Method Of Extending Engine Service Life And Angular Displacement-Limiting Clip For Same
A clip includes a one-piece metal body having a holder and an attached hanger. The clip is configured to couple with a valve lifter to form a lifter assembly for varying the position of a valve in an internal combustion engine. The holder may be C-shaped, and the hanger may be U-shaped. The one-piece metal body further includes an anti-scuffing outer profile, and a first and a second fillet transitioning from the holder to the hanger, for diffusing stresses induced in the clip at an angular displacement-limiting stop position defined by contact between the hanger and a wall portion of a cylinder block. Related methodology is disclosed.
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This application claims priority to Indian Patent Application Serial No. 3650/DEL/2011, filed Dec. 14, 2011 with the same title.
TECHNICAL FIELDThe present disclosure relates generally to valve lifters for internal combustion engines, and relates more particularly to extending engine service life via inhibiting fatigue failure of a displacement-limiting clip for a valve lifter.
BACKGROUNDValve lifters are used in internal combustion engines to convert rotational motion of an engine cam into linear motion, for controlling the position of gas exchange valves. A typical design includes a lifter body coupled with a pushrod configured to actuate a rocker arm of one or more gas exchange valves. The lifter body includes a roller positioned in contact with the engine cam, such that rotation of the engine cam causes the valve lifter to slide within a lifter bore formed in the engine housing. Sliding of the valve lifter adjusts the pushrod, which in turn moves the rocker arm in a well-known manner.
The roller may be generally cylindrical and contacts an outer surface of the cam, such that a desired interface between the roller and the cam outer surface is essentially linear. During service in the engine, valve lifters may become misaligned with the cam via rotation of the valve lifter within the lifter bore. The causes of such misalignment appear to vary from engine to engine. Even seemingly identical engine designs can exhibit different misalignment issues of their valve lifters over the course of the engine's service life. Adding to the complexity, some valve lifters tend to rotate more, or differently than other valve lifters even within the same engine.
Various strategies have been proposed over the years to limit valve lifter rotation. One technique employs a guide mechanism coupled with the valve lifter. U.S. Pat. No. 3,886,808 to Weber teaches such a design. In Weber, the guide mechanism includes a vertically disposed leg which seats in a slot formed on the valve lifter, and a pair of cylindrically shaped arms which seat in a circumferential groove also formed on the valve lifter. A hook connected to the leg seats in a bore in a cylinder block of the engine, apparently preventing the guide and valve lifter from rotation.
Variations on the basic guide design taught by Weber have been developed over the years. As engine designs, duty cycles, and performance characteristics change with continued progress of the art, however, both the nature and extent of valve lifter rotation and its consequences in an engine can change as well. Certain strategies for limiting or otherwise controlling valve lifter rotation that may have been satisfactory in the past have become unsuitable. As is the case with many engineering solutions, such strategies may also have been imperfect to begin with. Failure or damage of a valve lifter and related components can necessitate costly servicing or repair, and shorten the service life of the engine. The poorly understood causes of valve lifter rotation coupled with the desire to avoid redesigning an engine, thus render the pursuit of solutions in this technical area complex and unpredictable.
SUMMARYIn one aspect, a method of extending a service life of an internal combustion engine includes transmitting a torque from a valve lifter rotating out of alignment with a cam to a clip. The clip includes a holder engaged about a lifter body of the valve lifter, and a hanger extending into a cutout formed in the lifter body. The method further includes rotating the clip concurrently with the valve lifter via the transmitted torque, and stopping rotation of the valve lifter and the clip at a stop position defined by contact between the hanger and a cylinder block of the internal combustion engine. The method further includes inhibiting fatigue failure of the clip, at least in part by diffusing stresses induced in the clip at the stop position via fillets transitioning from the holder to the hanger.
In another aspect, a clip for limiting angular displacement of a valve lifter within a cylinder bore formed in a cylinder block of an internal combustion engine includes a one-piece metal body having a holder, and a hanger. The one-piece metal body includes a first jaw and an opposed second jaw, and a base connecting the first and second jaws, such that the holder forms a C-shape in a first plane. Each of the first and second jaws includes a proximal end adjoining the base, and a free distal end. The holder further includes an open side defined by the free distal ends, for clipping the holder about the valve lifter to form the lifter assembly. The hanger projects from the holder in a direction normal to the first plane, and has a straight proximal section connecting to the base and positionable within a cutout formed within the valve lifter to rotationally couple the clip thereto. The hanger further has a distal section forming a U-shape in a second plane normal to the first plane, for coupling the lifter assembly with a wall portion of a cylinder block adjacent the lifter bore. The one piece metal body further includes an anti-scuffing outer profile configured to inhibit interference between the base and the lifter bore during rotating the lifter assembly to and from an angular displacement-limiting stop position defined by contact between the hanger and the wall portion. The one-piece metal body further includes a first and a second fillet transitioning from the base to the straight proximal section, for diffusing stresses induced in the clip at the angular displacement-limiting stop position.
In still another aspect, a clip for limiting angular displacement of a valve lifter is provided, the angular displacement being induced by engine dynamics during service of an assembly of the valve lifter and the clip in an internal combustion engine. The clip includes a one-piece metal body having a holder, and a hanger. The holder includes a first jaw and an opposed second jaw, and a base connecting the first and second jaws, such that the holder forms a C-shape. Each of the first and second jaws includes a proximal end adjoining the base, and a free distal end. The holder further includes an open side defined by the free distal ends, such that spreading apart the free distal ends enlarges the open side for clipping the holder about the valve lifter to form the assembly. The hanger projects from the holder and has a distal section forming a U-shape, for coupling the assembly with a wall portion of a cylinder block adjacent a lifter bore in the internal combustion engine. The hanger further includes a straight proximal section connecting to the base and being positionable within a cutout formed in the valve lifter to rotationally couple the clip thereto, such that angular displacement of the valve lifter is limited at a stop position via contact between the hanger and the wall portion. The clip further includes means, including a shape and a thickness of the one-piece metal body, for inhibiting fatigue failure of the hanger in response to stresses induced at the stop position.
Referring to
Assembly 30 may include a valve lifter 42, and an angular displacement-limiting clip 92 coupled with valve lifter 42. Valve lifter 42 may have a proximal end 44, a distal end 46, and a lifter roller 48 positioned within distal end 46 and configured to contact cam 28. Clip 92 may include a holder 94 engaged with valve lifter 42 and a hanger 96 attached to holder 94 and coupling valve lifter assembly 30 with a portion of cylinder block 14, in particular a wall portion described below. Referring also now to
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It will be recalled that clip 92 may include a planar inboard surface which is positionable in opposition to and parallel to back surface 82 and relief surface 90 of lifter body 50. In
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Referring to the drawings generally, engine 10 operates via combustion of a mixture of fuel and air in cylinder 16, driving piston 20 to rotate crankshaft 24 in a conventional manner. Rotation of crankshaft 24 will induce camshaft 26 to rotate, causing cam 26 to rotate against roller 48 and sliding valve lifter 42 upward within lifter bore 18 to open valve(s) 36. Biasing springs coupled with rocker arm 34 will tend to return valve lifter 42 toward camshaft 26, and close valve(s) 36. It will be recalled that clip 92 is rotationally coupled to valve lifter 42 in service in engine 10. During operation of engine 10, valve lifter 42 may rotate out of alignment with cam 28. Due to the rotational coupling of clip 92 to valve lifter 42, a torque which rotates valve lifter 42 is transmitted to clip 92 such that clip 92 rotates concurrently with valve lifter 42. In particular, torque may be transmitted at least predominantly via contacting straight portions 86 of sidewalls 76 with straight section 110 of hanger 96. Hanger 96 is coupled with wall portion 19 in engine 10. Clearances will typically exist between hanger 96 and each of an outer side and an inner side of wall portion 19, in contrast with earlier designs where the clip contacted at least the inner side of a cylinder block wall portion. Inner side 23 and outer side 21 of wall portion 19 are shown in
In
Those skilled in the art will be familiar with the concept of engine dynamics. As an internal combustion engine operates, many different linear and rotational forces, vibrations, thermally-induced dimensional changes, and other factors, can combine, add, subtract, and otherwise interact with one another in cross-coupled and unpredictable ways. Accordingly, any given component or process, despite best engineering efforts, can behave, perform, or take place in ways different from what is intended. Even seemingly miniscule changes in component geometry, engine operating parameters, or other features can have substantial and unpredictable effects on engine dynamics. As alluded to above, substantial variation among seemingly identical engines, and variation in phenomena even among seemingly identical parts within an engine, is commonly observed. Rotation of valve lifters is one phenomenon that is believed to result from the complex phenomena of engine dynamics. Challenges in fully characterizing engine dynamics have contributed to the difficulty in solving the problems of lifter rotation, and prevented various possible solutions to lifter rotation and its consequences from being predictable.
In earlier clip designs, such as the design shown in comparison to clip 92 in
It will be recalled that wear marks 33 may form on cam 28 during service from contact with lifter roller 48, as illustrated in
Referring to
Upon observing wear patterns on many different cams, including those coupled with both inherently misaligned and self-aligning lifter assemblies, it was discovered that the inherent misalignment may result in a distinctive wear pattern on the corresponding cam that has similarities with, but is not identical to, wear patterns observed on cams associated with failed clips. By still further examining the features of engines and many lifter assemblies where clips have failed, it was further concluded that inherently misaligned lifter and clip assemblies are themselves associated with increased risk of failure. The similarities in wear pattern, and apparent shared likelihood of fatigue failure of the clip, ultimately led to the hypothesis that failed clips were likely to have experienced service conditions analogous with that of inherently misaligned clips. While the nature of these service conditions still remained unknown, additional observations as to scuff marks on the lifter bore finally led to the conclusion that various factors must have been causing clips to “hang-up” within the lifter bore and fail to self-align, resulting in stresses sufficient to eventually result in fatigue failure. This conclusion itself ran counter to the conventional wisdom that valve lifters would always tend to self-align. Once the phenomenon of lifter assemblies, and in particular the clip, hanging-up began to be revealed, it became possible to investigate the potential reasons. It is now believed that variations from engine to engine, and amongst lifter assemblies, results in a tendency for some lifter assemblies to experience constraints on their rotation based on interaction with the cylinder block, whilst others can rotate more freely. Variations in the dimensions of cylinder block wall portions from one engine to another may be one specific reason why some valve lifters behave differently than others, and fail to reliably return from a displaced position to an aligned position. Regardless of the specific causes behind failure to self-align, bending and twisting loads on the clip, ultimately leading to the observed failure modes, are believed to be most acute where a lifter assembly hangs up at the angular displacement limiting stop position(s), and the lifter roller is then contacted by the rotating up-ramp and nose of the associated cam.
The present disclosure addresses the problems of clip failure in valve lifter assemblies such that a service life of an engine may be extended, at least in part by designing clip 92 to be more tolerant of such bending and twisting loads, and by designing valve lifter 42 to optimally accommodate clip 92. As discussed above, clip 92 and valve lifter 42 each differ in a number of ways from known designs. These differences complement each other such that the failure modes discussed above can no longer occur, or take so long to occur during normal engine operation, that the service life of lifter assembly 30 exceeds a service life of engine 10. Those skilled in the art will be familiar with the undesirability of changing an overall engine design, incorporating new components, changing spatial footprints of components or assemblies, and other radical and expensive changes. As discussed above, engine dynamics may change in substantial and unpredictable ways even when small changes are made. Solutions to one challenge or problem may be effective, but quite commonly create new and unexpected failure modes or have other disadvantages, not to mention additional costs.
The features of clip 92 and valve lifter 42, and the manner in which those features interact with one another as well as other parts of engine 10, however, conservatively advance over known designs without creating new failure modes and without requiring modifications to an engine itself. Clip 92 may be thicker and differently shaped than known designs, as noted above. The thickness of clip 92 is believed to make body 93 more robust, whereas fillets 114 diffuse stresses which might otherwise cause fatigue failure, and the anti-scuffing outer profile prevents drag of the clip against lifter bore 18 as the clip rotates to and from an angular displacement-limiting stop position. In a practical implementation strategy, clip 92 may be designed such that distal ends 118 have a relatively mild interference fit with lifter bore 18, and the rest of holder 94 does not interfere at all. Clips contemplated herein may also have reduced or eliminated interference between the hanger and the wall portion of the cylinder block, contrasting with prior designs in which the lower part of the hanger bulged outwardly somewhat and created what is now recognized as undesirable interference with the lifter bore. In the case of valve lifter 42, the relieved outer surface 90 enables a snugger and better matched fit with clip 92, the relatively deeper cutout 74 accommodates the increased thickness of clip 92, and taper 80 ensures that sidewalls 76 will not impinge upon fillets 114. Lifter assembly 30 will typically have a spatial footprint such that lifter assembly 30 can be installed within engine 10 without requiring any other modification to hardware or operating strategy. Thus, the present disclosure may be understood in certain respects as reallocating a fixed quantity of material from one component to another, without changing the spatial footprint from the footprint available for existing valve lifter assemblies. Engines where valve lifter assemblies have failed, or where failure is deemed possible, can thus be serviced by swapping out existing valve lifter assemblies for lifter assemblies according to the present disclosure.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. For instance, while certain features of clip 92 and lifter 42 have been described herein as having example dimensional and geometric attributes, the present disclosure is not thereby limited and alternative implementations may be developed based on the teachings. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.
Claims
1. A method of extending a service life of an internal combustion engine comprising the steps of:
- transmitting a torque from a valve lifter rotating out of alignment with a cam to a clip, the clip having a holder engaged about a lifter body of the valve lifter and a hanger extending into a cutout formed in the lifter body;
- rotating the clip concurrently with the valve lifter via the transmitted torque;
- stopping rotation of the valve lifter and the clip at a stop position defined by contact between the hanger and a wall portion of a cylinder block of the internal combustion engine; and
- inhibiting fatigue failure of the clip, at least in part by diffusing stresses induced in the clip at the stop position via fillets transitioning from the holder to the hanger.
2. The method of claim 1 wherein the step of transmitting further includes transmitting the torque via contacting straight sidewalls of the cutout forming a proximal channel, with a straight section of the hanger.
3. The method of claim 2 further comprising a step of maintaining clearances between arcuate sidewalls of the cutout forming a distal taper, and the fillets, during the stopping step.
4. The method of claim 3 further comprising a step of decreasing clearances between a U-shaped section of the hanger and the wall portion during the step of rotating, and wherein the step of stopping further includes stopping the rotation via reducing the clearances to zero.
5. The method of claim 4 wherein the clip includes a one-piece metal body having a uniform thickness, and each of the fillets defines a radius which is greater than the uniform thickness.
6. The method of claim 5 wherein the step of rotating further includes rotating the clip such that interference between the clip and a lifter bore formed in the cylinder block occurs predominantly at distal ends of the holder and the holder rotates without scuffing the lifter bore.
7. A clip for limiting angular displacement of a valve lifter within a lifter bore formed in a cylinder block of an internal combustion engine, the clip comprising:
- a one-piece metal body including a holder, and a hanger;
- the holder having a first jaw and an opposed second jaw, and a base connecting the first and second jaws, such that the holder forms a C-shape in a first plane, each of the first and second jaws including a proximal end adjoining the base, and a free distal end, and the holder further having an open side defined by the free distal ends, for clipping the holder about the valve lifter to form a lifter assembly;
- the hanger projecting from the holder in a direction normal to the first plane, and having a straight proximal section connecting to the base and being positionable within a cutout formed in the valve lifter to rotationally couple the clip thereto, and the hanger further having a distal section forming a U-shape in a second plane normal to the first plane, for coupling the lifter assembly with a wall portion of the cylinder block adjacent the lifter bore; and
- the one-piece metal body having an anti-scuffing outer profile configured to inhibit interference between the base and the lifter bore during rotating the lifter assembly to and from an angular displacement-limiting stop position defined by contact between the hanger and the wall portion, and the one-piece metal body further including a first and a second fillet transitioning from the base to the straight proximal section, for diffusing stresses induced in the clip at the angular displacement-limiting stop position.
8. The clip of claim 7 wherein the one-piece metal body forms a T-shape in a third plane normal to each of the first and second planes.
9. The clip of claim 8 wherein the holder includes a planar upper edge surface, and a non-planar lower edge surface, and wherein each of the first and second fillets arcs upwardly from the planar upper edge surface to the hanger.
10. The clip of claim 9 wherein each of the first and second fillets defines a radius in the third plane which is from about 2 millimeters to about 4 millimeters.
11. The clip of claim 10 wherein the radiuses defined by the first and second fillets are equal to about 3 millimeters.
12. The clip of claim 9 wherein the anti-scuffing outer profile includes a first arcuate segment defined by the first jaw, a second arcuate segment defined by the second jaw, and a linear segment defined by the base, in the first plane.
13. The clip of claim 12 wherein the linear segment is defined by a planar outboard surface of the base, and the proximal straight section further includes another planar outboard surface adjoining the planar outboard surface located on the base.
14. The clip of claim 13 wherein the one-piece metal body includes a uniform thickness which is from about 2.0 millimeters to about 3.0 millimeters.
15. The clip of claim 7 wherein the first jaw includes a first distal end surface, and the second jaw includes a second distal end surface, and wherein the distal end surfaces define an angle which is about 110° or greater, and wherein the first and second jaws each have an arcuate configuration and are mirror images of one another.
16. The clip of claim 15 wherein the holder further includes an installation assist taper narrowing in a direction opposite the direction of projection of the hanger.
17. A clip for limiting angular displacement of a valve lifter, where the angular displacement is induced by engine dynamics during service of an assembly of the valve lifter and the clip in an internal combustion engine, the clip comprising:
- a one-piece metal body including a holder, and a hanger;
- the holder having a first jaw and an opposed second jaw, and a base connecting the first and second jaws, such that the holder forms a C-shape, each of the first and second jaws including a proximal end adjoining the base, and a free distal end;
- the holder further having an open side defined by the free distal ends, such that spreading apart the free distal ends enlarges the open side for clipping the holder about the valve lifter to form the assembly;
- the hanger projecting from the holder, and having a distal section forming a U-shape, for coupling the assembly with a wall portion of a cylinder block adjacent a lifter bore in the internal combustion engine;
- the hanger further having a straight proximal section connecting to the base and being positionable within a cutout formed in the valve lifter to rotationally couple the clip thereto, such that angular displacement of the valve lifter is limited at a stop position via contact between the hanger and the wall portion; and
- the clip further having means, including a shape and a thickness of the one-piece metal body, for inhibiting fatigue failure of the hanger in response to stresses induced at the stop position.
18. The clip of claim 17 wherein the one-piece metal body further includes a first and a second fillet transitioning from the holder to the hanger and each having a stress diffusing arcuate shape defining a radius, and wherein the base includes an anti-scuffing outer profile configured to inhibit interference between the holder and the lifter bore.
19. The clip of claim 18 wherein the one-piece metal body includes a uniform thickness which is from about 2 millimeters to about 4 millimeters, and the radiuses are from about 2 millimeters to about 4 millimeters.
20. The clip of claim 19 wherein the uniform thickness is less than the radiuses.
Type: Application
Filed: Jan 20, 2012
Publication Date: Jun 20, 2013
Applicant: CATERPILLAR, INC. (Peoria, IL)
Inventors: Satish Remala (Peoria, IL), Sathishkumar Raman (Paramakudi)
Application Number: 13/354,825
International Classification: F01L 1/14 (20060101);