JP5988287B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for controlling an internal combustion engine that causes a low temperature oxidation reaction (LTO) to occur in a fuel in an air-fuel mixture filled in a cylinder.

  By setting the atmosphere in the combustion chamber of the cylinder to a certain pressure and temperature zone during the period from the end of the compression stroke to the initial stage of the expansion stroke that ignites the air-fuel mixture, the fuel in the air-fuel mixture is easily burned by a low-temperature oxidation reaction. There is known an internal combustion engine that is in a state (see, for example, Patent Document 1 below). In the low temperature oxidation reaction, intermediate products such as OH radicals are induced by an increase in the pressure and temperature of the gas mixture.

  Recently, an “active ignition” method has been attempted in which microwaves or high-frequency waves are radiated into the combustion chamber when the air-fuel mixture is ignited (see, for example, Patent Documents 2 and 3 below). According to the active ignition method, a microwave or high-frequency electric field is formed, and an intermediate product such as an OH radical is induced in the electric field, and a large flame nucleus is formed as a plasma grows to start flame propagation combustion. Is done.

  By the way, there are conditions for the low-temperature oxidation reaction, and a low-temperature oxidation reaction cannot be obtained under any operating conditions. In particular, when the engine speed is low, the intake air amount is low, or the intake air temperature is low, the low-temperature oxidation reaction may not occur in the combustion chamber. Torque falls. Therefore, there is a tendency that a torque step occurs due to the presence / absence of a low-temperature oxidation reaction (change in combustion state due to a low-temperature oxidation reaction) in a transient region such as acceleration or deceleration.

JP 2002-038991 A JP 2011-159477 A JP 2011-0664162 A

  The present invention has been made by paying attention to the above-mentioned problem for the first time, and an object thereof is to suppress fluctuations in the output torque of the engine due to the presence or absence of a low-temperature oxidation reaction.

The present invention controls an internal combustion engine that causes a low-temperature oxidation reaction to a fuel in an air-fuel mixture in a combustion chamber, and the internal combustion engine performs microwave radiation or formation of a high-frequency electric field in the combustion chamber. A generator or electric field generator is provided, and a microwave or a high frequency is applied to the center electrode of the spark plug so that a microwave is radiated from the center electrode to the combustion chamber or a high frequency electric field is formed in the space between the center electrode and the ground electrode. If a predetermined condition is assumed that a low-temperature oxidation reaction is not expected in the transition period from the compression stroke to the expansion stroke of a certain cycle executed in the cylinder, the expansion cycle of the same cycle just before ignition, or to generate a microwave or high frequency electric field at the same time the combustion chamber immediately after or ignition, compared with the case where the predetermined condition is not satisfied in the expansion stroke of the cycle Immediately before the ignition, to constitute a control apparatus for an internal combustion engine, characterized in that to increase the strength of the microwave or a high frequency electric field is generated at the same time the combustion chamber just after or ignition.

  That is, when a low-temperature oxidation reaction does not occur in a certain cycle, electromagnetic waves are radiated into the combustion chamber in the same cycle to promote combustion instead of the low-temperature oxidation reaction.

  According to the present invention, it is possible to suppress fluctuations in engine output torque caused by the presence or absence of a low-temperature oxidation reaction.

The figure which shows schematic structure of the internal combustion engine and electric field generator in one Embodiment of this invention. The circuit diagram of the spark ignition device in the embodiment. The timing which shows transition of each in-cylinder pressure at the time of normal combustion and unstable combustion in the same embodiment, ion current, and a microwave generation flag. The figure which shows schematic structure of the electric field generator as a modification of this invention. The figure explaining the specific structure of the electric field generator in the modification. The circuit diagram of the H bridge which is an element of the electric field generator in the modification.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. This internal combustion engine is of a direct injection type, and includes a plurality of cylinders 1 (one of which is shown in FIG. 1), an injector 10 that injects fuel into each cylinder 1, An intake passage 3 for supplying intake air to the cylinder 1, an exhaust passage 4 for discharging exhaust from each cylinder 1, an exhaust turbocharger 5 for supercharging intake air flowing through the intake passage 3, and an exhaust passage And an external EGR device 2 that recirculates EGR gas from 4 toward the intake passage 3.

  The internal combustion engine in the present embodiment burns the fuel component contained in the air-fuel mixture charged in the cylinder 1 by low-temperature oxidation reaction during the period from the end of the compression stroke in the cycle to the initial stage of the expansion stroke that ignites the air-fuel mixture. It is intended to make it easy. In the low-temperature oxidation reaction, by placing the air-fuel mixture at a certain pressure and temperature range, it promotes the generation of intermediate products such as OH radicals, and as a pre-stage that generates a hot flame with a clear exotherm, Or blue flame), and work by heat generation before ignition.

  A spark plug 13 is attached to the ceiling of the combustion chamber of the cylinder 1. FIG. 2 shows an electric circuit for spark ignition. The spark plug 13 receives spark voltage generated by the ignition coil 12 and causes spark discharge between the center electrode and the ground electrode. The ignition coil 12 is integrally incorporated in a coil case together with an igniter 11 that is a semiconductor switching element.

  When the igniter 11 receives an ignition signal i from an ECU (Electronic Control Unit) 0 that is a control device for the internal combustion engine, the igniter 11 is first ignited and a current flows to the primary side of the ignition coil 12, and at the ignition timing immediately thereafter. The igniter 11 is extinguished to interrupt this current. Then, a self-induction action occurs, and a high voltage is generated on the primary side. Since the primary side and the secondary side share the magnetic circuit and the magnetic flux, a higher induced voltage is generated on the secondary side. This high induction voltage is applied to the center electrode of the spark plug 13, and spark discharge occurs between the center electrode and the ground electrode.

  Moreover, in this embodiment, the microwave generator which is one of the electric field generators is attached. The microwave generator includes a magnetron 14 that uses a battery as a power source and a control circuit 15 that controls the magnetron 14. The microwave generator is electrically connected to the spark plug 13 via a waveguide, a coaxial cable, etc., and applies the microwave output from the magnetron 14 to the spark plug 13, and the cylinder 1 It is possible to radiate into the combustion chamber.

  The microwave generated by the magnetron 14 is applied substantially simultaneously with the start of the spark discharge, immediately before the start of the spark discharge or immediately after the start of the spark discharge. The microwave generated by the magnetron 14 and the high induced voltage generated by the ignition coil 12 can be superimposed and applied to the center electrode of the spark plug 13.

  The intake passage 3 takes in air from the outside and guides it to the intake port of the cylinder 1. On the intake passage 3, an air cleaner 31, a compressor 51 of the supercharger 5, an intercooler 32, an electronic throttle valve 33, a surge tank 34, and an intake manifold 35 are arranged in this order from the upstream side.

  The exhaust passage 4 guides the exhaust generated by burning the fuel in the cylinder 1 from the exhaust port of the cylinder 1 to the outside. An exhaust manifold 42, a drive turbine 52 for the supercharger 5, and a three-way catalyst 41 are disposed on the exhaust passage 4. In addition, an exhaust bypass passage 43 that bypasses the turbine 52 and a waste gate valve 44 that is a bypass valve that opens and closes the inlet of the bypass passage 43 are provided. The waste gate valve 44 is an electric waste gate valve that can be opened and closed by inputting a control signal l to the actuator, and a DC servo motor is used as the actuator.

  The exhaust turbocharger 5 is configured such that the drive turbine 52 and the compressor 51 are connected and linked in a coaxial manner. Then, the driving turbine 52 is rotationally driven by using the energy of the exhaust gas, and the compressor 51 is pumped by using the rotational force, whereby the intake air is pressurized and compressed (supercharged) and sent to the cylinder 1.

  The external EGR device 2 realizes a so-called high-pressure loop EGR. The inlet of the external EGR passage is connected to a predetermined location upstream of the turbine 52 in the exhaust passage 4. The outlet of the external EGR passage is connected to a predetermined location downstream of the throttle valve 33 in the intake passage 3, specifically to a surge tank 34. An EGR cooler 21 and an EGR valve 22 are also provided on the external EGR passage.

  The ECU 0 is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor for detecting the vehicle speed, an engine rotation signal b output from an engine rotation sensor for detecting the rotation angle and engine speed of the crankshaft, an accelerator pedal depression amount or a throttle. An accelerator opening signal c output from an accelerator opening sensor that detects the opening of the valve 33 as an accelerator opening (so-called required load), and a temperature for detecting the intake air temperature in the intake passage 3 (particularly, the surge tank 34). An intake air temperature signal d output from the sensor, an intake air pressure signal e output from a pressure sensor that detects the intake pressure (or supercharging pressure) in the intake passage 3 (particularly, the surge tank 34), and the cooling water temperature of the internal combustion engine The cooling water temperature signal f output from the water temperature sensor for detecting the air temperature is output from the cam angle sensor at a plurality of cam angles of the intake camshaft. Cam signal g, the ion current signal h or the like to be output from the detection circuit for detecting an ion current caused by the combustion of the product and the gas mixture of the plasma in the combustion chamber are inputted. The engine rotation sensor generates a pulse signal b every 10 ° CA (crank angle). The cam angle sensor generates a pulse signal g at an angle obtained by dividing 720 ° CA by the number of cylinders, or every 240 ° CA for a three-cylinder engine. The ion current detection circuit according to the present embodiment uses an ion current flowing through the ignition plug 13 in a secondary circuit of the ignition coil 12 (for example, a secondary winding of the ignition coil 12 or a microwave generator is connected to the ignition plug 12). 13) (as a secondary voltage generated at the connecting end connected to 13).

  From the output interface, an ignition signal i for the igniter 11, a microwave generation command signal j for the control circuit 15 of the magnetron 14, an opening operation signal k for the throttle valve 33, and an opening operation signal k for the waste gate valve 44. Degree operation signal l, an opening degree operation signal m to the EGR valve 22, a fuel injection signal n to the injector 10, and the like.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, and h necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and is filled in the cylinder 1. Estimate the intake volume. Based on the engine speed and the intake air amount, the required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, ignition timing, Various operation parameters such as whether to generate a wave electric field, an EGR amount (or EGR rate), and an opening degree of the EGR valve 22 are determined. As the operation parameter determination method itself, a known method can be adopted, and the description thereof will be omitted. The ECU 0 applies various control signals i, j, k, l, m, and n corresponding to the operation parameters via the output interface.

  Therefore, in the present embodiment, when a predetermined condition that the low temperature oxidation reaction is assumed not to occur in the combustion chamber of the cylinder 1 is satisfied, a microwave electric field is generated in the combustion chamber, and combustion is performed instead of the low temperature oxidation reaction. To promote.

  The low-temperature oxidation reaction does not occur unless the pressure (in-cylinder pressure) and temperature (in-cylinder temperature) of the air-fuel mixture are higher than a certain level at the end of the compression stroke and in the vicinity of the compression top dead center. Therefore, it can be said that the low-temperature oxidation reaction hardly occurs when the engine speed is low, the intake air amount is small (engine load is small), the intake air temperature is low, or the like.

  The ECU 0 performs an intake air amount (fresh air amount and / or EGR gas amount), intake air temperature, etc. at each cycle (intake-compression-expansion-exhaust cycle in a 4-stroke engine) executed in each cylinder 1. Referring to Fig. 4, an estimated value of the pressure and temperature of the air-fuel mixture before ignition near the compression top dead center, that is, before ignition, is obtained. The estimated values of the pressure and temperature of the air-fuel mixture may be calculated by substituting the intake air amount and the intake air temperature into a predetermined function formula, or the estimated air pressure and temperature of the air-fuel mixture and the pressure and temperature of the air-fuel mixture. When map data defining the relationship with values is stored in the memory in advance, the map data may be searched for and acquired. Further, corrections based on the outside air temperature, the cooling water temperature of the engine, or the like may be added to the estimated values of the pressure and temperature of the air-fuel mixture.

  Then, the ECU 0 makes a determination as to whether or not a low-temperature oxidation reaction occurs in the fuel in the mixture in the combustion chamber of the cylinder 1 based on the estimated values of the pressure and temperature of the mixture. FIG. 3 illustrates the relationship between the estimated values of the pressure and temperature of the air-fuel mixture and the estimation of whether or not the low-temperature oxidation reaction has occurred.

  In addition to this, when the engine speed falls below the threshold, the intake air amount (or engine load) falls below the threshold, and the intake air temperature falls below the threshold, it is assumed that the low temperature oxidation reaction does not occur. It doesn't matter.

  When the ECU 0 estimates that a low-temperature oxidation reaction does not occur in a certain cycle (transitional period from the compression stroke to the expansion stroke) executed in the cylinder 1, the spark immediately before the ignition in the expansion stroke of the same cycle, that is, the spark ignition, Immediately after ignition or simultaneously with spark ignition, a microwave is applied to the ignition plug 13 from the microwave generator, and control is performed to radiate the microwave from the center electrode into the combustion chamber.

  Alternatively, if microwaves are radiated into the combustion chamber during the expansion stroke regardless of whether or not a low-temperature oxidation reaction occurs, the intensity of the microwave radiated into the combustion chamber when it is assumed that a low-temperature oxidation reaction does not occur It is set higher than the intensity of microwaves emitted when it is assumed that an oxidation reaction will occur.

  By such control, plasma is induced under the microwave electric field in the combustion chamber to enhance the flame, and / or the air-fuel mixture is heated under the microwave electric field in the combustion chamber. Can be made.

  In the present embodiment, the internal combustion engine that causes a low-temperature oxidation reaction to occur in the fuel in the air-fuel mixture in the combustion chamber of the cylinder 1 is satisfied, and a predetermined condition presumed that the low-temperature oxidation reaction does not occur is satisfied. In addition, the control device 0 is configured to perform control for generating a microwave electric field in the combustion chamber or increasing the intensity of the microwave electric field generated in the combustion chamber as compared with the case where the predetermined condition is not satisfied.

  According to the present embodiment, combustion can be promoted in place of the low temperature oxidation reaction even under an operating condition in which the low temperature oxidation reaction does not occur. Therefore, it is possible to suppress fluctuations in the engine output torque due to the presence or absence of the low-temperature oxidation reaction, and to improve the robust performance of the engine operation control, increase the engine output torque, and improve the fuel consumption.

  The present invention is not limited to the embodiment described in detail above.

  The electric field generator that generates an electric field in the combustion chamber for the purpose of generating plasma in the combustion chamber and / or heating the air-fuel mixture in the combustion chamber is not limited to the microwave generator. In other words, instead of radiating microwaves into the combustion chamber, high frequencies may be radiated.

  As an electric field generator other than the microwave generator, an AC voltage generator circuit that applies a high-frequency AC voltage, a pulsating voltage generator circuit that applies a high-frequency pulsating voltage, or the like can be employed. The pulsating voltage generation circuit may be any circuit that generates a DC voltage whose voltage periodically changes, and its waveform may be arbitrary. The pulsating voltage includes a pulse voltage that varies from a reference voltage (which may be 0V) to a constant voltage in a constant cycle, a voltage obtained by half-wave rectifying an AC voltage, a voltage obtained by adding a DC bias to the AC voltage, and the like. The high-frequency voltage oscillated by the electric field generator preferably has a frequency of about 200 kHz to 1000 kHz and an amplitude of about 3 kVp-p to 10 kVp-p.

  As shown in FIGS. 4 to 6, the electric field generator for generating a high frequency includes a circuit that uses a battery as a power source and converts low-voltage direct current into high-voltage alternating current. Specifically, a DC-DC converter 61 that boosts the battery 6 voltage of about 12V to 300V to 500V, an H bridge circuit 62 that converts direct current output from the DC-DC converter 61 into alternating current, and an H bridge circuit 62 are provided. The boosting transformer 63 that boosts the output alternating current to a higher voltage is used as an element.

  A first diode 64 and a second diode 65 are preferably provided at the output end of the electric field generator. The first diode 64 has a cathode connected to the signal line of the secondary winding of the step-up transformer 63 and an anode connected to a mixer 66 that is a node with the ignition coil 12. The second diode 65 has an anode connected to the ground line of the secondary winding of the step-up transformer 63 and a cathode grounded. The first diode 64 and the second diode 65 play a role of blocking the negative high voltage pulse current flowing from the secondary side of the ignition coil 12 at the ignition timing.

  The high-frequency voltage oscillated by the electric field generator is normally applied to the center electrode of the spark plug 13 almost simultaneously with the start of the spark discharge, immediately before the start of the spark discharge or immediately after the start of the spark discharge. As a result, a high-frequency electric field is formed in the space between the center electrode of the spark plug 13 and the ground electrode. Then, a plasma is generated by performing a spark discharge in a high-frequency electric field, and this plasma generates a large radical plasma flame nucleus that starts flame propagation combustion.

  In the above, the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge are vibrated and meandered by the influence of the electric field, resulting in a long path length and a dramatic increase in the number of collisions with surrounding water and nitrogen molecules. This is due to the 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 also ionized and changed to a plasma state. The ignition range for the air-fuel mixture increases and the flame kernel also increases. As a result, the two-dimensional ignition by only the spark discharge is amplified to the three-dimensional ignition, and the combustion rapidly propagates into the combustion chamber and expands at a high combustion speed.

  Whether or not a low temperature oxidation reaction occurs in the fuel in the air-fuel mixture in the combustion chamber of the cylinder 1 may be determined in consideration of the opening / closing timing of the intake valve and / or the exhaust valve by the variable valve timing mechanism. The opening / closing timing of the intake / exhaust valve affects the effective compression ratio. If the other conditions are the same, the higher the compression ratio, the easier the low-temperature oxidation reaction will occur, and the lower the compression ratio, the less likely the low-temperature oxidation reaction will occur. .

  If the internal combustion engine is provided with a variable compression ratio mechanism, it is desirable to estimate whether or not a low-temperature oxidation reaction has occurred, taking into account the compression ratio correctly. That is, if the compression ratio exceeds a threshold value (this threshold value may vary depending on the engine speed, required load, intake air amount, intake air temperature, etc.), it is presumed that a low temperature oxidation reaction will occur. I guess. Incidentally, as the variable compression ratio mechanism, the movable part including the cylinder block and the cylinder head is moved relative to the crankcase along the axial direction of the cylinder, or reciprocating in the cylinder by a multi-link piston-crank. An aspect in which the position of the top dead center is displaced along the axial direction of the cylinder by changing the stroke of the piston is known.

  In the above embodiment, the presence or absence of the low-temperature oxidation reaction is estimated by referring to the index such as the intake air amount and the intake air temperature. However, the pressure of the air-fuel mixture in the cylinder 1 during the period from the compression stroke to the expansion stroke is If actual measurement can be performed via the internal pressure sensor, it is possible to determine whether or not the low temperature oxidation reaction has occurred by referring to the transition of the actual measurement value of the pressure. The pressure of the air-fuel mixture before ignition (ignition) near the compression top dead center when the low temperature oxidation reaction does not occur is lower than that when the low temperature oxidation reaction occurs. Therefore, if the pressure of the air-fuel mixture before ignition near the compression top dead center exceeds a threshold value (this threshold value can vary depending on the engine speed, required load, intake air amount, intake air temperature, etc.), a low temperature oxidation reaction has occurred. If it falls below, it can be judged that the low temperature oxidation reaction did not occur.

  Further, the pressure of the air-fuel mixture in the cylinder 1 from the end of the compression stroke to the early stage of the expansion stroke is predicted based on the intake air amount, the intake air temperature, the outside air temperature, the engine coolant temperature, the engine speed, etc. in the cycle. Although it can be estimated, whether or not a low-temperature oxidation reaction has occurred can be estimated from the difference between this and the actually measured pressure of the air-fuel mixture. When the deviation is large, there is a low temperature oxidation reaction, and when the deviation is small, there is no low temperature oxidation reaction.

  Although the internal combustion engine in the above embodiment is a spark ignition internal combustion engine (gasoline engine), it is naturally allowed to apply the present invention to a compression ignition internal combustion engine (diesel engine).

  Other specific configurations of each part can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to an internal combustion engine mounted on a vehicle or the like.

0 ... Control unit (ECU)
DESCRIPTION OF SYMBOLS 1 ... Cylinder 13 ... Spark plug 14, 15 ... Electric field generator 61, 62, 63 ... Electric field generator

Claims (1)

Controlling an internal combustion engine that causes a low-temperature oxidation reaction to the fuel in the air-fuel mixture in the combustion chamber,
An internal combustion engine is equipped with a microwave generator or an electric field generator for generating microwave radiation or a high-frequency electric field in a combustion chamber, and combustion occurs from the center electrode by applying the microwave or high-frequency to the center electrode of the spark plug. A microwave is radiated to the chamber or a high frequency electric field is formed in a space between the center electrode and the ground electrode,
If a predetermined condition is assumed that a low-temperature oxidation reaction does not occur in the transition period from the compression stroke to the expansion stroke executed in a cylinder , immediately before, immediately after, or ignition in the expansion stroke of the same cycle At the same time , a microwave or a high-frequency electric field is generated in the combustion chamber, or a microwave generated in the combustion chamber immediately before, immediately after, or simultaneously with the ignition in the expansion stroke of the same cycle as compared with the case where the predetermined condition is not satisfied. Or the control apparatus of the internal combustion engine characterized by raising the intensity | strength of a high frequency electric field.

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