Patent Publication Number: US-2009223075-A1

Title: Gage for measuring drum brake inside diameter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional of on that and makes no claim of priority. This application is a non-provisional of, and makes claim of the benefit of priority to, U.S. provisional patent application Ser. No. 61/034,655, filed 7 Mar. 2008, which is incorporated by reference as if fully recited herein. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of gages, particularly, to the field of gages for measuring the largest inside diameter of a drum brake. 
     BACKGROUND OF THE ART 
     In the field of maintaining drum brakes, it is important and known to measure certain aspects of a drum brake to a high degree of accuracy and precision. One measurement that is required is a determination of the largest inside diameter that is encountered in the brake. 
     While it is desirable that a drum brake have a consistent value of the inside diameter as one moves around the circumference of a drum brake, actual observation is that the inside diameter will vary. 
     At least two problems exist in the known prior art gages for measuring drumbrake inside diameters. First, obtaining a consistently diametric value is difficult, as it is easy with many gages to skew the gage slightly off of the diameter. Second, and in part due to the first problem, the known gages make the act of obtaining accurate results and simultaneously recording these results in a useful manner a difficult task. 
     Therefore, it is an unmet objective of the prior art as known to provide a gage for both accurately and precisely measuring the inside diameter of a drum brake. 
     SUMMARY OF THE INVENTION 
     This and other objectives are achieved by a gage for measuring a drum brake with a generally planar beam. A readout member is mounted for sliding movement along the length of the beam. A face of the readout member is adapted for display of a measurement reading and the readout member is provided with a means for measuring a distance of the sliding movement along the length of the beam. One example of the means for measuring distance is a vernier. 
     First and second measuring jaws are also provided. The first measuring jaw extends outwardly from the beam in a direction that is normal to both a longitudinal and a transverse axis of the beam and the second measuring jaw extends outwardly from the readout member on a side thereof opposite the face, so that it is parallel to the first measuring jaw. 
     The first measuring jaw is affixed to the beam inward from a first end of the beam, leaving a portion of the beam between the first end and the first measuring jaw and is provided with a measuring tip that extends parallel to the beam longitudinal axis of the beam, in the direction of the first end of the beam. 
     To accommodate the second measuring jaw, the beam is provided, in some instances, with a longitudinal slot through which the second measuring jaw extends. IN other instances, the readout member extends around the transverse edges of the beam to allow the second measuring jaw to extend in the same direction as the first measuring jaw. 
     Each of the measuring jaws is provided with a measuring tip. The measuring tips are aligned with each other, although they extend in opposite directions. 
     In many aspects of the invention, means for effecting translation of the readout member relative to the beam are provided on at least one of the readout member and the beam. A typical means would be a knob for a user to grasp. The beam should be sufficiently long to span the inside diameter of the drum brake to be measured. When a portion of the beam between the first end and the first measuring jaw is rested upon the rim of the drum brake with the respective jaws extending into the central cavity of the drum brake, the inside diameter may be readily determined by securing the first measuring jaw into place and moving the second measuring jaw along the opposite circumference, recognizing that the lengths of the chords being measured thereby will be maximized when the beam is aligned along the true diameter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the invention will be had by reference to the accompanying figures, wherein identical parts are identified by identical part numbers and wherein: 
         FIG. 1  is a side elevation view of a drum brake gage as known in the prior art; 
         FIG. 2  is a side elevation view of an embodiment of the drum brake gage, in isolation; 
         FIG. 3  is a perspective view of the  FIG. 2  embodiment; 
         FIG. 4  is a schematic depiction of an exemplary readout member of the  FIG. 2  embodiment, showing particular details of the display face; 
         FIG. 5  is a side elevation view of the  FIG. 2  embodiment, operatively engaged in a drum brake; and 
         FIG. 6  is a perspective view of the operative engagement shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring first to  FIG. 1 , a digital drum brake gage  10  as is generally known in the prior art is shown in a side elevation view. In this view, the gage  10  is seen as having a generally planar beam  12 , with a first measuring jaw  14  that extends outwardly from the beam in an essentially co-planar manner and a second measuring jaw  16 . The second measuring jaw  16  also extends outwardly from the beam  12  in an essentially co-planar manner. However, instead of being affixed to the beam  12 , as the first measuring jaw  14  is affixed, the second measuring jaw  16  is affixed to a readout member  18  that is slidingly mounted on the beam. The readout member has a face  20  on which a measurement reading may be displayed. The first jaw  14  is a fixed jaw, and is affixed at an end of the beam  12 . 
     Each of the measuring jaws  14 ,  16  has a measuring tip, with tip  24  on jaw  14  and tip  26  on jaw  16 . The respective jaws and tips are arranged so that the tips  24  and  26  face away from each other and, as tip  26  moves relative to tip  24  when readout member  18  slides along beam  12 , the tips move along a line parallel to a longitudinal axis of the beam  18 . 
     In the known arrangement illustrated, the face  20  of the readout member is located on a plane that is parallel to the plane of the beam  12 . As seen in  FIG. 1 , the body of the readout member  18  is wider than the beam, particularly on the side of the beam from which the jaws extend. 
     Moving now to  FIGS. 2 and 3 , an embodiment of the drum brake gage  110  containing the inventive aspects of this application is shown in side elevation and perspective views, respectively. One immediately notable feature is the placement of the jaws  114 ,  116 . In this embodiment, the jaws are deployed normal to the plane of generally planar beam  112 , rather than being essentially co-planar. The first measuring jaw  114  is affixed to the beam  112  slightly inward from a first end of the beam, the portion  130  of the beam between the first end and the first jaw  114  providing a valuable function, as will be explained below. First measuring jaw  114  is provided with a measuring tip  124  that extends parallel to a longitudinal axis of the beam  112 , in the direction of the first end of the beam. The second measuring jaw  116  is affixed to a readout member  118  that slidingly rides atop the beam  112 . The readout member  118  has a face  120  on which a measurement reading may be displayed. 
     To allow the readout member  118  to ride atop the beam and the second measuring jaw  116  to extend normal to the beam on the opposite side of the beam from the readout member, as seen in  FIGS. 2 and 3 , either the beam is provided with an open slot through which the second jaw extends, or the readout member extends around the beam. Second measuring jaw  116  is equipped with tip  126 . In the manner shown in the prior art example, the respective jaws  114 ,  116  and their tips  124 ,  126  are arranged so that the tips face away from each other. As tip  126  moves relative to tip  124  when readout member  118  slides along beam  112 , the tips move along a line parallel to a longitudinal axis of the beam  12 . 
       FIGS. 2 and 3  show that a first knob  134  is fixed to the combined beam  112 /first measuring jaw  114 , the first knob extending from the beam opposite the first jaw, at least as shown in the illustrated embodiment. A second knob  136  is fixed to the combined readout member  118 /second measuring jaw  116 , the second knob extending from the readout member opposite the second jaw, at least as shown in the illustrated embodiment. 
     While not explicitly shown in either the prior art embodiment  10  of  FIG. 1  or the inventive embodiment  110  of  FIGS. 2 and 3 , the respective readout members  18 ,  118  will be understood by those of skill in the art to each be provided with a vernier or similar mechanism, through which a distance between the respective tips is determined 
     Movement of the readout member  118  along the beam  112  is delimited at the first end by the fixed first measuring jaw  114 . At the second end of the beam  112 , an end stop of some manner should be provided, with an exemplary end stop  140  shown in  FIGS. 2 and 3 . 
     Additional detail of the readout member  118 , and, especially, the display face  120  is shown in top plan view in  FIG. 4 . Prominent on the display face  120  is a display area  140 , which will be filled by a display means, typically a liquid crystal diode (LCD). Various control buttons are depicted. Among these are an “on/off” function button  142 , a units selection button  144 , a “hold” button  146 , a “set” button  147  and a “max” button  148 . Of particular note is the “max” button  148 . Internal to the readout member is a digital chip for operating the readout member  118 , as well as a power source, typically a small battery. Integral to the digital chip is a logic circuit that allows the maximum measured distance value to be stored in a memory register. Use of the “max” button  148  causes the value stored in the memory register to be displayed. 
     Use of the device  110  on a typical drum brake  60  is shown in  FIGS. 5 and 6 . Beam  112  has a length sufficient to span the inside diameter of the drum brake  60 , with enough additional length to allow a flat lower surface of beam  112  to be placed on the rim  62  thereof, with the jaws  114 ,  116  extending in to the central cavity of the drum brake. Because fixed first jaw  114  is positioned inwardly from the first end of the beam  112 , the beam portion  130  rests on the rim, such that first knob  134  and tip  124  of jaw  114  are useful in snugging the first end of the device against the inside wall of the drum brake  60 . From this point, a visual alignment of the device  110  is made across the top rim  62 , with the intent of aligning the tips  124 ,  126  with the diameter. Obviously, this process is preferably started with the second tip (and with it, the readout member  118 ) drawn inwardly from the second end of the beam. 
     With the device  110  positioned in this manner, the digital chip of the readout member  118  powered up and the maximum value register either “zeroed” or set to a value that is clearly smaller than the diameter, the second jaw  116  is moved towards the second end of the beam  112 , using the second knob  136  and keeping the second end of the beam in resting contact with the top rim surface, until the tip  126  contacts the inside face. Keeping in mind that the longest chord of a circle is its diameter, and keeping the tips  124 ,  126  in contact with the inside wall surface, slight lateral movement of the tips will seek out the true diameter, which will be recorded as the maximum value.