U.S. patent application number 12/604074 was filed with the patent office on 2011-04-28 for non-magnetic camshaft journal and method of making same.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Shekhar G. Wakade.
Application Number | 20110097233 12/604074 |
Document ID | / |
Family ID | 43898600 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110097233 |
Kind Code |
A1 |
Wakade; Shekhar G. |
April 28, 2011 |
NON-MAGNETIC CAMSHAFT JOURNAL AND METHOD OF MAKING SAME
Abstract
A camshaft journal and method of producing the same. The method
uses dynamic magnetic compaction in conjunction with austenitic
manganese steel powder metal precursors. Journals formed along the
camshaft are configured to cooperate with complementary bearing
surfaces, and can be used in cooperation with one or more sensors
such that the journal does not magnetically interfere with signals
travelling to such sensors. The journals may also be subjected to
machining, sintering or both once the dynamic magnetic compaction
has been completed.
Inventors: |
Wakade; Shekhar G.; (Grand
Blanc, MI) |
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
43898600 |
Appl. No.: |
12/604074 |
Filed: |
October 22, 2009 |
Current U.S.
Class: |
419/38 ; 419/66;
420/8 |
Current CPC
Class: |
B22F 5/106 20130101;
C22C 33/0278 20130101; C22C 38/02 20130101; B22F 3/162 20130101;
F01L 2303/00 20200501; F01L 2001/0476 20130101; F01L 2820/041
20130101; F01L 2001/0473 20130101; B22F 3/087 20130101; C22C 38/04
20130101; B22F 7/08 20130101; F01L 1/047 20130101; F01L 2301/00
20200501 |
Class at
Publication: |
419/38 ; 419/66;
420/8 |
International
Class: |
B22F 3/12 20060101
B22F003/12; B22F 3/087 20060101 B22F003/087; C22C 38/00 20060101
C22C038/00 |
Claims
1. A method of fabricating a camshaft journal using dynamic
magnetic compaction, said method comprising: providing a camshaft
die with an interior profile that substantially defines an exterior
profile of said journal; placing, within at least a part of said
interior profile a powdered austenitic manganese steel such that
upon formation of said journal with said camshaft die, at least the
portion of said exterior profile that corresponds to said journal
is made from said austenitic manganese steel; and subjecting said
powdered austenitic manganese steel in said camshaft die to said
dynamic magnetic compaction.
2. The method of claim 1, wherein said dynamic magnetic compaction
comprises compacting said powdered austenitic manganese steel into
a green precursor.
3. The method of claim 2, further comprising consolidating said
green precursor.
4. The method of claim 3, wherein said consolidating said green
precursor comprises sintering.
5. The method of claim 3, wherein said consolidating said green
precursor comprises machining.
6. The method of claim 3, further comprising forming an additional
shape in said journal prior to said sintering.
7. The method of claim 1, further comprising arranging a position
sensor in signal cooperation with said journal such that said
journal's substantially lack of magnetic properties prevent it from
substantially causing any degradation to a signal extending between
a rotated camshaft to which said journal is coupled and said
sensor.
8. A camshaft journal made by the method of claim 1.
9. A method of fabricating a camshaft journal, said method
comprising: providing a die with an interior profile that
substantially defines an exterior surface of said journal; placing
a compactable austenitic manganese steel within at least a portion
of said interior profile of said die; and forming said journal
using dynamic magnetic compaction.
10. The method of claim 9, wherein said austenitic manganese steel
is in powder form prior to placement into said die.
11. The method of claim 9, further comprising heat treating said
journal after said forming.
12. The method of claim 11, wherein said heat treating comprises
sintering.
13. The method of claim 9, further comprising machining said
journal after said forming.
14. The method of claim 13, further comprising sintering said
journal after said machining and forming.
15. The method of claim 13, wherein said machining said journal
after said forming takes place prior to sintering in a protective
atmosphere.
16. The method of claim 9, further comprising machining and heat
treating said journal after said forming.
17. A method of making a camshaft journal, said method comprising:
providing a die with an interior profile that substantially defines
an exterior surface of said journal; placing a compactable
austenitic manganese steel within at least a portion of said
interior profile of said die; and forming at least said journal
using dynamic magnetic compaction.
18. The method of claim 17, wherein said compactable austenitic
manganese steel is in powdered form prior to said forming.
19. The method of claim 18, further comprising performing at least
one of machining and heat treating said journal after said
forming.
20. A method of making a camshaft journal from multiple precursor
compositions, said method comprising: defining a form that
substantially corresponds to a shape of said journal; arranging a
first steel precursor in a first portion of said form, said first
steel precursor configured such that said portion of said journal
that corresponds thereto possesses relatively machinable
properties; arranging a second steel precursor in a second portion
of said form, said second steel precursor configured such that said
portion of said journal that corresponds thereto possesses
substantially non-magnetic properties; and applying dynamic
magnetic compaction to said first and second steel precursors in
said form.
21. The method of claim 20, further comprising connecting said
journal onto a camshaft.
22. The method of claim 20, wherein said first portion of said form
corresponds to at least a portion of the outer surface of said
journal and said second portion of said form corresponds to at
least a portion of the inner surface of said journal.
23. The method of claim 20, wherein said first and second portions
of said form are situated along a rotational axis of said journal
such that said first and second steel precursors occupy
substantially distinct axial portions of said journal.
24. The method of claim 23, further comprising forming at least one
signal-generating interruption in a portion of said journal that
corresponds to said first portion of said form.
25. The method of claim 24, wherein said at least one
signal-generating interruption corresponds to a cutout in a
peripheral portion of said journal.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to the manufacture
of non-magnetic steel automotive components using a powder
metallurgy process, and more particularly to the manufacture of
austenitic camshaft journals using a dynamic magnetic compaction
(DMC) process.
[0002] Automotive engine camshafts are used to open and close
valves in synchronization with the movement of pistons, fuel and
oxygen in an internal combustion engine. A typical camshaft
includes a rotating shaft with a number of lobes arranged in groups
(or packs) mounted along the shaft's length, where each group is
configured to cooperate with one or more valves within each of the
engine's cylinders. Upon rotation of the camshaft, the lobes
selectively force the spring-loaded valves to open or close,
depending on what stage of operation cycle a corresponding piston
is in.
[0003] The camshaft is mounted to the camshaft housing, cylinder
head or related engine structure through cooperation of numerous
journals on the camshaft and a complementary-shaped bearing formed
in the housing. The camshaft journals are intermittently spaced
along the shaft length such that they segment each of the groups of
cams. During operation, the journal and bearing are technically not
in contact, as oil or a related lubricant is inserted therebetween
to form a thin film in the region between their adjacent surfaces.
Throughout the remainder of this disclosure, the placement of the
journal and the bearing in contact with one another will be
construed to also cover the situation discussed above where the two
surfaces are separated only by the thin film of lubricant.
[0004] Even with such lubrication, the environment is harsh, as
high temperatures, rotational speeds and attendant radial loads,
coupled with the need for long-term care-free operation, dictate
that the journal used for a camshaft be made from high-strength
materials that can be formed to very tight tolerances. Moreover,
large-scale production dictates that the journal be as inexpensive
to make as possible.
[0005] Austenitic manganese steels (also known as Hadfield steels
or Sheffield steels) exhibit many desirable attributes that, for
reasons set forth below, may be useful in camshaft journals. Such
attributes include good wear resistance, toughness, ductility and
non-magnetic behavior, this last attribute important for allowing
the journal to be in the close proximity of one or more magnetic
position sensors that can be used to provide information relating
to camshaft rotation or related engine operating conditions.
Traditionally, manganese austenitic steels have been produced in
cast form; however, casting has a tendency to produce numerous
brittle carbides at the grain boundaries. Heat treatment (for
example, heating to the austenitic region and followed by water
quenching) breaks down the carbides to allow for machining and
other post-casting operations, but necessitates an additional
processing step. Other difficulties also arise in cast austenitic
manganese steels. For example, only a minimal amount of grinding is
permitted, as such causes the material to go through a significant
increase in work hardening and concomitant decrease in
machinability. Hot forging of sintered powder compacts at elevated
temperatures (for example, up to 1100.degree. C.) may also be used;
however, this method is not suitable for large-scale production,
and is therefore not commercially viable. To avoid these
difficulties in machinability, most components that are cast from
austenitic manganese steels forego these extra steps, which
unfortunately results in components that cannot take full advantage
of the capability of the materials.
[0006] Still other approaches to producing austenitic manganese
steels, such as powder metallurgy (PM), have been contemplated. In
PM, the processing route typically includes pressing (or
compacting) a powder, followed by sintering. Unfortunately, the
resulting components tend to have mechanical properties that are
inferior to that of the conventional casting discussed above.
Specifically, the high oxygen affinity of the alloy's manganese and
chromium results in a material with high porosity and accompanying
reduction in mechanical properties. Moreover, some degree of
post-sintering machining is required, and as mentioned above,
austenitic manganese steels are not amenable to machining. Other
processes, such as dynamic hot pressing (DHP), where sintered
powder compacts are further processed (such as by forging) at
elevated temperatures, may be used. These, too have drawbacks, as
problems with production scale-up, dimensional control and
uniformity of microstructure may prevent such an approach from
gaining acceptance.
[0007] It is therefore desirable to develop a method of producing a
manganese austenitic steel that is amenable to large-scale
production while being capable of taking full advantage of its
structural properties. It is more particularly desirable to produce
camshaft journals and other high-volume production components based
on manganese austenitic steels to be made using a process that is
capable of producing near net shape with minimal or no
machining.
BRIEF SUMMARY OF THE INVENTION
[0008] These desires can be met by the present invention, wherein
improved engine components and methods of making such components
are disclosed. According to a first aspect of the invention, a
method of fabricating a non-magnetic camshaft journal using DMC is
disclosed. The method includes providing a die or related tool with
an interior profile that is substantially similar to the exterior
profile of the camshaft journal being formed, where the formulated
powder that would ultimately produce an austenitic manganese steel
can be used. In the present context, the term "substantially"
refers to an arrangement of elements or features that, while in
theory would be expected to exhibit exact correspondence or
behavior, may, in practice embody something slightly less than
exact. As such, the term denotes the degree by which a quantitative
value, measurement or other related representation may vary from a
stated reference without resulting in a change in the basic
function of the subject matter at issue.
[0009] In one form, the austenitic manganese steel is powdered. In
addition, the method may optionally include placing a second
material within a part of the die interior profile of the journal.
As discussed above, this method is especially relevant to the
production of the end journal that either holds (or is close to)
the position sensor. By incorporating two different powders (i.e.,
one that would produce austenitic manganese steel and the other
with enhanced machinability), a hybrid approach to creating a
journal with tailored properties can be adopted. Such an approach
could be used to produce an outer layer that takes advantage of a
work hardenable material, while also keeping the non-magnetic
properties of the manganese austenitic steel in certain journal
locations, such as the aforementioned position sensor. In this way,
the austenitic manganese steel can be placed judiciously, thereby
allowing a more machinable, less expensive or other second
material, which (in addition to possessing different magnetic
properties) may possess different wear, friction or related
tribological properties from the austenitic manganese steel. Such a
second powder can be selected from metal powders, ceramic powders
and a combination of both. For example, having a material with
better machinability and formability would allow the journal to be
assembled on the cam shaft using any conventional assembly
methods.
[0010] Other optional steps may be employed. For example, the DMC
may be used to compact the austenitic manganese steel into a green
(i.e., prior to sintering) precursor, after which such precursor
can be consolidated. Such consolidating of the green precursor may
include sintering. Furthermore, one or more additional shapes can
be formed in the journal prior to the sintering. In one form,
machining in the green state may be used to form the lubricant
passageways. In configurations where oil passageways may be useful,
their formation in a green state may be beneficial. Such machining
may take place prior to any heat treating or related consolidation
techniques. In one form, the DMC is achieved by placing the
austenitic manganese steel in powder form inside an electrically
conductive sleeve or related armature, and then passing electric
current through a coil that is placed around the powder material
and the armature such that the current induces a magnetic field and
consequent magnetic pressure pulse that is imparted to the armature
and the powder metal contained therein. In another option,
machining of the journal after forming can be done prior to
sintering in an inert or related protective atmosphere.
[0011] According to another aspect of the invention, a method of
fabricating a camshaft journal is disclosed. The method includes
providing a die, template or related structure with an interior
profile that substantially defines an exterior surface of the
camshaft journal, into which a compactable austenitic manganese
steel is placed. As with the previous aspect, one significant
advantage over the prior art DMC process is that non-axisymmetric
and related irregular component shapes can be formed.
[0012] Optionally, the austenitic manganese steel is in powder form
prior to placement into the die. In other options, additional
steps, such as sintering or related heat treating, machining or a
combination of the above can be performed to place the camshaft in
a more permanent form. As with the first aspect, this aspect may
also include materials with tribologically different properties
than the austenitic manganese steel. In this way, metal alloys of
specific composition can be strategically placed on portions of the
exterior surface of the camshaft journal to tailor the material
properties to the camshaft journal's needs. Alternatively, a more
machinable or steel powder of magnetizable composition could be
placed in the interior of the journal.
[0013] According to yet another aspect of the invention, a method
of making a camshaft journal is disclosed. The method includes
providing a die with an interior profile that substantially defines
an exterior surface of a journal, placing a compactable austenitic
manganese steel within at least a portion of the die interior
profile and forming at least the journal using DMC.
[0014] Optionally, the method includes using powdered austenitic
manganese steel. In a more particular form, machining, heat
treating or both can be performed on the journal after it has been
formed by the DMC process. For example, and as discussed above, the
passageway can be machined into the journal when the latter is
still in the green state.
[0015] According to still another embodiment of the invention, a
method of making a journal from multiple precursor composition is
described. The method including using steel powders one of which
corresponds to a relatively machinable alloy suitable for a portion
of the journal, and the other of which corresponds to a
substantially non-magnetic alloy suitable for use in another
portion of the journal.
[0016] In one optional form, the method includes the connection or
related assembly of the journal onto the camshaft. In another
option, the relatively machinable composition would be possessive
of relatively magnetic properties, and its use would accordingly be
limited to an internal portion of the journal. Furthermore, the
substantially non-magnetic composition, such as those typical of
Hadfield steels, would be used in an exposed, exterior portion of
the journal. In another option, the first and second portions of
the form are situated along a rotational axis so that when a
journal produced by the form is formed, the first and second steel
precursors (which correspond to a magnetic and non-magnetic steel,
for example) occupy substantially distinct axial portions of the
journal. In another form, the magnetic material part may be formed
from a separate disk or plate that can be placed at or near one
axial end of the journal so that in circumstances where a sensor is
used to pick up rotational information about the camshaft, the disk
or plate (which can be made to rotate along with the camshaft and
journal), it can do so in conjunction with discontinuities,
interruptions or related variances formed in the disk or plate
periphery.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0017] The following detailed description of the present invention
can be best understood when read in conjunction with the following
drawings, where like structure is indicated with like reference
numerals and in which:
[0018] FIGS. 1A through 1C shows a the various steps used in the
DMC process of the prior art for making a cylindrical-shaped powder
component;
[0019] FIG. 2 shows a top-down view of a cylindrical part made from
the DMC process of the prior art;
[0020] FIG. 3 shows a view of a camshaft with journals made by a
modified DMC process according to an aspect of the present
invention;
[0021] FIG. 4 shows another view of one of the camshaft journals
from FIG. 3;
[0022] FIGS. 5A and 5B show a simplified die and camshaft journal,
both prior to (FIG. 5A) and after (FIG. 5B) the modified DMC
process of the present invention; and
[0023] FIG. 6 shows a partial cutaway view of an automotive engine
with a camshaft employing one or more journals made by the modified
DMC process of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Referring initially to FIGS. 1A through 1C and 2, a
conventional DMC process is shown, where a generally
cylindrical-shaped component is produced. FIG. 1A shows a powder
material 10 placed within an electrically conductive cylindrical
armature 20 (also called a sleeve). A coil 30 is connected to a
direct current power supply (not shown) such that electric current
can be passed through the coil 30. The powder material 10
substantially fills the electrically conductive armature 20.
Referring with particularity to FIG. 1B, a large quantity of
electrical current 40 is made to flow through the coil 30; this
current induces a magnetic field 50 in a normal direction that in
turn sets up magnetic pressure pulse 60 that is applied to the
electrically conductive container 20. This radially inward pressure
acts to compress the container 20, causing the powder material 10
to become compacted into a fully densified part in a very brief
amount of time (for example, less than one second) and at
relatively low temperatures. In addition, this operation can (if
necessary) be performed in a controlled environment to avoid
contaminating the consolidated material. By way of example, the
current flow through the coil 30 may be in the order of 100,000
amperes at a voltage of about 4,000 volts, although it will be
appreciated that other values of current and voltage may be
employed, depending on the characteristics of the container 20 and
the powder material 10 inside. Referring with particularity to FIG.
1C, the armature 20 and powder material 10 are shown compressed
(occupying a smaller transverse dimension than previous size of
FIG. 1A) as a result of the DMC process.
[0025] Referring with particularity to FIG. 2, a top-down view of a
notional cylindrical DMC containment structure according to the
prior art is shown, where the loosely held powder 10 is placed in
the electrically conductive round container 20 to await the
compacting force that arises from the magnetic field set up by a
sudden passage of a large amount of current through the coil 30.
This induced current produces a second magnetic field which, by its
magnitude and direction, repels the first magnetic field. This
mutual repulsion causes container 20 to be compressed, which in
turn applies pressure on the powder 10, causing its compaction.
Coil 30 is placed inside an external containment shell 70 to
restrain the coil 30 against radially-outward expansion when
repelled by the second magnetic field.
[0026] The chemical composition of austenitic manganese steels is
preferably about 1.0 to 1.4 weight percent carbon (C), about 10.0
to 15.0 weight percent manganese (Mn), about 0.3 to 1.5 weight
percent silicon (Si), up to about 0.07 weight percent phosphorous
(P), and up to about 0.07 weight percent sulfur (S), with a balance
of iron (Fe). Use of DMC to compact the specially formulated
powders into desirable shape with desirable chemical composition
would allow a novel way of processing this hard to process class of
materials. As discussed above, the component could be subsequently
machined in the green state and later sintered in a protective
atmosphere as needed. In addition to avoiding the PM porosity, DMC
does not require expensive, time-consuming preheating, making it
compatible with green component machining and subsequent heat
treating.
[0027] Referring next to FIG. 3, a camshaft 100 that defines a
generally elongate shaft body with numerous cam groups 110, 120,
130 and 140 spaced axially along the length of the body is shown.
Using the first cam group 110 as an example, numerous cams 110A,
110B and 110C are angularly offset relative to one another to
perform the opening and closing of engine valves (not shown) in a
manner known to those skilled in the art. As will also be
understood by those skilled in the cam art, a lobe extends from
each cam 110A, 110B and 110C to define its generally
non-axisymmetric axial profile. While the camshaft 100 shown has
four separate cam groups 110, 120, 130 and 140 (which could be used
as an intake or exhaust camshaft for a four or eight cylinder
engine), it will be appreciated by those skilled in the engine art
that different camshaft configurations consistent with the needs of
a particular engine are also within the scope of the present
invention.
[0028] Journals 150, 160, 170, 180 and 190 are spaced between each
of the cam groups 110, 120, 130 and 140, and transmit the
rotational loads of camshaft 100 to a camshaft housing, cylinder
head or related engine structure (none of which are shown) through
bearings that define a generally smooth surface formed as part of
such structure. Unlike the cams within the various cam groups 110,
120, 130 and 140, the journals 150, 160, 170, 180 and 190 define a
generally axisymmetric profile to facilitate smooth rotational
cooperation with the respective bearings. Cam caps (also not shown)
can be used to form the remaining inner race of the bearings as a
way to secure the journals 150, 160, 170, 180 and 190 within the
bearings. In one form, the journals 150, 160, 170, 180 and 190 can
be secured to the camshaft 100 through shrink-fitting or other
known methods. Camshaft 100 may include additional components
formed on or mounted to the body, such as a gear 200 that can
engage a crankshaft gear (not shown), and a gear 210 that can be
used to drive a distributor cap or oil pump (neither of which is
shown). As discussed above, a premixed powder of the desired
composition can be introduced into a die cavity formed in the shape
of the various components of camshaft 100, especially the journals
150, 160, 170, 180 and 190.
[0029] Referring next to FIG. 4, one of the journals 150 is shown
coupled to a part of the camshaft 100 where a gear (such as gear
210 shown in FIG. 3) or other component may be placed. A thin disk
300 of conventional steel is placed axially adjacent or in contact
with one end of the journal 150, and includes one or more slots 305
formed at the periphery thereof. In one form, the disk 300 can be
rigidly affixed to the shaft by known means so that it rotates at
the same rate as the journal 150 and by extension, the camshaft
100. The disk 300, which can be made from a conventional powder
metal approach or be formed and then have the slots 305 cut into
them, can be used in conjunction with magnetic sensor 400 to
generate a signal that corresponds to the passage of the slots 305
(and their concomitant magnetic field discontinuity), which in turn
provide indicia of the rotational state of camshaft 100. A wire 405
conveys the sensed signal from sensor 400 to a controller (not
shown) or related device to provide timing or other operating
information. The manganese steel composition and its attendant
non-magnetic property would be beneficial for the journal 150, as
otherwise its presence in a magnetic metal form would interfere
with the generation of signals in sensor 400. In one optional
feature, an oil (or lubricant) passageway (not shown) can be formed
in journal 150 in order to deliver lubricant to the bearing and
journal 150 through an internal fluid coupling formed inside the
journal 150.
[0030] DMC tooling (including the wiring that will allow the
passage of electrical current) is placed around the die cavity.
Upon the passage of electric current (and the consequent creation
of a pair of opposing magnetic fields), the powder in the die
cavity compacts into a near-net shape. Likewise, any sintering, if
needed, can be achieved in a controlled atmosphere furnace, wherein
the amount of oxygen in the furnace is tightly controlled, This
step may be followed by controlled cooling that may or may not
include water quenching. By performing any of the machining or
other post-compaction operations prior to a final sintering step,
the present method overcomes the difficulty that fully-processed
austenitic manganese steels (with their attendant hardness) of the
prior art have experienced. In this way, austenitic manganese steel
journals can be made that were hitherto not feasible as a
large-scale production material.
[0031] Referring next to FIGS. 5A and 5B, a setup 500 used to make
the camshaft journal using the DMC process according to an aspect
of the present invention is shown. An electrically-conducting coil
530 is wound around a sleeve 525 (made from a highly electrical
conductive material, such as copper) that is placed
circumferentially around a powder mass 540 contained in a die 550.
As shown, a gap (for example, and air gap) 135 is situated between
coil 530 and sleeve 525. As with conventional DMC, the present
DMC-based process exploits the electric current flowing through
coil 530 in order to impart a magnetically-compressive force onto
the sleeve 525, die 550 and the powder precursor materials 540
within. The inner surface of die 550 is similarly shaped to the
desired outer shape of the journal 150 of the camshaft 100 being
formed. The die 550 may include numerous reusable segments that can
come in various shapes (for example, quartered), not shown). A
central bore can be formed in the journal 150 through the inclusion
of an appropriately-shaped mandrel or core rod 560 during the
forming process. Sleeve 525 is compressed by the magnetic forces
generated by coil 530, as is die 550; this in turn causes the
powder precursor materials 540 to be deformed by the compressive
forces, resulting in formation of a green or un-sintered journal
150 that may subsequently undergo conventional sintering, machining
and related finishing steps (none of which are shown). As discussed
above, a separate disk 300 (shown in FIG. 4) can be coupled to one
or more of the journals 150, 160, 170, 180 and 190 to allow the use
of a sensor or related device to derive operational parameters
(such as rotational attributes) from the camshaft 100.
[0032] Referring with particularity to FIG. 6, portions of the top
of an automotive engine 1000 incorporating a camshaft 100 with one
of the cams 110A of cam group 110 is shown for a notional
direct-acting tappet overhead cam design. A cylinder head 1200
includes intake ports 1240 and exhaust ports 1250 with
corresponding intake and exhaust valves 1400, 1500 to convey the
incoming air and spent combustion byproducts, respectively that are
produced by a combustion process taking place between the piston
1300 and a spark plug (not shown) in the cylinder. When the lobed
portion of the cam 110A rotates into engagement with top of valve
1500, it pushes the valve 1500 downwards to overcome the bias
formed by spring 1600, thereby forcing the valve 1500 to open and
allowing exhaust gas built up in the cylinder above piston 1500 to
escape. As discussed previously, camshaft 100 is driven from an
external source, such as a crankshaft (not shown) through the gear
200 depicted in FIG. 4. It will be appreciated that similar
structure is included for the intake valve 1400, but is removed
from the present drawing for clarity. The hardness of the
austenitic manganese steel ensures that the journals 150, 160, 170,
180 and 190 can endure significant loads over prolonged periods of
operation, while is nonmagnetic character ensures that it will not
interfere with magnetic-based sensors (such as sensor 300 shown in
FIG. 4) disposed nearby. It will be appreciated by those skilled in
the art that the valve train architecture shown associated with
engine 1000, which includes a direct-acting tappet, is merely
representative, and that camshaft 100 and its journals 150, 160,
170, 180 and 190 manufactured using the DMC process as described
herein are equally applicable to other valve train architectures
(not shown).
[0033] While certain representative embodiments and details have
been shown for purposes of illustrating the invention, it will be
apparent to those skilled in the art that various changes may be
made without departing from the scope of the invention, which is
defined in the appended claims.
* * * * *