Abstract:
The present invention is directed to a rotary air coupling that distributes air to tires mounted on a rotating hub of a driven axle. The coupling is positioned outside of the axle and hub bearings avoiding interference with the wheel assembly. And the rotary coupling is connected to the brake mounting plate and the wheel hub to take advantage of existing space between these members with minimal change to existing wheel assemblies.

Description:
BACKGROUND OF THE PRESENT INVENTION 
     a) Field of the Invention 
     The present invention is directed to a rotary air coupling that provides a means to distribute air from an air supply to vehicle tires mounted on a rotating hub of a vehicle drive axle. 
     b) Description of Related Art 
     Automatic central tire inflation systems (CTIS) are becoming popular with the trucking industry. Various types of tire inflation system have been developed, both for trailer axles and tractor drive axles. 
     A central tire inflation system allows the operator to control the air pressure of the tires for improved performance of the tires and of the vehicle. However, the central tire inflation systems currently available suffer from two primary drawbacks. The axle and hub and possibly other parts must be extensively modified in order to accommodate a conventional system. 
     Central tire inflation systems in general are an important feature. Specifically, an off-road vehicle will often drive on soft, muddy surfaces and then switch to harder surfaces, such as paved roads. To obtain proper traction on soft, muddy surfaces, the tire should be operated at a relatively low pressure. To obtain proper traction and optimal fuel mileage on harder surfaces, the tires should be operated at relatively high pressures. 
     The differences between preferred high tire pressures (hard surfaces) and preferred low tire pressures (soft surfaces) may be quite large. For example, some truck tire manufacturers recommend a maximum tire pressure of 120 psi for highway conditions and 8 to 15 psi for extremely soft conditions such as sand, mud and swamps. A tire pressure for intermediate road conditions may be approximately 40 psi. Of course, in the case of trailers, the preferred tire pressure will also be dependent upon the weight of the goods or equipment carried in the trailer. 
     Another reason justifying the employment of central tire inflation systems is road surface deterioration. It is known that over-inflated tires are a major cause of road surface deterioration. Road repair and road building have become increasingly expensive and it is therefore foreseeable that governmental entities may begin penalizing the operators of trucks and tractor-trailers for operating equipment on public roads with improperly inflated tires or over-inflated tires. 
     Of course, another reason justifying central tire inflation systems is fuel economy. Soft tires on highways reduce gas or fuel mileage. A central tire inflation system that automatically controls the air pressures of trailer tires on a highway will increase fuel efficiency as well as improve road surface longevity. 
     Existing air distribution systems for tire inflation systems on drive axles direct the supply air through the bearings of the hub. Distribution through the bearings demand smaller bearings and require additional seals in the hub. The seal life is shortened due to the increased seal friction caused by pressure loading of the seal lips. 
     The need exists for a rotary air coupling designed to distribute supply air to the tires mounted on drive axles in which the air coupling is positioned externally of the drive axle and the hub bearings 
     SUMMARY OF THE INVENTION 
     The present invention is particularly directed to a rotary air coupling designed to distribute supply air to the tires mounted on drive axles in which the air coupling is positioned externally of the drive axle and the hub bearings. Therefore, the improved rotary air coupling of the present invention by being mounted outside the bearings of the hub has no effect on existing hub bearings. 
     The present improved rotary air coupling takes advantage of the known dimension of existing wheel systems by connecting the stationary component of the coupling to the brake mounting plate directly or through the axle housing, while the rotary component of the coupling is press-fit onto the hub. 
     One of the advantages of the present invention is that the rotary coupling of the present invention does not interfere with the drive axle, bearings or lubrications as internal axle type air couplings can. Thus, there is no interference in the strength of existing vehicle components, which can lead to lengthy testing delays. Another advantage is the accessibility of the present rotary coupling. The present rotary coupling can be accessed as easily as brake shoes and will not cause mechanical difficulty in re-assembly. 
     The present invention is directed to an improvement in a rotary air coupling in a tire inflation system having a driven axle, a hub rotatable on hub bearings, a brake mounting plate, and a brake drum connected to the hub. The coupling includes an annular stationary housing positioned externally of the hub bearings, and connected to the brake mounting plate, and an annular rotatable housing positioned externally of the hub bearings and connected to the hub. Seal means are provided sealing between the stationary housing and the rotatable housing. An air supply inlet is connected to the stationary housing, and an air outlet is connected to the rotatable housing. The stationary housing and the rotatable housing include an air passageway therethrough communicating between the air inlet and the air outlet. 
     The present invention is further directed to the improvement in an air inflation system for tires on a vehicle having a driven axle with at least one pneumatic tire at each end of the axle, a hub rotatable on hub bearings, a brake mounting plate, and a brake drum connected to the hub of a rotary air coupling which distributes supply air to the tires. The rotary air coupling includes an annular stationary seal housing having a seal chamber with an radially facing opening in which the stationary housing is positioned externally of the hub bearings and connected to the brake mounting plate. The radially facing opening of the stationary seal housing and the radially facing opening of the rotatable seal housing are positioned adjacent to and face each other. A pair of stationary high pressure seals are provided having a sealing face and are positioned in the seal chamber of the stationary housing. 
     An air supply inlet is connected to the stationary seal housing and in communication with the stationary component. An air outlet is connected to and is in communication with the rotatable component. 
     Other and further features and advantages will be apparent from the following description of a presently preferred embodiment of the invention, given for the purpose of disclosure, and taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a half cross-sectional view of a driven axle type of wheel assembly with the rotary air coupling of the present invention, 
     FIG. 2 is cross-sectional view of the rotational component and stationary component with the wheel and brake assembly being omitted, 
     FIG. 3 is a cross-sectional view of the rotational component, 
     FIGS. 4 and 5 are perspective views of the rotational component of FIG. 3, 
     FIG. 6 is a cross-sectional view of the stationary component, and 
     FIGS. 7 and 8 are perspective views of the stationary component of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An central tire inflation system (CTIS) in which the air and rotating tires are controlled through an air connection between the trailer air supply and each of the tires on a driven axle and such a disclosure is provided by this invention. 
     Referring to FIG. 1, the reference numeral  10  generally indicates a wheel assembly of a driven axle vehicle having a driven axle or spindle within the axle housing  12  upon which a wheel hub  14  is supported therefrom by bearings  16  and  17 . Lug bolts  18  extend from the hub  14  for receiving and supporting a wheel and tire (not shown), and a brake drum  20 , all of which rotate. A stationary component includes a brake assembly  22  including a mounting plate to which is connected the brake spider, the brake S cam and the brake shoe  28 . The above components of the wheel and brake assembly are conventional. 
     The present invention is directed to providing a rotary air coupling generally indicated by the reference numeral  30  to distribute supply air from an air supply on the vehicle to tires mounted on the drive axle or spindle. Existing air distribution systems for tire inflation systems on drive axles direct the supply air through the bearings of the hub which require smaller bearings, additional seals, which causes the seal life to be shortened. 
     One of the features of the present rotary coupling  30  is that it does not interfere with the conventional drive axle and axle housing  12 , bearings  16  and  17  or lubrication as do internal type axle couplings. Therefore, there is no interference in the strength of existing vehicle components. It is noted from FIG. 1 that the rotary air coupling  30  of the present invention is positioned around the outside of the axle housing  12  and externally of the hub bearings  16  and  17 . However, the present air coupling  30  consists of a rotary or dynamic component  33  and a stationary or static component  34 . It is important that the components  33  and  34  be closely aligned with tight tolerances; however, the various components in the wheel assembly  10  have variable and loose tolerances such a quarter of an inch or even greater. Nevertheless, the tolerances between the brake drum  20  and the brake shoe  28  must be maintained with close tolerances which requires that the tolerances between the brake mounting plate  22  and the hub  14  is a well defined dimensional relationship since the other brake members are interconnected from the brake mounting  22  and hub  14 . Therefore, it is another feature of the present invention to support the stationary components  34  and the rotating component  33  of the coupling  30  from the brake mounting plate  22  and the hub  14 , respectively, thereby allowing the components  33  and  34  to maintain the required close tolerances between themselves. 
     Referring now to FIGS. 1 and 2, the stationary component  34  includes a stationary seal chamber  36  which, in conjunction with a pair of high pressure seals  37  and  38 , defines a radially facing opening (see direction line  40 ). The stationary seal housing  36  is positioned externally of the hub bearing  16  and  17  and the axle housing  12 , and is connected to the brake mounting plate  22  and supported therefrom such as by bolts  42 . The pair of high pressure stationary ring seals  37  and  38  each having a sealing face  37   a,   38   a  is positioned in the seal chamber  36  with each sealing face  37   a,    38   a  oriented in the radial direction. 
     The high pressure seals  37 ,  38  are formed of a metal body portion that is press-fit into the annular opening of the components  33 ,  34 . The sealing face  37   a,    38   a  is formed with an appropriate spring-loaded rubber sealing member, and preferably a Teflon or other wear resistant surface is provided at the sealing interface. In the preferred embodiment, the sealing member is designed to withstand a pressure spike of about 125-130 psi. Of course, the exact sealing specifications may be altered to satisfy the sealing conditions at hand. 
     Referring now to FIG. 2, the rotating component  33  and stationary component  34  are illustrated with the wheel and brake assembly omitted. The two radially oriented, high-pressure seals  37 ,  38  provide a sealed interface between the rotating and stationary components  33 ,  34 ; thereby defining an airflow path shown with a series of arrows  39  in FIG.  2 . 
     Referring to FIGS. 1 and 2, an air supply inlet  90  is connected to the stationary component  34  and is adapted to be connected to the air supply on the vehicle thereby placing air in communication with the tire via the air path shown in FIG.  2 . The air outlet port  92  provides a connection via lines (not shown) to the pneumatic tires (not shown). 
     FIG. 3 is a cross sectional view of the rotational component  33  showing an annular hub portion with seal engaging surfaces  33   a,    33   b,  and a cylindrical delivery member  33   c.  FIGS. 4 and 5 are perspective views of the rotational component  33  of FIG. 
     FIG. 6 is a cross sectional view of the stationary component  34  showing an annular hub portion with seal mounting surfaces  34   a,    34   b,  and a cylindrical delivery member  34   c.  The stationary member is mounted to a brake mounting member via mounting holes  34   d  receiving the bolts  42 . FIGS. 7 and 8 are perspective views of the stationary component of FIG.  6 . 
     In operation, the present air coupling may be conveniently located outside of the axle and connected to known dimension parts; the stationary component is preferably connected to the brake mounting plate  22  by the bolts  42 , and the rotational component  33  is preferably press-fit onto the hub to thereby rotate with the tire. These components  33 ,  34  are mounted with the assurance that the tolerances of these available mounting services are always tightly controlled because it is important that the brake shoes  28  be aligned with the drum  20 . The location of these components also has the advantage of accessibility. The coupling  30  does not interfere with the drive axle or axle housing  12 , bearings  16  and  18 , or lubrication. The rotary union  30  can be accessed as easily as the brake shoes and may be easily reassembled and there is no interference with the existing vehicle components. An airline is connected to the vehicle air supply and connected to the inlet connection  90  to provide a supply air for supplying to the rotatable tires. Suitable air lines are connected between the tires and the outlet  92 . 
     The vehicle air supply will now be described. The onboard tire pressure inflation system may comprise a control which will typically be located in the vehicle operator&#39;s cab. The control may have a lever which is selectively movable to two or more positions for selecting a desired tire pressure. Typically, in a heavy duty vehicle, in highway (i.e. over-the-road) conditions it is desired that the driving tires be inflated to a pressure of about 75 pounds per square inch, in off-the-road conditions it is desired that the driving tires be inflated to a pressure of about 40 pounds per square inch and for desert operating conditions it is desired that the tires be inflated to a pressure of about 8-14 pounds per square inch. Of course, other pressures and/or other settings may be selected by the control and will fall within the scope of the present invention. The control may also include an infinitely variable control member whereby the operator may select any pressure within a given range of pressures. The control is attached to a pressure regulator by a line which may be hydraulic and/or electric or the like. The pressure regulator is connected to a source of pressurized fluid by a fluid connection and to a vent or exhaust. The pressure regulator will supply selectively pressurized fluid to the inlet  90  which communicates with the tire inflation structure shown in FIG.  1 . Pressure regulator is effective to supply pressurized fluid to fluid connections, or to vent fluid connections, in accordance with the setting of control. A pressure gauge may also be provided, preferably in the operator&#39;s cab, indicating the pressure level of pressurized fluid in the system. Typically, the pressurized fluid will be pressurized air and the source of pressurized fluid will be the vehicles onboard air system and/or a pressurized air accumulator. 
     Therefore, as the wheels rotate, air from the air supply flows through the inlet, into the chamber  36 , past the high pressure seals  37 ,  38  while their seal faces engage to the rotational component  33  to prevent escape of the air, into the rotational component  33 , and out of the outlet connection  92  to the tires. 
     As apparent from the foregoing description, the system of this invention consists of two machined pieces (the rotational component and stationary component) and two high pressure seals. The rotational component is designed to press fits onto the hub and rotates with the wheel. The stationary component pilots on the axle tube and is mounted using the brake assembly mounting bolts; the stationary member also holds the two high pressure seals in place. 
     To inflate the tire(s), a positive pressure is applied to the inboard side of the stationary component. Air is thereby delivered to the rotational component through the interface created by the two high-pressure seals. A hose then delivers the air to the tire for inflation. To deflate the tire(s), a negative pressure is applied to the inboard side of the stationary component; thereby reducing the air pressure in the tire(s). 
     The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned as well as others inherent therein. While a presently preferred embodiment of the invention has been given for the purpose of disclosure, numerous changes in the details of construction, and arrangement of parts will be readily apparent to those skilled in the art and which are encompassed within the spirit of the invention and the scope of the appended claims.