WO1994020744A1

WO1994020744A1 - Piston for an internal combustion engine

Info

Publication number: WO1994020744A1
Application number: PCT/BR1994/000005
Authority: WO
Inventors: Miguel Norberto Dalcomo Azevedo; Waldir Oliveira JORDÃO; Sylvio Chiquito Filho
Original assignee: Metal Leve S/A. Indústria E Comércio
Priority date: 1993-03-01
Filing date: 1994-02-28
Publication date: 1994-09-15
Also published as: BR9300444A

Abstract

Piston for an internal combustion engine, comprising a top upper portion (10), provided with a piston ring region (11) and a skirt lower portion (20), provided with a pair of hubs (21) for the articulating pin of the connecting rod. The piston ring region (11) disposed above the hubs (21) is provided with at least one peripheral groove (12) for a compression ring (32) and at least one peripheral groove (14) for an oil ring (34), located below the hubs (21), the relation between the compression height (HC) of the piston (P) and the diameter (D) of the cylinder (C) being inferior to 1:3.

Description

PISTON FOR AN INTERNAL COMBUSTION ENGINE

Field of the Invention

The present invention refers to mechanical engineering and, particularly, to internal combustion engines.

More specifically, it refers to Otto cycle pistons for internal combustion engines.

Background of the Invention

One of the most difficult tasks for the piston manufacturers has been the need to design components which can impart to the engines high power with a high degree of compactness.

The solutions for these objectives presented up to now have not, in most of the cases, complied with the specifications of the design, mainly because they proved to be economically infeasible.

It is known that in an internal combustion engine, between the generation of thermal power (explosion) and its conversion to mechanical power, there is a considerable loss due to the weight of the reciprocating masses, such as the connecting rods and pistons, said weight being still very high in the construction of more compact engines.

Specifically with the aim to reduce the weight of the pistons, new alloys, which are lighter and more resistant, have been developed. Nevertheless, though the technical result of this solution has been most of the time acceptable, the above mentioned economical aspect still makes these constructions impractible. Examples of new alloys are described in some Patent documents, such as JP-60166158, in the name of Susumi

Yoshihiro.

Another solution, which also aims to reduce the piston weight and which is usually carried out, is the development of new geometric forms for the piston profile. As opposed to the first solution, this solution offers more economical designs, presenting an acceptable technical performance. A change in the piston geometry that results in a weight reduction is achieved by reducing the compression height, i.e., the axial dimension comprised between the longitudinal axis of the piston pin and its top face. Such reduction is required so that the compression height reaches such a degree that the relation between the piston and the diameter of the cylinder in which it is located is considered optimum.

Such dimensional relation between the piston compression height and the diameter of the respective cylinder (HC/D) usually varies from 0.34 to 0.63, in the cases in which a favorable reduction of the piston height has been achieved. The smaller the HC/D value, the more favorable it will be, because it allows to obtain the desired reduction of the piston weight, as well as of the height of the engine block, thereby permitting the construction of vehicles having more aerodynamic profiles. Another advantage that has also been obtained with reduced values of the HC/D relation is the possibility to increase the length of the connecting rod, thus reducing the lateral efforts applied to the piston and consequently the noise of the engine operation caused by these efforts (piston slap) . For this purpose, it is necessary to reduce the axial dimension of the piston ring region, since the minimum dimension for installing the larger eye of the connecting rod is already being practiced. The conventional pistons are provided with three or more piston rings. There are usually two upper rings for sealing or compression purposes and an oil ring at the lowermost position. The uppermost rings, i.e., the compression rings, have the purpose of confining the combustion gases, in order to prevent them from escaping to the engine crankcase (blowby phenomenon) , while the oil ring is designed to remove the excess of oil from the cylinder, thus preventing said oil from going up to the upper combustion compartment (which increases the oil consumption) , and making the oil return to the engine crankcase through orifices provided on its respective groove.

A solution that aims to reduce the compression height of the piston is described in the Brazilian Patent Application PI 8600530, by Brian Leonard Ruddy and Jeremy W. Halt.

According to this application, it is possible to substitute two conventional rings for only one ring, by providing a recess in the form of a groove at the internal face of the compression ring, where an auxiliary sealing ring is installed, in contact with the bottom of the groove. Though at first it seems to be advantageous, this solution involves the obligation to use rings that do not belong to the specifications of the market, thus increasing the cost of the product. Another document that shows the reduction of the number of piston rings is the US 4,672,921, in the name of Angel . Quaglino Jr. In this case, the provision of only two piston rings, each located close to one of the upper and lower ends of the piston, forms a recess on the central wall of the skirt thereof. The function of said recess is to accumulate lubricant oil, thus improving the piston motion inside the cylinder. Nevertheless, even using two rings, the height of the piston has not been reduced, besides the fact that it is possible to foresee an undesirable "polymerization" of the lubricant oil that may be confined in the recess, producing acids that will deteriorate the inside of the engine. Other attempts have been made to reduce the height of the ring region. Nevertheless, there always occur problems relating to dimensional instability or loss of the sealing and scraping capacities of the rings, since both the walls between the grooves and the rings themselves present very thin dimensions. Disclosure of the Invention The main object of the present invention is to propose a new piston design, which improves the solutions known up to now, mainly relating to the reduction of the piston weight and to the better condition of the piston to move inside the cylinder, and which allows to obtain such a reduced compression height that an optimum compression height/cylinder diameter relation is obtained.

This objective is attained through the provision of an oil ring groove below the pin hubs, which permits to reduce the HC height, as described in claim 1 of the present specification. Brief Description of the Drawings

For illustrative purposes, some examples for carrying out the invention will be presented, by way of the attached drawings, in which:

Fig. 1 illustrates schematically the right section in axial elevation of an embodiment of the piston according to the present invention,- and Fig. 2 illustrates, also schematically, the right section in axial elevation of the preferred embodiment of the piston according to the present invention. Best Way of Carrying Out the Invention

According to figure 1, the piston P is installed within a cylinder C of diameter D and is formed by a top upper portion 10 and a skirt lower portion 20.

The top upper portion 10 presents a ring region 11, provided with two peripheral grooves 12, in order to lodge respective compression rings 32, which are thus located at the region of the piston P that defines the compression height HC thereof.

In the constructive form of figure 1, the peripheral groove 12 located closer to the skirt lower portion 20 may be provided with a plurality of radial orifices 13, that allow the oil return to the engine crankcase. The skirt lower portion 20 incorporates a pair of hubs 21, which are provided with a respective orifice 22, in order to mount a pin (not shown) for the articulation of the larger eye of the connecting rod (not shown) . In the particular illustrated embodiment, the skirt lower portion 20 is further provided with recessed areas 23. Still according to figure 1, the skirt lower portion 20 is provided, below the hubs 21, i.e., below the piston region that defines the compression height HC, with a peripheral groove 14, to lodge a respective oil ring 34. Though figure 1 illustrates a piston P with only one groove 14 for an oil ring, it should be understood that multiple peripheral grooves 14 for an oil ring can be provided, positioned below the hubs 21 of the skirt lower portion 20. The groove 14 for the oil ring in figure 1 is provided with a plurality of radial orifices 15 for the oil return to the engine crankcase. In the alternative embodiment of figure 2, there is provided only one peripheral groove 12 for the compression ring 32, at the ring region 11 located above the hubs 21, thus permitting to reduce even more the compression height HC of the piston P and consequently the relation between said compression height HC and the diameter D of the cylinder C of the engine. Besides reducing the relation between the compression height HC of the piston P and the diameter D of the cylinder C for values inferior to 1:3, the solution proposed by the present invention allows to achieve a favorable performance, because the excess of oil from the wall of the cylinder C can return to the engine crankcase, after said oil has been scraped by the oil ring 34.

Claims

1. Piston for an internal combustion engine, comprising a top upper portion (10) , provided with a piston ring region (11) and a skirt lower portion (20) , provided with a pair of hubs (21) for the articulating pin of the connecting rod, characterized in that it presents at least one peripheral groove (12) for a compression ring (32) at the piston ring region (11) disposed above the hubs (21) and at least one peripheral groove (14) for an oil ring (34) located below the hubs (21) , the relation between the compression height (HC) of the piston (P) and the diameter (D) of the engine cylinder

(C) in which the piston will be applied being inferior to 1:3.

2. Piston, according to claim 1, characterized in that the piston ring region (11) , which is disposed above the hubs (21) , is provided with only one peripheral groove (12) for the compression ring (32) .

3. Piston, according to claim 1, characterized in that the piston ring region (11) , which is disposed above the hubs (21) , is provided with two peripheral grooves (12) for the compression ring (32) .

4. Piston, according to claim 3, characterized in that the peripheral groove (12) for the compression ring

(32) located closer to the hubs (21) is provided with at least one radial orifice (13) for the oil return to the engine crankcase.

5. Piston, according to claim 1, characterized in that the peripheral groove (14) for the oil ring (34) is provided at least with a radial orifice (15) for the oil return to the engine crankcase.