Brakes – Internal-resistance motion retarder – Thrust member or piston structure
Reexamination Certificate
1998-06-08
2001-02-20
Oberleitner, Robert J. (Department: 3613)
Brakes
Internal-resistance motion retarder
Thrust member or piston structure
Reexamination Certificate
active
06189663
ABSTRACT:
TECHNICAL FIELD
This invention relates to piston rods for automobile shock absorbers and suspension struts. More specifically, it relates to the provision of thermal and kinetic spray coatings, instead of electrodeposited chromium, on such rods for corrosion protection and abrasion resistance.
BACKGROUND OF THE INVENTION
Automotive vehicles are suspended on springs to reduce the loads or vertical accelerations transmitted from the wheel to the body and its occupants. Springs store and release the energy imparted to the vehicle from the road surface. Cars and trucks also use suspension dampers (also known as shock absorbers and suspension struts) to convert the kinetic energy of the vehicle and springs into thermal energy and dissipate it to the atmosphere and the vehicle chassis. Such suspension dampers are necessary for the safety and comfort of the occupants of the vehicle.
Suspension dampers usually come in two forms on automotive vehicles, and a plurality of the dampers are used on each vehicle. A shock absorber is typically a hydraulic device that controls the sprung and unsprung masses of the vehicle by converting the kinetic energy into thermal energy. It is usually used in combination with a spring operating between the vehicle chassis and an axle to dampen the compression of the spring. A strut damper is more of a structural member of an automotive system that is designed to be capable of withstanding the forces and bending moments resulting from braking, acceleration and handling maneuvers. A strut damper, of course, also serves as a shock absorber. A typical shock absorber or strut damper comprises a cylindrical piston rod that slides in and out of a cylinder tube in sealing engagement with a closure portion of the tube. One end of the tube and one end of the piston rod are respectively connected to the chassis and axle. The other end of the rod is connected to a suitable piston structure that reciprocates within the tube. The piston, of course, displaces hydraulic fluid which is the shock absorbing medium of the device.
Piston rods for shock absorbers, strut dampers and the like are produced by the millions each year. Typically, the rods are formed of a suitable steel to provide the strength for its function. The exposed portion of the rod outside of the damper cylinder tube encounters water, salt, air and other aggressive materials that can cause corrosion of the rod. Since the rod must have a true round sealable surface for engagement with the seal portion of the device, corrosion must be minimized. For this reason, piston rods have traditionally been provided with an electroplated chromium coating. The chromium coating provides both corrosion resistance in the environment in which the damper operates and some abrasion resistance for the engagement of the rod with the sealing portion of the damper cylinder. Such electroplated chromium coatings have served well in damper piston rods for years. However, the hexavalent chromium plating bath and vapors are toxic to workers and present a disposal problem in the environment. There is a need for an alternative to the electroplated chromium coating practice for protecting automotive suspension damper piston rods.
SUMMARY OF THE INVENTION
This invention provides certain metallic and ceramic thermal and kinetic sprayed coatings on piston rods for automotive suspension dampers. These cylindrical shafts are typically made of a suitably strong, load bearing metal alloy such as a carbon steel. In accordance with the invention, a thermal spray or kinetic spray coating of an alloy is applied that is resistant to corrosion in the wet and often salty environment encountered by the automobile underbody. The coating is also resistant to abrasion as the rod slides in and out of the end closure means of the damper cylinder. Suitable alloys for thermal spray application include, e.g., nickel-chromium-iron alloys, iron-chromium-carbon alloys and iron-chromium alloys. Chromium-containing alloys are preferred. In another embodiment of the invention, suitable thermal spray coating materials include alumina-based ceramics.
Suitable thermal spray application processes include plasma spray, wire arc spray, high velocity oxy-fuel spray and flame spray processes. In these thermal spray processes, the wire or powdered starting material is melted in a gun and rapidly transported to a workpiece where it is deposited as individual molten droplets. The coating is thus applied drop by drop. It solidifies drop by drop and is therefore somewhat porous. Such pores typically make up 1% to 10% of the volume of the coating. In the case of metal alloy coatings, it is usually necessary to seal the porous coating to prevent water encroachment and electrochemical corrosion. The sealing may be accomplished by infiltration of the pores with a suitable polymer or by momentary thermal reflow of the metal alloy coating to fill the pores. In the case of ceramic coatings, especially electrically insulative alumina-based coatings, the sealing step is usually unnecessary. The alumina coatings may be porous but do not present a corrosive potential.
Kinetic spray processes involve suspending suitable coating particles in a gaseous stream and propelling the particles at supersonic speed against a roughened substrate to be coated. The gas may be heated to increase its velocity but not to soften or melt the particles. The particles are mechanically flattened and bonded on the substrate where they adhere without phase or composition change. Sealing may also be required for kinetic spray applied metallic coatings.
It is usually preferred to grind or otherwise finish the surface of the coating to assure roundness, the specified rod diameter and, very importantly, a smooth surface to minimize abrasion of the seal member of the damper housing for sealing engagement with the enclosure means on the cylinder member of the suspension damper.
REFERENCES:
patent: 3007550 (1961-11-01), Long, Jr.
patent: 3695149 (1972-10-01), Eberhart
patent: 3723165 (1973-03-01), Longo, et al.
patent: 4397452 (1983-08-01), Fouts
patent: 4526839 (1985-07-01), Herman et al.
patent: 4557808 (1985-12-01), Strunck et al.
patent: 4592964 (1986-06-01), Buran et al.
patent: 4669658 (1987-06-01), Nevgod et al.
patent: 4678511 (1987-07-01), Yasuoka et al.
patent: 4692305 (1987-09-01), Rangaswamy et al.
patent: 4822689 (1989-04-01), Fukubayashi et al.
patent: 4974498 (1990-12-01), Lemelson
patent: 5077139 (1991-12-01), Van der Heyden
patent: 5196471 (1993-03-01), Rangaswamy et al.
patent: 5338577 (1994-08-01), Burdette, II
patent: 5480536 (1996-01-01), Suehiro et al.
patent: 5504307 (1996-04-01), Hayashi et al.
patent: 5558908 (1996-09-01), Lukacs, III et al.
patent: 5778918 (1998-07-01), McLelland
patent: 5810130 (1998-09-01), Mc Candless
patent: 6000627 (1999-12-01), Chernyshov
patent: 0053521 (1982-09-01), None
patent: 609644 (1948-10-01), None
patent: 1120299 (1968-07-01), None
patent: 58-146762 (1983-01-01), None
patent: 60023671 (1985-06-01), None
Herman, “Plasma-Sprayed Coatings,”Scientific American, Sep. 1988, pp. 112-117.
Leivo et al, “Wear and Corrosion Properties of Plasma Sprayed A12O3and Cr2O3Sealed by Aluminum Phosphates,”Journal of Thermal Spray Technology, vol. 6(2), Jun. 1997, pp. 205-210.
Meng Wen-Jin
Smith John Robert
Van Steenkiste Thomas Hubert
General Motors Corporation
Oberleitner Robert J.
Sigler Robert M.
Talavera Melanie
LandOfFree
Spray coatings for suspension damper rods does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spray coatings for suspension damper rods, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spray coatings for suspension damper rods will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2584898