Method of manufacturing a poppet valve

Abstract

 A poppet valve is employed in an internal combustion engine of a motor vehicle. A valve stem and a valve head of the poppet valve are separately made. A bore is formed on the upper end of the valve head, and an engagement portion having an annular groove is formed at the lower portion of the valve stem. The engagement portion of the valve stem is engaged in the bore of the valve head, and a circumferential wall of the bore is pressed from the outside towards a vertical axis of the valve stem and plastically deformed, so that the valve stem is joined to the valve head to make the poppet valve.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method of manufacturing a poppet valve.

[0002] A poppet valve that consists of a valve stem and a valve head at the lower end of the valve stem is generally manufactured according to four methods as below:

(a) A long cylindrical material is shrunken by electric upset forging machines to form a spherical enlarged portion at one end as an intermediate, and the enlarged portion is molded by hot forging to make a poppet valve that has a valve head at one end of a valve stem.

(b) A heated large-diameter short material is made by hot-choking forging to form a valve stem having an enlarged portion at one end as an intermediate. Thereafter, the enlarged portion is made by hot forging to form a poppet valve having a valve head at one end of the valve stem.

(c) A heated short material is made by hot forging to form a valve head, which is welded to a valve stem to form a poppet valve.

(d) A cylindrical material is made through a plurality of cold-forging steps such as four steps to mold a poppet valve having a valve head at one end of a valve stem.

[0003] In the method (a), it takes relatively long time to form the intermediate. So four or five expensive electric upset forging machines are required to form the intermediate to increase cost.

[0004] In the method (b), it is difficult to determine the size of the material. To manufacture a larger-diameter valve, a larger-external-diameter material leads decrease in the size and accuracy and increase in squeezing resistance to reduce life of a die. In the meantime, to improve extrusion capability, smaller external diameter of the material leads decrease in size and accuracy of the valve head.

[0005] In the method (c), it is advantageous to join the valve head to the valve stem made of material different from the valve head. But, it is impossible to join two materials that are difficult to weld owing to difference in melting point, thereby limiting the kinds of materials.

[0006] In the method (d), the number of molding steps is too many to lead low productivity, and defective products are likely to be made owing to poor cold-forging capability in general heat-resistant steels.

[0007] In the methods except (c), the valve stem and the valve head are integrally molded, and it is impossible to employ different materials depending on use.

SUMMARY OF THE INVENTION

[0008] In view of the disadvantages as above, it is an object of the present invention to provide a method of manufacturing a poppet valve for joining a valve stem to a valve head easily to decrease manufacturing cost.

[0009] To achieve the object, according to the present invention, there is provided a method of manufacturing a poppet valve, comprising the steps of making a valve stem and a valve head separately, one of the valve stem and the valve head having an engagement portion that has an annular groove on an outer circumferential surface, the other having a bore; engaging the engagement portion with the bore; and pressing a circumferential wall of the bore from an outside toward an axis of the valve stem to deform it plastically so as to join the valve stem to the valve head integrally.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The features and advantages of the present invention will become more apparent from the following description with respect to embodiments as shown in appended drawings wherein:

Fig. 1 is a partially cut-away front view of a poppet valve made by the first embodiment of a method according to the present invention;

Fig. 2 is a front elevational view of a valve stem and a valve head before joining in the first embodiment;

Fig. 3 is a partially cut-away front view of the poppet valve in which the lower end of the valve stem is engaged with a bore of the valve head;

Fig. 4 is a partially cut-away front view of the poppet valve in which the valve stem is joined to the valve head by a pressing jig;

Fig. 5 is a front view of the lower end of a valve stem in the second embodiment according to the present invention;

Fig. 6 is a partially cut-away front view of a poppet valve in which the valve stem is joined to a valve head by pressing rollers

Fig. 7 is a front view of a valve stem and a valve head before joining in the third embodiment of a method according to the present invention; and

Fig. 8 is a partially cut-away front view of a poppet valve in which the valve stem is joined to the valve head by pressing rollers

DETAILED DESCRIPTION OF PREFERED EMBODIMENTS

[0011] Embodiments of the present invention will be described with respect to appended drawings.

[0012] Fig. 1 is a partially cut-away front view of the first embodiment of a poppet valve 1 according to the present invention.

[0013] The poppet valve 1 comprises a valve stem 2 and a valve head 3 which are joined to each other as below.

[0014] As shown in Fig. 2, on the outer circumferential surface of the lower end of the valve stem 2 which a cylindrical material is cut out to form, an annular groove 4 which becomes deeper upwards is formed. The annular groove 4 is formed on an engagement portion 2a.

[0015] In the middle of the valve head 3 formed by cold or hot forging, a bore 5 that has internal diameter and depth enough to be engaged with the engagement portion 2 is formed.

[0016] First, as shown in Fig.3, the engagement portion 2a of the valve stem 2 is engaged in the bore 5 of the valve head 3. Then, as shown in Fig. 4, the valve head 3 is positioned on a press device (not shown). Thereafter, the valve stem 2 is inserted into a pressing jig 7 which has an axial hole 6 which has an enlarged portion 6a at the lower end.

[0017] By the inner surface of the enlarged portion 6a of the axial hole 6, a circumferential wall 8 at the upper end of the valve head 3 is strongly pressed and plastically deformed towards the annular groove 4 of the engagement portion 2a, so that the valve stem 2 is joined to the valve head 3.

[0018] Figs. 5 and 6 illustrate the second embodiment of the present invention. An annular groove 9 having equal depth is formed on the outer circumferential surface at the lower portion of the valve stem 2, and the circumferential wall 8 at the upper end of the valve head 3 is strongly pressed by a pair of pressing rollers 10,10 each of which rotates in the same direction around a vertical axis, so that it is plastically deformed towards a vertical axis of the valve stem 2. Thus, the circumferential wall 8 is put into the annular groove 9 and caulked.

[0019] Accordingly, the valve stem 2 is joined to the valve head 3. The annular groove 9 of the valve stem 2 increases unfastening resistance to tensile load compared with the first embodiment. In this embodiment, the annular groove 9 may be formed to be concave.

[0020] Figs. 7 and 8 illustrate the third embodiment of the present invention. In this embodiment, on the contrary to the foregoing embodiments, a bore 11 is formed at the lower portion of a valve stem 2, and an engagement portion 12 is provided at the upper portion of the valve head 3. An annular groove 13 is formed to be concave0. The engagement portion 12 is inserted in the bore 11, and the outer circumferential surface of a circumferential wall 14 including the bore 11 is strongly pressed towards a vertical axis of the valve stem 2 by a pair of pressing rollers 10 similar to the above, so that the valve stem 2 is joined to the valve head 3. The annular groove 13 may be formed as the same shape as above.

[0021] As described above, in the foregoing embodiments, the valve stem 2 and the valve head 3 are separately made, and the ends of them are engaged with each other. The circumferential walls 8, 14 of the engagement bores 5,11 of the valve head 3 or the valve stem 2 are plastically deformed towards an axis of a valve stem 2, so that the valve stem 2 is integrally formed with the valve head 3, thereby facilitating manufacturing of the poppet valve 1.

[0022] Therefore, compared with conventional methods, manufacturing cost can be decreased.

[0023] In view of use, cost and lightening of the poppet valve, materials of the valve stem 2 and the valve head 3 can be suitably determined. For example, the valve stem 2 may be made of low-cost material such as carbon steel or alloy steel for mechanical structure, and the valve head 3 may be made of heat-resistant steel, thereby decreasing total cost. The valve stem 2 may be made of low-density material such as Al alloy, Ti alloy or Mg alloy to lighten the poppet valve 1.

[0024] The valve stem 2 and the valve head 3 are separately formed. Thus, a poppet valve having different diameter of the valve head may be made or different diameter of the valve stem can be easily made. Even if they are made of different materials such as heat-resistant steel and Al alloy that are difficult to weld owing to difference in melting points, they can be easily joined.

[0025] The valve head 3 can be molded by cold forging that provides high accuracy in size to omit later working to decrease cost.

[0026] The foregoing merely relates to embodiments of the present invention. Various changes and modifications may be made by a person skilled in the art without departing from the scope of claims wherein:

Claims

1. A method of manufacturing a poppet valve, comprising the steps of:

making a valve stem and a valve head separately, one of the valve stem and the valve head having an engagement portion that has an annular groove on an outer circumferential surface, the other having a bore;

engaging the engagement portion with the bore; and

pressing a circumferential wall of the bore from an outside toward an axis of the valve stem to deform it plastically so as to join the valve stem to the valve head.

2. A method as claimed in claim 1 wherein the engagement portion is provided on the lower end of the valve stem, while the bore is formed at an upper end of the valve head.

3. A method as claimed in claim 1 wherein the bore is formed at a lower end of the valve stem, while the engagement portion is provided at an upper end of the valve head.

4. A method as claimed in claim 2 wherein the annular groove is tapered upwards, the valve stem being inserted in an axial hole of a pressing jig, said axial hole having an enlarged portion at a lower end, the engagement portion of the valve stem engaged in the bore of the valve head being pressed by downward movement of the pressing jig, whereby the enlarged portion strongly presses the circumferential wall of the bore of the valve head.

5. A method as claimed in claim 2 wherein the circumferential wall of the bore of the valve head in which the engagement portion of the valve stem is engaged is pressed by a plurality of pressing rollers each of which rotates around a vertical axis.

6. A method as claimed in claim 3 wherein the circumferential wall of the bore of the valve stem in which the engagement portion of the valve head is engaged is pressed by a plurality of pressing rollers each of which rotates around a vertical axis.

Drawing