JP2008019729A - Control device of cylinder injection type engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of a cylinder injection type engine capable of suitably improving even emission, while restraining a torque shock when returning from a fuel cut. <P>SOLUTION: This control device (an ECU 60) of the cylinder injection type engine 10 comprises a program for supplying fuel supplied for combustion of a period equivalent to combustion cycle 2-periods just after returning from its fuel cut when the fuel cut is performed, by injecting and supplying the fuel by a quantity of becoming rich in the air-fuel ratio into its engine cylinder at a compression stroke (particularly, the latter period of the compression stroke) of the engine 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an in-cylinder injection engine that controls the fuel injection mode of a cylinder injection engine (so-called direct injection engine) that directly injects fuel into the cylinder to perform control such as fuel cut. The present invention relates to a control device.

  The in-cylinder injection type engine directly injects fuel into the cylinder (cylinder) in contrast to the intake port injection type engine known as the most common engine at present, that is, an engine that supplies fuel to the intake port. This is an engine to be supplied, and is generally known as an engine capable of improving engine output by a cooling effect due to vaporization latent heat of fuel directly injected into a cylinder. In-cylinder injection engines mainly allow two types of combustion. Specifically, fuel is injected into the engine cylinder by fuel injection in the intake stroke, and homogeneous combustion is performed to ignite an air-fuel mixture having a uniform stoichiometric ratio, and fuel injection in the compression stroke. There are two types of combustion modes: stratified combustion, in which fuel is injected into the engine cylinder and the ignition is performed with a partially rich air-fuel ratio in the vicinity of the spark plug while the air-fuel ratio is lean overall. It is possible to improve the fuel consumption rate (fuel consumption) by performing stratified combustion in a low rotation low load region (partial load region).

However, in the stratified combustion, combustion is performed at a lean air-fuel ratio in which the proportion of oxygen is higher than the stoichiometric air-fuel ratio, so that generation of NOx (nitrogen oxides) that is subject to regulation as a cause of acid rain and the like is generated. It tends to be promoted. For this reason, in the current in-cylinder injection type engine, the engine is basically operated by the homogeneous combustion in almost all operating regions except for some low load regions such as idling. For example, see Patent Document 1).
JP 2001-248482 A

  By the way, also in such an in-cylinder injection engine, fuel cut control for improving fuel consumption and deceleration is performed at the time of deceleration, similarly to the intake port injection engine. For example, in the case of an engine mounted on an automobile, a fuel cut is performed at the time of deceleration when the vehicle is sufficiently accelerated, and when accelerating again, the fuel is returned from the fuel cut and fuel is supplied again. become.

  However, when returning from a fuel cut, there is a concern that a large torque shock may occur due to a sudden (discontinuous) torque change from the fuel cut state (the state where the generated torque is zero), resulting in a deterioration in drivability. Become so. Therefore, conventionally, there is known a control device (first conventional device) for a direct injection engine in which the ignition timing is retarded to reduce the torque immediately after returning from the fuel cut. However, since there is a possibility of misfire if the ignition timing is retarded significantly, there is a limit to the amount of torque reduction with this device, and depending on the engine, it is possible to achieve torque reduction to the ideal torque value. May not be possible.

  In addition, regarding the above-described emission (NOx generation), since the oxygen concentration around the engine is high when returning from the fuel cut, the generation of NOx (nitrogen oxide) is promoted. Therefore, when the fuel cut is restored in the high load range, the homogeneous injection operation of the in-cylinder injection engine that performs the homogeneous combustion operation at the rich air-fuel ratio in which the fuel ratio is higher than the theoretical air-fuel ratio is performed instead of the homogeneous combustion at the theoretical air-fuel ratio. A control device (second conventional device) has also been proposed. However, even with this apparatus, the reduction of NOx is not sufficient, and the required emission improvement is not necessarily obtained.

  FIG. 9 and FIG. 10 show the results of experiments conducted by the inventor on an apparatus that combines the above-described characteristic configurations of the first and second conventional apparatuses. FIGS. 9A to 9G are timing charts showing transitions of control parameters when engine control (control related to a vehicle) is executed by this device. FIG. 10 shows the air-fuel ratio (solid line LE11) and the HC (one-dot chain line LE12) and NOx (two-dot chain line) detected in the exhaust pipe (tail pipe) of the engine when engine control is executed by the apparatus. It is a graph which shows the transition about each with LE13).

  As shown in FIG. 9, in this control, in order to decelerate a vehicle that has been sufficiently accelerated, for example, by steady combustion at the stoichiometric air-fuel ratio (combustion by intake stroke injection) during steady operation, at timing t11. When the amount of operation of the accelerator pedal (accelerator opening) by the driver is reduced (the throttle opening also follows), fuel cut is executed (fuel cut execution flag = ON). When the driver depresses the accelerator pedal again at timing t12 to return from fuel cut (fuel cut execution flag = OFF), the ignition timing is retarded to the retard limit Y1 for a predetermined period (t12 to t13). Along with (FIG. 9C), the target air-fuel ratio is set to be rich for a longer period (t12 to t14) (FIG. 9F). However, as shown in FIG. 9G, when the fuel cut is restored, the actual torque (solid line LT11) greatly deviates from the required torque (one-dot chain line LT12) (the actual torque is the required torque). Even with this device, torque reduction to the ideal torque value could not be achieved.

  In addition, as shown in FIG. 10, HC (maximum “5 ppm”) and NOx (maximum “12 ppm”) are generated immediately after returning from the fuel cut, as shown in FIG. Is not necessarily obtained.

  The present invention has been invented in view of such a situation, and it is an in-cylinder injection engine that can suitably improve the emission while suppressing the torque shock at the time of return from the fuel cut. The main purpose is to provide a control device.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  According to the first aspect of the present invention, in the in-cylinder injection engine control device that controls the fuel injection mode of the in-cylinder injection engine that directly injects fuel into the cylinder, the fuel cut is performed. The fuel supplied for combustion in the fuel cut return period, which is an arbitrary period immediately after the fuel cut return, is supplied in an amount sufficient to make the air-fuel ratio rich in the engine cylinder during the compression stroke of the engine. It is characterized by comprising a fuel cut return means for performing injection supply.

  In the above-described configuration including the fuel cut return means, the fuel is injected and supplied in the compression stroke slower than the intake stroke at the time of return from the fuel cut, taking advantage of the characteristics of the in-cylinder injection engine. Thereby, the possibility of misfire is reduced, and the ignition timing can be retarded more than in the intake stroke. In the inventor's experiment, the retard limit that was in the vicinity of “ATDC 5 ° CA (5 deg after top dead center)” in the intake stroke was determined, and “ATDC 20 ° CA (20 deg after top dead center) in the compression stroke”. "I was able to delay to near. Since the engine output torque is reduced by retarding the ignition timing as described above, according to the above configuration, by setting the ignition timing on the retard side with respect to the retard limit in the case of intake stroke injection, It becomes possible to accurately suppress the torque shock described above, which is a concern when returning from a fuel cut.

  The inventor also stated that the NOx is not sufficiently reduced even by the above-mentioned second conventional apparatus because the catalyst is in an oxidizing atmosphere at the time of return from fuel cut, and the catalyst (especially a catalyst made of a noble metal) Since the surface was covered with oxygen ions, the oxygen ions caused catalyst performance deterioration, and the oxidation / reduction reaction in the catalyst was considered to be delayed. Through various experiments, it was found that oxygen ions on the catalyst were removed by sending high-temperature exhaust gas having a rich air-fuel ratio to the catalyst. In this regard, according to the above-described configuration, the flame propagation speed after combustion is reduced and the time from combustion to emission is shortened by retarding the ignition timing more greatly as described above. As a result, the exhaust gas temperature is raised during the fuel cut recovery period. Moreover, the air-fuel ratio at this time is adjusted to a rich air-fuel ratio in which the proportion of fuel is higher than the stoichiometric air-fuel ratio (stoichiometric). Accordingly, even when the catalyst surface is covered with oxygen ions, this high-temperature exhaust rich in the air-fuel ratio can be suitably removed, and as a result, the above-described emission can be greatly improved. In general, the exhaust purification device (catalyst) provided in the exhaust system is more suitable when high-temperature exhaust is sent (for example, during high-speed travel) than when low-temperature exhaust is sent (for example during low-speed travel). Etc.), the emission performance can be improved by the influence. Furthermore, the generation of NOx (nitrogen oxide) is also suppressed by simply lowering the oxygen concentration in the exhaust gas.

  As described above, according to the above configuration, it is possible to suitably improve the emission while suppressing the torque shock when returning from the fuel cut. The present invention (apparatus) can be applied to engines in a wide field (for example, ships and aircrafts) that are not limited to automobiles, but it is particularly useful to be applied (mounted) to automobiles. It is as follows.

  In order to obtain such an effect, the fuel injection timing in the fuel cut return period is particularly useful when set in the latter half of the compression stroke in the compression stroke.

  Further, the fuel supply during the fuel cut return period may be a constant pattern or an indefinite pattern for each compression stroke. For example, the fuel may be supplied in different patterns (for example, a single injection pattern and a divided injection pattern, etc.) at each compression stroke corresponding to the crank cycle.

  According to a second aspect of the present invention, in the apparatus according to the first aspect, the fuel cut return means performs fuel supply in the fuel cut return period by split injection.

  When the fuel injected into the engine cylinder cannot be completely vaporized in the combustion chamber, the fuel remains in liquid form and adheres to the piston top surface, which affects the air-fuel ratio in the combustion chamber and prevents stable combustion. Or cause smoke. In this regard, if the divided injection is positively performed as in the above-described configuration, the amount to be injected at one time can be reduced, so that the amount of vaporization is accelerated and the amount that cannot be completely evaporated is reduced, and thus stable. Combustion will be realized.

  In addition, since various modes can be considered as the mode of split injection, it is desirable to adopt an optimal mode according to the engine specifications and the like. For example, a configuration in which injection is performed a plurality of times (for example, twice or three times) in a compression stroke, or a configuration in which divided injection is performed in an intake stroke and a compression stroke (for example, once) is effective in practice. It is believed that there is.

  According to a third aspect of the present invention, in the apparatus according to the first or second aspect, the fuel cut return period varying means for varying the fuel cut return period in accordance with a required engine torque value for the in-cylinder injection engine. It is characterized by providing.

  By the way, the optimum length of the fuel cut return period varies depending on the required engine torque value, in particular, the degree of fluctuation of the value at the time of fuel cut return. For example, when the required engine torque value suddenly increases at the time of fuel cut return, it is desirable to set the fuel cut return period to a shorter period and quickly shift to combustion by intake stroke injection. In this regard, according to the above configuration, in response to such a case, the fuel cut return period variable means sets the fuel cut return period as a shorter period, thereby promptly shifting to combustion by intake stroke injection. Is possible. Conversely, even if the required engine torque value is set such that the fuel cut return period is set to a longer period, it is possible to flexibly cope with this. In other words, with the above configuration, the length of the fuel cut return period can be optimized by the fuel cut return period variable means.

  According to a fourth aspect of the present invention, in the apparatus according to any one of the first to third aspects, the fuel cut return for setting the end timing of the fuel cut return period based on the ignition timing of the direct injection engine. A period setting unit; and an injection mode switching unit that switches the fuel injection mode of the in-cylinder injection engine to the injection supply in the intake stroke when the fuel cut return period ends.

  Comparing the combustion by the intake stroke injection and the combustion by the compression stroke injection, generally, the combustion by the intake stroke injection is superior in terms of engine output characteristics and emission if both are the same ignition timing. Therefore, when a sufficient amount of time elapses from the return of fuel cut and the ignition timing enters the stable combustion range of the intake stroke injection (advanced side from the retard limit), the combustion can be quickly shifted to combustion by the intake stroke injection. desirable. In this regard, according to the above configuration, the compression stroke injection is stopped when the ignition timing enters the stable combustion range of the intake stroke injection by the fuel cut return period setting means, and the fuel injection mode is changed to the intake stroke injection by the injection mode switching means. It becomes possible to switch. This makes it possible to realize a more preferable combustion mode, and thus an engine operation mode, as a control device for the direct injection engine.

  Also, as described above, at the same ignition timing, the combustion by the intake stroke injection is superior to the combustion by the compression stroke injection in terms of engine output characteristics and emission. Therefore, in view of these points, the compression stroke injection It is desirable that the period of combustion by is as short as possible. The inventor has clarified that the effect of suppressing the torque shock and the effect of improving the emission are particularly remarkable in the case of one or two compression stroke injections through various experiments. As a result, in order to achieve compatibility with the above-mentioned inconvenience due to the combustion by the compression stroke injection, the configuration in which the compression stroke injection is performed once or twice is effective as the configuration of the control device. I understood. In ordinary applications, one time is basically effective, and in applications where torque shock is large, two times are effective when giving priority to torque shock suppression over the above disadvantages. Therefore, as described in claim 5, in the device according to any one of claims 1 to 4, the length of the fuel cut return period is from one cycle to two cycles of the combustion cycle of the engine. It is effective to have a configuration that is set to a minute (in terms of the crank cycle), the crankshaft rotates twice (720 ° CA) and the crankshaft rotates four times (720 ° CA × 2). is there. In the case of a multi-cylinder configuration, it is desirable to set the length of the fuel cut return period for each cylinder to one to two cycles of the combustion cycle of each cylinder.

  According to a sixth aspect of the present invention, in the apparatus according to any one of the first to fifth aspects, the fuel provided for combustion in a rich operation continuation period that is an arbitrary rich operation period following the fuel cut return period. In the intake stroke of the engine, there is provided rich operation means for injecting and supplying fuel in an amount sufficient to make the air-fuel ratio rich into the cylinder of the engine.

  When the engine is installed in an automobile or the like, the vehicle body usually has to be accelerated after the fuel cut is restored, so if the torque shock is sufficiently suppressed, the ignition timing is immediately shifted to the advance side. It is desirable to increase the torque. However, as described above, even if the problem of torque shock is solved, the problem of emissions remains. In view of this, a configuration has been invented in which the intake stroke injection is continuously performed at a rich air-fuel ratio without returning the air-fuel ratio to the stoichiometric air-fuel ratio even after the end of the fuel cut return period. That is, in order to optimize the engine combustion mode, as described above, a fuel cut return period in which compression stroke injection is performed with a rich air-fuel ratio, and an intake stroke with a rich air-fuel ratio following this fuel cut return period. It is effective to provide rich operation continuation periods in which injection is performed, and to set the lengths of these periods individually according to the degree of torque shock, the degree of deterioration of emissions, and the like.

  Further, in this case, as in the seventh aspect of the invention, at least one of the length of the rich operation continuation period and the air-fuel ratio in the rich operation continuation period is set as the total fresh air amount (new air amount during the fuel cut). It is effective to include a means that can be varied according to the estimated value (for example, fuel cut execution time or engine speed).

  As the total amount of fresh air during fuel cut increases, the oxidation concentration around the engine increases, and the generation of NOx is promoted. For this reason, in order to improve emissions, the above configuration is adopted, and as the total amount of fresh air during fuel cut increases, the rich operation continuation period is lengthened or the air-fuel ratio during the same period is made richer. It is effective to set the fuel ratio.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment in which a control device for a direct injection engine according to the present invention is embodied will be described with reference to the drawings. In addition, the apparatus of this embodiment is mounted in the fuel-injection control system about the cylinder injection type engine (internal combustion engine) employ | adopted, for example in a four-wheeled motor vehicle.

  First, the configuration of this system will be described in detail with reference to FIG.

  FIG. 1 is a configuration diagram showing an outline of a vehicle control system in which a control device for a direct injection engine according to this embodiment is mounted. As an engine of the present embodiment, a multi-cylinder spark ignition reciprocating engine is assumed. However, in FIG. 1, only one cylinder is shown for convenience of explanation.

  As shown in FIG. 1, this system is constructed by an in-cylinder injection gasoline engine 10, various sensors for controlling the engine 10, various actuators, an ECU (electronic control unit) 60, and the like. .

  The engine 10 basically includes a cylinder (cylinder) 12 formed by a cylinder block 11. The cylinder block 11 is provided with a cooling water passage 11a serving as a cooling water passage and a cooling water temperature sensor 11b for detecting the cooling water temperature, and the engine 10 is cooled by the cooling water. Also, a piston 13 having a cavity 13a for generating a swirl flow or a tumble flow on the top surface is accommodated in the cylinder 12, and a reciprocating motion of the piston 13 causes a crankshaft as an output shaft (not shown). Is designed to rotate. A crank angle sensor 12a that outputs a rectangular crank angle signal for each predetermined crank angle (for example, at a cycle of 30 ° CA) is disposed on the outer peripheral side of the crankshaft so that the rotation angle of the crankshaft can be detected. Has been. A cylinder head 15 is fixed to the upper end surface of the cylinder block 11, and a combustion chamber 16 is formed between the cylinder head 15 and the upper surface of the piston 13.

  The cylinder head 15 is formed with an intake port 17 and an exhaust port 18 that open to the combustion chamber 16, and the intake port 17 and the exhaust port 18 are respectively connected to an intake valve 21 and an exhaust gas driven by cams 21a and 22a. The valve 22 is opened and closed. The intake port 17 is connected to an intake pipe 23 (intake manifold) for sucking outside air into each cylinder of the engine 10, and the exhaust port 18 is supplied with combustion gas (exhaust gas) from each cylinder of the engine 10. An exhaust pipe (exhaust manifold) 24 for discharging is connected, and in the middle of the intake pipe 23, a surge tank 23a whose passage area is enlarged (expanded diameter) for the purpose of preventing intake pulsation and intake interference is provided. Is provided.

  The intake pipe 23 is provided with an air flow meter 31 for detecting the amount of fresh air drawn through an air cleaner (not shown) at the most upstream portion of the intake pipe 23. Further, on the downstream side of the air flow meter 31, an electronically controlled throttle valve 32 whose opening is electronically adjusted by an actuator such as a DC motor, and the opening and movement (opening fluctuation) of the throttle valve 32 are provided. A throttle opening sensor 32a for detection is provided, and the amount of air sent to the surge tank 23a provided downstream thereof can be adjusted. The surge tank 23a is provided with an intake pipe pressure sensor 23b for detecting the intake pipe pressure (intake pipe negative pressure or the like), and in the vicinity of the intake port 17 is a swirl in the cylinder 12 that affects the flame propagation speed or the like. An airflow control valve 17a is provided for controlling airflow strength such as flow strength and tumble flow strength.

  On the other hand, the exhaust pipe 24 is provided with a catalyst 35 made of a three-way catalyst or the like for purifying CO, HC, NOx and the like in the exhaust gas, and exhausted from the cylinder 12 on the upstream side of the catalyst 35. An oxygen concentration sensor 35a (for example, a linear detection type A / F sensor, a binary detection type O2 sensor, or the like) is provided for detecting the air-fuel ratio or rich / lean of the air-fuel mixture using exhaust as a detection target.

  On the other hand, an electromagnetically driven injector (fuel) for supplying fuel (gasoline) for combustion in the combustion chamber 16 directly into the cylinder 12 (in-cylinder) is supplied to the combustion chamber 16 in the cylinder 12. 27) is provided. Here, for the sake of convenience, only the injector 27 provided in one cylinder (cylinder 12) is illustrated, but such an injector is provided for each cylinder of the engine 10. Each injector of the engine 10 including the injector 27 is connected to the fuel tank 41 so that the fuel in the fuel tank 41 pumped up by the fuel pump 42 is supplied to each injector through the fuel pipe 43. It has become. A fuel pressure sensor 44 for detecting the fuel pressure is provided in the middle of the fuel pipe 43 so that the fuel pressure of each injector of the engine 10 can be managed.

  Further, an ignition plug that ignites (sparks ignition) the fuel in the air-fuel mixture when a high voltage is applied to the combustion chamber 16 through an ignition coil (not shown) at a desired ignition timing based on an instruction from the ECU 60. 28 etc. are also attached. That is, during the operation of the engine 10, intake air is introduced into the combustion chamber 16 from the intake pipe 23 by opening the intake valve 21, and this air is mixed with the fuel injected and supplied directly from the injector 27 into the cylinder 12. . Then, the air-fuel mixture is ignited by the spark plug 28 in a compressed state, ignited and combusted, and the exhaust valve 22 is opened to discharge the combusted exhaust gas to the exhaust pipe 24. As described above, the fuel supply timing in the direct injection engine is not limited to the intake stroke before compression, and fuel can be supplied even during the compression stroke.

  The system further includes an EGR device for recirculating a part of the exhaust gas to the intake system as EGR (Exhaust Gas Recirculation) gas. The EGR device basically includes an EGR pipe 51 provided so as to communicate the intake pipe 23 and the exhaust pipe 24, and an electromagnetic valve that adjusts the passage area of the EGR pipe 51 according to the valve opening degree. And an EGR valve 52. In the EGR device, based on such a configuration, part of the exhaust gas is recirculated to the intake system through the EGR pipe 51, and the generation of NOx is reduced by lowering the combustion temperature.

  In addition to the above sensors, the vehicle (not shown) is further provided with various sensors for vehicle control. For example, an accelerator opening sensor 61 that detects an operation amount (accelerator opening) of an accelerator pedal by the driver is provided.

  The ECU 60 that controls the vehicle as an electronic control unit includes a known microcomputer (not shown), and controls the engine 10 by driving the various actuators based on detection signals sequentially input from the various sensors. is there. The microcomputer mounted on the ECU 60 basically includes a CPU (basic processing device) that performs various operations, a RAM as a main memory, a ROM (read only storage device) as a program memory, and a data storage memory. Are composed of various arithmetic devices and storage devices such as an EEPROM (electrically rewritable nonvolatile memory). The ROM stores various programs and control maps related to engine control including programs related to fuel injection timing control and ignition timing control, and the data storage memory (EEPROM) stores engine 10 design data. Various types of control data such as those are stored in advance.

  FIG. 2 is a block diagram showing various functions related to engine control of the present embodiment mounted on the ECU 60. These various functions are used to calculate various parameters based on required engine torque and the like for optimizing the operating state of the engine 10, and in particular, the fuel after the fuel cut is executed. Various parameters relating to fuel injection and ignition in a period immediately after the cut return (fuel cut return period) are calculated.

  As shown in FIG. 2, the ECU 60 is configured to have various functional blocks including a calculation block for each parameter. In the throttle opening calculation unit 60a, the accelerator opening, the engine rotation speed, etc. The required torque value (required engine torque) is obtained based on the above, and the throttle opening corresponding to this required torque value is calculated. The basic ignition timing calculation unit 60b calculates the basic ignition timing Sb based on the engine load (for example, intake pipe negative pressure) and the engine rotation speed. The ignition timing correction amount calculation unit 60c calculates the ignition timing correction amount Sc based on the engine speed and the like. The arithmetic unit 60d takes in the basic ignition timing Sb and the ignition timing correction amount Sc from the basic ignition timing calculation unit 60b and the ignition timing correction amount calculation unit 60c, respectively, and calculates the ignition timing correction amount Sc from the basic ignition timing Sb. The subtracted value (= Sb−Sc) is calculated. The calculation unit 60d changes its output in accordance with the counter value C1 of the counter 60g. While the counter value C1 is smaller than the threshold value (threshold value 1), the ignition timing S is “Sb”. When the counter value C1 is equal to or greater than “threshold 1”, the value “Sb−Sc” is output as the ignition timing S. The injection timing calculation unit 60e takes in the ignition timing S output from the calculation unit 60d, and calculates the injection timing FT based on the ignition timing S and the engine speed. Further, the target air-fuel ratio calculating unit 60f also changes its output in accordance with the counter value C2 of the counter 60g, similarly to the calculating unit 60d. In the target air-fuel ratio calculating unit 60f, while the counter value C2 is smaller than the threshold value (threshold value 2), a predetermined rich air-fuel ratio (for example, A / F (weight ratio of air / fuel)) is set as “13. )), But when the counter value C2 is equal to or greater than “threshold 2”, the stoichiometric air-fuel ratio (stoichiometric) is output as the target air-fuel ratio.

  The configuration of the vehicle control system according to the present embodiment has been described in detail above. That is, the vehicle (automobile) on which the engine 10 (FIG. 1) is mounted is controlled by such a system. In this system, for example, the optimal fuel injection amount, injection timing, injection pressure, ignition timing, EGR amount, etc. according to the operating state of the engine 10 are calculated by the ECU 60 and executed by various programs. The engine 10 is sequentially calculated based on engine operation information such as the engine speed, throttle opening, and air-fuel ratio, and feedback control is performed on the engine 10 based on the calculated parameters.

  Hereinafter, the engine control of the present embodiment will be described in detail with reference to FIGS.

  FIG. 3 is a flowchart showing a processing procedure for engine control executed by the apparatus of the present embodiment, and FIGS. 4A to 4H are transitions of control parameters when the processing of FIG. 3 is executed. It is a timing chart which shows. 3 is basically executed by a program stored in the ROM by the ECU 60, so that after the engine 10 is warmed up, each cylinder of the engine 10 is set at a predetermined crank angle. (For example, every TDC (top dead center)) or sequentially in a predetermined cycle. The values of various parameters used in the processing of FIG. 3 are stored as needed in a storage device such as a RAM or EEPROM mounted in the ECU 60, and updated as necessary.

  As shown in FIG. 3, in this series of processing, first, in step S101, the fuel cut execution flag F1 (FIG. 4B) indicating whether or not the fuel cut is being executed is set to “OFF”. Judge whether or not.

  That is, for example, in order to decelerate a vehicle that has been driven by homogeneous combustion at the stoichiometric air-fuel ratio (combustion by intake stroke injection) during steady operation and sufficiently accelerated, the amount of operation of the accelerator pedal by the driver (at timing t1 in FIG. 4) When the accelerator opening is decreased (see FIG. 4A), the ECU 60 executes fuel cut. In this case, “ON” is set in the flag F1 (see FIG. 4B), and it is determined in step S101 that “flag F1 = OFF” is not satisfied.

  If it is determined in step S101 that “flag F1 = OFF” is not satisfied, in subsequent step S102, a fuel cut return period passage flag F2 indicating whether or not the fuel cut return period has passed (FIG. 4E). Set “ON” to. Next, in step S103, "0" is set to the counter values C1 and C2 of the counter 60g (FIG. 2) (counter value reset). Thus, during the fuel cut execution (period t1 to t2 in FIG. 4), the processes in steps S101 to S103 are repeatedly executed. Note that the required torque value indicated by the alternate long and short dash line LT2 in FIG. 4H is obtained by the throttle opening calculation unit 60a (FIG. 2) as described above, and the throttle opening shown in FIG. Is controlled to a value that matches this required torque value.

  Thereafter, when the driver depresses the accelerator pedal again at timing t2 in FIG. 4 to return from the fuel cut, it is determined in step S101 that “flag F1 = OFF”. Accordingly, in the subsequent step S104, it is determined whether or not the flag F2 is “ON”. Immediately after the return from the fuel cut, “ON” is set in the flag F2 by the processing of the previous step S102, and therefore it is determined in this step S104 that “flag F2 = ON”. Accordingly, in the following step S105, for example, a basic map is referred to while referring to a predetermined map, more specifically, a two-dimensional map in which the basic ignition timing Sb corresponding to the predetermined engine ignition and engine rotation speed values is uniquely determined. The basic ignition timing Sb is calculated by the ignition timing calculation unit 60b (FIG. 2).

  Next, in step S111, it is determined whether or not the counter value C1 is smaller than “threshold 1” (C1 <threshold 1). The threshold value 1 is set as a fixed value corresponding to the period of timing t2 to t3 in FIG. 4, that is, the period for executing the compression stroke injection (fuel cut return period). Specifically, the ignition timing S is set to the intake stroke injection. Is set as a period (for example, two cycles of the combustion cycle) in which the timing t3 becomes the initial stage of the stable combustion range by predicting the time when the stable combustion range (advanced side from the retard limit Y1) is entered. . If it is determined in step S111 that the counter value C1 is smaller than “threshold value 1”, it is determined that the compression stroke injection is in a period of execution, and in step S112, for example, referring to a predetermined map, The ignition timing correction amount Sc is calculated by the ignition timing correction amount calculation unit 60c (FIG. 2). FIG. 5 shows an example of a map used for calculating the ignition timing correction amount Sc.

  As shown in FIG. 5, this map shows the ignition timing corresponding to each value of the number of ignitions and the engine speed (unit: “rpm”) after fuel cut return (after timing t2 in FIG. 4). It is a two-dimensional map in which the correction amount Sc is uniquely determined. This map defines the correspondence as shown in FIG. 5 so that as the number of ignitions after returning from fuel cut increases and the engine speed that affects the required torque increases, the map is set based on these values. The ignition timing correction amount Sc (retard amount) becomes small. It should be noted that the number of ignitions after returning from the fuel cut basically increases with the rotation of the crankshaft, in other words, with the passage of time. According to this map, the graph of FIG. The transition of the ignition timing as shown is obtained.

  Next, in step S113, using the calculation formula “S = Sb−Sc”, the calculation unit 60d (FIG. 2) calculates a value obtained by subtracting the ignition timing correction amount Sc from the basic ignition timing Sb. The final ignition timing S is set. Specifically, as shown in FIG. 4C, the ignition timing S is a compression stroke located on the retard side from the retard limit Y1 (for example, near “ATDC5 ° CA”) in the case of intake stroke injection. The delay angle limit Y2 in the case of injection (for example, near “ATDC 20 ° CA”) is set.

  In the subsequent step S114, the injection timing FT is calculated by the injection timing calculation unit 60e (FIG. 2) while referring to a predetermined map, for example, to execute the compression stroke injection. FIG. 6 shows an example of a map used for calculating the injection timing FT.

  As shown in FIG. 6, this map corresponds to the ignition timing S (BTDC (before top dead center), the unit is “deg”) and the engine rotation speed (unit is “rpm”). It is a two-dimensional map in which the injection timing FT to perform is uniquely determined. This map defines the corresponding relationship as shown in FIG. 6, so that the engine speed can be increased regardless of the ignition timing S taking any value from “20” to “−30 (negative sign indicates ATDC)”. As the speed increases, the injection timing FT is set to a more advanced side. As the engine speed increases (the crankshaft rotates faster), the ignition cycle and the injection cycle become shorter. Therefore, the injection timing FT is set to a more advanced side in order to secure an interval necessary for fuel vaporization. Then, during the period from the timing t2 to the timing t3 in FIG. 4, the injection timing FT of the graph as shown in FIG. 4F is obtained based on this map. Specifically, the injection timing FT is the latter half of the compression stroke (for example, “ BTDC 30 ° CA (near 30 deg. Before top dead center) ”is set.

  Next, in step S115, the counter value C1 is counted up (C1 = C1 + 1) by the counter 60g (FIG. 2). In this way, the processing of steps S112 to S115 is repeatedly executed during the period from timing t2 to t3 in FIG.

  Next, in step S121, it is determined whether or not the counter value C2 is smaller than “threshold 2” (C2 <threshold 2). The threshold value 2 is variably set as a period between timings t2 and t4 in FIG. 4, that is, a period during which the target air-fuel ratio is rich. Specifically, the fuel cut is executed as an estimated value of the total fresh air amount during the fuel cut. The longer the period (t1 to t2), the longer the period (t2 to t4) is set. If it is determined in step S121 that the counter value C2 is smaller than the “threshold value 2”, it is determined that the target air-fuel ratio is in a rich period, and in step S122, the target air-fuel ratio calculating unit 60f (FIG. 2) A rich air-fuel ratio (for example, A / F “13”) is output and set as the target air-fuel ratio. In the next step S123, the counter value C2 is counted up (C2 = C2 + 1) by the counter 60g (FIG. 2). In this way, during the period from the timing t2 to t4 in FIG.

  The air-fuel ratio is adjusted to be rich in the period from timing t2 to t4 in FIG. 4 by the processing in steps S122 to S123, but the period (t2 to t3) determined by the threshold 1 at timing t3 in FIG. After that, it is determined in the previous step S111 that “C1 <threshold 1” is not satisfied (C1 ≧ threshold 1). Therefore, in the subsequent step S116, the basic ignition timing Sb calculated by the basic ignition timing calculation unit 60b (FIG. 2) is set as the final ignition timing S as it is (S = Sb). In the subsequent step S117, the injection timing FT is calculated by the injection timing calculation unit 60e (FIG. 2) while referring to a predetermined map, for example, to execute the intake stroke injection. FIG. 7 shows an example of a map used for calculating the injection timing FT.

  As shown in FIG. 7, in this map as well as the map shown in FIG. 6, if the values of the ignition timing S and the engine speed are determined, the corresponding injection timing FT is uniquely determined. It is a dimension map. This map defines the corresponding relationship as shown in FIG. 7, so that the engine speed can be increased regardless of whether the ignition timing S takes any value between “40” and “−10 (negative sign indicates ATDC)”. As the speed increases, the injection timing FT is set to a more advanced side. Again, since the ignition cycle and the injection cycle become shorter as the engine speed increases, the injection timing FT is set to a more advanced side in order to secure an interval necessary for fuel vaporization. In the period from timing t3 to t4 in FIG. 4 (rich operation continuation period), the injection timing FT shown in FIG. 4F is obtained based on this map. An intake stroke (for example, near “BTDC 300 ° CA”) is set.

  Further, after the period (t2 to t4) determined by the threshold 2 has passed, it is determined that “C2 <threshold 2” is not satisfied (C2 ≧ threshold 2) at the timing t4 in FIG. Will come to be. Therefore, in the following step S124, the target air-fuel ratio calculation unit 60f (FIG. 2) outputs the stoichiometric air-fuel ratio (stoichiometric) and sets this as the target air-fuel ratio. Then, in subsequent step S125, in order to indicate that the fuel cut return period (t2 to t3) has passed, “OFF” is set to the fuel cut return period passing flag F2 (FIG. 4E) (flag reset). . That is, it is determined in the previous step S104 that “flag F2 = ON” is not established, and until the next fuel cut execution (for example, before timing t1 in FIG. 4), the above steps S101, S104, S103 are performed. This process is repeatedly executed. Note that the counter values C1 and C2 relating to the process of step S103 need only be reset during the fuel cut execution, and therefore, the process may be terminated without passing through step S103 in the period before the fuel cut execution. .

  As shown in FIG. 4 (h), in this embodiment, the actual torque (solid line LT1) is more faithfully represented by the required torque (solid line LT1) including when the fuel cut is restored by repeatedly executing the series of processes of FIG. It follows the one-dot chain line LT2). Thereby, the torque shock at the time of return from a fuel cut is suppressed. This also greatly improves emissions. In the present embodiment, as described above, the ignition timing is retarded more greatly (retarded to the retard limit Y2), so that the exhaust temperature is raised during the fuel cut return period (t2 to t3). The air-fuel ratio is adjusted to be rich (for example, A / F “13”) in the period from timing t2 to t4 in FIG. 4 including the fuel cut return period. Due to this high-temperature exhaust rich in the air-fuel ratio, the above-described system according to the present embodiment suitably removes the oxygen ions covering the catalyst surface described above, and as a result, the emission is greatly improved.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  (1) When the fuel cut is performed as the control device (ECU 60) of the direct injection engine 10, combustion in the period immediately after the return from the fuel cut (timing t2 to t3 in FIG. 4, the fuel cut return period) A program (fuel cut return means) for supplying the fuel to be supplied to the engine 10 by injecting and supplying an amount of fuel sufficient to make the air-fuel ratio rich in the engine cylinder during the compression stroke of the engine 10 (particularly at the latter stage of the compression stroke) ). According to such a configuration, it is possible to suitably improve the emission while suppressing the torque shock when returning from the fuel cut.

  (2) The length of the fuel cut return period (t2 to t3) (corresponding to the threshold value 1) is set to be equal to two combustion cycles for each cylinder (in terms of the crank period, the period during which the crankshaft rotates four times (720 °). CA × 2)). As a result, a large effect can be obtained with a small number of compression stroke injections.

  (3) As fuel to be used for combustion in the rich operation continuation period (t3 to t4) following the fuel cut return period, an amount of fuel sufficient to make the air-fuel ratio rich in the engine cylinder during the intake stroke of the engine 10 It was set as the structure provided with the program (rich operation means) which injects and supplies. This makes it possible to individually set the length of the fuel cut return period and the rich operation continuation period (corresponding to the thresholds 1 and 2) (steps S111 and S121), thereby suppressing the torque shock and improving the emission. It becomes possible to achieve both.

  (4) The rich operation continuation period (t3 to t4) is configured to include a program for variably setting the fuel cut execution time (t1 to t2). As a result, the emission can be improved more appropriately.

  The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  A program (fuel cut return period setting means) for setting the end timing (timing t3) of the fuel cut return period based on the ignition timing of the in-cylinder injection engine 10, and the direct injection engine 10 with the end of the fuel cut return period And a program (injection mode switching means) for switching the fuel injection mode to injection supply in the intake stroke. That is, in this case, for example, as shown in FIG. 8 (timing chart corresponding to FIG. 4), the compression stroke injection is stopped when the ignition timing enters the stable combustion range of the intake stroke injection (timing t3 in FIG. 8). At the same time, the fuel injection mode is switched to intake stroke injection (FIG. 8 (f)). Thus, by performing fuel supply (injection) in the intake stroke as much as possible, it is possible to realize a more preferable combustion mode, and thus an engine operation mode, as a control device for a direct injection engine. It becomes like this.

  The fuel supply in the fuel cut return period (t2 to t3) is not limited to the latter half of the compression stroke, and may be performed in the first half or the middle of the compression stroke. Also in this case, an effect similar to the effect (1) can be obtained.

  In the above embodiment, the fuel supply in one injection is assumed as the fuel supply in the fuel cut return period (t2 to t3), but the fuel supply in the same period is performed by split injection, for example, A configuration in which injection is performed a plurality of times (for example, two times or three times or more) in a compression stroke, a configuration in which divided injection is performed in an intake stroke and a compression stroke (for example, once), or the like may be employed. With such a configuration, since the amount injected at one time is small, the fuel vaporization is promoted, and the amount that cannot be completely vaporized is reduced, so that stable combustion is realized.

  Furthermore, the fuel supply during the fuel cut return period (t2 to t3) may be a constant pattern or an indefinite pattern for each compression stroke. For example, the fuel may be supplied in different patterns (for example, a single injection pattern and a divided injection pattern, etc.) at each compression stroke corresponding to the crank cycle.

  In the above embodiment, the length of the fuel cut return period (t2 to t3) (corresponding to the threshold value 1) is set to two periods of the combustion cycle with priority given to torque shock suppression. The length is basically arbitrary. In the normal use, if the period of synchronization is set to one period of the combustion cycle, basically, an effect similar to the effect (2) can be obtained.

  In the above embodiment, the fuel cut execution time (t1 to t2) is used as the estimated value of the total fresh air amount (the integrated value of the fresh air amount) during the fuel cut, and the rich operation continuation period according to this estimated value The length (t3 to t4) is variably set. However, this estimated value is sufficient if it can estimate the total amount of fresh air during the fuel cut. For example, the engine speed (the higher the speed, the larger the amount of fresh air) is taken as the fuel cut execution time. It may be used instead. However, in order to increase the estimation (calculation) accuracy, it is more effective to obtain the total fresh air amount during the fuel cut by calculation.

  A configuration in which the rich operation continuation period is fixed and the air-fuel ratio (for example, A / F “about 11 to 14”) in the rich operation continuation period is variably set according to the total fresh air amount during fuel cut or an estimated value thereof. Also good. That is, in this case, the air-fuel ratio (A / F) is set to a richer air-fuel ratio (smaller value) as the total amount of fresh air during fuel cut increases (for example, the longer the fuel cut execution time). Even with such a configuration, an effect similar to the effect of the above (4) can be obtained.

  The setting of the rich operation continuation period (t3 to t4) that is the rich operation period following the fuel cut return period is not an essential condition. For example, at the same time when the fuel cut return period ends, the combustion may be shifted to the combustion by the intake stroke injection at the stoichiometric air-fuel ratio (homogeneous combustion).

  A program (fuel cut return period variable means) that makes the fuel cut return period (t2 to t3) variable in accordance with the required engine torque value for the in-cylinder injection engine 10 (dashed line LT2 in FIG. 4 (h)) It is also effective to provide a configuration. For example, when the required engine torque value suddenly increases at the time of fuel cut return (the slope of the graph becomes steeper), the fuel cut return period (t2 to t3) is set as a shorter period so as to quickly Then, the combustion shifts to intake stroke injection. As a result, the length of the fuel cut return period is optimized.

  In the above embodiment, various software (programs) are used. However, some or all of the various functions (see FIG. 2) including the counter function (counter 60g) are dedicated circuits or the like. The same function may be realized by hardware.

  The system configuration shown in FIG. 1 is merely an example of a configuration to which the present invention can be applied. Even when the configuration is appropriately changed, the present invention is applied basically in the same manner as in the above embodiment. be able to. For example, the present invention can be applied to a configuration in which the arrangement of the EGR device is omitted or a configuration in which a variable valve mechanism and a turbocharger are further provided. And this invention is effective also about uses other than a motor vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS The configuration diagram which shows the outline of the vehicle control system to which this apparatus was applied about one Embodiment of the control apparatus of the direct injection type engine which concerns on this invention. The block diagram which shows the various functions which concern on the engine control mounted in the apparatus. The flowchart which shows the process sequence of the engine control performed by the same apparatus. (A)-(h) is a timing chart which shows transition of the control parameter when the process of FIG. 3 is performed, respectively. A map used when calculating an ignition timing correction amount (ignition delay correction amount). The map used when calculating the injection timing in the fuel cut return period. The map used when calculating the injection timing in the rich operation continuation period. (A)-(h) is a timing chart which shows another example of a fuel-injection aspect. (A)-(h) is a timing chart which shows the result of the experiment which the inventor performed about the apparatus which combined the partial structure of the conventional apparatus. The graph which shows the exhaust characteristic of the apparatus which concerns on the same experiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine, 27 ... Injector (fuel injection valve), 28 ... Spark plug, 60 ... ECU (electronic control unit), 60a ... Throttle opening calculation part, 60b ... Basic ignition timing calculation part, 60c ... Ignition timing correction amount calculation Part, 60d ... arithmetic part, 60e ... injection timing calculation part, 60f ... target air-fuel ratio calculation part, 60g ... counter.

Claims (7)

In a cylinder injection engine control apparatus for controlling a fuel injection mode of a cylinder injection engine that directly injects fuel into a cylinder,
When a fuel cut is performed, the fuel supplied for combustion in the fuel cut return period, which is an arbitrary period immediately after the return from the fuel cut, is supplied to the engine cylinder during the compression stroke of the engine. An in-cylinder injection engine control device comprising a fuel cut return means for performing injection by supplying an amount of fuel to be injected.   The in-cylinder injection engine control device according to claim 1, wherein the fuel cut return means performs fuel supply by split injection in the fuel cut return period.   The in-cylinder injection engine control device according to claim 1 or 2, further comprising fuel cut return period variable means for changing the fuel cut return period in accordance with a required engine torque value for the in-cylinder injection engine. Fuel cut return period setting means for setting an end timing of the fuel cut return period based on an ignition timing of the direct injection engine;
An injection mode switching means for switching the fuel injection mode of the in-cylinder injection engine to the injection supply in the intake stroke at the end of the fuel cut return period;
The control apparatus of the cylinder injection type engine as described in any one of Claims 1-3 provided with these.   The in-cylinder injection engine control device according to any one of claims 1 to 4, wherein a length of the fuel cut return period is set to one cycle to two cycles of a combustion cycle of the engine.   An amount of fuel sufficient to make the air-fuel ratio rich in the engine cylinder is injected during the intake stroke of the engine as fuel to be used for combustion in the rich operation continuation period that is an arbitrary rich operation period following the fuel cut return period. The in-cylinder injection engine control device according to any one of claims 1 to 5, further comprising a rich operation means for supplying.   The means for making at least one of the length of the rich operation continuation period and the air-fuel ratio in the rich operation continuation period variable according to the total fresh air amount or the estimated value during the fuel cut is provided. In-cylinder injection engine control device.

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