Abstract:
A fixture for measuring the resistance of a piston ring in a cylinder, comprising an elongate member having a first end and a second end and a central axis extending therebetween, and an expandable platform attached to the second end of the stem, the platform having a top surface facing towards the first end, the top surface being perpendicular to the central axis, the top surface including first, second and third points movable radially outward from the central axis, and methods of use thereof.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention pertains to a tool or a fixture for more easily measuring the drag of a piston ring in a cylinder and methods of use thereof. 
       BACKGROUND 
       [0002]    A piston ring is an open-ended or closed ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine. The three main functions of piston rings in reciprocating engines are sealing the combustion/expansion chamber, supporting heat transfer from the piston to the cylinder wall., and regulating engine oil consumption. Rings may be gapless or gapped. The gap in a gapped piston ring compresses to a few thousandths of an inch when inside the cylinder bore. 
         [0003]    Most automotive pistons have three rings: The top two while also controlling oil are primarily for compression sealing (compression rings); the lower ring is for controlling the supply of oil to the liner which lubricates the piston skirt and the compression rings (oil control rings). Typical compression ring designs will have an essentially rectangular cross section or a keystone cross-section. The periphery will then have either a barrel profile (top compression rings) or a taper form (second compression rings). There are some taper-faced top rings and on some old engines simple plain faced rings were used. 
         [0004]    Oil control rings typically are of three types: (1) single piece cast iron, (2) helical spring backed cast iron or steel, or (3) multi-piece steel. The spring backed oil rings and the cast iron oil rings have essentially the same range of peripheral forms which consist of two scraping lands of various detailed form. The multi-piece oil control rings usually consist of two rails or segments (these are thin steel rings) with a spacer expander spring which keeps the two rails apart and provides the radial load. 
         [0005]    During certain engine building , rebuilding or repair procedures, the resistance or drag of a piston ring in a cylinder bore is measured. In the typical prior art method, the piston ring is placed on the piston, which is then inserted into the cylinder bore. The piston is then attached to a spring weighing scale and pulled out of the piston. The resistance of the ring is related to the weight measurement on the scale. This can be an inconvenient or ungainly procedure and thus there is need for a fixture which allows a procedure which is more convenient and faster than the method described above. 
       SUMMARY 
       [0006]    Embodiments pertain to fixtures and methods for performing a piston ring resistance test. An adjustable fixture is substituted for the piston and one or more piston rings are placed on the fixture, and the resistance of the rings is measured while the piston ring or rings is pulled out from the piston cylinder. A spring scale, strain gauge with digital readout or other suitable device is used to measure the resistance or drag caused by the piston ring. 
         [0007]    One fixture according to an embodiment includes a stem for connecting a force measurement device to a platform for carrying one or more piston rings. The platform may include a central plate and a plurality of arms rotably connected to the central plate. The arms may be rotated outward to adjust the size of a piston ring carrying surface. The piston ring carrying surface is preferably flat, perpendicular to the stem and facing the stem. There may be two, three or more arms. The arms may be disposed in a radially symmetric fashion about the stem. The arms may have a thickness that is at least 0.3, 0.4, 0.45, 0.469, 0.5, or 0.6 inches. The arms may have a curved outer profile such as that of a circle arc segment or a French curve. The arms may be fixable in place after adjustment through the use of screws, a clamp or the like. 
         [0008]    One method of use involves adjusting the arms of the fixture so that the fixture just fits within the particular cylinder bore that is part of the test. The outermost part of each arm should preferably extend a distance away from the central axis that is slightly less than the radius of the cylinder bore. Further, the outermost part of the arm should also extend far enough out from the central axis so that the arms can support the piston ring or rings being tested. This means that each arm should extend out from the central axis such that the outermost part of the arm is further away from the central axis than the inner radius of the piston ring. When adjusted properly there arms are able to support the piston cylinder while having a small gap between the arms and the cylinder bore when the fixture is inserted into the cylinder bore. When the arms are properly positioned, they may be fixed in place, by tightening the fasteners as appropriate. A piston ring is disposed on the piston ring support surface of the arms and the fixture is inserted within the cylinder bore. The fixture is pulled directly out through the cylinder bore while making readings using a force measurement device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an isometric view illustrating a fixture  10  according to a first embodiment; 
           [0010]      FIG. 2  is an isometric view of the bottom of fixture  10 ; 
           [0011]      FIG. 3  is a view of fixture  10  having a piston ring disposed thereon; and 
           [0012]      FIG. 4  illustrates fixture  10  having a piston ring thereon and disposed in a cylinder bore. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  illustrates a first embodiment of a fixture  10  for measuring the force or drag of piston rings in a cylinder bore. Fixture  10  may include a plate  12  have a plurality of arms  14  attached thereto. A central axis  16  runs through the center of and perpendicular to plate  12 . A stem  18  is attached to plate  12  and preferably runs along the central axis  16 . The arms  14  are preferably rotatably attached to plate  14  at points  20  by a screw, nut and bolt or other fastener that can be tightened and loosened. 
         [0014]    A force measurement device  30  may be attached to the stem  18  opposite the plate  12 . The force measurement device may be any suitable device that can measure force along axis  16 . A digital device with a strain gauge and a spring scale are examples of suitable force measurement devices. 
         [0015]    In the embodiment shown, there are three arms  14 , and the three arms  14  are disposed in a radially symmetric fashion about the central axis  16 . Each of the arms rotates about an axis that passes through a respective point  20  and which is parallel to the central axis  16 . This allows the arms to rotate outwards as illustrated by the three arrows in  FIG. 2  so that the arms  14  are nearer to or farther away from the central axis  16  as desired. The arms  14  collectively define a top surface  32 . This surface is preferably flat and perpendicular to axis  16 . The top surface  32  is used to support one or more piston rings during a measurement procedure. It can be appreciated that by adjusting the arms, piston rings of various sizes can be supported. The arms preferably have a curved outer profile. This curved outer profile may be in the shape of an arc segment of a circle or in the shape of a French curve. In the embodiment shown, the arms have an outer profile in the shape of an arc segment of a circle. The arms are arranged relative to each other such that there is a position of the arms where the outer profiles of the arms define portions of the same circle. While the embodiment shown illustrates three arms  14  arranged in a radially symmetric manner, it can be appreciated that in other embodiments there may be fewer or more arms and the arms need not be arranged in a symmetric fashion. 
         [0016]    In the embodiment shown the arms  14  are attached to the plate using screws, bolts or the like, which are tightened or loosened as desired to allow for adjustment of the fixture. In another embodiment, the arms  14  are rotatably attached to the plate  12  tightly enough so that the arms  14  stay in place but where the arms may be adjusted without adjusting the fasteners. In other words, in this contemplated embodiment, there may be a degree of friction between the arms  14  and the plate that may be overcome manually to adjust the position of the arms. 
         [0017]    The stem  18  may be a rigid elongate element as shown in the figures or may be a flexible element such as a chain. 
         [0018]    The plate  12  and arms  14  may have each have a thickness. For example, the plate  12  may have a thickness that is at least 0.3, 0.4, 0.45, 0.469, 0.5, or 0.6 inches and each of the arms  14  may have a thickness that is at least 0.3, 0.4, 0.45, 0.469, 0.5, or 0.6 inches. Each of the arms  14  preferably has the same thickness and the arms  14  may or may not have the same thickness as the plate  12 . The outer profile  28  of the plate  12  may extend parallel to axis  16 . In one preferred embodiment, the plate has a circular outer profile. The outer profiles of the arms  14  may also extend parallel to axis  16 . The shapes of the plate  12  and arms  14  together with their thickness may effectively orient the fixture properly within the cylinder bore. 
         [0019]    With reference to  FIGS. 3 and 4 , in use, the arms  14  may be adjusted to just fit within the particular cylinder bore  38  of the engine block  36  that is part of the test. The outermost part of each arm  14  should preferably extend a distance away from the central axis  16  that is slightly less than the radius of the cylinder bore  38 . Further, the outermost part of the arm  14  should also extend far enough out from the central axis  16  so that the arms  14  can support the piston ring  34  being tested. This means that each arm  14  should extend out from the central axis  16  such that the outermost part of the arm  14  is further away from the central axis  16  than the inner radius of the piston ring  34 . The idea is to support the piston ring  34  with the arms  14  while being able to have a small gap between the arms  14  and the cylinder bore  38  when the fixture  10  is inserted into the cylinder bore  38 . When the arms  14  are properly positioned, they may be fixed in place by tightening fasteners as appropriate. The fixture  10  may be attached to a force measuring device  30 . A piston ring  34  may be disposed on the top surface  32  of the arms  14  and the fixture  10  is then inserted within the cylinder bore  38 . The fixture  10  may then be pulled through the cylinder bore  38  along axis  16  while making readings using the force measurement device  30 . 
         [0020]    In another example method of adjusting the arms, the arms may be adjusted so S that the outermost tips of the arms are within the ring created by two circles, the first circle having a diameter equal to the outer diameter of the piston ring and the second circle having a diameter having a diameter equal to the inner diameter of the piston ring. Such a method may allow one to adjust the arms on a template, for example. 
         [0021]    In another method of use, two or three piston rings  34  are stacked on the top surface  32  of arms  14 , and the process of measurement as described above is made while the several rings  34  are on the fixture. 
         [0022]    There have been described and illustrated herein several examples of a fixture and methods of use thereof. While particular embodiments and applications of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, while particular dimensions and configurations have been disclosed, it will be appreciated that others could be utilized. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as so claimed.