Metal working – Means to assemble or disassemble – Spring applier or remover
Reexamination Certificate
2000-03-08
2003-01-21
Wilson, Lee (Department: 3723)
Metal working
Means to assemble or disassemble
Spring applier or remover
C029S215000, C029S263000, C029S255000
Reexamination Certificate
active
06507985
ABSTRACT:
TECHNICAL FIELD
This invention relates to a tool for installing a snap ring retainer into operative assembly position in a piston and more particularly to new and improved tooling for seating a snap ring retainer into an annular slot formed in a wrist pin receiving bore of a piston to maintain the wrist pin in a central position such that the ends of the wrist pin are maintained in a desired spaced relationship away from the engine's cylinder wall. This invention further relates to a new and improved method of installing a snap ring retainer into an annular slot formed in the wrist pin receiving bore of the pistons.
BACKGROUND OF THE INVENTION
In internal combustion engines, a fall floating wrist pin are used to pivotally attach an end of a connecting rod to a piston for the purpose of accommodating reciprocating stroking movement of a piston in an associated cylinder of an internal combustion engine. Such a wrist pin support advantageously provides two stages or levels of wrist pin freedom during piston operation tending to reduce pin and bearing friction and wear. When properly installed in a piston and connecting rod assembly, a free floating wrist pin has the capability of relative rotation with respect to the connecting rod and with respect to a bearing or bore formed in the piston. This wrist pin bore in the piston consists of a pair of aligned bores extending through spaced apart boss-like portions of the piston.
During engine operation, the wrist pin is typically subjected to thrust loads in the lateral direction or axially of the wrist pin. This usually is caused by sideways moments of the associated connecting rod during piston stroking in the associated engine cylinder. If the wrist pin is allowed to be displaced a distance where an end of the pin physically contacts and rubs against the cylinder wall during engine operation, the cylinder wall and the piston may be damaged which might necessitate expensive repairs. To prevent such an occurrence, each piston utilizes snap ring retainers or wire end locks made of spring steel located at each end of the wrist pin. Specifically, the snap ring retainer is operatively mounted in an annular blind retainer slot or groove formed in the piston's wrist pin bore positioned at the outboard end of the wrist pin. A snap ring retainers at each end of the wrist pin maintains the wrist pin in centered position with each end portion spaced away the respective cylinder wall thus eliminating any potential damage to the cylinder wall and the piston.
Previously, punches and other similar hand tools have been used to force the snap ring into a radially constricted configuration and into the end portion of the pin bore for subsequent radial expansion into its annular blind retainer slot. Specifically, a tubular guide sleeve has been used to feed or move a snap ring retainer into and along wrist pin bores. However, use of this tubular guide sleeve has proven difficult especially for initially aligning the retainer and maintaining alignment once in the wrist pin bore. Even those having a high level of mechanical skill experience pop-out of a snap ring retainer from the guide sleeve at either the inboard or outboard end of the wrist pin bore rather than desired seating in the associated annular blind retainer slot. Thus, difficulties are often encountered by use of such tools in the installation of resilient snap ring retainers partly due to the problem of sensing exactly when the snap ring retainer is aligned with the annular blind retainer slot. Use of such tools frequently overcompresses the snap ring retainers in an inward radial direction which results in a weakened outward radial retention force necessary for the snap ring retainer to maintain its retention in the annular blind retainer slot. Use of these tools also imposes significant side loads on the snap ring retainers sufficient to distort and overstress the snap ring retainer and the damage is often sufficient to prevent a proper seating of the snap ring retainer in the annular blind retainer slot. Resultantly, this damage sometimes results in a disengaging movement or “popping-out” of the snap ring retainer from it's annular blind retainer slot which may possibly permit undesirable contact of an end of the wrist pin with the cylinder wall.
SUMMARY OF THE INVENTION
An object of this invention is to provide a new and improved installation tool for seating a snap ring type retainer into an associated annular blind retainer slot formed in a piston's wrist pin bore so as to properly maintain the wrist pin in a centered relationship with the piston. The tool further ensures that the snap ring retainer is not subjected to any substantial deformation which might damage the snap ring retainer and cause it to subsequently pop-out of its annular blind retainer slot. Typically, each piston utilizes two snap ring retainers, each seated in its own annular blind retainer slot formed in the piston's wrist pin receiving bores. One of the snap ring retainers is located at each of the opposite ends of the wrist pin for controlling axial movements of the wrist pin. Difficulties occur both in initially constricting the snap ring retainers in a radial direction and in then inserting and moving the snap ring retainer along the wrist pin bore. In addition, it is difficult to sense when the snap ring retainer has been axially displaced into a desired position where the snap ring retainer is free to radially expand or snap outward into the annular blind retainer slot which slots are hidden during installation of the snap rings.
By use of the subject installation tool, the snap ring retainer is gradually constricted radially to a predetermined diameter insufficient to result in over-compression as it is moved progressively into and along the piston's wrist pin bore. This simplifies the overall installation of the snap ring retainer from its initial loading into a guide and installation sleeve portion to its final insertion where the snap ring retainer expands into it's annular blind retainer slot. Further, the use of this tool is very straight forward so that it is readily used by persons even with minimal mechanical skills. Further, the subject tool fully contains and confines the snap ring retainers during installation thus minimizing any opportunity for the snap ring retainer to pop out or be damaged from over stressing.
Another object of this invention is to initially position and support the snap ring retainer in a guide and installation portion of the tool which has a fixed diameter bore adapted to receive the snap ring retainer and further having another portion with a tapered or funnel-like configuration to move the snap ring retainer and simultaneously radially constrict the snap ring retainer. This structure maintains the snap ring retainer in a natural transverse orientation and evenly loads it during displacement toward the annular blind retainer slot and also importantly minimizes the extent of the snap ring retainer's radial constriction. Accordingly, the radial compression or constriction of the snap ring retainer is carried out by the progressively tapered inner bore of the installation sleeve which has a minimum internal diameter corresponding to only a just sufficient minimum diameter equal to the diameter of the piston's wrist pin bore so as to prevent overcompression of the snap ring retainer and thus any chance of damage.
Another object of this invention is to simplify installation of wrist pin snap ring retainers and minimize loss or damage of such snap ring retainer during installation. The tool includes an installation sleeve with a tapered bore having a minimum internal diameter equal to the piston's wrist pin bore diameter for preventing over constriction or compression of the snap ring retainer. Cooperating with the installation sleeve is a specialized plunger assembly having a forward pin setting portion for piloting the snap ring retainer into the internal diameter of the piston's wrist pin bores. The plunger assembly inclu
Emmer Eric D
Loughlin Neil W
Bacon, Jr. Edwin W.
DaimlerChrysler Corporation
Wilson Lee
LandOfFree
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