Patent Application
20200080587
The present invention relates to internal combustion engines and, more specifically, to a cross-head piston for use in diesel engine.
Internal combustion engines, such as diesel and gasoline engines, are heat engines in which the burning of a fuel occurs in a confined space to create gases of high temperature and pressure. The gasses expand in the engine to do work. Typically, an internal combustion engine includes a cylinder into which fits a piston. The fuel is burned in the space between the cylinder and the piston, driving the piston outwardly when the burning gasses expand. The piston is usually coupled to a connecting rod, which transfers the reciprocating lateral motion of the piston to a crank shaft. The crankshaft translates the lateral motion to rotary motion, which is ultimately applied to perform useful work.
A typical piston includes a piston crown member, which includes a piston head having a diameter corresponding to the diameter of the cylinder into which the piston fits. Two spaced apart connecting ears extend from the piston head and connect the piston head to the connecting rod. Each connecting ear includes a pin bore into which fits a pin to which the connecting rod is coupled.
One type of existing piston is a cross-head piston, in which the connecting rod is bolted to the pin (also referred to as a “cross pin”). The connecting rod includes an elongated oil passage and the cross pin defines a passage therethrough that is in alignment with the oil passage of the connecting rod. In this way, oil passes through the elongated oil passage into an area around the piston, thereby providing lubrication and cooling.
Older cross-head pistons were cast from iron and machined to form surfaces in moving contact with other parts (e.g., the cylinder, the pin, etc.). The pin bore of a typical cross-head piston includes a replaceable bushing. The bushings wear out frequently and are costly to replace. Also, cast iron pistons are subject to fatigue.
Fatigue is a significant problem in cast iron pistons. As trucking companies desire to increase the loads that they carry, they often adjust their engine control systems to increase the horsepower output of their engines. With extended use at higher horsepower, cracks in the piston form which can result in catastrophic dome separation. Dome separation occurs when the piston head breaks away from the rest of the crown portion and usually requires a complete engine overhaul.
Another type of piston is a forged steel piston, which has an advantage over cast iron of being less susceptible to fatigue and can handle higher horsepower settings. However, because of the nature of the forging process, forged pistons cannot distribute oil from the elongated oil passage in the piston rods employed in older engines. Because stagnant oil in such passages would result in other types of failures, when cast iron pistons are replaced with forged steel pistons, the piston rods and piston pins must also be replaced. While replacing a piston is relatively straightforward and inexpensive, replacing a piston rod can be complicated and expensive.
Large commercial vehicles often employ diesel engines that are used for many years. The pistons in such engines are replaced at regular service intervals. Because existing cross-head pistons employ connecting rods that must be bolted to the corresponding cross-pins, forged steel pistons cannot be used as replacement parts in engines employing cross-head pistons without also replacing the connecting rods. Purchasing new connecting rods to replace serviceable connecting rods is costly and wasteful.
Therefore, there is a need for a forged steel piston that is compatible with existing piston rods.
There is also a need for a method of making a cross-head piston from forged steel.
The disadvantages of the prior art are overcome by the present invention which, in one aspect, is a piston unit for coupling to a crosshead piston rod with a crosshead piston pin That includes a piston crown member and an integrated crosshead pin support and skirt member. The piston crown member consists essentially of forged steel. The integrated crosshead pin support and skirt member consists essentially of forged steel. The integrated pin support and skirt member is affixed to the piston crown member and is configured to support the crosshead piston pin.
In another aspect, the invention is a crosshead piston including a crosshead piston unit consisting essentially of forged steel.
In yet another aspect, the invention is a method of making a crosshead piston in which a piston crown member is forged from steel. An integrated crosshead pin support and skirt member is forged from steel. The piston crown member is welded to the integrated crosshead pin support and skirt member.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.
A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. Unless otherwise specifically indicated in the disclosure that follows, the drawings are not necessarily drawn to scale. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” Also, as used herein “diamond-like carbon” (DLC) includes sp3 bonded carbon atoms of crystalline carbon polytype. In one embodiment, DLC includes tetrahedral amorphous carbon sp3 bonded carbon atoms and metastable form of hydrogenated amorphous carbon (a-C:H) containing significant sp3 bonding.
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The interior cylindrical member 130 defines a cooling cavity 123 therein. The interior cylindrical member 130 also defines a plurality of oil jet openings 124 passing therethrough so that the cooling cavity 123 is in fluid communication with the ring-shaped void 134. Each of the oil jet openings 124 is disposed between two different ones of the struts 122.
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A pin support frame 164 is disposed within the void region 170 and extends downwardly from the bottom side of the top member 168. The pin support frame 164 extends from a first side 174 of the vertical skirt wall 162 to a second side 175 of the vertical skirt wall 162. The pin support frame 164 defines a cylindrical pin bore 166 concentric therewith and opens to the first side 174 of the vertical skirt wall 162 and the second side 175 of the vertical skirt wall 168. The pin support frame 164 also defines a rod connection opening 176 between the pin support bore 166 and the void region 170.
The first mating surface 132 of the crown member 110 is welded to the second mating surface 178 of the integrated crosshead pin support and skirt member 160. The first mating surface 132 may be friction welded to the second mating surface 178. (In alternate embodiments, other welding techniques known to the art, such as laser welding, chemical welding, etc., may be used.)
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There are several advantages over existing crosshead pistons and forged steel pistons resulting from the present invention. For example, the present invention provides the strength of a forged steel piston while allowing it to be retrofitted with an existing crosshead piston rod and an existing crosshead pin. The invention can include such beneficial items as a cooling cavity within the piston (which can be molded in cast iron crosshead pistons, but which cannot be forged into conventional forged steel pistons). The invention eliminates the need for pin bushings required in existing cast iron crosshead pistons. The invention, when retrofit into older engines employing crosshead pistons, can allow the engines to operation at a substantially higher horsepower (e.g., 550 hp vs 350 hp) without a substantial increased probability of piston failure. The pin support frame of the invention is broader than the pin support ears of conventional forged steel pistons, which increases support for the pin and eliminates pin bending moment that can increase wear. The invention increases oil cooling of the piston over that of conventional forged steel pistons. The elimination of pin bushings in the invention strengthens the crosshead piston and reduces its cost. The use of steel in all of the piston parts (including an integrated steel piston skirt, instead of a separate aluminum skirt used in many existing pistons) ensures expansion and contraction at a constant rate among the different components of the piston, thereby reducing wear and increasing efficiency. Also, the invention is lighter and more efficient than conventional crosshead pistons.
Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description. It is understood that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. The operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set. It is intended that the claims and claim elements recited below do not invoke 35 U.S.C. 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim. The above described embodiments, while including the preferred embodiment and the best mode of the invention known to the inventor at the time of filing, are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.
