Title: Piston for magneto-rheological fluid systems and method for its manufacture
Abstract: The piston for a magneto-rheological fluid system is manufactured from a piston skirt of a material having a high magnetic permeability and a piston plate which closes one end of the piston skirt having a low magnetic permeability and therefore must be made out of a material such as stainless steel. The piston is manufactured by placing the plate on one electrode and clamping another set of electrodes against the outer circumferential surface of the piston ring or skirt. The plate and ring are brought into contact with one another while applying a current through the piston ring and the piston plate, thereby heating interfering portions of the ring and plate and permitting the plate to be forced inside of the ring while at the same time allowing the softened or plastic portions of the ring and plate to intermingle with one another and thus form a solid state bond.
Patent Number: 6,860,371 Issued on 03/01/2005 to Ananthanarayanan, et al.
| Inventors:
|
Ananthanarayanan; Venkatasubramanian (Beavercreek, OH);
Froning; Michael Henry (Bellbrook, OH);
Lonbani; Sohrab Sadri (Xenia, OH);
Goldasz; Janusz Pawel (Krakow, PL);
Hornback; Michael Everett (Xenia, OH);
Hopkins; Patrick Neil (West Carollton, OH);
Kruckemeyer; William Charles (Beavercreek, OH)
|
| Assignee:
|
Delphi Technologies, Inc. (Troy, MI)
|
| Appl. No.:
|
325191 |
| Filed:
|
December 20, 2002 |
| Current U.S. Class: |
188/322.22; 188/267 |
| Intern'l Class: |
F16F 009//00 |
| Field of Search: |
188/322.22,322.15,267,267.1,267.2
|
References Cited [Referenced By]
U.S. Patent Documents
| 4106171 | Aug., 1978 | Basiulis.
| |
| 4673067 | Jun., 1987 | Munning et al. | 188/266.
|
| 5277281 | Jan., 1994 | Carlson et al. | 188/267.
|
| 5878851 | Mar., 1999 | Carlson et al. | 188/269.
|
| 6260675 | Jul., 2001 | Muhlenkamp | 188/267.
|
| 6279700 | Aug., 2001 | Lisenker et al. | 188/267.
|
| 6311810 | Nov., 2001 | Hopkins et al. | 188/267.
|
| 6318519 | Nov., 2001 | Kruckemeyer et al. | 188/267.
|
| 6318520 | Nov., 2001 | Lisenker et al. | 188/267.
|
| 6382369 | May., 2002 | Lisenker.
| |
| 6390252 | May., 2002 | Namuduri et al. | 188/267.
|
| 6419058 | Jul., 2002 | Oliver et al.
| |
| 6471018 | Oct., 2002 | Gordaninejad et al. | 188/267.
|
| 6481546 | Nov., 2002 | Oliver et al. | 188/267.
|
| 6497308 | Dec., 2002 | Lisenker | 188/267.
|
| 6497309 | Dec., 2002 | Lisenker | 188/267.
|
| 6525289 | Feb., 2003 | Ananthanarayanan et al.
| |
| 6612409 | Sep., 2003 | Lun et al.
| |
| 6637560 | Oct., 2003 | Oliver et al.
| |
| Foreign Patent Documents |
| 3304903 | Aug., 1984 | DE.
| |
Primary Examiner: Siconolfi; Robert
Attorney, Agent or Firm: Smith; Michael D.
Parent Case Text
This is a division of application Ser. No. 09/775,192 filed on Feb. 1, 2001
now U.S. Pat. No. 6,525,289.
Claims
What is claimed is:
1. Piston for magneto-rheological fluid systems, comprising a
magneto-rheological piston ring made of a material having a relatively
high magnetic permeability and a piston plate made of a material having a
low magnetic permeability, said ring having an inner circumferential
surface defining an inner diameter of said ring, said ring terminating in
an end face, said plate having an edge portion received within said inner
diameter of said ring with an interference fit upon heating of said ring
and said plate sufficiently to permit the ring to receive said plate, said
edge portion and said inner diameter of said ring being heated
sufficiently to soften the interfering portion of the plate and the
corresponding portion of the ring engaged by the interfering portion of
the plate to permit the interfering portion of the plate to flow together
with the corresponding portion of the ring to thereby form a solid state
bond between the ring and the plate.
2. Piston as claimed in claim 1, wherein said inner circumferential surface
of said piston ring is stepped to define larger and smaller diameter
sections with a shoulder therebetween, said larger diameter section
defining said corresponding portion of the ring, said plate engaging said
shoulder.
3. Piston as claimed in claim 2, wherein said plate includes outwardly
projecting segments defining the interfering portion of the plate.
Description
TECHNICAL FIELD
This invention relates to a piston and a method of manufacturing a piston
for use in magneto-rheological fluid systems.
BACKGROUND OF THE INVENTION
Suspension dampers, such as shock absorbers, have been used for many years
to control the ride quality of automotive vehicles. In many vehicles, it
is desirable to control suspension stiffness. Recently,
magneto-rheological fluids have become available for use in vehicle
suspension dampers. Magneto-rheological fluids permit the viscosity of the
damping fluid to be changed in response to an applied magnetic field. Ride
stiffness may thereby be controlled by controlling current in an electric
coil within the damper. In magneto-rheological suspension systems, a
magnetic field is generated and is applied to the magneto-rheological
damping fluid, thereby permitting the viscosity of the fluid to be
modified depending upon ride conditions. Accordingly, the stiffness of the
suspension system may be easily controlled.
Magneto-rheological suspension systems require a piston rod and a
suspension piston in which a coil is mounted. The coil circumscribes the
piston rod, and the fluid is communicated through passages circumscribing
the piston rod between the coil and the piston ring or skirt. The piston
includes a piston skirt or ring, which is held in place by a piston plate
which is mounted on the piston rod and supports the piston ring.
Accordingly, in order that the magnetic field be applied to the
magneto-rheological fluid communicated through the passages, the portion
of the piston rod extending through the coil and the piston skirt or ring
must be made of a magnetically soft material exhibiting high magnetic
permeability and high saturation magnetization. The piston plate, which
extends between the piston ring and the piston rod, is desirably a
magnetic insulator exhibiting low magnetic permeability and serves only to
hold the other components in place. Accordingly, the rod and piston ring
define a magnetic circuit in which the electrodes are the piston rod and
piston ring. This magnetic circuit is energized by the coil and the
magnetic field is generated by electrical current flowing through the
coil.
Since the piston ring must be made of a material having high magnetic
permeability and the piston plate is desirably a magnetic insulator having
extremely low magnetic permeability, it is desirable to manufacture the
piston ring and rod out of low carbon soft magnetic steel, while the plate
is desirably made out of non-magnetic stainless steel. Because the plate
and piston ring are made out of materials having different properties,
joining the plate to the ring has been difficult. Conventional welding and
brazing techniques have proven to be unreliable. Welding dissimilar
materials of the type used in the piston ring and plate disclosed herein
is inherently difficult and often results in inconsistent and cracked or
failed welds.
SUMMARY OF THE INVENTION
According to the invention, the ring is clamped in two nearly semi-circular
electrodes whose inner diameter matches the outer diameter of the ring
closely. The semi-circular electrodes are connected together electrically
and connected to one of the terminals of a power supply of a resistance
welding machine. The plate is supported on a deflectable pin that extends
coaxially through the ring so that the plate is supported coaxial with the
ring. The plate is engaged by another electrode which is connected to the
other terminal of the power supply of the resistance welding machine. The
ring is urged against the ring with a predetermined weld force. Electrical
current is then caused to flow through the ring and the plate. The
magnitude of the current is adjusted so that the portions of the ring and
the plate which engage one another are heated to a temperature causing the
portions in both components engaging one another to become pliable or
plastic. When this occurs, the plate is forced into the piston, thereby
causing the plasticized material at the interface to mix with one another,
thereby forming a solid state bond between the components. Because of the
intermingling of the portions of the components, the strength of the bond
is greater than the strength of either of the components. Although the
invention has been specifically described with respect to a
magneto-rheological suspension damper, the piston of the present invention
may be used in other types of magneto-rheological fluid systems.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of a piston assembly using a piston made
according to the present invention;
FIG. 2 is an exploded view in perspective of a piston made according to the
present invention;
FIG. 3 is an assembled view in perspective of the piston illustrated in
FIG. 2;
FIG. 4 is a side elevation view, partly in section of the piston skirt and
piston plate comprising the piston illustrated in FIGS. 2 and 3
immediately before the piston plate is installed on the piston skirt;
FIGS. 5-7 are views similar to FIG. 4, but illustrating the various steps
required to manufacture the piston illustrated in FIGS. 2 and 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, a suspension damper generally indicated by
the numeral 10 is designed to operate with a magneto-rheological damping
fluid to control suspension stiffness. Magneto-rheological fluids are
commercially available and generally comprise a synthetic hydrocarbon or
silicone based fluid in which magnetically soft particles (such as iron
microspheres) are suspended. In the absence of a magnetic field, the
particles exhibit a random orientation within the fluid. Fluid viscosity
is relatively low. When a magnetic coil generates a magnetic field in the
vicinity of the fluid, the applied magnetic field aligns the magnetic
particles into fibrous structures, thereby changing the fluid viscosity to
a much higher value. By controlling current in the electromagnetic coil,
the strength of the applied magnetic field may be varied, thus permitting
gradations in the viscosity of the fluid. Referring to the damper 10 of
FIG. 1, a piston generally indicated by the numeral 12 is slidably
received within a conventional damping tube 14. The piston 12 includes a
piston ring or skirt 16 and a piston plate 18 which closes one end of the
skirt 16. A piston rod 20 is coaxial with the plate 18 and is secured
thereto. Circumscribing the piston rod 20, and secured thereto, is a coil
carrier 22, which holds an electrical coil 24. Circumferentially spaced
passages 26 extend through the plate 18 and permit communication of
damping fluid through the piston 12. Accordingly, the coil 24 energizes a
magnetic circuit comprising the piston rod 20 and skirt 16. It is,
accordingly, desirable that the piston ring or skirt 16 be held away from
the core defined by the piston rod 20 with a fixed annular gap.
Accordingly, while it is desirable that the piston skirt 16 and rod 20 and
coil carrier 22 be made out of a soft magnetic material having high
magnetic permeability and high saturation magnetization, it is desirable
that the plate 18 act as a magnetic insulator between the core of the
magnetic circuit (piston 20 and coil carrier 22) and the piston skirt 12,
which defines a flux ring. Accordingly, it is desirable, in order to
minimize the hysterisis loop of the magnetic circuit and minimize energy
losses when current is applied to the coil 24, that the plate 18 have a
low or minimum permeability (ideally approaching that of a vacuum) and low
magnetization. A typical material which permits the plate to act as a
magnetic insulator is nonmagnetic stainless steel. However, as discussed
above, securing the plate 18 to the skirt for ring 16 has proven to be
difficult, as brazing and mechanical attachment (crimping) of the plate to
the skirt have been undesirable, and most welding techniques generate hot
cracks in the stainless steel and otherwise yield poor weld quality.
The skirt or piston ring 16 includes an outer diameter surface 28 and inner
diameter surface 30, which is stepped to defined a larger diameter portion
32 and a smaller diameter portion 34 with a shoulder 36 therebetween.
Piston plate 18 is provided with a central opening 38 through which piston
rod 20 extends and is attached. Plate 18 also defines an outer
circumferential surface 40, which is less than the smaller diameter
portion 34 of skirt 16 and cooperates with inner circumferential surface
30 to define the passages 26 therebetween. Segments of the outer
circumferential surface 40 extend between radially outwardly projecting
portions 42 of the plate 18. As can be seen on FIG. 3, the diameter of the
plate 18 taken across the tips of the outwardly projecting portions 42 is
slightly greater than the larger diameter portion 32 of the piston skirt
16, so that the plate 18 interferes with the larger diameter portion.
Referring now to FIGS. 4-6, when the piston plate 18 is to be secured to
the ring 12, the ring 12 is clamped between two nearly semicircular copper
alloy electrodes 44, 46 in an alternating current resistance welding
machine, which are mounted on actuators (not shown) which cause the
clamping members 44, 46 to move radially with respect to the ring 12. The
semi-circular electrodes 44, 46 are typically made from a fully circular
copper alloy electrode which is then separated into two halves. The
electrodes 44, 46 are shorted together electrically and connected to a
terminal of the weld machine power supply 52. Accordingly, when the piston
12 is assembled, the clamping members 44, 46 are operated to engage and
hold the outer circumferential surface 28 of the piston ring or skirt 16,
as shown in FIG. 5.
As also shown in FIGS. 4 and 5, the plate 18 is supported on a pin 51 which
extends coaxially through the ring 12 in order to assure that the ring and
plate remain concentric as the plate is secured to the ring. The pin
includes a smaller diameter portion which extends into the aperture 38 in
the plate 18 so that the plate 18 rests on the shoulder 50 defined between
the larger and smaller diameter portions of the pin 51. The pin 51 is
mounted such that it deflects in response to an axial force applied to the
pin. An upper copper electrode 48 of a diameter substantially the same,
but slightly smaller than, the outer diameter surface 40 of the plate 18
is brought into engagement with the plate 18. The electrode 48 is then
urged downwardly viewing the Figures to apply a weld force on the plate
18, urging the portions 42 of the plate against the ring 12. The plate 18
is urged against the shoulder 36.
Due to interference of the projections 42 of the plate 18, the plate 18
does not enter the ring 12 with the application of the weld force alone
(but instead engages the end face 54), as indicated by FIG. 5. When an
appropriate weld current is applied for a short period typically not
exceeding one second, the heat and pressure make the plate 18 move into
the ring 12, without significant melting at the weld interface, as shown
in FIG. 6. The portions 42 of the plate 18 and the portions of the skirt
engaged by projections 42 become plastic and intermingle with one another,
forming a solid state weld. The clamping electrodes 44, 46 are then moved
away to release the completed assembly, as shown in FIG. 7.
*
