JP2014088778A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable reliable ignition and combustion even when the air-fuel ratio of mixture is prominently lean or an EGR rate is high.SOLUTION: An internal combustion engine includes discharge means for generating corona discharge E in a combustion chamber of a cylinder, and electric field producing means for producing high-frequency electric fields or microwave electric fields near electrodes 121, 122 where the corona discharge E is generated by the discharge means. Interaction between the corona discharge E and the high-frequency electric fields or the microwave electric fields causes the ignition of mixture in the combustion chamber. The magnitude of a voltage to be applied to the electrodes for the corona discharge E to be generated by the discharge means is changed depending on the magnitude of a pressure in the cylinder at a timing for generating the corona discharge E.

Description

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

  In a spark ignition internal combustion engine that causes a spark discharge between the center electrode and the ground electrode of the spark plug to ignite the air-fuel mixture in the combustion chamber, a high-frequency oscillator is placed around these electrodes at the same time as the spark discharge. Attempts have been made to "active ignition" that emits high-frequency waves output from or microwaves output from magnetrons (see, for example, the following patent document). According to the active ignition method, a high-frequency or microwave electric field is formed in the space between the electrodes, and plasma generated in the electric field grows to generate a large flame nucleus that starts flame propagation combustion. As a result, stable combustion can be obtained.

  However, when the air-fuel ratio of the air-fuel mixture is remarkably lean, or when the EGR (Exhaust Gas Recirculation) rate is high, there is still a risk of misfire even if active ignition is performed. In the spark discharge, since only one passage of extremely fine charged particles that connects the center electrode and the ground electrode of the spark plug is formed, the initial fire type that ignites the air-fuel mixture is small. In addition, when the fuel component contained in the air-fuel mixture is small, the flame is lowered in temperature and the flame propagation speed is also reduced. Therefore, there is a possibility that the flame kernel may misfire at a small stage due to the temperature drop in the cylinder accompanying the movement (lowering) toward the bottom dead center of the piston in the expansion stroke.

JP 2011-0664162 A JP 2011-159477 A

  An object of the present invention is to ensure ignition and combustion even when the air-fuel ratio of the air-fuel mixture is remarkably lean or when the EGR rate is high.

  In order to solve the above-described problems, in the present invention, discharge means for generating corona discharge in the combustion chamber of a cylinder, and electric field generation means for generating a high-frequency electric field or a microwave electric field in the vicinity of an electrode where corona discharge is generated by the discharge means. An internal combustion engine that ignites an air-fuel mixture in a combustion chamber by interacting a corona discharge with a high-frequency electric field or a microwave electric field, and a voltage applied to an electrode by the discharge means to generate the corona discharge. An internal combustion engine in which the magnitude is changed according to the magnitude of the pressure in the cylinder at the timing of generating the corona discharge is configured.

  According to the present invention, it is possible to reliably ignite and burn even when the air-fuel ratio of the air-fuel mixture is remarkably lean or when the EGR rate is high.

The figure which shows schematic structure of the internal combustion engine in one Embodiment of this invention. The circuit diagram of the ignition device in the embodiment. The figure explaining the structure of the electric field generator in the embodiment. The circuit diagram of the H bridge which is an element of the electric field generator in the embodiment. The principal part side sectional view which expands and shows the electrode part of the ignition plug in the embodiment. The bottom view of the ignition plug in the embodiment. The principal part side sectional view which expands and shows the electrode part of the spark plug in the modification of this invention. The bottom view of the ignition plug 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. The internal combustion engine of the present embodiment is a four-stroke gasoline engine and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1.

  An intake passage 3 for supplying intake air to the cylinder 1 of the internal combustion engine takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for exhausting the exhaust from the cylinder 1 guides the exhaust generated as a result of burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

  An external EGR device 2 may be attached to the internal combustion engine. The external EGR device 2 shown in FIG. 1 realizes a so-called high-pressure loop EGR, and an EGR passage 21 that communicates the upstream side of the catalyst 41 in the exhaust passage 4 and the downstream side of the throttle valve 32 in the intake passage 3. The EGR cooler 22 provided on the EGR passage 21 and the EGR valve 23 that opens and closes the EGR passage 21 and controls the flow rate of the EGR gas flowing through the EGR passage 21 are used as elements. The inlet of the EGR passage 21 is connected to the exhaust manifold 42 in the exhaust passage 4 or a predetermined location downstream thereof. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, specifically to a surge tank 33.

  FIG. 2 shows an electric circuit of an ignition device for igniting the air-fuel mixture in the combustion chamber of the cylinder 1. The discharge means of this embodiment generates corona discharge in the combustion chamber. The discharging means includes an ignition coil 14, a capacitor 15, a semiconductor switching element 13, and a spark plug 12 as constituent elements.

  The ignition coil 14 is a set of a primary coil and a secondary coil that share a magnetic circuit and magnetic flux with each other. The capacitor 15 is supplied with electric power from a DC-DC converter 16 that uses an in-vehicle battery as a power source and boosts a DC low voltage of about 12 V provided by the battery to a high voltage of about 200 V, and stores electric charge. A high voltage charged in advance in the capacitor 15 is applied to the primary coil of the ignition coil 14 at the timing of ignition. Then, the current flowing through the primary coil suddenly increases, and a high-voltage induced voltage is induced in the secondary coil at that moment. The induced voltage is applied to the center electrode 121 of the spark plug 12. Energization from the capacitor 15 to the primary coil is performed via the semiconductor switching element 13 such as a thyristor or a power transistor.

  The spark plug 12 that has received the induction voltage from the secondary coil generates a corona discharge between the center electrode 121 and the ground electrode 122 in the combustion chamber of the cylinder 1. As shown in FIGS. 5 and 6, the center electrode 121 of the spark plug 12 of this embodiment is covered with an insulator (dielectric) 123 and is not exposed to the combustion chamber side facing the ground electrode 122. . Therefore, the discharge between the center electrode 121 and the ground electrode 122 becomes a barrier discharge. The ground electrode 122 has a cylindrical shape surrounding the center electrode 121 and the insulator 123. The tip (lower end) of the ground electrode 122 protrudes further forward (downward) than the tip of the center electrode 121 and is substantially flush with the tip of the insulator 123.

  The corona discharge is caused by an applied voltage lower than the spark discharge in the spark plug of the spark ignition type internal combustion engine. As schematically shown in FIG. 6, in the corona discharge, a plurality of paths E of charged particles that connect the center electrode 121 and the ground electrode 122 are formed. The ignition by the corona discharge can ignite the air-fuel mixture in a wider range as compared with the ignition by the spark discharge, and a plurality of fire types or a large-volume fire type can be generated in the combustion chamber.

  The electric field generating means of this embodiment generates a high frequency electric field in the vicinity of the electrodes 121 and 122 where corona discharge occurs. The electric field generating means includes the electric field generator 6 and the antenna 121 as constituent elements.

  The electric field generator 6 mainly includes an AC voltage generation circuit that applies a high-frequency AC voltage to the antenna 121. As shown in FIG. 3 and FIG. 4, the electric field generator 6 uses a vehicle-mounted battery as a power source and converts low-voltage direct current to high-voltage alternating current. The low-voltage direct current of about 12V provided by the battery is converted to a high voltage of 100V to 500V. A DC-DC converter 61 that boosts the current to DC, an H-bridge circuit 62 that converts direct current output from the DC-DC converter 61 into alternating current, and a boost transformer 63 that boosts the alternating current output from the H-bridge circuit 62 to a higher voltage. It is a component. Note that the DC-DC converter 61 may be common to the DC-DC converter 16.

  A first diode 64 and a second diode 65 are preferably provided at the output end of the electric field generator 6. 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 14. 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 14 at the ignition timing.

  The high-frequency voltage oscillated by the electric field generator 6 is applied to the antenna 121 that faces the combustion chamber of the cylinder 1 and radiates a high-frequency electric field into the combustion chamber. In the present embodiment, the center electrode 121 of the spark plug 12 is used as an antenna for electric field radiation. The high-frequency voltage is applied to the center electrode of the spark plug 12 at the same time as the start of the corona discharge by the spark plug 12, immediately before the start of the corona discharge or immediately after the start of the corona discharge. In short, the high frequency voltage from the electric field generator 6 is superimposed on the induced voltage from the secondary coil of the ignition coil 14. As a result, a high-frequency electric field is formed in a region near the electrodes 121 and 122 where corona discharge occurs. Then, corona discharge is strengthened in a high-frequency electric field, and plasma is generated in and around the path E of charged particles, 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, that is, a plasma state. In addition, the region of ignition of the air-fuel mixture increases and the flame kernel also increases. As a result, the combustion propagates rapidly in the combustion chamber, in other words, the flame expands at a high combustion rate.

  Incidentally, as the electric field generator 6, a pulsating voltage generating circuit for applying a high-frequency pulsating voltage may be adopted. The pulsating voltage generation circuit only needs to generate a DC voltage whose voltage periodically changes, and the waveform thereof 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 pulsating voltage preferably has a frequency of about 200 kHz to 3000 kHz and an amplitude of about 3 kVp-p to 10 kVp-p.

  An ECU (Electronic Control Unit) 0 that controls operation of the internal combustion engine 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 that detects the actual vehicle speed of the vehicle, a crank angle signal b output from an engine rotation sensor that detects the rotation angle and engine speed of the crankshaft, and depression of an accelerator pedal. An accelerator opening signal c output from a sensor that detects the amount or the opening of the throttle valve 32 as an accelerator opening (so-called required load), and a brake pedaling amount signal d output from a sensor that detects the amount of depression of the brake pedal The intake air temperature / intake pressure signal e output from the temperature / pressure sensor for detecting the intake air temperature and the intake pressure in the intake passage 3 (particularly, the surge tank 33), and the output from the water temperature sensor for detecting the cooling water temperature of the engine. Output from sensor (or shift position switch) to know coolant temperature signal f and shift lever range Shift range signal g that is, the cam angle signal h or the like to be output from the cam angle sensor is input in a plurality of cam angle of the intake camshaft or an exhaust camshaft.

  From the output interface, the ignition signal i for the semiconductor switching element 13, the fuel injection signal j for the injector 11, the opening operation signal k for the throttle valve 32, and the electric field (ie, high frequency) for the electric field generator. ) The opening command signal m and the like are output to the generation command signal 1 and the EGR valve 23

  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, the intake air amount, etc., the required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, ignition timing, required EGR rate (or EGR rate) Various operating parameters such as volume). As the operation parameter determination method itself, a known method can be adopted. The ECU 0 applies various control signals i, j, k, l and m corresponding to the operation parameters via the output interface.

  The ECU 0 of the present embodiment sets the magnitude of the voltage applied from the secondary coil of the ignition coil 14 to the center electrode 121 of the spark plug 12 so as to generate corona discharge in the combustion chamber when the mixture in the combustion chamber is ignited. Then, it is changed according to the pressure in the cylinder 1 at the timing of generating the corona discharge.

  If the voltage applied to the center electrode 121 is too high, spark discharge or glow discharge occurs between the electrodes 121 and 122 instead of corona discharge. In the spark discharge or the glow discharge, only one passage E of charged particles is formed. Accordingly, it is impossible to ignite the air-fuel mixture over a wide range, and it is impossible to generate a plurality of fire types or large-volume fire types in the combustion chamber.

  On the contrary, if the voltage applied to the center electrode 121 is too low, no electric discharge is generated in the first place and the air-fuel mixture cannot be ignited.

  The magnitude of the applied voltage that is necessary for corona discharge and does not lead to spark discharge or glow discharge causes corona discharge between the electrodes 121 and 122 of the spark plug 12 (the semiconductor switching element 13 is turned on). The higher the pressure (or density) of the air-fuel mixture in the cylinder 1 at the timing of arcing, that is, at the ignition timing, the greater.

  The cylinder 1 internal pressure at the ignition timing can be estimated from the amount of intake air charged into the cylinder 1 (estimated from the intake pressure, intake air temperature and engine speed), the temperature of the internal combustion engine (cooling water temperature) at that time, and the like. Is possible. The ECU 0 estimates the pressure in the cylinder 1 at the ignition timing, and controls the ignition device so that the induced voltage applied from the ignition coil 14 to the center electrode 121 increases as the pressure increases.

  The induced voltage applied to the center electrode 121 is determined according to the amount of voltage charged in the capacitor 15 immediately before the ignition timing. Therefore, the ECU 0 adjusts the charging voltage of the capacitor 15 so that an induced voltage corresponding to the cylinder 1 internal pressure at the ignition timing is applied to the center electrode 121. For example, in the electric circuit of the ignition device, the size of the resistor 17 connected in parallel with the capacitor 15 is changed. The larger the resistance 17, the higher the charging voltage of the capacitor 15. The resistor 17 may be one using a variable resistor, or a plurality of resistors having different resistance values are arranged in parallel, and a resistor connected to the electric circuit can be switched via a switch. It may be as described above.

  The radiation period of the high-frequency electric field that enhances corona discharge may be adjusted according to the operating region of the internal combustion engine. Combustion is likely to be unstable when the air-fuel ratio of the air-fuel mixture is lean, when the EGR rate is high (both the fuel injection amount is small), when the engine speed is low, and the like. Therefore, the ECU 0 applies a high-frequency electric field from the electric field generator 6 to the center electrode 121 as an antenna as the air-fuel ratio is leaner, the EGR rate is higher, the fuel injection amount is smaller, and / or the engine speed is lower. The ignition device is controlled so that the period (crank angle (° CA) or time) is applied.

  In the present embodiment, a discharge means for generating a corona discharge in the combustion chamber of the cylinder 1 and an electric field generation means for generating a high-frequency electric field in the vicinity of the electrodes 121 and 122 where the corona discharge is generated by the discharge means are provided. Is an internal combustion engine that interacts with a high-frequency electric field to ignite an air-fuel mixture in the combustion chamber, and the voltage applied to the electrode 121 by the discharge means to generate the corona discharge is determined by the timing at which the corona discharge is generated. The internal combustion engine which changes according to the magnitude | size of the pressure in the cylinder 1 in was comprised.

  In this embodiment, the corona discharge is strengthened by superimposing the high-frequency electric field immediately before, simultaneously with or immediately after the occurrence of the corona discharge at the electrodes 121 and 122 of the spark plug 12, and the air-fuel mixture can be reliably ignited. Grow to discharge. Corona discharge occurs in a plurality of paths E between the electrodes 121 and 122, and can ignite a wide range or a large number of locations of the air-fuel mixture in the combustion chamber.

  According to this embodiment, even when the air-fuel ratio of the air-fuel mixture is remarkably lean or when the EGR rate is high, the air-fuel mixture can be reliably ignited and burned. By the multipoint ignition, the time until the combustion flame propagates and reaches the bore inner peripheral surface of the cylinder 1 is shortened. Since the flame propagation speed can follow the speed of the movement toward the bottom dead center of the piston in the expansion stroke, the possibility of misfire during the combustion is reduced. Since resistance to the lean air-fuel ratio and the increase in the amount of EGR gas is improved, the fuel injection amount can be further reduced, which contributes to the improvement of practical fuel consumption.

  In addition, since the center electrode 121 is covered with the insulator (or dielectric) 123, the center electrode 121 is not worn. Therefore, the center electrode 121 can be manufactured using nickel without using a highly durable rare metal (platinum or iridium), which can be effective in reducing the cost.

  The present invention is not limited to the embodiment described in detail above. For example, the specific shapes of the electrodes 121 and 122 of the spark plug 12 are not limited to those shown in FIGS. The tip of the ground electrode 122 may be sharpened as a needle electrode, and / or the tip of the center electrode 121 may be sharpened as a needle electrode. In the example shown in FIG. 7, both the center electrode 121 and the ground electrode 122 are needle electrodes. As shown in FIG. 8, the position where the needle electrode 122x is formed can control the generation position of corona discharge or the path E of charged particles to some extent. Since the electric field concentrates on the needle electrode 122x, plasma by corona discharge E is preferentially formed. Regardless of how the pressure field and temperature field in the combustion chamber of the cylinder 1 change, it becomes possible to generate a stable number of corona plasmas E, and the ignition performance to the air-fuel mixture is enhanced.

  The magnitude of the induced voltage applied from the secondary coil of the ignition coil 14 to the center electrode 121 of the ignition plug 12 is adjusted according to the air-fuel ratio of the air-fuel mixture filled in the cylinder 1 and the amount of fuel injection. Also good. At this time, the ECU 0 determines that the induced voltage (that is, the capacitor prior to the ignition timing) applied to the center electrode 121 to cause corona discharge as the air-fuel ratio becomes leaner and / or as the fuel injection amount decreases. 15).

  The electric field generating device that is an element of the electric field generating means is not limited to an AC voltage generating circuit that applies a high-frequency AC voltage or a pulsating voltage generating circuit that applies a high-frequency pulsating voltage. A microwave generator may be adopted as the electric field generator, and a microwave electric field may be generated in the combustion chamber of the cylinder instead of the high frequency electric field.

  The microwave generator is mainly a magnetron that uses a vehicle-mounted battery as a power source. The microwave generator is electrically connected to the center electrode of the spark plug via a waveguide, a coaxial cable, etc., applies the microwave output from the magnetron to the center electrode, and uses the center electrode as an antenna to burn the cylinder It is possible to radiate indoors.

  The microwave is also applied simultaneously with the start of corona discharge, immediately before the start of corona discharge, or immediately after the start of corona discharge. At this time, the ECU inputs an electric field (ie, microwave) generation command signal to a control circuit that controls the magnetron. It is also conceivable to apply the microwave by the magnetron and the high induction voltage by the ignition coil in a superimposed manner to the center electrode of the spark plug.

  In the above embodiment, the center electrode 121 of the spark plug 12 is used as an antenna for radiating an electric field (high frequency or microwave). However, the center electrode 121 is dedicated for radiating an electric field in the combustion chamber, which is different from the spark plug. These antennas may be mounted on each cylinder of the internal combustion engine.

  The ignition device for an internal combustion engine in the above embodiment is of a so-called CDI (Capacitive Discharge Ignition) type. In addition to this, a so-called direct ignition that induces a high induced voltage in the secondary coil by cutting off the current that is passed through the primary coil of the ignition coil (via a semiconductor switching element (igniter) such as a transistor). It is also conceivable to employ a type of ignition device. In the direct ignition type ignition device, in order to control the magnitude of the induced voltage applied from the secondary side coil to the center electrode of the spark plug, the magnitude of the current flowing in the primary side coil is adjusted just before the interruption. do it.

  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 12 ... Spark plug 121 ... Center electrode (antenna)
E ... Corona discharge

Claims (1)

A discharge means for generating a corona discharge in the combustion chamber of the cylinder; and an electric field generation means for generating a high-frequency electric field or a microwave electric field in the vicinity of an electrode where the corona discharge is generated by the discharge means. An internal combustion engine that ignites an air-fuel mixture in a combustion chamber by interacting with a wave electric field,
An internal combustion engine in which the magnitude of a voltage applied to an electrode for generating corona discharge by a discharge means is changed in accordance with the magnitude of pressure in the cylinder at the timing of generating corona discharge.

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