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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0005]      FIG. 1  is a front view of tire and rim assembly showing two peristaltic pump assemblies. 
           [0006]      FIG. 2  is a cross-sectional view of the pump outlet mechanism. 
           [0007]      FIG. 3  illustrates the operation of the pump when the tire rotates. 
           [0008]      FIG. 4  is a partial section view through the tire in the bead area showing the pump tube location next to the rim. 
           [0009]      FIG. 5  is an exploded cross-sectional view of a first embodiment of a pressure regulator; 
           [0010]      FIG. 6  is a cross-sectional view of the pressure regulator of  FIG. 5  showing the adjustability feature; 
           [0011]      FIG. 7  is a cross-sectional view of the pressure regulator of  FIG. 5  shown in operation in the closed position; and 
           [0012]      FIG. 8  is a cross-sectional view of the pressure regulator of  FIG. 5  shown in operation in the open position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    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  extending from opposite bead areas  34  to a crown or tire tread region  38 . The tire and rim enclose a tire cavity  40 . 
         [0014]    As shown in  FIG. 4 , the peristaltic pump assembly  14  includes a pump  41  that is 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. The pump  41  has a first end  41   a  in fluid communication with an outlet passageway of a regulator device  100 . The pump has a second end  42   b  in fluid communication with the tire cavity  30  as shown in  FIG. 2 .  FIG. 2  further illustrates that each outlet end  41   b  may further comprise a check valve  56  to prevent backflow of air into the pump. 
         [0015]    The pump  41  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. The tube may also be integrally formed in the tire sidewall. 
         [0016]    A first embodiment of a valve device  200  is shown in  FIGS. 5-9 . The valve device functions to regulate the flow of air into a pump  41 . The valve device has a housing  202  having a first end  204  and a second end  206 . The housing has an inlet passageway  207  that is in fluid communication with ambient air and a central bore  208 . The central bore  208  extends from the first end  204  of the housing to a valve seat  210  formed in the interior of the housing. The valve seat extends from the sidewall of the central bore  208 , and is located near the second end  206 . The valve seat may be made as a discrete component that is affixed to the sidewall of the central bore  208 . A flexible annular diaphragm  220  having a central hole  222  is located in the second end  206  and positioned on the valve seat  210 . A cap  205  is positioned in the second end  206  of the housing  202 . The cap has a hole  207  for communicating fluid from the valve device to the tire cavity. 
         [0017]    A flexible diaphragm  211  has an outer side that is positioned adjacent the cap. The cap is secured to the second end of the housing. The cap  205 , housing  202  and diaphragm  211  cooperate to form a pressure chamber  213  in pressure communication with the tire cavity via the hole in cap. The diaphragm seals the valve seat  210  when the tire cavity pressure is sufficient, preventing flow from entering fluid outlet passageway  230 . 
         [0018]    The diaphragm is biased into an open position by a spring  240 . The spring has a first end  242  mounted in a channel  244  of a spring housing  245 . The spring housing  245  is adjustably mounted within the first end  204  of the housing  202 . The spring has a second end  246  that is wrapped about an actuator  250 . The actuator  250  is a T shaped component mounted in the central bore  208 . The upper portion  252  has a plurality of holes  254  through channel  256 . Channel  256  communicates fluid from central bore  208  to outlet passageway  230  when the diaphragm is in the open position. Spring  240  exerts force on actuator  250 , which biases actuator  250  in a direction away from the spring. The actuator cap  252  engages the legs  262  of diaphragm actuator  260 , biasing the diaphragm into the open position. In operation, when the desired preset pressure is reached, the air pressure (from the tire cavity) acting on the diaphragm overcomes the preload force applied by the spring. The diaphragm closes off flow to outlet passageway  230 , preventing flow into the pump. 
         [0019]    In order to provide temperature compensated pressure regulation, the design of the valve device is as follows. The material of the housing  202  and spring housing  245  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. 
         [0020]    It is additionally preferred that the material of the outer cap  205  and valve seat be made of a low coefficient of thermal expansion in the range of about 75 to 150×10−6 m/m K, more preferably in the range of about 100 to about 125×10−6 m/m K. 
         [0021]    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 valve seat and diaphragm increases due to expansion of the housing. 
         [0022]    In a second 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 30 to 120 degrees F. 
         [0023]    The operation of the system may now be described. The diaphragm  211  is responsive to the pressure in the tire cavity, the pressure in the chamber  213  and the spring  240 . When the tire pressure is sufficiently high, the diaphragm overcomes the spring force and is forced into engagement with the valve seat  210 , thus sealing off flow to the inlet end 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 diaphragm away from the valve seat as shown in  FIG. 8 , allowing outside, filtered air to enter the central bore  208  via inlet passageway  207 , through channel  256 , into outlet passageway  230  and then into the inlet end of pump  41 . The inlet regulator device  200  may be adjusted by screwing (rotating) the adjustable spring housing  245  in either direction in order to increase or decrease the spring pressure, thus altering the pressure at which flow will be shut off to the pump. 
         [0024]    As will be appreciated from  FIG. 3 , the inlet regulator device  200  is in fluid communication with the circular air pump  41  and positioned generally 360 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  41   a  as shown at numeral  106 . Flattening of the segment  110  of the pump  41  forces a portion of air located between the flattened segment  110  and the outlet end  41   b,  in the direction shown by arrow  84  towards the pump outlet  41   b.    
         [0025]    As the tire continues to rotate in direction  88  along the ground surface  98 , the pump tube  41  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 exit into the tire cavity. 
         [0026]    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  200  in direction  90  continues until the outlet device  46 , rotating counterclockwise as shown with the tire rotation  88 , passes the tire footprint  100 . 
         [0027]    As the temperature of the tire rises, the thermal expansion of the housing occurs at a higher rate than the cap, increasing the gap distance d between the valve seat. 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. 
         [0028]    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.