JP2002235587A - Method and device for controlling fuel injection pressure of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for controlling the fuel injection pressure of an internal combustion engine capable of suppressing the noise of the internal combustion engine caused by a temporary activation of combustion resulting from the delay of an air intake system. SOLUTION: When the engine is in a fuel cut state until fuel is just burned (exfco = ON and exfc = OFF), the air sucked into a combustion chamber is led into the combustion chamber as intake air through an exhaust gas recirculating passage and an EGR valve without being consumed for combustion. Thus, when a control device judges YES in step 340, the temporary activation of combustion is expected to be caused. Accordingly, a decompression item initial value EPCINDWN is set in a fuel cut return time decompression item pcdwn (S345). By this, a fuel injection pressure is reduced temporarily (S390) to act in the direction of deactivating a combustibility. Thus the activation of the combustion can be suppressed to suppress noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling fuel injection pressure in an internal combustion engine such as a diesel engine.

[0002]

2. Description of the Related Art In a vehicle equipped with a diesel engine, the injection pressure of fuel injected into a combustion chamber is adjusted in accordance with an operating state. In this case, when the vehicle suddenly decelerates from high-speed running, the target value of the fuel injection pressure is rapidly reduced in accordance with the operation state.
However, since the fuel injection pressure does not immediately decrease even if the target value changes suddenly, at the beginning of deceleration, the high injection rate makes the atomization of fuel unnecessarily good and the combustion is temporarily activated. Occurs. This may cause the diesel engine to temporarily deteriorate combustion noise. In order to solve such a problem, there has been proposed a technique for executing a process of gradually changing the target value itself of the fuel injection pressure at the time of rapid deceleration (Japanese Patent Laid-Open No. Hei 5 (1994)).
-187301).

[0003]

An exhaust gas recirculation (hereinafter, referred to as "EGR") system for improving emissions and fuel efficiency by recirculating exhaust gas from an internal combustion engine to an intake system is known. In an internal combustion engine provided with such an EGR system, the EGR amount is adjusted according to a change in the operating state of the internal combustion engine. In this case, when it is necessary to rapidly increase the EGR amount due to a change in the operating state, the EGR valve is rapidly opened. It takes a long time for the exhaust gas to reach the fuel chamber. Therefore,
Even if the fuel injection system has already changed according to the operating state, the EGR amount is not sufficient because the response of the intake system is further low,
As a result, there is a possibility that combustion is temporarily activated and combustion noise is deteriorated.

[0004] In an internal combustion engine employing a system for stopping fuel injection during operation of the internal combustion engine, that is, a so-called fuel cut system, even if the EGR system is operating during the fuel cut, it is actually restarted. It is the air that is circulated, not the exhaust, which is essentially EGR
Is not running. For this reason, when returning from the state in which the fuel cut has been performed to the fuel injection state, the air that has been supplied from the EGR path to the intake system side is switched to the exhaust. However, also in this case, it takes a long time for the exhaust gas to reach the fuel chamber via the EGR route. Therefore, the EGR amount in accordance with the operating state of the internal combustion engine is insufficient, so that the combustion is temporarily activated and the combustion noise of the internal combustion engine may be deteriorated.

An object of the present invention is to provide a method and apparatus for controlling the fuel injection pressure of an internal combustion engine which can suppress the noise of the internal combustion engine caused by the temporary combustion activation caused by the delay of the intake system. .

[0006]

The means for achieving the above object and the effects thereof will be described below. The fuel injection pressure control method for an internal combustion engine according to the first aspect of the present invention temporarily reduces the injection pressure of fuel injected into a combustion chamber of the internal combustion engine when combustion is temporarily activated in the internal combustion engine. The noise of the internal combustion engine is suppressed.

As described above, when the combustion of the internal combustion engine is temporarily activated, the fuel injection pressure is temporarily reduced. Reducing the fuel injection pressure in this manner acts in the direction of inactivating the combustibility due to the deterioration of the atomization state or the like. Therefore, activation of the combustion is suppressed, and noise of the internal combustion engine can be suppressed.

[0008] In the fuel injection pressure control method according to the second aspect, in the configuration according to the first aspect, the temporary combustion activation in the internal combustion engine is performed by injecting fuel from a fuel injection stop state during exhaust gas recirculation. It is characterized by being caused by return.

As described above, as the temporary combustion activation,
One example is that caused by the return of fuel injection from the fuel injection stop state during exhaust gas recirculation.
That is, since the fuel injection was stopped immediately before, the air sucked into the combustion chamber is introduced into the intake passage via the exhaust gas recirculation passage without being used for combustion. For this reason, immediately after the return of the fuel injection, there is excess air in the combustion chamber more than expected, so that temporary combustion activation is caused. However, at this time, since the injection pressure of the fuel is temporarily reduced, an effect of temporarily inactivating the combustibility is generated. Therefore, even at the time of fuel injection return, activation of combustion is suppressed, and noise of the internal combustion engine can be suppressed.

According to a third aspect of the present invention, in the fuel injection pressure control method according to the first aspect, the temporary combustion activation in the internal combustion engine is caused by a sharp increase in the exhaust gas recirculation control amount. It is characterized by being.

As described above, the temporary combustion activation includes:
Examples include those caused by a sharp increase in the exhaust gas recirculation control amount. That is, since the amount of exhaust gas recirculation was small until immediately before, a large amount of air was introduced into the combustion chamber. Then, in such a state, when the exhaust gas recirculation control amount sharply increases, the internal combustion engine is controlled on the assumption that the actual exhaust gas recirculation amount also increases. However, actually, it takes a long time until the exhaust gas recirculation amount corresponding to the operating state is introduced into the combustion chamber via the exhaust gas recirculation path and the intake path.

For this reason, the internal combustion engine is controlled on the assumption that the actual amount of exhaust gas recirculation increases even though excess air is present in the combustion chamber more than expected. Activation is triggered. But,
At this time, since the fuel injection pressure is temporarily reduced,
This has the effect of temporarily inactivating the flammability. Therefore, even when such an exhaust recirculation control amount is sharply increased, activation of combustion is suppressed, and noise of the internal combustion engine can be suppressed.

According to a fourth aspect of the present invention, in the first aspect, the temporary combustion activation in the internal combustion engine is caused by stopping the pilot fuel injection. And

As described above, as the temporary combustion activation,
Examples include those caused by stopping the pilot fuel injection. That is, since the pilot fuel injection has been executed until immediately before, the intake air amount and the exhaust gas recirculation control amount are suitable for the pilot fuel injection. Then, in such a state, when the pilot fuel injection stops and the normal fuel injection is performed, the control of the internal combustion engine also changes accordingly. However, in fact, it takes a long time until the intake system changes, so that temporary combustion activation is caused. However, since the fuel injection pressure is temporarily reduced when the pilot fuel injection is stopped, an effect of temporarily inactivating the combustibility occurs. Therefore, even when such pilot fuel injection is stopped, activation of combustion is suppressed, and noise of the internal combustion engine can be suppressed.

According to a fifth aspect of the present invention, there is provided the internal combustion engine fuel injection pressure control method according to any one of the first to fourth aspects.
When returning from the temporary decrease in the fuel injection pressure, the fuel injection pressure is gradually restored.

Incidentally, it is necessary to return to the normal fuel injection pressure after temporarily reducing the fuel injection pressure. In this case, the fuel injection pressure is gradually restored so that the fuel injection pressure can be restored. Is prevented, and a stable operating state of the internal combustion engine can be maintained.

According to a sixth aspect of the present invention, there is provided a fuel injection pressure control method for an internal combustion engine according to any one of the first to fifth aspects.
When one or both of the internal combustion engine speed and the internal combustion engine load are smaller than a reference value, execution of the temporary reduction of the fuel injection pressure is permitted.

The temporary reduction of the fuel injection pressure may be permitted when one or both of the internal combustion engine speed and the internal combustion engine load are smaller than a reference value. When the internal combustion engine speed or internal combustion engine load is high,
This is because the normal operation noise of the internal combustion engine is relatively high, and the noise accompanying the temporary combustion activation is relatively inconspicuous. By limiting the temporary reduction of the fuel injection pressure in this way, the combustion activation state can be maintained, so that the emission can be further improved.

According to a seventh aspect of the present invention, there is provided the internal combustion engine fuel injection pressure control method according to any one of the first to fifth aspects.
The internal combustion engine is mounted on the vehicle for driving the vehicle, and when one or more of the internal combustion engine speed, the internal combustion engine load, and the vehicle speed is smaller than a reference value, the fuel injection pressure is temporarily reduced. Execution is permitted.

The temporary reduction of the fuel injection pressure may be permitted when at least one of the internal combustion engine speed, the internal combustion engine load and the vehicle speed is smaller than a reference value. . When the internal combustion engine speed, the internal combustion engine load, or the vehicle speed is high, the normal operation noise of the internal combustion engine is relatively high, and the noise due to the temporary combustion activation is relatively inconspicuous. . By limiting the temporary reduction of the fuel injection pressure in this way, the combustion activation state can be maintained, so that the emission can be further improved.

According to a fuel injection pressure control method for an internal combustion engine according to an eighth aspect, in the configuration according to any one of the first to seventh aspects,
The internal combustion engine is a diesel engine. By applying the above-described invention to a diesel engine, the activation of combustion is suppressed as described above, and the noise of the diesel engine can be suppressed.

According to a ninth aspect of the present invention, in the fuel injection pressure control method for an internal combustion engine according to the eighth aspect, the diesel engine includes a common rail type fuel injection system.

In particular, when the diesel engine is provided with a common rail type fuel injection system, the control of the fuel injection pressure is easy, and the above-mentioned effects are remarkable.

According to a tenth aspect of the present invention, there is provided a fuel injection pressure control apparatus for an internal combustion engine for adjusting an injection pressure of fuel injected into a combustion chamber of the internal combustion engine in accordance with an operation state of the internal combustion engine. Activation estimating means for estimating temporary combustion activation in the internal combustion engine based on the operating state of the internal combustion engine, and when the temporary combustion activation is estimated by the activation estimating means, Fuel injection pressure reducing means for temporarily reducing the injection pressure of the fuel injected into the combustion chamber to suppress noise of the internal combustion engine.

When the activation estimating means estimates the temporary combustion activation, the fuel injection pressure reducing means temporarily reduces the fuel injection pressure. Reducing the fuel injection pressure in this manner acts in the direction of inactivating the combustibility due to the deterioration of the atomization state or the like. Therefore, activation of the combustion is suppressed, and noise of the internal combustion engine can be suppressed.

[0026] In the fuel injection pressure control device according to the eleventh aspect, in the configuration according to the tenth aspect, the internal combustion engine includes an exhaust gas recirculation system and a fuel injection stop system during operation of the internal combustion engine, and the activation estimating means. It is assumed that during the exhaust gas recirculation by the exhaust gas recirculation system, if there is a fuel injection return from the fuel injection stop state by the fuel injection stop system, temporary combustion activation in the internal combustion engine will occur. Features.

During the exhaust gas recirculation by the exhaust gas recirculation system, if there is a fuel injection return from the fuel injection stop state by the fuel injection stop system, temporary combustion activation occurs. That is, since the fuel injection has been stopped immediately before due to the function of the fuel injection stop system, the air sucked into the combustion chamber is introduced into the combustion chamber as intake air by the exhaust gas recirculation system without being used for combustion. As described above, immediately after the return to the fuel injection, since there is excess air in the combustion chamber more than expected, temporary combustion activation is caused.

Therefore, the activation estimating means is configured to infer that temporary combustion activation in the internal combustion engine will occur when fuel injection returns in such a situation. Can temporarily reduce the fuel injection pressure at an appropriate timing. Thus, the activation of combustion is suppressed even immediately after returning to the fuel injection, and the noise of the internal combustion engine can be suppressed.

According to a twelfth aspect of the present invention, in the fuel injection pressure control system according to the tenth aspect, the internal combustion engine includes an exhaust gas recirculation system, and the activation estimating means includes an exhaust gas recirculation system. The present invention is characterized in that when there is a sharp increase in the circulation control amount, it is assumed that temporary combustion activation in the internal combustion engine will occur.

When there is a sharp increase in the exhaust gas recirculation control amount by the exhaust gas recirculation system, temporary combustion activation occurs. That is, since the amount of exhaust gas recirculation was small until immediately before, a large amount of air was introduced into the combustion chamber. Then, in such a state, when the exhaust gas recirculation control amount sharply increases, the internal combustion engine is controlled on the assumption that the actual exhaust gas recirculation amount also increases. However, in practice, it takes a long time before the exhaust gas recirculation amount corresponding to the operating state is introduced into the combustion chamber via the exhaust gas recirculation path and the intake path. For this reason, the internal combustion engine is controlled assuming that the actual amount of exhaust gas recirculation has increased despite the presence of excess air in the combustion chamber more than expected, so that temporary combustion activation is performed. Is caused.

Therefore, the activation estimating means is configured to infer that temporary combustion activation in the internal combustion engine will occur when there is such a rapid increase in the exhaust gas recirculation control amount. The injection pressure reducing means can temporarily reduce the injection pressure of the fuel at an appropriate timing. As a result, even when the exhaust gas recirculation control amount is rapidly increased, activation of combustion is suppressed, and noise of the internal combustion engine can be suppressed.

According to a thirteenth aspect of the present invention, in the fuel injection pressure control device according to the tenth aspect, the internal combustion engine includes a pilot fuel injection control system, and the activation estimating means uses the pilot fuel injection control system. When the pilot fuel injection is stopped from the pilot fuel injection state, it is estimated that temporary combustion activation in the internal combustion engine will occur.

When the pilot fuel injection is stopped from the pilot fuel injection state by the pilot fuel injection control system, temporary combustion activation occurs. That is, since the pilot fuel injection has been executed until immediately before, the intake air amount and the exhaust gas recirculation control amount are suitable for the pilot fuel injection. When the pilot fuel injection stops in this state and normal fuel injection is performed, the control of the internal combustion engine also changes accordingly.
However, in fact, it takes a long time until the intake system changes, so that temporary combustion activation is caused.

For this reason, the activation estimating means is configured to infer that temporary combustion activation in the internal combustion engine will occur when the pilot fuel injection is stopped. The fuel injection pressure can be temporarily reduced at an appropriate timing. Thus, even when the pilot fuel injection is stopped, the activation of combustion is suppressed, and the noise of the internal combustion engine can be suppressed.

According to a fourteenth aspect of the present invention, in the fuel injection pressure control device according to any one of the tenth to thirteenth aspects, the fuel injection pressure reducing means may return from a temporary reduction in the fuel injection pressure. Is characterized by gradually returning the fuel injection pressure.

It is necessary to temporarily reduce the fuel injection pressure and then return to the normal fuel injection pressure. In this case, however, the fuel injection pressure reducing means must gradually reduce the fuel injection pressure. Accordingly, it is possible to prevent a shock at the time of returning the fuel injection pressure and maintain a stable operation state of the internal combustion engine.

According to a fifteenth aspect of the present invention, in the fuel injection pressure control device according to any one of the tenth to fourteenth aspects, the fuel injection pressure reducing means includes a means for activating the temporary combustion by the activation estimating means. By temporarily reducing the injection pressure of the fuel injected into the combustion chamber of the internal combustion engine when the activation is estimated and one or both of the internal combustion engine speed and the internal combustion engine load are smaller than the reference value. The noise of the internal combustion engine is suppressed.

The fuel injection pressure reducing means includes not only the condition that the activation estimating means estimates the temporary combustion activation,
Further, when one or both of the internal combustion engine speed and the internal combustion engine load satisfy a condition that is smaller than a reference value, the injection pressure of the fuel injected into the combustion chamber of the internal combustion engine is temporarily reduced. It may be configured as follows.

When the internal combustion engine speed or the internal combustion engine load is high, the normal operating noise of the internal combustion engine is relatively high, and the noise associated with the temporary combustion activation becomes inconspicuous.
Therefore, by adding such a condition, by limiting the temporary reduction of the fuel injection pressure, the activated state of fuel combustion can be maintained, so that the emission can be further improved.

According to a sixteenth aspect of the present invention, in the fuel injection pressure control device for an internal combustion engine according to any one of the tenth to fourteenth aspects, the internal combustion engine is mounted on a vehicle for driving the vehicle and the fuel injection pressure reduction is performed. Means for determining whether or not the temporary combustion activation is estimated by the activation estimating means and when one or more of the internal combustion engine speed, the internal combustion engine load, and the vehicle speed are smaller than reference values. The noise of the internal combustion engine is suppressed by temporarily reducing the injection pressure of the fuel injected into the combustion chamber.

When the internal combustion engine is mounted on a vehicle for driving the vehicle, the fuel injection pressure reducing means includes not only the condition that the activation estimating means estimates the temporary combustion activation, but also the Temporarily reduce the injection pressure of the fuel injected into the combustion chamber of the internal combustion engine when one or more of the internal combustion engine speed, the internal combustion engine load, and the vehicle speed also satisfy a condition that is smaller than a reference value. May be configured.

When the internal combustion engine speed, the internal combustion engine load, or the vehicle speed is high, the normal operation noise of the internal combustion engine is relatively high, and the noise due to the temporary activation of combustion becomes inconspicuous. Therefore, by restricting the temporary reduction of the fuel injection pressure by adding such a condition, the fuel combustion activation state can be maintained, so that the emission can be further improved.

According to a seventeenth aspect of the present invention, there is provided a fuel injection pressure control system for an internal combustion engine, wherein the internal combustion engine is a diesel engine.

By applying the invention described above to a diesel engine, the activation of combustion is suppressed as described above, and the noise of the diesel engine can be suppressed.

In the fuel injection pressure control device according to the eighteenth aspect, in the configuration according to the seventeenth aspect, the diesel engine is provided with a common rail type fuel injection system.

In particular, when the diesel engine is provided with a common rail type fuel injection system, control of the fuel injection pressure is easy, and the above-described effects are remarkable.

[0047]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a schematic configuration diagram showing an accumulator type diesel engine (common rail type diesel engine) 1 as a first embodiment and a control system thereof. The pressure accumulating diesel engine 1 is an internal combustion engine mounted on a vehicle for driving an automobile.

The diesel engine 1 is provided with a plurality of cylinders (four cylinders in the present embodiment, but only one cylinder is shown) # 1, # 2, # 3, # 4. Injectors 2 are provided for the combustion chambers of cylinders # 1 to # 4, respectively. Fuel injection from the injector 2 to each of the cylinders # 1 to # 4 of the diesel engine 1 is controlled by turning on / off an injection control solenoid valve 3.

The injector 2 is connected to a common rail 4 serving as a pressure accumulating pipe common to each cylinder. While the injection control solenoid valve 3 is open, fuel in the common rail 4 is supplied from the injector 2 to each cylinder # 1. ♯4 are injected into the combustion chamber. A relatively high pressure corresponding to the fuel injection pressure is accumulated in the common rail 4. In order to realize this pressure accumulation, the common rail 4
Discharge port 6a of supply pump 6 via supply pipe 5
It is connected to the. In the middle of the supply pipe 5, a check valve 7 is provided. Due to the presence of the check valve 7, the supply of fuel from the supply pump 6 to the common rail 4 is permitted, and the backflow of fuel from the common rail 4 to the supply pump 6 is restricted.

The supply pump 6 is connected to a fuel tank 8 via a suction port 6b, and a filter 9 is provided on the way. The supply pump 6 draws fuel from the fuel tank 8 via the filter 9. Also,
At the same time, the supply pump 6 reciprocates the plunger by a cam (not shown) synchronized with the rotation of the diesel engine 1 to increase the fuel pressure to a required pressure, thereby supplying high-pressure fuel to the common rail 4.

Further, the discharge port 6a of the supply pump 6
A pressure control valve 10 is provided in the vicinity. The pressure control valve 10 is for controlling the fuel pressure (ie, injection pressure) discharged from the discharge port 6a toward the common rail 4. When the pressure control valve 10 is opened, excess fuel not discharged from the discharge port 6a is supplied to the return port 6c provided in the supply pump 6.
Through the return pipe 11 to the fuel tank 8.

An intake passage 13 and an exhaust passage 14 are connected to the combustion chamber of the diesel engine 1, respectively. A throttle valve 15 is provided in the intake passage 13. By adjusting the opening of the throttle valve 15 according to the operating state of the diesel engine 1, the flow rate of the intake air introduced into the combustion chamber is adjusted.

An exhaust recirculation path 16 is formed from the intake path 13 to the exhaust path 14. An EGR valve 17 is provided in the middle of the exhaust gas recirculation path 16 to adjust the amount of EGR to the intake passage 13 due to exhaust gas discharged from the combustion chamber to the exhaust passage 14.

A glow plug 18 is provided in the combustion chamber of the diesel engine 1. The glow plug 18 is a start-up assist device that glows red when an electric current is applied to the glow relay 18a immediately before the start of the diesel engine 1 and a part of fuel spray is sprayed on the glow relay 18a to promote ignition and combustion. is there.

The diesel engine 1 is provided with the following various sensors and the like, which detect the operating state of the diesel engine 1 in the first embodiment.
That is, an accelerator sensor 20 for detecting the accelerator opening ACCP is provided in the vicinity of the accelerator pedal 19, and a fully-closed signal (in the case where the depression amount of the accelerator pedal 19 is zero) is provided in the vicinity of the accelerator sensor 20. ON) is provided.

An intake air amount sensor 22 is provided in the intake passage 13 to detect an intake air amount GN flowing through the intake passage 13. The cylinder block of the diesel engine 1 is provided with a water temperature sensor 24 for detecting the temperature of the cooling water (cooling water temperature THW).

The return pipe 11 is provided with a fuel temperature sensor 26 for detecting a fuel temperature THF. Further, the common rail 4 is provided with a fuel pressure sensor 27 for detecting the pressure of the fuel in the common rail 4 (injection pressure PC).

In the first embodiment, an NE sensor 28 is provided near a pulsar (not shown) provided on a crankshaft (not shown) of the diesel engine 1. Further, the rotation of the crankshaft is transmitted via a timing belt or the like to a camshaft (not shown) for opening and closing the intake valve 31 and the exhaust valve 32. The camshaft is set to rotate at a rotation speed of 1/2 of the crankshaft. Near the pulsar (not shown) provided on this camshaft,
A sensor 29 is provided. Then, the first embodiment
Here, the engine speed NE, the crank angle CA, and the top dead center (TDC) of each of the cylinders # 1 to # 4 are calculated based on the pulse signals output from these two sensors 28 and 29.

A transmission speed sensor 30 for detecting a vehicle speed SPD from the rotation speed of the output shaft is provided on the output shaft of the transmission (not shown). In the first embodiment, an electronic control unit (ECU) 40 for controlling various controls of the diesel engine 1 is provided.
The CU 40 performs processing for controlling the diesel engine 1 such as fuel injection amount control. The ECU 40
A central processing controller (CPU), a read-only memory (ROM) in which various programs and maps are stored in advance, and a random access memory (R) in which the calculation results of the CPU are temporarily stored.
AM), a backup RAM for storing calculation results, pre-stored data, and the like, a timer counter, and the like, as well as an input interface and an output interface. These components are connected by a bus.

The above-described accelerator sensor 20, intake air amount sensor 22, water temperature sensor 24, fuel temperature sensor 26, fuel pressure sensor 27, etc. are respectively composed of a buffer, a multiplexer,
It is connected to the input interface via a / D converter (neither is shown). NE sensor 28,
The G sensor 29 and the vehicle speed sensor 30 are connected to the input interface via a waveform shaping circuit (not shown). Further, the fully closed switch 21 is directly connected to the input interface. The CPU reads the signals from the sensors via the input interface.

The solenoid valve 3, the pressure control valve 10, the throttle valve 15, the EGR valve 17, and the glow relay 18a
Are connected to the output interface via respective drive circuits (not shown). The CPU performs a control operation based on the input value read through the input interface, and controls the solenoid valve 3, the pressure control valve 10, the throttle valve 15, the EGR through the output interface.
The valve 17 and the glow relay 18a are suitably controlled.

Next, in the first embodiment, the ECU 4
The fuel injection amount control process executed at step S0 will be described with reference to the flowchart of FIG. This processing is interrupted at every injection, here, at every 180 ° crank angle because the diesel engine 1 has four cylinders. Steps in the flowchart corresponding to each processing content are represented by “SＳ”.

When the fuel injection amount control process is started, first, the operation state of the diesel engine 1, that is, the engine speed NE, the accelerator opening ACCP, the injection pressure PC, and the like are stored in a work area provided in the RAM of the ECU 40. It is read (S110). Then, based on the map shown in FIG. 3, the fuel injection amount command value QFIN is calculated from the engine speed NE and the accelerator opening ACCP (S120).

As shown in FIG. 3, the engine speed N
When E is Nei and the accelerator opening ACCP is 40%, the value of Qi is calculated as the fuel injection amount command value QFIN. The position indicated by the broken line in FIG. 3 is the fuel injection amount command value QFIN = 0, and the value below the broken line is set to the fuel injection amount command value QFIN <0. Therefore, when the fuel injection amount command value QFIN is calculated in the area below the broken line and the broken line based on the values of the engine speed NE and the accelerator opening ACCP, the fuel from the injector 2 is kept running even when the diesel engine 1 is operating. No injection is performed, and the fuel injection is stopped, that is, a so-called fuel cut is executed.

The valve opening time of the solenoid valve 3 of the injector 2 provided in the cylinder corresponding to the fuel injection timing is controlled by the fuel injection amount command value QFIN and the injection pressure PC detected by the fuel pressure sensor 27. (S13
0). As a result, a fuel amount corresponding to the fuel injection amount command value QFIN is injected into the combustion chamber of the corresponding cylinder and burned.

Next, the fuel injection pressure control process executed by the ECU 40 will be described with reference to the flowchart of FIG. This process is executed by interruption every injection, here, immediately after execution of the above-described fuel injection amount control process (FIG. 2).

When the fuel injection pressure control process is started, first, the operating state of the diesel engine 1, that is, the engine speed NE and the injection pressure PC, are read into a work area provided in the RAM of the ECU 40 (S210). . Then, based on the map shown in FIG.
E and the temporary target injection pressure tPF from the fuel injection amount command value QFIN obtained in the fuel injection amount control process (FIG. 2).
IN is calculated (S220). As shown in FIG. 5, when the engine speed NE is Nei and the fuel injection amount command value QFIN = Qi, the temporary target injection pressure tP
The value of Pi is calculated as FIN.

Then, a target injection pressure PFIN calculation process is executed (S230). This target injection pressure PFI
FIG. 6 shows details of the N calculation process. This target injection pressure PFI
In the N calculation process, first, the fuel injection amount control process (FIG. 2)
It is determined whether or not the fuel injection amount command value QFIN obtained in is equal to or greater than a fuel cut determination value EQFC which is a value for determining that the fuel is cut (S31).
0). As the fuel cut determination value EQFC, for example, a value of “−10 mm 3/1 injection” is set.

If QFIN ≧ EQFC (“YES” in S310), the fuel injection amount command value QFIN is a value for judging the state of returning from the fuel cut state to the normal fuel injection state. Fuel cut return judgment value EQ
It is determined whether it is equal to or greater than PCDON (S320). As the fuel cut return determination value EQPCDON, for example, a value of “−5 mm 3/1 injection” is set.

If QFIN ≧ EQPCDON (S3
20 "YES"), and then the fuel cut execution flag ex
fc is set to "OFF" (S330). Then, it is determined whether or not all the conditions for temporarily reducing the target injection pressure PFIN described later are satisfied (S34).
0).

This condition is as follows. (1) The previous fuel cut execution flag exfco indicating the content of the fuel cut execution flag exfc set one control cycle before is “ON”.

(2) Current fuel cut execution flag exf
c is “OFF”. (3) The engine speed NE is the execution upper limit speed ENEON
(For example, less than 2000 rpm).

(4) Vehicle speed SPD is execution upper limit vehicle speed ESPD
It is less than ON (for example, 10 km / h). (5) Accelerator opening ACCP is execution upper limit accelerator opening E
ACCPON (for example, 10%) or less.

Of these conditions, both (1) the previous fuel cut execution flag exfco = “ON” and (2) the fuel cut execution flag exfc = “OFF”, the diesel engine 1 has returned from the fuel cut state. It captures timing.

Further, (3) engine speed NE <execution upper limit rotation speed ENEON, (4) vehicle speed SPD <execution upper limit vehicle speed E
SPDON, (5) Accelerator opening ACCP ≦ Execution upper limit accelerator opening EACCPON, the normal operation sound of the diesel engine 1 is relatively low, and the process of temporarily reducing the target injection pressure PFIN, which will be described later, is substantially performed. This is to determine a state that is required in a practical manner.

Here, assuming that the operation state is such that fuel injection is continued, exfco = “OFF” and exfco = “OFF”
Since fc = “OFF”, the condition (1) is not satisfied (“NO” in S340). For this reason,
Next, a condition for determining whether or not to continue the attenuation calculation of the pressure reduction term pcdwn at the time of return from fuel cut described later is determined (S350).

This condition is as follows. If any one of these conditions is satisfied, the process proceeds to step S3.
It is determined to be "YES" at 50. (A) The fuel injection amount command value QFIN is equal to or greater than a pressure reduction term attenuation determination injection amount EQFCOFF (0 mm3 / 1 injection here) described later.

(B) The engine speed NE is equal to or higher than the execution upper limit speed ENEON. (C) The vehicle speed SPD is equal to or higher than the execution upper limit vehicle speed ESPDON. Here, in the state where the fuel injection is continued, QFIN ≧
Since the condition of EQFCOFF is satisfied (S3
("YES" at 50), and then a process of attenuating the pressure reduction term pcdwn at the time of return from fuel cut is performed as shown in the following equation 1 (S)
360).

[0079]

Equation 1 pcdwn ← pcdwn−EPCRADD ... [Equation 1] Here, the pressure-decreasing term attenuation value EPCRADD is gradually increased from the target injection pressure PFIN, which is reduced by the fuel-cut recovery pressure-decreasing term pcdwn, as described later. Pressure PF
A value for returning to IN, for example, “0.3 MPa”
Is set to

Next, the pressure reduction term pc at the time of fuel cut return
It is determined whether dwn is “0 MPa” or more (S37)
0). When the normal fuel injection is continued, the pressure reduction term pcdwn at the time of returning from the fuel cut is returned to “0 MPa”. Therefore, according to the calculation of Expression 1, pcdwn <“0M
Pa "(" NO "in S370). For this reason, the pressure reduction term pcdwn at the time of fuel cut recovery is set to “0 MPa”
Is set (S380).

Next, as shown in the following equation 2, the target injection pressure P
FIN is calculated (S390).

[0082]

[Equation 2] PFIN ← tPFIN−pcdwn [Expression 2] If fuel injection is continued, the pressure reduction term p at the time of fuel cut recovery is obtained.
Since cdwn = “0 MPa”, the value of the temporary target injection pressure tPFIN is set as the target injection pressure PFIN without being corrected for pressure reduction.

Then, the last fuel cut execution flag exf
The value of the current fuel cut execution flag exfc is set to co (S400), and the process once exits. Next, returning to the fuel injection pressure control process (FIG. 4), the control of the pressure control valve 10 is executed by the target injection pressure PFIN, and the fuel pressure sensor 2
7 is the target injection pressure PFIN
(S240).
Then, the fuel injection pressure control process ends once.

As long as fuel injection continues, the above-described processing continues. When the driver operates the accelerator pedal 19 or changes in conditions, the vehicle enters the fuel cut region shown in FIG. 3 and the fuel injection amount command value QFIN <“− 10 mm 3 /
If "1 injection" has been reached ("NO" in S310), "ON" is set in the fuel cut execution flag exfc (S310).
315).

Next, it is determined whether all of the above-mentioned conditions (1) to (5) are satisfied (S340). Here, since exfc = “ON” (“NO” in S340), it is next determined whether any of the above-described conditions (a) to (c) is satisfied (S350).

If any one of (a) to (c) is satisfied ("YES" in S350), the pressure reduction term pcdwn <0M when returning from the fuel cut is obtained according to the above equation (1).
Pa ”(S360). And then step S3
By the determination at 70 and the process at step S380, the pressure reduction term pcdwn at the time of fuel cut return is returned to "0 MPa".

If none of (a) to (c) is satisfied ("NO" in S350), the pressure reduction term pcdwn at the time of fuel cut recovery is equal to "0 MPa"("YES" in S370). )), Pressure reduction term p when returning from fuel cut
cdwn = “0 MPa” is maintained.

Then, according to the equation (2), the target injection pressure PF
IN is set (S390), but also at this time,
Since the pressure reduction term pcdwn = “0 MPa” when returning from the fuel cut, the value of the temporary target injection pressure tPFIN is set as the target injection pressure PFIN without being corrected for pressure reduction. Then, in this control cycle, the fuel cut execution flag exfc = “ON”, so the previous fuel cut execution flag exfco is set to “ON” (S400), and the process once exits.

Thereafter, the fuel cut state continues, and the fuel injection amount command value QFIN <the fuel cut determination value EQFC (S3
10 is “NO”) or the fuel injection amount command value QFIN <
Fuel cut return determination value EQPCDON ("N" in S320
O ”), the fuel cut execution flag exfc is set to“ ON ”(S315) or“ ON ”.
Since the state is maintained, "NO" in step S340.
Is determined. As a result, the state of the pressure reduction term pcdwn = “0 MPa” at the time of return from fuel cut is maintained, and the state where the value of the temporary target injection pressure tPFIN is set as the target injection pressure PFIN as it is (S390) is continued.

Immediately before the operation state of the diesel engine 1 deviates from the fuel cut region of FIG. 3, the fuel injection amount command value QFIN ≧ the fuel cut return determination value EQPCD
When it is turned ON (“YES” in S320), “OFF” is set in the fuel cut execution flag exfc (S33).
0).

As a result, (1) the previous fuel cut execution flag exfco = “O” in step S340
N ”and (2) the current fuel cut execution flag exfc =
The condition of "OFF" is both satisfied. At this time, (3),
Assuming that both of the conditions (4) and (5) are satisfied ("YES" in S340), the pressure-reduction term initial value EPCINDWN (for example, "10 MPa") is then added to the fuel-cut return pressure-reduction term pcdwn. It is set (S345).

Next, the pressure reduction term pc at the time of fuel cut return is given.
It is determined whether dwn is equal to or greater than “0” (S370).
Here, immediately after the pressure reduction term initial value EPCINDWN is set in the fuel reduction return pressure reduction term pcdwn in step S345, the fuel cut recovery pressure reduction term pcdwn> 0.
(“YES” in S370), then, the target injection pressure PFIN is calculated by substantially subtracting the fuel cut return-time pressure-reducing term pcdwn from the temporary target injection pressure tPFIN according to the equation (2). (S390).

That is, if the state is immediately before the fuel cut return, since pcdwn> 0, the target injection pressure P
FIN is set to a value smaller than the temporary target injection pressure tPFIN indicating the value of the target injection pressure to be set at the normal time. As a result, the injection pressure PC is reduced in pressure.

The last fuel cut execution flag exf
The value of the current fuel cut execution flag exfc “OF
F "is set (S400), and the process once exits. Next, returning to the fuel injection pressure control process (FIG. 4), the control of the pressure control valve 10 is executed by the target injection pressure PFIN,
Feedback control is performed so that the injection pressure PC detected by the fuel pressure sensor 27 becomes the target injection pressure PFIN (S240). At this time, the injection pressure PC is set to the temporary target injection pressure t, which is the target injection pressure to be set at the normal time.
The fuel pressure is adjusted so as to be reduced by PFIN by the pressure reduction term pcdwn when returning from the fuel cut.

When the target injection pressure PFIN calculation processing (FIG. 6) is executed in the next control cycle, steps S310 and S310 are executed.
It is determined as “YES” in 320, and the fuel cut execution flag exfc is set to “OFF” (S330). And
Since the previous fuel cut execution flag exfco = “OFF”, the condition (1) is not satisfied (S340).
Is "NO"), and it is then determined whether any of the above conditions (a), (b), and (c) is satisfied (S3).
50). Here, when the fuel injection amount command value QFIN is equal to or greater than the pressure-decrease term attenuation determination injection amount EQFCOFF and the fuel is completely recovered from the fuel cut, the condition (a) is satisfied ("YES" in S350). Therefore, next, the damping process of the pressure reduction term pcdwn at the time of returning from the fuel cut is executed by the above equation (S360). As a result, the pressure reduction term pcdwn when returning from fuel cut is reduced to the pressure reduction term initial value EPCIN.
It is reduced by the decompression term attenuation value EPCRADD from the value of DWN (here, “10 MPa”).

Then, the pressure reduction term pc when returning from the fuel cut is still obtained.
Since dwn> “0 MPa” (“Y” in S370)
ES "), and then the target injection pressure PFIN
Is calculated (S390). In the calculation according to Equation 2,
Since the pressure reduction term pcdwn at the time of fuel cut recovery is smaller by the pressure reduction term attenuation value EPCRADD than the previous time, the target injection pressure PFIN slightly approaches the temporary target injection pressure tPFIN. Then, after the process of step S400, the process once exits.

Hereinafter, the fuel cut execution flag exfc =
"OFF" continues, "NO" in step S340,
As long as “YES” is determined in step S350, the pressure reduction term pcdwn at the time of return from fuel cut is gradually attenuated by the processing in step S360. As a result, as shown in the timing chart of FIG. 7, immediately after returning from the fuel cut state (time t0 to t1) (time t1), the injection pressure PC once becomes the normal fuel injection pressure (30 MPa in FIG. 7). From the pressure reduction term initial value EPCINDWN (10 MPa in FIG. 7), and then gradually returned to the normal injection pressure PC (from time t).
2).

Then, the process of step S360 is repeated for each control cycle, so that the pressure reduction term pcdwn at the time of return from fuel cut decreases and pcdwn <“0 MPa” (“NO” in S370), pcdwn = “0MP”
a ”(S380), and this state is maintained after returning to the normal injection pressure PC (after time t2).

The throttle valve 15 and the EGR valve 1
The opening control of 7 is executed by the opening control process shown in the flowchart of FIG. This process is repeatedly executed in the same cycle as the fuel injection amount control process (FIG. 2).

When the opening degree control process is started, first, data such as an intake air amount GN, an engine speed NE, and an accelerator opening ACCP necessary for control are read into a work area in the RAM of the ECU 40 (S510). ). Next, from the throttle valve opening map shown in FIG.
The throttle valve opening EACCP is calculated based on E and the accelerator opening ACCP, and is set as a required value for a throttle valve opening control process (not shown) (S520). This allows the throttle valve 15
Is driven so as to have the throttle valve opening EACCP obtained in step S520. In step S520, when the increasing speed of the accelerator opening ACCP is large enough to determine that the operation is an acceleration operation, the throttle valve opening EACCP is set to 100% (fully open).

Next, the target air-fuel ratio λTRG is calculated from the target air-fuel ratio map based on the engine speed NE and the fuel injection amount command value QFIN calculated in the fuel injection amount control process (S530). Then, the fuel injection amount command value QF
The target intake air amount GNTRG is calculated from the product of IN and the target air-fuel ratio λTRG (S540).

Next, a deviation ΔGN of the actual intake air amount GN with respect to the target intake air amount GNTRG is calculated as shown in the following equation 3 (S550).

[0103]

ΔGN ← GN−GNTRG (Equation 3) The EGR opening DEFIN is calculated based on the deviation ΔGN, and the EGR opening DEFIN is not shown in the EG.
It is set as a required value for the R valve opening control process (S
560). That is, a correction value is calculated according to the difference ΔGN, and the integrated correction value is calculated by integrating the correction values. Then, the integrated correction value is added to the EGR opening degree DEFIN calculated in the previous control cycle or integrated and corrected, thereby obtaining a new EGR opening degree DEFIN.
To ask. Therefore, throttle valve 1
If there is no abnormality in the EGR valve 5 and the EGR valve 17 and the operation of the diesel engine 1 is stable, the deviation ΔGN is absorbed by the integrated correction value and approaches the deviation ΔGN = 0.

As a result, the EGR valve 17 is driven so as to have the EGR opening DEFIN determined in step S560. In step S560, when the increasing speed of the accelerator opening ACCP is large enough to determine that the operation is an acceleration operation, the EGR opening DEFIN = 0%
(Fully closed). Thus, the present process is once ended.

By performing such an opening control process, for example, when returning from the fuel cut, the throttle valve opening EACCP is closed and the EGR valve 17 is opened. For this reason, immediately after returning from the fuel cut, a large amount of air is temporarily introduced from the exhaust passage 14 and the exhaust recirculation passage 16 to activate the combustion. By reducing the injection pressure, combustion activation is suppressed.

In the configuration of the first embodiment described above, the condition determination processing of (1) and (2) in step S340 is replaced with the processing of step S340 as the activation estimating means.
(3) to (5) condition determination processing and step S
Steps 345 to S390 correspond to processing as fuel injection pressure reducing means.

According to the first embodiment described above, the following effects can be obtained. (I). If it is determined in step S340 that the fuel injection has returned or is returning from the fuel cut state according to the condition determinations (1) and (2), the fuel cut state is maintained until immediately before. You can see that. In this state, the air sucked into the combustion chamber is not used for combustion and is used as it is in the exhaust recirculation path 16 and the EGR valve 1.
This is a state in which the air is introduced into the combustion chamber as intake air via. Therefore, immediately after returning to the fuel injection, there is excess air in the combustion chamber more than expected, and if fuel injection is performed normally in such a combustion chamber, temporary combustion activation may be caused. I can guess.

As described above, the condition (1) of step S340
When temporary combustion activation is estimated by (2),
In step S345, pressure reduction term pcdw when returning from fuel cut
Set the pressure reduction term initial value EPCINDWN to n. As a result, the fuel injection pressure can be temporarily reduced. As a result, the atomization state of the fuel is deteriorated, and the fuel is made to act to deactivate the combustibility. For this reason, combustion activation is suppressed, and the noise of the diesel engine 1 can be suppressed.

(B). Step S340 further includes conditions (3), (4) and (5). These conditions mean conditions where the noise of the diesel engine 1 is inconspicuous. That is, when the engine speed NE, the accelerator opening ACCP (corresponding to the engine load), or the vehicle speed SPD is high, the normal operation sound of the diesel engine 1 is relatively high, and the normal combustion sound is accompanied by temporary combustion activation. Noise is less noticeable. Therefore, by adding such conditions, it is possible to improve the emission by limiting the temporary reduction of the fuel injection pressure.

(C). Further, once the fuel injection pressure is greatly reduced, the fuel injection pressure is gradually returned to the normal fuel injection pressure by the process of step S360.
As a result, a shock at the time of fuel injection pressure return can be prevented, and a stable operating state of the diesel engine 1 can be maintained.

[Second Embodiment] In a second embodiment, a target injection pressure PFIN calculation process shown in a flowchart of FIG. 10 is executed instead of the target injection pressure PFIN calculation process (FIG. 6) in the first embodiment. Is different.
The other configuration is the same as that of the first embodiment unless otherwise described.

The target injection pressure PFIN calculation processing of FIG. 10 will be described. When this processing is started, first, the EGR opening degree DEFI obtained in the opening degree control processing (FIG. 8)
The value of N is stored as the current opening value pegbse (S
610). Then, as shown in the following equation 4, the previous opening value p corresponding to the current opening value pegbse in the previous control cycle
The change opening value from egbseo is calculated as the EGR opening change amount d
It is calculated as a peg (S620).

[0113]

## EQU4 ## Then, it is determined whether or not all the conditions for temporarily reducing the target injection pressure PFIN described later are satisfied (S630).

This condition is as follows. (1) The EGR opening change amount dpeg exceeds the EGR opening change amount determination value EDPEG (for example, equivalent to 20%).

(2) The engine speed NE is lower than the execution upper limit engine speed ENEON (for example, 2000 rpm). (3) The vehicle speed SPD is lower than the execution upper limit vehicle speed ESPDON (for example, 10 km / h).

(4) The accelerator opening ACCP is equal to or less than the execution upper limit accelerator opening EACCPON (for example, 10%). Among these conditions, the condition of (1) dpeg> EDPEG is as follows:
This is to capture the timing when the EGR valve 17 opens rapidly.

Also, (2) engine speed NE <execution upper limit rotation speed ENEON, (3) vehicle speed SPD <execution upper limit vehicle speed E
SPDON, (4) accelerator opening ACCP ≦ execution upper limit accelerator opening EACCPON, as described in the first embodiment, the normal operation sound of the diesel engine 1 is relatively low, and the target injection pressure described later This is to determine a state in which processing for temporarily reducing PFIN is substantially required.

Here, assuming that dpeg ≦ EDPEG is not the state in which the EGR valve 17 is rapidly opened,
Since the condition (1) is not satisfied (S63
0 and “NO”), and then the EGR sudden opening pressure reduction term pgdwn is attenuated as shown in the following Expression 5 (S64).
0).

[0119]

Pgdwn ← pgdwn−EPGRADD (Equation 5) Here, the pressure-reducing term attenuation value EPGRADD is the target injection pressure PFI reduced by the pressure-reducing term pgdwn when the EGR is rapidly opened.
This is a value for gradually returning N to the normal target injection pressure PFIN, and is set to, for example, “0.5 MPa”.

Next, the pressure-reducing term pgdw at the time of EGR sudden opening
It is determined whether or not n is equal to or greater than “0 MPa” (S65)
0). If the EGR valve 17 is not suddenly opened, the EGR
The sudden opening pressure reduction term pgdwn returns to “0 MPa”. For this reason, pgdwn <“0”
MPa (“NO” in S650), so “0 MPa” is set in the EGR sudden opening pressure reducing term pgdwn (SMP).
660).

Next, as shown in the following equation 6, the target injection pressure P
FIN is calculated (S670).

[0122]

[Equation 6] PFIN ← tPFIN−pgdwn [Equation 6] If the EGR valve 17 is not in the rapid opening state, the EGR rapid opening pressure reduction term pgdwn = “0 MPa”. The value of the target injection pressure tPFIN is set as it is without pressure reduction correction.

Then, the value of the current opening value pegbse is set to the previous opening value pegbseo (S680), and the process once exits. Next, returning to the fuel injection pressure control process (FIG. 4), the control of the pressure control valve 10 is executed by the target injection pressure PFIN so that the injection pressure PC detected by the fuel pressure sensor 27 becomes the target injection pressure PFIN. (S240). Then, the fuel injection pressure control process ends once.

As long as the EGR valve 17 is not suddenly opened, the above-described processing is continued. Then, the EGR opening degree DEFIN rapidly opens due to the driver's operation of the accelerator pedal 19 or a change in the situation, and a value exceeding the EGR opening degree change amount determination value EDPEG is calculated as the EGR opening degree change amount dpeg. Consider the case.

In this case, of the above-mentioned conditions (1) to (4), the condition of (1) dpeg> EDPEG is satisfied. At this time, assuming that the conditions (2) to (4) are also satisfied ("YES" in S630), then, the pressure-reducing term initial value EPGINDWN (for example, "15 MPa") is added to the pressure-reducing term pgdwn at the time of EGR sudden opening. Is set (S635).

Next, the EGR sudden opening pressure reduction term pgdw
It is determined whether n is equal to or greater than “0” (S650). Here, in step S635, the EGR sudden opening pressure reduction term pgdw
Immediately after setting the pressure-reducing term initial value EPGINDWN to n, since the pressure-reducing term pgdwn> 0 at the time of the rapid opening of EGR (“YES” in S650),
The target injection pressure PFIN is calculated by substantially subtracting the EGR sudden opening pressure reduction term pgdwn from the temporary target injection pressure tPFIN (S670).

That is, if the EGR valve 17 is suddenly opened, since pgdwn> 0, the target injection pressure PF
IN is set to a value smaller than the temporary target injection pressure tPFIN indicating the value of the target injection pressure to be set at the normal time. As a result, the injection pressure PC is reduced in pressure.

Then, the value of the current opening value pegbse is set to the previous opening value pegbseo (S680), and the process once exits. Next, returning to the fuel injection pressure control process (FIG. 4), the control of the pressure control valve 10 is executed by the target injection pressure PFIN so that the injection pressure PC detected by the fuel pressure sensor 27 becomes the target injection pressure PFIN. (S240). At this time, the injection pressure P
C is a depressurization term pgd at the time of EGR sudden opening, which is lower than the temporary target injection pressure tPFIN which is a target injection pressure to be set at the normal time.
It is adjusted so that the pressure is reduced by wn.

When the target injection pressure PFIN calculation process (FIG. 10) is executed again, as long as the above conditions (1) to (4) are satisfied ("YES" in S630), step S is executed.
The setting of the EGR sudden opening pressure reduction term pgdwn in 635 is continued. Then, the change in the opening degree of the EGR valve 17 decreases,
The EGR opening change amount dpeg is equal to the EGR opening change amount determination value E.
If DPEG or less, condition (1) is not satisfied (“NO” in S630).
The process of attenuating the sudden opening pressure reduction term pgdwn is executed (S640). Accordingly, the pressure-reducing term pgdwn at the time of the rapid opening of the EGR is smaller than the value of the pressure-reducing term initial value EPGINDWN (here, “15 MPa”).
ADD is reduced.

Then, the pressure reduction term pgdw at the time of the rapid opening of EGR is still obtained.
n> “0 MPa” (“YE in S650”
S "), then, the target injection pressure PFIN is calculated by the above equation 6 (S670). In the calculation according to Equation 6, the target injection pressure PFIN slightly approaches the temporary target injection pressure tPFIN because the EGR sudden opening pressure reduction term pgdwn is reduced by the pressure reduction term attenuation value EPGRADD from the previous time. Then, after the process of step S680, the process once exits.

Thereafter, if there is no sudden opening of the EGR valve 17 ("NO" in S630), the EGR suddenly opening pressure reducing term pgdwn is gradually attenuated by the processing of step S640.
As a result, as shown in the timing chart of FIG. 11, immediately after the EGR valve 17 is rapidly opened (time t10), the injection pressure PC temporarily becomes equal to the normal fuel injection pressure (FIG. 1).
1, the decompression term initial value EPGINDW than 50 MPa)
N (15 MPa in FIG. 11), and then gradually returned to the normal injection pressure PC (to time t11).

Then, the process of step S640 is repeated for each control cycle, so that the EGR sudden opening pressure reduction term p
When gdwn decreases and pgdwn <“0 MPa” (“NO” in S650), pgdwn = “0 MPa”
Is set (S660). Therefore, after returning to the normal injection pressure PC (after time t11), this state is maintained.

In the configuration of the second embodiment described above, the condition determination processing of (1) in step S630 is replaced with the processing of (2) to (4) in step S340 and the processing of step S635 in step S340. ~
S670 corresponds to the processing as the fuel injection pressure reducing means.

According to the second embodiment described above, the following effects can be obtained. (I). When the opening of the EGR valve 17 suddenly increases, a large amount of air is introduced into the combustion chamber because the control amount for the EGR amount was low until immediately before.
In spite of the fact that excess air is present in the combustion chamber more than expected, the control of the fuel injection and the like of the diesel engine 1 is performed assuming that the amount of exhaust gas recirculation has increased as controlled. Combustion activation is caused.

For this reason, it is assumed that temporary combustion activation in the diesel engine 1 will occur when the opening of the EGR valve 17 suddenly increases, and the fuel injection pressure is temporarily reduced at this timing. . Thus, the EGR valve 1
Activation of combustion at the time of rapid opening of the fuel cell 7 is suppressed, and noise of the diesel engine 1 can be suppressed.

(B). The effects (b) and (c) of the first embodiment are obtained. [Embodiment 3] Embodiment 3 is based on Embodiment 1 described above.
On the other hand, in order to maintain a good operating state in emission and the like according to the operating state of the diesel engine 1, a process of switching the injection mode between pilot fuel injection and normal fuel injection is executed. Specifically, as shown in FIG. 12, according to the fuel injection amount command value QFIN and the engine speed NE, the pilot fuel injection is executed on the left side (low engine speed NE side) of the dashed boundary line. On the right side (on the high engine speed NE side) of the dashed boundary line, the pilot fuel injection is stopped to execute the normal main injection only. Note that, by switching the injection mode, the temporary target injection pressure tPFIN map shown in FIG. 5 and the throttle valve opening map shown in FIG. Can be switched.

Further, the third embodiment is different from the first embodiment in that the target injection pressure PFIN calculation process shown in the flowchart of FIG. 13 is executed instead of the target injection pressure PFIN calculation process (FIG. 6). different. The other configuration is the same as that of the first embodiment unless otherwise described.

The target injection pressure PFIN calculation processing of FIG. 13 will be described. When the process is started, first, it is determined whether the operation state of the diesel engine 1 is in the pilot injection range shown in FIG. 12 (S710). If it is in the pilot injection range ("YES" in S710), "ON" is set in pilot injection execution flag exfp (S720). If it is in the normal injection range ("NO" in S710), the pilot injection execution flag exfp is set to "O".
“FF” is set (S730).

Next, it is determined whether or not all the conditions for temporarily reducing the target injection pressure PFIN described later are satisfied (S740). This condition is as follows.

(1) The previous pilot injection execution flag exfpo indicating the content of the pilot injection execution flag exfp set one control cycle before is "ON". (2) The current pilot injection execution flag exfp is set to “O
FF ".

(3) The engine speed NE is less than the upper limit execution speed ENEON (for example, 2000 rpm). (4) The vehicle speed SPD is lower than the execution upper limit vehicle speed ESPDON (for example, 10 km / h).

(5) The accelerator opening ACCP is equal to or less than the execution upper limit accelerator opening EACCPON (for example, 10%). Among these conditions, (1) the previous pilot injection execution flag e
Both conditions of xfpo = “ON” and (2) pilot injection execution flag exfp = “OFF” capture the timing when the diesel engine 1 switches from the pilot injection range to the normal injection range.

Also, (3) engine speed NE <execution upper limit rotation speed ENEON, (4) vehicle speed SPD <execution upper limit vehicle speed E
SPDON, (5) Accelerator opening ACCP ≦ Execution upper limit accelerator opening EACCPON, as described in the first embodiment, the normal operation sound of the diesel engine 1 is relatively low, and the target injection described later This is to determine a state in which the process of temporarily reducing the pressure PFIN is substantially required.

Here, assuming that the operation state is that pilot fuel injection is continued, exfpo = “ON”, and
Since exfp = “ON”, the condition (1) is not satisfied (“NO” in S740).
Next, as shown in the following equation 7, the process of attenuating the pressure reduction term ppdwn when the pilot injection is stopped is executed (S750).

[0145]

Ppdwn ← ppdwn-EPPRADD [Equation 7] Here, the pressure reduction term attenuation value EPPRADD gradually reduces the target injection pressure PFIN reduced in the pilot injection stoppage pressure reduction term ppdwn to the normal target injection pressure PFIN. This is a value for returning, for example, set to “0.3 MPa”.

Next, it is determined whether or not the pressure reduction term ppdwn at the time of the pilot injection stop is equal to or more than "0 MPa" (S
760). If it is not immediately after switching from the pilot injection range to the normal injection range, since the pilot injection stop pressure reduction term ppdwn has returned to “0 MPa”, ppdwn <“0 MPa” by the calculation of the equation (7) ( ("NO" in S760). Therefore, “0 MPa” is set in the pressure reduction term ppdwn when the pilot injection is stopped (SMP).
770).

Next, as shown in the following equation 8, the target injection pressure P
FIN is calculated (S780).

[0148]

[Expression 8] PFIN ← tPFIN−ppdwn [Expression 8] Unless immediately after switching from the pilot injection range to the normal injection range, the pilot injection stop pressure reduction term ppdwn =
Since it is “0 MPa”, the target injection pressure PFIN
, The value of the temporary target injection pressure tPFIN is set as it is without the pressure reduction correction.

Then, the previous pilot injection execution flag e
The current pilot injection execution flag exfp is set in xfpo (S790), and the process once exits. Next, returning to the fuel injection pressure control process (FIG. 4) described in the first embodiment, the pressure control valve 1 is controlled by the target injection pressure PFIN.
0 is performed, and feedback control is performed so that the injection pressure PC detected by the fuel pressure sensor 27 becomes the target injection pressure PFIN (S240). Then, the fuel injection pressure control process ends once.

As long as the pilot injection range is not switched to the normal injection range, the above-described processing is continued. Then, consider a case where the pilot injection range shown in FIG. 12 is switched to the normal injection range.

In this case, among the conditions (1) to (5) described above, (1) the previous pilot injection execution flag exfpo
= “ON”, and (2) the condition of the current pilot injection execution flag exfp = “OFF” is satisfied. At this time,
If the conditions of (3) to (5) are also satisfied (S7
("YES" at 40), and then a pressure reduction term initial value EPPINDWN (for example, "10 MPa") is set as the pilot injection stop pressure reduction term ppdwn (S745).

Then, it is determined whether or not the pressure reduction term ppdwn at the time of the pilot injection stop is equal to or more than "0" (S76).
0). Here, in step S745, the pressure reduction term initial value EPPINDWN is added to the pressure reduction term ppdwn when the pilot injection is stopped.
Immediately after setting the pressure reduction term ppdwn> 0 when the pilot injection is stopped (“YE in S760”).
S "), and the temporary target injection pressure tP
Substantially reduced pressure term ppd from stop of pilot injection from FIN
The target injection pressure PFIN is calculated by subtracting wn (S780).

That is, if the timing has been switched from the pilot injection range to the normal injection range, ppdwn> 0
Therefore, the target injection pressure PFIN is set to a value smaller than the temporary target injection pressure tPFIN indicating the value of the target injection pressure to be set at the normal time. As a result, the injection pressure PC is reduced in pressure.

Then, the previous pilot injection execution flag e
xfpo is the current pilot injection execution flag exfp =
"OFF" is set (S790), and the process once exits. Next, returning to the fuel injection pressure control process (FIG. 4),
The control of the pressure control valve 10 is executed by the target injection pressure PFIN, and the injection pressure PC detected by the fuel pressure sensor 27.
Is subjected to feedback control so as to become the target injection pressure PFIN (S240). At this time, the injection pressure PC is lower than the temporary target injection pressure tPFIN, which is the target injection pressure to be set at the normal time, by the pilot injection stop pressure reduction term pp.
The pressure is adjusted so as to be reduced by dwn.

When the target injection pressure PFIN calculation process (FIG. 13) is executed again, since the previous pilot injection execution flag exfpo = “OFF”, the condition (1) is not satisfied (“NO” in S740). ). For this reason, the process of attenuating the pressure drop term ppdwn at the time of the stop of the pilot injection shown in Expression 7 is executed (S750). As a result, the pressure reduction term ppdwn when the pilot injection is stopped becomes the pressure reduction term initial value EPPINDWN (here, “10MP
a)) is reduced by the pressure reduction term attenuation value EPPRADD.

Since the pilot injection stop pressure reduction term ppdwn is still greater than “0 MPa” (“YES” in S760), the target injection pressure PF
IN is calculated (S780). In the calculation according to this equation 8, the pressure reduction term ppdwn at the time of the pilot injection stop compared to the previous time
Since the pressure reduction term attenuation value EPPRADD has been reduced, the target injection pressure PFIN is slightly reduced to the target injection pressure t.
Approach PFIN. Then, after the process of step S790, the process once exits.

Thereafter, by the processing in step S750, the pressure reduction term ppdwn when the pilot injection is stopped gradually decreases. As a result, as shown in the timing chart of FIG. 14, immediately after switching from the pilot injection range to the normal injection range (time t20), the injection pressure PC is temporarily reduced.
Is lower than the normal fuel injection pressure (40 MPa in FIG. 14) by the pressure reduction term initial value EPPINDWN (10 MPa in FIG. 14).
a) A lower setting is made. Thereafter, the injection pressure PC is gradually returned to the normal injection pressure PC (to time t21).

By repeating the process of step S750 for each control cycle, the pressure reduction term ppdwn when the pilot injection is stopped is reduced, and ppdwn <“0MP
a ”(“ NO ”in S760), ppdwn =
It is set to "0 MPa" (S770). For this reason, after returning to the normal injection pressure PC (time t21)
After that, this state is maintained.

In the configuration of the third embodiment described above, the condition determination processing of (1) and (2) in step S740 is replaced with the processing of the activation estimating means in step S740.
(3) to (5) condition determination processing and step S
Steps 745 to S780 correspond to processing as fuel injection pressure reducing means.

According to the third embodiment described above, the following effects can be obtained. (I). Immediately after switching from the pilot injection range to the normal injection range, since the pilot fuel injection has been executed until immediately before, the combustion activity suitable for the pilot fuel injection in the intake air amount, the exhaust recirculation control amount, etc. Also, an atmosphere having a high combustion activity remains on the intake system side. However, since the pilot fuel injection is stopped on the control side, the atmosphere of the remaining intake system is not suitable for normal fuel injection, and temporary combustion activation is caused.

For this reason, when switching from the pilot injection range to the normal injection range, it is estimated that temporary combustion activation in the diesel engine 1 will occur, and the fuel injection pressure is temporarily reduced at this timing. Thus, the activation of combustion when the pilot fuel injection is stopped is suppressed, and the noise of the diesel engine 1 can be suppressed.

(B). The effects (b) and (c) of the first embodiment are obtained. [Other Embodiments] In each of the above-described embodiments, the state in which combustion is temporarily activated in the internal combustion engine is regarded as the return from the fuel cut, the rapid opening of the EGR valve, or the stop of the pilot injection. However, besides this, a state in which combustion is temporarily activated in the internal combustion engine is determined based on a change in an operating state that causes a return from a fuel cut, a rapid opening of an EGR valve, or a stop of a pilot injection. May be.

In each of the above embodiments, a common rail type (accumulation type) injection system for supplying high-pressure fuel to the common rail 4 is used as the fuel injection system. HEUI (Hydraulicall) that pressurizes the fuel to the injection pressure with the pressure increasing piston
y actuated Electronically controlled Unit Injecto
The invention can also be applied to a fuel injection system such as an r) type fuel injection system.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a pressure accumulating diesel engine and a control system thereof according to a first embodiment.

FIG. 2 is a flowchart of a fuel injection amount control process executed by an ECU according to the first embodiment.

FIG. 3 is a map configuration diagram for calculating a fuel injection amount command value QFIN from an engine speed NE and an accelerator opening ACCP used in the fuel injection amount control process.

FIG. 4 is a flowchart of a fuel injection pressure control process executed by an ECU according to the first embodiment.

FIG. 5 is a map configuration diagram for calculating a temporary target injection pressure tPFIN from an engine speed NE and a fuel injection amount command value QFIN used in the fuel injection pressure control process.

FIG. 6 is a flowchart of a target injection pressure PFIN calculation process executed by the ECU according to the first embodiment.

FIG. 7 is a timing chart showing an example of control according to the first embodiment.

FIG. 8 is a flowchart of an opening control process executed by the ECU according to the first embodiment;

FIG. 9 is a configuration diagram of a throttle valve opening map for obtaining a throttle valve opening EACCP from an engine speed NE and an accelerator opening ACCP used in the opening control process.

FIG. 10 is a flowchart of a target injection pressure PFIN calculation process executed by the ECU according to the second embodiment.

FIG. 11 is a timing chart showing an example of control according to the second embodiment.

FIG. 12 is a map configuration diagram for setting a pilot fuel injection mode and a normal fuel injection mode used in the third embodiment.

FIG. 13 is a flowchart of a target injection pressure PFIN calculation process executed by the ECU according to the third embodiment.

FIG. 14 is a timing chart showing an example of control according to the third embodiment.

[Explanation of symbols]

1. Accumulation type diesel engine, 2. Injector, 3
... solenoid valve, 4 ... common rail, 5 ... supply pipe, 6 ... supply pump, 6a ... discharge port, 6b ... suction port, 6
c: return port, 7: check valve, 8: fuel tank, 9
... Filter, 10 ... Pressure control valve, 11 ... Return piping,
13: intake passage, 14: exhaust passage, 15: throttle valve, 16: exhaust recirculation passage, 17: EGR valve, 18 ...
Glow plug, 18a glow relay, 19 accelerator pedal, 20 accelerator sensor, 21 fully closed switch,
22: intake air amount sensor, 24: water temperature sensor, 26: fuel temperature sensor, 27: fuel pressure sensor, 28: NE sensor, 29
... G sensor, 30 ... vehicle speed sensor, 31 ... intake valve, 32 ...
Exhaust valve, 40 ... ECU.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) F02M 25/07 570 F02M 25/07 570D F-term (Reference) 3G062 AA01 BA02 BA05 BA06 CA06 GA01 GA04 GA08 GA15 GA21 3G092 AA02 AA17 BA01 BA04 BB02 BB04 BB08 BB10 BB13 DC03 DC09 DE01S DE09S DG09 EA01 EA02 EA22 EB03 EC01 FA14 FA15 GA13 HA01X HA01Z HA11Z HB01X HB01Z HB03X HB03Z HB04Z HE01Z HE03Z HE05Z HE06Z HE08Z11 HF09 HA03Z21 MA25 MA28 NA04 NE03 NE06 PA01A PA01Z PB01Z PB03Z PB08A PB08Z PF01Z PF04Z

Claims (18)

[Claims] When the combustion is temporarily activated in an internal combustion engine, the noise of the internal combustion engine is suppressed by temporarily reducing the injection pressure of fuel injected into a combustion chamber of the internal combustion engine. A method for controlling fuel injection pressure of an internal combustion engine. 2. The structure according to claim 1, wherein the temporary combustion activation in the internal combustion engine is caused by a return of fuel injection from a fuel injection stop state during exhaust gas recirculation. An internal combustion engine fuel injection pressure control method. 3. The internal combustion engine fuel injection pressure according to claim 1, wherein the temporary combustion activation in the internal combustion engine is caused by a sudden increase in an exhaust gas recirculation control amount. Control method. 4. The method according to claim 1, wherein the temporary combustion activation in the internal combustion engine is caused by stopping a pilot fuel injection. 5. In the configuration according to any one of claims 1 to 4, when returning from the temporary reduction of the fuel injection pressure,
A fuel injection pressure control method for an internal combustion engine, wherein the fuel injection pressure is gradually restored. 6. A fuel injection system according to claim 1, wherein one or both of the internal combustion engine speed and the internal combustion engine load are smaller than a reference value. A method for controlling fuel injection pressure of an internal combustion engine, characterized in that execution is permitted. 7. The vehicle as claimed in claim 1, wherein the internal combustion engine is mounted on the vehicle for driving the vehicle, and at least one of an internal combustion engine speed, an internal combustion engine load, and a vehicle speed. A fuel injection pressure control method for permitting execution of the temporary reduction of the fuel injection pressure when is smaller than a reference value. 8. A method according to claim 1, wherein said internal combustion engine is a diesel engine. 9. A fuel injection pressure control method for an internal combustion engine according to claim 8, wherein the diesel engine has a common rail type fuel injection system. 10. An internal combustion engine fuel injection pressure control device for adjusting an injection pressure of fuel injected into a combustion chamber of an internal combustion engine in accordance with an operation state of the internal combustion engine. Activation estimating means for estimating temporary combustion activation, and when the temporary combustion activation is estimated by the activation estimating means, the injection pressure of the fuel injected into the combustion chamber of the internal combustion engine is temporarily reduced. A fuel injection pressure control device, comprising: a fuel injection pressure reducing unit that reduces noise of the internal combustion engine by reducing the fuel injection pressure. 11. The exhaust gas recirculation system according to claim 10, wherein the internal combustion engine includes an exhaust gas recirculation system and a fuel injection stop system during operation of the internal combustion engine. The fuel injection pressure control device for an internal combustion engine, which estimates that temporary combustion activation in the internal combustion engine will occur when the fuel injection is stopped by the fuel injection stop system. 12. The structure according to claim 10, wherein the internal combustion engine is provided with an exhaust gas recirculation system, and the activation estimating means is configured to determine whether the amount of exhaust gas recirculation controlled by the exhaust gas recirculation system increases rapidly. An internal combustion engine fuel injection pressure control device which estimates that temporary combustion activation in an internal combustion engine will occur. 13. The system according to claim 10, wherein the internal combustion engine includes a pilot fuel injection control system, and the activation estimating means stops the pilot fuel injection from a pilot fuel injection state by the pilot fuel injection control system. A fuel injection pressure control device for an internal combustion engine, which estimates that temporary combustion activation in the internal combustion engine will occur when the internal combustion engine is activated. 14. The fuel injection pressure reducing means according to any one of claims 10 to 13, wherein when returning from the temporary reduction of the fuel injection pressure, the fuel injection pressure reducing means gradually recovers the fuel injection pressure. A fuel injection pressure control device for an internal combustion engine. 15. The fuel injection pressure reducing means according to any one of claims 10 to 14, wherein said activation estimating means predicts said temporary combustion activation and said internal combustion engine speed and When one or both of the internal combustion engine loads are smaller than the reference value, the noise of the internal combustion engine is suppressed by temporarily reducing the injection pressure of the fuel injected into the combustion chamber of the internal combustion engine. Internal combustion engine fuel injection pressure control device. 16. An apparatus according to claim 10, wherein said internal combustion engine is mounted on a vehicle for driving the vehicle, and said fuel injection pressure reducing means is provided with said activation estimating means for said temporary operation. Combustion activation is estimated,
In addition, when one or more of the internal combustion engine speed, the internal combustion engine load, and the vehicle speed are smaller than the reference values, the injection pressure of the fuel injected into the combustion chamber of the internal combustion engine is temporarily reduced to reduce the internal combustion engine An internal combustion engine fuel injection pressure control device characterized by suppressing noise. 17. The fuel injection pressure control device according to claim 10, wherein the internal combustion engine is a diesel engine. 18. The fuel injection pressure control device for an internal combustion engine according to claim 17, wherein the diesel engine has a common rail type fuel injection system.