CAMSHAFTS AND METHODS OF MAKING SAME

Abstract: A plastic stabilized composite camshaft and method is described in which a hollow polished tube (22) is positioned within appropriately aligned and fixtured annular cam elements (28, 30) and a flowable, hardenable material (33) is injected through the tube (22) to fill the voids between the tube (22) and the cam elements (28, 30) for securing the cam elements (28, 30) to the tube (22). The surfaces (24) of the tube (22) and of the cam elements (28, 30) are preground to finish dimensions. In one embodiment, the annular cam elements (28, 30) are originally circular and formed into their final configuration in the mold (32) by appropriately configured side acting shuttles. In another embodiment, the shaft (54) is of drawn metal and includes a plurality of ribs (56) and the cam elements (44, 46, 48, 50) are precast of powdered metal and have a common interior configuration arranged to approximately match the ribbed configuration of the tube (54).

Description: CAMSHAFTS AND METHODS OF MAKING SAME This invention relates generally to shaft mounted cam elements and particularly to camshafts that are used in internal combustion engines. Camshafts for internal combustion engines are well-known. A camshaft comprises an elongate cylindri¬ cal metal shaft-having one or more bearing surfaces and one or more angularly positioned cam elements precisely located along the length thereof. The angu¬ lar positioning is with respect to the centerline of the cylindrical shaft. The cam elements control the opening and closing of the intake and exhaust valves of the internal combustion engine in the appropriate sequence as the camshaft rotates. Camshafts are manu¬ factured by forging or casting. They are then subjected to a number of very exacting and expensive machining operations to grind and polish, the circulator bearing surfaces and ' the oval-shaped cam element surfaces. Conventional camshafts are quite massive and contribute significantly to the weight of the automobile engine. Recently, the-automotive industry has devoted a great deal of effort to improve vehicle gasoline mileage, that is the number of miles a vehicle can travel for each, gallon of fuel consumed. In an effort to reduce weight, engines have been downsized and redesigned to use a lesser amount of material as well as to incorporate lighter weight materials. A feature that is growing in popularity, because of its reduced weight and higher efficiency, is the overhead camshaft. An overhead camshaft is supported above the cylinder head (outside of the engine block) and is driven in timed relationship with the engine crankshaft by means of gears and a timing belt. Its use obviates the need for push rods and rocker arms. One drawback is that an overhead camshaft generally makes a lot more noise than a conventional in-the-b.lock camshaft. There is also great impetus to achieve more power and efficiency from an engine. Newer designs often incorporate two intake valves per cylinder to assist in getting sufficient air/fuel mixture into the cylinder. Such, engines require two camshafts and emphasize the desirablity for lighter and more economical camshafts. The prior art has addressed this problem in a couple of ways. Camshafts have been proposed that use a hollow cylindrical tube as a shaft member with the individual cam elements being separately fabricated and either brazed or welded in position along the hollow tube. Because of the thermal expansions experienced by the separate elements, camshafts made in this manner still require expensive grinding operations. Therefore, while the w.eight of the finished camshaft is reduced, its cost is. not significantly impacted. Another technique involves positioning preformed cam elements, with apertures therein for reception of a shaft, in a support .fixture. The . fixture holds the*powdered metal cam elements in appropriate positions and a hol¬ low camshaft is. inserted through, the apertures. High. pressure is applied to the inside of the hollow camshaft to bulge i.t out where permitted, i.e., where it passes through, the cam elements.. This, action locks the cam elements to the shaft in a press: fit. Here again, the resulting camshaft is lighter in weight, but the forces involved necessitate expensive grinding of the camshaft bef? re it can be used. Thus there still exists a need in the art for a lightweight, low cost camshaft. The invention therefore is aimed to provide a novel camshaft and especially one that is lightweight and economical to manufacture. A camshaft characterized by a shaft member, a cam element positioned around said shaft member, a hardened, flowable material secur¬ ing said cam element and said shaft member in fixed relationship to each, other. A further aim of the invention is to provide a novel method for manufacturing a lightweight camshaft. The method of fabricating a camshaft characterized by the steps of positioning a shaft with respect to an annular cam element, and securing said cam element in position on said snaft by filling the voids between said shaft and said annular cam element with, a flow¬ able, hardenable material. Further features and advantages of the in¬ vention will be apparent upon reading the following description of preferred embodiments of the invention taken in conjunction with the drawings, in which: FIG, 1 is a perspective view of a prior art camshaft; FIG. 2 is. a representation of a portion of a camshaft cons.tructed in accordance with, the invention; FIG, 3 is a partial section through a portion of a camshaft constructed in accordance with thein¬ vention; FIG. 4 is. a cross section of FIG. 3 taken a long the line 4-4; FIGS, 5 and 6 are representations depicting one aspect of the invention in which the cam elements are formed in place; FIG. 7 is a partial cross section of a cam- shaft being manufactured in accordance with the inven¬ tion; FIG. 8 is a sectional view taken along line 8-8 of FIG. 7; and FIG. 9 is a cross section through a shaft and cam element constructed in accordance with a preferred form of the invention. Referring to FIG. 1, a prior art camshaft 10 includes a plurality of eccentric or oval-shaped cam elements 11 interspersed with cylindrical bearing surfaces 12 on an elongated, solid cylindrical shaft 13. Such a camshaft, when constructed in accordance with prior art techniques, is either forged or cast and thereafter subjected to a plurality of expensive grind¬ ing operations for polishing and finishing the surfaces 11 and 12 to the required degree of precision. Such camshafts have been manufactured for many years and de-. tails of their construction are well-known, In FIG * 2, a portion of a composite camshaft 20, constructed in accordance with the invention is shown. For purposes of clarity, the plastic fill material, e.g., the flowable, hardenable material that, in accordance with the invention, binds the cam elements to the shaft proper, is omitted. In this connection, the term plastic is used to denote a characteristic of a material and not as the name for any particular mat¬ erial. Thus metals are plastic when molten so as to be flowable. An elongated, hollow, cylindrical tube 22 is shown positioned within a pair of annular cam elements 28 and 30. Hollo tube or shaft 22 has a plurality of holes 26 formed therein, juxtaposed to respective ones of cam elements.28 and 30. **' As will be discussed, in accordance with, one form of the invention, the outer surface of hollow tube 22 is polished to finished dimensions of the camshaft, at least at the bearing surfaces of the camshaft. Two such bearing surfaces 24, indicated in dashed lines, are shown and are com¬ parable to the surfaces.12 in the prior art camshaft of FIG. l t Also, as will be explained, the outer surfaces of cam elements 28 and 30 are polished to their finished condition prior to being "installed" in proper position with, respect to hollow tube 22. In FIGS. 3 and 4, tube 22 is shown positioned in a mold cavity, generally indicated by reference numeral 32, that precisely holds, or "fixtures" cam elements 28 and 30 in their respective correct positions. The cam elements occupy different positions along hol¬ low tube 12 and have precise, but different, angular orientations, with, respect to the centerline of hollow tube 22. The parting line for 'the. two halves of the mold are offset for each, cam element to enable opening and closing of the mold without interference with the finished camshaft. The mold will also include ap¬ propriately located injection holes and vent holes for enabling the injection of plastic, i.e., flowable, hardenable material, generally indicated by reference numeral 33, to fill the voids between tube 22 and cam elements ' 28 and 30. Material 33 may comprise a glass filled polyester, although other types of plastic, hardenable materials may be used, including metals such as aluminum. The mold configuration or contour, il- lustrated by reference numeral 35, defines the precise " final configuration of the finished camshaft. Thus the exterior surface of tube 22 precisely matches the interior configuration of the mold where external bearing surfaces, such as surface 24, are desired. Consequently, no plastic material contacts bearing sur¬ face 24. The mold interior configuration also pre¬ cisely matches, the outer surfaces of cam elements 28 and 30, thus ■ preventing plastic material ifrom-contacting these surfaces. Similarly, the contour of the mold defines the outer configuration of the plastic, har¬ denable stabilizing material 33. As seen, the provision of holes 26 in tube 22 enables the flowable, hardenable material 33 to form interlocking elements between the tube ad cam elements which, provide excellent torsional resistance to preclude movement of cam elements 28 and 30 with, respect to tube 22. While only a limited number of holes 26 are illustrated, more may be intro¬ duced if required for increased torsional resistance, The techniques of molding on a mass produc¬ tion basis, utilizing side acting shuttles for po¬ sitioning parts, is also well-known. The preferred technique for constructing a plastic, stabilized com- posite camshaft is to provide a mold having an offset parting line for accommodating the various cam elements in their precise angular displacements with respect to the tube and to include individual side acting shut¬ tles, for automatically feeding prefinished cam elements into their respective positions. Similarly, the tubular shaft is inserted in the mold and through the fix- tured cam elements when the shuttles have completed their operations and the mold is closed. After closure of the mold, the hardenable, plastic material is in- jected into suitable entry ports to fill all cavities for rigidly affixing the individual cam elements in s their precise positions, and with, proper angular orienta¬ tions with, respect to the tube, upon hardening of the- material. When that occurs, the mold is opened and the finished camshaft is removed. Preferably, two methods of forming the cam elements are contemplated by the invention. In one method, the cam elements are preformed to their ec¬ centric shapes and finish, ground to precise tolerances. side acting shuttle mechanisms automatically feed and locate the finished cam elements in their appropriate respective positions in the mold cavity. In an- other, and presently preferred approach, for small engine applications., the cam elements are initially circular and formed into their final shape upon closure of the mold. The cam elements are preferably '-'sliced" from prefinished malleable tubing of appropriate diameter. They are formed into their eccentric final configura¬ tions in the process of being loaded into the mold by the shuttles and the final closure of the mold. The latter approach is illustrated in FIGS. 5 and 6 where the mold 32. is split into two portions 32a and 32b with matching parting lines 38 and 40. The interior surfaces 34 and 36 are precisely machined to the exterior dimensions of the finished cam element 28. Cam ring 28 ! is shown in an eccentric (oval) cross section (having originally been circular) . As indicated by the heavy arrows, during final closure of the mold 32,- its two portions 32a and 32 b are forced together at parting lines 38 and 40 as illustrated in FIG. 6. In so doing, cam ring 28* is forced into the appropriate configuration defined by the highly finished interior surfaces 34 and 36 of the mold portions 32a and 32b to form cam element 28, The spaces between tube 22 and cam element 28 will of course be filled with the flowable, hardenable stabilizing material 33 to maintain cam element 28 in a fixed position relative to tube 22. In practice, while hollow tube 12 has obvious, advantages from a weight standpoint, the invention contemplates the use of solid axle or shaft members as well. In such, case, the mold will be gated to inject the plastic, hardenable material adjacent the cam elements for fabricating a plastic stabilized composite camshaft. The cam elements and axle may be fabricated of heat treated steel. The cam elements may also be made of cast or powdered metal that is appropriately treated and finished, ' hile the exact dimensions of the cam elements and hollow tube will depend upon the intended use of the camshaft, it is presently contem¬ plated to use tubing having a wall thickness of 0.090" (0.228 cm) . The presently preferred embodiments of the invention for large engine applications, are illustrated in FIGS. 7-9. In these embodiments, cam elements are precast of powdered metal and the shaft or tube is drawn and has a generally ribbed exterior. The cam elements are cast with, oversized interior openings that cor¬ respond generally to the cross sectional configuration of the shaft to permit a relatively small space there- between for the flowable hardenable plastic stabilizing material. With, reference to FIGS. 7 and 8, the cross section along the length of tube or shaft 54 is seen to be non-symmetrical because of the ribbed configura- tion.of shaft 54. Camshaft 40 includes oval-shaped cam elements 44, 46, -.48 and 50 that are each precisely positioned in a mold 42 with respect to shaft 54. Flowable, hardenable plastic stabilizing material 58 fills the spaces between shaft 54, the cam elements and mold.40. A cylindrical bearing element 52 is also shown and is affixed to shaft 54 in the same manner. In these embodiments, the plastic material is conven¬ tionally injected or gated to the mold via a sprue 59, that feeds a header 60 that, in turn, supplies a plurality of runners 62, 64 and 66. As best seen in FIG. 8, shaft 54 has a plurality of protrusions, in the form of ribs or flutes 56, and the interiors of the cam elements team element 46 is shown) are configured to match the contour of the shaft cross section, but are oversized to allow space for the plastic material 58. It will be readily seen by those skilled in the art that it is desirable to arrange the flutes or ribs to place the interface of plastic, hardenable material 58 in compression rather than in shear when the camshaft is in operation. The precise configura¬ tions to be used are therefore a matter of design choice and the invention is not to be limited to any specific disclosed configuration. FIG. 9 shows a configuration of a further preferred embodiment of the invention for use in an automotive engine application. Computer modelling of the loads, using a commercially available high tem- perature engineering resin, has indicated very adequate strength and stability for the desing. As shown, a generally star-shaped interior cross section of the cam element 70 has "depressions" 74 matched with "pro¬ trusions or points" 76 on shaft 72, except for portions 78. An interface 80 of flowable plastic material sep¬ arates the points and depressions with reservoir areas 82 being interspersed to help in the injection pro¬ cess. The configuration has a symmetry that permits a single design cam element 70 to be used in each position of the camshaft by simply changing its angle of orientation. Obviously the angle θ between the ribs or points must be selected with the engine cam angle in mind to permit this degree of interchangeability. It will also be noted that minor interior dimensional differences are compensated for in the assembly process wherein the mold interior precisely defines the alignment of the cam elements with the tube or shaft. It will be appreciated that other changes in the described embodiments of the invention could be made which, would be apparent to those skilled in the art and which, therefore would be within the scope of the invention.

Claims: CLAIMS 1. A camshaft characterized by a shaft member; a cam element positioned around said shaft member, a hardened, flowable material securing said cam element and said shaft member in fixed relation¬ ship to eac other. 2. The camshaft of claim 1 characterized in that said cam element is annular and wherein said shaft member comprises a hollow tube with an orifice communicating with, the interior of said annular cam element. 3. The camshaft of claim 1 or 2 char¬ acterized in that said shaft member has a polished bearing surface. 4. The camshaft of claim 1 or 2 char¬ acterized in that said annular cam element is fabricated of cast material or malleable metal. 5. A camshaft characterized by a shaft member, a cam element having an inner surface adapted to fit over said shaft member, and interlocking means including hardenable, flowable material between said shaft member and said cam element for rigidly main¬ taining said cam element in position with respect to saidshaft member-. 6. The camshaft of claim 5, characterized in that said interlocking means further include one or more protrusions and depressions on said surface_of said shaft member and said inner surface of said cam element. 7. The camshaft of claim 6, char¬ acterized in that said protrusions comprise extended ribs on said surface of said shaft member and wherein said depressions comprise grooves on the inner surface of said cam element corresponding to said surface of said shaft member. 8. The camshaft of claim 7 characterized in that said ribs are arcuately spaced by an angle θ such that the inner configuration of said surface of said cam element permits a common cam element construc¬ tion for use in all required angular spacings of cam elements along said shaft member. 9. The camshaft of claim 5, 6, 7 or 8, characterized in that shaft member is formed of drawn metal and wherein said cam element is precast of powdered metal. 10. A.camshaft characterized by an elongated, drawn metal shaft member, a plurality of ribs extending along the length of said shaft member, a plurality of powdered metal cam elements positioned along the length of said shaft member in predetermined angular relationships thereto, a plurality of grooves in each of said cam elements, approximately located with re¬ spect to said ribs and defining generally contiguous spaces between the exterior of said shaft member and the interior of each said cam element and a plastic, flowable, hardenable material in said spaces for main¬ taining said cam elements in fixed positions on said shaft member. 11. The method of fabricating a camshaft characterized by the steps of positioning a shaft with respect to an annular cam element, and securing said cam element in position on said shaft by filling the voids between said shaft and said annular earn e ement with a flowable, hardenable material. 12. The method of claim 11, characterized in that said shaft is hollow and is provided with a hole in a wall juxtaposed to said cam element for increasing the torsional resistance between said cam element and said shaft. 13. The method of claim 12 wherein an open- ablemold cavity is provided for accurately supporting said cam element when closed and further characterized by the steps of inserting said hollow shaft in said mold; and injecting a hardenable, plastic material through said hollow shaft and said hole to fill the voids between said shaft and said cam element. 14. The method of claim 13, char¬ acterized in that said shaft is polished and defines at least one external bearing surface and wherein said mold cavity is configured such to prevent said har¬ denable, plastic material from contacting said bearing surface. 15. The method of claim 11 or 12, char¬ acterized in that an openable mold cavity is provided for accurately supporting said cam element when closed and wherein-, said annular cam element comprises a short section of malleable tubing and further comprising the step of; forming said section of malleable tubing to match, the interior contour of said mold cavity by closure of said mold. 16. The method of fabricating a camshaft characterized by the steps of positioning a shaft member having a generally ribbed exterior surface axially within a plurality of cam elements, each - having an interior configuration generally matching said exterior rib surface, and defining spaces there¬ between, and securing said cam elements in position relative to said shaft member by filling the spaces between said shaft member and said annular cam elements with a flowable, hardenable material, 17. The method of claim 16, characterized in that said ribs are regularly spaced about the periphery of said shaft member and wherein said cam elements are the same shape and have a common inner configuration that permits said cam elements to occupy different angu¬ lar positions with, respect to said shaft member. 18. The method of claim 16 or 17, char¬ acterized in that said shaft member is formed of drawn metal and wherein said cam elements are formed of cast powdered metal.

Inventors: HUSTED ROYCE H, HUSTED, ROYCE, H.
Applicants: HUSTED ROYCE HILL, HUSTED, ROYCE, H.
Application year: 1988
Main classification: F16H53
IPC codes: B29C37, B29C39, B29C45, B29C70, B29L31, F01L1, F16H53