JP5000622B2 - Control method for spark ignition internal combustion engine - Google Patents

Description

  The present invention relates to a method for controlling a spark ignition internal combustion engine mounted on a vehicle, particularly an automobile.

  In a spark-ignition internal combustion engine, an ignition plug is used to spark discharge the spark plug without applying a higher voltage than before, to reliably ignite the air-fuel mixture in the combustion chamber and to obtain a stable flame. Is controlled to expand the ignitable region of the air-fuel mixture by generating plasma in the discharge region around the center electrode of the electrode and performing arc discharge in the plasma atmosphere in the discharge region (for example, Patent Document 1). ).

By the way, conventionally, in an internal combustion engine, that is, an engine, it has been required to reduce the exhaust gas restriction substance contained in the exhaust gas of the automobile, and the exhaust gas restriction substance is reduced by utilizing the purification action by the air-fuel ratio control and the catalyst. Reduced. However, the effect of the catalyst is effective after the temperature of the catalyst reaches a certain level and the catalyst is activated. When the catalyst is cold immediately after starting the engine, the exhaust emission control substance is discharged as it is. End up. In order to solve such problems, control of an internal combustion engine that activates the catalyst early by accelerating the temperature rise of the catalyst by retarding the ignition timing than usual immediately after starting and increasing the exhaust gas temperature. Is known (for example, Patent Document 2).
JP 2007-032349 A JP 2008-180184 A

  By the way, in the former mentioned above, when performing the arc discharge to a plasma atmosphere and igniting the air-fuel mixture in the combustion chamber, since the combustion is improved by the plasma atmosphere, an ignition method in which the exhaust gas temperature does not use plasma. Low compared to the engine. For this reason, for example, at the time of cold start such as winter, it takes a long time to reach a temperature at which the catalyst functions, resulting in inadequate purification of exhaust gas.

  Accordingly, the present invention focuses on the above-described problems, and in a spark ignition type internal combustion engine that can improve combustion by reacting plasma and spark ignition, sparks are activated so as to activate the catalyst at an early stage. It aims at controlling an ignition type internal combustion engine.

  In a control method for an internal combustion engine according to the present invention made to solve the above problems, a spark ignition internal combustion engine comprising a spark plug for generating a spark by discharge in a combustion chamber and a catalyst for purifying exhaust gas. In this case, the gas mixture is ignited in the absence of plasma in the combustion chamber by spark discharge from the spark plug until the catalyst is activated, and after the catalyst is activated, the plasma generated in the combustion chamber reacts with the spark. The mixture was ignited.

  That is, until the catalyst is activated, spark ignition is performed in the absence of plasma, and the internal combustion engine is controlled so that priority is given to an increase in exhaust gas temperature over improvement in combustion by plasma. If it is such, the temperature rise of a catalyst will be accelerated | stimulated by the raise of exhaust gas temperature, and a catalyst will be activated early. In addition, after the catalyst is activated, by controlling the spark generated by the discharge in the combustion chamber and the plasma in the combustion chamber to react and ignite the air-fuel mixture, compared to spark ignition using only the spark plug. Thus, the combustion temperature can be increased to accelerate the activation of the catalyst.

  According to the present invention, by igniting the air-fuel mixture only by spark discharge, the combustion temperature is increased compared with the case where the air-fuel mixture is ignited by reacting plasma and spark discharge, and the activity of the catalyst is increased. The exhaust gas can be accelerated and the exhaust gas can be purified at an early stage even during cold start.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

An engine 100 schematically showing the configuration of one cylinder in FIG. 1 is a three-cylinder for an automobile. The intake system 1 of the engine 100 is provided with a throttle valve 2 that opens and closes in response to an accelerator pedal (not shown), and a surge tank 3 is provided downstream of the throttle valve 2. A fuel injection valve 5 is further provided in the vicinity of the end on the cylinder head 4 side where the surge tank 3 communicates, and the fuel injection valve 5 is controlled by the electronic control unit 6. An ignition plug 8 and an antenna 9 for generating plasma are attached to the ceiling portion of the combustion chamber 7. The antenna 9 in this embodiment is a horn type antenna and is attached to a position near the spark plug 8 on the ceiling of the combustion chamber 7. An ignition coil 10 that is integrally provided with an igniter is attached to the ignition plug 8 in a replaceable manner. The antenna 9 has a horn shape, and a tip portion facing the combustion chamber 7 is closed by a dielectric 27 such as ceramics, and is connected to a high voltage AC generator 11 via a waveguide (not shown). Yes. In the exhaust system 12, a three-way catalyst (hereinafter referred to as catalyst 13) is disposed in a pipe line leading to a muffler (not shown), and an O ₂ sensor 14 is attached upstream thereof.

  The high-voltage AC generator 11 includes a magnetron 15 and a control circuit 16 that controls the magnetron 15. The microwave output from the magnetron 15 is applied to the antenna 9 through a waveguide. Further, the control circuit 16 is configured to receive the high-voltage AC generation signal n output from the electronic control unit 6, and the control circuit 16 is configured to output the microtron output from the magnetron 15 based on the input high-voltage AC generation signal n. It controls the wave output timing and output power.

  The electronic control unit 6 is mainly configured by a microcomputer system including a central processing unit 18, a storage device 19, an input interface 20, and an output interface 21. The central processing unit 18 controls the operation of the engine 100 by executing a program described later stored in the storage device 19.

Information necessary for controlling the operation of the engine 100 is input to the central processing unit 18 via the input interface 20, and the central processing unit 18 sends a control signal to the fuel via the output interface 21. Output to the injection valve 5 or the like. Specifically, the input interface 20 includes an intake pressure signal a output from an intake pressure sensor 22 for detecting the pressure of intake air in the surge tank 3, and a rotation speed sensor 23 for detecting the engine speed. , An engine speed signal b output from the idle switch 24 for detecting the open / closed state of the throttle valve 2, and a water temperature signal output from the water temperature sensor 25 for detecting the cooling water temperature of the engine 100. d, an intake air temperature signal e output from the intake air temperature sensor 26 for detecting the temperature of fresh air taken in by the engine 100, and an oxygen concentration in the exhaust gas discharged from the combustion chamber 7 through the exhaust valve. The voltage signal g output from the O ₂ sensor 14 is input. On the other hand, the output interface 21 outputs a fuel injection signal p to the fuel injection valve 5, an ignition signal m to the igniter, a high-voltage AC generation signal n to the high-voltage AC generator 11, and the like. Yes.

  The electronic control device 6 uses the intake pressure signal “a” output from the intake pressure sensor 22 and the rotation speed signal “b” output from the rotation speed sensor 23 as main information, and is determined according to various operating conditions of the engine 100. The basic injection time is corrected by the correction coefficient to determine the opening time of the fuel injection valve 5, that is, the final energization time of the injector, and the fuel injection valve 5 is controlled by the determined energization time so that the fuel corresponding to the engine load is supplied. A program for injecting fuel into the intake system 1 from the fuel injection valve 5 is incorporated.

  In the engine 100, in the normal operation state after warming up, the microwave generated by the high-voltage AC generator 11 is radiated from the antenna 9 into the combustion chamber 7 in accordance with the output timing controlled by the control circuit 16, The plasma generated thereby reacts with the spark discharge generated by the spark plug 8 to ignite the air-fuel mixture. When plasma is generated, microwaves are applied to the antenna 9, whereby a high-frequency electric field is formed in the combustion chamber 7 in a direction perpendicular to the spark discharge by the spark plug 8.

  Thus, upon ignition, a spark discharge is generated in the spark plug 8 by the ignition coil 10, and a high-frequency electric field is generated by microwaves almost simultaneously with or immediately after the spark discharge to generate plasma, thereby generating a combustion chamber. 7 is a configuration in which the air-fuel mixture in 7 is rapidly burned.

  Specifically, the spark discharge by the spark plug 8 becomes plasma in a high-frequency electric field, and the flame becomes large.

  This is because the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge oscillate and meander due to the influence of the high-frequency electric field, resulting in a longer path length and the number of collisions with surrounding water and nitrogen molecules. This is due to a dramatic increase. Water molecules and nitrogen molecules that have been struck by ions and radicals become OH radicals and N radicals, and the surrounding gas that has been struck by ions and radicals is ionized, in other words, a plasma state. The flame will increase dramatically.

  As a result, the air-fuel mixture is ignited by the spark discharge increased by reacting with the high-frequency electric field, so that the ignition region is expanded and the two-dimensional ignition of only the spark plug 8 is changed to the three-dimensional ignition. Therefore, the initial combustion is stabilized, the combustion rapidly propagates into the combustion chamber 7 with the increase of the radicals described above, and the combustion expands at a high combustion rate.

  On the other hand, at the time of start-up, as described below, the ignition plug 8 is ignited only by spark discharge and the ignition is performed by reacting plasma and spark discharge. Therefore, after the catalyst 13 is activated, the electronic control device 6 ignites the air-fuel mixture in the absence of plasma in the combustion chamber 7 by spark discharge by the spark plug 8 until the catalyst 13 is activated. Stores a control program for the engine 100 that ignites the air-fuel mixture by reacting the plasma generated in the combustion chamber 7 with sparks.

  Hereinafter, a schematic procedure for controlling the internal combustion engine 100 will be described with reference to a flowchart shown in FIG. The control program for the internal combustion engine 100 is executed for each ignition of each cylinder and when the engine 100 is idling after being started. Therefore, when the accelerator pedal is operated, that is, when the throttle valve 2 is opened, the processing ends.

  In step S1, the air-fuel mixture is ignited by spark discharge by the spark plug 8. Specifically, by outputting the ignition signal m from the output interface 21 to the igniter, a spark discharge is generated between the center electrode and the ground electrode of the spark plug 8 to ignite the air-fuel mixture. In this case, in order to raise the temperature of the catalyst 13 at an early stage, the ignition timing is retarded by a larger amount of the same retardation than the ignition timing, for example, when the ignition timing in the idle operation state is used as a reference. By retarding the ignition timing in this way, combustion continues to near the start timing of the exhaust stroke, and the temperature of the exhaust gas reaching the catalyst 13 becomes higher than when the ignition timing is advanced. Therefore, even when engine 100 is started when it is cold, the temperature of catalyst 13 can be raised to a temperature necessary for activation at an early stage.

  Next, in step S2, it is determined whether the catalyst 13 has been activated based on the elapsed time after startup. The elapsed time after start-up is set based on the time measured from start-up, that is, ignition on, and the outside air temperature, and is set longer as the outside air temperature is lower. The outside air temperature may be detected by the intake air temperature or the engine temperature (including the cooling water temperature and the lubricating oil temperature).

  If it determines with the catalyst 13 not having been activated in step S2, it will return to step S1.

  If it determines with the catalyst 13 having been activated in step S2, the plasma produced | generated in the combustion chamber 7 and a spark will react and an air-fuel mixture will be ignited (step S3). In step S <b> 3, a high-frequency AC generation signal n is output from the output interface 21 to the high-voltage AC generator 11, thereby generating a high-frequency electric field in the combustion chamber 7 via the antenna 9. This high-frequency electric field is generated perpendicular to the spark discharge, whereby plasma is generated in the peripheral region including the spark discharge portion of the spark plug 8.

  In such a configuration, in the combustion by only the spark discharge, the combustion temperature is higher than in the case of using plasma, so that the exhaust gas temperature rises and the catalyst 13 is heated. As a result, the temperature rise of the catalyst 13 is promoted, and the catalyst 13 is activated early. Thereby, the time until the temperature of the catalyst 13 becomes a constant temperature at which the action of the catalyst 13 becomes effective can be shortened, and the exhaust gas such as unburned hydrocarbons contained in the exhaust gas by the activated catalyst 13. The amount of gas-regulated substances can be reduced.

  After the catalyst 13 is activated, the spark discharge of the spark plug 8 reacts with the plasma to ignite the air-fuel mixture, so that the combustion can be improved, and the exhaust gas synergizes with the activation of the catalyst 13. Gas purification can be further promoted.

  The present invention is not limited to the above embodiment.

  In step S2 of the present embodiment, whether or not the catalyst has been activated is determined based on the elapsed time. However, the determination is made by estimating from the engine temperature, that is, the intake air temperature, the coolant temperature, the lubricating oil temperature, and the load. You may go. Further, when the exhaust temperature sensor 28 for measuring the exhaust gas temperature is provided on the downstream side of the catalyst 13, the catalyst temperature may be estimated using the exhaust temperature obtained by the exhaust temperature sensor 28. Good.

  In addition to the above-described magnetron, the high frequency generation source may be a traveling wave tube or the like, and may further include a semiconductor microwave oscillation circuit.

  Further, in this embodiment, a horn type antenna in which the tip facing the combustion chamber is covered with a dielectric is used as an antenna for generating plasma by microwaves. It may be made of a dielectric such as. Furthermore, instead of the horn type antenna, for example, a monopole antenna such as an inverted L-shaped antenna or a beam type antenna may be attached to the ceiling of the combustion chamber. In the case of using a monopole antenna or the like as the antenna in the present embodiment, considering the heat resistance of the tip portion facing the combustion chamber, the antenna is made highly heat-resistant such as tungsten, or It is conceivable to use the antenna by covering it with a dielectric.

  Furthermore, the center electrode of the spark plug may function as an antenna to form a high frequency power supply unit. In this case, if the high frequency is continuously applied to the center electrode at a constant voltage, the temperature of the center electrode rises excessively, so the high frequency voltage is set to be lower than the upper limit temperature set based on the heat resistance temperature of the center electrode. It is something to control.

  Other specific configurations of the respective parts are not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows schematic structure of one Embodiment of this invention. The flowchart which shows the outline of the control procedure of the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Engine 8 ... Spark plug 13 ... Catalyst

Claims (1)

In a spark ignition internal combustion engine comprising an ignition plug that generates sparks by discharge in a combustion chamber and a catalyst that purifies exhaust gas,
Until the catalyst is activated, spark discharge by the spark plug ignites the mixture without plasma in the combustion chamber,
A method for controlling a spark ignition internal combustion engine in which, after activation of a catalyst, plasma generated in a combustion chamber reacts with sparks to ignite an air-fuel mixture.

Images