PISTON ASSEMBLY WITH OPPOSING INJECTION REGIONS FOR AN OPPOSED-PISTON ENGINE
A piston for an opposed-piston, internal combustion engine includes a crown with an end surface having a bowl shaped to form a combustion chamber with an end surface of an opposing piston in the opposed-piston engine. A substantially circumferential top land of the crown meets the end surface at a substantially circular peripheral edge, and a skirt comprising a sidewall extends from a substantially circumferential belt region of the crown. A wristpin bore with a wristpin axis opens through the sidewall. The end surface of the piston includes a pair of injection regions across which fuel is injected into the bowl. The injection regions are disposed in substantially diametrically-opposed quadrants of the end surface which are defined by the wristpin axis and a connecting rod envelope axis substantially orthogonal to the wristpin axis. Each injection region extends along a respective arc concentric with the substantially circular peripheral edge.
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This application is a continuation of International Patent Application PCT/US2018/049214, “Piston Assembly With Opposing Injection Regions for an Opposed-Piston Engine, filed Aug. 31, 2018, which claims priority to U.S. Provisional Application 62/555,201, “Piston Assembly With Opposing Injection Regions for an Opposed-Piston Engine”, filed Sep. 7, 2017. This application contains subject matter related to the subject matter of the U.S. patent application Ser. No. 13/136,955, filed Aug. 15, 2011, for “Piston Constructions for Opposed-Piston Engines,” now U.S. Pat. No. 9,163,505, issued Oct. 20, 2015; U.S. patent application Ser. No. 13/776,656, filed Feb. 25, 2013, for “Rocking Journal Bearings for Two-Stroke Cycle Engines,” now U.S. Pat. No. 9,175,725, issued on Nov. 3, 2015; U.S. patent application Ser. No. 14/075,926, filed Nov. 8, 2013, for “Lubricating Configuration For Maintaining Wristpin Oil Pressure In A Two-Stroke Cycle, Opposed-Piston Engine,” now U.S. Pat. No. 9,038,593, issued on May 26, 2015; and U.S. patent application Ser. No. 14/199,877, filed Mar. 6, 2014, for “Piston Cooling Configurations Utilizing Lubricating Oil From a Bearing Reservoir in an Opposed-Piston Engine,” now U.S. Pat. No. 9,470,136, issued on Oct. 18, 2016.
FIELD OF THE INVENTIONThe present invention is directed to a piston with a unique end surface construction which makes it particularly suited for use in an opposed-piston internal combustion engine with direct side injection of fuel.
More specifically, the piston has a construction with an end surface configuration in which injection regions have a unique orientation with respect to wristpin and connecting rod features of the piston, which enables stationary oil jets to provide coolant for piston thermal management from positions favorable for achieving a compact engine configuration.
The present invention also relates to a piston construction with a unique location of diametrically-opposed injection regions on the end surface which permits fuel injectors to be positioned more favorably in an opposed-piston engine.
BACKGROUND OF THE INVENTIONThe related '725 patent describes a piston construction designed for an opposed-piston engine which includes a wristpin support structure mounted within the interior of the piston skirt. An upper portion of the wristpin support structure provides a wall for an interior annular cooling gallery. Inlet openings in the wall permit streams of liquid coolant enter the annular coolant gallery. The annular cooling gallery achieves an optimal cooling effect when the streams of coolant are aligned with injection trenches on the piston end surface by which fuel emitted through diametrically-opposed fuel injectors enters a combustion chamber. However, the features necessary for attachment of the wristpin bearing support structure to the interior of the skirt greatly restrict design options for placement of stationary oil jets that deliver the streams of coolant to the annular cooling gallery. Furthermore, the restrictions on oil jet placement result in a cascade of additional design restrictions regarding other elements including injection trenches and fuel injectors that limit progress toward realization of good piston thermal management in a compact opposed-piston engine.
Replacement of the separate wristpin support structure with a wristpin bore formed integrally with the piston skirt eliminates the attachment features that restrict placement of stationary oil jets and fuel injectors, thereby enabling a unique piston construction for an opposed-piston with direct side injection that permits stationary oil jets and fuel injectors to be positioned more favorably in an opposed-piston engine.
SUMMARY OF THE INVENTIONIn an aspect of the invention, a piston for an opposed-piston engine is provided having a crown with an end surface in which a bowl is configured to form a combustion chamber in cooperation with an adjacent end surface of an opposing piston. A substantially circumferential top land of the crown meets the end surface at a substantially circular peripheral edge, and a skirt comprising a sidewall extends axially away from the substantially circumferential top land. A wristpin bore with a wristpin bore axis is formed in the sidewall. The wristpin bore is provided for receiving a wristpin that couples the piston to a connecting rod that swings in an envelope of motion defined by an envelope axis which is substantially orthogonal to the wristpin bore axis. The end surface of the piston includes a pair of injection regions across which fuel is injected into the bowl. The injection regions are disposed in substantially diametrically-opposed quadrants of the end surface which are defined by the wristpin bore axis and the envelope axis. Each injection region extends along a respective arc concentric with the substantially circular peripheral edge. In some cases, the arcuate extent of each injection region may subtend an angle of about 50-70 degrees with the vertex of the angle being at the center of the substantially circular peripheral edge.
Preferably, the wristpin bore has a first opening formed in a first pin boss in a first wall portion of the sidewall and a second opening formed in a second pin boss in a second wall portion of the sidewall, and the openings are coaxially aligned along the wristpin bore axis.
In some aspects, an injection trench is formed in each injection region and injection trench extends from the substantially circular peripheral edge to the bowl.
In other aspects, the end surface has two diametrically opposed injection trenches, each injection trench being formed in a respective injection region and being shaped for guiding a spray of injected fuel into the bowl.
In another aspect of the invention, an opposed-piston engine has a cylinder block with a plurality of cylinders disposed in an inline array along a length of the cylinder block. A pair of pistons is disposed in opposition in each cylinder. Each piston has a wristpin with a wristpin axis, which couples the piston to a connecting rod that swings in a connecting rod motion envelope having an envelope axis. The envelope axis is substantially orthogonal to the wristpin axis. The piston has a crown with an end surface and a bowl in the end surface configured to form a combustion chamber in cooperation with a bowl of an adjacent end surface of an opposing piston. The end surface includes a pair of injection regions across which fuel is injected into the bowl. The injection regions are disposed in respective diametrically-opposed quadrants of the end surface that are defined by the wristpin axis and the envelope axis. Each injection region extends along a respective arc concentric with the substantially circular peripheral edge.
These features of the invention result in advantages that will be readily understood when the following detailed description of the invention is considered in conjunction with the below-described drawings.
Opposed-Piston Engine:
By way of background, an opposed-piston engine is an internal combustion engine in which two pistons are disposed in opposition in the bore of a cylinder. During engine operation, combustion takes place in a combustion chamber formed in the bore between the end surfaces of the two pistons when the pistons move through respective top center locations in the bore. When used herein, the term “combustion chamber” refers to the minimum volume within the cylinder that is bounded by the end surfaces of the pistons and the annular portion of the bore between the end surfaces during operation of the engine during each cycle of engine operation.
As seen in
In the engine 10, a lubrication system that supplies oil to lubricate moving parts of the engine 10 includes an oil reservoir 44 from which pressurized oil is pumped by a pump 42 to a main gallery 40. The main gallery 40 supplies pressurized oil to the crankshafts 30 and 32, typically through drillings 36 to the main bearings (not seen). From grooves and/or passageways in the main bearings, pressurized oil is provided to grooves in the big end bearings of the connecting rods 28. From there, pressurized oil flows through passageways formed in the connecting rods 28 to the wristpins 26.
The pistons 18 and 20 are cooled by provision of streams of oil emitted by stationary oil jets 46 that are mounted in the engine near respective ends of the cylinder 12. Each oil jet 46 comprises a nozzle aimed through an open end of the cylinder 12 at an inlet passage of the annular cooling gallery of the piston.
In some aspects, which are not intended to be limiting, the engine 10 is equipped with an air management system 50 that may include one or more of a turbocharger 52, a supercharger 54, and an EGR channel 56.
The operational cycle of an opposed-piston engine according to
Piston Constructions:
A piston for an opposed-piston engine (an “opposed piston”) is constructed differently from a conventional piston that forms a combustion chamber against the cylinder head of an engine where valve-controlled intake and exhaust ports are located. In opposed-piston engines the pistons move together in a ported cylinder to form a combustion chamber between their end surfaces. In addition, the movements of the opposed pistons control the opening and closing of the cylinder ports to allow charge air to flow into and exhaust to flow out of the engine's cylinders.
In the first instance, the end surface of a conventional piston typically includes a bowl shaped to enable the mixing of charge air with a spray of fuel injected along the axis of the cylinder in which the piston moves. Such a bowl has a shape that is symmetric with respect to the piston's axis. In contrast, the end surface of an opposed piston has a bowl whose features must accommodate fuel injection in a radial or tangential direction of the cylinder, typically from a pair of diametrically opposed fuel injectors. Such a bowl is not symmetric with respect to the piston's axis.
In the second instance, a conventional piston supports one ring band region and a wristpin. However, in addition to these features, an opposed piston must support a second ring band region near an open end of the piston in order to scrape excess oil from the cylinder bore and maintain the seal of an intake port or an exhaust port when the piston moves through top center. The second ring band necessitates a longer piston skirt for an opposed piston than for a conventional piston.
A third feature which characterizes an opposed piston is a linkage assembly including a wristpin bearing support that allows for the interaction of a connecting rod, a wristpin, and the piston in an environment where the wristpin undergoes continuous compressive loading throughout the operational cycle of the engine. U.S. Pat. No. 9,470,136 describes and illustrates a piston bearing assembly in an opposed-piston engine wherein a biaxial wristpin/bearing interface induces periodic separation of axially distributed bearing segments to permit lubricant to reach the opposing external surfaces of the wristpin and the bearing. The wristpin is supported in a generally cubic structure which is installed in the interior of the piston, where the structure is completely enclosed in the piston skirt.
The wristpin support structure is separate from the cylinder skirt, and so the exterior of the skirt is free of bosses and wristpin bores such that it presents a continuous cylindrical aspect to the cylinder bore, thereby providing a highly effective seal between the combustion chamber and crankcase when outfitted with nothing more than two sets of piston rings. However, the price paid is a complex and costly construction which necessitates multiple assembly steps and adds weight to the piston. Further, although the continuous cylindrical aspect of the skirt enables an effective seal between the combustion chamber and the crankcase, it also results in generation of friction in the interface between the skirt and the cylinder bore.
With reference to
Elimination of the Wristpin Support Structure:
A construction for a simpler, lighter piston for an opposed-piston engine eliminates the internal wristpin support structure of the prior art.
An outer ring belt region 323 is formed in a circumferential portion 325 of the sidewall 322 near the outer end 321 of the piston. The sidewall 322 is formed with two opposing curved sidewall portions 327 separated from one another by two opposing box wall portions 328. The curved sidewall portions 327 extend away from the crown 310 toward the open end 321. Relative to the longitudinal axis 302, the curved sidewall portions 327 may have the same radius as the crown 310 and the circumferential portion 325 of the sidewall. In other instances, the curved sidewall portions may have shapes and dimensions adapted for accommodating thrust differentials experienced during engine operation. The box wall portions 328 are inset from the curved sidewall portions 327 and run longitudinally in portions of the sidewall 322 between the inner ring belt region 314 and the outer ring belt region 323. The box wall portions 328 have wristpin bosses 333 in which diametrically-opposed, laterally-spaced wristpin bore openings 335 are formed at respective ends of a wristpin bore 336. The wristpin bore openings 335 are coaxially aligned along a wristpin bore axis 337. A particular piston bearing embodiment will now be described, although this embodiment is presented for the purpose of illustration only. Other bearing constructions are contemplated, although all will utilize the laterally-spaced wristpin bore openings 335.
With reference to
Opposing Injection Regions:
The piston construction thus far described eliminates any need for the wristpin support structure of the prior art piston of
The usual prior art locations of the inlet passageways as constrained by the prior art wrist pin support structure shown in
The injection regions 430 and 432 are disposed in respective diametrically-opposed quadrants of the end surface 311. The figure shows the injection regions 430 and 432 disposed in quadrants I and III, but this is not meant to be limiting as they may alternatively be in quadrants II and IV, together with the inlet passageways 433. Each one of the injection regions 430 and 432 extends along a respective arcuate section of the substantially circular peripheral edge 313 and is concentric with the substantially circular peripheral edge. The injection regions 430 and 432 may or may not be aligned in diametric opposition. Preferably, the arcuate extent of each of the injection regions 430 and 432 subtends an angle α of about 50-70 degrees with the vertex of the angle being at the center of the substantially circular peripheral edge, which is coincident with the longitudinal axis 302.
As per
The shapes of injection trenches often present edges and other surface irregularities where hot spots occur in the piston end surface during combustion. Hot spots lead to asymmetrical thermal stress, wear, and possibly piston crown fracture. Even in cases where the surface contour is less emphatic, such as without trenches, the injection regions may endure a higher thermal load than end surface regions closer to the interior of the bowl. In any event, it is desirable to provide directed cooling to the portions of the crown undersurface that are beneath the injection regions. Thus, in the example shown in
The materials and methods of construction of the piston 300 may be conventional for light, medium and/or heavy duty use or for large bore applications. For example, the crown and skirt part may be formed separately of compatible and/or complementary materials (e.g., forged steel crown, cast iron skirt part) and joined by welding or brazing. Additionally, or alternatively, forming technology including printing technology can be used to form some or all of the piston 300 and its components. Materials can include laminated structures, hybrid structures, composite structures, and the like, including thermal barrier coatings, ceramic-metal composites (e.g., cermets), high-temperature metal alloys, and laser ablated/structured surfaces.
Engine Application.
Those skilled in the art will appreciate that the specific embodiments set forth in this specification are merely illustrative of the invention and that various modifications are possible and may be made thereto without departing from the scope of the invention.
Claims
1. A piston for an opposed-piston engine, comprising:
- a crown with an end surface comprising a bowl configured to form a combustion chamber in cooperation with an adjacent end surface of an opposing piston;
- a substantially circumferential top land of the crown which meets the end surface at a substantially circular peripheral edge;
- a skirt comprising a sidewall extending away from the crown;
- a wristpin bore that opens through the sidewall, the wristpin bore having a wristpin bore axis;
- the wristpin bore configured to receive a wristpin that couples the piston to a connecting rod that swings in an envelope of motion defined by an envelope axis, the envelope axis being substantially orthogonal to the wristpin bore axis; and,
- the end surface including a pair of injection regions across which fuel is injected into the bowl;
- in which the injection regions are disposed in respective diametrically-opposed quadrants of the end surface, the diametrically-opposed quadrants being defined by the wristpin bore axis and the envelope axis; and,
- in which each injection region extends along a respective arc concentric with the substantially circular peripheral edge.
2. The piston of claim 1, the wristpin bore comprising a first opening formed in a first pin boss in the sidewall and a second opening formed in a second pin boss in the sidewall, the openings being coaxially aligned along the wristpin bore axis.
3. The piston of claim 1, the end surface further comprising a pair of injection trenches, each injection trench being formed in a respective injection region and extending from the substantially circular peripheral edge to the bowl.
4. The piston of claim 3, in which the injection trenches are situated in diametrically opposed locations.
5. The piston of claim 1, the end surface further comprising two diametrically-opposed injection trenches, each injection trench being formed in a respective injection region and being shaped for guiding a spray of injected fuel into the bowl.
6. The piston of claim 1, the crown further comprising an interior annular cooling gallery defined at least partially by an inner surface of the substantially circumferential top land, and inlet passageways positioned in the interior annular cooling gallery substantially in alignment with the injection trenches.
7. The piston of claim 6, the wristpin bore comprising a first opening formed in a first pin boss in the sidewall and a second opening formed in a second pin boss in the sidewall, the openings being coaxially aligned along the wristpin bore axis.
8. The piston of claim 6, the end surface further comprising two diametrically-opposed injection trenches, each injection trench being formed in a respective injection region and being shaped for guiding a spray of injected fuel into the bowl.
9. The piston of claim 8, in which the injection trenches are situated in diametrically opposed locations.
10. The piston of claim 6, in which the arcuate extent of each injection region subtends an angle of about 50-70 degrees with the vertex of the angle being at the center of the substantially circular peripheral edge.
11. The piston of claim 1, in which the arcuate extent of each injection region subtends an angle of about 50-70 degrees with the vertex of the angle being at the center of the substantially circular peripheral edge.
12. A piston assembly for an opposed-piston engine, comprising:
- a crown with an end surface comprising a bowl configured to form a combustion chamber in cooperation with an adjacent end surface of an opposing piston;
- a substantially circumferential top land of the crown which meets the end surface at a substantially circular peripheral edge;
- a skirt comprising a sidewall extending away from the crown;
- a wristpin bore in the sidewall;
- a wristpin with a wristpin axis received in the wristpin bore;
- a connecting rod coupled to the wristpin for swinging in an envelope of motion defined by an envelope axis, the envelope axis being substantially orthogonal to the wristpin axis;
- a pair of injection trenches in the end surface at the substantially circular peripheral edge through which fuel is injected into the bowl; and,
- the injection trenches being situated in respective diametrically-opposed quadrants of the end surface defined by the wristpin axis and the envelope axis.
13. The piston assembly of claim 12, the wristpin bore comprising a first opening formed in a first pin boss in the sidewall and a second opening formed in a second pin boss in the sidewall, the openings being coaxially aligned along the wristpin axis.
14. The piston assembly of claim 12, each injection trench extending from the substantially circular peripheral edge to the bowl.
15. The piston assembly of claim 14, in which the injection trenches are situated in diametrically opposed locations of the end surface.
16. The piston assembly of claim 12, each injection trench being shaped for guiding a spray of injected fuel into the bowl.
17. The piston assembly of claim 12, the crown further comprising an interior annular cooling gallery defined at least partially by an inner surface of the substantially circumferential top land region and inlet passageways positioned in the interior annular cooling gallery substantially in alignment with the injection trenches.
18. The piston assembly of claim 17, the wristpin bore comprising a first opening formed in a first pin boss in the sidewall and a second opening formed in a second pin boss in the sidewall, the openings being coaxially aligned along the wristpin axis.
19. The piston assembly of claim 18, each injection trench extending from the substantially circular peripheral edge to the bowl.
20. The piston assembly of claim 19, in which the injection trenches are situated in diametrically opposed locations of the end surface.
21. The piston assembly of claim 12, in which the injection trenches are positioned along respective arcuate portions of the substantially circular peripheral edge, each arcuate portion spanning about 70° and being substantially centered in one of the diametrically-opposed quadrants.
22. An opposed-piston engine, comprising:
- a cylinder block with a plurality of cylinders disposed in an inline array along a length of the cylinder block;
- a pair of pistons disposed in opposition in each cylinder;
- each piston comprising a wristpin with a wristpin axis, the wristpin coupling the piston to a connecting rod that swings in a connecting rod motion envelope having an envelope axis that is substantially orthogonal to the wristpin axis, the piston further comprising a crown with an end surface and a bowl in the end surface configured to form a combustion chamber in cooperation with a bowl of an adjacent end surface of an opposing piston, the end surface including a pair of injection regions across which fuel is injected into the bowl;
- in which the injection regions are disposed in respective diametrically-opposed quadrants of the end surface, the diametrically-opposed quadrants being defined by the wristpin axis and the envelope axis; and,
- in which each injection region extends along a respective arc concentric with the substantially circular peripheral edge.
23. The engine of claim 22, the wristpin bore comprising a first opening formed in a first pin boss in the sidewall and a second opening formed in a second pin boss in the sidewall, the openings being coaxially aligned along the wristpin axis.
24. The engine of claim 22, the end surface further comprising a pair of injection trenches, each injection trench being formed in a respective injection region and extending from the substantially circular peripheral edge to the bowl.
25. The engine of claim 24, in which the injection trenches are situated in diametrically opposed locations.
26. The engine of claim 22, the end surface further comprising two diametrically opposed injection trenches, each injection trench being formed in a respective injection region and being shaped for guiding a spray of injected fuel into the bowl.
27. The engine of claim 22, the crown further comprising an interior annular cooling gallery defined at least partially by an inner surface of a substantially circumferential top land of the crown, inlet passageways positioned in the interior annular cooling gallery in alignment with the injection regions.
28. The engine of claim 27, the wristpin bore comprising a first opening formed in a first pin boss in the sidewall and a second opening formed in a second pin boss in the sidewall, the openings being coaxially aligned along the wristpin axis.
29. The engine of claim 27, the end surface further comprising a pair of injection trenches, each injection trench being formed in a respective injection region and extending from the substantially circular peripheral edge to the bowl.
30. The engine of claim 29, in which the injection trenches are situated in diametrically opposed locations.
31. The engine of claim 27, the end surface further comprising two diametrically opposed injection trenches, each injection trench being formed in a respective injection region and being shaped for guiding a spray of injected fuel into the bowl.
32. The engine of claim 22, in which the arcuate extent of each injection region subtends an angle of about 50-70 degrees with the vertex of the angle being at the center of the substantially circular peripheral edge.
Type: Application
Filed: Feb 13, 2020
Publication Date: Jun 18, 2020
Applicant: ACHATES POWER, INC. (San Diego, CA)
Inventor: RYAN G. MACKENZIE (San Diego, CA)
Application Number: 16/790,552