Abstract:
A constant velocity joint has an outer joint part, an inner joint part, a ball cage and a plurality of balls located in the cage. The outer surface of the inner joint part is provided with two radii and the inner surface of the ball cage is provided with two radii resulting in a joint that is more compact, more durable and lubricated better than known joints.

Description:
FIELD OF INVENTION 
     The present invention relates to a vehicle joint, such as a plunging type constant velocity joint. 
     BACKGROUND OF THE INVENTION 
     As shown in  FIGS. 1A and 1B , a conventional double offset joint  10  comprises an outer joint part  12 , an inner joint part  14 , a cage  16  and at least one ball  18 . Typically, a plurality of balls  18  are provided. The outer joint part  10  has a cylindrical shape formed with a plurality of circumferentially spaced linear guide tracks  20  having a gothic arc or an elliptical form. The inner joint part  14  has circumferentially spaced linear guide tracks  22  formed on an outer spherical surface  24 . The cage  16  retains the plurality of balls  18  in a plurality of pockets  26  circumferentially spaced about the cage  16 . The cage  16  has an inner concave spherical surface at R 2  and an outer convex spherical surface at R 1 . R 1  and R 2  are offset by e to the opposite sides of point O to points O 1 , O 2  in the axial direction from the center of the ball pocket in which the outer convex spherical surface at R 1  contacts a cylindrical bore  28  of the outer joint part  12 . The inner concave spherical surface of the cage  16  at R 2  contacts the outer convex spherical surface  24  of inner joint part  14 . The inner joint part  14  also has an inner surface  30  for connection with a shaft (not shown). 
     In such a joint construction, if a certain torque is applied to the joint  10 , a load acts on ball track  20 ,  22  or balls  18  in the direction normal to the ball track  20 ,  22 . Another load derived partly from the load on the ball track  20 ,  22  acts on surfaces  32 ,  34  of the ball pockets  26  of the cage in axial direction Z, at an articulation angle. In this condition, the balls  18  contacts a track  20 ,  22  at the pressure angle A. A contact area CA is generated, taking the form of an ellipse defined by the longer length of elliptical contact a between the convex ball  18  and the concave track  22  and the shorter length of elliptical contact b made between the convex ball and the cylindrical formed track  20 . However, a becomes equal to b on the surfaces  32 ,  33  of ball pocket  26 , so the contact area takes a form of a circle, because a ball contacts a flat surface. The longer length of elliptical contact a on the ball track (hereafter contact ellipse length on ball track) and contact length on ball pocket (hereafter the contact length on the ball pocket) are design parameters to determine the cylindrical bore diameter of the outer joint part  12  in contact with outer spherical surface R 1  of the cage  16  and the outer sphere diameter R 2  of the inner joint part  14  in contact with the inner sphere diameter R 2  of the cage  16 . From this perspective, it is desirable that they (the cylindrical bore diameter of the outer joint part  12  and the outer sphere diameter of the inner joint part  14 ) be determined for the contact ellipse length a and not be cut off. If the contact ellipse length on the ball track or the ball pocket is cut off, contact stress on the ball track and the ball pocket increases by the amount of the cut off and affects durability of the joint  10 . 
     In the event that a joint  10  rotates at an articulation angle B, best seen in  FIG. 1C , a ball  18  reciprocates on the track  22  of the inner joint part  14  and the track  20  of the outer joint part  12 . During the reciprocation of the ball  18 , the distance between the pressure angle point and the bore diameter of outer joint part Lo does not vary along the ball track, due to its cylindrical shape, while that of the inner joint part Li varies along the ball track, due to its spherical shape defined by R 2 . More specifically, as the articulation angle increases, a ball  18  gets closer to the ends of the thickness of the inner joint part  14  on the ball track  22  and decreases the distance between the pressure angle point and the sphere diameter of the inner joint part Li, indicating that inner joint part  14  is inferior to the outer joint part  12  in terms of durability associated with the margin of contact in ellipse length a on the ball track. Furthermore, since the center of the outer sphere surface R 2  is offset to a side O 2  from the center O of the ball pocket at zero articulation angle, its diameter at the center of the ball pocket becomes RIO, as shown in  FIG. 1A , so the inner joint part  12  is even inferior to the outer joint part  10  in terms of Li by difference of R 2 −RIO even at zero articulation angle. 
     At the same time, when a ball  18  reciprocates on the track, as shown in  FIG. 1C , the ball  18  also moves in the radial direction and the circumferential direction on the surface of ball pocket  26 . During the movement, one ball  18 A moves closer to the edge of the outer spherical surface R 1 , while another ball  18 B gets closer to the edge of the inner spherical surface R 2  simultaneously in the radial direction, but it depends on the phase of the ball. In the worst case that either R 1  or R 2  is selected inadequately, a ball  18  could be derailed from the pocket  26 . To prevent a ball  18  from being derailed from the pocket  26 , the distance between the ball contact point and the inner spherical diameter (hereafter called cage inner spherical margin) S 1  should be secured properly, as seen in  FIG. 1A . Although a ball is not derailed from the ball pocket  26 , contact stress on the surface of the ball pocket will increase by the contact length cut off, in case that S 1  is smaller than the contact length a or b on the surface of the ball pocket  26 . On the other hand, the rear opening diameter Rr should be greater than the outer spherical surface  22  diameter of the inner joint part  14  to get the inner joint part  14  assembled into the cage  16 . It tends to make the distance between the rear opening diameter and the ball contact point on the ball pocket (hereafter called cage rear opening margin) S 2  smaller than S 1 . Any attempt to increase the contact ellipse length a on the ball track  22  of the inner joint part  14  or on the ball track  20  of the outer joint part  12  without adjusting the other design parameters eventually causes the cage inner spherical margin S 1 , the cage rear opening margin S 2  or the cage outer spherical margin SS 1 , SS 2  to get smaller. Therefore, the contact ellipse length on ball track a and the contact length on the ball pocket a or b or the cage inner spherical margin S 1 , the cage outer spherical margin SS 1 , SS 2 , the cage rear opening margin S 2  should be simultaneously considered for determining a bore diameter, outer spherical diameter, and inner spherical diameter, especially in terms of a compact design. 
     Recently, a lot of effort associated with compact design has been made to reduce the outside diameter of the outer joint part by increasing the number of balls, reducing the ball size, reducing the pitch circle diameter, and adjusting other design parameters, such as pressure angle and conformity ratio(=ball track radius/ball size). However, simple dimensional adjustments of design parameters in the conventional construction of double offset joint are not enough to achieve the compact design, due to the design constraints stated above, meaning that either the margin of the contact length on the ball pocket or the margin of contact of the ellipse length on the ball track is meant to be sacrificed to achieve the compact design, causing a reduction in either durability of the ball track or the durability of the cage ball pocket. 
     SUMMARY OF THE INVENTION 
     A plunging type constant velocity joint with a compact design and increased durability is provided by two partial spherical surfaces with different radii formed on the inner spherical surface of the cage and two partial spherical surfaces with different radii formed on the outer surface of inner joint part. 
     The plunging joint comprises an outer joint part having a cylindrical inner surface formed with a plurality of circumferentially spaced linear guide tracks, an inner joint part having an outer surface formed with the linear guide tracks matching those of the outer joint part, a plurality of torque-transmitting balls disposed within the ball tracks, and a cage retaining the balls in a plurality of pockets circumferentially spaced. 
     The claimed device is advantagous over the prior art for several reasons. Firstly, a partial spherical surface with a larger spherical radius formed on the outer surface of the inner joint part toward the rear opening of the cage provides more margin of contact ellipse length on the ball track, resulting in increased joint durability and a reduced joint size by the increment in the margin on the ball track. Secondly, a partial spherical surface with a smaller spherical radius formed on the inner surface of the cage toward the front opening of the cage provides more margin of contact length on the surface of ball pocket, resulting in increased joint durability and a reduced joint size by the increment in the margin on the ball pocket. Thirdly, an open space formed between the two different spherical surfaces with their different radii provides a better lubrication mechanism as the open space gets wider at a phase angle of zero degrees and gets narrower at a phase angle of 180 degrees. In other words, as a joint rotates at an articulation angle, meaning grease is filled when the open space becomes wider and grease is squeezed out and pumped into chasm between the parts when the open space becomes narrower. Therefore friction is reduced between the cage and the inner joint part thus providing better performance of the joint, and provides sufficient lubrication between a ball and a ball track. This feature also increases durability of the joint and reduces the size of the joint. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: 
         FIG. 1A  is an enlarged side sectional view of a portion of a conventional joint; 
         FIG. 1B  is an enlarged cross sectional view of the joint in  FIG. 1A ; 
         FIG. 1C  is a view showing the operation of the joint in  FIGS. 1A-1B ; 
         FIG. 2A  is an enlarged side sectional view of a portion of a joint depicting a first embodiment; 
         FIG. 2B  is a view showing the differences between a conventional cage and the embodiment in  FIG. 2A ; 
         FIG. 2C  is a view showing the differences between a conventional inner joint part and the embodiment in  FIG. 2A ; 
         FIG. 3A  is a view showing a second embodiment of the joint; 
         FIG. 3B  is a view showing the differences between a conventional cage and the embodiment in  FIG. 3A ; 
         FIG. 3C  is a view showing the differences between a conventional inner joint part and the embodiment of  FIG. 3A ; 
         FIG. 4A  is a view showing the operation of a joint of the present application; 
         FIG. 4B  is a view showing the differences between a conventional inner joint part and an embodiment of the joint at zero articulation angle; 
         FIG. 4C  is a view showing the differences between a conventional inner joint part and the present joint at the maximum articulation angle and at zero phase angle; 
         FIG. 4D  is a view showing the differences between a conventional inner joint part and the present joint at a maximum articulation angle and at 180 degrees of phase angle; 
         FIG. 5A  is a view showing a third embodiment of the joint; 
         FIG. 5B  is a view showing the cage of the embodiment in  FIG. 5A ; and 
         FIG. 6  is a view showing a fourth embodiment of the joint of the present application. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless the claims expressly state otherwise. 
     Now an embodiment that differs from the above-described prior art will be described below with reference to the accompanying drawings.  FIG. 2A  shows a double offset constant velocity joint  36  according to a first embodiment. The constant velocity joint  36  comprises an outer joint part  38  having a cylindrical inner surface  40  formed with a plurality of circumferentially spaced linear guide tracks  42 . An inner joint part  44  is also provided having an outer surface  46  formed with linear guide tracks  48  complimentary to those in the outer joint part  38 . A plurality of torque-transmitting balls  50  are disposed within the ball tracks  42 ,  48 . A cage  52  retains the balls  50  in a plurality of circumferentially spaced pockets  54 . The cage  52  also comprises an inner concave spherical surface  56  and an outer convex spherical surface  58  offset to the opposite sides O 1 , O 2  in the axial direction from the center of ball pocket O. The outer convex spherical surface  58  contacts the cylindrical inner surface  40  of the outer joint part  38 , via the tracks  42 , while the inner concave spherical surface  56  contacts the outer convex spherical surface  58  of inner joint part  44 . 
     The center of the inner joint part  44  is offset to a side O 1  facing its front opening Rf and a ball  50  mainly reciprocates more on the portion of the tracks  42 ,  48  facing the rear opening Rf of cage  52  than on the portion of the tracks  42 ,  48  facing the front opening of cage  52  by the offset amount. The center of the cage  52  may also be offset to a side (not shown). 
     With respect to the center line O 1  of the outer convex spherical surface  46  of inner joint part  44 , two partial spherical surfaces  60 ,  62  with their different radii R 21 , R 22  are formed on the outer surface  46  of the inner joint part  14  with respect to the center O 1  offset from the center of the ball  50 , respectively. An inner partial spherical surface  64  having the center O 1  is formed on the inner surface  56  of the cage  52  facing the front opening Rf of the cage  16  from a position L offset to the front opening of the cage  16 . 
     Another partial spherical surface  66  with a larger spherical radius having the same center O 1  is formed on the inner surface  56  of the cage  16  facing the rear opening Rr of the cage  16 . An open space K is provided between the two different spherical surfaces  60 ,  62 ,  64 ,  66  with their different radii R 21 , R 22  to allow the inner joint part  14  to rotate relatively to the cage  16  along the spherical surfaces  60 ,  62 ,  64 ,  66 . The size of open space K is determined by a relative circumferential movement of the inner joint part  14  to point O 2 , which is equivalent to half an articulation angle. 
       FIG. 2B  shows a difference in cage  52  between a conventional cage and the present case, in which RC represents an inner sphere radius of a conventional cage, as shown in the dotted line. The two radii R 21 , R 22 , of the partial spherical surfaces of the inner joint parts  60 ,  62  are depicted. The location of surface  62  is formed from a position equivalent to half of a ball diameter D/2 toward the front beginning opening of the cage Rf. 
       FIG. 2C  shows a difference in the inner joint part  44  between a conventional inner joint part and the present inner joint part in which RI represents the outer sphere radius of a conventional inner joint part, as shown in dotted line. As an advantage of the present joint, the partial spherical surface  62  with the larger spherical radius R 22  formed on the outer surface  46  of the inner joint part  44  toward the rear opening Rr of the cage  52  is larger than a spherical radius of the conventional art RI. This provides more margin of contact ellipse length (=R 22 −RI) on a ball track, thus increasing joint durability and decreasing the size of the joint  36  by the increment in the radius of the spherical surface (=R 22 −RI). The partial spherical surface  60 , with the smaller spherical radius R 21  formed on the inner joint part  44  toward the front opening of the cage  52 , has a smaller spherical radius than that of the conventional art RI. This provides more margin of contact length (=R 22 −Rc=SS 1 ) on the surface of the ball pocket, thus increasing joint durability and decreasing the size of the joint  36  by the difference in the radius of the spherical surface of cage (=R 22 −Rc). 
       FIG. 3A  shows a double offset constant velocity joint  68  according to another embodiment. The same reference numbers from  FIGS. 2A ,  2 B and  2 C are used for the same features in  FIGS. 3A ,  3 B and  3 C. One difference between the embodiment depicted in  FIG. 2A  and the embodiment depicted in  FIG. 3A  is that a flat cylindrical surface  70  defined by L 1  and RO 1  is formed additionally on the partial spherical surface  60  of the inner joint part  44 ′ to assemble the inner joint part  44 ′ into the cage  52  through the rear opening diameter Rr of cage  52 . The partial spherical surface  62  should be cut off at the central portion O of the inner joint part  44 ′ and also R 22  should not be greater than the rear opening diameter RO 1 . 
       FIG. 3B  and  FIG. 3C  show detailed drawings with regards to  FIG. 3A .  FIG. 3B  shows a difference in cage  52  between a conventional cage and the present case. As in  FIG. 2B , Rc in  FIG. 3B  represents an inner sphere radius of a conventional cage. The two radii R 22 , R 21  of the partial spherical surfaces  60 ,  62  of the inner joint part  44 ′ are depicted. The location of surface  64  is formed from a position equivalent to half a ball diameter D/2 toward the front opening of cage Rf. 
       FIG. 3C  shows a difference in the inner joint part  44 ′ between a conventional inner joint part and the present inner joint part where RI represents the outer sphere radius of a conventional inner joint part, as shown in dotted line. The advantages of joint  36  are thus achieved in the joint design for joint  68 . 
       FIG. 4A  is a view showing the operation of the joint  36  at a maximum articulation angle of B max, in which a first ball  72  having a phase angle of zero degrees travels toward a front opening diameter Rf of the cage  52  on the ball track  48  of the inner joint part  44  by T 1 , while a second ball  74  having a phase angle of 180 degrees travels toward the rear opening diameter Rr of the cage  52  on the ball track  48  of the inner joint part  44  by T 2 . While joint  36  is depicted in  FIG. 4A , it can be readily appreciated that the operation depicted in  FIGS. 4A-4D , can be readily applied to joint  68  of  FIGS. 3A-3C . 
       FIG. 4B  is a view showing the difference in contact ellipse length margin on the outer spherical surface  46  of the inner joint part  44  between a conventional inner joint part and the inner joint part  44  of the present joint  36  at zero articulation angle. The conventional inner joint part outer spherical surface is depicted in dashed lines. 
       FIG. 4C  is a view showing the difference in contact ellipse length margin on the outer spherical surface  46  of the inner joint part  44  between a conventional inner joint part and the inner joint part  44  of the present joint  36  at a maximum articulation angle and at a zero phase angle. Again, the conventional inner joint part outer spherical surface is depicted in dashed lines. 
       FIG. 4D  is a view showing the difference in contact ellipse length margin on the outer spherical surface  46  of the inner joint part  44  between a conventional inner joint part and the present joint  36  at a maximum articulation angle and at a phase angle of 180 degrees. The conventional inner joint part outer spherical surface is depicted in dashed lines. 
     As shown in  FIG. 4B  to  FIG. 4D , joint  36  has more margin of contact ellipse length than the conventional art by DEL at e meaning zero articulation angle. It also has more margin of contact ellipse length than the conventional art by DEL meaning T 2  and maximum articulation and a phase angle of 180 degrees than the conventional art. However, it does not have any more contact ellipse length margin than the conventional art at T 1  meaning maximum articulation and a phase angle of zero degrees, which means the present joint is equivalent to the conventional art at maximum articulation angle and at T 1 . However, since the margin of contact ellipse length at T 1  still becomes greater than that at T 2 , it is not necessary to secure more contact ellipse length margin on the central portion of the outer spherical surface  46  of the inner joint part  44  in terms of a margin in balance. Consequently, present joint  36  has increased durability, while achieving a reduction of weight and size. On the other hand, the present joint  36  is designed in a fashion that the open space L, at zero articulation angle gets wider to LL at a phase angle of zero degrees and gets narrower to zero (LL=0) at a phase angle of 180 degrees, as shown in  FIG. 4A . Therefore, the mechanism of the present joint  36  provides a better lubrication system, meaning that grease is filled, when the open space becomes wider, while grease is squeezed out and pumped into the chasm between the parts when the open space becomes narrower. Therefore, it can reduce friction between the cage  52  and the inner joint part  44 , eventually providing better NVH performance of the joint  68 . Additionally, it also can supply a sufficient amount of lubrication between a ball  72  or  74 , and a ball track  48 , thus increasing the durability of the joint  36  and allowing the joint  36  to be made more compact in size. 
       FIGS. 5A and 5B  show a double offset constant velocity joint  76  according to a preferred third embodiment that is intended to allow an inner joint part  78  to move in the axial direction Z for the purpose of improving NVH characteristics related to engine idling. To achieve this objective, a first partial spherical surface  80  with a radius R 221  having a center O 12  offset from the center of cage inner surface O 1  is formed on an inner surface  82  of a cage  84  facing the rear opening Rr of the cage  84 . A first flat cylindrical surface L 22  with inner diameter R 221  is smoothly formed to be directly adjacent to the first partial spherical surface  80 . A second partial spherical surface  86  defined by R 22  is adjacent to the first flat cylindrical surface L 22  and is extended approximately to a position offset from the center of the cage inner surface. The second partial spherical surface  86  has a center O 1  and faces the rear opening Rr of the cage  84 . R 22  is less than R 221 . 
     A third partial spherical surface  88  with a radius R 211  having a center O 11  offset from the center of the cage inner surface O 1  is formed on the inner surface of the cage  84  facing a front opening Rf of the cage  96 . R 211  is smaller than R 221 . A second flat cylindrical surface L 21  with an inner diameter equal to the third partial spherical surface  88  is smoothly formed to be adjacent to the third partial spherical surface  88  and extends to cage front opening Rf. 
     A fourth partial spherical surface  90  with radius R 21  having a center O 1  is formed on the outer surface  92  of the inner joint part  78  facing the front opening Rf of the cage  84 , in which a convex spherical surface defined by L 11  and R 211  is additionally formed and a flat cylindrical surface defined by R 212  and L 23 , smaller than the convex spherical surface in diameter, is additionally formed to get the convex spherical surface to contact the flat surface L 21 . R 21  is smaller than R 22 . 
       FIG. 6  shows a double offset constant velocity joint  94  according to the preferred fourth embodiment that is intended to allow an inner joint part  96  to move in the axial direction Z for the purpose of improving NVH characteristics related to engine idling. To achieve this objective, a first partial spherical surface  98  with radius R 211  having a center O 12  offset from a center O 1  of the inner surface  100  of a cage  102  is formed on an outer surface of the inner joint part  96  facing a front opening Rf of the cage  102 . A second partial spherical surface  106  with radius R 221  having a center O 11  offset from the center O 1  of the cage inner surface  100  is formed on the outer surface  104  of the inner joint part  96  facing the rear opening Rf of the cage  102 . A third partial spherical surface  108  with radius R 21  having a center O 1  is formed on the inner surface  100  of the cage  102  facing the front opening Rf of the cage  102 . A fourth partial spherical surface  102  with radius R 22  having a center O 1  is formed on the inner surface  100  of the cage  102  facing the rear opening Rr of cage  102 . Therefore, the inner joint part  96  is allowed to move in the axial direction Z by DL 21  and DL 22   
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.