Patent Description:
The present invention relates generally to a piston ring for providing a seal between the piston and a cylinder of the engine, an assembly including the piston ring between the piston and cylinder, and methods of manufacturing the same.

Typical internal combustion engines are provided with at least one piston assembly which reciprocates within a cylinder of an engine block. In general, each piston assembly includes a piston body with a plurality of ring grooves, each of which typically receives and operably supports a piston ring. In operation, the piston rings remain in the ring grooves and travel with their respective piston bodies in a reciprocating motion within cylinders of an engine block. Among other things, the pistons rings function to seal combustion gasses in a combustion chamber above the piston body, to transfer heat from the piston body to the cylinder wall, to restrict the passage of oil from the crank case to the combustion chamber and to provide a generally uniform oil film on the cylinder wall. Piston rings are oftentimes coated to reduce wear and friction, and thus improve performance. Reduced manufacturing cost is also desired.

<CIT> discloses a piston ring according to the preamble of claim <NUM>.

One aspect of the present invention provides a piston ring for an engine. The piston comprises a body portion including a running surface, a flank surface, and a transition surface between the running surface and the flank surface. The running layer is disposed over the running surface and over at least a portion of the transition surface. The running layer is formed of chromium nitride. A flank layer is disposed over the flank surface and over at least a portion of the transition surface. The flank layer is formed of chromium. A portion of the flank layer and a portion of the running layer overlap one another. The running layer and the flank layer provide outermost surfaces of the piston ring.

Another aspect of the invention provides a piston assembly comprising a piston including a ring groove, and a piston ring is disposed in the ring groove of the piston. The piston ring includes a running surface, a flank surface, and a transition surface between the running surface and the flank surface. The piston ring includes a running layer disposed over the running surface and over at least a portion of the transition surface. The running layer is formed of chromium nitride. The piston ring also includes a flank layer disposed over the flank surface and over at least a portion of the transition surface. The flank layer is formed of chromium. A portion of the flank layer and a portion of the running layer overlap one another. The running layer and the flank layer provide outermost surfaces of the piston ring, and the overlapping portion of the flank layer and the running layer are spaced from the ring groove of the piston.

A method of manufacturing a piston ring is also provided. The piston ring comprises a body portion including a running surface, a flank surface, and a transition surface between the running surface and said flank surface. The method includes applying a running layer over the running surface and over at least a portion of the transition surface by a physical vapor deposition process; and applying a flank layer over the flank surface and over at least a portion of the transition surface by a galvanic deposition process such that a portion of the flank layer overlaps a portion of the running layer.

These and other features and 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 coated piston ring <NUM> designed for a piston <NUM> of an internal combustion engine. <FIG> and <FIG> show a portion of the piston ring <NUM> disposed around the piston <NUM> and engaging a cylinder <NUM> of the internal combustion engine according to example embodiments. The piston ring <NUM> is disposed in a ring groove <NUM> of the piston <NUM> and provides a seal between the piston <NUM> and the cylinder <NUM>.

As shown in the Figures, the piston ring <NUM> includes a body portion <NUM> formed of metal, and preferably an iron-based material. According to example embodiments, the iron-based material is cast iron or steel. The body portion <NUM> has a generally circular or oval shape and extends around a center axis A. The body portion <NUM> of the piston ring <NUM> includes an upper flank surface <NUM> for engaging an upper surface <NUM> of the ring groove <NUM>, a lower flank surface <NUM> for engaging a lower surface <NUM> of the ring groove <NUM>, and a running surface <NUM> for engaging the cylinder <NUM>. The running surface <NUM> is typically parallel to the center axis A, and the upper and lower flank surfaces <NUM>, <NUM> are typically transverse or generally perpendicular to the center axis A. For example, the transverse flank surfaces <NUM>, <NUM> can extend at an angle relative to the center axis A, as shown in the <FIG> and <FIG>. The body portion <NUM> also preferably includes at least one transition surface <NUM> between the lower flank surface <NUM> and the running surface <NUM>.

The body portion <NUM> of the piston ring <NUM> can have various different designs. In the example embodiment of <FIG>, the body portion <NUM> includes the lower flank surface <NUM> extending generally parallel to the lower surface <NUM> of the ring groove <NUM>, the upper flank surface <NUM> extending generally parallel to the upper surface <NUM> of the ring groove <NUM>, and a single transition surface <NUM>, wherein the majority of the transition surface <NUM> extends at an angle from the lower flank surface <NUM> toward the running surface <NUM>. The body portion <NUM> includes a first sharp corner <NUM> between the transition surface <NUM> and the lower flank surface <NUM>, and the transition surface <NUM> rounds as it approaches the running surface <NUM>. In this case, the round portion of the transition surface <NUM> presents a convex shape. During operation of the piston <NUM> in the internal combustion engine, the transition surface <NUM> is spaced from both the cylinder <NUM> and the lower surface <NUM> of the ring groove <NUM>. A portion of the lower flank surface <NUM> is also disposed outwardly of the ring groove <NUM>.

In the example embodiment of <FIG>, the body portion <NUM> includes the lower flank surface <NUM> extending generally parallel to the lower surface <NUM> of the ring groove <NUM>, the upper flank surface <NUM> extending generally parallel to the upper surface <NUM> of the ring groove <NUM>, and the transition surface <NUM>, wherein the majority of the transition surface <NUM> extends at an angle from the lower flank surface <NUM> toward the running surface <NUM>. According to this embodiment, the transition surface <NUM> rounds as it approaches both the lower flank surface <NUM> and the running surface <NUM>. However, the transition surface <NUM> presents a concave shape as it approaches the lower flank surface <NUM>, and a second sharp corner <NUM> is located between the transition surface <NUM> and the lower flank surface <NUM>. The round portion of the transition surface <NUM> which approaches the running surface <NUM> presents a convex shape. During operation of the piston <NUM> in the internal combustion engine, the transition surface <NUM> is spaced from both the cylinder <NUM> and the lower surface <NUM> of the ring groove <NUM>. A portion of the lower flank surface <NUM> is also disposed outwardly of the ring groove <NUM>.

In the example embodiment of <FIG>, the body portion <NUM> includes the lower flank surface <NUM> extending generally parallel to the lower surface <NUM> of the ring groove <NUM>, the upper flank surface <NUM> extending generally parallel to the upper surface <NUM> of the ring groove <NUM>, and the transition surface <NUM>, wherein the majority of the transition surface <NUM> curves from the lower flank surface <NUM> to the running surface <NUM>. In this case, the round transition surface <NUM> presents a convex shape. During operation of the piston <NUM> in the internal combustion engine, the transition surface <NUM> is spaced from both the cylinder <NUM> and the lower surface <NUM> of the ring groove <NUM>.

As best shown in <FIG>, <FIG>, a coating <NUM> is applied to the body portion <NUM> of the piston ring <NUM> to reduce wear and friction, and thus improve performance of the piston <NUM> in the internal combustion engine. The coating <NUM> includes at least two layers <NUM>, <NUM>, including a flank layer <NUM> disposed over the lower flank surface <NUM> of the piston ring <NUM> and a running layer <NUM> disposed over the running surface <NUM> of the piston ring <NUM>. The flank layer <NUM> and the running layer <NUM> both provide an outermost surface of the coating <NUM> and also an outermost surface of the piston ring <NUM>. According to one embodiment, the flank layer <NUM> is disposed directly on the lower flank surface <NUM> and the running layer <NUM> is disposed directly on the running surface <NUM>. However, the coating <NUM> can optionally include one or more additional layers beneath the flank layer <NUM> and/or the running layer <NUM>.

According to the exemplary embodiments, the running layer <NUM> is formed of chromium nitride. The running layer <NUM> is applied on the running surface <NUM>, or applied to another layer disposed on the running surface <NUM>, by physical vapor deposition (PVD). As shown in the Figures, the running layer <NUM> is also applied to at least a portion of the transition surface <NUM>. In the embodiment of <FIG>, the running layer <NUM> is applied to the running surface <NUM> and a portion of the transition surface <NUM>. In the embodiment of <FIG>, the running layer <NUM> is applied to the running surface <NUM> and the entire transition surface <NUM>. In the embodiment of <FIG>, the running layer <NUM> is applied to the running surface <NUM> and the entire transition surface <NUM>.

According to the exemplary embodiments, the flank layer <NUM> is formed of chromium. The flank layer <NUM> is applied to the lower flank surface <NUM>, or applied to another layer disposed on the lower flank surface <NUM>, preferably by an economical process, such as galvanic deposition. As shown in the Figures, the flank layer <NUM> can be applied to a portion of the transition surface <NUM>. The flank layer <NUM> is also applied to a portion of the running layer <NUM> located on or over the transition surface <NUM>. In the embodiment of <FIG>, the flank layer <NUM> is applied to the lower flank surface <NUM> and a portion of the running layer <NUM>. According to this embodiment, the flank layer <NUM> is applied over the entire transition surface <NUM> and may be applied over a very small portion of the running surface <NUM>. In the embodiment of <FIG>, the flank layer <NUM> is applied to the lower flank surface <NUM> and a small portion of the running layer <NUM>. According to this embodiment, the flank layer <NUM> is applied over a small portion of the transition surface <NUM>. In the embodiment of <FIG>, the flank layer <NUM> is applied to the lower flank surface <NUM> and a portion of the running layer <NUM>. According to this embodiment, the flank layer <NUM> is applied over a majority of the transition surface <NUM>.

As shown in the Figures, a portion of the flank layer <NUM> overlaps the running layer <NUM> which is formed by PVD, and the flank layer <NUM> is preferably disposed outward of the running layer <NUM>. As previously discussed an overlapping portion <NUM> of the flank layer <NUM> and the running layer <NUM> is located along the transition surface <NUM> of the body portion <NUM> of the piston ring <NUM>. Preferably, no additional layers are disposed outward of the running layer <NUM> or the flank layer <NUM>.

According to example embodiments, the piston ring <NUM> also includes the transition surface <NUM> between the upper flank surface <NUM> and the running surface <NUM>. Thus, the piston ring <NUM> can include the flank layer <NUM> on the upper flank surface <NUM> instead of, or in addition to, on the lower flank surface <NUM>. For example, as shown in <FIG> and <FIG>, the upper and lower halves of the piston ring <NUM> can be mirror images of one another. Alternatively, the piston ring <NUM> can be flipped so that the lower flank surface <NUM> is at the top of the piston ring <NUM>.

During operation of the engine, the coated piston ring <NUM> is disposed in the ring groove <NUM> of the piston <NUM> and slides along the cylinder <NUM>. A majority of the running layer <NUM> engages the cylinder <NUM> during operation, and a majority of the flank layer <NUM> engages the lower surface <NUM> of the ring groove <NUM> during operation. A small portion of the running surface <NUM> and a small portion of the running layer <NUM> may be spaced from the cylinder <NUM>, as shown in <FIG> and <FIG>. Typically, a portion of the lower flank surface <NUM> and a portion of the flank layer <NUM> is located outward of the lower surface <NUM> of the ring groove <NUM>. The overlapping portion <NUM> of the flank layer <NUM> and the running layer <NUM> is preferably located outward of the lower surface <NUM> of the ring groove <NUM> and is spaced from the cylinder <NUM> during operation. Alternatively, a majority of the overlapping portion <NUM> of the flank layer <NUM> and the running layer <NUM> is preferably located outward of the lower surface <NUM> of the ring groove <NUM> and is spaced from the cylinder <NUM> during operation. Thus, the overlapping portion <NUM> does not engage the cylinder <NUM> or ring groove <NUM> and thus is not subject to significant wear and friction during operation.

It has been observed that the coating <NUM> experiences less friction and exhibits less wear after use in an engine relative to comparative piston rings. The cost to manufacture the coated piston ring <NUM> is also typically lower than comparative costed piston rings due to the PVD and galvanic methods used to apply the running layer <NUM> and the flank layer <NUM>. More specifically, the running layer <NUM> experiences low friction and exits low wear and is also resistant to bore scoring. The flank layer <NUM> is applied cost effectively and experiences less friction and wear relative to comparative coated piston rings, such as nitride rings.

Claim 1:
A piston ring (<NUM>), comprising a body portion (<NUM>)
including a running surface (<NUM>), a flank surface (<NUM>), and a transition surface (<NUM>) between said running surface and said flank surface;
a running layer (<NUM>) disposed over said running surface and over at least a portion of said transition surface, said running layer being formed of chromium nitride;
a flank layer (<NUM>) disposed over said flank surface and over at least a portion of said transition surface, said flank layer being formed of chromium; and
a portion of said flank layer and a portion of said running layer overlapping one another, characterised by
said running layer and said flank layer providing outermost surfaces of said piston ring.