Piston-and-connecting rod assembly

A piston-and-control rod assembly includes a hollow piston having a skirt; axially spaced, circumferential piston ring grooves provided in the skirt; a radial crown having an inner face; and a bearing block projecting from a central portion of the inner face and having a bearing bore oriented radially to the piston axis. The bearing bore is situated in a zone approximately radially adjacent the piston ring grooves. The assembly further includes a connecting rod having a main connecting rod body; a head portion located at an end of the main connecting rod body and being laterally offset relative thereto in a direction of offset; and a piston pin affixed to the head portion and projecting unilaterally therefrom in a direction opposite to the direction of offset. The piston pin is received in the bearing bore.

CROSS REFERENCE TO RELATED APPLICATION 
This application claims the priority of German Application No. P 43 37 
473.5 filed Nov. 3, 1993, which is incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
This invention relates to a piston-and-connecting rod assembly, 
particularly for internal combustion engines. To the head of the 
connecting rod a piston pin is affixed which is supported in a bearing 
mounted centrally in the inner piston base approximately at the height of 
the compression piston rings held circumferentially on the piston skirt. 
A great number of constructions are known where the piston is provided with 
two diametrically opposite bearing holes through which a piston pin 
extends which itself passes through an opening provided in the head of the 
connecting rod. In structures of this type it is not feasible to relocate 
the piston pin axially (with respect to the piston axis) to such an extent 
towards the piston bottom that the piston pin is situated radially 
adjacent a piston ring groove, because in such a case the bore holes in 
the piston skirt would pass through the piston ring grooves with the 
result that the piston rings can no longer perform their sealing function. 
To avoid the above-outlined difficulty, it is known to make multi-part 
pistons. Thus, German Offenlegungsschrift (application published without 
examination) 32 35 220 discloses a piston which has a first part forming 
the piston body and the piston skirt and a second, inner part which forms 
a bearing (articulation) for a connecting rod. The second part has two 
cylindrical bore holes which are oriented perpendicularly to the piston 
axis and which serve as bearings for a piston pin. As a first step in 
assembling the piston, the second part is coupled with the connecting rod 
and thereafter the second part is secured to the piston bottom by means of 
screws. Thus, in such prior art arrangements several individual components 
have to be manufactured, assembled, fitted to one another and bolted 
together. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved 
piston-and-connecting rod assembly of the above-outlined type in which the 
number of individual components is reduced and which, at the same time, 
permits an easier assembly of the individual parts without increasing the 
structural height of the piston. 
This object and others to become apparent as the specification progresses, 
are accomplished by the invention, according to which, briefly stated, the 
head of the connecting rod is laterally offset relative to the length of 
the connecting rod body and the piston pin is secured to the connecting 
rod head such that it projects unilaterally from the connecting rod head 
against the direction of the offset. 
By virtue of the construction according to the invention it is feasible to 
form the connecting rod bearing as a one-piece component with the piston. 
The connecting rod may be coupled to the piston by simply inserting the 
piston pin into the connecting rod bearing without the need of additional 
connecting elements such as screws. Therefore, the invention provides that 
the piston-and-connecting rod unit may be reduced to two individual 
components whose assembly may be automated in a simple manner. Preferably, 
the connecting rod head is offset in such a manner that the force exerted 
on the pin extends through the middle of the pin and the effective force 
path coincides with the center line of the main connecting rod body with 
respect to which the connecting rod head is offset. It is further feasible 
to form the piston pin on the connecting rod head as a one-piece, unitary 
component therewith. 
According to a further feature of the invention, the connecting rod head 
has, adjacent the pin, a supporting bearing face axially engaging the 
piston bottom. In this manner a direct force transmission from the piston 
to the connecting rod is achieved without exerting a bending stress on the 
piston pin. The force exerted on the piston pin and the support bearing 
is, by means of an appropriate offset of the connecting rod head guided 
through the piston center and the force path coincides with the 
longitudinal axis (longitudinal center line) of the main connecting rod 
body. For enhancing lubrication of the connecting rod bearing, the lateral 
faces of the piston pin are flattened at diametrically opposite locations.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates a piston-and-connecting rod assembly according to a 
preferred embodiment of the invention, generally designated at 1. The 
assembly includes a hollow piston 2 which is a one-piece construction and 
which has a cylindrical skirt provided with a plurality of axially spaced 
piston ring grooves 3. From the inner face 4' of the piston crown 4 there 
projects a connecting rod bearing block 5 which has no contact with the 
cylindrical skirt of the piston 2 and which has a radially oriented bore 
hole (bearing bore) 6. 
The piston-and-connecting rod assembly 1 further includes a connecting rod 
generally designated at 12 which has a main body 8 and a head 9. Stated 
differently, as shown in FIG. 1a, the connecting rod head 9 is offset by a 
distance a in the direction B relative to the length dimension of the main 
body 8 of the connecting rod 12, represented by the longitudinal center 
line C of the main body 8. It is further seen that the piston pin 7 
extends from the head 9 in a direction opposite to the direction B. In 
FIG. 1a, the upper part of the piston pin 7 and the head 9 is shown in 
section to illustrate that the pin 7 and the head 9 constitute a 
one-piece, unitary component. As indicated at 10, the connecting rod head 
9 is offset laterally relative to the length of the main body 8, that is, 
radially relative to the piston axis A and carries, as a one-piece, 
unitary component, a piston pin 7 which extends radially in a direction 
opposite to the direction of offset of the head 9. The piston pin 7 is 
received in the bearing bore 6 of the connecting rod bearing block 5. The 
connecting rod head 9 has an arcuate outer face 13 which is axially 
supported on a counterface 14 of an elevation 15 formed on the inner face 
4' of the piston crown 4. 
For installing the connecting rod 12, the latter is introduced axially into 
the piston 2 in such a manner that the pin 7 is first situated radially 
adjacent the bearing bore 6 and then the connecting rod 12 is shifted 
radially so that the pin 7 may penetrate into the bearing bore 6, whereby 
the connecting rod 12 and the piston 2 are hooked together. 
FIG. 2 shows that the pin 7 is provided with diametrically opposite 
flattened portions 11 which facilitates the lubrication of the bearing 
bore 6. 
FIG. 3 shows that the connecting rod 12 serves as an axial support as the 
arcuate head surface 13 engages the complemental bearing surface 14 of the 
elevation 15 formed on the inner face 4' of the piston crown 4. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.