Rotary air coupling for tire inflation system

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.

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.

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 37a,38a is positioned in the seal chamber 36 with each
 sealing face 37a, 38a 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 37a, 38a 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 33a, 33b, and a
 cylindrical delivery member 33c. 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 34a, 34b, and a
 cylindrical delivery member 34c. The stationary member is mounted to a
 brake mounting member via mounting holes 34d 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'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'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.