US20150020932A1

US20150020932A1 - Method of remanufacturing a rocker arm

Info

Publication number: US20150020932A1
Application number: US14/510,165
Authority: US
Inventors: Taylor Young; Kegan Luick; Jonathan R. Eggemeyer
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2014-10-09
Filing date: 2014-10-09
Publication date: 2015-01-22

Abstract

A method of remanufacturing a rocker arm is provided. The rocker arm includes a body defining a center hole for receipt of a shaft, a first arm extending radially away from the center hole, and a second arm extending radially away from the center hole in a direction opposite the first arm. The second arm is configured to be operatively engaged with a valve mechanism and includes a contact surface configured to engage with a braking member. The contact surface includes a worn upper hardened surface. The method includes machining the contact surface to a depth less than a predefined tolerance limit to remove the worn upper hardened surface and create a generally planar unhardened contact surface. The method further includes hardening the unhardened contact surface using a laser to create a repaired contact surface with a surface hardness of greater than at least Rockwell C 50.

Description

TECHNICAL FIELD

The present disclosure relates to a method of remanufacturing a rocker arm.

BACKGROUND

Rocker arms are typically used in an engine to actuate various valve train components, such as intake and exhaust valves. During normal operation of the engine, the rocker arms may be controlled by a camshaft to actuate the intake and exhaust valves. Such rocker arms may also perform an additional engine braking function. An engine braking system may actuate the rocker arm to open the exhaust valves in order to achieve engine braking. Typically, a component of the engine braking system engages with the rocker arm for actuation. This may lead to wear of the rocker arm. Such wear may have an adverse effect on engine braking performance. Therefore, the rocker arm may require replacement.
Many methods for manufacturing rocker arms are known in the art. U.S. Pat. No. 4,872,429 (the '429 patent) discloses a low friction finger follower rocker arm which is fabricated from a flat metal strip sheet stock having a stamped configuration with a centralized opening adapted to be bent later into a channel. The shaping and hardening of the stock section is carried out prior to such bending. The '429 also discloses a method of manufacturing the rocker arm. The method includes shaping the stock to have a pair of aligned journal openings, a pivot surface at one end, a stud contacting surface at the other end, and a pair of grooves aligned with the extremities of the centralized opening and containing the surface therebetween. The method also includes locally hardening the surfaces and the edges of the opposed openings and bending the shaped stock along the grooves to form a partial channel having side walls with an included angle of no greater than 40 degrees and with the journal openings approaching alignment on a common axis. Local hardening may be carried out by a laser. The method further includes inserting a journalized low friction wear assembly in the opposed journal openings, and then completing the bending of the stock so that the sides of the channel are substantially parallel.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a method of remanufacturing a rocker arm is provided. The rocker arm includes a body defining a center hole for receipt of a shaft, a first arm extending radially away from the center hole for engaging a camshaft, and a second arm extending radially away from the center hole in a direction opposite the first arm. The second arm is configured to be operatively engaged with a valve mechanism. The second arm includes a contact surface configured to engage with a braking member. The contact surface includes a worn upper hardened surface. The method includes machining the contact surface to a depth less than a predefined tolerance limit to remove the worn upper hardened surface and create a generally planar unhardened contact surface. The method further includes hardening the unhardened contact surface using a laser to create a repaired contact surface with a surface hardness of greater than at least Rockwell C 50.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a partial sectional view of an exemplary engine having a rocker arm;

FIG. 2 illustrates a perspective view of the rocker arm with a contact surface;

FIG. 3 illustrates a method of remanufacturing the rocker arm, according to an embodiment of the present disclosure;

FIG. 4 illustrates a top view of the rocker arm with a machined contact surface, according to an embodiment of the present disclosure; and

FIG. 5 illustrates a top view of the rocker arm with a hardened contact surface, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts.
FIG. 1 shows a partial sectional view an exemplary engine 100 having an engine braking system 102. The engine 100 may be any internal combustion engine used in various types of industries, for example, construction, transportation, mining, power generation, and the like. The engine 100 may also be used to power various types of machines, for example, excavators, loaders, dozers, mining trucks, electric generators, and the like.
Referring to FIG. 1, the engine 100 may include a cylinder head 103 and a cylinder block (not shown). The cylinder block may include one or more cylinders. Each of the cylinders may slidably receive a piston (not shown) therein. Each cylinder may include a valve mechanism 105 including a pair of intake valves (not shown) and a pair of exhaust valves 104. Alternatively, the valve mechanism 105 may include any number of intake valves and exhaust valves 104. As shown in FIG. 1, the exhaust valves 104 may be biased to a closed position by a spring 106. Further, the valve mechanism 105 may also include a valve bridge 108 connected to the exhaust valves 104. A rocker arm 110 may selectively actuate the exhaust valves 104 from the closed position via the valve bridge 108.
The rocker arm 110 may include a body 112 having a first end 114 and a second end 116. The body 112 may further define a center hole 118 configured to receive a shaft 119 therein. The rocker arm 110 may be configured to rotate relative to the shaft 119. The rocker arm 110 may further include a first arm 120 extending radially away from the center hole 118 and a second arm 122 extending in a direction opposite to the first arm 120. The second arm 122 may include a channel 124 proximate to the second end 116. The channel 124 may receive an actuating member 126 therethrough. The channel 124 may include threads 125 (shown in FIG. 2) configured to engage with corresponding threads (not shown) of the actuating member 126. The actuating member 126 may be coupled to the rocker arm 110 and the valve bridge 108. Thus, the second arm 122 may be operatively engaged with the valve mechanism 105 via the actuating member 126.
Further, the first arm 120 may include two extensions 128 at the first end 114 of the rocker arm 110. Each of the extensions 128 may include apertures 130 that receive a roller 132 therebetween. The roller 132 may be rotatable relative to the extensions 128. The roller 132 may engage with a lobe 134 of a camshaft 136. Thus, the first arm 120 may be engaged with the camshaft 136 via the roller 132. The camshaft 136 may be rotatably disposed in the cylinder head 103. A person ordinarily skilled in the art may appreciate that the camshaft 136 may include a plurality of lobes along a length in order to actuate corresponding rocker arms associated with the intake valves and the exhaust valves 104 of the cylinders of the engine 100.
As shown in FIG. 1, the second arm 122 may include a contact surface 138. The contact surface 138 may be configured to operatively engage with the engine braking system 102. Specifically, the engine braking system 102 may include a housing 140 defining a hollow portion 142. A brake piston 144 may be slidably received within the hollow portion 142. A brake spring 143 may bias the brake piston 144 to a retracted position. A pin 145 may be coupled to the brake piston 144. The pin 145 may engage with the contact surface 138 of the second arm 122. The brake piston 144 may be hydraulically actuated from the retracted position against the biasing of the brake spring 143 in order to achieve engine braking.
The rocker arm 110, as described above, is for illustrative purposes only, and the rocker arm 110 may be of any alternative configuration within the scope of the present disclosure. Further, the rocker arm 110 may also be used for actuating the intake valves or any other component in a valve train of the engine 100.
During normal operation of the engine 100, the brake piston 144 may be in the retracted position. Based on the rotation of the camshaft 136, the lobe 134 may engage the roller 132. The rocker arm 110 may rotate about the shaft 119 and actuate the exhaust valves 104 from the closed position against the biasing of the springs 106. During engine braking, the brake piston 144 may be hydraulically actuated from the retracted piston. The pin 145 may move the rocker arm 110 and actuate the exhaust valves 104 from the closed position, thereby achieving engine braking Therefore, during engine braking, a force applied by the pin 145 on the contact surface 138 may have to overcome the biasing of the springs 106. Prolonged engagement of the pin 145 with the contact surface 138 may lead to wear of a portion of the contact surface 138, explained hereinafter in detail with reference to FIG. 2.
FIG. 2 illustrates a perspective view of the rocker arm 110. As shown in FIG. 2, the contact surface 138 may be substantially planar. Further, the contact surface 138 may be hardened by various methods known in the art. In an embodiment, a substrate material of the contact surface 138 may have a hardness of Rockwell 15N 85 with a case depth of at least 0.2 mm. Due to prolonged contact with the pin 145, a portion of the contact surface 138 may undergo wear. A worn upper hardened surface 202 is shown in FIG. 2 to illustrate the wear of the contact surface 138. The worn upper hardened surface 202 may be formed due to rubbing with the pin 145 during normal operation of the engine 100 and/or force exerted by the pin 145 during engine braking The worn upper hardened surface 202 may form a recessed area relative to a surrounding portion of the contact surface 138. Dimensional changes in the worn upper hardened surface 202 may alter a braking performance of the engine braking system 102. Specifically, actuation of the exhaust valves 104 from the closed position may change for a given movement of the pin 145. Therefore, the rocker arm 110 may have to be remanufactured so that the rocker arm 110 may provide an intended actuation of the exhaust valves 104 corresponding to a given movement of the pin 145.
FIG. 3 illustrates a method 300 of remanufacturing the rocker arm 110, according to an embodiment of the present disclosure. FIG. 4 illustrates a top view of the rocker arm 110 after machining the contact surface 138 (shown in FIG. 2), according to an embodiment of the present disclosure. Referring to FIGS. 3 and 4, at step 302 the method 300 may include machining the contact surface 138 to a depth less than a predefined tolerance limit to remove the worn upper hardened surface 202 and create a generally planar unhardened contact surface 204. A portion 206 of the unhardened contact surface 204 may illustrate the removed worn upper hardened surface 202. The machining may include grinding, honing, milling, turning, or a combination thereof. The predefined tolerance limit may include a permissible deviation from a design dimension of the contact surface 138. The design dimension may be a dimension of the contact surface 138 required for achieving optimum engine braking performance. The case depth of the contact surface 138 may also be removed due to machining In an embodiment, the worn upper hardened surface 202 may be removed incrementally by multiple machining steps and a dimension of a resultant surface after each machining step may be measured to determine if the resultant surface falls within the predefined tolerance limit.
FIG. 5 illustrates a top view of the rocker arm 110 after hardening the unhardened contact surface 204 (shown in FIG. 4), according to an embodiment of the present disclosure. Referring to FIGS. 3 and 5, at step 304, the method 300 may include hardening the unhardened contact surface 204 using a laser to create a repaired contact surface 208 with a surface hardness of greater than at least Rockwell C 50. In an example, a case depth of the repaired contact surface 208 may be at least 0.4 mm.
A laser beam may be used to heat the unhardened contact surface 204. The laser beam may be emitted by any laser system known in the art, for example, a pulsed laser system. The laser beam may heat the unhardened contact surface 204 in one or more passes. After heating by the laser beam, a quenching operation may be carried out to obtain a martensitic grain structure. The quenching operation may include air blasting the heated surface. Thus, a hardened contact surface may be obtained after heating by the laser beam and the subsequent quenching. In an embodiment, one or more finishing processes may be performed on the hardened contact surface to result in the repaired contact surface 208. The one or more finishing processes may include polishing the hardened contact surface to remove any oxidation marks.

INDUSTRIAL APPLICABILITY

The present disclosure is related to the method 300 for remanufacturing the rocker arm 110. The rocker arm 110, after remanufacturing, may include the repaired contact surface 208. Dimensions of the repaired contact surface 208 may be within the predefined tolerance limit which is required for optimum braking performance. Further, the hardness of the repaired contact surface 208 may be sufficiently high in order to withstand wear during operation. In an embodiment, the hardness of the repaired contact surface 208 may be higher than the hardness of the contact surface 138. The repaired contact surface 208 may consequently sustain reduced wear and have a longer operational life. Moreover, the method 300 may enable an existing rocker arm with wear to be remanufactured so as to be reusable in an engine. This may be cost efficient as compared to replacement of the existing rocker arm with a new rocker arm.
Further, the unhardened contact surface 204 may be hardened using a laser. Laser hardening may enable improved control of a heat treated area and non-contact processing. Further, distortion of a heat treated area may be minimized.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

Claims

What is claimed is:

1) A method of remanufacturing a rocker arm, the rocker arm including a body defining a center hole for receipt of a shaft, a first arm extending radially away from the center hole for engaging a camshaft, and a second arm extending radially away from the center hole in a direction opposite the first arm, the second arm configured to be operatively engaged with a valve mechanism and having a contact surface configured to engage with a braking member, the contact surface having a worn upper hardened surface, the method comprising:

machining the contact surface to a depth less than a predefined tolerance limit to remove the worn upper hardened surface and create a generally planar unhardened contact surface; and

hardening the unhardened contact surface using a laser to create a repaired contact surface with a surface hardness of greater than at least Rockwell C 50.