BACKGROUND Some engine componentry, particularly crankshafts and thrust bearings, oftentimes requires surface finishes of higher quality than surface finishes of other engine components. The finishing, or"superfinishing,"of such engine componentry has been effectuated in the related art by removing the subject component from the engine, fixturing the part, and applying an oscillatory motion of a superfinishing stone to the part. The superfinishing stone is appropriately geometrically and abrasively formed. The engagement of the superfinishing stone and the subject component and the oscillatory motion of the stone on the surface of the component creates the desired surface finish. Pressure applied to the surface through the stone is adjustable depending upon the desired final finish, thereby allowing extremely high quality finishing to be achieved.

Devices of the related art available for the superfinishing of surfaces generally require that the particular component to be finished be removed from the machine before the finishing process can be executed. The time required for superfinishing of the componentry of the machine generally results in a considerable amount of downtime of the operation of the machine. A significant amount of such downtime is often attributed to the disassembly of the machinery in order to allow the components requiring superfinishing to be removed therefrom.

Other downtime is attributable to the superfinishing operation itself as well as the reassembly of the machinery. Such downtime may significantly increase the overall costs associated with the machine.

SUMMARY An apparatus for the in situ superfinishing of crankshaft thrust bearing surfaces is described herein. The apparatus includes an oscillator, an oscillation arm connected to the oscillator such that the oscillation arm is reciprocable by the oscillator, a caliper disposed on the oscillation arm in a location remote from the oscillator, and at least two abrasive pads disposed on the caliper.

The oscillation arm is configured, positioned, and dimensioned to facilitate the extension of the arm into the engine to cause the abrasive pads to engage the bearing. The abrasive pads are configured to abrasively superfinish the surfaces of the bearing.

A method for the in situ superfinishing of the surfaces of the bearing includes operably locating a superfinishing apparatus adjacent the engine, extending the abrasive pads into the engine, causing the abrasive pads to engage the surfaces to be superfinished, and oscillating the abrasive pads in contact with the surfaces to be superfinished.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic end view of a crankshaft and thrust bearing with an in situ superfinishing apparatus mounted on the exterior of the engine wall and engaged with the thrust bearing.

FIGURE 2 is a side view of the oscillation arm.

FIGURE 3 is a top plan view of the oscillation arm.

FIGURE 4 is a top plan view of the caliper.

DETAILED DESCRIPTION Referring to FIGURE 1, a crankshaft assembly is shown generally at 8. Crankshaft assembly 8 comprises a crankshaft 10 positioned adjacent to an inner wall of an engine block 12 of an engine (not shown) into which crankshaft assembly 8 is incorporated. Crankshaft 10 provides articulated movement to connecting rods and pistons (not shown) of the engine during operation thereof. A thrust bearing 14 is maintained in operable association with crankshaft 10.

An in situ superfinishing apparatus for use with crankshaft assembly 8 is shown generally at 15 and is hereinafter referred to as"superfinishing apparatus 15."Superfinishing apparatus 15 comprises an oscillator arm 24, a caliper 36 extending substantially coaxially from one end of oscillator arm 24 and mounted thereon via pins 40, and abrasive pads 42 disposed on an end of caliper 36 distal from oscillator arm 24. Abrasive pads 42 are maintained in mechanical communication with thrust bearing 14. An opposing end of oscillator arm 24 extends through an outer wall of engine block 12 and includes an oscillator 22 mounted thereon. An adjuster support, shown generally at 20, is disposed on oscillator arm 24 intennediate oscillator 22 and the outer wall of engine block 12.

Adjuster support 20 is pivotally mounted to the outer wall of engine block 12 using a pin 19 extending therethrough. Ends of pin 19 are secured by a clevis 18 mounted on a bracket 16. Pivotal adjustment of adjuster support 20 is effectuated by the repositioning of a set screw 21 disposed through adjuster support 20 and mounted into bracket 16. The degree of lateral movement of oscillator arm 24 depends upon the length of pin 19 along which adjuster support 20 can laterally translate as well as the width of adjuster support 20. The range of lateral movement is preferably about one half to two inches. Operative portions of oscillator 22 are fixedly connected to oscillation arm by fasteners (not shown) extending through oscillator 22.

Referring now to FIGURES 2 and 3, oscillation arm 24 is illustrated in greater detail. Oscillator arm 24 is fabricated from a lightweight material such as aluminum and comprises an attachment end 28 through which holes 26 extend, an extension section 30 disposed on attachment end 28, and a caliper attachment section 32 disposed on extension section 30. Caliper attachment 32 is an offset clevis having an opening 34 appropriately dimensioned to receive the caliper. Pin openings 38 extend through the offset clevis to provide access for the pins that connect the caliper to caliper attachment 32. The dimensions of the offset clevis and an opening 34 thereof are such that the caliper can be maintained on caliper attachment section 32 with some degree of play between the caliper and the defining surfaces of the offset clevis. Tolerances between the outer surfaces of the

pins and pin openings 38 are such that the pins may axially rotate in pin openings 38, thereby enhancing the flexibility of the caliper relative to oscillation arm 24.

Referring now to FIGURE 4, caliper 36 is shown in greater detail.

Caliper 36 comprises a first caliper finger 36a and a second caliper finger 36b, each being individually connected to caliper attachment section 32 by a pin extending through a corresponding pin opening 38. Caliper fingers 36a, 36b are spacedly arranged to enable each abrasive pad 42 to maintain mechanical communication with respective opposing surfaces of the thrust bearing. Materials of construction of caliper fingers 36a, 36b include, but are not limited to, aluminum and other lightweight materials having rigidity sufficient to reduce the effects of cantilevered weight on the oscillator.

Caliper fingers 36a, 36b are furthermore biased together with a biasing element. The biasing element, as shown in FIGURE 4, comprises an arrangement of tension springs 44 disposed between each caliper finger 36a, 36b.

Tension springs 44 are sized for caliper 36 to provide a tensile force selected for maintaining appropriate frictional communication between each abrasive pad 42 and its respective surface for which finishing is desired. The tensile force provided by the arrangement of tension springs 44 is selected such that between about 3 and about 5 lb/in2 of compressive force is maintained on abrasive pads 42 when abrasive pads 42 are maintained in operable contact with the thrust bearing.

Providing the finishing force at caliper 36 utilizing the biasing element reduces bending movement that would otherwise be required along the oscillation arm, thereby deflecting such bending movement from the oscillation arm and imposing the stresses associated therewith on the oscillator itself and its bracketry. By avoiding such bending movement, a much simpler design can be realized while superior finishing characteristics can be maintained.

Abrasive pads 42 comprise an abrasive material disposed on a backing material. The abrasive material is generally finely graded diamond particles securely anchored to the backing material with a metal plated bond or resin bond. Abrasive pads 42 are dimensioned to enable operation of the, superfinishing apparatus in a space having clearance of less than about 3/8 inches.

Such abrasive pads are known as flexible diamond products and are commercially available from various suppliers including 3M in Minneapolis, Minnesota.

Referring back to FIGURE 1, the operation of superfinisl-iing apparatus 15 is described. The rotational motion of crankshaft 10 during operation of the engine necessitates the rotational motion of thrust bearing 14. Caliper 36 extends from caliper attachment section 32 such that mechanical communication can be maintained between abrasive pads 42 disposed on the caliper fingers and the outer surfaces of thrust bearing 14. The biasing element effectuates the mechanical communication to ensure that frictional contact is maintained between abrasive pads 42 and the outer surfaces of thrust bearing 14. Upon rotation of thrust bearing 14 and the oscillation of oscillation arm 24, the frictional contact between abrasive pads 42 and the outer surfaces of thrust bearing 14 causes the superfinishing of the surfaces of thrust bearing 14. Because of the flexibility provided in caliper attachment 32 via pins 40 disposed in the pin openings, caliper 36 is self-centering with respect to thrust bearing 14. Self-centering of caliper 36 necessitates the equal application of pressure by abrasive pads 42 to the surfaces of thrust bearing 14, thereby ensuring that a proper and even finish is applied to thrust bearing 14.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.