FIELD OF THE DISCLOSURE

The present disclosure generally relates to internal combustion engine piston design, and more particularly to a piston design having insulating air gaps formed by additive manufacturing.

BACKGROUND

A significant portion of the fuel energy used in an internal combustion engine is lost as heat transferred from the combustion chamber to the coolant (e.g., oil). Thus, a reduction in this heat loss through the pistons results in an improvement to the engine's efficiency. It is known that a reduction in the heat transfer through the piston often results in an increase in exhaust temperatures, which can be beneficial for the turbine, after-treatment system and waste heat recovery system.

One approach to reduce heat loss through pistons is to include air gaps (or pockets) below the crown of the pistons to provide a layer of insulation between the high temperatures at the crown and the piston cooling gallery. While such air gaps may be created by welding an upper portion of the piston to a lower portion of the piston, a relatively large height piston is needed to facilitate the welding process. The engine industry, however, is moving toward smaller compression height pistons because they result in reduced friction and more compact engine packaging. As such, piston manufacturers face a difficult challenge in providing short compression height pistons with air gaps formed using conventional manufacturing processes.

It is also known that decreases in heat transfer through the piston result in temperature increases at the piston crown. If the crown temperatures exceed the oxidation limit of the piston materials, piston failure may result. Thus, an improved approach is needed for providing short compression height pistons with air gaps for reduced heat transfer through the pistons and an anti-oxidation protective coating on the crown surface.

SUMMARY

According to one embodiment, the present disclosure provides a piston, comprising: a skirt having an upper body portion; and a crown formed on the upper body portion by an additive manufacturing process, the crown including at least one air gap. In one aspect of this embodiment, the at least one air gap is formed and positioned to reduce heat transfer from combustion to at least one cooling gallery formed in the piston. In a variant of this aspect, the cooling gallery is formed between the crown and the skirt adjacent a perimeter of the piston. In another aspect, the additive manufacturing process includes laser metal deposition. In yet another aspect, the at least one air gap includes an outer peripheral air gap and a central air gap. In a variant of this aspect, the crown includes an upper surface, a bowl rim, an outer wall and a central wall, the outer peripheral air gap being formed between an inner surface of the outer wall and the upper body portion of the skirt, and the central air gap being formed between the central wall and the upper body portion of the skirt. Another variant further comprises an anti-oxidation coating applied to at least one of the upper surface of the crown, the bowl rim, the inner surface of the outer wall, and the upper surface of the central wall. In a further variant, the anti-oxidation coating includes at least one of an aluminum chrome oxide coating or a chrome oxynitride coating. In still a further variant, the anti-oxidation coating has a thickness of less than 50 micrometers. In another variant of this aspect, the anti-oxidation coating has a thickness of between 5 micrometers and 10 micrometers.

In another embodiment, the present disclosure provides a method of forming a piston, comprising: providing a skirt having an upper body portion; and forming a crown on the upper body portion by an additive manufacturing process, the crown including at least one air gap formed and positioned to reduce heat transfer from combustion to at least one cooling gallery formed in the piston. In one aspect of this embodiment, forming a crown on the upper body portion by an additive manufacturing process includes using a laser metal deposition process. In another aspect, the cooling gallery is formed between the crown and the skirt adjacent a perimeter of the piston. In another aspect, the at least one air gap includes an outer peripheral air gap and a central air gap. In a variant of this aspect, forming a crown on the upper body portion by an additive manufacturing process includes forming an upper surface of the crown, a bowl rim of the crown, an outer wall of the crown and a central wall of the crown, the outer peripheral air gap being formed between an inner surface of the outer wall and the upper body portion of the skirt, and the central air gap being formed between the central wall and the upper body portion of the skirt. Another variant further comprises applying an anti-oxidation coating to at least one of the upper surface of the crown, the bowl rim, the inner surface of the outer wall, and the upper surface of the central wall. In a further variant, the anti-oxidation coating includes at least one of an aluminum chrome oxide coating or a chrome oxynitride coating. In yet another variant, the anti-oxidation coating has a thickness of less than 50 micrometers.

In yet another embodiment, the present disclosure provides a piston prepared by a process, comprising: providing a skirt having an upper body portion; and forming a crown on the upper body portion by an additive manufacturing process, the crown including at least one air gap. In one aspect of this embodiment, the crown is formed and positioned to reduce heat transfer from combustion to at least one cooling gallery formed in the piston. In another aspect, the at least one air gap includes an outer peripheral air gap and a central air gap. In yet another aspect, forming a crown on the upper body portion by an additive manufacturing process includes forming an upper surface of the crown, a bowl rim of the crown, an outer wall of the crown and a central wall of the crown, the outer peripheral air gap being formed between an inner surface of the outer wall and the upper body portion of the skirt, and the central air gap being formed between the central wall and the upper body portion of the skirt.

In yet another embodiment, the present disclosure provides a piston, comprising: a skirt having an upper body portion; and a crown disposed on the upper body portion; wherein the skirt and the crown are formed by an additive manufacturing process, the crown including at least one air gap. In one aspect of this embodiment, the crown is formed and positioned to reduce heat transfer from combustion to at least one cooling gallery formed in the piston.

