Abstract:
A groove defined by groove sidewalls is positioned within the bending region of a tire sidewall. An elongate air tube positioned within the sidewall groove is in contacting engagement with the groove sidewalls and resiliently squeezes and collapses segment by segment as the groove constricts segment by segment within the rolling tire footprint. A longitudinally oriented projecting locking rib extends from a tube sidewall and registers within a complementary configured and located detent extending adjacent the groove to deter lateral movement of the tube within the groove after insertion. An annular projecting ridge extends from the groove for engaging the sidewalls of the air tube to deter an axial movement of the tube within the groove after insertion.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to air maintenance tires and, more specifically, to an air maintenance and tire pumping assembly. 
       BACKGROUND OF THE INVENTION 
       [0002]    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 dependant upon the driver taking remedial action when warned to re-inflate a tire to recommended pressure. It is a desirable, therefore, to incorporate an air maintenance feature within a tire that will maintain air pressure within the tire in order to compensate for any reduction in tire pressure over time without the need for driver intervention. 
       SUMMARY OF THE INVENTION 
       [0003]    In one aspect of the invention, a groove defined by groove sidewalls is positioned within the bending region of the first tire sidewall. An elongate air tube positioned within the sidewall groove is in contacting engagement with the groove sidewalls and resiliently squeezes and collapses segment by segment as the groove constricts segment by segment within the rolling tire footprint. One or more longitudinally oriented projecting locking ribs extend from a tube sidewall and registers within a complementary configured and located detent extending adjacent the groove to deter lateral movement of the tube within the groove after insertion. 
         [0004]    In another aspect, a pair of longitudinal ribs are directed in opposite directions from tube sides and into respective complementary detents adjacent the groove to deter lateral movement of the tube within the groove. 
         [0005]    According to another aspect, the tube further includes one or more annular projecting ridges along the air tube for engaging the sidewalls of the groove to deter an axial movement of the tube within the groove after insertion. 
       DEFINITIONS 
       [0006]    “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. 
         [0007]    “Asymmetric tread” means a tread that has a tread pattern not symmetrical about the center plane or equatorial plane EP of the tire. 
         [0008]    “Axial” and “axially” means lines or directions that are parallel to the axis of rotation of the tire. 
         [0009]    “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. 
         [0010]    “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction. 
         [0011]    “Equatorial Centerplane (CP)” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of the tread. 
         [0012]    “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. 
         [0013]    “Groove” means an elongated void area in a tire dimensioned and configured in section for receipt of an elongate air tube therein. 
         [0014]    “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. 
         [0015]    “Lateral” means an axial direction. 
         [0016]    “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. 
         [0017]    “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. 
         [0018]    “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. 
         [0019]    “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. 
         [0020]    “Peristaltic” means operating by means of wave-like contractions that propel contained matter, such as air, along tubular pathways. 
         [0021]    “Radial” and “radially” means directions radially toward or away from the axis of rotation of the tire. 
         [0022]    “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. 
         [0023]    “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. 
         [0024]    “Tread element” or “traction element” means a rib or a block element defined by having a shape adjacent grooves. 
         [0025]    “Tread Arc Width” means the arc length of the tread as measured between the lateral edges of the tread. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0027]      FIG. 1 ; Isometric exploded view of tire and tube assembly. 
           [0028]      FIG. 2 ; Side view of tire/tube assembly. 
           [0029]      FIG. 3A through 3C ; Details of outlet connector. 
           [0030]      FIG. 4A through 4E ; Details of inlet (filter) connector. 
           [0031]      FIG. 5A ; Side view of tire rotating with air movement ( 84 ) to cavity. 
           [0032]      FIG. 5B ; Side view of tire rotating with air flushing out filter. 
           [0033]      FIG. 6A ; Section view taken from  FIG. 5A . 
           [0034]      FIG. 6B ; Enlarged detail of tube area taken from  FIG. 6A , sidewall in non-compressed state. 
           [0035]      FIG. 7A ; Section view taken from  FIG. 5A . 
           [0036]      FIG. 7B ; Enlarged detail of tube area taken from  FIG. 7A , sidewall in compressed state. 
           [0037]      FIG. 8A ; Enlarged detail of the preferred tube &amp; groove detail taken from  FIG. 2 . 
           [0038]      FIG. 8B ; Detail showing the preferred tube compressed and being inserted into groove. 
           [0039]      FIG. 8C ; Detail showing the preferred tube fully inserted groove at ribbed area of groove. 
           [0040]      FIG. 8D ; Exploded fragmented view of tube being inserted into ribbed groove. 
           [0041]      FIG. 9 ; Enlarged detail taken from  FIG. 2  showing the “first” rib profile area located on both side of the outlet to cavity connector. 
           [0042]      FIG. 10A ; Enlarged detail of groove with “first” rib profile. 
           [0043]      FIG. 10B ; Enlarged detail of tube pressed into “first” rib profile. 
           [0044]      FIG. 11 ; Enlarged detail taken from  FIG. 2  showing the “second” rib profile area located on both side of the outlet to cavity connector. 
           [0045]      FIG. 12A ; Enlarged detail of groove with “second” rib profile. 
           [0046]      FIG. 12B ; Enlarged detail of tube pressed into “second” rib profile. 
           [0047]      FIG. 13A ; Enlarged view of a “second” embodiment of a tube &amp; groove detail. 
           [0048]      FIG. 13B ; Detail showing tube from  FIG. 13A  being compressed and inserted into groove. 
           [0049]      FIG. 13C ; Detail showing tube from  FIG. 13A  fully inserted into groove. 
           [0050]      FIG. 14A ; Enlarged view of a “third” embodiment of a tube &amp; groove detail. 
           [0051]      FIG. 14B ; Detail showing tube from  FIG. 14A  being compressed and inserted into groove. 
           [0052]      FIG. 14C ; Detail showing tube from  FIG. 14A  fully inserted into groove. 
           [0053]      FIG. 15A ; Enlarged view of a “forth” embodiment of a tube &amp; groove detail. 
           [0054]      FIG. 15B ; Detail showing tube from  FIG. 15A  being compressed and inserted into groove. 
           [0055]      FIG. 15C ; Detail showing tube from  FIG. 15A  fully inserted into groove. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0056]    Referring to  FIGS. 1 ,  2 , and  6 A, a tire assembly  10  includes a tire  12 , a peristaltic pump assembly  14 , and a tire rim  16 . The tire mounts in conventional fashion to a pair of rim mounting surfaces  18 ,  20  adjacent outer rim flanges  22 ,  24 . The rim flanges  22 ,  24 , each have a radially outward facing flange end  26 . A rim body  28  supports the tire assembly as shown. The tire is of conventional construction, having a pair of sidewalls  30 ,  32  extending from opposite bead areas  34 ,  36  to a crown or tire tread region  38 . The tire and rim enclose a tire cavity  40 . 
         [0057]    As seen from  FIGS. 2 and 3A ,  3 B,  3 C,  6 B and  8 A, the peristaltic pump assembly  14  includes an annular air tube  42  that encloses an annular passageway  43 . The tube  42  is formed of a resilient, flexible material such as plastic or rubber compounds 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 purposes described herein and allowing a positioning of the tube in an operable location within the tire assembly as will be described. In the configuration shown, the tube  42  is of elongate, generally elliptical shape in section, having opposite tube sidewalls  44 ,  46  extending from a flat trailing tube end  48  to a radiussed leading tube end  50 . The tube  42  is configured having a longitudinal outwardly projecting pair of locking detent ribs  52  of generally semi-circular cross-section and each rib extending along outward surfaces of the sidewalls  44 ,  46 , respectively. As referenced in  FIG. 8A , the tube  42  has a length L 1  within a preferred range of 3.65 to 3.8 mm; a preferred width of D 1  within a range of 2.2 to 3.8 mm; a trailing end preferred width of D 3  within a range of 0.8 to 1.0 mm. The protruding detent ribs  52 ,  54  each have a radius of curvature R 2  within a preferred range of 0.2 to 0.5 and each rib is located at a position distance L 3  within a preferred range of 1.8 to 2.0 mm of the trailing tube end  48 . The leading end  50  of the tube  42  has a radius R 1  within a range of 1.1 to 1.9 mm. The air passageway  43  within the tube  42  is likewise of generally elliptical cross-section having a length L 2  within a preferred range of 2.2 to 2.3 mm; and a preferred width D 2  within a range of 0.5 to 0.9 mm. 
         [0058]    The tube  42  is profiled and geometrically configured for insertion into a groove  56 . The groove  56  is of elongate, generally elliptical configuration having a length L 1  within a preferred range of 3.65 to 3.8 mm in complement to the elliptical shape of the tube  42 . The groove  56  includes a restricted narrower entryway  58  having a nominal cross-sectional width D 3  within a preferred range of 0.8 to 1.0 mm. A pair of groove rib-receiving axial detent channels  60 ,  62  of semi-circular configuration are formed within opposite sides of the groove  56  for complementary respective receipt of the tube locking ribs  52 ,  54 . The channels  60 ,  62  are spaced approximately a distance L 3  within a range of 1.8 to 2.0 mm of the groove entryway  58 . Detent channels  60 ,  62  each have a radius of curvature R 2  within a preferred range of 0.2 to 0.5 mm. An inward detent groove portion  64  is formed having a radius of curvature R 1  within a preferred range of 1.1 to 1.9 mm and a cross-sectional nominal width D 1  within a preferred range of 2.2 to 3.8 mm. 
         [0059]    As best seen from  FIGS. 8D ,  9 ,  10 A and  10 B, the tire further formed to provide one or more compression ribs  66  extending the circumference of and projecting into the groove  56 . The ribs  66  form a pattern of ribs of prescribed pitch, frequency, and location as will be explained. For the purpose of explanation, the seven compression ribs are referred to generally by numeral  66  in the first rib profile pattern shown, and specifically by the rib designations D 0  through D 6 . The ribs D 0  through D 6 , as will be explained, are formed in a preferred sequence and pitch pattern in order to render the pumping of air through the tube passageway  43  more efficient. The ribs  66  each have a unique and predetermined height and placement within the pattern and, as shown in  FIG. 8D , project outward into the groove  56  at a radius R 3  ( FIG. 8A ) within a preferred range of 0.95 to 1.6 mm. 
         [0060]    With reference to  FIGS. 1 ,  2 ,  3 A through  3 C, and  4 A through E, the peristaltic pump assembly  14  further includes an inlet device  68  and an outlet device  70  spaced apart approximately 180 degrees at respective locations along the circumferential air tube  42 . The outlet device  70  has a T-shaped configuration in which conduits  72 ,  74  direct air to and from the tire cavity  40 . An outlet device housing  76  contains conduit arms  78 ,  80  that integrally extend from respective conduits  72 ,  74 . Each of the conduit arms  78 ,  80  have external coupling ribs  82 ,  84  for retaining the conduits within disconnected ends of the air tube  42  in the assembled condition. The housing  76  is formed having an external geometry that complements the groove  56  and includes a flat end  86 , a radius generally oblong body  88 , and outwardly projecting longitudinal detent ribs  90 . So configured, the housing  76  is capable of close receipt into the groove  56  at its intended location with the ribs  90  registering within the groove  56  as represented in  FIG. 8A . 
         [0061]    The inlet device  68  as seen in  FIGS. 1 ,  2 ,  4 A through  4 E includes an elongate outward sleeve body  94  joining to an elongate inward sleeve body  96  at a narrow sleeve neck  98 . The outward sleeve body is generally triangular in section. The inward sleeve body  96  has an external geometry of oblong section complementary to the groove  56  and includes a pair of detent ribs  100  extending longitudinally along the body  96 . An elongate air entry tube  101  is positioned within the inward sleeve body  96  and includes opposite tube ends  102  and a pattern of entry apertures  104  extending into a central tube passageway. External ribs  106 ,  108  secure the tube ends  102  into the air tube  42  opposite the outlet device  70 . 
         [0062]    As will be appreciated from  FIGS. 6A ,  6 B,  7 A,  7 B,  8 A through D, the pump assembly  14  comprising the air tube  42  and inlet and outlet devices  68 ,  70  affixed in-line to the air tube  42  at respective locations 180 degrees apart, is inserted into the groove  56 . The groove  56  is located at a lower sidewall region of the tire that, when the tire  12  is mounted to the rim  16 , positions the air tube  42  above the rim flange ends  26 .  FIG. 8B  shows the air tube  42  diametrically squeezed and collapsed to accommodate insertion into the groove  56 . Upon full insertion, as shown in  FIG. 8C , the ribs  52 ,  54  register within the groove channels  60 ,  62  and the flat outer end  48  of the tube  42  is generally coplanar with the outer surface of the sidewall of the tire  12 . Once fully inserted, the air passageway  43  of the tube  42  elastically restores into an open condition to allow the flow of air along the tube during operation of the pump. 
         [0063]    Referring to  FIGS. 1 ,  2 ,  5 A,  5 B,  6 A,  6 B,  7 A,  7 B,  8 A through  8 D, the inlet device  68  and the outlet device  70  are positioned within the circumference of the circular air tube  42  generally 180 degrees apart. The tire  12  with the tube  42  positioned within groove  56  rotates in a direction of rotation  110 , causing a footprint  120  to be formed against the ground surface  118 . A compressive force  124  is directed into the tire from the footprint  120  and acts to flatten a segment of the air tube passageway  43  opposite the footprint  120  as shown at numeral  122 . Flattening of the segment of the passageway  43  forces air from the segment along tube passageway  43  in the direction shown by arrow  116 , toward the outlet device  70 . 
         [0064]    As the tire continues to rotate in direction  110  along the ground surface  118 , the tube  42  will be sequentially flattened or squeezed opposite the tire footprint segment by segment in a direction opposite to the direction of tire rotation  110 . A sequential flattening of the tube passageway  43  segment by segment will result and cause evacuated air from the flattened segments to be pumped in the direction  116  within tube passageway  43  to the outlet device  70 . Air will flow through the outlet device  70  and to the tire cavity as shown at  130 . As referenced by arrow  130 , air exiting the outlet device is routed to the tire cavity  40  and serves to re-inflate the tire to a desired pressure level. A valve system to regulate the flow of air to the cavity when the air pressure within the cavity falls to a prescribed level is shown and described in pending U.S. patent applicant Ser. No. 12/775,552, filed May 7, 2010, and incorporated herein by reference. 
         [0065]    With the tire rotating in direction  110 , flattened tube segments are sequentially refilled by air flowing into the inlet device  68  in the direction  114  as shown by  FIG. 5A . The inflow of air into the inlet device  68  and then into the tube passageway  43  continues until the outlet device  70 , rotating counterclockwise as shown with the tire rotation  110 , passes the tire footprint.  120 .  FIG. 5B  shows the orientation of the peristaltic pump assembly  14  in such a position. In the position shown, the tube  42  continues to be sequentially flattened segment by segment opposite the tire footprint by compressive force  124 . Air is pumped in the clockwise direction  116  to the inlet device  68  where it is evacuated or exhausted outside of the tire. Passage of exhaust air as shown at  128  from the inlet device  68  is through the filter sleeve  92  which is formed of a cellular or porous material or composite. Flow of air through the sleeve  92  and into the tube  101  is thus cleansed of debris or particulates. In the exhaust or reverse flow of air direction  128 , the sleeve  92  is cleansed of trapped accumulated debris or particles within the porous medium. With the evacuation of pumped air out of the inlet device  68 , the outlet device is in the closed position and air does not flow to the tire cavity. When the tire rotates further in counterclockwise direction  110  until the inlet device  44  passes the tire footprint  120  (as shown in  FIG. 5A ), the airflow resumes to the outlet device  70  and causes the pumped air to flow out and into the tire cavity  40 . Air pressure within the tire cavity is thus maintained at a desired level. 
         [0066]      FIG. 5B  illustrates that the tube  42  is flattened segment by segment as the tire rotates in direction  110 . A flattened segment  134  moves counterclockwise as it is rotated from the footprint while an adjacent segment  132  moves opposite the tire footprint and is flattened. Accordingly, the progression of squeezed or flattened tube segments can be seen to move air toward the outlet device  70  ( FIG. 5A ) or the inlet device  68  ( FIG. 5B ) depending on the rotational position of the tire relative to such devices. As each segment is moved by tire rotation away from the footprint  120 , the compression forces within the tire from the footprint region are eliminated and the segment is free to resiliently reconfigure into an unflattened state as it refills with air from passageway  43 .  FIGS. 7A and 7B  show a segment of the tube  42  in the flattened condition while  FIGS. 6A and 6B  show the tube segment in an expanded, unflat configuration prior and after leaving a location opposite the tire footprint. In the original non-flattened configuration, segments of the tube  42  resume an oblong generally elliptical shape in section. 
         [0067]    The above-described cycle is then repeated for each tire revolution, half of each rotation resulting in pumped air going to the tire cavity and half of the rotation the pumped air is directed back out the inlet device filter sleeve  92  to self-clean the filter. It will be appreciated that while the direction of rotation  110  of the tire  12  is as shown in  FIGS. 5A and 5B  to be counterclockwise, the subject tire assembly and its peristaltic pump assembly  14  will function in like manner in a (clockwise) reverse direction of rotation as well. The peristaltic pump is accordingly bi-directional and equally functional with the tire assembly moving in a forward or a reverse direction of rotation. 
         [0068]    A preferred location for the air tube assembly  14  is as shown in  FIGS. 5A ,  5 B,  6 A,  6 B,  7 A and  7 B. The tube  42  is located within the groove  56  in a lower region of the sidewall  30  of the tire  12 . So located, the passageway  43  of the tube  42  is closed by compression strain bending the sidewall groove  56  within a rolling tire footprint as explained above. The location of the tube  42  in the sidewall  30  affords the user freedom of placement and avoids contact between the tube  42  and the rim  16 . The higher placement of the tube  42  in the sidewall groove  56  uses the high deformation characteristics of this region of the sidewall as it passes through the tire footprint to close the tube. 
         [0069]    The configuration and operation of the groove sidewalls, and in particular the variable pressure pump compression of the tube  42  by operation of ridges or compression ribs  66  within the groove  56  will be explained with reference to  FIGS. 8A through 8D ,  9 ,  10 A and  10 B. In the shown embodiment, the ridges or ribs are referred to generally by numeral  66  and individually as D 0  through D 6 . The groove  56  is preferably of uniform width circumferentially along the side of the tire with the molded in ridges D 0  through D 6  formed to project into the groove  56  in a preselect sequence, pattern or array. The ridges D 0  through D 6  act to retain the tube  42  in its preferred orientation within the groove  56  and also apply a variable sequential constriction force to the tube  42 . 
         [0070]    The uniformly dimensioned pump tube  42  is positioned within the groove  56  as explained previously, preferably by a procedure initiated by mechanically spreading the entryway D 3  of the groove  56  apart. The tube  42  is then inserted into groove enlarged opening. The opening to the groove  56  is thereafter released to return to close into the original spacing D 3  and thereby capture the tube  42  inside the groove. The longitudinal locking ribs  52 ,  54  are thus captured into longitudinal grooves  60 ,  62 . The locking ribs  52 ,  54  resultingly operate to lock the tube  42  inside the groove  56  and prevent unwanted ejection of the tube from the groove during tire operation. Alternatively, if so desired, the tube  42  may be press inserted into the groove  56 . The pump tube  42 , being of uniform width dimensions and geometry, is capable of being manufactured in large quantities. Moreover, a uniform dimensioned pump tube  42  reduces the overall assembly time and material cost and the complexity of tube inventory. From a reliability perspective, this results in less chance for error. 
         [0071]    The circumferential ridges D 0  through D 6  projecting into the groove  56  increase in frequency (number of ridges per axial groove unit of length) toward the inlet passage end of the tube  42  represented by the outlet device  70 . Each of the ridges D 0  through D 6  has a common radius dimension R 4  within a preferred range of 0.15 to 0.30 mm. The spacing between ridge D 0  and D 1  is the greatest, the spacing between D 1  and D 2  the next greatest, and so on until the spacing between ridges D 5  and D 6  is nominally eliminated altogether. While seven ridges are shown, more or fewer ridges may be deployed at various frequency along the groove if desired. The projection of the ridges into the groove  56  by radius R 4  serve a twofold purpose. First, the ridges D 0  through D 6  engage the tube  42  and prevent the tube  42  from migrating or “walking” along the groove  56  during tire operation from the intended location of the tube. Secondly, the ridges D 0  through D 6  act to compress the segment of the tube  42  opposite each ridge to a greater extent as the tire rotates through its rotary pumping cycle as explained above. The flexing of the sidewall manifests a compression force through each ridge D 0  through D 6  and constricts the tube segment opposite such ridge to a greater extent than otherwise would occur in tube segments opposite non-ridged portions of the groove  56 . As seen in  FIGS. 10A and 10B , as the frequency of the ridges increases in the direction of air flow, a pinching of the tube passageway  43  progressively occurs until the passageway constricts to the size shown at numeral  136 , gradually reducing the air volume and increasing the pressure. As a result, with the presence of the ridges, the tube groove  56  provides variable pumping pressure within the pump tube  42  configured to have uniform dimension therealong. As such, the sidewall groove  56  may be said to constitute a variable pressure pump groove that functions to apply a variable pressure to a tube situated within the groove. It will be appreciated that the degree of pumping pressure variation will be determined by the pitch or ridge frequency within the groove  56  and the amplitude of the ridges deployed relative to the diametric dimensions of the tube passageway  43 . The greater the ridge amplitude relative to tube passageway diameter, the more air volume will be reduced in the tube segment opposite the ridge and pressure increased, and vice versa.  FIG. 9  depicts the attachment of the tube  42  to the outlet device  70  and the direction of air flow on both sides into device  70 . 
         [0072]      FIG. 11  shows a second alternative rib profile area located on both sides of the outlet to cavity connector device  70 .  FIG. 12A  shows an enlarged detail of the groove  56  with the alternative second rib profile and  FIG. 12B  shows an enlarged detail of the tube  42  pressed into the second rib profile. With reference to  FIGS. 11 ,  12 A,  12 B, the ridges or ribs D 0  through D 6  in the alternative embodiment have a frequency pattern similar to that described above in reference to  FIGS. 10A ,  10 B but each rib is also formed having a unique respective amplitude as well. Each of the ribs D 0  through D 6  is generally of semi-circular cross-section having a respective radius of curvature R 1  through R 7  respectively. The change radii of curvatures of ridges or ribs D 0  through D 6  are within preferred exemplary ranges: Δ=0.02 to 0.036 mm. 
         [0073]    The number of ridges and respective radii of each may be constructed outside the preferred ranges above to suit a particular dimension preference or application if desired. The increasing radius of curvature in the direction of air flow results in the ribs D 0  through D 6  projecting at an increasing amplitude and to an increasing extent into the tube channel  43  toward the outlet device  70 . As such, the passageway  43  will constrict to a narrower region  138  toward the outlet device and cause a commensurately greater increase in air pressure from a reduction in air volume. The benefit of such a configuration is that the tube  42  may be constructed smaller than otherwise necessary in order to achieve a preferred desired air flow pressure along the passageway and into the tire cavity from the outlet device  70 . A smaller sized tube  42  is economically and functionally desirable in allowing a smaller groove  56  within the tire to be used, whereby resulting a minimal structural discontinuity in the tire sidewall. 
         [0074]      FIGS. 13A  through C show a second embodiment of a tube  42  and groove  56  detail in which the detent ribs  90  in the  FIGS. 8A through 8C  embodiment are eliminated as a result of rib and groove modification. In the second embodiment of  FIGS. 13A through 13C , the tube  42  is configured having an external geometry and passageway configuration having indicated dimensions within preferred ranges specified as follows: 
         [0075]    D 1 =2.2 to 3.8 mm; 
         [0076]    D 2 =0.5 to 0.9 mm; 
         [0077]    D 3 =0.8 to 1.0 mm; 
         [0078]    R 4 =0.15 to 0.30 mm; 
         [0079]    L 1 =3.65 to 3.8 mm; 
         [0080]    L 2 =2.2 to 2.3 mm; 
         [0081]    L 3 =1.8 to 2.0 mm. 
         [0082]    The above ranges are preferred exemplary values that may be modified to suit a particular dimensional preference, tire geometry, or tire application if desired. As shown, the external configuration of the tube  42  includes beveled surfaces  138 ,  140  adjoining the end surface  48 ; parallel and opposite straight intermediate surfaces  142 ,  144  adjoining the beveled surfaces  138 ,  140 , respectively; and a radius nose or forward surface  146  adjoining the intermediate surfaces. As seen from  FIGS. 13B and 13C , the tube  42  is compressed for press insertion into the groove  56  and, upon full insertion, expands. The constricted opening of the groove  56  at the sidewall surface functions to retain the tube  42  securely within the groove  56 . 
         [0083]      FIGS. 14A through 14C  show a third alternative embodiment of a tube  42  and groove  56  configuration.  FIG. 14A  is an enlarged view of the third embodiment detail;  FIG. 14B  a detail view showing the third embodiment tube  42  being compressed and inserted into the groove  56 ; and  FIG. 14C  a detail view showing the tube  42  fully inserted into the groove  56 . The tube  42  is generally of elliptical cross-section inserting into a like-configured groove  56 . The groove  56  is formed having a narrow entryway formed between opposite parallel surfaces  148 ,  150 . In the third embodiment of  FIGS. 14A through 14C , the tube  42  is configured having an external geometry and passageway configuration having noted dimensions within preferred ranges specified as follows: 
         [0084]    D 1 =2.2 to 3.8 mm; 
         [0085]    D 2 =0.5 to 0.9 mm; 
         [0086]    D 3 =0.8 to 1.0 mm; 
         [0087]    R 4 =0.15 to 0.30 mm; 
         [0088]    L 1 =3.65 to 3.8 mm; 
         [0089]    L 2 =2.2 to 2.3 mm; 
         [0090]    L 3 =1.8 to 2.0 mm. 
         [0091]    The above ranges are preferred exemplary values that may be modified to suit a particular dimensional preference, tire geometry, or tire application if desired. 
         [0092]      FIGS. 15A through 15C  show a fourth alternative embodiment of a tube  42  and groove  56  configuration.  FIG. 15A  is an enlarged view of the fourth embodiment detail;  FIG. 15B  a detail view showing the fourth embodiment tube  42  being compressed and inserted into the groove  56 ; and  FIG. 15C  a detail view showing the tube  42  fully inserted into the groove  56 . The tube  42  is generally of parabolic cross-section inserting into a like-configured groove  56 . The groove  56  is formed having an entryway sized to closely accept the tube  42  therein. The ridges  66  engage the tube  42  once it is inserted into the groove  56 . In the fourth embodiment of  FIGS. 15A through 15C , the tube  42  is configured having an external geometry and passageway configuration having noted dimensions within preferred ranges specified as follows: 
         [0093]    D 1 =2.2 to 3.8 mm; 
         [0094]    D 2 =0.5 to 0.9 mm; 
         [0095]    D 3 =2.5 to 4.1 mm; 
         [0096]    L 1 =3.65 to 3.8 mm; 
         [0097]    L 2 =2.2 to 2.3 mm; 
         [0098]    L 3 =1.8 to 2.0 mm. 
         [0099]    The above ranges are preferred exemplary values that may be modified to suit a particular dimensional preference, tire geometry, or tire application if desired. 
         [0100]    From the forgoing, it will be appreciated that the subject invention provides a bi-directionally peristaltic pump for air maintenance of a tire. The circular air tube  42  flattens segment by segment and closes in the tire footprint  100 . The air inlet device  68  may include an outer filter sleeve  92  formed of porous cellular material and thereby render device  68  as self-cleaning. The outlet device  70  employs a valve unit (see co-pending U.S. patent application Ser. No. 12/775,552, filed May 7, 2010, incorporated herein by reference). The peristaltic pump assembly  14  pumps air under rotation of the tire in either direction, one half of a revolution pumping air to the tire cavity  40  and the other half of a revolution pumping air back out of the inlet device  68 . The peristaltic pump assembly  14  may be used with a secondary tire pressure monitoring system (TPMS) (not shown) of conventional configuration that serves as a system fault detector. The TPMS may be used to detect any fault in the self-inflation system of the tire assembly and alert the user of such a condition. 
         [0101]    The tire air maintenance system further incorporates a variable pressure pump groove  56  configured having one or more inwardly directed ridges or ribs that engage and compress a segment of the air tube  42  opposite to such rib(s). The pitch or frequency of the rib series is preferred to increase toward the outlet device  70  to gradually reduce the air volume within the passageway  43  by compressing the tube  42 . The reduction in air volume increases the air pressure within the tube passageway  43  and thereby facilitates a more efficient air flow from the tube into the tire cavity. The increase in tube pressure is achieved by engagement by the ribs  66  of the groove  56  and the tube  42  having uniform dimensions along the tube length. The tube  42  may thus be made of uniform dimension and of relatively smaller size without compromising the flow pressure of air to the tire cavity necessary to maintain tire air pressure. The pitch and amplitude of the ridges  66  may both be varied to better achieve the desired pressure increase within the tube passageway. 
         [0102]    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.