JP2007285276A - Spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress generation of a pre-ignition by a second ignition plug without degrading the fuel consumption, in a spark ignition internal combustion engine for performing a homogeneous combustion by igniting the homogeneously mixed gas by both a first ignition plug arranged around an upper portion of a cylinder, and the second ignition plug arranged substantially around the upper portion of the cylinder. <P>SOLUTION: In a spark ignition internal combustion engine for performing the homogeneous combustion by igniting a homogeneously mixed gas by both a first ignition plug 2a arranged around an upper portion of a cylinder, and a second ignition plug 2b arranged substantially around the upper portion of the cylinder, the homogeneously mixed gas is ignited only by the first ignition plug when detecting a condition of generation of pre-ignition by the second ignition plug or a condition immediately before generation thereof. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a spark ignition internal combustion engine.

  A homogeneous combustion is known in which a homogeneous mixture is formed in a cylinder and the homogeneous mixture is ignited and combusted at the ignition timing at the end of the compression stroke. In a cylinder injection spark ignition internal combustion engine equipped with a fuel injection valve that directly injects fuel into the cylinder, switching between homogeneous combustion and stratified combustion that forms a combustible mixture only in the vicinity of the spark plug In addition, it has been proposed to separately provide a homogeneous combustion ignition plug disposed around the cylinder upper portion and a stratified combustion ignition plug disposed substantially in the center of the cylinder upper portion (see, for example, Patent Document 1). .

  In the above-described in-cylinder spark ignition internal combustion engine, the use of two spark plugs for homogeneous combustion is not disclosed, but if a homogeneous mixture is ignited and combusted by two spark plugs, the combustion speed is reduced. It can be accelerated to improve homogeneous combustion. However, the spark plug disposed substantially at the center of the upper part of the cylinder is likely to generate pre-ignition due to a high temperature. In order to suppress the occurrence of pre-ignition, it has been proposed to cool the spark plug with the injected fuel when the occurrence of pre-ignition or the situation immediately before the occurrence is detected (see, for example, Patent Document 2).

JP 2004-44434 A JP 2003-206796 A JP 2002-339780 A

  However, as described above, if fuel injection is performed only to cool the spark plug at the time of occurrence of pre-ignition or just before the occurrence, fuel consumption is deteriorated.

  Accordingly, an object of the present invention is to perform homogeneous combustion by igniting a homogeneous mixture by both the first spark plug disposed around the upper part of the cylinder and the second spark plug disposed substantially at the center of the upper part of the cylinder. In the spark ignition internal combustion engine, the occurrence of pre-ignition by the second spark plug is suppressed without deteriorating fuel consumption.

  A spark ignition internal combustion engine according to claim 1 of the present invention is configured to provide a homogeneous mixture by both a first spark plug disposed around a cylinder upper portion and a second spark plug disposed substantially at the center of the cylinder upper portion. In a spark ignition internal combustion engine that ignites and performs homogeneous combustion, when the occurrence of pre-ignition by the second spark plug or the situation immediately before the occurrence is detected, the homogeneous mixture is ignited only by the first spark plug. It is characterized by.

  A spark ignition internal combustion engine according to a second aspect of the present invention is the spark ignition internal combustion engine according to the first aspect, further comprising a fuel injection valve that injects fuel directly into a cylinder, and is compressed by the fuel injection valve. It is also possible to perform stratified combustion in which a combustible mixture is formed in the vicinity of the second spark plug by the fuel injected in the second half of the stroke, and the combustible mixture is ignited by the second spark plug.

  A spark ignition internal combustion engine according to a third aspect of the present invention is the spark ignition internal combustion engine according to the first or second aspect, wherein the in-cylinder gap formed by the cylinder head and the piston at the end of the compression stroke is the first portion. A second portion, the first portion is narrow, the second portion is wider than the first portion, an ignition gap of the first spark plug is located in the first portion, and the second spark plug An ignition gap is located in the vicinity of the boundary between the first part and the second part, and at the time of homogeneous combustion, the second spark plug is ignited immediately after ignition of the first spark plug, and the first spark plug By igniting the air-fuel mixture in the first portion, a mixed air flow is ejected from the first portion toward the second portion, and an arc generated in an ignition gap of the second spark plug is the mixed air flow. Wherein the igniting the air-fuel mixture in the second portion is more extended to the second portion within.

  According to the spark ignition internal combustion engine of the first aspect of the present invention, homogeneous mixing is performed by both the first spark plug disposed around the cylinder upper portion and the second spark plug disposed substantially at the center of the cylinder upper portion. In a spark ignition internal combustion engine that ignites gas and performs homogeneous combustion, when the occurrence of pre-ignition by the second spark plug or the situation immediately before the occurrence is detected, the homogeneous mixture is ignited only by the first spark plug. It has become. Thereby, the temperature of the second spark plug is lowered as compared with the case where the second spark plug is used for ignition of the homogeneous mixture, and the occurrence of pre-ignition by the second spark plug can be suppressed.

  According to the spark ignition internal combustion engine according to claim 2 of the present invention, the spark ignition internal combustion engine according to claim 1 is provided with a fuel injection valve for directly injecting fuel into the cylinder. It is also possible to perform stratified combustion in which a combustible mixture is formed in the vicinity of the second spark plug by the fuel injected in the latter half of the compression stroke, and this combustible mixture is ignited by the second spark plug. Accordingly, since the second spark plug is used not only for homogeneous combustion but also for stratified combustion and easily reaches a high temperature, when the occurrence of pre-ignition due to the second spark plug or the situation immediately before the occurrence is detected, the second spark plug is detected. The temperature is lowered without using the spark plug for ignition of the homogeneous mixture, and the occurrence of preignition due to the second spark plug is suppressed.

  According to the spark ignition internal combustion engine of claim 3 according to the present invention, in the spark ignition internal combustion engine of claim 1 or 2, the in-cylinder gap formed by the cylinder head and the piston at the end of the compression stroke is The first portion is narrower, the second portion is wider than the first portion, the ignition gap of the first spark plug is located within the first portion, and the ignition gap of the second spark plug is Located near the boundary between the part and the second part, the second spark plug is ignited immediately after the ignition of the first spark plug during homogeneous combustion. Thereby, the air-fuel mixture in the first part can be surely combusted by ignition with the first spark plug, and the mixed air flow is ejected from the first part toward the second part, and the ignition gap of the second spark plug Since the arc generated in (2) is extended into the second portion by the mixed airflow, the air-fuel mixture in the second portion starts to burn simultaneously from a relatively large area in contact with the extended arc. In this way, the combustion rate is considerably increased and good homogeneous combustion can be realized.

  1 to 3 are schematic longitudinal sectional views showing an embodiment of a spark ignition internal combustion engine according to the present invention. FIG. 1 shows the ignition timing of homogeneous combustion at the end of the compression stroke, FIG. 2 shows the fuel injection timing of homogeneous combustion at the end of the intake stroke, and FIG. 3 shows the fuel injection timing of stratified combustion in the latter half of the compression stroke. In these drawings, reference numeral 1 denotes a fuel injection valve that is disposed substantially at the center of the cylinder upper portion and directly injects fuel into the cylinder. Although not shown in FIGS. 1 to 3, two intake valves are arranged on the right side of the upper part of the cylinder, and two exhaust valves are arranged on the left side.

  The spark ignition internal combustion engine of the present embodiment directly injects fuel into the cylinder at the end of the intake stroke by the fuel injection valve 1, thereby forming a homogeneous mixture in the cylinder at the ignition timing at the end of the compression stroke, This homogeneous mixture is ignited with sparks to perform homogeneous combustion. As described above, the present embodiment is an in-cylinder injection type. However, in order to perform homogeneous combustion, the fuel injection valve injects fuel into the intake port synchronously or asynchronously with intake air, and the fuel is injected into the cylinder together with intake air from the intake port. To form a homogeneous mixture.

  The spark ignition internal combustion engine of the present embodiment ignites a homogeneous air-fuel mixture by both the first spark plug 2a disposed around the cylinder upper portion and the second spark plug 2b disposed substantially at the center of the cylinder upper portion. Perform homogeneous combustion. Thereby, since the homogeneous air-fuel mixture is ignited at two points, the time until all the fuel is burned is shortened and the combustion speed can be increased. Thereby, homogeneous combustion can be made favorable.

  In general, the second spark plug 2b disposed substantially at the center of the upper part of the cylinder is generally made relatively thin due to restrictions from the mounting position. In such a spark plug, since the radial distance between the center electrode portion and the surrounding grounding portion is shortened, the center electrode portion protrudes relatively large from the grounding portion, and the center electrode portion and the grounding portion are The insulation distance between the two is satisfied by the axial distance. The second spark plug 2b in which the center electrode portion protrudes greatly in this way is referred to as a burnt type, and the center electrode portion is not easily cooled and easily maintained at a high temperature, so that it is likely to be a heat source for preignition.

  The present embodiment uses an ion sensor as means for detecting the occurrence of pre-ignition or the situation immediately before the occurrence. Preignition is a type of combustion that is different from normal combustion. Before the original ignition by the spark plug, for example, the center electrode of the spark plug maintained at a high temperature is used as a heat source to ignite the mixture. It is a phenomenon. It is known that when preignition occurs, ions are generated, and when the ions reach the ignition gap of the spark plug, an ion current flows through the spark plug. The ion sensor detects this ionic current and detects the occurrence of preignition. Specifically, when the ion current detected by the ion sensor is greater than or equal to a set value, it is determined that the pre-ignition has occurred or has just occurred.

  In this embodiment, when it is determined that the pre-ignition is generated or just before the occurrence, in this embodiment, the homogeneous mixture is ignited only by the first spark plug 2a, and the homogeneous combustion is performed. Since the temperature of the center electrode of the two spark plugs 2b is lower than when the second spark plug 2b is used to ignite a homogeneous mixture, the occurrence of preignition by the second spark plug 2b is suppressed. Can do.

  By the way, in this embodiment, as shown in FIG. 1, the cylinder gap formed by the cylinder head and the piston 3 at the end of the compression stroke has a first portion s1 and a second portion s2, and the first portion s1 is narrow and the second portion s2 is wider than the first portion s1. The ignition gap of the first spark plug 2a is positioned in the first portion s1, and the ignition gap of the second spark plug 2b is positioned in the vicinity of the boundary between the first portion s1 and the second portion s2.

  The second ignition plug 2b is ignited immediately after the ignition of the first ignition plug 2a at the ignition timing of homogeneous combustion at the end of the compression stroke when preignition has not occurred. Accordingly, in general, the flame hardly enters a narrow gap such as the first portion s1, and it is difficult to burn all the air-fuel mixture in the first portion s1, but the first spark plug 2a causes the first portion to be burned. By directly igniting the air-fuel mixture in s1, the air-fuel mixture in the first portion s1 can be reliably burned.

  Further, by igniting the air-fuel mixture in the first part s1, the air-fuel mixture in the first part s1 expands rapidly, and as indicated by the dashed line arrow in FIG. 1, from the first part s1 toward the second part s2. A mixed air current is ejected. At this time, the second spark plug 2b is ignited, and the arc A generated in the ignition gap of the second spark plug 2b is extended into the second portion s2 by this mixed airflow, and the second The air-fuel mixture in the portion s2 starts combustion simultaneously from a relatively large area in contact with the stretched arc A. Thus, the overall combustion rate is considerably increased and good homogeneous combustion can be achieved.

  In the present embodiment, the combustion of the air-fuel mixture in the first portion s1 at the beginning of combustion is not so fast, and only the combustion speed of the air-fuel mixture in the second portion s2 is considerably accelerated. Compared with a case where the speed is increased, heat release is suppressed and high thermal efficiency can be realized.

  The spark plug generally has an L-shaped electrode on the ground side and a center electrode on the high voltage side, and an ignition gap is formed between the L-shaped electrode and the center electrode. As described above, in order to satisfactorily extend the arc A into the second portion s2 by the mixed air flow in the second spark plug 2b, in particular, the L-shaped electrode 21b is located on the downstream side of the mixed air flow in the ignition gap of the second spark plug 2b. It is preferable not to be closed by. For example, as shown in FIGS. 1 to 3, it is preferable that the width direction of the L-shaped electrode 21b of the second spark plug 2b is substantially parallel to the mixed airflow. Of course, the second ignition shown in FIGS. The L-shaped electrode arrangement of the plug 2b may be an arrangement rotated 180 degrees when viewed from the inside of the cylinder, and only an arrangement rotated 90 degrees clockwise as viewed from the inside of the cylinder is not preferable.

  In the present embodiment, the first portion s1 of the in-cylinder gap at the end of the compression stroke is formed by the intake valve side of each of the cylinder head and the piston 3, and the second portion s2 is the exhaust valve side of each of the cylinder head and the piston 3. It is formed by. The first spark plug 2a is disposed on the intake valve side around the cylinder upper portion with an ignition gap positioned in the first portion s1. The second spark plug 2b has an ignition gap positioned in the vicinity of the boundary between the first portion s1 and the second portion s2, and is disposed substantially at the center of the cylinder upper portion. The above-mentioned effects are not limited to such a configuration. For example, a configuration in which the intake valve side and the exhaust valve side are reversed may be used, and a first portion is formed on one intake valve and exhaust valve side. However, the second portion may be formed on the other intake valve and exhaust valve side.

  In the present embodiment, a cavity 3 a is formed on the exhaust valve side of the top surface of the piston 3. As shown in FIG. 2, in the intake stroke, a tumble flow T is formed that descends the exhaust valve side in the cylinder and rises the intake valve side by the intake air. The cavity 3a on the top surface of the piston 3 has a partial arc-shaped cross section parallel to a longitudinal cross section (cross section of FIGS. 1 to 3) passing between the two intake valves and between the two exhaust valves, and is a compression stroke. Thus, even when the space in the cylinder becomes narrow, the tumble flow T functions along the cavity 3a so as to suppress the attenuation of the tumble flow T.

  Thereby, in the cavity 3a as the second portion s2 at the end of the compression stroke, the turbulence due to the tumble flow can easily exist, and the combustion speed of the air-fuel mixture in the second portion s2 can be further increased. Further, in the present embodiment, fuel injection is performed at the end of the intake stroke by the fuel injection valve 1 (for example, the fuel injection start crank angle according to the fuel injection amount so that the fuel injection end crank angle is in the vicinity of the intake bottom dead center) Or the fuel injection start crank angle is set in the latter half of the intake stroke regardless of the fuel injection amount).

  The fuel injection direction of the fuel injection valve 1 is directed to the exhaust valve side of the cylinder bore as shown in FIG. The penetration force of the fuel F injected from the fuel injection valve 1 is set so that the front end of the fuel 1 ms after the start of fuel injection reaches 60 mm or more. When the fuel F having such a strong penetrating force is injected obliquely downward toward the exhaust valve side of the cylinder bore from the substantially upper center of the cylinder, the tumble flow T formed in the cylinder can be strengthened by the fuel penetrating force. it can. The strengthened tumble flow T is reliably maintained until the end of the compression stroke, and the turbulence due to the tumble flow can surely exist in the cavity 3a as the second portion s2, so that the mixture in the second portion s2 The burning rate is further increased.

In the present embodiment, the air-fuel ratio of homogeneous combustion is made leaner than the stoichiometric air-fuel ratio (preferably, the lean air-fuel ratio in which the amount of NO _x produced is suppressed) to suppress fuel consumption. In addition, the combustion tends to be slow, and it is particularly effective to increase the combustion speed as described above. However, at high engine loads that require high engine output, the air-fuel ratio of homogeneous combustion may be the stoichiometric air-fuel ratio or rich air-fuel ratio. In this case as well, it is effective to increase the combustion speed.

  In addition, when high engine output is not required, especially at low loads, it is not homogeneous combustion, but it is better to perform stratified combustion by forming a combustible mixture near the spark plug and igniting it. Can be reduced. In the present embodiment, the second spark plug 2b is protruded relatively large into the cylinder, and a part of the fuel injected from the fuel injection valve 1 toward the exhaust valve side of the cylinder bore is the second spark plug 2b. It is arranged so as to pass through the ignition gap.

  Accordingly, as shown in FIG. 3, if fuel is injected by the fuel injection valve 1 in the latter half of the compression stroke, the injected fuel is easily vaporized by friction with the high-pressure intake air in the latter half of the compression stroke, and becomes a combustible mixture. The ignition gap of the second spark plug 2b can be positioned in the combustible mixture. Thus, good stratified combustion can be realized by igniting the combustible air-fuel mixture with the second spark plug 2b at the ignition timing at the end of the compression stroke. For such stratified combustion, the cavity 3a on the top surface of the piston 3 is not necessarily required. However, if the cavity 3a is formed as in this embodiment, the combustible mixture is reliably maintained in the cavity 3a. Therefore, the stratified combustion can be further improved.

  When the second spark plug 2b is also used for stratified combustion as in the present embodiment, the second spark plug 2b is easily maintained at a high temperature, and is greatly protruded into the cylinder for stratified combustion. If so, the second spark plug 2b is more likely to be maintained at a higher temperature by heat during stratified combustion and homogeneous combustion. Accordingly, since the pre-ignition is easily generated by the second ignition plug 2b, as described above, the ignition of the homogeneous mixture by the second ignition plug 2b is prohibited in the situation immediately before the occurrence of the pre-ignition. It is important to suppress the occurrence of pre-ignition.

  The shape of the fuel spray injected from the fuel injection valve 1 can be arbitrarily set, and may be, for example, a solid or hollow cone shape, or a solid column shape. Moreover, it is good also as a comparatively thin substantially fan-shaped fuel spray injected from a slit-shaped nozzle hole. Moreover, it is good also as a fuel spray of a comparatively thin arc-shaped cross section or a polygonal line cross section by the combination of an arc-shaped slit nozzle hole or a some linear slit nozzle hole. In any case, it is preferable that the fuel spray has a strong penetration force as described above to accelerate the tumble flow in the cylinder.

  In the present embodiment, the fuel injection valve 1 and the second ignition plug 2b are both arranged substantially at the upper center of the cylinder, and in particular, the fuel injection valve 1 is on the intake valve side of the second ignition plug 2b. 1 may be on the exhaust valve side of the second spark plug 2b. In this case, in order to perform stratified combustion, it is preferable to guide the injected fuel to the vicinity of the second spark plug 2b using the cavity on the top surface of the piston.

1 is a schematic longitudinal sectional view at the end of a compression stroke showing an embodiment of a spark ignition internal combustion engine according to the present invention. FIG. 2 is a schematic longitudinal sectional view at the end of an intake stroke of the spark ignition internal combustion engine of FIG. 1. FIG. 2 is a schematic longitudinal sectional view of the latter half of a compression stroke of the spark ignition internal combustion engine of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel injection valve 2a 1st spark plug 2b 2nd spark plug 3 Piston T Tumble flow F Injection fuel

Claims (3)

  In a spark ignition internal combustion engine that performs homogeneous combustion by igniting a homogeneous air-fuel mixture by both a first spark plug disposed around the cylinder upper portion and a second spark plug disposed substantially in the center of the cylinder upper portion, A spark ignition internal combustion engine characterized by igniting a homogeneous air-fuel mixture only with the first spark plug when the occurrence of pre-ignition due to the second spark plug or a situation immediately before the occurrence is detected.   A fuel injection valve for directly injecting fuel into the cylinder, the fuel injected by the fuel injection valve in the second half of the compression stroke forms a combustible mixture in the vicinity of the second spark plug, and the combustible mixture is The spark ignition internal combustion engine according to claim 1, wherein stratified combustion that is ignited by the second spark plug is also possible.   An in-cylinder gap formed by the cylinder head and the piston at the end of the compression stroke has a first portion and a second portion, the first portion is narrow, the second portion is wider than the first portion, and the first portion An ignition gap of the spark plug is located in the first part, and an ignition gap of the second spark plug is located in the vicinity of the boundary between the first part and the second part. Immediately after ignition of the second spark plug, by igniting the air-fuel mixture in the first part by the first spark plug, a mixed air flow is ejected from the first part toward the second part, The arc generated in the ignition gap of the second spark plug is extended into the second part by the mixed airflow to ignite the air-fuel mixture in the second part. Spark ignition internal combustion engine as set forth.

Images