WO1994007016A1

WO1994007016A1 - Piston for an internal combustion engine

Info

Publication number: WO1994007016A1
Application number: PCT/BR1993/000034
Authority: WO
Inventors: Alan Stanton Brown; José Manoel Martins LEITES; José do CARMO SOUZA RIBEIRO
Original assignee: Metal Leve S/A. Indústria E Comércio
Priority date: 1992-09-18
Filing date: 1993-09-17
Publication date: 1994-03-31
Also published as: BR9203717A

Abstract

Piston for an internal combustion engine, in which there is reduced the passage of combustion gases into the lower region of the engine, thereby presenting a reduction in the consumption of lubricating oil, by providing 'J' shaped circumferential recesses (13), inclined at the longitudinal face (10) of the piston (2), said recesses being located between the sealing rings (6 and 7), said recesses advantageously increasing the volume of the compartment (11) defined by said sealing rings (6 and 7) and allowing the balance between the pressures originated from the combustion and the pressures generated due to the dynamic of the gases, during the downward movement of the piston (2) towards the lower dead center of the engine (not shown).

Description

PISTON FOR AN INTERNAL COMBUSTION ENGINE

Technical Field

The present invention refers to an improvement for pistons of internal combustion engines. More specifically, the present invention refers to an improvement in the construction of a piston region, defined by the piston rings, also called sealing rings, in order to reduce the comsumption of lubricating oil by the engine. Background Art

The pistons for internal combustion engines are generally provided with at least two peripheral grooves, at the upper portion or head of the piston, each groove receiving a circumferential piston ring.

The piston rings disposed inside the grooves, located closer to the top or upper grooves, are called sealing rings, which have the main function of confining the region above the piston, where the combustion of the fuel takes place, so that all pressure generated from this combustion can be used to impel the piston. In order to execute this task, the so called sealing rings should be precisely adjusted between the sides of the grooves and the cylinder wall. As an additional function, the sealing rings further promote the scraping of the excess of lubricating oil from the cylinder wall, thus preventing the oil from passing into the fuel combustion region above the piston, thereby achieving the advantages mentioned above.

A third piston ring, which is optionally installed inside a groove immediately below the upper grooves, has the function of scraping the lubricating oil from the cylinder wall, so that the rings of the grooves disposed thereabove are not overloaded with oil.

In the four-stroke internal combustion engines, such as the Diesel engines, the combustion of the fuel generates a certain pressure above the piston that impels said piston downwardly, the pressure presenting its maximum value at the beginning of the combustion stroke, decreasing gradually as the piston moves downwardly towards the lower dead center, and reaching the room pressure at the end of the discharge stroke. Nevertheless, during the piston downward travel to the lower dead center, at an angle of the engine cycle between 360 and 540 degrees, as well as when reinitiating its upward travel, at an angle between 540 and 600 degrees, it has been observed that, at the compartment defined by the compression rings, the cylinder face and the piston longitudinal face located between said rings, there is formed a pressure field, due to the dynamic of the gases. Such pressure generates a force in an opposite direction, which in some points is higher than the remaining downward pressure originated from the fuel combustion. The difference of the higher pressure in said compartment over the remaining combustion pressure during the piston travel, causes the displacement of the upper ring towards the upper side of its groove, thereby practically seating the intermediate ring on the lower side of the intermediate groove.

During this axial movement of the sealing rings, particularly due to the upward movement of the upper ring, a clearance is created between the portion of the rings internal to the groove and the upper and lower sides of its groove, through which clearance the combustion gases pass towards the lower part of the engine, this phenomenum being known as "blow-by", which accelerates the thermochemical degradation of the lubricating oil, thereby highly increasing its consumption.

With the aim of guaranteeing the balance between the combustion pressure, which propagates forces in the downward direction, and that pressure which arises in the compartment between the sealing rings and whose force is ascending, in order to avoid the axial movement of the sealing rings during the engine cycles, it is common to attenuate the pressure inside said compartment between the sealing rings, by increasing the volume of said compartment through the provision of a "C" shaped peripheral concave recess at the piston longitudinal face located between the upper grooves.

Such a recess, although initially achieving the desired effect, presents a construction that allows the deposition and build up of solid particles originated from the degradation of the lubricating oil, thereby causing the quick reduction of its volume, being thus incapable of promoting the balance of the pressures. Another known solution also refers to the provision of a recess at the same region of the piston, but in the form of a peripheral step, whose larger side is positioned transversely to the piston longitudinal axis. This solution has the disadvantage of not giving a supporting face at the upper portion of the sealing ring, located at the intermediate groove, thereby reducing its capacity for sealing and scraping the oil in the cylinder.

Disclosure of the Invention

The object of the present invention is to provide a solution for equalizing said upward and downward pressures, which tend to axially move the sealing rings of said pistons, thereby overcoming the deficiencies presented by the solutions known heretofore. According to the invention, there is provided a construction for a peripheral recess, which presents from 1.5 to 2.5 times, preferably twice the volume of the compartment defined by the piston sealing rings, the wall portion of the cylinder and the piston longitudinal face located between the two sealing ring grooves, said peripheral recess being provided at the piston longitudinal face located between the sealing ring grooves, and presenting the shape of a "J" inclined at an angle of 60 to 80 degrees relative the longitudinal axis of said piston, in order to permit the exit of said solid particles from the inside of said peripheral recess, said recess further providing a support for the ring of the intermediate groove, thereby assuring its sealing and scraping capacities. Brief Description of the Drawings

The invention will be described now, with reference to the attached drawings, in which there are initially shown two graphics, one being relative to the behavior of the combustion pressure and the pressure inside the compartment between the rings, while the other is relative to the axial movement of the sealing rings due to said pressure difference. By way of example, the data shown in the graphics relate to a 41 / 4 cylinder Diesel engine.

There are further shown solutions which are already known from the prior art.

Two possible embodiments of the invention are presented in figures 5 and 6. In the drawings: Fig. 1 shows a Gas Pressure (MPa) X Angle of Engine Cyc1e (degrees) graphic;

Fig. 2 shows an Axial Displacement of the Sealing Rings (%) X Angle of Engine Cycle (degrees) graphic; Fig. 3 is a longitudinal partial section view of a cylinder, in whose inside there is shown the upper portion of a piston for internal combustion engines, said portion being provided with a "C" shaped peripheral concave recess at the piston longitudinal face located between the upper grooves of its sealing rings, according to a known technique;

Fig. 4 illustrates, in a similar view to that of fig. 3, a second piston presenting another known solution, but in the form of a peripheral step, whose larger side is oriented in a direction transversal to the longitudinal axis of the piston; Fig. 5 illustrates a first preferred embodiment of the invention, in the form of a "J" shaped peripheral recess, provided at the piston longitudinal face located between the upper grooves of said piston, according to the same longitudinal section view made to illustrate the solutions of figures 3 and 4; and

Fig. 6 illustrates a second possible way for executing the invention, which is also shown according to the same partial longitudinal section view. Best Mode of Carrying Out the Invention Referring to fig. 1, at the axis of the ordinates, there are illustrated the four strokes of said engine, namely admission, compression, combustion and discharge. It can be seen that the peak of the pressure originated during combustion (line 1) , takes place at the beginning of ^* the combustion stroke, and decreases till reaching the room pressure at the discharge stroke. Nevertheless, the ascending pressure (line 2) , which is originated at the region defined by the sealing rings 6 and 7 located at the upper grooves 3 and 4, the wall portion of cylinder 1 and the longitudinal piston face 10 (figs. 3-6), assumes greater values than those of the descending pressure originated from combustion (line 1) , at a rotational angle of the engine of about 360 to 600 degrees (not shown) , more specifically at the regions delimited by the circles A and B, resulting in the problems already mentioned above.

From figure 2, it can be seen that there is a substantial axial movement of the sealing ring 6 located at the groove 3 (line 1) , during the combustion stroke and beginning of the discharge stroke, corresponding to the regions A and B of fig. 1, and an imperceptible displacement of the sealing ring 7 in the groove 4.

In figures 3 and 4, there is shown a portion of a cylinder 1, in which inside is located a piston 2, provided with grooves 3 and 4 for sealing rings 6 and 7, and with a groove 5 for an oil scraping ring 8. Optionally, said piston 2 can present a notch 9, in order to improve the fuel combustion. At the region defined by the sealing rings 6 and 7, the wall portion of the cylinder 1 and the respective piston longitudinal face 10, there is formed a compartment 11. After combustion, a certain pressure is generated inside the notch 9 above the piston 2, thereby making the latter move downwardly. When the piston is at an angle of the engine cycle (not shown) between 360 and 600 degrees, another pressure field is created in the compartment 11, the forces of said pressure field acting in an opposite direction to that of the combustion pressure and with more intensity (A, B - fig. 1) at some points of the piston travel, thereby axially upwardly moving the sealing ring 6, towards the upper side 3S of the groove 3, and practically seating the sealing ring 7 on the lower side 4i of the groove 4. Upon moving upwardly, the sealing ring 6 leaves a clearance 12, through which the gases resulting from combustion flow towards the engine (not shown) . In order to overcome this problem, there are provided peripheral grooves 13, in the form of a concave "C" (fig. 3) , or presenting an inverted step (fig. 4) , in order to increase the volume inside the compartment 11 and, therefore reduce the value of the pressure existing therein. Nevertheless, this provision is not a satisfactory solution, as it permits the build up of solid particles (not shown) inside said recess, according to the construction of fig. 3, or fails to give an upper supporting surface for the sealing ring 7, by removing a portion of the upper side 4S from the groove 4, as shown in fig. 4. According to the invention, which is shown in the embodiments of figures 5 and 6, the pressure generated in the compartment 11 is equalized with the pressure generated in the combustion taking place in the notch 9 above the piston 2, by providing a "J" shaped cicumferential recess 13 at the piston longitudinal face 10. Since the recess 13 presents one of its sides 14 defined by an inclined straight portion relative the longitudinal axis E of the piston 2, and the remaining side being defined by an arc segment 14a, tangent to said straight portion 14 and matching therewith, it becomes possible the exit of undesirable particles upon the reciprocation of the piston 2. Moreover, there is further provided a supporting area 15 for the sealing ring 7, thereby guaranteeing its capacity for sealing and scraping the oil which eventually has not been collected by the oil ring 8.

The embodiments and examples presented herein are merely illustrative, thereby obviously allowing variations, provided that they are contained within the scope of the invention.

Claims

1. Piston for an internal combustion engine, provided with grooves (3 and 4) presenting sealing rings (6 and 7) , said piston being optionally provided with an upper notch (9) and a groove (5) with an oil ring (8) , said piston being characterized in that it presents, at the piston longitudinal face (10) , located between the sealing rings (6 and 7) , a "J" shaped circumferential recess (13) , with one side (14) thereof being defined by a straight line, inclined relative the longitudinal axis (E) of the piston (2) , and presenting a remaining portion (14a) in the form of a concave arc segment, tangent to said straight portion (14) and projected towards the inside of the piston (2) .

2. Piston, according to claim 1, characterized in that the positioning of the recess (13) , facing the sealing ring (7) is at a position closer to the upper groove (3) .

3. Piston, according to claim 1, characterized in that the positioning of the recess (13) facing the sealing ring (6) is at a position closer to the groove (4) .