U.S. patent application number 11/118198 was filed with the patent office on 2006-11-02 for stabilizer bar.
This patent application is currently assigned to Meritor Suspension System Company, U.S.. Invention is credited to Michael P. Binno, Thomas D. Haiderer.
Application Number | 20060243355 11/118198 |
Document ID | / |
Family ID | 36702836 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060243355 |
Kind Code |
A1 |
Haiderer; Thomas D. ; et
al. |
November 2, 2006 |
Stabilizer bar
Abstract
A tubular stabilizer bar for a vehicle suspension is formed from
an as-quenched steel material that is not subjected to a tempering
process, and which has a hardness of at least 40 Rockwell C. The
stabilizer bar includes an ultimate tensile strength that is
greater than 200 ksi with a ratio of yield strength to ultimate
tensile strength that is no more than 0.9. The stabilizer bar is
significantly harder and has significantly improved fatigue life
without compromising ductility, when compared with prior
designs.
Inventors: |
Haiderer; Thomas D.;
(Goodrich, MI) ; Binno; Michael P.; (Troy,
MI) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Assignee: |
Meritor Suspension System Company,
U.S.
|
Family ID: |
36702836 |
Appl. No.: |
11/118198 |
Filed: |
April 29, 2005 |
Current U.S.
Class: |
148/593 ;
148/320 |
Current CPC
Class: |
C21D 9/02 20130101; C21D
9/08 20130101; C21D 1/18 20130101; B60G 2206/427 20130101; B60G
2206/012 20130101; B60G 21/055 20130101; B60G 2206/84 20130101;
B60G 2206/8106 20130101 |
Class at
Publication: |
148/593 ;
148/320 |
International
Class: |
C21D 9/08 20060101
C21D009/08 |
Claims
1. A method for forming a tubular stabilizer bar including: (a)
quenching stabilizer bar tubing material formed from a lower carbon
content steel having a carbon content of approximately 0.07-0.40%
to produce an as-quenched stabilizer bar tube; and (b) forming a
final stabilizer bar from the as-quenched stabilizer bar tube from
step (a) having a hardness of at least 40 Rockwell C.
2. The method according to claim 1 including the steps of applying
a paint to the as-quenched stabilizer bar tube and curing the paint
subsequent to steps (a) or (b).
3. The method according to claim 2 wherein step (a) provides the
as-quenched stabilizer bar tube with a first hardness value and
wherein curing the paint provides the as-quenched stabilizer bar
tube with a second hardness value that is less than the first
harness value.
4. The method according to claim 1 wherein step (b) includes
providing the hardness of at least 40 Rockwell C without tempering
the as-quenched stabilizer bar tube subsequent to step (a).
5. The method according to claim 4 including providing the final
stabilizer bar with an ultimate tensile strength of at least 200
ksi.
6. The method according to claim 1 wherein step (a) is the only
heat treating step applied to the stabilizer bar tubing
material.
7. The method according to claim 1 wherein the hardness is at least
42 Rockwell C.
8. The method according to claim 1 wherein the carbon content is
approximately 0.20-0.35%.
9. A stabilizer bar for a suspension assembly comprising: a tubular
body having a hardness of at least 40 Rockwell C without
tempering.
10. The stabilizer bar according to claim 9 wherein said tubular
body is comprised of an as-quenched lower carbon steel
material.
11. The stabilizer bar according to claim 10 wherein said tubular
body is non-tempered.
12. The stabilizer bar according to claim 9 wherein said tubular
body includes a cured paint coating.
13. The stabilizer bar according to claim 9 wherein said tubular
body is formed from a material having a ratio of yield strength to
ultimate tensile strength that is less than 0.9.
14. The stabilizer bar according to claim 13 wherein said material
has an ultimate tensile strength of at least 200 ksi.
15. The stabilizer bar according to claim 9 wherein said hardness
is at least 42 Rockwell C.
16. The stabilizer bar according to claim 9 wherein said tubular
body has a percent elongation property of at least 15% and a
percent reduction in area property of at least 46%.
17. The stabilizer bar according to claim 9 wherein said tubular
body is formed from a lower carbon content steel having a carbon
content of approximately 0.07-0.40%.
18. The stabilizer bar according to claim 17 wherein the carbon
content is approximately 0.20-0.35%.
Description
TECHNICAL FIELD
[0001] The subject invention relates to a tubular stabilizer bar
made from an as-quenched, low carbon steel, which provides a
desired hardness to improve fatigue life.
BACKGROUND OF THE INVENTION
[0002] Stabilizer bars for vehicle suspensions are typically formed
from a medium or high carbon content steel that is quenched,
tempered, and then painted. Quenching produces martensite, which is
very hard but brittle. Brittle material has a tendency to crack,
which can result in an overall reduction in fatigue life of a
component. The stabilizer bars are tempered to reduce the
brittleness.
[0003] One disadvantage with this tempering process is that while
brittleness is reduced, the overall hardness, ultimate tensile
strength, and yield strength are also reduced. This traditional
quench and temper process provides a hardness, ultimate tensile
strength, and yield strength combination that produces a stabilizer
bar with a less than desired fatigue life. The application of
paint, which requires a curing process, can further reduce
hardness, ultimate tensile strength, and yield strength.
[0004] A stabilizer bar made according to this traditional process
typically has a ratio of yield strength to ultimate tensile
strength of about 0.95. Further, the stabilizer bar made according
to this process has a hardness value that is typically around 37
Rockwell C. This combination of properties provides a less than
desired fatigue life for a stabilizer bar.
[0005] Thus, it is desirable to have a heat treat process for a
stabilizer bar that produces an improved combination of hardness,
ultimate tensile strength, and yield strength to provide a
stabilizer bar having an improved fatigue life.
SUMMARY OF THE INVENTION
[0006] A stabilizer bar for a vehicle suspension includes a tubular
body that is processed to provide a minimum hardness of at least 40
Rockwell C. The hardness of at least 40 Rockwell C is provided by
an as-quenched steel material that is not subjected to tempering.
The as-quenched steel material has a carbon content of 0.07-0.40%.
The tubular body has an ultimate tensile strength of at least 200
ksi and has a ratio of yield strength to ultimate tensile strength
that is no more than 0.9. Further, the ductility properties are
satisfactorily maintained and are indicated by a percent elongation
that is generally greater than 15.5% and a percent reduction in
area that is greater than 46%.
[0007] In one example, paint is applied to the tubular body to
provide a protective coating. The paint is then cured. Curing the
paint provides a reduction in ultimate tensile strength and
hardness. However, the ultimate tensile strength is at least 200
ksi and the hardness is at least 40 Rockwell C even after
curing.
[0008] By eliminating tempering from a stabilizer bar manufacturing
process, manufacturing costs are reduced. Further, the as-quenched
stabilizer bar provides increased hardness and significantly
improved fatigue life, without compromising ductility, when
compared to prior designs.
[0009] These and other features of the present invention can be
best understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view of a stabilizer bar for a
vehicle suspension incorporating the subject invention.
[0011] FIG. 2 is a cross-section view taken at lines 2 of FIG.
1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] A stabilizer bar is shown generally at 10 in FIG. 1. The
stabilizer bar 10 is formed to have a U-shape with a center portion
12 and first and second transversely extending legs 14, 16.
Radiused bends 18 transition from the center portion 12 to the
first and second transversely extending legs 14, 16. The first and
second transversely extending legs 14, 16 are each attached to a
suspension trailing arm or lower control arm (not shown) as
known.
[0013] The stabilizer bar 10 includes a tubular body 20 (see FIG.
2). The tubular body 20 includes an outer surface 22 and an inner
surface 24 that are spaced apart to define a wall thickness 26.
Wall thickness 26 can vary as needed to provide desired vehicle
roll resistance.
[0014] The subject invention provides a stabilizer bar 10 that is
made from a lower carbon content steel material that is subjected
to a heat treating process that does not include tempering. Any
type of lower carbon content steel can be used. Typically, a lower
carbon content steel includes, by weight, about 0.07-0.40% carbon
(C), in addition to other known elements. Preferably, the carbon
content is approximately 0.20-0.35%. The stabilizer bar 10 is
preferably made from this type, or a similar type, of lower carbon
content steel, however, it should be understood that the subject
invention could provide benefits for carbon steels having lower or
higher ranges of carbon content.
[0015] As mentioned, the material that forms the stabilizer bar 10
is processed with a heat treat that does not include tempering. Due
to the low carbon content of the steel used to form the stabilizer
bar 10, quenching is all that is required to achieve a desired
combination of hardness, ultimate tensile strength, and yield
strength. As known, quenching involves heating a material to a
desired temperature for a desired length of time and then immersing
the heated material in a liquid bath to cool the material. This
process provides a desired microstructure for the material.
Temperatures, times, and types of liquid baths can be varied as
known to achieve a final desired microstructure.
[0016] The subject invention provides a stabilizer bar 10 formed
from the low carbon content steel, which is quenched to achieve a
hardness of at least 40 Rockwell C. Preferably, the hardness is at
least 42 Rockwell C or higher. During quenching, the low carbon
content steel forms self-tempered martensite having a desired
combination of properties that do not require any additional heat
treat. The stabilizer bar 10 made from this process includes an
ultimate tensile strength of at least 200 ksi and a yield strength
of at least 170 ksi. Further, a ratio of yield strength to ultimate
tensile strength is approximately 0.9 or less. No tempering is
required to achieve this combination of material properties and
ductility properties are not compromised.
[0017] The stabilizer bar 10 formed from the material subjected to
this process has sufficient ductility, such that the previously
required tempering step can be eliminated.
[0018] In one example, a paint coat 28 is applied to the outer
surface 22 of the stabilizer bar 10. The paint coat 28 is cured, as
known, to achieve desired coating characteristics. Curing the paint
coat 28 provides a reduction in ultimate tensile strength and
hardness. However, the ultimate tensile strength is at least 200
ksi and the hardness is at least 40 Rockwell C even after
curing.
[0019] When compared with a tubular stabilizer bar made from the
traditional process where the stabilizer bar was quenched,
tempered, and painted, the subject stabilizer bar 10 has
significantly higher ultimate tensile strength, yield strength, and
hardness properties. Additionally, fatigue life (B10) of the
stabilizer bar 10 is also improved.
[0020] For an as-quenched stabilizer bar 10 that does not include a
paint coat 28, yield strength is about 112%, ultimate tensile
strength is about 145%, and hardness is about 130% of that of the
corresponding properties for the traditionally processed stabilizer
bar. Fatigue life is about 150% of that of the traditionally
processed stabilizer bar. In one example, the as-quenched
stabilizer bar 10 without the paint coat 28 includes an ultimate
tensile strength of 242 ksi, a yield strength of 180 ksi (ratio of
yield strength to ultimate tensile strength being 0.75), and a
hardness of 47 Rockwell C.
[0021] Further, ductility is not compromised as percent elongation
is maintained at at least 15.5% and percent reduction of area is at
least 46%. The percent elongation is thus at least 86% of that
which would be achieved with the traditional process. Percent
reduction in area is at least 80% of that achieved with the
traditional process. These percentages provide a desired ductility
level for the stabilizer bar 10, without requiring tempering. This
significantly reduces processing costs.
[0022] For an as-quenched stabilizer bar 10 that includes the paint
coat 28, yield strength is about 108%, ultimate tensile strength is
about 120%, and hardness is about 116% of that of the corresponding
properties for the traditionally processed stabilizer bar. Fatigue
life is about 130% of that of the traditionally processed
stabilizer bar. In one example, the as-quenched stabilizer bar 10
with the paint coat 28 includes an ultimate tensile strength of 202
ksi, a yield strength of 174 ksi (ratio of yield strength to
ultimate tensile strength being 0.86), a percent elongation of 16%,
a percent reduction of area of 49.5%, and a hardness of 42 Rockwell
C. This can be compared to a stabilizer bar that is quenched,
tempered, and painted. This traditionally formed stabilizer bar has
an ultimate tensile strength of 167 ksi, a yield strength of 161
ksi, a hardness of 36 Rockwell C, a percent elongation of 18%, and
a percent reduction area of 58%.
[0023] Using a lower carbon content steel and eliminating tempering
from the heat treat process for a stabilizer bar increases
hardness, improves fatigue life, and provides a lower cost process
than traditionally used. By utilizing an as-quenched material, a
desired combination of material properties is achieved, which
results in a significant increase in fatigue life compared to prior
stabilizer bars.
[0024] Although a preferred embodiment of this invention has been
disclosed, a worker of ordinary skill in this art would recognize
that certain modifications would come within the scope of this
invention. For that reason, the following claims should be studied
to determine the true scope and content of this invention.
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