Brakes – Internal-resistance motion retarder – Electroviscous or electrorheological fluid
Reexamination Certificate
2001-01-05
2002-03-26
Graham, Matthew C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Electroviscous or electrorheological fluid
C188S315000
Reexamination Certificate
active
06360856
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a shock absorber for use in a motor vehicle; and, more particularly, to a double-tube shock absorber using a magnetorheological (MR) fluid and a hydraulic fluid.
BACKGROUND OF THE INVENTION
Typically, motor vehicles are equipped with a suspension system to improve road-adherence and to provide ride-comfort for occupants. The suspension system includes springs and shock absorbers. The shock absorbers are disposed in parallel with the springs to damp the vibration of the springs.
The shock absorbers utilize a fluid flow system incorporating therein either a hydraulic fluid having a constant viscosity or a fluid having a changeable viscosity, e.g., magnetorheological (MR) fluid. The use of MR fluid is advantageous in that the viscosity thereof can be controlled with the application of a magnetic field in order to adjust a damping force being exerted on the springs depending on a traveling condition.
Particularly, MR fluid is a free-flowing liquid with a viscosity. Exposure to a magnetic field can transform the liquid into a near-solid in milliseconds; and with the removal of the magnetic field, the fluid can be returned to its liquid state just as quickly. The degree of change in the viscosity of the MR fluid is proportional to the magnitude of the applied magnetic field.
FIGS. 1 and 2
are a cross sectional view illustrating a conventional shock absorber using an MR fluid and an enlarged cross sectional view depicting a piston assembly shown in FIG. 1, respectively, disclosed in U.S. Pat. No. 5,284,330 entitled “MAGNETORHEOLOGICAL FLUID DEVICE” issued on Jan. 11, 1994.
The shock absorber
10
comprises two principal components: a housing
20
and a piston assembly
30
. The housing
20
includes a volume of magnetorheological (MR) fluid. The fluid includes carbonyl iron particles suspended in silicone oil.
The housing
20
is generally of a cylindrical tube with a first closed end
22
. A cylindrical sleeve
25
may be affixed to an inner cylinder by any conventional means, e.g., press fit, welding or adhesive to increase the cross-sectional surface area of the housing
20
. The cylinder is closed at a second end thereof by an end member
26
. A first seal
27
extends about an outer periphery of the end member
26
to prevent fluid leakage between the housing
20
and the end member
26
. A second annular seal
28
is housed in a groove in an inner periphery of the end member
26
and seals against a piston rod
32
. A scraper
29
can be used to wipe the MR fluid off the surface of piston rod
32
so as to minimize the loss of MR fluid past the second annular seal
28
.
The housing
20
is provided with a floating piston
21
to separate the MR fluid from a pressurized accumulator
23
. The pressurized accumulator
23
is necessary to accommodate a fluid displaced by the piston rod
32
as well as to allow for thermal expansion of the fluid.
The piston assembly
30
is shown in greater detail in
FIG. 2. A
piston head
34
is spool shaped with an upper outwardly extending flange
36
and a lower outwardly extending flange
38
. A coil
40
is wound upon the spool-shaped piston head
34
between the upper flange
36
and the lower flange
38
. The piston head
34
is made of a magnetically permeable material, such as low carbon steel. Guide rails
42
are attached around an outside of the piston head
34
at particular intervals. As shown in
FIGS. 1 and 2
, four guide rails
42
are shown spaced uniformly about a periphery of the piston head
34
.
An electrical connection is made to the coil
40
through the piston rod
32
by lead wires
45
and
47
. The first lead wire
45
is connected to a first end of an electrically conductive rod
48
which extends through the piston rod
32
to a Phono-jack connector
46
. A center connection of the Phono-jack
46
is connected to a first end
39
of the coil
40
. A second end
41
of windings of the coil
40
is attached to a “ground” connection on an outside of the Phono-jack
46
. An electrical return path, then, includes the piston rod
32
and the ground lead
47
.
However, such an MR shock absorber has some inherent drawbacks. First, since the MR fluid has a higher viscosity than the conventional hydraulic fluid even in the absence of a magnetic field, the MR shock absorber tends to exert a harder damping force against external forces applied thereto, resulting in a deteriorated ride-comfort under certain circumstances. Furthermore, the MR fluid is costly, increasing the manufacturing cost of the shock absorber.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a double-tube shock absorber using a magnetorheological fluid and a hydraulic fluid.
In accordance with the present invention, there is provided a double-tube shock absorber comprising: an outer cylinder having a first working chamber; an inner cylinder located inside the first working chamber and having a second working chamber, wherein the first and the second working chamber are filled with a hydraulic fluid and a magnetorheological fluid, respectively; a first piston movably inserted into the first working chamber; a second piston having a coil movably inserted into the second working chamber, wherein each of the pistons includes one or more orifices; one or more first piston rods for leading the first piston in a reciprocating motion; and a second piston rod for leading the second piston in a reciprocating motion.
REFERENCES:
patent: 4896752 (1990-01-01), Shtarkman
patent: 5284330 (1994-02-01), Carlson et al.
patent: 5316112 (1994-05-01), Kimura et al.
patent: 5366048 (1994-11-01), Watanabe et al.
patent: 5956951 (1999-09-01), O'Callaghan
patent: 4200977 (1993-07-01), None
patent: 0607545 (1994-07-01), None
patent: 2267947 (1993-12-01), None
patent: 9927273 (1999-06-01), None
Anderson Kill & Olick PC
Graham Matthew C.
Mando Corporation
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