Piston having a barrel of forged steel and a cooling channel

A piston with a cooling channel having a basic piston barrel made from forged steel and a box-shaped shaft, bosses and boss supports and connecting walls between the boss supports as well as a combustion trough. The piston increases the rigidity of the ring part. To accomplish this, the piston has a wall extending all around above the boss bores. A structural component is welded in between the wall and the piston head and limits the cooling channel. This design increases the rigidity of the ring part in pistons.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to piston with a basic piston barrel of 
forged steel and a cooling channel. In particular, this invention relates 
to a piston in which deformation in the region of the ring band is 
minimized. 
2. The Prior Art 
This type of a piston and a process for its manufacture are known from 
German Patent No. 44 46 726 Al. However, the piston shown in this patent 
has the drawback that the ring band is tied to the basic piston barrel 
only via the piston head. Thus, the ring band is consequently susceptible 
to deformation. 
A piston made of cast iron is known from PCT Application WO 80/02308, where 
the top part and the boss part are welded together. This piston has a rib 
extending all around above the bosses; however, this rib is not welded to 
the top part and has no stiffening function. 
Another piston of this type is shown in German Patent No. DE 24 34 902 A, 
where sections of the ring band and a radially outward section of the 
piston head are formed by a welded-in component. This measure, however, 
exclusively forms a cooling channel. This is a problem which has been 
solved already in the relevant state of the art by closing the machined 
cooling channel with a metal sheet. 
Another piston is shown in German Patent No. DE 30 32 671 A, where a top 
part made of heat-resistant steel and a bottom part made of flow-pressed 
steel are welded together. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to minimize deformation in the 
region of the ring band of pistons of this type. 
This and other objects of the invention are achieved by a piston comprising 
a basic piston barrel made of forged steel having a carbon equivalent of 
at least 0.3% and having a box-shaped shaft. There are a cooling channel 
and bosses with boss bores and boss supports formed in the piston barrel. 
The boss supports have connecting walls between them. There is a wall 
extending all around the piston barrel and disposed axially above the boss 
bores. The wall extends radially outside of the boss supports and the 
connecting walls and is integrally formed with the basic piston barrel. 
There is a combustion trough formed in the piston barrel. 
In the piston according to the invention, at least part of the ring band 
and piston head are formed by a structural component which is welded to 
the basic barrel of the piston by two welding seams. The rigidity of the 
ring section is therefore distinctly increased. The structural part forms 
at least part of a ring band and part of a piston head disposed outwardly 
radially on the piston barrel. The welding seams are produced by 
MIG-welding, MAG-welding, laser welding or electron beam welding. The wall 
of the basic piston barrel and the structural component jointly form a 
radially outer and axially lower limiting wall of the cooling channel, 
resulting in a bending-resistant zone in the region of the ring band. 
In a preferred embodiment, there is an elastic metal sheet in the interior 
of the piston, which forms a lower limitation of an inner cooling space. 
The metal sheet is fixed in the region of the boss support by its own 
initial stress. 
The box-shaped shaft can be separated from the ring band either by a recess 
in the pressure/counter-pressure direction as shown in the drawings, or it 
can be connected with the ring band and the surrounding wall.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring in detail to the drawings, FIGS. 1-4 show piston 1, which 
consists of a basic piston barrel 2 and a structural component 3 welded to 
barrel 2. Component 3 comprises part of the ring section and the piston 
land as well as part of piston head 5. The ring portion and the piston 
land are jointly denoted by reference numeral 4. A combustion trough 6 is 
arranged in piston head 5. The basic piston barrel consists of the bosses, 
which have a boss bore 7, boss supports 8 and connecting walls 9 between 
the bosses. There is a wall 10 shaped by molding above boss bores 7 and 
extending all around and radially disposed outside of the bosses and the 
connecting walls 9 between the bosses. There is also a well as piston head 
5 with combustion trough 6. 
Wall 10, which runs all around, starts to extend from the bosses or 
connecting walls between the boss supports and runs upwardly and is 
slanted radially to the outside. 
The welding seams are in the form of an axial seam in the outer region of 
the piston head, and in the form of a radial seam in the region of the 
ring band between the second and third grooves. 
The box-shaped shaft 11 can be connected either only to the bosses or also 
with ring band 4. 
Wall 10 substantially forms a lower limitation of a cooling channel 12, and 
the welded-in structural component 3 substantially forms a radially outer 
limitation of cooling channel 12. 
There is an elastic metal sheet 13 in the interior of the piston, which 
forms a lower limitation of an inner cooling space. Metal sheet 13 is 
fixed in the region of boss support 8 by its own initial stress. 
Accordingly, while only a few embodiments of the present invention have 
been shown and described, it is to be understood that many changes and 
modifications may be made thereunto without departing from the spirit and 
scope of the invention as defined in the appended claims.