Note: Descriptions are shown in the official language in which they were submitted.
i7
MET~IOD AND APPAR~.TUS FOR ~CHINING E~ORES
FIELD OF THE INVENTION
The present invention relates to the machininq of a
bore in a workpiece and, in particular, to the machining
with an expant~lable tool of a thin wall defining a bore in a
workpiece and separating the bore from an adjacent passage.
BACKGROUND OF THE INVENTION
In the manllfacture or engine blocks for vehicles, the
cylinder bores are subjected to a honing operation to
provide bore dimensions withln very close tolerances. In
the pas., the maintenance of bore dimensions within the
required tolerance range has sometimes been dif.icult
especially when the cylinder block is designed and cast to
have relatively thin walls separating the bores from
adjacent coolant passages primarily for weight reduction
purposes. This difficultY has been compounded when the
cross-section of the wall varies considerably from one
location to another as a result of engine design
considerations or core shift when casting the engine block.
During honing, the honing stones are expanded radially
against the bore wall to exert an abrading action thereon, a
honing pressure in the range of 100 to 400 psi, typicall~-
200-250 psi, being used. This tool exp2nsion orc~ has
caused thin bore walls or thin portions thereo~ to be
distorted during honing, resulting in finish~d bore geometry
out o~ required tolerances.
U.S. Patent 4,117,633 issued Oct. 3, 1975 to
C. L. Yother describes a honing plate attachabie to the
cylinder block during honing to simulate the normal
operating stresses and distortions of an engine block caused
. ~ .
. .
.. . , , " ... ~ .,, , . .. ~ .. . . .. . ... . . . . . . .... . . . . . . .. . . . .. ..
-- 2 --
by bolt-on components such as cylinder heads and intake
manifolds. Re-boring and honing are effected with the plate
attached to allegedly increase the accuracy of the '~oring
and honing operations. However, this patent does not deal
with the problem of distortion of thin bore walls by the
honing tool itself, in particular by the tool e~pansion
force or pressure needed or honing engagement.
U.S. Patent 3,542,354 issued Nov. 24, 1970 to
P. Fitzpatrick and U.S. Patent 3,751,050 issued Aug. 7, 1973
to I. W. Wades et al. disclose so-called workpiece chucks or
fixtures for holding a cylindrical cylinder liner during a
machining operation such as honing without distorting the
cylinder liner. Each patent uses an expansible component to
grip and hold the workpiece around its exterior in response
to fluid pressure exerted on the expansible component.
These patents seek to minimize distortion of the cylinder
liner workpiece caused by the clamping or fixturing means.
The aforementioned prior art workers did not deal with
the problems of honing thin bore walls in engine blocks or
other articles wherein the honing tool itself causes
distortion of the thin walls and out of tolerance bore
geometry.
SUUUARY OF THE INVENTION
The present invention relates to a method and apparatus
for machining a workpiece bore, in particular a thin bore
wall separating a workpiece borG from another adjacent
passage such as a coolant passage and the like, with a tool
expandable asainst the thin wall whersin pressurizing means
applies a fluid pressure to the adjacent passage in the
workpiece during machining acting to exert a force or
pressure on the thin wall counter to the distorting force o~
the expandable tool against the wall. Distortion ~ the
57
thin wall is thereby substantially xeduced during
machining to provide a more accurate machined bore
geometry.
The apparatus according to the present invention
includes a means adapted for releasable attachment to
the workpiece to seal the passage in.. fluid pressure
tight manner and means for introducing fluid pressure
into the sealed passage during machining. Tool means
is expandable agaist the wall and is movable relative
thereto to effect machining so that the fluid pressure
in the passage acts counter to any distortion force
exerted on the wall by the expandable tool means to
reduce distortion thereof during machining whereas to
provide a closer tolerance bore geometry.
In a specific embodiment of the invention, the
coolant jacket or passages of an engine block are fluid
pressurized to a pressure level of for example 30 psi
during honing of the cylinder bores to substantially
reduce distortion of thin cylinder walls by the expansion
force of the honing tool thereagainst. Considerable
improvement in bore geometry has been achieved in this
manner.
. BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partial cross-sectional view through a four
cylinder engine block showing the walls separating the
cylinder bores ~1 and ~2 from adjacent coolant passages.
Figure 2 is a schematic end elevational view showing the
apparatus of the invention for Eluid pressurizing the
coolant passages of -the engine block while the cylinder
bores are honed.
Figure 3 is a schematic side eleva-tional view of the
apparatus of Fig. 2.
;7
Figure 4 is a schematic top view of the apparatus of
Fig. 3.
DESCRIPTION OF PREFERRED EMBODIMENTS
Fig. l illustrates a partial cross-section
through a typical engine block 10 including cylinder
bores 12 de~ined by walls 14 having relatively thick
portions 14a at the top end and relatively thin portions
14b therebelow. It is apparent that the walls 14 may
vary in cross-sectional shape or dimension along their
lengths. The thin walls 14b
.~
- 3a -
-- 4
terminate at their bottom ends in thicker suppor~ walls 15
which are not honed. As is apparent, the thin walls 14
separate the cylinder bores from adjacent coolant passages
16 formed in the engine block.
Fig~. 2-4 show an appara~us for use in the invention
comprising a simulated cylinder head 20 adapted to be bolted
to the engine block. To this end, the head includes a
plurality of holes 22 for receiving standard bolts (not
shown) and a bottom surface 24 to rest against the top
surface 26 of the engine block and close off the coolant
passages in known manner where the passages open to the top
surface 26. A resilient gasket 28 is interposed between
head surface 24 and block surface 26 to provide a fluid
pressure tight seal therebetween. The head 20 also includes
a plurality of bores 30 coaxially alisned with the cylinder
bores 12, the head bores 30 being slightly greater in
diameter than the c~linder bores to allow entry of the
honing tools 34 to the cylinder bores for the honing
operation. Honing tools used in the method of the invention
are cormmercially available and include a plurality or
abrasive stones 35 or an abrasive sleeve expandable radially
outward by various means such as tapered arbors, to engage
and contact the bore wall at a selected honing pressure to
effect honing, usually in the range of 100 psi to 400 psi,
typically 200 psi to 250 psi.
The apparatus also includes a cover 36 bolted over the
water pump opering 38 in the front side or the engine block.
A resilient gas.cet 40 is placed between the cover 36 and
engine block to provide a fluid pressure tight seal
therebetween. In addition, all other side or lateral
openings 44 in the engine block e~tending to the ~oolant
jacket or passages are plugged fluid pressure tlght by
expandable plugs 46 or other means.
To introduce fluid pressurizing means such as
pressurized liquid or gas into the coolant jacket including
passages 16, a conduit 50 is attached to the engine ~lock at
the engine temperature thermocouple opening 52. Of course,
the conduit is connected to a suitable source 54 o~
pressurized fluid such as pressurized liquid or gas. Honing
trials using the above-described apparatus were carried out
using air pressure o~ 30 p5i introduced into the coolant
passages 16 from a conventional pressurized air source and
using a pressure regulator 56 in the air supply conduit 50
to the block 10. The coolant used in the honing operation
could also be used as the pressurized fluid (from source
54).
Table I shows the roundness deviation of ~ores in a
4-cylinder automobile cast iron engine before honing by the
invention and afterwards. Honing was carried out using an
expandable honing tool with 9 abrasive stones of 230 grit
with approximately 200 psi hone pressure during a 33-second
h¢ning stage followed by a hone pressure of approximately 80
psi during a 5-second run-out stage. Roundness measurements
were taken with a commercially available "Talyrond" gage at
the top, center and bottom of each cylinder bore in known
~ashion.
. . . - .. , , :
~ 6 ~
TABLE I
DEVIATION DEVIATION
RO~IDNESS ROUNDNESS
(BEFORE) (AFTER)
(ten thousands of inch) (ten thousands of inch)
Bore ~1 Top
Center 3 1
Bottom 8 4
Bore ~2 Top 5 0
Center 13 o
Bottom 12
Bore #3 Top 2
Center 7
~ottom 12 O
Bore ~4 Top 2
Center 6
~ot~om 3
It is apparent that a marked improvement in bore
roundness is achieved by the honing method of the invention.
The increased out-o~-roundness of bore #l relative to the
other bores iq attributable to the greater thickness of
portions o the cast wall defining this bore (see Fig. 1)
compared to the other bores. Bore #l would correspond to
the ~irst bore at the front of the engine. The roundness of
bore ~1 was nevertheless considerably improved by the honing
method of the invention~ The present invention is
especially effective in improving roundness of bores with
the relatively thinner cast walls such as walls associated
with the inner bores #2 and ~3 and, depending on engine
block design, rear bore #4.
... ... . . . . .. .... ... . ... ..... . . .
-- 7 --
While there have been described what are considered to
be certain preferred embodimen~s of the invention, other
modifications, additions and the like may occur to those
skilled in the art and it is intended to cover in the
appended claims all such modifications as fall within the
spirit and scope of the invention.
