Abstract:
A self-inflating tire assembly includes an adjustable valve having: a housing having first end and a second end, and a central bore which extends from the first end to the second end; a piston slidably mounted within the central bore at the first end of the housing, a cap mounted in the second end of the housing forming a chamber with the housing, wherein a spring is mounted within the chamber and having a first end for engagement with the piston and a second end for engagement with a bottom wall of the chamber, said cap further comprising a fluid chamber projecting from the bottom wall of the chamber, wherein the piston is movable to seal the fluid chamber, wherein the housing is made from a material having a higher coefficient of thermal expansion than the material of the fluid chamber.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to self-inflating tires and, more specifically, to a pump mechanism for such tires. 
       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 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. 
         [0003]    Self-inflating tire systems regulates the tire pressure. One problem is that the pressure of a tire changes with temperature. This may be due to the temperature increase due to the rise in ambient temperature, the operation of the tire, hysteresis losses, and as a result in the increase in vehicle speed. Generally, self-inflating tire systems allow inflation of a tire when the tire cavity pressure falls below a selected value. This selected value may not account for the increase in temperature. If the temperature rise is significant from an increase due to ambient temperature or vehicle speed, the system may not inflate the tire resulting in an underinflated tire. Thus it is desired to provide a temperature compensated pressure regulation system for air maintenance tires. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention provides in a first aspect a self-inflating tire assembly comprising a tire mounted to a rim, 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. The assembly further includes an air tube connected to the tire and defining an air passageway, the air tube being composed of a flexible material operative to allow a portion of the air tube segment near a tire footprint to substantially close the annular passageway. The assembly further includes an inlet regulator device connected to an inlet end of the air tube, the inlet regulator device includes an insert mounted in the tire, wherein the insert has a bore therethrough having a first end located in the tire cavity, and a second end which extends through the tire, wherein a pressure membrane is received within the first end of the insert, and a regulator body is received within the second end of the insert, wherein the regulator body has an interior passageway which extends from a first end to a distal end, wherein the distal end extends into a cavity of the insert, wherein the pressure membrane is responsive to the cavity tire pressure and the outside air pressure, wherein the pressure membrane is positioned for engagement with the distal end of the regulator body when the tire pressure reaches a set value. 
         [0005]    The invention provides in a second aspect a self-inflating tire assembly comprising a tire mounted to a rim, 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. The invention further includes an air tube connected to the tire and defining an air passageway, the air tube being composed of a flexible material operative to allow a portion of the air tube segment near a tire footprint to substantially close the annular passageway. The assembly also has an inlet regulator device connected to an inlet end of the air tube, the inlet regulator device includes an insert mounted in the tire, wherein the insert has a bore therethrough having a first end located in the tire cavity, a middle portion forming a chamber, and a second end which extends through the tire and which is in fluid communication with the outside air and the chamber, wherein a piston is slidably mounted within the first end of the insert, and a regulator body is received within the chamber and positioned to engage a stop, the chamber having a hole for fluid communication with a pump inlet air tube, a spring mounted within the chamber and having a first end for engagement with the piston and a second end for engagement with a bottom wall of the chamber wherein the regulator body has a interior passageway which extends from a first end to a distal end, wherein the distal end extends into a cavity of the insert. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0007]      FIG. 1  is a front view of tire and rim assembly showing two peristaltic pump assemblies. 
           [0008]      FIG. 2  is a cross-sectional view of the pump outlet mechanism. 
           [0009]      FIG. 3  illustrates the operation of the pump when the tire rotates. 
           [0010]      FIG. 4  is a partial section view through the tire in the bead area showing the pump tube location next to the rim. 
           [0011]      FIG. 5  is a cross-sectional view of a first embodiment of a pressure regulator; 
           [0012]      FIG. 6  is a cross-sectional view of the pressure regulator of  FIG. 5  showing the adjustability feature; 
           [0013]      FIG. 7  is a cross-sectional view of the pressure regulator of  FIG. 5  shown in operation in the closed position; 
           [0014]      FIG. 8  is a cross-sectional view of the pressure regulator of  FIG. 5  shown in operation in the open position; and 
           [0015]      FIG. 9  is an enlarged cross sectional view of the tire and rim assembly with the pressure regulator of  FIG. 5  shown mounted in the tire. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring to  FIGS. 1 and 4 , 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  22 . The outer rim flanges  22  have an outer rim surface  26 . 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 . 
         [0017]    As shown in  FIG. 1 , the peristaltic pump assembly  14  includes a first and second pump  41 , 42  that are mounted in a passageway  43  located in the sidewall area of the tire, preferably near the bead region. The air passageway is preferably molded into the sidewall of the tire during vulcanization and is preferably annular in shape. Each pump  41 , 42  has a first end  41   a,   42   a  joined together by an inlet device  44  and a second end  41   b,   42   b  joined together by an outlet device  46 . Each pump  41 , 42  is comprised of a tube formed of a resilient, flexible material such as plastic, 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 may be utilized. 
         [0018]    As shown, the inlet device  44  and the outlet device  46  are spaced apart approximately 180 degrees at respective locations forming two 180 degree pumps  41 , 42 . 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. As shown in  FIGS. 3A and 3B , the outlet device  46  is a connector having a body  47  having a first port  48  that connects to pump  41  outlet end  41   b.  The first port  48  is in fluid communication with outlet port  52 . Outlet port  52  extends into the tire cavity so that the pump end  41   b  is in fluid communication with the tire cavity. The outlet device further includes a second port  50  that connects to pump  42  outlet end  42   b.  The second port  50  is connected to an outlet port  54  that is located in the tire cavity so that the pump end  42  is in fluid communication with the tire cavity.  FIG. 2  further illustrates that each outlet end  52 , 54  may further comprise a check valve  56 , 58  to prevent backflow of air into the pump. The outlet ends  52 , 54  of the outlet device  46  extend into the tire cavity so that the outlet ends are in fluid communication with the internal tire cavity  40 . 
         [0019]    A first embodiment of a valve device  200  is shown in  FIGS. 5-9 . The valve device functions to regulate the inlet flow of both pumps  41 , 42 . The valve device  200  includes an outer T shaped insert  210  that may be molded into a green tire and then cured.  FIG. 9  illustrates the inlet device installed in the sidewall  32  of a tire, wherein the T shaped portion of the insert is located on the interior portion of the tire sidewall, facing the tire cavity  40 . An outer cap  212  is secured to the insert. The outer cap  212  has an outer surface  213  that is preferably flush with the tire sidewall  32 . The sidewalls  222  of the T shaped insert cooperates with the bottom wall  224  of the outer cap  212  to form an inner chamber  220 . Two holes  226 , 228  are located in the inner chamber sidewall  222  for fluid communication with inlet tube ends  41 , 42   a  of the pumps  41 , 42 . 
         [0020]    A regulator piston  230  is slidably received within the inner chamber  220  of the insert. The regulator piston  230  has an outer flanged surface  232  which is slidably received within a slot  234  of the chamber sidewall. An outer stop  236  located on the upper chamber wall of the T shaped insert retains the piston  230  within the chamber. An optional outer membrane  221  is received over the top of the piston  230  to make the system airtight and to prevent leakage of air between the piston and the cylinder  234 . The regulator piston has an interior threaded bore  240  in which an adjustable member  242  is received. The adjustable member  242  is positioned to engage an inner stop  250  located on an inlet port  252 . The inlet port  252  is in fluid communication with outside air via passageway  266  in the cap. A spring  260  is positioned in the insert chamber  220  with a first end  261  engaging the piston end wall  262  and a second end  263  engaging the bottom wall of the chamber  224 . The spring biases the piston and the adjustable member away from the inner stop  250 . 
         [0021]    In order to provide temperature compensated pressure regulation, the design of the valve device is as follows. The material of the T shaped insert is selected from a material to have a high coefficient of expansion, in the range of 150 to 300×10−6 m/m K, more preferably in the range of 175 to 250×10−6 m/m K. One example of a material suitable for use is polyethylene with a coefficient of thermal expansion of 200×10−6 m/m K. 
         [0022]    It is additionally preferred that the material of the outer cap  212 , including the inlet port  252  be made of a material having a low coefficient of thermal expansion. It is additionally more preferred that the material of the regulator piston  230  and the adjustable member  242 , be made of a low coefficient of thermal expansion. The material may have a coefficient of thermal expansion in the range of about 50 to 150×10−6 m/m K, more preferably in the range of about 75 to about 100×10−6 m/m K. 
         [0023]    The idea of the invention is to select two different materials, one with a high coefficient of thermal expansion and one with a low coefficient of thermal expansion in order to increase the gap distance d required for the valve to close. Temperature compensation of the pressure regulator is achieved by increasing the gap between the stop  250  and piston  242 . The housing is selected to have a high coefficient of thermal expansion, while the piston regulator and adjustable member is selected to be made from materials having a low coefficient of thermal expansion. Thus the gap distance d between the stop  250  and piston  242  increases due to expansion of the housing. 
         [0024]    In a third embodiment of the invention, the spring  260  is formed from a shape memory alloy. The spring is made from a shape memory alloy, more preferably a nickel titanium spring selected to have an austenite-martensite transition in the range of temperatures 0 degrees C. to 50 degrees C. 
         [0025]    The operation of the system may now be described. The regulator piston  230  is responsive to the pressure in the tire cavity, the pressure in the insert chamber  220  and the spring  260 . The pressure in the chamber is similar to the pressure in the outside air. When the tire pressure is sufficiently high, the regulator piston overcomes the spring force and is forced into engagement with the stop  250  of the insert, thus sealing off flow to the inlet ends of the pump, as shown in  FIG. 7 . As the tire pressure decreases, the spring force overcomes the force from the tire pressure, pushing the piston  230  away from the stop  250  as shown in  FIG. 8 , allowing outside, filtered air to enter the chamber  220  and into the inlet ends of the pumps  41 , 42  via side holes  226 , 228  in the chamber walls. The inlet regulator device  200  may be adjusted by screwing (rotating) the adjustable member  242  in either direction in order to increase or decrease the gap distance d from the distal end of the adjustable member to the stop  250 , thus altering the pressure at which flow will be shut off to the pumps. 
         [0026]    As will be appreciated from  FIG. 3 , the inlet device  44  and the outlet device  46  are in fluid communication with the circular air tube  42  and positioned generally 180 degrees apart. 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  a as shown at numeral  106 . Flattening of the segment  110  of the pump  42  forces a portion of air located between the flattened segment  110  and the outlet device  46 , in the direction shown by arrow  84  towards the outlet device  46 . 
         [0027]    As the tire continues to rotate in direction  88  along the ground surface  98 , the pump tube  42  will be sequentially flattened or squeezed segment by segment in a direction  90  which is opposite to the direction of tire rotation  88 . The sequential flattening of the pump tube  42  segment by segment causes the column of air located between the flattened segments to and the outlet device  46  be pumped in the direction  84  within pump  42  to the outlet device  46 . 
         [0028]    With the tire rotating in direction  88 , flattened tube segments are sequentially refilled by air  92  flowing into the inlet device  44  along the pump tube  42  in the direction  90  as shown by  FIG. 3 . The inflow of air from the inlet device  44  in direction  90  continues until the outlet device  46 , rotating counterclockwise as shown with the tire rotation  88 , passes the tire footprint  100 . 
         [0029]    As the temperature of the tire rises, the thermal expansion of the T shaped insert occurs at a higher rate than the cap and piston, increasing the gap distance d between inlet port  252  and the lower surface of the piston. The major benefit of the invention is that the valve system is better able to control the set pressure of the tire, and not prematurely close (preventing inflation of the tire) due to the artificial temperature induced temperature increase. 
         [0030]    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  80  to self-clean the filter. It will be appreciated that while the direction of rotation  88  of the tire  12  is shown in  FIG. 3  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 to that shown at numeral  88 . The peristaltic pump is accordingly bi-directional and equally functional with the tire assembly moving in a forward or a reverse direction of rotation. 
         [0031]    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.