D E S C R I PT I O N

The present invention deals with a piston for internal combustion engines. Briefly, internal combustion engines are thermal motive machines which transform into mechanical work part of the thermal energy freed by burning fuels inside the machine itself; said transforming occurs by means of a working fluid (mixture of fuel air) which, by being expanded and compressed, exchanges energy with moving machine members. The classification criteria of internal combustion engines are several and can be based, for example, on the following parameters:

• Mode of starting the working fluid combustion: with controlled ignition, with spontaneous ignition;

• Described cycle length: complete piston cycle in four strokes, two strokes, etc.;

• Nature of used fuel: gasoline, alcohol, diesel oil, etc.;

• Air supply: aspirated engine, supercharged engine, turbo- supercharged engine; '

• Fuel supply: carburetion, cylinder (direct) injection, suction manifold (in direct) injection;

• Load adjustment due to variation of mixture composition (adjusting the fuel amount), of amount of charge inserted into the cylinder (with constant composition).

However, apart from the above parameters, the most used type of internal combustion engines is the one providing for the burning of a suitable mixture inside a combustion chamber composed of a cylinder

closet on its lower part by a un piston and on its upper part by an head; said head has fluid inlet valves, discharge gas exhaust valves and possibly an injector and/or a spark plug to generate a spark.

A connecting rod is hinged, through a connection piston pin, to the piston in order to transform the alternate straight motion into a rotary motion.

For the correct operation of an engine, a correct combustion is essential; this occurs by suitably designing the combustion chamber in order to allow the fluid to obtain a quick advancement of the combustion phase; consequently, there will be a higher specific power, a lower cyclic dispersion, an efficiency gain and a better emission control.

In fact, the combustion chamber design affects its filling placing limitations to maximum valve diameter and shape of suction and discharge duct outlets. In addition, a good combustion chamber prevents anomalous combustion phenomena, spark advancing or delaying in time the compressed mixture ignition.

Among the most severe anomalies, there is the detonation one which limits performances and efficiency (preventing from exceeding certain compression ratio values).

Moreover, under particularly severe conditions, a detonation can cause the damaging of mechanical engine members.

It is known from the prior art to obtain combustion chambers directly from the piston crown (or head), to create swirling movements of the input charge, favour mixing between fuel and oxygen and improving thermal process speed.

A piston having the above stated geometry is known with the term "cup piston"; such cup can assume different shapes, in particular having straight or re-entering edges.

Among the geometric parameters which define an internal combustion engine, there are bore and stroke.

The adoption of a more or less high stroke with respect to bore changes the engine field of use.

Generally, a bore lower than the stroke is kept for normal engines, with a daily use. On the contrary, in sports competitions in which maximum performances are searched, it is mandatory to keep high bore ratios with respect to the stroke and to allow reducing the mean piston speed or, alternatively, to increase the number of engine revolutions (and therefore the power) with the same mean piston speed (worsening the consumptions which however do not become the major choice factor).

Object of the present invention is making available a piston for internal combustion engines which allows placing the connecting rod small end as near as possible to the piston top, namely in the recess tunnel obtained under the piston crown. Another object is providing a convexity obtained in the head which is able to induce better turbulences of the fresh charter inside the piston cup.

Among the advantages which the present invention has, the following can be cited:

• optimisation of the swirling motion due to the simultaneous generation of two vortexes coupled inside the chamber obtained in the piston itself caused by the convexity;

• almost complete concentration of fresh charge inside the piston cup;

• due to the high bore allowed by the combustion chamber geometry, the valves can be advantageously placed in a vertical position with respect to the piston head;

• stroke reduction due to the chance of using a wider bore and the presence of the concavity obtained under the piston crown which allows keeping the pin axis, and therefore the connecting rod small end, nearer to the piston barycentre, with a high reduction of oscillating effects during sliding inside the cylinder.

The above objects and advantages are all obtained by the piston for internal combustion engines, subject of the present invention, which is characterised by what is stated in the below listed claims. These and other characteristics will be better pointed out by the following description of some embodiments shown, merely as a non-limiting example, in the attached tables of drawing, in which:

- figure 1 shows a piston for internal combustion engine, subject of the present invention, in a perspective view; - figure 2 shows, from a different angle, the piston of figure 1 ;

- figure 3 shows the top plane view of the piston of figure 1 ;

- figure 4 shows section B-B of figure 3;

- figure 5 shows section A-A of the piston of figure 3.

With reference to figures 1 , 2, 3 and 4, a piston 1 is shown in whose head 2 a cup-type combustion chamber is obtained, designated with 4.

From the bottom of such combustion chamber 4, a convexity 3 rises

towards the head (2) and forms a back in the chamber 4 itself.

As better shown in figure 5, it must be noted how the relative maximum point of the convexity 3 is placed next to the centre distance of the head 2 and projects from the combustion chamber 4 bottom. The convexity 3 is preferably arranged according to the direction of axis 5 of the connection piston pin of the connecting rod with piston 1 and extends for the whole combustion chamber 4 diameter.

It must further be observed that the convexity 3 is substantially symmetrical with respect to the centre distance of the head 2, according to a sectional median plane transverse to the piston pin axis.

In part 2a below the head 2, there is a recess 3b, next to the convexity 3 above and also arranged according to the insertion axis of the piston pin.

Similarly, the recess 3b is substantially symmetrical with respect to the centre distance of the head 2, according to a sectional transverse plane to the piston pin axis.

The configuration shown in the example allows taking the axis 5 of the connection piston pin of the connecting rod with piston 1 as near as possible to the piston 1 barycentre, with the connecting rod eye contained in the recess 3b.

The example of piston 1 is subjected to numerous variations as regards the shape of the combustion chamber 4, the possible placement of valve prints on the head, the number of rings or scraper rings being present and so on. According to a not-shown variation of the piston 1 , convexity 3 and concavity 3b can be placed in an asymmetrical position with respect to a

sectional median plane transverse to the piston pin axis 5.

According to a not-shown variation of the piston 1 , the convexity 3 extends for a shorter length than the cup diameter of the combustion chamber 4.