Plunging constant velocity joint for a propshaft tuned for energy absorption

[0001] 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.

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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's axial travel distance, especially when the normal operational range of the joint has been surpassed.

[0008] 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).

[0009] 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.

[0010] 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.

[0011] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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, 5B and 5C, 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.