Connecting rod for piston-operated machines, especially compressors, and process for its production

In a connecting rod with a split big-end, the unmachined part is preferably aluminum die-casting in which notches are made along the subsequent line of separation. The big-end is separated substantially along the intended break line by means of a shearing tool capable of widening the eye in the region of intended bore reliefs in such a way that subsequent opening out is unnecessary.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention relates to a connecting rod for a piston and more 
specifically as well as to a process for producing such a connecting rod. 
Diecast connecting rods, such as aluminum diecast connecting rods for 
compressors, are known which are constructed as closed connecting rods or 
as split connecting rods. Split connecting rods are produced, for example, 
of two cast parts which are provided with fixing noses. Also known are 
connecting rods which are split mechanically and are fixed with respect to 
one another by close-tolerance bolts or pins or profilings. 
For the finishing of split connecting rods, before the machining of the 
bore of the split big end, its top part must be screwed to its bottom part 
and must be marked in a suitable manner. The construction of lateral bore 
reliefs in the form of opened-out areas is not easily possible and, if at 
all, can be provided in the unmachined part. Connecting rods of the known 
type will still require a mechanical finishing with increased expenditures 
of time and cost. 
In addition, the screwing of the top part to the bottom part, which 
precedes the finishing, presents problems because, even in the case of the 
most exact centering of the parts, a slight offset must always be 
accepted. Such a spatial offset disadvantageously influences the 
lubricating film which, after the mounting on the crank pin, exists 
between it and the interior circumference of the big end eye; that is, 
forms during the rotation of the crank pin relative to the eye. 
Based on the above, it is an object of the invention to provide a 
connecting rod for piston-operated machines, particularly compressors, 
which, with respect to its splitting, can be manufactured with low 
expenditures of time and cost and nevertheless permits an extremely 
precise manufacturing, mainly in the area of the splitting of the big end 
and of the big-end eye. 
It is also an object of the invention to provide a process for 
manufacturing a connecting rod of this type. 
The process of the invention and the product manufactured by means of it 
have the advantage that the unmachined part of the connecting rod can be 
finished like a closed connecting rod and is split only before the 
mounting in the compressor of other machines by a suitable 
separating-breaking tool at the separating point, that is, along a desired 
breaking line. In this case, it is a special advantage that the profile 
(toothing) of the breaking point which forms during the breaking is 
subsequently used as a fixing device for the connection and at the same 
time for a protection with respect to an exchange. In the case of a 
corresponding construction of the breaking-shearing tool and taking into 
account the separating forces and deformations, it is possible to achieve 
the optimal construction of the big end eye without requiring a mechanical 
finishing. In particular, it is possible to subsequently shape opened-out 
areas serving as bore reliefs on the interior circumference of the big end 
eye by means of the shearing tool.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 of the drawing illustrates a connecting rod which consists of a 
spherical part 1, a connecting rod shank 3 and a big end 5 and which, 
according to the invention, is prepared for a split extending along the 
plane A. The connecting rod is preferably made of a diecast aluminum 
material and is illustrated as an unmachined part; that is, the 
illustrated connecting rod produced as a die-casting has the eye of the 
spherical head, the eye 9 of the big end and optionally the passages 11 
for (not shown) fastening screws. 
In the area of the plane A, the unmachined part of the connecting rod 
illustrated in FIG. 1 is provided with notches 13 and 15 extending on the 
interior side on the interior circumference of the eye 9 and on the 
exterior side respectively. In the sectional view and as an enlarged 
individual view, the FIGS. 2 and 3 show the possible contouring of the 
notches 13 and 15. 
Starting from the unmachined part illustrated in FIG. 1, the connecting rod 
will then be subjected to a finishing; that is, the eyes 7 and 9 are 
drilled with the required precision; likewise, the passages 11 are 
provided with internal threads 17, as required. With the exception of the 
area of the notch 13, the eye 9 has a circular shape which, in the course 
of the splitting to be carried out subsequently, may experience a 
deviating of the contour. 
As illustrated above, the unmachined part of the connecting rod is 
finished, specifically with respect to all areas to be subjected to a 
manufacturing. The connecting rod will at first exist as a closed 
connecting rod and will be split only before the mounting in the 
compressor by means of a corresponding tool and measures at the separation 
point (plane A) of the unmachined part. In this case, a correspondingly 
constructed shearing tool will be used which takes into account the 
separating forces and deformations which occur during this operation, 
whereby an optimal construction of the bearing form is achieved without 
the requirement of a mechanical finishing. An exemplary tool S is shown in 
FIG. 5 interior the eye 9 as having two halves. The tool S separates in 
the direction F shown by the arrows to simultaneously create the 
separating forces and deformations. 
As an enlarged, partially cut lateral view, FIG. 5 reflects Line B of the 
course of the break at the big end 5. In the left sectional half according 
to FIG. 5, C indicates the circular course of the bore of the eye 9 before 
the breaking along Line B, while, in the right sectional half according to 
FIG. 5, D indicates the course on the interior circumference of the eye 9 
after the separation or after the break of Line B. A comparison of the two 
contours C and D shows that, when the connecting rod head 5 is separated 
by means of a suitable tool, opened-out areas 19 and therefore 
indentations are created which are expedient for receiving lubricants in 
the case of such connecting rods, specifically in the area of the pressure 
relief of the crank pin. 
During the mounting of the connecting rod split in the above-mentioned 
manner on a crank pin (connecting rod bearing pin), thus during the 
joining of the top part and the bottom part, it is particularly 
advantageous that an essentially arbitrary toothing was formed during the 
breaking. This toothing profile permits an absolutely noninterchangeable 
joining and screwing to the crank pin, specifically without any offset. 
List of Reference Numbers 
1 spherical head 
2 connecting rod shank 
5 big end 
7 eye 
9 eye 
11 passage 
13 notch 
15 notch 
17 internal thread 
19 opened-out area