A method of securing a tip in a tappet

Abstract: In a tappet for use in an internal combustion engine, a tip is fitted in an engage bore between the top wall of the tappet and an engine valve shaft. The tip has a chamfered portion over which a circumferential projection is pressed by a punch so as to fix the tip in the engage bore firmly. A caulking groove is formed by the punch around the engage bore on the top wall. Owing to the cahmfered portion of the tip, a cracking is prevented at the bottom of the groove.

Description: BACKGROUND OF THE INVENTION The present invention relates to a method of securing a tip in a tappet, and particularly, to a method of securing a wear-resistant metal tip between an engine valve shaft and the top wall of the tappet of a direct-acting valve operating mechanism in an internal combustion engine. Recently, in order to increase allowable maximum speed and maximum brake power in an internal combustion engine, a DOHC-type valve operating mechanism has been used. In order to make the valve operating mechanism lighter, a tappet (valve lifter) in the valve operating mechanism has been made of an aluminium alloy instead of conventional steel. Such aluminium alloy tappets have lower strength, rigidity and wear resistance than steel tappets, so a wear resistant metal is applied between a rotary cam and an axial end of an engine valve. US-A-2 187 661 discloses a method of securing threaded and other inserts into valve tappets. EP-A-0 509 541 discloses a direct driven valve operating system in which a tip member is affixed to a cover portion by means of plastic deformation of a peripheral edge of said cover portion. Fig. 10 illustrates a known tappet in a direct-acting valve operating mechanism. The numeral 101 denotes a cylinder head which a tappet body 102 slidably contacts, the tappet being a cylinder the upper surface of which is closed. A circular wear resistant plate 105 made of wear resistant metal fits in a larger diameter circular recess 104 on the upper surface of a top wall 103, and a smaller diameter tip 107 made of wear resistant metal fits in an engage bore 106 on the lower surface of the top wall 103. The lower surface of the tip 107 contacts the axial end of an engine valve connected to a cylinder head 101 by a pair of opposing cotters 108 and 108; a spring retainer 109 holds the cotters; and a valve spring 110 urges the spring retainer 109 upwardly. A rotary cam 112 disposed substantially above the axis of the engine valve slidably contacts the upper surface of the wear resistant plate 105. To fix the tip 107 in the engage bore 106 of the tappet 102, there is a known method as shown in Fig. 11, which illustrates the tappet 102 inverted to the one in Fig. 10 to illustrate a position during working. The bottom of the tappet 102 is upwardly placed. The circular tip 107 made of wear resistant metal fits in the engage bore 106, around which a circumferential projection 113 is pressed by a caulking punch 120. On the lower surface of the punch, there are provided a plurality of inverted triangle-sectioned blades 121 arranged in a circle having a diameter larger than that of the engage bore 106. The punch 120 is pressed downwardly, so that the caulking blades 121 push into the upper surface of the top wall 103 of the tappet 102 in Fig. 11. Thus, the circumferential projection 113 around the engage bore 106 is plastically deformed inwardly so as to fix the tip 107. In the known art, there is a smaller engage area between the circumferential projection 113 around the engage bore 106 and the upper surface(in Fig. 11) of the tip 107, and the circumferential projection 113 has a relatively smaller inward deformation, so that the tip 107 is not sufficiently fixed. If the tip 107 is not sufficiently fixed within the engage bore 106, there is a clearance between the tip 107 and the tappet 102, or the tip 107 and the shaft 111 of the engine valve, which results in clattering during operation, thereby causing one-sided wear. Further if such abnormal movement occurs in the valve operating mechanism, the tip 107 may drop out. To fix the tip 107 firmly, the caulking blade 121 of the punch 120 may be made a larger size, thereby providing a large plastic deformation of the engage bore 106. However, in such a case, a crack 114 is liable to be formed at the bottom of a triangle-sectioned groove (hereinafter refer to "caulking groove") on the upper surface of the top wall of the tappet 102. The caulking blade 121 in the known punch 120, for example, comprises a plurality of separate arcs in a circumference as shown in Fig. 12, a bottom view of the punch. In Fig. 12, there are provided six caulking blades 121 the arc of each being subtended over 40 degrees of a central angle at intervals of 20 degrees. The sides of the caulking blade 121 intersect a circumferential portion substantially at a right angle. Accordingly, the sides of the caulking groove in the tappet 102 are formed at a sharp angle as well, so that the crack 114 is liable to be formed. In order to solve the foregoing disadvantages in the prior art, the object of the present invenion is to provide a method of securing a tip in a tappet in an internal combustion engine the method providing high durablity and reliability by increasing the caulking force on the tip and thereby fixing the tip in an engage bore of the tappet firmly. According to one aspect of the present invention, there is provided a method of securing a tip in a tappet of an internal combustion engine as claimed in claim 1. According to another aspect of the present invention, there is provided a method of securing a tip to a tappet in an internal combustion engine, as claimed in claim 8. A advantages of the present invention are as follows. The circumferential projection of the top wall of the tappet body is plastically deformed inwardly, and the engaged area between the tip and the engage bore is increased. Therefore, the caulking force on the tip is increased and the tip is firmly fixed in the engage bore. If a chamfered portion is formed on the tip, the contact area between the circumferential projection around the engage bore and the tip becomes larger and adhesiveness is increased, so that the tip is more firmly fixed. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other advantages and features of this invention will become more clear based on the following description with respect to drawings wherein: Fig. 1A is a longitudinal sectional front view of one embodiment of a tappet for an internal combustion engine according to the prior art in which a tip is provided; Fig. 1B is a side view which illustrates another priort art embodiment of the tip, Fig. 2 is an enlarged sectional view of a main part in Fig. 1; Fig. 3 is a top plan view of one embodiment of the present invention showing a tip engage portion formed by pressing in the above embodiment; Fig. 4 is a top plan view of another embodiment of a tip engage portion formed by pressing in the same embodiment; Fig. 5 is a longitudinal sectional view which shows another embodiment of a tappet according to the present invention; Fig. 6 is a partial sectional view of a main part in Fig. 5 in further embodiment of the present invention Fig. 7 is a longitudinal sectional view of yet another embodiment of a tappet according to the present invention in which a tip is mounted; Fig. 8 is an enlarged partial sectional view of in which the tappet in Fig. 7 is inverted; Fig. 9 is a bottom plan view of Fig. 7. Fig. 10 is a central longitudinal sectioned front view of a known tappet in a direct-acting valve operating mechanism; Fig. 11 is a longitudinal sectional view which iilustrates a known caulking method; and Fig. 12 is a bottom view of a known punch for forming caulking grooves. Figs. 1A, 1B and 2, show an aluminium alloy tappet 1 of the prior art comprising a cylinder in which the upper end is closed by a top wall 2. When the tappet 1 is in use, the tappet body 1 is inverted as shown in Fig. 1A; so the top and bottom of the tappet will be hereinafter mentioned with respect to Fig. 1A. There is provided a thickened portion 3 on the upper surface of the top wall 2 of the tappet body 1 and coaxial with the body 1. Within the thickened portion 3, there is provided a blind engage bore 5 in which a tip 4 is to be fitted. The tip 4 is formed as a disc made of wear resistant metal having a chamfered portion 6 at its upper surface. Before the following caulking process, the engage bore 5 is cylindrical as shown by the two-dotted line in Fig. 2 so that the tip 4 may fit in the engage bore 5. After the tip 4 has been inserted into the engage bore 5, a caulking blade is pressed on the upper surface of the thickened portion 3 around the engage bore 5 by the known punch of Fig. 11. On the upper surface of the thickened portion 3, there is formed a triangle-sectioned groove 7, so that an upper circumferential projection 8 is plastically deformed in an inward direction around the engage bore 5. Since a chamfered portion 6 is formed on the upper surface of the tip 4, the upper projection 8 is deformed over an inclined surface of the chamfered portion 6. Thus, compared with a known method having no chamfered portion, the contact area between the upper projection 8 and the tip 4 is increased, thereby causing a larger holding force and keeping the tip 4 stable and strong even if the pressing force of the caulking blade is relatively smaller. Preferably a chamfered portion 6 may be formed on both the upper and lower surfaces of the tip 4 as shown in Fig. 1B. Thus, when the tip 4 is inserted into the engage bore 5, it will not be necessary to discriminate which is the top or bottom of the tip 4, thereby increasing working efficiency. Figs. 3 and 4 are top plan views of the present invention which illustrate an embodimenti of the tip engage portion after it is formed by pressing of the caulking blade. Fig. 3 shows a groove formed by a punch having a continuous circular caulking blade. In this case, there is no corner to generate a crack, and thus cracking is prevented during working. The upper projection 8 of the engage bore 5 to be deformed over the chamfered portion 6 of the tip 4 is equally formed over the whole circumference, thereby keeping the tip 4 firm and strong In Fig. 4, with a punch having a plurality of separate, arcuate caulking blades, there are formed a plurality of arcuate grooves 10 the sides of which are formed as a semicircular or semi-elliptical surface. In this case, there are no sharp corners like the known example shown in Fig. 12, and no cracking can be generated by pressing. Further, in Fig. 4, the pressing force in use is smaller than that of the circular caulking groove 9, so that lighter and smaller pressing means for deforming the upper projection 8 could be provided. Figs. 5 and 6 illustrate an embodiment in which increased caulking force fixes a tip 34 firmly in an engage bore 35, similar to Figs. 1A and 2. A tappet body 1 is closed by a top wall 32 at the end. In Fig. 5, the tip 34 is made of wear resistant metal formed as a disc in which its thickness is slightly smaller than the depth of the engage bore 35, and a chamfered portion 36 is formed at angle of 45 degrees. The tip 34 will be fitted in the engage bore 35 as follows. Firstly, as shown in Fig. 5, into the engage bore 35 of the inverted tappet body 31 is fitted the tip 34 having the chamfered portion 36 at the upper surface. Then, the upper surface of a thickened portion 33 is strongly pressed by a punch 43 having on its lower surface an inverted isosceles triangle sectioned caulking blade 42 in which an inner concaved surface 41 is formed. On the thickened portion 33, an annular groove 37 corresponding to the caulking blade 42 is formed, and at the same time, an upper projection 38 of the engage bore 35 is plastically deformed inwardly over the chamfered portion 36 of the tip 34, so that the tip 34 is caulked. Preferably, the tip end of the caulking blade 42 may be slightly rounded to prevent any stress concentration at the bottom of the groove 37. By caulking the tip 34 as above, the concaved surface 41 of the caulking blade 42 makes the upper projection of the engage bore 35 smoothly deformed, thereby increasing the inward plastic deformation rate. Thus, the contact area between the upper projection 38 and the tip 34 is increased, and the chamfered portion 36 is strongly pressed onto the inner surface of the upper projection 38. As a result, by increasing pressing or caulking force of the tip 34 into the engage bore 35, the tip 34 is firmly fixed within the engage bore 35. Fig. 6 illustrates a further embodiment of the present invention, in which the chamfered portion 36 is formed as a convexed surface. Accordingly, the material contents are smoothly flown, thereby increasing adherence between the chamfered portion 36 and the upper projection 38 which acts to press the load onto the whole chamfered portion effectively. Thus, the caulking force is further increased, so that force required to remove the tip 34 from the tappet body is increased. In this embodiment, the tip 34 is continuously caulked, but a plurality of points around the tip 34 may be caulked by a punch 43 which comprises a plurality of separate caulking blades 42. Figs. 7 and 8 illustrate an embodiment for increasing caulking force on a tip 54 and are similar to Figs. 1A and 2. A tappet body 51 is closed by a top wall 52 at the end. The tip 54 is formed as a disc having a thickness slightly smaller than the depth of the engage bore 55 and its lower outer circumference has a chamfered portion 56 at an angle of about 45 degrees. As shown in Fig. 8, in an inverted tappet body 51, the tip 54 fits in the engage bore 55, and, then, the upper surface of the thickened portion 53 is strongly pressed by a punch 63 which comprises at it's lower surface a circular caulking blade 62 having an inverted isocles triangle section intersected at a right angle. Accordingly, on the upper surface of the thickened portion 53, there is formed an inverted triangle-sectioned groove 57 corresponding to the caulking blade 62, so that an upper projection 58 of the engage bore 55 is plastically deformed inwardly over a whole circumference. Meanwhile, the stroke of the punch 63 is determined so that the tip end of the caulking blade 62 may reach to a depth beyond the lower edge 56a of the chamfered portion 56 of the tip 54, or so that the height "H 1 " between the bottom 57a of the groove 57 and the upper surface of the tip 54 may be slightly larger than the height "H 2 " of the chamfered portion 56. In order not to concentrate stress at the bottom 57a of the groove 57, preferably, the tip end 64 of the caulking blade 62 may be slightly rounded. Thus, caulking of the tip 54 increases the contact area between the upper projection 58 and the tip 54, and the starting point of the upper projection 58 is lower than the lower edge 56a of the chamfered portion 56, so that inward plastic deformation is increased and a large pressing load acts over the whole surface and the lower portion of the chamfered portion 56. Thus, the caulking or fastening force on the tip 54 is increased and the tip 54 is firmly fixed in the engage bore 55. Instead of caulking the whole circumference of the tip 54 into a circular form, several points may be preferably caulked with a punch 63 which has a plurality of separate caulking blades 62. The tip 54 is not limited to a circular form, but may be elliptical or other form. To determine strength of the caulking force, it is generally necessary to measure the relative rotary force or rotary torque between the tip engage portion (tappet body) and the tip, and the applicant confirms that significant larger slip torque is available compared with a known tappet when the tip is caulked by the forgoing method.

Claims: A method of securing a tip (4, 34) in a tappet (1, 31) of an internal combustion engine comprising inserting the tip (4, 34) in a blind engage bore (5, 35) formed in the inner surface of the top wall(2, 32)of the tappet body, said tappet body having a closed upper end; and pressing the top wall (2, 32) around the blind engage bore (5, 35) with a caulking punch (43) characterised in that the caulking punch (43) is provided with a triangle section caulking blade (42) having a concave surface (41) at an inner side thereof adapted to attain inward plastic deformation of a circumferential projection (38). A method as claimed in claim 1 wherein the tip (34) is provided with a chamfered portion (36) on an upper surface. A method as claimed in claim 1 wherein the tip has a chamfered portion (36) on both the upper and lower surfaces. A method as claimed in claims 2 and 3 wherein the chamfered portion (36) extends around the entire circumference of the tip. A method as claimed in claims 2 - 4 wherein the chamfered portion (36) is formed as a convex surface. A method as claimed in any of the preceding claims wherein there is provided a plurality of caulking blades (42) which form a caulking groove comprising a plurality of arcuate grooves (10) arranged around the engage bore, each groove having arcuate ends. A method as claimed in any of the preceding claims wherein the edge of the caulking blade (42) is rounded as to prevent any stress concentration at the bottom of the caulking groove. A method of securing a tip (54) in a tappet (51) of an internal combustion engine comprising inserting the tip (54) in a blind engage bore (55) formed in the inner surface of the top wall of the tappet body (51) said tappet body having a closed upper end; and pressing the top wall (52) around the blind engage bore (55) with a caulking punch (63) characterised in that the tip (54) is provided with a chamfered portion 56 at its circumference and the caulking punch (63) is provided with a triangle section caulking blade (62) which is pressed into the top walls (52) around the blind engage bore (55) until an edge of the caulking blade (62) reaches to a depth beyond the lower edge (56a) of the chamfered portion (56) of the tip (54) thereby attaining inward plastic deformation of a circumferential projection (58). A method as claimed in claim 7 wherein the tip (54) has a chamfered portion on both the upper and lower surfaces. A method as claimed in claims 8 and 9 wherein the chamfered portion (56) extends around the entire circumference of the tip (54). A method as claimed in claims 8 - 10 wherein the chamfered portion (56) is formed as a convex surface. A method as claimed in claims 8 - 11 wherein there is provided a plurality of caulking blades (62) which form a caulking groove comprising a plurality of arcuate grooves arranged around the engage bore, each groove having arcuate ends. A method as claimed in claims 8 - 12 wherein the edge 54 of the caulking blade (62) is rounded so as to prevent any stress concentration at the bottom (57a) of the caulking groove (57).

Inventors: HARA NOBUO, HARA, NOBUO
Applicants: FUJI VALVE, FUJI OOZX INC.
Application year: 1993
Main classification: F01L1
IPC codes: F01L1