Abstract:
The pressure gauge is designed for operative engagement with a gas pressurized system such as a pneumatic tire. It includes a housing having a pressurized gas inlet orifice and a cylindrical bore formed within the housing. A pressure reactive piston is slidably engaged within the cylindrical bore, and a resistance means is disposed within the cylinder to provide a resistive force to the movement of the piston. A calibration rod is disposed proximate the piston, whereby movement of the piston will cause movement of the rod. A pressure indicator bar, which is threadably engaged to the rod, provides an indication of the pressure level of the gas. The calibration rod has a user accessible end, and rotation of the rod causes a calibration adjustment of the pressure indicator bar due to the threaded engagement of the rod with the pressure indicator bar.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to pressure gauges and more particularly to an improved pressure gauge including a movable piston pressure sensing element and a gauge calibration element.  
         [0003]     2. Description of the Prior Art  
         [0004]     One embodiment of the present invention is designed to be similar in size and shape to truck tire gauge, to act as a replacement for it. The present invention generally utilizes a piston-type pressure element having a coil spring to provide a reactive force. Gauges of this general configuration are known in the prior art, and they are calibrated following assembly and before sale to the public. A problem with such prior art tire pressure gauges is that they can become inaccurate through usage, and it would be desirable to provide a mechanism for the user to accomplish a re-calibration of the gauge. Also, where the manufactured tire pressure gauge is calibrated at a manufacturer&#39;s selected calibration pressure, it is also desirable for the user to be able to re-calibrate the tire pressure gauge to obtain maximum accuracy at another user chosen pressure. The present invention provides a means for the user to re-calibrate a tire pressure gauge after it has been manufactured and calibrated by the manufacturer.  
       SUMMARY OF THE INVENTION  
       [0005]     The pressure gauge is designed for operative engagement with an air pressurized system such as a pneumatic tire for an automobile or truck. It includes a housing having a pressurized air inlet orifice and a cylindrical bore formed within the housing. A pressure reactive piston is slidably engaged within the cylindrical bore, and a resistance means is disposed within the cylinder to provide a resistive force to the movement of the piston. A calibration rod is disposed proximate the piston, whereby movement of the piston will cause movement of the rod. A pressure indicator bar, which is threadably engaged to the rod, provides an indication of the pressure level of the air. The calibration rod has a user accessible slotted end, and rotation of the rod causes a calibration adjustment of the pressure indicator bar due to the threaded engagement of the rod with the pressure indicator bar.  
         [0006]     It is an advantage of the present invention that it provides a pressure gauge that is relatively easy to manufacture.  
         [0007]     It is another advantage of the present invention that it provides a pressure gauge that is easy to calibrate.  
         [0008]     It is a further advantage of the present invention that it provides a pressure gauge that can be calibrated to a high degree of accuracy by the user.  
         [0009]     It is yet another advantage of the present invention that provides a first calibration mechanism that is calibrated by the manufacturer, and a second user adjustable calibration mechanism, such that the device can remain re-calibrated throughout its lifetime.  
         [0010]     The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments, which make reference to the several figures of the drawings.  
     
    
     IN THE DRAWINGS  
       [0011]      FIG. 1  is a side elevational view, with cross-sectional portions of a truck tire type pressure gauge of the present invention;  
         [0012]      FIG. 2  is a more complete cross-sectional view of the gauge depicted in  FIG. 1 ;  
         [0013]      FIG. 3  is an end elevational view of the gauge depicted in  FIG. 1 ;  
         [0014]      FIG. 4  is a cutaway view depicting components of the gauge depicted in  FIG. 1 ;  
         [0015]      FIG. 5  is an enlarged, partially cross-sectional view of the piston element of the device depicted in  FIGS. 1-4 ; and  
         [0016]      FIG. 6  is a graph depicting the operation of the re-calibration mechanism of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     The present invention comprises a truck tire type pressure gauge, as depicted in  FIGS. 1-4 . The gauge  10  includes a cylindrical housing  14  enclosing a cylindrical piston bore  18 . A piston member  22  having an O-ring seal  26  and a calibration nut  30  is disposed within the bore  18 . A coil spring  40  is disposed within the bore  18  between the calibration nut  30  and the upper end  44  of the cylindrical housing  14 . A dual-foot air chuck  50 , or a dual-valve air chuck including nuts  54  and an air check (not shown) are engaged to the lower end  56  of the housing  14 . The piston  22 , O-ring seal  26 , calibration nut  30  and coil spring  40  are substantially identical in form and function to those elements described the inventor&#39;s U.S. Pat. No. 5,965,822, and are generally described herebelow with the aid of  FIG. 5 .  
         [0018]     A push type plunger pressure indicator bar  60  has a lower end  64  which resides within the bore  18  and an outer, calibrated end  68  that projects outwardly through the upper end  44  of the housing  14 . A bar guide  72 , having an opening  76 , is fixedly engaged within the upper end  44 . The indicator bar  60  is slidably engaged within the guide opening  76 , and the lower end  64  of the indicator bar  60  has a projecting stop pin  78 , such that it will not pass through the opening  76 , whereby the indicator bar  60  is retained within the housing  14 . With particular reference to the end elevational view of  FIG. 3 , the indicator bar  60  is generally rectangular in cross-section, and the opening  76  in the bar guide  72  is similarly rectangular, such that the indicator bar  60  is slidably engaged with the guide  72 , but will not rotate within the guide  72 .  
         [0019]     With particular reference to  FIGS. 2 and 3 , the pressure indicator bar  60  is formed with a central bore  80  that projects along the longitudinal central axis of the bar, and a calibration rod  84  is disposed within the bore  80  along its central axis. The upper end  88  of the bar bore  80  is threaded  92 , and the upper end  96  of the calibration rod  84  is similarly threaded  98 , such that the calibration rod  84  is threadably engaged within the bore threads  92  of the indicator bar  60 . The inner end  100  of the calibration rod  84  extends beyond the inner end  64  of the indicator bar  60 , such that the inner end  100  of the calibration rod  84  rests upon, but is not engaged to, the upper surface of the piston  22 . As is best seen in  FIG. 3 , the upper end  88  of the calibration rod is slotted  104 , such that a screwdriver  108  or similar instrument may be used to rotate the calibration rod  84  in its threaded engagement with the indicator bar  60 . Due to the non-rotatable engagement of the indicator bar  60  within the guide  72 , the indicator bar  60  will not rotate when the calibration rod  84  is rotated by a user&#39;s application of a screwdriver  108  to the slotted outer end  88  of the calibration rod  84 .  
         [0020]     As is best seen with the aid of  FIG. 5 , the movable piston  22  is a generally cylindrical member including a generally widened lower section  114  and a generally narrowed upper section  118  having external threads  122  formed thereon. The internally threaded gauge calibration nut  30  is threadably engaged to the threaded upper section  118  of the piston  22 . The calibration nut  30  is utilized to calibrate the gauge during the assembly and testing of the gauge components, as is discussed hereinbelow. An O-ring seal  26  having an outwardly projecting lip  132  is disposed within an O-ring groove  136  formed within the lower section  114 . It is to be understood that the O-ring seal is disposed to make a moving pressurized seal with the inner walls of the housing bore  18 . The lower end  140  of the coil spring  40  rests upon an upper surface of the calibration nut  30 , and the upper end of the coil spring  40  presses against the upper end  44  of the housing  14 , such that when the piston  22  moves upwardly, the coil spring  40  is compressed between the calibration nut  30  and the upper end  44  of the housing  14 .  
         [0021]     It is therefore to be understood that when the gauge  10  is utilized to determine the air pressure within a pneumatic tire that pressurized air from the tire enters through a gauge valve member  50  into the air tube  56  and passes through the air inlet hole  160 . The pressurized air will then pass into the piston bore  18  to push the piston  22  upwardly against the resistance of the coil spring  40 , thus pushing the calibration rod  84  with its threadably engaged indicator bar  60  outwardly. When the gauge  10  is removed from the tire, the air pressure within the cylinder  18  will decrease to atmospheric pressure and the piston  22  will return to its initial position. However, because the calibration rod  84  is not engaged to the piston, the indicator bar will remain at its extended position to indicate the maximum pressure which was detected by the gauge  10 . The user of the device  10  must manually push the indicator bar  60  back into the cylindrical housing  14  after having read the indicated pressure.  
         [0022]     While the use of a coil spring  40  to provide a restoring force is generally useful, because the spring&#39;s resistive force is directly proportional to the compressive force, a problem with the use of coil springs in the manufacturing of accurate instruments is that the spring constant of identically appearing coil springs can vary enough to greatly complicate quality control during manufacturing. That is, several manufactured gauges that appear to be identical in all details can report significantly different pressure readings due to the different spring constants of the different coil springs  40  disposed within the gauges. The inventor&#39;s prior art solution to this problem, as described in the inventor&#39;s prior art U.S. Pat. No. 5,965,882, is the utilization of the calibration nut  30  during the manufacturing process to correct this problem, as is next discussed.  
         [0023]     During the manufacturing assembly steps for each pressure gauge  10 , the various specific components of a particular gauge are chosen and assembled outside of the housing  14 . In this assembly process a particular coil spring  40  will have been chosen. Those skilled in the art will understand that a completed, calibrated pressure gauge  10  will be most accurate at the pressure to which the gauge was calibrated and less accurate at pressure levels that are significantly different from the calibration pressure level. Thus, if it is known beforehand that a pressure gauge will be used in a situation where the greatest accuracy is required at approximately a specific pressure, the gauge  10  can be calibrated to that specific pressure, such that its greatest accuracy will occur there.  
         [0024]     At a nearly finished manufacturing stage, the assembled gauge  10  is tested to a known pressure level which is preferably, though not necessarily close to the typical user&#39;s expected pressure reading on the gauge  10 . In this test set up, the calibration nut  30  is generally initially disposed at approximately the mid-point of its threaded engagement range with the piston  22 ; the indicator bar  60  is likewise initially disposed at approximately the mid-point of its threaded engagement range with the calibration rod  84 . Owing to the particular spring constant of the particular coil spring  40  within the gauge  10 , the actual reading of the gauge  10  may differ significantly from the known test pressure level. The gauge  10  is then calibrated to read the correct test pressure level by rotating the threaded calibration nut  30  in the upward or downward direction that is required to move the piston  22 , relative to the spring  40 , such that the calibration rod  84  and its attached indicator bar  60  moves inwardly or outwardly. The calibration nut  30  is rotated to apply the selected calibration force on the piston  22  until the pressure indicator bar  60  accurately reflects the known test pressure level. Thereafter, the gauge is removed from the test set up, and the calibration nut  30  is permanently engaged in its test position by an appropriate method to the inner portion  114  of the piston  22 . In the preferred embodiment, the calibration nut  30  is permanently affixed by soldering it  166  in position to the piston  22 , however other equivalent methods for engaging the calibration nut  30  to the piston  22  are contemplated to be within the scope of the invention. Thus, in manufacturing a plurality of pressure gauges, each including a spring  40  having a different spring constant, the use of the calibration nut and calibration process will result in a plurality of gauges that are all most accurate at the same test pressure level.  
         [0025]     Often, through ongoing usage, the spring constant or other spring parameters will change and the tire gauge will become less accurate. A user operable re-calibration means is then desirable, and the re-calibration means of the present invention includes the calibration rod  84  upon which the pressure indicator bar  60  is threadably mounted. As indicated above, the upper end  96  of the calibration rod  84  includes a screw head slot  104 , such that it can be rotated by a screwdriver  108 , with the user holding onto the pressure indicator bar  60 .  
         [0026]     Therefore, after extended usage, when the tire gauge no longer reads as initially calibrated, the user rotates the calibration rod  84  (such as by use of a screwdriver  108 ), whereupon the pressure indicator bar  60  will move inwardly or outwardly (depending upon the direction of rotation) due to its threaded engagement with the calibration rod  84 , such that the indicator bar  60  will once again read as initially calibrated when measuring a test air pressure source.  
         [0027]      FIG. 6  is a graph depicting the operation of the invention. The vertical axis represents a master test gauge reading and the two horizontal axes represents tire gauge indicator bar readings of the present invention. Initially, assuming the manufacturer&#39;s calibration pressure point is 80 PSI, it can be seen that the tire gauge reading before re-calibration (top horizontal axis) properly reads 80 PSI. However, the tire gauge pressure reading line (the dashed line) is not collinear with the reference gauge line; this represents the well known linear performance error of this type of gauge. Therefore, it can be seen that where the master test gauge reading is 100 PSI, the tire gauge reading before re-calibration may be 102 PSI. Now, if the user desires to re-calibrate the tire gauge such that it is accurate at 100 PSI, the user will use the screwdriver to turn the calibration rod  84 , such that the indicator bar  60  is moved towards the right (lower horizontal axis) in  FIG. 6  (see arrow  170 ) until the indicator bar properly reads 100 PSI. Therefore, after re-calibration, the tire gauge is re-calibrated to read 100 PSI to correspond with a master test gauge reading of 100 PSI.  
         [0028]     Upon reading the specification and drawings provided hereabove, it is to be understood that a significant feature of the embodiments described hereinabove is the utilization of the calibration rod in its threaded engagement with the pressure indicator bar to provide a means for the user to re-calibrate the gauge. Such a calibration is desirable due to the varying usage factors of the gauges subsequent to the initial factory calibration.  
         [0029]     While the invention has been disclosed and described with regard to specific preferred embodiments, it is intended by the inventor that the following claims cover not only the specific embodiments described herein but other and further altered devices that would occur to those skilled in the art upon reviewing the specification and drawings provided herein. It is therefore intended that the following claims cover all such alterations and modifications which nevertheless include the true spirit and scope of the this invention.