Abstract:
A system for air injection into tires, comprising a rotary air chamber secured to a hub cap wherein the rotary air chamber is configured to inject air into at least one tire when tire pressure drops below a first adjustable preset value and to release air from the at least one tire when tire pressure rises above a second adjustable preset value, an air shaft extending through the hub cap and into the rotary air chamber, an air line attached to the air shaft, and ball bearings affixed between the air shaft and the hub cap. A bracket can be fastened to the hub cap such that the rotary air chamber is fastened to the bracket. The hub cap and air shaft are fastened to the axle such that an air line extends from inside the axle through the air shaft to the rotary air chamber.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation-in-part of U.S. application Ser. No. 10/408,815, filed on Apr. 7, 2003, entitled “Tire Inflation System,” which is entirely incorporated herein by reference, which claims priority to Provisional Application No. 60/371,305, filed on Apr. 10, 2002. This application also claims the benefit of U.S. provisional application entitled, “Trailer Axle—Tire Inflation System”, having Ser. No. 60/652,544 filed Feb. 14, 2005, which is entirely incorporated herein by reference. 

   TECHNICAL FIELD 
   Various embodiments are generally related to over the road trailers and, more particularly, are related to systems and methods for maintaining correct air pressure in various type trailer tires. 
   BACKGROUND 
   Over 7 million trailers haul 94% of the nation&#39;s cargo transporting items as diverse as fresh fruit, computers, steel, flowers, cattle, plastic, oil, compressed gas, US Mail and more. Other trailer classifications are dry bulk, reefers (refrigerated) and tankers, dry and liquid. Many trailers are now used as warehouses on wheels, often waiting several days and tires can loose air pressure in any number of ways. 
   Tires in most trailers normally operate at approximately 100 psi. However, traveling through hot climates such as the Arizona desert can cause the pressure in the tires to increase to dangerous levels increasing likelihood of a blow-out or other catastrophic failure. Traveling through mountainous terrain increases tire wear dramatically. Oil tankers that require proportionately more turning also increases wear on the tires. Additionally, improper air pressure significantly reduces the life of tires, as much as 50% in many cases. 
   A typical long haul trailer will experience tire pressure loss of up to 10% psi per week causing accelerated tire wear of 20-30%. Additionally the under inflated tires cause up to a 5.8% increase in fuel consumption. It has been estimated that over 20 million tires are damaged annually due to road hazards such as fallen bolts from other units, large pot holes, washboard interstates and railway tracks. The rubber compound that makes up the tire will also leak air over time. 
   The three largest operating costs associated with transporting goods are fuel, salaries of drivers, and tires. It has been estimated that tire failures account for more than 50% of all road cost. Air injection directly into trailer tires while traveling at high speed has been available only via cumbersome and cost prohibitive measures such as using a separate air compressor or pressurizing axles, for example. Maintaining correct air pressure in trailer tires could significantly reduce costs associated with transporting goods, by extending tire life up to 80%. Consequently, systems and methods are needed for maintaining the correct air pressure in trailer tires. 
   SUMMARY 
   Systems and methods for injecting air into tires for various over the road trailers are disclosed. Briefly described, one embodiment is a system comprising a rotary air chamber secured to a hub cap wherein the rotary air chamber is configured to inject air into at least one tire when tire air pressure drops below a first adjustable preset value and to release air from the at least one tire when tire air pressure rises above a second adjustable preset value, an air shaft extending through the hub cap and into the rotary air chamber, an air line attached to the air shaft, and ball bearings affixed between the air shaft and the hub cap. The hub cap and air shaft are fastened to the axle such that an air line extends from inside the axle to the air shaft and the air shaft extends into the rotary air chamber. 
   Another embodiment is a method comprising causing air to flow through an air line running through an axle, the air flow continuing through an air shaft into a rotary air chamber secured to a hub cap, injecting air into at least one tire when a check valve in the rotary air chamber indicates that tire pressure drops below a first preset value, and releasing air from the at least one tire when a relief valve in the rotary air chamber indicates that tire pressure rises above a second preset value. 
   Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Many aspects of the invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the current invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is an illustration of the tire inflation system affixed to the hub cap of a trailer. 
       FIG. 2  is the tire inflation system of  FIG. 1 . 
       FIG. 3  is a cut-away view of the tire inflation system of  FIG. 1 . 
       FIG. 4  is an illustration of air flow through the tire inflation system of  FIG. 3 . 
       FIG. 5  is a tire inflation system of  FIG. 1  fastened directly to the hub cap of a trailer. 
       FIG. 6  is a flowchart illustrating an embodiment of a process for maintaining correct air pressure in trailer tires. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates an embodiment of the tire inflation system  10  for a trailer axle on a trailer  13 . The rotary air chamber  28  of a tire inflation system  10  is shown affixed to a hub cap  24  of a tire  11 . Two pressure gauges  32  indicate the current pressure for both the outermost tire  11  and the tire behind it. The tire inflation system  10  maintains the tire  11  pressure between adjustable predetermined values. Typically, the operating air pressure for tires  11  on a trailer  13  is maintained between 100 and 110 psi. For situations where the trailer  13  load requires different air pressures in the tires  11 , the lower and upper values of the desired tire  11  air pressure range can be adjusted. 
   An embodiment of the tire inflation system  10  is shown in  FIG. 2 . A rotary air chamber  28  is fastened to a bracket  26 . The bracket  26  is fastened to a hub cap  24 . The hub cap  24  is fastened to the rim or wheel (not shown). An air shaft  40  extends from the axle  20  through the hub cap  24 , the bracket  26  and into the rotary air chamber  28 . High speed bearings  38  are affixed between the air shaft  40  and the hub cap  24 . The air shaft  40  is inserted into the axle  20  via an axle plug  22 , so that the air shaft  40  remains stationary, thus allowing air to flow through the passage while the wheel and the hub cap  24  rotate. As discussed further below, the rotary air chamber  28  also contains high speed bearings between the rotary chamber  28  and the air shaft  40 . Two pressure gauges  32  allow visual inspection of the operating air pressure in the tires. Fittings  42  on either end of the rotary air chamber  28  allow for connection to tires  11  (see  FIG. 1 ) through air hoses  44 . Two pressure relief valves  30  will release air pressure from the respective tire  11  when the tire  11  air pressure exceeds a preset upper limit. As a non-limiting example, the tire  11  air pressure could exceed the preset upper limit during hot weather. This preset upper limit may be adjusted to accommodate changing load and temperature conditions. 
   Air pressure flows to the tire  11  from a pressurized air tank  12  through an air line  18 . A shut off valve  14  and an air pressure regulator  16  are inserted into the air line  18  between the air tank  12  and the axle  20 . The pressurized air tank  12  is typically available to service air brakes and other similar equipment on the tractor and/or trailer. The air pressure regulator  16  sets the desired pressure for the tire inflation system  10  independently of other air pressure systems that may be present. As a non-limiting example, if it is desired to operate the tires  11  at 100 psi, then the air pressure regulator  16  is set for 100 psi. Air pressure will then flow through the air line  18  at 100 psi. The air line  18  extends through the axle  20  and continues to the air shaft  40 . The air shaft  40  extends through the hub cap  24  and the bracket  26  and into the rotary air chamber  28 . Of course, the air line  18  may extend in both directions to air shafts  40  at both ends of the axle  20 . It should be noted that the shut off valve  14  and the air pressure regulator  16  could be operated manually or remotely. Additionally, the shut off valve  14  and the air pressure regulator  16  could be operated automatically or could even be computer controlled. 
   The air flow for the tire inflation system  10  operates on a positive pressure if small leaks occur in a tire  11  as, in a non-limiting example, when a bolt or nail becomes stuck in the tire  11 . The tire inflation system  10  will increase flow rate to maintain the predetermined tire pressure. Again, the predetermined air pressure may be changed by adjusting the air pressure regulator  16 . 
   An alternative embodiment of the tire inflation system  10  would allow for adding a coolant such as nitrogen to the pressurized air. A coolant could be added to the pressurized air by, for example but not limited to, providing a fixed bleed into the air line  18 . 
   Further details of the tire inflation system  10  are illustrated in  FIG. 3 . As noted above, the air line  18  extends through the axle  20  and continues to the air shaft  40 . The air shaft  40  extends through the hub cap  24 , the bracket  26  and into the rotary air chamber  28 . High speed bearings  38  are affixed between the air shaft  40  and the hub cap  24 . Additionally, the rotary air chamber  28  has high speed bearings  34  affixed between the inside of the rotary air chamber  28  and the air shaft  40 . Thus, the air shaft  40  remains stationary while the hub cap  24 , the bracket  26  and the rotary air chamber  28  rotate with the wheel and tire  11 . Air flows through the air line  18  into an air chamber  35  inside the rotary air chamber  28 . A high pressure air seal  36  is affixed between the air line  18  and the air chamber  35 . 
   Pressure relief valves  30  operate to release air pressure from the tires  11  when the tire  11  air pressure exceeds an adjustable predetermined value. The predetermined value may be set for an appropriate maximum tire  11  air pressure dependent upon weather and/or load conditions. Check valves  41  operate to cause air to flow into the tires  11  when the tire  11  air pressure drops below the desired pressure as set by the air pressure regulator  16 . Additionally, the check valves  41  operate to prevent loss of pressure in one tire  11  in the event of a catastrophic failure of the other tire, as in for example a blow-out. If the check valve  41  detects an increased air flow rate, it will close off air flow through the check valve  41 . The check valve  41  will prevent air from flowing back into the air chamber  35  from the still operable tire  11  in an attempt to equalize the pressure with the failed tire. 
   The rotary air chamber  28  prevents trailer tires from loosing air pressure due to “non air back flow technology.” The rotary air chamber  28  causes air transfer to each tire  11  as needed. As the tire  11  air pressure increases to unsafe levels, air is released via the relief valves  30 . A pressure gauge  32  corresponds to each tire and the rotary air chamber  28  is equipped with a non flow-back check valve  41 , which also prevents air flow from one tire to another due to catastrophic failure of a tire. The rotary air chamber  28  also includes auxiliary inlet air fill valves (not shown) through which nitrogen or other coolants can be introduced if desired. 
   Arrows representing air flow  15  in  FIG. 4  illustrate the passage of air through the tire inflation system  10 . Air flows from the air tank  12  through the air line  18 . Typically a shut off valve  14  and an air pressure regulator  16  are present in the air line  18  between the air tank  12  and the axle  20 . Air flow  15  continues through the air line  18  to the end of the axle  20 , and then continues through the air shaft  40  and into the rotary air chamber  28 . Air hoses  44  are connected to the fittings  42  on either end of the rotary air chamber and air flow  15  continues through the air hoses  44  to the tires  11 . 
   An alternative embodiment of the tire inflation system  15  allows the rotary air chamber  28  to be secured directly to the hub cap  24  as shown in  FIG. 5 . The intervening bracket is not used in this embodiment. Aside from the bracket not being present the tire inflation system  15  operates as in previous embodiments. As noted above, the air line  18  extends through the axle  20  and continues to the air shaft  40 . The air shaft  40  extends through the hub cap  24  and into the rotary air chamber  28 . The high speed bearings  34  (not shown in  FIG. 4 , see  FIG. 3 ) are affixed between the inside of rotary air chamber  28  and the air shaft  40 , such that the air shaft  40 , which is secured to the axle  20  via an axle plug  22 , remains stationary while the hub cap  24  and the rotary air chamber  28  rotate with the wheel and tire  11 . 
   Pressure relief valves  30  operate to release air pressure from the tires  11  when the tire  11  air pressure exceeds an adjustable predetermined value. The predetermined value may be set for an appropriate maximum tire  11  air pressure dependent upon weather and/or load conditions. Check valves  41  (not shown, see  FIG. 3 ) operate to cause air to flow into the tires  11  when the tire  11  air pressure drops below the desired pressure as set by the air pressure regulator  16 . As above, the check valves  41  operate to prevent loss of pressure in one tire  11  in the event of a catastrophic failure of the other tire, as in for example a blow-out. The check valve  41  and air seal  36  prevent air from flowing back into the air chamber  35  (not shown, see  FIG. 3 ) of the rotary air chamber  28  from the still operable tire  11  in an attempt to equalize the pressure with the failed tire. 
   It should be noted that the pressure gauges  32 , as shown in  FIG. 2 ,  FIG. 3 ,  FIG. 4  and  FIG. 5  could include sensors and/or transmitters equipped to indicate the air pressure in tire  11 . The transmitter could send tire  11  air pressure to a monitoring system in a vehicle or to other wireless connection points and could thus provide air pressure measurements to the monitoring system. In this way the driver could monitor the tire  11  air pressure from inside the vehicle. 
     FIG. 6  shows a flowchart  50  illustrating the operation of the tire inflation system  10 . Step  54  shows that the air flows through an air line, through the axle, and into a rotary air chamber secured to a hub cap. The tire inflation system continuously monitors the tire air pressure as in step  56 . If the air pressure is below a predetermined minimum value, air is injected into the tire in step  58 . The tire inflation system also continuously monitors the tire air pressure as in step  60 . If the air pressure is above a predetermined maximum value, air is released from the tires in step  62 . The nature of steps  56  and  60  is such that the order of the steps may be switched or occur simultaneously. 
   It should be emphasized that the above-described embodiments are merely examples of the disclosed system and method. Many variations and modifications may be made to the above-described embodiments. All such modifications and variations are intended to be included herein within the scope of this disclosure.