The present invention relates to a rocker arm and method for making a rocker arm for an internal combustion engine having internal oil passages. More particularly, the invention relates to an improved rocker arm having internal oil passages formed by joining pre-fabricated sections that have oil passages as an integral feature of at least one of the sections.
Conventional methods for manufacturing rocker arms generally involve stamping or casting procedures. The formed pieces are thereafter processed to remove material by machining e.g. drilling, milling, etc. to form oil passages in the rocker arm. Such methods by machining, drillings, milling, etc. require the removal of material to create the necessary oil passages. Additionally, passages formed in that manner are often less precise in dimensions and location. Also, prior art drilling or machining of oil passages, as a practical matter, must comprise a straight line and be of a size compatible with the drilling process and cannot take the form of a “worm” groove formed so as to provide the optimum advantage. Additionally, deeper holes, e.g. those in excess of about 10 drill-diameters deep, require the use of slower, relatively costly drilling process i.e., gun drilling. A method for production which pre-fabricates sections and the resulting product with precisely formed and located oil passages and joins such sections to form a finished rocker arm would be advantageous in cost and time savings.
The novel rocker arm of the invention is characterized by joining the pre-fabricated sections of sintered metal particles, generally two halves that are symmetrical to a central plane and wherein the mating surfaces of one or both halves incorporate grooves which upon assembly form one or more passageways for oil. The resulting product results in a significant reduction in mass and is found to produce an increase in structural stiffness. The pre-fabricated sections, preferably of powdered metal composition, are joined together by any convenient known technique such as by metallurgical brazing or by chemical or mechanical means.
The rocker arm of the invention comprising the pre-fabrication of separate mating sections, preferably two sections, is manufactured conveniently such as by furnace brazing together the sections, preferably formed of a powdered metal and containing integrally formed grooves in one or both mating sections. Additional machining or drilling to form internal passageways is avoided.
The metal is atomized by methods in which a stream of molten metal is struck with air or water jets and the formed metal particles are collected, sieved and annealed. In processing, the powdered metal particles, including mixtures of different metals, are shaped into the desired suitable form such as by flowing the metal powder usually at room temperature into a die cavity shaped as the finished part, and then applying pressure from above and below to form a compact. After ejection from the die, the compact is heated (sintered) to form a coherent mass with the configuration of the original die and properties related to the metals used. The pressure applied affects the density as well as the strength of the formed piece; the greater pressure the higher the strength. A low density porous compact may be formed by pouring the powder into a die and then heating it without first applying pressure. The shape and size of the die cavity can be exactly as required by the finished part. However, if desired, this invention contemplates the use of any suitable metal or metal alloy powder and preferable powders of iron or iron alloys.
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Although the invention has been described with respect to a preferred specific embodiment, many variations and modifications will become apparent to those skilled in the art. It is therefore the intention that the claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.