Abstract:
A self-inflating tire assembly includes an air tube mounted within a tire sidewall groove. The air tube is in contacting engagement with opposite angled groove surfaces surrounding the air tube. A segment of the air tube is flattened from an expanded diameter to a flat diameter by bending and compression of the groove in a rolling tire footprint to force air evacuated from the flattened segment along a tube air passageway. A tube is positioned within the groove, wherein the tube has a circular cross-sectional shape and an outside diameter D, and the groove does not have a circular cross-sectional shape, wherein said groove has a width W and a length L, wherein D is greater than W.

Description:
STATEMENT OF FEDERAL FUNDING 
       [0001]    The invention was made with government support under DE-EE0005447 awarded by the Department of Energy. The government has certain rights in the invention. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to air maintenance tires and, more specifically, to a tire assembly incorporating an air pumping mechanism into a tire for maintaining tire air pressure. 
       BACKGROUND OF THE INVENTION 
       [0003]    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 self-maintain the tire air pressure in order to compensate for any reduction in tire pressure over time without a need for driver intervention. 
       SUMMARY OF THE INVENTION 
       [0004]    According to an aspect of the invention, a self-inflating tire assembly includes a rim having a tire mounting surface extending between first and second rim flanges; a tire mounted to the rim tire mounting surface, the tire having a tire cavity, and first and second sidewalls extending respectively from first and second tire bead regions to a tire tread region. A sidewall groove is positioned within a compression zone of the tire, and an air tube is positioned within the sidewall groove in contacting engagement with opposite groove surfaces at least partially surrounding the air tube. The sidewall groove operatively bends within the compression side of the bending region responsive to a bending strain within the rolling tire footprint to compress the air tube from an expanded diameter to a flat diameter adjacent the rolling tire footprint, whereby forcing evacuated air from a flattened air tube segment along the air passageway. 
       DEFINITIONS 
       [0005]    “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. 
         [0006]    “Asymmetric tread” means a tread that has a tread pattern not symmetrical about the center plane or equatorial plane EP of the tire. 
         [0007]    “Axial” and “axially” means lines or directions that are parallel to the axis of rotation of the tire. 
         [0008]    “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. 
         [0009]    “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction. 
         [0010]    “Equatorial Centerplane (CP)” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of the tread. 
         [0011]    “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. 
         [0012]    “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. 
         [0013]    “Lateral” means an axial direction. 
         [0014]    “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. 
         [0015]    “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. 
         [0016]    “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. 
         [0017]    “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. 
         [0018]    “Peristaltic” means operating by means of wave-like contractions that propel contained matter, such as air, along tubular pathways. 
         [0019]    “Radial” and “radially” means directions radially toward or away from the axis of rotation of the tire. 
         [0020]    “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. 
         [0021]    “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. 
         [0022]    “Tread element” or “traction element” means a rib or a block element defined by having a shape adjacent grooves. 
         [0023]    “Tread Arc Width” means the arc length of the tread as measured between the lateral edges of the tread. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0025]      FIG. 1  is a front view of tire, rim and pump assembly. 
           [0026]      FIG. 2  is a cross-sectional view of the tire of  FIG. 1 ; 
           [0027]      FIG. 3A  is an enlarged fragmentary view of the sidewall passageway shown in  FIG. 2 ; 
           [0028]      FIG. 3B  illustrates a round pump tube that has been inserted in the tire of  FIG. 2 . 
           [0029]      FIG. 3C  illustrates a close up cross-sectional view of the end cap inserted over the opening of the round pump tube. 
           [0030]      FIG. 3D  illustrates a close up cross-sectional view of the pump tube after assembly into the pump sidewall passageway. 
           [0031]      FIG. 4A  illustrates a close up cross-sectional view of the pump tube in the pump sidewall passageway under load and in the open position. 
           [0032]      FIG. 4B  illustrates a close up cross-sectional view of the pump tube in the pump sidewall passageway under load and in the closed position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Referring to  FIGS. 1 and 2 , a tire assembly  10  includes a tire  12 , a peristaltic pump assembly  14 , and a tire wheel  16 . The tire mounts in conventional fashion to the wheel  16 . The wheel  16  has a rim  28  with rim mounting flanges  26 . The tire is of conventional construction, having a pair of sidewalls  32  extending from opposite bead areas  34  to a crown or tire read region  38 . The tire  12  and wheel  16  enclose a tire cavity  40 . 
         [0034]    As shown in  FIGS. 1, 2 and 3 , the pump assembly  14  includes an air tube  50  mounted in a passageway  60 . The tube  50  is formed of a resilient, flexible material such as plastic or rubber compounds that are capable of withstanding repeated deformation cycles. So constructed, the tube may deform within a tire into a flattened condition subject to external force and, upon removal of such force, return to an original sectional configuration. In the embodiment shown, the cross-section of the tube  50  in an unstressed state is generally circular with an inner round hole  52  formed by tube wall  54 . The tube is of a diameter sufficient to operatively pass a requisite volume of air sufficient for the purpose of pumping air into the tire cavity  40  to maintain the tire  12  at a preferred inflation pressure. While the air tube  50  shown in this embodiment is annular for a 360 degree pump, the air tube need not be annular and may have any sufficient length for example, a 180 degree pump. 
         [0035]    As shown in  FIGS. 1 and 2 , the peristaltic pump assembly  14  may further include a regulator device  70  and an air intake and filter assembly  75 . The regulator device  70  functions to prevent air from entering the peristaltic pump through the air intake and filter assembly  75  if the tire air pressure in cavity  40  of the tire is greater than a selectable set point pressure. If the tire cavity pressure is below the set point pressure, the regulator  70  opens an air passage connected to the pump inlet of the peristaltic pump to allow outside air to flow into the peristaltic pump. The regulator may be as described in U.S. patent application No. 61/931,916 filed on Jan. 27, 2014, and which is hereby incorporated by reference. 
         [0036]    As the tire rotates, the sidewall of the tire undergoes compression as it enters the tire footprint. A compressive force  104  is directed into the tire from the footprint  100  and acts to flatten a portion of the air tube passageway as shown in  FIG. 4B . As the tire continues to rotate, the pump tube will be sequentially flattened or squeezed opposite the tire footprint in a segment by segment manner in a direction opposite to the direction of tire rotation. The sequential flattening of the tube passageway  50  segment by segment causes evacuated air from the flattened segments to be pumped to the outlet, into the regulator device and then into the tire cavity  40 . In addition, as the tire rotates, the flattened tube segments are refilled with air from the air intake filter assembly  75  until the regulator shuts off flow to the pump when the set pressure is reached. 
         [0037]    A preferred location for the air tube assembly  14  is as shown in  FIG. 2 . The air tube assembly  14  is preferably mounted in an area of the tire that undergoes bending strain. Utilizing the bending strain within a bending region of a sidewall avoids the need to compress the air tube by pinching the air tube against a relatively hard barrier such as the tire assembly rim. Potential damage to the air tube from contact with the rim is thus avoided and the structural integrity of the air tube is preserved throughout the life cycle of the tire. The tube  50  is located within a groove  60 . The groove  60  is preferably located in the lower sidewall  32  of the tire  12 , and more preferably, in the lower sidewall area radially outward of the upper rim flange when mounted on a wheel, as shown in  FIG. 2 , where bending deformation of the tire helps to achieve tube pinching. 
         [0038]    The tube  50  is closed by compression strain bending the groove  60  within a rolling tire footprint. The location of the tube  50  in the sidewall  30  affords the user freedom of placement and avoids contact between the tube  50  and the rim flange  26 . The higher placement of the tube  50  in the groove  60  uses the deformation of the sidewall as it passes through the tire footprint to close the tube. 
         [0039]    The groove  60  is shown in an unloaded state in  FIG. 3A .  FIG. 3A  illustrates the tube in phantom positioned within the groove  60 . The tube  50  has a diameter D greater than the width of the groove  60 , such that there is an interference fit of the tube  50  in the width direction, when the tube  50  is mounted in the groove  60 . The groove  60  has a length L that is in the range of 2 to 4 times the width W, and more preferably in the range of 3-4 times the width W. The outside diameter D of the tube  50  is preferably greater than the width W of the groove, and more preferably in the range of 1.5 to 2 times the width W of the groove. The length of the groove L is greater than the outside diameter D of the tube  50 , so that when the tube is inserted in the groove  60 , the tube  50  does not fill the entire groove  60  leaving a gap  110 . The gap  110  allows room for filing the entire groove  60  with an adhesive to secure the tube within the groove. Thus with respect to the groove length, the tube does not have an interference fit with respect to the groove length. The groove  60  further includes a neck portion  65  with a reduced width N located at the groove inlet. The reduced width N is in the range of 40-60% of the width W. The groove  60  is defined by a first and second sidewalls  62 , 63 , a portion of which are in parallel relation to each other. The first and second sidewalls  62 , 63  join together at the terminal end  64  of the groove  60 . 
         [0040]    After the tube  50  is inserted into the groove  60 , a coverstrip  130  is inserted into the groove inlet to secure the tube inside the tire. The coverstrip  130  has a circular recessed face  132  that is positioned against the curved outer surface  51  of the tube  50 . The coverstrip  130  has two opposed neck portions  134 , 136  that are received against the groove neck  65 . The coverstrip  130  has outer end portions  138 , 140  that are mounted in the beveled portion  69  of the groove  60 .  FIG. 3D  illustrates the tube and groove in the assembled position when the tire is in an unloaded state. When the tube is mounted into the groove, the tube cross-sectional shape is generally elliptical.  FIG. 4A  illustrates the groove and tube assembly when the tire is rotating under load, showing the tube in the open position.  FIG. 4B  illustrates when the groove and tube assembly has rotated into the footprint area, so that the tire sidewall  32  is under compression, and the tube  52  is in the closed position. 
         [0041]    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.