Connecting rod made of fiber reinforced plastic material

A connecting rod has at one end thereof two leg portions formed in forked configuration defining therebetween an intermediate groove having a recess of semi-circular cross section on the inside thereof and having oppositely located bolt insertion holes at the leading ends thereof, respectively. In the other side of the intermediate groove is fitted a block having a semi-circular recess defining a crankshaft bearing hole in opposed relationship with said semi-circular recess of the intermediate groove and having a bolt insertion hole formed therethrough and extending coaxially with each of the bolt insertion holes so as to tighten up and fixedly secure the block between the leg portions by a bolt and nut unit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a connecting rod, and more particularly to a 
connecting rod of a fiber reinforced plastic material. 
2. Description of the Prior Art 
The connecting rods which have so far been employed are constructed as 
disclosed in the Japanese Laid-open Publication Nos. 56-155122 and 
56-157420 of Japanese Utility Model Applications, such that the body of 
connecting rod has a bearing hole for a piston pin of a small diameter 
formed at one end thereof into which is inserted the piston pin and, at 
the other end thereof, is provided with a semi-circular recess forming a 
half part of a bearing hole for a crankshaft of a larger diameter 
connected to the crankshaft and with a block having a semi-circular recess 
corresponding to said recess and fixedly secured to the other end of the 
body by tightening up a pair of bolts thereby defining a crankshaft 
bearing hole. The purpose of this is to allow a back pressure to be 
exerted on the crankshaft bearing hole in the longitudinal direction of 
the rod member. 
Accordingly, it is necessary to form longitudinally extending holes in the 
connecting rod body on both sides of the recess thereof and on both sides 
of the block (that is; in the critical part of the connecting rod). 
Therefore, in the case where the connecting rod is formed by a fiber 
reinforced plastic material, the fiber itself is interrupted or cut off by 
the bolt insertion holes to thereby reduce the effective sectional area of 
the critical part of the connecting rod and both ends of the fiber in the 
vicinity of the bolt insertion holes are cut off. Consequently, the load 
caused by tightening up the bolts and that due to the inertia force 
exerted in the crankshaft bearing hole portion will be borne by the 
shearing strength of the carbon fiber reinforced plastic material in the 
periphery of the recess on the side of the crankshaft bearing hole and 
also in the periphery of the recess on the side of the block. Therefore, 
there is a risk that the fiber reinforced plastic material cannot endure 
the loads caused on the crankshaft bearing hole portion with the result 
that the connecting rod is damaged or broken. 
SUMMARY OF THE INVENTION 
The present invention has been contemplated in view of the foregoing 
circumstances, and has for its object to provide a connecting rod made of 
a fiber reinforced plastic material wherein the mechanical strength of the 
portion of the rod on both sides of the crankshaft bearing hole is 
increased so as to bear the load caused on that portion and to prevent the 
failure thereof and a back pressure can be exerted in the crankshaft 
bearing hole in the longitudinal direction of the connecting rod body. 
Another object of the present invention is to provide a connecting rod of 
light weight wherein an inertia force reduction effect and a noise level 
reduction or suppressing effect resulting from improved vibration 
attenuation characteristic can be obtained. 
In order to obtain the foregoing objects or aspects of the present 
invention, there is provided a connecting rod comprising a body thereof; 
one end of the body having a piston pin bearing hole; two leg portions 
formed in forked configuration at the other end of the body and having a 
recess of semi-circular cross-section formed on one side of an 
intermediate groove defined between the leg portions, the leg portions 
respectively having oppositely located bolt insertion holes formed in the 
leading ends thereof; a block adapted to be fitted in the other side of 
the intermediate groove and having a semi-circular recess defining a 
crankshaft bearing hole in opposed relationship with said semi-circular 
recess formed on one side of the intermediate groove, the block having a 
bolt insertion hole formed therethrough and extending coaxially with each 
of the bolt insertion holes formed in the leg portions; a bolt adapted to 
be passed through said three bolt insertion holes; and a nut for 
tightening up and fixedly securing said block between said two leg 
portions in co-operation with the bolt. 
In accordance with another aspect of the present invention, there is 
provided a connecting rod comprising a body thereof; one end of the body 
having a piston pin bearing hole; two leg portions formed in forked 
configuration at the other end of the body and having a recess of 
semi-circular cross section formed on one side of an intermediate groove 
defined between the leg portions, the leg portions respectively having 
oppositely located bolt insertion holes formed in the leading ends 
thereof; a block adapted to be fitted in the other side of the 
intermediate groove and having a semi-circular recess defining a 
crankshaft bearing hole in opposed relationship with said semi-circular 
recess formed on one side of the intermediate groove, the block having a 
bolt insertion hole formed therethrough and extending coaxially with each 
of the bolt insertion holes formed in the leg portions, respectively, and 
notches respectively formed in both open ends of the bolt insertion hole 
thereof; a bolt adapted to be passed through said three bolt insertion 
holes; a nut for tightening up and fixedly securing said block between 
said two leg portions in co-operation of the bolt; and wedge pieces each 
being pushed into each of the notches formed in the block by tightening up 
the nut threadably engaged with the bolt thereby pressing the block 
against the longitudinal inside of the body. 
In accordance with a further aspect of the present invention, there is 
provided a connecting rod wherein a body thereof is made of a fiber 
reinforced plastic material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Formed at one end of a body 10 is a piston pin bearing hole 11 which 
rotatably supports a piston pin (not shown) and in which a bushing 12 is 
fitted. 
The other end of the above-mentioned body 10 is of forked configuration 
comprising one leg portion 10a and another leg portion 10b. Formed beween 
the leg portions 10a and 10b is a groove 15 comprised of a semi-circular 
recess 13 and opposed faces 14 and 14 in parallel relationship with each 
other. 
Formed in the leg portions 10a and 10b, respectively, at positions nearer 
to their open ends and away from a circular are with a radius 
corresponding to the radius .gamma. of the recess 13 are bolt insertion 
holes 16, 16 which are in opposed relationship and which extend in the 
direction at right angles to the longitudinal direction of the body 10. 
Further, fitted in each of the bolt insertion holes 16 and 16 is a 
metallic insert 17. 
The fiber 18 used as the constituent material of the body 10 extends 
continuously in the longitudinal direction thereof and bend along the 
periphery of the piston pin bearing hole 11 and the bolt insertion hole 
16. Thus, the fiber 18 extends uninterruptedly in the direction of the 
body 10 thereby to form the body 10. 
A metallic block 19 is inserted in the above-mentioned groove 15. The 
metallic block 19 has a semi-circular recess 20 having a radius 
substantially equal to the radius of the aforementioned semi-circular 
recess 13. Further, a hole 21 for the insertion of a bolt is formed 
opposite to the aforementioned bolt insertion hole 16, and both the 
semi-circular recess 13 and the recess 20 form a crankshaft bearing hole 
22. A nut 24 is threadably engaged with the bolt 23 which passes through 
the aforementioned bolt insertion hole 16 and is tightened up to fixedly 
secure the bolt and the nut. 
Moreover, the bushing 12 and the insert 17 are embedded into the connecting 
rod when it is molded of a fiber reinforced plastic material such as for 
example a carbon fiber reinforced plastic material. 
Another embodiment of the present invention will be described below with 
reference to FIGS. 3 to 7. 
This embodiment has the substantially same construction as the first 
embodiment shown in FIGS. 1 and 2, and like parts are shown by the same 
reference numerals. This embodiment differs from the first embodiment in 
that a half-split metal 130 is fitted into the aforementioned 
semi-circular recess 13, and also a half-split metal 200 is fitted into 
the semi-circular recess 20 formed in the block 19. Thus, the aforesaid 
half-split metals 130 and 200 form a crankshaft bearing hole 22. Another 
difference of this embodiment from the first embodiment resides in that 
the inside diameter of the bolt insertion hole 21 of the above-mentioned 
block 19 is larger than the outside diameter of the bolt 23 and the bolt 
insertion hole 21 has outwardly enlarged semi-circular notches 25 formed 
in both ends thereof and in each of which is fitted a generally 
semi-circular wedge piece 26 the inner peripheral surface of which 
corresponds with the outer peripheral surface of the bolt 23. According to 
this second embodiment, when the nut 24 is threadably engaged with the 
bolt 23 and tightened up, the wedge piece 26 is pressed by the insert 17 
into the notch 25 so that the outer peripheral surface of the wedge piece 
26 may be pressed against the inner wall surface of the notch 25 of the 
block 19 by a wedging action thus urging the block 19 always towards the 
semi-circular recess 13 (that is; in the direction shown by arrow Y). In 
this case, the urging or pressing force exerted by the wedge piece 26 
against the block 19 is determined, as shown in FIG. 7, by a difference 
.delta. between the inner wall surface 25a of the notch 25 and an outer 
peripheral surface 26a of the wedge pieces 26, the inclination angle 
.theta. of the outer peripheral surface 26a and the amount l of the wedge 
piece 26 to be pushed in. 
Further, the wedge piece 26 and the insert 17 may be formed as an integral 
unit, and the wedge piece 26 and the notch 25 may be formed in a square 
shape. 
By forming the connecting rod by a fiber reinforced plastic material as 
mentioned hereinabove, the fiber extends uninterruptedly along the 
periphery of the crankshaft bearing hole 22 so as to increase the 
effective sectional area of the connecting rod so that the loading due to 
the inertia force can be borne by the compression, bending and shearing 
strength thus increasing the mechanical strength of the rod per se to 
substantially increase the resistance thereof to failure. 
Further, the pushing-in of the metal 130 in the direction shown by arrow Y 
resulting from pressing of the block 19 by the insertion of the wedge 
piece 26 into the notch 25 enables a back pressure to be exerted on the 
crankshaft bearing hole 22 thereby enabling the complete roundness of the 
metal 130 to be secured. 
Furthermore, by forming a connecting rod by a fiber reinforced plastic 
material, an improved inertia force reduction effect resulting from a 
reduction in weight and a considerable noise suppressing effect due to 
improved vibration attenuation characteristics can be expected. 
It is to be understood that the foregoing description is merely 
illustrative of preferred embodiments of the invention, and that the scope 
of the invention is not to be limited thereto, but is to be determined by 
the scope of the appended claims.