Abstract:
A tire pressure indication device is provided that continuously monitors pressure of a tire and instantaneously generates a visual display having an easy to read indication as soon as the tire pressure falls below a safe threshold limit. This device includes a dome shaped upper end. A two color dome shaped indicator element is disposed therein having two colors or other visually distinguishable markings which are visible through viewing areas. The dome element is rotatable in response to sensed tire pressure to provide a visual indication of low pressure and another visually distinct indication of safe pressure. The lower end of the body includes a connector to be fitted or threaded onto the valve stem of a tire. Multiple seals are provided within the device to substantially eliminate air or gas from escaping to the atmosphere. Thereby, the device can remain on the tire valve and monitor pressure for long periods of time.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) to provisional patent application Ser. No. 60/173,837 filed Dec. 30, 1999, the disclosure of which is hereby incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     BACKGROUND OF THE INVENTION 
     This invention is directed to a low tire pressure indicator which is of simple and efficient construction and which can readily be installed on the valve stems of vehicle tires to provide a highly visible indication of tire pressure lower than a predetermined limit. 
     Proper maintenance of tire pressure is essential for optimizing the operation of a vehicle, as underinflation is the leading cause of tire failure. By maintaining the proper tire inflation, the life of the tire will be increased, the gas mileage of the vehicle will be improved, and the safety of the vehicle will be enhanced. 
     Tire failure is generally caused by overheating which typically results from one or a combination of tire defects, underinflation, or overloading. Tire heating is caused by the normal bending motion, or flex, in the sidewalls of a tire that occurs as a vehicle bounces up and down or moves side to side in turns. If the tires are properly inflated, the sidewalls will be stiff and the amount of flex will be minimized. However, if the tires are underinflated, they will become less stiff and the amount of flex will increase. Thereby, the tires will become more susceptible to overheating and failure. 
     The need for proper tire inflation has created a long time demand for various tire pressure devices. For instance, hand-held tire pressure gauges are well known and widely used. The user typically slides such a pressure gauge over the valve stem of the tire until the gauge sufficiently fits over the valve stem to create a seal that minimizes pressure escape between the tire and the gauge. Once the gauge has been appropriately positioned, the user notes the pressure value displayed on the gauge. The user then compares this value to the pressure value recommended by the manufacturer of the tire. The user must either refer to a manual or other source for this information or commit this value to memory. 
     Presently, all of the known tire pressure gauges either require a great deal of user intervention or do not provide a constant and instantaneous indication of whether the tire pressure has a value that is below a safe threshold limit. Most people seldom check tire pressure due to the inconvenience of these known gauges. Therefore, people fail to take an important role in preventing premature tire failure. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed towards providing a tire pressure indication device that continuously monitors the tire pressure and instantaneously generates a visual display having an easy to read indication as soon as the tire pressure falls below a safe threshold limit. The device of the present invention includes a dome shaped upper end. A two color dome shaped indicator element is disposed therein having two colors or other visually distinguishable markings which are visible through viewing areas. The dome element is rotatable in response to sensed tire pressure to provide a visual indication of low pressure and a visually distinct indication of safe pressure. A low pressure indication is provided, for example, by having a visible color distinct from the color of the dome cover present in the viewing area while one continuous color is displayed when a safe pressure is sensed. The lower end of the body includes a fitting to be fitted or threaded onto the valve stem of a tire. 
     The tire pressure causes displacement of a piston within the indicator body, which cooperates with a camming mechanism, to cause rotation of the indicator dome for displaying first and second visual indicator markings. The indicator is calibrated such that the dome element rotates sufficiently to provide the visual indication of low pressure in the viewing areas when the pressure falls below the threshold limit. Pressure which is lower than normal but not as low as the threshold limit provides less rotation of the indicator dome and therefore displays decreased but not completely low pressure. 
     The device includes multiple seals to substantially eliminate air from escaping to the atmosphere. Thereby, the device may be left on the tire valve and monitor tire pressure for long periods of time. Furthermore, the rotational movement of the indicator dome can be provided in a non-linear manner by appropriate design of cammed surfaces on top of the piston such that the indicator dome quickly rotates to a warning position when the pressure is sufficiently low. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention will be more fully understood by reference to the following detailed description of the invention in conjunction with the drawings, of which: 
     FIG. 1 is an exploded view of an embodiment of the present invention; 
     FIG. 2 is an exploded view illustrating the interaction between the cam mechanism and retainer in an embodiment of the present invention; 
     FIG. 3 illustrates the contact between the display dome and the cam mechanism in an embodiment of the present invention; 
     FIGS.  4 ( a ) and  4 ( b ) illustrate pressure indication conditions for an embodiment of the present invention; and 
     FIGS.  5 ( a ) and  5 ( b ) are cross sectional views illustrating safe and low pressure conditions for an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, a low tire pressure indicator according to an embodiment of the present invention will be described. Specifically, as shown in FIG. 1, the indicator includes an indicator dome  100 , a cam mechanism  200 , a seal  300 , and a valve connector  400 . 
     The indicator dome  100  includes a dome cover  110  that is directly connected to the cam mechanism  200 . Viewing portions  112  and closed portions  114  are uniformly spaced around the surface of the dome cover  110 . FIGS. 1-3 illustrate an embodiment of the present invention where the dome cover  110  includes four viewing portions  112  and four closed portions  114 . The dome cover  110  is divided into eight equal areas in this embodiment so that the viewing portions  112  and closed portions  114  are uniformly spaced. 
     The dome cover  110  may preferably be a two color injection molded plastic. For example, the closed portions  114  may be made of a black plastic and the viewing portions  112  may be made of a clear plastic. It is readily apparent that many manufacturing techniques and color combinations may be used for the dome cover  110 . However, the viewing portions  112  are preferably made of a clear plastic. This allows the dome cover  110  to be completely sealed while providing viewing areas for a low or warning pressure indication. By completely sealing the dome cover  110 , the device elements will be protected from the environment and the device will be pressurized to prevent air from escaping out of the tire. 
     A dome display  120  is also included in the indicator dome  100 . The dome display  120  is positioned within the dome cover  110  and is rotatably connected to the cam mechanism  200 . The dome display  120  has alternating safe and warning indication portions  122  and  124  which correspond to the uniformly spaced viewing portions  112  and closed portions  114  of the dome cover  110 . The safe indication portions  122  are used to indicate that the pressure is above a threshold limit and the warning indication portions  124  are used to indicate that the pressure is below the threshold limit. The two sets of alternating indication portions  122  and  124  may be distinguished by having one color for a set of indication portions and another color or visually distinguishable markings for the other set. 
     One embodiment of the present invention is illustrated in FIG. 1 where the dome display  120  is divided into eight equal areas to match the viewing portions  112  and closed portions  114  of the dome cover  110 . For example, the safe indication portions  122  may be black and the warning indication portions  124  may be yellow. The safe indication portions  122  preferably match in color to the closed portions  114  of the dome cover  110  (black in this example) and the low pressure indication portions  124  have a different color or markings (such as yellow, orange, or another bright color or distinct markings) which visually contrasts from the color or markings on the closed portions  114 . 
     When the dome display  120  is in a safe pressure condition, the dome cover  110  and the dome display  120  will appear to be one continuous color as illustrated by the regions having a like shading in FIG.  4 ( a ). If a low pressure condition is detected, the dome display  120  will then rotate so that the contrasting warning color or markings will be readily apparent from a quick visual glance as represented by the different cross hatched patterns on the dome cover  110  and the dotted patterns on the display dome  120  in FIG.  4 ( b ). It is readily apparent that many manufacturing techniques and color combinations or markings may be used for the display dome  120 . The display dome  120  is preferably made of a lightweight and durable material, such as plastic from a two color injection molding process. 
     The dome display  120  further includes ribs  126  for interacting with the cam mechanism  200  and rotating the dome display  120  as a change in pressure is detected. The ribs  126  may extend along an inside surface of the dome display  120  as illustrated in FIGS. 3 and 5. The ribs  126  and the cam mechanism  200  cooperatively engage to rotate the dome display  120 . The shape of the top surface of the cam mechanism  200  which contacts the ribs  126  may be varied to achieve the desired nonlinear rotational displacement of the dome display  120 . A guide  128  at the top center of the dome display  120  may also be included so that the dome display  120  will rotate freely and ensure proper orientation of the indication portions  122  and  124 . 
     The cam mechanism  200  includes a piston  210 , a linear spring  220 , and a retainer  230 . The piston  210  includes a base  212  having cam legs  214  extending up from its surface. The spring  220  fits outside of the base  212  and inside of the retainer  230  so that the linear spring  220  may expand and contract therebetween. The retainer  230  includes cam openings  232  on its top surface which correspond in number to the cam legs  214 . The cam openings  232  should be designed to be slightly larger than the cam legs  214  for allowing the retainer  230  to slide freely about the axis of the cam legs  214 . The surfaces of the cam legs  214  may then be exposed to engage with the dome display  120  and achieve the desired nonlinear rotational displacement. In the illustrative embodiment of FIG. 2, three cam legs  214  fit inside of three openings  232 . However, it is apparent that various numbers of cam legs  214  and openings  232  may be used as long as they are corresponding in number. 
     The piston  210  also includes a circular neck  216  at its base  212  having a circumference larger than the circumference of the piston  210 . Extending below the top surface of the retainer  230  is a cylindrical tube  240  for a distance greater than the length of the base  212 . The inner circumference of the cylindrical tube  240  should only be slightly larger than the circumference of the neck  216 . Thereby, the piston  210  may slide freely along the axis of the cam legs  212  with a minimal amount of wobble about this axis. 
     The linear spring  220  fits around the piston  210  and the neck  216  out from the base  212  to a sufficient distance for allowing the linear spring  220  to rest thereon. The cylindrical tube  240  is placed over the piston  210  and its neck  216  so that the inner surface of the cylindrical tube  240  fits snugly around the neck  216 . The length of the cylindrical tube  240  extends down from the top surface of the retainer  230  to a sufficient distance for allowing the piston  210  to slide without becoming disengaged from the cylindrical tube  240 . The linear spring  220  translates air pressure to linear displacement of the piston  210 . The type of linear spring  220  is chosen and calibrated according to the pressure threshold that is to be detected and may be interchanged based on the desired pressure threshold. 
     The retainer  230  also includes a torsion spring  250  wrapped around a shaft  252 . The shaft  252  extends up from the top surface of the retainer  230  and helps to properly position the dome display  120  in combination with the torsion spring  250 . A torsion rib  254  may also be placed on the top surface of the retainer  230  for locking the torsion spring  250  in place. The dome display  120  is positioned on the shaft  252  so that it may rotate about the shaft  252 . 
     The dome cover  110  is carefully attached so that the safe and warning indication portions  122  and  124  of the dome display  120  line up with the viewing and closed portions  112  and  114 . More specifically, when the pressure increases above the threshold limit and the piston  210  is forced upward as illustrated in FIG.  5 ( a ), the dome cover  110  should be attached so that the safe indication portions  122  align with the viewing portions  112 . Thereafter, as the pressure decreases, the warning indication portions  124  rotate toward and align with the viewing portions  112  as illustrated in FIG.  5 ( b ). 
     The dome cover  110  is attached directly to the top surface of the retainer  230 . Gluing, snapping, or other known attaching techniques may accomplish this attachment as long as a seal is maintained to prevent air or gas from escaping the device to the atmosphere. Again, the retainer  230  and the piston  210  are preferably made of a lightweight and durable material, such as plastic made for example in an injection molding process. 
     The device further includes the seal  300  and valve connector  400  as illustrated in FIGS. 1-3, and  5 . The top surface of the valve connector  400  has a ledge  410  of a circumference slightly smaller than the circumference of the seal  300 . The seal  300  is placed on top of the ledge  410  of the valve connector  400  and the bottom surface of the cylindrical tube  240 . Then, the retainer  230  and the valve connector  400  may be attached in a known manner, such as gluing, snapping, or the like. The seal  300  is preferably a flexible membrane, such as an elastomer diaphragm seal and moves in response to the contacted pressure for actuating the piston  210 . The seal  300  serves as part of the multiple seal structure to ensure that pressure from the valve does not escape to the atmosphere. 
     As illustrated in FIG.  5 ( a ), when pressure flows through the valve connector  400  towards the seal  300 , the seal  300  is forced upwards. This in turn forces the piston  210  upward which engages the cam legs  214  with the dome display  120  and displays the appropriate pressure indication in the viewing portions  112 , such as the safe indication portions  122 . FIG.  5 ( b ) illustrates a decreased amount of pressure being exerted on the seal  300 , which causes the height of the seal  300  to be reduced. The piston  210  is then forced downward which engages the cam legs  214  with the dome display  120  and displays the appropriate pressure indication in the viewing portions  112 , such as the warning indication portions  122 . 
     The valve connector  400  includes an opening  410  for allowing pressure to flow from the tire or source to the device. Additionally, the valve connector  400  includes threads  420  or another connecting structure for connecting the device to the valve of the tire. The valve connector  400  is preferably a chrome plated brass part. A stem  430  extends downward from the bottom surface of the valve connector  400  for depressing the valve core of the tire and thereby pressurizing the device. An O-ring seal  440  is preferably attached below the bottom surface of the valve connector  400  and above the threads  420  for maintaining a seal between the device and the valve of the tire. These multiple seals substantially eliminate any leakage from the valve to the atmosphere so that the device can remain attached to the valve for long periods of time. 
     Having described preferred embodiments of the invention it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts may be used. Accordingly, it is submitted that the invention should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the appended claims.