Abstract:
A universal joint is provided with a rotation shaft having a ball portion provided at an end thereof and a pair of projections formed on a diameter line of the ball portion, and a rotation body having guide grooves formed for receiving insertion of the respective projections of the rotation shaft and a holding hole formed for holding the ball portion, the ball portion being rotatable about an axis line of the projections and rotatable while inclining the projections along the guide grooves. In the universal joint pins serving as a stopper are provided in the holding hole for inhibiting the ball portion from slipping off.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a universal joint having a rotation body and a rotation shaft which cause bending in any direction. 
   2. Description of the Related Art 
     FIG. 4  to  FIG. 8  show an example conventionally known as the above type of universal joints. The conventional universal joint in  FIGS. 4 to 8  has ball portions  2  and  3  respectively provided at the ends of a rotation shaft  1 . The ball portions  2  and  3  have the respective pairs of projections  4  and  5  formed on the diameter lines of the ball portions  2  and  3 . 
   Two rotation bodies  6  and  7 , which are coupled to the rotation shaft  1 , are formed in a tubular shape and respectively have holding holes  8  and  9  formed on their axis. The holding holes  8  and  9  respectively receive the ball portions  2  and  3  and allow them to slide in the axis direction. The rotation body  6  has guide grooves  10  formed in positions 180 degrees out of phase with each other, and the rotation body  7  has guide grooves  11  formed in a like manner. The guide grooves  10  slidably receive the respective projections  4  of the ball portion  2  which is placed in the holding hole  8 , and likewise the guide grooves  11  slidably receive the respective projections  5 . 
   By placing the ball portions  2  and  3  in the respective holding holes  8  and  9  in this manner, the ball portions  2  and  3  can rotate about the axis line of the projections  4  and  5 , and further rotate while tilting the projections  4  and  5  in the guide grooves  10  and  11 . Thus the rotation shaft  1  is capable of rotating in any direction with respect to the rotation bodies  6  and  7 . 
   For example, a universal joint structured as described above is used to couple a drive wheel of a radio-controlled car or the like to an output shaft or the like. When a drive wheel of a radio-controlled car is coupled to an output shaft, the rotation body  6  is coupled to the drive wheel as shown in  FIG. 6 . Specifically, the rotation body  6  is mounted, via bearings  14  and  15 , in a ring portion  13  formed in a steering knuckle arm  12  for the drive wheel. The drive wheel  17  is fixed to an axle  16  provided integrally with the rotation body  6 . Accordingly, upon the rotation of the rotation shaft  1 , the rotation body  6  rotates and the drive wheel  17  rotates with the rotation of the rotation body  6 . The knuckle arm  12  moves rotationally in directions of the arrows  18  shown in  FIG. 6 , and the center of the rotational motion is a point X corresponding to the center of a kingpin (not shown). 
   The other rotation body  7 , which is located opposite to the rotation body  6 , is coupled to an output shaft (not shown) and rotates in conjunction with the output shaft. Therefore, the torque of the rotation body  7  rotating along with the output shaft is transmitted through the rotation shaft  1  to the rotation body  6 . After the torque is transmitted to the rotation body  6  in this manner, the torque is transferred also to the drive wheel  17  to produce rotation of the drive wheel  17 . At this point, if the knuckle arm  12  moves rotationally in either of the directions of the arrows  18 , the drive wheel  17  is changed in direction. 
   When the knuckle arm  12  moves rotationally in either of the directions of the arrows  18  about the X point where the kingpin is provided as described above, a virtual distance between the opposing rotation bodies  6  and  7  increases. For example, when the rotation bodies  6  and  7  are on the same axis, the distance between the rotation bodies  6  and  7  is L 1  as illustrated in  FIG. 7 . When the rotation bodies  6  and  7  are placed on the same axis as described above, the rotation center X of the rotation body  6  and the rotation center Y of the ball portion  2  are considered to align with each other. 
   If the rotation body  6  rotates from the above position about the rotation center X, the distance between the rotation bodies  6  and  7  becomes L 2  as shown in  FIG. 8 . The distance L 2  becomes longer than the distance L 1 . However, even if the opposite distance between them increases from L 1  to L 2  as described above, the rotation shaft  1  is not extendable, and therefore a difference between the two distances is absorbed by moving the ball portions  2  and  3  in the holding holes  8  and  9  of the rotation bodies  6  and  7  in the axial direction. 
   A specific examination is not made for the conventional example. 
   Regarding conventional universal joints structured as described above, for example, when the rotation body  6  rotates about the position X, the distance between the rotation bodies  6  and  7  is increased by a length “L 2 −L 1 ”. For example, it is assumed that the increased length is absorbed in the rotation body  6  of the two rotation bodies. If the increased distance is absorbed in the rotation body  6  in this manner, the rotation center Y of the ball portion  2  becomes out of alignment with the rotation center X of the rotation body  6  as shown in  FIG. 8 . 
   The misalignment caused between the rotation center X of the rotation body  6  and the rotation center Y of the ball portion  2  as described above makes it impossible for the rotation body  6  to rotate about the center X. Still, the knuckle arm  12  continues to rotate about the center X in order to change the direction the drive wheel  17  travels. However, at this point, the rotation body  6  rotates while pulling the rotation center Y of the ball portion  2  to the rotation center X. In other words, the rotation body  6  rotates while moving the rotation shaft  1  toward the rotation body  6  in such a manner as to draw the ball portion  3  located at the other end of the rotation shaft  1  out from the holding hole  9  of the rotation body  7 . 
   If the rotation body  6  rotates while pulling the ball portion  2  inward as described above, the resistance is increased, thereby making it difficult to smoothly change the direction the drive wheel  17  travels. Further, every time the direction the drive wheel  17  travels is changed as described above, the rotation shaft  1  moves in the axial direction. Thus, a smooth change in the direction the drive wheel  17  travels is made difficult. 
   Note that the foregoing description is given of an example of integrating the drive mechanism of the drive wheel  17  and the steering mechanism with each other and systematically rotating the rotation body  6  of the two rotation bodies about the center X. However, in the aforementioned conventional universal joints, the rotation of the rotation body is not caused systematically, but is caused as a consequence. In this case, problems as described in the forgoing also arise. 
   Any problem as described in the forgoing does not arise if the rotation center Y of the ball portion  2  in the holding hole  8  and the rotation center X of the rotation body  6  are in alignment with each other at all times. However, in view of the cost merits, the conventional universal joint as described above is not designed such that the rotation center Y of the ball portion  2  in the holding hole  8  and the rotation center X of the rotation body  6  are systematically aligned with each other. In order to achieve the positional alignment between the rotational center Y of the ball portion  2  in the holding hole  8  and the rotation center X of the rotation body  6 , this type of inexpensive universal joint is considered incompetent, and the use of a higher precision universal joint is considered necessary. 
   Further, the holding hole  8  needs to be deepened for ensuring the amount of movement of the center Y of the ball portion  2 . However, when the ball portion  2  is positioned close to the closed end of the holding hole  8 , if the rotation shaft  1  moves toward the rotation body  6 , disadvantageously, the rotation shaft  1  is pressed against the opening edge of the holding hole  8  and causes damage to the opening edge. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a universal joint that is of an inexpensive form of inserting a ball portion into a holding hole but is capable of maintaining a ball portion in position in a holding hole. 
   The present invention is based on a universal joint that is provided with a rotation shaft having a ball portion provided at an end of the rotation shaft and a pair of projections formed on a diameter line of the ball portion, and a rotation body having guide grooves formed for receiving insertion of the respective projections of the rotation shaft and a holding hole formed for holding the ball portion, the ball portion being rotatable about an axis line of the projections and rotatable while inclining the projections along the guide grooves. 
   Based on the universal joint, a first characteristic of the present invention is that a stopper is provided in the holding hole for inhibiting the ball portion from slipping off, and misalignment of a rotation center when the ball portion rotates about the axis line of the projections is prevented. 
   A second characteristic of the present invention is that a pin is inserted into the rotation body, is placed on at least one side of the rotation shaft placed in the rotation body, and serves as the stopper. 
   A third characteristic of the present invention is that a ball is embedded in a face of the holding hole of the rotation body, and is in contact with the ball portion placed in the holding hole, and serves as the stopper. 
   According to these characteristics, because the stopper is provided for specifying the position of the ball portion in the holding hole, it is possible to align the rotation center of the ball portion and the rotation center of either the rotation body or a bearing or the like fitted to the rotation body with each other at all times. Because the rotation centers of the ball portion and the rotation body or the like are able to be always aligned with each other in this manner, it is possible to rotate the rotation body extremely smoothly. Hence, when the universal joint according to the present invention is used as, for example, a drive shaft of a drive wheel with a steering mechanism in a radio-controlled car, it becomes possible to align the rotation center of the ball portion with the position of the kingpin provided on the knuckle arm at all times, leading to an extreme smooth change in the direction the drive wheel travels. 
   A distinctive feature of this type of universal joint is inexpensiveness. Without loss of this “inexpensiveness”, the present invention is able to positively resolve the conventional problems. That is, an adequate improvement in performance is achieved only by placing a ball portion in a rotation body in a conventional universal joint and using a stopper to trap the ball portion. The cost merit caused by this is immeasurable. 
   A fourth characteristic of the present invention is that an opening end of the holding hole is placed close to the stopper. 
   According to the fourth characteristic, because the ball portion is subject to a positional limit within the holding hole of the rotation body, the holding hole does not need to be deepened. In consequence, even when the rotation shaft moves toward the rotation body, the rotation shaft has less tendency to come into contact with the opening end of the holding hole. Thus, the opening end of the holding hole is not damaged by the rotation shaft. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view illustrating an essential part of the present invention. 
       FIG. 2  is a partially sectional view of the present invention associated with a drive wheel provided in a steering mechanism of a radio-controlled car. 
       FIG. 3  is a sectional view of a rotation body. 
       FIG. 4  is a front view illustrating a conventional universal joint. 
       FIG. 5  is a perspective view of a conventional ball portion formed on a rotation shaft. 
       FIG. 6  is a partially sectional view of a conventional universal joint associated with a drive wheel provided in a steering mechanism of a radio-controlled car. 
       FIG. 7  is a sectional view illustrating a pair of rotation bodies located on the same axis in the conventional universal joint. 
       FIG. 8  is a sectional view illustrating the pair of rotation bodies of which one rotation body rotates in the conventional universal joint. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 to 3  illustrate an embodiment of using the universal joint of the present invention for a radio-controlled car. The universal joint has ball portions  22  and  23  respectively provided at the ends of a rotation shaft  21 . The ball portions  22  and  23  have respective pairs of projections  24  and  25  placed on their diameter lines. 
   Further, the two ends of the rotation shaft  21  are respectively coupled to two rotation bodies. One rotation body  26  of the two rotation bodies has features as the present invention, and the other rotation body is the same as that conventionally used. Therefore, a detailed description of the other rotation body is omitted and, when required, a description will be given by using the same reference numbers as those in the description of the conventional example. 
   The rotation body  26  is formed in a tubular shape and has a holding hole  27  drilled on the axis line of the rotation body  26 . The ball portion  22  is placed in the holding hole  27 . The rotation body  26  structured in this manner has two guide grooves  28  formed in positions 180 degrees out of phase with each other and extending in the axis direction of the rotation body  26 . The guide grooves  28  receive respective projections  24  of the ball portion  22  which is placed in the holding hole  27 , and allow the projections  24  to move therein. 
   By placing the ball portion  22  in the holding hole  27  in this manner, the ball portion  22  can rotate about the axis of the projections  24 , and further rotate while tilting the projections  24  in the guide grooves  28 . Thus, the rotation shaft  21  is capable of rotating in any direction with respect to the rotation body  26 . 
   For example, the universal joint structured as described above is used in a radio-controlled car together with a steering mechanism to provide the coupling between a drive wheel and an output shaft or the like. This use is the same as that described in the conventional example, and the structural components of the steering mechanism and the drive mechanism are described by use of the same reference numerals as those in the conventional example. 
   The rotation body  26  is connected to a drive wheel  17  as illustrated in  FIG. 2 . The rotation body  26  is fitted, via bearings  14  and  15 , in a ring portion formed in a steering-system knuckle arm  12  of the drive wheel  17 . Then, the drive wheel  17  is fixed to an axle  29  provided integrally with the rotation body  26 . Accordingly, upon the rotation of the rotation shaft  21 , the rotation body  26  rotates, and in turn the drive wheel  17  rotates with the rotation of the rotation body  26 . Then, the knuckle arm  12  moves rotationally in directions of the arrows  18  shown in  FIG. 8 , and the center of the rotational motion is a point X corresponding to the center of a kingpin (not shown). 
   The other rotation body  7 , which is located opposite to the rotation body  26 , is connected to an output shaft (not shown) as in the case of the conventional example and rotates in conjunction with the output shaft. Therefore, the rotation body  7  rotates along with the output shaft and the torque of the rotation body  7  is transmitted through the rotation shaft  21  to the rotation body  26 . After the torque is transmitted to the rotation body  26  in this manner, the torque is transferred also to the drive wheel  17  to produce rotation of the drive wheel  17 . At this point, if the knuckle arm  12  moves rotationally in either of the directions of the arrows  18 , the drive wheel  17  is changed in direction. 
   The rotation body  26  structured as described above has a pair of through holes  30  and  31  formed therein so as to cross the holding hole  27  as is clear from  FIGS. 1 to 3 . A pair of pins  32  and  33  corresponding to a stopper of the present invention is inserted into the respective through holes  30  and  31 . The pins  32  and  33  thus inserted in the through holes  30  and  31  are in contact with the ball portion  22  in the holding hole  27  to perform the function of preventing the ball portion  22  from slipping off. Hence, the ball portion  22  is subject to a positional limit by the pins  32  and  33 . The rotation center X of the knuckle arm  12  and the rotation center Y of the ball portion  22  are designed to align with each other in the limited position. 
   Accordingly, even if the knuckle arm  12  rotates about the kingpin, the center of relative rotation between the ball portion  22  and the rotation body  26  is not displaced. Because there is no displacement of the relative rotation center, the knuckle arm  12  smoothly rotates about the kingpin. In other words, all inconveniences caused by a misalignment between the rotation body  26  and the ball portion  22  as occurring in the conventional example is eliminated. In the embodiment, one rotation body  26  of the two rotation bodies has the pins  32  and  33  provided for trapping the ball portion  22  in the rotation body  26 , but the other rotation body  7  is structured as in the case of the conventional example. Hence, when the knuckle arm  12  rotates and the distance between the rotation bodies  26  and  7  is changed from L 1  to L 2  as described earlier, this change is completely absorbed by the other rotation body  7 . 
   Further, according to the embodiment, there&#39;s no need to secure the amount of movement of the center Y of the ball portion  2  as is done conventionally. In turn, this eliminates the need for increasing the depth of the holding hole  27 . In consequence, the opening end of the holding hole  27  and the pins  32  and  33  can be positioned close to each other. This makes it possible for an allowable angle of relative rotational movement between the rotation shaft  21  and the rotation body  26  to be set large. If the allowable angle of bending can be increased in this manner, even when the rotation shaft  21  and the rotation body  26  greatly move rotationally relative to each other, the rotation shaft  21  will not cause any damage to the opening end of the holding hole  27 . 
   Further, the universal joint of the present invention is successfully achieved simply by placing the ball portion  22  in the holding hole  27  of the rotation body  26  and mounting the pins  32  and  33  corresponding to the stopper for preventing the ball portion  22  from slipping off. As a result, it is possible to reliably eliminate the problems associated with conventional universal joints as illustrated in  FIG. 4  to  FIG. 7  while taking full advantage of inexpensiveness of the conventional universal joints. In the embodiment, a pair of pins  32  and  33  is used. However, the ball portion  22  may be trapped by only one pin. Whether one pin or two pins is used depends on costs, required accuracy of dimension, or the like. 
   In the embodiment, the pins  32  and  33  are used as the stopper. However, for example, a ball may be embedded in the inner face of the holding hole  27  in such a manner as to be in contact with the ball portion in the holding hole  27 . In this case, the ball constitutes the stopper of the present invention. In either case, in the present invention, the structure of the stopper is not specifically limited as long as the stopper is capable of being in contact with the ball portion  22  in the holding hole  27  so as to prevent the ball portion  22  from slipping off.