Abstract:
A constant velocity (CV) joint includes a shield to protect a J-boot from damage due to projectiles such as stones and to prevent ballooning. A rigid portion of the shield is fixed to a ring, which is adapted for fixation to a powertrain component such as a transmission. A flexible portion of the shield prevents projectiles from entering through the opening created by non-coincident axes of the shaft and ring. The flexible portion has a number of truncated conical panels with alternating orientation that accommodate the variable size opening by flexing in an accordion-like fashion.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to the field of vehicle drivelines. More particularly, the disclosure pertains to a constant velocity universal joint having a protective shield. 
       BACKGROUND 
       [0002]      FIG. 1  schematically illustrates a rear wheel drive vehicle powertrain with an independent rear suspension. Solid lines indicate shafts capable of transferring torque and power. Engine  10  converts chemical energy in the fuel into mechanical power. Transmission  12  modifies the speed and torque to suit current vehicle requirements. At low vehicle speed, the transmission provides torque multiplication for improved performance. At cruising vehicle speed, the transmission increases speed permitting the engine to run at a fuel efficient operating point. The output of transmission  12  is coupled to the input of differential  14  by rear driveshaft  16 . Two components are coupled when rotating either component by one revolution causes the other component to rotate by one revolution. Differential  14  distributes the power to left rear wheel  18  and right rear wheel  20  via left axle shaft  22  and right axle shaft  24  respectively. Differential  14  changes the direction of rotation by 90 degrees and multiplies the torque by a final drive ratio. Differential  14  provides approximately equal torque to each wheel while permitting slight speed differences as the vehicle turns a corner. 
         [0003]    In a four wheel drive vehicle based on the powertrain of  FIG. 1 , a transfer case fixed to the transmission divides power between the rear driveshaft  16  and a front driveshaft that directs power to the front wheels via a front differential. In a front wheel drive powertrain, the front differential is typically integrated with the transmission in an assembly called a transaxle. In a four wheel drive vehicle based on a front wheel drive powertrain, a power take-off unit fixed to the transaxle drives a rear driveshaft and a rear drive unit fixed to the rear differential selectively transfers power to the rear differential. Throughout this document, the term transmission should be interpreted to include any transfer case or power take-off unit. Similarly, the term differential should be interpreted to include any rear drive unit. 
         [0004]    Engine  10 , transmission  12 , and rear differential  14  are mounted to vehicle structure. Wheels  18  and  20  are supported via a suspension that allows the wheels to move vertically over road bumps while limiting the vertical movement of the vehicle body. The axis of rotation of engine  10  and transmission  12  may be offset slightly from the input axis of differential  14 . Universal joints  26  and  28  accommodate this offset by transmitting torque and power between shafts that rotate about intersecting but not coincident axes. Similarly, universal joints  30 ,  32 ,  34 , and  36  accommodate the offset between the output axis of differential  14  and the axes of rotation of wheels  18  and  20  even though the axes of rotation of the wheels fluctuates as the wheels absorb road bumps. In some rear wheel drive vehicles, the differential  14  is not mounted directly to the vehicle frame but is instead supported by left and right axles  22  and  24 . This eliminates the need for universal joints  30  and  34  but universal joints  26  and  28  must then accommodate a fluctuating offset between the transmission output axis and the differential input axis. 
         [0005]    A variety of types of universal joints are known. In the simplest types of universal joint, although the driving shaft and driven shaft are coupled, the instantaneous speed of the driven shaft differs slightly from the instantaneous speed of the driving shaft as a function of rotational position. Consequently, although the driving shaft may have a constant speed, the driven shaft speed may oscillate at a frequency proportional to the driving shaft speed. Due to the inertia associated with the driven shaft, this results in an oscillating torque level. The oscillating torque level may be perceived by vehicle occupants, especially if the frequency is close to a natural frequency of the driveline. Therefore, universal joints that maintain equal instantaneous speeds between the driving and driven shafts, called Constant Velocity (CV) joints, are desirable. Several types of CV joint mechanisms are known. Among known CV joint types, tripod joints and Rzeppa joints are common in automotive drivelines. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    A constant velocity joint includes a ring, a shaft, a flexible boot, and a protective shield. The ring is adapted for fixation to a flange of a powertrain component such as a transmission. The ring and the shaft are coupled to rotate at the same rotational speed, but their axes are not constrained to be coincident. The flexible boot seals a cavity containing lubricating fluid. The protective shield includes a rigid portion and a flexible portion. The rigid portion, which is fixed to the ring, extends axially over the boot to protect the boot from projectiles and to prevent ballooning. An outer edge of the flexible portion is fixed to the ring while an inner edge of the flexible portion maintains contact with the shaft, preventing projectiles from reaching the flexible boot around the rigid portion. The flexible portion may define a plurality of truncated conical panels with alternating orientation such that the flexible portion deflects accordion fashion to accommodate the non-coincident axes of the ring and shaft. Both the rigid portion and the flexible portion of the protective shield may be formed in multiple circumferential segments for ease of assembly. 
         [0007]    A vehicle driveshaft includes a shaft, a ring, a flexible boot, a rigid shield, and a flexible shield. The shaft is adapted for fixation to a differential at one end and is coupled to the ring at the opposite end. The shaft and the ring have non-coincident axes. A flexible boot is fixed to the ring and to the shaft. The rigid shield fixed to the ring extends axially over the flexible boot to protect the boot from projectiles and to prevent ballooning. An outer edge of the flexible shield is fixed to the rigid shield while an inner edge of the flexible shield contacts the shaft. The flexible portion may define a plurality of truncated conical panels with alternating orientation such that the flexible portion deflects accordion fashion to accommodate the non-coincident axes of the ring and shaft. Both the rigid portion and the flexible portion of the protective shield may be formed in multiple circumferential segments for ease of assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic diagram of a vehicle powertrain. 
           [0009]      FIG. 2  is side cross section of a CV joint suitable for use in several locations in the powertrain of  FIG. 1 . 
           [0010]      FIG. 3  is an end cross section of the CV joint of  FIG. 2 . 
           [0011]      FIG. 4  is a pictorial view of the CV joint of  FIG. 2 . 
           [0012]      FIG. 5  is a side cross section of the CV joint of  FIG. 2  with a protective shield. 
           [0013]      FIG. 6  is a pictorial view of the CV joint of  FIG. 2  with a protective shield. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0015]      FIGS. 2-4  illustrate a Rzeppa-type CV joint suitable for use at  26 ,  28 ,  30 ,  32 ,  34 , and/or  36  in  FIG. 1 .  FIG. 2  is a cross section in the plane defined by the centerlines  50  and  52  of the two sides of the joint. Ring  54  is adapted for fixation to the driveline component such as the transmission output shaft, the wheel, or the differential as described in detail below. Stub shaft  56  is adapted for fixation to driveshaft  16  or to an axle shaft  22  or  24 . Stub shaft  56  may be fixed to the shaft by welding at the circumference of flange  58 , for example. Six concave grooves  60  are formed in ring  54  and six convex grooves  62  are formed in stub shaft  52 . Six balls  64 , each positioned within a concave groove  60  and a convex groove  62 , position stub shaft radially with respect to ring  54 . The balls can roll within the grooves to accommodate the angle between axis  50  and axis  52 . For example, as shown in  FIG. 2 , the ball at the top has rolled toward the left of the groove in ring  54  and has rolled toward the right end of the groove in stub shaft  56 . The ball on the bottom has rolled the opposite direction. As either the ring or the stub shaft rotates about its respective axis, the balls force the other member to rotate by an equal amount such that the grooves line up at the ball locations. The balls may be retained by a cage (not shown). 
         [0016]    Proper function of the joint requires lubrication, typically in the form of grease. A back plate  66  and a flexible boot  68  seal a cavity to retain the grease and to prevent contaminants from entering. Flexible boot  68  may be a J-shaped boot fixed to front plate  72  which, in turn, is fixed to ring  54 . Boot  68  is made of a flexible material to accommodate the different axes of rotation. During each revolution of the shafts, a particular circumferential portion of the boot changes from the shape shown at the top of  FIG. 2  to the shape shown at the bottom of  FIG. 2  and then back. In some applications, such as the underside of an off-road vehicle, the joint may be vulnerable to projectiles that may puncture the J-boot. If the grease leaks out or contaminants get in, friction may lead to rapid temperature increase and joint failure. 
         [0017]    Another failure mode, called ballooning, occurs when the pressure builds up inside the grease cavity. This may occur, for example, due to friction causing the temperature of the grease and air in the cavity to increase. Centrifugal forces also contribute to internal pressure in the cavity. The increased pressure may cause boot  68  to deform such that the convex surface facing the grease cavity becomes concave. This type of deflection weakens the boot material over time, eventually leading to loss of sealing function and eventual joint failure. 
         [0018]      FIG. 3  is a cross section taken through the plane defined by the six balls  64 .  FIG. 4  is a pictorial view of the joint. Ring  54  defines six holes  70  that are used to fix the ring to the component, such as the transmission, differential, or wheel. Specifically, six bolts are inserted through the holes  70 , from the side with the J-boot, into threaded holes in a flange of the component. Washers may be inserted to distribute the compressive force from the bolt head across the face of the front plate  72 . In some cases, it may be necessary to rotate the shaft after inserting some of the bolts in order to be able to reach the remaining bolts with an appropriate tool. The shaft may be welded to the stub shaft  54  prior to positioning the shaft assembly into the vehicle. 
         [0019]      FIGS. 5 and 6  show the CV joint of  FIGS. 2-4  with a protective shield.  FIG. 5  is a cross section in the same plane as  FIG. 2 . The protective shield includes a rigid portion  74  and a flexible portion  76 . The rigid portion  74  is fixed to the ring. For example, the rigid portion may be fixed to the ring by the same bolts  78  that fix the ring to the driveline component. A flange of the rigid portion may be compressed between the washer  80  and the front plate. The rigid portion  74  also constrains boot  68  from ballooning outward. The rigid portion protects the flexible J-boot from damage. The flexible portion seals off the gap between the rigid portion and the shaft, preventing any projectiles from reaching the J-boot and potentially rupturing it. In order to accommodate the non-coincident axes of rotation, an inner edge of the flexible portion must be capable of moving to a position not concentric with an outer edge. This may be accomplished, for example, by forming the flexible portion with an accordion shape having a number of truncated conical panels with alternating orientation. Unlike the flexible J-boot, however, the flexible portion of the protective shield does not need to form a seal against the shaft. If a projectile, such as a rock, creates a small hole in the flexible portion, the universal joint will continue to function properly. 
         [0020]      FIG. 6  is a pictorial view of the CV joint with protective shield  74  and  76 .  FIG. 6  also shows the six bolts  78  and the washers  80  used to fasten ring  54  to a component flange. Note that both the rigid portion  74  and the flexible portion  76  of the shield may be formed from multiple circumferential segments which collectively surround the circumference of the J-boot. Each circumferential portion can be fastened to the CV joint separately. 
         [0021]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.