Patent Document

TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a motor vehicle propeller shaft assembly and a constant velocity joint (CVJ) cap of such an assembly. 
     BACKGROUND OF THE INVENTION 
     For safety reasons, propeller shaft assemblies for motor vehicles which are oriented longitudinally with constant velocity joints are typically designed with a shock absorption capability during telescopically collapse of the shaft assembly in the event of a frontal impact. These assemblies also need proper sealing against lubricant leakage on the one hand and a venting system on the other hand. All these requirements make the construction of a propeller shaft assembly complex. 
     SUMMARY OF THE INVENTION 
     The present invention simplifies the propeller shaft assembly by providing a cap inserted into or abutting the outer race of a constant velocity joint (CVJ) that enables both proper sealing and venting without interfering with the energy absorption capability of the assembly. 
     The grease retention and vent cap of this invention may enable a collapse of the propeller shaft assembly in various ways. In a first example, the grease retention and vent cap has a rim pressed into or adjacent the outer race of the CVJ which stays rigid during a vehicle crash. If the propeller shaft is fabricated with a beaded weld which projects into the inside diameter of the shaft, this rim may be retained or broken by the weld bead during a crash. Internal CVJ components abut a central portion of the cap and cause this central portion to break away from the cap rim and pass through the tubular propeller shaft ahead of the internal joint components, allowing the propeller shaft assembly to collapse telescopically. 
     Alternatively, the entire rim of the cap can disintegrate into pieces small enough to enter the tubular propeller shaft. 
     For applications for a propeller shaft which does not have an inwardly protruding weld bead, the entire cap may be pushed into the tubular propeller shaft without breaking. The cap has an arrangement of vent ducts leading from the internal components of the CVJ to a radial annular groove surrounding the entire circumference of the cap. From there, a connection to the atmosphere is established by radial bores in the outer race of the CVJ in the axial area of the annular groove at any angular position on the tubular shaft. The invention thus encompasses both a venting system incorporated into the cap and a crash feature for a propeller shaft assembly, eliminating the need for two separate systems for such features. 
     Grease is retained inside the outer race of the CVJ in the propeller shaft assembly by providing a vent hole for communication with the interior components of the CVJ in the axial center of the cap, thereby ensuring that the vent hole is never at the bottom of the tubular shaft, regardless of the orientation of the cap. The rim thus forms a seal along the entire circumference of the cap. 
     In this configuration, the cap will act as a venting system, provides grease retention for the CVJ, and allows for crash optimization. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a side view of a first illustrative example of a cap in accordance with this invention; 
         FIG. 2  depicts the cap of  FIG. 1  in a first perspective view showing one of two major surfaces of the cap; 
         FIG. 3  depicts the cap of  FIG. 1  in a second perspective view showing the other one of the two major surfaces of the cap; 
         FIG. 4  is a longitudinal cross-sectional view of a propeller shaft assembly according to this invention showing the components thereof during normal vehicle operation; and 
         FIG. 5  is a longitudinal cross-sectional view of a propeller shaft assembly according to this invention showing the components thereof following a vehicle crash. 
         FIG. 6  depicts a first perspective view of a grease retention and vent cap according to a second exemplary embodiment of the invention. 
         FIG. 7  depicts a second perspective view of the grease retention and vent cap of  FIG. 6 . 
         FIG. 8  depicts a cross-sectional view of the venting system in the grease retention and vent cap of  FIG. 6 . 
         FIG. 9  depicts a side view on the grease retention and vent cap of  FIG. 6   
         FIG. 10  depicts the grease retention and vent cap of  FIG. 6  within a propeller shaft system during normal vehicle operation. 
         FIG. 11  depicts the grease retention and vent cap of  FIG. 6  within a propeller shaft system during a vehicle crash. 
         FIG. 12  depicts the grease retention and vent cap of  FIG. 6  within a first propeller shaft system after a vehicle crash. 
         FIG. 13  depicts the grease retention and vent cap of  FIG. 6  within a second propeller shaft system after a vehicle crash. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The figures of the drawings are provided for purely illustrative purposes and are not intended to limit the scope of the invention. 
     Referring to  FIGS. 1 through 3 , a first exemplary embodiment of a grease retention and vent cap  1  has a rim  2  dimensioned to be placed and retained in an outer race  9  of a CVJ. As shown, CVJ has a counter-bored region for receiving cap  1 . Other embodiments (not shown) can provide an inside diameter surface for retaining cap  1  adjacent to the CVJ. Retaining the rim  2  in the outer race  9  may be accomplished by a slight radial annular indent placed on a corresponding annular protrusion in the outer race  9 . 
     Axially adjacent to the rim  2  is an axial area forming a hollow chamber  3  that extends radially across the entire width of the cap  1 . The hollow chamber  3  is open at both radial ends and terminates in an annular groove  4  that extends around the entire circumference of the cap  1 . An axial vent hole  5  is located centrally in cap wall  18  that bounds the hollow chamber  3  at an axial end opposite the rim  2 . The vent hole  5  establishes fluid communication of the hollow space  3  to the outside of the cap  1 . 
     Referring now to  FIG. 4 , the cap  1  is pressed into a recessed inside diameter portion of the outer race  9  of a propeller shaft CVJ and retained at its outer diameter by rim  2 . The cap  1  separates internal components of a CVJ, such as a stub shaft  12 , an inner race, a cage and balls (known as the internal joint components and referred to by reference number  8 ) from a tubular shaft portion  11  of the propeller shaft. A dust boot  13  seals the gap between the stub shaft  12  and the outer race  9  to prevent contamination. Air is allowed to pass from the internal components  8  of the CVJ to the cap hollow chamber  3  through the vent hole  5 , which is centrally located in the cap  1  and extends axially through a face of the cap  1  into the hollow chamber  3 . This allows atmospheric pressure venting which prevents the development of pressure differentials between the area of the joint internals  8  and atmosphere, which can lead to the introduction of contaminants which can degrade the service life of the CVJ. 
     The vent hole  5  is located on a major face of the cap wall  18  and oriented to face the internal CVJ components  8 . Air is then allowed to pass from the hollow air chamber  3  of the cap  1  through the radially open ends of the hollow chamber  3  into the radial annular groove  4  that runs 360 degrees around the outer periphery of the cap  1 . The air then passes through bores  17  drilled into the outer race  9  of the CVJ to the atmosphere. 
     The hollow air chamber  3  in the cap  1  has a cavity volume which ensures that the propeller shaft CVJ does not allow water ingress during an event in which the CVJ is hot and then cooled quickly, for example by water submersion during operation of the associated motor vehicle. In such a situation, the rapid quenching can cause water to be sucked into the cap  1 . By providing sufficient volume in the internal hollow chamber  3  of the cap  1 , the sucked-in water will be retained in the hollow chamber  3  and will not reach the internal joint components  8  through vent hole  5 . The exact volume of the hollow chamber  3  depends on anticipated temperature differences and on physical properties of the propeller shaft assembly, such as enclosed air volume. The central location of vent hole  5  ensures that the vent hole  5  is never at the bottom of the hollow chamber, regardless of the angular orientation of the cap  1  inside the propeller shaft assembly. Therefore, any water accumulated at the bottom of the hollow chamber  3  cannot flow into the area of the internal joint components  8 . 
     The tubular shaft  11  of the propeller shaft assembly is connected to the outer race  9  via a weld  10 . The weld  10  as shown, has a bead which extends both radially outwardly, and also inwardly from the inside diameter of shaft  11 , which is typical in a friction welding process. To not interfere with axial movement of a cap, machining of the bead of weld  10  would be required. In order to still allow for a telescopic collapse during a frontal impact without interior machining of the weld  10 , the cap  1  is configured to withstand axial displacement of the internal joint components  8  in direction  14  only to a limited extent. Upon a vehicle crash exceeding such displacement, the rim  2  of the cap  1  are retained inside the CVJ outer race  9 . A central portion  6  of the cap  1  shears away, separating from the rim  2 , and allows the internal joint components  8  to escape from the outer race  9  into the tubular shaft  11 . 
     The cap  1  is made of a material, for instance a suitable plastic material, that is tunable to collapse at a certain energy produced by the vehicle during a crash. The exact energy and resulting force to trigger a separation of the central portion  6  from the rim  2  can be empirically determined and depends on several factors that may include vehicle weight and spatial dimensions inside the vehicle. 
       FIG. 4  depicts the cap  1  used within a propeller shaft system during normal vehicle operation. The cap  1  is pressed inside the outer race  9 . The internal joint components  8  are retained and sealed by the cap  1 . Grease is retained within the outer race  9  by the cap  1 . The air vent bores  17  in the outer race  9  allow venting from the internal joint components  8  through the axial vent hole  5 , via the hollow chamber  3  and the bores  17  to the atmosphere. 
       FIG. 5  depicts the cap  1  used within a propeller shaft system during a vehicle crash. During the impact, forces acting on the vehicle transmission shift the stub shaft  12 , producing displacement in the direction shown by the arrow  14 . The internal joint components  8  impact the cap  1 , forcing the cap toward the tubular shaft  11  until the rim  2 , acting as a low force retention feature, contacts the interior bead of the weld  10 . The rim  2  remains in contact with the weld  10 , while the impact causes the central portion  6  of the cap  1  to shear and break away. The central portion  6  exits the outer race  9  ahead of the internal joint components  8  and enters the tubular shaft  11 , giving way for the internal joint components  8  to follow. 
     The internal joint components  8  are small enough to pass from the outer race  9  through the tubular propeller shaft  11  following a backward shift of an engine or transmission during a vehicle collision, to absorb the energy created by the vehicle collision, thereby enabling the telescopic effect described earlier. 
     The cap  1  may be used in a propeller shaft which uses either a friction weld, gas metal arc weld or magnetic arc weld to join the CVJ outer race  9  to the tubular propeller shaft  11 . With the use of a friction weld  10 , during a collision, the cap  1  contacts the internal bead of the weld  10  and the central portion  6  of the cap  1  is sheared away from the rim portion  2  as described above. 
     With the use of either a gas metal arc weld or magnetic arc weld forming a smooth surface at the inner tube diameter, the cap  1  may be made with a diameter small enough such that it is able to pass through the weld portion and into the tubular propeller shaft  11 . Accordingly, absent an interior weld bead, the grease retention and vent cap  1  remains intact during the collision. In the drawings, the cap  1  of  FIG. 4  would simply move to the right as a whole, ahead of the internal CVJ components, without shearing of the cap. 
     Referring now to  FIGS. 6 through 9  showing an alternative embodiment of cap  101 , axes x, y, and z of a virtual coordinate system are indicated in the drawings to illustrate the respective perspectives of the individual drawing figures. In a second exemplary embodiment of the present invention, a grease retention and vent cap  101  has a rim  102  dimensioned to be placed and retained in an outer race  109  of a CVJ. Retaining the rim  102  in the outer race  109  may be accomplished by a slight radial annular indent or expansion matched with a corresponding annular shape in the outer race  109 . 
     Axially adjacent to the rim  102  is an axial area forming a plurality of hollow channels  103  that extend parallel across the entire radial width of the cap  101 . The hollow channels  103  are separated by parallel walls  107  arranged in such a way that the radial center of the cap  101  is not obstructed by a wall  107 . The hollow channels  103  are open at both radial ends. A radial annular groove  104  in end portions of the walls  107  extends around the entire circumference of the cap  101 . An axial vent hole  105  is located centrally in a radially extending wall  118  that bounds the hollow channels  103  at an axial end opposite the rim  102 . The vent hole  105  establishes an axial communication of that one of the hollow channels  103  that extends across the central location to the axial outside of the cap  101 . 
       FIG. 6  shows optional reinforcing webs  115  supporting the rim  102 , the thickness as well as radial and axial dimensions of these webs  115  can be dimensioned to meet specifications regarding a threshold force along the arrow  114  (shown in subsequent figures) required to separate the rim  102  from the central portion  106  of the cap  101  or to disintegrate the rim as explained in more detail in connection with  FIGS. 10 through 12 . 
     Referring now to  FIG. 10 , the cap  101  is pressed into the outer race  109  of a propeller shaft CVJ and retained at its outer diameter at rim  102 . The cap  101  separates a stub shaft  112 , an inner race, a cage and balls (known as the internal joint components and collectively identified by reference number  108 ) from a tubular portion  111  of the propeller shaft. The stub shaft  112  and the outer race  109  are sealed via a dust boot  113  to prevent contamination. Air is allowed to pass from the internal components  108  of the CVJ to the central one of the hollow channels  103  through the vent hole  105  which is centrally located in the cap  101  and extends axially through a face of the cap  101  into the hollow channel  103 . 
     The vent hole  105  is located on a major face of the cap  101  oriented to face the internal CVJ components  108 . Air is then allowed to pass from the central hollow channel  103  of the cap  101  through the radially open ends of the hollow channel  103  into the radial annular groove  104  that runs 360 degrees around the outer periphery of the cap  101 . The air then passes through bores  117  drilled into the outer race  109  of the CVJ to the atmosphere. 
     The hollow air channels  103  in the cap  101  have a cavity volume which ensures that the propeller shaft CVJ does not allow water ingress during an event in which the CVJ is hot and then cooled quickly, for example by water submersion. In such a situation, the rapid quenching can cause water to be sucked into the cap  101 . By providing sufficient volume in the internal hollow channels  103  of the cap  101 , the sucked-in water will be retained in the hollow channels  103  and will not reach the internal joint components  108  through vent hole  105 . The exact volume of the hollow channels  103  depends on anticipated temperature differences and on physical properties of the propeller shaft assembly, such as enclosed air volume. 
     The central location of vent hole  105  ensures that the vent hole  105  is never at the bottom of the hollow channels  103 , regardless of the angular orientation of the cap  101  inside the propeller shaft assembly. Therefore, water accumulated at the bottom of the hollow channels  103 , even in the central hollow channel  103 , cannot flow into the area of the internal joint components  8 . 
     The tubular shaft  111  of the propeller shaft assembly is connected to the outer race  109  via a weld  110 . The weld  110  of the type shown has an interior bead that would require machining to remove. In order to still allow for a telescopic collapse during a frontal impact without interior machining of the weld  110 , the cap  101  is configured to withstand axial forces from the internal joint components  108  in direction  114  only to a limited extent. Upon a vehicle crash exceeding such limited force, the rim  102  of the cap  101  is retained inside the CVJ outer race  109 . The central portion  106  of the cap  101  gives way, separates from the rim  102 , and allows the internal joint components  108  to escape from the outer race  109  into the tubular propeller shaft  111 . The rim  102  is configured to break into pieces at the time of separation from the central portion  106 . The pieces of the rim  102  are small enough to disperse into the tubular propeller shaft  111  without impeding the telescopic movement of the internal joint components  108  into the tubular propeller shaft  111 . 
     The cap  101  is made of a material, for instance a suitable plastic material, that is tunable to collapse at a certain energy produced by the vehicle during a crash. The exact energy and resulting force to trigger a separation of the central portion  106  from the rim  102  or to break the rim  102  can be empirically determined and depends on several factors that may include vehicle weight and spatial dimensions inside the vehicle. The dimensions of the webs  115  can be utilized for fine-tuning the cap properties to given demands, for instance by model simulations or by experimentation. 
     The cap  101  may be used in a CVJ outer race  109  that is joined to a tubular propeller shaft  111  by welding. When the joining method is friction welding, during a collision the grease retention and vent cap  101  contacts the weld  110  and collapses as illustrated in  FIGS. 11 and 12 . Upon a frontal impact, the walls  107  may collapse when the cap  101  first abuts the interior bead of the weld  110  as illustrated in  FIG. 11 . This collapse leaves the webbed axial surface of the cap  101  intact. Once the rim  102  reaches the weld, it may either be retained as shown in the embodiment of  FIGS. 1 through 5 , or it may break into pieces that may disperse inside the tubular propeller shaft  111  as illustrated in  FIG. 12 . In  FIG. 12 , the stub shaft  112  has been pushed so far into the tubular shaft  111  that the dust boot  113  is torn. The rim  102  of the cap  101  is destroyed and broken into many small pieces dispersed in the tubular shaft  111 . The pieces are small enough not to impede the movement of the internal joint components  108 . 
     If the CVJ and tubular propeller shaft  111  are fabricated by a process other than friction welding, such as a magnetic arc welding or gas metal arc welding, no interior bead is created. In this approach, the cap  101  may be small enough to pass through the connection between the CVJ and the tubular propeller  111  shaft into the tubular propeller shaft  111  during a collision, without breaking the cap as shown in  FIG. 13 . 
     The caps  1  and  101  are dimensioned to be sufficiently robust to withstand general handling and operation during normal use over the entire lifetime of a propeller shaft. 
     The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Technology Category: 4