Patent Application
20130133609
1. Technical Field
This invention relates generally to internal combustion engines, and more particularly to pistons and their method of construction.
2. Related Art
Engine manufacturers are encountering increasing demands to improve engine efficiencies and performance, including, but not limited to, improving fuel economy, improving fuel combustion, reducing oil consumption, and increasing the exhaust temperature for subsequent use of the heat within the vehicle. In order to achieve these goals, the engine running temperature in the combustion chamber needs to be increased. However, while desirable to increase the temperature within the combustion chamber, it remains necessary to maintain the piston at a workable temperature. As such, it is known to incorporate outer and inner cooling galleries, both open and closed, within the piston head through which engine oil is circulated to reduce the operating temperature of the piston head. The outer cooling galleries typically circulates about an upper land of the piston including a ring groove region while the inner cooling gallery is typically beneath an upper combustion surface of the piston head, commonly referred to as undercrown, which commonly includes a recessed combustion bowl. As such, both the ring belt region and the combustion surface benefit from cooling action of the circulated oil. However, over time the circulated oil begins to degrade and oxidize as a result of contacting the high temperature surfaces, and thus, carbon deposits form on the inner surfaces of the upper land and undercrown. As the carbon build-up continues, an insulation layer is formed on the respective surfaces. As such, the cooling effects of the circulated oil are diminished, which in turn leads to surface oxidation and erosion, as well as over tempering of the upper land and combustion surface regions. As such, the mechanical properties of the piston material are diminished, which can lead to crack formation, particularly as high stressed regions, such as a combustion bowl rim.
A piston constructed in accordance with this invention overcomes the aforementioned disadvantages brought on by the formation of carbon build-up by reducing the tendency for oil deposits to accumulate surfaces contacted by cooling oil. As such, a piston constructed in accordance with this invention realizes enhanced running efficiencies, maintains the strength and durability of the base material throughout use and provides an enhanced useful operating life.
In accordance with one aspect of the invention, a piston for an internal combustion engine is provided. The piston includes a piston body having an upper combustion surface configured for direct exposure to combustion gases within a cylinder bore with an undercrown surface located beneath the upper combustion surface. The piston body also includes a ring belt region configured for receipt of at least one piston ring adjacent the upper combustion surface with a cooling gallery configured radially inwardly and in substantial radial alignment with the ring belt region. The piston further includes a non-stick coating material bonded to at least one of the undercrown surface and at least a portion of the cooling gallery, wherein the non-stick coating material inhibits the build-up of carbon deposits thereon.
In accordance with another aspect of the invention, the piston body includes an upper crown constructed of a first piece of material and a lower crown constructed from a second piece of material separate from the upper crown. The upper crown is fixed to the lower crown and the non-stick coating material is bonded to at least one of the upper crown and lower crown.
In accordance with another aspect of the invention, the non-stick coating material is bonded to the upper crown and the lower crown is free of the non-stick coating material.
In accordance with another aspect of the invention, both the cooling gallery and the undercrown surface have the non-stick coating material bonded thereto.
In accordance with yet another aspect of the invention, a method of constructing a piston for an internal combustion engine is provided. The method includes the following: forming a piston body having an upper combustion surface configured for direct exposure to combustion gases within a cylinder bore and an undercrown surface beneath the upper combustion surface; forming a ring belt region configured for receipt of at least one piston ring adjacent the upper combustion surface; forming a cooling gallery radially inwardly and in substantial radial alignment with the ring belt region; and bonding a non-stick coating material to at least one of the undercrown surface and at least a portion of the cooling gallery, the non-stick coating material being resistant to the build-up of carbon deposits thereon.
In accordance with another aspect of the invention, the method includes keeping the lower crown free of the non-stick coating material.
In accordance with another aspect of the invention, the method includes bonding the non-stick coating material to the undercrown surface and at least a portion of the cooling gallery.
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 12 has an upper crown region 26 and a lower crown region 28. The lower crown region 28 provides a pair of pin bosses 30 depending from the upper crown region 26 to provide laterally spaced pin bores 32 coaxially aligned along a pin bore axis 34 that extends generally transverse to the central longitudinal axis 14. The pin bosses 30 are joined to laterally spaced skirt portions 36 via strut portions 38. The skirt portions 36 are diametrically spaced from one another across opposite sides the pin bore axis 34 and have convex outer surfaces contoured for cooperation within the cylinder bore to maintain the piston 10 in a desired orientation as it reciprocates through the cylinder bore.
The upper combustion surface 16 is represented as having a recessed combustion bowl 40 to provide a desired gas flow with the cylinder bore. At least in part due to the combustion bowl 40, relatively thin regions of piston body material are formed between the combustion bowl 40, the cooling gallery 22 and the undercrown surface 18. As such, in use, these regions need to be properly cooled, such as via oil flowing through the cooling gallery 22 and against the undercrown surface 18 with a central gallery region between the pin bosses 30. The undercrown cooling could be provided by oil splashes, oriented cooling oil jets or via oil within the central gallery region. Further, an outer wall 42 of the upper crown region 26 extends downwardly from the upper combustion surface 16. The outer wall 42 is formed having at least one, and shown as a plurality of annular ring groove 44 in the ring belt region 20 for receipt of corresponding piston rings (not shown), wherein the rings typically float freely within their respective ring groove 44. As with the aforementioned relatively thin regions, the annular wall extending between the cooling gallery 22 and the ring belt region 20 is relatively thin, and thus, also needs to be properly cooled during use.
To facilitate proper cooling of the upper combustion surface 16, including the combustion bowl 40, and the ring belt region 20 during use over an extended useful life of the piston 10, the non-stick coating material 24 is bonded to at least a portion of surface bounding the cooling gallery 22 and also to the undercrown surface 18. The non-stick coating material 24 is selected from materials that resist the build-up of carbon thereon, including from the group consisting of: chrome, chrome-diamond, nickel, diamond-like coating, chrome-nitride, ceramic and polymer materials. In the embodiment shown in
In addition to the cooling gallery 22 having a layer of the non-stick coating material 24 bonded thereto, the undercrown surface 18 is shown having a layer of the non-stick coating material 24 bonded thereto and extending completely therealong. As such, carbon deposits are prevented from accumulating on the undercrown surface 18, thereby preventing an insulation layer of carbon deposits from forming that would otherwise inhibit the cooling effectiveness of the oil splashing against the undercrown surface 18. Thus, by allowing proper cooling of the upper combustion surface 16, including the entire combustion bowl 40, the material of the piston body 12 in this region is also prevented from becoming weakened via unintended tempering. Accordingly, the material of the upper combustion surface 16 retains its high strength and resistance to crack propagation.
A piston 110 constructed in accordance with another aspect of the invention is shown in
The piston body 112 has an upper part, referred to as an upper crown region 126 and a lower part, referred to as a lower crown region 128 extending to a pair of pin bosses 130 having laterally spaced pin bores 132. Unlike the piston 10 discussed above, the upper and lower crown regions 126, 128 are constructed from separate pieces of material and subsequently fixed to one another, such as via a welding or other joining process.
A first weld joint 50 unites a portion of the separately made upper and lower crown regions 126, 128 of the piston 110. The first weld joint 50 extends through an upstanding wall of a combustion bowl 140 above an annular valley 52 of the combustion bowl 140. Thus, the first weld joint 50 is open to the combustion bowl 140 above the valley 52. In addition to the first weld joint 50 extending through the wall of the combustion bowl 140, a second weld joint 54 extends through an outer wall 142 in a ring belt region 120. The upper crown region 126 may thus include a pair of upper joining surfaces, including a radially inner, downwardly facing joining surface 56 and a radially outer, downwardly facing upper joining surface 57 of the ring belt region 120. Meanwhile, the lower crown region 128 may thus include a pair of lower joining surfaces, including a radially inner, upwardly facing lower surface 58 and a radially outer, upwardly facing lower joining surface 59. The associated lower and upper joining surfaces 56, 57; 58, 59 may be united by a selected joining process, such as induction welding, friction welding, resistance welding, charge carrier rays, electron beam welding, laser welding, stir welding, brazing, soldering, hot or cold diffusion, etc.
The upper crown region 126 provides an upper portion of the cooling gallery 122, having a generally U-shape in cross-section taken along a central longitudinal axis 114 of the piston 110. The lower crown region 128 provides a lower portion of the cooling gallery 122, having a generally U-shape in cross-section taken along the central longitudinal axis 114 and also the wall of the upper combustion surface 116 and undercrown surface 118. Accordingly, prior to joining the upper crown region 126 to the lower crown region 128, the non-stick coating material 124 can be bonded to the desired surfaces of the separate upper and lower parts 126, 128, including the undercrown surface 118 and/or one or both of the generally U-shaped surfaces bounding the cooling gallery 122, shown in
A piston 210 constructed in accordance with another aspect of the invention is shown in
A piston 310 constructed in accordance with another aspect of the invention is shown in
The piston body 312, as discussed for the piston body 112 of
A first weld joint 350 unites a portion of the separately made upper and lower crown regions 326, 328 of the piston 310. However, unlike the piston 110, the first weld joint 350 does not extend through an upstanding wall of a combustion bowl 340 above an annular valley 352 of the combustion bowl 340, but rather, the first weld joint 350 is formed beneath the combustion bowl 340. The combustion bowl 340 is formed entirely of the material of the upper crown region 326, including the upstanding wall of the combustion bowl. In addition to the first weld joint 350, a second weld joint 354 extends through an outer wall 342 in a ring belt region 320. The upper crown region 326 may thus include a pair of upper joining surfaces, including a radially inner, downwardly facing joining surface 356 extending below the combustion bowl 340 and a radially outer, downwardly facing upper joining surface 357 within the ring belt region 320. Meanwhile, the lower crown region 328 may thus include a pair of lower joining surfaces, including a radially inner, upwardly facing lower surface 358 and a radially outer, upwardly facing lower joining surface 359. The associated lower and upper joining surfaces 356, 357; 358, 359 may be united by a selected joining process, such as induction welding, friction welding, resistance welding, charge carrier rays, electron beam welding, laser welding, stir welding, brazing, soldering, hot or cold diffusion, etc.
The upper crown region 326 provides an upper portion of the cooling gallery 322, having a generally U-shape in cross-section taken along a central longitudinal axis 314 of the piston 310. The lower crown region 328 provides a lower portion of the cooling gallery 322, having a generally U-shape in cross-section taken along the central longitudinal axis 314. Accordingly, prior to joining the upper crown region 326 to the lower crown region 328, the non-stick coating material 324 can be bonded to the desired surfaces of the separate upper and lower parts 326, 328, including the undercrown surface 318 and/or one or both of the generally U-shaped surfaces bounding the cooling gallery 322, shown in
Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.
