JP5626145B2 - Engine control device - Google Patents

Description

  The present invention relates to an engine control device, and more particularly to an engine control device including a fuel injection valve that injects fuel directly into a cylinder.

  Conventionally, an in-cylinder injection type in which fuel is directly injected into a cylinder is known as an engine. In this in-cylinder type engine, a rich atmosphere tends to be locally generated, so that particulate matter (PM) is likely to be generated with combustion of the engine. In view of this, various techniques for suppressing PM emissions have been proposed for in-cylinder injection engines (see, for example, Patent Document 1).

  Conventionally, a three-way catalyst is known as a catalyst for purifying HC, CO, NOx, etc. contained in the exhaust of the engine. In a port injection type or in-cylinder injection type gasoline engine, the oxygen of the three-way catalyst is known. Exhaust gas purification is performed using storage capacity.

  Here, during engine operation, the fuel injection by the fuel injection valve may be temporarily stopped to bring the engine to a combustion stop state in accordance with establishment of a predetermined fuel cut condition. In this case, when air containing no fuel is supplied to the catalyst, the catalyst is in an excessive oxygen storage state, and as a result, the NOx purification ability of the catalyst may decrease immediately after returning from the fuel cut. Therefore, it has been proposed to reduce the oxygen storage amount of the catalyst by correcting the fuel injection amount temporarily (immediately after returning from the fuel cut) (by changing the air-fuel ratio to the rich side) ( For example, see Patent Document 2).

JP 2003-206786 A JP 2003-172176 A

  However, when the air-fuel ratio is made rich so as to reduce the oxygen storage amount of the catalyst, there is a concern that PM is likely to be generated as the rich fuel is burned. In particular, in an in-cylinder injection type engine, local enrichment is more likely to occur, and PM is likely to occur due to combustion in a state where fuel and air are not uniform.

  The present invention has been made in view of the above problems, and controls an engine that can suppress the generation of particulate matter even when the air-fuel ratio is temporarily made rich in order to recover the purification capability of the exhaust purification device. The main purpose is to provide a device.

  The present invention employs the following means in order to solve the above problems.

The present invention is applied to an engine provided with a fuel injection valve for directly injecting fuel into a cylinder and having an exhaust purification device having an oxygen storage capacity disposed in an exhaust passage. In addition, the first configuration includes fuel cut means for temporarily stopping fuel injection and executing fuel cut when a predetermined fuel cut condition is satisfied, and a predetermined release condition is satisfied during execution of the fuel cut. Accordingly, when canceling the fuel cut, the rich control means for temporarily controlling the air-fuel ratio on the rich side, and the pressure of the fuel supplied to the fuel injection valve based on the engine operating state each time When the air fuel ratio is temporarily controlled on the rich side by the first fuel pressure control means for controlling a certain fuel pressure of the injection valve and the rich control means, the fuel cut is canceled by the first fuel pressure control means. And a second fuel pressure control means for controlling at a fuel pressure higher than the fuel pressure of the injection valve in the case of controlling based on the subsequent engine operating state.

  In short, immediately after canceling the fuel cut, the rotational speed and load of the engine are relatively small, and the injection valve fuel pressure set in such an engine operating state is relatively low. On the other hand, in the above configuration, when the air-fuel ratio is temporarily made rich after the fuel cut is released, the injection valve fuel pressure is set higher than the injection valve fuel pressure set based on the engine operating state after the fuel cut is released. Use fuel pressure. This increase in fuel pressure promotes atomization of the fuel, and as a result, generation of PM can be suppressed even under a situation where the air-fuel ratio is temporarily rich to recover the purification capability of the exhaust purification device.

  In the enrichment control, as the oxygen storage amount of the exhaust purification device during fuel cut increases, the richness of the air-fuel ratio is increased to quickly recover the purification capability of the exhaust purification device while suppressing excessive enrichment. Can do. On the other hand, the ease of PM generation differs depending on the richness of the air-fuel ratio, and the greater the richness of the target air-fuel ratio, the more easily the engine combustion chamber becomes locally rich. This is likely to occur.

In view of that point, in the second configuration , target setting means for variably setting a target air-fuel ratio when the air-fuel ratio is controlled on the rich side by the enrichment control means according to the oxygen storage amount of the exhaust purification device is provided. And the enrichment control means controls the air / fuel ratio temporarily on the rich side by controlling the actual air / fuel ratio with the target air / fuel ratio set by the target setting means, and the second fuel pressure control means The injection valve fuel pressure is variably controlled according to the target air-fuel ratio set by the target setting means. According to this configuration, the fuel pressure of the injection valve can be made variable according to the ease of PM generation, and generation of PM can be suitably suppressed while suppressing excessive enrichment of the air-fuel ratio.

In a third configuration , a fuel cut time measuring unit that measures a duration of the fuel cut is provided, and the target setting unit varies the target air-fuel ratio according to the duration measured by the fuel cut time measuring unit. Set to.

  The amount of oxygen stored in the exhaust purification device during fuel cut differs depending on the duration of fuel cut. The longer the fuel cut duration, the longer the contact time between the exhaust purification device and air. The amount increases. Therefore, it is preferable to set the target air-fuel ratio at the time of air-fuel ratio enrichment according to the duration of fuel cut as in the above configuration. At this time, it is better to increase the rich degree of the target air-fuel ratio during the enrichment control as the duration of the fuel cut is longer.

In the fourth configuration , the predetermined release condition includes that the engine is in a predetermined operation state during execution of the fuel cut and that an accelerator operation is performed before the engine is in the predetermined operation state. The target setting means is configured such that the fuel cut is released when the engine enters the predetermined operating state and the fuel cut is released when the accelerator operation is performed. Set the air-fuel ratio to be variable.

  When the condition for canceling the fuel cut is that the engine is in a predetermined operation state (for example, an idle operation state), a sufficient time for recovering the purification ability of the exhaust purification device can be secured. On the other hand, when the fuel cut is canceled in accordance with the accelerator operation, it is desirable to quickly recover the exhaust purification performance so as to promptly shift to the engine output control according to the driving request of the driver. In order to quickly recover the exhaust purification performance, it is conceivable to increase the rich degree of the target air-fuel ratio when the air-fuel ratio is enriched. On the other hand, PM is more likely to occur as the richness of the target air-fuel ratio is increased. In view of this point, in the above configuration, the target air-fuel ratio at the time of air-fuel ratio enrichment is made variable depending on whether the fuel cut is canceled based on the accelerator operation or not. Specifically, the target air-fuel ratio of the enrichment control may be set to the rich side when the fuel cut is canceled by the accelerator operation compared to when the fuel cut is not performed.

In the fifth configuration , a temperature detection means for detecting the temperature of the exhaust purification device is provided, and the target setting means variably sets the target air-fuel ratio according to the temperature detected by the temperature detection means.

  The oxygen storage amount of the exhaust purification device during the fuel cut differs depending on the temperature of the exhaust purification device. Generally, the oxygen storage amount increases as the temperature increases. Therefore, it is preferable to set the target air-fuel ratio at the time of enrichment of the air-fuel ratio according to the temperature of the exhaust purification device as in the above configuration. At this time, the target air-fuel ratio at the time of enriching the air-fuel ratio may be set to the rich side as the temperature of the exhaust purification device is higher. As the temperature detection means, there is provided a configuration for detecting the temperature of the exhaust purification device by calculating (estimating) the temperature of the exhaust purification device based on the engine operating state, and a temperature sensor for detecting the temperature of the exhaust purification device. And a configuration in which the sensor directly detects the same.

In the sixth configuration , the second fuel pressure control means controls the injection valve fuel pressure based on the engine operating state after the fuel cut is released by the first fuel pressure control means during execution of the fuel cut. Set the fuel pressure higher than the fuel pressure of the injection valve. In this configuration, in consideration of the time required for the fuel pressure increase of the injection valve fuel pressure, the injection valve fuel pressure is raised to a predetermined fuel pressure before the enrichment of the air-fuel ratio accompanying the cancellation of the fuel cut is performed. As a result, when the air-fuel ratio is enriched in order to recover the purification capability of the exhaust purification device, the fuel pressure of the injection valve can be brought to a high pressure state from the beginning of the enrichment, and PM generation can be suitably suppressed. it can.

1 is an overall schematic configuration diagram of an engine control system. The flowchart which shows the process sequence of fuel cut control. The flowchart which shows the process sequence of catalyst neutralization control. The flowchart which shows the process sequence of fuel pressure control. The figure which shows the relationship between the target air fuel ratio at the time of neutralization control, and a target fuel pressure. The time chart which shows the specific aspect of fuel pressure control. The time chart which shows the specific aspect of the fuel pressure control of other embodiment. The flowchart which shows the fuel pressure control of other embodiment. The time chart which shows the specific aspect of the fuel pressure control of other embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. In this embodiment, an engine control system is constructed for an in-cylinder injection type on-vehicle multi-cylinder four-cycle gasoline engine that is an internal combustion engine. In this control system, an electronic control unit (hereinafter referred to as ECU) is used as a center to control the fuel injection amount, control the ignition timing, and the like. FIG. 1 shows an overall schematic configuration diagram of the engine control system.

  In the engine 10 shown in FIG. 1, an air cleaner 12 is provided at the most upstream portion of the intake pipe 11, and an air flow meter 13 for detecting the intake air amount is provided downstream of the air cleaner 12. A throttle valve 14 whose opening degree is adjusted by a throttle actuator 15 such as a DC motor is provided on the downstream side of the air flow meter 13. The opening degree of the throttle valve 14 (throttle opening degree) is detected by a throttle opening degree sensor built in the throttle actuator 15.

  A surge tank 16 is provided on the downstream side of the throttle valve 14, and an intake pipe pressure sensor 17 for detecting the intake pipe pressure is provided in the surge tank 16. An intake manifold 18 for introducing air into each cylinder of the engine 10 is connected to the surge tank 16. The intake manifold 18 is further connected to the intake port of each cylinder.

  An intake valve 21 and an exhaust valve 22 are provided at an intake port and an exhaust port of the engine 10, respectively. The air in the surge tank 16 is introduced into the combustion chamber 23 by the opening operation of the intake valve 21, and the exhaust gas after combustion is discharged to the exhaust pipe 24 by the opening operation of the exhaust valve 22.

  A fuel injection valve 19 that directly supplies fuel into the combustion chamber 23 is attached to the upper part of each cylinder of the engine 10. A fuel tank 38 is connected to the fuel injection valve 19 via a fuel pipe 25, and an electromagnetically driven feed pump 39 is disposed at the most upstream portion of the fuel pipe 25, and downstream of the feed pump 39. A mechanically driven high pressure pump 26 is arranged. The fuel in the fuel tank 38 is pumped up by the feed pump 39 and pressurized to a predetermined feed pressure (for example, 0.3 MPa), and then pumped to the high-pressure pump 26. In the high-pressure pump 26, the feed pressure fuel pumped from the feed pump 39 is further increased (for example, 4 to 20 MPa) and pumped to the delivery pipe 27, and supplied from the delivery pipe 27 to the fuel injection valve 19 of each cylinder. The Thereafter, the fuel is injected into the combustion chamber 23 by the fuel injection valve 19.

  A spark plug 29 is attached to the cylinder head of the engine 10. A high voltage is applied to the spark plug 29 at a desired ignition timing through an ignition device (not shown) including an ignition coil. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 29, and the air-fuel mixture in the combustion chamber 23 is ignited and used for combustion.

  The exhaust pipe 24 is provided with a three-way catalyst 31 as a catalyst for purifying CO, HC, NOx and the like in the exhaust gas. The three-way catalyst 31 has an oxygen storage capability of storing oxygen in a lean atmosphere and releasing oxygen in a rich atmosphere. In this system, exhaust gas purification is performed using the oxygen storage ability of the three-way catalyst 31.

  The exhaust pipe 24 is provided with a sensor that detects the air-fuel ratio (oxygen concentration) of the air-fuel mixture using exhaust as a detection target. Specifically, in the exhaust pipe 24, a wide-area detection type air-fuel ratio sensor 32 that outputs a wide-range air-fuel ratio signal proportional to the oxygen concentration in the exhaust gas is provided upstream of the catalyst 31, and downstream of the catalyst 31. Is provided with an electromotive force output type O2 sensor 33 that generates a binary electromotive force due to a difference in oxygen concentration between the atmosphere and exhaust gas. The O2 sensor 33 generates different electromotive force depending on whether the air-fuel ratio is rich or lean. Specifically, the O2 sensor 33 outputs about 0.9 V when the fuel is rich and outputs about 0 V when the fuel is lean. In this system, a catalyst (three-way catalyst or the like) 34 is further provided on the downstream side of the O 2 sensor 33.

  In addition, the engine 10 includes a cooling water temperature sensor 35 that detects the cooling water temperature, a crank angle sensor 36 that outputs a rectangular crank angle signal at every predetermined crank angle of the engine 10 (for example, at a cycle of 10 ° CA), and a delivery pipe. A fuel pressure sensor 37 for detecting the fuel pressure in the fuel tank 27 is attached.

  As is well known, the ECU 40 is mainly composed of a microcomputer (hereinafter referred to as a microcomputer) 41 composed of a CPU, ROM, RAM, and the like, and executes various control programs stored in the ROM, so that the engine operation state can be changed each time. In response, various controls of the engine 10 are performed. That is, the microcomputer 41 of the ECU 40 inputs detection signals from the various sensors described above, calculates the fuel injection amount, ignition timing, etc. based on the various detection signals, and drives the fuel injection valve 19 and the ignition device. Control etc.

  Specifically, regarding the engine control, the microcomputer 41 performs air-fuel ratio control based on the output value of the air-fuel ratio sensor 32. Specifically, the target air-fuel ratio is calculated based on the engine operating state (for example, engine speed and engine load), and the calculated target air-fuel ratio and the actual air-fuel ratio detected by the air-fuel ratio sensor 32 are calculated. Air-fuel ratio feedback control is performed to eliminate the deviation. Further, the microcomputer 41 performs fuel pressure control in the delivery pipe 27 based on the output value of the fuel pressure sensor 37, and specifically, based on the engine operating state (for example, engine speed and engine load). Thus, the target fuel pressure, which is the target value of the fuel pressure in the delivery pipe 27, is calculated, and fuel pressure feedback control is performed to eliminate the deviation between the calculated target fuel pressure and the actual fuel pressure detected by the fuel pressure sensor 37. In addition, by controlling the fuel pressure in the delivery pipe 27, the fuel pressure of the injection valve, which is the pressure of the fuel supplied to the fuel injection valve 19, is controlled. Further, the above fuel pressure control based on each engine operating state corresponds to the fuel pressure control performed by the first fuel pressure control means.

  Further, the microcomputer 41 of the ECU 40 temporarily stops fuel injection by the fuel injection valve 19 (performs fuel cut) and executes fuel cut when a predetermined fuel cut condition is satisfied during vehicle deceleration. When a predetermined release condition is satisfied, control for releasing the fuel cut and returning the engine 10 from the combustion stopped state to the combustion state is performed. Here, the fuel cut condition includes, for example, that the accelerator operation amount is 0 and the engine speed is equal to or higher than a predetermined fuel cut speed (for example, 1000 rpm). The release conditions include, for example, that the engine rotational speed has become equal to or lower than a predetermined return rotational speed (for example, idle rotational speed or the vicinity thereof) during fuel cut, and the engine rotational speed is reduced to a predetermined return rotational speed. This includes that an accelerator operation was performed before

  By the way, in the state where the combustion of the engine 10 is stopped by the fuel cut, the exhaust pipe 24 is in an atmospheric atmosphere, so the catalyst 31 is in an excessive oxygen storage state, and the NOx of the catalyst 31 is caused by the excessive oxygen storage. Purifying ability may decrease. In such a case, the NOx contained in the exhaust gas cannot be completely purified by the catalyst 31 immediately after returning from the fuel cut, and the NOx emission amount may increase.

  In view of this, in this system, when the fuel cut is canceled and the engine 10 is returned from the fuel stop state to the combustion state, the catalyst neutralization control for temporarily controlling the air-fuel ratio to the rich side is performed. . That is, immediately after canceling the fuel cut, considering that the oxygen storage amount of the catalyst 31 becomes excessive, by temporarily performing rich combustion, reduction of HC, CO, etc. in the exhaust discharged during the combustion is performed. The oxygen storage amount of the catalyst 31 is reduced by the components.

  On the other hand, when the air-fuel ratio is temporarily controlled to the rich side by catalyst neutralization control, it is considered that particulate matter (PM) is likely to be generated during combustion. In particular, in a direct injection engine, a rich atmosphere is likely to be locally formed in the combustion chamber 23, and PM is likely to be generated.

  Therefore, in the present embodiment, during the period in which the air-fuel ratio is temporarily controlled on the rich side by the catalyst neutralization control, the fuel pressure of the injection valve, which is the pressure of the fuel supplied to the fuel injection valve 19, is set after the fuel cut is released. Control is performed at a fuel pressure higher than the fuel pressure set on the basis of the engine operating state. This fuel pressure control corresponds to the fuel pressure control performed by the second fuel pressure control means. In other words, when the air-fuel ratio is rich by the catalyst neutralization control, the atomization of the fuel is promoted by increasing the fuel pressure of the injection valve, so that PM emission is suppressed even under the air-fuel ratio rich condition for recovering the catalytic performance. I have to.

  Next, fuel cut control, catalyst neutralization control, and fuel pressure control in this system will be described with reference to the flowcharts of FIGS. Here, FIG. 2 shows a processing procedure for fuel cut control, FIG. 3 shows a processing procedure for catalyst neutralization control, and FIG. 4 shows a processing procedure for fuel pressure control. These processes are executed at predetermined intervals by the microcomputer 41 of the ECU 40, respectively.

  First, fuel cut control which is a premise of the present system will be described with reference to FIG. 2, in step S101, it is determined whether or not the engine is operating. If the engine is operating, the process proceeds to step S102 to determine whether or not a predetermined fuel cut condition is satisfied. When the fuel cut condition is satisfied, the process proceeds to step S103, the fuel cut flag Ffc is turned on, and the fuel supply by the fuel injection valve 19 is stopped.

  If the engine 10 is in the combustion stop state, a negative determination is made in step S101, and the process proceeds to step S104. In step S104, it is determined whether or not a fuel cut is being executed. If the fuel cut is being executed, the process proceeds to step S105 to determine whether or not a predetermined release condition for releasing the fuel cut is satisfied. At this time, if the release condition is not satisfied, the present process is temporarily terminated and the fuel cut is continued as it is. On the other hand, if the release condition is satisfied, the process proceeds to step S106, the fuel cut flag Ffc is turned off, and the fuel supply by the fuel injection valve 19 is restarted.

  Next, the catalyst neutralization control will be described with reference to FIG. In FIG. 3, in step S201, it is determined whether or not it is time to switch the fuel cut flag Ffc from on to off. When an affirmative determination is made in step S201, the process proceeds to step S202, and the neutralization execution flag Fri is turned on. Further, the neutralization air-fuel ratio λtga is acquired as the target air-fuel ratio during execution of catalyst neutralization. Note that the neutralized air-fuel ratio λtga is a richer value than the theoretical air-fuel ratio, and in this embodiment, is calculated before the catalyst neutralization is performed by the fuel pressure control of FIG. Therefore, the value calculated by the fuel pressure control is acquired here. In the following step S203, the actual air-fuel ratio λat detected by the air-fuel ratio sensor 32 is acquired. In step S204, the air-fuel ratio feedback is performed so that the acquired actual air-fuel ratio λat matches the target air-fuel ratio (neutralized air-fuel ratio λtga). Execute control.

  If it is not the timing for canceling the fuel cut, a negative determination is made in step S201, and the process proceeds to step S205. In step S205, it is determined whether or not the neutralization execution flag Fri is on. If Fri = on (when catalyst neutralization is being executed), the process proceeds to step S206, and the output value of the O2 sensor 33 is acquired. In step S207, it is determined whether or not the output value is a rich output (about 0.9 V). At this time, in the case of a lean output (about 0V), the enrichment control based on the neutralized air-fuel ratio λtga is continued by executing the processing of steps S203 and S204. On the other hand, in the case of rich output, the process proceeds to step S208, and the neutralization execution flag Fri is switched off. Thereby, the temporary enrichment of the catalyst 31 is terminated, and the routine proceeds to the normal air-fuel ratio control.

  Next, the fuel pressure control of this embodiment will be described with reference to FIG. In FIG. 4, in step S301, it is determined based on the fuel cut flag Ffc whether or not the fuel cut is being executed. If the fuel cut is not being executed, the process proceeds to step S302, and it is determined whether or not the catalyst neutralization is being executed based on the neutralization execution flag Fri. At this time, if the catalyst neutralization is not being executed, the process proceeds to step S303, and the target fuel pressure Ptg in the delivery pipe 27 is calculated based on the engine operating state each time. Here, the target fuel pressure Ptg is calculated based on the engine rotation speed and the engine load (for example, intake air amount).

  On the other hand, if the fuel cut is being executed, the process proceeds to step S304, and a neutralized air-fuel ratio λtga, which is a target air-fuel ratio at the time of neutralizing the catalyst that is performed after canceling the fuel cut, is calculated. In this embodiment, the temperature (catalyst temperature) of the catalyst 31 at the start of fuel cut is detected, and the neutralized air-fuel ratio λtga is variably set based on the detected catalyst temperature. Specifically, in consideration of the fact that during the fuel cut, the oxygen storage amount of the catalyst 31 increases as the catalyst temperature increases, the value on the rich side is set as the neutralized air-fuel ratio λtga as the catalyst temperature increases. Here, the catalyst temperature may be calculated (estimated) based on the engine operating state, or a temperature sensor that detects the temperature of the catalyst 31 may be provided, and the catalyst temperature may be directly detected by the sensor. . While the fuel cut is being executed, the target air-fuel ratio at the time of neutralizing the catalyst is calculated. However, since the air-fuel ratio control is not performed, the target air-fuel ratio at the time of fuel cut is not calculated.

  In the subsequent step S305, the target fuel pressure Ptg in the delivery pipe 27 is calculated. During the fuel cut, the target fuel pressure Ptg is variably set based on the neutralized air-fuel ratio λtga. Specifically, as shown in FIG. Ptg is set to a high fuel pressure. Further, the target fuel pressure Ptg set here is a value higher than the target fuel pressure that can be set based on the engine operating state for a predetermined period (for example, several seconds) immediately after canceling the fuel cut. In this embodiment, the target fuel pressure Ptg A value slightly lower than the maximum value of the control range is set as the minimum target fuel pressure, and a value on the higher pressure side than the minimum target fuel pressure Ptg1 is set. Specifically, if the control range of the fuel pressure is 4 to 20 MPa, for example, 15 to 20 MPa is set as the target fuel pressure Ptg. In this case, immediately after returning from the fuel cut, it is assumed that the engine operation state is a low load / low rotation state. In particular, this is naturally the case when the fuel cut is canceled when the engine rotation speed becomes the return rotation speed. In such an operating state, the fuel pressure is usually not set near the upper limit value, but in this embodiment, even if the engine operating state immediately after the release of the fuel cut is assumed to be a low load / low rotation A relatively high fuel pressure (fuel pressure near the upper limit value) is set as the target fuel pressure Ptg.

  In step S306, the actual fuel pressure Pat detected by the fuel pressure sensor 37 is acquired. In step S307, the driving of the high-pressure pump 26 is controlled so that the acquired actual fuel pressure Pat matches the target fuel pressure Ptg.

  Now, when a predetermined release condition is satisfied during execution of the fuel cut and the fuel cut is released, neutralization (air-fuel ratio enrichment) of the catalyst 31 is started. In this case, a negative determination is made in step S301, an affirmative determination is made in step S302, and the processes in steps S306 and S307 are executed. That is, during catalyst neutralization, the target fuel pressure at the time of fuel cut (target fuel pressure calculated based on the neutralized air-fuel ratio Ptga) is used, and the high-pressure pump 26 is driven so that the target fuel pressure Ptg and the actual fuel pressure Pat coincide. To control. Further, in the present embodiment, the fuel pressure in the delivery pipe 27 is set to a high pressure state in advance before the start of the catalyst neutralization, more specifically during the execution of the fuel cut. Fuel at the fuel pressure is injected from the fuel injection valve 19.

  Next, a specific aspect of the fuel pressure control of the present embodiment will be described using the time chart of FIG. In the figure, (a) is the transition of the accelerator pedal depressing / depressing, (b) is the transition of the vehicle speed, (c) is the transition of the engine speed, (d) is the transition of the fuel cut flag Ffc, (e) is The transition of the neutralization execution flag Fri, (f) the transition of the target air-fuel ratio, and (g) the transition of the fuel pressure in the delivery pipe 27. In (g), the solid line indicates the actual fuel pressure Pat, and the alternate long and short dash line indicates the target fuel pressure Ptg.

  In FIG. 6, while the vehicle is running (before t11), the target fuel pressure Ptg of the delivery pipe 27 is calculated based on the engine speed and the engine load (for example, intake air amount). Further, the driving of the high-pressure pump 26 is controlled based on the calculated target fuel pressure Ptg. When the accelerator pedal is depressed from the depressed state at the timing t11 during vehicle travel, the fuel cut flag Ffc is turned on on condition that the engine rotational speed is equal to or higher than the predetermined fuel cut rotational speed. The fuel injection by the fuel injection valve 19 is stopped. Along with this fuel cut, the air sucked into the engine 10 is supplied to the exhaust passage as it is, so that the oxygen storage amount of the catalyst 31 increases. Further, at the timing t11, as the fuel cut is started, a neutralized air-fuel ratio Ptga that is a target air-fuel ratio at the time of catalyst neutralization is calculated, and the target fuel pressure Ptg in the delivery pipe 27 is calculated based on the neutralized air-fuel ratio Ptga. Is calculated.

  When the engine rotation speed becomes equal to or lower than the predetermined return rotation speed Nr at timing t12 during execution of fuel cut, the fuel cut flag Ffc is switched from on to off, and fuel injection by the fuel injection valve 19 is resumed. Further, at timing t12, the neutralization execution flag Fri is turned on, and air-fuel ratio control based on the neutralization air-fuel ratio λtga is started. In this air-fuel ratio rich period (t12 to t13), the fuel pressure control at the target fuel pressure Ptg calculated based on the neutralized air-fuel ratio λtga is continued.

  Here, the engine operating state after release of the fuel cut is low rotation and low load, and the target fuel pressure calculated based on these engine operating state parameters (for example, target fuel pressure P1 during idling operation, corresponding to “fuel pressure after release”) When the fuel pressure control (first fuel pressure control) is performed, the fuel pressure of the injection valve is low, and there is a concern that the PM emission amount increases with the combustion of the rich fuel. On the other hand, in the present embodiment, in the air-fuel ratio rich period (t12 to t13), the actual fuel pressure is not controlled with the target fuel pressure set based on the engine operating state, but the fuel pressure on the higher fuel pressure side than this. By implementing the control (second fuel pressure control), fuel atomization is promoted.

  When the rich output is detected by the O2 sensor 33, the neutralization execution flag Fri is switched from on to off at the timing t13. At timing t13, the target fuel pressure Ptg is reset based on the engine operating state (engine speed and engine load) after each fuel cut is released. In FIG. 6, it is assumed that the engine 10 is in an idle operation state after the fuel cut, and at the timing t13, the target fuel pressure P1 (for example, 4 MPa) during the idle operation is set. By changing the target fuel pressure, the fuel pressure in the delivery pipe 27 is lowered to the fuel pressure corresponding to the current engine operating state.

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

  When performing catalyst neutralization control that temporarily brings the air-fuel ratio to the rich side after canceling the fuel cut, the fuel pressure of the injector is higher than the fuel pressure set based on the engine operating state after canceling the fuel cut. It was set as the structure controlled by. As a result, atomization of the fuel can be promoted during the catalyst neutralization control, and as a result, even in a situation where the air-fuel ratio is temporarily rich to recover the purification capacity of the catalyst 31, the PM Occurrence can be suppressed.

  The neutralized air-fuel ratio λtga, which is the target air-fuel ratio when the air-fuel ratio is controlled on the rich side by the catalyst neutralization control, is variably set according to the oxygen storage amount of the catalyst 31, and more specifically, at the start of fuel cut The temperature of the catalyst 31 (catalyst temperature) is detected, and the neutralized air-fuel ratio λtga is variably set based on the detected catalyst temperature. When the target air-fuel ratio at the time of neutralization of the catalyst is made constant regardless of the oxygen storage amount, it is conceivable that the time required for catalyst neutralization increases as the oxygen storage amount of the catalyst 31 increases. In this case, since the target air-fuel ratio is set according to the oxygen storage amount during the fuel cut, the purification capacity recovery of the catalyst 31 by the catalyst neutralization control can be performed promptly. Further, since the fuel injection valve fuel pressure is variably controlled according to the set neutralized air-fuel ratio λtga, the fuel injection valve fuel pressure can be made variable according to the ease of PM generation, and the generation of PM is suitable. Can be suppressed.

  Since the fuel pressure of the injector is kept high during the fuel cut, more specifically, from the first fuel pressure control that calculates the target fuel pressure based on the engine operating state at the fuel cut start timing, the neutralization of the catalyst is performed. The control is switched to the second fuel pressure control that calculates the target fuel pressure based on the target air-fuel ratio in the control, so that the fuel injection valve fuel pressure is raised to the predetermined fuel pressure before the air-fuel ratio is enriched when the fuel cut is cancelled. I can keep it. As a result, high-pressure fuel can be injected from the beginning of enrichment of the air-fuel ratio for recovery of the purification capability of the catalyst 31.

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

  The duration of fuel cut is measured, and the neutralized air-fuel ratio λtga, which is the target air-fuel ratio at the time of catalyst neutralization, is variably set according to the measured duration. The oxygen storage amount of the catalyst 31 differs depending on the duration of the fuel cut, and the longer the fuel cut duration, the longer the contact time with the air. As a result, the oxygen storage amount of the catalyst 31 increases. Therefore, it is better to set the target air-fuel ratio at the time of neutralizing the catalyst to the rich side as the duration of the fuel cut is longer.

  FIG. 7 is a time chart showing a specific aspect of this configuration. In the figure, (a) shows the change in engine speed, (b) shows the change in fuel cut flag Ffc, (c) shows the change in fuel cut time counter, (d) shows the change in neutralization execution flag Fri, (e) Is the change in the target air-fuel ratio, and (f) is the change in the fuel pressure in the delivery pipe 27. In (f), the solid line indicates the actual fuel pressure Pat, and the alternate long and short dash line indicates the target fuel pressure Ptg.

  In FIG. 7, when a predetermined fuel cut condition is satisfied at timing t21 and the fuel cut flag Ffc is turned on, the fuel cut time counter starts counting up. Further, the neutralized air-fuel ratio λtga is calculated based on the catalyst temperature at the start of fuel cut, and the target fuel pressure Ptg is calculated using the neutralized air-fuel ratio λtga as a parameter. Here, λ1 is set as the neutralized air-fuel ratio λtga. When the fuel cut time counter exceeds the determination value TH at the timing t22 during execution of fuel cut, the neutralized air-fuel ratio λtga is changed to λ2 having a richness higher than λ1, and the empty air after the change is changed. The target fuel pressure Ptg is reset to the high fuel pressure side based on the fuel ratio λ2. Here, the target fuel pressure Ptg is changed to a value of high fuel pressure by ΔP with respect to the current set value. Further, when the fuel cut is released at timing t23, the neutralization air-fuel ratio λtga is set to λ2, and the air-fuel ratio control is performed, whereby the neutralization of the catalyst 31 is performed.

  ・ When canceling the fuel cut, there is an accelerator operation while the fuel cut is being executed, and when shifting to normal engine control based on the accelerator operation amount, or when there is no accelerator operation during the fuel cut, to avoid engine stall May return to combustion. Here, when the fuel cut is canceled in accordance with the accelerator operation, it is desirable to quickly recover the exhaust purification performance so as to promptly shift to the engine output control according to the driving request of the driver. In order to quickly recover the exhaust purification performance, it is conceivable to increase the rich degree of the target air-fuel ratio when the air-fuel ratio is enriched. On the other hand, PM is more likely to occur as the richness of the target air-fuel ratio is increased. In view of this, in this configuration, when the fuel cut is canceled during the fuel cut execution and the accelerator operation is not performed, the engine is in a predetermined operating state without the accelerator operation (for example, the engine rotational speed is equal to or lower than the predetermined return rotational speed). The target air-fuel ratio (neutralized air-fuel ratio) at the time of neutralizing the catalyst is set to a different air-fuel ratio when the fuel cut is canceled as the engine becomes neutral. Specifically, when the fuel cut is released by the accelerator operation, the target air-fuel ratio at the time of neutralizing the catalyst is set to the rich side compared to the case where the accelerator operation is not performed.

  FIG. 8 is a flowchart showing a processing procedure of fuel pressure control according to the present embodiment. This process is executed at predetermined intervals by the microcomputer 41 of the ECU 40. In FIG. 8, the same processes as those in FIG. 4 are denoted by the same step numbers as those in FIG. In FIG. 8, it is determined in step S401 whether or not a fuel cut is being executed. If the fuel is being cut, the same processes as in steps S304 to S307 in FIG. 4 are executed in steps S404 to S407. On the other hand, after canceling the fuel cut, a negative determination is made in step S401, and the process proceeds to step S408. In step S408, it is determined whether or not it is the timing for switching the fuel cut flag Ffc from on to off, that is, the timing for canceling the fuel cut. When an affirmative determination is made in step S408, the process proceeds to step S409, and it is determined whether or not the fuel cut cancellation has been executed in accordance with the accelerator operation. At this time, if the accelerator operation is not performed, the target air-fuel ratio at neutralization (neutralized air-fuel ratio λtga) calculated in step S404 and the target fuel pressure Ptg calculated in step S405 are maintained as they are. On the other hand, in the case of the accelerator operation, the process proceeds to step S410, the neutralized air-fuel ratio λtga is changed to the rich side, and the target fuel pressure Ptg is reset based on the changed neutralized air-fuel ratio.

  In FIG. 9, the time chart showing the specific aspect of the said structure is shown. In the figure, (a) is the transition of depression / depressing of the accelerator pedal, (b) is the transition of the fuel cut flag Ffc, (c) is the transition of the neutralization execution flag Fri, (d) is the transition of the target air-fuel ratio, (E) shows the transition of the fuel pressure in the delivery pipe 27. In (e), the solid line indicates the actual fuel pressure Pat, and the alternate long and short dash line indicates the target fuel pressure Ptg.

  In FIG. 9, when the fuel cut is executed at timing t31, the target fuel pressure Ptg is calculated with the neutralized air-fuel ratio λtga (here, λ1) set based on the catalyst temperature at that time as a parameter. When the fuel cut is released at the timing t32 during execution of the fuel cut and the fuel cut is released, the neutralized air-fuel ratio is changed to λ3, which is richer than λ1, and Based on the changed air-fuel ratio λ3, the target fuel pressure Ptg is reset to the high fuel pressure side. When the fuel cut is canceled at timing t32, air-fuel ratio control is performed with the neutralized air-fuel ratio λtga as λ3, whereby neutralization of the catalyst 31 is performed.

  In the above embodiment, the neutralized air-fuel ratio that is the target air-fuel ratio at the time of neutralizing the catalyst is made variable according to the catalyst temperature at the start of fuel cut, but the neutralized air-fuel ratio is set as a predetermined fixed value. Also good. In this case, a fixed value is also set for the target fuel pressure when the catalyst is neutralized.

  ・ Catalyst temperature detected each time during fuel cut execution (calculated based on engine operating condition or directly detected by sensor) instead of calculating neutralized air-fuel ratio according to catalyst temperature at start timing of fuel cut The neutralized air-fuel ratio may be calculated based on the above. During the fuel cut, the air sucked into the engine 10 is supplied to the catalyst 31 as it is, so that it is conceivable that the catalyst temperature changes each time and the oxygen storage amount changes with the temperature change. Therefore, with the above configuration, the target air-fuel ratio can be set according to the oxygen storage amount when the catalyst is neutralized, and as a result, the purification capacity recovery of the catalyst 31 can be performed quickly. Further, at that time, since the injection valve fuel pressure is variably controlled according to the rich degree of the air-fuel ratio, PM emission can be suitably suppressed.

  In the above embodiment, at the fuel cut start timing t11, control (first fuel pressure control) for calculating the target fuel pressure based on the engine operating state (first fuel pressure control), control for calculating the target fuel pressure based on the neutralized air-fuel ratio λtga (second fuel pressure) By switching to control, the fuel pressure of the injection valve is set higher than the fuel pressure of the injection valve corresponding to the engine operating state after cancellation of the fuel cut during the fuel cut. In contrast, in the present configuration, the first fuel pressure control is switched to the second fuel pressure control at the catalyst neutralization start timing t12. In this case, the change of the fuel pressure in the delivery pipe 27 to the high pressure side is started at the same timing as the start of the catalyst neutralization. However, also in this configuration, the fuel pressure of the injection valve (delivery pipe 27 when the catalyst neutralization is executed). The internal combustion pressure) can be brought to a high pressure state, and the effect of suppressing the PM emission amount associated with the neutralization of the catalyst can be obtained. Or it is good also as a structure which switches from 1st fuel pressure control to 2nd fuel pressure control at the timing in the middle of execution of fuel cut.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 19 ... Fuel injection valve, 26 ... High pressure pump, 27 ... Delivery pipe, 31 ... Three-way catalyst (exhaust gas purification device), 32 ... Air-fuel ratio sensor, 33 ... O2 sensor, 37 ... Fuel pressure sensor, 38 ... Fuel Tank, 39 ... feed pump, 40 ... ECU, 41 ... microcomputer (fuel cut means, enrichment control means, first fuel pressure control means, second fuel pressure control means, target setting means, fuel cut time measurement means, temperature detection means) .

Claims (5)

A fuel injection valve for directly injecting fuel into the cylinder and an exhaust purification device having an oxygen storage capacity are applied to an engine disposed in the exhaust passage,
Fuel cut means for temporarily stopping fuel injection and executing fuel cut with the establishment of a predetermined fuel cut condition;
Enrichment control means for temporarily controlling the air-fuel ratio on the rich side when the fuel cut is released when a predetermined release condition is satisfied during execution of fuel cut by the fuel cut means;
First fuel pressure control means for controlling an injection valve fuel pressure, which is a pressure of fuel supplied to the fuel injection valve, on the basis of an engine operating state each time;
When the air-fuel ratio is temporarily controlled on the rich side by the enrichment control means, the injection valve when the fuel pressure of the injection valve is controlled by the first fuel pressure control means based on the engine operating state after the fuel cut is released A second fuel pressure control means for controlling the fuel pressure at a fuel pressure higher than the fuel pressure;
Target setting means for variably setting a target air-fuel ratio when the air-fuel ratio is controlled on the rich side by the enrichment control means according to the oxygen storage amount of the exhaust purification device,
The enrichment control means controls the air-fuel ratio temporarily on the rich side by controlling the actual air-fuel ratio at the target air-fuel ratio set by the target setting means,
The second fuel pressure control means variably controls the injection valve fuel pressure in accordance with a target air-fuel ratio set by the target setting means . Comprising fuel cut time measuring means for measuring the duration of the fuel cut;
The engine control device according to claim 1 , wherein the target setting means variably sets the target air-fuel ratio in accordance with a duration time measured by the fuel cut time measuring means. The predetermined release condition includes that the engine is in a predetermined operation state during execution of the fuel cut and that an accelerator operation is performed before the engine is in the predetermined operation state,
The target setting means is configured to detect the target empty state when the fuel cut is released when the engine enters the predetermined operating state and when the fuel cut is released when the accelerator operation is performed. The engine control device according to claim 1 or 2 , wherein the fuel ratio is variably set. Comprising a temperature detection means for detecting the temperature of the exhaust purification device;
The engine control device according to any one of claims 1 to 3 , wherein the target setting means variably sets the target air-fuel ratio in accordance with the temperature detected by the temperature detection means. The second fuel pressure control means is higher than the injection valve fuel pressure when the fuel pressure is controlled based on the engine operating state after the fuel cut is canceled by the first fuel pressure control means. The engine control device according to any one of claims 1 to 4 , wherein the fuel pressure is set.

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