CA2177631A1 - Connecting rod - Google Patents

Abstract

A connecting rod for an internal combustion engine, compressor or other machine; a structure for aligning the shank and cap parts of a two-piece connecting rod. The alignment structure being on one side a V-junction with contact only between slanting walls and on the other side a junction of two single-plane walls.

Description

, A , 2 1 7 7 6 3 1 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 2 1 77~,3 1 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 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.

~ 2 1 7763 ~

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 ~ 21 77631 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 2 1 776~ ~

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 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 2 ~ 77~
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 ' ~ 2177631 g 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 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 2 1 7763 ~
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 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 2 1 7763 l 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.

Claims (3)

1. 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 surface;
(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 for 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 tongue and the groove being formed 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 coplanar third junction 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.

2. A connecting rod as recited in claim 1, wherein an end of the tongue is truncated, forming a non-contact space in the groove between the first shank leg and the first arc-end.

3. A connecting rod as recited in claim 1, wherein the first tongue wall and the second tongue wall are at right angles to each other and the first groove wall and the second groove wall are at right angles to each other.