Patent Abstract:
A constant velocity joint has an outer part, an inner part, a plurality of torque transmitting balls, and a cage having windows for retaining the balls in the ball tracks of the outer and inner parts. The balls are retained in a constant velocity plane by the cage and guided by corresponding pairs of outer and inner ball tracks. The cage has an outer spherical face guided in contact by an inner bore of the outer part and inner concave face rotatably guided in contact by the convex face of the inner part. The outer part having a normal axial range, an extended axial range, and at least one energy absorption surfaces located in the extended axial range. Wherein the energy absorption surface interferes with at least one of the torque transmitting balls when the joint is operated beyond said normal axial range.

Full Description:
TECHNICAL FIELD 
   The present invention relates generally to motor vehicle propeller shafts, and more particularly concerns a constant velocity joint having improved crash-worthiness and energy absorption capabilities within a propeller shaft of a motor vehicle. 
   BACKGROUND OF THE INVENTION 
   Constant velocity joints are common components in automotive vehicles. Typically, constant velocity joints are employed where transmission of a constant velocity rotary motion is desired or required. Common types of constant velocity joints include end motion or plunging and fixed motion designs. Of particular interest is the end motion or plunging type constant velocity joints, which include a tripod joint, a double offset joint, a cross groove joint, and a cross groove hybrid. Of these plunging type joints, the tripod type constant velocity joint uses rollers as torque transmitting members, and the others use balls as torque transmitting members. Typically, these types of joints are used on the inboard (toward the center of the vehicle) on front sideshafts and on the inboard or outboard side for sideshafts on the rear of the vehicle and on the propeller shafts found in rear wheel drive, all wheel drive, and four-wheel drive vehicles. 
   Propeller shafts are commonly used in motor vehicles to transfer torque and rotational movement from the front of the vehicle to a rear axle differential such as in a rear wheel and all wheel drive vehicles. Propeller shafts are also used to transfer torque and rotational movement to the front axle differential in four-wheel drive vehicles. In particular, two-piece propeller shafts are commonly used when larger distances exist between the front drive unit and the rear axle of the vehicle. Similarly, sideshafts are commonly used in motor vehicles to transfer torque from a differential to the wheels. The propeller shaft and sideshafts are connected to their respective driving input and output components by a joint or series of joints. Joint types used to connect the propeller shaft and sideshaft interconnecting shafts include Cardan, Rzeppa, tripod and various ball type joints. 
   In addition to transferring torque and rotary motion, in many automotive vehicles the propeller shaft and axle drives allow for axial motion. Specifically, axial motion is designed into two-piece propeller shafts by using an end motion or plunging type constant velocity joint. 
   Besides transferring mechanical energy and accommodating axial movement, it is desirable for plunging constant velocity joints to have adequate crash-worthiness. In particular, it is desirable for the constant velocity joint to be shortened axially preventing the propeller shaft from buckling, penetrating the passenger compartment, or damaging other vehicle components in close proximity of the propeller shaft or drive axle. In many crash situations, the vehicle body shortens and deforms by absorbing energy that reduces the vehicle acceleration; further protecting the occupants and the vehicle. As a result, it is desirable for the propeller shaft be able to reduce in length during the crash, allowing the constant velocity joint to travel beyond its operation length. It is also desirable for the constant velocity joint within the propeller shaft to absorb a considerable amount of the deformation energy during the crash. Propeller shaft length reduction during a crash situation is often achieved by having the propeller shaft telescopically collapse and energy absorb thereafter. 
   In telescopic propeller shaft assemblies, the joint must translate beyond the constant velocity joint limitation before the telescopic nature of the propeller shaft is effectuated. In some designs, the propeller shaft must translate the torque as well as maintain the ability to telescope. In other designs, the telescopic nature of the joint only occurs after destruction of the joint, joint cage or some type of joint retaining ring. Still in other designs, the joint must first translate the balls off the race area before the telescopic attribute can be used for axial joint displacement. The limitation of the telescopic ability is that the constant velocity joint must be compromised before axial displacement can occur in a crash situation. Therefore, there is a desire to have a constant velocity joint that can accommodate the axial displacement during a crash. 
   Furthermore, the energy absorption only occurs after the functional limit or end of the constant velocity joint has been surpassed. This causes a time delay in the energy absorption of the propeller shaft. Then and only then, the energy absorption is accomplished and typically has a force step or impulse energy absorption pattern. After the initial energy absorption, typically, there is no further energy absorption in the propeller shaft. In another situation there is further energy absorption, but only after the joint balls successfully translate off the joint race and onto the propeller shaft. Therefore, there is a desire to have a constant velocity joint that has a controlled or tuned force energy absorption profile over a range of the joint&#39;s axial travel distance, especially when the normal operational range of the joint has been surpassed. 
   It would be advantageous to have the above mentioned features in the double offset joint. The double offset constant velocity joint is commonly known by automotive manufactures and suppliers as a DO type joint and the invention, here below, relates to this type of joint. Double offset joints are used for accommodating angular and axial displacements in a propeller shaft. Propeller shafts, in turn, are used to connect a drive unit, i.e. transmission, to a rear differential. The differential has an outer joint part in which a plurality of linear ball tracks are axially formed on an inner cylindrical surface thereof. This outer joint part contains an inner joint part in which a plurality of linear ball tracks are axially formed on an outer spherical surface thereof and an equal number of torque transmitting balls retained by cage windows in a ball cage and located in a pair of outer and inner ball tracks. Since the spherical center of the outer spherical face of the cage and the spherical center of the inner concave face thereof are offset to the opposite side in the axial direction from the center of the cage windows, they are called “double offset type”. When this kind of joint transmits a torque while taking an operating angle, the cage rotates to the position of the torque transmitting balls moving in the ball tracks in response to the inclination of the inner joint part to retain the torque transmitting balls on the constant velocity plane bisecting the operating angle. Furthermore, as the outer joint part and the inner joint part relatively displace in the axial direction, a slipping occurs between the outer spherical face of the cage and the inner cylindrical surface of the outer joint part to ensure a smooth axial displacement (plunging). 
   SUMMARY OF THE INVENTION 
   The present invention is directed toward a constant velocity joint for use in a vehicle driveline having at least one energy absorption element for improved crash-worthiness and energy absorption. In particular, at least one energy absorption element of the constant velocity joint, described herein, is tuned to control joint energy absorption for axial displacement beyond the normal axial travel range of the joint. 
   The present invention provides an energy absorbing plunging constant velocity joint for improved crash-worthiness. In particular, a constant velocity joint has an outer joint part, an inner joint part, a plurality of torque transmitting balls, and a ball cage having cage windows for retaining the torque transmitting balls in the outer and the inner ball tracks of the outer and the inner joint parts. The torque transmitting balls are retained in a constant velocity plane by the ball cage and guided by corresponding pairs of the outer and the inner ball tracks. The ball cage has an outer spherical face guided in contact by an inner bore of the outer joint part and an inner concave face rotatably guided in contact by the convex face of the inner joint part. The outer joint part having a normal axial range, an extended axial range, and at least one energy absorption surfaces located in the extended axial range. Wherein the energy absorption surface interferes with at least one of the torque transmitting balls when the joint is operated beyond the normal axial range, allowing the joint to absorb the thrust energy. 
   An advantage of the present invention is that the constant velocity joint absorbs energy within an extended axial range when the joint is thrust beyond its normal axial range. The present invention itself, together with further objects and intended advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of this invention, reference should now be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention. 
     In the drawings: 
       FIG. 1  shows a plan view of a four wheel drive vehicle driveline in which the present invention may be used to advantage. 
       FIG. 2  shows a half-sectional view of a vehicle propeller shaft assembly comprising one or more constant velocity joints in accordance with one embodiment of the present invention. 
       FIG. 3  shows a half-sectional view of a constant velocity joint in accordance with one embodiment of the present invention in a propeller shaft assembly. 
       FIG. 4  shows a partial view of a constant velocity joint in accordance with alternative embodiment of the present invention. 
       FIGS. 5A–5C  show a partial view of a constant velocity joint in accordance with an alternative embodiment of the present invention, and details of alternative energy absorption surfaces. 
       FIG. 6  shows a layout view of an outer ball track according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following description, various operating parameters and components are described for one constructed embodiment. These specific parameters and components are included as examples and are not meant to be limiting. 
   While the invention is described with respect to an apparatus having improved crash-worthiness within a propeller shaft of a vehicle, the following apparatus is capable of being adapted for various purposes including automotive vehicle drive axles, and other vehicles and non-vehicle applications which require collapsible propeller shaft assemblies. 
   Referring now to  FIG. 1 , there is shown a plan view of four-wheel drive vehicle driveline  10  wherein a constant velocity joint  11  in accordance with the present invention may be used to advantage. The driveline shown in  FIG. 1  is typical for a four wheel drive vehicle, however, it should be noted that the constant velocity joint  11  of the present invention can also be used in rear wheel drive only vehicles, front wheel drive only vehicles, all wheel drive vehicles, and four wheel drive vehicles. The vehicle driveline  10  includes an engine  14  that is connected to a transmission  16  and a power takeoff unit such as a transfer case  18 . The front differential  20  has a right hand sideshaft  22  and left hand sideshaft  24 , each of which are connected to a wheel and deliver power to the wheels. On both ends of the right hand front sideshaft  22  and the left hand front sideshaft  24  are constant velocity joints  12 . A front propeller shaft  25  connects the front differential  20  to the transfer case  18 . A propeller shaft  26  connects the transfer case  18  to the rear differential  28 , wherein the rear differential  28  is coupled to a rear right hand sideshaft  30  and a rear left-hand sideshaft  32 , each of which is connected to a respective wheel. Constant velocity joints  12  are located on both ends of the sideshafts  30 ,  32  that connect the rear wheels to the rear differential  28 . The propeller shaft  26 , shown in  FIG. 1 , is a two-piece propeller shaft. Each end includes a rotary joint  34  which may comprise a cardan joint or any one of several types of constant velocity or non-constant velocity joints. Between the two pieces of the propeller shaft  26  is a high speed constant velocity joint  11  in accordance with the present invention as well as a support  36  such as an intermediate shaft bearing. The constant velocity joints  11 ,  12 ,  34  transmit power to the wheels through the propeller shaft  26 , front propeller shaft  25  and sideshafts  22 ,  24 ,  30 ,  32  even if the wheels or the shafts  25 ,  26  have changing angles due to the steering or raising or lowering of the suspension of the vehicle. The constant velocity joints  11 ,  12 ,  34  may be any of the standard types known and used to advantage, such as a plunging tripod, a cross-groove joint, a cross-groove hybrid joint, or a double offset joint or any other type of constant velocity joints. 
     FIG. 2  shows a half-sectional view of a vehicle propeller shaft  26  assembly comprising one or more constant velocity joints  11 ,  34  in accordance with one embodiment of the present invention such as is shown in  FIG. 1 . The propeller shaft  26  assembly may include one, two or a combination of constant velocity joints  11 ,  34 . The constant velocity joint can be of a monobloc, disc, flanged, or other styles of design know to those in the art. The propeller shaft  26  assembly transfers torque from the transmission  16  to the rear differential  28  by way of the propeller shaft  26 . The constant velocity joints  11 ,  34  are axially plungeable. The constant velocity joints  11 ,  34  have an inner joint part  38  and an outer joint part  40 . The outer joint part  40  of constant velocity joint  11  is connected to one end of a hollow shaft  42  by, for example, a friction weld. The hollow shaft  42  being defined as having cylindrical shell having an inner diameter that is smaller than its outer diameter and two open ends. The other end of the hollow shaft  42  is connected to a rotary joint  35  that is connectable to a rear differential  28  or a transmission  16  depending upon the directional orientation of propeller shaft  26 . Into the inner joint part  38  there is inserted a connecting shaft  44  which, at a certain distance from the joint  11 , is supported by a shaft bearing  36 . 
   Similarly, in combination or alternatively, the outer joint part  40  of constant velocity joint  34  is connected to one end of a hollow shaft  43  by, for example, not shown, a bolted connection. The other end of the hollow shaft  43  is connected to a shaft bearing  36  on the opposite side of connecting shaft  44 . Into the inner joint part  38  there is inserted a connecting shaft  45  which is connectable to a transmission  16  or a rear differential  28  depending upon the directional orientation of propeller shaft  26 . The propeller shaft  26  assembly transfers torque from the transmission  16  to the rear differential  28  by way of the propeller shaft  26 . 
   In addition to torque transfer, the propeller shaft  26  can accommodate axial and angular displacements within the constant velocity joints  11 ,  34 . Where axial movement and articulation of the hollow shafts  42 ,  43  is relative to the connecting shafts  44 ,  45 . Axial movement is relative to the shaft centerlines. In certain crash situations, however, the connecting shaft  44 ,  45  will thrust axially toward the shafts  42 ,  43 , beyond the joints normal operating range while engaging a tuned energy absorption surface. The tuned energy absorption surface extends over an extended axial range of the constant velocity joints  11 ,  34 . Energy may be absorbed until the extended axial range is exceeded and the joint parts are released into the hollow shafts  42 ,  43  or are impeded by the hollow shafts  42 ,  43 . The required thrust for axial movement may be increased or decreased by increasing or decreasing the amount of interference caused by the energy absorption surface. 
     FIG. 3  shows a half-sectional view of a constant velocity joint  11  in accordance with one embodiment of the present invention in a propeller shaft assembly. The joint  11  is an axially plungeable constant velocity joint of the double offset type. The constant velocity joint  11  comprises an outer joint part  50 , an inner joint part  52 , a ball cage  54  and more than one torque transmitting balls  56  each held in a cage window  58 . The outer joint part  50  comprises an inner bore  64 , a cylindrical open end  66  located at the end of the inner bore  64  and proximate to the hollow shaft  42 , more than one outer ball tracks  60  which longitudinally extend over the length of the outer joint part  50 , a normal axial range N and an extended axial range E. The inner joint part  52  comprises a convex guiding face  70 , and more than one inner ball tracks  61  which longitudinally extend over the length of the inner joint part  52 . Each inner ball track  61  has a corresponding outer ball track  60 . Thus, the outer joint part  50  and the inner joint part  52  are driveably connected through the torque transmitting balls  56  located in axially straight ball tracks  60 ,  61 ; there being one torque transmitting ball  56  for each corresponding pair of ball tracks  60 ,  61 . The torque transmitting balls  56  are positioned and maintained in a constant velocity plane by the ball cage  54 . The ball cage  54  is located between the two joint parts  50 ,  52  and has an axially offset outer spherical face  62  and an inner concave guiding face  63  that defines a constant velocity plane. The constant velocity joint  11  permits axial movement since the convex guiding face  70  of the inner joint part  52  positionably engages the inner concave guiding face  63  of the ball cage  54  and the inner bore  64  of the outer joint part  50  guides the outer spherical face  62  of the ball cage  54 . 
   The outer joint part  50  is connected to a hollow shaft  42  which is fixed to the outer joint part by, for example, a friction weld. The hollow shaft  42  may also be flanged and connected to the outer joint part by way of, for example, bolts. 
   Into the inner joint part  52  there is inserted a connecting shaft  44 . A plate cap  46  is secured to the outer joint part  50 . A convoluted boot  47  seals the plate cap  46  relative to the connecting shaft  44 . The other end of the joint  11  at the cylindrical open end  66 , i.e., towards the hollow shaft  42 , is sealed by a grease cover  48 . In addition, the cover  48  may provide some energy absorption should the connecting shaft  44  be thrust beyond the extended axial range E of constant velocity joint  11 . That is, the grease cover  48  is displaceable when the joint travels beyond the extended axial range. The constant velocity joint  11  is designed to operate in its normal axial range N until, however, compression from a crash or an unintended thrust is applied forcing the inner joint part  52 , the ball cage  54 , and the torque transmitting balls  56  into or through the extended axial range E. 
   In this embodiment of the present invention there is a tuned energy absorption surface  74 , which is a circlip  76 . The circlip  76  is circumferentially located in the extended axial range E and coupled to the inside surface  51  of the outer joint part  50 . The circlip  76 , in this embodiment, is an annular ring, made from a deformable material, preferably metal or plastic, and positionable in the outer joint part  50  so as to reside in the outer ball tracts  60 . When the connecting shaft  44  along with the inner joint part  52 , the torque transmitting balls  56  and the ball cage  54  are thrust, as a result of an unintended force, such as a crash, beyond the normal axial range N and into the extended axial range E of the joint  11 , the torque transmitting balls  56  will interfere with or be impeded by the circlip  76 . The impediment of the circlip  76  causes an increase in the thrust required for axial motion, thereby allowing energy to be absorbed by the constant velocity joint  11  and the propeller shaft  26 . The circlip  76  can be a tuned so as to achieve different force levels, allowing for the design of a controlled energy absorption profile within the constant velocity joint  11 . The tuning can be accomplished by changing the size, the shape, the material, or the location of the circlip  76 . There may be more than one circlip  76 , although not shown, located within the extended axial range E of the constant velocity joint  11 . 
   Thus, under normal operating conditions, the torque transmitting balls  56  will operate in the normal axial range N of the constant velocity joint  11 . In certain crash situations, however, the connecting shaft  44  along with the inner part  52 , the ball cage  54  and the torque transmitting balls  56  will be thrust toward the hollow shaft  42  allowing track and bore energy to be absorbed along the extended axial range E caused by the impediment of the circlip  76  upon the inside surface  51  of the outer joint part  50 . It is contemplated that the circlip  76  could be a foreign body residing upon the extended axial range E absorbing plastic energy. 
     FIG. 4  shows a partial view of a constant velocity joint in accordance with alternative embodiment of the present invention. In this embodiment, there is a tuned energy absorption surface  80 , which is a bore surface  82 . The bore surface  82  is circumferentially located in the extended axial range E, has an inclination θ and is coupled to the inner bore  64  of the outer joint part  50  between any two adjacent outer ball tracks  60 . In addition to or as an alternative, the bore surface  82  can have multiple inclinations, stepped inclination, or variable inclination. The bore surface  82  may be located between any set of one or more outer ball tracks  60  or upon the entire inner bore surface  64  in the extend axial range E. The bore surface  82  may be manufactured by layering, i.e. welding, material upon the inner bore surface  64  or by undercutting, while machining, the inner bore surface  64 . One embodiment contemplates the bore surface  82  to be manufactured from the same material as the outer joint part  50  by reducing the inner bore  64  diameter forming an inclination θ in the extended axial range E during the machining process. However, one in the trade would recognize that the bore surface  82  could be accomplished, among other ways, by tacking, staking, or riveting a material upon the inner bore  64 . Thus, when the connecting shaft  44  along with the inner joint part  52 , the torque transmitting balls  56 , and the ball cage  54  are thrust, as a result of an unintended force, such as a crash, beyond the normal axial range N and into the extended axial range E of the joint  11 , the ball cage  54  will interfere with or be impeded by the bore surfaces  82 . The impediment of the bore surfaces  82  causes an increase in the thrust required for axial motion allowing energy to be absorbed by the constant velocity joint  11  and the propeller shaft  26 . The bore surfaces  82  can be tuned, so as to achieve different force levels, allowing for design of a controlled energy absorption profile within the constant velocity joint  11 . The tuning may be accomplished by changing the size, the shape, the material, or the location of the bore surfaces  82 . Any number of bore surfaces  82  may be combined with any number of circlips  76 , as in  FIG. 3 , in the extended axial range E of the constant velocity joint  11  to achieve a tuned and controllable energy absorption rate. 
   Thus, under normal operating conditions, the ball cage  54  will operate in the normal axial range N of the constant velocity joint  11 . In certain crash situations, however, the connecting shaft  44  along with the inner part  52 , the ball cage  54  and the torque transmitting balls  56  will be thrust toward the hollow shaft  42  allowing bore energy to be absorbed along the extended axial range E caused by the impediment of the bore surface  82  upon the inside surface  51  of the outer joint part  50 . 
     FIG. 5A  shows a partial view of a constant velocity joint in accordance with alternative embodiment of the present invention. In this embodiment, there is a tuned energy absorption surface  86 , which is a track surface  88 . The track surface  88  having a taper  90  and is longitudinally located in the extended axial range E of an outer ball track  60  of the outer joint part  50 . There can be one or more track surfaces  88  located on anyone of the other outer ball tracks  60 . The taper  90  may extend linearly over the extended axial range E as shown in the layout view of  FIG. 6 . Alternatively, as shown in the detail of  FIGS. 5B and 5C , the track surface may have a variable taper  91  or a step taper  92  of increasing or decreasing size. As can also be seen in  FIGS. 5A ,  5 B and  5 C, the track feature  88  may be made from the same material piece as the outer joint part  50 . Thus, when the connecting shaft  44  along with the inner joint part  52 , the torque transmitting balls  56 , and the ball cage  54  are thrust, as a result of an unintended force, such as a crash, beyond the normal axial range N and into the extended axial range E of the joint  11 , the torque transmitting balls  56  will interfere with or be impeded by the track surface  88 . The impediment of the track surface  88  causes an increase in the thrust required for axial motion allowing energy to be absorbed by the constant velocity joint  11  and the propeller shaft  26 . The track surface  88  can be tuned to achieve different force levels, allowing for the design of a controlled energy absorption profile within the constant velocity joint  11 . The tuning may be accomplished by changing the size, the shape, the material, or the location of the track surface  88 . The circlip  76  is combined with the track surface  88  as shown in  FIG. 5 , but is not required. 
     FIG. 5A  also shows the “double offset” nature of the joint  11 , wherein the center O o  of the outer spherical surface of the cage  54  and the center O i  of the inner spherical surface of the cage  54  are offset from each other by an equal amount in opposite directions of the center O of the cage windows. 
   Thus, under normal operating conditions, the torque transmitting balls  56  will operate in the normal axial range N of the constant velocity joint  11 . In certain crash situations, however, the connecting shaft  44  along with the inner joint part  52 , the ball cage  54  and the torque transmitting balls  56  will be thrust toward the hollow shaft  42  allowing track energy to be absorb along the extended axial range E caused by the impediment of the track surface  88  upon the inside surface  51  of the outer joint part  50 . 
   The one or more track surfaces  88 , the one or more circlips  76 , and the one or more bore surfaces  82  are combinable to achieve a controlled and tuned energy absorption rate when the constant velocity joint  11  is operated beyond its normal axial range N. 
     FIG. 6  shows a layout view of an outer ball track  60  according to one embodiment of the present invention. The layout view is representative of an outer ball track  60  having a track surface  88  with a taper  90  located in the extended axial range E of a constant velocity joint  11 . 
   From the foregoing, it can be seen that there has been brought to the art a new and improved crash-worthy constant velocity joint. While the invention has been described in connection with one or more embodiments, it should be understood that the invention is not limited to those embodiments. On the contrary, the invention covers all alternatives, modifications, and equivalents as may be included within the spirit and scope of the appended claims.

Technology Classification (CPC): 8