Patent Publication Number: US-7895982-B2

Title: Refurbished camshaft and method

Description:
TECHNICAL FIELD 
     This patent disclosure relates generally to rotating eccentric shafts for use in internal combustion engines and, more particularly, to refurbished or repaired camshafts having had worn or damaged lobes. 
     BACKGROUND 
     Rotating shafts having eccentric features formed on portions of their outer surfaces are commonly used in various machines requiring cyclically timed mechanical events or actuations of various components. For example, an internal combustion engine may use a rotating camshaft for timed actuation of intake or exhaust valves controlling the flow of air and exhaust into and out from one or more combustion chambers. Camshafts are typically unitary structures having lobes or eccentric features protruding therefrom. The lobes are arranged to periodically push onto a roller or follower connected to another engine component, where the roller or follower tracks an outer periphery or race of each lobe. 
     In a typical camshaft application, each lobe is continuously in contact with a roller or follower. The interface between the cam lobe and follower is continuously subject to compressive forces and friction, causing wear and/or damage to the lobe during prolonged use, or when a defective condition is present. For example, in instances where inadequate lubrication of the interface is provided and/or situations when the follower is not properly aligned with its respective lobe, wear and/or damage to the lobe may occur. A damaged lobe may directly affect the motion of the follower and, hence, operation of the engine. 
     SUMMARY 
     The disclosure describes, in one aspect, a method of refurbishing a camshaft having at least one defective lobe. The method includes removing material from the at least one defective lobe to create a neck region. An alignment feature is introduced in the neck region indicative of a previous orientation of the defective lobe. A lobe blank is installed around the neck region and oriented with respect to the alignment feature. The lobe blank is refined to match a lobe profile of the defective lobe. 
     In another aspect, the disclosure describes a refurbished camshaft. The refurbished camshaft includes a camshaft core having a centerline. The neck region and at least one alignment feature are formed at an axial location on the camshaft core. A lobe blank having a neck opening surrounds the neck region. Proper orientation of the lobe blank is accomplished by the alignment feature formed in the neck region. The lobe blank includes at least two portions connected to each other to form a rigid structure around the neck region. In an alternate embodiment, the refurbished camshaft includes at least two portions that are connected to each other via the lobe blank, which is a single piece, to form a rigid structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross section of a camshaft installed in an internal combustion engine in accordance with the disclosure. 
         FIG. 2  is a side view of a camshaft having a damaged lobe in accordance with the disclosure. 
         FIG. 3  is a partial outline view of a camshaft having a neck region resulting from the removal of a damaged lobe in accordance with the disclosure. 
         FIG. 4  is a partial outline view of an alignment feature formed in the neck region of a camshaft in accordance with the disclosure. 
         FIG. 5  is a breakaway view of a segmented camshaft during installation of a lobe blank in accordance with the disclosure. 
         FIG. 6  is an assembled view of a segmented camshaft having a lobe blank installed onto the neck region in accordance with the disclosure. 
         FIGS. 7-9A  are alternative embodiments of lobe blanks having various alignment features in accordance with the disclosure. 
         FIGS. 10-13  are alternative embodiments of segmented lobe blanks having various connection configurations and various alignment features in accordance with the disclosure. 
         FIG. 14  is an alternate embodiment for a lobe blank having a lobe-shaped alignment feature in accordance with the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure relates to camshafts for use with internal combustion engines. The disclosure provides various embodiments for the apparatus and methods associated with reworking or refurbishing a camshaft having a worn or damaged lobe in a remanufacturing facility, to avoid scrapping the returned camshaft in favor of a new one. The camshaft described herein is configured for use in actuating fuel injectors for a unit injection system. The devices and methods described and used herein, nevertheless, have broad applicability not only to camshafts used to operate other systems on an internal combustion engine, but also to different applications for camshafts in general, for example, camshafts operating valves in reciprocating pumps, and so forth. 
       FIG. 1  is a partial section view of a camshaft  100  used to operate a unit fuel injector  102  installed on an internal combustion engine  104 . The camshaft  100  includes a central shaft portion or camshaft core  106 , which typically has a circular cross section, and a plurality of lobes  108  successively positioned along the camshaft core  106 . Each lobe  108  has a base portion  110 , which is typically circular in cross section and surrounds the camshaft core  106 , and an actuator portion  112 , which extends eccentrically from the base portion  110  and which follows a path  114  as the camshaft  100  rotates. 
     In this exemplary application the camshaft  100  is arranged for operating the injector  102 , and other injectors, by cyclically actuating a plunger  116  of the injector  102 . The injector  102 , being a unit injector, is capable of compressing fuel by motion of the plunger  116 , which acts as a reciprocating piston pump within the injector  102 . As the camshaft  100  rotates and the actuator portion  112  of the lobe  108  follows the path  114 , the lobe  108  comes into contact with the plunger  116 , pushing it in a compressing direction. Fuel compressed within the injector  102  by motion of the plunger  116  exits the injector  102 , typically as a mist, via a plurality of openings formed in a nozzle portion  118  of the injector  102 . 
     The nozzle portion  118  of the injector  102  is located within a combustion cylinder  120  of the engine  104 . The combustion cylinder  120  has a variable volume defined between a bore  122  formed in a crankcase  124  of the engine  104 , a cylinder head  126 , and a reciprocating piston  128  located within the bore  122 . During operation of the engine  104 , air and fuel are compressed within the combustion cylinder  120  and ignited, pushing the piston  128  and generating work. Work is transferred from the piston  128  to a crankshaft (not shown) via a connecting rod  130 , thus generating power while the engine  104  operates. 
       FIG. 2  is a side view of the camshaft  100 . As shown here, the camshaft  100  is arranged to operate an engine having four cylinders, each cylinder associated with three lobes  108  that operate, respectively, the intake valves, exhaust valves, and injector associated with each cylinder. Each lobe  108  has a different orientation or phase shift with respect to adjacent lobes  108 . The lobes  108  are arranged in sets of three with bearing portions  202  occupying the space between each set. While the lobes  108  are eccentric, the bearing portions  202  are cylindrical and concentric with a centerline  204  of the camshaft  100 . The bearing portions  202  are used to provide support along various locations along the centerline  204  when the camshaft  100  is installed into an engine. 
     Wear or damage to the lobes  108  and/or bearing portions  202  may occur in situations when inadequate lubrication, misalignment, or another failure occurs that affects the working interface between each lobe  108  and another component of the engine  104 , for example, the plunger  116  shown in  FIG. 1  or, in general, any follower component contacting the lobe. Such conditions can cause excessive wear or scuffing of one or more of the lobes  108  or bearing portions  202 , which can lead to replacement and scrapping of the camshaft  100 . For illustration, a defective lobe  206  is shown in  FIG. 2  having scuff marks or scratches  208  formed thereon, but other lobes  108  or bearing portions  202  may be damaged. Up to now, the camshaft  100  having the defective lobe  206  or bearing portion  202  would have been scrapped and replaced with a new one because repair or reconditioning was deficient if not impossible. The camshaft  100 , however, may advantageously be rebuilt or reconditioned as described below. 
     When the camshaft  100 , or others having similar failures, are returned to a remanufacturing facility, they may first be inspected to determine conformance with dimensional specifications. For example, some camshafts may fail this inspection because their centerlines  204  are skewed from their desired linearity. In such situations, these camshafts will fail in the same or a similar fashion even if a defective lobe or bearing is replaced, and are either scrapped or undergo a process to restore the linearity of their centerlines. In cases, however, when the only defect is the defective lobe  206  or bearing portion  202 , then the camshaft  100  may progresses on to be reworked and have the defective lobe  206  or bearing portion  202  replaced with a new one. 
     The rebuilding process may begin with a grinding or machining operation to remove the defective lobe  206 . As shown in the partial view of  FIG. 3 , the defective lobe  206  is ground down at least partially or, in this case entirely, leaving a neck region  302  in its place. The neck region  302  may be formed, for example, by turning the camshaft  100  on a lathe or subjecting the camshaft  100  to a single or multi axial machining process. When a lathe is used, the neck region  302  may have a cylindrical shape and be concentric with the centerline  204  of the camshaft  100 . As can be appreciated, more than one defective lobe  206  may be ground at the same time. Optionally, the neck region  302  may be ground to have an outer diameter that is smaller than a diameter of the camshaft core  106  of the camshaft  100  to create a shoulder  304  on either side of the neck region  302  along the centerline  204 . If a shoulder  304  is not deemed necessary, the neck region  302  may be formed with either a larger or smaller diameter than the diameter of the camshaft core  106 . 
     After the neck region  302  has been defined, the camshaft  100  may be oriented in a fixture and a key or alignment feature  402  may be formed in the neck region  302 . The alignment feature  402 , in this case, is a flat portion  404  formed in the neck region  302  by cutting away material from the camshaft core  106 . Orientation of the flat portion  404  with respect to the remaining lobes  108  of the camshaft  100  is important because the flat portion  404  will be used to orient a replacement lobe in a subsequent process. As can be appreciated, the alignment feature  402  may take on many different forms depending on the design selected and is not limited to one or more flat portions being formed in the neck region  302 . 
     The camshaft  100  in the state shown in  FIG. 4  is ready to receive a replacement lobe or bearing portion blank. As shown, the camshaft  100  is adapted to receive a lobe blank, but the processes and methods disclosed herein are equally adaptable for replacement of a bearing portion. Two embodiments are disclosed herein for connecting a replacement lobe to the camshaft  100  having the neck region  302  and flat portion  404  formed thereon. The description will be focused on replacement of a lobe, which requires a more precise alignment to the camshaft  100 , but the methods can easily be adapted for a bearing blank. In the first embodiment, the camshaft  100  is cut along a surface  500  as shown in  FIG. 5 . The cut, which can be performed after an alignment feature has been formed in the neck region  302 , separates the camshaft  100  into a first and second portions  502  and  504  at a cut location  506  along the centerline  204 . Each of the first and second portions  502  and  504  advantageously retains at least a portion of the alignment feature or flat portion  404  thereon to aid in proper re-assembly of the camshaft  100 . The surface  500  shown in  FIG. 5  is planar and intersects the centerline  204  perpendicularly. Of course, the surface  500  may be non planar, or may even intersect the centerline  204  at a different angle to facilitate alignment during re-assembly of the first and second portions  502  and  504 . Moreover, dowel holes or other alignment features may be formed in the neck region or surface  500  to facilitate re-assembly of the camshaft  100 . 
     After the first portion  502  has been separated from the second portion  504 , a lobe blank  508  having a neck opening  510  may be inserted over the neck region  302  between the first portion  502  and second portion  504 . The neck opening  510  may be circular and have an internal diameter forming a clearance fit with the outer diameter of the neck region  302 . In the configuration illustrated where the neck region  302  has a flat portion  404 , the lobe blank  508  may have a ledge  512  formed on one side of the neck opening  510  that fits over the flat portion  404  to align the lobe blank  508  with respect to the remaining lobes  108  and also to align the first portion  502  with the second portion  504  of the camshaft  100 . Alternatively, the fit between the neck opening  510  and the neck region  302  may be an interference fit requiring a press-fit operation to push the first portion  502  and second portion  504  together and within the lobe blank  508 . 
     After the lobe blank  508  has been installed and the first portion  502  has been pushed together with the second portion  504 , the camshaft  100  may be inspected for linearity of the centerline  204  and for its total length before being permanently connected, for example, by welding the lobe blank  508  into place along two seams  602  (only one visible) to create a rigid structure. As can be appreciated, this permanent connection can be used to fuse the lobe blank  508  with each of the first portion  502  and second portion  504  to yield a unitary structure. Alternative methods of connecting the first and second portions  502  and  504  with the lobe blank  508  include press-fitting, brazing, use of adhesives, and so forth. 
     In a final and optional operation, the shape of the lobe blank  508  may be refined to match a desired lobe profile. In cases, for example, where more than one type of camshafts are reconditioned in the same facility, a single lobe blank piece may be used to repair any defective camshafts. Moreover, lobe blanks may be used to replace bearing portions of the camshaft. In this case, the blank would be refined to remove any eccentricity to yield a cylindrical bearing portion. In the case of lobe replacement, because different camshafts may be processes in a single facility and each of the camshafts may have different lobe shapes, the lobe blanks may be shaped in a machining or grinding operation to achieve the desired contour. 
     Three different embodiments of lobe blanks are shown in  FIGS. 7 through 9 . These lobe blanks may also be used to replace bearing portions or, alternatively, bearing blanks that are generally cylindrical may be used. In  FIG. 7 , the lobe blank  508  described thus far is presented. As stated previously, the lobe blank  508  has a neck opening  510  that defines a flat spot or ledge  512 . The ledge  512  helps not only to align the lobe blank  508  with respect to the camshaft  100 , but is also useful in aiding the lobe blank  508  to withstand torsional loading during operation. A second embodiment for a lobe blank  808  is shown in  FIG. 8 . The lobe blank  808  also has a neck opening  810  but, in this case, the neck opening  810  is surrounded by a hexagonal key feature having six symmetrically arranged sides  812 . In this case, the neck region of a corresponding camshaft would have a hexagonal shape corresponding to the shape of the neck opening  810 . It can be appreciated that a shape such as this, even if more difficult to manufacture, is better suited to withstand torsional loading tending to shear the interface between the lobe or bearing blank and the neck region of the camshaft. 
     A third embodiment for a lobe blank  908  is shown in  FIG. 9 . In this embodiment, a neck opening  910  of the lobe blank  908  has two opposing flat spots or ledges  912  formed around the neck opening  910 . This arrangement is easier to manufacture than the second embodiment shown in  FIG. 8 , and is more effective in dealing with torsional stresses causing shear along the interface between the lobe blank and the neck region than the first embodiment shown in  FIG. 7 . 
     A cross section of a variation on the third embodiment for a lobe blank is shown in  FIG. 9A . This variation includes an optional spacer  914  disposed within neck opening  910 . The spacer  914 , which may be formed unitarily or added as a separate piece with not just the lobe blank  908  but with any of the lobe blanks described in this disclosure, can be used to correct the overall length of the camshaft  100 . As can be appreciated, some material from the neck region  302  may be lost when the camshaft  100  is cut. For example, if the camshaft  100  is cut using a band saw, a segment of material corresponding to a length of the camshaft  100  that is about equal to the thickness of the cutting blade on the band saw will be lost during the cut. The spacer  914  can advantageously restore the material lost during cutting of the camshaft  100  and bring the overall length of the re-assembled camshaft  100  close to its original length. Of course, the spacer  914  can also be used when replacing a bearing portion of the camshaft  100 . 
     The different configurations for key features presented thus far are not deemed exhaustive and are used simply for illustration. Other configurations are possible and considered to be within the scope of the present disclosure. One similarity between the embodiments for lobe blanks presented in  FIGS. 7-9  is that each lobe blank is made from a single piece of material, typically metal or ceramic, that fully surrounds the neck opening. Therefore, installation of such lobe blanks requires cutting of the camshaft at the neck region, as described, installation of the lobe blank, and then re-assembly and alignment of each camshaft portion to yield a reconditioned camshaft. 
     In an alternate method, the lobe or bearing blank may be segmented instead of the camshaft to avoid the processes of re-assembling and re-aligning the portions of the camshaft. This alterative embodiment is similar to the embodiment described above up to the point when the camshaft  100  is brought to the state described and shown in  FIG. 4 , namely, after the defective lobe  206  or bearing portion  202  of the camshaft  100  is removed and the neck region  302  and flat portion  404  are formed. Following this operation, a segmented lobe blank  1008  is inserted directly over the neck region  302  instead of cutting the camshaft  100 . The description below relates to a replacement lobe for illustration of the process used for reconditioning the camshaft, but is equally applicable to replacement of a bearing blank. 
     One example of a segmented lobe blank  1008  is shown in  FIGS. 10 and 11 . The segmented lobe blank  1008  in this example is made by connecting a first section  1010  and a second section  1012 . Each section  1010  and  1012  has a concave feature formed therein, which when the first section  1010  is connected to the second section  1012 , forms a neck opening  1014  that surrounds the neck region  302  of the camshaft  100 . Features aiding the alignment between the first section  1010  and second section  1012  include a protrusion  1016  formed in one section and corresponding to an opening  1018  in the other section, and a fastener opening  1020  configured to receive a fastener  1022  and arranged to secure the two sections  1010  and  1012  to each other. Similarly, a ledge or other features of the lobes described thus far may be used to align each or both of the first and second sections  1010  and  1012  to the neck region  302 . Of course, even though one fastener is shown here connecting the first and second sections  1010  and  1012  to each other, it can be appreciated that more than one fasteners or more than one protrusions can be used to connect and align the various sections of a lobe blank to each other. 
     An alternate embodiment for a segmented lobe blank  1208  is shown in  FIG. 12 . In this embodiment, the segmented lobe blank  1208  includes a first portion  1210  and a second portion  1212 . When connected, the first and second portions  1210  and  1212  form a symmetrical opening  1214  that surrounds a neck region  1216  of the camshaft. Alignment of the assembled segmented lobe blank  1208  with the neck region  1216  is accomplished by a fastener  1218  passing through the first portion  1210 , the neck region  302 , and the second portion  1212 . In this case, the alignment feature is an opening that accepts the fastener  1218 . The fastener  1218  passes through a first opening  1220  in the first portion  1210 , a neck opening  1222  formed in the neck region  1216  and oriented along a diameter thereof corresponding to the desired orientation of the lobe, and a second opening  1224  formed in the second portion  1212  and having threads engaging the fastener  1218 . Additional alignment features on the neck region  1216  and/or the segmented lobe blank  1208  may not be required for this embodiment because alignment may be accomplished by simply assembling the fastener  1218  by connecting the first and second portions  1210  and  1212  through the neck opening  1222 . 
     Even though fasteners have been illustrated thus far to connect the various segments or portions of the segmented lobe blanks, other methods or combination of methods can be used. For example, a segmented lobe blank  1308  including a first portion  1310  and a second portion  1312  is shown in  FIG. 13 . The segmented lobe blank  1308  is shown assembled around a neck region  1314  having two flat portions  1316  along the interface therebetween. The first portion  1310  and second portion  1312  are welded to each other along two weld beads  1318 . Welding is a practical mode of connection between the first and second portions  1310  and  1312  inasmuch as any weld spatter or protrusion of weld material beyond the desired lobe profile may be ground or machined off when the segmented lobe blank  1308  is refined by machining its outer portion to the desired contour. Alternatively, welding or a plug may be used to secure the head of a fastener to the lobe blank to prevent loosening or “walking out” of the fastener during service. Further, weld material may be used to fill-in the opening around the head of the fastener. Optionally, one may even forego use of welding or fasteners in favor of adhesives, for example various epoxies, brazing, or soldering processes to connect the various portions of the lobe blanks to each other and even to the neck region of the camshaft. 
     The foregoing description relative to the neck region of the camshaft has included a grinding or machining process to entirely remove the defective lobe or, alternatively, a defective bearing portion, leaving a cylindrical neck section on the camshaft. A damaged lobe or bearing will typically have damage or wear along an outer portion or surface thereof. Therefore, the machining operation performed to remove the damaged or worn portions of the damaged lobe or bearing may advantageously be limited to the damaged or worn outer portion. Hence, the damaged lobe or bearing on a camshaft may undergo a limited machining to remove a layer of material from its outer portion, leaving a neck region having, respectively, a lobe-shaped or cylindrical profile. A lobe blank for such a situation would have a lobe-shaped neck opening. Such a lobe blank  1408  is shown in  FIG. 14 . The lobe blank  1408 , shown as a single structure for illustration, has a neck opening  1410  which follows the external profile of the lobe blank  1408  such that a wall thickness  1412  is substantially uniform. As can be appreciated, the lobe blank  1408  may be segmented into two or more portions, or may even be formed by a strip of material that is bent and formed around the neck region of the camshaft being reconditioned. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to the remanufacturing of engine components among other applications. More particularly, the methods described herein are well suited for repairing, reconditioning, or refurbishing camshafts having worn or damaged lobes. Various features and aspects are described in conjunction with specific embodiments, but it can be appreciated that individual features may be combined in ways not illustrated depending on the specific application. 
     When a worn or damaged camshaft is returned to a remanufacturer&#39;s facility, it can be first inspected to determine the nature and extent of damage. Even though some damaged camshafts may be scrapped, some or a majority of them will have acceptable dimensional characteristics overall, but also wear or scuffing damage to one or more of their lobes or bearings. For such camshafts, a reconditioning or rebuilding process may be applied to yield dimensionally and operationally acceptable components for re-use in service. 
     After a camshaft having one or more defective lobes and/or bearings has been identified, a machining operation may be used to remove either a layer of material from the damaged feature or the damaged feature entirely, leaving a relatively smooth neck region for attachment of a replacement blank. The neck region may take on any shape that is appropriate for connecting with a lobe or bearing blank. For example, the neck region may be cylindrical, with or without flat portions formed thereon for alignment. In general, the neck region may be circular or non circular, such as hexagonal or square, in cross section. Various alignment features may be formed in the neck region, for example, flat portions, openings, and so forth, before a blank is installed and connected to the camshaft forming a rigid structure. 
     Installation of the blank may be accomplished by first segmenting the camshaft at an axial location along its centerline intersecting the neck region. The blank may then be installed around the neck region before re-assembling the camshaft portions. Alternatively, the blank may be segmented and installed in two or more pieces around the neck region formed in the camshaft. In this instance, segmentation of the camshaft may not be necessary. The two or more blank portions may then be connected to each other and/or to the camshaft to form a rigid structure. 
     It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. 
     All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.