Load transfer point offset of rocking journal wristpins in uniflow-scavenged, opposed-piston engines with phased crankshafts

Patent metadata

Field	Value
Publication number	US-9841049-B2
Application number	US-201514732588-A
Country	US
Kind code	B2
Filing date	Jun 5, 2015
Priority date	Jun 5, 2015
Publication date	Dec 12, 2017
Grant date	Dec 12, 2017

Abstract

Load transfer point offset of rocking journal bearings in uniflow-scavenged, opposed-piston engines with phased crankshafts includes differing offsets for the load transfer points of opposed pistons. More specifically, under the condition that a first crankshaft leads the second crankshaft, an angular offset of a rocking journal wristpin of a piston coupled to the first crankshaft proportional to an offset of the first crankshaft relative to the second crankshaft is made to ensure adequate oil film thickness to the wristpin when it experiences a peak combustion pressure during a power stroke.

First claim

The invention claimed is:

1. A uniflow-scavenged, opposed-piston engine having first and second rotatable crankshafts, one or more cylinders each with a first piston interconnected by a first connecting rod with the first crankshaft and a second piston opposing the first piston and interconnected by a second connecting rod with the second crankshaft, a first rocking journal bearing situated between the first piston and the first connecting rod and including a plurality of sets of bearing surfaces, a second rocking journal bearing situated between the second piston and the second connecting rod and including a plurality of sets of opposed bearing surfaces, each rocking journal bearing having a respective load transfer point at which a compressive load transfer occurs from one set of opposed bearing surfaces to another set of opposed bearing surfaces during successive cycles of engine operation, wherein:
the first crankshaft is positioned so as to lead the second crankshaft during engine operation by an angle;
the load transfer point of the first rocking journal bearing being selected such that a load transfer from one set of opposed bearing surfaces to another set of opposed bearing surfaces occurs during each cycle following a top center position of the first piston and closely preceding the occurrence of a cyclic peak load; and,
the load transfer point of the second rocking journal bearing being selected such that a load transfer from one set of opposed bearing surfaces to the another set of opposed bearing surfaces occurs during each cycle closely preceding the occurrence of the cyclic peak load;
wherein, the plurality of sets of bearing surfaces of the first rocking journal includes a plurality of axially-spaced, eccentrically-disposed journal segments formed on a wristpin and a plurality of corresponding axially-spaced, eccentrically-disposed surface segments formed on a segmented bearing surface of a sleeve, and when the first piston is at a top center or a bottom center the wristpin journal segments are rotated by an angular offset φ with respect to the bearing surface segments, in which a first wristpin rocking journal segment has a centerline A and second wristpin rocking journal segments share a centerline B that is offset from the centerline A, and the angular offset φ is measured between a longitudinal axis of the first connecting rod and a line that joins the centerlines A and B.

2. The uniflow-scavenged, opposed-piston engine according to claim 1 , wherein the angle by which the first crankshaft leads the second crankshaft has a value x in the range of 4°<x<12°.

3. The uniflow-scavenged, opposed-piston engine according to claim 2 , wherein the angular offset φ has a value in the range of 2°<φ<4°.

4. The uniflow-scavenged, opposed-piston engine according to claim 3 , wherein the wristpin is mounted to a small end of the first connecting rod for rocking oscillation against the segmented bearing surface of the sleeve.

5. The uniflow-scavenging, opposed-piston engine according to claim 1 , wherein the angle is fixed or variable.

6. The uniflow-scavenging, opposed-piston engine according to claim 5 , wherein the first crankshaft is an exhaust crankshaft and the second crankshaft is an intake crankshaft.

7. A method of operating the uniflow-scavenging, opposed-piston engine according to claim 1 , by:
causing the first and second crankshafts to rotate in response to combustion in a combustion chamber formed in the uniflow-scavenging, opposed-piston engine between end surfaces of the first and second pistons;
causing rotation of the first crankshaft to lead rotation of the second crankshaft;
causing the load transfer point of the first rocking journal to occur at a first crank angle measured with respect to rotation of the first crankshaft; and,
causing the load transfer point of the second rocking journal to occur at a second crank angle measured with respect to rotation of the second crankshaft;
wherein the first crank angle is greater than the second crank angle.

8. A two-stroke cycle, opposed-piston engine having first and second rotatable crankshafts a cylinder, a first piston disposed in a bore of the cylinder and interconnected by a connecting rod with the first crankshaft, a second piston disposed in the bore in opposition to the first piston and interconnected by a connecting rod with the second crankshaft, a first rocking journal bearing acting between the first piston and its connecting rod and including a plurality of sets of bearing surfaces, a second rocking journal bearing acting between the second piston and its connecting rod and including a plurality of sets of opposed bearing surfaces, each rocking journal bearing having a respective load transfer point at which a compressive load transfer occurs from one set of opposed bearing surfaces to another set of opposed bearing surfaces during successive cycles of engine operation, wherein:
the first crankshaft is positioned so as to lead the second crankshaft during engine operation by a fixed or variable angle;
the load transfer point of the first rocking journal bearing being selected such that a load transfer from one set of opposed bearing surfaces to another set of opposed bearing surfaces occurs during each cycle after a top center position of the first piston and preceding the occurrence of a cyclic peak load; and,
the load transfer point of the second rocking journal bearing being selected such that a load transfer from one set of opposed bearing surfaces to another set of opposed bearing surfaces occurs during each cycle preceding the occurrence of the cyclic peak load;
wherein, the plurality of sets of bearing surfaces of the first rocking journal includes a plurality of axially-spaced, eccentrically-disposed journal segments formed on a wristpin and a plurality of corresponding axially-spaced, eccentrically-disposed surface segments formed on a segmented bearing surface of a sleeve, and when the first piston is at a top center or a bottom center the wristpin journal segments are rotated by an angular offset φ with respect to the bearing surface segments, in which a first wristpin rocking journal segment has a centerline A and second wristpin rocking journal segments share a centerline B that is offset from the centerline A, and the angular offset φ is measured between a longitudinal axis of the first connecting rod and a line that joins the centerlines A and B.

9. The two-stroke cycle, opposed-piston engine according to claim 8 , wherein the fixed or variable angle by which the first crankshaft leads the second crankshaft has a value x in the range of 4°<x<12°.

10. The two-stroke cycle, opposed-piston engine according to claim 8 , wherein angular offset φ has a value in the range of 2°<φ<4°.

11. The two-stroke cycle, opposed-piston engine according to claim 10 , wherein the wristpin is mounted to a small end of the first connecting rod for rocking oscillation against the segmented surface of the sleeve.

12. The two-stroke cycle, opposed-piston engine according to claim 11 , wherein the first crankshaft is an exhaust crankshaft and the second crankshaft is an intake crankshaft.

13. A method of operating a two-stroke cycle, opposed-piston engine according to claim 8 , by:
causing the first and second crankshafts to rotate in response to combustion in a combustion chamber formed in the uniflow-scavenging, opposed-piston engine between end surfaces of the first and second pistons;
causing rotation of the first crankshaft to lead rotation of the second crankshaft; causing the load transfer point of the first rocking journal to occur at a first crank angle measured with respect to rota

Assignees

• Achates Power Inc

Inventors

• Klyza Clark A

Classifications

• F16C3/06

  Crankshafts · CPC title

• F16C17/24

  with devices affected by abnormal or undesired positions, e.g. for preventing overheating, for safety · CPC title

• F16J1/16

  with gudgeon-pin; Gudgeon-pins · CPC title

• F16C9/04 Primary

  Connecting-rod bearings; Attachments thereof · CPC title

• F16C2361/00

  Apparatus or articles in engineering in general · CPC title