Patent Application
20160169153
This disclosure relates generally to internal combustion engines and, more particularly, to pistons operating within engine bores.
Internal combustion engines typically include one or more pistons interconnected by connecting rods to a crankshaft. The pistons are typically disposed to reciprocate within bores formed in a crankcase. A typical piston includes a head portion, which at least partially defines a combustion chamber within each bore, and a skirt, which typically includes a pin opening and other support structures for connection to the connecting rod of the engine. In general, a piston is formed to have a generally cupped shape, with the piston head forming the base, and the skirt portion being connected to the base and surrounding an enclosed gallery of the piston. In typical applications, lubrication oil from the engine is provided within the gallery of the piston during operation to convectively cool and lubricate various portions of the piston.
A typical piston head also includes an outer cylindrical wall having one or more circumferentially continuous grooves formed therein. These grooves typically extend parallel to one another and are appropriately sized to accommodate sealing rings therewithin. These sealing rings create sliding seals between each piston and the crankcase bore it is operating within. Typically, the groove located closest to the skirt of the piston accommodates a scrapper ring, which is arranged to scrape oil clinging on the walls of the piston bore during a down-stroke of the piston. Oil that may remain wetting the walls of the bore following the down-stroke of the piston may enter the combustion chamber and combust during operation of the engine.
In general, the piston operates by reciprocating within a bore formed in a cylinder case of the engine, which creates a variable volume that can compress a fuel/air mixture provided therein. The combusting fuel/air mixture expands and pushes the piston to increase the variable volume, thus producing power. Fuel can be provided directly or indirectly within the variable volume, while air and exhaust gas is provided or removed from the variable volume through one or more intake and exhaust valves that selectively fluidly connect the variable volume with intake and exhaust collectors.
The materials used to construct the walls of the engine cylinders, the piston, the various valves associated with the variable volume, and other surrounding engine structures, are selected to withstand high temperatures and pressures that are present during engine operation. Various features of the piston are also shaped to promote the efficient burning of fuel within the piston, reliability of the various engine components associated with the engine cylinders, and other considerations. However, it is always desired to increase the reliability and service life of these and other engine components, as well as promote the efficient operation of the engine in terms of reducing fuel consumption and emissions and increasing power and efficiency.
In one aspect, the disclosure describes a piston for an internal combustion engine. The piston includes a piston body forming a crown portion and a skirt portion. The skirt portion includes a pin bore that is arranged to receive a pin for connecting the piston to a connecting rod. The skirt portion further forms two guide surfaces along outer margins of the skirt portion. The crown portion forms a generally cylindrical surface surrounding the crown portion. The generally cylindrical surface forms at least two grooves therein that extend parallel to one another. The at least two grooves define a top land surface, a bottom land surface, and at least one intermediate land surface along the generally cylindrical surface.
In one disclosed embodiment, the top land surface has a height in a direction along a centerline of the piston, and the piston has a nominal outer diameter that is configured to permit the piston to operate within a bore having a nominal inner diameter. A ratio between the height of the top land surface and the nominal inner diameter of the bore is between 3% and 4.5%. Further, each guide surface extends on an outer portion of the skirt portion over a height in the direction along the centerline of the piston, and the pin bore has a diameter that extends entirely within the respective heights of the two guide surfaces in the direction along the centerline of the piston, such that the skirt portion fully supports the piston during operation within a piston bore by counteracting forces and moments present in the piston and applied through the piston bore.
This disclosure relates to pistons for use in internal combustion engines. In one aspect, the disclosure provides various embodiments for engine pistons having features that can set up flow fields and turbulence to promote combustion of fuel within the cylinder. Such features of the piston, depending on the type of engine operation, for example, spark ignition or compression ignition, can operate to contain, mix and/or direct various fuel containing masses within the piston to increase engine efficiency, decrease heat rejection, shorten burn time, and also control component temperatures, thus increasing component reliability and service life. As discussed herein, the mixing or directing of material within the cylinder may occur at least for an instant and may last no more than a few thousandths of a second while an injection of fuel and/or a combustion flame is present within the cylinder, or over portions of that period.
For purpose of illustration of certain features of an engine piston in accordance with the disclosure, a fragmented view of a piston 100 for an engine is shown from a side perspective in
In reference now to
More specifically, the crown portion 102 includes piston ring grooves 110 in the outer cylindrical wall 112. The piston ring grooves 110 accommodate ring seals (not shown) that slidably and generally sealably engage the walls of the engine cylinder in which the piston 100 is reciprocally disposed. An outer diameter of the two guide surfaces 105 and the secondary guide surface 108 is arranged such that the piston is prevented from rotating or binding within the bore in which it is reciprocally disposed during operation. Moreover, the two guide surfaces 105 and secondary guide surface 108 collectively cover a length along the centerline, C, of the piston that entirely includes along the same direction the pin bore 106 such that full coverage is provided.
Regarding other functional features of the piston 100, in reference to the orientation of the piston 100 as shown in
Around the center of the bowl is a convex surface 120 that is centrally disposed with respect to the piston 100. The convex surface 120 has a radius, R1, of about 155 mm, but other radii can also be selected. From a functional standpoint, the radius of the convex surface 120 determines the overall volume of the bowl 114, which in turn determines the volume of the combustion chamber when the piston is at the top dead center position within the bore and also the compression ratio of the engine. Thus, the radius R1 of the convex surface 120 can be selected depending on the desired compression ratio of the particular engine in which the piston is installed and will operate.
Surrounding the convex surface 120 and disposed within the frusto-conical wall surface 117 is a concave surface 122. The concave surface 122 is formed at a radius of about 10 mm and extends peripherally around the convex surface 120. In the illustrated embodiment, the rim 116 is relatively sharp or formed at a relatively small de-burr chamfer, for example, of about 0.25 mm or less. During operation, the piston 100 forms various features that operate to redirect and/or contain various moving masses within the cylinder. In various embodiments, these features operate to split the hot injector fuel plume that is provided to the cylinder when the piston is close to a top dead center position in the cylinder, and also which may be provided while the piston is approaching the top dead center position (e.g., pilot injection events) and/or is moving away from the top dead center position (e.g. post injection events during a combustion stroke). The fuel plume, a fuel atomization cloud, and/or a flame of burning fuel during these times of engine operation can be redirected in terms of flow direction and material dissipation in a fashion that reduces exposure of the various surrounding in-cylinder combustion surfaces to flame temperatures. By insulating cylinder surfaces from flame temperatures, retained heat and heat transfer to the metal of the surrounding engine components can be reduced, which in turn can provide a higher power output and/or higher power density to the engine, and also improve component reliability and service life. In the illustrated embodiment, the piston 100 achieves flow detachment along the crown surface 118 and material turbulation within the bowl 114 by the combined effects or primarily the frusto-conical wall surface 117 and the rim 116 having a sharp transition. These features operate to keep the burning fuel away from the edges of the piston.
To illustrate an additional feature of the piston 100, an enlarged view of the crown portion 102 is shown in
For forming the annular oil gallery 130, in the illustrated embodiment, machining tools are used to remove material from an original piston casting made of metal. An enlarged detail view of a portion of the piston 100 is shown in
To alleviate these and other issues, an alternative design for a piston 200 is shown in
As can be seen in
The present disclosure is applicable to pistons for internal combustion engines, which can be used in any application such as land or marine based applications, as well as for mobile or stationary applications. The various embodiments for piston features described herein have been found to have advantages in improving engine operation by increasing power output, decreasing fuel consumption and also decreasing emissions.
In one analysis, the heat release rate of a cylinder as a function of crankshaft angle rotation in degrees (CAD), for three piston designs was considered. The three piston designs included a baseline piston, in which the bowl includes a peripherally extending wall surface that is shallow or, stated differently, the inclination angle of the baseline piston bowl that corresponds to the angle, β (see
More specifically, where the peak IHRR for the baseline piston was determined to be at about 0.032 (1/CAD), the peak IHRR for the second piston was at about 0.037, and for the third piston at about 0.042, which represents an increase of more than 30% in the IHRR for the cylinder from the baseline piston, which was unexpected. In other tests, a peak IHRR as high as 0.055 (1/CAD) was observed, which is about a 72% increase over the baseline piston. In this analysis, the test conditions for measuring the reported peak IHRR values were run on a gas, spark-ignited engine operating at 2220 kPa IMEP, generating about 180 ppm NOx, having an intake manifold absolute temperature of about 51 deg. C. (IMAT), and ignition timing at 24 deg. before top dead center (BTDC). It is contemplated that the increase in IHRR for the piston 100, as described herein, may be attributed to an increase in the so-called squish velocity, which describes the velocity of fluids within the cylinder in the area above the crown surface 118 (see
More particularly, it is difficult to realize efficiency benefit when the IHRR increases, because increasing squish velocity leads to increasing losses the cylinder air system such as air system breathing, heat transfer, and the like, which outweigh any benefit to engine efficiency because of IHRR increases. Similarly, slower squish velocities, which lead to lower IHRRs, can affect and are too low for high engine brake efficiencies. In general, engine efficiency tends to flatten off above IHRR of about 4.5%/CAD, while a re-entrant bowl design, such as the bowl design for the piston 100 (
Another feature of the piston 100 (
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the disclosed embodiments (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this disclosure are described herein. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. Skilled artisans are expected to employ such variations as appropriate. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.
