CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims an invention which was disclosed in a provisional application filed May 16, 2012, application Ser. No. 61/647,968, entitled “Dual Wheels with Internal Air Passageways”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     This invention pertains generally to the field of devices used to maintain equal pressure in a pair of dual tires—such as those typically used on trucks, buses and other types of vehicles—without the need for external hoses or piping. More specifically, the invention teaches a system by which, in the event of one tire experiencing a rapid air loss, a valve mechanism will prevent the other tire from going flat. 
     A major problem with dual tires is that the pressure in one dual tire is frequently different than the pressure in the mating dual tire. Pressure differences occur due to lack of maintenance, gradual leakage, and temperature differences. Even if two dual tires start with exactly the same pressure, as a vehicle is driven the tires can heat up unevenly. The inner dual is subject to brake heat and less air flow which causes the pressure in the inner dual tire to be greater than the outer dual tire. 
     The need for equal pressure in dual tires is well known in the industry. First, equal tire pressure improves dual tire tread life—If one dual tire has a higher pressure than the other, then the effective outside diameter of the tire will be greater. Thus, as the tires are forced to roll together, the difference in circumferences will cause the tires to drag and prematurely wear. When dual tires are maintained at an equal inflation pressure, the tread wear is reduced. Second, equal tire pressure improves fuel economy—if the tires drag due to differences in diameter, then fuel economy is reduced. Low air pressure also decreases fuel efficiency. According to Federal Motor Carrier Safety Administration (FMCSA) research, improper tire inflation, as little as 10 psi lower than the target pressure, reduces fuel economy by about one percent. Third, equal tire pressure maintains proper tire load carrying capability. For every 5 psi drop in tire pressure, a 12R22.5 tire loses 160 pounds of load carrying capability. This load must be carried by the other dual tire, which can become overloaded. Fourth, improper dual tire inflation can cause excessive tire bulge in the footprint area which can cause dual tires to rub together (or “kiss”) and significantly reduce the tire life. 
     Consequently, there have been numerous attempts to produce systems and/or devices to alleviate the problems associated with unequal pressure in dual tires. These systems have hoses that connect to the valve stems of each wheel. The other ends of the hoses connect to a valve that equalizes the pressure in the dual tires and provides a single point for tire inflation. In the event of a tire or hose blowout, the valve will close off the good tire from going flat. 
     However, though effective, there are several disadvantages to these systems. First, the valve and hoses used in these products are bulky. The weight of the valve and hoses add extra weight to the vehicle, and can cause imbalance in the assembly. Second, the valve and hoses are unsightly. Many truck owners take great pride in their vehicle to the point of buying premium polished aluminum wheels or chrome-plated wheels. But these valves and hoses detract from the wheel and vehicle appearance. Third, the valve assembly bolts to the lug, hub cap, or drive axle end. If the connection is not tight then the mounting is not secure. Fourth, the hose connections add additional potential leak points in the system. Fifth, the external valve and hoses can be snagged by brush in off-road applications, such as farm trucks, brush fire trucks, or military trucks. Sixth, the valve and hoses make the wheels difficult to clean. Seventh, the equalizing valve and hoses must be removed before removing the duals for service. Eighth, different mounting brackets are needed to mount the equalizing valve to various wheel and hub configurations. Previous devices in the field of the invention had even more disadvantages than the current art devices just described. 
     In contrast to the foregoing, the new design taught herein not only equalizes dual tire pressures, but also isolates a good tire from a bad tire in case of a blow-out or broken hose. This design can sense low the pressures or over-pressurized conditions. However, it does not necessarily utilize electronics to equalize pressure, and thus reliability is improved. None of the previous devices, systems and/or other attempts to alleviate the problems associated with unequal pressure in a pair of dual tires has fully satisfied the needs in the field of the invention, or anticipates the unique features and advantages of the instant invention. 
     SUMMARY AND OBJECTS 
     In view of the foregoing, it is an object of this invention to provide improved dual wheels with balanced pressures that significantly reduce the number of components and reduce the potential for leaks. Fewer components also reduce the cost, weight, and complexity of the system. Another object of this invention is to eliminate external hoses and piping to improve wheel balance, decrease complexity, decrease assembly and disassembly time, make the assembly more robust, and make wheel end maintenance easier. Still another object of this invention is to provide an improved means to incorporate an inflation valve to provide a single point for tire inflation, and in the event of a tire blowout, an integrated valve that will close off the good tire from going flat. The integrated valve assembly decreases the risk of damage from curbs, rocks, tree and shrub branches, and the like. The integrated valve assembly reduces weight, improves wheel assembly balance while reducing the need for external mounting brackets and provides easy access to the wheels for maintenance. 
     The inner and outer wheels in a dual wheel configuration are typically identical one-piece wheels. Dual wheels are typically mounted on the vehicle hub with both wheel disc faces in direct contact with each other. To ensure equal pressure in both tires, this invention has air passageways machined into the wheels such that the air passageways meet at the interface between the wheels, and the junctions are sealed by a rubber seal or gasket. Both tires can then be inflated or deflated simultaneously through a standard air valve. It is also common practice in the trucking industry to use an identical wheel as a single on the front axle wheel end. In this case, the air passageway on a single wheel can be sealed by a plug. 
     Two-piece bolt together wheels can be configured into a dual arrangement in a similar way, but they may require the use of an intermediate piece between the dual wheels (depending on wheel geometry). Air passageways can connect the two-piece wheels in a similar manner as described above with the air passageways going through the common intermediate piece, and a plug can be used to seal off the air passageway for front singles as described above. In another configuration, two-piece wheels may be used as duals without an intermediate wheel disc. Air passageways connect the dual tire air chambers as described above. In still another configuration (not shown), demountable rims can be joined by an air passageway to maintain equal pressure in the tires. 
     External dual pressure equalizing valves are well known in the industry, but heretofore pressure equalizing valves have not been embedded into the wheels as part of an integral system. In this invention, an integral pressure equalizing valve is embedded in the wheels and/or an intermediate piece between the dual wheels and connects to wheel internal air passageways. This results in a robust design that reduces cost, weight, size, and eliminates the need for separate mounting brackets, but also provides the means to prevent a good tire from going flat in the event that there is a rapid pressure loss in the other tire. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross sectional view of the internal passageways of two one-piece wheels and tires configured in a dual arrangement. 
         FIG. 1B  is a cross sectional view of the standard inflation valves of two one-piece wheels and fires that are configured in a dual arrangement. 
         FIG. 1C  is a cross sectional view of the blocked-off internal passageway of one-piece wheel as configured for a single (front wheel) applications. 
         FIG. 2  is a cross sectional view of the internal passageways of two two-piece wheels and tires with an intermediate wheel disc between the dual wheels configured in a dual arrangement. 
         FIG. 3  is a close-up partial sectional view of the internal passageways of two-piece wheels with an intermediate piece configured for a dual wheel configuration. 
         FIG. 4  is a close-up partial sectional view of the internal passageways of a two-piece wheel configured for a single wheel configuration. 
         FIG. 5  is a cross sectional view of the internal passageways of two two-piece wheels and tires without an intermediate piece between the dual wheels configured in a dual arrangement. 
         FIG. 6  is a perspective view of a cartridge-type valve that can isolate and maintain the pressure in a good tire from a bad tire in case of a blow-out. 
         FIG. 7  is an exploded view of a cartridge-type valve that can isolate and maintain the pressure in a good tire from a bad tire in case one tire has a rapid pressure loss. 
         FIG. 8  is a sectional view of a cartridge-type valve that can isolate and maintain the pressure in a good tire from a bad tire in case one tire has a rapid pressure loss. 
         FIG. 9  is a partial cross sectional view of two two-piece wheels and tires with an intermediate piece between the dual wheels configured in a dual arrangement and with a cartridge-type valve that can isolate and maintain the pressure in a good tire from a bad tire in case one tire has a rapid pressure loss. 
         FIGS. 10A, 10B, and 10C  provide further details related to the air passageways in the port end of the cartridge valve. 
         FIG. 11  is a cross sectional view of the internal passageways of two two-piece wheels and tires with an intermediate wheel disc between the dual wheels configured in a dual arrangement, and equipped with a central tire inflation system valve. 
         FIG. 12  is a cross sectional view of the internal passageways of two two-piece wheels and tires with an intermediate wheel disc between the dual wheels configured in a dual arrangement, and a tire pressure monitoring system sensor. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1A  tires  22 A and  22 B are assembled to wheels  21 A and  21 B in a traditional manner. During assembly, air pressure is sometimes needed to seat the tire beads  50 A,  50 B,  50 C, and  50 D to tire bead seats  51 A,  51 B,  51 C, and  51 D. Plug  40  (shown in  FIG. 1C ) can be temporarily installed in threads  28 A and  28 B to seal off air passageways  25 A and  25 B while the tire cavities  24 A and  24 B are inflated to a low pressure via tire valves  23 A and  23 B (shown in  FIG. 1B ) to seat the tire beads  50 A,  50 B,  50 C, and  50 D. Once the tire beads are seated, the air in tire cavities  24 A and  24 B can be exhausted via the inflation valves  23 A and  23 B. Plug  40  is then removed from wheels  21 A and  21 B. 
     Inner dual wheel assembly  20 B and outer dual wheel assembly  20 A are attached to the hub  29  with lug studs  32  and lug nuts  33 . Seal  27  is placed in the outer and inner half seal grooves  26 A and  26 B to seal air passageways  25 A and  25 B. Once the inner dual wheel assembly  20 B and outer wheel assembly  20 A are in place, tire cavities  24 A and  24 B can be pressurized by injecting air through inflation valve  23 A or  23 B. As either tire cavity  24 A or  24 B is pressurized, air pressure is immediately transferred to the other tire cavity through the air passageways  25 A and  25 B. 
     During service, the pressure in both tires cavities  24 A and  24 B will always be equal because air can freely flow through air passageways  25 A and  25 B. For single wheels ( FIG. 1C ), the air passageway  25 C is closed off by plug  40  that is installed in threads  28 C. The tire is then inflated normally through the inflation valve (not shown) just like any other single wheel. 
     Dual wheels may also be made as 2-piece bolt together wheels  65 A and  65 B as shown in  FIG. 2 . Depending on the offset needed for the wheels, an intermediate wheel disc  66  may be placed between the wheels  65 A and  65 B. Air passageways  62 A,  62 B,  62 C,  62 D and  62 E may be sealed with seals  63 A,  61 A,  61 B, and  63 B. Plug  40  (not shown) can be screwed into threads  68 A or  68 B to temporarily seal off air passageways  62 B and  62 D when mounting the tires (not shown) to the wheels  65 A and  65 B. The plugs  40  are then removed prior to assembling wheels  65 A and  65 B and intermediate wheel disc  66  to the vehicle hub (not shown). During assembly, seals  61 A and  61 B are placed between the dual wheels  65 A and  65 B and the intermediate wheel disc  66 . Once assembled, the tires are inflated by means of inflation valve  62 A. As air passes through the inflation valve  62 A, it travels through the air passageways  67 A,  62 A,  62 B,  62 C,  62 D,  62 E and  67 B to inflate both tires (not shown). In a similar manner as described above, both tires will maintain the same pressure because air can freely flow through air passageways  67 A,  62 A,  62 B,  62 C,  62 D,  62 E and  67 B. 
     Any of the seals may be of various types or configurations, and as an example, a rectangular seal  70  is shown in one location in  FIG. 3  in place of an o-ring type seal. Equally obvious, a gasket or some other sealing method may be used instead of the o-ring seals shown throughout the invention. 
       FIG. 4  shows a single 2-piece wheel  65 C mounted on a front hub  72 . For single wheel applications, the inflation valve  64 C is installed in the threads  68 C, and plug  71  is used to seal off air passageway  75 . The tire is pressurized by putting pressurized air through inflation valve  64 C. Air flows to the tire cavity via air passageways  73 ,  74  and  76 , and air leakage between the wheel halves is prevented due to seal  63 C. 
       FIG. 5  shows dual wheels may also be made as 2-piece bolt together wheels  80 A and  80 B and butted together without an intermediate center disc. This design functions the same as the design shown in  FIGS. 2, 3, and 4 . Except it has no intermediate center disc. Likewise, it is obvious that this wheel can be configured with a plug and inflation valve to function like the one shown in  FIG. 4 . 
       FIG. 6  shows a cartridge valve  100  that equalizes pressure between the dual tires but seals off a good tire from a bad tire in case one tire has a rapid loss (such as a tire blowout). As shown in  FIGS. 7 and 8 , this valve has a valve port end  101 , diaphragm  102 , follower  103 , spring  104 , valve closed end  105 , vent  106 , and plugs  107  and  108 . The valve may consist of additional parts (not shown) to identify low, correct, or high pressure conditions or seals (not shown).  FIGS. 10A, 10B and 10C  show how air passageways may be connected in valve port end  101 . The cartridge valve described here functions similarly to the valves described in U.S. Pat. No. 4,476,803 and other US patents, but it is a cartridge design rather than an external design. 
       FIG. 9  shows the cartridge valve  100  installed in an intermediate wheel disc  110  used with two 2-piece wheels  120 A and  120 B. To assemble the tires (not shown) to the wheels  120 A and  120 B, the inflation valve  126 A or  126 B) may be installed in the threads  134 A and  134 B. Air pressure is applied through the inflation valve to seat the tire beads. Once the beads are seated, the air pressure is relieved and the inflation valves  126 A and  126 B are removed from threads  134 A and  134 B and screwed into the wheels as shown in  FIG. 9 . 
     Once the tires are installed on the wheels  120 A and  120 B, then inner dual wheel  120 B, intermediate wheel disc  110  with cartridge valve  100 , outer dual wheel  120 A and various seals as shown are attached to the hub  29  (not shown) with lug studs  32  (not shown) and lug nuts  33  (not shown). Orienting pin  109  can orient the cartridge valve  100  to the intermediate wheel disc  110 , and orienting pins  111  and  112  can orient the wheels  120 A and  120 B to the intermediate wheel disc  110 . Obviously other means can be employed to orient the parts without departing from the spirit of the invention. 
     Once assembled, both tires can be inflated using inflation valve  126 A. Air flows through air passageways  127 A and  128 A into the cartridge valve  100 . The valve  100  allows the air to flow to air passageways  132 A,  131 A,  130 A as well as air passageways  133 ,  132 B,  131 B,  130 B and into the tires (not shown). Once the tires are inflated, the cartridge valve  100  maintains equal pressure between the dual tires but seals off a good tire from a had tire in case one tire has a rapid pressure loss (such as a tire blowout). Seals  121 A,  121 B,  122 A,  122 B,  123 ,  124 , and  125 A seal the air passageways from leakage. Vent  140  prevents pressure build up on the closed end of the cartridge valve. 
     Inflation valve  126 A can be used to deflate both tires simultaneously if needed. Details of the air passageways in the port end of the cartridge valve  100  are shown in  FIGS. 10A, 10B, and 10C . The internal passageways maintain equal pressure in the dual tires even if a temperature differential develops between the inner and outer dual tires. The equalized pressure reduces tire drag, scuffing and wear, and improves fuel economy. Tires with balanced pressure carry the load more equally which can result in longer life in the tires and wheels. Tire pressure maintenance is much easier since one inflation valve is easy to reach and both dual tires are inflated or deflated at the same time. 
     The internal cartridge valve (if used) prevents a good tire from going flat in case the mating dual tire has a rapid pressure loss. The internal air passageways and cartridge valve reduce assembly imbalance to provide better ride quality, longer tire life, have less rotating mass, and a “clean appearance” that makes custom wheels easy to see and clean. The internal air passageways and cartridge valve also mean there are no external hoses, brackets, or external valve that may be damaged by rocks or snagged by brush in off-road applications. 
     It should be obvious that the cartridge valve  100  can be placed in one of the dual wheels to make a dual wheel configuration without the intermediate wheel disc  110 . It should also be obvious that the porting configuration on the port side of the balancing valve can be made as a separate manifold piece to match the wheel internal air channels as necessary. It should also be obvious that the same design principles can be used with demountable dual rims. 
       FIG. 11  shows a dual tire arrangement similar to the one in  FIG. 2  except with an added central tire inflation system (CTIS) valve  150  incorporated into the design. In this embodiment the dual tires can be remotely inflated or deflated by pressing a control button on the dashboard in the cab (not shown, but well known in the art). The CTIS valve can be surface mounted, partly embedded, or fully embedded in the intermediate wheel disc  66  or either one of the wheels. In a configuration with a CTIS, a person of ordinary skill in the art will readily recognize that the spacing between the dual tires may need to be changed based on tire or wheel sizes, inflation pressures, tire load, and other factors in order to prevent damage to the tires from contacting each other. 
       FIG. 12  shows a tire pressure monitoring system (TPMS) sensor mounted to the intermediate wheel disc  66 . In this arrangement the pressure of both tires can be monitored via a TPMS. Usually the TPMS sensor must be mounted inside the tire cavity where there are harsh conditions of heat, pressure, moisture, etc. Our invention allows the TPMS sensor to be mounted outside of the tire to avoid these harsh conditions. 
     The following parts list for the drawing figures may be found to be of assistance in understanding more fully the concepts of our invention:
       20 A Outer dual wheel assembly     20 B Inner dual wheel assembly     20 C Single wheel assembly     21 A Outer dual wheel     21 B Inner dual wheel     21 C Single wheel     22 A Outer dual tire     22 B Inner dual tire     22 C Single tire     23 A Outer dual wheel inflation valve     23 B Inner dual wheel inflation valve     24 A Outer dual tire cavity     24 B Inner dual tire cavity     24 C Single tire cavity     25 A Outer dual wheel air passageway     25 B Inner dual wheel air passageway     25 C Single wheel air passageway     26 A Outer dual wheel half Seal groove     26 B Inner dual wheel half Seal groove     27  Seal     28 A Outer dual wheel threads     28 B Inner dual wheel threads     28 C Front wheel threads     29  Hub     30  Hub/wheel interface     31  Wheel to wheel interface     32  Lug studs     33  Lug nuts     40  Plug     50 A Tire head     50 B Tire bead     50 C Tire bead     50 D Tire bead     51 A Tire bead seat     51 B Tire bead seat     51 C Tire bead seat     51 D Tire bead seat     60  Mounting area of intermediate wheel disc     61 A Seal     61 B Seal     62 A Air passageway     62 B Air passageway     62 C Intermediate wheel disc air passageway     62 D Air passageway     62 E Air passageway     63 A Seal     63 B Seal     63 C Seal     64 A Inflation valve     64 B Inflation valve     64 C Inflation valve     65 A Outer 2-piece dual wheel     65 B Inner 2-piece dual wheel     65 C Single 2-piece wheel     66  Intermediate wheel disc     67 A Air passageway     67 B Air passageway     68 A Threads     68 B Threads     68 C Threads     70  Square seal     71  Plug     72  Front hub     73  Air passageway     74  Air passageway     75  Air passageway     76  Air passageway     80 A Outer 2-piece wheel dual     80 B Inner 2-piece wheel dual     81 A Air passageway     81 B Air passageway     81 C Air passageway     81 D Air passageway     100  Cartridge valve     101  Valve port end cap     102  Diaphragm     103  Follower     104  Spring     105  Valve closed end     106  Vent hole     107  Plug     108  Plug     109  Orientation pin     110  Intermediate wheel disc     111  Orientation pin     112  Orientation pin     120 A Outer 2-piece dual wheel     120 B Inner 2-piece dual wheel     121 A Seal     121 B Seal     122 A Seal     122 B Seal     123  Seal     124  Seal     125 A Seal     125 B Seal     126 A inflation valve     126 B Inflation valve     127 A Air passageway     127 B Air passageway     128 A Air passageway     128 B Air passageway     129 A Threads     129 B Threads     130 A Air passageway     130 B Air passageway     131 A Air passageway     131 B Air passageway     132 A Air passageway     132 B Air passageway     133  Air passageway     134 A Threads     134 B Threads     140  Vent     150  Central tire inflation system valve     151  Air passageway     152  Air passageway     153  Plug     160  Tire pressure monitoring system sensor     161  Air passageway   

     Finally, although the preferred embodiments shown in the figures illustrate a cartridge valve that is fully embedded within the parts, the valve may be only partially embedded or may be mounted directly to the surface of the wheel or intermediate wheel disc. Further, although preferred embodiments are illustrated and discussed, it should be clear to any person skilled in the art of wheels and pressure balancing valves that a variety of configurations may be utilized without departing from the spirit of the invention. Thus, numerous variations are possible without deviating from and/or exceeding the spirit and scope of the invention. Moreover, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the claims that follow.
This invention describes a system to maintain equal pressure in a pair of dual tires, and also incorporates a valve mechanism that will prevent one dual wheel tire from going flat in the event the other dual wheel tire experiences a rapid air loss. Dual wheels are typically mounted on the vehicle hub with both wheel disc faces in direct contact with each other. To ensure equal pressure in both tires, this invention has air passageways machined into the wheels such that the air passageways meet at the interface between the wheels where the wheel disc faces are in direct contact. These junctions are sealed by a rubber seal or gasket. Both tires can then be inflated or deflated simultaneously through a standard air valve located on either wheel. Where a dual wheel arrangement requires the use of an intermediate piece between the dual wheels, air passageways can connect the two-piece wheels via intermediate air passageways going through the common intermediate piece. A dual pressure equalizing valve is connected to the air passageways and embedded into the wheels or intermediate piece.