Abstract:
An exemplary constant velocity joint includes a first member and a second member rotatably engaging the first member. A clutch pack is disposed between and engages the first and second members. A fastener is used to attach the first member to the second member. The fastener is fixedly connected to the second member and rotatably engages the first member. The fastener exerts a biasing force for urging the first and second members into engagement with the clutch pack.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application 61/022,771, filed Jan. 22, 2008, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Constant velocity joints connecting shafts to drive units are common components in vehicles. The drive unit typically has an output shaft or an input shaft for receiving the joint. Typically, the drive unit is an axle, transfer case, transmission, power take-off unit, or other torque device, all of which are common components in automotive vehicles. Typically, one or more joints are assembled to the shaft to form a propeller or drive shaft assembly. It is the propeller shaft assembly which is connected, for instance, at one end to the output shaft of a transmission and, at the other end, to the input shaft of a differential. The shaft may be solid or tubular with ends adapted to attach the shaft to an inner race of the joint thereby allowing an outer race connection to a drive unit. The inner race of the joint is typically press-fit, splined, or pinned to the shaft making the outer race of the joint available to be bolted or press-fit to a hub connector, flange or stubshaft of the particular drive unit. At the other end of the propeller shaft, the same typical or traditional connection is made to a second drive unit when connecting the shaft between the two drive units. Optionally, the joint may be coupled to a shaft for torque transfer utilizing a direct torque flow connection. 
     In many off road vehicle environments considerable torque is applied through the constant velocity joint. All terrain vehicles and utility vehicles often have drivelines that are subject to intermittent high torque values during unusual or extreme operating conditions. Such operating conditions may arise, for example, when the vehicle lands after jumping off irregular terrain. The impact upon landing generates considerable torque in the drivelines. This torque is subsequently imparted into the individual components of the constant velocity joint as the wheels of the vehicle regain traction. When the torque imparted into the constant velocity joint components exceeds design considerations, the components can experience failure. A common design response to these extreme conditions has been to increase the size of the CV joint components in order to increase their maximum torque weathering capacity. 
     In addition to the extreme conditions, designers are utilizing higher capacity engines in vehicle designs. These higher capacity engines increase the power passed through the drivelines and therefore increase the overload torques experienced during extreme conditions. Existing methods of compensation require continued upsizing of the drivelines in order to accommodate the increased power and resulting increased overload torques. Continued upsizing, however, results in increases in mass of the driveline components with subsequent mass increases to the vehicle itself. Upsizing, therefore, poses undesirable restrictions on vehicle designers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of an exemplary drive system for a typical four-wheel drive vehicle employing an exemplary constant velocity joint having torque overload protection. 
         FIG. 2  is a partial cross-sectional view of the exemplary constant velocity joint employing a clutch pack having an outer circumference attached to a joint stem and an inner circumference attached to a joint housing. 
         FIG. 3  is a partial cross-sectional view of the exemplary constant velocity joint employing a clutch pack having an inner circumference attached to the joint stem and an outer circumference attached to the joint housing. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the discussion that follows and also to the drawings, illustrative approaches to the disclosed systems and methods are shown in detail. Although the drawings represent some possible approaches, the drawings are not necessarily to scale and certain features may be exaggerated, removed, or partially sectioned to better illustrate and explain the present invention. Further, the descriptions set forth herein are not intended to be exhaustive or otherwise limit or restrict the claims to the precise forms and configurations shown in the drawings and disclosed in the following detailed description. 
     While the invention is described with respect to a constant velocity universal joint with torque overload protection for use in an all-terrain vehicle, the following apparatus is capable of being adapted for various purposes including automotive vehicles drive axles, motor systems that use a propeller shaft, or other vehicles and non-vehicle applications that require shaft assemblies for torque transmission. 
     An exemplary drive system  12  for a typical four-wheel drive vehicle is shown in  FIG. 1 . While a 4-wheel drive system is shown and described, the concepts herein presented could apply to a single drive unit system or multiple drive unit system, including rear wheel drive only vehicles, front wheel drive only vehicles, all wheel drive vehicles, and four wheel drive vehicles. In this example, the drive system  12  includes an engine  14  that is connected to a transmission  16  and a power take-off unit  18 . A front differential  20  has a right hand side half shaft  22  and left hand side half shaft  24 , each of which are connected to a wheel  21  and deliver power to the wheels. Attached to the ends of the right hand side half shaft  22  and left hand side half shaft  24  are constant velocity joints  10 . 
     A propeller shaft  26  connects the front differential  20  to a rear differential  28 . The rear differential  28  includes a rear right hand side shaft  30  and a rear left hand side shaft  32 . Attached to each side shaft  30 ,  32  is a wheel  21 . Constant velocity joints  10  may be attached to the ends of the half shafts  30 ,  32  that connect to the wheels  21  and the rear differential  28 . 
     The propeller shaft  26 , shown in  FIG. 1 , is a three-piece propeller shaft that includes a plurality of Cardan joints  34  and one high-speed constant velocity joint  10 . The propeller shaft  26  includes interconnecting shafts  23 ,  25 ,  27 . The constant velocity joints  10  transmit power to the wheels through the propeller shaft  26  even if the wheels or the propeller shaft  26  have changed angles, such as may occur due to steering and/or raising or lowering of the suspension of the vehicle. 
     The constant velocity joints  10  may have any of a variety of configurations, such as a plunging tripod, a cross groove joint, a fixed ball joint, a fixed tripod joint, or a double offset joint, to name a few. The constant velocity joints  10  allow for transmission of constant velocities at angles typically encountered in the off road travel of all-terrain vehicles in both the half shafts, interconnecting shafts and propeller shafts of these vehicles. Optionally, each Cardan joint  34  may be replaced with any other suitable type of joint, including constant velocity joint types. The constant velocity universal joint with torque overload protection may be utilized for any of the above mentioned joint locations. 
     The shafts  22 ,  23 ,  24 ,  25 ,  27 ,  30 ,  32  may have a variety of configurations, such as solid or tubular with ends adapted to attach each shaft to an inner race or an outer race of a joint, thereby allowing the outer race or inner race to be connected to a hub connector  36 , a flange  38 , or stubshaft  40 , of each drive unit, as appropriate for the particular application. Thus, any of the connections identified in  FIG. 1  at  10  or  34  may employ a constant velocity universal joint with torque overload protection. 
     Referring now to  FIG. 2 , an exemplary constant velocity universal joint with torque overload protection  50  is illustrated. The constant velocity joint  50  may include a housing  52  configured to support a bearing  53 . The housing  52  may be configured to engage a propeller shaft. Bearing  53  may include an inner bearing race  54  configured to engage a journal of a drive unit and a plurality of torque transmitting balls  56  positioned between inner bearing race  54  and housing  52 . It should be understood that the constant velocity joint  50  may also be configured such that the housing  52  engages a drive unit and the inner bearing race  54  engages a propeller shaft. A ball cage  58  may be positioned between the housing  52  and inner race  54 , and retains the plurality of torque transmitting balls  56 . 
     The housing  52  may include a semi-spherical internal bore  60  forming a bearing cavity  61  in which bearing  53  is disposed. Bearing cavity  61  is at least partially defined by an inner surface  62 , a conical opening  64  disposed adjacent inner surface  62 , and an opposed rear-internal surface  66 . Located on an outer surface  68  of the housing  52  is at least one circumferential channel  70  extending around the entire outer periphery of the housing  52 . A boot or another protective cover may be secured to the channel to prevent dirt and contaminants from entering the bearing cavity. The housing  52  may generally be made of a steel material, however, it should be noted that any other type of metal material, hard ceramic, plastic, or composite material, to name a few, may also be used for the housing  52 . It is desirable that the selected material be capable of withstanding the high speeds, temperatures and contact pressures of the constant velocity joint  50  for extended periods. 
     The housing  52  may also include a plurality of axially opposed outer ball tracks  72  located on the inner surface  62  thereof. The tracks  72  form a generally spherical shaped path within the inner surface  62  of the housing  52 . The tracks  72  may be axially opposed, such that one half of the outer ball tracks  72  open to a side of the housing  52  opposite to that of the other half of the outer ball tracks  72  in any number of patterns. Depending on the configuration of the constant velocity joint, the ball tracks all may open or axially align on the same side of the outer race. The outer ball tracks  72  may also be of a gothic or elliptical shape provided the pressure angle and conformity are maintained, or may have other configurations depending on the requirements of the particular application. The outer ball tracks  72  located on the inner surface  62  of the housing  52  may also be double offset tracks. Further, it is to be understood that the constant velocity joint  50  may be a fixed constant velocity joint, including without limitation a VL, RF, AC, DO, or a tripod joint including other fixed constant velocity joints. 
     The inner bearing race  54  generally has a circumferential shape. The inner bearing race  54  is arranged within the bore  60  of the housing  52 . The inner bearing race  54  includes a drive unit side  84 , an inner joint bore  86  that includes a plurality of splines  88 , and a circlip groove  90  on the inner surface  92  thereof, for axially retaining the constant velocity joint in a rotationally fixed way to a driveshaft. It should be understood, however, that axial retention of the inner bearing race  54  to a shaft may also be accomplished in other ways. 
     An outer surface  94  of the inner bearing race  54  may include a plurality of inner ball tracks  96  that may be axially opposed. The inner ball tracks  96  generally have a spherical shape and are aligned radially with the ball tracks  72  on the housing  52 , such that the axial angle will open in a similar or the same direction as the ball track  72  directly aligned above it on the housing  52 . The inner bearing race  54  may be made of steel, or another material, such as a metal composite, hard plastic, and ceramic, to name a few. 
     The ball cage  58  generally has a ring-like configuration. The ball cage  58  is arranged within the bore  60  of the housing  52  such that it is not in contact with the inner surface of the housing  54 . The cage  58  has a plurality of oblong-shaped orifices or windows  98  that extend through the cage. The number of windows  98  may match the number of ball tracks  72 ,  96  on the housing  52  and inner bearing race  54  of the constant velocity joint  50 . The number of balls and windows may, however, differ. The cage  58 , along with the inner bearing race  54 , may be made of a steel material, but any other hard metal material, plastic, composite, or ceramic, to name a few, may also be used. 
     The balls  56  are each arranged within a separate orifice  98  of the cage  58  and within a ball track  72 ,  96  of the housing  52  and the inner bearing race  54 , respectively. Therefore, the balls  56  will be capable of rolling in the axially opposed tracks  72 ,  96  aligned in the same direction. It is contemplated that a pocket region  99  may be formed between the outer ball tracks  72  and the rear internal surface  66 . The pocket region  99  may be configured to provide clearance for the inner bearing race  54  during angled positioning. 
     Attached to the housing  52  is a stem  100  having a housing engagement end  102 . The stem  100  includes a connector  104  arranged at the housing engagement end  102  of the stem  100  for attaching the stem to the housing  52 . The housing  52  includes a correspondingly configured connector  106  that slidably engages the connector  104  of the stem  100 . The connector  104  of the stem  100  may include a cylindrical shaped region  108 . A longitudinal axis of the cylindrically shaped region  108  substantially coincides with a longitudinal axis of the stem  100 . The connector  106  of the housing  52  similarly includes a cylindrical shaped region  110  having a longitudinal axis that substantially coincides with a longitudinal axis of the bearing  53 . The cylindrical region  110  of the housing  52  engages the cylindrical region  108  of the stem  100  when the two members are interconnected. The connector  104  of the stem  100  has a diameter sized smaller than a diameter of the connector  106  of the housing  52  to enable the two members to rotate relative to one another when connected. With the stem  100  attached to the housing  52 , the bearing  53 , the housing  52 , and the stem  100  are aligned substantially along a common axis. A stem o-ring channel  112  and an o-ring element  114  may be used to axially seal the stem  100  within the housing  52 . 
     Also arranged at the housing engagement end  102  of the stem  100  is a recessed region  116  configured to receive a clutch pack  118 . The stem recessed region  116  may include a generally cylindrical sidewall  122  having a longitudinal axis that substantially coincides with the longitudinal axis of the stem  100 . The sidewall  122  engages an outer circumference  124  of the clutch pack  118 . A rear wall  126  of the recessed region  116  is arranged generally perpendicular to the longitudinal axis of the stem  100  and engages a side  128  of the clutch pack  118 . 
     The housing  52  may include a cylindrically shaped clutch mounting flange  130 . An outer circumferential surface  132  of the flange  130  engages an inner diameter of the clutch pack  118 . Extending generally radially outward from the flange  130  is a housing surface  134  that engages a side  136  of the clutch pack  118  that is opposite the side  128 . With the stem  100  connected to the housing  52 , the cylindrical sidewall  122  and rear wall  126  of the recessed region  116  of the stem  100 , and the outer surface  132  of the clutch mounting flange  130  and the sidewall  134  of the housing  52 , together define a clutch chamber  137  in which the clutch pack  118  is disposed. 
     The stem  100  may be secured to the housing  52  by means of a fastener  138 . The fastener  138  extends through a bore  140  in the housing  52 . The housing  52  is free to rotate about the fastener  138 . The fastener  138  may include a threaded end  142  that engages a correspondingly threaded aperture  144  in the stem  100 . An opposite end  146  may include a head  148  configured to enable torque to be applied to the fastener  138 . For example, the fastener head  148  may include an external hex  150  that can be engaged with an appropriately sized socket wrench, or may include a recessed socket  152  configured to receive a suitably configured key, such as a hex key or Torx™ wrench. The head  148  of the fastener  138  is disposed within the bearing cavity  61  and may be accessed through the bore  86  of the inner bearing race  54 . 
     A biasing member  154  may be disposed between the rear internal surface  66  of the bearing housing  52  and an underside of the fastener head  148 . The biasing member  154  may include, but is not limited to, a coil spring, wave spring, leaf spring, ring of elastic material, as well as other types of biasing devices. The biasing member  154  produces a biasing force that tends to draw the stem  100  and the housing  52  toward one another, thereby causing the housing  52  and the stem  100  to exert a compressive force on the clutch pack  118 . The magnitude of the compressive force applied to the clutch pack  118  can be selectively controlled by adjusting how far the end  142  of the fastener  138  is threaded into the threaded aperture  144  of the stem  100 . 
     Although a variety of clutch packs  118  and attachment configurations are contemplated, one exemplary configuration contemplates the use of a plurality of slip clutch plates  156  held in compression between the stem  100  and the housing  52 . Each clutch plate  156  is splined either at the inner diameter of the plate or the outer diameter of the plate. The clutch plate spline engage a corresponding spline  157 ,  159  formed on the cylindrical side wall  124  of the recessed region  116  of the stem  100  and surface  132  of clutch mounting flange  130 , respectively. Generally the clutch plates  156  are arranged such that every other clutch plate is splined at the inner diameter, for example clutch plates  158  are splined at the inner diameter, and the intermediate plates  160  are splined at the outer diameter. The clutch plates  156  may be slid axially relative to the stem  100  and housing  52 , but are prevented from rotating relative to the housing or the stem, depending on which component the clutch plate is splined. The torque transfer path through the constant velocity joint  50  travels from the spline  88  located in the bore  86  of the inner bearing race  54 , through torque transmitting balls  56  to housing  52 , at which point the torque is transmitted to the clutch plate  158  splined at the inner diameter to the housing  52 , across a clutch plate interface  162  to the adjoining clutch plate  160  that is splined at the outer diameter to the stem  100 , and ending at the spline  117 . 
     The fastener  138  may be utilized to set a torque threshold of the clutch pack  118 . When the fastener  138  is tightened, the compression force being applied by the housing  52  and the stem  100  on the clutch pack  118  increases, thereby producing a corresponding increase in the torque threshold. Conversely, loosening fastener  138  reduces the compression on the clutch pack  118 , and the corresponding torque threshold is reduced. The biasing member  154  disposed between the head  148  of the fastener  138  imparts a generally constant axial compressive load on the clutch plates  156  of the clutch pack  118 . The fastener  138  may be installed and pre-tensioned prior to assembly of the inner bearing race  54  into the housing  52 . The fastener  138  tension may also be set through the inner joint bore  86  after assembly. 
     The clutch pack  118  is disposed within the clutch chamber  137  and engages the outer race stem  100  and the housing  52 . The clutch pack  118  is configured such that the outer race stem  100  and the housing  52  rotate in unison below a pre-set overload torque value. When the overload torque reaches a predetermined threshold, the designed frictional resistance of the plurality of slip clutch plates  156  is overcome and independent rotation is allowed. Once the overload torque value threshold is crossed, the outer race stem  100  and the housing  52  are allowed to rotate independently, thereby preventing damaging torque from being imparted into the constant velocity joint  50  internal components. When the torque values drop below the overload threshold, the clutch pack  118  re-engages and the outer race stem  100  and housing  52  resume rotating in unison. 
     With reference to  FIG. 3 , housing  52  and stem  100  may be configured such that the outer circumference  124  of the clutch pack  118  engages the housing and the inner circumference  133  of the clutch pack  118  engages the stem. Housing  52  includes a recessed region  164  configured to receive the clutch pack  118 . The housing recessed region  164  may include a generally cylindrical sidewall  166  having a longitudinal axis that substantially coincides with the longitudinal axis of the bearing  53 . The sidewall  166  engages the outer circumference  124  of the clutch pack  118 . A rear wall  168  of the recessed region  164  is arranged generally perpendicular to the longitudinal axis of the bearing  53  and engages the side  136  of the clutch pack  118 . 
     The stem  100  may include a cylindrically shaped clutch mounting flange  170 . An outer circumferential surface  172  of the flange  170  engages the inner diameter  133  of the clutch pack  118 . The clutch mounting flange  170  extends through a bore  173  in the housing  52 . The housing  52  is free to rotate about the clutch mounting flange  170 . Extending generally radially outward from the flange  170  is a stem side wall  174  that engages the side  128  of the clutch pack  118  that is opposite the side  136 . With the stem  100  connected to the housing  52 , the cylindrical sidewall  166  and rear wall  168  of the recessed region  164  of the stem  100 , and the outer surface  172  of the clutch mounting flange  170  and the sidewall  174  of the stem  100 , together define a clutch chamber  176  in which the clutch pack  118  is disposed. 
     The stem  100  may be secured to the housing  52  my means of a fastener  178 . The fastener  178  may include a threaded end  180  that engages a correspondingly threaded aperture  182  in the stem  100 . An opposite end  184  may include a head  186  configured to enable torque to be applied to the fastener  178 . For example, the fastener head  186  may include an external hex  188  that can be engaged with an appropriately sized socket wrench, or may include a recessed socket  190  configured to receive a suitably configured key, such as a hex key or Torx™ wrench. The head  186  of the fastener  178  is disposed within the bearing cavity  61  and may be accessed through the bore  86  of the inner bearing race  54 . 
     A biasing member  154  may be disposed between the rear internal surface  66  of the bearing housing  52  and an underside of the fastener head  186 . The biasing member  154  may include, but is not limited to, a coil spring, wave spring, leaf spring, ring of elastic material, as well as other types of biasing devices. The biasing member  154  produces a biasing force that tends to draw the stem  100  and the housing  52  toward one another, thereby causing the housing  52  and the stem  100  to exert a compressive force on the clutch pack  118 . The magnitude of the compressive force applied to the clutch pack  118  can be selectively controlled by adjusting how far the end  180  of the fastener  178  is threaded into the threaded aperture  182  of the stem  100 . 
     The clutch pack  118  may be attached to the housing  52  and the stem  100  in a similar manner as previously described with respect to the configuration illustrated in  FIG. 2 . For example, each of the clutch plates  156  may be splined either at the inner diameter of the plate or the outer diameter of the plate. The clutch plate spline engages a corresponding spline  192 ,  194  formed on the cylindrical side wall  166  of the recessed region  164  of the housing  52  and surface  172  of clutch mounting flange  170 , respectively. The clutch plates  156  may be slid axially relative to the stem  100  and housing  52 , but are prevented from rotating relative to the housing or the stem, depending on which component the clutch plates are splined. The torque transfer path through the constant velocity joint  50  travels from the spline  88  located in the bore  86  of the inner bearing race  54 , through torque transmitting balls  56  to housing  52 , at which point the torque is transmitted to the clutch plate  156  splined at the outer diameter to the housing  52 , across the clutch plate interface to the adjoining clutch plate  156  that is splined at the inner diameter to the stem, and ending at the spline  117 . 
     The fastener  178  may be utilized to set a torque threshold of the clutch pack  118 . When the fastener  178  is tightened, the compression force being applied by the housing  52  and the stem  100  on the clutch pack  118  increases, thereby producing a corresponding increase in the torque threshold. Conversely, loosening the fastener  178  reduces the compression on the clutch pack  118 , and the corresponding torque threshold is reduced. The biasing member  154  disposed between the head  186  of the fastener  178  imparts a generally constant axial compressive load on the clutch plates  156  of the clutch pack  118 . The fastener  178  may be installed and pre-tensioned prior to assembly of the inner bearing race  54  into the housing  52 . The fastener  178  tension may also be set through the inner joint bore  86  after assembly. 
     The clutch pack  118  is disposed within the clutch chamber  176  and engages the outer race stem  100  and the housing  52 . The clutch pack  118  is configured such that the outer race stem  100  and the housing  52  rotate in unison below a pre-set overload torque value. When the overload torque reaches a predetermined threshold, the designed frictional resistance of the plurality of slip clutch plates  156  is overcome and independent rotation is allowed. Once the overload torque value threshold is crossed, the outer race stem  100  and the housing  52  are allowed to rotate independently, thereby preventing damaging torque from being imparted into the constant velocity joint  50  internal components. When the torque values drop below the overload threshold, the clutch pack  118  re-engages and the outer race stem  100  and housing  52  resume rotating in unison. 
     With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously or generally simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claimed invention. 
     It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent to those of skill in the art upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation and is limited only by the following claims. 
     All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those skilled in the art unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.