Patent Application
20190257265
This invention relates generally to pistons for internal combustion engines, and methods of manufacturing the same.
Modern heavy duty diesel engines are being pushed towards increased efficiency under emissions and fuel economy legislation. To achieve greater efficiency, the engines must run at higher temperatures. For example, some internal combustion engines are being designed to run hotter, and some types of steel pistons are designed to run at temperatures 100 to 250° C. hotter than standard pistons in some zones.
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. Alternatively, the piston can have a galleryless design and thus has an open undercrown region for exposure to cooling oil. Both the ring belt region and the undercrown surface benefit from cooling action of the circulated oil. However, over time. the circulated oil begins to degrade and oxidize. The oxidation is driven by heating of the oil due to contact with the high temperature piston surfaces, and thus, deposits can form on the surfaces of the piston, also referred to as coking. The increased temperatures of the pistons during operation contributes to the risk of increased coking, especially in the undercrown and land regions of the piston. As the deposit build-up continues, an insulation layer is formed on the respective surfaces. Due to the coking deposits, the cooling effects of the circulated oil can be diminished, which in turn leads to combustion bowl surface oxidation and erosion, as well as over tempering of the surface. As such, the mechanical properties of the piston material are diminished, which can lead to crack formation.
One aspect of the invention provides a piston for an internal combustion engine which includes a coating for mitigating, reducing, or avoiding carbon deposits or coking during operation of the piston in the engine. The piston includes a body portion formed of a ferrous material, and the coating is disposed on the body portion. The body portion includes a crown presenting a combustion surface and an undercrown surface, and a ring belt region depending from the combustion surface. The body portion also includes a pair of pin bosses depending from the crown and spaced from one another by a pair of skirt sections. The coating includes a fluoropolymer and has a thickness of 25 microns to 1 millimeter.
Another aspect of the invention provides a method of manufacturing a piston. The method includes the steps of: providing a body portion formed of a ferrous material. The body portion includes a crown presenting a combustion surface and an undercrown surface, and a ring belt region depending from the combustion surface. The body portion also includes a pair of pin bosses depending from the crown and spaced from one another by a pair of skirt sections. The method further includes disposing a coating on the body portion. The coating includes a fluoropolymer and has a thickness of 25 microns to 1 millimeter.
These and other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
One aspect of the invention provides a piston 20 with a coating 22 for use in an internal combustion engine, such as a heavy duty diesel engine or alternatively a gasoline engine. The coating 22 reduces or avoids coking deposits during operation of the piston 20 in the engine at temperatures ranging from 200 to 400° C. Thus, the piston 20 can provide for improved cooling effects of the circulated oil, which in turn leads to reduced surface oxidation and erosion, as well as reduced tempering of the surface. As such, the mechanical properties of the piston 20 are improved, and crack formation is reduced. Examples of the piston 20 are shown in
According to the example embodiments of
The body portion 24 further includes a ring belt region 36 depending from the combustion surface 32. The ring belt region 36 includes a plurality of ring grooves 36a spaced from one another by lands 36b. The ring belt region 36 is located at an outer diameter of the body portion 24 and extends circumferentially about the center axis A of the body portion 24.
The body portion 24 further includes a pair of pin bosses 38 depending from the crown 30 and spaced from one another by a pair of skirt sections 40. The pin bosses 38 and the skirt sections 40 extend from the crown 30 to the lower end 28, and the pin bosses 38 define a pin bore for receiving a wrist pin (not shown).
According to the example embodiment of
According to the example embodiment of
The coating 22 of the piston 20 is disposed on at least a portion of the ferrous body portion 24. For example, the coating 22 is disposed on at least one of the undercrown surface 34, at least one of the ring grooves 36a, at least one of the lands 36b, at least one of the pin bosses 38, and at least one of the skirt sections 40. In the example embodiments of
As stated above, the coating 22 reduces or avoids the bonding of the carbon deposits on the body portion 24 of the piston 20, also referred to as coking, during operation of the piston 20 in the engine at service temperatures ranging from 200 to 400° C. The coating 22 includes a fluoropolymer and has a thickness of 25 microns to 1 millimeter. The thickness of the coating 22 is measured after the coating 22 is dried and cured. For example, the fluoropolymer of the coating 22 can include polytetrafluoroethylene (PTFE), fluorosilane, fluorocarbon, fluoroplastic resin, and/or perfluoroplastic. According to one embodiment, the coating 22 further includes silicone, polysilane, and/or polysilazane, and the coating 22 may be silicone-based. The coating 22 could alternatively be another non-stick formulation which includes a fluoropolymer. For example, the coating 22 could be hydrocarbon based. In another embodiment the coating 22 includes a thermoset binder. For example, the thermoset can include phenolic, epoxy, polyester, polyamide-imide or any combination of the thermoset resins. The fluoropolymer is added to the uncured thermoset resin(s) and mixed before application to one or more surfaces of the piston 20 followed by curing. Alternatively, the fluoro-polymer can be added to the thermoplastic resin as uncured components and co-polymerized in the curing step of the coating 22. In both methods, the fluoropolymer components segregate to the surface of the coating 22 over time and provide the non-stick effect.
Another aspect of the invention provides a method of manufacturing the piston 20. The method includes providing the body portion 24 formed of a ferrous material. The body portion 24 can include the design described above, or can have a different design.
The method further includes disposing the coating 22 on the body portion 24. The coating 22 includes the fluoropolymer as described above. The step of disposing the coating 22 on the body portion 24 includes disposing the coating 22 on at least one of the following: the undercrown surface 34, at least one ring groove 36a of the ring belt region 36, at least one land 36b of the ring belt region 36, at least one of the pin bosses 38, and at least one of the skirt sections 40. The coating 22 is preferably applied by spraying, dipping, brushing, ink-jet, rolling, pipetting or transfer stamping.
The coating step is preferably a rapid and atmospheric method. According to an example embodiment, the spraying step is conducted using an airbrush dispenser. The spraying should be capable of directing the coating 22 to specific regions of the body portion 24. The method can also include masking a portion or portions of the body portion 24, to prevent the coating 22 from being applied to that portion or portions, during the spraying step. The method can also include moving the body portion 24 relative to the airbrush dispenser during the spraying step. When manufacturing multiple pistons 20, a part handling and manipulation system can be used to pick and place the body portions 24 and move them appropriately in a spray jet. Alternatively a system of linear axis slides or a robot could manipulate the spray gun relative to the body portion 24. The method next includes drying and curing the coating 22. A convection oven or infrared lamps can be used to dry and/or cure the coating 22. The thickness of the coating 22 is 25 microns to 1 millimeter after the drying and curing steps.
The method of manufacturing the coated piston 20 has no need for vacuum chambers or special atmospheres that would be needed in physical vapor deposition or chemical vapor deposition. Thus, the process of manufacturing the coated piston 20 is a production friendly, minimally invasive process. It can fit with current production methods, and the coating 22 could be applied over the top of a finished phosphated piston. Initial testing conducted in an engine run at full power for 25 hours showed coking deposits on the undercrown of non-coated, standard pistons, but the coated piston 20 run in the same test had the coking deposits significantly reduced (by 66%).
Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the following claims. In particular, all features of all claims and of all embodiments can be combined with each other, as long as they do not contradict each other.
