Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: BROACHING BEARINGS IN AN ENGINE B~OC~
This invention relates generally to broaching and
refers more particularly toa broach for, and method of,broaching
the aligned crankshaft bearings in an engine block.
~ACKGROUND AND SUMMARY
When broaching a ~eries of aligned bearing~, such as
the crankshaft bearing bores of an engine block, care must be
taken to insure that the bores are cut true, that is, that they
are rosnd and in line. The problem is particularly troublesome
when the bearings are formed of different materials having
different machining characteristics. As an exa~ple, the
cran~shaft bearings of a cast aluminum engine bloc~ may have
ductile iron bearing caps, 80 that one half of each bearing i8
aluminum and one half i- iron. The aluminum portion of each
bearing is softer and gummier and prone to tearing, wherea~ the
ductile iron bearing cap~ are abrasive and have a higher cutting
force con~tant. Thi~ causes the broach to stray off line ana
pu~h into the softer aluminum material. As a result, the broach
may cut holes that are off line and egg-shaped rather than
round. Also, the forces generated by the broaching process may
cause the bearing caps to deflect during broaching, causing an
out-of-round condition in the final bore~.
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In accordance with the present invention, the broach
has a front piloting section to guide the block over the broach.
This front piloting section preferably is completely in the
block before cutting begin~. The broach is designed with
alternate cutting and piloting section~, 80 that no two ad~acent
bearing ~ournals are broached at the same time. While one
broaching section is broaching one bearing bore, the ad~acent
piloting section is guiding the broach in the next bearing bore.
This provide~ 8 gu~ded movement of the broach and prevents the
broach from straying off line.
Each piloting section which follows a broa~hing
section is desiqned to guide behind that particular broaching
section. Therefore, each piloting section is slightly larger
in diameter based on the stock removal of the broaching ~ection
which precedes it. $his a~ures that the broach will not drift
away from the iron bearing caps and into the aluminum engine
block.
Preferably the broaching sections are de~igned with
spiral gullets to obtain a continuous engagement throughout the
part. The broach may be rotated 360 while lt is broaching ~o
that every point on the cutting edge~ will engage in the aluminum
for half a stroke and in the ductile iron the other half.
Rotating the broach will apply uniform wear pattern~ on the
cutting edge~. This will al~o aid in minimizing drifting of
the tool.
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The last broaching section may be a burnishlng shell
to improve the finish of the broached holes.
It is an object of this invention to provide a broach,
and a method of broaching, having the foregoing features and
capable of achieving the results indicated.
Another ob~ect is to provide a broach which i~ rugged
and durable, composed of a relatively few ~imple parts, capable
of being inexpens~vely manufactured, and well designed for the
accomplishment of it~ intended function.
These and other ob~ects, features and advantages of
the invention will become more apparent as the following
description proceeds, especially when considered in con~unction
with the accompanying drawings.
BRIEF DESCRIPTION OF THF DRAWINGS
Figure lisan elevational view of a broach constructed
ln accordance with the invention.
Figure 2 i~ a fragmentary elevatlonal view showing
the retriever end of the broach connected to a lead bar.
Figure 3 is a sectional view taken on the line 3--3
in Figure 1.
Figure 4 is a sectional view taken on the line 4--
~in Figure 1.
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Fiqure~ SA - 5D show the broach in several posltions
as it is pulled through the aligned bearing bore~ for the
crankshaft of an engine block to broach the bore~ in sequence.
Pigure 6 is an elevational view showing one of the
pilot ~hell~ of the broach.
Figure 7 i8 an end view of the pilot shell a~ viewed
fro~ the left in Figure 6.
Figure 8 is an end view of the pilot shell as viewed
from the right in Figure 6.
Figure 9 is an elevational view of one of the broaching
shells of the broach.
; Figure 10 is an end view of the broaching shell as
viewed from the left in Figure 9.
Fiqure 11 i~ an end view of the broaching ~hell as
viewed from the right in Figure 9.
Figure 12 i~ an enlarged fragmentar,v view of a portion
of the broaching shell showing the cutting teeth.
Figure 13 is an elevational view of the burnishing
shell of the broach.
Figure 14 i~ an enlarged frag~entary view ~howing a
portion of the burni~hing ~hell.
DETAILED DESCRIPTION
Referring now more particularly to the drawinq~, the
broach 10 is used to broach the bearing bores for the crankshaft
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of an engine block 12. The engine block 12 comprises in this
instance an aluminum casting 14 havinq a plurality of spaced
bearing formations 15, 16, 18, 20 and 22 each shaped with a
semi-circular recess 24 forming one-half of a bearing bore.
Secured to each bearing formation by fastener~ 26 1~ a bearing
cap 28 of ductile lron having a 3emi-cyllndrical reces~ 27
providing the other half of the bearing bore. The bearlng bores
are numbered 29, 30, 32, 34 and 36 snd are cylindrical, axi~lly
spaced, and aligned, and each 1~ formed one-half of aluminum
and one-half of ductile iron.
The broach comprises an elongated, solid, unitary
draw bar 40 having a pull bead 42 for connection to a power
device such as a hydraulic piston-cylinder assembly (not shown)
and at the other end having a retriever 44 which can be attached
to a lead bar ~6 by any sultable coupllng 48.
The broach has a front piloting section 50 and a rear
~iloting section 52. Between the front and rear pllotlng
sectlons are a plurality of axially spaced broachlng sect~on~
54, 56, 58, 60 and 62 with lntermediate pllotinq sectlons 64,
66, 68 and 70 in the spaces between the broaching sectlons.
The front pilotinq section 50 18 formed of a plurality
of cyllndrical ~hell~ 72 sleeved on the draw bar whlch are
stacked together end-to-end. The shells are all of the same
outside diameter and may be of the came or differing lengths,
but together form the front piloting section 50 which is of
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greater length than the overall distance between the five
bearings. The diameter of the shells 72 is designed to provide
a close guiding fit in the bearing bores before broaching.
The rear piloting section 52 is in this instance an
integral cylindrical portion of the draw bar and iQ of uniform
diameter throughout its length. The diameter of the rear
piloting section 52 is designed to provide a clo~e guiding fit
in the bearing bores after broaching.
The broaching section~ 54 - 62 are in the form of
cylindrical shells sleeved on the draw bar and preferably having
spiral gullets 73 between the continuous spiral cutting teeth.
Spiral cutting teeth are preferable on a finishing broach, but
not necessary on a roughing broach. The teeth are preferably
formed with spaced flats 75 to break up the chips. These flats
are non-aligned when the broach rotates, so that the next tooth
~ill not have a flat at the same location. The broaching
sect$ons, starting with the ~ection 54 nearest to the front end
of the broach, are progres ively larger in diameter ~o that
each takes a cut in the gradual removal of stock and the broaching
of the bores to a predetermined final dlameter.
The rearmost broaching section 62 in this instance is
burnishing shell in which the teeth have rounded crest 63
to pack or compress the material forming the bores in a finishing
operation. A burnishing shell improve~ the finish and quality
of the broached bores. How~ver, a burnishing shell is not
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always required, and usually is not employed for rough cutting~
In those instances where a burnishing shell is not needed, the
rearmost section 62 will be replaced by a broaching shell with
the same type of cutting teeth as shells 54, 56, 58 and 60.
The piloting sections 64 - 70 are in the form of
cylindrical sbells sleeved on the draw bar and with smooth
cylindrical radially outer surfaces. Each plloting section is
designed to guide specifically behind the broaching section
immedlately ahead of it. The diameter of the pilotinj sections
is based on the stock removal of the broaching section whlch
precedes it and, therefore, the piloting sections, starting
with section 64 nearest the front end, are progressively larger
in diameter. Thus after a hole is broached by one broaching
section, the piloting section immediately to the rear thereof
guides in that hole and is dimensioned to have a close fit
therein in order to guide properly.
The broaching sections 54 - 62 and piloting sections
64 - 70 are interlocked to prevent them frQm rotating on the
draw bar 40. Thus the burnishing shell 62 has a slot 7~ cut
across one end which receives a central projection 76 on the
ad~acent end of the rear piloting section 52. The parallel
sides 78 and 80 of the ~lot 74 engage the parallel sides of the
pro~ection 76 so that the burnishing shell is held from rotation.
~he opposite end of the burnishing shell 62 has a pro~ection
similar to the projection 76 on the rear piloting section
2 ~ 9t~
S2 which engages in a slot in the piloting shell 70 to prevent
the latter from rotating. There is a ~imilar pro~ection/slot
interengagement between the ends of the other broaching and
piloting shells so that they are all interlocked with the draw
bar and prevented from rotating. The shells 72 making up the
front piloting section 70 may or may not be interlocked to
prevent rotation. In thls instance, tbe shells 72 are not
~nterlocked and thus are free to rotate.
The lead bar ~6 has helical grooves 84 in which one
or more stationary pins 86 engage so that the lead bar, and
hence the broach, rotate in the direction of the arrow 85 as
the broach is pulled through the bearings of the engine block
in the direction of the arrow 87. Preferably the broach is
thus rotated 360 or one full revolution when broaching while
pulled through the engine block 80 that every point on the
cutting edges will engage in the aluminum of the block for half
a ~troke and in the ductile iron of the bearing cap for the
other half of the stroke. Rotating the broach will apply unlform
wear patterns on the cutting edges of the broaching sections,
further alding in minimizing drifting of the broach. The spiral
gullets also achieve a re continuous engagement with the
bearing bores throughout the broaching action.
A nut 77 is threaded on the front end of the draw bar
40 and packs the various shells sleeved on the draw bar into
tight end-to-end contact, holdinq the slot and pro~ection
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interengagement between the broaching shells and intermed$ste
piloting shells so they are not free to rotate on the draw bar.
A set screw 79 carried by the nut is advanced into engagement
with an annular groove 81 in the draw bar to hold the nut clamped
against the shells.
Figures 5A - 5D ~how the broach a~ it i~ pulled through
the bearing bores of the engine block. It will be noted in
Figure 5A that initlally the front piloting section 50 i8
completely within all five bearing bores. Figures 5B and 5C
show the alternate broaching of the bearing bores and guiding
in the broached bores as the broach advances. Figure 5D shows
the position of the broach after broaching has been completed
and the rear piloting section 52 extends through all of the
broached bearing bores.
A~ noted in Figures 5B and 5C, the broach is designed
in relation to the spacing of the bearing bores so that no two
ad~acent bearing ~ournal~ are broached at the same time. While
one broaching section i8 broaching one bearing bore,the ad~acent
piloting section is guiding the broach in the ne~t bearing bore.
Thus a guidea movement of the broach is provided, preventing
the broach from ~traying off line.
Although the broach 10 is described and illu~trated
as composed of an assembly of separable part3 in which the front
piloting ~ection 50 is formed of a plurality of shells 72 sleeved
on the draw bar 40, and the broaching sections 54 - 62 and
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intermediate piloting sections 64 - 70 are Also formed of
cylindrical shells sleeved on the draw bar, it ~hould be
understood that the broach may, if desired, be formed 89 one
solid piece in which all parts, including the draw bar, front
piloting section50,rearpiloting section 52, broachlng sectlon~
S4 - 62 and intermediate piloting sections 64 - 70 ~re
manufactured as a single integral unit.
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