JP2013068144A - Piston of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston of an internal combustion engine which can achieve the robust mixing, eventually, the combustion of fuel and air though a configuration is simple and low in cost, is excellent in reliability, can reduce the exhaust amount of soot by increasing an air use factor in a combustion chamber over a wide operating range to promote the improvement of combustion, and can improve thermal efficiency by reducing a heat loss from a wall surface demarcating the combustion chamber.SOLUTION: In this piston 100 of an internal combustion engine which includes a piston combustion chamber 110 constituting a part of the combustion chamber of the internal combustion engine, the piston combustion chamber 110 is recessed semi-spherically in the upper surface of the piston, and includes a ring-shaped projection 120 which projects from a bottom 130 and is disposed around the center axis of the piston combustion chamber 110. A fuel spray is made to collide with the ring-shaped projection 120, and a part of the fuel spray advances inward of the ring-shaped projection 120 and the remaining part is dispersed outward of the ring-shaped projection 120.

Description

  The present invention relates to a technology for a piston of an internal combustion engine.

  Purifying the exhaust from the internal combustion engine to suppress the expansion of air pollution is an important issue, but as one of the systems (apparatus) for this purpose, a part of the exhaust from the internal combustion engine is returned to the combustion chamber. A so-called EGR (Exhaust Gas Recirculation) system is known for reducing the concentration (exhaust amount) of nitrogen oxides (hereinafter referred to as NOx) in exhaust gas by reducing the combustion temperature by recombusting the exhaust gas. ing.

  In order to further reduce the NOx emission amount from the internal combustion engine, it is effective to increase the EGR rate (= EGR gas amount / (new air amount + EGR gas amount) × 100 (%)). On the other hand, the oxygen that can be used for combustion in the combustion chamber of the internal combustion engine decreases, and the amount of black smoke (soot) emission increases.

  For this reason, while improving the utilization rate (air utilization rate) of air (oxygen) in the combustion chamber and promoting combustion improvement, the emission of black smoke (soot) is reduced and the wall surface defining the combustion chamber It is desired to improve the thermal efficiency by reducing the heat loss.

  Here, conventionally, in an internal combustion engine, in particular, in a diesel combustion engine, the specifications of the injection holes of the fuel injection nozzle that injects and supplies the fuel (injection hole diameter, number of injection holes, cone angle, etc.) and intake air flow such as intake swirl In order to improve the air utilization rate, the optimization is implemented.

  However, the fuel spray injected from the fuel injection nozzle (fuel spray) is a combustion chamber recessed in the top surface of the piston (the combustion chamber is a combustion chamber of an internal combustion engine formed with a cylinder head and a cylinder wall). It is collided with the inner wall of the gas (in part), and mixing with the air is promoted in combination with the air flow, but depending on the operating conditions such as the rotation speed and load of the internal combustion engine, the collision of the fuel spray In addition to the change in the piston side position, the influence of the airflow also changes, so there is a situation that it is difficult to always create the targeted diffusion mixing state in all operating states.

  Even in mass production, in order to maintain output performance, exhaust performance, fuel efficiency performance, etc. at specified levels, it is necessary to strictly control the variation in the fuel spray collision position, and it is more robust (less susceptible to disturbances). It is desirable to achieve combustion by mixing fuel and air.

JP 07-42558 A

  Here, for example, in Patent Document 1, as shown in FIG. 10, a combustion including a bottomed cylindrical protrusion 16 that protrudes from the bottom of a piston combustion chamber 14 that is recessed in the top surface of the piston 10. The room is listed.

  In the low load operation, the fuel spray injected from the fuel injection valve 15 collides with the upper inner wall 16b of the protrusion 16 and is burned mainly inside the protrusion 16 (inner chamber 14a). To suppress NOx generation by preventing the combustion temperature from becoming too high, and at the same time unburned due to excessive mixing. Suppresses the production of hydrocarbons.

  Further, during the high load operation, the fuel injection amount increases and the injection period becomes longer. Therefore, if the injection start timing is the same, the injection end timing is delayed from that during the low load operation. Therefore, during the predetermined period from the start of injection, combustion is performed inside the protrusion 16 (inner chamber 14a) in the vicinity of the top dead center of the piston to suppress the generation of NOx and the generation of unburned hydrocarbons. In the latter half, the piston 10 descends from the vicinity of the top dead center, so that the fuel spray passes over the upper end 16b of the protrusion 16 and is supplied to the outside of the protrusion 16 (outer chamber 14b). As a result, the mixing ratio in the inner chamber 14a and the outer chamber 14b becomes uniform, and the black smoke and the fuel consumption are prevented from deteriorating.

  As described above, according to the combustion chamber described in Patent Document 1, comparison is made so that combustion suitable for low load operation can be performed during low load operation and combustion suitable for high load operation can be performed during high load operation. It is configured to perform good combustion in a wide operating range.

  However, even in the combustion chamber described in Patent Document 1, whether or not the fuel spray stays in the inner chamber 14a or diffuses to the outer chamber 14b without exceeding the protrusion 16 depends on the amount of protrusion of the lower surface of the cylinder head of the fuel injection valve. It is difficult to achieve the target combustion state over a wide operating range because it is subject to variations, piston processing accuracy variations, and airflow effects such as squish and swirl (affected by the manufacturing accuracy of intake ports). There is the actual situation.

  Further, since the protrusion 16 in the combustion chamber described in Patent Document 1 has a shape that rises suddenly from the bottom of the piston combustion chamber 14, stress concentration occurs due to thermal stress or the like, and damage such as cracks is likely to occur. There is also the risk of worry.

  The present invention has been made in view of the above circumstances, and realizes a more robust mixing of the fuel and air and combustion in a relatively simple and low-cost configuration while being more robust (not easily affected by disturbance). In addition to being able to achieve high reliability, the exhaust rate of black smoke is reduced by improving the air utilization rate in the combustion chamber and promoting combustion improvement over a wide operating range. An object of the present invention is to provide a piston for an internal combustion engine having a piston combustion chamber capable of improving thermal efficiency by reducing heat loss from a wall surface defining the combustion chamber.

For this reason, the piston of the internal combustion engine according to the present invention is
A piston of an internal combustion engine having a piston combustion chamber that constitutes a part of the combustion chamber of the internal combustion engine,
The piston combustion chamber is configured to have a hemispherical recess on the upper surface of the piston, and an annular protrusion that protrudes from the bottom of the piston combustion chamber and is disposed around the central axis of the piston combustion chamber.
The fuel spray injected from the fuel injection valve collides with the annular protrusion, a part of the fuel spray advances to the inside of the annular protrusion, and the remaining part diffuses to the outside of the annular protrusion. It is characterized by.

  In the present invention, the outer edge of the fuel spray injected from the fuel injection valve is located slightly inward from the top of the annular projection within a range of about 10 ° before and after the top dead center of the compression stroke at the crankshaft rotation angle. It can be characterized by being set as follows.

  In the present invention, a concave portion is formed in the vicinity of the collision position of the fuel spray on the annular projection.

  In the present invention, the angle between the fuel spray central axes when viewed from the direction orthogonal to the reciprocating direction of the piston is set to about 110 ° to about 120 °.

  According to the present invention, although it is a relatively simple and low-cost configuration, more robust (hard to be affected by disturbance) fuel and air can be realized and combustion can be realized. On the other hand, by improving the air utilization rate in the combustion chamber and promoting combustion improvement over a wide operating range, it is possible to reduce the emission of black smoke (soot) and to define the combustion chamber. It is possible to provide a piston of an internal combustion engine having a piston combustion chamber capable of improving thermal efficiency by reducing heat loss from the wall surface formed.

It is sectional drawing (sectional drawing cut | disconnected along the piston reciprocation direction) which showed schematically the piston combustion chamber of Example 1 which concerns on embodiment of this invention. It is the top view which looked at the piston combustion chamber of FIG. 1 from the piston reciprocating motion upper direction. It is an example of the combustion simulation result (oxygen concentration, combustion temperature) which showed the piston combustion chamber of an Example same as the above, and the conventional toroidal type combustion chamber. It is an example (a soot amount (soot generation | occurrence | production / reoxidation history) in a combustion chamber) of the combustion simulation result shown by comparing the piston combustion chamber of an Example same as the above, and the conventional toroidal type combustion chamber. It is sectional drawing (sectional drawing cut | disconnected along the piston reciprocation direction) which showed schematically the piston combustion chamber of Example 2 of this invention. It is sectional drawing (sectional drawing cut | disconnected along the piston reciprocation direction) which showed schematically the piston combustion chamber of Example 3 of this invention. It is an example of the combustion simulation result (oxygen concentration) which compared and showed the piston combustion chamber of Example 3 same as the above, and the piston combustion chamber of Example 1 same as the above. It is a top view which shows an example at the time of providing a notch in a part of circumferential direction of the annular projection part of the piston combustion chamber of Example 1. FIG. It is sectional drawing which shows an example of the toroidal type combustion chamber recessedly provided in the piston top surface of the normal internal combustion engine. It is sectional drawing which shows the piston combustion chamber shape recessedly provided in the piston top surface of the internal combustion engine of patent document 1. FIG.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. The present invention is not limited to the embodiments described below.

  The piston combustion chamber 110 formed in a concave shape on the upper surface of the piston 100 used in the internal combustion engine according to Example 1 of the present embodiment is formed in a concave shape on the upper surface of a normal piston 500 (see FIG. 9). In place of the conical protrusion 520 provided at the center of the toroidal piston combustion chamber 510 so as to protrude from the bottom surface, the center of the protrusion 520 is shaved, as shown in FIGS. And an annular projection 120 having a shape like an egg stand.

  Further, the bottom portion 130 of the piston combustion chamber 110 is formed to be substantially flat except for the base of the annular projection 120.

  Further, the corner portion 140 can be formed so as to be smoothly connected with a certain amount of R, but in the drawing, a part of R is omitted.

  In the internal combustion engine according to the first embodiment, the intake port (not shown) has an intake swirl so that the swirl ratio is about 0 to 0.5, which is much lower than the conventional 1.5 to 2.0. Is formed. The swirl is the circumferential swirl flow of air in the combustion chamber (cylinder), and the swirl ratio is the ratio of the flow rate of the swirl flow in the circumferential direction to the flow rate in the axial direction (piston reciprocating motion direction). .

  Here, with respect to fuel spray (fuel spray) injected from a fuel injection valve (not shown), the conventional fuel spray angle (a sandwich angle between fuel sprays: cone angle) is about 145 to 155 °. In this embodiment, the angle is set to a narrow angle of about 110 to 120 °, and the fuel spray is set to collide with the bottom 130 of the piston combustion chamber 110 during the fuel injection period.

  The number of injection holes of the fuel injection valve (the number of holes through which fuel is injected) can be 6 to 9 injection holes, but is not limited to this.

  In the recess 150 at the center of the piston combustion chamber 110, the outer edge of the fuel spray injected from the fuel injection valve in the range of about 10 ° (degree) before and after the compression stroke top dead center at the crankshaft rotation angle is the annular protrusion 120. It arrange | positions so that it may become a position slightly inside from the vertex (corner part 140) of (refer FIG. 3 (A)).

  As a result, the tip of the fuel spray injected near the top dead center of the compression stroke collides with the annular protrusion 120 arranged in an annular shape, and a part of the fuel spray diffuses inside the annular protrusion 120. However, in other parts, the spray volume is enlarged due to the impact. Then, after the fuel spray that has traveled along the fuel spray center axis also collides with the bottom portion 130, it proceeds (develops) in the radial direction of the piston combustion chamber 110 along the flat bottom shape (FIG. 3A). )reference).

  Further, when the injection period is long (for example, when the fuel injection amount is large and the load is high), the fuel spray injected beyond about 10 ° after the top dead center of the compression stroke rises from the bottom 130 of the piston combustion chamber 110. It does not interfere with the annular protrusion 120 and proceeds (develops) toward the bottom 130 as it is, and is guided from the side wall 170 to the outside (squish area) 160 of the piston combustion chamber 110 in an unburned state.

  For this reason, the equivalence ratio at the center of the piston combustion chamber 110 does not increase regardless of the total amount of fuel injection (the change in equivalence ratio is small), and soot is generated at the center of the piston combustion chamber 110 due to insufficient oxygen. Combustion can be performed at a good air-fuel ratio without incurring such problems. Moreover, since local temperature becomes the maximum in the position away from the bottom part 130, since the heat loss to a wall surface (wall surface heat loss) can be reduced, the improvement of thermal efficiency can also be expected.

  In the piston combustion chamber 110 according to the first embodiment, the soot generation / reoxidation history obtained by performing the combustion simulation under the optimized condition of the spray angle of the fuel spray as a narrow angle is shown in FIG. Shown in comparison with the combustion chamber.

  From FIG. 4, it can be confirmed that the amount of generated soot can be reduced when the piston combustion chamber 110 according to the first embodiment is used as compared with the case of a normal toroidal combustion chamber.

  As described above, according to the first embodiment, unlike the conventional spray characteristics or the combustion characteristics, the spray angle of the fuel spray injected from the fuel injection valve is set to a narrow angle (narrow angle), and the fuel is pistoned. While spraying toward the bottom 130 of the combustion chamber 110, a part of the fuel spray is caused to collide with the annular protrusion 120 protruding from the bottom 130 of the piston combustion chamber 110 to promote spray diffusion. As a result, the air utilization rate is improved, soot generation can be effectively suppressed, air flow such as swirl is reduced, and the portion where the combustion temperature becomes high is separated from the wall surface of the piston combustion chamber 110 so that the wall surface heat is reduced. Since loss can be reduced, thermal efficiency can be improved and fuel consumption can be improved.

  In particular, in a region where the rotational speed of the internal combustion engine is low or a region where the load is small, while improving the air utilization rate inside the annular projection 120 and performing good combustion, the region where the rotational speed of the internal combustion engine is high In a region where the load is large, the fuel spray and thus the combustion is expanded to the outside of the annular projection 120, so that the air outside the annular projection 120 is effectively used and the combustion gas becomes a high temperature portion. By separating from the wall surface of the piston combustion chamber 110, it is possible to reduce the wall surface heat loss and improve the thermal efficiency and to perform good combustion.

  In the first embodiment, the swirl is less affected by the manufacturing variation of the intake port and the like, and the dependency on the promotion of mixing of the fuel and the air by the intake swirl is reduced, and the annular protrusion 120 is relatively gentle from the bottom 130. The piston combustion chamber structure is used, and the direction of the collision with the fuel spray is less affected by variations in the spray angle of the fuel spray. In addition to being able to be realized, it is possible to realize a piston combustion chamber having a small thermal load and excellent reliability.

  Further, by flattening the bottom portion 130 of the annular projection 120, the spread of the fuel spray in the radial direction can be made smooth and with little variation, and this also makes it possible to mix the fuel and air in a robust manner. Therefore, combustion can be realized.

  That is, according to the present invention, in addition to a relatively simple and low-cost configuration, more robust (not easily affected by disturbance) fuel and air can be mixed and combustion can be realized. While improving reliability, it is possible to reduce the amount of black soot emission by improving the air utilization rate in the combustion chamber and promoting combustion improvement over a wide operating range, It is possible to provide a piston for an internal combustion engine having a piston combustion chamber that can improve thermal efficiency by reducing heat loss from the wall surface that defines the above.

  The injection direction of the fuel spray applied to the piston combustion chamber 210 of the piston 200 according to the second embodiment of the present embodiment is the same as the first embodiment shown in FIG. 1, the fuel spray angle (the sandwich angle between the fuel sprays). Is set to about 110 to 120 °. As a result, as shown in FIG. 5, the fuel spray can reach slightly outside the annular projection 220 provided so as to protrude from the bottom 230 of the piston combustion chamber 210.

  The fuel spray that has collided with the annular projection 220 is dispersed outside and inside the annular projection 220, and the fuel spray is generated by the vertical vortex generated as an airflow accompanying the fuel spray (fuel spray accompanying airflow). Spreading is promoted.

  In FIG. 5, compared with the annular protrusion 120 of the first embodiment, the collision surface of the annular protrusion 220 with the fuel spray is widened, and the robustness is improved against variations in the fuel injection direction.

  Specifically, as shown in FIG. 5, the spreading direction of the fuel spray is made wider by widening the width of the convex portion of the annular protrusion 220.

  Further, the tumble airflow (vortex formed around the fuel spray) accompanying the fuel spray can be strengthened by reducing the curvature of the convex portion of the annular projection 220.

  Furthermore, since the volume at the center of the piston combustion chamber 210 (the inner volume of the annular protrusion 220) is smaller than the volume on the outer peripheral side of the annular protrusion 220, a desired volume can be obtained by increasing the depth direction. Can do. That is, the depth of the central portion of the piston combustion chamber 210 (inside the annular protrusion 220) and the depth of the outer peripheral portion of the annular protrusion 220 can be made different.

  In the third embodiment, as shown in FIG. 6, with respect to the annular protrusions 120 and 220 that are convex toward the fuel spray, such as the piston combustion chambers 110 and 210 of the first and second embodiments described above, This is an example in the case where the concave portion 321 is formed at a position where the annular protrusion 320 collides with the fuel spray.

  Thus, by providing the recess 321 at the fuel spray collision position of the annular protrusion 320, the diffusion of the initial fuel spray can be promoted by the collision of the fuel spray to the recess 321. The utilization rate of the unused air in the upper part can be improved.

FIG. 7 shows the result of the combustion simulation.
From FIG. 7, the oxygen concentration when the piston combustion chamber 310 of Example 3 was employed and burned at 40 ° (crank angle) after piston compression top dead center was the piston combustion chamber 110 of Example 1. Compared with the oxygen concentration in the case, it is confirmed that the unused air in the upper part of the piston combustion chamber is reduced.

  Thus, also in the second and third embodiments, as in the first embodiment, the spray angle of the fuel spray injected from the fuel injection valve is narrow (narrow) unlike the conventional spray characteristics or the combustion characteristics. ), And the fuel is injected toward the bottom portions 230 and 330 of the piston combustion chambers 210 and 310, and a part of the fuel spray is projected from the bottom portion 230 of the piston combustion chamber 210 so as to protrude. Since the spray diffusion is promoted by colliding with 220, 320, the air utilization rate can be improved and soot generation can be effectively suppressed, the air flow of swirl and the like is reduced, and the combustion temperature is high. Since the wall surface heat loss can be reduced by separating the portion to be separated from the wall surfaces of the piston combustion chambers 210 and 310, the thermal efficiency can be improved and the fuel consumption can be improved.

  In particular, in a region where the rotational speed of the internal combustion engine is low or a region where the load is small, the air utilization rate is improved inside the annular projections 220 and 320 to achieve good combustion, while the rotational speed of the internal combustion engine is high. In the region and the region where the load is large, the fuel spray and the combustion are expanded to the outside of the annular projections 220 and 320, so that the air outside and outside the annular projections 220 and 320 is effectively used. At the same time, by separating the portion where the combustion gas becomes hot from the wall surfaces of the piston combustion chambers 210 and 310, it is possible to reduce the wall surface heat loss and improve the thermal efficiency, thereby allowing good combustion.

  In the second and third embodiments, the swirl is less affected by the manufacturing variation of the intake port and the like, and the dependency on the promotion of mixing of fuel and air by the intake swirl is reduced. Since the piston combustion chamber structure that is relatively gently raised from 230 and 330, and the direction of the collision with the fuel spray is less fluctuating with respect to the variation in the spray angle of the fuel spray, the robust fuel and air In addition to being able to realize combustion by mixing, it is possible to realize a piston combustion chamber having a small thermal load and excellent reliability.

  Further, by flattening the bottom portions 230 and 330 of the annular projections 220 and 320, the fuel spray can be smoothly spread in the radial direction with little variation, and this also ensures robust fuel and air. Combustion can be realized by mixing with.

  In other words, according to the second and third embodiments, it is possible to realize a more robust mixing of the fuel and air (combustion less susceptible to disturbance) and combustion while having a relatively simple and low-cost configuration. In addition, while being excellent in reliability, it is possible to reduce the emission of black smoke by improving the air utilization rate in the combustion chamber and promoting combustion improvement over a wide operating range. Further, it is possible to provide a piston for an internal combustion engine having a piston combustion chamber that can improve thermal efficiency by reducing heat loss from the wall surface that defines the combustion chamber.

  According to the piston combustion chamber 210 of the second embodiment, the annular protrusion 220 is formed in a circular shape that is convex upward in the cross section shown in FIG. 5, and the width of the collision portion of the annular protrusion 220 with the fuel spray is widened. The fuel spray can be diffused in a wider range, reducing the influence of disturbances, etc., and achieving even better mixing of fuel and air and combustion can do.

  Further, as shown in FIG. 6, according to the piston combustion chamber 310 of the third embodiment, the recess 321 is provided at the fuel spray collision position of the annular projection 320, so that the fuel spray to the recess 321 is prevented. Since the collision of the initial fuel spray can be promoted by the collision, the utilization rate of the unused air in the upper part of the piston combustion chamber 310 can be improved, and the fuel and air can be mixed and further combusted. Can be realized.

  By the way, the annular protrusion 120 (same for 220 and 320) is not limited to the shape as shown in FIG. 2, and for example, as shown in FIG. ) In at least a part in the circumferential direction.

  The present invention is not limited to the embodiments of the invention described above, and various modifications can be made without departing from the gist of the present invention.

100, 200, 300 Piston 110, 110, 210 Piston combustion chamber 120, 220, 320 Toroidal protrusion 130, 230, 330 Bottom 140 Corner 150 Recess 160 External (Squish area)
170 Side wall 321 Recess

Claims (4)

A piston of an internal combustion engine having a piston combustion chamber that constitutes a part of the combustion chamber of the internal combustion engine,
The piston combustion chamber is configured to have a hemispherical recess on the upper surface of the piston, and an annular protrusion that protrudes from the bottom of the piston combustion chamber and is disposed around the central axis of the piston combustion chamber.
The fuel spray injected from the fuel injection valve collides with the annular protrusion, a part of the fuel spray advances to the inside of the annular protrusion, and the remaining part diffuses to the outside of the annular protrusion. A piston for an internal combustion engine characterized by the above.   The outer edge of the fuel spray injected from the fuel injection valve is set so as to be slightly inward from the top of the annular protrusion within a range of about 10 ° before and after the top dead center of the compression stroke at the crankshaft rotation angle. The piston of the internal combustion engine according to claim 1, wherein   The piston of the internal combustion engine according to claim 1, wherein a recess is formed in the vicinity of the collision position of the fuel spray of the annular protrusion.   4. A sandwich angle between fuel spray central axes when viewed from a direction orthogonal to the piston reciprocating direction is set to about 110 [deg.] To about 120 [deg.]. The piston of the internal combustion engine described in 1.