Process for manufacturing a spool valve

Abstract: Disclosed are a spool valve which comprises: a shaft (1) having plural small diameter portions (2) formed at required intervals on the circumferential surface of the shaft; a pair of circular convex portions (3) having a diameter larger than the inner diameter of a collar (4), provided on the outer circumferential faces of each small diameter portion; and the collar (4) subjected to quenching processing, arranged between the circular convex portions (3) so that the side faces of the circular convex portions are in close contact with circular concave portions (6) formed at both ends of a center hole of the collar (4) or both side faces themselves of the collar (4), and a process for manufacturing the same.

Description: BACKGROUND OF THE INVENTION This invention relates to a spool valve such as an oil valve for automatic transmission, which is integrated into a hydraulic control circuit of automatic transmission or the like of an automobile and conducts switching of oil passage, and a process for manufacturing the same. In a conventional spool valve to be used as an oil valve for automatic transmission or the like, it is common that a rod-shaped material 20 made of a metal as shown in Fig. 10 is cut by a lathe or the like, and a shaft 21 on which a valve body is carved out is prepared as shown in Fig. 11. Therefore, there are problems that a large amount of a material is cut and wasted as chips, and time is required for machining of material to worsen productivity. Moreover, in order to give abrasion resistance to such a shaft, after machining of material, it is necessary to subject the whole surface of the shaft to carburization quenching processing as shown in Fig. 12. However, due to carburization quenching processing, thermal strain of the shaft is necessarily induced, so that after carburization quenching processing, it is necessary to subject it to straightening as shown in Fig. 13. Thus, there are problems that productivity is bad, and cost is high. A method of manufacturing a spool valve is described in British Patent No. GB1450380, according to the preamble of claim 1. In the method of GB1450380, the spool valve collars are secured to the shaft using cement. European Patent Publication No. EP 0340128 discloses the method of manufacturing a cam shaft in which a knurling tool is used to deform the shaft adjacent to the cams in order to secure the cams to the shaft by mechanical bonding. The method of EP 0340128 has the disadvantage that the knurling tool forms a deep depression in the surface of the shaft adjacent to the cam. SUMMARY OF THE INVENTION An object of the present invention is to provide a process for manufacturing a spool valve in which productivity is high and wasting of a material can be reduced, and a thus-obtained spool valve. This invention provides a process for machining a spool valve which comprises the steps of: providing a shaft material; providing plural collars subjected to quenching process wherein each collar has a central hole therein which inner diameter is slightly larger than an outer diameter of the shaft material; fitting each of the collars to the shaft material so that the collar is arranged at required position; characterised by each collar having circular concave portions chamfered in a tapered shape at both ends of an inner surface of the collar; and by contracting the diameter of the shaft material in the vicinity of the inner surface of each collar and to form a pair of small diameter portions by rolling die, whereby to cause plastic flow of a metal constituting said shaft material, to fill said metal into said circular concave portions, and to form a pair of circular convex portions having a diameter larger than the inner diameter of the collar on an outer surface of the shaft material so that a side face of each circular convex portion is in close contact with the circular concave portion at the chamfered portion thereof formed at the inner surface of the collar to fix the collars to the shaft material. In the manufacturing process of the present invention, it is one of embodiments that the length of the above shaft material has a length corresponding to plural spool valves; the number of the collars to be fitted to the above shaft material is a number of collars required for the respective spool valves; and at the time of completion of the above step of forming the circular convex portions by the rolling dies, said shaft material is cut into the respective spool valves. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front view illustrating a spool valve produced by the process of the present invention (collars are shown by sections thereof). Fig. 2 is a front view illustrating a shaft material to be used in one embodiment of the process for manufacturing a spool valve according to the present invention. Fig. 3 is sectional views of collars to be used in one embodiment of the process for manufacturing a spool valve according to the present invention. Fig. 4 is a front view showing a manufacturing step for fitting collars to a shaft material in one embodiment of the process for manufacturing a spool valve according to the present invention (the collars are shown by sections thereof). Fig. 5 is a front view showing a manufacturing step for clinching collars to a shaft material in one embodiment of the process for manufacturing a spool valve according to the present invention (the collars are shown by sections thereof). Fig. 6 is an enlarged view of a clinching step in one embodiment of the process for manufacturing a spool valve according to the present invention. Fig. 7 is an enlarged view of another embodiment of a clinching step in one embodiment of the process for manufacturing a spool valve according to the present invention. Fig. 8 is a front view showing a manufacturing step for clinching collars to a shaft material in another embodiment of the process for manufacturing a spool valve according to the present invention. Fig. 9 is a side view of a rolling die in another embodiment of the process for manufacturing a spool valve according to the present invention. Fig. 10 is a front view of a shaft material to be used for manufacturing a conventional spool valve. Fig. 11 is a front view of a cutting step of a conventional shaft material. Fig. 12 is a front view of carburization quenching processing of a conventional shaft material. Fig. 13 is a front view of a straightening step of a conventional shaft. DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, a preferred embodiment of the process for manufacturing a spool valve of the present invention is explained in detail by taking the case of an oil valve for transmission (see Fig. 1). 1 is a cold or warm headed shaft, and said shaft 1 has a flange 1a for bearing a spring, formed on one end thereof and also has plural small diameter portions 2 formed at required intervals and at predetermined positions of said shaft. On the outer circumferential faces of each small diameter portion of said shaft, a pair of circular convex portions 3 having a diameter larger than the inner diameter of a collar 4 described below are arranged at predetermined intervals so that they are faced to each other. A collar 4 is a collar having a surface subjected to quenching processing such as carburization, and at both ends of a center hole 5 of said collar, circular concave portions 6 chamfered in a taper shape are formed. Said circular convex portions are processed and formed so that the circular concave portions 6 are in close contact with the side faces thereof, whereby said collar is fixed to said shaft to form a valve body. The spool valve constituted as described above is integrated into a hydraulic control circuit of automatic transmission or the like, and the valve body switches oil passage by moving the shaft 1 in the shaft direction thereof. The side faces of a pair of the circular convex portions 3 formed on the outer circumferential faces of the small diameter portions 2 of said shaft are in close contact with the taper-shaped circular concave portions 6 of the center hole 5, formed at both ends of the collar 4 as a valve body, whereby the collar 4 is fixed to said shaft securely and stably. Moreover, the surface of said collar is subjected to carburization quenching processing, so that said collar is not abraded even by oil passage-switching movement, whereby oil passage-switching movement can be carried out securely for a long time. In the embodiment, after clearance fit of said collar to said shaft is carried out, the side faces of said circular convex portions are in close contact with said circular concave portions chamfered in a taper shape to hold said collar 4 by said circular convex portions. However, said circular concave portions may have a stepped shape in place of a taper shape as a matter of course. Further, when interference fit of said collar is carried out, a pair of circular convex portions touching both side faces themselves of said collar may be formed on the outer circumferential faces of the small diameter portions 2 of the shaft 1 in place of forming said circular concave portions on said collar, as a matter of course. Next, a preferred embodiment of the process for manufacturing a spool valve according to the present invention is explained in detail by referring to Fig. 2 to Fig. 7. As shown in Fig. 2, 10 is a shaft material having a flange 1a for bearing a spring, formed on one end thereof by cold or warm heading. As shown in Fig. 3, 4 is a collar made by cold or warm heading so that it has an inner diameter slightly larger than the outer diameter of the shaft material 10. At both ends of a center hole 5 of said collar, circular concave portions 6 chamfered in a taper shape are formed, and the surface of said collar is subjected to quenching processing such as carburization for heightening abrasion resistance. Further, the position at which said collar is provided on the shaft and the length of said collar itself are different depending on the position of oil passage to be switched in a hydraulic control circuit (in the embodiment, collars having three kinds of lengths are used). In manufacture of a spool valve, after clearance fit of said collars to required positions of said shaft material is carried out, respectively, as shown in Fig. 4, the diameters of the portions of said shaft material in the vicinity of both ends of said collars are contracted by rolling dies 7 as shown in Fig. 5, whereby plastic flow of a metal is caused, and the contracted metal of said portions flows into the circular concave portions 6 formed at both ends of the center holes 5 of the collars 4 and are in close contact therewith. At this time, the circular concave portions 6 are processed to have a taper shape, so that as shown in Fig. 6 and Fig. 7, plastic flow of the metal toward the tapered surfaces is caused, and gaps existing between said circular concave portions and the shaft 1 are filled with the metal. As a result, irrespective of existence of clearance between the outer diameter of the shaft material 10 and the inner diameters of the collars 4, said collars are fixed to the shaft 1 securely and stably. Thus, said collars are fixed to said shaft to become valve bodies. In the embodiment, said circular concave portions are processed to have a taper shape so that mobility of the metal is improved, but for the object of fixing said collars to said shaft, said circular concave portions may have a stepped shape as a matter of course. Fig. 8 and Fig. 9 each show a further embodiment of the manufacturing process of the present invention, i.e. a preferred embodiment of the manufacturing process by which plural spool valves (two spool valves in Fig. 8) can be manufactured simultaneously. There are formed circular concave portions 6 which has an inner diameter slightly larger than the outer diameter of a shaft material 10, are chamfered in a taper shape and are provided at both ends of center holes 5. Clearance fit of a large number of collars 4 having a surface subjected to carburization quenching processing, for two spool valves to required positions of the shaft material 10 having a length corresponding to two spool valves is carried out (a right side portion of Fig. 8 shows this state). As shown in Fig. 8 and Fig. 9, by clinching die teeth 15b of a rolling die 15 having a halving die tooth 15a formed at the center of an upper surface and a large number of the clinching die teeth 15b formed on an upper surface, the diameters of the portions of said shaft material in the vicinity of both ends of said collars 4 are contracted, whereby plastic flow of a metal of said portions is caused, and the contracted metal moves to gaps existing between said circular concave portions formed at both ends of said center holes of said collars and a shaft 1 and are in close contact with said circular concave portions. At this time, said circular concave portions are processed to have a taper shape, so that the mobility of said metal is good as in the embodiment described above. Further, simultaneously with formation of circular convex portions 3 by clinching, the diameter of the center portion of the shaft material 10 is gradually contracted by the halving die tooth 15a, and said shaft material is separated and cut by the tooth at the highest position of said halving die tooth (a left side portion of Fig. 8 shows a state immediately before this state). In this embodiment, the same two spool valves are manufactured, but a large number of the same or different spool valves may be manufactured as a matter of course. As clearly seen from the above explanation, according to the present invention, valve bodies are formed by fixing separately prepared collars subjected to quenching processing such as carburization to a cold or warm headed shaft, so that it is not necessary to subject the shaft to machining of material for obtaining valve bodies, and wasting of a material generated by machining of material can be reduced. Further, each collar is fixed by being in close contact with a pair of circular convex portions formed by clinching the shaft by a rolling die, so that the collars are stable even when they are used for a long time. Moreover, only the surfaces of the collars as the valve bodies which are abraded by switching of oil passage are subjected to carburization quenching processing, and it is not necessary to subject the shaft as a whole to carburization quenching processing, so that it is not necessary to subject it to a straightening step for removing thermal strain induced by subjecting the shaft to carburization quenching processing, whereby cost can be reduced by simplification of steps, productivity is improved, and therefore manufactured spool valves can be made inexpensive. Further, by clinching a large number of collars 4 subjected to carburization quenching processing, for plural spool valves to a shaft material having a length corresponding to plural spool valves; and then separating and cutting the shaft material, a large number of spool valves can be manufactured simultaneously in a short time, so that the present invention has various advantages for heightening productivity to a great extent. Thus, the present invention provides a spool valve the problems in the art of which have been solved and a process for manufacturing the same, and therefore greatly contributes to development of the art.

Claims: A process for manufacturing a spool valve which comprises the steps of providing a shaft material (1); providing plural collars (4) subjected to quenching process wherein each collar (4) has a central hole (5) therein which inner diameter is slightly larger than an outer diameter of the shaft material; fitting each of the collars to the shaft material so that the collar is arranged at required position; characterised by each collar having circular concave portions (6) chamfered in a tapered shape at both ends of an inner surface of the collar; and by contracting the diameter of the shaft material in the vicinity of the inner surface ofeach collar and to form a pair of small diameter portions (2) by rolling die, whereby to cause plastic flow of a metal constituting said shaft material, to fill said metal into said circular concave portions, and to form a pair of circular convex portions (3) having a diameter larger than the inner diameter of the collar on an outer surface of the shaft material so that a side face of each circular convex portion is in close contact with the circular concave portion at the chamfered portion thereof formed at the inner surface of the collar to fix the collars to the shaft material. The process according to claim 1, wherein the length ofthe above shaft material has a length corresponding to plural spool valves; the number of the collars to be fitted to the above shaft material is a number of the collars required for the respective spool valves; and at the time of completion of the above step of forming the circular convex portions by the rolling die, said shaft material is cut into the respective spool valves.

Inventors: KATO KEIGO, MIZUNO MASATAKA, KATO, KEIGO, MIZUNO, MASATAKA, Kato, Keigo, c/o Aoyama Seisakusho Co Ltd.,, Mizuno, Masataka, c/o Aoyama Seisakusho Co Ltd.,
Applicants: AOYAMA SEISAKUSHO, AOYAMA SEISAKUSHO CO., LTD.
Application year: 1997
Main classification: B23P15
IPC codes: F16K11, B23P11, F16K3, F16K25, B23P15