Patent Publication Number: US-2006003848-A1

Title: Sliding type constant velocity universal joint

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to sliding type constant velocity universal joints for transmitting torque between input and output shafts while accommodating angular and axial displacements therebetween, and more particularly to such constant velocity universal joints having boots for preventing entrance of contaminants and lubricant leakage.  
      2. Description of the Related Art  
      A conventional tripod type constant velocity universal joint, which is one type of a sliding type constant velocity universal joint, is described below with reference to  FIG. 5  and  FIG. 6 . As shown, the tripod type constant velocity universal joint includes an outer joint member  10 , an inner joint member  20 , and roller assemblies  30 , as main components. The outer joint member  10  has a cylindrical inner surface  11  including three linear track grooves  12  extending in an axial direction, and roller guide surfaces  13  formed on both circumferential sides of each linear track groove  12 . The inner joint member  20  has a tripod member  22  with three radially projecting trunnions. The tripod member  22  is inserted in the outer joint member  10  and a shaft  23  extends from the tripod member  22  to the outside of the outer joint member  10 . The roller assemblies  30  have rollers  31  inserted in the linear track grooves  12  of the outer joint member  10  and are rotatably fitted to the trunnions  21  of the tripod member  22  with needle bearings  32  therebetween.  
      When torque is applied to the tripod type constant velocity universal joint configured as above with an angular displacement between the outer joint member  10  and the inner joint member  20 , the roller assemblies  30  slide back and forth along the roller guide surfaces  13  of the outer joint member  10  as the inner joint member  20  rotates. Any contaminants present between the roller guide surfaces  13  and rollers  31  cause friction resistance therebetween and may inhibit the torque transmission between the outer joint member  10  and the inner joint member  20 . In some tripod type joints inside of which is filled with lubricant, lubricant leakage from the inside of the joint will lead to lubrication failure and may inhibit the torque transmission between the outer joint member  10  and the inner joint member  20 . To prevent such entrance of contaminants and lubricant leakage, the above described tripod type constant velocity universal joint is generally provided with a boot  40  for sealing the inside of the joint.  
      As shown in  FIG. 5 , the boot  40  has a boot body  41  made of resilient material such as rubber or plastic, and a boot adaptor  42  that connects the boot body  41  with the outer joint member  10 . The boot body  41  has a substantially U-shape cross section and an annular shape, and its inner peripheral edge  43  is tightened to the shaft  23  of the inner joint member  20  using a boot band  44 . The boot adaptor  42  is generally cylindrical, having one end crimped to the outer peripheral edge  45  of the boot body  41 . As shown in the enlarged view of  FIG. 5 , the other end of the cylindrical boot adaptor  42  has a fitting portion  46  and a swaged portion  47  extending from the fitting portion  46 . The fitting portion  46  is hermetically fitted to a seal portion  14  of the outer joint member  10 . The swaged portion  47  is swaged radially inwardly to engage with a corresponding portion  15  of the outer joint member  10 .  
      The outer joint member  10  further includes an annular groove  16  formed in the seal portion  14  as shown in the enlarged view of  FIG. 5 . An O-ring  17  made of resilient material such as rubber or plastic is mounted in the groove  16  to enhance the seal between the outer joint member  10  and the boot adaptor  42 .  
      While the boot mounting design of the above-described conventional example is that of tripod type constant velocity universal joints, Japanese Patent Laid-Open Publication No. 2003-056590 shows a substantially identical boot mounting design for cross-groove type constant velocity universal joints, which are another type of sliding type constant velocity universal joints. A cross-groove type constant velocity universal joint typically includes an outer joint member having a cylindrical inner surface formed with a plurality of linear track grooves, an inner joint member having a spherical outer surface formed with a plurality of linear track grooves opposite the linear track grooves of the outer joint member, a plurality of balls interposed in the track groove cross section between the outer joint member and the inner joint member, and a retainer accommodated in an annular spacing between the outer joint member and the inner joint member for retaining the balls.  
      When assembling this conventional sliding type constant velocity universal joint, the tripod member  22  and roller assemblies  30  (or inner race and balls in the case with the cross-groove joint) are assembled to the outer joint member  10 , and the shaft  23  with the boot body  41  fitted thereon is press-fitted into the tripod member  22  (or inner race in the case with the cross-groove joint), while the boot adaptor  42  is press-fitted onto the seal portion  14  of the outer joint member  10 . As the inside of the joint is sealed by the fitting portion  46  of the boot adaptor  42  rubbing against the seal portion  14  of the outer joint member  10 , when the boot adaptor  42  is press-fitted from the open end to the fitting end of the outer joint member  10 , the air inside the joint is compressed and the inside pressure builds up. This pressure buildup causes deformation of the boot body  41  so as to render the cross section of which in a generally C-shape as indicated by broken lines in  FIG. 5 . Relative axial movement of the outer joint member  10  and inner joint member  20  and torque application to the outer and inner joint members  10  and  20  with angular displacement therebetween bend or reverse the boot body  41  leading the boot body to rub against the shaft  23  and resulting in the boot body  41  getting wear or cracks, because of which the durability of the boot body  41  is reduced.  
      It has been the practice to reduce the pressure inside the joint by creating a gap in the mating parts between the boot body  41  and the shaft  23  using a tool to release the air inside the joint so that the boot body  41  returns to its original shape. While such depressurization prevents wear of the boot body  41  and increases the life of the same, there is the danger that the tool may damage the boot body  41  or the shaft  23  leading to the gas tight deterioration of the joint.  
     SUMMARY OF THE INVENTION  
      Based on the foregoing, an object of the present invention is to provide a sliding type constant velocity universal joint which can be assembled without causing an inside pressure buildup so that the durability of the boot body is improved.  
      To achieve the object, the invention provides a sliding type constant velocity universal joint for transmitting torque between an outer joint member and an inner joint member fitted in the outer joint member while accommodating angular and axial displacements therebetween, including a boot having a boot body made of resilient material and a boot adaptor attached to one end of the boot body. The boot adaptor is fitted onto the outer surface of the outer joint member while the boot body is fitted onto a shaft extending from the inner joint member to the outside of the outer joint member to seal the inside of the joint. The outer joint member is provided with a seal portion in the outer surface on the far end side of a portion that mates with a fitting portion of the boot adaptor. The fitting portion of the boot adaptor is fitted to the seal portion in an airtight manner. The outer joint member further includes a small diameter portion having a smaller diameter in a region nearer to the open end than the seal portion the diameter of which is smaller than that of the seal portion, so that a gap is formed between the small diameter portion of the outer joint member and the fitting portion of the boot adaptor.  
      Because of the small diameter portion having a smaller diameter than the outside diameter of the seal portion, a gap is formed between the small diameter portion of the outer joint member and the fitting portion of the boot adaptor. This gap allows communication between inside and outside of the joint until the boot adaptor is completely fitted with the seal portion of the outer joint member and prevents a pressure buildup inside the joint. That is, if the mating parts between the outer joint member and the boot adaptor have the same length as that of conventional joints, the air inside the joint in the portion between the fitting portion of the boot adaptor and the small diameter portion of the outer joint member is not compressed. Deformation of the boot body when fitting the boot adaptor to the outer joint member is thus suppressed.  
      As discussed above, according to the sliding type constant velocity universal joint of the present invention, because of the small diameter portion having a smaller diameter than the outside diameter of the seal portion in a region nearer to the open end than the seal portion, a gap is formed between the small diameter portion of the outer joint member and the fitting portion of the boot adaptor. Therefore, the air inside the joint in the portion between the fitting portion of the boot adaptor and the small diameter portion of the outer joint member is not compressed, and deformation of the boot body caused by a pressure buildup inside the joint is suppressed. Thus, wear of the boot body due to its rubbing against the shaft of the inner joint member is prevented, and the durability of the boot body is improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the accompanying drawings:  
       FIG. 1  is a cross-sectional view of one embodiment of a tripod type constant velocity universal joint, which is one type of a sliding type constant velocity universal joint, of the present invention, part of which is enlarged to a greater scale;  
       FIG. 2  is a diagram for explaining how a boot adapter is assembled to an outer joint member;  
       FIG. 3  is an enlarged cross-sectional view illustrating relevant part of a modified example of the sliding type constant velocity universal joint of the invention;  
       FIG. 4  is an enlarged cross-sectional view illustrating relevant part of a modified example of the sliding type constant velocity universal joint of the invention;  
       FIG. 5  is an axial cross-sectional view of a conventional sliding type constant velocity universal joint; and  
       FIG. 6  is a cross-section view in a direction orthogonal to the axis of the conventional sliding type constant velocity universal joint. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings.  
       FIG. 1  is a cross-sectional view of one embodiment of a tripod type constant velocity universal joint, which is one type of a sliding type constant velocity universal joint, of the present invention. The tripod type constant velocity universal joint of  FIG. 1  generally includes, as the main components, an outer joint member  10 , an inner joint member  20 , and roller assemblies  30  as with the conventional example described in the foregoing. A boot  40  is fitted to an outer peripheral edge of the outer joint member  10  and to the shaft  23  of the inner joint member  20  to seal the inside of the joint. Since the inner joint member  20 , the roller assemblies  30 , and the boot  40  are the same as the conventional example, these are given the same reference numerals and detailed description thereof is omitted. The outer joint member  10 , which has the characteristic feature of the invention, will be described below.  
      The outer joint member  10  includes a seal portion  14  on the far end side of a portion that mates with a fitting portion  46  of the boot adaptor  42 . The seal portion  14  is fitted with the fitting portion  46  of the boot adaptor  42  in an air tight manner. A step is formed in a region nearer to the open end than the seal portion  14  where the diameter is smaller than that of the seal portion  14  to define a small diameter portion  18 . The seal portion  14  has a diameter that is generally the same as the inside diameter of the fitting portion  46  of the cylindrical boot adaptor  42  so that it is air-tightly fitted with the fitting portion  46  of the boot adaptor  42 . The small diameter portion  18  has a slightly smaller diameter than the inside diameter of the fitting portion  46  of the boot adaptor  42  to define an air passage gap between itself and the fitting portion  46  as well as to reduce rattling of the boot adaptor  42  due to the loose fitness thereof.  
      When the fitting portion  46  of the boot adaptor  42  is fitted to the open end of the outer joint member  10 , this small gap between the small diameter portion  18  of the outer joint member  10  and the fitting portion  46  of the boot adaptor  42  allows communication between inside and outside of the joint until the fitting portion  46  reaches the seal portion  14 , as shown in  FIG. 2 , thereby preventing a pressure buildup inside the joint. That is, when the boot adaptor  42  is completely fitted to the fitting end of the outer joint member  10 , the air inside the joint in the portion between the fitting portion  46  of the boot adaptor  42  and the small diameter portion  18  of the outer joint member  10  has not been compressed. Deformation of the boot body  41  due to pressure buildup inside the joint is thus suppressed. As the boot body  41  is thereby prevented from wear due to rubbing against the shaft  23  of the inner joint member  20 , improved durability of the boot body  41  is obtained.  
      The boot adaptor  42  is not incurred with press-fitting load until it comes to the seal portion  14  of the outer joint member  10 . As reduced is the accumulated load on the boot adaptor  42  when it is fitted to the outer joint member  10 , the strength of the boot adaptor  42  against the press-fitting load can be decreased without incurring any danger of damage to the boot adaptor  42  when it is fitted to the outer joint member  10 . Accordingly, the boot adaptor  42  can be made thinner and lighter.  
      While the invention has been described in the form of a preferred embodiment, the invention is not limited to the form described, and numerous modifications may be made to the above-described embodiment. For example, while the small diameter portion  18  of the outer joint member  10  is formed as a stepped surface having a smaller diameter than the seal portion  14 , the small diameter portion  18  may be tapered as shown in  FIG. 3 , or may have any other shape as long as it has a smaller diameter than the seal portion  14 .  
      In the above-described embodiment, the small diameter portion  18  of the outer joint member  10  has a slightly smaller diameter than the outside diameter of the seal portion  14  for the purpose of reducing rattling of the fitting portion  46  of the boot adaptor  42  due to the loose fitness thereof. Alternatively, a plurality of ribs  19  may be provided on the small diameter portion  18  as shown in  FIG. 4 . As such ribs accommodate the fitting looseness, the diameter of the small diameter portion  18  can be further reduced. The ribs  19  may extend longitudinally to make line contact with the boot adaptor  42 , or they may be pins to make point contact with the boot adaptor  42 .  
      While the sliding type constant velocity universal joint of the invention has been described as a tripod type constant velocity universal joint having single roller type roller assemblies  30 , the invention may be applied to a tripod type constant velocity universal joint having double roller type roller assemblies, or to other types of sliding type constant velocity universal joints such as cross-groove joints.