Piston for internal combustion engines

A piston for internal combustion engines, especially for motors of the Diesel type. On purpose to reduce the heat diffusion from the piston crown to the piston portion where are fitted the sealing piston rings, provision is made of an internal circular groove intended to reduce the thickness of the connection portion between the piston crown and the side portion where are fitted the sealing rings, an external cut tangentially formed in the piston side portion substantially at the connection thereof with the piston crown, i.e. above the grooves of the piston rings, being substituted for the circular groove which is interrupted below the regions of the piston crown provided with any recess which would cause the thickness of the connection portion to be too slight.

This invention relates to an improved piston for internal combustion 
engines, particularly for motors operating at high temperatures and 
pressures, such as motors of the Diesel type. 
In motors of the afore-stated type, the piston surface areas which are 
subjected to the detonation stress must withstand, as soon as the engine 
is started, to these operating high temperatures and pressures. On the 
contrary, the area where the piston rings are located and particularly the 
so-called "fire" or compression ring, must be protected against the 
stresses due to the detonation of the gases at high temperatures as to 
avoid a quick carbon deposit. 
A known arrangement intended to solve these problems consists in 
manufacturing of composite pistons having an upper portion made of either 
cast-iron or steel and opposite to the combustion chamber, said upper 
portion being maintained at a temperature higher than that to which is 
subjected a lower portion made of light alloy and intended to bear the 
piston rings, said portions being associated to a conventional piston 
structure on which the upper portion made of cast-iron or steel is mounted 
either by assembling thereto or as an insert-shaped portion on which the 
lower portion made of light alloy is directly cast. 
In French patent application No. 78/09460 on behalf of the Applicant, there 
was described a composite piston of this type, which comprises an upper 
face made of steel and mounted thereto by means of a well known screwed 
assembly on a lower portion made of light alloy, said piston being 
characterized in that said lower portion comprises a circular inwardly 
open channel which is concentric to the piston rings and closely located 
on the bottom of the ring grooves, said circular channel being covered by 
the upper portion made of steel. 
The aim of the present patent application is to solve the afore-mentioned 
problem by providing an improved piston structure easier to manufacture, 
which results in a lower building cost. 
To this end, the piston for internal combustion engines, especially for 
motors of the Diesel type, which is the object of this invention, is 
characterized in that, on purpose to reduce the heat diffusion from the 
piston crown to the piston portion where are fitted the sealing piston 
rings, provision is made of an internal circular groove intended to reduce 
the thickness of the connection portion between the piston crown and the 
side portion where are fitted said sealing rings, an external cut 
tangentially formed in the piston side portion substantially at the 
connection thereof with the piston crown, i.e. above the grooves of the 
piston rings, being substituted for said circular groove which is 
interrupted below the regions of the piston crown provided with any recess 
which would cause the thickness of said connection portion to be too 
slight. 
As an advantageous feature of said embodiment, the invention enables either 
composite pistons comprising two parts or pistons made in one piece to be 
manufactured.

The piston upper portion shown, by way of example, on these figures mainly 
comprises the bushes 1 for connecting the piston to the small end of the 
connecting rod, the legs 2 and ribs 3 thereof for connecting said bushes 
to the bottom face 4 of the piston crown 5, and the side portion 6 in 
which are provided the grooves 7 for the oil sealing rings. 
In accordance with the present invention and on purpose to reduce the heat 
diffusion flowing from the crown 5 to the side portion 6 in which are 
formed the grooves 7 for the sealing rings, provision is made of a 
circular internal groove 8 so shaped as to reduce the thickness 9 of the 
connection portion between the crown 5 and said side portion 6 where are 
fitted in grooves 7 the sealing rings. 
Below regions of the crown 5 where are provided recesses 10, such as 
bottoms of any pre-ignition chamber, which could weaken said connection 
part 9 at such an extent that a perforation of the crown 5, made by a 
torch effect due to the gases flowing from the pre-ignition chamber, could 
occur, the groove 8 is interrupted at a convenient distance from said 
recesses 10. Further, on purpose to maintain in said regions a connection 
thickness sufficient to reduce the heat diffusion from the crown 5 to the 
side part 6 where sealing rings are fitted in grooves 7, a cut or slot 12 
tangentially formed on the external face of said side part 6 substantially 
at the connection area thereof with the crown 5, i.e. above said grooves 
7, is substituted for the groove 8. 
The scope of this invention is not limited to the embodiment herein-above 
described. Particularly, as previously stated in this Specification, this 
invention may be applied to the manufacture of composite bimetallic 
pistons as well as to monobloc pistons. Further, the shape and sizes of 
cut 12 may also vary substantially with respect to the thermo-electric 
properties of the alloy or metal to be used, as well as to the shape and 
location of the recesses 10 in the compression face 5 of the piston.