US007574795B2

(12) United States Patent (10) Patent N0.: US 7,574,795 B2

Ishida et al. (45) Date of Patent: Aug. 18,2009
(54) METHOD OF MANUFACTURING 4,768,694 A * 9/1988 Fabris et a1. ................ .. 225/94
CONNECTING ROD 5,568,891 A * 10/1996 Hoag et a1. ....... . . . . . . .. 225/93

5,974,663 A * 11/1999 Ikeda et a1. ..... .. 29/888.09

(75) Inventors: Masao Ishida, Saitama (JP); Toyotaka 6,312,159 B1* 11/2001 Ishida et a1. .............. .. 384/294
6,427,326 B1 * 8/2002 Soga et a1. ........... .. 29/888.092
Kinoshita, Saitama (JP) 6,474,526 B1* 11/2002 Hahnel et a1. 225/100
(73) Assignee: Honda Motor Co., Ltd., Minato-Ku
6,817,505 B2 * 11/2004 Hahnel et a1. ..... . . . . . . . .. 225/2

6,961,997 B2 * 11/2005 Kubota et a1. .......... .. 29/888.09

Tokyo (JP) 7,299,716 B2 * 11/2007 Nakajima et a1. ........... .. 74/593

(*) Notice: Subject to any disclaimer, the term of this FOREIGN PATENT DOCUMENTS
patent is extended or adjusted under 35
JP 2-19328 A 1/1990
U.S.C. 154(b) by 329 days. JP 2000-179535 A 6/2000

(21) Appl. N0.: 11/403,864 * cited by examiner

(22) Filed: Apr. 14, 2006 Primary ExamineriDavid P Bryant

Assistant ExamineriRyan J Walters
(65) Prior Publication Data (74) Attorney, Agent, or FirmiBirch, Stewart, Kolasch &
Birch, LLP
Us 2006/0231164 A1 Oct. 19, 2006
(57) ABSTRACT
(30) Foreign Application Priority Data
Apr. 15, 2005 (JP) ........................... .. 2005-117820 To manufacture a connecting rod including positioning
grooves having a function of positioning a bearing metal at
(51) Int. Cl. loW cost. A big end part of a split type connecting rod is
B23P 1 7/00 (2006.01) fractured in tWo after inserting an approximately cylindrical
(52) US. Cl. ............................ .. 29/888.092; 29/888.09; die into a bearing hole. The die has projections corresponding
29/413; 384/294; 384/430; 225/100 to locking grooves on an outer circumferential surface
thereof. The die includes a pair of split dies having tapered
(58) Field of Classi?cation Search ................. .. 29/412,
faces, each expanding an opening on an edge of an end face of
29/413, 414, 888.09, 888.92, 888.092; 148/206; each of the split die halves. The tapered faces are formed by
384/294, 430; 225/100
See application ?le for complete search history. partially notching mating surfaces by pressing the inner cir
cumferential surface of the bearing hole With the projections
(56) References Cited by a movement of the pair of split dies in a radial direction of
the bearing hole.
U.S. PATENT DOCUMENTS
4,569,109 A * 2/1986 Fetouh .................. .. 29/888.09 20 Claims, 8 Drawing Sheets
US. Patent Aug. 18, 2009 Sheet 1 of8 US 7,574,795 B2

FIG. 1
US. Patent Aug. 18, 2009 Sheet 2 of8 US 7,574,795 B2

FIG. 2

“9,471,
k:- f _ _c
F ) A:
2mm T '6“
L 17050
US. Patent Aug. 18, 2009 Sheet 3 of8 US 7,574,795 B2

FIG. 3(a)
I00
\ ,--22

lI
‘130 13b‘

FIG. 3(1))
I00
I30 ‘ '

II
200 22/49
US. Patent Aug. 18, 2009 Sheet 4 of8 US 7,574,795 B2

FIG. 4(a)

I50 'IJOD
12%
I40- 23‘)
- “14::

FIG. 4(1))

I40 '5 {43 [0b

'2 /
US. Patent Aug. 18, 2009 Sheet 5 of8 US 7,574,795 B2

FIG. 5
US. Patent Aug. 18, 2009 Sheet 6 of8 US 7,574,795 B2

FIG. 6(a)

55 55
50a 5/0
50b
52
53 56I") /\56
5|

FIG. 6(b)
‘a " " /Z_,,70

52 F ’ .. "A. ~54
5' 56 ~ I 56
US. Patent Aug. 18, 2009 Sheet 7 of8 US 7,574,795 B2

FIG. 7

L.

5|

53o

. 52

50

53 50a
US. Patent Aug. 18, 2009 Sheet 8 of8 US 7,574,795 B2

FIG. 8(a)
 US 7,574,795 B2
1 2
METHOD OF MANUFACTURING end part of the connecting rod are formed by cutting each of
CONNECTING ROD the halves. Thus, costs for manufacturing the separate-type
connecting rod are generally increased. In the case of manu
CROSS-REFERENCE TO RELATED facturing by fracture-splitting, it is required to perform cut
APPLICATIONS ting to form a bearing hole so as to alloW bottoms of the
locking grooves and bottoms of the V-shaped grooves to be on
This nonprovisional application claims priority under 35 the same plane, in order to form one continuous fracture
U.S.C. § 119(a) on PatentApplication No. 2005-1 17820, ?led surface after fracture. Moreover, if it is tried to perform cut
in Japan on Apr. 15, 2005, the entirety of Which is incorpo ting ?nish for the locking grooves in a state Where an inte
rated herein by reference. grally formed material of the split type connecting rod is
fractured into tWo halves at a position of the V-shaped groove
BACKGROUND OF THE INVENTION and, thereafter, the tWo halves are attached to each other and
assembled on the fracture surface, it is impossible to perform
1. Field of the Invention cutting to form the locking grooves so as to be located at
The present invention relates to a method of manufacturing different positions With each other in an axial direction of a
a connecting rod. More particularly, the present invention bearing hole across the fracture surface. Thus, only a pair of
relates to a method of manufacturing a connecting rod, Which locking grooves that face each other across the fracture sur
achieves a reduction in manufacturing costs, an improvement face and communicate With each other can be formed by
in positioning accuracy for a bearing metal, and the like. cutting.
2. Description of Background Art 20 Consequently, Without adopting a method of performing
In the background art, a bearing metal is inserted into a cutting to form the locking grooves located at axially different
bearing hole in a big end part of a split type connecting rod positions across the fracture surface, a method of integrally
(Which includes a rod side upper half, on Which a piston is forming locking grooves by die-pressing While applying a
provided, and a cap side loWer half, Which is fastened onto the compressive load in the axial direction of the big end part of
rod side upper half) of an internal combustion engine (engine) 25 the connecting rod may be adopted. HoWever, When the con
used for a vehicle and the like. Speci?cally, the bearing metal necting rod is formed by applying the compressive load in the
is formed of a pair of bearing metal halves, each of Which has axial direction of the big end part, only a locking groove
a semi-arc-shaped cross section and is made of soft metal opened in an end face in the axial direction of the big end part
such as aluminum and brass. Moreover, lubricating oil circu can be formed. Thus, in order to axially position the bearing
lating inside the engine forms an oil ?lm betWeen the bearing 30 metal inserted into the bearing hole of the big end part, it is
metal and a crank pin. Thus, lubrication betWeen the connect required to provide locking grooves at tWo spots (on one end
ing rod and the crank pin is achieved When the engine is face in the axial direction of the big end part and the other end
operating. face thereof). Thus, it is required to similarly form projections
In general, the pair of bearing metal halves as described of the respective bearing metal halves, Which are engaged
above are positioned so as not to move in a circumferential 35 With the locking grooves, at tWo spots. Accordingly, costs for
direction and in an axial direction and are attached to the rod processing the bearing metal are increased.
side upper half and the cap side loWer half, respectively, on
the big end part of the split type connecting rod. SUMMARY OF THE INVENTION
In Japanese Examined Patent Publication No. Hei 2 1990
19328 and Japanese Patent Laid-Open No. 2000-17953, a 40 In consideration of the problems described above, it is an
projection that projects radially outWard is formed on an end object of the present invention to provide a method of manu
on either side in a circumferential direction of each bearing facturing a connecting rod, Which reduces costs for manufac
metal half having a semi-arc-shaped cross section. Moreover, turing locking grooves engaged With projections of a bearing
a locking groove is formed on a mating surface side of an metal and improves a function of positioning the bearing
inner circumferential surface of each of upper and loWer metal.
halves of a big end part of a split type connecting rod. Accord In order to achieve the foregoing object, a method of manu
ingly, positioning of the bearing metal halves inserted into a facturing a connecting rod according to the present invention
bearing hole of the big end part is performed by engagement is a method of manufacturing a connecting rod including a big
betWeen the projection and the locking groove on the con end part Which supports a crankshaft With a bearing, a small
necting rod side. 50 end part Which supports a piston pin With a bearing, and a rod
A method of manufacturing a split type connecting rod is part Which integrally connects the big end part to the small
classi?ed roughly into a separate-split type connecting rod end part. The big end part is split in tWo by fracture on a split
and a fracture-split type connecting rod. Speci?cally, the surface Which passes an approximately central axis of a bear
separate-split type connecting rod is used by separately form ing hole formed in the big end part With an approximately
ing a rod side upper half and a cap side loWer half of a big end 55 circular cross section and Which is approximately perpen
part of a connecting rod and bonding both halves together. dicular to a center line connecting the big end part to the small
The fracture-split type connecting rod is used by integrally end part and dividing the rod part into right and left sides. The
die-forming a Whole connecting rod including a rod side big end part is split into a rod side upper half obtained by
upper half and a cap side loWer half, fracturing the connecting integrating an upper half of the big end part With the small end
rod into tWo parts including a rod side half including an upper part by use of the rod part and a cap side loWer half formed of
half of a big end part and a cap side half that is the same as a a loWer half of the big end part. The connecting rod is used in
loWer half of the big end part after the die-forming, and a state Where the rod side upper half and the cap side loWer
assembling both halves so as to attach fracture surfaces to half are bonded on the split surface in a state Where a bearing
each other. metal having an arc-shaped cross section is attached to an
Among those described above, as to the separate-split type 65 inner circumferential surface of the bearing hole. Further
connecting rod, locking grooves formed on an inner circum more, the connecting rod has positioning grooves (for
ferential surface of each of upper and loWer halves of the big example, locking grooves 511 and 5b in an embodiment) for
 US 7,574,795 B2
3 4
?xing the bearing metal on the inner circumferential surface bearing hole. Accordingly, the projections are ?rmly ?xed in
of the bearing hole. The method includes the steps of: insert the axial direction, and movement thereof in the axial direc
ing an approximately cylindrical die into the bearing hole, the tion is restricted. Thus, it is only necessary to form one posi
die having projections corresponding to the positioning tioning groove for ?xing the bearing metal (halves) in the
grooves on an outer circumferential surface and including a axial direction.
pair of split dies in Which at least one of mating surfaces is Since it is only necessary to form one positioning groove
partially notched to form a tapered face extended Wider for ?xing the bearing metal in the axial direction as described
toWard an end face of one end of the split die; pressing the above, it is only necessary to form one projection correspond
inner circumferential surface of the bearing hole With the ing thereto, Which is provided on the bearing metal to be ?xed
projections by sliding a tapered Wedge along the tapered face to the positioning groove on the bearing hole. Thus, it is
and moving the pair of split dies in a radial direction of the possible to reduce manufacturing costs for performing cut
bearing hole While separating the mating surfaces from each ting to form the projections on the bearing metal.
other; and forming the positioning grooves on the inner cir Furthermore, When the positioning grooves can be formed
cumferential surface of the bearing hole. All of these steps are at arbitrary positions in the axial direction of the bearing hole
carried out before fracturing the big end part. according to the positions of the projections on the die and a
Moreover, in the method of manufacturing a connecting pair of bearing metal halves having an approximately arc
rod having the con?guration described above, it is preferable shaped cross section are attached so as to face each other in
that convex parts for forming fracture grooves for facilitating the bearing hole, When the pair of bearing metal halves are
fracture of the big end part on the inner circumferential sur inserted into the bearing hole, end faces of the respective
face of the bearing hole are provided on the outer circumfer 20 projections formed on the pair of bearing metal halves butt a
ential surface of the die, While being extended in the axial fracture surface of the big end part. Thus, compared With the
direction of the die. When the inner circumferential surface of case Where a pair of positioning grooves facing each other
the bearing hole is pressed, the positioning grooves are across the fracture surface and communicating With each
formed and the fracture grooves are formed in the axial direc other are formed, a positioning function for the bearing metal
tion on the inner circumferential surface of the bearing hole. 25 halves in the circumferential direction by the positioning
According to the method of manufacturing a connecting grooves is suf?ciently achieved.
rod according to the present invention, the big end part is split In addition, if the peripheral part of the die is con?gured so
in tWo by fracture after integrally die-forming the entire con as to form notched fracture grooves, of Which bottoms are on
necting rod, unlike the manufacturing method by Which the the same plane as bottoms of the positioning grooves,
rod side upper half and the cap side loWer half of the big end 30
together With the positioning grooves on the inner circumfer
part of the connecting rod are formed as separate bodies. ential surface of the bearing hole (if positions of the projec
Thus, it is possible to omit a step of cutting the big end part. tions and the convex parts are aligned), the fracture grooves
Moreover, in the manufacturing method by Which the big end are set to be starting points of fracture When the big end part
part is split in tWo by fracture, if the rod side upper half and the is fracture-split and fracture is facilitated. Moreover, one con
cap side loWer half are bonded so as to attach fracture surfaces 35 tinuous fracture surface is likely to be formed at the time of
thereof to each other, both halves can be bonded to ?t per fracture.
fectly to each other Without misalignment. Thus, it is not Further scope of applicability of the present invention Will
required to cut mating surfaces to form positioning holes or become apparent from the detailed description given herein
projections. Moreover, drilling of bolt holes for bonding both after. HoWever, it should be understood that the detailed
halves, Which has been required for each of the rod side upper 40
description and speci?c examples, While indicating preferred
half and the cap side loWer half, may be performed once embodiments of the invention, are given by Way of illustration
before fracture-splitting. As described above, various only, since various changes and modi?cations Within the
machining steps can be omitted. Thus, the connecting rod can spirit and scope of the invention Will become apparent to
be manufactured at a loW cost. those skilled in the art from this detailed description.
In addition to the effect as described above, in the manu 45
facturing method according to the present invention, before BRIEF DESCRIPTION OF THE DRAWINGS
fracture of the big end part, positioning grooves for ?xing the
bearing metal are formed by pressing the bearing hole in the
The present invention Will become more fully understood
big cnd part by use of the die having projcctions correspond from the detailed description given hereinbeloW and the
ing to the positioning grooves. Thus, it is not required to form 50
accompanying draWings Which are given by Way of illustra
the positioning grooves by cutting. From this vieWpoint, the tion only, and thus are not limitative of the present invention,
connecting rod can be manufactured at loW cost.
and Wherein:
In addition, in the manufacturing method according to the
present invention, unlike a manufacturing method such as FIG. 1 is a front vieW of a split type connecting rod accord
die-pressing by applying a compressive load in the axial 55
ing to the present invention;
direction of the bearing hole, the positioning grooves are FIG. 2 is a schematic front vieW shoWing an inner circum
formed by pressing the inner circumferential surface of the ferential surface of a big end part of the split type connecting
bearing hole in the radial direction. Thus, Without being lim rod, When vieWed from a direction A in FIG. 1;
ited to formation of positioning grooves opened in an end face FIG. 3 (a) is a side vieW and FIG. 3 (b) is a bottom vieW
in the axial direction of the bearing hole, the positioning 60 shoWing an upper bearing metal half attached to the big end
grooves can be formed at arbitrary positions in the axial part of the split type connecting rod shoWn in FIG. 1;
direction of the bearing hole according to positions of the FIG. 4 (a) is a top plan vieW and FIG. 4 (b) is a side vieW
projections on the die. As described above, When the proj ec shoWing a loWer bearing metal half attached to the big end
tions of the bearing metal are ?xed to positioning grooves not part of the split type connecting rod shoWn in FIG. 1;
opened in the end face in the axial direction of the bearing 65 FIG. 5 is an exploded perspective vieW shoWing the split
hole, the projections come into contact With both Wall sur type connecting rod shoWn in FIG. 1 and a bearing metal
faces of the positioning grooves in the axial direction of the attached to the big end part thereof.
 US 7,574,795 B2
5 6
FIG. 6 (a) is a plan vieW and FIG. 6 (b) is a side vieW separate bodies from the beginning. The connecting rod
showing a die for forming positioning grooves and the like to according to the present invention is a fracture-split type
?x the bearing metal halves to the big end part of the split type connecting rod manufactured by integrally die-forming the
connecting rod; rod side half 4 and the cap side half 3. Thereafter, the inte
FIG. 7 is a partial perspective vieW shoWing a portion grally die-formed body is fractured and split into tWo separate
around a projections on the die; and bodies. Therefore, the split surface C is a fracture surface C
FIGS. 8 (a) and 8 (b) are vieWs shoWing the steps of formed by the fracture described above.
forming the positioning grooves and the like by use of the die, In the split type connecting rod 1 that is fractured and split
Wherein FIG. 8 (a) shoWs a state before the positioning into the rod side half 4 and the cap side half 3, an inner
grooves and the like are formed in the big end part and FIG. 8 circumferential surface of the big end part 111 is ?nished by
(b) shoWs a state after the positioning grooves and the like are machining such as cutting When both halves are assembled.
formed in the big end part. Thus, the bearing hole 1d is formed.
In the upper half2 of the big end part 111 of the split type
DETAILED DESCRIPTION OF THE PREFERRED connecting rod 1, a lubricating oil passage 1e having an
EMBODIMENTS opening in the inner circumferential surface of the big end
part 111 is formed at a position that avoids a connection part
The present invention Will noW be described With reference betWeen the big end part 111 and the rod part 10 Which con
to the accompanying draWings, Wherein the same or similar nects the big end part 111 to the small end part 1b.
elements Will be identi?ed With the same reference numerals. A relatively soft metal such as brass and aluminum alloy is
With reference to FIGS. 1 to 8, an embodiment of the 20 used as a material of a bearing metal 10. As shoWn in FIG. 5,
present invention Will be described beloW. First, With refer the bearing metal 10 is formed of a pair of upper and loWer
ence to FIGS. 1 to 5, description Will be given of a structure of bearing metal halves 10a and 10b, each of Which has a semi
a connecting rod manufactured by use of a method of manu arc-shaped cross section. As shoWn in FIGS. 3 and 4, on
facturing a connecting rod according to the present invention. mating surfaces 13 and 14 of the upper and loWer bearing
FIG. 1 is a front vieW of a split type connecting rod according 25 metal halves 10a and 10b, Which are used to butt the upper
to the present invention. FIG. 2 is a schematic front vieW and loWer bearing metal halves 10a and 10b With each other
shoWing an inner circumferential surface of a big end part of into a cylindrical shape, projections 11 and 12 that project
the split type connecting rod, When vieWed from a directionA radially outWard are formed by press Working, respectively.
in FIG. 1. FIG. 3 (a) is a side vieW and FIG. 3 (b) is a bottom The mating surfaces 13 and 14 of the upper and loWer
vieW shoWing an upper bearing metal half attached to the big 30 bearing metal halves 10a and 10b include mating surface
end part of the split type connecting rod shoWn in FIG. 1. FIG. portions 13a and 13b and mating surface portions 14a and
4 (a) is a top plan vieW and FIG. 4 (b) is a side vieW showing 14b on both ends in a circumferential direction of the upper
a loWer bearing metal half attached to the big end part of the and loWer bearing metal halves 10a and 10b, respectively.
split type connecting rod shoWn in FIG. 1. FIG. 5 is an The projection 11 is formed on the mating surface portion
exploded perspective vieW shoWing the split type connecting 35 13a, and the projection 12 is formed on the mating surface
rod shoWn in FIG. 1 and a bearing metal attached to the big portion 14a. Speci?cally, the projections 11 and 12 are
end part thereof. Moreover, FIG. 6 (a) is a plan vieW and FIG. formed at axially different positions With each other.
6 (b) is a side vieW shoWing a die for forming positioning On a peripheral Wall of the upper bearing metal half 1011, an
grooves and the like to ?x the bearing metal halves to the big oil hole 22 is formed at a position corresponding to the open
end part of the split type connecting rod. FIG. 7 is a partial 40 ing of the oil passage 1e formed in the upper half 2 of the big
perspective vieW of the die. FIGS. 8 (a) and 8 (b) are vieWs end part 111 of the split type connecting rod 1. An oil hole 23
shoWing the steps of forming the positioning grooves and the is formed on a peripheral Wall of the loWer bearing metal half
like by use of the die. Speci?cally, FIG. 8 (a) shoWs a state 10b at a position facing the oil hole 22 across the mating
before the positioning grooves and the like are formed in the surfaces of both bearing metal halves 10a and 10b.
big end part, and FIG. 8 (b) shoWs a state after the positioning 45 The upper and loWer bearing metal halves 10a and 10b
grooves and the like are formed in the big end part. described above are attached to the upper and loWer halves 2
As shoWn in FIG. 1, a split type connecting rod 1 includes: and 3 of the big end part 111 of the fracture-split type connect
a big end part 111 Which holds a crank pin of an unillustrated ing rod 1, respectively, in the folloWing manner.
crankshaft; a small end part 1b Which holds a piston pin of an In an upper half 2 side portion and a loWer half 3 side
unillustrated piston; and a rod part (shaft part) 10 Which 50 portion of the bearing hole 1d that is the inner circumferential
connects the big end part 111 to the small end part 1b. surface of the big end part 111 of the fracture-split type con
The split type connecting rod 1 is manufactured in the necting rod 1, a pair of locking grooves 511 and 5b are formed.
folloWing manner. Speci?cally, the split type connecting rod The locking grooves 511 and 5b are located at positions dif
1 is split in tWo on a split surface C Which passes an approxi ferent from each other in the axial direction of the big end part
mately central axis of a crank pin bearing hole 1d in the big 55 111 as shoWn in FIG. 2, When vieWed from a direction of the
end part 111 and Which is perpendicular to a center line of the arroW A in FIG. 1, beloW and above the fracture surface C,
split type connecting rod 1. The center line extends from the respectively. The locking grooves 511 and 5b described above
big endpart 1a to the small endpart 1b and divides the rodpart are formed by cold forging using a die 50 as described later.
10 into right and left sides. Accordingly, a rod side half 4 and When the upper and loWer bearing metal halves 10a and
a cap side half 3 are prepared. Speci?cally, the rod side half 4 60 10b are attached to the big end part 1a, the projection 11 is
is formed by integrating an upper half (rod side upper half) 2 engaged With the locking groove 5a and the projection 12 is
of the big end part 1a, the small end part 1b and the rod part engaged With the locking groove 5b respectively. Thus,
10. Thus, both halves 4 and 3 are bonded on the split surface movement of the upper and loWer bearing metal halves 10a
C and integrated. The cap side half 3 and a loWer half (cap side and 10b in the circumferential direction and in the axial
loWer half) 3 of the big end part 111 are the same body. 65 direction is restricted.
There is also a separate-split type connecting rod in Which In the case of the upper and loWer bearing metal halves 10a
the rod side half 4 and the cap side half 3 are die-formed as and 10b shoWn in FIGS. 3 and 4, When the upper bearing
 US 7,574,795 B2
7 8
metal half 1011 is attached to the upper half 2 of the big end end part 111 is cut on the fracture surface C, and is die-formed
part 1a, the projection 11 of the upper bearing metal half 1011 during the cold forging using the die 50.
is engaged With the locking groove 5b of the upper half 2. With reference to FIGS. 6 and 7, description Will be given
Moreover, When the loWer bearing metal half 10b is attached of the die 50 for forming the locking grooves 511 and 5b
to the loWer half 3 of the big end part 1a, the projection 12 of formed on the inner circumferential surface of the bearing
the loWer bearing metal half 10b is engaged With the locking hole 1d of the big end part 1a. The die 50 is formed ofa pair
groove 5a of the loWer half 3. of split die halves 50a and 50b. When the pair of split die
For example, When the loWer bearing metal half 10b is halves 50a and 50b are attached to each other on mating
attached to the loWer half 3 of the big end part 1a, in engage surfaces 55 and 55 thereof, an approximately cylindrical
ment betWeen the projection 12 and the locking groove 5a, a shape is formed as a Whole. Tapered faces 56 and 56 are
locking surface 15a of the projection 12 is engaged With a formed on the mating surfaces 55 and 55 of the split die halves
locking surface 16a of the locking groove 5a. Moreover, a 50a and 50b. Each of the tapered faces 56 and 56 is formed by
ceiling surface of the projection 12 is engaged With a locking partially notching each of the mating surfaces and expanding
surface 17a of the locking groove 5a. Note that the locking an opening on an edge of an end face of each of the split die
surface 17a is on the mating surface of the upper half 2 in the halves 50a and 50b.
position of the fracture surface C. Note that an alloy tool steel for a cold die can be used as a
Accordingly, movement of the loWer bearing metal half material of the die 50. For example, it is preferable to use one
10b in the axial direction is restricted by the engagement employed for a press die, such as SKS 31 containing tungsten
betWeen the locking surface 15a and the locking surface 16a. or SKD 12 that is high-carbon high-Cr steel.
Moreover, by the engagement betWeen the ceiling surface of 20 On an outer circumferential surface of the split die half
the projection 12 and the locking surface 17a, the loWer 5011, a convex part 53 is formed so as to extend in the axial
bearing metal half 10b is positioned in the circumferential direction of the die 50. Speci?cally, the convex part 53 has a
direction and movement of the loWer bearing metal half 10b V-shaped cross section and corresponds to the concave
in the circumferential direction is restricted. groove 21 on the inner circumferential surface of the bearing
Similarly, When the upper bearing metal half 1011 is 25 hole 1d of the big end part 1a. Similarly, on an outer circum
attached to the upper half 2 of the big end part 1a, movement ferential surface of the other split die half 50b, a convex part
of the upper bearing metal half 1011 in the axial direction is 54 is formed so as to extend in the axial direction of the die 50.
restricted by engagement betWeen a locking surface 20a of Speci?cally, the convex part 54 has a V-shaped cross section
the projection 11 and a locking surface 16b of the locking and corresponds to the concave groove 24 on the inner cir
groove 5b. Moreover, by engagement betWeen a bottom sur
cumferential surface of the bearing hole 1d of the big end part
face of the projection 11 and a locking surface 17b of the 111.
locking groove 5b, the upper bearing metal half 1011 is posi On the outer circumference of the split die half 50a, pro
tioned in the circumferential direction and movement of the jections 51 and 52 corresponding to the locking grooves 511
upper bearing metal half in the circumferential direction is and 5b on the inner circumferential surface of the bearing hole
restricted. Note that the locking surface 17b is on the mating 1d of the big end part 111 are formed across the convex part 53
surface of the loWer half 3 in the position of the fracture While projecting outWard in a radial direction of the die 50.
surface C. The projections 51 and 52 are not located at positions facing
each other across the convex part 53 but are located at posi
As described above, the upper and loWer bearing metal tions shifted from each other in the axial direction of the die
halves 10a and 10b are respectively attached to the upper and 50.
loWer halves 2 and 3 of the big end part 111 of the fracture-split
With reference to FIGS. 8 (a) and 8 (b), the steps of a
type connecting rod 1 in a state Where movement thereof in
method of manufacturing a split type connecting rod con?g
the circumferential direction and in the axial direction is
ured as described above Will be sequentially described.
restricted.
As a material of the split type connecting rod 1, alloy steel
As shoWn in FIG. 2, on the inner circumferential surface 45 for machine structural use is used, Which contains a relatively
(the bearing hole 1d) of the big end part 111 of the fracture-split loW concentration of carbon by a mass ratio of about 0.13 to
type connecting rod 1, a concave groove 21 having a notch 0.23%. Compared With carbon steel, such alloy steel can have
part that is a starting point of fracture is formed along the a suf?cient hardness even if a member With a diameter of
fracture surface C. The concave groove 21 has a V-shaped about 15 mm or more is used. Since the alloy steel described
cross section and a bottom of theV shape forms the notch part. 50 above contains a relatively loW concentration of carbon, a
The concave groove 21 is die-formed together With the lock hardness thereof at room temperature is loWer than that of
ing grooves 511 and 5b during the cold forging using the die 50 high-carbon alloy steel. Moreover, mechanical properties
as described later. A formation position of the concave groove thereof are suitable for cold forging to be performed later.
21 is Where the big end part 111 is fractured on the fracture CriMo steel (for example, one having a mass ratio of C:
surface C. 55 0.13 to 0.18%, Mn: 0.60 to 0.85%, Cr: 0.90 to 1.20%, Mo:
The concave groove 21 formed as described above facili 0.15 to 0.30%, Si: 0.15 to 0.35%, P: 0.03% or less and S:
tates a fracture operation during fracture of an integrally 0.03% or less) or Cr steel (for example, one having a mass
formed material of the fracture-split type connecting rod 1. ratio of C: 0.13 to 0.18%, Mn: 0.60 to 0.85%, Cr: 0.90 to
The concave groove 21 also serves to chamfer the respective 1.20%, Si: 0.15 to 0.35%, P: 0.03% or less and S: 0.03% or
mating surfaces of the upper and loWer halves 2 and 3 of the 60 less) is selected. Note, hoWever, that the compositions
big end part 111 of the fracture-split type connecting rod 1. described above are merely examples. The material of the
Furthermore, on the inner circumferential surface (the split type connecting rod 1 does not necessarily have such a
bearing hole 1d) of the big end part 111 of the fracture-split composition as long as alloy steel for machine structural use
type connecting rod 1, a concave groove 24 that has a notch is used.
part as a starting point of fracture is also formed along the 65 First, a round bar made of a material having a composition
fracture surface C so as to face the concave groove 21. The as described above is subjected to volume distribution (rough
concave groove 24 is also formed at the position Where the big forming) by roll forging or the like. The material is put
 US 7,574,795 B2
10
between dies carved into a shape of a product and is hot After the carburiZing treatment, a quenching treatment is
forged by heating to a recrystallization temperature or more. performed with the material heated to the austenite range. By
The material formed by hot forging has a rough shape of the such quenching treatment after the carburiZing, quench hard
product with a burr around it. Thereafter, the burr produced ening occurs in the surface layer of the material, into which
around the shape of the product in the hot forging step is carbon has penetrated during the carburiZing treatment. Thus,
removed by pressing. Furthermore, an end mill is used to cut abrasion resistance and fatigue resistance are improved to
a surface of the material including a portion to be a bearing make the material suitable to be used as a connecting rod.
hole 1d ofa big end part 1a. The integrally formed material subjected to the heat treat
Next, by use of a die 50 as described above, cold-forging is ment is set in the fracturing machine for fracture-splitting the
performed to form locking grooves 511 and 5b and concave material. In this step, an impact force is applied to the big end
grooves 21 and 24 in the portion that is to be the bearing hole part 111 of the integrally formed material by the fracturing
1d ofthe big end part 1a. machine. Thus, the big end part 111 of the integrally formed
The cold forging is performed by inserting the die 50, material is fracture-split into a rod side half 4 and a cap side
which is obtained by putting together split die halves 50a and half 3.
50b on mating surfaces 55 and 55, into the bearing hole 1d of By such fracture-splitting, the big end part 111 of the inte
the big end part 111 (see FIG. 8 (11)). In the above state, a grally formed material is split into the rod side half 4 and the
tapered wedge 70 is inserted from its tip side so as to follow cap side half 3. Thus, compared with a method of cutting the
tapered faces 56 and 56 of the die 50 (see FIG. 6 (b)). big end part 111 of the integrally formed material, the time
Thereafter, by use of a fracturing machine as described required to split the big end part in two can be shortened.
later, which is used to fracture-split the big end part 111 in two, 20 Moreover, when the two split members are assembled, both
the wedge 70 is pressed downward in an axial direction of the members can be attached to ?t perfectly to each other without
die 50 by pressing an upper surface of the wedge 70. In this misalignment by attaching fracture surfaces thereof to each
event, a peripheral side face of the big end part 111 is ?rmly other.
?xed so as not to move the big end part 1a, which diverts the If a peripheral part of the die 50 is con?gured so as to form
applied force to the die 50 from the wedge 70. 25 bottoms of the locking grooves 511 and 5b and bottoms of the
Along with movement of the wedge 70 downward in the concave grooves 21 and 24 within the same plane on the inner
axial direction of the die 50, the wedge 70 slides along the circumferential surface of the bearing hole 1d by the cold
tapered faces 56 and 56 of the die 50. In this event, a compo forging (if the convex part 53 is formed so as to allow the both
nent of force applied to the die 50 from the wedge 70 in a of projections 51 and 52 to come into contact with a pointed
radial direction of the die 50 presses the die 50 in the radial 30 end 5311 of the convex part 53), the bottoms of the locking
direction. Accordingly, the split die half 50a on the left side in grooves 511 and 5b and the bottoms of the concave grooves 21
the plan view direction is moved to the left (in a direction of and 24 are set as a starting point of fracture when the big end
the arrow D) in FIG. 8 (a) and the split die half 50b on the right part 111 is fracture-split. Thus, fracturing the big end part 111 is
side is moved to the right (in a direction of the arrow E) facilitated. Moreover, during the fracture, one continuous
similarly in FIG. 8 (a) (see FIG. 8 (b)). Speci?cally, along 35 fracture surface C is likely to be formed.
with the downward movement of the wedge 70, the left and In the split type connecting rod 1 after the fracture-split
right split die halves 50a and 50b put together on the mating ting, the rod side half 4 and the cap side half 3 of the big end
surfaces 55 and 55 at the beginning are separated from each part 111 are integrated again by attaching the fracture surfaces
other. Along with the separation of the left and right split die thereof to each other. Thereafter, in the state where the rod
halves 50a and 50b, an inner circumferential surface of the 40 side half 4 and the cap side half 3 are assembled, the inner
bearing hole 1d is pressed in a radial direction of the bearing circumferential surface of the bearing hole 1d is subjected to
hole 1d by the die 50. a ?nishing process. In this ?nishing process, the inner circum
To be more speci?c, the inner circumferential surface of the ferential surface of the bearing hole 1d is subjected to ?ne
bearing hole 1d is pressed by projections 51 and 52 formed on polishing using ?ne abrasive grains, for example a honing
an outer circumference of the die 50. Similarly, the inner 45 process. By such ?ne polishing, a surface having a surface
circumferential surface of the bearing hole 1d is pressed by roughness of 1 pm or less is obtained in the bearing hole 1d.
convex parts 53 and 54 formed on the outer circumference of As described above, the split type connecting rod 1 having
the die 50. the big end part 111 subjected to the ?nishing process is pro
The larger the distance between the left and right split die vided as a product in the following manner. Speci?cally, in a
halves 50a and 50b is, the larger the force pressing the inner 50 state where the bearing metal halves 10a and 10b are inserted
circumferential surface of the bearing hole 1d in the radial into the bearing hole 1d, the upper bearing metal half 1011 is
direction by the convex parts 53 and 54 and the projections 51 ?xed to the locking groove 5b and the lower bearing metal
and 52 becomes. Accordingly, the inner circumferential sur half 10b is ?xed to the locking groove 5b, the bearing metal
face of the bearing hole 1d undergoes plastic deformation so halves 10a and 10b are elastically deformed so as to reduce a
as to form concave parts. Thus, the locking grooves 511 and 5b 55 radius of curvature thereof. Thereafter, the rod side half 4 and
and the concave grooves 21 and 24 are formed in the inner the cap side half 3 are assembled by fastening with bolts.
circumferential surface of the bearing hole 1d. By setting the projections 51 and 52 in the peripheral part
Next, heat treatment is performed for the material in which of the die 50 to project outside of the die 50 by approximately
the locking grooves 511 and 5b and the concave grooves 21 and the same length, the depths of the locking grooves 511 and 5b
24 are formed as described above. As the heat treatment step, 60 formed on the inner circumferential surface of the bearing
?rst, a carburiZing treatment is performed. Gas carburiZing is hole 1d are set approximately the same. Thus, when the rod
used as the carburiZing treatment, for example. In the gas side half 4 and the cap side half 3 are fastened with bolts and
carburiZing, the material heated to an austenite range is the bearing metal halves 10a and 10b are ?xed respectively,
exposed in hydrocarbon gas. Thus, a carbon concentration in the bearing metal halves 10a and 10b are attached to each
a surface layer of the material is increased. Note that the 65 other on the mating surfaces 13a and 14a thereof without
carburiZing treatment is not limited to gas carburiZing, but being radially shifted from each other. Accordingly, the bear
may be pack carburiZing or liquid carburiZing. ing metal 10 is ?xed to have an approximately cylindrical
 US 7,574,795 B2
11 12
cross section. Therefore, When a crank pin is installed to the Speci?cally, the cold forging after the sintering step is
big end part 111 and lubricating oil is supplied betWeen an effective not only for forming the locking grooves 511 and 5b
outer circumferential surface of the crank pin and an inner and the concave grooves 21 and 24 but also for improving the
circumferential surface of the bearing metal 10, the lubricat hardness of the sintered body by eliminating the air holes in
ing oil is distributed around the crank pin While evenly ?oW the forging step and densifying the sintered body. Moreover,
ing therearound so as to make the gap betWeen the outer in the case of manufacturing by poWder metallurgy, it is
circumferential surface of the crank pin and the inner circum possible to obtain a shape close to a product (near net shape)
ferential surface of the bearing metal 10 uniform in the cir only by putting metal poWder that is a raW material in a
cumferential direction. Thus, a lubricating oil ?lm is su?i predetermined die and sintering it. Thus, there is also an
ciently secured. advantage that a high yield is achieved (it is not required to
Although the embodiment of the present invention has discard an unnecessary portion produced in the step of hot
been described above, the scope of the present invention is not forging the ingot steel).
limited to the embodiment described above. In the embodi Effects achieved by the present invention are as described
ment described above, the tWo locking grooves 511 and 5b are beloW. Speci?cally, in the method of manufacturing a con
formed on the inner circumferential surface of the bearing necting rod according to the present invention, the big end
hole 1d by using the die 50 having a pair of proj ections 51 and part is split in tWo by fracture, unlike the manufacturing
52 in the peripheral part. On the other hand, a locking groove method by Which the rod side upper half and the cap side
is formed by cold forging using a die having one projection in loWer half of the big end part of the connecting rod are formed
its peripheral part. Thereafter, a bearing metal With a proj ec as separate bodies. Thus, it is possible to omit a step of cutting
tion (the bearing metal not being one split into a pair of 20 the big end part. Moreover, in the manufacturing method by
bearing metal halves but being one integrated) corresponding Which the big end part is split in tWo by fracturing, if the rod
to the locking groove described above is inserted into a bear side upper half and the cap side loWer half are bonded so as to
ing hole. And then, the connecting rod is assembled. attach fracture surfaces thereof to each other, both halves can
In the embodiment described above, as a material of the be bonded to ?t perfectly to each other Without misalignment.
split type connecting rod 1, loW-carbon alloy steel for 25 Thus, it is not required to cut mating surfaces of the halves to
machine structural use is used. Medium-carbon alloy steel for form positioning holes or projections. Moreover, drilling of
machine structural use (for example, CriMo steel having C: bolt holes for bonding both halves, Which has been required
0.33 to 0.38% or Cr steel having C: 0.38 to 0.43%) may be for each of the rod side upper half and the cap side loWer half,
used. As described above, When medium-carbon alloy steel is may be performed at one time before fracture-splitting. As
used, a method of manufacturing a connecting rod is different 30 described above, various machining steps can be omitted.
from the one described above in the folloWing point. In the Thus, the connecting rod can be manufactured at loW cost.
heat treatment step after formation of the locking grooves 5a Before fracturing the big end part, positioning grooves for
and 5b and the concave grooves 21 and 24 by the cold forging, ?xing the bearing metal are formed by pressing the bearing
processing (re?ning process) for improving ductility may be hole in the big end part by use of a die having projections
performed instead of the carburiZing treatment. Speci?cally, 35 corresponding to the positioning grooves. Thus, it is not
in the re?ning processing, oil quenching is performed With required to perform cutting to form the positioning grooves.
the material heated to the austenite range, and, thereafter, From this vieWpoint, the connecting rod can be manufactured
tempering is performed. The method of manufacturing a con at a loW cost.
necting rod according to the present invention is suitable for Furthermore, unlike a manufacturing method such as die
formation of the locking grooves 511 and 5b and the concave 40 pressing by applying a compressive load in the axial direction
grooves 21 and 24 by cold forging. This is because the mate of the bearing hole, the positioning grooves are formed by
rial is of loW hardness at the point Where the cold forging is pressing the inner circumferential surface of the bearing hole
performed since the heat treatment step is performed after the in the radial direction of the bearing hole. Thus, not limited to
cold forging. forming positioning grooves opened in an end face in the
To form the locking grooves 511 and 5b and the concave 45 axial direction of the big end part, the positioning grooves can
grooves 21 and 24 on the inner circumferential surface of the be formed at arbitrary positions in the axial direction of the
bearing hole 1d, instead of the alloy steel for machine struc bearing hole according to positions of the projections on the
tural use, medium carbon steel (for example, one obtained by die. As described above, When the projections of the bearing
adding a small amount of niobium or vanadium to C: 0.30 to metal are ?xed to positioning grooves not opened in the end
0.45% in order to miniaturiZe crystal grain siZe) is used as a 50 face in the axial direction of the bearing hole, the projections
material of the split type connecting rod 1. The cooling rate is come into contact With both Wall surfaces of the positioning
controlled in the hot forging step to precipitate very small grooves in the axial direction of the bearing hole. Accord
carbide particles to obtain predetermined hardness. The ingly, the projections are ?rmly ?xed in the axial direction,
resultant material is then subjected to cold forging. and movement in the axial direction is restricted. Thus, it is
Furthermore, the locking grooves 511 and 5b and the con 55 only necessary to form one positioning groove for ?xing each
cave grooves 21 and 24 may be formed in the folloWing bearing metal (half) in the axial direction.
manner. Speci?cally, instead of using ingot material as a Since it is only necessary to form one positioning groove
material and die-forming the material by hot forging, a poW for ?xing a bearing metal half in the axial direction, it is only
der of alloy steel for machine structural use is die-formed into necessary to form one projection corresponding thereto,
a shape of a connecting rod, Which is sintered and subjected to 60 Which is provided on the bearing metal half to be ?xed to the
cold forging as described above. In the case of a manufactur positioning groove on the bearing hole. Thus, it is possible to
ing method of such poWder metallurgy, a sintered body that is cut manufacturing costs for performing cutting to form the
not yet subjected to cold forging (as-sintered), has air holes projections of the bearing metal.
remaining therein and is not suf?ciently densi?ed. Thus, the Furthermore, When the positioning grooves can be formed
sintered body, Which has loW sintered density and loW hard 65 at arbitrary positions in the axial direction of the bearing hole
ness, is suitable for the cold forging to be subsequently per according to the positions of the projections on the die and a
formed. pair of bearing metal halves are inserted into the bearing hole,
 US 7,574,795 B2
13 14
end faces of respective projections of the pair of bearing metal 2. The method of manufacturing a connecting rod accord
halves butt a fracture surface of the big end part. Thus, com ing to claim 1, further comprising the steps of:
pared With the case Where a pair of positioning grooves facing providing convex parts on the outer circumferential surface
each other across the fracture surface and communicating of the die for forming fracture grooves on the inner
With each other are formed, a positioning function for the circumferential surface of the bearing hole for facilitat
bearing metal halves in the circumferential direction by the ing fracture of the big end part, the convex parts extend
positioning grooves is suf?ciently achieved. ing in the axial direction of the die;
Moreover, if the peripheral part of the die is con?gured so forming the positioning grooves When the inner circumfer
as to form notched fracture grooves, together With the posi ential surface of the bearing hole is pressed; and
tioning grooves on the inner circumferential surface of the forming the fracture grooves in the axial direction on the
bearing hole, the bottoms of the fracture grooves being on the inner circumferential surface of the bearing hole When
same plane as bottoms of the positioning grooves (if positions the inner circumferential surface of the bearing hole is
of the projections and the convex parts are aligned), the frac pressed.
ture grooves are set to be starting points of fracture When the 3. The method according to claim 2, further comprising the
big end part is fracture-split and fracture of the big end part is 5 step of locating the projections on the die at positions spaced
facilitated. Moreover, a single continuous fracture surface is from each other in the axial direction to form the positioning
likely to be formed at the time of fracture. grooves on the inner circumferential surface of the bearing
The invention being thus described, it Will be obvious that hole at positions spaced in the axial direction.
the same may be varied in many Ways. Such variations are not 4. The method according to claim 2, further comprising the
to be regarded as a departure from the spirit and scope of the 20 step of performing a carburiZing treatment to the connecting
invention, and all such modi?cations as Would be obvious to rod after the formation of the positioning grooves and the
one skilled in the art are intended to be included Within the fracture grooves and prior to fracture of the big end part.
scope of the folloWing claims. 5. The method according to claim 4, further comprising the
step of quenching the connecting rod after the carburiZing
What is claimed is: 25 treatment and prior to fracture of the big end part.
1. A method of manufacturing a connecting rod, the con 6. The method according to claim 5, further comprising the
necting rod including a big end part that has an approximately steps of:
circular cross section for supporting a crankshaft With a bear setting the connecting rod into a fracture-splitting machine
ing, a small end part for supporting a piston pin With another after the quenching step; and
bearing, and a rod part integrally connecting the big end part 30 applying a force to the big end part to fracture the big end
to the small end part, Wherein the big end part is split in tWo part along the split surface.
by fracture on a split surface that passes through an approxi 7. The method according to claim 1, further comprising the
mately central axis of a bearing hole formed in the big end step of locating the projections on the die at positions spaced
part and is approximately perpendicular to a center line that from each other in the axial direction to form the positioning
extends from the big end part to the small end part and divides 35 grooves on the inner circumferential surface of the bearing
the rod part into right and left sides, the big end part is split hole at positions spaced in the axial direction.
into a rod side upper half obtained by integrating an upper half 8. The method according to claim 1, further comprising the
of the big end part With the small end part by use of the rod step of performing a carburiZing treatment to the connecting
part and a cap side loWer half formed of a loWer half of the big rod after the formation of the positioning grooves and the
end part, and the rod side upper half and the cap side loWer 40 fracture grooves and prior to fracture of the big end part.
half are integrated by bonding on the split surface in a state 9. The method according to claim 8, further comprising the
Where a bearing metal having an arc-shaped cross section is step of quenching the connecting rod after the carburiZing
attached to an inner circumferential surface of the bearing treatment and prior to fracture of the big end part.
hole, the inner circumferential surface of the bearing hole 10. The method according to claim 9, further comprising
having positioning grooves prior to fracture of the big endpart 45 the steps of:
for ?xing the bearing metal, said method comprising the steps setting the connecting rod into a fracture-splitting machine
of: after the quenching step; and
inserting an approximately cylindrical die into the bearing applying a force to the big end part to fracture the big end
hole, the die including a pair of split dies, each of the part along the split surface.
split dies having a tapered face and a mating surface 50 11. A method of manufacturing a connecting rod, the con
extending directly from the tapered face doWnWardly, necting rod including a big end part having a bearing hole for
one of the pair of split dies having projections on an supporting a crankshaft With a bearing, a small end part for
outer circumferential surface thereof corresponding to supporting a piston pin With another bearing, and a rod part
the positioning grooves on the inner circumferential sur integrally connecting the big end part to the small end part,
face of the bearing hole; 55 said method comprising the steps of:
pressing the inner circumferential surface of the bearing inserting an approximately cylindrical die into the bearing
hole With the projections by sliding a tapered Wedge hole, the die including a pair of split dies, each of the pair
along the tapered face and moving the pair of split dies in of the split dies having a tapered face and a mating
a radial direction of the bearing hole While separating the surface extending directly from the tapered face doWn
mating surfaces from each other, Wherein the mating 60 Wardly, one of the pair of split dies having projections
surface of one of the pair of the split dies is in contact formed on an outer circumferential surface thereof that
With the mating surface of the other one of the pair of the correspond to positioning grooves to be formed on an
split dies after the pair of split dies is inserted into the inner circumferential surface of the bearing hole, the
bearing hole and before the tapered Wedge is slid along positioning grooves being for ?xing the bearing Within
the tapered face; and 65 the bearing hole;
forming the positioning grooves on the inner circumferen pressing the inner circumferential surface of the bearing
tial surface of the bearing hole. hole With the projections by sliding a tapered Wedge
 US 7,574,795 B2
15 16
along the tapered face and moving the pair of split dies in ing rod after the formation of the positioning grooves and the
a radial direction of the bearing hole While separating the fracture grooves and prior to fracture of the big end part.
mating surfaces from each other, Wherein the mating 15. The method according to claim 14, further comprising
surface of one of the pair of the split dies is in contact the step of quenching the connecting rod after the carburiZing
With the mating surface of the other one of the pair of the treatment and prior to fracture of the big end part.
split dies after the pair of split dies is inserted into the 16. The method according to claim 15, further comprising
bearing hole and before the tapered Wedge is slid along the steps of:
the tapered face; and setting the connecting rod into a fracture-splitting machine
forming the positioning grooves on the inner circumferen after the quenching step; and
tial surface of the bearing hole. applying a force to the big end part to fracture the big end
12. The method of manufacturing a connecting rod accord part along the split surface.
ing to claim 11, further comprising the steps of: 17. The method according to claim 11, further comprising
providing convex parts on the outer circumferential surface the step of locating the projections on the die at positions
of the die for forming fracture grooves on the inner spaced from each other in the axial direction to form the
circumferential surface of the bearing hole for facilitat positioning grooves on the inner circumferential surface of
ing fracture of the big end part, the convex parts extend the bearing hole at positions spaced in the axial direction.
ing in the axial direction of the die; 18. The method according to claim 11, further comprising
forming the positioning grooves When the inner circumfer the step of performing a carburiZing treatment to the connect
ential surface of the bearing hole is pressed; and ing rod after the formation of the positioning grooves and the
20 fracture grooves and prior to fracture of the big end part.
forming the fracture grooves in the axial direction on the
19. The method according to claim 18, further comprising
inner circumferential surface of the bearing hole When
the inner circumferential surface of the bearing hole is
the step of quenching the connecting rod after the carburiZing
treatment and prior to fracture of the big end part.
pressed. 20. The method according to claim 19, further comprising
13. The method according to claim 12, further comprising 25 the steps of:
the step of locating the projections on the die at positions setting the connecting rod into a fracture-splitting machine
spaced from each other in the axial direction to form the after the quenching step; and
positioning grooves on the inner circumferential surface of applying a force to the big end part to fracture the big end
the bearing hole at positions spaced in the axial direction. part along the split surface.
14. The method according to claim 12, further comprising
the step of performing a carburiZing treatment to the connect * * * * *