Ceramic valve supporting structure in use for internal combustion engine
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a ceramic valve which in turn moves to open and close an intake and exhaust port of an engine cylinder, and particularly concerns to an improved structure to movably support a ceramic valve. 
     2. Description of the Prior Art 
     In recent years, high rotation with high power has been required for an internal combustion engine in use for an automobile. A valve, adapted to open and close an intake and exhaust port of an engine cylinder, is exposed to severe environment both mechanically and thermally. Light weight and heat-resistant ceramics is considered to apply to the valve so as to endure the severe environment. 
     In this instance, a valve (b) supports its stem (s) by a retainer (r) through a cotter (c) as seen in FIG. 14a. The outer surface of the cotter (c) and the inner surface of the retainer (r) are both tapered to tightly engage each other by the action of wedge. 
     In accompaniment with the valve action, the cotter (c) acts to engage with the stem (s) more tightly by the effect of wedge, the maximum intensity of which works at the lowest end (n) of the retainer (r). The retainer (r) makes its end (n) tightly act to the stem (s) through the lowest end (m) of the cotter (c), leading to stress concentration at the stem (s) so as to result in crack or breakage as seen at denotation (k) in FIG. 14a. 
     Another problem is shown by the prior structure, in which the cotter (c) provides a lock projection (p) semi-circular in section at the inner surface to interfit an annular groove (g) provided at the outer surface of the stem (s) as shown in FIG. 7c. 
     In association with the action of the valve (b), the projection (p) acts to tightly engage with the open ended portion of the groove (g), thus leading to establish stress concentration so as to end up in crack or breakage as seen at denotation (k) in FIG. 7c. 
     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 wedge effect. The lengthwise sharp edge (e) of each piece tightly engages with the outer surface of the stem (s) so as to cause stress concentration, resulting in crack or breakage as seen at denotation in FIG. 7d. 
     Therefore, it is an object of this invention to provide a ceramic valve supporting structure which is capable of preventing stress concentration from being developed upon a valve stem in a structure in which the ceramic valve is supported by way of a cotter. 
     It is another object of this invention to provide a ceramic valve supporting structure which is capable of obtaining a long servicing life with simple structure and minimum cost. 
     According to this invention, there is provided a ceramic valve supporting structure comprising a ceramic valve having an integral stem, the upper portion of which is provided with a circular groove in concentrical relationship with said stem, and arranged to axially displace so as to alternately open and close an intake and exhaust passageway communicating with a combustion chamber of an internal combustion engine, a cotter the outer surface of which is tapered, and formed by butting a pair of semi-cylindrical pieces, and having a lock member placed into said groove when secured concentrically to the outer surface of said stem, a cylindrical retainer concentrically secured to the outer surface of said cotter so as to support said valve through said cotter, said retainer being provided with the inner surface tapered in a direction so as to make said cotter tightly engage with the outer surface of said stem by means of wedge effect against said tapered cotter due to the urging force of a spring member axially exerted on said retainer, and a stress relief means provided so as to avoid the predetermined portion of said cotter from locally engaging against the outer surface of said stem. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: 
     FIGS. 1a through 4a shows first embodiment of the invention in which; 
     FIG. 1a is a longitudinal cross sectional view of main component of a valve supporting structure; 
     FIG. 2a is a longitudinal cross sectional view of a cotter; 
     FIG. 3a is a longitudinal cross sectional view of a retainer; 
     FIG. 4a is a partial view of an internal combustion engine associated with the invention; 
     FIGS. 5a through 8a are views of main part of supporting structure according to second through fifth embodiments of the invention; 
     FIG. 9a is a view similar to FIGS. 5a through 8a according to sixth embodiment of the invention; 
     FIG. 10a is a view similar to FIGS. 5a through 8a according to seventh embodiment of the invention; 
     FIG. 11a is a view similar to FIGS. 5a through 8a according to eighth embodiment of the invention; 
     FIG. 12a is a view similar to FIGS. 5a through 8a according to nineth embodiment of the invention; 
     FIG. 13a is a view similar to FIGS. 5a throguh 8a according to tenth embodiment of the invention; 
     FIG. 1b is a view similar to FIG. 1a according to eleventh embodiment of the invention; 
     FIG. 2b is a logitudinal cross sectional view of a cotter according to eleventh embodiment of the invention; 
     FIG. 3b is a longitudinal cross sectional view of a retainer according to eleventh embodiment of the invention; 
     FIGS. 5b through 7b are longitudinal cross sectional views of a main views of a main component according to twelfth through fourteenth embodiments of the invention; 
     FIG. 1c is a view similar to FIG. 1a according to fifteenth embodiment of the invention; 
     FIG. 2c is a longitudinal cross sectional view of a cotter according to fifteenth embodiment of the invention; 
     FIG. 3c is a cross sectional view of a retainer according to fifteenth embodiment of the invention; 
     FIG. 5c is an exploded cross sectional view of a valve supporting structure according to sixteenth embodiment of the invention; 
     FIG. 6c is a longitudinal cross sectional view of a valve supporting structure according to sixteenth embodiment of the invention; 
     FIG. 1d is a view similar to FIG. 1a according to seventeenth embodiment of the invention; 
     FIG. 2d is a cross sectional view of a cotter according to seventeenth embodiment of the invention according to seventeenth embodiment of the invention; 
     FIG. 3d is a cross sectional view of a retainer according to seventeenth embodiment of the invention; 
     FIGS. 5d and 6d are cross sectional views of a valve supporting structure according to eighteenth and nineteenth embodiment of the invention; 
     FIG. 1e is a view of valve similar to FIG. 1a according to twentieth embodiment of the invention; 
     FIG. 2e is a view similar to FIG. 1a according to the twentyfirst embodiment of the invention. 
     FIG. 3e is a plan view of a ring according to modified form of twentieth or twentyfirst embodiment; and 
     FIG. 14a, FIG. 7c and FIG. 7d are each cross sectional view and plan view of prior art valve supporting structure. 
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     Each embodiment of the invention is described hereinafter in reference with the drawings. 
     In a first embodiment of the invention, an exhaust valve 1, which is employed in a combustion chamber of an internal combustion engine described hereafter, is made of ceramics such as silicon nitride material, and has a column-shape stem 1b formed in integrally with a valve head 1a as shown in FIG. 1a. The valve 1 provides a circumferential groove 2 semi-circular in section with the upper portion of the stem 1b. A metallic cotter 3 comprising a pair of split pieces, substantially forms a cylinder when combined as seen in FIG. 2a. 
     Into the stem 1b of the valve 1, is the cotter 3 telescoped, the inner surface of which has an integral lock projection 3a semi-circular in section placed into the groove 2. A retainer 4 which is comprised a cylindrical portion 4a and a flange 4b formed in integral with the top of the portion 4a, is interfit into the outer surface of the cotter 3 through the cylindrical portion 4a. In this instance, the retainer 4 provides a tapered inner surface with the cylindrical portion 4a to make face-to-face contact with an oppositely tapered outer surface of the cotter 3. 
     Now, attention is called to a heat-resistant portion designated at 50 which serves as a stress-relief layer coated to the inner surface of the cotter 3. The stress relief layer 50 is not less than at least 5 micron at its thickness which is formed by means of electrical plating of metal such as nickel, copper, silver or the like. Instead of the plating, such means as fluorine-based plastic coating or spattering may be employed to form a layer 50. 
     With above structure, the cotter 3 engages with the stem 1b through the stress-relief layer 50. 
     The valve 1 thus far described, is incorporated into a cylinder head 5 of an internal combustion engine as shown in FIG. 4a. 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 air-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 repeatedly displaces upward and downward to alternately close and open the exhaust passage 8. In compliance with the up-and downward displacement of the valve 1, the retainer 4 tightly engages with the cotter 3 through each tapered surface by means of wedge effect. This causes the cotter 3 to tightly engages against the outer surface of the stem 1b through the stress-relief layer 50. In this situation, the layer 50 approprietely deforms itself according to the stress from the cotter 3, so that the cotter 3 uniformly engages against overall inner surface of the stem 1b through the layer 50. This avoids the upper end of the cotter 3 from locally enaging against the stem 1b so as not to undergo stress concentration, leading to conducive to a long servicing life, in opposition to the counterpart supporting structure in which stress concentration applied on a stem may result in crack or breakage. 
     In addition, all required to avoid the stress concentration upon the stem 1b is only the stress relief layer 50 so as to substantially maintain a simple and cost-saving structure. To take an example as a layer, it is found that a copper plating of 15 micron thick renders immune to crack or breakage even at an excessively high revolution range of the engine. 
     In further reference with the drawings of FIG. 4a, numeral 9 designates a tubular guide to receive the stem ib of the valve 1, numeral 10 designates a cam connected to a shaft 11, numeral 12 being a swing arm, one end of which engages against the upper end of the stem 1b, while the other end of which is supported by a spherical support 13. The rotation of the cam 10 causes to oscillate the swing arm 12 so as to axially displace the stem 1b. Numeral 14 designates an intake valve which acts to alternately open and close an air-intake passage 15 through a valve seat 16. Numeral 17 designates a valve guide, numeral 18 a compression coil spring, numeral 19 a swing arm, one end of which engages 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, and rotation of the cam 21 causes the swing arm 19 to oscillate so as to axially displace the valve 14. Numeral 23 designates a cylinder block, numeral 24 being a piston which lengthwisely reciprocates within the cylinder block 23 in a conventional manner. 
     Now, the second through fifth embodiment of the invention is described in reference with the drawings of FIGS. 5a through 8a. 
     In the second embodiment at FIG. 5a, the stress relief layer 50 is provided with overall outer surface of the cotter 3. 
     In the third embodiment at FIG. 6a, the stress relief layer 50 is provided with the outer surface of the stem 1b instead of the cotter 3. 
     In the fourth embodiment at FIG. 7a, the stress relief layer 50 is provided with the stem 1b as of FIG. 6a in addition to the cotter 3 of the first embodiment. 
     In the fifth embodiment at FIG. 8a, the stress relief layer 50 is provided with the cotter 3 in a manner similar to the second embodiment in addition to the stem 1b of the third embodiment. 
     Now, the sixth through tenth embodiment of the invention respectively is shown in FIGS. 9a through 13a. In the sixth through tenth embodiment, the cotter 3 has the lock projection 3a positioned somewhat remote from the upper end toward the central portion, and each modified to correspond to the first through fifth embodiment. That is to say, the sixth embodiment of FIG. 9a shows the stress relief layer 50 provided with the inner surface of the cotter 3. The seventh embodiment of FIG. 10a shows the same layer 50 provided with the inner and outer surface of the cotter 3. The eighth embodiment of FIG. 11a shows the layer 50 provided with the stem 1. The nineth embodiment of FIG. 12a shows the layer 50 provided with the inner surface of the cotter 3 in addition to the stem 1. The tenth embodiment of FIG. 13a shows the layer 50 provided with the inner and outer surface of the cotter 3 in addition to the stem 1. 
     In the second through tenth embodiment, the reference numerals corresponding to components being identical to those in the first embodiment, and only the structural parts other than those in the first embodiment is described. 
     It is noted that the case in which the layer 50 is provided with overall surface of the cotter 3 is preferrable owing to eliminating the need of coating or marking partially. 
     Further, it is noted that the lock projection 3a of the cotter 3 may be rectangular in section instead of semi-circular section. In this case, the groove 2 of the stem 1 corresponds to the shape of the lock projection 3a. 
     In addition, the stress relief layer 50 is not limited only to metal such as nickel, copper, silver or the like instead of those material, the layer 50 may be made of such materials as to be elastically expansible and developable, at the same time, heat-resistant. 
     Referring to FIGS. 1b through 3b, eleventh embodiment of the invention is described hereinafter. 
     In the eleventh embodiment, instead of the stress-relief layer 50, a novel structure is provided as follows: 
     That is, the lengthwise dimension of the retainer 4 is determined substantially equal to that of the cotter 3. The retainer 4 has a semi-circularly rounded bevel portion 4c in the form of an arch at the lowerest end in the circumferential direction. The bevel portion 4c acts as a stress relief means to position 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 eleventh embodiment, the bevel portion 4c effectively avoids it from tightly engaging against the lower end of the cotter 3, thus leading to a long service life, in opposition to the counterpart supporting structure in which stress concentration applied to a stem may result in crack or breakage. 
     Attention is called to the drawings of FIG. 5b in which twelfth embodiment of the invention is shown. 
     In the twelfth embodiment, instead of the bevel portion 4c of the eleventh embodiment, the retainer 4 provides a circumferentially notched portion 4d at the lowest inner side to position 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. 
     Attention is called to the drawings of FIGS. 6b and 7b  in which thirteenth and fourteenth embodiment are respectively shown. 
     In the thirteenth embodiment of FIG. 6b, the cotter 3 determines its lower end greater in length than that of the eleventh embodiment so as to somewhat extend downward beyond the lower end of the retainer 4. 
     In the fourteenth embodiment of FIG. 7b, the cotter 3 determines its lower end greater in length than that of the twelfth embodiment in a similar manner as above so as to somewhat extend downward beyond the lower end of the retainer 4. 
     Now, attention is called to FIG. 1c in which fifteenth embodiment of the invention is shown. In the fifteenth embodiment, the cotter 3 determines its lengthwise dimension (L) 1.4 times as great as the diametric dimension (d) of the stem 1b as seen in FIG. 1c. 
     In this instance, the lengthwise dimension (L) of the cotter 3 may fall within an extent ranging from 1.1 times to 1.5 times greater than the diametric dimension (d) of the stem 1b. 
     Such is the dimensional arrangement between the cotter 3 and the stem 1b, that the lengthwise dimension (l) in which the cotter 3 substantially contacts against the stem 1b is determined to fall within an extent ranging from 0.6 times to 1.1 times greater than the diametric dimension (d) of the stem 1b. 
     According to the embodiment of the invention, the lengthwise dimension (L) of the cotter 3 is 1.4 times greater than the diametrical dimension (d) of the stem 1b, so that the cotter 3 brings its inner surface uniformly into engagement with overall outer surface of the stem 1b, in opposition to the counterpart in which a cotter tightly engages its lock projection against the open ended portion of a groove to result in stress concentration. 
     Experimentation conducted with the stem 5.5 mm in diameter (d), the cotter 7.8 mm in length (L), the contacting length (l) 6 mm and with the valve made of ceramic material such as, for example, silicon nitride (Si 3  N 4 ), shows that no crack or no breakage was found on the valve with the revolution range from 1.0×10 4  rpm idling to 1.2×10 4  rpm racing at full load. 
     Further, attention is called to FIGS. 5c and 6c in which sixteenth embodiment of the invention is shown. In this embodiment, such is the arrangement between the cotter 3 and the retainer 4 that the cotter 3 determines the tapered degree (y) slightly smaller than that (x) of the retainer by an angle of such as, for example, 0.5 degrees. Such arrangement allows to lessen the engagement degree of the projection 3a against the open-ended portion of the groove 2, so that overall inner surface of the cotter 3 uniformly engages with the outer surface of the stem 1b, thus preventing the projection 3a from locally engaging against the open-ended portion of the groove 2 so as to avoid stress concentration. 
     It is noted that the angular difference between tapered degree of the cotter 3 and that of the retainer 4 should be 0.7 degree at most, taking the wedge effect into consideration. 
     Attention is also called to FIG. 1d in which seventeenth embodiment is shown. In this embodiment, the cotter 3 determines its inner diameter slightly greater than the outer diameter of the stem 1b by the length of such as, for example, 0.08 mm. 
     Such is the structure of the seventeenth embodiment that the cotter 3 brings its overall inner surface into uniform engagement with the outer surface, thus avoiding stress concentration, in opposition to the counterpart of FIG. 7d in which the lengthwise sharp edge tightly engages with the stem. 
     Attention is called to FIG. 5d in which eighteenth embodiment of the invention is shown. In this embodiment, a valve 30 slightly reduces the diameter of the stem 31 to be smaller than the inner diameter of a cotter 32 by the length of between 0.01 and 0.08 mm, in opposition to the seventeenth embodiment in which the cotter 3 increases its diameterical dimension to be greater than the diameter of the stem 1b. 
     Attention is also paid to FIG. 6d in which nineteenth embodiment of the invention is shown. In this embodiment, a cotter 33 provides a lock projection 33a somewhat remote from its upper end toward the central portion. 
     Referring to FIGS. 1e and 2e in which twentieth and twentyfirst embodiment of the invention are shown. In the twentieth embodiment of FIG. 1e, the cotter 3 provides a groove 3g in corresponding with the groove 2 of the stem 1b, instead of the projection 3a of preceding embodiments. A circular solid ring R fits the inner circumference portion into the groove 2 of the stem 1b while outer circumference portion into the groove 3g of the cotter 3, so that the cotter 3 support the valve 1 through the ring R. The ring R may preferably be made from titanium or titanium-based alloy which has small Young&#39;s modulus of 11,000 kg/mm 2 , compared to that of conventional metal of 21,000 kg/mm 2 . 
     According to the twentieth embodiment, the ring R elastically deforms to effectively absorb the engagement force of the cotter 3 against the stem 1b, thus avoiding tight engagement against the open-ended portion of the groove 2. 
     Experimentation conducted with the cotter 3 from SCM 435, the ring R from 99% titanum, and the valve 1 from 94% sintered silicon nitride, shows no crack or no breakage was found on the valve 1 with the revolution range from idling rpm to 1.2×10 4  rpm racing at the cycle of 2×10 4  repeatedly. 
     Refering to FIG. 2e, the twentyfirst embodiment is shown in which the ring R is in the form of hollow to readily deform. Instead of close-looped ring, such open-looped type as seen in FIG. 3e may be employed to obtain ready securement to the stem 1b. 
     It is appreciated that the ring R may be made from shape memory alloy to deform reducing the diameter so as to be tightly placed at the groove 2 at the time of high ambient temperature with the engine running. 
     While various changes may be made in the detail construction, it is understood such manage will be within the spirit and scope of the present invention.