Method and apparatus for forming surfaces on piston rings

Apparatus is described for machining the exterior peripheral surface of piston rings for internal combustion engines, particularly piston rings having a transverse shape other than circular, for example, oval or elliptical. A jig arrangement usable with the apparatus is adapted to temporarily deform the workpieces in order to produce exterior surfaces having a conical taper.

BACKGROUND OF INVENTION 
The field of the present invention is the production of piston rings for 
use in internal combustion engines. 
In conventional internal combustion engines, pistons are employed which 
typically include a circular transverse sectional shape. Piston rings used 
with such pistons are themselves circular and are easily formed. The 
exterior surface of such rings may be easily finished by simply rotating a 
stack of piston ring blanks about the axial centerline thereof while 
applying a cutting tool to the exterior surface. 
Internal combustion engines have also been developed which employ cylinders 
and pistons located therein which are noncircular in transverse section. 
These cylinders are elongated in plan in order to accommodate the more 
efficient intake and exhaust valve arrangement providing greater effective 
port area. One such device is illustrated in U.S. Pat. No. 4,350,126, 
granted Sept. 21, 1982 to Shoichi Honda, the disclosure of which is 
incorporated herein by reference. The corresponding piston rings for such 
noncircular pistons are, of necessity, also noncircular, being oval, 
elliptical or otherwise of an elongated shape. Consequently, the exterior 
surface of such rings cannot be formed by the aforementioned conventional 
procedure. 
In certain circumstances, piston rings have been used which employ an 
external peripheral surface that is conically tapered. The foregoing 
problem of not being able to easily machine piston rings of noncircular 
plan is compounded in that the ring blanks cannot be coaxially stacked in 
a single jig. Instead, they must be stacked with spacers in between each 
ring blank. Specialized rotary cutting tools having a series of precisely 
formed cutting teeth of conical shape have been employed. Such devices are 
illustrated in FIG. 7. Processing the piston ring blanks in this manner to 
achieve a conical exterior surface is disadvantageous because of the 
required effort to assemble and disassemble the blanks and spacers from 
the jig and because of the expensive tooling required. 
SUMMARY OF THE INVENTION 
The present invention is directed to an improved method and apparatus for 
the production of piston rings for internal combustion engines. According 
to a first aspect of the present invention, rings of noncircular plan may 
be finished through controlled displacement of a cutting tool relative to 
angular orientation of the work piece. To this end, the apparatus may 
include a jig rotatable about an axis normal to the plan of the ring 
blank. A cutting tool may be controlled to move perpendicular to that axis 
relative to the angular orientation of the jig. The jig may further 
include mechanisms to enhance the location and removal of pluralities of 
work pieces. 
According to a second aspect of the present invention, method and apparatus 
are provided capable of machining a conical taper on the exterior 
peripheral surface of piston ring blanks. To this end, a jig may be 
employed having a reduced diameter portion with a transverse sectional 
shape conforming to the internal shape of the ring blanks to be processed. 
The blanks, being flat, relatively thin, cylindrical members are 
relatively resilient to movement of the inner periphery axially relative 
to the outer periphery. The jig may employ this resilience by providing 
outwardly extending conical faces, between which may be positioned the 
ring blanks. Distortion of the blanks between the conical faces is such 
that, when deformed, a cylindrical surface may be machined from the 
exterior surface of the ring blanks. When released, the exterior surface 
of each ring assumes a conical configuration. 
It is, therefore, an object of the invention to provide a method and 
apparatus for production of ring-shaped workpieces, such as piston rings 
for internal combustion engines. For a better understanding of the 
invention, its operating advantages and the specific objectives obtained 
by its use, reference is made to the accompanying drawings and description 
that relate to the preferred embodiments thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With particular regard to FIGS. 1 to 4, the illustrated internal combustion 
engine includes a piston 1 whose transverse sectional shape is 
non-circular, being formed with an oblong cylinder curvature obtained by 
joining points spaced distally in a direction normal to a reference curve 
having continuous curvature. Pistons having a transverse section that is 
substantially oval or elliptical may also be employed. On the peripheral 
surface of the piston 1, are formed a plurality of parallelly disposed 
grooves 2 for reception of piston rings 3. 
As shown in FIGS. 2 and 4, the piston ring has a substantially continuous 
body having parallel upper and lower surfaces 5 and inner and outer 
peripheral surfaces 6 and 7, respectively, whose transverse shape is 
elliptical or one that approximates an ellipse. The blanks for the piston 
rings, indicated as 4, can be individually formed by casting or pressing, 
or can be cut in round slices from a hollow casting. The inner surface of 
each piston ring 3 is precisely finished to the desired shape by broaching 
or by profile cutting of the blank through the medium of electric 
discharge cutting. As shown in FIG. 4, the piston rings 3 preferably 
possess a transverse slot 8 to permit their assembly into the piston 
grooves 2. 
The exterior peripheral surface 7 of the blanks 4 forming rings 3 is 
machined employing apparatus 10 illustrated generally in FIGS. 5 and 6. 
Such apparatus includes a workpiece supporting jig 11 whose exterior 
surface conforms, or may be slightly larger for fitting considerations, to 
the inner surface 6 of the blanks 4. The jig 11 is adapted to mount a 
plurality of ring blanks 4 arranged in a stack. As shown in FIG. 6, the 
jig 11, according to one aspect of the invention, is a body having an 
axial bore 12 and a base that is detachably secured to a turntable 14 by 
means of bolt 15. The jig 11 is coaxially positioned on the turntable 14 
and fixed for rotation therewith. The turntable 14 is adapted to be 
rotatably driven at a suitable angular velocity by turning and driving 
mechanisms (not shown). 
The jig 11 is attached to the turntable 14 by means of a clamping 
arrangement which includes a connector 17 adapted to fit into an enlarged 
diameter portion of the bore 12. The connector 17 threadedly receives the 
lower end of a headed clamp bolt 19. As shown, springs 16 encircle the 
bolt 19 and are disposed in a space between the facing surfaces of the 
connector 17 and the enlarged bore portion 13. The head of the bolt 19 
clampingly engages a transversely slotted clamp washer 18 against the 
upper end of the jig 11 for axially securing the stacked ring blanks 4 
thereto. 
Mounted on the turntable axis A within space provided therein beneath the 
connector 17 is a clamp operator comprising hydraulically activated 
cylinder 20 having an extendable piston adapted to engage the adjacent end 
of the connector and to move it upwardly against the force of the springs 
16. During operation of the apparatus 10 the piston in cylinder 20 is in 
its retracted position whereby the connector 17 and clamp bolt 19 are 
urged downwardly by the springs 16 to secure the stacked ring blanks 4 to 
the jig 11. Actuation of the cylinder 20 extends the piston into 
engagement with the connector 17 for moving it and the actuated clamp bolt 
19 axially upwardly whereupon the clamp washer 18 can be laterally removed 
from beneath the bolt head and the blanks released from the jig 11. 
The stationary support for the turntable 14 includes a laterally spaced 
upstanding portion 21 within which is positioned a hydraulically operated 
lifting cylinder having an axially movable and rotatable piston spindle 
23. The spindle 23 fixedly secures a work overarm 24 on the base of which 
is a positioning projection 25 adapted to fit in a recess 26 in the upper 
face of the support portion 21. When the spindle 23 is extended, the 
projection is raised from the recess 26, following which, rotation of the 
spindle 23 permits the overarm to be rotated out of its operational 
position. The upper surface of the support portion 21 may be formed as a 
sliding surface to permit the lower end of the projection 25 to engage the 
surface in order to provide support for the overarm 24 in its 
non-operational position. 
The overarm 24 carries at its upper end a clamp joint in the form of a 
spring biased, shouldered centering pin 27 having a conical tip adapted 
for reception in a mating recess in the head of clamp bolt 19. With the 
overarm 24 in its operation position the pin 27 provides axial support for 
the upper end of the assembled jig and clamp assembly. 
Oppositely adjacent the overarm 24 is a movable toolholder 28 for mounting 
a milling cutter 29. The toolholder 28 supports the cutter 29 at its ends 
such that it is caused to rotate about an axis parallel to the axis of the 
assembled clamp bolt 19. The cutter 29 is rotably driven by a motor (not 
shown). The toolholder is structurally mounted for movement by mechanism 
(not shown) in a straight-line direction, indicated as X, perpendicular to 
the axis A of the clamp bolt 19. 
A computer (not shown) controls the driving mechanism of the turntable 14 
and the mechanism for moving the toolholder 28. The computer is designed 
to calculate the turning angle of the turntable 14 and the amount of 
displacement of the milling cutter axis required to form the desired 
external peripheral surface 7 on the workpiece blanks 4. 
The apparatus 10 disclosed in FIGS. 5 and 6 is operated as follows. With 
the stack of ring blanks 4 assembled on the jig 11, the milling cutter 29 
and turntable 14 are rotatively driven at substantially constant 
velocities about their respective axes and the computer is activated. A 
control signal from the computer causes the toolholder 28 to move the 
milling cutter 29 in the X direction perpendicular to the turntable axis 
which corresponds to the axis A of the clamp bolt 19. Movement of the 
toolholder 28 in the X direction is thereafter controlled in response to 
the calculated position of the exterior peripheral surface of the stacked 
blanks as they rotate with the turntable 14. Therefore, the exterior 
peripheral surface 7 of the blanks 4 can be accurately formed to the 
desired elliptical shape. 
Thus, since the inner peripheral surfaces 6 of the blanks 4 for the rings 3 
are initially accurately formed and since their surfaces are constrainedly 
fitted on the jig 11, the processing accuracy of the exterior surface 7 is 
high. 
In the disclosed arrangement, since the position in the X direction of the 
milling cutter 29 with respect to the axis A of the turntable 14 as the 
milling cutter and turntable are driven, is controlled by means of 
numerically controlled operation of the computer to coincide with the 
desired shape of the exterior surface of the blanks 4, deviation of the 
desired shape from a circular shape, as for example, to an elliptical 
shape, can be accurately obtained. 
While the above description involves use of a numerically controlled 
controller for determining the relative position in the X direction of the 
milling cutter 29 with respect to the central axis of the clamp bolt 19, 
it should be understood that the invention also contemplates formation of 
the outer peripheral surface 7 of the piston rings 3 by means of profile 
copy processing. In such case, a profile copy model formed in a shape 
identical to the desired shape of the external peripheral surface 7 of the 
piston ring 3 or in a shape along a curve obtained by joining points 
spaced a predetermined distance in a direction normal to the curve of the 
surface 7 can be mounted coaxially by the turntable 14 with a disc having 
the same diameter as the cutter 29 mounted coaxially thereof. Thus the 
profile copy is obtained by causing the disc to follow the model. 
According to the foregoing description, the exterior peripheral surface of 
non-circular ring-like blanks can be easily and positively formed with a 
high degree of accuracy into the desired shape by suitably turning the 
workpieces about their central axis and moving the rotating cutter for 
forming the outer surface in the lateral direction in response to rotation 
of the workpieces. Accordingly, the productivity of piston ring production 
can be improved by increased accuracy and reduced cost. 
The above described apparatus can be readily adapted for forming the 
exterior peripheral surface of piston rings having conically tapered 
surfaces rather than cylindrically-formed surfaces, thereby avoiding the 
need to employ less effective production means, such as that illustrated 
in FIG. 7. As shown, this prior art means involves the coaxial mounting of 
the plurality of blanks 30 to be processed on a rotatable mandrel 31 with 
reduced diameter spacers 32 interposed between each blank and wherein the 
desired taper is cut into the cylindrical surface by means of a 
specialized tool 33 having blades 34 with tapered peripheries that may be 
attached to an engine lathe or the like. Such production means is 
undesirable for the intended purpose in that, since the spacers 32 are 
required to separate each blank 30, the time and effort required to 
install and remove the blanks with respect to the mandrel is 
objectionable. Also, the need for a specialized cutting tool having blades 
provided with accurately formed, shape conforming cutting edges, increases 
tool costs whereby production costs increase. 
FIG. 8 illustrates an exploded view showing the jig device according to 
this aspect of the invention as comprising a jig body 35 and a clamp plate 
36 adapted for attachment thereto. The jig body 35 has a large diameter 
portion 37 and a reduced diameter portion 38 extending therefrom. The 
transverse sectional shape of the reduced diameter portion 38 is intended 
to correspond substantially with the inner peripheral shape of the ring 
blanks 4a to be processed. The reduced diameter portion 38 is axially 
elongated for receiving a plurality of blanks 4a in coaxially stacked 
array. As the illustrated jig device can accommodate blanks having inner 
peripheral surfaces that may be either circular or non-circular, the 
following description will be directed to a processing operation for 
blanks having a circular inner periphery, it being understood that blanks 
having a non-circular inner periphery can be similarly processed employing 
apparatus hereinbefore described. 
In the arrangement illustrated in FIGS. 7 through 12, the reduced diameter 
portion 38 of the jig body 35 is provided with a cylindrical shape having 
an outer diameter substantially equal to the inner diameter of the ring 
blanks 4a. The transition portion between reduced diameter portion 38 and 
large diameter portion 37 is formed as a shoulder 39 having a conically 
tapered surface facing the reduced diameter portion. The angle .theta. 
that the surface of shoulder 39 makes with respect to a plane normal to 
the axis of the reduced diameter portion 38 is substantially equal to the 
angle .theta. (FIG. 11) of the taper to be formed on the outer peripheral 
of the ring blanks 4a. The axial end 43 of the reduced diameter portion 38 
is a flat surface extending normal to the axis of the body 35. Its 
peripheral edge 44 is preferably conically formed with a taper inclined at 
the angle .theta.. 
Clamp plate 36 has a cylindrical exterior of a diameter substantially the 
same as the portion 37 of the jig body 35. The upper surface of the clamp 
plate 36 is provided with a dish-like recess 40, an annular peripheral 
edge portion of which has a conically tapered surface 41 inclined at the 
same angle .theta. as that of the surface of the jig body shoulder 39. The 
central portions of the recess 40 presents a circular bottom surface 42 
extending normal to the axis of plate 36 and adapted to engage the axial 
end face 43 of the reduced diameter portion 38 of jig body 35. 
The clamp plate 36 is adapted to be detachedly connected to the end of the 
reduced diameter portion 38 of jig body 35 by means of bolts 45 that 
extend through holes 46 in the plate and whose threaded ends engage 
corresponding threads in holes 47 that penetrate the end surface 42 on the 
jig body 35. 
It will be appreciated that, when the clamp plate 36 is attached to the jig 
body 35, the respective tapered surfaces 39 and 41 on each project 
radially outwardly from the peripheral surface of the reduced diameter 
portion 38 and in facing parallel relation to each other. 
In processing the ring blanks, first, as shown in FIG. 9, a plurality of 
blanks 4a, having unprocessed, generally cylindrical outer peripheral 
surfaces 48 are stacked upon the reduced diameter portion 38 of the jig 
body 35. Following this, the clamp plate 36 is attached by means of bolts 
45 to the end of the jig body 35. Thus, the stacked ring blanks 4a are 
clamped between the opposed, conically tapered surfaces 39 and 41 
whereupon, as shown in FIG. 10, the blanks 4a are caused to deform 
resiliently into a conical shape conforming with the shape of the surfaces 
39 and 41. 
The taper angle .theta., shown exaggeratedly in the respective drawing 
figures is in practice, an angle of from 1 to 3 degrees. Accordingly, due 
to the resiliency in the axial direction of the ring blanks 4a, the 
required deformation is readily achieved and, as shown best in FIG. 11, 
when the deformation is accomplished, the outer peripheral surface 50 of 
each blank 4a is caused to be inclined at the angle .theta. with respect 
to a line parallel to the axis of each blank. The entire assemblage of 
ring blanks 4a at this stage of the procedure presents a serrated outer 
peripheral surface. 
Following this, the assembled jig carrying the plurality of deformed blanks 
4a is mounted on a turntable, such as that shown at 14 in FIGS. 5 and 6, 
for rotation about the central axis, indicated as 1 in FIG. 10, and 
rotatingly brought to bear against the cutting edge of milling cutter 51, 
or the like, having a rotation axis L' parallel to the rotation of the 
turntable-mounted jig axis L. The outer peripheral surfaces 50 of the 
stacked blanks 4a so-machined becomes a cylindrical surface, as shown by 
the dotted line C in FIG. 11. This cylindrical surface is inclined at the 
angle .theta. to the original outer peripheral surfaces of the blanks and 
to their upper surfaces 52. 
Removal of the machined ring blanks 4a from the jig, due to the resiliency 
of their material returns them to their original, flat shape as shown in 
FIG. 12. The original cylindrical outer peripheral surface 50 of FIG. 11 
becomes a surface 50' that is conically tapered at the angle .theta.. 
FIG. 13 illustrates another embodiment of a jig structure useful in the 
described invention. In this embodiment, the ring blanks 4a are mounted on 
a jig arrangement in two groups, indicated as 4a' and 4a". Reference 
numeral 35a indicates a jig body similar to the body 35 in the previously 
described embodiment. To the jig body 35a is clamped a second jig body 35b 
provided on its upper end with an enlarged diameter portion 37a containing 
a conically tapered, dish-like recess similar to the recess 40 of the 
previously described clamp plate 36. The ring blanks 4a are clamped and 
deformed between the conically tapered surfaces 39a and 41a on the 
respective jig bodies. Also, the jig body 35b is provided with a conically 
tapered surface 39b similar to the surface 39 of the previously described 
jig body and mounts a clamp plate 36' that is substantially the same as 
the clamp plate 36. The other group of ring blanks 4a" is mounted between 
the conically tapered surfaces 39b and 41 on the enlarged diameter portion 
37b and the clamp plate 36, respectively. Clamping pressure for the 
assemblage is provided by the axial force developed between an axially 
disposed headed clamp bolt 53 whose shaft extends through holes in the 
members 35a and 35b and a bolt 8' similar to the previously described 
bolts 8, that threadedly engages the end of the clamp bolt 53. By 
arranging the ring blanks 4a in two groups, as shown, a greater number of 
blanks can be readily and more positively deformed. 
As previously mentioned, the above described invention is equally adaptable 
to accommodate non-circular ring blanks for machining of their exterior 
peripheral surfaces by means of the apparatus described in FIGS. 1 through 
6. In such case, the profile shapes in the transverse section of the 
reduced diameter portion 38 of the jig body 35 and the conically tapered 
surfaces 39 on the jig body 35 and 41 on the clamp plate 36, are provided 
with a transverse shape conforming with that of the ring blank to be 
processed. The cutting process may be performed by a numerically 
controlled milling cutter as described in connection with FIGS. 1 to 6 
hereof wherein, as shown in FIG. 10, the rotational axis L' of the cutter 
51 may be moved transversely forward and backward with respect to the axis 
L as shown by the arrow "a". Alternatively, of course, the axis L could be 
similarly moved with respect to the axis L'. 
From the foregoing description, it will be appreciated that the present 
invention provides improved means for machining the exterior peripheral 
surfaces of large numbers of piston ring blanks on a production scale and 
in a manner that positively insures the accuracy of the surface being 
unachieved. 
It will be understood that various changes in the details, materials and 
arrangement of parts which have been herein dboltibed and illustrated in 
order to explain the nature of the invention, may be made by those skilled 
in the art within the principle and scope of the invention as expressed in 
the appended claims.