Abstract:
Provided is a slidable constant velocity universal joint which holds an elastic member (coil spring) in a stable attitude even if an associated shaft makes an oscillating motion, thereby achieving an improvement in terms of stability in torque transmission. The slidable constant velocity universal joint includes an outer joint member ( 4 ) connected to a power transmission member ( 2 ), and an inner joint member ( 5 ) connected to an end portion of a shaft ( 1 ), with torque transmission being possible between the outer joint member ( 4 ) and the inner joint member ( 5 ) while allowing angular displacement and axial displacement. At a forward end of the shaft ( 1 ), there is provided an elastic member ( 21 ) for elastically urging the outer joint member ( 4 ) toward the power transmission member ( 2 ), and, between the elastic member ( 21 ) and the forward end of the shaft ( 1 ), there is interposed a bearing member ( 24 ) for guiding the forward end of the shaft ( 1 ) while in contact therewith.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a slidable constant velocity universal joint for use in a power transmission system for automobiles, various industrial machines or the like and, more specifically, to a slidable constant velocity universal joint which is capable of transmitting rotary motion at constant velocity even when driving and driven shafts to be joined together are at an angle (operating angle) with respect to each other and which allows a relative axial movement between driving and driven shafts. 
         [0003]    2. Description of the Related Art 
         [0004]    As shown in  FIG. 5 , for example, in the power transmission system of a conventional vehicle such as an agricultural tractor, two power transmission shafts  120  and  130  and both ends of a propeller shaft  150  arranged between them are operationally connected with each other via cross joints  100   a  and  100   b , respectively (see, for example, JP05-178105A and JP2003-300422A). The mounting structure for the cross joints and the power transmission shafts will be described with reference to  FIG. 5 ; in the case of one cross joint  100   a  (the one on the left-hand side as seen in the drawing), a cylindrical portion  101   a  with a female spline groove formed therein is fitted onto a spline shaft  121  of the mating power transmission shaft  120  with a male spline groove formed therein, with a bolt  105  being engaged with a recess  122  formed in the outer periphery of the spline shaft  121 . 
         [0005]    In the case of the other cross joint  100   b  (the one on the right-hand side as seen in the drawing), a cylindrical portion  101   b  with a female spline groove formed therein is fitted onto a spline shaft  131  of the mating power transmission shaft  130  with a male spline groove formed therein. That is, the right-hand cross joint  100   b  is axially slidable with respect to the power transmission shaft  130 , whereby, even if the relative position between the two power transmission shafts is changed due to engine vibration or the like, it is possible to absorb any glitch at each connecting portion due to the relative positional deviation. As a result, the fit-engagement between the members is properly maintained, and rotational torque is transmitted in a satisfactory manner. 
         [0006]    However, in the conventional example shown in  FIG. 5 , the right-hand cross joint  100   b  is fit-engaged with the spline shaft  131  so as to be slidable, so that wear occurs at the fit-engagement portion. Further, the left-hand cross joint  100   a  has to be fixed to the power transmission shaft  120  by the bolt  105 , and the mounting operation involved is a bother. 
         [0007]    To solve the above-mentioned problems, the present applicant has already proposed a slidable constant velocity universal joint in which, as shown in  FIG. 6 , coil springs  201  are provided between the ends of a shaft  200  and receiving members  205  arranged inside outer rings  202  (see JP 2006-299351 A). Due to the use of the coil springs  201 , the distance between the slidable constant velocity universal joints at both ends is variable, whereby the slidable constant velocity universal joints can be easily mounted to two power transmission members  203  spaced apart from each other by a predetermined interval. 
         [0008]    In the slidable constant velocity universal joint shown in  FIG. 6 , when the shaft  200  assumes an operating angle, cap members  204  provided at the forward ends of the coil springs  201  slide on the receiving members  205  arranged inside the outer rings  202 . That is, the coil springs  201  are also inclined in conformity with the shaft  200 , so that if the sliding motion of the cap members  204  relative to the receiving members  205  is not effected smoothly, the coil springs  201  may be bent, making it impossible to maintain a stable attitude. This may lead to deterioration in stability in torque transmission. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the above-mentioned problem, it is an object of the present invention to provide a slidable constant velocity universal joint which keeps an elastic member (coil spring) in a stable attitude even if a shaft makes an oscillating motion to thereby achieve an improvement in terms of stability in torque transmission. 
         [0010]    A slidable constant velocity universal joint according to a first aspect of the present invention includes: an outer joint member connected to a power transmission member; and an inner joint member connected to an end portion of a shaft, with torque transmission being possible between the outer joint member and the inner joint member while allowing angular displacement and axial displacement, in which the shaft is provided with, at a forward end thereof, an elastic member for elastically urging the outer joint member toward the power transmission member, and in which the elastic member and the forward end of the shaft are provided with a bearing member interposed therebetween for guiding the forward end of the shaft while in contact therewith. 
         [0011]    When the shaft makes an oscillating motion with respect to the power transmission member, the forward end of the shaft is guided by the bearing member while in contact therewith. Thus, the elastic member is scarcely affected by the oscillating motion of the shaft, making it always possible to maintain a stable attitude. 
         [0012]    A slidable constant velocity universal joint according to a second aspect of the present invention, in the first aspect of the invention, further includes, a cap member, provided at the forward end of the shaft, having at its forward end a spherical convex surface portion is, in which the bearing member has a spherical concave surface portion for guiding the spherical convex surface portion while in contact therewith. 
         [0013]    Since the spherical convex surface portion of the cap member and the spherical concave surface portion of the bearing member are in contact with each other, the contact friction between the members is reduced, thus making it possible to effect smooth sliding. As a result, the influence of the oscillating motion of the shaft on the elastic member can be further mitigated. 
         [0014]    A slidable constant velocity universal joint according to a third aspect of the present invention, in the second aspect of the invention, further includes: a flat surface portion formed at the center of the forward end portion of the cap member; and an annular spherical convex surface portion formed around the flat surface portion. 
         [0015]    Not the flat surface portion but the annular spherical convex surface portion of the cap member is held in contact with the bearing member. In this way, the cap member and the bearing member can be held in contact with each other in an annular fashion, thereby allowing stable sliding. 
         [0016]    According to a slidable constant velocity universal joint of a fourth aspect of the present invention, in the second or third aspect of the invention, the spherical convex surface portion has a radius of curvature set smaller than that of the spherical concave surface portion. 
         [0017]    Due to this setting, it is possible to diminish the contact range between the cap member and the bearing member, thereby making it possible to further reduce the contact friction between the members. 
         [0018]    According to the present invention, even if the shaft makes an oscillating motion with respect to the power transmission member, the elastic member is scarcely affected by the oscillating motion of the shaft, making it always possible to maintain a stable attitude. Thus, the elastic member (coil spring) is not bent as in the case of the slidable constant velocity universal joint shown in  FIG. 6 , making it possible to achieve an improvement in terms of stability in torque transmission. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In the accompanying drawings: 
           [0020]      FIG. 1  is a sectional view of a slidable constant velocity universal joint according to an embodiment of the present invention; 
           [0021]      FIG. 2  is a sectional view of the slidable constant velocity universal joint with a coil spring therein compressed; 
           [0022]      FIG. 3  is a sectional view of the same with a shaft assuming an operating angle; 
           [0023]      FIG. 4  is a sectional view of the same with the shaft assuming a maximum operating angle; 
           [0024]      FIG. 5  is a sectional view of a conventional propeller shaft; and 
           [0025]      FIG. 6  is a sectional view of a slidable constant velocity universal joint of a comparative example as applied to a propeller shaft. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    In the following, an embodiment of the present invention will be described with reference to the accompanying drawings. 
         [0027]    The present invention relates to a slidable constant velocity universal joint for use in a power transmission system, for example, a propeller shaft, used in a vehicle such as a passenger car or an agricultural tractor, in which both ends of a shaft arranged between two power transmission members, one constituting a driving shaft and the other a driven shaft, are respectively connected to two power transmission members so as to allow an oscillating motion. A pair of slidable constant velocity universal joints connected to both ends of this shaft are of a similar (symmetrical) structure, so that solely the slidable constant velocity universal joint at one end of the shaft will be described. 
         [0028]    As shown in  FIG. 1 , a slidable constant velocity universal joint according to the present invention is mainly composed of an outer ring  4 , an inner ring  5 , balls  6  serving as torque transmission members, and a retainer  7 . 
         [0029]    The outer ring  4  constituting an outer joint member is a member formed by coaxially integrating a large diameter cylindrical portion  8  and a small diameter cylindrical portion  9  with each other. In the inner peripheral surface of the small diameter cylindrical portion  9 , there is formed an axially extending female spline groove  10 , and, in the outer peripheral surface of a spline shaft  11  of a power transmission member  2 , there is formed a male spline groove  12  to be engaged with the female spline groove  10 . That is, the power transmission member  2  and the outer ring  4  are axially slidable and detachable with respect to each other. 
         [0030]    The large diameter cylindrical portion  8  of the outer ring  4  contains therein an accommodation space  13  capable of accommodating the inner ring  5 , the balls  6 , the retainer  7 , etc., and, in the inner peripheral surface of the large diameter cylindrical portion  8 , there are formed a plurality of axially extending ball grooves  14  arranged at equal circumferential intervals. Further, a boot  20  formed of rubber or the like is provided between the open end of the large diameter cylindrical portion  8  and a shaft  1 . 
         [0031]    The inner ring  5  serving as an inner joint member has in its inner peripheral surface an axially extending female spline groove  16  to be engaged with a male spline groove  15  formed in the outer peripheral surface of the end portion of the shaft  1 . And, a retaining ring  17  for preventing detachment of the shaft  1  from the inner ring  5  is attached to a portion in the vicinity of the forward end of the shaft  1  inserted into the inner ring  5 . 
         [0032]    Further, a plurality of axially extending ball grooves  18  are formed in the outer peripheral surface of the inner ring  5  at equal circumferential intervals, with the ball grooves  18  of the inner ring  5  and the ball grooves  14  of the outer ring  4  being opposed to each other. The opposing ball grooves  14  and  18  of the inner and outer rings  4  and  5  define tracks, in each of which one ball  6  is incorporated so as to be capable of rolling. 
         [0033]    The retainer  7  has a plurality of pockets  19  extending therethrough and formed at equal circumferential intervals. The retainer  7  is interposed between the outer ring  4  and the inner ring  5 , with each pocket  19  accommodating one ball  6 . The inner peripheral surface of the retainer  7  and the outer peripheral surface of the inner ring  5  are in spherical contact with each other, whereby the shaft  1  can assume an operating angle (i.e., make an angular displacement). Further, the balls  6  can roll along the ball grooves  14  of the outer ring  4 , so that the balls  6 , the shaft  1 , the inner ring  5 , and the retainer  7  can move integrally in the axial direction (i.e., make an axial displacement) with respect to the outer ring  4 . That is, in the slidable constant velocity universal joint, torque transmission is possible between the outer ring  4  and the inner ring  5  while allowing angular displacement and axial displacement. 
         [0034]    Further, a retaining ring  30  such as a circlip is attached to the inner peripheral edge of the open end of the outer ring  4 , and the retaining ring  30  and the balls  6  interfere with each other, whereby detachment of the inner ring  5 , the shaft  1 , etc. from the outer ring  4  is prevented. 
         [0035]    In the accommodation space  13  of the outer ring  4 , there is provided an elastic member  21  capable of expanding and contracting in the axial direction. In  FIG. 1 , the elastic member  21  is a coil spring. A shallow-plate-like seal plate  23  is fit-engaged with a recess  22  formed in a step surface connecting the inner peripheral surface of the large diameter cylindrical portion  8  of the outer ring  4  and the inner peripheral surface of the small diameter cylindrical portion  9  thereof, and one end of the coil spring  21  is attached to the seal plate  23 . Attached to the other end of the coil spring  21  is a shallow-plate-like bearing member  24 . The bearing member  24  has a convex spherical configuration protruding toward the seal plate  23 . On the shaft  1  side surface of the bearing member  24  thus formed, there is provided a spherical concave surface portion  25 . The seal plate  23  and the bearing member  24  have short-cylinder-like edge portions  23   a  and  24   a , respectively. The end portions of the coil spring  21  are respectively retained in the edge portions  23   a  and  24   a , whereby movement of the coil spring  21  in a direction orthogonal to the axis thereof (decentering) is prevented. 
         [0036]    A cap member  26  is provided at the forward end of the shaft  1 , which is held in contact with the bearing member  24  through the intermediation of the cap member  26 . The cap member  26  has at its forward end a flat surface portion  27  formed at the center and an annular spherical convex surface portion  28  formed in the periphery of the flat surface portion  27 . From the viewpoint of the ease with which it can be mounted to the shaft  1  and the ease with which it can be shaped, it is desirable for the cap member  26  to be formed of resin. 
         [0037]    In the state of  FIG. 1 , the coil spring  21  is compressed in the axial direction, and the cap member  26  and the bearing member  24  are held in press contact with each other by the elastic urging force of the coil spring  21 . More specifically, the spherical convex surface portion  28  of the cap member  26  and the spherical concave surface portion  25  of the bearing member  24  are held in contact with each other. The radius of curvature of the spherical convex surface portion  28  is set smaller than the radius of curvature of the spherical concave surface portion  25 , so that the spherical convex surface portion  28  and the spherical concave surface portion  25  are held in line contact with each other in an annular fashion. 
         [0038]    The coil spring  21  is provided within the outer ring  4  in a compressed state. That is, the coil spring  21  is capable of imparting elastic force in both ways in the axial direction over the axial movable range for the balls  6 , in other words, over the entire range of the sliding stroke of the slidable constant velocity universal joint  3 . 
         [0039]    To be described will be a method of mounting the slidable constant velocity universal joints thus provided at both ends of a shaft respectively to two power transmission members spaced apart from each other by a predetermined interval. 
         [0040]    First, the small diameter cylindrical portion  9  of one slidable constant velocity joint  3  is fitted onto the spline shaft  11  of the mating power transmission member  2  by causing it to slide thereon in the axial direction (see  FIG. 1 ). In this state, the axial distance between the forward end of one slidable constant velocity universal joint  3  and the forward end of the other slidable constant velocity universal joint  3  is larger than the interval dimension between the power transmission members  2 . Thus, as shown in  FIG. 2 , an axial pressurizing force A is imparted to the other slidable constant velocity universal joint  3 , bringing the coil springs  21  in both slidable constant velocity universal joints  3  into a compressed state. That is, by compressing the coil springs  21  by imparting the pressurizing force A thereto, the axial distance between the forward ends of the slidable constant velocity universal joints  3  can be made smaller than the interval dimension between the power transmission members  2 . And, the small diameter cylindrical portion  9  of the other slidable constant velocity universal joint  3  is fitted onto the spline shaft  11  of the mating power transmission member  2  by causing it to slide axially thereon, whereby the mounting operation is completed. 
         [0041]    In the state in which the mounting has been completed, the outer rings  4  of the slidable constant velocity universal joints  3  are pressed against the mating power transmission members  2  by the elastic urging force of the coil spring  21 , thereby maintaining the fit-engagement between the slidable constant velocity universal joints  3  and the power transmission members  2 . The shaft  1  is held at a position where the opposing elastic forces of the coil springs  21  at both ends thereof are in equilibrium with respect to each other. 
         [0042]    The mounting method is not restricted to the above-mentioned one; for example, it is also possible to pressurize the slidable constant velocity universal joints  3  on both sides toward the shaft  1  to shorten them in the axial direction; thereafter, the slidable constant velocity universal joints  3  are successively or simultaneously fitted onto the power transmission members  2 . 
         [0043]    In detaching the completely mounted slidable constant velocity universal joints  3  from the power transmission members  2 , procedures reverse to those for the mounting as described above are to be taken, so a description of the detachment method will be omitted. 
         [0044]      FIG. 3  shows a state in which the two power transmission members are at an angle (operating angle) with respect to each other, that is, a state in which the shaft  1  assumes an operating angle θ. When transition is effected from the state of  FIG. 1 , in which the operating angle is 0°, to the state of  FIG. 3 , in which the operating angle is θ, the cap member  26  at each end of the shaft  1  slides on the spherical concave surface portion  25  of the bearing member  24 . The spherical convex surface portion  28  of each cap member  26  is brought into line contact with the spherical concave surface portion  25  in an annular fashion, whereby a smooth and stable sliding movement is effected. On the other hand, each coil spring  21  is arranged so as to be parallel to the axial direction and is held in a stable attitude. 
         [0045]      FIG. 4  shows a case in which the shaft  1  assumes a maximum operating angle θ′, with the spherical convex surface portion  28  of each cap member  26  being in line contact with the spherical concave surface portion  25  of the bearing member  24 . In this case also, the coil spring  21  is held parallel to the axial direction and in a stable attitude. In this way, even if the shaft  1  oscillates with respect to the power transmission members  2 , each coil spring  21  is always held in a stable attitude, so that it is possible to realize a stable torque transmission. From the viewpoint of keeping them in a stable attitude, it is desirable for the diameter of the coil springs  21  to be relatively large. 
         [0046]    The present invention is not restricted to the above-mentioned embodiment but naturally allows various modifications without departing from the gist of the invention. For example, the slidable constant velocity universal joint of the present invention may be connected solely to one end of a shaft instead of connecting the same to both ends thereof. Further, the elastic members may also be members other than coil springs; for example, they may also be bellows-like elastic metal members. Further, the ends of the shaft may be held in direct contact with the bearing members; in this case, it is possible to form a flat surface portion and a spherical convex surface portion at each end of the shaft.