JP2010223039A - Method for controlling misfire inhibition in transient state of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein if fuel quantity, combustion chamber wall temperature, ignition timing and the like change from steady operation state in combustion of a former cycle and in-cylinder burned gas temperature, namely internal EGR temperature is different from a state in which the steady state adapted value is measured, in transient operation in which engine speed and load change, heavy knocking and pre-ignition occurs when internal EGR temperature is higher than a steady state adapted value and ignition fails and misfire occurs when internal EGR temperature is lower than the steady state adapted value, in an HCCI engine. <P>SOLUTION: In an in-cylinder fuel injection type internal combustion engine executing premixed compression self ignition combustion by controlling air fuel mixture temperature by mixing fresh air and burned gas staying in a cylinder, in-cylinder maximum pressure during execution of premixed compression self ignition combustion is detected, and fluctuation state of each cycles is obtained by the detected in-cylinder maximum pressure. Indication of misfire is determined and air fuel mixture temperature is raised (S7) if the obtained fluctuation state increases right after reduction deviating a prescribed range (S6). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a transient misfire suppression control method for an internal combustion engine that performs premixed compression auto-ignition combustion (hereinafter referred to as HCCI) in accordance with an operating state.

  2. Description of the Related Art Conventionally, in an internal combustion engine equipped with a spark plug, for example, an engine fueled with gasoline, when moving from an exhaust stroke to an intake stroke, the exhaust valve and the intake valve are closed simultaneously, a so-called negative overlap period (hereinafter referred to as NVO). An HCCI engine that operates by causing the air-fuel mixture to self-ignite by compressing the air-fuel mixture by heating the air-fuel mixture with the heat of the remaining fuel gas is known. ing.

  For example, in the HCCI engine described in Patent Document 1, the first fuel injection for forming a substantially uniform air-fuel mixture in the combustion chamber and the second fuel injection for unevenly distributing fuel in the vicinity of the spark plug In this configuration, the rich mixture in the vicinity of the spark plug is ignited by the spark plug, and then the mixture around the rich mixture is self-ignited. The combustion state at the time of self-ignition is detected by a parameter that correlates with the combustion speed or combustion timing, for example, the maximum in-cylinder pressure, and the fuel supply or ignition timing is controlled based on the detected parameter.

JP 2002-188486 A

  By the way, in such an HCCI engine, in the case of a transient operation in which the engine speed or load changes, the amount of fuel, the combustion chamber wall temperature, the ignition timing, etc. change from the steady operation state in the previous cycle combustion, and the in-cylinder The fuel gas temperature, that is, the internal EGR (exhaust gas recirculation) temperature is different from the state in which the steady conformity value is measured.

  For example, during acceleration with a substantially constant torque, the required value of the internal EGR temperature is also substantially constant. However, when the engine speed increases, the internal EGR temperature rises because heat transfer to the wall surface also decreases even if the amount of fuel used in one cycle is constant. For this reason, the HCCI engine is adapted to reduce the internal EGR rate. However, when the engine speed and torque change transiently, the actual wall temperature differs from the wall temperature at the time of adaptation. For this reason, the internal EGR temperature may not rise as much as the steady state of conformity.

  As described above, when the internal EGR temperature is different from the steady matching value, there is a high possibility that various problems will occur. Specifically, when the internal EGR temperature is higher than the steady conformity value, heavy knocking or pre-ignition occurs, and conversely, when the internal EGR temperature is low, ignition does not occur, so there is a possibility of misfire.

  Therefore, the present invention aims to eliminate such problems.

  That is, the transient misfire suppression control method for an internal combustion engine according to the present invention is an in-cylinder in which premixed compression self-ignition combustion can be performed by controlling the mixture temperature by mixing the burned gas and fresh air remaining in the cylinder. In a fuel-injection type internal combustion engine, the maximum in-cylinder pressure when premixed compression auto-ignition combustion is performed is detected, and the fluctuation state for each cycle is determined by the detected maximum in-cylinder pressure, and the detected fluctuation state is within a predetermined range. In the case where it increases immediately after deviating from the above, the temperature of the air-fuel mixture is raised by judging the sign of misfire.

  According to such a configuration, it is possible to estimate a decrease in the mixture temperature due to a fluctuation state that increases immediately after decreasing outside the predetermined range, and by this estimation, there is no sign of misfire, in other words, ignitability. By determining the decrease, the control for increasing the mixture temperature can be executed before the misfire. Thereby, it becomes possible to stabilize combustion and ignition by suppressing the occurrence of misfire in advance.

  The present invention is configured as described above, and by suppressing the occurrence of misfire, combustion and ignition can be stabilized, and in the transient operation state, the HCCI is almost equivalent to that in the steady operation. An operation area can be secured. Therefore, the effects of reducing fuel consumption and improving the amount of environmental pollutants in exhaust gas can be utilized to the maximum.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic structure explanatory drawing which shows schematic structure of the engine of embodiment of this invention. The flowchart which shows the control procedure of the embodiment. Action | operation explanatory drawing of the same embodiment.

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

  The spark ignition type and in-cylinder fuel injection type engine 100 of this embodiment is an engine equipped with a variable valve timing mechanism 30, and in order to implement HCCI, only the normal spark ignition is performed with a compression ratio. It is higher than the engine that does. Except for setting the compression ratio, it is the same as that of a normal spark ignition type engine provided with the variable valve timing mechanism 30.

  Specifically, an engine 100 schematically showing the configuration of one cylinder in FIG. 1 is a three-cylinder engine for an automobile, and its intake system 1 is an electronic throttle that opens and closes in response to an accelerator pedal (not shown). A valve 2 is provided, and a surge tank 3 is provided on the downstream side thereof, and intake air from the surge tank 3 is drawn into the cylinder 38 via the intake port 11 and the intake valve 37. The intake system 1 is provided with a bypass passage 1a that is a bypass for bypassing the throttle valve 2, and the bypass passage 1a is provided with a flow control valve 1b for controlling the amount of air passing through the bypass passage 1a. It is. The flow rate control valve 1b is controlled mainly when the idle rotation control of the engine 100 is executed.

An injector 5 is provided for the combustion chamber 35 provided in the cylinder head 12 so that fuel can be directly injected into the combustion chamber 35. The injector 5 is configured to be controlled by an electronic control device 6 described later. In the exhaust system 20, an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas discharged from the combustion chamber 35 through the exhaust valve 36 is disposed in a pipe line until reaching a muffler (not shown). It is attached at a position upstream of the three-way catalyst 22.

  The variable valve timing mechanism 30 is, for example, a mechanical type that is operated by hydraulic oil, and can control the open / close timing of the exhaust valve 36 and the intake valve 37 independently in cooperation with the electronic control unit 6. is there. That is, the variable valve timing mechanism 30 that operates by controlling the hydraulic oil according to the signal output from the electronic control device 6 advances and retards the operation center that fully opens the exhaust valve 36 and the intake valve 37. At the same time, the operating angles of the exhaust valve 36 and the intake valve 37 are controlled. The variable valve timing mechanism 30 controls the exhaust valve 36 and the intake valve 37 so that the opening periods of the exhaust valve 36 and the intake valve 37 overlap during spark ignition, and during the HCCI, intake from the exhaust stroke is performed. During the transition to the stroke, the exhaust valve 36 and the intake valve 37 are controlled to be closed simultaneously for a predetermined period in which the piston 39 is located near the exhaust top dead center. This predetermined period is NVO.

The electronic control unit 6 that controls the operation of the engine 100 together with the variable valve timing mechanism 30 is mainly a microcomputer system including a central processing unit 7, a storage unit 8, an input interface 9, and an output interface 10. It is configured. The input interface 9 outputs an intake pressure signal a output from an intake pressure sensor 19 for detecting the pressure in the surge tank 3, that is, an intake pipe pressure, and an output from a rotation speed sensor 14 for detecting the engine rotation speed NE. The rotational speed signal b, the crank angle signal m output from the crank sensor 41, the intake cam signal n output from the timing sensor 42, and the IDL output from the idle switch 16 for detecting the open / closed state of the throttle valve 2 A signal d, a water temperature signal e output from the water temperature sensor 17 for detecting the cooling water temperature of the engine 100, a voltage signal h output from the O ₂ sensor 21, and the like are input. On the other hand, from the output interface 10, a drive pulse as a fuel injection signal f is output to the injector 5, and an ignition signal g is output to the spark plug 18 when spark ignition is performed.

  The spark plug 18 is connected to an ion current detection circuit 60 and an ignition circuit 61 including an ignition coil and a switching transistor in order to detect an ion current. The ion current detection circuit 60 includes a power source that applies a voltage for detecting an ion current to the spark plug 18 during operation of the engine 100, and also includes a resistor and a voltage sensor for detecting the ion current. Therefore, even in the case of HCCI, the energization signal g is output to the ignition circuit 61.

  In such a configuration, the electronic control unit 6 uses the intake pressure signal a output from the intake pressure sensor 19 and the rotation speed signal b output from the rotation speed sensor 14 as main information, and the operating state of the engine 100. The basic injection time (basic injection amount) is corrected by various correction coefficients determined according to the above, the fuel injection valve opening time, that is, the final injector energization time T is determined, and the injector 5 is controlled by the determined energization time. A program for injecting fuel corresponding to the engine load into the intake system 1 is incorporated.

  In addition, the electronic control unit 6 detects the in-cylinder maximum pressure in the transient operation in which the HCCI is performed, grasps the fluctuation state for each cycle based on the detected in-cylinder maximum pressure, and the grasped fluctuation state is predetermined. A transient misfire suppression control program is built in that increases the mixture temperature by judging the sign of misfire when it increases immediately after decreasing outside the range R.

  An outline control procedure of the transient misfire suppression control program in this embodiment will be described with reference to FIG. In this transient misfire suppression control program, the fluctuation state is grasped by the fluctuation rate of the in-cylinder maximum pressure. Therefore, a predetermined number of in-cylinder maximum pressures calculated in each cycle is temporarily stored in the storage device 8 in order to calculate the variation rate for each cycle.

  First, in step S1, an ionic current is detected. In the case of normal combustion, the ionic current generated after ignition once increases after ignition, then continues to increase after decreasing, reaches a maximum current value near the top dead center where the combustion pressure becomes maximum, and then gradually attenuates. . Utilizing such ion current characteristics, in step S2, the in-cylinder maximum pressure is estimated from the detected ion current. In this case, the in-cylinder maximum pressure may be estimated by calculation using a two-dimensional map of the maximum current value of the ionic current and the in-cylinder maximum pressure, or by multiplying the maximum current value by the converted value.

  In step S3, the fluctuation rate of the in-cylinder maximum pressure for each cycle is calculated based on the estimated in-cylinder maximum pressure. The variation rate is calculated based on, for example, the moving average of the in-cylinder maximum pressure in a predetermined number including the currently calculated in-cylinder maximum pressure and the standard deviation of the in-cylinder maximum pressure in the predetermined number.

  In step S4, it is determined whether or not the calculated variation rate is within a predetermined range R. That is, in order to grasp the fluctuation state of the in-cylinder maximum pressure, it is determined whether the calculated fluctuation rate is the same as or different from the previous cycle, in other words, whether an abnormal decrease or increase has occurred. Is. As shown in FIG. 3, the predetermined range R is set so that the fluctuation rate calculated in the steady operation is entirely within the predetermined range R, with the fluctuation rate being zero. Specifically, the predetermined range R is set, for example, with a fluctuation rate of 0 at the center and a positive / negative width of 0.1. If it is determined in step S4 that the calculated variation rate deviates from the predetermined range R, that is, the variation rate is 0.1 or more, whether positive or negative, the process proceeds to step S5. Otherwise, the current program The execution of is terminated.

  In step S5, it is determined based on the previous calculation result of the fluctuation rate stored in the storage device 8 whether or not the fluctuation rate has decreased outside the predetermined range R in the cycle immediately before the current cycle. If it is determined in step S5 that the rate of change has decreased in the previous cycle, the process proceeds to step S6. Otherwise, the execution of the current program is terminated.

  In step S6, it is determined whether or not the variation rate calculated this time has increased, that is, whether or not the current cycle is a cycle immediately after decreasing in the previous cycle and the variation rate has increased. Based on this determination, the presence or absence of a sign of misfire is determined.

  When the combustion state becomes slightly unstable, part of the fuel in the air-fuel mixture does not burn and the combustion stroke ends. In this case, since a part of the fuel is in an unburned state, the combustion pressure does not increase by the amount of unburned fuel, and the in-cylinder maximum pressure decreases. In the exhaust stroke subsequent to such a combustion stroke, unburned fuel or unburned gas remains in the cylinder as internal EGR gas. As a result, in the next cycle, the remaining unburned fuel is larger than the fuel amount set for that cycle, that is, the total amount of fuel in this cycle is increased by the amount of unburned fuel. The maximum in-cylinder pressure is higher than that in the case of the set fuel amount.

  In step S7, the mixture temperature is raised. In this embodiment, the opening timing of the exhaust valve 36 is controlled in order to increase the mixture temperature. Specifically, the timing for closing the exhaust valve 36 by the variable valve timing mechanism 30 is advanced, and with this configuration, the amount of burned gas is reduced and the burned gas remaining in the cylinder is reduced. This increases the amount of internal EGR. Accordingly, a larger amount of burned gas than before is mixed with the sucked fresh air, and the mixture temperature rises.

  When the operating state of the engine 100 is changed from the steady operation state to the transient operation state, the internal EGR temperature is changed by changing the fuel amount, the combustion chamber temperature, or the ignition timing from the previous steady operation state. There is. When the combustion state changes due to the change in the internal EGR temperature and the change appears in the in-cylinder maximum pressure, the transient misfire suppression control program maintains the operation state at that time or the mixture gas mixture. It is determined whether to control the exhaust valve 36 so as to increase the temperature.

  Then, as described above, by calculating the rate of change of the maximum in-cylinder pressure and determining the change, it is possible to determine the presence or absence of signs of misfire due to the lack of the mixture temperature. It is possible to take countermeasures, that is, to increase the mixture temperature by increasing the timing of closing the exhaust valve 36. As a result, combustion can be stabilized and the occurrence of misfire can be suppressed in advance.

  In addition, this invention is not limited to the above-mentioned embodiment.

  In the above-described embodiment, the sign of misfire is determined based on the fluctuation rate of the in-cylinder maximum pressure, but based on the pressure difference between the in-cylinder maximum pressure in the previous cycle and the in-cylinder maximum pressure in the current cycle. It may be one that determines signs of misfire. Even in this case, the maximum in-cylinder pressure decreases outside the predetermined range R in the previous cycle and changes so that the maximum in-cylinder pressure increases outside the predetermined range R in the current cycle. It is for judging signs.

  The in-cylinder maximum pressure is detected or measured directly by a pressure sensor provided along the combustion chamber 35 or the cylinder instead of the method of estimating based on the maximum current value of the ionic current as in the above-described embodiment. It may be. Such a pressure sensor includes a spark plug seat type pressure sensor and a knock sensor.

  In the above-described embodiment, the variable valve timing mechanism 30 that varies the valve timing of the exhaust valve 36 and the intake valve 37 has been described. However, a variable valve lift mechanism that can change at least the valve lift amount of the exhaust valve 36 is described. It is also possible to reduce the valve lift amount of the exhaust valve 36, thereby reducing the amount of burned gas to be discharged and increasing the mixture temperature.

  In this way, instead of reducing the valve lift amount of the exhaust valve 36, the valve lift amount of the intake valve 37 is reduced to reduce the amount of fresh air to be sucked. As a result, the new amount of burned gas remaining is reduced. The air volume ratio may be increased by decreasing the volume ratio, that is, by relatively increasing the internal EGR rate.

  Further, a variable valve mechanism having both the variable valve timing mechanism 30 and the valve lift variable mechanism may be provided for increasing the mixture temperature, and the above-described valve timing control and valve lift amount control may be performed. May be configured to raise the mixture temperature.

  If the engine includes a turbocharger, the mixture temperature may be increased by controlling the back pressure of the turbocharger. That is, the back pressure control of the turbocharger is performed by controlling the opening degree of the waste gate, and in the case of the variable nozzle type, by closing the nozzle.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  The present invention can be utilized in an internal combustion engine mounted on a vehicle, particularly an automobile.

DESCRIPTION OF SYMBOLS 5 ... Injector 6 ... Electronic control unit 7 ... Central processing unit 8 ... Memory | storage device 9 ... Input interface 10 ... Output interface 35 ... Combustion chamber R ... Predetermined range

Claims (1)

Premixed compression self-ignition combustion is performed in an in-cylinder fuel injection internal combustion engine that can perform premixed compression self-ignition combustion by controlling the temperature of the mixture by mixing the burned gas remaining in the cylinder with fresh air The maximum in-cylinder pressure when
Grasping the fluctuation state for each cycle based on the detected maximum in-cylinder pressure,
A transient misfire suppression control method for an internal combustion engine in which a misfire indication is determined and an air-fuel mixture temperature is increased when the grasped fluctuation state increases immediately after deviating from a predetermined range.