Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1992-12-03
1994-11-29
Walsh, Donald P.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
148513, 148514, 419 28, 419 39, 419 48, 419 55, 419 57, 420549, B22F 314, C22C 104, C22C 2102
Patent
active
053686292
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a rotor for an oil pump such as an oil pump for use in an automatic transmission (A/T).
BACKGROUND ART
Demand for cars that consume less fuel is strong these days. One way to improve the fuel efficiency is to reduce the overall weight of a car. In order to reduce the car weight, efforts are being made to reduce the weight of individual component parts of a car.
In this respect, it is considered highly important to reduce the weight of an oil pump, because 1) by reducing the weight of the pump and its peripheral parts and 2) by reducing the weight of frictional and rotary parts thereof, one can expect improved pumping capacity. For example, in case of a conventional oil pump for use in an automatic transmission, its part (pump case) is made of iron (mainly cast or diecast iron) and it weighs more than 5 kg. If the same part is made of an aluminum alloy, its weight will be less than 2 kg, which corresponds to about 60% weight reduction. Such a lightweight pump will show improved pumping capacity.
Heretofore, in generating a high-precision toothed part (gear) configured in a trochoid or involute curve by using a ferrous sintered part, the sizing technique has been employed in which pores remaining in the sintered part at the rate of 10-20% are partially closed by applying pressure, thus locally deforming the sintered part into the shape complementary to the metal mold, without giving any noticeable plastic deformation. The gear thus made has a high dimensional accuracy.
On the other hand, it is virtually impossible to apply such a sintering process to a part made of aluminum powder alloy, because, in case of an aluminum alloy powder, the oxide layer formed on the surface thereof tends to inhibit the diffusion and sintering. Sintering is applicable only in a eutectic liquid phase which appears at an extremely high temperature. But such a sintering operation tends to severely damage the microscopic and uniform metastable alloy phase obtained by the rapidly solidifying method or the mechanical alloying method and is thus practically meaningless. Furthermore, if a material made by solidifying aluminum powder should have pores at the rate of 10-20% as in the case of a ferrous sintered material, such a material could never be used for sliding members because its strength is extremely low.
Also, in generating a member made of aluminum powder alloy using the powdered metal technique, the aluminum alloy powder is molded and solidified in the cold and then is hot-forged. The heat produced by hot-forging tends to expand and shrink the mold and the solidified material, thus causing a change in the dimensions of the solidified material. It was therefore difficult to generate a part which is comparable in dimensional accuracy to a ferrous sintered part, with the heat-forging technique alone. If the solidified powder compact has a true density, what is done will be re-forging rather than sizing. Thus, it is impossible to improve the dimensional accuracy.
Also, if a rotor of an oil pump is made of one of various known aluminum alloys, such a rotor will have the following problems. heretofore been used as a slide member such as a piston or a bearing, such as AC8B and A390, its tooth surface would suffer severe wear damage resulting from pitching wear due to insufficient strength against frictional wear between aluminum alloys and surface pressure fatigue. Also, severe adhesion wear will appear at the end face and the outer peripheral portion due to seizure between the pump and the case. Further, when the rotor is rotating at high speed, fatigue failure may occur at the joint portion with the shaft due to insufficient strength of the rotor. Also, since cold forging cannot generate a precise and complicated shape, machining is further needed. As the percentage of Si increases, the primary crystal of Si becomes too coarse. This reduces the strength and toughness. On the other hand, in order to attain a sufficient high-strength temperature, the content of Fe has to be between 3
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Kondo Katsuyoshi
Takeda Yoshinobu
Mai Ngoclan T.
Sumitomo Electric Industries Ltd.
Walsh Donald P.
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