JP2015187394A - internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the stabilization of stratified combustion in a low load region of a direct-fuel-injection internal combustion engine.SOLUTION: An internal combustion engine directly injecting a fuel into a combustion chamber of each cylinder 1 and capable of closing an intake valve at earlier timing than intake bottom dead center, can realize the stabilization of stratified combustion in a low load region in which an accelerator opening is equal to or lower than a predetermined value by closing the intake valve at the earlier timing than the intake bottom dead center and implementing fuel injection after closing the intake valve.

Description

  The present invention relates to an in-cylinder direct injection internal combustion engine that directly injects fuel into a combustion chamber of a cylinder.

  In an ignition device mounted on a general spark ignition type internal combustion engine, a high voltage generated in the ignition coil when the igniter extinguishes is applied to the center electrode of the ignition plug, so that the center electrode of the ignition plug is grounded. A spark discharge is caused between the electrodes and ignited.

  Recently, in order to ensure that the air-fuel mixture in the combustion chamber of the cylinder is ignited and a stable flame can be obtained, the high frequency output from the high frequency oscillator or the microwave output from the magnetron is radiated into the combustion chamber. An “active ignition” method has been attempted (see, for example, the following patent document). According to the active ignition method, a high-frequency electric field or a microwave electric field is formed in the space between the center electrode and the ground electrode, and the plasma generated in this electric field grows to form a large flame nucleus that starts flame propagation combustion. Can be generated.

JP, 2014-029128, A

  In-cylinder direct injection internal combustion engines aim to improve fuel efficiency, and stratified combustion (stratified combustion) can be performed in a partial load region (operation region where the accelerator opening is not fully open or close to full open). It is customary. Stratified combustion is stratification of an air-fuel mixture in which the air-fuel ratio is lean for the entire combustion chamber of the cylinder, and an air-fuel mixture close to the stoichiometric air-fuel ratio suitable for ignition combustion is placed near the electrode of the spark plug. This establishes lean combustion.

  However, in the low load region where the accelerator opening is small, the fuel injection amount is remarkably reduced, the fuel injected into the combustion chamber does not diffuse sufficiently and has an air-fuel ratio suitable for ignition around the spark plug electrode. There is a problem that it is difficult to place a combustible mixture.

  An object of the present invention is to realize stabilization of stratified combustion in a low load region of a direct injection type internal combustion engine.

  The present invention is an in-cylinder direct injection internal combustion engine that directly injects fuel into a combustion chamber of a cylinder, and is capable of closing an intake valve at a timing earlier than the intake bottom dead center. In the low load region below a predetermined level, the internal combustion engine is configured such that the closing timing of the intake valve is advanced from the intake bottom dead center and fuel injection is performed after the intake valve is closed.

  ADVANTAGE OF THE INVENTION According to this invention, stabilization of the stratified combustion in the low load area | region of the direct injection internal combustion engine can be implement | achieved.

The figure which shows schematic structure of the internal combustion engine of one Embodiment of this invention. The circuit diagram of the ignition system of the internal combustion engine of the embodiment. The figure explaining the structure of the electric field generator accompanying the ignition system of the internal combustion engine of the embodiment. The circuit diagram of the H bridge which is an element of the electric field generator. The figure which shows the variable valve timing mechanism incidental to the internal combustion engine of the embodiment.

  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 direct injection type four-stroke gasoline engine, and includes a plurality of cylinders 1 (for example, a three-cylinder engine, one of which is shown in FIG. 1). Yes. Each cylinder 1 is provided with an injector 11 for injecting fuel at a position facing the intake port. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1.

  FIG. 2 shows an electric circuit of the ignition system. The ignition coil 14 supplies a high voltage for spark discharge to be applied to the spark plug 12, and is integrally incorporated in a coil case together with an igniter 13 which is a semiconductor switching element. When the igniter 13 receives an ignition signal i from an ECU (Electronic Control Unit) 0 which is a control device of the internal combustion engine, the igniter 13 is first ignited and a current flows to the primary side of the ignition coil 14, and at the ignition timing immediately thereafter. The igniter 13 is extinguished to interrupt this current. Then, a self-induction action occurs, and a high voltage is generated on the primary side of the ignition coil 14. 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 induced voltage is applied to the center electrode of the spark plug 12, and a spark discharge is generated between the center electrode and the ground electrode.

  In the internal combustion engine of the present embodiment, an electric field generator 6 for generating an electric field in the combustion chamber of the cylinder 1 is attached to the ignition system. The electric field generator 6 generates a high frequency for the purpose of generating plasma in the combustion chamber. Specific examples of the electric field generator 6 include an AC voltage generation circuit that outputs a high-frequency AC voltage, a pulsating voltage generation circuit that outputs a high-frequency pulsating voltage, and the like.

  As shown in FIGS. 3 and 4, the electric field generation device 6 includes a circuit that converts a low-voltage direct current into a high-voltage alternating current using a vehicle-mounted battery as a power source. Specifically, a DC-DC converter 61 that boosts a DC voltage of about 12 V provided by the battery to 100 V to 500 V, and an AC oscillator that outputs an AC high frequency using the DC voltage output from the DC-DC converter 61. The constituent elements are a high-frequency generator circuit 62 and a step-up transformer 63 that boosts an alternating-current high-frequency output from the high-frequency generator circuit 62 to a higher voltage.

  The DC-DC converter 61 can change the magnitude of the direct-current drive voltage applied to the high-frequency generation circuit 62 in response to the instruction 1 from the ECU 0, and consequently the amplitude of the high-frequency voltage downstream of the step-up transformer 63. Can be changed. The high-frequency voltage downstream of the step-up transformer 63 preferably has a frequency of about 200 kHz to 3000 kHz and an amplitude of about 3 kVp-p to 10 kVp-p.

  In the present embodiment, the high frequency generation circuit 62 is an H bridge circuit that converts the DC voltage output from the DC-DC converter 61 into an AC voltage. FIG. 4 shows a configuration example of this H-bridge circuit.

  A first diode 64 and a second diode 65 are interposed 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 rectify the high frequency of alternating current by half-wave rectification downstream of the step-up transformer 63 and pulsate the negative high-voltage pulse current flowing from the secondary side of the ignition coil 14 at the ignition timing. Play a role of blocking.

  Incidentally, when a pulsating voltage generation circuit is employed as the electric field generator 6, 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 mentioned here includes a pulse voltage that varies from a reference voltage (which may be 0 V) to a constant voltage at a constant period, a voltage obtained by adding a DC bias to an AC voltage, and the like.

  A high-frequency pulsating voltage generated by the electric field generator 6 is applied to the center electrode of the spark plug 12 via the mixer 66. That is, the center electrode of the spark plug 12 facing the combustion chamber of the cylinder 1 is an antenna that radiates an electric field. Thereby, a high frequency electric field is formed in the space between the center electrode of the spark plug 12 and the ground electrode in the combustion chamber. 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, 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 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.

  In the case of performing active ignition, the timing at which a high frequency is applied to the center electrode of the spark plug 12 is usually almost simultaneously with the start of spark discharge, immediately before the start of spark discharge, or immediately after the start of spark discharge.

  Of course, the internal combustion engine of the present embodiment can also ignite the air-fuel mixture by conventional spark ignition that is not active ignition, that is, spark discharge that does not involve emission of a high-frequency electric field from the center electrode of the spark plug 12. In situations where it is easy to ignite and burn stably (it is unlikely to cause a combustion failure), it is conceivable to perform conventional spark ignition to suppress power consumption.

  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.

  The external EGR (Exhaust Gas Recirculation) device 2 realizes a so-called high pressure loop EGR, and an EGR passage 21 communicating 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.

  As shown in FIG. 5, in the internal combustion engine of the present embodiment, a timing chain 74 is wound around a crank sprocket 71, an intake side sprocket 72, and an exhaust side sprocket 73, and the rotational driving force provided from the crankshaft by this timing chain 74. Is transmitted to the intake camshaft via the intake side sprocket 72 and to the exhaust camshaft via the exhaust side sprocket 73.

  In addition, a variable valve timing mechanism 8 is interposed between the intake side sprocket 72 and the intake camshaft. The VVT mechanism 8 in the present embodiment changes the opening / closing timing of the intake valve by changing the rotational phase of the intake camshaft with respect to the crankshaft.

  The housing 81 of the VVT mechanism 8 is fixed to the intake side sprocket 72, and the intake side sprocket 72 and the housing 81 rotate together in synchronism with the crankshaft. On the other hand, the rotor 82 fixed to one end of the intake camshaft is accommodated in the housing 81 and can be rotated relative to the intake-side sprocket 72 and the housing 81. A plurality of fluid chambers into which hydraulic fluid flows in and out are formed inside the housing 81, and each fluid chamber is partitioned into an advance chamber 812 and a retard chamber 811 by a vane 821 formed on the outer periphery of the rotor 82. Is done.

  The hydraulic fluid stored in the oil pan 831 is supplied from the hydraulic pump 832 to the hydraulic pressure (particularly hydraulic) circuit of the VVT mechanism 8. The hydraulic pump 832 is driven by power from the internal combustion engine. An OCV (Oil Control Valve) 9 that is a switching control valve is provided between the hydraulic pump 832 and the VVT mechanism 8. By operating the flow rate and direction of the hydraulic fluid via the OCV 9, the hydraulic fluid pumped from the oil pan 831 can be selectively supplied to the advance chamber 812 or the retard chamber 811. Then, the housing 81 rotates relative to the rotor 82, and the opening / closing timing of the intake valve can be advanced or retarded.

  The OCV 9 is a so-called electromagnetic four-way spool valve. The spool 96 is driven by a solenoid 97. That is, the advance / retreat distance of the spool 96 changes according to the duty ratio of the pulse current (or voltage) input to the solenoid 97 as the control signal n.

  When the duty ratio of the control signal n is relatively large, the hydraulic fluid pressure discharged from the hydraulic pump 832 is supplied to the advance chamber 812 through the A port 92, while already stored in the retard chamber 811. The hydraulic fluid flows down toward the oil pan 831 through the B port 93, and the vane 821 and the rotor 82 rotate so that the volume of the advance chamber 812 is increased and the volume of the retard chamber 811 is reduced. As a result, the rotational phase of the intake camshaft, in other words, the displacement angle of the intake camshaft with respect to the crankshaft is advanced, and the valve timing of the intake valve is advanced.

  On the other hand, when the duty ratio of the control signal n is relatively small, the hydraulic fluid pressure discharged from the hydraulic pump 832 is supplied to the retard chamber 811 through the B port 93 while being already stored in the advance chamber 812. The hydraulic fluid that has flowed down flows toward the oil pan 831 through the A port 92, and the vane 821 and the rotor 82 rotate so that the volume of the retard chamber 811 is expanded and the volume of the advance chamber 812 is decreased. . As a result, the displacement angle of the intake camshaft with respect to the crankshaft is retarded, and the valve timing of the intake valve is retarded.

  The ECU 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 degree signal c output from a sensor that detects the amount or the opening degree of the throttle valve 32 as an accelerator opening degree (so-called required load), and a brake switch or master cylinder pressure sensor that detects the depression amount of the brake pedal. Brake pedal amount signal d, intake air temperature / intake pressure signal e output from temperature / pressure sensor for detecting intake air temperature and intake pressure in intake passage 3 (especially surge tank 33), and cooling water temperature of internal combustion engine are detected. The cooling water temperature signal f output from the water temperature sensor, the intake camshaft or the exhaust camshaft A cam angle signal g at the cam angle is output from the cam angle sensor, an atmospheric pressure signal h or the like to be outputted from the atmospheric pressure sensor for detecting the atmospheric pressure is inputted.

  From the output interface, an ignition signal i for the igniter 13 associated with the spark plug 12, a fuel injection signal j for the injector 11, an opening operation signal k for the throttle valve 32, and a DC-DC converter 61. A voltage command signal l for instructing the magnitude of the drive voltage output from the DC-DC converter 61, an opening operation signal m for the EGR valve 23, a control signal n for the OCV 9, and the like are output.

  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, intake air amount, etc., the required fuel injection amount, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, ignition timing, and high-frequency electric field applied to the combustion chamber Various operating parameters such as whether or not to perform, the strength of the electric field, the required EGR rate (or EGR amount), the opening and closing timing of the intake valve, and the like are determined. The ECU 0 applies various control signals i, j, k, l, m, and n corresponding to the operation parameters via the output interface.

  In the internal combustion engine of the present embodiment, in the partial load operation region where the accelerator opening is not fully open or close to full open, the entire combustion chamber of the cylinder 1 is in the vicinity of the electrode of the spark plug 12 while making the air-fuel ratio lean. It is possible to carry out stratified combustion in which an air-fuel mixture close to the stoichiometric air-fuel ratio suitable for ignition combustion is placed and ignited.

  Although there are several methods for realizing the stratification of the air-fuel mixture, a so-called spray guide method is assumed in the present embodiment. The spray guide method is a method in which fuel is injected directly from the injector 11 toward the electrode of the spark plug 12 during the compression stroke of the cylinder 1. Since the interval from fuel injection to ignition is short, it is possible to prevent excessive diffusion of the fuel and to suppress the collision of the fuel with the piston, so there is little emission of unburned fuel components (especially HC) and high combustion efficiency. There is an advantage that can be realized.

  On the other hand, in the spray guide system, the fuel injected from the injector 11 must be reliably guided to the vicinity of the electrode of the spark plug 12, and ignition must be performed at a timing when the injected fuel passes near the electrode of the spark plug 12. There is. In a low load region where the accelerator opening is small, the amount of fuel injection is remarkably reduced, the fuel injected into the combustion chamber does not diffuse sufficiently, and a combustible mixture having an air-fuel ratio suitable for ignition in the vicinity of the electrode of the spark plug 12 It is difficult to place Qi layers.

  Therefore, in the present embodiment, in the low load operation region where the accelerator opening is equal to or less than a predetermined value, the closing timing of the intake valve in the intake stroke of each cylinder 1 via the VVT mechanism 6 is a certain level or more than the intake bottom dead center. While performing early closing control to advance the angle, fuel injection is executed after the intake valve is closed.

  More specifically, the intake valve is closed at a timing earlier than the intake bottom dead center, and after the intake valve is closed, before intake bottom dead center or after intake bottom dead center (intake bottom dead center). Fuel is injected from the injector 11 into the combustion chamber at the beginning or middle of the compression stroke in which the crank angle from the point is within the predetermined range, that is, when the in-cylinder pressure (combustion chamber pressure of the cylinder 1) is low. Then, the injected fuel vaporizes under reduced pressure and diffuses from the injector 11 into the combustion chamber. As a result, it is possible to arrange a layer of combustible air-fuel mixture in the vicinity of the electrode of the spark plug 12 at least in the amount of fuel injection, and to obtain stable stratified combustion.

  In addition, the early closing control of the intake valve also realizes a mirror cycle that effectively shortens the stroke length of the compression stroke than the stroke length of the expansion stroke, reducing the amount of exhaust heat while reducing the pumping loss. The thermomechanical conversion efficiency can be further increased.

  However, if the early closing control of the intake valve is performed in the low load region, the in-cylinder temperature (combustion chamber temperature) at the intake bottom dead center of the cylinder 1 is remarkably lowered, and in some cases, reaches the freezing point. There is a concern that a decrease in the in-cylinder temperature may lead to instability of the ignition and combustion of the air-fuel mixture. When the intake valve is controlled to be closed early in a low load region where the accelerator opening is equal to or less than a predetermined value, it is preferable to execute the above-described active ignition so that the air-fuel mixture is ignited and burned reliably.

  In the present embodiment, the cylinder 1 is a direct injection type internal combustion engine that directly injects fuel into the combustion chamber of the cylinder 1. The intake valve can be closed earlier than the intake bottom dead center. In the low load region where the degree is less than or equal to a predetermined value, the internal combustion engine is configured such that the closing timing of the intake valve is advanced from the intake bottom dead center and fuel injection is performed after the intake valve is closed.

  According to this embodiment, it becomes easy to arrange the combustible air-fuel mixture around the electrode of the spark plug 12 even in a low load region where the fuel injection amount is small. That is, since stable stratified combustion can be obtained in a low load region, it contributes to reduction of fuel consumption and suppression of emission of unburned fuel components (improvement of fuel consumption and emission).

  In addition, ignition is performed only by spark discharge during normal times except during stratified combustion in low-load regions where the stability of the combustion of the air-fuel mixture decreases, and early closing control is only possible during stratified combustion in low-load regions. At the same time, it is possible to perform an ignition combustion of the air-fuel mixture by active ignition. In this case, power consumption due to electric field emission into the combustion chamber can be reduced.

  The present invention is not limited to the embodiment described in detail above. For example, when performing stratified combustion accompanied by intake valve early closing control in a low load region, it is not always necessary to execute active ignition. If the mixture can be ignited, the mixture may be burned by conventional spark ignition.

  The electric field generator 6 for applying an electric field to the combustion chamber of the cylinder 1 is not limited to an AC voltage generating circuit for applying a high-frequency AC voltage or a pulsating voltage generating circuit for applying a high-frequency pulsating voltage. A magnetron or the like that outputs a microwave may be employed as the electric field generator 6, and active ignition may be performed by applying a microwave electric field into the combustion chamber of the cylinder 1.

  In the above-described embodiment, the center electrode of the spark plug 12 is an antenna for electric field radiation. However, an antenna separate from the spark plug 12 is provided in the cylinder 1, and a high-frequency electric field or micro wave is provided in the combustion chamber of the cylinder 1 through this antenna. A wave electric field may be emitted.

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

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

0 ... Control unit (ECU)
DESCRIPTION OF SYMBOLS 1 ... Cylinder 12 ... Spark plug, antenna 6 ... Electric field generator

Claims (1)

A direct injection type internal combustion engine that directly injects fuel into the combustion chamber of the cylinder, and can close the intake valve at a timing earlier than the intake bottom dead center,
An internal combustion engine in which, in a low load region where the accelerator opening is equal to or less than a predetermined value, the closing timing of the intake valve is advanced from the intake bottom dead center and fuel injection is performed after the intake valve is closed.

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