KR100503818B1 - Piston for medium and heavy duty spark ignition lean burn engine - Google Patents

Abstract

The present invention relates to a piston for a medium to large ignition ignition lean combustion engine capable of rapid combustion in which combustion is completed in the shortest possible time.

A piston for a medium to large ignition ignition lean combustion engine according to the present invention includes: a piston head portion in which a bowl-shaped recess is formed to form a part of a combustion chamber at an upper end of the piston; A ring portion in which a plurality of ring grooves are formed at predetermined intervals along an outer circumferential surface of the upper end of the piston, and a compression ring or an oil ring is fitted into each of the ring grooves; And a skirt portion formed at a lower end of the piston to receive side pressure when the piston reciprocates up and down, wherein the side wall of the bowl-shaped recess formed in the piston head portion has a predetermined angle α with the upper surface of the piston head portion. A first inclined portion inclined downward inwardly downward, a vertical portion descending downwardly perpendicularly to an upper end surface of the piston head portion at a lower end of the first inclined portion, and a predetermined portion at the lower end of the vertical portion; It comprises a second inclined portion inclined downward inwardly while forming an angle β.

Description

Piston for medium and large ignition ignition lean burn engines {PISTON FOR MEDIUM AND HEAVY DUTY SPARK IGNITION LEAN BURN ENGINE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for a vehicle engine, and more particularly, to a piston for a medium to large ignition lean lean combustion engine capable of rapid combustion in which combustion is completed in the shortest possible time.

In general, in a vehicle engine, a piston reciprocates inside a cylinder and receives a gas pressure of high temperature and high pressure in a power stroke, which generates rotational force on the crankshaft through a connecting rod.

The gasoline engine supplies gasoline to the sucked air with a carburetor or a fuel injector to form a mixer having a combustible mixing ratio (13 to 18: 1), and then ignites it with an electric flame. The flame forms a flame surface and propagates at a rate of 10 to 10 m per second to complete combustion.

On the other hand, the diesel engine inhales and compresses only air and injects light oil into a cylinder at high temperature and high pressure to self-ignite. The injected fuel has a ignition delay period, and then one or several ignition nuclei are formed at a position where the mixing ratio is most suitable, and the combustion proceeds explosively.

As such, the gasoline engine and the diesel engine have different combustion methods, and thus the pistons that form part of the combustion chamber are also manufactured differently. That is, in the gasoline engine, since combustion starts by electric ignition, the shape of the piston is determined to maintain the compression ratio of about 9 to 10 and favor the combustion. However, the diesel engine has a high compression ratio of about 16 to 20 because combustion proceeds by self-ignition, and therefore, a piston of a diesel engine, which is commonly used, is manufactured to form a recess that is semicircularly concave in its head. Is common.

The pistons for medium and large ignition engines cannot use the pistons of ordinary small and medium-sized gasoline engines. The pistons of the existing large diesel engines are modified to reduce the compression ratio for ignition ignition. Accordingly, as shown in FIGS. 5 and 6, a semicircular concave recess 52 is formed in the piston head to form a part of the combustion chamber together with a cylinder (not shown).

Piston 50 modified in this way does not cause a problem during normal operation, but in the case of the lean burn applied in order to obtain the advantages such as reducing the heat load of the engine or increase the thermal efficiency, it does not achieve rapid combustion and operating performance is poor Rather, it falls greatly.

In other words, the lean combustion method has a relatively low pumping loss, an increase in specific heat ratio than normal combustion, and not only improves the engine thermal efficiency, but also reduces the nitrogen oxide (NOx) by lowering the maximum combustion temperature. However, there is a merit that the harmful emissions are reduced due to the decrease of) .However, the conventional pistons for medium and large engines do not achieve rapid combustion , and the combustion ratio becomes unstable as the air-fuel ratio becomes lean during lean combustion, resulting in torque fluctuations. Have.

The present invention has been made to solve the above problems, the object of which is to secure a strong turbulence strength and combustion by optimizing the shape of the head portion of the piston to increase the squish area and to ensure a sufficient flame area It is to provide a piston for a medium to large ignition ignition lean combustion engine that can achieve stability and optimize the ignition timing and extend the lean driving limit.

In order to achieve the above object, the present invention transmits the pressure received from the explosion stroke to the crankshaft through the connecting rod while reciprocating in the cylinder up and down to generate a rotational force and transfer power from the crankshaft in the suction, compression, exhaust An engine piston for receiving a function, comprising: a piston head portion formed with a concave bowl-shaped recess at an upper end of the piston to form part of a combustion chamber; A ring portion in which a plurality of ring grooves are formed at predetermined intervals along an outer circumferential surface of the upper end of the piston, and a compression ring or an oil ring is fitted into each of the ring grooves; And a skirt portion formed at a lower end of the piston to receive side pressure when the piston reciprocates up and down, wherein the side wall of the bowl-shaped recess formed in the piston head portion has a predetermined angle α with the upper surface of the piston head portion. A first inclined portion inclined downward inwardly downward, a vertical portion descending vertically downward from the lower end of the first inclined portion relative to an upper end surface of the piston head portion, and the vertical portion and the Provided is a piston for a medium to large ignition ignition lean burn engine including a second inclined portion inclined downward inwardly while forming a set angle β.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a perspective view showing a ignition ignition lean combustion engine piston according to the present invention, Figure 2 is a plan view of Figure 1, Figure 3 is a cross-sectional view seen from the A-A direction of FIG.

The piston 10 basically transfers the pressure received from the explosion stroke to the crankshaft (not shown) through the connecting rod (not shown) while reciprocating up and down the cylinder to generate rotational force, and the crankshaft in the suction, compression, and exhaust stroke. It acts by receiving power from the piston, and comprises a piston head portion 12, a ring portion 20 to which the compression ring or oil ring is fitted, and a skirt portion 23 at the bottom thereof.

The piston head 12 includes a recess 19 formed in a concave bowl shape on top of the piston 10, which recess 19 is part of the combustion chamber together with a cylinder (not shown). Will be configured.

The side wall of the recess 19 is divided into three parts according to the inclination angle, that is, the first inclination part 14, the vertical part 16, and the second inclination part.

Referring to FIG. 3, the first inclined portion 14 is inclined downward toward the inner side of the recess 19 while forming a predetermined angle α with the upper end surface of the piston head portion 12. At this time, it is preferable to manufacture so that the angle (alpha) which the surface of the 1st inclination part 14 and the upper end surface of the piston head part 12 make exists in the range of 130 degrees-140 degrees. If the angle is less than 130 °, there is a disadvantage in that the flame area is secured as the vertical portion 16 is reduced, and if the angle exceeds 140 °, the turbulence strength is difficult to secure as the area of the upper squish is reduced.

The vertical portion 16 descends downwardly perpendicular to the top surface of the piston head portion 12 at the lower end of the first inclined portion 14.

Thus, by providing the first inclined portion 14 and the vertical portion 16 on the side wall of the recessed portion 19, the contact area S with the flame while maintaining the entire volume V of the recessed portion 19 as in the prior art. You can widen it. Therefore, the volume ratio with respect to area can be made small compared with the past.

In the narrow space between the piston 10 and the cylinder head (not shown), the upward movement of the piston at the end of the compression stroke generates a flow of gas into the combustion chamber, which is called a squish flow. This squeegee flow creates a turbulent flow towards the center of the combustion chamber and serves to increase the flame propagation rate.

According to the piston head portion 12 of the present invention, by reducing the volume ratio with respect to the area of the recessed portion 19, the squishy flow can be more active, thereby resulting in advantageous stratification of fuel (lean fuel and air) To separate the fuel components around the igniter). In addition, if the area (squeegee area) where the squeegee flow can be increased, strong turbulence strength can be secured at the end of the compression during combustion, so it is possible to rapidly burn during ignition, which is very advantageous for the expansion of the lean driving limit.

The second inclined portion 18 is inclined downward from the lower end of the vertical portion 16 to form a predetermined angle β with the vertical portion 16 at the inner side of the recessed portion 19. At this time, the angle β formed between the surface of the second inclined portion 18 and the surface of the vertical portion 16 is set based on the surface of the vertical portion 16 and ranges from 130 ° to 140 °. It is preferable to manufacture so that it belongs to. If it exceeds 140 °, there is a disadvantage in securing the flame area as the vertical portion 16 is reduced, and if it is less than 130 °, the endurance stability of the piston is too close from the oil gallery 25 to be described below. There is a disadvantage.

An oil gallery 25 is provided between the upper recess 19 and the ring 20 of the piston 10. The oil gallery 25 is an essential element in order to maintain the durability of the piston, and is appropriate from the recess 19 of the piston head 12 exposed to strong impact by providing the second inclined portion 18. The distance can be kept to prevent breakage. For example, the distance between the second inclined portion 18 and the oil gallery 25 may be maintained at about 1.0 cm.

On the other hand, the piston head 12 according to the present invention is a percentage ratio (% ratio, P / of the depth P of the recessed portion 19 to the top surface diameter (D) while maintaining the combustion chamber bottom thickness at 1.0 cm D x 100) is preferably in the range of 17 to 21%. At this time, when the piston is less than 17%, the top land of the piston is lowered, and the thermal durability of the piston may be lowered. There is a problem that the suppression effect of the knocking phenomenon does not occur.

This range is a slightly cut top of the top land of the piston for a conventional medium / large ignition type engine which was manufactured by remodeling a diesel engine piston. . By doing so, it is possible to suppress the occurrence of knocking phenomenon due to excessive compression.

It is preferable that the convex portion formed by the first inclined portion 14 and the vertical portion 16 meet and the concave portion formed by the vertical portion 16 and the second inclined portion 18 meet as smoothly as possible.

The ring portion 20 has a plurality of ring grooves 21 formed at predetermined intervals along the outer circumferential surface of the upper end of the piston 10, and each ring groove 21 is fitted with a compression ring or an oil ring. The ring groove 21 may be formed about three to four as needed, the piston ring fitted into the ring groove 21 serves to maintain the airtight and to prevent oil from entering the combustion chamber.

The skirt 23 is formed at the lower end of the piston 10 and is a portion that receives side pressure when the piston 10 reciprocates up and down.

Hereinafter, specific embodiments will be described in detail.

Example

In accordance with the prior art and the present invention, the pistons used in the 11L engine were manufactured, and the flame contact area (squish area) and the top land height of the main portion of each piston head were measured. That is, the squish area of the medium-large ignition engine piston according to the prior art (hereinafter 'Comparative Example') is 2782 mm 2 and the top land height is 15.68 mm, the piston for medium-large ignition engine according to the present invention (hereinafter 'Example) The squishy area of ') is 3590 mm 2 and the top land height is 14.00 mm.

As shown in FIG. 4, a performance stabilization curve of a large LPG engine when each piston is manufactured as described above is derived. The engine test was conducted by applying the optimum ignition timing under the same conditions of compression ratio 9.3, 1200rpm, and full load conditions, respectively. Here, the optimum ignition timing is to measure the combustion pressure of the engine by changing the ignition timing in the engine test and calculate the output (imep or bmep) and stability (COV) of the ignition timing from the values. Among them, the ignition timing that shows the best output and stability is usually called MBT ignition timing and this is called optimized ignition timing.

In the graph shown in FIG. 4, the vertical axis represents the stability performance of combustion (COV-imep, Coefficient of imep Variation), and the region where the output cycle variation does not exceed 5% is a region in which stable operation is possible, that is, a lean operation limit. The horizontal axis represents the excess air ratio (λ), which means the ratio between fuel and air, and the higher the value, the less fuel is included.

As shown in FIG. 4, in the case of the comparative example, the lean driving limit is up to about 1.5 excess air ratio (λ), but in the case of the example, the lean driving limit is up to about 1.6 excess air ratio (λ). In other words, the lean driving limit is extended in the case of the example compared with the comparative example.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

As described above, according to the piston for the medium to large ignition ignition lean combustion engine according to the present invention, by optimizing the shape of the head portion of the piston to increase the squish area and secure a sufficient flame area, to secure a strong turbulence strength and combustion Stability can be achieved and optimizing the ignition timing and extending the lean driving limit can be achieved.

In addition, by cutting the top surface further by reducing the height of the top land than the piston remodeling the existing piston for the diesel engine can suppress the occurrence of knocking phenomenon due to excessive compression, and also ensure the durability and mass production.

1 is a perspective view showing a ignition ignition lean combustion piston according to the present invention.

2 is a plan view showing a ignition ignition lean combustion engine piston according to the present invention.

3 is a cross-sectional view seen from the direction A-A of FIG. 1.

4 is a graph comparing combustion stability of an engine according to a piston shape.

Fig. 5 is a plan view showing a conventional ignition ignition lean combustion piston.

FIG. 6 is a cross-sectional view seen from the direction B-B of FIG. 5.

* Description of the symbols for the main parts of the drawings *

10: piston 12: piston head portion

14: first inclined portion 16: vertical portion

18: second inclined portion 19: main portion

20: ring 21: ring groove

23: Skirt 25: Oil Gallery

Claims (4)

In the piston for the engine that acts by receiving power from the crankshaft in the intake, compression, and exhaust strokes by transmitting the pressure received from the explosion stroke to the crankshaft through the connecting rod while reciprocating in the cylinder. A piston head portion in which a bowl-shaped recess is formed to form a part of a combustion chamber at an upper end of the piston; A ring portion in which a plurality of ring grooves are formed at predetermined intervals along an outer circumferential surface of the upper end of the piston, and a compression ring or an oil ring is fitted into each of the ring grooves; And It is formed on the lower end of the piston includes a skirt that receives the side pressure when the piston reciprocates up and down, The side wall of the bowl-shaped recess formed in the piston head portion has a first inclined portion which is inclined downward inwardly while forming a predetermined angle α with the upper surface of the piston head portion, and the piston at a lower end of the first inclined portion. A medium-sized part including a vertical part which descends downwardly perpendicularly to an upper end surface of the head part, and a second inclined part which tilts downward inwardly at a lower end of the vertical part at a predetermined angle β with the vertical part; Pistons for ignition lean burn engines. The method of claim 1, Medium and large ignition ignition lean burn, characterized in that the predetermined angle (α) formed by the upper surface of the piston head portion and the first inclined portion meets the range of 130 ° to 140 ° with respect to the fixed center of the first inclined portion Pistons for the engine. The method of claim 1, Piston for medium and large ignition ignition lean combustion engine, characterized in that the predetermined angle (β) formed by the meeting the vertical portion and the second inclined portion is in the range of 130 ° to 140 ° with respect to the fixed center of the second inclined portion . The method of claim 1, The piston head portion is characterized in that the percent ratio (% ratio) of the bowl-shaped recess depth (P) to the top surface diameter (D) in the range of 17 to 21% while maintaining the bottom thickness of the combustion chamber 1.0 cm Pistons for medium and large ignition lean combustion engines.