JP2015187392A - internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To complete starting a direct-fuel-injection internal combustion engine as early as possible while suppressing the occurrence of undesired pre-ignition at a time of starting the engine.SOLUTION: An internal combustion engine that is a direct-fuel-injection internal combustion engine directly injecting a fuel into a combustion chamber of each cylinder and that can implement active ignition for producing plasmas in the combustion chamber by the interaction between plasma discharge generated between a center electrode and a ground electrode of an ignition plug and an electric field emitted into the combustion chamber via an antenna facing the interior of the combustion chamber and thereby igniting the fuel, emits the electric field into the combustion chamber or implements the active ignition before fuel injection in the cylinder in which the fuel injection and ignition can be first carried out after starting cranking for restarting the engine.

Description

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

  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, Patent Document 1 below). 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.

  Recently, it has become common to implement idle stop for stopping idle rotation of an internal combustion engine mounted on a vehicle when the vehicle is temporarily stopped such as waiting for a signal (for example, see Patent Document 2 below). In the existing idling stop system, when the vehicle speed is below a predetermined value, the brake pedal is depressed above a threshold value, and the conditions such as the cooling water temperature of the internal combustion engine and the voltage of the vehicle battery are sufficiently high, the internal combustion engine Stop the engine. During idling stop, the internal combustion engine is restarted when there is a restart request such as when the driver removes his foot from the brake pedal or depresses the accelerator pedal, or when a predetermined time has elapsed in the idling stop state.

JP, 2014-029128, A JP 2012-137018 A

  When starting an in-cylinder direct injection internal combustion engine, particularly when restarting after idling stop in an idling stop vehicle, intake air containing unburned fuel may remain in the combustion chamber of the cylinder. When the cylinder is in the compression stroke immediately after the cranking is started under the condition where the in-cylinder temperature (combustion chamber temperature) is high, the piston reciprocates when the fuel is injected into the intake air that already contains unburned fuel. Coupled with the slow speed of this, it may cause preignition that ignites and explodes due to compression pressure. When pre-ignition occurs, abnormal noise is generated during startup of the internal combustion engine, and the internal combustion engine may be damaged.

  In order to avoid such pre-ignition, a cylinder that can undergo fuel injection and ignition in the first compression stroke after the start of cranking is intentionally not fuel-injected and ignited. It is conceivable to take a procedure of once exhausting intake air that may contain unburned fuel.

  However, the start of the internal combustion engine is required to be completed as quickly as possible. This is especially true when restarting from an idle stop when the vehicle is stopped, such as when waiting for a signal. Refraining from fuel injection despite the compression stroke of the cylinder means that the generation of engine torque and the acceleration of the internal combustion engine (crankshaft) are delayed, and the cranking period is likely to be extended. is there.

  An object of the present invention is to make the completion of the start as early as possible while suppressing the occurrence of an undesired pre-ignition at the start of the direct injection 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, via a spark discharge generated between a center electrode and a ground electrode of a spark plug and an antenna facing the combustion chamber. It is possible to perform active ignition that interacts with the electric field radiated in the combustion chamber to generate plasma in the combustion chamber and ignite the fuel, and after starting the cranking for restarting, the fuel first An internal combustion engine that radiates an electric field in the combustion chamber or performs active ignition in a cylinder that enables injection and ignition before fuel injection is configured.

  ADVANTAGE OF THE INVENTION According to this invention, completion | finish of start-up can be advanced, suppressing generation | occurrence | production of the undesired preignition at the time of start-up of the direct injection internal combustion engine.

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.

  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 an in-cylinder direct injection type four-stroke gasoline engine that directly injects fuel into the combustion chamber of the cylinder 1, and includes a plurality of cylinders 1 (for example, a three-cylinder engine. Are shown). Each cylinder 1 is provided with an injector 11 for injecting fuel at a position facing the combustion chamber. 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 generator 6 includes a circuit that converts the low-voltage direct current into the high-voltage alternating current by using the on-board battery 8 as a power source. Specifically, a DC-DC converter 61 that boosts a DC voltage of about 12 V provided by the battery 8 to 100 V to 500 V, and an AC that outputs an AC high frequency using the DC voltage output from the DC-DC converter 61. The high frequency generation circuit 62 as an oscillator and the step-up transformer 63 that boosts the alternating high frequency output from the high frequency generation circuit 62 to a higher voltage are used as components.

  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 the mixer 7, which 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.

  The 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 7. 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.

  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.

  The crank angle sensor senses the rotation angle of a rotor that is fixed to the crankshaft and rotates integrally with the crankshaft. The crank angle sensor typically transmits a pulse signal as a crank angle signal b every time the crankshaft rotates by 10 ° CA (crank angle). However, the crank angle sensor does not output 36 pulses during one rotation of the crankshaft. For example, the 17th, 18th, 20th, and 20th pulses are missing. . The ECU 0 can know the absolute angle of the crankshaft based on the missing pulse train of the received crank angle signal b.

  The cam angle sensor also senses the rotation angle of a rotor that is fixed to the cam shaft and rotates integrally with the cam shaft. The cam angle sensor transmits a pulse signal as a cam angle signal g every time the cam shaft rotates at least an angle obtained by dividing one rotation by the number of cylinders 1. In the case of a three-cylinder engine, a pulse signal is transmitted every time the camshaft rotates 120 °. Since the camshaft is driven and rotated by receiving rotational torque from the crankshaft via a winding transmission mechanism (chain and sprocket, not shown) and the like, the rotational speed is half that of the crankshaft. Therefore, the pulse interval of the cam angle signal g corresponds to 240 ° CA in terms of the crank angle. This pulse of the cam angle signal g indicates a timing at which the cylinder 1 is advanced by a predetermined crank angle (a value within a range of 30 ° CA to 70 ° CA) from the compression top dead center of each cylinder 1. Further, in an internal combustion engine with a so-called phase change type variable valve timing mechanism, the cam timing signal g also represents a valve timing adjusted by the mechanism.

  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 commanding the magnitude of the drive voltage output by the DC-DC converter 61, an opening operation signal m, etc. are output to 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, 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, and the required EGR rate (or EGR amount) are determined. 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 inputs a control signal o to an electric motor (starter (cell motor) or motor generator (not shown)) when the internal combustion engine is started (a cold start or a return from an idle stop). Then, cranking is performed in which the crankshaft is rotationally driven by an electric motor. Cranking ends when the internal combustion engine starts from the first explosion to a continuous explosion and the engine speed, that is, the rotation speed of the crankshaft, exceeds a judgment value determined according to the coolant temperature, etc. (assuming that the explosion has been completed) To do.

  The ECU 0 of the present embodiment performs an idle stop that stops the idle rotation of the internal combustion engine when the vehicle stops due to a signal waiting or the like. The ECU 0 determines whether the vehicle speed is equal to or less than a predetermined value (for example, a value of 10 km / h to 13 km / h) and the brake pedal is depressed by the driver (the brake switch is ON) or the brake operation amount (the brake pedal depression amount). Or the master cylinder pressure) exceeds the determination threshold, the cooling water temperature of the internal combustion engine and the voltage of the in-vehicle battery 8 are each higher than a predetermined value, and the vehicle speed is a predetermined value (for example, 10 km / h after the most recent restart of the internal combustion engine). (I.e., a value of 13 km / h) or more, the fact that all the conditions such as the history of rising are all established is determined that the idle stop condition is satisfied, and the idle stop is executed.

  After the idle stop condition is established, the ECU 0 determines that the driver has released his / her foot from the brake pedal (the brake switch is OFF) or the brake operation amount (the brake pedal depression amount or the master cylinder pressure) has fallen below the determination threshold. The brake pedal was further depressed (the brake pedal depression amount or the master cylinder pressure further increased), the accelerator pedal was depressed, a predetermined time (for example, 3 minutes) passed in the idle stop state, etc. When any one of them is satisfied, it is determined that the idle stop end condition is satisfied, and the internal combustion engine is restarted.

  After starting the cranking for restarting the internal combustion engine, the ECU 0 performs cylinder discrimination for confirming the current stroke of each cylinder 1 based on the crank angle signal b and the cam angle signal g. As a cylinder discrimination method itself, a known method may be adopted. When the cylinder discrimination is completed, synchronous injection in which fuel is injected from the injector 11 in the compression stroke is performed on the cylinder 1 that reaches the compression stroke thereafter, and ignition is performed at a timing near the compression top dead center thereafter. It becomes possible.

  However, particularly when the internal combustion engine is restarted after the idle stop, there is a possibility that the intake air containing unburned fuel (fuel injected before the idle stop) remains in the combustion chamber of the cylinder 1. When the fuel is injected into the intake air that already contains unburned fuel in the cylinder 1 that reaches the compression stroke immediately after the start of cranking under a situation where the in-cylinder temperature is high, the fuel self-ignites due to the compression pressure and explodes. May cause pre-ignition.

  Therefore, in this embodiment, in order to suppress the occurrence of pre-ignition at the time of restart of the internal combustion engine, after starting cranking for restart, in the cylinder 1 where fuel injection and ignition can be performed first, Prior to synchronous injection, which is regular fuel injection for obtaining torque, a high frequency electric field is radiated from the center electrode of the spark plug 12 into the combustion chamber in advance, or the center electrode of the spark plug 12 is grounded together with the radiation of the high frequency electric field. Active ignition that causes spark discharge between the electrodes is performed.

  As a result, even if the intake air containing unburned fuel remains in the combustion chamber of the cylinder 1, the intake air absorbs the energy of electromagnetic waves radiated from the spark plug 12 and activates it to perform synchronous injection. The unburned fuel can be self-ignited and burned before performing, or the unburned fuel can be forcibly activated and burned before performing synchronous injection. As a result, even if synchronous injection is executed during the compression stroke of the cylinder 1, preignition does not occur, and an excessive increase in the in-cylinder pressure (combustion chamber pressure) is prevented, so that no loud noise is generated and the internal combustion engine No damage.

  Field emission or active ignition for avoiding undesired pre-ignition (processing of unburned fuel before synchronous injection) is as early as possible in the compression stroke after the intake bottom dead center of the cylinder 1 (according to the intake bottom dead center). It is preferable to execute at a time (closer and further from the compression top dead center). Needless to say, this is because the unburned fuel remaining in the combustion chamber of the cylinder 1 needs to be processed before the timing of the synchronous injection.

  The above-described field emission or active ignition is not necessarily performed during the compression stroke of the cylinder 1. The cylinder 1 in which fuel injection and ignition can be performed first after completion of the cylinder discrimination, that is, the cylinder 1 that will reach the compression stroke first after completion of the cylinder discrimination, was in the exhaust stroke or the intake stroke when the cylinder discrimination was completed. However, the above-described field emission or active ignition may be performed immediately without waiting for the transition to the compression stroke. However, there is a possibility that it cannot be absolutely stated that there is no risk of afterfire or backfire by burning unburned fuel in the combustion chamber of the cylinder 1 when the exhaust valve or intake valve is open. is there. In addition, leakage of electromagnetic waves radiated into the combustion chamber to the outside of the combustion chamber may be a problem. If backfire, afterfire or electromagnetic wave leakage is a concern, it is appropriate to perform the field emission or active ignition described above during the compression stroke when both the exhaust and intake valves are closed.

  In order to speed up the completion of the restart of the internal combustion engine, that is, to shorten the cranking period, after performing the above-mentioned field emission or active ignition in the cylinder 1 that will reach the compression stroke first after completion of the cylinder discrimination, Synchronous injection, which is normal fuel injection, is executed during the first compression stroke, and the fuel injected at the timing near the compression top dead center is ignited to realize the original combustion (outputting engine torque) .

  In this embodiment, it is an in-cylinder direct injection internal combustion engine that directly injects fuel into the combustion chamber of the cylinder 1, and an antenna that faces the spark discharge generated between the center electrode and the ground electrode of the spark plug 12 and the combustion chamber. It is possible to perform active ignition that interacts with the electric field radiated into the combustion chamber via (the center electrode of the ignition plug 12) to generate plasma in the combustion chamber and ignite the fuel, for restarting After starting the cranking, an internal combustion engine that radiates an electric field into the combustion chamber or performs active ignition before the fuel injection in the cylinder 1 in which fuel injection and ignition can be performed first is configured.

  According to the present embodiment, when the internal combustion engine is restarted under a situation where the in-cylinder temperature is already high, an undesired preignition that generates a large noise or damages the internal combustion engine is caused. It can be effectively avoided. In addition, fuel injection and ignition are first performed in the cylinder 1 where fuel injection and ignition are possible, and the internal combustion engine can be started quickly. In addition, since it is not necessary to reduce the compression ratio of the cylinder 1 for the purpose of preventing pre-ignition, it is effective for securing sufficient engine torque and improving fuel efficiency.

  The present invention is not limited to the embodiment described in detail above. For example, 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 that applies a high-frequency AC voltage or a pulsating voltage generator circuit that applies 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.

  The internal combustion engine to which the present invention is applied is not limited to a so-called gasoline direct injection engine. Naturally, it is also conceivable to apply the present invention to a diesel engine, a HCCI (homogeneous-charge compression ignition) engine, or the like.

  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 7 ... Mixer

Claims (1)

This is an in-cylinder direct injection internal combustion engine that directly injects fuel into the combustion chamber of the cylinder, and radiates it into the combustion chamber via the spark discharge generated between the center electrode and the ground electrode of the spark plug and the antenna facing the combustion chamber. An active ignition that interacts with the generated electric field to generate plasma in the combustion chamber and ignite the fuel,
An internal combustion engine that radiates an electric field in a combustion chamber or performs active ignition before fuel injection in a cylinder in which fuel injection and ignition can be performed first after starting cranking for restart.

Images