Minimizing oil leakage from rocking journal bearings of two-stroke cycle engines

Abstract

A rocking journal bearing is provided in a piston coupling mechanism of a two-stroke cycle engine. The bearing includes a sleeve and a wristpin constructed with two sets of eccentrically-disposed bearing surfaces which alternate in accepting a compressive load during an operational cycle of the bearing. The sleeve includes a network of grooves to transport oil to the bearing surfaces. Lubricating oil flow through the bearing is minimized by limiting provision of pressurized oil from the wristpin to the network of grooves to portions of the cycle when one or the other of the sets of bearing surfaces receives the compressive load.

Claims

1. A rocking journal bearing for a two-stroke cycle engine, comprising: a bearing sleeve including a generally cylindrical bearing surface with a plurality of axially-spaced, eccentrically-disposed surface segments separated by circumferential oil grooves in the bearing surface for transporting oil in a circumferential direction of the bearing surface; a plurality of circumferentially-spaced, axial oil grooves in the bearing surface that run across the surface segments and intersect the circumferential oil grooves for transporting oil in an axial direction of the bearing surface; a wristpin including a plurality of axially-spaced, eccentrically-disposed journal segments engaged for rocking oscillation with corresponding surface segments; and, an oil-receiving space in the wristpin with oil outlet passages acting through the journal segments for delivering oil to the bearing surface; in which, there are no oil outlet passages in the wristpin that are aligned with the circumferential oil grooves in the bearing surface; and, at least one oil outlet passage in each journal segment is positioned to cross at least one axial oil groove during said rocking oscillation; wherein, the plurality of journal segments includes a first journal segment formed in an intermediate portion of the wristpin, between two second journal segments and the two second journal segments are formed on opposite ends of the wristpin, on respective sides of the first journal segment; positioning of a first oil outlet passage locates the first oil outlet passage in the first journal segment at a first arcuate distance from one side of a cut plane containing the longitudinal axis of the wristpin and a radius forming an axis of an oil inlet passage in the wristpin for transporting oil to the oil-receiving space; and, positioning of two second oil outlet passages locates each second oil passage in a respective one of the second journal segments at a second arcuate distance from the opposite side of the cut plane; in which the first and second arcuate distances are in opposite directions; and, wherein, when a rotational position of the wristpin relative to the sleeve is at a load transfer point of the rocking journal bearing, the first and second oil outlet passages are positioned between first and second axial oil grooves, with the first oil outlet passage being relatively nearer to the first axial oil groove, and the second oil outlet passages being relatively nearer to the second axial oil groove.

2. A rocking journal bearing according to claim 1, wherein, when the wristpin is at rotational position relative to the sleeve where first journal and surface segments are fully loaded, while second journal and surface segments are separated, the first oil outlet passage is aligned with the first axial oil groove for enabling oil to enter the first axial oil groove from the first oil outlet passage.

3. A rocking journal bearing according to claim 2, in which the separation between the second journal and surface segments enables the second oil outlet passages to deliver oil to space between the second journal and surface segments.

4. A rocking journal bearing according to claim 1, wherein, when the wristpin is at a rotational position relative to the sleeve where second journal and surface segments are fully loaded, while first journal and surface segments are separated, the second oil outlet passages are aligned with the second axial oil groove for enabling oil to enter the second axial oil groove from the second oil outlet passages.

5. A rocking journal bearing according to claim 4, in which the separation between the first journal and surface segments enables the first oil outlet passage to deliver oil to space between the first journal and surface segments.

6. A rocking journal bearing for a two-stroke cycle engine, comprising: a bearing sleeve including a generally cylindrical bearing surface with a plurality of axially-spaced, eccentrically-disposed surface segments separated by circumferential oil grooves in the bearing surface for transporting oil in a circumferential direction of the bearing surface; a plurality of circumferentially-spaced, axial oil grooves in the bearing surface that run across the surface segments and intersect the circumferential oil grooves for transporting oil in an axial direction of the bearing surface; a wristpin including a plurality of axially-spaced, eccentrically-disposed journal segments engaged for rocking oscillation with corresponding surface segments; and, an oil-receiving space in the wristpin with oil outlet passages acting through the journal segments for delivering oil to the bearing surface; in which, there are no oil outlet passages in the wristpin that are aligned with the circumferential oil grooves in the bearing surface; and, at least one oil outlet passage in each journal segment is positioned to cross at least one axial oil groove during said rocking oscillation; wherein the plurality of journal segments includes a first journal segment having a first centerline and two second journal segments sharing a second centerline that is offset from the first centerline, and the first journal segment is disposed between two second journal segments, in which: positioning of a first oil outlet passage locates the first oil outlet passage in the first journal segment at a first arcuate distance from one side of a cut plane containing the longitudinal axis of the wristpin and a radius forming the axis of an oil inlet passage in the wristpin for transporting oil to the oil-receiving space; positioning of two second oil outlet passages locates each second oil passage in a respective one of the second journal segments at a second arcuate distance from the opposite side of the cut plane; and, the first and second arcuate distances are in opposite directions; and, wherein, when a rotational position of the wristpin relative to the sleeve is at a load transfer point of the rocking journal bearing, the first and second oil outlet passages are positioned between first and second axial oil grooves, with the first oil outlet passage relatively nearer to the first axial oil groove, and the second oil outlet passages relatively nearer to the second axial oil groove.

7. A rocking journal bearing according to claim 6, wherein, when the wristpin is at rotational position relative to the sleeve where first journal and surface segments are fully loaded, while second journal and surface segments are separated, the first oil outlet passage is aligned with the first axial oil groove for enabling oil to enter the first axial oil groove from the first oil outlet passage.

8. A rocking journal bearing according to claim 7, in which the separation between the second journal and surface segments enables the second oil outlet passages to deliver oil to space between the second journal and surface segments.

9. A rocking journal bearing according to claim 6, wherein, when the wristpin is at a rotational position relative to the sleeve where second journal and surface segments are fully loaded, while first journal and surface segments are separated, the second oil outlet passages are aligned with the second axial oil groove for enabling oil to enter the second axial oil groove from the second oil outlet passages.

10. A rocking journal bearing according to claim 9, in which the separation between the first journal and surface segments enables the first oil outlet passage to deliver oil to space between the first journal and surface segments.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic representation of a two-stroke cycle, opposed-piston engine, and is properly labeled Prior Art.

(2) FIG. 2 is an exploded perspective view of a piston coupling mechanism including a rocking journal bearing, and is properly labeled Prior Art.

(3) FIG. 3 is a schematic diagram illustrating the bearing surfaces of the rocking journal of FIG. 2, and is properly labeled Prior Art.

(4) FIG. 4 is a perspective view showing a bearing surface of a rocking journal sleeve.

(5) FIGS. 5A-5C show a rocking journal wristpin constructed to provide oil for lubricating a rocking journal bearing comprising the sleeve of FIG. 4, and are properly labeled Prior Art.

(6) FIG. 6 is a perspective view of a rocking journal wristpin according to this disclosure.

(7) FIG. 7 is an end elevation view of a rocking journal bearing according to this disclosure comprising the sleeve of FIG. 4 and the wristpin of FIG. 6.

(8) FIG. 8A is a side elevation view and FIGS. 8B-8D are cross-sectional views of the rocking journal bearing of FIG. 7 showing details of bearing lubrication at a load transfer point of the bearing.

(9) FIG. 9A is a side elevation view and FIGS. 9B-9D are cross-sectional views of the rocking journal bearing of FIG. 7 showing details of bearing lubrication at a first loading point of the bearing.

(10) FIG. 10A is a side elevation view and FIGS. 10B-10D are cross-sectional views of the rocking journal bearing of FIG. 7 showing details of bearing lubrication at a second loading point of the bearing.

(11) FIG. 11 is a graph showing an operational cycle of the rocking journal bearing of FIG. 7.

(12) FIGS. 12A-12C illustrate flow paths of pressurized oil delivered to the rocking journal bearing of FIG. 7 at respective points in the operational cycle of the bearing shown in FIG. 11.

DETAILED DESCRIPTION

(13) FIG. 6 shows a wristpin 100 according to this disclosure that is combined with the sleeve 46 of FIG. 4 to form a rocking journal bearing 200 as shown in FIG. 7 in which the flow of excess pressurized oil from the bearing 200 is reduced throughout its operational cycle. In this regard, pressurized oil is provided intermittently instead of continuously to the network of oil grooves in the bearing surface of the sleeve. The view in FIG. 6 is toward a contacting portion 102 of the wristpin outer surface 103 that is in contact with the sleeve bearing surface 47 during oscillation of the bearing. The wristpin is constructed with axially-offset surface segments J.sub.1 and J.sub.2 as per FIG. 3. As best seen in FIG. 8C, an oil inlet passage 105 is formed in the non-contacting portion of the J.sub.1 segment of the wristpin. As per FIG. 6, at least one oil outlet passage 107 is formed in the contacting portion of the J.sub.1 journal segment. At least one oil outlet passage 109 is formed in the contacting portions of each of the J.sub.2 journal segments. The oil outlet passages 107 and 109 open through the wristpin sidewall to oil gallery space 111 within the wristpin, and are offset along the wristpin's longitudinal axis 113 relative to the circumferential grooves 115 that separate the segments J.sub.1 and J.sub.2. There are no oil outlet passages along either of the circumferential grooves 115. The wristpin 100 is assembled to the sleeve 46 with the journal segments J.sub.1-J.sub.2 in engagement with the surface segments J.sub.1-J.sub.2 and the circumferential grooves 115 of the wristpin 100 aligned with the circumferential grooves 70 of the bearing surface 47. As relative oscillation occurs between the wristpin 100 and the sleeve 46, pressurized oil flows to the space between the separated segments from the oil grooves 70, 72, and 115 and from the outlet passages 107 and 109 located in the separated journal segments of the wristpin.

(14) With reference to FIGS. 6 and 8C, to carry out the purposes of a rocking journal bearing construction according to this disclosure, the positioning of the oil outlet passage 107 locates the oil outlet passage in the J.sub.1 journal segment at a first arcuate distance D.sub.1 from one side of a cut plane P containing the longitudinal axis 113 of the wristpin and a radius 117 forming the axis of the oil inlet passage 105. The positioning of the oil outlet passages 109 locates these oil outlet passages in respective J.sub.2 journal segments at a second arcuate distance D.sub.2 from the opposite side of the cut plane P. Thus, as the rocking journal 200 is viewed as per FIGS. 8A-8D, in which the rotational position of the wristpin 100 relative to the sleeve 47 is 0, as would occur when the load transfer point of the bearing 200 is traversed, the oil outlet passages 107 and 109 are positioned between the axial oil grooves 72 and 73 of the sleeve 46, with the oil outlet passage 107 relatively nearer (for example, adjacent) to the axial oil groove 72 and the oil outlet passages 109 relatively nearer (for example, adjacent) to the axial oil groove 73. In this relative rotational position, the bearing interfaces J.sub.1-J.sub.1 and J.sub.2-J.sub.2 are equally loaded.

(15) With reference to FIGS. 9A-9D, presume that the wristpin 100 revolves in the CCW direction from the 0 position relative to the sleeve 46 to a point where the segments J.sub.1-J.sub.1 are fully loaded, while the segments J.sub.2-J.sub.2 are separated. As a result of movement in this direction, the oil outlet passage 107 moves across the axial oil groove 72, which enables a pulse of pressurized oil to enter the oil groove from the oil outlet passage, while the separation between the segments J.sub.2-J.sub.2 allows the oil outlet passages 109 to deliver pressurized oil to the space therebetween.

(16) With reference to FIGS. 10A-10D, presume that the wristpin 100 revolves in the CW direction from the 0 position relative to the sleeve 46 to a point where the segments J.sub.2-J.sub.2 are fully loaded, while the segments J.sub.1-J.sub.1 are separated. As a result of movement in this direction, the oil outlet passages 109 cross the axial oil groove 73, which enables a pulse of pressurized oil to enter the oil groove from each of the oil outlet passages, while the separation between the segments J.sub.1-J.sub.1 allows the oil outlet passage 107 to deliver pressurized oil to the space therebetween.

(17) FIG. 11 is a graph showing an exemplary operational cycle of a rocking journal bearing as may be observed when the bearing is incorporated into the piston coupling mechanisms of a two-stroke cycle opposed-piston engine such as the engine 8 of FIG. 1. The graph shows wristpin-to-sleeve clearance for the J.sub.1-J.sub.1 interface and J.sub.2-J.sub.2 interfaces as a function of the crank angle position (in degrees) of the one of the crankshafts to which the coupling mechanism connects its associated piston. The graph shows a full cycle of crankshaft operation, with the understanding that this represents the operational cycles of each of the two crankshafts seen in FIG. 1 (with or without a phase difference). Further, the graph is representative of the two-stroke cycle operation of the opposed-piston engine of FIG. 1. This graph is based upon load transfer occurring at 0 (TC) and 180 (BC), although this condition should not be considered to be limiting. At a crank angle of 0, with the piston at TC, the compressive load is about equally divided between the J.sub.1-J.sub.1 and J.sub.2-J.sub.2 interfaces, as the crank angle advances, the load is increasingly received by the J.sub.1-J.sub.1 interface while the J.sub.2-J.sub.2 segments begin to separate. At a crank angle of 90 the compressive load is maximally borne by the J.sub.1-J.sub.1 interface, while the J.sub.2-J.sub.2 segments are maximally separated. At this point, the compressive load begins shifting from the J.sub.1-J.sub.1 interface to the J.sub.2-J.sub.2 interface and the J.sub.2-J.sub.2 surface segments begin to close. At 180, with the piston at BC, the compressive load is about equally divided between the J.sub.1-J.sub.1 and J.sub.2-J.sub.2 interfaces. As the crank angle advances the load is increasingly received by the J.sub.2-J.sub.2 interface while the J.sub.1-J.sub.1 segments begin to separate. At a crank angle of 270 the compressive load is maximally borne by the J.sub.2-J.sub.2 interface, while the J.sub.1-J.sub.1 segments are maximally separated. At this point, the compressive load begins shifting to the J.sub.1-J.sub.1 interface from the J.sub.2-J.sub.2 interface and the J.sub.1-J.sub.1 segments begin to close. At 360, the compressive load is about equally divided between the J.sub.1-J.sub.1 and J.sub.2-J.sub.2 interfaces, and the cycle repeats.

(18) FIGS. 12A-12C show the pressurized oil flow patterns through the sleeve oil grooves 70, 72, and 73 for load transfer points (0 and 180), for maximum J.sub.1 loading, and maximum J.sub.2 loading during an engine operating cycle shown in FIG. 11. At 0 and 180 oscillation, no oil outlet passages align with the sleeve axial grooves 72 and 73, and since all three interfaces are equally loaded, no significant oil is added to the interfaces. At the maximum J.sub.1 loading point (90), the J1 oil outlet passage 107 is aligned with the axial oil groove 72 and oil flows freely through the oil grooves 70, 72, and 73 to fill the J.sub.2 lifted segment areas. At the maximum J.sub.2 loading point (90), the two J.sub.2 oil outlet passages 109 align with the axial oil groove 73 and oil freely flows into the oil grooves 70, 72, and 73 to fill the J.sub.1 lifted segment area.

(19) The column of oil in the piston connecting rod oil passage 64 applies peak positive and negative pressures to the volume of oil in the wristpin gallery when at TC and BC piston positions, respectively. By using the intermittent alignment system described and illustrated above, and in the absence of oil outlet passages positioned in alignment with the circumferential grooves, the only path for oil to flow through during these peak pressure events is between the equally-loaded J.sub.1-J.sub.1 and J.sub.2-J.sub.2 surface segments, which is quite restrictive. As a result, this construction has the additional benefit of reducing the system sensitivity to oil pressure fluctuations in the wristpin gallery.

(20) Although this disclosure describes particular embodiments for minimizing oil leakage from journal wristpins in two-stroke cycle, opposed-piston engines, these embodiments are set forth merely as examples of underlying principles of this disclosure. Thus, the embodiments are not to be considered in any limiting sense.