U.S. patent application number 12/793525 was filed with the patent office on 2011-12-08 for friction brake component and method for manufacturing the same.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Ronnie T. Brown, Lisa G. Devoe, Michael D. Hanna, Michael L. Holly, Kee Hyuk Im, Donna Y. Sekulovski, James A. Webster.
Application Number | 20110297495 12/793525 |
Document ID | / |
Family ID | 45063616 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110297495 |
Kind Code |
A1 |
Hanna; Michael D. ; et
al. |
December 8, 2011 |
FRICTION BRAKE COMPONENT AND METHOD FOR MANUFACTURING THE SAME
Abstract
A ferritically nitrocarburized rotational member of a vehicle
brake is disclosed, including a rotational member having a friction
surface configured for braking engagement with a corresponding
friction material. A compound zone is disposed at the friction
surface. An exposed surface of the compound zone is exposed to an
atmosphere. The area of the exposed surface includes from about 0
percent to about 14 percent graphite.
Inventors: |
Hanna; Michael D.; (West
Bloomfield, MI) ; Holly; Michael L.; (St. Clair
Shores, MI) ; Brown; Ronnie T.; (Bloomfield Hills,
MI) ; Webster; James A.; (Washington Township,
MI) ; Devoe; Lisa G.; (Ortonville, MI) ;
Sekulovski; Donna Y.; (Novi, MI) ; Im; Kee Hyuk;
(Rochester Hills, MI) |
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
DETROIT
MI
|
Family ID: |
45063616 |
Appl. No.: |
12/793525 |
Filed: |
June 3, 2010 |
Current U.S.
Class: |
188/218R ;
451/38 |
Current CPC
Class: |
F16D 65/12 20130101;
F16D 2250/0038 20130101; F16D 2200/0013 20130101; F16D 2200/0021
20130101; F16D 2200/0017 20130101; F16D 65/10 20130101; B60T 1/065
20130101 |
Class at
Publication: |
188/218.R ;
451/38 |
International
Class: |
F16D 65/12 20060101
F16D065/12; B24C 1/00 20060101 B24C001/00; F16D 65/10 20060101
F16D065/10 |
Claims
1. A ferritically nitrocarburized rotational member of a vehicle
brake, comprising: a rotational member, including: a friction
surface configured for braking engagement with a corresponding
friction material; a compound zone disposed at the friction
surface; and an exposed surface of the compound zone exposed to an
atmosphere wherein an area of the exposed surface includes from
about 0 percent to about 14 percent graphite.
2. The rotational member as defined in claim 1 wherein the area of
the exposed surface includes from about 1 percent to about 10
percent graphite.
3. The rotational member as defined in claim 1 wherein the area of
the exposed surface includes from about 2 percent to about 5
percent graphite.
4. The rotational member as defined in claim 1 wherein the area of
the exposed surface includes from about 3 percent to about 14
percent graphite.
5. The rotational member as defined in claim 1 wherein the
rotational member is formed from gray cast iron, steel, or
stainless steel.
6. The rotational member as defined in claim 1 wherein the
rotational member further comprises a brake rotor, a brake drum, or
combinations thereof.
7. The rotational member as defined in claim 1 wherein the
corresponding friction material exhibits a wear of less than 0.4 mm
per 1000 stops at about 350.degree. C.
8. The rotational member as defined in claim 1 wherein the compound
zone exhibits a hardness of between about 56 HRC and about 64
HRC.
9. The rotational member as defined in claim 1 wherein the
rotational member exhibits a coefficient of friction of at least
0.32.
10. The rotational member as defined in claim 1 wherein less than
15 percent of the exposed surface exhibits visible red rust after 1
week in humid air with a temperature of at least about 10.degree.
C. (50.degree. F.).
11. A method for increasing useful life of a rotational member of a
vehicle brake, comprising removing graphite flakes from a friction
surface of the rotational member prior to nitrocarburizing the
friction surface.
12. The method as defined in claim 11 wherein removing the graphite
flakes is accomplished by a process selected from sand blasting,
grit blasting, grinding, and combinations thereof.
13. The method as defined in claim 11 wherein graphite comprises
from about 0 percent to about 14 percent of the friction surface
after removing the graphite flakes.
14. The method as defined in claim 11 wherein nitrocarburizing
includes a gas nitrocarburizing process, a plasma nitrocarburizing
process, or a salt bath nitrocarburizing process.
15. The method as defined in claim 11 wherein the nitrocarburizing
comprises: immersing at least the friction surface of the
rotational member into a nitrocarburizing salt bath; and then
immersing the at least the friction surface of the rotational
member into an oxidizing salt bath.
16. A rotational member formed by the method of claim 11 wherein
the rotational member is formed from gray cast iron, and the
rotational member includes a brake rotor, a brake drum, or a
combination thereof.
17. The rotational member as defined in claim 16 wherein a
corresponding friction material exhibits wear of less than 0.4 mm
per 1000 stops at 350.degree. C.
18. The rotational member as defined in claim 16 wherein a compound
zone exhibits hardness of between about 56 HRC and about 64
HRC.
19. The rotational member as defined in claim 16 wherein the
friction surface of the rotational member exhibits a coefficient of
friction of at least 0.32.
20. The rotational member as defined in claim 16 wherein less than
15 percent of an exposed portion of the friction surface exhibits
visible red rust after 1 week in humid air with a temperature of at
least about 10.degree. C. (50.degree. F.).
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to a friction brake
component and method of manufacturing.
BACKGROUND
[0002] Friction brake components, such as, e.g., brake rotors and
brake drums may be used in a vehicle brake system. It may be
desirable for a brake rotor or brake drum to have a high
coefficient of friction with a friction material while promoting
long life of the friction material and the brake rotor or brake
drum.
SUMMARY
[0003] A ferritically nitrocarburized rotational member of a
vehicle brake has a rotational member, including a friction surface
configured for braking engagement with a corresponding friction
material. A compound zone is disposed at the friction surface. The
compound zone may have a surface that is exposed to an atmosphere.
The area of the exposed surface includes from about 0 percent to
about 14 percent graphite.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Features and advantages of examples of the present
disclosure will become apparent by reference to the following
detailed description and drawings, in which like reference numerals
correspond to similar, though perhaps not identical, components.
For the sake of brevity, reference numerals or features having a
previously described function may or may not be described in
connection with other drawings in which they appear.
[0005] FIG. 1 is a perspective view of a disc brake assembly in an
example of the present disclosure;
[0006] FIG. 2 is a side view of a drum brake assembly in an example
of the present disclosure;
[0007] FIG. 3 is a graph comparing experimental wear vs.
temperature results for an example of the present disclosure and a
prior art brake;
[0008] FIG. 4 is a schematic depiction of a section view showing a
compound layer in an example of the present disclosure at a
microscopic enlargement;
[0009] FIG. 5 is a perspective view of a brake disc in an example
of the present disclosure;
[0010] FIG. 6 is a microscopic enlargement of a surface of the
brake disc shown in FIG. 5;
[0011] FIG. 7 is a perspective view of a brake drum in an example
of the present disclosure;
[0012] FIG. 8 is a perspective view showing the inside of the brake
drum depicted in FIG. 7;
[0013] FIG. 9 is a perspective view of a drum-in-hat rotational
member;
[0014] FIG. 10 is a cross sectional view of the drum-in-hat
rotational member depicted in FIG. 9; and
[0015] FIG. 11 is a flow diagram depicting an example of a method
according to the present disclosure.
DETAILED DESCRIPTION
[0016] A brake 10 is an energy conversion system used to retard,
stop, or hold a vehicle. While a vehicle in general may include
spacecraft, aircraft, and ground vehicles, in this disclosure, a
brake 10 is used to retard, stop, or hold a wheeled vehicle with
respect to the ground. More specifically, as disclosed herein, a
brake 10 is configured to retard, stop, or hold at least one wheel
of a wheeled vehicle. The ground may be improved by paving.
[0017] A vehicle brake 10 may be a disc brake 20, drum brake 50,
and combinations thereof. FIG. 1 depicts an example of a vehicle
brake, in particular, a disc brake 20. In a disc brake 20, a
rotational member 12 is typically removably attached to a wheel
(not shown) at a wheel hub 40 by a plurality of wheel studs 24
cooperatively engaged with lug nuts (not shown). The rotational
member 12 in a disc brake 20 may be known as a brake disc (or
rotor) 39. The rotor 39 may include vent slots 38 to improve
cooling and increase the stiffness of the brake disc 39. When
hydraulic fluid is pressurized in a brake hose 34, a piston (not
shown) inside a piston housing 32 of a caliper 28, causes the
caliper 28 to squeeze the brake disc 39 between brake pads 36,
thereby engaging the disc brake 20. The brake pads 36 may include a
friction material 44 that contacts a friction surface 46 of the
brake disc 39 when the disc brake 20 is engaged. If the wheel is
rotating at the time the disc brake 20 is engaged, kinetic energy
of the moving vehicle is converted to heat by friction between the
brake pads 36 and the brake disc 39. Some of the heat energy may
temporarily raise the temperature of the brake disc 39, but over
time, the heat is dissipated to the atmosphere surrounding the
vehicle.
[0018] Referring now to FIG. 2, a drum brake 50 in an example is
shown. The rotational member 12' is a brake drum 56 (see also FIGS.
7 and 8). The brake drum 56 is removably fastened to a wheel (not
shown). The brake drum 56 may include fins 68 to improve cooling
and increase the stiffness of the brake drum 50. When hydraulic
fluid is pressurized in a wheel cylinder 52, a piston 54 causes the
brake shoes 62 to press a brake lining 66 against the brake drum
56, thereby engaging the drum brake 20. It is to be understood that
the brake lining 66 is a friction material 44'. Alternatively, a
drum brake 56 may be engaged mechanically by actuating an emergency
brake lever 64 via an emergency brake cable 58. The emergency brake
lever 64 causes the shoes 62 to press the brake lining 66 against
the brake drum 56. If the wheel is rotating at the time the drum
brake 50 is engaged, kinetic energy of the moving vehicle is
converted to heat by friction between the brake lining 66 and the
brake drum 56. Some of the heat energy may temporarily raise the
temperature of the brake drum 56, but over time, the heat is
dissipated to the atmosphere surrounding the vehicle.
[0019] FIG. 7 shows a perspective view of a brake drum 56 in an
example of a rotational member 12'. FIG. 8 is a rotated perspective
view of the brake drum 56 shown in FIG. 7, showing an inside view
of the brake drum 56. The friction surface 46' is visible in FIG.
8. As shown in both FIGS. 7 and 8, examples of a brake drum 56 may
include fins 68.
[0020] It is to be understood that a disc brake 20 may be combined
with a drum brake 50. As shown in FIGS. 9 and 10, a drum-in-hat
rotational member 12'' may be included in such a combination. In a
drum-in-hat type brake, small brake shoes may be mechanically/cable
actuated as an emergency brake, while the flange portion acts as a
typical disc brake.
[0021] The rotational member 12, 12', 12'' includes a friction
surface that is engaged by a friction material 44, 44' of the brake
pad 36 or the brake shoe 62. As a brake is engaged to retard a
vehicle, mechanical wear and heat may cause small amounts of both
the friction material 44, 44' and the rotational member 12, 12',
12'' to wear away. It may be possible to reduce the rate of wear of
the rotational member 12, 12', 12'' or the friction material 44,
44' by reducing the coefficient of friction between the two, but a
lower coefficient of friction may make the brake 10 less effective
at retarding the vehicle.
[0022] In the production of a gray cast iron brake disc 39 or drum
56, graphite flakes may be embedded in the cast iron at the
friction surface 46, 46'. Gray iron is a cast iron in which free
graphite, in the form of flakes, precipitates throughout a metallic
matrix. It is the graphite flakes which account for the excellent
machinability, wear resistance, damping capacity, low shrinkage
characteristics during solidification, and generally higher thermal
conductivity of gray cast iron during operation. Due to galvanic
scale differences between graphite and the metal matrix in which it
is embedded, the graphite flakes may be initiation sites for
corrosion of the cast iron, leading to pitting and roughness. In
cast iron, corrosion is mainly the formation of iron oxides. Iron
oxides are very hard and abrasive. Thus, corrosion may lead to
undesirably rapid wear of the friction surface 46, 46' and the
corresponding friction material 44, 44'. Graphite flakes may act as
tiny masks during ferritic nitrocarburization. Thus, if graphite
flakes are dislodged during brake use, they leave a small crevice
which has not been ferritically nitrocarburized and may act as an
initiation site for corrosion.
[0023] It is to be understood that graphite generally has high
lubricity when interposed between sliding surfaces. Furthermore,
the lubricity of graphite may reduce the coefficient of friction
between the friction material 44, 44' and the friction surface 46,
46' during brake engagement, at least until corrosion begins.
[0024] Ferritic nitrocarburization has been used to produce a
friction surface 46, 46' that resists corrosion and wear. Ferritic
nitrocarburization may be used to dispose a compound zone 70 on the
rotational member 12, 12', 12'' of the brake 10. In an example, a
rotational member 12, 12', 12'' has a compound zone 70 disposed at
the friction surface 46, 46'. The compound zone 70 may have an
exposed surface in contact with an atmosphere, for example,
air.
[0025] It is to be understood that a gray cast iron normally
includes flakes of graphite. However, in an example, the rotational
member 12, 12', 12'' has an exposed surface of the compound zone 70
having from about 0 percent to about 14 percent graphite. In
another example, the exposed surface may include from about 1
percent to about 10 percent graphite. In yet another example, the
exposed surface may include from about 2 percent to about 5 percent
graphite. Still further, an example may have an exposed surface
including from about 3 percent to about 14 percent graphite. The
percentage of graphite is the ratio of the area of the exposed
surface that is graphite to the total area of the exposed surface
expressed as a percentage. A sample calculation is as follows:
(area of graphite:11.78 in.sup.2)/(total area of exposed
surface:117.8 in.sup.2)*100=10%
[0026] As depicted in FIG. 4, the compound zone 70 further may
include an oxide layer 72 having Fe.sub.3O.sub.4 disposed at the
exposed surface. An iron nitride layer 74 including epsilon
Fe.sub.3N iron nitride and gamma prime Fe.sub.4N iron nitride may
be generally subjacent the oxide layer 72 and containing a majority
of epsilon Fe.sub.3N iron nitride. Further, the oxide layer 72 may
have a thickness 73 ranging from about 5% to about 50% of a
thickness 75 of the iron nitride layer 74. As shown in FIG. 4, a
diffusion layer 77 is subjacent the iron nitride layer 74 and is a
transition between the iron nitride layer 74 and a portion of the
rotational member that is beyond the reach of ferritic
nitrocarburization (not shown).
[0027] FIG. 3 is a graph comparing experimental wear vs.
temperature results for an example and a prior art brake. The
improved wear-vs.-temperature curve 76 for a friction material
against a low graphite concentration friction surface is shown
compared to the wear-vs-temperature curve 78 against a standard
friction surface. In an example, a ferritically nitrocarburized
rotational member 12, 12', 12'' with low graphite concentration at
the friction surface 46, 46' exhibits a friction material 44, 44'
wear of less than 0.4 mm per 1000 stops at about 350.degree. C. An
experiment using the test procedure in Surface Vehicle Recommended
Practice J2707, Issued February 2005 by SAE International gave the
results shown at 76 in FIG. 3. An Akebono NS265 Non Asbestos
Organic (NAO) friction material was used in the experiment.
[0028] Referring now to FIG. 5, a perspective view of a brake disc
39 in an example is shown. Rotational member 12 is a brake disc 39
with vent slots 38. FIG. 6 is a depiction of a microscopic
enlargement of a friction surface 46 of the brake disc 39 shown in
FIG. 5. In the example shown in FIG. 6, microscopic crevices 48 are
present in the friction surface 46. A scale indicator 80 is
provided in FIG. 6 to facilitate estimation of the size of crevices
48 and their relative density on a friction surface 46. It is noted
that graphite flakes (not shown) are substantially absent according
to an example of the present disclosure.
[0029] The rotational member 12, 12', 12'' may be made from gray
cast iron, steel, or stainless steel. It is to be understood that
the rotational member may be cast, stamped, forged, formed from
powdered metal or any suitable forming process. The compound zone
70 disposed at the friction surface 46, 46' may exhibit a hardness
of between about 56 HRC and about 64 HRC. Alternatively, the
compound zone 70 may exhibit a hardness on gray cast iron of at
least 300 HK100 per SAE AMS2757b or SAE AMS2753. Hardness is
directly related to wear resistance.
[0030] A method 100 for increasing useful life of a rotational
member 12, 12', 12'' of a vehicle brake 10 is disclosed herein and
shown schematically in FIG. 11. The method 100 includes step 110,
removing graphite flakes from a friction surface 46, 46' of the
rotational member 12, 12', 12'' prior to step 120, nitrocarburizing
the friction surface 46, 46'. The graphite flakes may be removed
by, for example, sand blasting, grit blasting, grinding, and
combinations thereof. After the graphite has been removed according
to examples of the method 100, graphite will comprise less than
about 14 percent of the friction surface 46, 46'. In an example,
the friction surface 46, 46' may include from about 1 percent to
about 5 percent graphite. In yet another example, the friction
surface 46, 46' may include from about 2 percent to about 10
percent graphite. Still further, an example may have a friction
surface 46, 46' including from about 3 percent to about 14 percent
graphite. The percentage of graphite is the ratio of the area of
the friction surface 46, 46' that is graphite to the total area of
the friction surface 46, 46' expressed as a percentage. A sample
calculation is as follows:
(area of graphite:11.78 in.sup.2)/(total area of friction
surface:117.8 in.sup.2)*100=10%
[0031] After the graphite has been removed according to the method
100, at least the friction surface 46, 46' of the rotational member
12, 12', 12'' is nitrocarburized. It is to be understood that
removal of the graphite before nitrocarburizing prevents the
graphite from masking tiny areas from nitrocarburization. If
nitrocarburization is performed before removing graphite flakes,
the tiny areas masked by the graphite flakes may act as initiation
sites for corrosion.
[0032] It is to be understood that nitrocarburizing includes a gas
nitrocarburizing process, plasma nitrocarburizing process, or salt
bath nitrocarburizing process. The salt bath nitrocarburizing
process may include immersing at least the friction surface 46, 46'
of the rotational member 12, 12', 12'' into a nitrocarburizing salt
bath, and then immersing at least the friction surface 46, 46' of
the rotational member 12, 12', 12'' into an oxidizing salt
bath.
[0033] The rotational member 12, 12', 12'' may be formed from gray
cast iron using the method 100 above. It is to be understood that
the rotational member 12, 12', 12'' may include a brake disc 39, a
brake drum 50, or a combination thereof. The rotational member 12,
12', 12'' formed using the disclosed method 100 may reduce the wear
in a corresponding friction material 44, 44'. For example, the
friction material 44, 44' used with the rotational member 12, 12',
12'' formed using the disclosed method 100 may exhibit wear of less
than 0.4 mm per 1000 stops at 350.degree. C. The compound zone 70
disposed at the friction surface 46, 46' may exhibit a hardness
between about 56 HRC and about 64 HRC. Alternatively, the compound
zone 70 may exhibit a hardness on gray cast iron of at least 300
HK100 per SAE AMS2757b or SAE AMS2753. Wear resistance of the
compound zone is directly related to hardness. It is to be
understood that friction material 12, 12', 12'' wear may be
determined using Surface Vehicle Recommended Practice J2707, Issued
February 2005 by SAE International.
[0034] The rotational member 12, 12', 12'' formed using the method
100 disclosed above may exhibit a coefficient of friction of at
least 0.32 between the friction surface 46, 46' and the
corresponding friction material 44, 44'. In an experiment, a
specimen of rotational member 12, 12', 12'' material made according
to the disclosed method was tested with an Akebono NS265 Non
Asbestos Organic (NAO) brake pad. A 50 N normal load was applied,
and the friction coefficient was determined by measuring a force in
opposition to an oscillating sliding force applied at 2 Hz. The
friction coefficient in the test was determined to be greater than
0.32 for at least 300 cycles. Further, the method 100 may improve
corrosion resistance. Less than 15 percent of the exposed portion
of the friction surface 46, 46' may exhibit visible red rust after
1 week in humid air with a temperature of at least about 10.degree.
C. (50.degree. F.). It is to be understood that for the purposes of
this disclosure, humid air has a relative humidity of greater than
about 40 percent. The corrosion resistance depends on the amount of
graphite that remains. If only 1 to 5 percent of the exposed area
of the friction surface 46, 46' is graphite flakes, then the
percentage of visible red rust would be in a lower part of the
disclosed range.
[0035] Numerical data have been presented herein in a range format.
It is to be understood that this range format is used merely for
convenience and brevity and should be interpreted flexibly to
include not only the numerical values explicitly recited as the
limits of the range, but also to include all the individual
numerical values or sub-ranges encompassed within that range as if
each numerical value and sub-range is explicitly recited. For
example, a surface area amount ranging from about 1% to about 10%
should be interpreted to include not only the explicitly recited
limits of about 1% to about 10%, but also to include individual
amounts such as 2%, 3%, 4%, etc., and sub-ranges such as 5% to 8%,
3% to 9%, etc.
[0036] While several examples have been described in detail, it
will be apparent to those skilled in the art that the disclosed
examples may be modified. Therefore, the foregoing description is
to be considered exemplary rather than limiting.
* * * * *