Two-piece piston assembly

Details Two-piece piston assembly Two-piece piston assembly

1999-08-31

2001-11-20

Ryznic, John E. (Department: 3745)

Expansible chamber devices

Piston

With separable means for pivotally mounting connecting rod...

C092S208000, C092S224000

Reexamination Certificate

active

06318243

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a two-piece piston assembly, and more particularly to a two-piece piston assembly which improves the efficiency of an internal combustion engine.
BACKGROUND OF THE INVENTION
Traditionally, pistons used in internal combustion engines (ICE) have been of a unitary construction. These pistons have been made from cast iron or steel. As fuel economy has become a more significant factor in ICE design, engine makers have had to develop lighter weight pistons capable of operating at higher temperatures for more efficient engines. These efforts have typically involved two different approaches; the use of lighter weight materials or the use of materials having higher melting temperatures.
The typical choice for a lighter weight material to replace cast iron or steel is aluminum. Aluminum has a lower density and is easily machinable. Aluminum also has high thermal conductivity and is corrosion resistant. Unfortunately, aluminum has lower yield strength than cast iron or steel at the normal operating temperatures of pistons.
The second approach to solving this problem typically involves the use of a material with a higher melting point. The operating temperature of an engine is increased by using higher melting point materials. The relationship between high operating temperatures and efficiency is well understood by those skilled in the art. Unfortunately, higher melting point materials are typically more expensive than cast iron or steel, or cannot be fabricated to solve the problem in a cost-efficient manner.
As a result, the two-piece piston assembly has been developed as a compromise. The two-piece assembly allows two different materials to be used in the construction of a piston. The design usually has a lighter weight, the side being composed of a lighter material with a heavier, more thermally stable, crown material. The two-piece piston assembly allows the vehicle manufacturer to obtain both advantages of the original solutions to this problem and optimize the performance of ICE's.
The present invention is particularly useful for conventional automobile ICE's but may also be used with diesel ICE's.
The present invention employs the concept of a two-piece piston assembly and introduces further refinements into the assembly. The invention teaches the proper selection of joining surfaces to couple the two pieces of the piston assembly to reduce weight. The invention also teaches a method of fastening the piston assembly to the piston rod to eliminate the external holes in the piston assembly.
The invention also teaches a piston that has a reduced “dead-air space.” Dead-air space is the space between the annular top ring groove on a piston crown and the top of a piston. The reduction of dead-air space improves fuel efficiency, increases engine power, reduces emissions, and improves engine performance.
DESCRIPTION OF THE RELATED ART
Applicant is aware of the following U.S. Patents concerning pistons:
U.S. Pat. No.
Inventor
Issue Date
Title
5,839,352
Ribeiro
11-24-1998
ARTICULATED PISTON
5,797,311
Gasthuber
08-25-1998
PISTON/LINER
ARRANGEMENT FOR
RECIPROCATING-PISTON
INTERNAL COMBUSTION
ENGINE
5,787,796
Ribeiro
08-04-1998
ARTICULATED PISTON
5,778,846
Mielke
07-14-1998
FORGED OR CAST PISTON
HEAD OF AN OSCIL-
LATING SHAFT PISTON
5,730,090
Kling
03-24-1998
RECIPROCATING PISTON
FOR INTERNAL
COMBUSTION ENGINES
5,499,572
Cobble
03-19-1996
BI-TECH PISTON
5,144,884
Kelly
09-08-1992
TWO-PART PISTON
ASSEMBLY DEVICE
2,621,092
Clark
12-09-1952
PISTON
2,051,546
Crist
08-18-1936
PISTON
1,940,629
Mahle
12-19-1933
PISTON ALLOY
1,704,393
Leary
03-05-1929
CONNECTING ROD
1,427,673
Allen
08-29-1922
UNIVERSAL PISTON ROD
CONNECTION
1,391,161
Atkinson
09-20-1921
FOOD PRODUCT AND
PROCESS OF PREPARING
1,017,498
Bittner
02-13-1912
PISTON FOR EXPLOSIVE
ENGINES
Ribeiro, U.S. Pat. No. 5,839,352, and Ribeiro, U.S. Pat. No. 5,787,796, both teach a two-piece piston assembly with opposing bores in the piston skirt. Neither patent teaches a piston crown and a piston skirt manufactured from different materials. Both patents teach a wrist pin that must be inserted through the exterior wall of the piston skirt and through the bores and bosses of the piston crown to retain the piston crown within the piston skirt. Neither patent teaches the use of a recession on the rim of a piston crown. The primary advantage of the Ribeiro pistons is that the piston skirt can be manufactured using conventional manufacturing or processes which reduces the cost of manufacturing.
Mielke, U.S. Pat. No. 5,778,846, teaches a multiple-piece piston assembly with a piston head and a ring section. The piston head may be manufactured from steel, cast iron, or aluminides including titanium aluminide. The ring section may consist of an aluminum piston alloy, a cast iron alloy, or other material. The piston head may be made from tempered steel or from a different, hardened material. Therefore, the patented piston assembly teaches a piston head and a ring section made from different materials. These materials may be joined by welding, soldering, frictional, or interlocking connection.
Cobble, U.S. Pat. No. 5,499,572, teaches a two-piece piston assembly with a piston head and a piston skirt. The piston assembly has a wrist pin that has been inserted through the exterior wall of the piston skirt. The piston crown and piston skirt are made from different materials. The piston crown is composed of metal. The piston skirt is composed of an epoxy resin. The piston crown and piston skirt are joined together by keying the piston skirt. The piston crown has no rim for joining the piston head to the piston skirt. Thus, the lower portion of the piston crown has a higher diameter than the upper portion of the piston skirt, which increases the weight of the piston structure. In addition, the piston crown has no recession on the rim.
Kelly, U.S. Pat. No. 5,144,884, teaches a two-part piston assembly having a piston skirt with a transverse bore. Kelly teaches a piston assembly with a piston pin attached to the piston skirt through the external bore. The piston crown is composed of a cast iron or steel. The piston skirt is composed of an aluminum alloy.
Clark, U.S. Pat. No. 2,621,092, teaches a piston head having a piston wrist pin for connecting the piston head to a connecting piston rod. The pin connects to the head through a special wrist pin retainer. The retainer allows for prevailing longitudinal movement of the pin while allowing rotation of the piston rod. Clark teaches an inner portion of the piston cap having piston bosses with holes through the bosses for accepting a wrist pin that is inserted through the exterior wall of a surrounding piston skirt.
Crist, U.S. Pat. No. 2,051,546, teaches a composite piston formed of a piston head and a piston skirt. The piston head and skirt may be made from different materials. The interior of the piston head has piston pin bosses which accept a wrist pin and which can be inserted through a hole in the exterior wall of a piston skirt.
Mahle, U.S. Pat. No. 1,940,629, teaches a piston head having a ring bearing portion composed of one material and having additional portions of the piston head made of different materials. Mahle also teaches a piston skirt with a portion that may be made of iron or other materials. The piston skirt has an extra hole therethrough for accepting a wrist pin.
Bittner, U.S. Pat. No. 1,017,498, teaches a piston head having a body and a head. Preferably, the body and head connect by a screw thread joint. The patented invention teaches that the piston body and head may screw together to form a piston having a hollow body. The piston head has a channel therethrough. The channel accepts a piston wrist pin that inserts through the piston head. The piston head attaches the piston rod to the piston head. The ends of the wrist pin extend within the piston body. The piston head ends flush with the outer sides of the piston part. The ends are internally located within the upper portion of the piston body so that the wrist pin may not ex

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