Abstract:
Alternate embodiments of a vehicle tire inflation system are illustrated wherein pressurized air from a source on the vehicle is supplied from an end of an axle to the rotating hub cap and thus to the tire through a flexible tube which compensates for misalignment of the axes of the axle and hub cap.

Description:
REFERENCE TO RELATED PROVISIONAL APPLICATION 
     This application claims the benefit of my Provisional Application No. 60/145,486 filed Jul. 16, 1999, and entitled “Vehicle Tire Inflation System”. 
    
    
     FIELD OF THE INVENTION 
     This application relates generally to a vehicle tire inflation system for continuously supplying air from the vehicle&#39;s axles to the rotating tires. In one of its aspects, it relates to a system of this type having an improved rotary union connection to transmit pressurized air from an axle end to the surrounding rotating hub cap by means of a tube received at one end near the center of the axle end and at the second end near the center of the hub. 
     BACKGROUND OF THE INVENTION 
     The commercial trucking industry is a large market in need of automatic tire inflation systems. Tractor and trailer rigs can typically have 18 tires, and because of their constant use and cost it can be justifiable for a fleet to purchase tire inflation systems for tire pressure maintenance. Properly inflated tires can greatly extend tire life and reduce hazardous blowouts. To meet the needs of the trucking industry, a low cost, low maintenance, and durable rotary union is essential. 
     A typical rotary union for such a system has one member fixed in relation to the end of the axle and another fixed in relation to the hub cap. Some will incorporate a smooth graphite face seal to serve as the dynamic wear seal and others use elastomer seals. Most existing designs have relatively large dynamic sealing surfaces and their size is proportional to the surface speed of the wearing surface. Large seals can compensate for misalignment between the axle and hub cap since the large cross-section will expand and contract with every half rotation. A larger seal helps guarantee sealing but generates more heat, costs more, and generally wears more quickly. Some tire inflation systems add expensive controls to provide air only momentarily to the rotary unions to extend their life, limiting the effectiveness of the inflation system. 
     As shown in U.S. Pat. No. 5,769,979, the rotary union is able to use a small dynamic seal by compensating for bearing wobble and misalignments between the hub and axle through the use of a pivoting rigid tube extending between two elastomer seals. Distortion of the elastomer seals while the tube pivots can impair their sealing ability and longevity. Providing sufficient clearance around the seals so the rigid tube can pivot freely can also be a detriment to a seal&#39;s performance since proper backing isn&#39;t provided for the seal. A rigid tube also is vulnerable to permanent bending during handling and installation. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide a system having an improved rotary union for durability and wear, wherein, as compared with other systems, the tube is flexible so as to compensate for bearing wobble and misalignment between the axis of the axle and the axis of the hub. Elongate openings in the rotary union&#39;s members affixed to the hub cap and to the axle, guide the flexible tube through the seal rings contained within the members. Thus, this invention also allows the ends of the tube to remain axially aligned with the seal rings to provide more reliable seals, and thus allow for greater misalignment than a pivoting rigid tube, as in U.S. Pat. No. 5,769,979. The improvement also allows for greater durability during installation and operation since the tube will not be weakened or destroyed if it is bent. 
     The flexible tube allows for another novel embodiment of the invention. Since substantial lengths of the tube ends are contained in the elongate openings, redundant seal rings can be added along the tube&#39;s length contained in the elongate openings. This provides the ability for air to be vented to the atmosphere in the event of a leak in the outermost seal contained within the member affixed to the hub cap. A redundant seal and a vent to the atmosphere between the two seals in this member will prevent air from entering the lubrication compartment between the axle end and hub cap. 
     In the preferred and illustrated embodiments of the invention, the tire inflation system includes a rotary union having a first member which is fixed in relation to a hollow axle, a second member fixed in relation to a hub, both having an elongate opening therethrough, and a flexible tube which is received at its first end within a first seal ring carried about the opening in the first member and received at its second end within a second seal ring carried about the second member near the hub&#39;s axis, at least one of which forms a dynamic seal during the hub&#39;s rotation, wherein misalignment between the hub axis and the axle axis is compensated for primarily by the flexibility of the tube. The seals prevent air passage from around the outer diameters of the flexible tube, and the elongate opening in each member aligns the end of the flexible tube so that segment of the flexible tube which passes through the seal ring remains coaxial with the opening during rotation. 
     In order for the system to inflate a tire, the vehicle requires a frame mounted source of air pressure to supply air as needed to the tires. Pressurized air passes through a system of valves and through the hollow axle to pressurize the seal ring of the rotary union&#39;s first member. Air then passes through the flexible tube to pressurize the seal ring carried about the opening in the rotary union&#39;s second member, and finally is sent from the second member through a pressure conduit to the tire. 
     The flexible tube is held in alignment with the small seals in each rotary union member, at least one of which is a dynamic, and a third dynamic seal can be added in line with the seal in the second member to divert air through a vent between the seals directly to the atmosphere in the event the first dynamic seal leaks. Thus, this improvement prevents unwanted pressurization of the lubricated bearing compartment, which when pressurized can destroy the wheel seal and purge the lubricant causing bearing failure. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a vehicle equipped with a tire system utilizing the new rotary union; 
     FIG. 2 is a cross section of one embodiment of the rotary union housed in the axle end and, hub cap; 
     FIG. 3 is a cross section of the rotary union similar to FIG. 2, but illustrating misalignment of the axes of the axle and hub; 
     FIG. 3A is an enlarged view of the rotary union to further illustrate misalignment; 
     FIG. 4 is a cross section of another embodiment of a rotary union equipped with an additional seal vent to atmosphere; 
     FIG. 5 is still another embodiment wherein the dynamic seal is mounted in the member of the rotary union on the axle; 
     FIG. 6 shows yet another embodiment having a modified static seal in the first member; and 
     FIG. 7 shows still another embodiment of rotary union wherein either or both of the seals may be dynamic. 
    
    
     DESCRIPTION OF THE INVENTION 
     With reference now to the details of the drawings, the vehicle tire inflation system of FIG. 1 is shown to include an air reservoir  1  mounted to the frame of the vehicle. A pressure protection valve  2  receives air from the reservoir. When a minimum amount of pressure is reached in the reservoir  1 , the pressure protection valve  2  opens and allows air to pass to the shut-off valve  3 . When the system is operating, the shut-off valve  3  will be manually opened to send air to the pressure regulator  4 . The pressure regulator  4  reduces the reservoir pressure to the desired pressure in the vehicle&#39;s tires. A pressure gauge  5  allows for proper adjustment of the pressure regulator  4 . 
     A manifold  6  then makes it possible to deliver air to a plurality of axles. A conduit  7  delivers air to the axle  8  which is hollow and sealed at both ends by the plugs  9 A and  9 B and their respective seals  10 A and  10 B. The axle  8  is pressurized with the air from the attached conduit  7 . The pressurized air in the axle then passes through a filter  11  and into the opening of the first rotary union member  12 , which is sealably connected to the axle plug  9 A and held near the axle&#39;s axis with pipe threads. 
     FIG. 2 is a closer view of the rotary union wherein the pressurized air is passed from the first rotary union member  12  to the flexible tube  13  and sealed by the static seal  15  carried about the opening through the member. A compression fitting  17 , in this case a collet, is used to hold the flexible tube in place. The flexible tube  13  then sends the pressurized air into the opening in the second member  14  of the rotary union which is attached near the axis of the hub cap  21 . A dynamic seal ring  16  is carried about the opening in the second member to form a rotatable seal between the flexible tube  13  and the second member  14 . Once the pressurized air is in the rotatable second member  14 , it is sent through a conduit  22  and a one-way check valve  23  into the pressurized area  24  formed by the tire  25  and the wheel  26 . 
     FIG. 1 illustrates a second axle  50  which is hollow but does not act as a pressurized conduit as does the first axle  8 . Instead, a conduit  51  is housed inside the axle  50  and the stabilizing plug  52  forms a union for the conduit  51  and the first member of the rotary union  53 . 
     FIG. 3 is illustrative of misalignment between the hub cap axis  31  and the axle axis  32  which may be created by slop in the bearings  28  and  29 , and manufacturing tolerances such as the placement of the hub cap  21  on the hub  27  and their attachment by the bolts  33  and  34 . However, this misalignment does not disturb the function of the rotary union, as will be apparent from enlarged FIG. 3A, wherein the axis  31  of the hub cap  21  is non-concentric with the axis  32  of the axle  8 . 
     Instead the ends of the rotary union&#39;s flexible tube  13  are able to bend and pass straight through both the seal ring  15  of the rotary union&#39;s first member&#39;s opening, as well as a seal ring  16  in the rotary union&#39;s second member&#39;s opening. The elongate opening  19  closely and guideably receives the tube  13  so it does not distort the seal ring  15  during rotation. The second member  14  is equipped with a similar elongate opening  18  so the flexible tube  13  does not distort seal ring  16 . This function is best illustrated in FIG.  3 A. FIG. 3A also shows a sleeve  66  tightly about a mid portion of the tube to prevent buckling which might occur if the first and second members are widely spaced. A bell-mouth  67  makes it possible to thread the supple tube  13  into the elongate opening  18  during installation. A radius  70  at the rim of the opening  18  prevents concentrated wear between the flexible tube  13  and the second member  14  during rotation. 
     FIG. 4 illustrates a modified version of the invention wherein the end of the flexible tube  13  passes coaxially through the dynamic seal ring  16  and an additional seal  36 , about the opening  18  inwardly of ring  16 . The third seal ring  36  is not a normally pressurized seal, but instead prevents pressurized air that might leak past the wear seal ring  16  from entering the bearing lubrication compartment  38  by diverting it out a vent  41 . The bearing lubrication compartment  38  is normally vented by an orifice  39 , however, without the seal ring  36  in place, added air pressure from a leak at the wear seal ring  16  could introduce contaminants into the lubrication compartment  38  and extra pressure can cause premature failure of the wheel seal  40 . 
     FIG. 5 is a modified version of the rotary union wherein the dynamic wear ring  43  is in the member  12 , and the collet  44  and the static seal ring  45  are housed in the rotary union&#39;s second member  14 . Bearing wobble and other misalignments are still compensated for with the flexible tube  13 . Here a bell-mouth  68  on the first member  12  makes it possible to thread the pliable tube  13  into the elongate opening  19  during installation. A radius  69  eliminates a sharp corner and prevents concentrated wear between the tube  13  and the first member  12  during rotation. 
     The modified version of the rotary union shown in FIG. 6 is similar to that of FIGS. 2 and 3 in that the dynamic seal ring  16  is carried by the second member  14 . The first member  12  differs, however, in the manner in which it holds and seals about the tube  13  to compensate for misalignment between the axle and the hub. Thus, a metallic compression ring  60  having one tapered end received in a tapered recess in the end of member  12  and the other tapered end received in the end of a tapered recess in the open end of the compression nut  61  threadedly connected about the member to force the compression ring  60  against the tapered recess of the first member  12  to form a seal therewith. The compression nut  61  holds the compression ring  60  which forms a seal against the outer diameter of the flexible conduit  13  forming a seal therewith and holding the tube  13  in place. The seal  62  is held rigidly while the tube  13  must flex for misalignment. 
     In the modified form of the rotary union shown in FIG. 7, the seal rings  15  and  16  carried about the elongate openings in both members of the rotary union are dynamic, or at least capable of same, having in mind that friction may cause one to be static. In this form, a flange  65  on the left outer end of tube  13  prevents it from being pushed out of the members  12  and  14 . As shown, the seal ring  16  is a lip type, rather than an O-ring as in the case of the seal ring  15 . 
     In each of the above described embodiments of the rotary union, the outer member  14  carrying the outer seal ring is so connected to the hub cap as by means of the threads that it may be removed from the outside of the cap to permit replacement of wear parts without removal of the cap. 
     The flexible tube is preferably made of any plastic material having the required characteristics of resistance to heat, wear, and fatigue. Preferably, however, in accordance with the preferred and illustrated embodiments, the tube is made of fluorocarbon polymer, which I believe to best perform the desired functions. 
     While preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptations of the preferred embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.