Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to connecting rods. More
particularly it relates to con~ecting rods used in
internal combustion engines and compressors to connect a
crankshaft to a piston.
In conventional internal combustion engines,
r~nnPct;ng rods transmit the reciprocating motion of the
pistons to the cranksha~t and thereby convert it to
rotary motion. For ease of assembly, the rod is usually
formed with a main shank that has a top bore for
receiving a p~ston connector and a lower part that
partially surrounds the crankshaft. The rod also has a
cap which extends the rest of the way around the
crankshaf t . The cap and shank are bolted together to
sandwich the crankshaf t .
Connecting rods are subj ect to stress, shock and
temperature (and thus wear) as they rapidly change from
being compressed to being tensed. Moreover, it is highly
desirable to make the connecting rods as light as
possible. This has lead to the use of aluminum, other
lightweight metals and even plastic. However, the use of
these materials creates other design problems.
The invention provides a structure for aligniIIg the
shank portion and the cap portion of a connecting rod
which requires little or no machining on the adj oining
faces of these two portions. This is particularly
helpful in the case of connecting rods made by an
extrusion process. Previously known connecting rods
require machining the alignment features of the shank and
cap parts to provide the precise tolerances needed to
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ensure full alignment of the alignment features. An
alternative approach has been inltially making the piston
rod i~ one piece and then broaching or fracturing it into
two pieces which have alignment features which
necessarily fit precisely together. Eliminating these
operations and using the parts "as is" can dramatically
reduce the manufacturing costs for: the connecting rod
because perfecting the fit of the alignment features
accounts for a substantial portion of the cost of
manuf acturing a prior art rod .
More specif ically, the invention provides a
connecting rod for linking a piston to a movable part of
a crankshaft assembly, the connecting rod comprising:
(a) a shank having a first end adapted for
connection to the piston and a forked opposite end having
a first leg and a second leg which define an arcuate
inner shank surf ace;
(b) a forked cap having a first arc-end and a
second arc-end which define an arcuate inner cap surface,
the inner shank surface and the inner cap surface forming
an aperture f or receiving the movable part when the shank
and the cap are adjoined;
(c~ wherein an end of the first shank leg or the
first arc-end is a tapered tongue having a planar first
tongue wall and a planar second tongue wall which slant
toward each other, and wherein an end of the other of the
first shank leg or the first arc-end has a tapering
groove having a planar first groove wall and a planar
second groove wall which slant toward each other, the
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tongue and the groove being f ormed so that when the shank
and the cap are adjoined to form the aperture the tongue
is engaged in the groove and the only contact between the
first shank leg and the first arc-end is a co-planar
first junction between the first tongue wall and the
first groove wall and a co-planar second junction between
the second tongue wall and the first groove wall;
(d) wherein the second shank leg culminates in a
single, planar shank wall and the second arc-end
culminates in a single, planar arc-end wall, the shank
wall and the arc-end wall abutting each other in a co-
planar third j unction when the shank and the cap are
adjoined to form the aperture; and
(e) a fastener adapted to secure the shank and the
cap together to form the aperture.
In one aspect, the two protrusion walls do not
intersect but rather are truncated ~o that the protrusion
has a clipped V-6hape. In another aspect, the protrusion
walls are at right angles to each other, and the
indentation walls are at right angles to each other.
These and still other objects and advantages of the
invention will be apparent from the description which
follows. The preferred embodiments will be described in
reference to the accompanying drawings. These
embodiments do not represent the full scope of the
invention. Rather, the invention may be employed in
other embodiments . Ref erence should therefore be made to
the claims herein f or interpreting the breadth of the
invent ~n.
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In the drawings:
Fig. 1 shows connecting rods embodying the present
invention installed in a V-2 engine;
Fig. 2 is a side elevational view of a connecting
rod o~ the present invention with fragments of the piston
and crankshaft showing;
Fig. 3 is an enlarged partial cross-sectional view
taken along line 3-3 o~ Fig. 2;
Fig. 4 is an enlarged side elevational view, with
parts broken away showing the j unctions of the shank and
the cap prior to fastening them together with the bolt;
Fig. 5 is similar to Fig. 4 except that the bolt has
been f astened;
Fig. 6 is an enlarged cross-sectional view showing a
preferred embodiment of the male/female junction;
Fig. 7 is an enlarged cross-sectional view of
another embodiment of that junction;
Fig. 8 is a schematic view of the preferred
extrusion process;
Fig . 9 is a schematic view of the pre~erred f ine
blanking process i
Figs. 10-12 illustrate three two-bolt connecting
rods which embody the alignment structure claimed herein;
and Fig. 13 illustrates an aluminum fastener.
Fig. 1 shows a two cylinder internal combustion
engine 8 having a connecting rods 10 embodying the
present invention. Each connecting rod 10 preferably
includes only three parts: a shank 12, an arcuate cap 14
and a bolt 16
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Shank 12 comprises an elongated central portion 17
which supports at one end an enlarged head 18 and at the
other end an enlarged cap -mounting portion 2 0 . The head
18 is conventionally formed to suitably receive a pin 22
of an engine piston 24. The cap-mounting portion 20 is
bifurcated into two legs, lugged leg 26 and ;n~ ntf~d
"female" leg 28. The facing, inner surfaces of legs 26
and 28 form a semicircular surface 30 which forms one-
half of the aperture for receiving the crankpin 32 of the
engine crankshaf t .
Lugged leg 26 o~ shank 12 extends outward and
downward (as viewed in Fig. 2) from central portion 16 in
an arcuate manner. The outer surface 34 bulges outward
at the end of leg 26 to form thumblike lug 36. Lug 36
includes a flat lower surface 38, which forms the bottom
of leg 26 and which merges into a semi-circular outwardly
protruding surface 40.
The outer surface 42 of leg 28 curls outward and
downward to form a lower leg 44. Lower leg 44 has an
internal threaded bore 46 whose longitudinal axis is
perpendicular to line 47 which extends between the lower .
ends 48 and 49 of the facing inner sur~aces of legs 26
ard 28 respectively.
In the embodiment of Fig. 6, the lower 6urface of
lower leg 44 is indented by a "female" groove 51 having
sloping sides 50 and 52 which join at valley 54. The
sides 50 and 52 of the groove may be straight as shown in
the figures, or they may be curvilinear. As will be
seen, the indented lower ~surface of lower leg 44 serves
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as a female component of a male/female mounting junction,
and in one particular aspect, as groove 51 o~ a tongue-
in-groove connection.
The second component of connecting rod 10, cap 14,
has a generally arcuate shape which comprises hook arc-
end 56 and male arc-end 58. The inner facing surfaces of
arc-ends 56 and 58 form a semi-circular surface 60 which
join with semi-circular surface 30 of shank 12 to form
the complete aperture for the crankpin 32.
~ ook arc-end 56 culminates in a hook 62 which (as
viewed in Fig. 2) curls upward and then inward. The
inner surface of hook 62 includes flat surface 64 which
can be aligned with flat surface 38 of lug 36 and a semi-
circular surface 66 which can be arlgned with semi-
circular sur~ace 40 of lug 36.
Male arc-end 58 of cap 14 has an internal through
bore 68 which is coaxially alignable with bore 46 when
cap 14 is fastened to shank 12. In the embodiment of
Fig. 6, the upper end of male arc-end 58 is tapered and
includes slanting sides 70 and 72 (referred to in the
claims as "planar first tongue wall" and "planar second
tongue wall" respectively) which are designed to align
with sides 50 and 52 (referred to in the claims as
"planar first groove wallU and "planar second groove
wall~ respectively) which form the groove in the end of
lower leg 44 of cap 14. As shown in Figs. 2, 4, 5 and 6,
the only areas of contact between leg 28 of the shank 12
and arc-end 58 of the cap 14 are the co-planar f irst
junction of slanting side 50 of lower leg 44 with
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slanting side 70 of arc-end 58 and the co-planar second
junction of slanting side 52 of lower leg 44 with
slanting side 72 of arc-end 58. That is, there are no
surfaces of lower leg 44 or arc-end 58 which are in
contact other than slanting sides 50 and 70 and slanting
sides 52 and 72 respectively. The peak or tongue 73 of
the tapered end is truncated by flat surface 74.
Fig . 7 shows another embodiment of the j unction of
lower leg 44 of the shank 12 with male arc-end 58 of cap
14. In this embodiment, lower leg 44 and male arc-end 58
have abutting surfaces 76 and 78 respectively which
adjoin sides 52 and 72 respectively and which are at
least partially transverse to the direction of sides 52
and 72. Alternatively, surfaces 76 and 78 could adjoin
surfaces 50 and 70 respectively.
The third and f inal ~ nmrnnC-nt of connecting rod 10
is threaded bolt 16. :~t is made of steel and is chosen
to be able to slidably move through bore 68 of arc-end 58
and to be threadably inserted into bore 46 of lower leg
44 of shank 12.
To assemble the conn~;n~ rod, semi-circular
surface 66 of hook 62 is juxtaposed to surface 40 of lug
36, and sides 50 and 52 of the groove of lower leg 44 are
juxtaposed with sides 70 and 72 respectively of male arc-
end 58. Bolt 16 is inserted from the bottom of male arc-
end 58 through bore 68 and is screwed into bore 46 of
lower leg 44.
In one aspect of the invention, the tongue 73 of
male arc-end 58 is slightly inset toward the crankpin
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aperture relative to the groove 51 of lower leg portion
44. For example, in one embodiment, the distance from
the outermost point on lug 36 to the middle of tongue 73
is 51. 3 millimeters while the corresponding distance to
the middle of groove 51 is 51 5 millimeter6.
As a resuit, when cap 14 is loosely juxtaposed
against the legs of shank 12, bores 68 and 46 do not
perfectly align and the crankpin opening is slightly out
of round. Tightening screw 16 cau6es male arc-end 58 to
move toward lower leg portion 44 approximately along an
axis perpendicular to line 47 and also causes cap 14 to
move to the lef t ( in the perspective of Fig . 2 )
approximately along the axis of line 47. This firmly
locks hook 62 against lug 3 6, rounds out the crankpin
opening and locks surface 72 against surface 52. The
resulting tension ~l;m;n;~hPf: the risk that bolt/fastener
16 will loosen and therefore continually maintains a
round crankpin opening.
To make the connecting rod shank by an extrusion
process as represented in Fig. 8, a die 80 is preferably
constructed which has the desired elevational (as in the
perspective of Fig. 2) shape. This die 80 is mounted at
the end of a heating chamber 82 into which a charge of
material, such as aluminum, is placed. The chamber is
then closed except for the outlet provided by the die.
The ~ m; nllm is then heated to a semi -molten state . The
semi-molten aluminum is then forced through the die hole
by an extrusion ram. As a result, there is extruded from
the die an aluminum piece 84 which has the Fig. 2
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elevational shape of the rr~nkR~ft shank. A saw 86 is
used to cut separate crankshaft shanks 87 each having the
desired width.
The one-bolt design, and the lack of any additional
parts, offsets the normal weight disadvantages of the
extrusion process. Also, the shapes of the connecting
portions of the apparatus aspect of=the present invention
are sufficiently rounded to be made effectively and
efficiently by such an extrusion process. Thirdly, the
nature of the present invention is such that relatively
loose tolerances can be used. The cap can be made in a
similar manner.
The connecting rod shank and cap of the present
invention may also advantageously be made using a "fine
blankingll process, which is represented schematically in
Fig. 9. A die plate 88 is formed to have an opening of
the size and shape of the periphery of the part. A punch
90 also of that size and shape is aligned with the
opening. In the opening of the die plate 88, there is a
moveable anvil 92, which is urged toward the punch by a
counterpunch pressure. A sheet 94 of material is
introduced between the punch 9 0 and the die plate 8 8 and
is immobilized relative to the die plate 88. The punch
90 is forced through the sheet of material and,
overcoming the counterpunch pressure, pushes a portion 96
of the material into the opening . The portion 9 6 has the
shape of the connecting rod part.
The male/female (also known aR tongue-in-groove)
junction illustrated in ~igR. 2, 4, 5 and 6 and described
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above may be employed (with or without a lateral offset)
in a two-bolt connecting rod as well as in a single-bolt
connecting rod as described above. Three embodiments of
such two-bolt connecting rods are illustrated in Figs.
10, 11 and 12_ In Figs. 10-12, ~he lower leg 44 of the
shank is the male component and the arc-end 58 of the cap
is the female component, which is the reverse of the
single-bolt embodiment shown in Figs. 2, 4, 5 and 6.
However, either arrangement of the male and female
components may be employed on any of the ~ nn~ t i n~
embodiments of the present invention. In Figs. 10-12,
t~e male slanting sides 70, 72 and the female slanting
sides 50, 52 are identified with the same numbers as used
for their counterparts in Figs. 2, 4, 5 and 6. They form
a V-junction 98.
It has been found advantageous to design the lower
leg 44 and the arc-end 58 80 that walls 70 and 72 are at
approximately right angles to each other, walls 50 and 52
are approximately at right angle~ to each other and the
area of contact between wall 70 and wall 50 is
approximately the same as the area of contact between
wall 72 ard wall 52. The tip 74 of the male portion of
lower leg 44 is truncated to avoid any contact between it
and the valley 54 of arc-end sa 80 that the only contact
is between slanting walls 70 and 50 and 72 and 52
respectively. The truncation of the tip 74 of the male
portion of the lower leg 44 leaves a non-contact space 99
between the tip 74 and the valley 54.
In the two-bolt embodiments of ~ig~. 10-12, the
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other junction (i.e., the junction of the lugged leg 26
of the shank with the hook arc-end 56 of the cap as seen
in Figs. 2, ~, 5 and 6) has been replaced by a single-
plane junction 100 To acco,mplish this, the thumb-like
lug 36 of leg 26 and the hook 62 of hook arc end 56 have
been eliminated so that the only point of contact between
leg 26a and arc-end 56a is the adjoining single plane of
surfaces 38 and 6a~ respectively. The junction 100
(referred to in the claims as ''co-planar third junction~)
is rn~int~;ner~ by a fastener, such as a bolt 16 ~ tf~ ;ng
longitudinally through a bore in leg 26a and arc-end 56a.
An advantage of the embodiments of Figs. 10-12 is
the elimination of the need to have precisely matching
features in the shank and the cap, thereby eliminating
machining, broaching or fracturing steps in the
manufacturing process. The V-junction 98 on one side and
the single-plane junction 100 on the other side allows
the shank and the cap portions to be used "as is"--i.e.,
as produced in the extrusion, blanking or casting
process. Specifically, if wall 70 and wa~l 50 (and/or
wall 72 and wall 52) deviated from single slanting
planes, so that the V-junction 98 included both slanting
walls and lateral surfaces, the piece~ would likely have
to be made or machined to precise tolerances to insure
that both the lateral surfaces and the slanting surfaces
were in full contact. Similar precision would be
re~uired on the other side if junction 100 included any
alignment feature.
In another aspect, the steel bolt 16 employed in the
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embodiments of Figs. 2-6 and 10-12 may be replaced by an
aluminum fastener in those applications in which the
connecting rod parts are made of aluminum. Because the
aluminum fastener and the aluminum shank and cap have
very similar coefficients of thermal expansion, the
aperture for the crankshift pin remains more nearly round
as the engine heats up, rather than becoming increasingly
oval as occurs when steel bolts are used. Fig. 13 shows
an embodiment of an aluminum fastener which could replace
steel bolt 16 It comprises an aluminum stud 102
threaded on both ends 104, 106 and a steel nut 108. In
the embodiments illustrated in the drawings, threaded end
104 is screwed into threaded bores in the shank legs and
the threaded end 106 passes freely through bores in the
cap arc ends and extends out of the cap to accept nut
108. The connecting rod parts and the stud 102 do not
have to be of exactly the same aluminum alloy because the
coefficients of thermal expansion of ~11 common aluminum
alloys fall in a fairly narrow range. It has been found
that a stud 102 made from 2024 T4 aluminum is
satisfactory. It is often preferable that stud 102 be
slightly wider than steel bolt 16 to achieve the
necessary strength. A steel (rather than aluminum) nut
has the advantages of being readily available as a stock
item and of in~reasing the strength of the j oint .
However, an aluminum nut could be used in some
applications, or an aluminum bolt could be used in lieu
of the aluminum stud and steel nut.
Although the especially preferred embodiments of the
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invention have bee~ described above, the invention
claimed is not so restricted. There may be other
modifications and changes to these embodiments which are
within the scope of the invention. For example, the bolt
can be extended through the shank leg and fastened in
place with a nut. Further, the hook-on-lug and the
male/female junctions may be shaped in many different
ways which are within the scope of the invention. For
example, the male and female parts could be more
cylindrical. Also, the female part could be on the cap,
with the male part on the leg. Moreover, the extrusion
and f ine blanking processes may be used with materials in
addition to ~lllm;~l~m Thus, the invention is not to be
limited by the specific description above, but rather
should be jud~ed by the claims that follow.
