U.S. patent application number 10/145494 was filed with the patent office on 2002-11-21 for precisely repositioning powder metal components.
Invention is credited to Cadle, Terry M., Eckstein, Lawrence E..
Application Number | 20020170161 10/145494 |
Document ID | / |
Family ID | 27360659 |
Filed Date | 2002-11-21 |
United States Patent
Application |
20020170161 |
Kind Code |
A1 |
Cadle, Terry M. ; et
al. |
November 21, 2002 |
Precisely repositioning powder metal components
Abstract
A sintered powder metal (P/M) component has an integrally formed
tapered boss surrounding its bolt hole which extends into
counterbores in a component to which it is assembled and produces
plastic conformance between the boss and the counterbore when the
boss is seated in the counterbore. The P/M component can then be
removed from the other component and reassembled to it, with the
boss fitting perfectly back into the bore with the plastically
deformed surfaces fitting back together precisely to determine the
relative positioning of the two components. The boss is tapered, a
moat may surround it, and the boss may be provided with axial
splines and/or be oblong in the axial direction. Bosses such as
these may be applied to two components in general, at least one of
which is powder metal, such as a main bearing cap, a sensor ring
for measuring the timing of an internal combustion engine and a
connecting rod bearing cap. Such bosses may also be applied to a
casting insert in which the boss is crushed when the die is closed
so as to seal off the surrounded hole during casting.
Inventors: |
Cadle, Terry M.; (Wauwatosa,
WI) ; Eckstein, Lawrence E.; (Beaver Dam,
WI) |
Correspondence
Address: |
QUARLES & BRADY LLP
411 E. WISCONSIN AVENUE
SUITE 2040
MILWAUKEE
WI
53202-4497
US
|
Family ID: |
27360659 |
Appl. No.: |
10/145494 |
Filed: |
May 14, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10145494 |
May 14, 2002 |
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09527791 |
Mar 17, 2000 |
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6422755 |
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10145494 |
May 14, 2002 |
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09155781 |
Oct 2, 1998 |
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6086258 |
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09155781 |
Oct 2, 1998 |
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PCT/US97/04050 |
Mar 12, 1997 |
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60168245 |
Dec 1, 1999 |
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60016852 |
May 3, 1996 |
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Current U.S.
Class: |
29/505 ; 29/525;
29/888.09 |
Current CPC
Class: |
Y10T 29/49288 20150115;
F16C 35/02 20130101; B22F 3/1035 20130101; C22C 33/0214 20130101;
Y10T 29/49908 20150115; B22F 5/00 20130101; F05C 2251/042 20130101;
Y10T 29/49945 20150115; F05C 2201/021 20130101; B22F 5/10 20130101;
B22F 2998/00 20130101; F16C 33/06 20130101; F16C 7/023 20130101;
F16C 9/04 20130101; F16C 43/02 20130101; B22F 2998/00 20130101;
Y10T 29/49291 20150115; F05C 2201/0436 20130101; F05C 2201/0439
20130101; F16C 9/02 20130101; F02F 7/0053 20130101 |
Class at
Publication: |
29/505 ; 29/525;
29/888.09 |
International
Class: |
B23P 011/00 |
Claims
What we claim is:
1. A method of precisely positioning two components relative to one
another in which at least one of said components is sintered powder
metal, comprising: forming said sintered powder metal component
with a boss protruding from a surface of said sintered powder metal
component; forming a hole in said other component to which said
sintered powder metal component is assembled, said hole being sized
and positioned to receive said boss with interference between said
boss and hole; inserting said boss into said hole with sufficient
force so as to cause plastic conformance between said boss and said
hole; removing said boss from said hole; and reinserting said boss
in said hole.
2. The method as defined in claim 1, further comprising the step of
tapering the boss such that the boss progressively tightens in the
hole as it is inserted.
3. The method as defined in claim 1, further comprising the step of
forming splines on the outside of the boss, the axial splines
deforming as the boss is inserted in the hole.
4. The method as defined in claim 1, wherein said sintered powder
metal is formed from a liquid phase sintering powder metal
material.
5. The method as defined in claim 1, further comprising the step of
forming a moat around a trailing end of the boss, the moat creating
a void into which material around the boss may expand.
6. The method as defined in claim 1, wherein the boss is formed to
be oblong in one direction to provide an interference fit with the
hole in that direction.
7. The method as defined in claim 1, further comprising the step of
forming the boss on a powder metal insert for casting, the insert
acting as a crush ring to seal molten casting metal from flowing
out of the hole.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/527,791 filed Mar. 17, 2000, which claims
the benefit of U.S. Provisional Patent Application Serial No.
60/168,245 filed Dec. 1, 1999 and is a continuation in part of U.S.
patent application Ser. No. 09/155,781 filed Oct. 2, 1998, which is
the national phase in the U.S. of International Patent Application
Serial No. PCT/US97/04050 filed Mar. 12, 1997, which claims the
benefit of U.S. Provisional Patent Application Serial No.
60/016,852 filed May 3, 1996.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to powder metallurgy, and in
particular to the application of powder metallurgy to produce
precisely repositionable components.
[0004] 2. Discussion of the Prior Art
[0005] International Patent Publication No. WO 97/42424 published
Nov. 13, 1997, which is hereby incorporated by reference, discloses
an integral dowel design solution for a problem where there was a
specific need for bearing caps to be accurately repositioned after
joint separation and reassembly. U.S. patent application Ser. No.
09/155,781 filed Oct. 2, 1998, which issued Jul. 11, 2001 as U.S.
Pat. No. 6,086,258, hereby incorporated by reference, is the
national phase in the U.S. of International Patent Application
Serial No. PCT/US 97/04050 filed Mar. 12, 1997 which was published
in the above identified International Publication No. WO
97/42424.
[0006] The essential function of a bearing cap is to retain and
locate a rotary shaft, or a bearing for a rotary shaft which in
turn retains and locates the shaft, relative to a support
structure. For example, the main bearing cap of an engine bolts to
a bulkhead of the engine crankcase and together with the bulkhead
retains and locates the crankshaft journal in place while the
crankshaft is rotating. The crankshaft journal runs against two
half shell bearings which are fitted to the main bearing cap and
the engine bulkhead semi-circular bores, respectively.
[0007] In this case, for vibration free, low friction and quiet
running, the roundness of the bore produced by the main bearing cap
and the bulkhead is very important. This roundness is achieved by a
machining operation called line boring. The main bearing caps are
bolted to the bulkheads of the engine block, and then a boring bar
fitted with a cutting tool is used to machine the bores in the
assembly. This ensures the two half rounds formed by the main
bearing cap and the bearing block form as near to a perfect circle
as possible. A finishing operation involving a grinding hone is
often used to achieve the extremely fine tolerances needed for
quiet running and efficient engine performance.
[0008] However, to install the crankshaft, it is necessary to
remove the main bearing caps from the engine block. After the
crankshaft is put in place, it is necessary to reposition the main
bearing caps to the bulkhead so that they are replaced in the
identical position they occupied during the line boring operation.
Any deviation from that original position produces an out-of-round
condition that, in turn, leads to vibration, noise and possibly
stiff, high friction crankshaft operation.
[0009] There are a number of conventional structures for
re-locating and attaching the main bearing caps to bulkheads when
installing the crankshaft. One such structure is shown in FIG. 1.
In this instance, the main bearing cap C has a very precisely
machined, snap-width W, which is the distance across the long axis
of the main bearing cap across the foot sections T of the bearing
cap. Similarly, a precision channel P is machined in the engine
block bulkhead B to produce a controlled interference fit with the
feet T when the main bearing cap C is refitted after crankshaft
installation.
[0010] This method does not, however, provide relocation in the
fore and aft direction (i.e., in the direction of the axis of the
journal bore J). The bolt holes H themselves are used to control
the axial repositioning, and since there is a substantial clearance
between the bolts F and the bolt holes H of the main bearing cap C,
this relocation accuracy is generally poor.
[0011] In addition, the interference fit between the main bearing
caps C and the channel P in the engine block B in this structure is
a variable which affects the final roundness of the bore J after
re-installation. A highly stressed main bearing cap C may stress
relieve during engine operation, thereby changing the roundness of
the bore. Also, the precision machining operations required on the
main bearing caps C to define the snap width W and on the block B
to form the channel P, so as to avoid an overstressed or loose main
bearing cap in this structure, are relatively expensive.
[0012] Another known method of location and attachment is shown in
FIG. 2. This involves the use of hollow dowels D. These dowels D
are pressed into counter-bored holes L in the engine block bulkhead
B. The dowels D then locate in precisely machined counterbores M in
the corresponding main bearing cap foot sections T. The accuracy of
installation of the hollow dowels D is dependent upon the precision
counterboring of the engine block and the main bearing cap. Both of
these operations have a finite tolerance which, when stacked up
with the tolerance on the dowel D outer diameter, can produce an
unacceptable variation in location of the main bearing cap C.
Additionally, this procedure has the added expense of purchasing
precision hollow dowels, their handling and installation, and the
costly machining of precision bores L in the bulkhead B and M in
the main bearing caps C.
[0013] In many cases where hollow dowels as shown in FIG. 2 are
used, the engine block channel/main bearing cap snap width
relocation method of FIG. 1 is also used. This combination is
expensive and, in fact, can produce a situation where the
interference fits between the snap-width and channel are in
conflict with the interference fits between the hollow dowels and
the main bearing cap or bulkhead holes.
[0014] It has also become clear that there are many other
applications that would benefit from an integral dowel design. One
example concerns the need for precise angular location of a toothed
sensor ring that measures the timing of an internal combustion
engine. FIGS. 27 and 28 show drawings of a portion of the sensor
ring and the flywheel or other component to which it is assembled.
The previous design of FIGS. 27 and 28 used bolts 601 with a
conical head shape that locates into a similar cone shape in a ring
602. This suffers from the problem of using the threaded hole 603
to provide angular location. As stated above, it is well known in
the engineering profession that using a threaded hole to both fix
and precisely locate two components is not good practice. The
reasons are that it is difficult to thread a hole concentrically,
and even harder to ensure that the bolt is concentric to the
threads.
[0015] This stack-up of errors reduces the precision of the fixture
to the point where a separate locating dowel 604 is often needed,
as illustrated in FIGS. 28a-d, similar to the separate dowel of
FIG. 2. As stated above, the two components must be precisely
oriented and clamped, then a precision hole 605 must be bored
through one component into the second one. Finally, a separate
dowel 604 must be pushed through both holes 605 to achieve the
desired location precision. This is expensive both in cost of
machining and the purchase of the dowel 604.
SUMMARY OF THE INVENTION
[0016] The present invention provides a structure and method of
permitting precise repositioning of two components relative to one
another where one of the components is made by powder metallurgy
(P/M). The P/M component has an integral boss protruding from it,
which is received in a bore of the part to which the component is
assembled. The boss is of a shape and ductility so that at least
one of the boss and bore plastically conform to one another when
they are brought together with force, for example in a pressing
operation or when they are bolted together for the first time. The
plastic deformation of the boss and bore creates a unique mating
surface fit between the two parts so that when the two parts are
taken apart and then put back together, they go back together in
the exact same, or near to the exact same, position.
[0017] In a preferred form, the boss is provided around a bolt hole
in the P/M component, and the boss fits into a counterbore of a
bolt hole in the part to which the P/M component is assembled.
Counterboring bolt holes is a standard process in manufacturing and
so the invention is readily adapted to be used without major
production line changes.
[0018] The boss is preferably tapered, so as to progressively
tighten in the bore as it is forced in. A lead-in radius may be
provided on a leading edge of the boss to help initially locate the
boss in the bore. Axial splines may be provided on the outside of
the boss to further contribute to unique plastic deformation
between the boss and bore, with the splines and boss conforming to
the bore if the bore is in a relatively hard material such as cast
iron, or bite into the bore if the bore is in a relatively soft
material such as an aluminum alloy.
[0019] Plastic conformance between the bore and the boss is
facilitated by the boss and remainder of the bearing cap being
sintered powder metal, which is not fully dense. However, it may
also need to be ductile, depending on the material of the bore, and
if so it is preferably a liquid phase sintering powder metal
material. Such a material preferably is a powder metal alloy of
iron containing phosphorus from ferrophosphorus powder with a
phosphorus content of 0.4 to 0.7% and a carbon content of 0 to
0.8%. Additional strength may be achieved with the addition of
copper in the amount of 0 to 4% without loss of ductility.
[0020] In another preferred aspect, a moat is formed around a
trailing end of the boss. The moat creates a void into which
material around the bore may bulge or expand when it is deformed by
the insertion of the boss.
[0021] In another aspect, the boss may be oblong in one direction,
so as to provide an interference fit with the bore in that
direction. Other means may be provided to accurately position the
components in the other direction.
[0022] These aspects may be applied to any of a number of different
components. Component applications specifically described are main
bearing cap, timing sensor ring and connecting rod bearing cap
applications, but the invention is not limited to only these
applications.
[0023] In another aspect of the invention, a deformable boss can be
formed on a powder metal insert for casting which acts as a crush
ring to seal molten casting metal from flowing into a hole or
crevice which the boss surrounds. The insert is placed in the
casting mold, and when the mold halves come together, the bosses
are crushed so as to form the seal.
[0024] In a method of the invention, two parts, one of which is
sintered powder metal, are brought together with enough force to
cause plastic conformance between the boss of the P/M part and the
hole into which it is inserted. The parts are taken apart and, when
reassembled, go back together to replicate the original assembled
position.
[0025] Other objects and advantages of the invention will be
apparent from the detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a cross-sectional view of a prior art main bearing
cap secured to an engine bulkhead;
[0027] FIG. 2 is a cross-sectional view of another prior art main
bearing cap secured to an engine bulkhead;
[0028] FIG. 3 is a side elevation view of a main bearing cap
incorporating the invention;
[0029] FIG. 4 is a bottom plan view of the main bearing cap of FIG.
3;
[0030] FIG. 5 is a fragmentary detail side elevation view of a foot
of the main bearing cap of FIGS. 3 and 4;
[0031] FIG. 6 is a fragmentary bottom plan view of the foot of FIG.
5;
[0032] FIG. 7 is a view similar to FIG. 5 but of an alternate
embodiment;
[0033] FIG. 8 is a bottom plan view of the foot of FIG. 7;
[0034] FIG. 9 is an enlarged fragmentary detail bottom plan view of
the foot of FIG. 8;
[0035] FIG. 10 is a partial cross-sectional view as viewed from the
plane of the line 10-10 of FIG. 9;
[0036] FIG. 11 is a partial cross-sectional view as viewed from the
plane of the line 11-11 of FIG. 9;
[0037] FIG. 12 is a partial cross-sectional view as viewed from the
plane of the line 12-12 of FIG. 11;
[0038] FIG. 13 is a partial cross-sectional view as viewed from the
plane of the line 13-13 of FIG. 11;
[0039] FIG. 14 is a view similar to FIG. 5 but of another alternate
embodiment of a foot for a bearing cap of the invention;
[0040] FIG. 15 is a bottom plan view of the foot of FIG. 14;
[0041] FIG. 16 is a view similar to FIG. 5 but of another alternate
embodiment of a foot for a bearing cap of the invention;
[0042] FIG. 17 is a bottom plan view of the foot of FIG. 16;
[0043] FIG. 18 is a view similar to FIG. 5 but of another alternate
embodiment of a foot for a bearing cap of the invention;
[0044] FIG. 19 is a bottom plan view of the foot of FIG. 18;
[0045] FIG. 20 is a side elevation view of another alternate
embodiment of a bearing cap of the invention, similar to FIG.
3;
[0046] FIG. 21 is a bottom plan view of the bearing cap of FIG.
20;
[0047] FIG. 22 is a detail bottom plan view of the left foot shown
in FIGS. 20 and 21;
[0048] FIG. 23 is a detail side elevation view of the foot shown in
FIG. 22;
[0049] FIG. 24 is a view of how a bearing cap can be loaded in
operation;
[0050] FIG. 25 is a bottom plan view of another alternate
embodiment of a bearing cap of the invention; and
[0051] FIG. 26 is a bottom plan view of another alternate
embodiment of the invention.
[0052] FIGS. 27a and 27b are cross-sectional views of a prior art
method of fastening and locating two components relative to one
another using a threaded bore in one of the components, a conical
counterbore in the other component and a conical headed threaded
fastener;
[0053] FIGS. 28a-d are cross-sectional views of a prior art method
of fastening and locating two components relative to one another
using a separate dowel fitted in holes bored in both
components;
[0054] FIGS. 29a and 29b are cross-sectional views, similar to
FIGS. 27 and 28, but illustrating an application of the present
invention to joining and locating the two components relative to
one another;
[0055] FIGS. 30a and 30b are cross-sectional views illustrating an
application of the present invention to securing and locating a
bearing cap relative to a connecting rod;
[0056] FIGS. 31a-e are cross-sectional views illustrating an
application of the present invention to securing and locating a die
casting mold insert in a die casting mold; and
[0057] FIGS. 32a-d are detail views illustrating how an integrally
formed crush ring of the insert of FIG. 31 is crushed to seal off
the bolt hole from the flow of casting metal.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0058] FIGS. 3 and 4 illustrate a main bearing cap 10 of the
invention. The cap 10 defines a semicircular bore 12 which together
with the semicircular bore of the engine bulkhead (see, for
example, FIG. 2) defines the bore J (FIG. 2) through which the
crankshaft of the engine extends and is journaled. Journal bearings
may be received in the bore between the surface of the crankshaft
and the surface of the bore J, as is well known. Cap 10 may be
notched as at 14 to receive an ear of the journal bearings so as to
prevent the journal bearings from rotating relative to the cap 10
and bulkhead B. The semicircular bore 12 extends through the
bearing cap 10 from the front side 16 to the rear side 18.
[0059] The bore 12 defines on each of its lateral sides a foot
portion 22 of the cap 10. A bridge portion 24 joins the two foot
portions 22. A bolt hole 26 extends through each foot portion 22
from the top side 32 to the bottom 34 of the cap 10. The cap 10 may
also be provided with threaded set screw holes 36 extending from
the lateral sides 38 and 39 at right angles into the respective
bolt holes 26 so as to lock the retaining bolts (F in FIG. 2) in
position after the cap 10 is bolted to the engine bulkhead (B in
FIG. 2) support structure.
[0060] Projecting from the bottom side 34 of each foot 22 around
the respective bolt hole 26 is a boss 40. Each bolt hole 26 extends
through its corresponding boss 40. FIGS. 5 and 6 show in detail the
structure of the boss 40. The two bosses 40 are identical, so only
one will be described in detail.
[0061] The boss 40 extends for 360.degree. around the bolt hole 26
and is itself surrounded by a recess or moat 44 which is formed in
the bottom surface 34 of the foot 22 for the purpose described
below.
[0062] The bolt hole 26 extends into the engine bulkhead B where it
is threaded so that bolts F, as shown in FIG. 2, may be used to
secure the cap 10 to the bulkhead B. The bulkhead bolt holes are
also counterbored, as shown at L in FIG. 2, so as to receive the
bosses 40 in the counterbores of the bulkhead. However, the
counterbores L of the bulkhead need not be as precise in diameter
or position as was necessary when using the precision hollow dowels
D as shown in FIG. 2, because the boss 40 is tapered and the boss
40 and counterbore L are conformable to one another.
[0063] To effect perfect mating of the parts during line boring and
subsequently thereafter when the crankshaft is installed, the main
bearing cap 10 is made by sintered powder metallurgy, with the
bosses 40 molded integrally with the feet 22 and remainder of the
bearing cap 10. As shown in FIGS. 5 and 6, the boss 40 tapers from
a minor diameter at its leading edge 46 to a larger, major diameter
at its trailing edge 48. The minor diameter is chosen to be less
than the diameter of the counterbore L in the bulkhead B, and the
major diameter is chosen to be equal to or slightly greater than
the diameter of the counterbore L. This tapering of the boss 40
ensures that the main bearing cap 10 is in the identical position
after crankshaft installation as it was when it was line bored. The
angle of the taper is preferably greater than 7.degree. so as to
ensure easy removal of the bearing cap 10 from the bulkhead after
line boring.
[0064] An alternate embodiment of the boss 40, designated 140, is
shown in FIGS. 7 and 8, with details shown in FIGS. 9-13. The boss
140 is identical to the boss 40, except as shown and described
below. The boss 140 shown in FIGS. 7 and 8 has linear splines 160
angularly spaced apart all the way around its circumference.
Leading edge 146 of the boss 140 defines the minor diameter of the
boss 140, which is less than the diameter of the counterbore in the
bulkhead into which the boss 140 fits, and the boss 140 tapers to
its major diameter at its trailing edge 148, which is somewhat
greater than the counterbore diameter into which the boss fits.
[0065] As shown in FIGS. 9-13, the linear splines 160 are flat from
leading edge 146 to line 162, which is at approximately the axial
midpoint of the boss 140, and are pointed and continue to taper
outwardly at a more shallow angle from the midpoint 162 to the
trailing edge 148. The underlying tubular body 164 of the boss 140
may also taper from leading edge 146 to midpoint 162 and may at
that point become constant in diameter to the trailing edge 148 so
as to provide adequate support to the splines 160.
[0066] FIGS. 14-19 show other alternate embodiments of the
invention. Elements corresponding to elements of the boss 140 are
labeled with the same reference numeral plus 100 for FIGS. 14 and
15, plus 200 for FIGS. 16 and 17 and plus 300 for FIGS. 18 and
19.
[0067] The boss 240 shown in FIGS. 14 and 15 is identical to the
boss 140, except that it is not provided with axially running
linear splines 160. The boss 340 shown in FIGS. 16 and 17 is
identical to the boss 40 of FIGS. 3-6, except that it does not
extend for 360.degree. around the bolt hole 26. The moat 344 is
also coterminous with the trailing edge 348 of the boss 340. The
boss 440 is the same as the boss 40, except that it is provided
with ribs or axially running linear splines 460 which are flat from
their leading edges to their trailing edges.
[0068] The exact design of the boss used for practicing the
invention will depend upon the application. There must be
sufficient conformance between the bosses 40 and the counterbores L
of the supporting structure so as to precisely locate the bearing
cap 10 relative to the support structure. If additional conformance
is needed, a design utilizing the linear splines such as 160 or 460
may be used. The combination of these linear splines and the fact
that the sintered powder metal is not fully dense, results in the
needed conformance between the boss and the corresponding bulkhead
counterbore.
[0069] Where the bulkhead material is an aluminum alloy, for
example, the linear splines bite into the softer counterbore to
make a perfect fit. Any bulging of the aluminum is accommodated by
the moat 44, 144, 244, 344, or 444. In the case of a cast iron
bulkhead, which is relatively hard and non-conforming, the splines
can condense and conform to the cast iron counterbore, and, again,
form a perfect fit.
[0070] FIGS. 20-23 illustrate another alternate embodiment of a
bearing cap of the invention. Elements corresponding to elements of
the boss 140 are labeled with the same reference numeral plus
400.
[0071] The boss 540 is the same as the boss 140, except that it is
oblong (which includes oval), having its longer dimension in the
direction of the crankshaft which is retained by the bearing cap,
i.e., in the axial direction of the bore 412. The result is that
the bosses 540 engage their round engine block bulkhead
counterbores in such a way as to prevent relative motion in the
axial direction but provide a clearance in the lateral direction,
which is the direction that the snap width (between surfaces 438
and 439) provides for location. Thereby, by the oblong bosses 540
providing an interference fit in the axial direction and the snap
width providing an interference fit in the lateral direction, the
bearing cap 410 is accurately located in all directions.
[0072] Since the boss 540 is oblong, the recess or moat 544, which
has a round outer periphery, varies in width as illustrated. The
hole 526 is a truncated round shape, having its round shape
truncated by laterally extending flats which are spaced far enough
apart in the axial direction to permit passage of the bolt F for
securing the cap 510. This shape allows substantial clearance with
the bolts in the lateral direction.
[0073] In FIGS. 20 and 21, a 360.degree. boss 540 is shown on the
left side and a boss 540 is shown on the right which extends for
less than 360.degree., extending for approximately 270.degree. with
its inward most quadrant absent. The moat 544 of the right boss 540
is also truncated. It should be understood that the bosses can be
different as shown, or can be the same, with both being 360.degree.
or 270.degree. bosses.
[0074] The precise installation of the main bearing cap 10, 110,
210, 310, 410 or 510 with any of the bosses described above can be
achieved by tightening the retaining bolts F alone, or
alternatively, by applying independent pressure to the assembly,
for example, from a hydraulic ram. After line boring, the bearing
cap is readily removed due to the tapered geometry of the
installation interface. After installing the crankshaft, the
bearing caps are replaced, and the integral bosses nest into their
preformed positions (preformed when the cap was initially mounted
to the support structure prior to line boring) with great
accuracy.
[0075] As stated above, the particular design of the boss will
depend on the application. The principal variables in the design
are the taper angle, the length of the boss, the relative lengths
of the tapered and straight portions of the boss, the number,
width, and radial height of any vertical splines, and the radial
wall thickness of the boss. The leading edge of the splines may be
tapered at a higher angle as shown in FIG. 10 or may have a small
lead-in radius as shown in FIG. 18 to aid in initial location of
the bearing cap bosses into the bulkhead counterbores. The
particular design of a bearing cap incorporating the invention will
depend upon various specific design details of the bulkhead, such
as whether a bearing notch is needed in the cap, wall thicknesses
needed between the bolt hole and the side of the bearing cap, the
material of the bulkhead, and the design of the bulkhead
counterbore hole, for example, with respect to lead-in chamfers or
even a preformed taper. In all cases, however, it is essential that
the sintered powder metal bearing cap boss produce a mating surface
to ensure identical relocation after installation of the
crankshaft, by plastically conforming to the counterbore, causing
the counterbore to plastically conform to the boss, or a
combination of both.
[0076] As mentioned above, for practicing the invention, the
bearing cap must be made of sintered powder metal. A desirable
quality of the powder metal material of the bearing cap for
carrying out the invention is ductility. Since the splines, or the
body in some cases, will yield plastically to some extent during
the initial installation process, it is important to avoid
cracking. Most powder metal ferrous materials are inherently
brittle. To overcome this potential difficulty, it is preferable to
use a material that has an adequate ductility.
[0077] There are a number of ways of improving the ductility of
sintered powder metal ferrous materials, but most of them are
expensive or inapplicable to bearing caps. However, an appropriate
liquid phase sintering system is particularly useful in providing
the necessary ductility in this application. An example of this
process involves the use of a phosphorus compound such as
ferrophosphorus. A small amount of ferrophosphorus powder is added
to the ferrous material powder during powder blending. After
compaction and during the thermal treatment stage (sintering), this
small amount of ferrophosphorus becomes molten and dramatically
increases the rate of atomic diffusion during the sintering
process. This enhanced diffusion produces a rounding of the
microporosity in the sintered powder metal component which, in
turn, provides increased ductility.
[0078] To achieve this, the composition of the powder metal
material from which the bearing cap of the invention is made should
contain 0.4 to 0.7% phosphorus (preferably 0.4 to 0.6% phosphorus),
a carbon content of 0 to 0.8% carbon (preferably 0.4 to 0.6%
carbon) and with the balance being essentially iron (neglecting
impurities). This material with the preferred percentages can
produce a tensile elongation of 3%, which is adequate for straight
spline conformance to a cast iron counterbore, and also strong
enough to indent a cast aluminum alloy bulkhead. Additional
strength can be attained by the addition of 0 to 4% copper in the
final mix of the material for making bearing caps of the invention
without loss of ductility.
[0079] In practicing the invention, it is important to ensure
dimensional consistency of the distance between the axial centers
of the bosses. It is relatively inexpensive to control the
counterbore L diameter hole centers in the engine block bulkhead by
the use of appropriate drill guides or computer controlled drill
heads. However, to control the distance between the boss centers of
bearing caps of the invention requires some form of dimensional
control during or after the sintering operation. One example of an
appropriate procedure is to repress the bearing cap in a set of
tools which will straighten and adjust the dimensions of the
component. This is a procedure well known in the powder metallurgy
industry as repressing (also known as sizing or coining). An
alternative approach is to use a fixture which locates and retains
the bearing cap holes in position during sintering. Such a fixture
could be made from either stainless steel or molybdenum and may
consist of a U-shaped staple like structure, the legs of which are
inserted into the bolt holes of the main bearing cap, thereby
avoiding distortion during the sintering operation.
[0080] A common problem encountered in main bearing cap joints is
"fretting". This is the relative micromovement of the clamped
contact surfaces of the bearing cap and bulkhead at high frequency
that results in damage to the surfaces. Fretting fatigue is a
possible outcome of this mechanism.
[0081] When a main bearing cap is constrained laterally in the
block by a snap width channel as shown in FIG. 1, it can still move
fore and aft (axially) and also from side to side (laterally) under
load. Fore and aft motion is due to crankshaft bending (especially
in V-engines) which causes a rocking motion. Since there is no
restraint in this direction other than bolt clamp pressure,
microsliding, and therefore fretting, can occur. Similarly, as
illustrated in FIG. 24, when the crankshaft loading X is pushing
the cap to the "right", the left foot is pulled away from the snap
channel as indicated by arrows Y to create a clearance at the area
indicated by the arrow Z.
[0082] The present invention, which provides an integral hollow
dowel on the bearing cap foot, improves this situation since the
dowel serves to fix the position of the foot relative to the block.
The fretting problem can be further mitigated by hollowing out the
footprint of the bearing cap, which has the effect of raising the
clamping pressure for a given bolt loading. By appropriate
geometry, the remaining metal forms a land that increases the
quality of clamping close to the bearing shell.
[0083] The technique of reducing area to raise clamping pressure is
not new. However, it is very costly to achieve in volume
production. The current predominant process of making bearing caps
is by casting and machining. To machine precision hollow forms in a
casting is prohibitively expensive. Using powder metallurgy,
however, hollows can be molded into the foot with great precision
for no extra cost beyond the initial tooling face form costs.
Examples of four suitable forms for producing the indicated void
areas V1-V4 (approximately 0.010- 0.020 inches deep) and
corresponding planar contact areas A1-A4 are shown in FIGS. 25 and
26. These voids may be used either with or without integral bosses
as described above and may be used in any combination.
Experimentation with pressure sensitive paper and finite element
analysis simulation shows that the hollowed out foot surface raises
the clamping pressure by the following percentages (the void area
given is for each void and there are two voids per foot as
illustrated):
1 Clamping Load Contact Area (in.sup.2) Void Area (in.sup.2)
Increase A1 = 1.0957 V1 = .2942 32% A2 = 1.1373 V2 = .2936 33% A3 =
1.0191 V3 = .2936 30% A4 = 1.0504 V4 = .3159 33%
[0084] The previously described structures, materials and methods
as applied to a bearing cap can also be applied to other powder
metal components. Thus, the present invention avoids the problems
of the prior art in locating two components of any suitable type
fastened by a bolt 601 (FIG. 29a-b) by using a precision drilled
counterbore 608 in one of the components 609 in combination with an
integral dowel 612 made by powder metallurgy. The counterbore 608
may be provided around a hole 614 in the component 609, which may
be tapped, as shown in FIGS. 29a and 29b. The counterbore 608 is
easily provided by commonly available computer numerically
controlled (CNC) machining units. The integral dowel 612 formed on
the mating component 616 engages the counterbore 608 and is
self-centering on account of the tapered or conical shape of the
integral dowel 612 fitting into and interfering with the
counterbore 608. The bolt 601 pulls the tapered lead angle of the
conical outer surface of the integral dowel 612 into the
counterbore 608 to give precise angular location. Plastic
deformation of the dowel 612 and/or counterbore 608 may occur, and
may be preferred in some applications, since such deformation
contributes to precise relocation. Another advantage of this
application is that it avoids the need for special conical-head
bolts, and can use low cost regular headed bolts.
[0085] Another example of the application of this invention is a
reciprocating engine connecting rod 620 and bearing cap 622 as
shown in FIGS. 30a and 30b. In this case, the cap 622 has to be
connected to the rod 620 prior to machining the bore 624, 626 in
which the crankshaft is journaled so that when the piston pin of
the crankshaft (not shown) is inserted in the bore 624, 626 after
machining, it locates in the correct location. This ensures
excellent roundness and quiet running of the engine piston. Current
solutions include a method where the cap is fractured away from the
rod, so that the fracture is used to precisely reassemble the rod
and cap. This is fine for essentially brittle materials, but is
inappropriate for the stronger, tougher materials used for highly
stressed engines, since instead of cracking, they tend to bend and
deform. In such cases, the current invention is an economical
solution. The cap 622 is molded with two integral dowels 630, 632
having outer conical surfaces that fit into and interfere with
counterbores 634, 636 formed around the drilled and threaded holes
638 in the rod 620. Again, this invention separates locating and
fixturing, which avoids the bolts bearing against the sides of the
bolt holes, which can introduce distortion and stresses that can
lead to engine failure.
[0086] Another application of the invention is to locate a powder
metal component in a die cavity that will be filled with molten
metal--especially aluminum. Often, it is necessary to reinforce an
aluminum casting with a powder metal (P/M) steel insert. For
example, such an application may include a main bearing insert in
the lower half of an aluminum alloy combustion engine cylinder
block or a bed plate. In such a case, the lower thermal expansion
of the steel of the insert compared to the aluminum alloy of the
crankcase is used to maintain bore-roundness when the engine
temperature rises during running and the aluminum tries to grow
away from the crankshaft, leaving a gap that can cause engine
noise.
[0087] It is difficult to accurately position the insert within the
die cast mold since the mold is open at insertion and closed during
casting. The integral dowels solve this problem by both locating
the bearing cap during mold closure and sealing off the bolt holes
from molten aluminum.
[0088] FIG. 31a shows the open die halves 650, 652 and FIG. 31b
show it with a main bearing cap insert 654 impaled on two
bullet-nosed pins 655, 657 that hold it in position on the left
half 650 of the die, while the opposite right side 652 of the die
advances as the mold is closed (FIG. 31c). The right die wall has
two shouldered bullet nosed pins 662, 664, one of which is shown in
detail in FIGS. 32a-d, that locate into the open ends of the holes
666 in the bearing cap insert 654, when the mold is almost closed,
as shown in FIGS. 32a-d. The die mold halves 650, 652 are finally
clamped closed under a very high load, sufficient to crush the
integral dowels and bring the mold halves together with sufficient
force so as to prevent high pressure molten aluminum 674 from
spurting out from the mold joint line. The shoulders 658, 660 on
the right hand set of pins 662, 664 crush the integral cone-shaped
dowels 670 to create a seal between the pins and the holes 666. The
seal prevents the molten aluminum 674 from entering the holes 666.
This action causes precise location of the cap 654 and eliminates
the need for expensive drilling-out of aluminum flash that
otherwise enters the bolt holes 666 where it solidifies. After
solidification of the aluminum, the mold is opened as shown in FIG.
31e, and the composite part is ejected.
[0089] The height of the integral dowel 670 (or crush ring) is
chosen to accommodate normal variation in mold closing distance and
to produce adequate resistance to provide a sealing pressure that
prevents aluminum penetration. It is the intrinsic microporous
nature of sintered powder metal that enables the material to behave
in this way to effect a crush ring seal. The traditional gray cast
iron that is often used for main bearing caps is very brittle and
would crack and fragment under the crushing load. Ductile cast iron
which is also used, would be more likely to deform without
cracking, but the cost to machine the integral dowel shapes around
the bolt holes would be prohibitive.
[0090] Experimental integral-dowel in-casting trials with a test
mold in a high pressure die cast machine enabled the crush ring
dimensions to be optimized. Subsequently these findings were
confirmed in a casting trial that involved substituting P/M steel
caps in a current production bed plate that contained five ductile
cast iron bearing cap inserts. The tests showed that a dowel height
of 0.04 inches (2 mm) with a 0.02 inches (0.5 mm) flat sealing face
radial thickness and an angle of 45 degrees (90 degrees included
cone angle) worked well in locating the in-cast insert. This also
gave 100% sealing against aluminum ingress of all the bolt holes in
a trial of 100 holes, compared to at least 70% of holes in the cast
iron which suffered aluminum leakage without the integral
dowels.
[0091] Preferred embodiments of the invention have been described
in considerable detail. Many modifications and variations to the
preferred embodiments described will be apparent to those skilled
in the art. Therefore, the scope of the invention should not be
limited to the preferred embodiments, but should be defined by the
claims which follow.
* * * * *