Abstract:
A dual type constant velocity universal joint solves the problems of greasing work efficiency and lubricating ability of a double Cardan Joint. The dual type constant velocity universal joint includes two constant velocity universal joints. Each constant velocity universal joint includes: a cylindrical outer ring in which a plurality of guiding grooves that extend in an axial direction are formed on a spherical inner circumferential surface; an inner ring in which a plurality of guiding grooves that extend in an axial direction are formed on a spherical outer circumferential surface; balls for torque transmission each of which is disposed in each of a plurality of ball tracks which are through coordination between the guiding grooves of the outer ring and the guiding grooves of the inner ring; and a cage  5  for holding the balls. The outer ring are coaxially integrated with back to back, and a place between the outer circumferential surface on the opening side of the outer ring and shafts connected to the inner ring is covered with a boot having a metal ring.

Description:
TECHNICAL FIELD 
     The present invention relates to a dual type constant velocity universal joint which is formed by integrating two pieces of constant velocity universal joints and which is mainly used for a drive axle of a vehicle. In particular, the present invention relates to a dual type constant velocity universal joint which is preferable for use as a constant velocity universal joint for a drive axle of a rough-terrain crane vehicle, farm tractor or the like that requires a large steering angle. 
     BACKGROUND ART 
     Conventionally, in many drive axles for farm tractors or the like that require a large steering angle, the differential gear output shaft is coupled to the wheels via a constant-velocity type double Cardan joint. While a double Cardan joint requires a long axial length and a large outer diameter, it can have an intersection angle exceeding 50°. The constant-velocity type double Cardan joint is ordinarily lubricated by grease that has been filled in an axle housing. In the meantime, a drive axle of a large vehicle such as a rough-terrain crane vehicle adapted to on-road driving uses one constant velocity universal joint of Rzeppa-type or ball-fixed type (hereinafter sometimes referred to as “BJ” or “BJ-type”) with bellows boot to simplify the mechanism (see Patent Document 1). The BJ type includes an outer ring on which a curved track groove is formed in an axial direction on a spherical inner diameter surface, an inner ring on which a curved track groove is formed in an axial direction on a spherical outer diameter surface, a plurality of balls for torque transmission disposed in ball tracks that are formed through coordination between the track groove of the outer ring and the track groove of the inner ring corresponding thereto, and a cage provided with pockets for holding the balls. 
     When a constant velocity universal joint of BJ-type is used for a drive shaft, an axle section (driven shaft) that integrally extends from one end of the outer ring in an axial direction is coupled to a wheel bearing, and a shaft (drive shaft) that is spline engaged with a shaft hole of the inner ring is coupled to a slide-type constant velocity universal joint. When there is an angular displacement between the two axes, that is, between an axle section of the outer ring and a shaft of the inner ring, the balls housed in the pockets of the cage are always held in an angle bisecting plane of any operating angle, whereby constant velocity of the joint can be maintained. The operating angle herein refers to an angle created by the axle section of the outer ring and the shaft of the inner ring. 
     In the meantime, a drive axle of a large vehicle such as a rough-terrain crane vehicle includes, in a section inside of the wheel hub, a so-called hub reduction including a reducer such as a planetary gear mechanism to prevent large drive torque from acting on the BJ-type constant velocity universal joint.
     Patent Document 1: Japanese Patent Laid-open Publication No. Heisei 4-358970   

     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     The drive axle including a BJ with a bellows boot must allow a large angle exceeding 30° when steering the wheels. Accordingly, such a drive axle has a longer axial direction length of the boot and a larger outer diameter than an ordinary drive axle. In the case of a rough-terrain crane vehicle including a hub reduction, the number of revolutions when the vehicle is driving straight at a high speed exceeds 1300 rpm. A synergetic effect of the high speed revolution and the large diameter of the BJ causes a problem that the boot swells and is deformed. To address this, although improvement is being made mainly on the shape of the bellows boot and on the material thereof to increase hardness of the bellows boot, such improvement is not enough to inhibit deformation of the boot. There are increasing cases where the problem of deformation of the boot cannot be solved merely by improvement of the shape and material of the bellows boot because of the relationship between the required BJ size and the number of revolutions. 
     In addition, in the case of a drive axle using one BJ, when excessive torque caused by sudden start or the like acts thereon in the case where the operating angle of the BJ has increased, damage can occur at a portion where the ball guiding groove is shallow. In other words, when the operating angle of the BJ has increased, the ball moves to the rear side of the ball guiding groove. The rear side of the ball guiding groove has a smaller groove depth. Accordingly, a contact ellipse of the ball in the ball guiding groove pushes out an edge of an edge chamfer of the ball guiding groove. When a large load accompanying excessive torque acts on the ball under this state, the outer spherical surface of the inner ring in the vicinity of the ball guiding groove rises and thus it is deformed. When the outer spherical surface of the inner ring is deformed, operability of the joint may sometimes be reduced or a chamfer edge of the ball guiding groove may be chipped. To prevent such damage, the outer diameter of the BJ must be increased. 
     Furthermore, there is a structural restriction in a drive axle using one BJ also that a king pin center, which is the center of steering rotation of the wheel, must match the center of the angled bending of the BJ (that is, the intersection of the 2 axes; the axle section of the outer ring and the shaft of the inner ring). 
     An object of the present invention is to provide a constant velocity universal joint which can inhibit deformation of a boot at a high speed revolution, which can have an operating angle exceeding 50° without increasing the size of the outer diameter size of the BJ, and which does not require precise position alignment with a king pin center. 
     Means for Solving the Problems 
     To solve the foregoing problem, the present invention includes two constant velocity universal joints. Each constant velocity universal joint includes: a cylindrical outer ring in which a plurality of guiding grooves that extend in an axial direction are formed on a spherical inner circumferential surface; an inner ring in which a plurality of guiding grooves that extend in an axial direction are formed on a spherical outer circumferential surface; balls for torque transmission each of which is disposed in each of a plurality of ball tracks which are formed through coordination between the guiding grooves of the outer ring and the guiding grooves of the inner ring; and a cage for holding the balls. The outer rings are coaxially integrated with back to back, and a portion between the outer circumferential surface on the opening side of the outer ring and a shaft connected to the inner ring is covered with a boot having a metal ring. 
     The dual type constant velocity universal joint according to the present invention uses a boot having a metal ring (of diaphragm type) in place of a conventional bellows boot. Therefore, the problem of deformation of the boot when rotating at a high speed can be resolved. Specifically, in the case where the reference axis diameter of the shaft to be coupled to the inner ring of the BJ is 2 inches, the maximum number of revolutions of a conventional bellows boot at the operating angle 0° would be approx. 1300 rpm. However, no problem of deformation will occur in the BJ according to the present invention which uses a boot having a metal ring, even when the number of revolutions is 2000 rpm or higher. 
     In addition, since the dual type constant velocity universal joint according to the present invention includes two BJs, the dual type constant velocity universal joint as a whole can actualize twice as large as the operating angle of one BJ. Specifically, tightening of two BJs of a compact disc type in an axial direction by a bolt enables reduction of the operating angle per BJ to 18° or less. As a result of this, even at an operating angle at which a part of a contact ellipse of the ball would push out the chamfer of the guiding grooves of the inner ring in a conventional joint, deformation of the chamfer of the guiding groove caused by load torque can be prevented without increasing the size of the outer diameter of the BJ. 
     To coaxially integrate the outer rings back to back, for example, a disk-shaped adapter flange having a center through-hole is sandwiched between two outer rings and a bolt is inserted in the two outer rings and the adapter flange to integrate them. Alternatively, two outer rings may be formed on opposite sides of a cylindrical component which has been integrated. 
     Advantage of the Invention 
     As described above, by integrating two constant velocity universal joints, the present invention can actualize an operating angle or an intersection angle that is twice as large as the dual type constant velocity universal joint as a whole. For example, in the case where the operating angle or the intersection angle for one constant velocity universal joint is 35°, the intersection angle which is twice as large as it, that is 70°, can be actualized as a whole. As a result of this, the operating angle is approximately half of the case where one constant velocity universal joint is used. In addition, deformation of the guiding grooves because the contact ellipse thereof has pushed out is also more advantageously prevented, whereby the size reduction of the constant velocity universal joint can be achieved. 
     In addition, adoption of a boot having a metal ring can inhibit formation of a boot when rotating at a high speed. Accordingly, the dual type constant velocity universal joint is preferable for a drive axle of a rough-terrain crane vehicle mounted with a hub reduction. 
     Use of two constant velocity universal joints eliminates the necessity of precise position alignment of the king pin center, which is the steering center of the wheel, with the bending center of the joint. Therefore, freedom in the design of a drive axle increases. 
     Use of a disc-type constant velocity universal joint and of a boot having a metal ring enables a compact joint which is short in an axial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view of a dual type constant velocity universal joint according to a first embodiment of the present invention in the state where the operating angle is 0°; 
         FIG. 2  is a longitudinal sectional view of the state where the joint has become close to the maximum operating angle; 
         FIG. 3  is a longitudinal sectional view of a dual type constant velocity universal joint according to a second embodiment of the present invention in the state where the operating angle is 0°; 
         FIG. 4  is a longitudinal sectional view of the case where one of the joints has the operating angle of 32°; and 
         FIG. 5  is a cross sectional view showing a surface pressure in the guiding groove of the inner ring. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be hereinafter described with reference to  FIGS. 1 to 5 .  FIGS. 1 and 2  show a first embodiment of a dual type constant velocity universal joint according to the present invention.  FIG. 1  shows the state where the operating angle is 0°, and  FIG. 2  shows the state where the operating angle is 32°. The dual type constant velocity universal joint has a structure formed by integrating two ordinary fixed-type constant velocity universal joints of same specifications. The constant velocity universal joint uses balls  4  as torque transmission component. A differential gear-side shaft  3  is connected to one of the joints, and a wheels-side shaft  10  is connected to the other joint. A distal end of the wheels-side shaft  10  is connected to a sun gear of a hub reduction. A slinger  9  is attached to the wheels-side shaft  10 . The outer diameter surface of the slinger  9  makes contact with a lip section of an oil seal for preventing leakage of lubricant from a planetary gear of the hub reduction. 
     For the sake of convenience, the embodiment will now be described with reference to mainly a one-side half of one side half the dual type constant velocity universal joint, that is, one of the two constant velocity universal joints. The one-side half of the dual type constant velocity universal joint, as shown in  FIG. 2 , includes a cylindrical outer ring  1 , an inner ring  2 , the shaft  3 , the balls  4  for torque transmission, a cage  5  and a boot  8 . In the cylindrical outer ring  1 , six curved guiding grooves  1   b  are formed in an axial direction on an inner diameter spherical surface  1   a  thereof. In the inner ring  2 , six curved guiding grooves  2   b  are formed in an axial direction on an outer diameter spherical surface  2   a  thereof. The inner ring  2  includes a spline (or serration) hole  2   c . One end of the shaft  3  is engaged with the spline hole  2   c . Each of the balls  4  for torque transmission is disposed in each of 6 ball tracks that are formed through coordination between the guiding grooves  1   b  of the outer ring  1  and the guiding grooves  2   b  of the inner ring  2 . The cage  5  holds the balls  4 . The boot  8  is disposed between the outer circumferential surface on the opening side of the outer ring  1  and the outer circumferential surface of the shaft  3  ( 10 ). Although both the numbers of the guiding grooves  1   b , and of the guiding grooves  2   b  are herein set as 6, they may sometimes be increased to 7, 8, 9, 10, or any preferable number. 
     The outer ring  1  has a structure formed by integrating the individual outer rings  1  of the two constant velocity universal joints. Specifically, the two outer rings  1  are coaxially integrated in the state where they are matched back to back with the opening sides thereof (on the shafts  3 ,  10  side) facing outwards. The insides of the right and left outer rings  1  are connected with each other. The term “integrated” herein includes both the case of connecting two outer rings  1  that have been made as separate bodies to integrate them (in the first embodiment) and the case of complete integral molding from a common material (in the second embodiment). In the first embodiment, the two outer rings  1  are integrated with the adapter flange  11  being sandwiched therebetween. When the dual type constant velocity universal joint is used for a drive axle, the center in the width direction of the adapter flange  11  substantially matches an axis of rotation of the king pin. 
     The adapter flange  11  is a disk-shaped component which has a center through-hole  11   a . Cylinder sections for position alignment  11   b ,  11   b  are formed in the peripheral part of the adapter flange  11  such that they project leftwards and rightwards. The size of the cylinder sections  11   b ,  11   b  is matched with that of the outer diameter of the outer ring. Bolt insertion holes  11   c  are formed at a plurality of locations in circumferential direction in a section inside of the cylinder section  11   b . The peripheral part of the outer ring at a portion where the ball guiding grooves  1   b  are located is thinner, and the bolt insertion holes  11   c  are formed at a portion excluding such thin portion, that is, at a plurality of locations at equal intervals in circumferential direction between the guiding grooves. After the positions of the bolt insertion holes  11   c  are aligned a bolt  12  is inserted thereinto, and a nut  13  is screwed into the distal end of the bolt  12 . Numerals  14 ,  15  denote spring washers. 
     The outer circumferential surface of the outer ring  1  is a cylindrical surface  11   d  around the axis line of the outer ring  1  as the center. A metal ring  16  of the boot  8  is engaged with the cylindrical surface  11   d  on the opening side. The metal ring  16  includes bolt insertion ports  16   a  at equal intervals in circumferential direction, and the metal ring  16  is tightened to the side surface of the outer ring  1  by the bolt  12  when the two outer rings  1 ,  1  are connected to the adapter flange  11  by the same bolt  12 . The metal ring  16  includes a large diameter section  16   b , a flange section  16   c  and a small diameter section  16   d . The large diameter section  16   b  is engaged with the outer circumferential surface of the outer ring  1 . The flange section  16   c  abuts with the side surface of the outer ring  1 . The small diameter section  16   d  projects in the direction to be separated from the outer ring  1 . A liquid packing is interposed between the flange section  16   c  and the side surface of the outer ring  1  for preventing leakage of grease enclosed in the interior of the joint. A large diameter end  8   a  of the disk-shaped boot  8  is integrated through vulcanization with the small diameter section  16   d  of the metal ring  16 . A small diameter end  8   b  of the disk-shaped boot is engaged with a ring-shaped concave section  3   a  ( 10   a ) that is formed on the outer circumferential surface of the shaft  3  ( 10 ). A band  17  is fixed to the outer circumferential surface of the small diameter end  8   b . The disk-shaped boot  8  has a structure, with a U-shaped cross section, in which the large diameter end  8   a  and the small diameter end  8   b  are opposite to each other in radial direction. 
     The distal end of the shaft  3  is engaged with the spline hole  2   c  of the inner ring  2 . At the same time, relative movement of the shaft  3  with the inner ring  2  is restricted by a rectangular circlip  19  and a round circlip  18  that are engaged with the ring-shaped grooves  3   c ,  3   b , respectively. A center hole  3   d  ( 10   d ) is formed on the distal end surface of the shaft  3  ( 10 ) for centering when lathing the shaft  3  ( 10 ). 
     Each of the right and left the constant velocity universal joints has a structure which is called as Rzeppa type, ball-fixed type, or double-offset type as a single unit. In the state where the operating angle is 0° as shown in  FIG. 1 , the respective centers O 1 , O 2  with radials R 1 , R 2  of the guiding grooves  1   b ,  2   b  of the outer ring  1  and the inner ring  2  are offset with respect to the common center O (that is, the center of the joint) of the inner diameter spherical surface  1   a  of the outer ring  1  and of the outer diameter spherical surface  2   a  of the inner ring  2  in opposite axial directions by an equal distance f. As a result of this, the ball track that is formed through coordination between the guiding grooves  1   b  and the guiding grooves  2   b  corresponding thereto has a wedge shape that is opened toward the opening side of the joint. 
     The cage  5  is formed of an annular component. The outer circumferential surface thereof is referred to as an outer diameter spherical surface  5   a  that makes a sliding contact with the inner diameter spherical surface  1   a  of the outer ring  1 , and the inner circumferential surface thereof is referred to as an inner diameter spherical surface  5   b  that makes a sliding contact with the outer diameter spherical surface  2   a  of the inner ring  2 . Windows  6  are formed through penetration by grinding, milling or the like on the peripheral wall of the cage  5 . The number of the windows  6  is the same as the number of the balls  4 . The windows  6 , which are for example rectangular, are formed at equal intervals in circumferential direction of the cage  5 . 
     The dual type constant velocity universal joint according to the present invention is configured as described above. In the state where the outer ring  1  and the inner ring  2  creates the operating angle 0° as shown in  FIG. 1 , the ball  4  is held in a plane which includes the center O of the joint and which is perpendicular to the rotational axis line due to the offset effect of respective curvature centers O 1 , O 2  of the guiding groove  1   b  of the outer ring  1  and of the guiding groove  2   b  of the inner ring  2 , respectively, and torque is transmitted in this state. 
     Next, in the state where the outer ring  1  and the inner ring  2  at the opposite sides of the dual type constant velocity universal joint are bent to the limit operating angle θ, the dual type constant velocity universal joint as a whole actualizes the operating angle 2θ. The torque transmission balls  4  of each joint are aligned in the plane that bisects the angle θ by the cage  5 , which ensures maintaining constant velocity of both joints. 
     In the case where the dual type constant velocity universal joint is used for a drive axle, the center in the width direction the adapter flange is substantially positioned at the rotational center of the king pin as described above. However, the joint of the present invention is a dual type constant velocity universal joint that is formed by connecting two BJs. Accordingly, unlike a conventional joint using only one BJ, there is no need for precise position alignment with the axis rotation of the king pin. 
       FIG. 3  shows a second embodiment of the present invention, in which an outer ring  1 ′ is of an integrated type and the adapter flange  11  as described before has been omitted. In other words, two outer rings are formed on opposite sides of an integrated cylindrical component. The metal ring  16  of the boot  8  is fixed to the side surface of the outer ring  1 ′ by a hexagonal socket bolt  20 . Other elements are the same as those in the first embodiment. Therefore, the same numerals are provided to portions corresponding to the portions in  FIG. 1  and  FIG. 2 , and the description thereof will be omitted. In the meantime, the state in the case where one of the BJs of the second embodiment has the operating angle 32° is shown in  FIG. 4 . In this state, a disadvantageous situation is generated in which the ball  4  at the rear side of the joint moves to a shallow portion at the rear of the guiding groove  1   b , thereby the guiding groove  1   b  being easily deformed. 
     The surface pressure at a ball contact point in the guiding groove  2   b  of the inner ring  2  will now be described.  FIG. 5  slightly exaggeratedly shows the relationship between a contact ellipse  21  and a ball contact point surface pressure curve P ball . The resultant force of the ball contact point surface pressures is expressed as P. The relationship of force relationship shown in  FIG. 5  is common to the first embodiment as described above and the second embodiment. With respect to the ball  4  expressed commonly, the outer diameter spherical surface  2   a  of the inner ring  2  when the operating angle is 0° is expressed in by the solid line. Meanwhile, the outer diameter spherical surface  2   a  when the operating angle of a conventional joint using one BJ is 32° is expressed by the dashed line. It is the relationship between the ball  4  at the rear side of the joint and the guiding groove  1   b  in  FIG. 4  that the dotted line indicates. 
     The outer diameter spherical surface  2   a  when the operating angle 32° of the joint of the present invention is shown by the dashed-dotted line. In the case where a conventional joint has the operating angle 32°, a shoulder section of the contact ellipse  21  of the ball  4  pushes out a chamfer  22  of the guiding groove  2   b . As a result of this, a large load in accordance with excessive torque acts on the ball  4 , whereby an edge load  23  causes the outer diameter spherical surface  2   a  of the inner ring in the vicinity of the ball guiding groove  2   b  to rise to deform. Such deformation of the outer diameter spherical surface  2   a  of the inner ring may cause reduced operability of the joint or cause chipping of the edge of the chamfer  22  of the ball guiding groove  2   b . According to the dual type constant velocity universal joint of the present invention, since the joint uses two BJs, each BJ requires only half of the operating angle the dual type constant velocity universal joint requires as a whole. Therefore, even when the same operating angle 32° is granted, the outer diameter spherical surface  2   a  of the inner ring  2  is located at the position as shown by the dashed-dotted line, and accordingly, there is a leeway in the depth of the guiding groove  2   b . Therefore, substantially no edge load is generated, which can suppress deformation caused by rising of the outer diameter spherical surface  2   a  of the inner ring. 
     Although the embodiments of the present invention have been so far described, the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea as described in the scope of the claims. 
     INDUSTRIAL APPLICABILITY 
     A dual type constant velocity universal joint of the present invention is not limited to use in drive axles of rough-terrain crane vehicles or farm tractors. It can also be applicable to drive axles of various vehicles and to industrial machines that require high operating angles.