Ceramic valve arrangement

Abstract: A ceramic valve supporting structure comprising in use for internal combustion engine; a ceramic valve (1) having an integral stem (1b), the upper portion of which is provided with a circular groove (2); a cotter (3) the outer surface of which is tapered, and formed by butting a pair of semi-cylindrical pieces, and having a lock projection (3a) placed into the groove (2) when secured concentrically to the outer surface of the stem, a cylindrical retainer (4) concentrically secured to the cotter surface of the cotter so as to support the valve (1) through the cotter (3); the retainer (4) being provided with the inner surface tapered in a direction so as to make the cotter (3) tightly engage with the outer surface of the stem (1b) by means of wedge effect against the tapered cotter (3) due to the urging force of a coil spring member (6) axially exerted to the retainer (4); and a stress relief means provided so as to avoid the predetermined portion of the cotter from locally engaging against the outer surface of the stem. Stress relief is provided by a bevelled portion (4c) at the end of the retainer (4) adjacent the valve head to provide a clearance between the retainer (4) and cotter (3) at the end of the cotter.

Description: This application is a divisional of EP 0249503, and relates to a ceramic valve arrangement having an axially reciprocable ceramic valve usable, for example, for opening and closing intake or exhaust ports of an engine cylinder. In recent years, high rotation speed with high power has been required from internal combustion engines in automobiles. Valves used to open and close intake or exhaust ports of engine cylinders are exposed to severe mechanical and thermal stresses. Lightweight and heat-resistant ceramics have been considered for such valves as they can endure the severe conditions, see for example US-A-4359022. Although the valve disclosed therein has no specific valve retaining means, commonly valves (b) having a stem (s) support a retainer (r) through a cotter (c), as seen in Fig. 6. The outer surface of the cotter (c) and the inner surface of the retainer (r) are both tapered to tightly engage each other by wedge action. Upon valve action, the cotter (c) acts to engage with the stem (s) more tightly due to the wedge action, the maximum intensity of the engagement falling on the lowest end (n) of the retainer (r). The end (n) of the retainer (r) acts tightly on the stem (s) through the lowest end (m) of the cotter (c), thus leading to stress concentrations in the stem (s) which result in cracks or breakage as seen at (k) in Fig. 6. Another problem can arise where cotter (c) has a semi-circular lock projection (p) fitted in an annular groove (g) provided in the outer surface of the stem (s) as shown in Fig. 7. In association with the action of the valve (b), the projection (p) acts to engage tightly with the open ended portion of the groove (g), leading to stress concentrations which create cracks or breakage as seen at (k) in Fig. 7. In addition, with the axial displacement of the valve (b), the cotter (c) comes to engage with the stem (s) more tightly under the influence of the wedge effect. A sharp edge (e) of each piece tightly engages with the outer surface of the stem (s) so as to cause stress concentrations, thus resulting in cracks or breakage as seen at (x) in Fig. 8. GB-A-1139657 discloses an axially reciprocable valve arrangement including a non-ceramic valve having a head and a stem, a groove in the stem remote from the valve head, a one-piece cotter surrounding the stem, a lock member extending into the groove and connecting the cotter to the stem, a cylindrical retainer surrounding the cotter, the cotter having a tapered outer surface and the retainer having an inner surface such that axial forces urging the retainer along the stem tighten the cotter on the stem. After assembly of the cotter around the valve stem, the assembled cotter and valve are fitted through a bore of the retainer and the end of the cotter nearest to the valve head is spread or flanged to form a lip of larger diameter than the retainer bore. The end of the retainer nearest to the valve head is provided with a bevelled mouth which is arranged to co-operate with the lip of the cotter to hold the cotter for limited free endwise movement in the retainer. According to the present invention there is provided an axially reciprocable valve arrangement including a ceramic valve having a head and a stem, a groove in the stem remote from the valve head, a two-part cotter surrounding the stem, a lock member extending into the groove and connecting the cotter to the stem, a cylindrical retainer surrounding the cotter, the cotter having a tapered outer surface and the retainer having a tapered inner surface such that axial forces urging the retainer along the stem tighten the cotter on the stem, and means for relieving creation of stress concentrations in the stem by the cotter, said means comprising a rounded bevel portion defined at the end of the retainer closest to the valve head to provide a clearance between the retainer and cotter at the end of the retainer. In order that the invention may be more clearly understood, the following description is given by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a partial view of an internal combustion engine associated with the invention; Fig. 2 is a longitudinal cross sectional view of the main components of a valve supporting structure according to a first embodiment of the invention; Fig. 3 is a longitudinal cross sectional view of the cotter of the first embodiment of the invention; Fig. 4 is a longitudinal cross sectional view of the retainer of the first embodiment of the invention; Fig. 5 is a longitudinal cross sectional view of a second embodiment of the invention; Figs. 6-8 are sectional views of prior art valve supporting structures. Each embodiment of the invention is described hereinafter in reference to the accompanying drawings, in which, in many cases, like numerals indicate like parts. In the first embodiment of the invention, an exhaust valve 1, which is employed in a combustion chamber of an internal combustion engine described hereinafter, is made of ceramic material such as silicon nitride, and has a column-shape stem 1b formed integrally with a valve head 1a. The valve 1 has a circumferential groove 2, semi-circular in cross section, in the upper portion of the stem 1b. A metallic cotter 3, comprising a pair of split pieces (two parts), substantially forms a cylinder when assembled. The stem 1b of the valve 1 has the cotter 3 around it. The inner surface of the cotter has an integral lock projection 3a, semi-circular in cross section, received in the groove 2. A retainer 4, which comprises a cylindrical portion 4a and a flange 4b formed integrally with the top of the portion 4a, fits onto the outer surface of the cotter 3. In this instance, the retainer 4 has a tapered inner surface in the cylindrical portion 4a to make face-to-face contact with an oppositely tapered outer surface of the cotter 3. The valve 1, thus far described, is incorporated into a cylinder head 5 of an internal combustion engine as shown in Fig. 1. Between the valve 1 and the cylinder head 5, is a compression coil spring 6 provided to urge the valve 1 upward in the axial direction so as to tightly close an exhaust passage 8 by the engagement of the valve head 1a against a valve seat 7. With the engine running, the valve 1 is repeatedly displaced upward and downward alternately to close and open the exhaust passage 8. In compliance with the up and downward displacement of the valve 1, the retainer 4 comes to engage tightly with the cotter 3 through the tapered surfaces by means of a wedge action. With further reference with the drawing of Fig. 1, numeral 9 designates a tubular guide to receive the stem 1b of the valve 1, numeral 10 designates a cam connected to a shaft 11, numeral 12 designates a swing arm, one end of which engages against the upper end of the stem 1b and the other end of which is supported by a spherical support 13. The rotation of the cam 10 causes the swing arm 12 to oscillate so as to displace axially the stem 1b. Numeral 14 designates an intake valve which acts to open and close alternately an air-intake passage 15 through a valve seat 16. Numeral 17 designates a valve guide, numeral 18 a compression coil spring and numeral 19 a swing arm, one end of the swing arm 19 engaging against the upper end of a valve 14 while the other end is supported by a spherical support 20. Numeral 21 designates a cam connected to a shaft 22, rotation of the cam 21 causing the swing arm 19 to oscillate so as to axially displace the valve 14. Numeral 23 designates a cylinder block and numeral 24 a piston which is axially reciprocable within the cylinder block 23 in the conventional manner. Referring to Figs. 2 to 4, the first embodiment of the invention will now be described. The lengthwise dimension of the retainer 4 is substantially equal to that of the cotter 3. The retainer 4 has at its lowest end a rounded bevel portion 4c in the form of a semi-circular are, extending in the circumferential direction. The bevel portion 4c acts as stress relief means located slightly remote from the outer surface of the cotter 3 so as to be in non-contacting relationship with the lower end of the cotter 3. According to the first embodiment, the bevel portion 4c effectively avoids tight engagement against the lower end of the cotter 3, thus leading to a long service life, in contrast to the known supporting structure in which stress concentrations applied to a stem may result in cracks or breakage. Attention is called to Fig. 5 in which a second embodiment of the invention is shown. In the second embodiment, the cotter 3 is longer than in the first embodiment so as to extend downward beyond the lower end of the retainer 4, which end is provided with a rounded bevel (4c).

Claims: An axially reciprocable valve arrangement including a ceramic valve (1) having a head (1a) and a stem (1b), a groove 2 in the stem remote from the valve head, a two-part cotter (3) surrounding the stem, a lock member (3a) extending into the groove and connecting the cotter to the stem, a cylindrical retainer (4) surrounding the cotter, the cotter having a tapered outer surface and the retainer having a tapered inner surface such that axial forces urging the retainer along the stem tighten the cotter on the stem, and means for relieving creation of stress concentrations in the stem by the cotter, said means comprising a rounded bevel portion (4c) defined at the end of the retainer (4) closest to the valve head to provide a clearance between the retainer (4) and cotter (3) at the end of the retainer (4). A valve assembly according to claim 1, wherein the rounded bevel is in the form of a semi-circular arc. A valve assembly according to claim 1 or 2, wherein the cotter (3) extends towards the valve head beyond the end of the retainer (4).

Inventors: KAGAWA JUNICHI, KAWAMURA MITSUYOSHI, NAGASAKI SHIGERU, SATO YASUSHI, TANIGUCHI MASATO, KAGAWA, JUNICHI, KAWAMURA, MITSUYOSHI, NAGASAKI, SHIGERU, SATO, YASUSHI, TANIGUCHI, MASATO
Applicants: NGK SPARK PLUG CO, NGK SPARK PLUG CO., LTD
Application year: 1987
Main classification: F01L3
IPC codes: F01L3