Piston assembly and method of manufacture

A piston assembly having a piston and a piston ring. The ring mates to the piston in a groove on the outer surface of the piston. The ring includes two side walls that connect between inner and outer peripheral walls. The side walls converge outwardly at different angles from the inner peripheral wall to the outer peripheral wall. The angles are different to produce a twist feature of the ring within the piston groove to generate a better seal by the ring. The groove of the piston is generally tapered and has top and bottom walls converging at angles approximately equal to the angles of the side walls of the ring. A method of manufacturing the piston assembly includes forming first and second side walls having first and second angles by outwardly converging from the inner peripheral wall to the outer peripheral wall.

TECHNICAL FIELD

The present invention relates to a piston assembly for an internal combustion engine and in particular to a piston assembly and method of manufacture having a piston ring with two side walls converging at dissimilar angles.

BACKGROUND OF THE INVENTION

There are traditionally two different types of piston rings, oil control rings and compression rings. Typically, the piston assembly includes one or more compression rings to generate a seal between the outer surface of the piston and an inner surface of the liner of the combustion chamber. An inner end of the compression ring fits into a tapered groove on the outer surface of the piston while an outer wall of the ring makes contact with the inner surface of the liner. The outer wall of the compression ring generates the seal in the space between the piston and the liner to prevent high-pressure combustion gases and air from escaping.

Typical prior art piston assemblies are shown inFIGS. 1aand1b. The assembly10includes a piston12and a piston ring14. The seal formed by the piston ring14prevents combustion gases and air from escaping the combustion chamber with each stroke of the piston12. The piston ring14includes an inner peripheral wall20, an outer peripheral wall22, a first side wall24and a second side wall26. The first side wall24and the second side wall26extend from the inner peripheral wall20to the outer peripheral wall22. As shown, the prior art piston rings14have angles, A, generated by the outward convergence of the side walls24,26. In the prior art, the angles, A, are equal, for example, each angle, A, would be approximately 7.5 degrees.

To improve the seal of the ring14, manufacturers have found it desirable to twist the ring14within a tapered groove30of a piston12. Twisting the ring14causes an edge28of the outer peripheral wall22of the ring14to bear against a liner (not shown) with an increased force as compared to the rest of the outer peripheral wall22. This increased force on the edge28of the outer peripheral wall22generates a more effective seal and prevents leakage of gases, air and lubricating-oils between the liner and the outer peripheral wall22. Furthermore, twisting the ring14within the groove30reduces the clearance between the ring14and the groove30to provide continuity of the seal. To twist the ring14, traditionally the first side wall24is beveled to generate an intermediate wall, B. The intermediate wall, B permits the ring14to twist within the tapered piston groove30and provide a better seal when contacting the liner and the piston12.

To manufacture the conventional piston ring14with the beveled intermediate wall, B, and the resultant twist feature, the piston ring14is first machined to generate the two side walls24,26at equal angles, A. Typically to produce the beveled intermediate wall, B, an additional machining process is necessary to remove the material from the first side wall24. This additional machining process is time consuming. Alternatively, other techniques for generating the beveled intermediate wall, such as making the ring14from near net shape wire to include the beveled intermediate wall, B, are commonly used in the industry.

SUMMARY OF THE INVENTION

The inventors of the present invention have recognized these and other problems associated with traditional piston assemblies described above. To this end, the inventors have developed a piston assembly including a piston and a piston ring having the twist feature without the need for the beveled intermediate wall.

Specifically, the invention comprises a piston assembly comprising a ring and a piston. The ring has inner and outer peripheral walls along with first and second side walls. The first side wall of the ring converges outwardly at a first angle from the inner peripheral wall to the outer peripheral wall. The second side wall of the ring also converges outwardly from the inner peripheral wall to the outer peripheral wall, but at a second angle that is different than the first angle.

The invention also describes a method of manufacture for a piston assembly. First, the first side wall is formed having a first angle outwardly converging from the inner peripheral wall to the outer peripheral wall of the piston ring. Next, the second side wall is formed having a second angle outwardly converging from the inner peripheral wall to the outer peripheral wall, wherein the first angle is different than the second angle.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As seen inFIGS. 2 and 3, a piston assembly is generally shown at100. Similar to the prior art, the assembly100includes a piston112and a piston ring114. The piston assembly100is housed within a combustion chamber116of an internal combustion engine (not shown). Within the combustion chamber116is a cylinder liner118. The ring114surrounds the piston112and contacts the cylinder liner118to form a seal. The piston ring114includes an inner peripheral wall120, an outer peripheral wall122, a first side wall124and a second side wall126. In accordance with the invention, the first side wall124outwardly converges from the inner peripheral wall120to the outer peripheral wall122. The intersection of the inner peripheral wall120and the first side wall124forms a first angle, A1. Similarly, the second side wall126also outwardly converges from the inner peripheral wall120to the outer peripheral wall122and the intersection of the inner peripheral wall120and the second side wall126forms a second angle, A2. Additionally, both the first side wall124and the second side wall126are linear and approximately equal in length.

In contrast to the prior art, the present invention has the first angle, A1, different from the second angle, A2. Preferably, the first angle, A1, is different than the second angle, A2, by at least one degree. It has been found that the greater the difference between the first angle, A1, and the second angle, A2, the greater the twisting feature that is produced. For example, the first angle, A1, would be approximately twelve degrees and the second angle, A2, would be approximately three degrees. The angles of approximately twelve degrees and approximately three degrees are a working example and the invention is in no way limited to these angle measurements. The difference between the first angle, A1, and the second angle, A2, produces a twisting feature of the piston ring114as best shown inFIG. 3. The twisting feature forces an edge128of the outer peripheral wall122to bear against the liner118and provides an effective seal to prevent gases and air from escaping. Unlike the prior art, the dissimilar first angle, A1, and second angle, A2, produce this twisting feature, therefore eliminating the need to create an intermediate wall, B, of the traditional prior art piston rings.

The piston112further includes a groove130that circumferentially surrounds an outer surface132of the piston112. The groove130receives the piston ring114to create the piston assembly100. The groove130has a top wall134and a bottom wall136. The top wall134extends from a base138of the groove130to the outer surface132of the piston112at an angle approximately equal to the first angle, A1, of the piston ring114. Similarly, the bottom wall136extends from the base138to the outer surface132at an angle approximately equal to the second angle, A2.

The present invention is also directed toward the method of manufacturing the piston assembly100. First, the first side wall124is formed having the first angle, A1. The first side wall124forms the first angle, A1, by outwardly converging from the inner peripheral wall120to the outer peripheral wall122. Similarly, the second side wall126is formed having the second angle, A2by outwardly converging from the inner peripheral wall120to the outer peripheral wall122. The first angle, A1, and the second angle, A2, are different. Finally, the ring114is inserted into the groove130of the piston112to form the piston assembly100.

It should be understood that the aforementioned and other various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.