Piston having a smooth outer crown surface in a sensitive area of deposits
By reducing the surface roughness to 0.0002 mm or less in the deposit-sensitive area of the piston crown of an internal combustion engine, the problem of difficult removal of piston deposits is solved, resulting in deposit reduction and improved lubricant distribution, thereby improving the performance of the internal combustion engine.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CATERPILLAR INC
- Filing Date
- 2021-11-11
- Publication Date
- 2026-05-19
AI Technical Summary
The formation and adhesion of deposits on internal combustion engine pistons are difficult to predict and mitigate, affecting lubricant distribution and increasing oil consumption. Furthermore, existing mechanical deposit management technologies have limited effectiveness.
In the deposit-sensitive area of the piston crown, the formation and adhesion of deposits are suppressed by reducing the average roughness (Ra) of the outer surface of the crown to 0.0002 mm or less.
It significantly reduces the thickness and coverage of deposits on the piston, lowers fuel consumption, reduces combustion gas leakage, and improves the efficiency and reliability of the internal combustion engine.
Smart Images
Figure CN114483360B_ABST
Abstract
Description
Technical Field
[0001] The present invention generally relates to a piston for an internal combustion engine, and more specifically to a piston having a selectively smoothed surface to inhibit deposit formation and / or adhesion. Background Technology
[0002] An internal combustion engine employs one or more pistons positioned within a combustion chamber and moved by a controlled combustion reaction within the chamber to rotate the crankshaft. Many different fuel supply, temperature, and pressure control strategies related to the combustion process have been proposed over the years. For example, fuel can be injected directly into the cylinder, port-injected, or vaporized into the intake airflow. In the case of direct injection internal combustion engines, typically operating with liquid hydrocarbon fuels such as diesel fractions, the fuel spray is usually directed into the combustion bowl in an effort to confine the combustion process within the bowl, although in some cases, the injected fuel can be directed or spilled onto the piston rim and wet the cylinder walls, typically formed by the cylinder liners. These and other operating and / or fuel supply strategies are used for a variety of purposes, including emissions reduction, efficiency optimization, and others. Engine oil is provided for distribution between the cylinder walls and the piston and piston rings to lubricate the interface.
[0003] In almost all engines, especially diesel engines, deposits typically accumulate on parts of the piston, regardless of operating and fuel supply conditions. Deposits are particularly noticeable on the piston and piston rings facing the cylinder wall. In dynamic combustion environments, variations in fuel delivery strategies, as described above, or disturbances to desired operating parameters, can make deposit formation relatively difficult to predict and mitigate. Furthermore, emission and efficiency targets, for example, are often prioritized over deposit reduction, even when the mechanisms of deposit accumulation are understood or suspected. Variations in fuel quality and type can further influence the manner and extent of deposit formation.
[0004] Engineers have previously experimented with mechanical deposit management techniques, such as deposit scrapers, in an effort to manage the formation of such deposits. Excessive piston deposits can interfere with lubricant distribution, increase oil consumption, and cause or exacerbate a phenomenon known as "leakage," in which combustion gases escape from the cylinder through the gap between the piston rings and the cylinder wall. An example of piston deposit mitigation efforts is presented in EP 3043054A1, which describes a carbon scraper ring that significantly helps to scrape unwanted deposits off the combustion surfaces. Summary of the Invention
[0005] In one aspect, a piston for an internal combustion engine includes a piston body having a piston crown defining a piston central axis and a piston skirt connected to the piston crown. The piston skirt includes an outer skirt surface and an inner skirt surface. The piston crown includes an outer crown surface and a combustion surface formed by an annular outer edge surface and a combustion bowl surface radially inward from the annular outer edge surface. The outer crown surface forms a plurality of piston platforms that alternate axially with a plurality of piston ring grooves, the piston platforms and piston ring grooves together defining a deposit-sensitive region. At least one of the outer or inner skirt surfaces has a roughness number (Ra) of 0.002 mm or greater, and the outer crown surface is smoothed to a Ra of 0.0002 mm or less within at least a portion of the deposit-sensitive region.
[0006] In another aspect, a piston for an internal combustion engine includes a piston body having a piston crown defining a piston central axis and a piston skirt connected to the piston crown. The piston crown includes an outer surface and a combustion surface formed by an annular outer edge surface and a combustion bowl surface radially inward from the annular outer edge surface. The outer surface of the crown forms a plurality of piston platforms that alternate axially with a plurality of piston ring grooves, the piston platforms and piston ring grooves together defining a deposit-sensitive region. The piston crown is entirely formed of a piston body material having an exposed surface smoothness varying within the piston crown and an average roughness (Ra) of 0.0002 mm or less within at least a portion of the deposit-sensitive region.
[0007] In another aspect, a method of manufacturing a piston for use in an internal combustion engine includes receiving a piston body, the piston including a piston crown defining a piston central axis and having a crown outer surface extending circumferentially around the piston central axis and formed by exposed piston body material extending through the piston crown. The method further includes reducing the surface roughness of the piston crown by removing or deforming at least one of the exposed piston body material in a deposit-sensitive region of the piston body, the deposit-sensitive region being defined by a plurality of piston platforms and a plurality of piston ring grooves, each piston ring groove being formed by the crown outer surface. The method also includes increasing the smoothness of the exposed piston body material based on a deposit suppression smoothness that reduces the surface roughness to at least an order of magnitude smoother than the smoothness in a deposit-insensitive region of the piston body. Attached Figure Description
[0008] Figure 1 This is a partial cross-sectional side view of an internal combustion engine according to one implementation scheme;
[0009] Figure 2 It is a simplified side view of a piston according to one embodiment, including a detailed enlarged view;
[0010] Figure 3 This is a schematic diagram of a piston in the manufacturing stage according to one implementation scheme.
[0011] Figure 4 This is a schematic diagram of a piston at another stage of processing according to one implementation scheme.
[0012] Figure 5 The image shows a scanned image of the piston according to the present invention after it has been used in an internal combustion engine.
[0013] Figure 6 It is measured with sediment filling. Figure 5 A view of a scanned image of the piston;
[0014] Figure 7 These are scanned images of pistons of known designs after they have been used in an internal combustion engine; and
[0015] Figure 8 It is measured with sediment filling. Figure 7 A view of a scanned image of the piston. Detailed Implementation
[0016] See now Figure 1 An internal combustion engine 10 according to one embodiment is shown. The internal combustion engine 10 includes a cylinder block 12 and an engine cylinder head 14 connected to the cylinder block 12. An intake manifold 16 and an exhaust manifold 18 are formed in the engine cylinder head 14. An intake valve 20 is movable to control fluid communication between the intake manifold 16 formed in the cylinder block 12 and a combustion cylinder 26. An exhaust valve 22 is movable to control fluid communication between the cylinder 26 and the exhaust manifold 18. A fuel injector 24 shown is supported in the engine cylinder head 14 and positioned to inject liquid fuel directly into the cylinder 26. The engine 10 also includes a connecting rod 28 connected to a piston 30 positioned within the cylinder 26 and operable to rotate a crankshaft in a conventional manner. The internal combustion engine 10 may include a compression-ignition engine operable on liquid hydrocarbon fuels (e.g., liquid diesel fraction fuels). Other fuels and fuel mixtures, such as biodiesel, may also be used. Cylinder 26 can be one of any number of cylinders in any suitable arrangement, such as a V-pattern, an inline pattern, or another. As will become clear further from the following description, piston 30 can be configured to reduce or eliminate the formation and / or adhesion of deposits (such as carbon or carbonized material) thereon.
[0017] Piston 30 includes a piston body 32 having a piston crown 34 defining a piston central axis 35. The piston body 32 also includes a piston skirt 36 connected to the piston crown 34. The piston crown 34 and piston skirt 36 can be formed from separate parts attached by any suitable process (e.g., friction welding), although a uniform, one-piece piston falls within the scope of this invention. The piston skirt 36 includes an outer skirt surface 38 and an inner skirt surface 40. Figure 1 The piston pin bore 44 is formed in the piston skirt 36 and supports the piston pin 42, which connects the connecting rod 28 to the piston 30 in a conventional manner.
[0018] Now for reference Figure 2 The piston crown 34 includes a crown outer surface 46 and a combustion surface 48 formed by an annular outer edge surface 58 and a combustion bowl surface 60 radially inward from the annular outer edge surface 58. The combustion bowl surface 60 forms a combustion bowl 62. The piston crown 34 and piston skirt 36 may also include a passage surface 65 forming a passage 64, which typically has one or more downward-opening ports or the like to receive a spray of cooling and lubricating oil injected upward from a conventional injector, and an exhaust port.
[0019] The outer surface 46 of the crown forms a plurality of piston platforms, including a top platform 66, a second platform 68, and a third platform 70. The piston platforms 66, 68, and 70 alternate axially with a plurality of piston ring grooves also formed by the outer surface 46 of the crown. The plurality of piston ring grooves may include a top ring groove 72, a second ring groove 74, and a third or bottom ring groove 76. Pistons having other numbers of piston platforms and / or piston ring grooves are within the scope of this invention. Each of the plurality of piston platforms and the plurality of piston ring grooves extends circumferentially around the piston central axis 35 and together defines a deposit-sensitive region 82.
[0020] In a practical implementation strategy, the piston crown 34 is formed throughout the piston body material. The piston skirt 36 can also be formed from the same piston body material. The piston body 32, including the piston crown 34 and piston skirt 36, can be formed by casting, forging, or by another suitable process (e.g., additive manufacturing). The piston body material can be iron, steel, stainless steel, aluminum, or various other metals and alloys. As described above, the piston 30 is adapted to inhibit the formation and / or adhesion of certain deposits.
[0021] For this purpose, the outer surface 46 of the crown may be smoothed to an average roughness (Ra) of 0.0002 mm (0.20 μm) or less within at least a portion of the sediment-sensitive region 82. According to another feature, the outer surface 46 of the crown may be smoothed to a root mean square (RMS) roughness of 11 microinches or less. In one improvement, the outer surface 46 of the crown is smoothed to Ra of 0.00015 mm or less within the main portion of the sediment-sensitive region 82, and in another improvement, it is smoothed to a mirror finish Ra of 0.000125 mm or less.
[0022] The smoothness of the main portion of the outer surface 46 of the crown is considered to limit or depend on usage conditions, potentially eliminating deposit formation and / or adhesion thereon. In some embodiments, the smoothness of the entire outer surface 46 of the crown may be Ra of 0.0002 mm or less, 0.00015 mm or less, or 0.000125 mm or less. It has been observed that increased smoothness of at least a portion of the deposit-sensitive region 82 relative to the deposit-insensitive region of the piston body 32 can provide some improvement regarding deposit formation and / or adhesion. “Increased” smoothness refers to a reduction in the average roughness Ra, a reduction in RMS roughness, or a reduction in roughness by some other measure relative to a given standard, such as the initial roughness of the target surface or the roughness of another surface that has not been so smoothed.
[0023] In some embodiments, less than the entire outer surface of the crown 46 and less than the entire deposit-sensitive region 82 may therefore be smoothed. For example, in one embodiment, the top plateau 66 is smoothed to Ra of 0.0002 mm or less, or smoothed to or less than one of the smoother Ra values listed herein. In another embodiment, the outer surface of the crown 46 is smoothed to Ra of 0.0002 mm or less within each top plateau 66, second plateau 68, and third plateau 70, or smoothed to or less than one of the smoother Ra values listed herein. In conjunction with the smoothing of one or more of the piston ring plates 66, 68, and 70, or independently, at least one of the piston ring grooves 72, 74, and 76 may be smoothed to Ra of 0.0002 mm or less, or smoothed to or less than one of the smoother Ra values listed herein.
[0024] As described above, some piston bodies 32, including some piston crowns 34, may be relatively smoother than other portions of the piston bodies 32 and / or piston crowns 34. Therefore, the piston body material forming the piston crowns 34 may have an exposed surface smoothness that varies within the piston crowns 34, for example, a smoothness on the combustion surface 48 that differs from the smoothness on the outer surface 34 of the piston crown within the deposition-sensitive region 82. In one embodiment, at least one of the outer skirt surface 38 or the inner skirt surface 40 may have a Ra of 0.002 mm or greater, wherein the piston body material has an exposed surface smoothness that is smoothest in the deposition-sensitive region 82 and varies by at least an order of magnitude between the deposition-sensitive region 82 and another less smooth surface of the outer skirt surface 38 or the inner skirt surface 40 or the piston body 32. In other words, within at least a portion of the deposition-sensitive region 82, the outer crown surface 34 may be at least ten times smoother than other surfaces of the piston crowns 32 and / or piston skirts 36. The outer surface 38 or the inner surface 40 of the skirt may be or include a deposit-insensitive area of the piston body 32, wherein deposit formation and / or adhesion are unlikely or not observed at all. The combustion surface 48 may also be or include a deposit-insensitive area of the piston body 32.
[0025] Figure 2 This includes a detailed magnified view showing the exposed piston body material forming the top platform 66, and another detailed magnified view showing the exposed piston body material on the outer skirt surface 38. At least under a microscope, differences in the smoothness of the piston body material forming the various surfaces can be expected to be observable. Machining marks on the outer skirt surface 38 may be blurry, but are visible and have a clear orientation under optical microscope magnification. On the top platform 66, machining marks may be visible at optical microscope magnification, but their apparent orientation may be invisible.
[0026] Now for reference Figure 3 The figure shows a piston 30, which may be present during a machining stage supported by a jig 102 in the processing unit 100. A tool 104, such as a grinding wheel, as shown, may contact the outer surface 34 of the crown and may be moved generally axially along the outer surface 34 of the crown and along the outer surface 38 of the skirt. The tool 104 may be used to remove or deform the exposed piston body material of the piston body 32 to obtain a specific surface texture including Ra. Also referenced... Figure 4 The image shows the piston 30 still supported by the clamp 102 in the processing unit 100, and now shows it alongside a different tool 106 for use only to remove or deform the deposit-sensitive area 82 of the outer surface 34 of the crown, which can be used with the piston body material exposed therein. Thus, tool 104 can be used... Figure 3The stage shown illustrates the machining of the piston crown 34 and piston skirt 36. Tool 106 can be used only for subsequent machining of the piston crown 34 to achieve the desired smoothness, as described herein. It is conceivable that tool 106, including polishing or grinding tools or other tools, can remove or plastically deform exposed piston body material in all piston platforms 66, 68, and 70, and may also plastically deform exposed piston body material in piston ring grooves 72, 74, and 76, but is not used for machining the piston skirt 36. Those skilled in the art will appreciate that a variety of different tools, techniques, and different processing units, jigs, or other equipment and techniques can be used. To obtain the desired Ra in the deposition-sensitive region 82, the outer surface 34 of the crown can be treated by polishing, electropolishing, laser polishing, or by other known techniques such as so-called supermachining. Therefore, tool 106 can take various forms.
[0027] In any practical implementation strategy employing any of the various possible technologies, the piston body 32 can be received to... Figure 3 and Figure 4 The piston body 32 is processed in stages, including stages where a basic shape has been produced, for example, by casting or forging, and rough machining has been performed to achieve the desired smoothness. Processing the piston body 32 will include reducing the surface roughness of the piston crown 34 by removing or deforming at least one of the piston body materials exposed in the deposit-sensitive region 82, and increasing the smoothness of the exposed piston body material based on the reduction of surface roughness to a deposit suppression smoothness that is at least an order of magnitude smoother than the smoothness in the deposit-insensitive region of the piston body 32. For example, the deposit suppression smoothness may be Ra of 0.0002 mm or less. As described above, the deposit-insensitive region of the piston body 32 may include the outer skirt surface 38, or, for example, another surface. The piston body 32 may also include one or more cast surfaces or one or more forged surfaces whose roughness may be an order of magnitude, or even multiple orders of magnitude, greater than the outer crown surface 34 in the deposit-sensitive region 82. For example, the inner skirt surface 40 may be cast or forged, and the channel surface 65 may be cast or forged.
[0028] Industrial applicability
[0029] According to the present invention, determining which surface features are suitable or optimal targets for smoothing can be determined through simulation or empirical means, for example by observing the location of deposits formed on the piston after use in an internal combustion engine. It is conceivable that factors such as fuel injection angle, combustion temperature and / or operating temperature range, lubricating oil flow rate, coolant flow rate, duty cycle, fuel type and / or quality, and many other factors can influence the formation location and deposit load experienced by any particular piston. Empirical observation can also help determine which portion of the outer crown surface, such as the entire outer crown surface, or only a plateau, a piston ring groove, multiple plateaus and multiple grooves, or some other combination, should be targeted for smoothing to inhibit or mitigate deposit formation and / or adhesion. The present invention is intended to be applicable to newly manufactured pistons as well as remanufactured pistons removed from use in internal combustion engines.
[0030] See now Figure 5 The image shows a piston 30 according to the invention, which may appear in a scanned image after it has been serviced in an internal combustion engine, showing the relative position and thickness of deposits 110 on the top plateau 66 and elsewhere. Scales in millimeters are indicated by reference numeral 120. Figure 6 A first image 150 includes a portion of a top platform 66, a top annular groove 72, and a second platform 68, wherein deposition thickness measurements are filled at several points, which can be used to calculate the average deposition thickness. The deposition thickness measurements are shown as numbers 151, 153, 155, and 157, and the deposition thickness scale in millimeters is shown as 159. Figure 6 It also includes an image 160 consisting of measurements of the maximum piston sediment thickness (including measurements 161 and 163) and a sediment thickness scale in millimeters at 165.
[0031] Now for reference Figure 7 The image shows a piston 230 of known design, having a top platform 266 and deposits 310 thereon. The deposition thickness scale in millimeters is shown at 320. Figure 8 Image 350 shows deposition thickness measurements 351, 353, 355, and 357 that can be used to calculate the average deposition thickness. At 359, the deposition thickness scale is shown in millimeters. Figure 8 It also includes another image 360 filled with the maximum deposition thickness measurements 361 and 363 and the deposition thickness scale 365.
[0032] Figure 5 and Figure 6 The piston and data shown represent actual test data for the piston according to the invention, wherein, after use in a diesel engine, the top platen 66 was smoothed to a mirror finish Ra of 0.000125 mm or less. Figure 7 and 8 The piston 230 shown represents actual test data for a known design in which the top plateau 266 is conventionally smoothed, for example to Ra 0.0002 mm or greater, and is essentially the same as piston 30 after use in a diesel engine. By... Figure 5 and Figure 6 Images and Figure 7 and Figure 8 A comparison of the images reveals that piston 30 exhibits a relatively smaller average thickness, a smaller maximum thickness, and a smaller overall sediment space coverage. The total accumulated amount in piston 30 can be more than 60% less than the total accumulated amount in piston 230.
[0033] This specification is for illustrative purposes only and should not be construed as narrowing the scope of the invention in any way. Therefore, those skilled in the art will understand that various modifications can be made to the currently disclosed embodiments without departing from the full and fair scope and spirit of the invention. Other aspects, features, and advantages will become apparent from reading the accompanying drawings and claims. As used herein, the article “a / an” is intended to include one or more items and is interchangeable with “one or more.” The term “a” or similar language is used where only one item is intended. Furthermore, as used herein, the terms “has / have / having” and the like are intended to be open-ended terms. Additionally, the phrase “based on” is intended to mean “at least partially based on” unless explicitly stated otherwise.
Claims
1. A piston for an internal combustion engine, comprising: A piston body, comprising a piston crown defining a piston central axis, and a piston skirt attached to the piston crown; The piston skirt includes an outer surface and an inner surface. The piston crown includes an outer surface of the crown and a combustion surface formed by an annular outer edge surface and a combustion bowl surface radially inward from the annular outer edge surface; The outer surface of the crown forms multiple piston platforms that alternate axially with multiple annular grooves and together define a deposit-sensitive region; At least one of the outer surface or the inner surface of the skirt has a roughness value (Ra) of 0.002 mm or greater; and in, The plurality of piston platforms include a top platform, a second platform, and a third platform, and the outer surface of the crown is smoothed within the top platform to a Ra of 0.0002 mm or less.
2. The piston as claimed in claim 1, wherein, The outer surface of the crown is smoothed to a Ra of 0.0002 mm or less within each of the top, second, and third platforms.
3. The piston as described in any of the preceding claims, wherein, The outer surface of the crown is smoothed to a Ra of 0.00015 mm or less within at least a portion of the sediment-sensitive area.
4. The piston as claimed in claim 3, wherein, The outer surface of the crown is smoothed to a mirror finish Ra of 0.000125 mm or less within the portion of the sediment-sensitive area.
5. A piston for an internal combustion engine, comprising: A piston body, comprising a piston crown defining a piston central axis, and a piston skirt attached to the piston crown; The piston crown includes an outer surface of the crown and a combustion surface formed by an annular outer edge surface and a combustion bowl surface radially inward from the annular outer edge surface; The outer surface of the crown forms multiple piston platforms that alternate axially with the multiple piston ring grooves, collectively defining a deposit-sensitive region. These multiple piston platforms include a top platform, a second platform, and a third platform. The piston crown is entirely formed of the piston body material, which has an exposed surface smoothness that varies within the piston crown, and the outer surface of the crown is smoothed within the top platform to an average roughness (Ra) of 0.0002 mm or less.
6. The piston as claimed in claim 5, wherein The piston skirt is formed throughout the piston body material and includes an inner surface and an outer surface of the skirt; The piston body material has an exposed surface smoothness that is smoothest in the deposit-sensitive region and varies by at least one order of magnitude between the deposit-sensitive region and at least one of the outer surface or inner surface of the skirt.
7. The piston as claimed in claim 5 or 6, wherein, The piston body material has a Ra of 0.0002 mm or less in a portion of the deposit-sensitive region, which includes at least one of the plurality of piston platforms.
8. A method for manufacturing a piston for use in an internal combustion engine, comprising: A piston body receiving the piston, the piston body including a piston crown defining a piston central axis and having a crown outer surface extending circumferentially around the piston central axis and formed of exposed piston body material extending through the piston crown, the crown outer surface forming a plurality of piston platforms alternating axially with a plurality of annular grooves and together defining a deposit-sensitive region, the plurality of piston platforms including a top platform, a second platform, and a third platform; and The surface roughness of the piston crown is reduced by removing or deforming at least one of the piston body material exposed in the deposit-sensitive region of the piston body, the deposit-sensitive region being defined by a plurality of piston platforms and a plurality of piston ring grooves, each piston ring groove being formed by the outer surface of the crown; and The smoothness of the exposed piston body material is increased by reducing the surface roughness to at least an order of magnitude smoother than the smoothness in the deposit-insensitive region of the piston body, and the outer surface of the crown is smoothed within the top platform to an average roughness (Ra) of 0.0002 mm or less.
9. The method of claim 8, wherein, Increased smoothness includes improving the smoothness to a mirror finish Ra of 0.000125 mm or less; and Reducing surface roughness includes reducing the surface roughness of the exposed piston body material forming at least one of the piston platforms.
10. The method of claim 8 or 9, wherein, The reduction in surface roughness includes reducing the surface roughness of the exposed piston body material forming at least one of the piston ring grooves; and The reduction in surface roughness includes reducing the surface roughness of the exposed piston body material that forms all piston platforms.