JPH0434258A - Manufacture of cam shaft - Google Patents

Abstract

PURPOSE:To manufacture a builtup cam shaft light in weight and excellent in wear resistance by building a cam piece and/or journal piece interposing a brazing material between junction surfaces in a piece assembly corresponding position and heating the piece to a junction temperature of brazing to be firmly fixed. CONSTITUTION:Column-shaped ceramic pieces 3, 4, having an external diameter in size a little smaller than an internal diameter of a steel pipe of a shaft part 2, are inserted to the inside of the shaft part and fixed by pressure molding the periphery. Next, a cam piece 7 and a journal piece 8 are built in a predetermined position in a condition that brazing materials 5, 6 are interposed between junction surfaces of the pieces 7, 8 and the periphery of the shaft part 2 by machining the periphery of the shaft part 2, corresponding to a position of mounting the ceramics-made cam piece 7 and journal piece 8, in the predetermined dimensional accuracy. Thereafter, this cam shaft assembly unit is set up to a jig and heated to about 700 to 850 deg.C in a furnace, and the ceramics- made cam piece 7 and journal piece 8 are connected by brazing to the predetermined position in the periphery of the shaft part 2.

Description

[Detailed description of the invention] [Purpose of the invention]

(Industrial Application Field) This invention relates to a method for manufacturing a camshaft used in manufacturing a camshaft used in a valve mechanism of an internal combustion engine, etc. (Prior Art) Conventional Internal Combustion Engine The manufacturing methods used for camshafts include casting methods that impart wear resistance by chilling the contact surface with the cam follower, which is the mating material, and a casting method that imparts wear resistance to the mating material after hot forging. A heat treatment method has been adopted in which the contact surface with the cam follower is induction hardened to impart wear resistance. Currently, internal combustion engines for automobiles are required to have higher performance than ever before, that is, to improve fuel efficiency, durability, and output. Improvement in abrasion resistance and weight reduction are desired. Under these circumstances, in recent years, technology has been developed to assemble and sinter-bond a shaft made of high-strength steel pipe with a cam piece, journal piece, etc. made of compacted iron-based wear-resistant powder. It was proposed that a lightweight, hollow-assembled camshaft with excellent wear resistance could be manufactured using a technology in which cam pieces, journal pieces, etc. made of molded and sintered iron-based wear-resistant powder were rolled around the hollow shaft by bulge forming. It has come to be incorporated into actual engines (for example, JP-A-62-97721, JP-A-62-9772).
No. 2). However, there is a natural limit to further improving the wear resistance and reducing the weight because the material is the same as before. As a possible means of further improving wear resistance and reducing weight, a hollow assembled camshaft using a lighter and more wear-resistant ceramic material as the cam piece and journal piece material may be considered. (Problem B to be solved by the invention) However, in the conventional manufacturing method of assembled camshafts for internal combustion engines, etc. as described above, there is a problem in joining the ceramic cam piece or ceramic journal piece to the shaft part. Therefore, it is difficult to firmly fix it. For example, by assembling a ceramic cam piece or a ceramic journal piece into a hollow shaft, fixing it in a mold, and applying hydrostatic pressure to the inside of the hollow shaft to form a bulge, the cam piece or journal can be attached to the hollow shaft. If you try to firmly fix the pieces, the stress inside the ceramic will increase and the ceramic will break. If you try to bulge-form the hollow shaft part by applying hydrostatic pressure to an extent that does not break the ceramic, the desired result will not be achieved. The disadvantage is that bonding strength cannot be obtained. In addition, there is a method for attaching a ceramic cam piece or a ceramic journal piece to a shaft and applying a diffusion agent to the contact area between the cam piece or journal piece and the shaft and heating it to perform diffusion bonding, or a method for diffusion bonding by heating the contact area between the cam piece or journal piece and the shaft. If you try to fix the material by sandwiching them and heating them in a furnace and brazing them, the difference in thermal expansion between the ceramic material of the cam piece and journal piece and the steel material of the shaft will cause the inside of the ceramic material around the joint to The drawback is that concentrated stress is generated in the ceramic, causing cracks in the ceramic and making it impossible to firmly bond the ceramic.Therefore, it has been a challenge to resolve these drawbacks. (Purpose of the Invention) This invention was made in view of the conventional problems associated with the manufacturing method of such hollow assembled camshafts, and has been developed to create a lightweight and wear-resistant ceramic material for use as a cam piece or journal piece. Even when the cam piece and journal piece are used, the cam piece and journal piece are firmly fixed to the hollow shaft part, and the ceramic cam piece and ceramic journal piece are lightweight and wear resistant so that they will not be damaged. It is an object of the present invention to provide a method for manufacturing a camshaft that makes it possible to manufacture an assembled camshaft with excellent quality.

[Structure of the invention]

Means for Solving Problems (1) A method for manufacturing a camshaft according to the present invention is as follows. The shaft portion of the camshaft is formed from a high-strength metal tube, and after assembling a ceramic cam piece and/or a ceramic journal piece to the shaft portion, the camshaft is manufactured by brazing. After arranging and fixing a cylindrical or cylindrical ceramic piece on the inner periphery of a position corresponding to the assembly of a ceramic cam piece and/or a ceramic journal piece, the cam piece and/or journal piece and the piece of the shaft are assembled. The cam piece and/or journal piece is assembled with a brazing material sandwiched between the joint surfaces with the outer periphery at the position corresponding to assembly, and the cam piece and/or journal piece is attached to the outer periphery of the shaft by heating to a brazing temperature. The camshaft is characterized by a structure that is firmly fixed, and the structure of such a camshaft manufacturing method is a means for solving the above-mentioned conventional problems. In an embodiment of the method for manufacturing a camshaft according to the present invention, a high-strength hollow steel tube is used as the high-strength metal tube, and in the same embodiment, the cylindrical or cylindrical ceramic piece is the ceramic cam piece and/or Alternatively, a ceramic material having a thermal expansion coefficient equivalent to that of the ceramic material constituting the journal piece may be used, and in the same embodiment, when fixing the columnar or cylindrical ceramic piece to the inner periphery of the shaft portion, The metal tube may be configured to be pressure-formed from the outer periphery of the metal tube, or the metal tube may be inserted into the heated state, and after cooling, the ceramic cam piece and/or journal piece may be tightly fitted inside the shaft portion. In the same embodiment, nickel or a nickel alloy, or copper or a copper alloy thin piece is sandwiched between the joint surfaces of the shaft portion and the cam piece and/or the journal piece, and brazing is performed, and the same embodiment is employed. In an embodiment, the outer circumferential surface of the columnar or cylindrical ceramic piece may have a barrel shape with an outer diameter smaller at the center than at both ends. (Function of the Invention) Since the method for manufacturing a camshaft according to the present invention has the above-described configuration, it is heated to a brazing temperature in a furnace or the like to produce a ceramic cam piece and/or a ceramic journal piece with high strength. When fixing the cam piece and journal piece to the metal tube, a cylindrical or cylindrical ceramic piece is fixed to the inner periphery of the metal tube at the fixed part of the cam piece or journal piece. Deformation due to thermal expansion of the tube can now be suppressed. Therefore, the stress caused by the difference in thermal expansion in and around the cam piece and journal piece is relaxed, and the ceramic cam piece and journal piece are completely fixed on the outer periphery of the shaft without cracking. It becomes possible to obtain a camshaft in which a lightweight ceramic cam piece and/or a ceramic journal piece, which are lightweight and have excellent wear resistance, are firmly fixed to a metal shaft portion. (Example) Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a partial cross-sectional view of a camshaft manufactured by an embodiment of the camshaft manufacturing method according to the present invention. Cylindrical or cylindrical (cylindrical in the example shown)
A ceramic cam piece 7 and a ceramic journal piece 8 are brazed to the outer periphery of the shaft portion 2 to which the ceramic piece 3.4 is fixed, via brazing materials 5 and 6. It forms a structure that is firmly fixed by joining. To explain the manufacturing method of the camshaft 1 having such a structure, first, as shown in FIG. 2, the shaft portion 2 is formed of a hollow steel tube, and the ceramic cam piece 7 and the ceramic journal piece A cylindrical ceramic piece 3.4 having an outer diameter slightly smaller than the inner diameter of the steel pipe of the shaft section 2 is inserted into the mounting position 8 of the shaft section 2, and then the outer periphery of the shaft section 2 is press-formed. By doing so, the ceramic piece 3.4 is fixed inside the shaft portion 2, as shown in FIG. Next, the shaft portion 2 corresponding to the mounting position of the ceramic cam piece 7 and the ceramic journal piece 8 is attached.
The outer periphery of the shaft portion 2 is machined to a predetermined dimensional accuracy, and the brazing materials 5 and 6 are sandwiched between the joint surfaces of the cam piece 7 and journal piece 8 and the outer periphery of the shaft portion 2, and then assembled at a predetermined position. Thereafter, this camshaft assembly is placed in a jig and heated in a furnace at approximately 700°C to 850°C to bond the ceramic cam piece 7 and journal piece 8 to a brazing material 5.6.
It is brazed to a predetermined position on the outer periphery of the shaft portion 2 via. In this embodiment, a cylindrical ceramic piece 3.4 having a coefficient of thermal expansion equivalent to that of the ceramic material of the cam piece 7 and the journal piece 8 is inserted into the shaft portion 2 at the mounting position of the ceramic cam piece 7. Because it is fixed, it is possible to suppress deformation due to thermal expansion of the steel shaft part 2 at each joint part during brazing joint in a furnace, as shown in Fig. 4 (a). This is clear from Figure 4 (b) (x-x' cross section) and Figure 4 (e) (Y-Y' cross section), which show the measurement results of residual stress at the x-x' cross section and the Y-Y' cross section, respectively. As described above, it was possible to alleviate stress in and around the bonding layer (5) between the ceramic cam piece 7 and the shaft portion 2 due to the difference in thermal expansion, and it was possible to prevent cracking of the ceramic. In addition, as another example, in order to further relieve the stress between the joint parts, as shown in FIG. If necessary, it is desirable to interpose a layer of nickel or copper, and in this case, a thin piece of nickel or copper is sandwiched between the brazing filler metals 5. It is also preferable to do it. Furthermore, as shown in FIG.
The outer peripheral surface of the ceramic piece 3.4, which is cylindrical in the illustrated example, can be shaped into a barrel so that the diameter is smaller at the center than at both ends, and in this case, as shown in FIG. In addition, the internal stress at both ends of the cam piece 7 (and/or journal piece 8) can be relaxed. As another example, the shaft part 2 made of a metal tube such as a steel pipe is heated to expand the inside diameter of the shaft part, and a ceramic material having an outside diameter slightly larger than the inside diameter of the shaft part 2 at room temperature is used. Pieces 3 and 4 are inserted, and after cooling, the ceramic pieces 3 and 4 are fixed inside the shaft portion 2 by interference fit. Thereafter, the ceramic cam piece 7 and/or journal piece 8 may be assembled in the same manner as described above.

【Effect of the invention】

As explained above, according to the method for manufacturing an assembled camshaft according to the present invention, the shaft portion of the camshaft is formed of a high-strength metal tube, and a ceramic cam piece and/or a ceramic cam piece with excellent wear resistance is formed. When manufacturing a camshaft by assembling a journal piece made of ceramic to the shaft part and then joining it by brazing, a cylindrical or cylindrical shape is formed on the inner periphery of the shaft part at a position corresponding to the assembly of the ceramic cam piece and/or the ceramic journal piece. The ceramic piece may be fixed by arranging and fixing the ceramic piece, for example, by pressure molding from the outer periphery of the shaft portion. Alternatively, for example, the ceramic piece is fixed by inserting the shaft in a heated state and, after cooling, tightly fitting the ceramic piece inside the shaft, and then the cam piece and/or journal piece and the shaft The cam piece and/or the cam piece are sandwiched between the joint surfaces of the cam piece and the outer periphery at the position corresponding to the piece assembly position.
Alternatively, the cam piece and/or journal piece is firmly fixed to the outer periphery of the shaft by heating the journal piece 2, for example, in a furnace to a brazing temperature, so that it can be used as a cam piece or journal piece in a lightweight and durable manner. Even when ceramics are used, which have excellent abrasion resistance, the ceramic pieces are fixed to the inner circumference of the cam piece or journal piece on the shaft, so they must be heated to the brazing temperature in a furnace, etc. At the same time, it suppresses deformation due to thermal expansion of the shaft at the cam piece or journal piece joint, and reduces stress in the joint between the ceramic cam piece or ceramic journal piece and the shaft and its surrounding area due to the difference in thermal expansion. To manufacture an assembled camshaft that is light in weight and has excellent wear resistance, in which the cam piece and/or journal piece can be bonded and fixed to the shaft portion without cracking the ceramic. This brings about an extremely superior effect.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a partial cross-sectional explanatory diagram of an assembled camshaft obtained by an embodiment of the camshaft manufacturing method according to the present invention, and FIGS. 2 and 3 are the same as those shown in FIG. A cross-sectional explanatory diagram showing the process of manufacturing an assembled camshaft, Figure 4 (
JL) is the position x-x when measuring the stress distribution of the ceramic cam piece-shaft bonding layer and surrounding area due to the difference in thermal expansion.
4(b) is a graph showing the measurement results of the stress distribution in the xx' cross section of FIG. 4(a), and FIG. 4(C) is an explanatory diagram showing the A graph showing the measurement results of the stress distribution on the Y-Y' cross section in FIG. The figure is an explanatory cross-sectional view of a cylindrical ceramic piece portion showing still another embodiment of the camshaft manufacturing method according to the present invention. DESCRIPTION OF SYMBOLS 1... Camshaft, 2... Shaft part, 3.4... Ceramic piece, 5.6... Brazing metal, 7... Ceramic cam piece, 8... Ceramic journal piece, Ri ...Stress relaxation layer.

Claims (1)

[Claims] (1) The shaft portion of the camshaft is formed from a high-strength metal tube, and after assembling a ceramic cam piece and/or a ceramic journal piece to the shaft portion, the shaft portion is joined by brazing to manufacture the camshaft. After arranging and fixing a cylindrical or cylindrical ceramic piece on the inner periphery of the ceramic cam piece and/or ceramic journal piece corresponding to the assembly position of the part, the cam piece and/or journal piece and the piece of the shaft part are assembled. The cam piece and/or journal piece is assembled with a brazing material sandwiched between the joint surfaces with the outer periphery at the position corresponding to assembly, and the cam piece and/or journal piece is attached to the outer periphery of the shaft by heating to a brazing temperature. A method for manufacturing a camshaft that is characterized by being firmly fixed.