Piston with anti-coking design features

A steel piston with anti-coking design features is provided. The piston includes an upper crown portion and a lower crown portion forming an outer cooling gallery therebetween. The outer cooling gallery is substantially closed except for an oil inlet, oil outlet, and optional oil passage(s) to a central cooling gallery. According to one embodiment, at least one anti-coking insert is disposed in the outer cooling gallery and sized to prevent escaping through the oil inlet or the oil outlet. For example, the insert(s) can comprise a helical coil, a plurality of steel balls, coil springs, or chips formed of polymer with abrasive filler. Alternatively, an outer gallery floor to the outer cooling gallery includes a plurality of anti-coking openings disposed sequentially in decreasing spaced relation from one another, or anti-coking openings with varying lengths.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to pistons for internal combustion engines, and more particularly to pistons having cooling galleries.

2. Related Art

Pistons for internal combustion engines oftentimes have a single outer cooling gallery, a central cooling gallery, or two cooling galleries (dual galleries). The dual gallery pistons have an annular, radially outer cooling gallery which is substantially closed and an open central cooling gallery formed between upper and lower crown portions. During operation, cooling oil is contained in or sprayed into the cooling galleries to reduce the temperature of the surround metal body. However, oil deposits oftentimes accumulate on the inner walls bounding the cooling galleries, particularly the closed or substantially closed outer cooling gallery. As the oil deposits accumulate, the cooling effectiveness of the oil circulating therein diminishes.

These oil deposits, also referred to as oil coking, in the cooling galleries, is generally associated with high thermally loaded steel pistons. To reduce oil coking, coatings have been applied to the inner surfaces of the cooling galleries. However, the coating solutions and other known solutions to oil coking, are oftentimes expensive or not preferred for other reasons.

SUMMARY OF THE INVENTION

One aspect of the invention provides a piston with anti-coking design features that are oftentimes preferred over the coatings and other known solutions to oil coking. The piston comprises a piston body including an upper crown portion with an upper combustion wall and a lower crown portion. The upper crown portion and the lower crown portion form an outer cooling gallery therebetween. The lower crown portion presents an outer gallery floor of the outer cooling gallery. The outer gallery floor has an oil inlet allowing oil to flow into the outer cooling gallery and an oil outlet allowing oil to flow out of the outer oil gallery. At least one insert is disposed in the outer cooling gallery, and the at least one insert is sized to prevent escaping of the at least one insert through the oil inlet or through the oil outlet.

According to another embodiment, the outer gallery floor of the piston includes a plurality of anti-coking openings, the anti-coking openings are disposed sequentially in decreasing spaced relation from one another.

According to yet another embodiment, the outer gallery floor of the piston includes a plurality of anti-coking openings, each of the openings has a length extending circumferentially around the outer cooling gallery, and the lengths of the anti-coking openings vary from one another.

Another aspect of the invention provides a method of manufacturing a piston with anti-coking design features. The method comprises the step of providing a piston body including a lower crown portion and an upper crown portion with an upper combustion wall, the upper crown portion and the lower crown portion forming an outer cooling gallery therebetween, the lower crown portion presenting an outer gallery floor of the outer cooling gallery, the outer gallery floor having an oil inlet allowing oil to flow into the outer cooling gallery and an oil outlet allowing oil to flow out of the outer oil gallery. The method also includes disposing at least one insert in the outer cooling gallery, and the at least one insert is sized to prevent the at least one insert from escaping through the oil inlet or the oil outlet.

According to another embodiment, the method includes providing a piston body including a lower crown portion and an upper crown portion with an upper combustion wall, the upper crown portion and the lower crown portion forming an outer cooling gallery therebetween, the lower crown portion presenting an outer gallery floor of the outer cooling gallery, the outer gallery floor including a plurality of anti-coking openings, and the anti-coking openings being disposed sequentially in decreasing spaced relation from one another.

According to yet another embodiment, the method includes providing a piston body including a lower crown portion and an upper crown portion with an upper combustion wall, the upper crown portion and the lower crown portion forming an outer cooling gallery therebetween, the lower crown portion presenting an outer gallery floor of the outer cooling gallery, the outer gallery floor presenting a plurality of anti-coking openings extending therethrough, each of the openings having a length extending circumferentially around the outer cooling gallery, and the lengths of the anti-coking openings varying from one another.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

One aspect of the invention provides a piston10designed with anti-coking features to reduce oil deposits caused by cooling oil during operating of the piston10and thus improve piston cooling. As shown inFIGS. 1 and 6, the piston10has a piston body12extending along a central axis14along which the piston body reciprocates within a cylinder bore (not shown). The piston body12is formed of metal, and preferably steel. The piston body12includes an upper crown portion16having dome or an upper combustion wall18, represented here, by way of example and without limitation, as having a recessed combustion bowl20, against which combustion forces directly act in the cylinder bore. The upper crown portion16has at least one, and shown here, by way of example and without limitation, as having a pair of annular upper ribs, referred to hereafter as an upper inner rib22and upper outer rib24, depending from the upper combustion wall18to respective free ends. The piston body12further includes a lower crown portion26having at least one, and shown here, by way of example and without limitation, as having a pair of annular lower ribs, referred to hereafter as a lower inner rib28and lower outer rib30, extending to respective free ends arranged in alignment for fixed abutment with the respective free ends of the upper inner and outer ribs22,24to form and separate an outer cooling gallery31from a central region of the piston10. The outer cooling gallery31presents an oil passage72extending circumferentially around the upper crown portion18. The outer cooling gallery31also surrounds a central cooling gallery33located in the central region of the piston10.

The lower crown portion26, by way of example and without limitation, is shown as having an inner gallery floor32extending radially inwardly from the lower inner rib28toward the central axis14. Further, the lower crown portion26has an outer gallery floor48extending laterally between the lower inner and outer ribs28,30. The lower inner rib28, the lower outer rib30, the upper inner rib22, the upper outer rib24, the upper combustion wall18, and the outer gallery floor48present an inner surface55defining the outer cooling gallery31. The lower inner rib28, the upper inner rib22, the upper combustion wall18, and the inner gallery floor32also present an inner surface57defining the central cooling gallery33therebetween. The inner gallery floor32includes a central opening53to the central cooling gallery33along the central axis14. According to another embodiment, the inner gallery floor32is not included and thus the central cooling gallery33is open.

According to certain embodiments, the outer gallery floor48has a through opening providing an oil inlet50to allow oil to flow into the outer gallery31and a through opening providing an oil outlet52to allow oil to flow outwardly from the outer gallery31. As such, oil from the crankcase is able to flow upwardly into the outer cooling gallery31through the oil inlet50, whereupon the oil is circulated about the outer cooling gallery31and then exits through the oil outlet52. To further yet facilitate cooling the piston10, the respective inlet and outlet oil flow openings50,52extend through the outer gallery floor48of the outer cooling gallery31in diametrically opposed relation to one another. The openings50,52are formed generally 45 degrees offset from the pin axis44.

According to the example embodiments shown inFIGS. 1 and 6, the outer cooling gallery31of the upper crown portion16has an annular outer oil gallery pocket56extending from the inner and outer rib free ends upwardly into an upper ring belt region58and an annular inner oil gallery cavity or pocket60forming part of the central crown region extending upwardly from the inner free end beneath the combustion bowl20. However, the outer cooling gallery31could comprise various other shapes. According to these embodiments, the lower crown portion26is formed, such as in a casting or forging process from steel or other metal, having an annular outer oil gallery pocket62extending from the inner and outer rib free ends downwardly into a lower ring belt region64. To further facilitate cooling the piston10, one or more oil flow passages can be provided in one or more of the inner ribs22,28to allow cooling oil to flow from the outer cooling gallery31to the central cooling gallery33. For example, as shown inFIG. 6, an intermediate oil passage66extends through the lower inner rib28in ascending relation from a lower most portion of the outer oil gallery31to a lower portion of the inner cooling gallery33. As such, oil from the crankcase is able to flow upwardly into the outer cooling gallery31through the inlet opening50, whereupon the oil is circulated about the outer cooling gallery31and channeled in part inwardly through the oil flow passage66into the central oil gallery33. Upon joining or attaching the upper crown portion16to the lower crown portion26, the central cooling gallery33is formed, and the annular outer oil gallery31is formed. The outer oil gallery31is substantially closed or sealed upon joining the upper crown portion16to the lower crown portion26, except for the oil inlet50, oil outlet52, intermediate oil passage66, and any other passage or small opening for conveying of cooling oil.

A pair of pin bosses36,38depend generally from the outer and inner gallery floors32,48to provide a pair of wrist pin bores40,42aligned along the pin axis44for receipt of a wrist pin (not shown) with a space46provided between the pin bosses38,40for receipt of a small end of a connecting rod (not shown).

The piston10is designed with at least one anti-coking feature to reduce oil deposits caused by cooling oil contained in the outer cooling gallery31during operation of the piston10and thus improve cooling of the piston10. For example, one aspect of the invention is directed to creating mechanisms inside the outer oil gallery31that motivates the oil to move directionally avoiding stagnation and coking, for example by partial drainage and coil approach. Coking in cooling galleries is a problem oftentimes found with highly thermally loaded steel pistons. Coking is a four-variable function, and the variables include cooling media activation energy level (EA), absolute surface temperature (T) of the metal of the piston body12, flux of cooling media (M), and residence time (RT) of the cooling media within the reactor, in this case the cooling oil in the outer cooling gallery31. The coking process inception is amenable to calculation. An inspection of the Arrhenius equation and extrapolating to real life conditions inside of the engine shows that there are few options for adjusting the activation energy level (EA) and absolute surface temperature (T) of the metal of the piston body12. The flux of the cooling media, i.e. lubricant oil, is limited by the expenditure of parasitic power to increase flow and the need to allow sufficient residual volume in the outer cooling gallery31, such as to promote an effective cocktail shaker effect. The sufficient residual volume is generally in the range of 50% to 75% of the total volume of the outer cooling gallery31. Therefore, the residence time (RT) of the cooling oil within the outer cooling gallery31is the remaining variable which can be adjusted to reduce coking.

According to one embodiment, at least one anti-coking insert54is disposed in the outer cooling gallery31to reduce the residence time of the cooling oil in the outer cooling gallery31and thus reduce coking. The insert(s)54is designed to clean the inner surface55of the outer cooling gallery31continuously during service and while the engine is running, thus preventing accumulation of oil deposits which could affect the cooling function of the outer cooling gallery31. The at least one insert54, also referred to as a flux capacitor, can comprise a variety of different sizes and shapes. However, each insert54is sized to prevent the insert54from escaping through the oil inlet50, through the oil outlet52, or through any other passage or opening for conveying cooling oil. For example, a minimum thickness t of each insert54is greater than a maximum diameter or dimension D1of the oil inlet50, greater than a maximum diameter or dimension D2of the oil outlet52, and greater than a maximum diameter or dimension of any other passage or opening to the outer cooling gallery31for conveying oil. The insert(s)54should also be shaped in a way that allows it to impact the upper combustion wall18of the outer cooling gallery31where oil deposits are likely. The insert(s)54should also be designed to not cause unacceptable noise, vibration, or harshness issues. The insert(s)54should also not impede oil flow significantly, and the insert(s)54should be durable to provide effective cleaning for the expected service life of the piston10.

According to one example embodiment, as shown inFIGS. 1, 2, and 2A, one insert54is disposed in the outer cooling gallery31, and the insert54is a helical coil. The helical coil presents a center coil opening68extending circumferentially around the outer cooling gallery31. The center coil opening68is aligned with the oil passage72of the outer cooling gallery31for allowing oil to flow therethrough. The helical coil could be provided by forming the inner surface55of the outer cooling gallery31into the shape of the coil, such that the helical coil is part of the piston body12. Alternatively, the helical coil could be a component disposed within the oil passage72separate from the piston body12. Due to the shape of the helical coil and the ingress of the oil pressure wave during use of the piston10, an inherent stabilized unidirectional flow towards the oil outlet52is established. An inner diameter d of the helical coil impedes to a degree any backflow, as the cooling fluid is either predominantly near the upper combustion wall18of the outer cooling gallery31or near the outer gallery floor48of the outer cooling gallery31. Thus, the helical coil minimizes the residence time (RT) of the cooling oil in the outer cooling gallery31and thus reduces oil coking.

According to another example embodiment, as shown inFIG. 3, the at least one insert54includes plurality of scallops spaced from one another circumferentially around the outer cooling gallery31. Each scallop has an inner diameter d presenting a scallop center opening70aligned with the oil passage72of the outer cooling gallery31for allowing oil to flow therethrough. The inner diameter d of each scallop decreases in a direction moving from the oil inlet50to the oil outlet52. For example, the scallops can be venturi-shaped. The scallops are typically fixed to the inner surface55of the outer cooling gallery31, as shown inFIG. 3. Due to the shape of the scallops and the ingress of the oil pressure wave during use of the piston10, an inherent directional flow towards the oil outlet52is established. The scallops impede to a degree any backflow, as the cooling oil is either predominantly near the upper combustion wall18of the outer cooling gallery31or near the outer gallery floor48of the outer cooling gallery31. The scallops speed up the flow of oil along the length of the outer cooling gallery31, minimize the residence time (RT) of the cooling oil in the outer cooling gallery31, and thus reduce oil coking. Although the anti-coking inserts54ofFIG. 3are shown as symmetrical along the length of the outer cooling gallery31, the anti-coking inserts54could be staggered along the length of the outer cooling gallery31without compromising their function.

According to yet another embodiment, the at least one insert54is free to move within the outer cooling gallery31during reciprocation of the piston body12in use. In this case, the outer cooling gallery31typically contains a plurality of the inserts54. As the inserts54move throughout the cooling gallery31during reciprocation, they impact the inner surface55bounding the outer cooling gallery31, thereby preventing or inhibiting the accumulation and build-up of oil deposits on the inner surface55. As such, optimal cooling results in the outer cooling gallery31without “coking” the oil on the inner surface55.

The inserts54can have various different designs, and example designs are shown inFIG. 6. The shape of the at least one insert54can be round, polygonal, square, triangular, prismatic, and/or toroidal. For example, the inserts54can include balls formed of steel, balls of coarse steel turnings, coil springs, or chips formed of high temperature resistant polymer with abrasive filler. According to one embodiment, the abrasive filler includes at least one of metal fibers and glass fibers. According to another embodiment, the at least one insert54includes at least one prismatic rod or prismatic wire having one axis significantly longer than two other axes.

According to another example embodiment, the at least one anti-coking feature includes a plurality of anti-coking openings70in the outer gallery floor48. In this case, the oil inlet50and the oil outlet52are not required. The anti-coking openings70can be the same size or difference sizes. For example, each anti-coking opening70can have a circular or oblong shape. The anti-coking openings70can be used alone or with the at least one anti-coking insert54.

In the example embodiment ofFIG. 4, the anti-coking openings70are disposed sequentially in decreasing spaced relation from one another. Preferably, the anti-coking openings70are spaced in a way which sequentially minimizes the residence time (RT) of the cooling oil in the outer cooling gallery31until it finds the next anti-coking opening70. Thus, due to drainage of the superheated cooling oil, the oil coking which would otherwise occur is avoided.FIG. 4shows the lengths L1, L2, LI between the anti-coking openings70, wherein L1<L2<LI.

In the example embodiment ofFIG. 5, each anti-coking opening70has a length L extending circumferentially around the outer cooling gallery31, and the lengths L of the anti-coking openings70vary from one another. For example, the anti-coking openings70can be drilled to the desired size, or drilled to form oblong slits as shown inFIG. 5.

Another aspect of the invention provides a method of manufacturing the piston10with the at least one anti-coking feature. The piston body12can be formed by forging or casting one piece or multiple pieces of metal. According to one embodiment, the method includes providing the piston body12including the lower crown portion26and the upper crown portion16with an upper combustion wall18. The upper crown portion16and the lower crown portion26form the outer cooling gallery31therebetween. The lower crown portion26presents an outer gallery floor48of the outer cooling gallery31, and the outer gallery floor48has an oil inlet50allowing oil to flow into the outer cooling gallery31and an oil outlet52allowing oil to flow out of the outer oil gallery31. The step of providing the piston body12typically includes joining the upper crown portion16to the lower crown portion26, for example by welding.

The method according to this embodiment also includes disposing the at least one insert54in the outer cooling gallery31, wherein the at least one insert54is sized to prevent the at least one insert54from escaping through the oil inlet50or the oil outlet52. The insert(s)54is typically disposed in the outer cooling gallery31before joining, for by example welding, the upper crown portion16to the lower crown portion26. After joining, the at least one insert54is contained with the resulting outer cooling gallery31. The at least one insert54can be disposed within one of the pockets56,62, as shown inFIG. 6. Alternatively, the step of providing the piston body12includes joining the upper crown portion16to the lower crown portion26, and the step of disposing the at least one insert54in the outer cooling gallery31is conducted after the joining step. In this case, the method can include compressing the least one insert54, such as a coil spring, through the oil inlet50and/or the oil outlet52, and then allowing the at least one insert54to expand inside the outer cooling gallery31to prevent escaping of the insert54back through the openings50,52during use. The insert(s)54which are in the form of a prismatic ‘rod’ or ‘wire’ with one axis significantly longer than the other two axes could also be inserted into the outer cooling gallery31through the oil inlet50or oil outlet52after joining the upper crown portion16to the lower crown portion26.

According to another example embodiment, the method of manufacturing the piston10includes providing the piston body12with the lower crown portion26and the upper crown portion16with the upper combustion wall18, wherein the upper crown portion16and the lower crown portion26form the outer cooling gallery31therebetween, the lower crown portion26presents the outer gallery floor48of the outer cooling gallery31, the outer gallery floor48includes a plurality of the anti-coking openings70, and the anti-coking openings70are disposed sequentially in decreasing spaced relation from one another.

According to yet another example embodiment, the method of manufacturing the piston10includes providing the piston body12including the lower crown portion26and the upper crown portion16with the upper combustion wall18, wherein the upper crown portion16and the lower crown portion26form the outer cooling gallery31therebetween, the lower crown portion26presents an outer gallery floor48of the outer cooling gallery31, the outer gallery floor48presents a plurality of the anti-coking openings70extending therethrough, each of the openings has a length L extending circumferentially around the outer cooling gallery31, and the lengths L of the anti-coking openings70vary from one another.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, it is contemplated that the piston could be constructed as a monolithic piece of material, such as by being formed in a single steel cast process. Further, it is contemplated that the piston, rather than having a “dual gallery” construction, could have a single “outer oil gallery” with a substantially open central crown region. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.