Abstract:
A self-inflating tire assembly includes an air tube connected to a tire and defining an air passageway, the air tube being composed of a flexible material operative to allow an air tube segment opposite a tire footprint to flatten, closing the passageway, and resiliently unflatten into an original configuration. The air tube is sequentially flattened by the tire footprint in a direction opposite to a tire direction of rotation to pump air along the passageway to an inlet device for exhaust from the passageway or to an outlet device for direction into the tire cavity. The inlet device is positioned within the annular passageway 180 degrees opposite the outlet device such that sequential flattening of the air tube by the tire footprint effects pumping of air along the air passageway with the tire rotating in either a forward or reverse direction of rotation. The invention further includes an outlet device for regulating the tire cavity pressure and flow into the cavity.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to self-inflating tires and, more specifically, to a pump mechanism for such tires. 
     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 dependant 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. 
     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. 
     “Buffer volume” means the pump minimum volume. 
     “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. 
     “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. 
     “Peristaltic pump tube” means a tube formed or molded in a tire or an embedded tube which may be inserted post cure or pre-cure. 
     “Pump minimum volume” or “buffer volume” means the smallest value of the pump variable volume. 
     “Pump maximum volume” means the volume of fluid located between the peristaltic pump tube inlet and the outlet valve. 
     “Pump variable volume” means the volume of fluid located between the pinched tube path and the entry of the outlet valve. 
     “Radial” and “radially” means directions radially toward or away from the axis of rotation of the tire. 
    
    
     
       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 an isometric view of the valve, tube and filter for a peristaltic pump assembly. 
         FIG. 2  is a side view of the assembly of  FIG. 1  shown mounted in a tire. 
         FIG. 3  is an enlarged partial cross sectional view of the tire and rim assembly with the pump valve mechanism shown mounted in the tire. 
         FIG. 3A  is an enlarged perspective view of the pump valve mechanism of  FIG. 3 . 
         FIG. 4  is a perspective view of a first embodiment of a regulator mechanism of the present invention. 
         FIG. 5  is a partial section view through the regulator mechanism of  FIG. 4  in the direction  5 - 5 . 
         FIGS. 6 and 7  are cross-sectional views of the regulator mechanism in operation, in the closed position and the open position, respectively. 
         FIG. 8  is a perspective view of a second embodiment of a regulator mechanism of the present invention shown in a first position. 
         FIG. 9  is perspective view of the regulator mechanism of  FIG. 8  shown in a second position. 
         FIG. 10  is a perspective view of the adjustable cap of the regulator mechanism of  FIG. 8 . 
         FIG. 11  is a perspective view of a second embodiment of a pump system of the present invention. 
         FIGS. 12A and 12B  illustrate front views of an interchangeable valve body. 
         FIGS. 13A ,  13 B and  13 C represent an illustration of the pump maximum volume, the pump variable volume, and the buffer or pump minimum value. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 through 3 , a tire assembly  10  includes a tire  12 , a peristaltic pump assembly  14 , and a tire rim  16 . The tire mounts in a conventional fashion to a pair of rim mounting surfaces  18  located adjacent outer rim flanges  20 . The outer rim flanges  20  have an outer rim surface  22  that engages the bead area of the tire. The tire is of conventional construction, having a pair of sidewalls  30  extending from opposite bead areas  34  to a crown or tire tread region  38 . The tire and rim enclose a tire cavity  40 . 
     As shown in  FIGS. 1-2 , the peristaltic pump assembly  14  includes a pump tube  42  that is mounted in a tire passageway  44 , which is preferably located in the sidewall area of the tire, preferably near the bead region. The tire passageway is preferably molded into the sidewall of the tire during vulcanization and is preferably annular in shape. The pump tube  42  has a first end  42   a  joined together by an inlet device  46  and a second end  42   b  joined together with an outlet device  50 . The pump tube  42  is comprised of a tube formed of a resilient, flexible material such as plastic, silicone, elastomer or rubber compounds, and is capable of withstanding repeated deformation cycles when 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. Preferably, the tube has a circular cross-sectional shape, although other shapes such as elliptical or lens shape may be utilized. Alternatively, the passageway  44  molded or formed into the tire sidewall may serve as the pump tube  42 . 
     As shown in  FIG. 2 , the inlet device  46  and the outlet device  50  are spaced apart a desired distance typically in the range of approximately 90 degrees or more, typically about 180 degrees to 360 degrees. If 180 degrees is selected, two 180 degree pumps may be used. The inlet and outlet device may be located adjacent each other, thus forming a single 360 degree pump. Other variations may be utilized, such as 270 degrees, etc. 
     The inlet device  46  in its simplest form may be the inlet tube end exposed to the atmosphere. The inlet device may optionally comprise a check valve and/or an optional filter. The outlet device  50  is a pressure and flow regulating device, and regulates the tire cavity maximum pressure. The outlet device  50  also functions to regulate the flow into and out of the tire cavity. The outlet device is described in more detail, below. 
     As will be appreciated from  FIG. 2 , the inlet device  46  and the outlet device  50  are in fluid communication with the circular air tube  42 . As the tire rotates in a direction of rotation  88 , a footprint  100  is formed against the ground surface  98 . A compressive force  104  is directed into the tire from the footprint  100  and acts to flatten a segment  110  of the pump  42 . Flattening of the segment  110  of the pump  42  forces a portion of air located between the flattened segment  110  and the outlet device  50 , in the direction shown by arrow  84  towards the outlet device  50 . The portion of air will then regulated through the outlet device  50 . If the pressure at the inlet of the outlet device is sufficiently high, the internal valve will open and fill the tire cavity, as described in more detail, below. 
     As the tire continues to rotate in direction  88 , the previously flattened tube segments  110 ,  110 ′,  110 ″ will be sequentially refilled by atmospheric air flowing into the inlet device  46  along the pump tube  42 . The inflow of air from the inlet device  46  continues until the outlet device  50  rotating counterclockwise as shown with the tire rotation  88 , passes the tire footprint  100 . 
     The location of the peristaltic pump assembly will be understood from  FIGS. 2-4 . In one embodiment, the peristaltic pump assembly  14  is positioned in the tire sidewall, radially outward of the rim flange surface  26  in the chafer  120 . So positioned, the air tube  42  is radially inward from the tire footprint  100  and is thus positioned to be flattened by forces directed from the tire footprint as described above. The segment  110  that is opposite the footprint  100  will flatten from the compressive force  114  from the footprint  100  pressing the tube segment against the rim flange surface  26 . Although the positioning of the tube  42  is specifically shown as between a chafer  120  of the tire at the bead region  34  and the rim surface  26 , it is not limited to same, and may be located at any region of the tire such as anywhere in the sidewall or tread. The diametric sizing of the peristaltic pump air tube  42  is selected to span the circumference of the rim flange surface  26 . 
     Pressure Regulating Outlet Device 
     The regulator device  50  is a pressure and flow regulating device, and regulates the tire cavity maximum pressure. The regulator device  50  also functions to regulate the flow into and out of the tire cavity. The regulator device has a valve body  52  having a first end  53  that has a valve passageway  54  that extends from the first end to a second end  56 . The first end of the valve body  52  is mounted through the tire sidewall as shown in  FIGS. 3 ,  3 A so that the valve passageway  54  is in fluid communication with the tire cavity  40 . The valve passageway  54  has an expanded portion  58  and a narrow portion  60 . A large ball  62  is received in the expanded portion  58  and positioned for engagement with the narrow portion  60 . A spring  64  is positioned within the valve passageway for engagement with the ball  62 . The spring  64  biases the ball into engagement with the narrow portion  60 , so that flow is blocked in the interior passageway  54 . 
     The second end  56  of the valve body has an outer threaded portion  57  that is received within a first threaded end  70  of an adjustable housing  72 . The adjustable housing has an internal cavity  74  that extends from the first threaded end  70  to the second threaded end  76 . The internal cavity  74  has a fixed buffer volume portion and an adjustable buffer volume portion. The fixed volume portion is defined by the non-threaded inner wall of the internal cavity having a length C. The fixed volume is equal to the cross-sectional area of the internal cavity times the length C. The adjustable volume portion is defined by the amount of the threaded length that is exposed within the internal cavity and is indicated as distance B. The adjustable volume is determined from the distance B times the cavity cross-sectional area. The distance B may be zero if the valve body is fully received within the adjustable housing. The adjustable housing and respective internal buffer volumes may be modified by substituting the adjustable housing as shown in  FIG. 12  A in order to increase the fixed buffer volume or by substituting the adjustable housing as shown in  FIG. 12   b  in order to decrease the fixed buffer volume. 
     The regulator device  50  further comprises an elbow fitting  80  having a first end  82  connected to the adjustable housing inlet end  76  and a second end  84  connected to the pump tube outlet  42   b . The second end of the elbow fitting  80  may comprise a flared fitting  86 . 
     The maximum air pressure delivered by the peristaltic pump can be fixed by setting the volume of the pump tube and the buffer volume located between the end of the tube and the check valve and the adjustable buffer chamber. The pump tube volume is selected by design with the tube dimensions and the tube length. As shown in  FIG. 11 , multiple pump tubes may be used, with the selection of the tube length and inner tube dimensions to tune the system. The buffer or dead volume can also be set by design. The air in the buffer volume chamber is not compressed, but functions to tune or adjust the maximum air pressure of the pump system. The buffer volume acts as a storage chamber for accumulating air mass for transfer to the tire cavity. Increasing the buffer volume will decrease the tire pressure, while decreasing the buffer volume will increase the tire cavity pressure. Thus, by adjusting the buffer volume, one can adjust the desired tire final pressure. 
     The operation of the system and the outlet device  50  can now be described. As shown in  FIG. 2 , the tire rotates in a direction of rotation  88 , and a footprint  100  is formed against the ground surface  98 . A compressive force  104  is directed into the tire from the footprint  100  and acts to flatten a segment  110  of the pump  42 . Flattening of the segment  110  of the pump  42  forces a portion of air located between the flattened segment  110  and the regulator device  50 , in the direction shown by arrow  84  towards the outlet device  50 . The portion of air will then be regulated through the outlet device  50 . If the pressure at the inlet  86  of the regulator device is sufficiently high, the fluid pressure will overcome the spring pressure  54  (cracking pressure), thus opening the internal check valve. Thus fluid from the pump outlet  42   b  will flow into the elbow fitting  80  and into the adjustable housing  72 . 
     If the pressure in the pump tube  42   b  is less than the tire pressure, the ball  62  will engage the narrow portion  60  and block flow from either direction. The check valve  62  when closed, blocks flow from communicating from the pump  42   b  into the tire cavity  40 , and also prevents back flow from the tire cavity into the pump  42 . When the check valve is closed, the pump compresses the air in the pump tube  42 . Air from the pump tube enters the elbow fitting  80  of the regulator device, and then enters the buffer volume chamber  74 . The buffer volume chamber will fill while the check valve remains closed. When the pressure in the inlet  56  of the regulator device exceeds the cracking pressure, the check valve opens and will allow air from the pump to fill the tire cavity. The check valve will close when the inlet pressure P T  falls below the cracking pressure. The cycle of opening and closing the check valve will allow the tire cavity to be filled as the tire rotates a specified distance. A maximum tire cavity will be reached based upon the pump volume and the buffer volume. The buffer volume may be adjusted by turning the valve body  52  relative to the adjustable housing. Increasing the buffer volume results in a decrease of tire final pressure, while decreasing the buffer volume results in an increase of the tire final pressure. The advantage of having an adjustable buffer volume allows the maximum system pressure of the tire cavity to be tuned for a specific tire. 
       FIGS. 8-10  illustrate a second embodiment of a pressure regulator  200 . The pressure regulator  200  comprises a valve body  202  having an internal passageway  204  that extends through the valve body  202 . The internal passageway  204  includes a movable check valve assembly  206 . The movable check valve assembly includes a ball  208 , a spring  210  housed within a receptacle  212 . The receptacle has a retainer  214  which retains the ball  208  within the check valve assembly. The outer edge of the receptacle may have external threads like a screw, so that the receptacle may be screwed into or out of the internal passageway  204 . A variable buffer volume  220  is located adjacent the movable check valve assembly, so that when the movable check valve assembly is rotated clockwise, the variable buffer volume decreases. The outer receptacle of the check valve may have notations on it to indicate to a user to indicate the relationship of the number of turns to the volume adjustment. Alternatively, the movable check valve may slide within the passageway  204 , with retaining means located within the passageway which allow the position of the movable check valve to be repeatedly adjusted and then fixed in position. 
     The valve body  202  of the pressure regulator  200  further comprises a second portion  222  which is at right angles to the first portion  224  of the valve body. The second portion has an interior fixed dead volume  230  which is in fluid communication with the variable volume  220 . Located adjacent the interior fixed dead volume  230  is an outlet  240 . The outlet  240  is connected to the pump tube outlet  42   b . The second portion  222  is mounted in the tire, typically in the sidewall and connected to the pump tube outlet  42   b . The first portion  224  of the valve body is mounted through the sidewall and into the tire cavity  40 . 
     The operation of the system and the outlet device  200  can now be described. As shown in  FIG. 2 , the tire rotates in a direction of rotation  88 , and a footprint  100  is formed against the ground surface  98 . A compressive force  104  is directed into the tire from the footprint  100  and acts to flatten a segment  110  of the pump  42 . Flattening of the segment  110  of the pump  42  forces a portion of air located between the flattened segment  110  and the regulator device  200 , in the direction shown by arrow  84  towards the outlet device  200 . The portion of air will then be regulated through the outlet device  200 . If the pressure at the inlet of the regulator device is sufficiently high, the fluid pressure will overcome the spring pressure (cracking pressure), thus opening the internal check valve. Thus fluid from the pump outlet  42   b  will flow into the regulator and out into the tire cavity through a hole in the adjustable check valve assembly. 
     If the pressure in the pump tube  42   b  is less than the tire pressure, the ball  208  will engage the narrow portion  214  and block flow from either direction. The check valve when closed, blocks flow from communicating from the pump  42   b  into the tire cavity  40 , and also prevents back flow from the tire cavity into the pump  42 . When the check valve is closed, the pump compresses the air in the pump tube  42 . Air from the pump tube enters the regulator device, and fills the buffer volume chambers  220 , 230 . When the pressure to the inlet of the regulator device exceeds the cracking pressure, the check valve opens and will allow air from the pump to fill the tire cavity. The check valve will close when the inlet pressure P T falls  below the cracking pressure. The cycle of opening and closing the check valve will allow the tire cavity to be filled as the tire rotates a specified distance. A maximum tire cavity will be reached based upon the pump volume and the buffer volume. The buffer volume may be adjusted by turning the adjustable check valve relative to the housing. Increasing the buffer volume results in a decrease of tire final pressure, while decreasing the buffer volume results in an increase of the tire final pressure. The advantage of having an adjustable buffer volume allows the maximum system pressure of the tire cavity to be tuned for a specific tire. 
     The table below indicates exemplary tires, all having the same internal tire volume of 38 L and initial tire pressure of 1.8 Bar. All of the exemplary pumps have a circumferential length of 180 degrees. Examples 1 and 2 have a pump size of 2×1 with a pump volume of 1036 mm3. For example 1 the buffer volume is selected to be 459 mm3, resulting in a desired final tire pressure of 2.2 bar. A distance of 241 km is needed to achieve the final tire pressure. If the buffer volume is decreased to 351 mm3, with all other variables being equal, the final tire pressure will be 2.9 bar (Ex. 2) as compared to 2.2 bar for Ex. 1. A longer distance of 490 km will be needed to achieve a higher final tire pressure of 2.9 bar. 
     Examples 3 and 4 illustrate a smaller tube size resulting in a smaller pump volume of 700 mm3. For a buffer volume of 310 mm3 (Ex 3) results in a final tire pressure of 2.2 bar and a needed distance of 355 km to achieve the final tire pressure. Ex 4 illustrates all the properties of Ex. 3, except for a smaller buffer volume of 237 mm3, resulting in a higher final tire pressure of 2.9 bar achieved in 727 km. 
     Examples 5-8 have the same properties as examples 1-4, with example 5 corresponding with example 1, etc. the cracking pressure of the valve is higher for examples 5-8 as compared to 1-4. A slightly lower buffer volume is needed in examples 5-8 to achieve the same final tire pressure as examples 1-4. The higher cracking pressure also results in a significantly shorter distance to be traveled by the pump/tire in order to result in the final tire pressure. The volume ratios of the buffer volume to pump volume may be used to determine a new buffer volume should the pump volume or cavity volume change. The buffer volume may be adjusted by rotating screw  66 . The number of turns of the screw (e.g. 5 turns) would result in a distance of 4 mm with a screw pitch of 75 mm. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Cavity 
                   
                 A 
                 B 
                 C 
                 D 
               
             
          
           
               
                 Cracking 
                   
                   
                 Volume 
                 Tire 
                 Initial Tire 
                 Buffer Volume 
                 Final Tire 
                 Needed 
                 Volumes 
               
               
                 Pressure 
                 Angle 
                 Size 
                 [mm3] 
                 Volume 
                 pressure 
                 [mm3] 
                 pressure 
                 Distance 
                 Ratio 
               
               
                   
               
             
          
           
               
                 0.1 bar 
                 180 
                 2 × 1 
                 1036 
                 38 L 
                 1.8 bar 
                 459 
                 2.2 bar 
                 241 km 
                 0.443 
               
               
                   
                 180 
                 2 × 1 
                 1036 
                 38 L 
                 1.8 bar 
                 351 
                 2.9 bar 
                 490 km 
                 0.339 
               
               
                   
                 180 
                 2.7 × 0.5 
                 699.5 
                 38 L 
                 1.8 bar 
                 310 
                 2.2 bar 
                 355 km 
                 0.443 
               
               
                   
                 180 
                 2.7 × 0.5 
                 699.5 
                 38 L 
                 1.8 bar 
                 237 
                 2.9 bar 
                 727 km 
                 0.339 
               
               
                 0.3 bar 
                 180 
                 2 × 1 
                 1036 
                 38 L 
                 1.8 bar 
                 422 
                 2.2 bar 
                 137 km 
                 0.407 
               
               
                   
                 180 
                 2 × 1 
                 1036 
                 38 L 
                 1.8 bar 
                 329 
                 2.9 bar 
                 324 km 
                 0.318 
               
               
                   
                 180 
                 2.7 × 0.5 
                 699.5 
                 38 L 
                 1.8 bar 
                 285 
                 2.2 bar 
                 203 km 
                 0.407 
               
               
                   
                 180 
                 2.7 × 0.5 
                 699.5 
                 38 L 
                 1.8 bar 
                 222.5 
                 2.9 bar 
                 485 km 
                 0.318 
               
               
                   
               
             
          
         
       
     
     The maximum air pressure delivered by a peristaltic pump embedded in a tire can be fixed by setting the right volume of the pump tube and the buffer volume. The pump tube volume can be set by design with the dimensions of the tube sections and tube length. The buffer volume can also be set by design but can also be easily manually changed by the mean of a dedicated device or by interchanging appropriate parts before the valve. This can be implemented with either a set of tube with different lengths or a set of small tanks to be inserted before the valve. 
     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.