U.S. patent application number 12/348032 was filed with the patent office on 2009-07-09 for surface treated rocker arm shaft.
This patent application is currently assigned to Roller Bearing Company of America, Inc. Invention is credited to Robert Lugosi, Steve Parkinson, James Prescavage.
Application Number | 20090173301 12/348032 |
Document ID | / |
Family ID | 40568591 |
Filed Date | 2009-07-09 |
United States Patent
Application |
20090173301 |
Kind Code |
A1 |
Lugosi; Robert ; et
al. |
July 9, 2009 |
SURFACE TREATED ROCKER ARM SHAFT
Abstract
A shaft for a rocker arm assembly is disclosed. The shaft
includes a substantially cylindrical outer surface at least a
portion of which defines a bearing surface thereon and an interior
core portion located radially inward of the bearing surface. The
bearing surface has a hardness greater than that of the core
portion, for providing wear resistance and deterring crack
initiation and propagation.
Inventors: |
Lugosi; Robert; (Oxford,
CT) ; Parkinson; Steve; (Lakeville, IN) ;
Prescavage; James; (Hainesport, NJ) |
Correspondence
Address: |
MICHAUD-DUFFY GROUP LLP
306 INDUSTRIAL PARK ROAD, SUITE 206
MIDDLETOWN
CT
06457
US
|
Assignee: |
Roller Bearing Company of America,
Inc
Oxford
CT
|
Family ID: |
40568591 |
Appl. No.: |
12/348032 |
Filed: |
January 2, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61019936 |
Jan 9, 2008 |
|
|
|
Current U.S.
Class: |
123/90.39 |
Current CPC
Class: |
F01L 2303/00 20200501;
F01L 1/18 20130101; F01L 1/053 20130101; F01L 2301/00 20200501 |
Class at
Publication: |
123/90.39 |
International
Class: |
F01L 1/18 20060101
F01L001/18 |
Claims
1. A shaft for a rocker arm assembly, said shaft comprising: a
substantially cylindrical outer surface at least a portion of which
defines a bearing surface thereon and an interior core portion
located radially inward of said bearing surface; said bearing
surface being configured to rotatably engage a mating surface
positioned in a receiving bore of a rocker arm; and said bearing
surface having a hardness greater than that of said core portion,
for providing wear resistance and deterring crack initiation and
propagation.
2. The shaft of claim 1, wherein said bearing surface has a
Rockwell C scale hardness of at least 59.
3. The shaft claim 1, wherein a concentration of at least one of
carbon and nitrogen at said bearing surface and extending radially
inward therefrom to an effective case depth of about 0.063 inches,
exceeds the concentration of at least one of said carbon and
nitrogen in said core portion.
4. The shaft of claim 1, wherein portions of said shaft outside of
an area wherein said bearing surface and said mating surface engage
one another, are masked prior to surface hardening said shaft to
prevent surface hardening of said masked area such that said masked
area has a hardness about equal to that of said core portion.
5. The shaft of claim 3, wherein said bearing surface has an
arithmetic mean roughness of less than about 2.5 micro inches.
6. The shaft of claim 1, wherein said bearing surface is
isotropic.
7. The shaft of claim 1, wherein said bearing surface has a
specular brightness.
8. A shaft for a rocker arm assembly, said shaft comprising: a
substantially cylindrical outer surface at least a portion of which
defines a bearing surface thereon; at least a portion of said
bearing surface having an arithmetic mean roughness of less than
about 2.5 micro inches, for providing wear resistance and deterring
crack initiation and propagation.
9. The shaft of claim 8, wherein said bearing surface is
isotropic.
10. The shaft of claim 8, wherein said bearing surface has a
specular brightness.
11. The shaft of claim 8, wherein said outer surface defines an
interior core portion located radially inward of said bearing
surface; and at least a portion of said bearing surface having a
hardness greater than that of said core portion, for providing wear
resistance and deterring crack initiation and propagation.
12. The shaft of claim 11, wherein said bearing surface has a
Rockwell C scale hardness of at least 59.
13. The shaft claim 10, wherein a concentration of at least one of
carbon and nitrogen at said bearing surface and extending radially
inward therefrom to an effective case depth of about 0.063 inches,
exceeds the concentration of at least one of said carbon and
nitrogen in said core portion.
14. The shaft of claim 8, wherein portions of said shaft are masked
prior to treatment of said shaft to prevent said at least a portion
of said bearing surface from having an arithmetic mean roughness of
less than about 2.5 micro inches.
15. A rocker arm assembly comprising: a substantially cylindrical
shaft having an outer surface at least a portion of which defines a
bearing surface thereon and an interior core portion located
radially inward of said bearing surface; a rocker arm having a
receiving bore extending therethrough; said bearing surface being
configured to rotatably engage a mating surface positioned in said
receiving bore; and said bearing surface having a hardness greater
than that of said core portion, for providing wear resistance and
deterring crack initiation and propagation.
16. The rocker arm assembly of claim 15, wherein a concentration of
at least one of carbon and nitrogen at said bearing surface and
extending radially inward therefrom to an effective case depth of
about 0.063 inches, exceeds the concentration of at least one of
said carbon and nitrogen in said core portion.
17. The rocker arm assembly of claim 16, wherein said bearing
surface has an arithmetic mean roughness of less than about 2.5
micro inches.
Description
FIELD OF THE INVENTION
[0001] The present invention is generally directed to a surface
treated rocker arm shaft for an internal combustion engine and is
more specifically directed to a surface hardened rocker arm shaft
having a case hardened and/or a highly polished surface that is
capable of improved wear resistance and deterrence of crack
initiation and propagation.
BACKGROUND OF THE INVENTION
[0002] Internal combustion engines, such as multi-cylinder diesel
engines, typically include a crankshaft, a camshaft and a rocker
arm shaft. The crankshaft is connected with a plurality of piston
rods, which in turn are connected with a plurality of corresponding
pistons. Reciprocating movement of the pistons within corresponding
combustion cylinders causes rotation of the crankshaft. The
crankshaft is typically interconnected with the camshaft via a gear
set and thereby rotatably drives the camshaft during operation. The
camshaft includes a plurality of cams, with each cam being
associated with an inlet valve, and an exhaust valve or a fuel
injector valve. More particularly, the rocker arm shaft carries a
plurality of rocker arms, with each rocker arm having a roller
follower that engages a corresponding cam on the camshaft. Rotation
of the camshaft causes oscillatory pivotal movement of the rocker
arms around the rocker arm shaft. The rocker arm shaft is subject
to cyclic bending moments as a result of forces applied thereto by
the roller follower and cam.
[0003] Typically, rocker arm shafts are manufactured from a high
strength through hardened steel such as AISI E52100. Through
hardening of the steel imparts a high hardness throughout the
entire shaft. The expense of some through hardened steels make them
impractical for use as rocker arm shafts in typical internal
combustion engines.
[0004] In addition, the above mentioned cyclic bending moments can
cause fatigue failure of the rocker arm shaft. Although the use of
the through hardened steel can improve wear resistance, fatigue
generated surface cracks can propagate inwardly through the core
portion. Such propagation of the cracks through the core portion
has resulted in catastrophic failure of the rocker arm shaft.
SUMMARY OF THE INVENTION
[0005] According to one aspect of the present invention, a shaft
for a rocker arm assembly for an internal combustion engine
includes a substantially cylindrical outer surface at least a
portion of which defines a bearing surface thereon and an interior
core portion located radially inward of the outer surface. At least
a portion of the outer surface has a hardness greater than that of
the core portion, for providing wear resistance and deterring crack
initiation and propagation.
[0006] Rocker arm shafts having a bearing surface that has a
hardness greater than that of the core portion can improve
resistance to the initiation and propagation of surface cracks
inwardly through the core portion.
[0007] In one aspect of the present invention, the bearing surface
has a Rockwell C scale hardness of at least 59. In another aspect
of the present invention, the bearing surface, has a concentration
of carbon and/or nitrogen at the outer surface. This concentration
extends radially inward from the outer surface to a depth of about
0.063 inches.
[0008] In yet another aspect of the present invention, the bearing
surface has an arithmetic mean roughness of less than about 2.5
micro inches.
DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a perspective view of a rocker arm assembly.
[0010] FIG. 2 is a schematic cross sectional view of a valve
actuating device and rocker arm assembly.
[0011] FIG. 3 is a schematic cross sectional view of a rocker arm
assembly.
[0012] FIG. 4 is a side cross sectional view of the rocker arm
assembly of FIG. 3.
[0013] FIG. 5 illustrates the rocker arm assembly of FIG. 3 with a
portion of the shaft masked.
[0014] FIG. 6 illustrates a schematic cross sectional view of the
rocker arm assembly having a bearing surface having an outer
surface treated with a surface finishing process.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] FIG. 1 illustrates a rocker arm assembly generally
designated by element number 1. The rocker arm assembly 1 includes
a hollow shaft 2 having a longitudinal axis A and four rocker arms
4 rotationally secured thereto. The rocker arms 4 rotationally and
cyclically pivot with respect to the rocker arm shaft 2 about the
longitudinal axis A as indicated by arrows marked P.
[0016] Referring to FIG. 2, a valve actuating device for an
internal combustion engine is generally referred to as numeral 6.
The valve actuating device 6 includes an intake valve 8 for
selectively opening and closing an intake port 10 of a combustion
chamber 12 defined in a cylinder head 14 of an internal combustion
engine. In addition, a camshaft 16 includes an intake valve drive
cam 18 for actuating the intake valve 8 and a pair of rocker arms
17A and 17B for jointly transmitting the lift of the intake valve
drive cam 18 to the intake valve 8. The rocker arm 17A is shown
rotatably mounted on a solid cylindrical rocker arm shaft 19.
[0017] FIGS. 3-4 illustrate a portion of a rocker arm assembly 20
for use in overhead valve cylinder deactivation valve trains
forming part of an internal combustion engine. The rocker arm
assembly 20 includes two rocker arms 22 rotatably mounted on a
solid, substantially cylindrical, rocker arm shaft 24 having a
longitudinal axis A. During operation, the rocker arms 22
cyclically pivot as illustrated by the arrow R about the axis A.
The rocker arm shaft 24 includes an outer surface 26 at least a
portion of which defines a bearing surface 28 thereon. Each of the
rocker arms 22 includes a substantially cylindrical inside wall 30
defining a bore extending therethrough. The inside wall 30
rotatably engages a contact portion 29 of the bearing surface 28.
The rocker arm shaft 24 is shown having a core portion 32 defined
by the outer surface 26 and located radially inward of the bearing
surface 28. The bearing surface 28 has a surface hardness greater
than that of the core portion 32, for improved wear resistance and
deterrence of crack initiation and propagation.
[0018] In one embodiment, the rocker arm shaft 24 is manufactured
from through hardened ASM 52100 steel and is further case hardened
by carburization for increased wear resistance and deterrence of
crack initiation and propagation. The carburization case hardening
process includes one of gas diffusion, pack diffusion and liquid
diffusion. In the carburization process the rocker arm shaft 24, in
particular the bearing surface 28 is exposed to a carbon rich
atmosphere (e.g., carbon monoxide, carbon powder, or a molten
carbon rich bath) for a predetermined period of time. During
carburization the carbon rich atmosphere is at a temperature
between approximately 1550.degree. F. to 1750.degree. F. The
temperature and time are selected based on a desired surface
hardness and penetration depth of the carbon. After carburization,
the rocker arm shaft 24 is cooled to a temperature of approximately
70.degree. F. to achieve a desired surface hardness. Cooling can be
accomplished by quenching in a liquid and/or by air cooling. The
carburization process causes the bearing surface 28 to have a
Rockwell hardness, C scale, of at least 59.
[0019] As illustrated in FIGS. 3-4 the carburization process causes
the bearing surface 28 and a portion of the shaft 24 radially
inward therefrom to an effective case depth d, to have a carbon
concentration greater than that of the core 32. The effective case
depth d is a distance from a case hardened exterior surface to a
furthest point, interior to the case hardened exterior surface, at
which the Rockwell hardness, C scale, is about 50. The effective
case depth d is measured perpendicular to the bearing surface. In
one embodiment, the case depth d is about 0.063 inch (1.6002
mm).
[0020] While the carburization process is described for hardening
the bearing surface 28, the present invention is not limited in
this regard as the present invention is adaptable to other
hardening processes including, but not limited to, nitriding
wherein nitrogen is diffused into the bearing surface,
carbonitriding wherein carbon and nitrogen are diffused into the
bearing surface, flame hardening, induction hardening, laser beam
hardening and electron beam hardening.
[0021] In addition, other surface treatment processes to provide
wear and impact resistance and deter crack initiation and
propagation can be used. Such a surface treatment process includes
lapping-like scratching of the surface under extremely high
compression of the surface to reduce slip planes, increase surface
hardness, increase impact resistance, and increase surface
compressive stresses by about twenty percent to a depth of about
0.012 inches. Surface roughness is reduced to less than 1 micro
inch. For example, Mikronite Technologies, Inc. of Eatontown, N.J.
has a Mikronite.RTM. brand surface treatment processes which can be
employed.
[0022] Another process that can deter crack initiation and
propagation and increase impact, wear and corrosion resistance is a
process using abrasive or non-abrasive media with or without
chemical solutions, applied by vibratory methods. Such a process
can provide: 1) a superfinished surface, defined as having an ISO
Standard No. 4287 Arithmetic Mean Roughness of less than or equal
to 2.5 micro inches; 2) an isotropic surface, defined as a surface
having no orientation to its surface irregularities; and 3) a
specular brightness, defined as a surface in which a clear
reflection of an object can be seen. For example, REM Chemicals,
Inc. of Southington, Conn. has an Isotropic Superfinish (ISF.RTM.)
process that can be employed.
[0023] In one embodiment, the case hardened bearing surface 28 of
FIG. 4 is treated with the Mikronite.RTM. and/or ISF.RTM.
processes, either before or after carburization case hardening,
such that the bearing surface 28 has an Arithmetic Mean Roughness
of less than or equal to 2.5 micro inches, a specular brightness
and/or is isotropic.
[0024] The rocker arm assembly of FIG. 5 is similar to that
illustrated in FIGS. 3-4. Therefore, like elements will be given
like numbers preceded by the numeral 1. FIG. 5 illustrates a rocker
arm assembly 120, including two rocker arms 122 rotatably mounted
on a solid, substantially cylindrical, rocker arm shaft 124 having
a longitudinal axis 1A. The rocker arm shaft 124 includes an outer
surface 126 at least a portion of which defines a bearing surface
128 on portions thereof as described below. Each of the rocker arms
122 includes a substantially cylindrical inside wall 130 defining a
bore extending therethrough. The inside wall 130 rotatably engages
the bearing surface 128 in the contact region 129. The rocker arm
shaft 124 is shown having a core portion 132 defined by the outer
surface and located radially inward of the bearing surface 128. The
contact region 129 of the bearing surface 128 is case hardened by
carburization to attain a surface hardness greater than that of the
core portion 132, for example a Rockwell hardness, C scale, of at
least 59. In addition, portions of the outer surface 126 beyond the
contact region 129 are not case hardened and have a hardness about
equal to that of the core portion 132. The effective case depth Id
of the case hardened surface of the contact region 129 is about
0.063 inch (1.6002 mm).
[0025] Portions of the outer surface 126 which do not require
hardening are coated with a mask 134 prior to initiation of the
case hardening process. The mask 134 is made up of a substance
impermeable to carbon, for example copper, to preclude diffusion of
carbon into the portions of the outer surface 126 which do not
require hardening. In one embodiment, the mask 134 is deposited on
the portions of the outer surface 126 which do not require
hardening by an electro-chemical plating process. After case
hardening, for example, carburizing, the mask 134 is removed.
Although the mask 134 is described as being copper, the present
invention is not limited in this regard as other coatings are also
suitable including but not limited to water soluble coatings.
[0026] In another embodiment, the portions of the outer surface 126
in the contact region 129, illustrated in FIG. 5, which are
selectively case hardened and/or the portions of the outer surface
126 which do not require hardening, are treated with the
Mikronite.RTM. and/or ISF.RTM. processes either before or after
case hardening, such that the bearing surface 128 and/or outer
surface 126 has an Arithmetic Mean Roughness of less than or equal
to 2.5 micro inches, a specular brightness and/or is isotropic. In
one embodiment, a mask 134, similar to that described above for
FIG. 5, can be applied to a portion of the outer surface 126, prior
to treatment of the rocker arm shaft 124 with the Mikronite.RTM.
and/or ISF.RTM. processes for selectively surface treating the
rocker arm shaft 124. The mask 134 is removed after such
treatment.
[0027] The rocker arm assembly of FIG. 6 is similar to that
illustrated in FIGS. 3-4. Therefore, like elements will be given
like numbers preceded by the numeral 2. FIG. 6 illustrates a rocker
arm assembly 220, including two rocker arms 222 rotatably mounted
on a solid, substantially cylindrical, rocker arm shaft 224 having
a longitudinal axis 2A. The rocker arm shaft 224 includes an outer
surface 226 at least a portion of which defines bearing surface 228
thereon. Each of the rocker arms 222 includes a substantially
cylindrical inside wall 230 defining a bore extending therethrough
which rotatably engages the bearing surface 228 in the contact
region 229. The rocker arm shaft 224 is shown having a core portion
232 defined by the outer surface 226 and located radially inward of
the bearing surface 228.
[0028] Referring again to FIG. 6, at least a portion of the bearing
surface 228 has a ISO Standard No. 4287 Arithmetic Mean Roughness
of less than or equal to 2.5 micro inches, providing a fine
polished finish for improved wear resistance and for deterring
crack initiation and propagation. In one embodiment the Arithmetic
Mean Roughness is less than 1 micro inch. In one embodiment, the
bearing surface 228 is isotropic having no orientation to its
surface irregularities. In one embodiment, the bearing surface 228
has a specular brightness, defined as a surface in which a clear
reflection of an object can be seen. In one embodiment, surface
compressive stresses are increased by about twenty percent above
pretreated conditions. Such increase in the surface compressive
stresses is affected to a depth of about 0.012 inches.
[0029] While that above rocker arm shafts 28, 128 and 228 are
illustrated as solid substantially cylindrical shafts, the present
invention is not limited in this regard as other shaft
configurations are adaptable for use in the present invention,
including but not limited to case hardening and/or surface
treatment of any portion of: hollow rocker arm shafts, rocker arm
shafts with grooves for receiving and/or guiding the rocker arms
and stepped rocker arm shafts having a plurality of different
diameters.
[0030] Although the present invention has been disclosed and
described with reference to certain embodiments thereof, it should
be noted that other variations and modifications may be made, and
it is intended that the following claims cover the variations and
modifications within the true scope of the invention.
* * * * *