REFERENCE TO RELATED PROVISIONAL APPLICATION 
     This application claims the benefit of my Provisional Application No. 60/150,680 filed Aug. 25, 1999, and entitled “Automatic Tire Inflation System Having a Pressure Regulator with an Integrated Leak Detection Switch”. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to automatic tire inflation systems for transportation vehicles, and specifically improvements in those that include an indicating device to signal when a tire is receiving air. 
     BACKGROUND OF THE INVENTION 
     Automatic tire Inflation systems provide air to a vehicle&#39;s tires even while the vehicle is in motion. In the event a tire has lost air pressure, the inflation system will send air to the leaking tire, usually from the frame of the vehicle through a rotary union aligned with the tire&#39;s rotational axis. When the inflation system is delivering air, it is beneficial for the driver to be alerted that a tire is requiring inflation. The alert system can be a visual light, a screen display, an audio alarm, or another electronically activated device to warn the driver. 
     A common alert system uses a pressure regulator and a pressure switch. The pressure regulator is placed between a source of air pressure and the tires to limit the system&#39;s inflation pressure and thereby prevent over inflation as shown in U.S. Pat. No. 3,276,503. A normally closed pressure switch is placed between the pressure regulator and the tires, and when a tire looses pressure, dynamic pressure losses cause the pressure downstream of the pressure regulator to drop and close the pressure switch. The signal ceases only when the pressure regulator delivers enough air to refill the tire and build enough pressure to open the pressure switch. 
     It is difficult for this method to be responsive because the pressure switch&#39;s open and close pressure must be adjusted precisely below the regulator&#39;s adjusted pressure. Temperature and friction change over time, and the dynamic components in both the pressure switch and pressure regulator do not always respond consistently. If the difference between the two adjusted settings is large, the signal will not be sent until a tire&#39;s pressure has greatly decreased. If the difference between the adjusted settings is small, it is possible the switch will close and falsely send a signal due to normal fluctuations in the regulator&#39;s output. Also, the presence of two adjustments leads to unnecessary complications in the field. 
     One design meant to overcome the insensitivity of the pressure regulator and pressure switch combination is the use of a flow switch, as in U.S. Pat. No. 5,767,398. Here the switch requires no adjustment and will close whenever the inflation system is sending air. One drawback to this system is that the operator will not be alerted if a tire has low air pressure and the system has no air pressure to deliver. If the automatic tire inflation system were turned off, the flow switch would not indicate low pressure in a tire to the driver since no air would flow through the switch. Another shortcoming is that a cluster of valves is difficult to package on a vehicle. 
     Proximity sensors have been used to remotely determine valves&#39; positions in many other applications. When a valve is used in processes where it is inaccessible, it can be desirable to know the valve&#39;s position using a sensor. Usually these sensors are used on shut-off type valves with remote actuators so the valve&#39;s position can be assured when remotely actuating the valves. The present invention is an improved sensor for detecting an air leak in a tire inflation system. Integrating a sensor directly into the tire inflation system&#39;s pressure regulating valve offers advantages over existing methods. 
     Objects and Advantages 
     Tire inflation system designers have always included additional pressure switches or valves to determine the tires&#39; pressure status, apparently because the benefits of integrating a switch into a pressure regulator were not considered or understood. The object of the present invention is to provide such a system with an alert switch which will indicate a low tire pressure situation, even when the source of air pressure is depleted or turned off, and without requiring the separate adjustment of a switch, while meeting the needs of a present day commercial tire inflation system. By building the switch into the pressure regulator the switch will respond with certainty to the system&#39;s operation. The only adjustment required is setting the pressure regulator. The need for additional valves or external switches is eliminated, helping to package the system within the vehicle. The switch will close immediately if a tire&#39;s pressure falls, greatly improving sensitivity. In the event of a low tire pressure situation when there is no pressure from the source, the switch will also close to warn of the condition. In accordance with the present invention a pneumatic valve used in an automatic tire inflation system comprises an inlet, an outlet, and a spring biased pneumatically controlled actuator responsive to the outlet air pressure and capable of opening a normally closed valve seat to allow air flow from the inlet to the outlet to control outlet air pressure, while actuating a switch to indicate a warning signal. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a partial cross-sectional view of a vehicle&#39;s automatic tire inflation system incorporating the valve with an integrated alert switch; 
     FIG. 2 is a cross-sectional drawing of the valve and switch of the system with the tires fully charged and the regulator in the closed position with the switch in the opened position; 
     FIG. 3 is a cross-sectional drawing of the valve and switch with at least one tire&#39;s air pressure below the pressure regulator&#39;s adjusted pressure, and the pressure regulator is open and the switch is closed; 
     FIG. 4 is a cross-sectional drawing of the valve and switch with too much outlet air pressure and the regulator is in the exhaust position and the switch is open; 
     FIG. 5 is a cross-sectional drawing of the invention with an encapsulated limit switch. 
    
    
     DESCRIPTION OF THE INVENTION 
     With reference now to the details of the drawings, FIG. 1 reveals a source of pressurized air  1  which communicates with a pressure protection valve  2 . When sufficient pressure is reached from the source  1 , the pressure protection valve  2  opens and passes air through the shut-off valve  3  if it is in the open position. The shut-off valve then sends pressurized air to the air inlet  40  of the pressure regulator and switch  4 , which, as will be described, regulates the pressure and according to this invention will complete the electrical circuit  30 ,  31 ,  32 ,  33 , and  34  if a tire should need air. Regulated air then exits the outlet  50  and is in communication with a conduit  7  that transports air into a hollow axle  8 . A pressure gage  5  makes it possible to properly set the pressure regulator  4 . 
     The pressurized air inside the hollow axle is contained at each end by a plug  9  and its corresponding seal  10 . A rotary union comprised of a stationary member  12 , a tube  13 , and a rotating member  14  passes the pressurized air from the axle end to the rotating hubcap  21 . This can be seen in detail by referring to patent application Ser. No. 60/145,486. A pressure conduit  22  sends the air through a one-way check valve  23  and into the pressurized area  24  contained within the tire  25  and the wheel  26 . 
     FIG. 1 also illustrates the electrical circuit having a power source  30  which, when a tire&#39;s air pressure is low and the electrical switch  4  is in its closed position, completes a circuit with electrically conductive materials  31 , 33 , and  34 , and an electronically activated alert device  32 . It should be understood by those familiar in the art that additional circuitry such as a relay switch can be added to the circuit and still provide an electronically triggered warning when the pressure regulator delivers air. 
     FIG. 2 shows a cross-section of the pressure regulator and switch  4  which includes a hollow body having an air inlet  40  which receives pressurized air to fill an inlet cavity  41  within the body. A face seal  42  is slightly biased by a spring  43  to seat against the sealing surface  44  to close the passage  70 . Air pressure inside a piston cavity  46  on the opposite side of the passage  70  forces the actuating member, in this case a piston  45 , and its corresponding seal  47 , reciprocal in the cavity  46 , against the main spring  48 . A diaphragm could also serve as the actuator in substitution of the piston  45  and seal  47 . 
     The main spring  48  can be adjusted by turning the threaded adjuster  49  to change the spring force and consequently the output pressure of the regulator. The pressure in the piston cavity  46  creates a force against the affective area of the piston  45  and its seal  47 , which are exposed to atmospheric pressure on their opposite side through the vent  72 . At a specific pressure in the piston cavity  46  the affective force created will compress the spring  48  to position the face seal  42  onto the sealing surface  44 . The main piston cavity  46  is in direct communication with the air outlet  50  which sends air to the tires as illustrated in FIG.  1 . 
     When a tire&#39;s pressure drops, the air pressure inside the main piston cavity  46  also drops, and as shown in FIG. 3, the main spring  48  forces the piston  45  to move the face seal  42  away from the sealing surface  44 . Now supply air from the air inlet  40  is free to pass from the lower cavity  41 , through the passage  70 , and into the upper piston cavity  46 . When the piston  45  is in this position, an electrically conductive material located on the lower end  56  of the piston conducts electricity between the two electrical contacts  51  and  52 . Each electrical contact is insulated from the body with a non-conductive material  53  about the contacts, and o-rings  54  and  55  prevent air passage between the body cavities  41  and  46 . 
     Only when the tire pressure has returned to its proper pressure will the air pressure inside the main piston cavity  46  force the piston  45  upwardly against the main spring  48 . This closes the face seal  42  and also breaks the electrical connection between the contacts  51  and  52 , consequently turning off the alert mechanism. 
     The valve  4  can take another position as shown in FIG.  4 . Here excessive air pressure has developed in the upper cavity  46 . To prevent over pressurization of the tires, the additional air pressure forces the piston  45  and its seal  47  to further compress the spring  48 . The piston  45 , which has as hollow passage  71 , moves away from the face seal  43 . In this position air pressure from the outlet  50  is exhausted through the passage  71  and to the atmosphere through a vent  72 . Only when the pressure inside the cavity  46  has dropped to the adjusted pressure will the piston  45  seat against the face seal  43  and stop air from venting. 
     FIG. 5 illustrates the invention using a self-contained switch  60  within the valve body. Air pressure regulation functions in the same way as the valve illustrated in FIGS. 2,  3 , and  4 . The piston  45 , when opening or closing the electrical circuit actuates a button  61  on the normally open or normally closed switch  60 . The switch  60  must be internally air tight in the case of this drawing. The o-ring  62  that is backed by a washer  63  and held by a nut  64 , which is threadably connected to the switch  60 , forms a seal around the switch&#39;s outer surface. Those familiar in the art should understand that the switch  60  could also be positioned on the non-pressurized side of the piston  45 . By placing the switch  60  on the atmospheric side of the piston  45 , the switch  60  would not need to be sealed but would still be actuated by the piston  45 . 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
     As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
Alternate embodiments of a vehicle tire inflation system equipped with a low tire pressure warning device are illustrated wherein a pressure regulating valve controls the pressure delivered to the tires from a pressurized air source and has an integrated electrical switch to indicate if the pressure regulating valve is supplying air to a tire.