The present disclosure relates generally to a piston for an internal combustion engine, and more particularly to a piston body having a chamfer adjoining a combustion bowl and a piston rim and being structured to balance heat dissipation with combustion properties of the piston.
A great many different operating strategies and component designs are known in the field of internal combustion engines. Research and development has progressed for decades in relation to the manner in which factors such as fueling, exhaust gas recirculation, turbocharging, and variable valve actuation can be varied to produce different results. In addition to variation in these and other operating parameters, a great deal of research and testing effort has gone into the different ways that engine components, such as pistons, can be shaped and proportioned, and formed from various materials. One motivation driving advancements in combustion science and related research has been the desire to reduce relative amounts of certain emissions in engine exhaust, such as particulate matter and oxides of nitrogen or NOx. Other motivations relate to improving or optimizing engine performance, reducing fuel consumption, limiting component wear and/or fatigue and still others.
Efforts to accommodate the various different patterns of engine operation and duty cycle have resulted in the great many engine operating strategies and component designs that can be seen in the art. For certain engines that are subjected to relatively harsh operating conditions, such as high temperatures and frequent temperature swings, one area of particular research and development interest has included piston geometry and materials. Other research efforts have been directed to preparing pistons that are well-suited to conditions of relatively extreme mechanical duress. Decades of combustion science, materials, and mechanical engineering research have generally revealed that factors such as emissions and efficiency can be affected significantly and often unpredictably by seemingly minor changes in piston shape and features. Commonly owned U.S. Pat. No. 8,978,621 to Easley et al. (“Easley”) is directed to a piston having a combustion bowl shaped to balance combustion efficiency and emissions properties. The Easley disclosure proposes a piston having a compound combustion bowl and a compound rim, with an abrupt transition between the compound combustion bowl and the compound rim, with the features together desirably affecting emissions such as particulate matter and NOx, without unduly sacrificing fuel efficiency.
In one aspect, a method of operating an internal combustion engine includes moving a piston in a cylinder in the internal combustion engine toward a top dead center position such that a pressure in the cylinder is increased up to or above an autoignition pressure, and directly injecting a fuel into the cylinder. The method further includes autoigniting a mixture of the fuel and air when the pressure in the cylinder is at or above the autoignition pressure, and heating material forming an end face of the piston by way of combustion of the autoignited mixture. The end face forms a combustion bowl, an annular piston rim extending circumferentially around a longitudinal piston axis and having a curved profile sloping toward the combustion bowl, and a heat-dissipating chamfer extending axially and radially between the combustion bowl and the annular piston rim. The method still further includes dissipating heat of the material forming the end face to oil conveyed through an oil gallery within the piston.
In another aspect, a piston for an internal combustion engine includes a piston body structured for reciprocation within a cylinder in the internal combustion engine to increase a pressure in the cylinder to an autoignition pressure for autoigniting a mixture of fuel and air. The piston body defines a longitudinal axis extending between a first axial piston body end including a piston end face having a combustion bowl formed therein and an annular piston rim extending circumferentially around the combustion bowl, and a second axial piston body end including a piston skirt and a wrist pin bore formed in the piston skirt. The combustion bowl includes a convex center section transitioning radially outward and axially downward to a combustion bowl floor, and a concave outer section transitioning radially outward and axially upward from the combustion bowl floor to an outer combustion bowl edge. The annular piston rim includes a curved profile and slopes radially inward and axially downward toward the combustion bowl. The piston body further has an oil gallery formed therein, and a chamfer extending circumferentially around the longitudinal axis and axially and radially between the outer combustion bowl edge and the annular piston rim. At least one of a size of the chamfer, an orientation of the chamfer, or a thickness of material of the piston body between the chamfer and the oil gallery is structured to balance heat dissipation to oil in the oil gallery with combustion properties of the piston.
In still another aspect, a piston crown includes a piston body crown piece structured for coupling with a piston body skirt piece to form a one-piece piston body having an oil gallery therein and being reciprocable within a cylinder in an internal combustion engine to increase a pressure in the cylinder to an autoignition pressure for autoigniting a mixture of fuel and air. The piston body crown piece defines a longitudinal axis and includes a piston end face having a combustion bowl formed therein and an annular piston rim extending circumferentially around the combustion bowl. The combustion bowl includes a convex center section transitioning radially outward and axially downward to a combustion bowl floor, and a concave outer section transitioning radially outward and axially upward from the combustion bowl floor to an outer combustion bowl edge. The annular piston rim includes a curved profile and slopes radially inward and axially downward toward the combustion bowl. The piston body crown piece further includes a chamfer extending circumferentially around the longitudinal axis and axially and radially between the outer combustion bowl edge and the annular piston rim. At least one of a size of the chamfer, an orientation of the chamfer, or a thickness of material of the piston body crown piece forming the chamfer is structured to balance heat dissipation to oil in the oil gallery with combustion properties of the piston.
Referring to
Piston 22 may be coupled with a wrist pin 24, positioned within a wrist pin bore 50, that is in turn coupled with a connecting rod 26 coupled with a crankshaft (not shown). Piston rings 38 are shown positioned upon piston 22. Although no cylinder liner is shown in
Engine 10 may experience a range of operating conditions during service, including compression ratios that can be more than 15:1 and in-cylinder pressures during combustion that are still higher, as well as temperatures within an engine cylinder that can regularly exceed 500° C. Although engine 10 and the components used therein are not limited to any particular operating strategy or set of operating conditions, the teachings of the present disclosure may find particular application in engines experiencing relatively high temperatures, typically above 450 degrees C., and in many instances above 500 degrees C. It is contemplated that material of which piston body 30 is formed can be heated to temperatures from about 515 degrees C. to about 535 degrees C., or potentially higher still. As will be further apparent from the following description, piston 22 may be uniquely configured to tolerate harsh operating conditions, especially with respect to the above-mentioned temperature extremes and thermal cycling. Engine 10 may be a relatively large bore diesel engine, having an engine cylinder diameter of about 100 mm to about 200 mm, although the present disclosure is not limited in this regard.
Referring also now to
Referring now also to
Also depicted in
As noted above, piston 22 is structured, including by way of chamfer 66, to balance heat dissipation with combustion properties. Those skilled in the art will appreciate that relatively minute changes to piston geometry, and in particular combustion bowl and piston rim geometry, can affect combustion properties such as production of particulate matter, production of oxides of nitrogen or NOx, and fuel efficiency. Those skilled in the art will also be aware that varying certain in-cylinder conditions, including temperature and pressure, can affect, commonly unpredictably, the foregoing and other combustion properties, as well as structural and/or material integrity and thermal fatigue life of a given piston. It will further be understood that much of the energy of combustion is converted into kinetic energy of a piston, however, some of the energy of combustion is transferred to heat energy of material of which the piston and other engine hardware is formed, and ultimately dissipated at least in part to cooling oil.
As described herein, certain optimal or target material thicknesses, ranges and relative proportions among the thicknesses may be employed in constructing piston 22. These material thicknesses can affect the extent to which and the rate at which heat is dissipated to oil conveyed through oil gallery 54. Chamfer 66 may be understood to shorten a distance that at least a part of piston end face 40 is spaced from oil gallery 54. If first thickness 130 were decreased further such as with a larger or deeper chamfer, heat could be dissipated relatively more rapidly to a given volume or flow of oil through oil gallery 54. Dissipating heat from material of which piston body 30 is formed to the oil too rapidly, however, could heat the oil too much, ultimately resulting in coking or other problems. If heat is not dissipated effectively enough, such as where chamfer 66 is not as large or deep, material of which piston body 30 is formed could be heated beyond temperatures for which it is designed, or at the least accelerate thermal fatigue of the material. Optimum material thickness, and variations in thickness across different parts of a piston end face, can also be dictated in part by structural specifications. Variations that are too large, or chamfer angles that are too steep or too shallow, could result in unevenness in heat dissipation, insufficient heat dissipation, increased thermal fatigue sensitivity, or still other problems. In parallel with the heat dissipation capability of chamfer 66 are concerns relating to production of particulate matter, production of NOx, a balance between particulate matter and NOx, and fuel efficiency. As discussed herein, seemingly minor variations to a piston design can have relatively large and often unpredictable effects on such combustion properties.
Referring to the drawings generally, operating internal combustion engine 10 can include moving piston 22, and such other pistons as engine 10 might include, in a corresponding cylinder 16 toward a top dead center position such that a pressure in cylinder 16 is increased up to or above an autoignition pressure. Just prior to or after pressure in cylinder 16 has been increased up to or above the autoignition pressure, fuel injector 20 can be operated to directly inject fuel into cylinder 16. The directly injected fuel in a mixture with air can autoignite within cylinder 16, and in particular within combustion bowl 42. The combustion of the autoignited mixture can heat material forming end face 40 of piston 22, by way of the energy release that results from burning of the injected fuel. The heat of the material forming end face 40, and other parts of piston 22, can be dissipated to oil conveyed through oil gallery 54. In particular, the dissipating of heat can further include dissipating heat of the material forming piston end face 40 to oil in contact with back side cooling surface 64 forming oil gallery 54 within crown 32 and piston 22. Oil sprayer 52 can meanwhile be spraying oil continuously into an inlet (not shown) that leads to oil gallery 54, with the sprayed oil once heated within oil gallery 54 draining through an outlet (not shown) and eventually to an oil sump, typically after passing through an oil to coolant heat exchanger or another suitable oil cooler apparatus.
Due to improved cooling capability, operation of engine 10 and other engines contemplated herein can occur under conditions that enable engine 10 to have a relatively higher power density than certain other known engines. In a practical implementation strategy, heating of the material forming end face 40 can include heating the material to a temperature of about 450 degrees C. or greater, and in some instances heating the material to a temperature from about 515 degrees C. to about 535 degrees C. Operation of engine 10 at such conditions can produce about 130 kilowatts per cylinder or greater power output of engine 10 at a brake mean effective pressure of about 2500 kilo Pascals or greater by way of the combustion of the autoignited mixture of fuel and air. Dissipating heat as described herein can further include transferring about 8% or less of the power output of engine 10 to oil conveyed through oil gallery 54. In one embodiment, the oil may be conveyed through oil gallery 54 at a flow rate of about 5 kilograms or less per kilowatt-hour of operation of internal combustion engine 10.
It should be appreciated that the foregoing description of operation of internal combustion engine 10 is but one example of a relatively high performance application. Piston rim temperatures in such instances might rise as high as 550 degrees C. at least for relatively short periods of time. In other instances, engine 10 could be operated at still higher power outputs, or at lower power outputs for extended periods of time. The present disclosure is contemplated to enable operation of certain engines at a power output of about 75 kilowatts or greater per cylinder at a brake mean effective pressure of about 1900 kilo Pascals, continuously for periods of time of several thousand hours. Such operating parameters could be obtained at a power output transfer to the oil and oil flow rates similar to those discussed above.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.
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6314933 | Iijima | Nov 2001 | B1 |
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Number | Date | Country |
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2857698 | Jan 2005 | FR |
Number | Date | Country | |
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20180058371 A1 | Mar 2018 | US |