Internal-combustion engines – Transmission mechanism from piston – Crankshaft and connecting rod
Reexamination Certificate
1999-12-13
2001-09-04
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Transmission mechanism from piston
Crankshaft and connecting rod
C123S147000
Reexamination Certificate
active
06283085
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a reciprocating engine, and more particularly an internal combustion engine, with at least two cylinders accommodating a reciprocating piston each, and with at least one primary connecting rod and at least one secondary connecting rod, whose small ends are connected to a piston each, and whose crankshaft ends, i.e., the ends opposite of the small ends of the connecting rods, are mounted on a common crank pin of a crankshaft, the crankshaft end of the primary connecting rod having at least one shoulder whose inner surface is rotatably connected to the crank pin via a first big end bearing, and whose outer surface constitutes a bearing surface for at least one secondary connecting rod.
DESCRIPTION OF THE PRIOR ART
In reciprocating engines, and in particular internal combustion engines where several cylinders are positioned approximately in a plane normal to the crankshaft axis, such as radial engines, a plurality of connecting rods act on a common crank pin. The challenge for the design engineer lies in the minimization of engine length. Several design solutions are known where a plurality of connecting rods are coupled to one and the same crank pin.
In U.S. Pat. No. 5,150,670 A an internal combustion engine is described in which assemblies of three connecting rods are coupled to a common crank pin each. The crankshaft ends of the connecting rods feature shoulders configured as cylinder segments whose inner surfaces engage the crank pin. The outer surfaces of the shoulders are radially secured by rings. This solution requires a certain amount of space and is only suitable for use with reciprocating engines provided with friction bearings between connecting rods and crank pin, where comparatively small inertial forces are encountered. For high-speed internal combustion engines, such as naturally aspirated four-stroke engines, this arrangement of connecting rods is not suitable.
U.S. Pat. No. 5,765,451 A is concerned with a reciproacting engine of the initially described kind, where three connecting rods in fan-type arrangement are coupled to a common crank pin in the same plane. The two outer connecting rods have shoulders configured as cylinder segments, whose inner surfaces engage the crank pin. The outer surfaces of the shoulders are defined as bearing surfaces for the third, i.e., center connecting rod, whose crankshaft end is divided and exhibits slots along its circumference. The shoulders of the two outer connecting rods are disposed within the eye on the crankshaft end of the center connecting rod, the shanks of the outer rods projecting from the eye on the crankshaft end of the central rod through the slots. The center connecting rod thus is supported on the outer surfaces of the shoulders of the outer rods. The length of the circumferential slots is essentially defined by the respective inclination angle between the cylinders. As above, this comparatively complex design can only be used with engines with friction bearings between connecting rods and crank pin.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a simple and compact solution for coupling a plurality of connecting rods to a crank pin in a reciprocating engine of the aforementioned type.
According to the invention this object is achieved by providing that the inner and outer surfaces constituting the bearing surfaces of the essentially tubular shoulder be configured as preferably cylindrical surfaces extending around the full periphery, and that the at least one secondary connecting rod have a crankshaft end with a non-divided, big eye surrounding the shoulder of the primary connecting rod, the inner surface of said eye being supported on the outer surface of the shoulder via a second bearing. This solution is independent of the inclination angles between the cylinders and is thus suited for both fan-type and radial cylinder arrangements.
In a preferred variant, the primary connecting rod has at least two shoulders, which are preferably disposed on either side of a center plane of the connecting rod normal to the crankshaft axis, and more preferably symmetrical to this plane, each shoulder bearing a secondary connecting rod. The two secondary connecting rods on the outer sides are thus supported on the shoulders of the primary connecting rod in the middle. Although the width of the primary connecting rod is somewhat greater than in conventional designs, this arrangement will help reduce overall width. The first big end bearing of the primary connecting rod constituting the master rod, in which the crank pin rotates, may be designed for high load. The secondary connecting rods placed on either side of the master rod will perform only tilting movements in the second big end bearings. On account of their larger diameters they will offer adequate load-bearing capacity despite the small width.
The first and/or second big end bearings may be configured as friction or antifriction bearings, and preferably as needle bearings. The use of needle bearings will reduce friction and improve emergency running properties. In order to avoid bending of the needle ends of the bearing between the primary connecting rod and the crank pin when the crank pin is bent strongly, the needle bearing preferably is configured as a double-row bearing.
Special preference is given to a variant in which the big end of the primary and/or secondary connecting rod has a non-divided eye and the crankshaft is configured as an assembled part. Due to the non-divided configuration of the big ends of the primary and secondary connecting rods reliable bearing properties are obtained, especially with the use of antifriction bearings. For assembly of the connecting rod and the non-split bearing cages of the antifriction bearings the crankshaft must be configured as an assembled part. Preferably, crankshaft and/or connecting rods are made of steel.
The design of the invention is particularly suitable for use with reciprocating engines where three connecting rods are coupled to a common crank pin each.
It may be further provided by the invention that at least two of the connecting rods differ in length. The length of the primary connecting rod may be smaller or greater than the length of the secondary connecting rod. This will permit high flexibility as regards cylinder arrangements.
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patent: 5537971 (1996-07-01), Pong
patent: 5615642 (1997-04-01), Coughlin
patent: 5655496 (1997-08-01), Pong
patent: 5765451 (1998-06-01), Carone
patent: 5894763 (1999-04-01), Peters
patent: 5950579 (1999-09-01), Ott
patent: 9004725 (1990-05-01), None
AVL List GmbH
Benton Jason
Dykema Gossett PLLC
Wolfe Willis R.
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