Rotary shafts – gudgeons – housings – and flexible couplings for ro – Coupling accommodates drive between members having... – Coupling transmits torque via radially directed pin
Reexamination Certificate
1999-07-01
2002-04-30
Browne, Lynne H. (Department: 3629)
Rotary shafts, gudgeons, housings, and flexible couplings for ro
Coupling accommodates drive between members having...
Coupling transmits torque via radially directed pin
C403S271000
Reexamination Certificate
active
06379254
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a method of fabricating automotive driveshafts and more specifically, to a method of attaching metal end-fittings such as an automotive U-joint yoke and splined tube shaft to tubular shafts which rotate at speeds and transmit torque and axial forces such as when in use as a vehicle driveshaft.
In general, a vehicular driveshaft transmits torque from a transmission to an axle to drive selected wheels of a vehicle. A driveshaft operates through changing relative angles between the transmission and the axle. Furthermore, a driveshaft expands and contracts in response to road conditions when the vehicle is operated. To accomplish these functions, driveshafts include well known universal joints and slip joints connected to driveshaft tubes.
A driveshaft tube includes a hollow cylindrical portion of a desired length, oftentimes terminating at one end in a tube yoke. The tube yoke includes a pair of opposed arms for receiving bearing cups mounted on trunnions of a cross. The tube yoke, cross and bearing can be combined with an end yoke to form a universal joint. The opposite end of the driveshaft tube can terminate in a splined tube shaft designed to receive an end yoke. The opposite end of the driveshaft tube can also terminate in a second tube yoke. Tube yokes and driveshaft tubes are conventionally formed from steel and are attached to the driveshaft tube by conventional welding processes.
In order to reduce vehicular weight, obtain smooth operation and improve fuel economy, driveshaft components have been formed from lighter materials such as aluminum. Pure aluminum does not make driveshaft components of acceptable strength, but alloys of aluminum have adequate strength. While aluminum alloys have been an acceptable material because of their strength and lighter weight, problems have been experienced using conventional welding techniques with such components. For example, aluminum components have been weakened by heat generated and transferred to them during conventional welding.
For the attachment of end-fittings to metal tubes, many other techniques are available with varying degree of success. Among these other methods are the use of pins, rivets, bolts, adhesives and such mechanical methods as splines, keyways, polygon matching shapes, shrink fits and press fits. However, these attachment methods are not as economical as desired, particularly when applied to driveshafts of vehicles.
In use today, with limited success, is one recent innovation known under the trademark MAGNAFORM. This technology employs a very high electromagnetic-induced force to swage aluminum tube onto a fitting, as is commonly used for non-driveshaft applications. Unfortunately, the results of such a method for attaching end fittings to driveshaft tubes have been less than satisfactory. Magnetic forming requires a non-circular, force-transmitting shape to transmit torque between two rotating parts. Aluminum, which is typically used in driveshafts, is a notch sensitive material, and is subject to cracking where it is stressed by being deformed into shapes having relatively large contours. Also, when torque is applied to the driveshaft in the vehicle, there is a small amount of slippage between the yoke and the driveshaft tube which produces a loud and irritating sound. This has resulted in a large number of consumer complaints. Besides that, magnetic pulse forming gives good mechanical strength results only as long as the torque is not too high. But with a high level of torque, as measured with fatigue tests, the life of the driveshaft is reduced considerably.
A large number of revisions have been made in order to attempt to solve those problems. Unfortunately, all of these have been unsatisfactory. There is therefore a need to provide a solution which permits the advantageous use of magnetic pulse fields for swaging a tube and the advantageous use of the welding process for joining the end-fitting and the aluminum driveshaft tube.
A known prior art method of pressure welding is based on the use of interaction of magnetic fields, produced by an inductor through which an impulse of high intensity current is passed. The parts to be welded are positioned in spaced relation at an angle therebetween and the method can be used for obtaining overlapping welded joints of thin-walled parts having different thickness and made from different materials without melting. This is described in U.S. Pat. No. 3,520,049, to Lysenko et al. This method is referred to as Magnetic Pulse Welding (MPW) and has been used in particular to weld the end of nuclear fuel rods and has also found application in other contexts in which the diameters of the parts to be joined are small (about 25 mm) and tubes made from mechanical strength metal. Diameters of parts to be welded can be larger (about 60 mm) if tubes are made from technically pure aluminum and have a wall thickness of about 1.5 mm.
The apparatus for MPW as used today in manufacturing has the same basic design as the apparatus for magnetic pulse forming. The main parts of each apparatus are a capacitor bank, inductor and high current switching device. The technological capability of conventional MPW apparatus is much less than what is necessary for magnetic pulse welding of driveshafts having tube diameter within the range of about 75 to 180 mm and wall thickness of 2 to 3 mm. Further, conventional MPW apparatus is not capable of magnetic pulse welding of end fittings with driveshafts made from high-strength aluminum alloys like 6061T.
An improvement in welding tubular parts of large diameter using MPW is described by Yablochnikov in “Apparatus for MPW Large Diameter, Thin-Walled Pipes”; Avt. Svarka, 1983, No. 4 pp. 48-51, 58. That apparatus, named the Arc Magnetic Pulse Equipment (AMPE) has two main features: first, using a special type of inductor and, second, using a special vacuum switch which has closely-spaced ring-like electrodes that are positioned close to the inductor. Between the electrodes there are insulators and a metallic housing. The contact surfaces of the insulators, the metallic housing and the electrodes are hermetically sealed to create a closed discharge chamber which is evacuated by a vacuum pump. Due to those features and extra-low inductance of the system connection bus bars, AMPE has minimal loss of energy in the process of discharge.
In principle, AMPE should permit tubes as large as a driveshaft to be welded using MPW, but there appear four problems which must be solved before this technology can become valuable from a manufacturing point of view. The first problem is the destruction and contamination of insulation elements of inductor by the powerful cumulative jet which flows axially along the welding surfaces (i.e., axially of the driveshaft tube) during the welding process. This cumulative jet is produced in the process of collision welding of metal when the impact velocity is high enough. The second problem is the low strength of the welding joint between high-strength aluminum alloy tubes and the end fitting if the latter is made from steel. The third problem is the possibility of premature breakdown of the vacuum switch. And the fourth problem is a long cycle time and resulting low productivity of AMPE. The last two problems are connected and contradictory to each other.
In the process of MPW welding, the surfaces of metal approach each other at an angle and collide with high relative velocity. The welding surfaces usually have oxide films and contaminants. To get a strong joint or weld, it is necessary to clean this contamination from the welding surfaces. In the process of MPW in the area where the surfaces collide with each other at high velocity, the cumulative jet includes material from the surface sheets and contaminants from the collision surfaces. This material carried with the cumulative jet acts to clean the welding surfaces.
The cumulative jet has supersonic velocity and creates a loud sound like thunder if allowed to escape to the atmosphere. If the cumulative je
Binda Greg
Browne Lynne H.
MacMillan Sobanski & Todd LLC
Spicer Driveshaft, Inc.
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