WO2026030001A1 - Piston - Google Patents

Abstract

A piston (102) includes an upper wall (104) and an outer wall (106) extending along a center axis (108) and around a periphery of and downward from the upper wall. The outer wall defines a first groove (110), a second groove (120), a third groove (130), a fourth groove (140), and a stepped groove (150). The first groove is disposed along a first plane (112) located a first distance along the center axis from the upper wall. The second groove is disposed along a second plane (122) located a second distance along the center axis from the upper wall. The third groove is disposed along a third plane (132) located a third distance along the center axis from the upper wall. The fourth groove is disposed along a fourth plane (142) located a fourth distance along the center axis from the upper wall. The stepped groove is disposed between the third groove and the fourth groove.

Description

PISTON

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001 ] The present application claims priority to United States Provisional Patent Application No. 63/676,994, filed July 30, 2024 and the contents of which are incorporated herein by reference.

TECHNICAL FIELD

[0002] The present application relates generally to piston assemblies for use in internal combustion engines.

BACKGROUND

[0003] Internal combustion engines combust a mixture of fuel (e.g., diesel, gasoline, natural gas, etc.) and air within a combustion chamber. The combustion of the air-fuel mixture causes a piston to move within the combustion chamber, which in turn generates power (e.g., for moving a vehicle, powering equipment, etc.).

SUMMARY

[0004] In one embodiment, a piston includes an upper wall and an outer wall extending along a center axis and around a periphery of and downward from the upper wall. The outer wall defines a first groove disposed along a first plane located a first distance along the center axis from the upper wall. The first groove receives a first ring. The outer wall further defines a second groove disposed along a second plane located a second distance along the center axis from the upper wall. The second distance is greater than the first distance. The second groove receives a second ring. The outer wall further defines a third groove disposed along a third plane located a third distance along the center axis from the upper wall. The third distance is greater than the second distance. The third groove receives a third ring. The outer wall further defines a fourth groove disposed along a fourth plane located a fourth distance along the center axis from the upper wall. The fourth distance is greater than the third distance. The fourth groove receives a fourth ring. The outer wall further defines a stepped groove disposed between the third groove and the fourth groove. The stepped groove is contiguous with the third groove.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the disclosure will become apparent from the description, the drawings, and the claims, in which:

[0006] FIG. 1 is a perspective view of a portion of a piston assembly, according to an example embodiment;

[0007] FIG. 2 is a perspective view of a piston, according to an example embodiment;

[0008] FIG. 3 is a schematic diagram of the piston assembly of FIG. 1, according to an example embodiment;

[0009] FIG. 4 is a top view of a first ring, according to an example embodiment;

[0 10] FIG. 5 is a top view of a second ring, according to an example embodiment;

[OOH ] FIG. 6 is a cross-sectional view of a ring having a straight face, according to an example embodiment;

[0012] FIG. 7 is a cross-sectional view of a ring having a tapered face, according to an example embodiment;

[0013] FIG. 8 is a cross-sectional view of a ring having a stepped face, according to an example embodiment; and

[0014| FIG. 9 is a cross-sectional view of a ring having a Napier face, according to an example embodiment. [0015| It will be recognized that the Figures are schematic representations for purposes of illustration. The Figures are provided for the purpose of illustrating one or more implementations with the explicit understanding that the Figures will not be used to limit the scope or the meaning of the claims.

DETAILED DESCRIPTION

|0016] Following below are more detailed descriptions of various concepts related to, and implementations of, a piston assembly of an internal combustion engine. The various concepts introduced above and discussed in greater detail below can be implemented in any of a number of ways, as the described concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

10017] FIG. 1 illustrates a portion of a piston assembly 100 according to an example embodiment. The piston assembly 100 can be part of an engine (e.g., an internal combustion engine), such as a spark-ignition engine or a compression-ignition engine. Examples of the engine include a hydrogen engine, a diesel engine, a gasoline engine, a propane engine, a dualfuel engine, a natural gas engine, etc. The engine is configured to combust at least one fuel (e.g., hydrogen, diesel, gasoline, propane, natural gas, etc., or any combination thereof) to produce energy that can be utilized by various outputs. For example, the engine can produce energy that is utilized to drive a movement member (e.g., wheel, tread, propeller, impeller, turbine, rotor, etc.) or power a generator. The engine can be implemented in a vehicle (e.g., truck, car, construction vehicle, freight vehicle, commercial vehicle, emergency vehicle, military vehicle, maritime vehicle, etc.).

| 0018] The piston assembly 100 can correspond to a combustion chamber assembly of the engine that is configured to combust fuel. For example, the combustion chamber assembly can include a cylinder (e.g., combustion chamber, etc.) configured to receive the piston assembly 100. The cylinder can include a cylinder liner or a cylinder wall that at least partially defines an internal volume. The cylinder is configured to receive air from an air intake and fuel from a fuel source. The air and fuel can be mixed before reaching the combustion chamber, or can be introduced independently . A mixture of the air and fuel can be combusted within the internal volume of the cylinder.

[0019] The piston assembly 100 includes a piston 102. The piston assembly 100 can be a part of a piston rod assembly. The piston rod assembly can include a connecting rod that is coupled to the piston 102 via a pin (e.g., a piston pin, etc.) received within a pin bore of the piston 102. The connecting rod can be configured to couple to a crankshaft of the engine. The piston 102 and the cylinder wall can jointly define the internal volume such that, when the air-fuel mixture is combusted, the piston 102 is translated axially within the cylinder by the force of the combustion. One or more rings (e.g., cylinder rings, etc.) can be disposed between the piston 102 and the cylinder liner. The cylinder rings are configured to form a seal between the combustion chamber and crankcase, being located by the piston 102 and the cylinder liner or bore.

[0020] FIGS. 1-3 illustrate the piston 102. The piston 102 comprises an upper wall 104 and an outer wall 106 extending along a center axis 108 and around a periphery of and downward from the upper wall 104. The outer wall 106 defines a first groove 110 disposed along a first plane 112 located a first distance dl along the center axis 108 from the upper wall 104. The first groove 110 is configured to receive a first ring 114. The outer wall 106 further defines a second groove 120 disposed along a second plane 122 located a second distance d2 along the center axis 108 from the upper wall 104. The second distance d2 is greater than the first distance dl. The second groove 120 is configured to receive a second ring 124. The outer wall 106 further defines a third groove 130 disposed along a third plane 132 located a third distance d3 along the center axis 108 from the upper wall 104. The third distance d3 is greater than the second distance d2. The third groove 130 is configured to receive a third ring 134. The outer wall 106 further defines a fourth groove 140 disposed along a fourth plane 142 located a fourth distance d4 along the center axis 108 from the upper wall 104. The fourth distance d4 is greater than the third distance d3. The fourth groove 140 is configured to receive a fourth ring 144. The outer wall 106 further defines a stepped groove 150 disposed between the third groove 130 and the fourth groove 140. The stepped groove 150 is contiguous with the third groove 130. [00211 The first groove 110 (e.g., a cavity, a recess, etc.), the second groove 120 (e.g., a cavity, a recess, etc.), the third groove 130 (e.g., a cavity, a recess, etc.), and the fourth groove 140 (e.g., a cavity, a recess, etc.) can be incontiguous (e.g., not contiguous (e.g., sharing a boundary, contacting, etc.), not share a boundary, not contact, etc.) with each other. The stepped groove 150 can be incontiguous with the fourth groove 140.

[0022] The first groove 110 can include a first groove upper edge 116 and a first groove lower edge 118 opposite of the first groove upper edge 116. In some embodiments, each of the first groove upper edge 116 and the first groove lower edge 118 include a first chamfer. In other embodiments, one of the first groove upper edge 116 and the first groove lower edge 118 includes the first chamfer.

100231 The second groove 120 can include a second groove upper edge 126 and a second groove lower edge 128 opposite of the second groove upper edge 126. In some embodiments, each of the second groove upper edge 126 and the second groove lower edge 128 include a second chamfer. In other embodiments, one of the second groove upper edge 126 and the second groove lower edge 128 includes the second chamfer.

[0024] In some embodiments, a chamfer angle of the first chamfer is equal to a chamfer angle of the second chamfer. In other embodiments, the chamfer angle of the first chamfer is greater than the chamfer angle of the second chamfer. In yet other embodiments, the chamfer angle of the first chamfer is less than the chamfer angle of the second chamfer. In some embodiments, a first chamfer length and a second chamfer length of the first chamfer and/or a third chamfer length and a fourth chamfer length of the second chamfer are between 0 millimeter (mm) and 0.5 mm. The first chamfer and/or the second chamfer provide for additional control of air and/or fluid volume capable of being held proximate the first groove upper edge 116, the first groove lower edge 118, the second groove upper edge 126, and/or the second groove lower edge 128. The first chamfer and/or the second chamfer can be manually sized.

[0025] The outer wall 106 (e.g., a ring belt, etc.) includes a first portion 160 (e.g., an upper portion, a top land, a head land, etc.) that extends between the first groove upper edge 116 and the upper wall 104 (e.g., a piston crown, etc ). The first portion 160 can be manufactured with reduced clearance such that a diameter of the first portion 160 is maximized while not contacting the cylinder wall, thereby minimizing unburned fuel, reducing emissions contribution, reducing propensity for localized combustion, and/or protecting the first ring 114.

[0026] The outer wall 106 includes a second portion 162 that extends between the first groove lower edge 118 and the second groove upper edge 126. The second portion 162 can be sized (e.g., a diameter of the second portion 162, etc.) such that the pressure within that fluid volume (encompassing air, fuel, oil, or any combination thereof) is greater than other portions of the outer wall 106 downward of the second portion 162 (i.e., in a direction away from the first portion 160, etc.), such that the oil and gas are pushed downward rather than upward (e.g., toward the upper wall 104, etc.).

[0027] The third groove 130 can include a third groove upper edge 136. The outer wall 106 includes a third portion 164 that extends from the second groove lower edge 128 to the third groove upper edge 136. The third portion 164 can be continuous (e.g., uninterrupted, smooth, lacks any grooves, etc.).

[0028] A fifth distance d5 can be defined between the first plane 112 and the second plane 122. In some embodiments, the fifth distance d5 can be greater than the first distance dl (i.e., distance between the upper wall 104 and the first plane 112). A sixth distance d6 can be defined between the second plane 122 and the third plane 132. In some embodiments, the sixth distance d6 can be less than the fifth distance d5. A seventh distance d7 can be defined between the third plane 132 and the fourth plane 142. In some embodiments, the seventh distance d7 can be less than the sixth distance d6. In other embodiments, the seventh distance d7 can be greater than the fifth distance d5.

[0029] The fifth distance d5, the sixth distance d6, and the seventh distance d7 can be configured such that a first pressure of the fluid volume proximate the fifth distance d5 (i.e., between the first plane 112 and the second plane 122) is greater than a second pressure of the fluid volume proximate the sixth distance d6 (i.e., between the second plane 122 and the third plane 132) that is greater than a third pressure of the fluid volume proximate the seventh distance d7 (i.e., between the third plane 132 and the fourth plane 142). For example, the stepped groove 150 can include a stepped groove lower edge 152. The fourth groove 140 can include a fourth groove upper edge 146. The outer wall 106 includes a fourth portion 166 that extends from the stepped groove lower edge 152 to the fourth groove upper edge 146. The fourth portion 166 can be continuous. A pressure of the fluid volume proximate the second portion 162 is greater than a pressure of the fluid volume proximate the third portion 164, and the pressure of the fluid volume proximate the third portion 164 is greater than a pressure of the fluid volume proximate the fourth portion 166. Such a configuration prevents oil and gases from flowing upwards and into the combustion chamber (e.g., above the upper wall 104, etc.).

[0030| The piston assembly 100 includes the first ring 114. The first ring 114 (e.g., a cylinder ring, a piston ring, an O-ring, a seal, etc.) is disposed within the first groove 110. The first ring 114 can include a first compression ring (e.g., a gas-sealing ring, etc.). The first compression ring is configured to create a first seal between the piston 102 and the cylinder wall to substantially maintain pressure of a fluid volume (e g., air, fuel, mixture of the air and fuel (e g., an air-fuel mixture, etc.), exhaust, etc.) between the piston 102 and the cylinder wall. As illustrated in FIG. 4, the first ring 114 includes a first ring first end 117 and a first ring second end 119 located a first circumferential distance cdl away from the first ring first end 117. In some embodiments, the first circumferential distance cdl is minimized while preventing contact between the first ring first end 117 and the first ring second end 119 under operational thermal and pressure conditions to minimize slip of the fuel, air, and/or the oil.

[00311 The piston assembly 100 includes the second ring 124 (e.g., a cylinder ring, an O- ring, a seal, etc.). The second ring 124 (e.g., a cylinder ring, a piston ring, an O-ring, a seal, etc.) is disposed within the second groove 120. The second ring 124 can include a second compression ring (e.g., a gas-sealing ring, etc.). The second compression ring is configured to create a second seal between the piston 102 and the cylinder wall to substantially maintain pressure of the fluid volume between the piston 102 and the cylinder wall. In some embodiments, the first seal of the first compression ring (e.g., the first ring 114) and the second seal of the second compression ring (e.g., the second ring 124) cooperate to substantially reduce blowby (i.e., where the fuel or the air-fuel mixture leaks between the outer wall 106 and the cylinder wall into a crankcase of the engine), thereby (i) reducing size and cost of a purge device of the engine that is configured to maintain appropriate levels of the fuel (e.g., hydrogen, etc.) within the crankcase and (ii) reducing parasitic losses due to the leaked fuel not contributing to the combustion.

[0032] As illustrated in FIG. 5, the second ring 124 includes a second ring first end 127 and a second ring second end 129 located a second circumferential distance cd2 away from the second ring first end 127. In some embodiments, the second circumferential distance cd2 is minimized while preventing contact between the second ring first end 127 and the second ring second end 129 under operational thermal and pressure conditions to minimize slip of the fuel and/or the oil. In some embodiments, the first circumferential distance cdl is greater than the second circumferential distance cd2, thereby maintaining a positive pressure differential along a length of the piston 102 and maximizing blockage of the fuel, the exhaust, and/or the oil. In other embodiments, the first circumferential distance cdl is equal to or greater than the second circumferential distance cd2. In yet other embodiments, the first circumferential distance cdl is equal to or less than the second circumferential distance cd2.

[0033] In some embodiments, at least one of the first ring 114 or the second ring 124 has a substantially rectangular or keystone cross-section that can substantially prevent oil (e.g., lubricant, etc.) from leaking between the outer wall 106 and the cylinder wall through the at least one of the first ring 114 or the second ring 124 towards the upper wall 104 and/or substantially prevent fuel, air, or air-fuel mixture from leaking between the outer wall 106 and the cylinder wall through the at least one of the first ring 114 or the second ring 124 into the crankcase. In some embodiments, at least one of the first ring 114 or the second ring 124 has an asymmetric barrel face that can at least partially scrap (e.g., clean, remove, etc.) the oil downward towards the crankcase. [0034| The piston assembly 100 includes the third ring 134 (e.g., a cylinder ring, an O-ring, a seal, etc.). The third ring 134 is disposed within the third groove 130. The third ring 134 can include a scraper ring. The scraper ring is configured to scrape the oil from the cylinder wall as the piston assembly 100 moves within the cylinder. The scraper ring can be configured to ride over the oil (e.g., substantially not scrape the oil, etc.) during an up-stroke of the piston assembly 100 (i.e., when the piston assembly 100 moves upward within the cylinder) and scrape the oil during a down-stroke of the piston assembly 100 (i.e., when the piston assembly 100 moves downward within the cylinder). The scraper ring can move the scraped oil downward towards the crankcase during the down-stroke. The stepped groove 150 can accumulate the oil scraped by the scraper ring until it can be drained downward towards the crankcase, thereby preventing, or reducing an amount of the oil from flowing upwards (e.g., to the upper wall 104, etc.).

[9035] As illustrated in FIG. 3, an eighth distance d8 can be defined between the outer wall 106 and a shortest edge of the third ring 134 (e.g., an edge of the third ring 134 closest to the center axis 108 and faces the cylinder liner or bore, an edge of the third ring 134 closest to the center axis 108 and faces away from the third groove 130, etc.). A ninth distance d9 can be defined between the outer wall 106 and the stepped groove 150. The ninth distance d9 can be a minimum distance, a maximum distance, a median distance, or a mean distance between the outer wall 106 and the stepped groove 150. In some embodiments, the ninth distance d9 is greater than the eighth distance d8.

|0036| The piston assembly 100 includes the fourth ring 144 (e.g., a cylinder ring, an O-ring, a seal, etc.). The fourth ring 144 is disposed within the fourth groove 140. The fourth ring 144 can include an oil ring. The oil ring is configured to cooperate with the piston 102 to scrape the oil downward towards the crankcase and/or substantially prevent the oil from leaking between the outer wall 106 and the cylinder wall towards the upper wall 104.

[0037] In some embodiments, the oil ring is a 2-piece oil ring that includes a housing ring and a spring received within the housing ring. In other embodiments, the oil ring is a 3-piece oil ring that includes an upper rail, a lower rail disposed below the upper rail, and a spacer or expander disposed between the upper rail and the lower rail.

[0038] As illustrated in FIG. 2, the outer wall 106 can define one or more apertures 170. The apertures 170 can be disposed at least partially within the fourth groove 140. The apertures 170 are configured to pass the oil therethrough to drain the oil received within the fourth groove 140 downward toward the crankcase.

|0039| As illustrated in FIG. 2, the piston 102 includes a skirt 172 disposed below the outer wall 106. The piston 102 can include a recess 174 between the outer wall 106 and the skirt 172. The recess 174 can have a diameter that is less than a diameter of the skirt 172, thereby aiding in drainage of the oil towards the crankcase. The diameter of the recess 174 can be less than a diameter of the outer wall 106.

[0040] FIG. 6 illustrates a cross-sectional view of a fifth ring 200 having a straight face 202. In some embodiments, at least one of the first ring 114, the second ring 124, the third ring 134, or the fourth ring 144 have the straight face 202.

[00411 FIG. 7 illustrates a cross-sectional view of a sixth ring 210 having a tapered face 212. In some embodiments, at least one of the first ring 114, the second ring 124, the third ring 134, or the fourth ring 144 have the tapered face 212.

[0042] FIG. 8 illustrates a cross-sectional view of a seventh ring 220 having a stepped face 222. In some embodiments, at least one of the first ring 114, the second ring 124, the third ring 134, or the fourth ring 144 have the stepped face 222.

[0043] FIG. 9 illustrates a cross-sectional view of an eighth ring 230 having a Napier face 232. In some embodiments, at least one of the first ring 114, the second ring 124, the third ring 134, or the fourth ring 144 have the Napier face 232. In some embodiments, the third ring 134 has one of the Napier face 232, the stepped face 222, or a mini-Napier face. [0044] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what can be claimed but rather as descriptions of features specific to particular implementations. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features can be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination can be directed to a subcombination or variation of a subcombination.

[0045] As utilized herein, “substantially” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to any precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the present disclosure.

[ 0046] The term “coupled” and the like, as used herein, mean the joining of two components directly or indirectly to one another. Such joining can be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining can be achieved with the two components or the two components and any additional intermediate components being integrally formed as a single unitary body with one another, with the two components, or with the two components and any additional intermediate components being attached to one another.

[0047] It is important to note that the construction and arrangement of the piston assembly shown in the various example implementations is illustrative only and not restrictive in character. All changes and modifications that come within the spirit and/or scope of the described implementations are desired to be protected. It should be understood that some features may not be necessary, and implementations lacking the various features can be contemplated as within the scope of the application, the scope being defined by the claims that follow. When the language “a portion” is used, the item can include a portion and/or the entire item unless specifically stated to the contrary.

|0048| Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. can be either X, Y, Z, X and Y, X and Z, Y and Z, or X, Y, and Z (i.e., any combination of X, Y, and Z). Thus, such conjunctive language is not generally intended to imply that certain embodiments require at least one of X, at least one of Y, and at least one of Z to each be present, unless otherwise indicated.

(0049] Additionally, the use of ranges of values (e.g., W1 to W2, etc.) herein are inclusive of their maximum values and minimum values (e.g., W1 to W2 includes W1 and includes W2, etc.), unless otherwise indicated. Furthermore, a range of values (e.g., W1 to W2, etc.) does not necessarily require the inclusion of intermediate values within the range of values (e.g., W1 to W2 can include only W1 and W2, etc.), unless otherwise indicated.

Claims

WHAT IS CLAIMED IS:

1. A piston comprising: an upper wall; and an outer wall extending along a center axis and around a periphery of and downward from the upper wall, the outer wall defining: a first groove disposed along a first plane located a first distance along the center axis from the upper wall, the first groove configured to receive a first ring, a second groove disposed along a second plane located a second distance along the center axis from the upper wall, the second distance greater than the first distance, the second groove configured to receive a second ring, a third groove disposed along a third plane located a third distance along the center axis from the upper wall, the third distance greater than the second distance, the third groove configured to receive a third ring, a fourth groove disposed along a fourth plane located a fourth distance along the center axis from the upper wall, the fourth distance greater than the third distance, the fourth groove configured to receive a fourth ring, and a stepped groove disposed between the third groove and the fourth groove, the stepped groove contiguous with the third groove.

2. A piston assembly comprising: the piston of claim 1; the first ring disposed within the first groove, the first ring comprising a first compression ring; and the second ring disposed within the second groove, the second ring comprising a second compression ring.

3. The piston assembly of claim 2, wherein: the first ring comprises a first ring first end and a first ring second end located a first circumferential distance away from the first ring first end; and the second ring comprises a second ring first end and a second ring second end located a second circumferential distance away from the second ring first end, the first circumferential distance being greater than the second circumferential distance.

4. The piston assembly of claim 2, wherein at least one of the first ring or the second ring has a substantially rectangular cross-section.

5. The piston assembly of claim 2, wherein at least one of the first ring or the second ring has an asymmetric barrel face.

6. A piston assembly, comprising: the piston of claim 1; the third ring disposed within the third groove, the third ring comprising a scraper ring; and the fourth ring disposed within the fourth groove, the fourth ring comprising an oil ring.

7. The piston assembly of claim 6, wherein the third ring has a Napier face.

8. The piston assembly of claim 6, wherein the third ring has a straight face.

9. The piston assembly of claim 6, wherein the third ring has a stepped face.

10. The piston assembly of claim 6, wherein the third ring has a tapered face.

11. The piston assembly of claim 6, wherein: the third ring comprises an edge closest to the center axis and that faces away from the third groove; and an eighth distance between the edge of the third ring and the outer wall is less than a ninth distance between the stepped groove and the outer wall.

12. The piston of claim 1, wherein a portion of the outer wall extending from a second groove lower edge of the second groove to a third groove upper edge of the third groove is continuous.

13. The piston of claim 1, wherein at least one of: each of a first groove upper edge and a first groove lower edge of the first groove comprise a first chamfer; or each of a second groove upper edge and a second groove lower edge of the second groove comprise a second chamfer.

14. The piston of claim 1, wherein a fifth distance between the first plane and the second plane is greater than the first distance.

15. The piston of claim 14, wherein a sixth distance between the second plane and the third plane is less than the fifth distance.

16. The piston of claim 14, wherein a seventh distance between the third plane and the fourth plane is less than the sixth distance.

17. The piston of claim 1, wherein the stepped groove is incontiguous with the fourth groove.

18. The piston of claim 1, wherein the outer wall defines one or more apertures that are at least partially disposed within the fourth groove, the one or more apertures configured to pass oil therethrough.

19. The piston of claim 1, further comprising: a skirt disposed below the outer wall; and a recess disposed between the outer wall and the skirt, the recess having a diameter less than a diameter of the skirt and a diameter of the outer wall.

20. The piston of claim 1, wherein the first groove, the second groove, the third groove, and the fourth groove are incontiguous with each other.