RU2208692C2 - Piston - Google Patents

Abstract

FIELD: mechanical engineering; internal combustion engines. SUBSTANCE: invention relates to mean speed four stroke internal combustion engines. Piston is provided with trunk with bosses of piston pin, and ring groove for upper oil control ring with drain holes. Cross sections in loaded zones of trunk in cut along ring groove for upper oil control ring from side of inner space of piston are concave, with radius of concavity equal to 0.6 of radius of ring groove inner surface. EFFECT: increased service life of piston. 3 dwg

Description

 The invention relates to the field of engine building, in particular to medium-speed four-stroke internal combustion engines.

 A known construction of a cast aluminum piston for medium-speed engines, for example, diesel engines of the type D50 (6CHN 31.8 / 33) 1, 6CHN 21/21, etc., in which the piston head ([1], figure 1) is thick-walled with a smooth transition from the bottom 1 to the walls of the tronk 2. The piston tronk has two bosses 3, in which the floating pin 4 is placed. In the annular groove under the upper oil scraper ring 5 holes are drilled (6; Fig. 2, position 1 [1]) to drain the oil removed from mirrors of the cylinder sleeve into the internal cavity of the piston (drainage holes). Cross sections, in particular, in the section along the annular groove in the loaded areas of the throne (NRT) located above the bosses of the piston pin, which transmit force from the pressure of the gases on the piston crown to the connecting rod, have a convex shape from the side of the internal cavity of the piston ([1] and FIG. .2, a).

 This design of the piston is simple and reliable, because in comparison with a composite piston it does not require taking into account the force and elastic bonds of its individual parts when working under load, the time required for fine-tuning, etc.

 However, in the case of a non-optimal configuration of the sections in the NCT of solid cast pistons and the associated non-constructive design of drainage holes in the grooves of the upper oil scraper rings, these pistons may fail. Thus, in the operation of 6D50M marine diesels, solid pistons failed systematically due to the formation of fatigue cracks on the sharp edges of the drainage holes [2], which then led to the separation of the piston heads.

 The non-optimal configuration of the NRT sections of the existing solid cast piston designs is that the convex cross-sectional shape in the NRT from the side of the piston’s internal cavity along the chord length (l chorus, Fig. 3, a and b) equal to the internal diameter of the boss db) does not correspond the nature of the distribution along the length of this chord of axial reactive loads due to the action of the force on the outer surface of the piston pin from the gas pressure on the piston crown. At the same time, the convex shape of the NCT sections from the side of the piston’s internal cavity, in particular in the section along the annular groove under the upper oil scraper ring, which in addition to compression deformation undergo bending deformation due to the deflection of the piston pin between the bosses and the gas pressure in the center of the piston crown, leads to sharp edges of the drainage holes on one side ([1] and FIG. 2a, positions 3, 6, 10 and 13), which, as the results of static strain gauging proved, due to a sharp increase in stress concentration on them (FIG. .2, b) significantly reduce the resistance to fatigue fracture of the tronk.

 The design of the NRT of solid-cast pistons with a convex shape of their cross sections from the side of the internal cavity of the piston is based on the assumption accepted in existing works, such as, for example, in [3], that the load on the outer surface of the piston pin is distributed according to the law of the cosine wave.

However, the results of static strain gauging of the experimental piston of a D50 diesel engine without drainage holes when installing strain gauges with a base of 3 mm on the inner surface of the tron along the weakened circular groove of the convex section of the NCT (Fig. 3, a) showed (Fig. 3, b) that the total stress (Σσ ) compression and bending vary along the length of the aforementioned chord inversely proportional to its current height (S _φ , Fig. 3, a). This indicates that axial reactive loads are distributed over sections of the NCT with constant intensity.

 The reasons for this are the large horizontal ovalization of the piston pin and the deformation of the inner surface of the hole in the boss due to the large difference in the Young's modulus of elasticity of the materials of the finger and tronka arising from the action of the gas pressure force on the piston crown during engine operation. So, for example, on D50 diesel engines, the horizontal ovalization of the piston pin with the ratio of its inner diameter to the outer one equal to 0.72 is 0.1 mm in the boss with a radial clearance of (0.03-0.05) mm, and the elastic modulus Jung's steel piston pin exceeds 3 times its value for an aluminum tron. In this case, the levels of maximum contact pressures acting in the middle part of the sections decrease, and at their ends increase, i.e. the pressure intensity is equalized along the horizontal diameter in the boss.

 In this case, as can be seen from Fig. 3, b, the level of normal total compressive and bending stresses on the runaway sections of the NCT sections (Σσ = 33.4 MPa) is almost 2 times higher than the value of these stresses (Σσ = 18 MPa) in the middle of the sections in particular in a section weakened by an annular groove under the upper oil scraper ring, which significantly reduces the bearing capacity of the piston tronka. In this regard, when designing the NRT of the pistons in question, it is unlawful to take their sections convex from the side of the internal cavity of the piston.

 The optimal configuration of the sections of the NCT of seamless pistons are sections having a concave shape from the side of the internal cavity of the piston (Fig.3, c). Moreover, as shown by the results of strain gauging of the working piston of a 6D50M diesel engine, the total axial compressive and bending stresses have a uniform distribution along the chord of the NCT sections (Fig. 3, d), and their maximum level, compared with the convex section, decreases from 33.4 to 24.5 MPa.

 As for the magnitude of the total compressive and bending stresses at the edges of the drainage holes in the concave section of the NCT in the section along the annular groove under the upper oil scraper ring (Fig. 3, d), compared with the convex section, it decreased from 86.6 to 39 MPa (Fig. .2, b and Fig. 3, d). Moreover, the resistance to fatigue failure at the edges of the drainage holes, taking into account the decrease in the stress concentration coefficient from 2.6 to 1.59, increases from 20.6 to 44.3 MPa, and the fatigue safety factor in a weakened section (A-A ) NRT of the claimed piston, shown in figure 1, increases, compared with the existing one, from 1.06 to 2 [4].

 Thus, the essence of the invention is to change the shape of the cross sections in the loaded zones of the tronka of the solid piston (in particular, in the section along the annular groove under the upper oil scraper ring) from the side of its internal cavity from convex to concave, with a radius of concavity equal to 0.6 radius the inner surface of the annular groove with the location of its center on the axis of the piston. Due to this, a uniform distribution of reactive loads is achieved, and therefore, a decrease in the maximum level of total normal compressive and bending stresses in the NCT sections due to the force exerted on the outer surface of the piston pin by the gas pressure on the piston crown during operation of the engine three, as well as the elimination of sharp edges with one side of the drainage holes in the annular groove under the upper oil scraper ring, which significantly increases the resistance to fatigue destruction of the piston throne. At the same time, a sufficient endurance strength of the tronka of a cast aluminum piston and an increase in its service life before overhaul are ensured.

 The implementation of the invention, i.e., the execution of a concave cross-sectional shape in the loaded areas of the tronka of the claimed solid aluminum piston (Fig. 1), three are used using its serial billet.

USED LITERATURE
1. Diesel 2D50. Album of drawings. Central Bureau of Technical Information. Saratov, 1966. 160s

 2. Sidorin I.D. The study of the strength of solid pistons of internal combustion engines. Processes in heat engines. Collection of scientific papers. M .: Univer. Friendship of Parods them. P. Lumumba, 1983. 144p.

 3. Vansheydt V.A. Design and strength calculations of marine diesel engines. L: Shipbuilding, 1969.640s.

 4. Sidorin I. D. Bearing capacity of the tronka of solid and composite pistons of medium-speed four-stroke engines // Dvigatelestroyeniye. 2001. 1. P.5-7.

Claims (1)

 Solid aluminum piston for medium-speed four-stroke internal combustion engines having a tronk with piston pin bosses, an annular groove for the upper oil scraper ring, and the loaded zones of the tronk located above the piston pin bosses are designed to transmit force from gas pressure on the piston crown to the connecting rod, characterized in that the cross sections in the loaded zones of the tronka in the section along the annular groove under the upper oil scraper ring from the side of the internal piston cavity are concave with a radius of concavity equal to 0.6 of the radius of the inner surface of the annular groove.

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