Abstract:
An air maintenance tire and air pump assembly is provided including a tire and an elongate tubular air passageway enclosed within a flexing region of a tire sidewall. A plurality of check valve devices are spaced apart and positioned along the air passageway into multiple air passageway segments. A check valve membrane opens to allow pressurized air to directionally pass through the check valve device from an upstream passageway segment to a downstream passageway segment and closes to prevent air from passing in an opposite direction through the check valve from the downstream segment to the upstream segment.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to air maintenance systems for a tire and, more specifically, to such systems that affix an air pump apparatus to a tire which maintains air pressure within the tire as the tire rotates. 
     BACKGROUND OF THE INVENTION 
     Normal air diffusion reduces tire pressure over time. The natural state of tires is under inflated. Accordingly, drivers must repeatedly act to maintain tire pressures or they will see reduced fuel economy, tire life and reduced vehicle braking and handling performance. Tire pressure monitoring systems have been proposed to warn drivers when tire pressure is significantly low. Such systems, however, remain dependent upon the driver taking remedial action when warned to re-inflate a tire to recommended pressure. It is a desirable, therefore, to incorporate a self-inflating feature within a tire that will self-inflate the tire in order to compensate for any reduction in tire pressure over time without the need for driver intervention. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, an air maintenance tire and air pump assembly is provided including a tire; an elongate tubular air passageway enclosed within a flexing region of a tire wall, the air passageway having an air inlet portal operable to admit air into the air passageway and an outlet portal spaced apart from the inlet portal operable to withdraw pressurized air from the air passageway, the air passageway operably closing segment by segment in reaction to induced forces from the tire flexing region as the flexing region of the tire wall rotates opposite to a rolling tire footprint. Multiple spaced apart check valve devices are seated within and along the axial air passageway, dividing the air passageway into multiple passageway segments. Each check valve device has an external dimension and configuration operable to substantially occupy the air passageway. A valve gate, such as a membrane, allows pressurized air to directionally pass through the check valve device from an upstream passageway segment to a downstream passageway segment. The valve gate in a closed position prohibits air from passing in an opposite direction through the check valve body from the downstream passageway segment to the upstream passageway segment. 
     In another aspect, the air passageway may alternatively be configured as an integrally formed passageway within the tire sidewall or as an axial passage provided by a flexible air tube that is assembled to the tire in a post-cure procedure. 
     According to another aspect, each check valve device is configured as a tubular body closely received within the air passageway, the tubular body having outwardly projecting retention barb(s) for securing the tubular body at a preferred location within the air passageway. The tubular body houses a flexible membrane member which serves as the valve gate. The membrane opens along a slit to admit pressurized air from one side of the check valve device to an opposite side. 
     The check valve devices, in another aspect, may be positioned and spaced along a continuous air passageway extending between the inlet and outlet portals, or, alternatively, serve to connect air tube segments together in a splicing check valve configuration. 
     DEFINITIONS 
     “Aspect ratio” of the tire means the ratio of its section height (SH) to its section width (SW) multiplied by 100 percent for expression as a percentage. 
     “Asymmetric tread” means a tread that has a tread pattern not symmetrical about the center plane or equatorial plane EP of the tire. 
     “Axial” and “axially” means lines or directions that are parallel to the axis of rotation of the tire. 
     “Chafer” is a narrow strip of material placed around the outside of a tire bead to protect the cord plies from wearing and cutting against the rim and distribute the flexing above the rim. 
     “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction. 
     “Equatorial Centerplane (CP)” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of the tread. 
     “Footprint” means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure. 
     “Groove” means an elongated void area in a tire tread dimensioned and configured in section for receipt of an air tube therein and where the tread may extend circumferentially or laterally about the tread in a straight, curved, or zigzag manner. Circumferentially and laterally extending grooves sometimes have common portions. The “groove width” is equal to tread surface area occupied by a groove or groove portion, the width of which is in question, divided by the length of such groove or groove portion; thus, the groove width is its average width over its length. Grooves may be of varying depths in a tire. The depth of a groove may vary around the circumference of the tread, or the depth of one groove may be constant but vary from the depth of another groove in the tire. If such narrow or wide grooves are substantially reduced depth as compared to wide circumferential grooves which the interconnect, they are regarded as forming “tie bars” tending to maintain a rib-like character in tread region involved. 
     “Inboard side” means the side of the tire nearest the vehicle when the tire is mounted on a wheel and the wheel is mounted on the vehicle. 
     “Lateral” means an axial direction. 
     “Lateral edges” means a line tangent to the axially outermost tread contact patch or footprint as measured under normal load and tire inflation, the lines being parallel to the equatorial centerplane. 
     “Net contact area” means the total area of ground contacting tread elements between the lateral edges around the entire circumference of the tread divided by the gross area of the entire tread between the lateral edges. 
     “Non-directional tread” means a tread that has no preferred direction of forward travel and is not required to be positioned on a vehicle in a specific wheel position or positions to ensure that the tread pattern is aligned with the preferred direction of travel. Conversely, a directional tread pattern has a preferred direction of travel requiring specific wheel positioning. 
     “Outboard side” means the side of the tire farthest away from the vehicle when the tire is mounted on a wheel and the wheel is mounted on the vehicle. 
     “Peristaltic” means operating by means of wave-like contractions that propel contained matter, such as air, along tubular pathways. 
     “Radial” and “radially” means directions radially toward or away from the axis of rotation of the tire. 
     “Rib” means a circumferentially extending strip of rubber on the tread which is defined by at least one circumferential groove and either a second such groove or a lateral edge, the strip being laterally undivided by full-depth grooves. 
     “Sipe” means small slots molded into the tread elements of the tire that subdivide the tread surface and improve traction, sipes are generally narrow in width and close in the tires footprint as opposed to grooves that remain open in the tire&#39;s footprint. 
     “Tread element” or “traction element” means a rib or a block element defined by having a shape adjacent grooves. 
     “Tread Arc Width” means the arc length of the tread as measured between the lateral edges of the tread. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described by way of example and with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of a tire and air pumping system assembly. 
         FIG. 2  is a side view of the tire with a 180 degree peristaltic tube and multiple check valves in place. 
         FIG. 3  is a side view of the tire with a 360 degree peristaltic tube alternative embodiment. 
         FIG. 4  is a side view of the tire with two 180 degree peristaltic tubes in an alternative embodiment. 
         FIG. 5  is a perspective view of a check valve prior to insertion into a peristaltic tube. 
         FIG. 6  is a section view of the check valve in the “open” flow position. 
         FIG. 7  is a section view of the check valve in the “closed” flow position. 
         FIG. 8  is a partial section view showing a check valve being introduced into an inflated tube by a rod. 
         FIG. 9  is a partial section view showing the check valve being seated in place in an inflated tube by the rod. 
         FIG. 10  is a partial section view showing a second check valve being introduced into the inflated tube by a rod. 
         FIG. 11A  is a perspective view of a clamp in the “open” position prior to placement over the valve and the tube. 
         FIG. 11B  is a perspective view of a clamp in the “closed” position. 
         FIG. 12  is a Perspective view of a tube with 3 valves in place. The right valve is retained in its intended location by a clamp. 
         FIG. 13  is a perspective view of an alternative splice-configured check valve. 
         FIG. 14A  is a section view showing a tube end going into position over one end of the splice-configure check valve. 
         FIG. 14B  is a section view showing a second tube end going into position over the other end of the check valve. 
         FIG. 14C  is a section view showing the check valve with two tubes attached. 
         FIG. 15  is a perspective view of the step shown in  FIG. 14B . 
         FIG. 16  is a section view taken from  FIG. 3  showing the tube. 
         FIG. 17  is a section view taken from  FIG. 3  showing the check valve in the tube. 
         FIGS. 18, 19, 20 and 21  show alternative embodiments of peristaltic tube configurations suitable for use with the check valves. 
         FIG. 22  is a graph showing segment pressure of an AMT Vein pump showing pressure vs. distance (km). 
         FIG. 23  is a graph of compression ratio effect on a vein pump showing chamber pressure vs. distance. 
         FIG. 24  is a graph of segment volume effect in a six segment tube having a 0.15 L Chamber. 
         FIG. 25  is a graph showing the effect of segment number on chamber pressure. 
         FIG. 26  is a graph showing check valve dead-end volume effect in a six segment tube configuration. 
         FIG. 27  is a graph comparing forward and backward tube performance. 
         FIG. 28  is a graph showing the effect of forward motion on the vein segments. 
         FIG. 29  is a graph showing the effect of backward motion on the vein pressure. 
         FIG. 30  is a graph comparing forward vs. backward chamber pressure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a tire  12  and air maintenance pump assembly  10  (forming an air maintenance tire or “AMT”) includes a tire and a vein pump assembly including an air tube  26 . The general operation of a peristaltic pump for use in a tire is described in U.S. Pat. Nos. 8,113,254 and 8,042,586 which were both filed on Dec. 12, 2009, and issued on Feb. 14, 2012, and Oct. 25, 2011, respectively, and are incorporated herein in their entirety by reference. The tire is constructed to provide a tread region  14 , a pair of sidewalls  16 ,  18  extending from opposite bead areas  22 ,  24  to the tire tread region  14 . The tire encloses a tire cavity  20 . The air maintenance assembly includes an elongate air tube  26  that encloses an annular passageway  28 . The tube  26  is formed of a resilient, elastomeric flexible material such as plastic or rubber compounds and composites that are capable of withstanding repeated deformation cycles wherein the tube is deformed into a flattened condition subject to external force and, upon removal of such force, returns to an original condition generally circular in cross-section. The tube is of a diameter sufficient to operatively pass a volume of air sufficient for the purpose of maintaining air pressure within the cavity  20 . The tube  26  is shown to follow a 180 degree semi-circular path in the configuration of  FIG. 1 . However, other configurations may be employed as will be described without departing from the invention. 
     The air maintenance vein pump assembly further includes an inlet device  30  and an outlet device  32  spaced apart approximately 180 degrees at respective opposite end locations of the air tube  26 . The outlet device  32  has a T-shaped configuration in which T-forming sleeves connect to an end of the tube  26  and an outlet conduit conducts air from the tube to the tire cavity  20 . The inlet device  30  likewise is of a T-shaped configuration, connecting to an opposite end of the tube  26  and having an inlet conduit which intakes outside air into the tube passageway  28 . The pending applications previously identified and incorporated herein provide the details of the outlet and inlet devices. Situated within the inlet and outlet devices are appropriate, commercially available valve mechanisms for controlling air intake into the tube  26  and outlet from the tube into the cavity  20 . 
     As will be appreciated from  FIG. 2 , the air tube  26 , inlet device  30 , and the outlet device  32  are positioned within an appropriately complementarily configured channel within one of the tire sidewalls. As the tire rotates in the direction of rotation indicated, a footprint is formed against a ground surface (not shown). A compressive force is thus directed into the tire from the footprint and acts to flatten a segment of the air tube  26  and passageway  28 . As the tire rotates further, the air tube and passageway are sequentially flattened and pump air in the direction  72  shown. Flattening of the tube segment by segment thereby forces air from the inlet along tube passageway  28 , until the pressurized air is directed from the outlet and into the tire cavity. Appropriate valve mechanism at the outlet will vent the air in the event that the tire cavity pressure is at or above the recommended tire pressure. Pumping of air occurs for one-half the revolution of the tire with the 180 degree air tube configuration shown. 
       FIG. 3  shows an alternative 360 degree air tube which functions as described above, with the exception that air is pumped along the air tube in direction  72  for the entire 360 degree revolution of the tire.  FIG. 4  shows a tire with two 180 degree peristaltic tubes as an alternative embodiment. In the  FIG. 4  embodiment, the pump will function in either direction of tire rotation shown by the directional arrows. The two air tubes are each operational in a respective direction of rotation to pump air into the tire cavity. 
     With reference to  FIGS. 5, 6 and 7 , pursuant to the invention a plurality of check valves  34  are provided for assembly into the passageway  28  of the vein tube  26 . The check valve  34  includes a cylindrical valve body  36 , composed of any suitable rigid or semi-rigid material. The body  36  has a rounded forward end rim  38 . An array of outwardly directed retention ribs or flanges  40  are spaced apart along the surface of the valve body  36 , each retention rib angling to the rear of the body. A flexible membrane member  42 , of suitable elastomeric composition, is assembled into a central through passage of the cylindrical valve body  36 . The membrane member  42  includes a cylindrical membrane body  44  captured within the valve body  36  by in turned end flanges  45 ,  47  of the valve body  36 . The membrane insert  42  further includes a central projecting nose  46  having a slit  48  therethrough. The nose  46  forms a gate through which pressurized air can flow in a forward direction  50  ( FIG. 6 ) but which prevents a back flow of air through the check valve in a rearward direction ( FIG. 7 ). 
       FIGS. 8, 9 and 10  show an assembly sequence whereby multiple check valves  34  may be inserted into the axial passageway  28  of the elastomeric flexible tube  26 . The multiple check valves  34  are designed to occupy spaced apart respective locations within the tube  26  in an orientation which facilitates a flow of pressurized air in a forward direction from the inlet  30  to the outlet  32  but which prevents a back flow of pressurized air in the reverse direction. As seen in  FIG. 8 , a pressurized air source  52  is positioned to inject pressurized air  54  into the tube passageway  28 , whereby radially expanding the tube in the direction  56  so that the passageway  28  assumes a temporary, oversized diameter. A stopper  57  is inserted into a forward end of the tube to prevent the flow  54  from escaping. At the location within the passageway  28  that a check valve  34  is to be located, a clamping collar  58  is affixed over the tube  26  and exerts a radial force  60  on the tube, thereby preventing the tube from expanding at that location. Thereafter, a check valve  34  is inserted into an open end of the tube with the membrane gate opening toward the outlet end of the tube. A rod  62  pushes the check valve  34  through the expanded tube  26  in the direction of arrow  64  until it reaches its intended location within passageway  28 , as shown in  FIG. 9 . 
     The clamping collar  58  may then be removed and relocated down the axial length of the tube  26  to a location where a second check valve  66  is to be located. The second check valve  66  is positioned at the open end of the tube and pushed by rod  62  through the diametrically expanded tube into the intended second check valve location  65  within the tube passageway  28 .  FIG. 10  illustrates insertion of the second check valve  66  by the rod  62 . The above procedure is repeated until all of the check valves  34  are in place within the tube  28 . Once the pressurized air flow  54  is withdrawn from the tube passageway, the tube  26  elastically radially contracts into its original unexpanded condition. The tube  26  in its resilient radial contraction, thus captures each placed check valve  34  and exerts a radial compression force on the check valve bodies  36  to hold the check valves in their intended locations within the passageway  28 . With the radial contraction of the tube, the retention flanges or barbs  40  on the sides of the cylindrical valve body of each check valve  34  engage into the sidewalls of the tube defining the passageway  28 , and thus function, in conjunction with the tube radial clamping force on the check valves, to retain the check valves  34  in their intended placement locations.  FIG. 12  show the check valves  34  assembled into the tube passageway with the tube in its original, unexpanded diameter and the retention flanges  40  of each valve body  36  engaging into the sidewalls of the tube forming the passageway  28 . 
     With reference to  FIGS. 11A and 11B , multiple secondary retention clamps  68 , each in the form of a cylindrical collar, may be deployed over respective locations along the tube  26  where the check valves  34  have been positioned. The clamps  68  are formed of flexible material such as plastic or metal. The clamps  68  open to facilitate receipt of the tube  26  through each clamp. Subsequently, the clamps  68  are closed into a circular configuration and overlapping locking flanges  70  engage to hold each clamp  68  in a closed circular configuration over the tube  26 . The opening through the clamps  68  is sized nominally smaller than the tube diametric dimension, so that the clamps  68  in a closed position press the tube radially inward over the check valves. 
       FIG. 12  shows the placement of the clamps  68  along the tube  26  over respective check valve locations. The resilient radially directed force of the tube  26  combined with engagement of each check valve&#39;s retention flanges  40  with internal tube sides and the clamps  68  provide redundant means for retaining each check valve in its intended location within the tube passageway  28 . Opening and closing of the check valves  34  during operation of the pump assembly will accordingly not act to dislocate any of the check valves from their positions within the tube passageway. 
     It will be appreciated from the drawings, particularly  FIGS. 12 and 14C , that the external configuration (geometry) of the air pumping tube remains unaltered by the presence of a check valve or check valves  76 . That is, the check valve or check valves  76  create substantially no bulge where present within the air tube  26 . As set forth, the tube  26  has a complementary dimension and external geometry to the groove in which the tube  26  is inserted. The groove sidewalls must exert a compressive force against the tube progressively as the tire rotates in order for the tube to efficiently pump and compress air along the tube. Should the presence of check valves at one or more locations along the tube create a bulge, the bulge would disrupt the compression of the tube in that location as the tire rotates. Such a disruption would interfere with smooth generation of compressed air along the tube. Accordingly, the system employed configures the exterior dimension of the check valves such that the check valve(s) operably substantially occupy the air passageway within the tube without disrupting the uniform external uninterrupted configuration and cross-sectional dimension of the air passageway within the tube. 
     Referring to  FIG. 13 , an alternatively configured check valve  76  is shown in a splice configuration. The check valve  76  has a relatively more elongate cylindrical valve body  78 . First and second arrays of retention flanges or barbs are provided, the first array  80  at a forward location along the body  78  and the second array  82  at a rearward location. The body  78 , as will be seen in  FIGS. 14A, 14B and 14C , has a centered membrane insert configured to operate in the manner previously explained. The elongate body  78  is used for the purpose of splicing two segments of tube  84 ,  88  together. An end  86 ,  90  of each of the tubes  84 ,  88  attaches over a respective end of the body  78  ( FIGS. 14A, 14B, 15 ), whereupon the barb arrays  80 ,  82  engage internal sidewalls of the tube ends  86  as shown in  FIGS. 14C and 15 . 
     With reference to  FIGS. 1, 3, 16 and 17 , upon completed assembly of the check valves  34  into the tube passageway  28 , the tube  26  is inserted into a complementarily configured channel formed within a tire sidewall  16 . The lower sidewall region shown in  FIGS. 16 and 17  above the bead region  22  flexes sufficiently to allow for the segment by segment air pumping action by the tube described previously. If desired, higher locations on the tire sidewall may be used as the location for the vein pump tube  26  without departing from the invention. One or both of the tire sidewalls may contain an air pumping tube if desired, and the system may be configured in a 180 degree, 360 degree (shown at  74  of  FIG. 3 ), or dual 180 degree tube configuration. 
     While the tube shown in  FIG. 1  is generally of circular cross-section, alternative tube sectional configurations may be used.  FIG. 18  shows in cross-section circular tube  26  having a circular through passageway  92 .  FIG. 19  shows a circular tube  26  modified to have an elliptical air passageway  94 .  FIG. 20  shows a mushroom shaped tube  96  having adjoining cap  98  and plug  102  tube components. The tube fits into a sidewall groove with the cap abutting an outer sidewall surface. An elliptical air passageway  100  extends through the tube.  FIG. 21  shows a mushroom shaped tube with a circular air passageway  104 . It will be understood that the check valves (such as  34 ) will have a complementary external shape and configuration to the shape of the air passageway into which the check valves are positioned. Likewise, the clamping mechanisms (such as  68 ) will be configured to fit over the tube configuration in order to impose a radial clamping force on a check valve. 
       FIG. 22  shows a chart for a multi-segment AMT Vein Pump and graphs absolute pressure (PSA) vs. distance travelled by the tire (km).  FIG. 22  illustrates the amplification of segment pressure as the tube forces air through the series of tube segments, adjacent segments being separated by a check valve. The check valves between the tube segments open only in a forward direction between air inlet and air outlet and do not allow any back flow of air within the tube in a reverse direction. In stringing a series of segments together, adjacent segments separated by a check valve, a vein-type system is constructed. The adjoining segments sequentially pump air segment to segment as the tire-mounted tube moves through a rolling tire footprint. The check valves prevent a back flow of air and operate to increase the pumping efficiency of the vein/tube system. Consequently, the vein/tube volumetric size may be as small as possible without compromising achievement of the requisite air pumping volume necessary for maintaining the tire at its rated pressure. The check valve and vein segment construction thus serves to improve to the air pressure level at the outlet portal beyond what would be attained from a single segment, non-check valve, tube of equal length. 
       FIG. 23  represents a case study graph on the compression ratio effect of the vein pump using a six segment assembly into a 0.15 L chamber. The compression ratios R=1.50, 1.35, 1.324, 1.291, 1.267 and 1.20 are graphed. As the distance (km) travelled increases, the chamber pressure increases, with R=1.5 yielding the greatest increase. 
       FIG. 24  shows a case study graph on the segment volume effect on a vein pump employing a six segment assembly delivering pressurized air to a 0.15 L chamber. The segment volumes graphed are 57.5, 114, 172.5 and 230 cubic mm. The chamber pressure vs. distance (km) travelled show the chamber pressure increasing with distance, with the larger segment volume attaining a higher pressure level. 
       FIG. 25  show a case study graph on the effect of segment number. The number of segments examined are vein pumps having 10, 7, 6, 5, 4 segments, each segment having a radius shown in  FIG. 25 . The chamber pressure is graphed against distance travelled. The graph indicates that the greater the number of segments utilized in the vein pump, the higher chamber pressure attained. The graphs for 10, 7 and 6 segments, however, are relatively coincidental, implying that increasing the number of segments beyond a certain point results does not provide significant benefit. 
       FIG. 26  graphs in the case study (six segments, 0.15 L chamber) the check valve dead-end volume effect resulting from a variance in segment radius. The chamber pressure vs. distance travelled lines show that the dead-end volume of 5 cubic mm results in a highest chamber pressure at a segment radius R—1.575. 
       FIG. 27  graphs a comparison between forward and rearward tire rotational direction under the controlled case study parameters. The chamber pressure vs. distance travelled is graphed for forward segment-6 pressure; forward chamber pressure; backward segment 6 pressure; and backward chamber pressure. The graph indicates a consistent performance of the vein pump in both forward and rearward directions. 
       FIG. 28  shows forward motion effect on the vein segments, graphing absolute pressure of each of the six segments vs. distance travelled. As shown thereby, the pressure increases from segment to segment, 1-6, with the greatest absolute pressure present in segment six. 
       FIG. 29  is a graph showing the effect of backward motion on the vein pressure. 
       FIG. 30  is a graph comparing forward vs. backward chamber pressure. 
     From the foregoing empirical verification, it will be understood that the subject vein pump assembly in a tire achieves significant advantage over a single, non-segmented peristaltic tube system. The vein concept utilizes one tube and multiple check valves inside a tubing, which is divided by the check valves into a series of tube segments. The check valves provide one-way air flow through the one-way check valves, each aligned to open toward an outlet port of the vein pump. Standard flexible tuber is used. The method of check valve placement contemplates: 
     (A) One end of the tubing is opened; 
     (B) A clamping fixture may be placed around the tube where a check valve is to be located; 
     (C) A check valve is dropped or forced into the tubing until positioned by the clamping fixture; 
     (D) The clamping fixture is moved to a second location along the tube where a second check valve is to be placed; 
     (E) A second check valve is dropped or forced into the tubing to its intended position within the tube passageway; 
     (F) Steps b through e are repeated until all of the check valves are in place; 
     (G) clamping collar may be affixed around the tube at each check valve location to hold the check valve in place. The check valve may further be oversized with respect to the tube passageway and include one or more retention flanges which engage sidewalls defining the tube passageway. 
     The above method may further be modified to include radial expansion of the air passageway by forced air injection so as to enlarge the passageway for receipt of the check valves therein. 
     The subject vein system may utilize a single, unitary tube length separated into segments by the inserted check valves, or multiple discrete tube segments joined together by the check valve bodies. As a result, the subject system controls the direction of air flow and eliminates loss of air from back flow. The vein pump requires a relatively low tire sidewall deformation to achieve a requisite pressure build. Consequently, the vein system is relatively forgiving and can accept tire or vein tube groove variation or non-uniformity. The vein system further is tolerant of rim variation. A higher efficiency is thus achieved by using a multi-segmented tube system resulting in a higher compression ratio at the final segment due to the amplification effect. Any issue with dead-end volume is also eliminated. 
     Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.