JP2009091937A - Control device for cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for a cylinder injection type spark ignition internal combustion engine, offering technology for compatibly improving the ignitability of mixture when the ignition gap of an ignition plug is relatively small and reducing required voltage when the ignition gap is large. <P>SOLUTION: The control device is provided for the cylinder injection type spark ignition internal combustion engine which has a cylinder fuel injection valve provided in a combustion chamber of the internal combustion engine for executing intake stroke injection in an intake stroke and compression stroke injection in a compression stroke, and the ignition plug. The device comprises a compression injection ratio control means for controlling a compression injection ratio as the ratio of a fuel injection amount relating to the compression stroke injection to a fuel injection amount relating to the intake stroke injection depending on an aging change in the ignition gap of the ignition plug. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an in-cylinder injection spark ignition internal combustion engine.

  In recent years, an in-cylinder spark ignition internal combustion engine that directly injects fuel into a combustion chamber of an internal combustion engine is known (see, for example, Patent Documents 1 and 2). The in-cylinder injection spark ignition internal combustion engine can perform fuel injection at any timing regardless of the opening / closing timing of the intake valve, so that the fuel is injected in the intake stroke and the compression stroke in which fuel is injected in the intake stroke. The injection ratio with the compression stroke injection can be changed according to the operating state of the internal combustion engine.

  For example, a combustion in which the fuel is locally and relatively fuel-rich in the vicinity of the spark plug by compression stroke injection (that is, fuel is unevenly distributed around the spark plug), and the air-fuel ratio in the entire cylinder is leaner than the stoichiometric air-fuel ratio. Is possible. In addition, ignition is performed in a state where fuel is uniformly dispersed in the cylinder by the intake stroke injection, and the intake air is cooled by the injected fuel, thereby increasing the charging efficiency of the intake air and contributing to the improvement of the engine output. It becomes possible.

  By the way, the discharge (spark discharge) by the spark plug breaks the insulation between the electrodes by applying a voltage between the electrodes of the spark plug (between the center electrode and the ground electrode), and sparks between the electrodes (spark). The electrodes are energized while generating On the other hand, the electrode of the spark plug is worn by being oxidized by an impact during discharge or an increase in the in-cylinder temperature. That is, as the operating time of the internal combustion engine and the travel distance of the vehicle increase, wear of the electrodes of the spark plug progresses, so that the ignition gap (distance between the electrodes of the spark plug) increases with time.

When the ignition gap becomes larger (wider) due to electrode wear in the spark plug, the required voltage (hereinafter simply referred to as “required voltage”) to the ignition power source that applies a voltage between the electrodes of the spark plug when the mixture is ignited. If the required voltage becomes excessively high, there is a high possibility that a fire error will occur. In contrast, when the initial gap, which is the initial value of the spark plug (ignition gap when the spark plug is new), is set to be small (narrow) in advance, the required voltage becomes relatively large with respect to the applied voltage. (Hereinafter also referred to as the “lifetime limit”).
JP 2001-248482 A JP-A-11-125131 JP-A-9-112321

  However, if the ignition gap is excessively small, the spark itself is likely to be generated even at a low voltage (that is, the required voltage is low), but the spark generation area is too narrow to reduce the flame kernel (fire type). It becomes difficult to grow large. Therefore, the ignitability of the air-fuel mixture deteriorates when the wear amount of the spark plug electrode is small (when the ignition gap is small) as a contradiction to prolonging the service life limit by setting the initial gap small in advance. There was a case.

  In addition, even if it is possible to prolong the service life limit by setting the initial gap small in advance, there is a limit to this, and it is desired to provide a technique for reducing the required voltage itself when the ignition gap becomes large. It was the actual situation.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to ignite an air-fuel mixture when an ignition gap of a spark plug is relatively small in a control device for a direct injection spark ignition internal combustion engine. It is an object of the present invention to provide a technique capable of achieving both improvement in performance and reduction in required voltage when the ignition gap is large.

In order to achieve the above object, a control device for a direct injection spark ignition internal combustion engine according to the present invention employs the following means.
That is, a control device for a cylinder injection spark ignition internal combustion engine, which is provided in a combustion chamber of the internal combustion engine and includes an in-cylinder fuel injection valve and an ignition plug that can execute an intake stroke injection in an intake stroke and a compression stroke injection in a compression stroke. In
Compression injection ratio control means for controlling a compression injection ratio, which is a ratio of a fuel injection amount related to the compression stroke injection to a fuel injection amount related to the intake stroke injection, according to a change with time of an ignition gap in the spark plug; It is characterized by providing.

  In a region where the ignition gap of the spark plug is relatively small, the ignitability of the air-fuel mixture is likely to deteriorate. Therefore, in the present invention, in a region where the ignition gap is relatively small, control for improving the ignitability of the air-fuel mixture by increasing the compression injection ratio (hereinafter also referred to as “ignitability improvement control”) is performed.

  That is, when the compression injection ratio is increased in the ignitability improvement control, the air-fuel mixture in the vicinity of the spark plug becomes locally more fuel-rich. According to this, it becomes possible to make more combustible fuel unevenly distributed in the vicinity of the spark plug, and it is possible to make the air-fuel mixture near the spark plug very easily ignited. Therefore, according to the ignitability improvement control of the present invention, the ignitability of the air-fuel mixture can be ensured even when the ignition gap is small.

  On the other hand, the required voltage of the spark plug increases as the spark gap increases due to electrode wear in the spark plug. Accordingly, in a region where the ignition gap is relatively large, the required voltage becomes excessive, and the possibility of occurrence of a spark fly error increases. Therefore, in the present invention, in a region where the ignition gap is relatively large, control for reducing the required voltage by increasing the compression injection ratio (hereinafter also referred to as “required voltage reduction control”) is performed.

  Here, when the compression injection ratio is increased, the local richness of the air-fuel mixture in the vicinity of the spark plug increases as described above. Focusing on the air-fuel ratio (mixture ratio of intake air and fuel) of the air-fuel mixture in the vicinity of the spark plug, the fuel-rich air-fuel mixture containing more liquid fuel that is easier to energize than the fuel-lean mixture containing more intake air Since it can be more unevenly distributed in the vicinity, a discharge at the time of ignition can be easily generated. Therefore, in the present invention, the required voltage can be reduced by performing the required voltage reduction control even when the ignition gap becomes large.

  Further, in the present invention, since the ignitability of the air-fuel mixture can be improved when the ignition gap is small, there is an effect that the initial gap can be set smaller than the conventional one while ensuring the ignitability. As a result, the end of the service life limit can be postponed compared to the conventional case. Further, since the required voltage itself can be reduced even if the ignition gap is increased, the arrival of the service life limit time can be further postponed.

  As a result, the service life of the spark plug and the travelable distance of the vehicle until the spark plug needs to be replaced become longer, so that the durability of the spark plug can be further improved. Therefore, user satisfaction can be improved and the commercial value of the spark plug can be increased.

  When attention is paid to the engine load of the internal combustion engine, the ignitability of the air-fuel mixture tends to deteriorate because the fuel injection amount is small in the low load operation. Therefore, it is more preferable that the ignitability improvement control in the present invention is performed particularly during low load operation of the internal combustion engine. Further, since the in-cylinder pressure increases during high load operation of the internal combustion engine, the required voltage tends to increase. This is because the density of the air-fuel mixture that insulates between the electrodes of the spark plug becomes higher. Therefore, it is more preferable that the required voltage reduction control in the present invention is performed particularly during high-load operation of the internal combustion engine.

  The compression injection ratio control means in the present invention may increase the compression injection ratio as the ignition gap is smaller when the ignition gap is equal to or smaller than the predetermined first threshold value. Here, the first threshold value is an upper limit value of the ignition gap that is determined to cause deterioration of the ignitability of the air-fuel mixture when the ignition gap is equal to or smaller than the threshold value and the spark generation region at the time of ignition is too narrow.

  Here, as the ignition gap increases with time, the ignitability of the air-fuel mixture is improved. Therefore, in the present invention, when the ignition gap is equal to or smaller than the predetermined first threshold, the compression injection ratio is increased as the ignition gap is smaller. In other words, the compression injection ratio is decreased as the ignition gap increases. According to this, the compression injection ratio can be controlled more finely according to the size of the ignition gap that changes over time.

  Further, after the ignition gap has become larger than the first threshold value, there is no possibility that the ignitability of the air-fuel mixture will deteriorate, so the compression injection ratio may be made substantially zero. Alternatively, when a compression injection ratio that matches the operating state (engine load, engine speed) of the internal combustion engine is referred to as a reference compression injection ratio, the compression injection ratio may be substantially matched with the reference compression injection ratio. As a result, an unnecessary increase in the compression injection ratio is suppressed, and an air-fuel mixture is formed in which the fuel is more uniformly dispersed in the cylinder. As a result, the air-fuel mixture can be burned more stably and the amount of unburned components and smoke discharged from the fuel can be reduced.

  Further, the compression injection ratio control means in the present invention may increase the compression injection ratio as the ignition gap increases when the ignition gap is equal to or greater than a predetermined second threshold value. Here, the second threshold value is a lower limit value of the ignition gap at which it is determined that when the ignition gap is equal to or greater than this threshold value, the required voltage rises excessively and it is difficult to generate a spark at the time of ignition. is there.

  Here, since the required voltage becomes higher as the ignition gap becomes larger, in the present invention, when the ignition gap is equal to or larger than the second threshold value, the compression injection ratio is increased as the ignition gap becomes smaller. According to this, the compression injection ratio can be controlled more finely according to the size of the ignition gap that changes over time. When the ignition gap is smaller than the second threshold value, the required voltage does not become excessively high. Therefore, when the ignition gap is smaller than the second threshold value, the compression injection ratio is substantially zero or the compression injection ratio is set to the standard compression. Stable combustion of the air-fuel mixture may be achieved by making it substantially coincide with the injection ratio.

  Here, when the ignitability improvement control or the required voltage reduction control is performed, the engine torque may decrease due to combustion fluctuations of the internal combustion engine. Therefore, in the present invention, a supercharger that makes the supercharging pressure variable, and a supercharging pressure increase control that increases the supercharging pressure so that the amount of decrease in engine torque due to the increase in the compression injection ratio becomes substantially zero. And a supercharging pressure control means to be implemented.

  According to this, even when the compression injection ratio is increased by the compression injection ratio control means, it is possible to suitably suppress the torque reduction of the internal combustion engine. That is, it is possible to improve the ignitability of the air-fuel mixture in a region where the ignition gap is relatively small and to suppress the required voltage of the spark plug in a region where the ignition gap is relatively large while suppressing the torque reduction.

  It should be noted that a torque decrease accompanying an increase in the compression injection ratio is likely to occur during high load operation of the internal combustion engine in which the fuel injection amount increases. Therefore, when the boost pressure increase control according to the present invention is performed at the time of high load operation of the internal combustion engine in which the possibility of torque reduction is high, the effect can be more remarkably exhibited.

  Here, in the case where the torque reduction is suppressed by performing the supercharging pressure increase control, the cylinder pressure of the internal combustion engine increases due to the increase of the supercharging pressure. As a result, the density of the air-fuel mixture that insulates the electrodes of the spark plug increases, and the required voltage of the spark plug increases. Therefore, when the compression injection ratio is increased to improve the ignitability of the air-fuel mixture or reduce the required voltage of the spark plug, the compression injection is taken into account the increase in the required voltage due to the supercharging pressure increase control. It is preferred to control the ratio.

  Therefore, in the present invention, target voltage decrease amount setting means for setting a target voltage decrease amount of the required voltage of the spark plug based on the ignition gap, and a decrease amount of the required voltage due to an increase in the compression injection ratio (hereinafter referred to as “ The total voltage decrease amount obtained by subtracting the required voltage increase amount (hereinafter also referred to as “voltage increase amount”) resulting from the supercharging pressure increase control from the “voltage decrease amount”) is set by the target voltage decrease amount setting means. Target compression injection ratio determining means for determining a target compression injection ratio of the compression injection ratio controlled by the compression injection ratio control means so as to be substantially equal to the target voltage decrease amount. The target voltage reduction amount is a target value of the reduction amount of the required voltage necessary for reducing the required voltage to the applied voltage.

  In the present invention, since the compression injection ratio is determined in consideration of the increase in the required voltage due to the boost pressure increase control, the amount of decrease in the required voltage is insufficient as a contradiction to suppress the torque decrease by the boost pressure increase control. Can be suppressed. In addition, when the present invention is applied to a case where the required voltage becomes high, such as when the ignition gap is large or the internal combustion engine where the in-cylinder pressure becomes high, such as during high load operation, the operational effects of the present invention become more prominent. Can play.

  Here, the voltage drop amount and the voltage increase amount described above increase as the compression injection ratio increases. This is because as the compression injection ratio increases, the degree of fuel richness in the vicinity of the spark plug increases, and the degree of decrease in engine torque increases. However, the gradient at which the voltage drop amount and the voltage rise amount change with respect to the change in the compression injection ratio is not constant.

  More specifically, in the region where the compression injection ratio is relatively small, the slope in which the voltage drop amount changes is larger than the slope in which the voltage increase amount changes, and in the process of shifting to a region where the compression injection ratio is larger, The magnitude relationship is reversed. Here, the total voltage drop obtained as a result of subtracting the voltage rise from the voltage drop is considered. In a region where the compression injection ratio is small, the total voltage drop amount increases as the compression injection ratio increases, but the slope of the total voltage drop amount gradually increases. When the compression injection ratio further increases, the total voltage decrease amount reaches the maximum value (hereinafter also referred to as “limit voltage decrease amount”), and thereafter, the total voltage decrease amount decreases as the compression injection ratio increases. To go.

  By the way, in order to ensure the functionality of the spark plug over the lifetime of the spark plug, it is important that the target voltage drop does not exceed the limit voltage drop during the lifetime. Here, in view of the fact that the target voltage drop increases as the electrode gap in the spark plug progresses and the spark gap increases, the spark gap at the end of the spark plug life (hereinafter referred to as the “life end gap”). If the target voltage drop amount corresponding to “No.” is equal to or less than the limit voltage drop amount, there is no possibility that the required voltage becomes excessively high during the service life.

Therefore, the initial gap in the present invention is the maximum value of the total voltage drop when the ignition gap is increased by a predetermined reference value that guarantees the durability of the spark plug with respect to the initial gap. It is preferable that it is determined to be equal to or less than the limit voltage drop amount. The predetermined reference value that guarantees the durability of the spark plug means the difference between the end-of-life gap and the initial gap, and the larger the amount of electrode wear guaranteed during the service life, the larger the reference value. Become.

  According to the present invention, the end-of-life gap is set in a range where the target voltage drop amount is equal to or less than the limit voltage drop amount, and the initial gap is set by subtracting the reference value from the end-of-life gap. According to this, it becomes possible to make the service life as long as possible while suppressing deterioration of the ignitability of the air-fuel mixture and excessive increase in the required voltage during the service life.

  The means for solving the problems in the present invention can be employed in combination as much as possible.

  According to the present invention, in the control device for a direct injection spark ignition internal combustion engine, the ignitability of the air-fuel mixture is improved when the ignition gap of the spark plug is relatively small, and the required voltage is reduced when the ignition gap is large. Can be made compatible.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

  Here, the case where the present invention is applied to a gasoline engine for driving a vehicle will be described as an example. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 and its intake / exhaust system in the present embodiment.

  The internal combustion engine 1 is a gasoline engine for driving a vehicle. The internal combustion engine 1 has a cylinder 2, and a piston 4 is slidably provided in the cylinder 2. An intake port 6 and an exhaust port 7 are opened in the combustion chamber 5 in the upper part of the cylinder 2.

Openings of the intake port 6 and the exhaust port 7 to the combustion chamber 5 are opened and closed by an intake valve 8 and an exhaust valve 9, respectively. The combustion chamber 5 is provided with an in-cylinder fuel injection valve 10 for directly injecting fuel into the combustion chamber 5 and an ignition plug 11 for igniting the fuel injected by the in-cylinder fuel injection valve 10. ing.

  The intake port 6 and the exhaust port 7 are connected to an intake passage 12 and an exhaust passage 13, respectively. A compressor housing 17 a of a variable displacement turbocharger (hereinafter simply referred to as “turbocharger”) 17 as a supercharger is installed in the middle of the intake passage 12. A turbine housing 17b of the charger 17 is installed. In this embodiment, the turbocharger 17 corresponds to the supercharger in the present invention.

  A compressor wheel 17c and a turbine wheel 17d are provided inside the compressor housing 17a and the turbine housing 17b, respectively. In the turbocharger 17, the turbine wheel 17d is rotated by the exhaust gas flowing into the turbine housing 17b, and the compressor wheel 17c rotates along with the rotation of the turbine wheel 17d, whereby the intake air (air) that flows into the compressor housing 17a. Is supercharged.

  A plurality of nozzle vanes (not shown) are provided around the turbine wheel 17d in the turbine housing 17b so as to be rotatable in the turbine housing 17b. And if a nozzle vane is rotated to the closing side, the flow path between adjacent nozzle vanes will become narrow and a supercharging pressure will increase. Further, when the nozzle vane is rotated to the open side, the flow path between the adjacent nozzle vanes widens and the supercharging pressure decreases.

  In addition, a pressure sensor 15 that outputs an electrical signal corresponding to the supercharging pressure by the turbocharger 17 is provided in the intake passage 12 on the downstream side of the compressor housing 17a. Further, the internal combustion engine 1 includes an accelerator opening sensor 16 that outputs an electric signal corresponding to the accelerator opening, and a crank position sensor 18 that detects a rotation angle of a crankshaft that rotates in conjunction with the reciprocating motion of the piston 4. Is provided.

  The internal combustion engine 1 configured as described above is provided with an ECU 20 for controlling the internal combustion engine 1. The ECU 20 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. Various sensors such as a pressure sensor 15, an accelerator opening sensor 16, and a crank position sensor 18 are connected to the ECU 20 via electric wiring, and these output signals are input to the ECU 20. The ECU 20 detects the engine load TQ of the internal combustion engine 1 from the output value of the accelerator opening sensor 16 and detects the engine speed NE of the internal combustion engine 1 from the output value of the crank position sensor 18.

  Further, the in-cylinder fuel injection valve 10 is electrically connected to the ECU 20, and the fuel injection timing and the fuel injection amount by the in-cylinder fuel injection valve 10 are controlled by the ECU 20. Specifically, the ECU 20 controls each fuel injection amount in the intake stroke injection that is the fuel injection in the intake stroke of the internal combustion engine 1 and the compression stroke injection that is the fuel injection in the compression stroke, and thereby the fuel injection related to the intake stroke injection. The ratio (hereinafter referred to as “compression injection ratio”) Rq of the fuel injection amount (hereinafter referred to as “compression stroke injection amount”) Qfc related to the compression stroke injection to the amount (hereinafter referred to as “intake stroke injection amount”) Qfi is controlled. The

  Further, the ignition plug 11 is electrically connected to the ECU 20 via an ignition power source 19 that applies a voltage to the ignition plug 11, and the ignition plug 11 is connected to the ECU 20 based on a command signal from the ECU 20. When the voltage is applied between the electrodes, the air-fuel mixture burns.

  The turbocharger 17 is electrically connected to the ECU 20, and the flow rate of the exhaust blown to the turbine wheel 17 d by controlling the opening amount of the nozzle vane (hereinafter referred to as “VN opening”) by the ECU 20, The amount or the like is adjusted, and the intake air amount, the supercharging pressure, or the like is adjusted.

  Next, a schematic configuration of the spark plug 11 in the present embodiment will be described with reference to FIG. The spark plug 11 includes a center electrode 21 and a ground electrode 22. In the spark plug 11 configured as described above, when a voltage from the ignition power supply 19 is applied to the center electrode 21, a discharge is caused between the center electrode 21 and the ground electrode 22 (hereinafter referred to as "ignition gap"). A spark (spark) is generated, and the air-fuel mixture ignited in the combustion chamber 5 is combusted by flame propagation.

  Next, the ignition request voltage Vr of the ignition plug will be described. Here, the ignition request voltage Vr is a voltage required for the ignition power source 19 necessary for generating a spark between the center electrode 21 and the ground electrode 22 when the mixture is ignited. In this embodiment, the required ignition voltage Vr corresponds to the required voltage in the present invention.

Here, the ignition request voltage Vr of the ignition plug increases as the ignition gap Gp increases. Since the center electrode 21 and the ground electrode 22 (hereinafter collectively referred to simply as “electrodes”) are worn by being oxidized due to an impact during discharge or an increase in the in-cylinder temperature, the ignition gap Gp is changed over time. Will increase. When the ignition request voltage Vr becomes relatively high with respect to the applied voltage of the ignition power source 19, the possibility of a flying mistake increases.

  On the other hand, when the ignition gap Gp is small, the spark (spark) itself is likely to be generated even at a low voltage (that is, the ignition request voltage Vr is low), but the spark generation region is too narrow, so It becomes difficult to grow well. Therefore, when the amount of wear of the electrode of the spark plug 11 is small and the ignition gap Gp is small, the ignitability of the air-fuel mixture may be deteriorated.

  Therefore, in the internal combustion engine 1 according to the first embodiment, when the ignition gap Gp is small, the ignitability improvement control for improving the ignitability of the air-fuel mixture is performed according to the change over time of the ignition gap Gp, and the ignition gap Gp is increased. When this happens, the required voltage reduction control for reducing the required ignition voltage Vr is performed. Specifically, the compression injection ratio Rq is controlled according to the ignition gap Gp.

  FIG. 3 is a diagram showing the relationship between the ignition gap Gp and the compression injection ratio Rq in the ignitability improvement control of the present embodiment. Here, the horizontal axis represents the ignition gap Gp, and the vertical axis represents the compression injection ratio Rq. Further, the reference compression injection ratio Rqb on the vertical axis is a compression injection ratio that matches the operating state (engine load TQ, engine speed NE) of the internal combustion engine 1, and is experimentally determined in advance for each operating state of the internal combustion engine 1. I ask you to.

  In the present embodiment, as shown in the drawing, when the ignition gap Gp is equal to or smaller than the first reference gap Gpb1, the compression injection ratio Rq is increased compared to the reference compression injection ratio Rqb, and the ignition gap Gp is larger than the first reference gap Gpb1. When it is larger, the compression injection ratio Rq is made to coincide with the reference compression injection ratio Rqb. Here, the first reference gap Gpb1 is an upper limit value of the ignition gap Gp that is determined that when the ignition gap Gp is equal to or smaller than this value, the spark generation region at the time of ignition is too narrow and the ignitability of the air-fuel mixture deteriorates. It is. In the present embodiment, the first reference gap Gpb1 corresponds to the predetermined first threshold value in the present invention.

  When the compression injection ratio Rq is increased, the local richness of the air-fuel mixture in the vicinity of the spark plug 11 can be further increased. That is, by making the fuel having combustibility more unevenly distributed in the vicinity of the spark plug 11, it is possible to form an air-fuel mixture that is particularly easily ignited in the vicinity of the spark plug 11, thereby improving the ignitability of the air-fuel mixture.

  Further, since the spark generation region is expanded as the ignition gap Gp increases, the ignitability of the air-fuel mixture is gradually improved. That is, as the ignition gap Gp increases, the required increase amount of the compression injection ratio Rq with respect to the reference compression injection ratio Rqb decreases. In the ignitability improvement control according to the present embodiment, the compression injection ratio Rq (specifically, the increase amount of the compression injection ratio Rq with respect to the reference compression injection ratio Rqb) is reduced as the ignition gap Gp increases, so that The compression injection ratio Rq is accurately controlled in accordance with the ignition gap Gp that changes with time.

  Further, after the ignition gap Gp becomes larger than the first reference gap Gpb1, there is no possibility that the ignitability of the air-fuel mixture will be excessively deteriorated, so the compression injection ratio Rq is maintained at the reference compression injection ratio Rqb. As a result, the unnecessary increase in the compression injection ratio Rq is suppressed, stable combustion of the air-fuel mixture is achieved, and the amount of unburned components and smoke discharged from the internal combustion engine 1 is reduced.

  Next, the required voltage reduction control of this embodiment will be described. FIG. 4 is a diagram showing the relationship between the ignition gap Gp and the compression injection ratio Rq in the required voltage reduction control of this embodiment. Here, the horizontal axis represents the ignition gap Gp, and the vertical axis represents the compression injection ratio Rq.

  In the present embodiment, as shown in the figure, when the ignition gap Gp is equal to or greater than the second reference gap Gpb2, the compression injection ratio Rq is increased compared to the reference compression injection ratio Rqb, and the ignition gap Gp is greater than the second reference gap Gpb2. Is smaller, the compression injection ratio Rq is matched with the reference compression injection ratio Rqb.

  The second reference gap Gpb2 is a lower limit of the ignition gap Gp at which it is determined that it is difficult to generate a spark at the time of ignition when the ignition gap is equal to or larger than this value and the required ignition voltage Vr increases excessively. Value. In the present embodiment, the second reference gap Gpb2 corresponds to the predetermined second threshold value in the present invention.

  In the required voltage reduction control in the present embodiment, attention is paid to the air-fuel ratio (mixture ratio of intake air and fuel) of the air-fuel mixture in the vicinity of the spark plug 11. When the compression injection ratio Rq is increased, the local richness of the air-fuel mixture in the vicinity of the spark plug 11 can be further increased. In other words, by making the fuel-rich mixture containing a larger amount of liquid fuel easier to energize than the fuel-lean mixture containing a larger amount of intake air near the ignition plug 11, discharge at the time of ignition of the ignition plug 11 is more likely to occur. As a result, the required ignition voltage Vr can be reduced.

  Further, since the required ignition voltage Vr increases as the ignition gap Gp increases, the required ignition voltage Vr needs to be further reduced. In the required voltage reduction control in this embodiment, as the ignition gap Gp increases, the compression injection ratio Rq (specifically, the amount of increase of the compression injection ratio Rq with respect to the reference compression injection ratio Rqb) is increased, so that The compression injection ratio Rq is accurately controlled in accordance with the ignition gap Gp that changes to.

  On the other hand, when the ignition gap Gp is smaller than the second reference gap Gpb2, there is no possibility that the ignition request voltage Vr becomes excessively high, so the compression injection ratio Rq is maintained at the reference compression injection ratio Rqb. As a result, the unnecessary increase in the compression injection ratio Rq is suppressed, stable combustion of the air-fuel mixture is achieved, and the amount of unburned components and smoke discharged from the internal combustion engine 1 is reduced.

  Here, FIG. 5 is a flowchart showing a control routine in the present embodiment. This routine is a program stored in the ROM of the ECU 20, and is a routine that is executed at predetermined intervals when the internal combustion engine 1 is in operation. In this embodiment, the ECU 20 that executes this routine corresponds to the compression injection ratio control means in the present invention. In this embodiment, the description will be made on the assumption that the above-described second reference gap Gpb2 is larger than the first reference gap Gpb1.

  When this routine is executed, first, in step S101, the operating state of the internal combustion engine 1 is detected. Specifically, the engine load TQ and the engine speed NE are detected based on output signals from the accelerator opening sensor 16 and the crank position sensor 18. In the subsequent step S102, based on the operating state of the internal combustion engine 1, the fuel injection amount Qf required for the internal combustion engine 1 and the reference compression injection ratio Rqb are calculated.

In step S103, the current ignition gap Gp is estimated. Specifically, the wear amount of the electrode in the spark plug 11 is estimated based on the operation history of the internal combustion engine 1 (for example, the total operating time of the internal combustion engine 1, the travel distance, etc.), and the wear amount and the initial gap Gps are calculated. Based on this, the current ignition gap Gp is estimated. The initial gap Gps is the size of the ignition gap Gp when the spark plug 11 is new.

  In step S104, whether the ignition gap Gp is equal to or less than the first reference gap Gpb1 (a determination), whether the ignition gap Gp is equal to or greater than the second reference gap Gpb2 (b determination), and whether the ignition gap Gp is the first. It is determined whether the value is larger than the reference gap and smaller than the second reference gap Gpb2 (c determination).

  Here, if a determination (Gp ≦ Gpb1) is made, it is determined that the ignitability of the air-fuel mixture needs to be improved, and the process proceeds to step S105. Further, when the b determination (Gp ≧ Gpb2) is made, it is determined that the ignition request voltage Vr needs to be reduced, and the process proceeds to step S106. Further, when the c determination (Gpb1 <Gp <Gpb2) is made, it is determined that there is no need to improve the ignitability of the air-fuel mixture and there is no need to lower the ignition request voltage Vr, and the process proceeds to step S107.

  In step S105, the above-described ignitability improvement control is executed. That is, the compression injection ratio Rq is obtained by substituting the reference compression injection ratio Rqb calculated in step S102 and the ignition gap Gp estimated in step S103 into the map shown in FIG. The intake stroke injection amount Qfi and the compression stroke injection amount Qfc are calculated based on the compression injection ratio Rq and the fuel injection amount Qf calculated in step S102, and fuel injection control is performed. Then, when the processing of this step is finished, this routine is once finished.

  In step S106, the above-described required voltage reduction control is executed. That is, the compression injection ratio Rq is obtained by substituting the reference compression injection ratio Rqb calculated in step S102 and the ignition gap Gp estimated in step S103 into the map shown in FIG. The intake stroke injection amount Qfi and the compression stroke injection amount Qfc are calculated based on the compression injection ratio Rq and the fuel injection amount Qf calculated in step S102, and fuel injection control is performed. Then, when the processing of this step is finished, this routine is once finished.

  In step S107, normal fuel injection control is executed. That is, the fuel injection control is performed based on the fuel injection amount Qf calculated in step S102 and the reference compression injection ratio Rq. That is, in this step, increase control of the compression injection ratio Rq for improving the ignitability of the air-fuel mixture or reducing the ignition request voltage Vr is not performed. Then, when the processing of this step is finished, this routine is once finished.

  As described above, according to the present embodiment, when the ignition gap Gp is small, the ignitability of the air-fuel mixture can be improved by executing the ignitability improvement control. In addition, this makes it possible to set the initial gap Gps to be smaller than in the prior art while ensuring the ignitability of the air-fuel mixture. As a result, the time when the ignition required voltage Vr becomes excessively high due to the increase of the ignition gap Gp can be postponed further than before.

  Further, even if the ignition gap Gp increases and the required ignition voltage Vr increases, the required ignition voltage Vr can be suitably reduced by executing the required voltage reduction control in this embodiment. Thereby, the durability of the spark plug can be further improved. Accordingly, the service life of the spark plug can be further extended, and the travelable distance of the vehicle until the spark plug needs to be replaced can be further increased. Therefore, the satisfaction of the user who uses the spark plug 11 can be improved, and the commercial value of the spark plug 11 can be further increased.

When attention is paid to the engine load TQ of the internal combustion engine 1 when performing the ignition performance improvement control or the required voltage reduction control in this embodiment, the fuel injection amount Qf is originally small during the low load operation of the internal combustion engine 1, and therefore mixing is performed. Qi ignitability is more likely to deteriorate. Further, since the in-cylinder pressure becomes higher during high load operation of the internal combustion engine 1, the ignition request voltage Vr tends to become higher. Therefore, the ignitability improvement control may be executed only during the low load operation of the internal combustion engine 1, and the required voltage reduction control may be executed only during the high load operation of the internal combustion engine 1.

  3 illustrates the relationship between the ignition gap Gp and the compression injection ratio Rq when the ignition performance improvement control is performed, but the lower the engine load TQ of the internal combustion engine 1 when the compression injection ratio Rq is controlled, You may control so that compression injection ratio Rq may become larger. In this case, the ignitability of the air-fuel mixture becomes worse as the fuel injection amount Qf decreases. Further, when the compression injection ratio Rq is controlled according to the ignition gap Gp, an upper limit value of the compression injection ratio Rq may be set in advance.

  4 illustrates the relationship between the ignition gap Gp and the compression injection ratio Rq when the required voltage reduction control is performed, but the engine load TQ or the supercharging pressure of the internal combustion engine 1 when controlling the compression injection ratio Rq. It may be controlled so that the compression injection ratio Rq becomes larger as the value becomes higher. In this case, the increase in the required ignition voltage Vr becomes more remarkable as the in-cylinder pressure increases. Similarly to the above, when the compression injection ratio Rq is controlled according to the ignition gap Gp, an upper limit value of the compression injection ratio Rq may be set in advance.

  3 and 4, the compression injection ratio Rq is continuously changed according to the ignition gap Gp, but the present invention is not limited to this. For example, of course, the compression injection ratio Rq may be changed stepwise according to the ignition gap Gp.

Next, a second embodiment of the present invention will be described. The internal combustion engine 1 and its intake / exhaust system in this embodiment are the same as those shown in FIG. Here, when the compression injection ratio Rq is increased with respect to the reference compression injection ratio Rqb during the above-described ignitability improvement control and required voltage reduction control, the vicinity of the spark plug 11 becomes excessively fuel-rich and combustion fluctuations occur. May occur. The engine load TQ may decrease due to this combustion fluctuation. Therefore, in this embodiment, when the compression injection ratio Rq is increased in accordance with the ignition gap Gp, supercharging pressure increase control is performed to increase the supercharging pressure so that the engine load decrease amount ΔTQd becomes zero. Therefore, the reduction in engine load TQ is suppressed.

  FIG. 6 shows an increase amount ΔRq of the compression injection ratio Rq with respect to the reference compression injection ratio Rqb (hereinafter referred to as “compression injection ratio increase amount”) ΔRq and a target boost pressure increase amount ΔPit in the supercharging pressure increase control of the present embodiment. It is a map which shows a relationship. This map is obtained in advance by experiments or the like and stored in the ECU 20. Here, as the compression injection ratio increase amount ΔRq is larger, the rich degree in the vicinity of the spark plug 11 is further increased, so that the engine load decrease amount ΔTQd is increased. Therefore, in this embodiment, the target boost pressure increase amount ΔPit is set to a larger value as the compression injection ratio increase amount ΔRq is larger as shown in the figure.

  When the ignitability improvement control or the required voltage reduction control is performed, the ECU 20 substitutes the compression injection ratio increase amount ΔRq into the map to derive the target boost pressure increase amount ΔPit and outputs the pressure sensor 15. The current supercharging pressure Pi is detected from the value. Then, the boost pressure increase control is performed by controlling the VN opening to the closed side so that the detected boost pressure Pi is increased by the target boost pressure increase amount ΔPit. In this embodiment, the ECU 20 that executes the boost pressure increase control corresponds to the boost pressure control means in the present invention.

As described above, according to the supercharging pressure increase control according to the present embodiment, it is possible to reliably suppress the engine load TQ from decreasing when the compression injection ratio Rq is increased according to the ignition gap Gp. Further, the decrease in the engine load TQ accompanying the increase in the compression injection ratio Rq is more likely to occur during the high load operation of the internal combustion engine 1 where the fuel injection amount Qf increases. Therefore, when the boost pressure increase control in the present embodiment is performed at the time of high load operation of the internal combustion engine 1, the operation effect can be exhibited more remarkably.

  Next, the required voltage reduction control when the above-described supercharging pressure increase control is performed will be described. Here, when the supercharging pressure increase control is performed, the density of the air-fuel mixture that insulates the electrodes of the spark plug 11 is further increased as compared with the case where the supercharging pressure increase control is not performed, so that the ignition request voltage Vr increases. It will be. Therefore, if the boost pressure increase control is performed when the required voltage reduction control described in the first embodiment is performed, the amount of decrease in the ignition request voltage Vr may be insufficient.

  Here, FIG. 7 shows the amount of decrease in the ignition request voltage (hereinafter simply referred to as “voltage decrease”) caused by the increase in the compression injection ratio increase amount ΔRq when the required voltage reduction control and the supercharging pressure increase control in the present embodiment are performed. FIG. 4 is a diagram showing ΔVrd (shown as L1) ΔVrd (referred to as “amount”) and an increase amount (hereinafter simply referred to as “voltage increase amount”) ΔVru of ignition request voltage Vr caused by supercharging pressure increase control.

  Here, the voltage decrease amount ΔVrd and the voltage increase amount ΔVru mean a decrease amount and an increase amount when the reference ignition request voltage Vrb, which is the value of the ignition request voltage Vr when the required voltage reduction control is not performed, is used as a reference. . In this embodiment, the voltage drop amount ΔVrd corresponds to the required voltage drop amount resulting from the increase in the compression injection ratio in the present invention, and the voltage rise amount ΔVru corresponds to the required voltage rise amount resulting from the boost pressure increase control. To do.

  As shown in the figure, the voltage drop amount ΔVrd and the voltage rise amount ΔVru both increase as the compression injection ratio increase amount ΔRq increases, but the slope at which the voltage drop amount ΔVrd changes and the slope at which the voltage rise amount ΔVru changes. It is not constant, and the slope changes according to the compression injection ratio increase amount ΔRq. That is, in the region where the compression injection ratio increase amount ΔRq is relatively small, the slope at which the voltage decrease amount ΔVrd changes is larger than the slope at which the voltage increase amount ΔVru changes, and the compression injection ratio increase amount ΔRq is in a region where the compression injection ratio increase amount ΔRq is relatively large. The transition reverses the relationship between the two.

  Here, when the voltage increase amount ΔVru (L2) is inverted with respect to the reference ignition request voltage Vrb and illustrated in L3, the ignition request voltage Vr substantially increased by increasing the compression injection ratio increase amount ΔRq in the required voltage reduction control. The amount of decrease (hereinafter, “total voltage decrease amount”) ΔVrda is equal to the difference between L1 and L3, that is, the value obtained by subtracting the voltage increase amount ΔVru from the voltage decrease amount ΔVrd.

  Therefore, in the required voltage reduction control in the present embodiment, the voltage increase amount ΔVru caused by the supercharging pressure increase control is taken into consideration, and the compression injection ratio increase amount ΔRq is determined based on the total voltage decrease amount ΔVrda.

  Here, FIG. 8 is a map showing the relationship between the ignition gap Gp and the target voltage drop amount ΔVrdt in the present embodiment. FIG. 9 is a map showing the relationship between the compression injection ratio increase amount ΔRq and the total voltage decrease amount ΔVrda in the present embodiment. These maps are obtained in advance by experiments or the like and stored in the ECU 20. Here, the target voltage drop amount ΔVrdt is a target value of the total voltage drop amount ΔVrda set when the required voltage reduction control is performed. The target voltage drop amount ΔVrdt may be set by adding a predetermined margin to the difference between the reference ignition request voltage Vrb and the applied voltage Vc.

In the present embodiment, referring to the map of FIG. 8, the target voltage decrease amount ΔVrdt is set to zero when the ignition gap Gp is smaller than the second reference gap Gpb2. When the ignition gap Gp is equal to or greater than the second reference gap Gpb2, the target voltage decrease amount ΔVrdt is set to a larger value as the ignition gap Gp is larger. Here, in this embodiment, the ECU 20 that sets the target voltage drop amount ΔVrdt corresponds to the target voltage drop amount setting means in the present invention.

  Then, the ECU 20 substitutes the target voltage decrease amount ΔVrdt set based on the map of FIG. 8 into the map of FIG. 9 to obtain the target value ΔRqt of the compression injection ratio increase amount. That is, the target value ΔRqt of the compression injection ratio increase amount is determined so that the total voltage decrease amount ΔVrda becomes equal to the target voltage decrease amount ΔVrdt. Then, the target value Rqt of the compression injection ratio is determined based on the target value ΔRqt of the increase amount of the compression injection ratio and the reference compression injection ratio Rqb described above. In this embodiment, the target value Rqt of the compression injection ratio corresponds to the target compression injection ratio in the present invention, and the ECU 20 that determines the target value Rqt of the compression injection ratio based on the maps of FIGS. It corresponds to a determination means.

  According to the required voltage reduction control in the present embodiment, the target value Rqt of the compression injection ratio is determined in consideration of the voltage increase amount ΔVru resulting from the supercharging pressure increase control. As a contradiction to suppress, it is possible to suitably suppress the decrease amount of the ignition request voltage Vr from being insufficient with respect to the target voltage decrease amount ΔVrdt.

  Next, the setting of the initial gap Gps in the present embodiment will be described. As described with reference to FIG. 7, in the region where the compression injection ratio increase amount ΔRq is relatively small, the slope at which the voltage decrease amount ΔVrd changes is larger than the slope at which the voltage increase amount ΔVru changes, but the compression injection ratio increase amount ΔRq. The relationship between the two is reversed as the value increases. Therefore, as shown in FIG. 9, the total voltage drop amount ΔVrda has a maximum value (hereinafter referred to as “limit voltage drop amount”) ΔVrdamax, and the total voltage drop amount ΔVrda has reached the limit voltage drop amount ΔVrdamax. After that, it gradually gets smaller.

  On the other hand, in general, a service life (for example, service life) is set for the spark plug 11, and in order to increase the commercial value of the spark plug 11, a longer service life is required. In order to ensure the function of the spark plug 11 over the lifetime of the spark plug 11, it is important that the target voltage drop amount ΔVrdt does not exceed the limit voltage drop amount ΔVrdamax during the lifetime. Therefore, in this embodiment, the initial gap Gps of the spark plug 11 is set so that the target voltage drop amount ΔVrdt is maintained below the limit voltage drop amount ΔVrdamax over the lifetime.

  In the present embodiment, in view of the fact that the target voltage decrease amount ΔVrdt increases as the ignition gap Gp increases, the ignition gap Gp when the target voltage decrease amount ΔVrdt becomes the limit voltage decrease amount ΔVrdamax is determined as the lifetime of the spark plug 11. The ignition gap at the end (hereinafter referred to as “end-of-life gap”) Gpe (shown in FIG. 9) was set.

  In addition, the wear amount of the electrode that wears during the service life is obtained in advance by experiments or the like, and the guaranteed gap increase amount ΔGp, which is the increase amount of the ignition gap corresponding to the wear amount, is obtained. In this embodiment, the initial gap Gps is set by subtracting the guaranteed gap increase amount ΔGp from the end-of-life gap Gpe. In this embodiment, the guaranteed gap increase amount ΔGp corresponds to a predetermined reference value in the present invention.

By setting the initial gap Gps in this manner, the target voltage drop amount ΔVrdt can be maintained below the limit voltage drop amount ΔVrdamax over the life of the spark plug 11. For example, when the service life of the spark plug 11 is set to be long, the guaranteed gap increase amount ΔGp is increased and the initial gap Gps is decreased. Even in this case, by executing the above-described ignitability improvement control, the ignitability of the air-fuel mixture can be improved even when the ignition gap Gp is at the initial gap Gps. According to this, it is possible to make the service life as long as possible while suitably suppressing deterioration of the ignitability of the air-fuel mixture and excessive increase in the ignition request voltage Vr during the service life of the spark plug 11. It becomes.

1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system in Embodiment 1. FIG. It is a figure which shows schematic structure of the ignition plug in Example 1. FIG. It is a figure which shows the relationship between the ignition gap Gp and the compression injection ratio Rq in the ignitability improvement control of Example 1. FIG. It is a figure which shows the relationship between the ignition gap Gp and the compression injection ratio Rq in the required voltage reduction control of Example 1. FIG. 3 is a flowchart illustrating a control routine in the first embodiment. 6 is a map showing a relationship between a compression injection ratio increase amount ΔRq and a target boost pressure increase amount ΔPit in the supercharging pressure increase control of the second embodiment. It is a figure which shows voltage fall amount (DELTA) Vrd and voltage rise amount (DELTA) Vru when implementing required voltage reduction control and supercharging pressure increase control in Example 2. FIG. 6 is a map showing a relationship between an ignition gap Gp and a target voltage drop amount ΔVrdt in Example 2. 6 is a map showing a relationship between a compression injection ratio increase amount ΔRq and a total voltage decrease amount ΔVrda in Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 5 ... Combustion chamber 10 ... In-cylinder fuel injection valve 11 ... Spark plug 12 ... Intake passage 13 ... Exhaust passage 15 ... Pressure sensor 16 ... Accelerator opening Degree sensor 17, turbocharger 18, crank position sensor 19, ignition power source 20, ECU
21 .. Center electrode 22 .. Ground electrode

Claims (6)

In a control apparatus for a cylinder injection spark ignition internal combustion engine, which is provided in a combustion chamber of an internal combustion engine and includes an in-cylinder fuel injection valve and an ignition plug that are capable of executing an intake stroke injection in an intake stroke and a compression stroke injection in a compression stroke.
Compression injection ratio control means for controlling a compression injection ratio, which is a ratio of a fuel injection amount related to the compression stroke injection to a fuel injection amount related to the intake stroke injection, according to a change with time of an ignition gap in the spark plug; A control apparatus for an in-cylinder injection type spark ignition internal combustion engine.   The in-cylinder injection type according to claim 1, wherein the compression injection ratio control means increases the compression injection ratio as the ignition gap is smaller when the ignition gap is equal to or less than a predetermined first threshold value. Control device for a spark ignition internal combustion engine.   3. The in-cylinder according to claim 1, wherein the compression injection ratio control means increases the compression injection ratio as the ignition gap is larger when the ignition gap is equal to or larger than a predetermined second threshold value. A control device for an injection spark ignition internal combustion engine. A turbocharger with variable supercharging pressure;
Supercharging pressure control means for performing supercharging pressure increase control for increasing the supercharging pressure so that the amount of decrease in engine torque caused by the increase in the compression injection ratio becomes substantially zero;
The control apparatus for a direct injection spark ignition internal combustion engine according to any one of claims 1 to 3, further comprising: Target voltage decrease amount setting means for setting a target voltage decrease amount of the required voltage of the spark plug based on the ignition gap;
The target voltage decrease amount setting means sets a total voltage decrease amount obtained by subtracting the increase amount of the required voltage due to the boost pressure increase control from the decrease amount of the required voltage due to the increase in the compression injection ratio. Target compression injection ratio determining means for determining a target compression injection ratio of the compression injection ratio controlled by the compression injection ratio control means so as to be substantially equal to the target voltage drop amount;
The control apparatus for a cylinder injection spark ignition internal combustion engine according to claim 4, further comprising: The initial gap, which is an initial value of the ignition gap, is the target voltage drop when the ignition gap is increased by a predetermined reference value that guarantees durability of the spark plug with respect to the initial gap. 6. The control apparatus for a direct injection spark ignition internal combustion engine according to claim 5, wherein the controller is determined so as to be equal to or less than a limit voltage decrease amount which is a maximum value of the decrease amount.

Images