1. Technical Field
This invention relates generally to internal combustion engines, and more particularly to pistons therefor.
2. Related Art
Engine manufacturers are encountering increasing demands to improve engine efficiencies and performance, including, but not limited to, improving fuel economy, reducing oil consumption, improving fuel systems, increasing compression loads and operating temperatures within the cylinder bores, reducing heat loss through the piston, improving lubrication of component parts, decreasing engine weight and making engines more compact, while at the same time decreasing the costs associated with manufacture.
While desirable to increase the compression load and operation temperature within the combustion chamber, it remains necessary to maintain the temperature of the piston within workable limits. Accordingly, although desirable to increase the compression load and operation temperature within the combustion chamber, achieving this goal comes with a tradeoff in that these desirable “increases” limit the degree to which the piston compression height, and thus, overall piston size and mass can be decreased. This is particularly troublesome with typical piston constructions having a closed or partially closed cooling gallery to reduce the operating temperature of the piston. The cost to manufacture pistons having upper and lower parts joined together along a bond joint to form the closed or partially closed cooling gallery is generally increased due to the joining process used to bond the upper and lower parts together. Further, the degree to which the engine weight can be reduced is impacted by the need to make the aforementioned “cooling gallery-containing” pistons from steel so they can withstand the increase in mechanical and thermal loads imposed on the piston.
One aspect of the invention provides a piston for an internal combustion engine designed to improve engine efficiency and performance. The piston is free of a cooling gallery along and undercrown surface and thus has a reduced weight and related costs, relative to known piston constructions, but still provides for exceptional cooling to maintain the temperature of the piston within workable limits. The piston comprises a piston body extending along a central longitudinal axis. The piston body has an upper wall forming an upper combustion surface and an annular ring belt depending from the upper combustion surface. The upper combustion surface has first and second portions, the first portion extends annularly along an outer periphery of the upper wall, and the second portion forms a combustion bowl depending radially inwardly from the first portion. The piston body further includes a pair of skirt panels depending from the ring belt, and a pair of pin bosses spaced from one another by the skirt panels providing a pair of laterally spaced pin bores. The undercrown surface is formed on an underside of the upper wall and is located opposite the second portion of the upper combustion surface, radially inwardly of the ring belt. The undercrown surface has an exposed 2-dimensional surface area, as viewed looking along the central longitudinal axis, ranging from 25 to 60 percent of a cross-sectional area defined by a maximum outer diameter of the piston body.
Another aspect of the invention provides a method of constructing a piston which is free of a cooling gallery along an undercrown surface. The method comprises forming a piston body extending along a central longitudinal axis by at least one of machining, forging, and casting. The piston body has an upper wall forming an upper combustion surface and an annular ring belt depending from the upper combustion surface. The upper combustion surface has first and second portions, the first portion extends annularly along an outer periphery of the upper wall, and the second portion forms a combustion bowl depending radially inwardly from the first portion. The piston body further includes a pair of skirt panels depending from the ring belt, and a pair of pin bosses spaced from one another by the skirt panels providing a pair of laterally spaced pin bores. The undercrown surface is formed on an underside of the upper wall and is located opposite the second portion of the upper combustion surface, radially inwardly of the ring belt. The undercrown surface has an exposed 2-dimensional surface area, as viewed looking along the central longitudinal axis, ranging from 25 to 60 percent of a cross-sectional area defined by a maximum outer diameter of the piston body.
These and other aspects, features and advantages of the invention will become more readily appreciated when considered in connection with the following detailed description of presently preferred embodiments and best mode, appended claims and accompanying drawings, in which:
Referring in more detail to the drawings,
The piston body has an upper head or top section providing an upper wall 14, which provides an upper combustion surface 16 that is directly exposed to combustion gasses within the cylinder bore of the internal combustion engine. The upper combustion surface 16 includes an annular first portion 18 formed as a substantially planar surface extending along an outer periphery of the upper wall 14 and a second portion 20 forming a combustion bowl. The second portion 20 of the upper combustion surface 16, which forms the combustion bowl, typically has a non-planar, concave, or undulating surface that depends from the planar first portion 18.
The piston 10 also includes an undercrown surface 24 formed on an underside of the upper wall 14, directly opposite the second portion 20 of the upper combustion surface 16 and radially inwardly of the ring belt 32. The undercrown surface 14 is preferably located at a minimum distance from the combustion bowl and is substantially the surface on the direct opposite side from the combustion bowl. The undercrown surface 24 is defined here to be the surface that is visible, excluding the pin bores 40, when observing the piston 10 straight on from the bottom.
The undercrown surface 24 can also be defined in view of a thickness t of the upper wall 14. The thickness t of the upper wall 14 extends from the upper combustion surface 16 to the underside of the upper wall 14. The portion of the underside of the upper wall 14 which is considered to be the undercrown surface 24 is typically a portion that is located a certain distance away from the second portion 20 of the upper combustion surface 16, and that distance is no more than two times the minimum thickness t of the upper wall 14 along the second portion 20. The undercrown surface 24 can also be define as a portion of the underside of the upper wall 14 which is located at a distance not greater than 10 mm away from the upper combustion surface 16. Accordingly, the undercrown surface 24 is generally form fitting to the combustion bowl of the upper combustion surface 16. The undercrown surface 24 is also openly exposed, as viewed from an underside of the piston 10, and it is not bounded by an enclosed or partially enclosed cooling gallery, or any other features tending to retain oil or a cooling fluid near the undercrown surface 24.
The annular first portion 18 of the upper wall 14 forms an outer periphery of the upper wall 14 and surrounds the second portion forming the combustion bowl, which depends therefrom. Thus, the second portion 20, including the combustion bowl, is recessed below the uppermost first portion 18 of the upper combustion surface 16. The combustion bowl of the second portion 20 also extends continuously through a central axis 30 and across the entire diameter of the piston 10, between opposite sides of the annular first portion 18. The combustion bowl typically comprises a concave surface extending continuously between the opposite sides of the annular first portion 18. Alternatively, the combustion bowl wall can be contoured, for example to provide an upper apex, also referred to as center peak (not shown), which may lie coaxially along the central axis 30 of the piston 10, or may be axially offset relative to the piston central axis 30. The top section of the piston 10 further includes a ring belt 32 that depends from the upper combustion surface 16 to provide one or more ring grooves 34 for receipt of one or more corresponding piston rings (not shown). In the example embodiments, at least one valve pocket 29 having a curved profile is formed in the annular first portion 18 of the upper wall 14. The combustion bowl does not include the valve pockets 29.
The piston body further includes a bottom section including a pair of pin bosses 38 depending generally from the upper wall 14. The pin bosses 38 each have a pin bore 40, preferably bushingless given the steel construction, wherein the pin bores 40 are laterally spaced from one another coaxially along a pin bore axis 42 that extends generally transversely to the central longitudinal axis 30. The pin bosses 38 have generally flat, radially outermost surfaces, referred to as outer faces 43, that are spaced from one another along the pin bore axis 40 a distance PB, shown as being generally parallel with one another. The PB dimension is minimized, thereby maximizing an exposed area of a recessed, generally cup-shaped region, referred to hereafter as undercrown pockets 50.
The undercrown pockets 50 are located radially outwardly of the pin bosses 38 and at least a portion of each pocket 50 forms a portion of the undercrown surface 24. In the example embodiment, the portions of the undercrown pockets 50 forming the portion of the undercrown surface 24 are located opposite the second portion 20 of the upper combustion surface 16 and radially inwardly of the ring belt 32, at a distance of no more than two times a minimum thickness of the upper wall 14, and at a distance of not greater than 10 mm from the upper combustion surface 16.
The undercrown pockets 50 also extend radially outwardly beyond the undercrown surface 24 along an underside surface of the annular first portion 18 of the upper combustion surface 16 and depend from the upper wall 14 along an inner surface of the ring belt 32. These portions of the undercrown pockets 50 are either located outwardly of the second portion 20 of the upper combustion surface 16, at a distance of greater than two times a minimum thickness of the upper wall 14, and/or at a distance of greater than 10 mm from the upper combustion surface 16, and thus they do not form a portion of the undercrown surface 24.
With the 2-dimensinional and 3-dimensional surface area of the pockets 50 being maximized, at least in part due to the minimized distance PB, the cooling caused by oil splashing or being sprayed upwardly from the crankcase against the exposed surface of the undercrown pockets 50 is enhanced, thereby lending to further cooling of the upper combustion surface 16, the undercrown surface 24, as well as a portion of the ring belt 34.
The pin bores 40 each have a concave uppermost load bearing surface, referred to hereafter as uppermost surface 44, disposed near the ring belt 32. As such, the compression height CH is minimized (the compressing height is the dimension extending from the pin bore axis 42 to the upper combustion surface 16). The pin bosses 38 are joined via outer panels, also referred to as struts 46, to diametrically opposite skirt panels, also referred to as skirt panels 48.
The pin bosses 38, skirt panels 48 and struts 46 bound an open region extending from a lowermost or bottom surface 51 of the struts 46 and skirt panels 48 to the undercrown surface 24. In the embodiments of
The open region along the underside of the piston 10 provides direct access to oil splashing or being sprayed from within the crankcase directly onto the undercrown surface 24, thereby allowing the entire undercrown surface 24 to be splashed directly by oil from within the crankcase, while also allowing the oil to freely splash about the wrist pin (not shown), and further, significantly reduce the weight of the piston 10. Accordingly, although not having a typical closed or partially closed cooling gallery, the generally open configuration of the galleryless piston 10 allows optimal cooling of the undercrown surface 24 and lubrication to the wrist pin joint within the pin bores 40, while at the same time reducing oil residence time on the surfaces near the combustion bowl, which is the time in which a volume of oil remains on the surface. The reduced residence time can reduce unwanted build-up of coked oil, such as can occur in pistons having a closed or substantially closed cooling gallery. As such, the piston 10 remains “clean” over extended use, thereby allowing it to remain substantially free of build-up.
Owing to the optimal cooling of the undercrown surface 24 is the percentage of the undercrown surface 24 directly underlying the upper combustion surface 16 that is directly exposed to the splashing and sprayed oil from the crankcase. The undercrown surface 24 of the piston 10 has greater a total surface area (3-dimensional area following the contour of the surface) and a greater projected surface area (2-dimensional area, planar, as seen in plan view) than comparative pistons having a closed or partially closed cooling gallery.
The total exposed surface area, defined as the 3-dimensional area Au3D following the contour of the undercrown surface 24, is an expansive area for contact by cooling oil while the piston 10 is in use. In the example embodiments, the 3-dimensional area Au3D of the undercrown surface 24 is greater than 30 percent of, and typically ranges from 40 to 90 percent of a cross-sectional area AOD defined by the maximum outer diameter OD of the piston 10.
The undercrown surface 24 can also have a projected surface area, defined as the 2-dimensional surface area Au2D seen looking generally along the central longitudinal axis 30 from the bottom of the piston 10 of greater than 25 percent, and typically ranging from 30 to 60 percent of the cross-sectional area defined by the maximum outer diameter OD of the piston 10. More preferably, the 2-dimensional surface area Au2D ranges from 30 to 55 percent of the cross-sectional area defined by the maximum outer diameter OD of the piston 10. As indicated above, a portion of the 2-dimensional surface area Au2D of the undercrown surface 24 is located within the pockets 50. The 2-dimensional surface area Au2D of the undercrown surface 24 can also be measured relative to the 2-dimensional surface area Ac2D of the combustion bowl along the upper combustion surface 16. In the example embodiments, the 2-dimensional surface area Au2D of the undercrown surface 24 ranges from 50 to 125 percent of the 2-dimensional surface area Ac2D of the combustion bowl. In addition, the valve pockets 29 are not included in the 2-dimensional surface area Ac2D of the combustion bowl.
The 3-dimensional surface area Au3D of the undercrown surface 24 can also be measured relative to the 3-dimensional surface area Ac3D of the combustion bowl along the upper combustion surface 16. In the example embodiments, the 3-dimensional surface area Au3D of the undercrown surface 24 ranges from 50 to 120 percent of the 3-dimensional surface area Ac3D of the combustion bowl. As indicated above, a portion of the 3-dimensional surface area Au3D of the undercrown surface 24 is located within the pockets 50.
As an example,
Further yet, the exposed area of the undercrown surface 24 typically has a diameter Du, as shown in
However, the percentages of relative surface areas and relative diameters can vary from the ranges disclosed above while still providing for enhanced cooling. The percentages of relative surface areas and relative diameters of the exposed undercrown surface 24 of the piston 10 are far in excess of conventional pistons, and in some cases, are upwards to three times greater or more. As such, the upper combustion surface 16 can be cooled directly via oil splashing upwardly from the crankcase, which can be coupled with the assistance from oil jets, if desired.
As mentioned above, at least a portion of the undercrown pockets 50 of the piston 10 define at least a portion of the undercrown surface 24, as well as a portion of an underside of the first portion 18 and a portion of an inner surface of the annular ring belt 32. In the example embodiments, the undercrown pockets 50 together have a total 2-dimensional surface area Ap2D ranging from 18 to 35 percent of the cross-sectional area AOD defined by the maximum outer diameter of the piston 10. The undercrown pockets 50 also have a total 3-dimensional area Ap3D ranging from 50 to 85 percent of the cross-sectional area SOD defined by the maximum outer diameter of the piston 10. An example of the 3-dimesnional area Ap3D of the undercrown pockets 50 is also shown in
However, it is noted that the 2-dimensional and 3-dimensional surface areas of the undercrown pockets 50 can vary from the ranges disclosed above while still being able to contribute significantly to the cooling of the regions of the upper combustion surface 16 located directly above the pockets 50.
Another significant aspect of the example pistons 10 shown in
Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that the invention may be practiced otherwise than as specifically described, and that the scope of the invention is defined by any ultimately allowed claims.
This U.S. Continuation-In-Part Application claims the benefit of U.S. Continuation patent application Ser. No. 14/940,416, filed Nov. 13, 2015, which claims the benefit of U.S. Utility patent application Ser. No. 14/535,839, filed Nov. 7, 2014, which claim the benefit of U.S. Provisional Application No. 61/901,287, filed Nov. 7, 2013, and the benefit of U.S. Provisional Application No. 62/011,876, filed Jun. 13, 2014, which are each incorporated herein, by reference, in their entirety.
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Number | Date | Country | |
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Child | 14940416 | US |
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Child | 14988885 | US |