunnion  11 , by allowing the metal flows  32  of the blank material to extend along the connecting portion A in this area, the metal flows  32  are prevented from being cut in the portion where the stress is concentrated, thereby being able to enhance the strength of the trunnion  11 . As a result of this, even when the load is input repeatedly, the trunnion is prevented against crack, which makes it possible to enhance the durability of the toroidal-type continuously variable transmission. 
     By manufacturing the trunnion  11  by forging in such a manner that the metal flows  32  are allowed to extend along the connecting portions A in these areas, the cutting operation of the trunnion can be reduced greatly. 
     By the way, in the above-mentioned embodiment, the circular hole  19 , which is used to hold the displacement shaft  10  rotatably through the needle bearing  20 , is formed by cutting in the main body plane portion  18  of the trunnion  11 . However, in case where the trunnion  11  is formed by forging in such a manner that the metal flows  32  extend around the circular hole  19 , the strength of the trunnion  11  can be increased further. 
     Also, the invention is not limited to a trunnion for use in a toroidal-type continuously variable transmission of a single cavity type but can also be applied to a trunnion for use in a cavity type. 
     In case that the metal flow that is nearest to the angular portion does not contact with the first and second surfaces, the inclination angles θ 1  and θ 2  can be defined at points that intersects the metal flow that is nearest to the angular portion with the imaginary lines extending from the first and second surfaces. That is, the inclination angles θ 1  and θ 2  can be defined by the nearest metal flow at the above points and the lines parallel to the first and second surfaces. 
     While only certain embodiments of the invention have been specifically described herein, it will apparent that numerous modifications may be made thereto without departing from the spirit and scope of the invention. 
     As has been described heretofore, according to a first aspect of the invention, since the two connecting portions between the main body plane portion of the trunnion and the pair of pivot shaft portions respectively formed in the two end portions of the trunnion integrally therewith respectively form continuous metal flows, even when the trunnion receives an excessive load repeatedly, the trunnion is prevented against damage, thereby being able to enhance the durability of the trunnion. 
     Also, according to a second aspect of the invention, due to the fact that the trunnion is manufactured by forging, not only the mechanical working of the trunnion can be reduced greatly but also continuous metal flows can be formed in the connecting portions, so that, even when the trunnion receives an excessive load repeatedly, the trunnion is prevented against damage, thereby being able to enhance the durability of the trunnion.