Abstract:
An apparatus for measuring tension of piston rings includes a cylindrical support fixture having a circumferential groove formed therearound for receiving and holding a piston ring. A rigid base supports a plurality of components of the apparatus. A strong, thin band, formed from a material sufficiently strong to withstand repeated applications of pulling force thereto, is mounted to the base, and is held between two clamps. The band has a loop formed therein, for receiving the support fixture with a piston ring mounted therein. The apparatus also includes reciprocally movable structure for tightening the band around the support fixture, such as a slidably movable clamp assembly at one end of the band. The apparatus further includes mechanism for measuring tension on the band, and fluid activatable mechanism for vertically reciprocating a portion of the support fixture. In a preferred embodiment, the reciprocating mechanism is pneumatically activatable, such as by compressed air.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the invention 
     The present invention relates to a method and apparatus for automated measurement of piston ring tension. More particularly, the present invention relates to a method and apparatus for compressing a piston ring in a measuring fixture, with a thin high-strength band, and measuring the force exerted on the band, by the outwardly expanding ring. Even more particularly, the present invention relates to a method and apparatus of the type described, in which a portion of the fixture and piston ring are vertically reciprocated, in order to help remove any looseness from the band, caused by friction between the piston ring and the compression band, before measurement takes place. 
     2. Description of the Background Art 
     A manually operated method of measuring piston ring tension has been known for many years, in which a steel band is formed into a loop which is wrapped around a piston ring to be measured. The band is then placed under tension by pulling on a handle which is attached to one end of the band, the other end of the band being clamped in place. In this known design, the base of the handle is pivotally anchored to a support. A spring-actuated load gauge is connected to the steel band, between the handle and the loop which surrounds the piston ring, and the tension of the ring may be read directly off of the load gauge. This early method and apparatus suffered from problems with consistency and reproducibility. 
     Some later known devices exist for compressively measuring piston ring tension. Two such known devices are described in U.S. Pat. Nos. 3,946,602 and 4,249,415. 
     Certain aspects of this type of apparatus have become relatively standardized. Referring now to FIGS. 1-3, a steel band  10  is shown having a rectangular hole  12  formed therein. The band  10  also includes a narrowed diameter portion  14 , and in order to form the band into a loop, a first end  15  of the band  10  is turned sideways, passed through the hole  12  in the band, and then straightened up as shown in FIG.  2 . After passing the first end  15  of the band through the hole  12 , the band  10  includes an integral loop  16  therein, with an adjustable size range which is determined by the length and spacing of the narrrowed diameter portion  14  in relation to the rectangular hole  12 . 
     Referring now to FIG. 3, the band  10  is shown wrapped around a cylindrical fixture  17  having a horizontally oriented circumferential groove formed therearound, which receives a piston ring  18  therein. The fixture  17  is provided to hold and stabilize a piston ring  18  during testing thereof. The same fixture  17  is used over and over again, to test many different piston rings. 
     Often, a standardized master ring is used which exhibits a known and calibrated diameter. The master ring is used as a comparison device, to ensure that a piston ring measuring apparatus is set correctly. Where used, the master ring is checked first, and the machine readouts are adjusted, if necessary, to show the known tension thereof. Then, an unknown ring is tested. 
     A common problem has been encountered with this band type of device, in that when a fixture  17  and piston ring  18  is placed into a loop  16  of the band  10 , and tension on the band  10  is increased, the band will not tighten down on the fixture and ring in a consistent and reprodudcible manner, unless the fixture and ring assembly is repeatedly tapped against a table top, or other work surface, as the band  10  is tightened therearound, to ensure that no looseness caused by friction remains in the loop  16 . Where the band  10  is placed under tension without tapping the fixture and ring against a work surface, test results tend to vary with a single piston ring from test to test, instead of being reliable and reproducible. Accordingly, a step of tapping the fixture and ring assembly against a table or other support, as the band  10  tightens therearound, became a necessary part of the normal process of piston ring tension measurement. 
     Unfortunately, the tapping procedure of a given machine operator might be different from one day to the next, as well as different from the tapping procedure of another operator using the same machine, perhaps on a later work shift. Because of this above-described variability in test procedure, efforts began to be made to standardize the tapping operation as a part of piston ring tension measurement. 
     A recent design for an apparatus which may be used to measure piston ring tension is described in Japanese laid-open Patent number 6-19299, published Oct. 8, 1996, naming Hattori as the inventor. The disclosure of Japanese laid-open Patent number 6-19299 is herein incorporated by reference. In the apparatus of Hattori, a number of components are mounted on a rigid base, including a horizontally reciprocally movable first clamp coupled to an electronic load cell. The first clamp holds a first end of a steel band which is formed into a loop, and a horizontally reciprocally movable second clamp holds a second end of the steel band. The steel band encircles a piston ring to be measured. The piston ring rests on a carrying stand, which is separate from the base. The second clamp is attached to an electronic length measuring device, as well as to the band. 
     In order to make sure that looseness caused by friction in the band is removed in a consistent and reproducible fashion, before tension in the piston ring is measured, the apparatus of Hattori also includes a vertically reciprocally movable vibration plate, which is located in between the piston ring and the carrying stand. The vibration plate is free at a first end thereof, and is pivotally attached to the carrying stand at a second end thereof. An electric motor is horizontally mounted below the base, and the motor rotatably drives an eccentric cam, to alternately lift the free end of the vibration plate and drop it against the carrying stand. After any looseness caused by friction has been taken out of the band by reciprocal movement of the first and second clamps, acting in conjunction with the above-described movement of the vibration plate, the tension of the piston ring may be measured by the load cell, in conjunction with the electronic length measuring device. 
     Although the method and apparatus of Hattori is useful, and advanced the known state of the art at the time it was published, Hattori&#39;s use of an electric motor and eccentric cam to actuate the mechanical vibration plate is subject to wear and tear, and these components may fail after some time in service. It would be advantageous if a method and apparatus could be provided for measuring piston ring tension, which replaced the vibration plate, electric motor and eccentric cam of the Hattori apparatus with a more reliable means of vertically reciprocating a section of a piston ring, in a measuring device, which would not be as prone to mechanical breakdown. 
     A need still exists in the art for an improved method and apparatus for measuring piston ring tension, which does not have the shortcomings of the apparatus according to the design of Hattori. 
     SUMMARY OF THE INVENTION 
     An improved method and apparatus for measuring piston ring tension includes a rigid base which supports a plurality of other components of the apparatus. A preferred apparatus for measuring tension of piston rings includes a strong, thin band, formed from a material sufficiently strong to withstand repeated applications of pulling force thereto, which is mounted to the base, and is held between two clamps. The band has a loop formed therein, for receiving a support fixture, with a piston ring mounted therein. The apparatus hereof, optionally, may include a cylindrical support fixture having a circumferential groove formed therearound for receiving and holding a piston ring. Preferably, the apparatus also includes horizontally reciprocally movable means for tightening the band around the support fixture, such as a slidably movable clamp assembly at one end of the band. The apparatus further includes means for measuring tension on the band, and fluid activatable means for vertically reciprocating a portion of the support fixture. In a most preferred embodiment of the present invention, the reciprocating means is pneumatically activatable, such as by compressed air. 
     Accordingly, it is an object of the present invention to provide an improved method and apparatus for measuring piston ring tension, which includes a superior means for vertically reciprocating a portion of the support fixture. It is another object of the present invention to provide an apparatus for measuring piston ring tension which will give consistently reproducible readings. For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view, partially cut away, of a prior art steel band usable in a piston ring tension measuring apparatus; 
     FIG. 2 is a perspective view of the prior art steel band of FIG. 1, wrapped around in a loop configuration; 
     FIG. 3 is a top plan view of the prior art steel band of FIGS. 1-2, wrapped around a cylindrical fixture holding a piston ring therein; 
     FIG. 4 is a top plan view, partially cut away, of a piston ring tension measuring apparatus in accordance with a first embodiment of the present invention; 
     FIG. 5 is a top plan view of a groove gauge fixture, usable in conjunction with the apparatus of FIG. 4, in accordance with the present invention; 
     FIG. 6 is a cross-sectional view of the groove gauge fixture of FIG. 4; 
     FIGS. 7A and 7B are sequential cross-sectional sequential views of a portion of the apparatus of FIG. 4 during operation thereof, taken along the line  7 — 7  in FIG. 4; and 
     FIGS. 8A and 8B are sequential cross-sectional sequential views, similar to FIGS. 7A and 7B, of a portion of a modified apparatus according to a second embodiment of the present invention, during operation thereof. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 4, an apparatus for measuring piston ring tension, in accordance with the present invention, is shown generally at  20 . The apparatus  20 , generally, includes the following main components which will be discussed in further detail below: a base  22 , a work support plate  24 , a groove gauge fixture  26 , a steel band  28 , length and tension measuring devices  42 ,  45 , respectively, and an air delivery system  50 . 
     The base  22  is preferably formed from a strong, rigid material such as cast iron. The base  22  has a generally flat upper surface which supports multiple components of the apparatus  20  thereon. A work support plate  24  is adjustably mounted to the base  22 , for supporting a groove gauge fixture  26  and a steel band  28  thereon. An open space  23  is provided around the work support plate  24  to allow adjustment thereof, in order to accommodate piston rings of different diameters. First and second locking members  25 ,  27  are provided for releasably fixing the position of the support plate  24  on the base  22 . An alignment tab  44  is adjustably mounted to the support plate  24 . The alignment tab  44  is preferably used as a rough guide to help guide an operator of the apparatus, in lining up the groove gauge fixture  26  on the support plate  24 , but the alignment tab  44  does not contact the band  28 , or the groove gauge fixture  26 , during actual testing. 
     The steel band  28  is substantially similar to the band  10  shown and described in connection with FIGS. 1-3, and includes an integral loop  29  therein. The steel band  28  is held at a first end  30  thereof by a first clamp  32 , which is reciprocally movable by a first reciprocating means  34 . The first reciprocating means  34  can be a conventional reciprocating means such as, e.g., a motor-driven cam arrangement, and acts to move the first end  30  of the band  28  linearly horizontally back and forth, in the direction of the band, exclusive of the loop. 
     The steel band  28  is further held at a second end  36  thereof by a second clamp  38 , which may also be reciprocally movable by a second reciprocating means  40 . The second reciprocating means  40 , where used, can also be a conventional reciprocating means such as, e.g., a motor-driven cam arrangement, and acts to move the second end  36  of the band  28  linearly horizontally back and forth, in the direction of the band, exclusive of the loop  29 . In a preferred embodiment of the apparatus  20  hereof, the first and second reciprocating means are synchronized to move in opposed directions, so that they are both putting the band  28  under tension, from opposite directions, at the same time. This opposed reciprocating movement acts to help remove any slack from the loop  29 , where it surrounds the groove gauge fixture  26 . The second clamp  38  is attached to a length measuring device  42 . 
     A tension measuring apparatus  45  is also provided to measure tension on the band  28 . A coarse adjustment wheel  56  and a fine adjustment knob  58  are also provided attached to the base  22 , and are operatively connected to the band  28 , for setting the tension thereon. 
     AIR DELIVERY SYSTEM 
     The air delivery system  50  provides an intermittent supply of compressed air to an outlet nozzle  60  located in the work support plate  24  adjacent the edge of the loop  29  in the steel band  28 , when the apparatus  20  hereof is connected to a supply of shop air. 
     An air fitting  46  is provided, at the exterior of the apparatus  20 , for connecting the apparatus to a source of shop air, preferably regulated to about 70-100 psi, most preferably about 85 psi. The air fitting  46  is preferred to be of the quick disconnect type. The air fitting  46  is in fluid communication with an air delivery line  48 , for providing compressed air to the apparatus  20 . 
     A valve  52  is provided in the air delivery line  48  for selectively and intermittently interrupting the flow of air therethrough. The valve  52  includes an electrically operable solenoid  53  in the preferred embodiment of the present invention. An electronic controller  49  is also provided as a part of the air delivery system  50 , and is electrically connected to the valve  52  for regulating the cycling speed thereof. The valve is operable to intermittently interrupt the flow of air to the nozzle  60  in the support plate  24 . 
     After the valve  52 , the air delivery line  48  feeds into, and is in fluid communication with a hollow bore  54  formed in the support plate  24 . The hollow bore  54  connects the air delivery line  48  to the nozzle  60 . The nozzle  60  provides an air outlet to the apparatus  20 . The nozzle may be formed as a slot, and is preferred to be located so as to not be completely covered, by the groove gauge fixture  26 , as this could lead to a partial vacuum being created in the air delivery system  50  at certain times and under certain conditions, such as, for example, after the apparatus  20  was shut off. The nozzle  60  in one embodiment, may be about 1-2 mm across. 
     THE GROOVE GAUGE FIXTURE 
     Referring now to FIGS. 5-7, the groove gauge fixture  26  which is usable with, or as a part of, the present invention is generally formed as a hollow disc having a cut out arcuate notch  62  formed in one side thereof. The groove gauge fixture  26  has a peripheral exterior side edge  64  with a circumferential groove  66  formed therein, which passes completely around the outside of the groove gauge fixture, as shown in phantom in FIG.  5 . The circumferential groove  66  is provided for supportably receiving a piston ring  68  therein (FIGS. 7A-7B) during a testing operation. 
     METHOD OF OPERATION 
     In use, a master piston ring, having a known diameter, is tested first to calibrate the apparatus. Shop air, at about 85 psi, is connected to the inlet fitting  46 . The ring is installed into the groove of the groove gauge fixture  26 , and rotated until the gap in the ring is aligned with the notch  62  in the groove gauge, as shown in FIG.  4 . The groove gauge fixture  26 , with the ring  68  in place thereon, is then manually placed into the loop  29  on top of the work support plate  24 , using the alignment tab  44  as a rough guide where to place the groove guage. It has been found helpful, in the practice of the present invention, to have high spots  65  placed on the work support plate  24  to avoid excessive contact between the lower surface of the groove gauge and the upper surface of the work support plate. These high spots  65  may be painted on. It will be seen from the foregoing that the high spots  65  provide a spacer means, between the rigid base and the support fixture, for creating a small gap when the groove gauge fixture  26  is resting on the rigid base defined by the work support plate  24 . 
     The apparatus is then turned on, to activate the valve  52  to begin providing an intermittent supply of compressed air through the bore  54  and out of the nozzle  60 . The rate of pulsation of the compressed air supply is controlled by the electronic controller  49  signaling the solenoid  53  when to open and close. The rate of pulsation is preferably in a range of 5-15 Hz, preferably 6-12 Hz, and most preferably 8-10 Hz. 
     This pulsating supply of air moves the edge of the groove gauge fixture, adjacent the nozzle  60 , up and down in a vertical reciprocal movement, as shown by the two-headed arrow in FIG.  7 B. Air being expelled from the nozzle  60  pushes on, and lifts the fixture, ring, and band loop  29  as a unit, on the side of the loop proximate the nozzle  60 , as shown in FIG.  7 B. It is expected that the edge of the fixture  26  may be raised approximately ⅛ inch to ¼ inch off of the work support plate  24 . As gravity moves the groove gauge fixture downwardly into contact with the work support plate  24  in between puffs of air, the groove gauge taps against the work support plate  24  in a completely consistent and reproducible manner. Used in conjunction with the reciprocating movement of the band clamps  32 ,  38 , this repeated tapping helps to remove any looseness caused by friction from the loop  29  in the band  28 , so that the loop  29  is in close contact with the piston ring  68  at all points therearound. 
     When the apparatus  20  is turned on, the reciprocating means  34 ,  40  also begin moving the first and second clamps  32 ,  38  alternately toward and away from each other, to remove looseness caused by friction from the loop  29  in the band  28 . Then, after all looseness caused by friction is removed from the loop  29 , the valve  52  is closed to shut off the supply of air through the nozzle  60 , and the reciprocating means  34 ,  40  is also shut off, to create a steady state condition in the band  28 . Then, the tension on the band  28  is adjusted, by turning the adjustment handles  56 ,  58 , until a predetermined band length is obtained between two reference points  70 ,  72 , as indicated on the length measuring device  42 . This predetermined band length should correspond to a known measurable gap in the piston ring  68 . When the predetermined band length is reached, a reading can be taken from the tension measuring device  45 . When using the master ring, the reading on the tension measuring device  45 , at this stage, should be a predictable and constant value such as the 2.000 kgf shown on the readout of the tension measuring device in FIG.  4 . If the reading varies from the expected value, the readout of the tension measuring device  45  may be adjusted to the expected value. 
     After reading the master ring, an unknown ring may then be substituted into the groove gauge fixture, and the process repeated until a reading on the tension measuring device is obtained for the unknown ring, at the same predetermined band length. 
     ALTERNATIVE EMBODIMENT 
     Referring now to FIGS. 8A and 8B, an alternative embodiment of an apparatus  120 , in accordance with the present invention, is shown. The apparatus  120  in this second embodiment is substantially identical to that shown and described herein with respect to the apparatus  20  according to the present invention, except that in this second embodiment, instead of the bore  54  being formed through the work support plate and communicating with the nozzle  60 , as in the first embodiment, a flexible hose  154  connects the air delivery line  48 , downstream of the valve  52 , to the top of the groove gauge fixture  126 . 
     In this embodiment, the groove gauge fixture  126  has a hollow vertical bore  155  formed therethrough, and a small cylindrical tube  160  is welded on to, or otherwise fixedly attached to, the top of the groove gauge fixture  126 , adjacent the vertical bore  155  and in fluid communication therewith. The flexible hose  154  fits sealingly over the cylindrical tube  160 , to intermittently provide pulses of air from the air delivery system to the vertical bore  155  of the groove gauge fixture  126 . 
     As seen from a comparison of FIGS. 8A and 8B, when air under pressure is supplied to the vertical bore  155 , it passes outwardly from an outlet aperture  161  at the bottom of the vertical bore  155 , beneath the groove gauge fixture  126 . This outwardly expelled air pulse pushes the edge of the groove gauge fixture, on the right side in the drawing, upwardly away from the work support plate  124  from about ⅛ inch to about ¼ inch. When air stops flowing through the hose  154  and the vertical bore  155 , the groove gauge fixture falls, under its own weight, back into contact with the work support plate  124 . When the groove gauge fixture contacts the work support plate  124 , it creates a tapping action which helps to remove looseness caused by friction from the band loop  29 . 
     Although the present invention has been described herein with respect to specific preferred embodiments thereof, the foregoing description is intended to be illustrative, and not restrictive. Those skilled in the art will realize that many equivalent modifications of the preferred embodiments could be made which would be operable. All such modifications, which are within the scope of the claims, are intended to be within the scope and spirit of the present invention.