BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improved rotary assembly for use in a central tire inflation system for automatically maintaining the inflation pressure of the pneumatic tires on moving vehicles such as tractor trailers.

2. Description of the Prior Art

Automatic central tire inflation systems for vehicle tires are well known and the subject of several U.S. patents, including U.S. Pat. Nos. 3,276,503; 4,387,931; 4,883,106; 5,287,906; 5,584,949; and 6,105,645, the disclosures of which are incorporated herein by reference.

The central tire inflation systems employed on typical tractor trailers utilize the air compressor on the tractor as a source of pressurized air to fill a leaking tire while the trailer is in motion. The compressor directs air to the reserve air brake tank on the trailer, which generally corresponds to the range of typical inflation pressures in the tires used on trailers. Air from the reserve air brake tank is first directed to the braking system to maintain the air pressure in the braking system. Excess air is directed from the tank through a pressure protection valve to a control box for the tire inflation system. The pressure protection valve only opens to direct the air to the control box when excess air pressure is present, thereby preventing air from being directed to the air inflation system which is needed for the trailer braking system. The control box contains a pressure regulator which is set to the cold tire pressure of the particular tires on the trailer so as to supply air to the tires at the desired pressure level in the event of a leak. Air is directed from the control box to the leaking tire through one of the trailer axles, which either carries an air line from the control box, or is sealed and functions as an air conduit. The pressurized air carried by the axles communicates with each pair of trailer tires mounted thereon through a rotary union assembly by which air flow is directed from a stationary air line to the valve stems on the rotating tires. Pressure responsive valves are employed between each rotary union assembly and its associated tires so that upon the occurrence of a leak in one of the tires, the resulting pressure loss will cause one of the valves to open and allow air flow from the rotary union assembly to pass therethrough to the leaking tire.

While these central tire inflation systems are well known and in widespread use, they suffer from several shortcomings. The rotary union assemblies employed in these systems have a relatively limited useful life span before the rotary seals begin to leak. The rotary seals, or rotary unions as they are frequently called, which are employed in these assemblies are generally located within the wheel lubrication compartments adjacent the ends of the axles. Accordingly, any air leakage in the rotary union seals causes an air pressure build up within the lubrication compartment which can damage the oil seals therein, and create an oil leak. If the wheel bearings lose their lubrication, they will seize up and can cause a fire. In addition to creating the potential for a dangerous fire, the positioning of the rotary union within the lubrication compartment of the wheel makes accessibility to the elements comprising the rotary union both difficult and awkward. As a result, the costs of repair and replacement are significantly increased.

Other problems facing central tire inflation systems include a lack of uniformity in tractor trailer wheel hub cap configurations and off-center mountings. The former situation results in variations in the axial distance between the ends of the axle spindles and end walls of the hub caps. This distance generally determines the spacing between the air inlet of the assembly and the rotary seal therein. It would be highly desirable to provide a rotary union assembly which could readily accommodate such dimensional variations and thereby obviate the need to provide differently sized assemblies or replacement components for different hub cap configurations. Preferably, the rotary union assembly should also accommodate off-center alignments of the axle spindle and hub caps without incurring additional wear on the air seals in the assembly which further shortens the life of the assembly.

Accordingly, the need remains for an improved rotary union assembly that better integrates with the tractor trailer wheel hub cap, includes improved venting from within the hub cap compartment, and provides improved accessibility for replacement of the rotary union assembly or wear parts thereof at the expiration of their lifespan.

SUMMARY OF THE INVENTION

A rotary union assembly for use with a tire inflation system includes a hollow tube configured to deliver air between proximal and distal ends, a bullet having a central axial aperture receiving the tube therethrough, a proximal retaining structure defined on the proximal end of the tube, and a distal retaining structure defined on a distal end of the tube, configured to retain the bullet on the tube therebetween. A cartridge is coupled to a distal end of the tube and includes one or more apertures on a sidewall thereof in fluid communication with the tube. In use, the rotary union assembly is coupled between a non-rotating axle of a vehicle and the rotating hubcap of a tire rotating about the axle and may be removed as a unit for repair and/or replacement of wear parts on the assembly. Pressurized air from within the axle is communicated through the rotary union assembly and out airlines coupled to air stems on the rotating hubcap and then to the tires themselves to maintain them at the proper inflation pressure.

The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention that proceeds with reference to the accompanying drawings.

