Ceramic tip cast in valve rocker arm

In a ceramic tip comprising a slipper block engaged by a cam arranged for rotation for causing opening and closing movement of an inlet valve on an exhaust valve of an engine, and a cast body block cast integrally with a valve rocker arm body, a round slope is formed at the conjoined boundary area between the slipper block and the cast body block to prevent occurrence of cracks, and retaining channels are formed on the cast body block to prevent escapement of the cast body block from the valve rocker arm body.

FIELD OF THE INVENTION 
This invention relates to a ceramic tip cast integrally with the body of a 
valve rocker arm for improving the reliability of the valve rocker arm 
from the aspect of mechanical strength. 
BACKGROUND OF THE INVENTION 
In vehicles, especially, those equipped with diesel engines, an exhaust gas 
recirculation system is most frequently incorporated for recirculation of 
a portion of engine exhaust gases as a part of new charge therely 
minimizing the amount of oxides of nitrogen contained in the exhaust 
gases. However, when such an exhaust gas recirculation system is used, 
solid carbon contained in the exhaust gases is also mixed into intake air, 
and the carbon tends to be contained in the engine oil. There has 
therefore been the tendency that articles of carbon flow into the area 
between, for example, cams arranged for rotation for causing opening and 
closing movement of inlet valves and exhaust valves of the engine and 
slipper faces of valve rocker arms swung by the cams, resulting in unusual 
abrasion of the slipper faces having a hardness lower than that of the 
surface of the cams. 
To avoid such a trouble, formation of this slipper portion from a ceramic 
material this kind of silicon nitride is disclosed in, for example, 
Japanese Patent Laid Open No. 217307/1984. The structure disclosed in the 
cited patent application is shown in FIG. 1. Referring to FIG. 1, a valve 
rocker arm body 102 is rotatably or rockably mounted on a rocker arm shaft 
101. One end of the valve rocker arm body 102 is engaged by the upper end 
of a valve stem 103 of an inlet valve or an exhaust valve in an engine. 
The valve stem 103 is normally biased upward by the force of a valve 
spring 104 through a spring retainer 105. A cam 106 driven from the engine 
engages the other or base end of the valve rocker arm body 102 for causing 
rocking movement of the valve rocker arm body 102 around the shaft 101. A 
ceramic tip 108 having a slipper face 107 actually engaged by the cam 106 
is provided integrally with the base end of the valve rocker arm body 102. 
Generally, this ceramic tip 108 is cast integrally in the base end of the 
valve rocker arm body 102 during casting of the valve rocker arm body 102. 
As shown in FIG. 2 which is an enlarged perspective external view of the 
prior art ceramic tip 108, a pair of wedge-like tapered retaining faces 
110 are formed on a cast body block 109 of the ceramic tip 108 for 
preventing escapement of the ceramic tip 108 from the valve rocker arm 
body 102. However, when, in the ceramic tip 108 having such a structure, 
an impulsive force generated due to the rotation of the cam 106 is 
repeatedly imparted, as moment of rotation, to a slipper block 111 having 
the slipper face 107, cracks tend to occur at the constricted basal part 
of the cast body block 109. Thus, the prior art ceramic tip has been shown 
to be defective in that the possibility of damage due to generation of 
cracks is very large resulting in a very low reliability. 
SUMMARY OF THE INVENTION 
With a view to obviate such a prior art defect, it is a primary object of 
the present invention to provide a ceramic tip cast in a valve rocker arm, 
which can exhibit a mechanical strength sufficient to withstand the impact 
imparted due to the rotation of the cam and which is therefore highly 
reliable. 
In accordance with the present invention which attains the above object, 
there is provided a ceramic tip cast in a valve rocker arm, comprising a 
slipper block having a part-cylindrical slipper face engaged by a cam 
arranged for rotation for causing opening and closing movement of an inlet 
valve or an exhaust valve of an engine, and a cast body block protruding 
from reverse side of the slipper face of the slipper block and cast 
integrally with the valve rocker arm body, wherein a round slope is formed 
at the conjoined boundary area between the slipper block and the cast body 
block to alleviate stress concentration on the conjoined boundary area, 
and a pair of retaining channels are formed on the cast body block to 
extend in an orthogonal direction with respect to a rocker arm shaft for 
preventing escapement of the cast body block from the valve rocker arm 
body.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
A preferred embodiment of the ceramic tip according to the present 
invention will be described in detail with reference to FIG. 3, which is a 
perspective external view thereof, and FIG. 4, which shows the state of 
the ceramic tip cast in a valve rocker arm body. 
Referring to FIGS. 3 and 4, the ceramic tip embodying the present invention 
is generally designated by the numeral 17 and comprises a cast body block 
12 cast in a valve rocker arm body 11. The cast body block 12 is formed 
integrally with a slipper block 14 having a part-cylindrical slipper face 
13 and protrudes from the face of the slipper block 14 remote from the 
slipper face 13, At the conjoined boundary area between the cast body 
block 12 and the slipper block 14, where the cast body block 12 is joined 
to the slipper block 14, a round slope 15 having a radius of curvature of 
more than 1.0 mm (for example, 1.5 mm) is formed to continuously extend 
along the conjoined boundary area so as to prevent stress concentration on 
the conjoined boundary area. Further, in order to prevent escapement of 
the cast body block 12 from the valve rocker arm body 11, a pair of 
retaining channels 16 having an arcuate sectional shape are formed on the 
cast body block 12 to extend in parallel to each other in a direction 
orthogonal with respect to a rocker arm shaft (not shown). The material of 
the ceramic tip 17 according to the present invention is preferably a fine 
ceramic material having a high hardness and a high resistance to heat, 
such as, silicon nitride, silicon carbide or boron nitride. 
Therefore, even when bending moment due to rotation of a cam (not shown) 
may be imparted to the ceramic tip 17 in the circumferential direction of 
the slipper face 13, the ceramic tip 17 can sufficiently withstand the 
impact and there is substantially no possibility of generation of cracks, 
since the cast body block 12 has not any constriction in the direction of 
impartation of the bending moment, as seen in FIG. 4. The round slope 15 
and retaining channels 16 may be formed after calcination. In such a case, 
the step of grinding can be simplified. Further, the ceramic tip 17 may be 
integrated with the valve rocker arm body 11 by any one of a such as die 
casting molding and so on. When, for example, die casting is utilized, the 
valve rocker arm body 11 is cast in a state in which the ceramic tip 17 is 
previously mounted in a predetermined position in a die casting mold. In 
this case, later finishing of the slipper face 13 is unnecessary. Further, 
although the slipper block 14 and the cast body block 12 of the ceramic 
tip 17 embodying the present invention are rectangular in shape, they may 
be columnar in shape. In such a case, it is preferable that the retaining 
channels 16 extend along the entire periphery of the cast body block 12. 
It will be understood from the foregoing detailed description that, in the 
ceramic tip according to the present invention, a slope for allevating 
stress concentration is formed at the conjointed boundary area between the 
slipper block and the cast body block, and a pair of retaining channels 
for preventing escapement of the ceramic tip from the valve rocker arm 
body are formed to extend in a direction orthogonal with respect to the 
rocker arm shaft, so that there is no change in the width of the cast body 
block along the direction of impartation of bending moment to the ceramic 
tip. Therefore, the resistance of the ceramic tip according to the present 
invention against an impact is greatly improved over that of the prior art 
one, and the ceramic tip of the present invention which eliminates 
substantially the possibility of generation of cracks due to the 
impartation of impact has a high reliability in use.