JP4247616B2 - Fuel injection control device for diesel engine - Google Patents

Description

  The present invention relates to a fuel injection control device for a diesel engine, and more particularly to a technique for suppressing smoke emission.

Diesel engines tend to generate smoke in low-rotation and high-load regions, and in order to suppress the generation of such smoke, the fuel injection amount is adjusted according to the amount of fresh air, supercharging pressure, etc. during the transitional period of operation. Technology to suppress has been developed.
Also, if the time staying in the low rotation / low load region is long, smoke is likely to be generated. Therefore, when the engine speed increases slowly and the time remaining in the low rotation / low load region is long, the engine rotation speed increases faster. Also, a technique for limiting the fuel injection amount has been developed (see Patent Document 1).
JP 2002-256945 A (Claim 1 etc.)

By the way, in a diesel engine, since the intake air amount is large and NOx is likely to be generated, EGR (exhaust gas recirculation) is mainly performed for the purpose of reducing NOx, and a part of the exhaust gas is recirculated to the intake system as EGR gas. In this case, the EGR gas amount is generally set according to the fuel injection amount.
Therefore, if the fuel injection amount is suppressed according to the fresh air amount, the supercharging pressure, or the like as described above, or according to the rising speed of the engine rotation speed, the EGR gas flow rate is determined according to the suppressed fuel injection amount. For example, a phenomenon may occur in which the fuel injection amount decreases while the EGR gas flow rate increases due to suppression.

If the EGR gas flow rate increases in this way, the amount of fresh air in the intake air will decrease, and the amount of fresh air will also decrease at the same time even though the fuel injection amount is suppressed, and smoke cannot be sufficiently suppressed. There is a problem.
Further, even when the suppression of the fuel injection amount is finished and the fuel injection amount returns to the normal state, the EGR gas flow rate cannot immediately respond to the fuel injection amount, that is, the EGR gas does not decrease with good responsiveness, Therefore, there is a problem that the amount of fresh air does not increase with good responsiveness and smoke cannot be sufficiently suppressed.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a fuel injection control device for a diesel engine that has a simple configuration and can sufficiently suppress smoke emission. It is in.

In order to achieve the above object, in the fuel injection control device for a diesel engine according to claim 1, the normal fuel injection amount is set based on the engine rotation speed and the accelerator operation amount, and the normal fuel injection amount and the engine rotation speed are set. The target excess air ratio setting means for setting the target excess air ratio based on the above, the EGR passage for returning a part of the exhaust gas to the intake system as EGR gas, and the EGR gas flow rate flowing through the EGR passage to the target excess air ratio EGR control means for controlling based on the limit, excess air ratio setting means for setting a limit excess air ratio that does not generate smoke according to the normal fuel injection amount and the engine speed, and a limit fuel based on the limit air excess ratio Limiting fuel injection amount calculating means for obtaining an injection amount; injection amount change degree detecting means for detecting a change degree of the normal fuel injection amount; and the normal fuel When the degree of change in injection amount exceeds a predetermined value, said a fuel injection means for performing fuel injection based on the normal fuel injection amount the limit fuel injection amount in place of, the EGR control means, the limit air Even when the limit excess air ratio is set by the excess ratio setting means, the EGR gas flow rate is controlled based on the target excess air ratio .

The fuel injection control device for a diesel engine according to claim 2 further includes in-cylinder excess air ratio estimating means for estimating an excess air ratio in the cylinder, wherein the limited fuel injection amount calculating means is provided in the estimated in-cylinder A limiting ratio of the excess air ratio is obtained by dividing the excess air ratio by the limit excess air ratio, and the restricted fuel injection amount is obtained from the product of the restriction ratio and the normal fuel injection amount.
In the fuel injection control device for a diesel engine according to claim 3, the fuel injection means can control the EGR gas flow rate by the EGR control means, and the degree of change in the normal fuel injection amount is a predetermined value or more. In this case, fuel injection is performed based on the limited fuel injection amount instead of the normal fuel injection amount.

  Further, in the fuel injection control device for a diesel engine according to claim 4, the fuel injection means starts fuel injection when the limited fuel injection amount becomes equal to or more than the normal fuel injection amount or based on the limited fuel injection amount. When a predetermined time elapses, fuel injection based on the limited fuel injection amount is terminated and fuel injection is performed using the normal fuel injection amount.

  According to the fuel injection control device for a diesel engine according to claim 1, when the degree of change in the normal fuel injection amount becomes a predetermined value or more, the fuel injection is performed by the limited fuel injection amount based on the limit excess air ratio instead of the normal fuel injection amount. On the other hand, since the EGR gas flow rate is controlled based on the target excess air ratio, it is prevented that the EGR gas flow rate increases in response to the limited fuel injection amount and the fresh air amount in the intake air decreases. Emission can be reliably suppressed.

Further, even when the fuel injection by the limited fuel injection amount is returned to the fuel injection by the normal fuel injection amount, the EGR gas flow rate does not immediately decrease and the fresh air amount cannot follow the increase in the fuel injection amount. Is prevented, and smoke emission can be reliably suppressed.
According to the fuel injection control device for a diesel engine according to claim 2, the estimated excess air ratio in the cylinder is divided by the limit excess air ratio to obtain a limit ratio of the excess air ratio. Since the limited fuel injection amount is obtained from the product of the amount, it is possible to reliably suppress smoke discharge with a simple configuration.

  According to the fuel injection control device for a diesel engine according to claim 3, when the EGR gas flow rate can be controlled by the EGR control means and the change degree of the normal fuel injection amount becomes a predetermined value or more, the normal fuel injection is performed. Since fuel injection is performed based on the limited fuel injection amount instead of the amount, for example, when the diesel engine is in the engine stall mode or the start mode and the control of the EGR gas flow rate is unstable, for example, the boost sensor fails When the EGR gas flow rate is large and the fresh air amount is small as in the case where the fuel is injected, the fuel injection amount is prevented from being inadvertently suppressed, preventing combustion deterioration, inability to start, engine stall (engine stall), etc. Can do.

  Further, according to the fuel injection control device for a diesel engine according to claim 4, a predetermined time has elapsed since the limit fuel injection amount becomes equal to or greater than the normal fuel injection amount or the fuel injection based on the limit fuel injection amount is started. Sometimes the fuel injection based on the limited fuel injection amount is terminated and the fuel injection based on the normal fuel injection amount is performed, so that the fuel injection at the limited fuel injection amount is minimized and the output performance of the diesel engine is not impaired. Can be.

Embodiments of a fuel injection control device for a diesel engine according to the present invention will be described below with reference to the drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of a fuel injection control device for a diesel engine according to the present invention mounted on a vehicle, which will be described below with reference to FIG.
Here, an in-line four-cylinder diesel engine (hereinafter simply referred to as an engine) is employed as the engine 1.

  The fuel supply system of the engine 1 is composed of, for example, a common rail system. In this system, an injector 2 is provided for each cylinder, and these injectors 2 are connected to a common rail (not shown). Each injector 2 is connected to an electronic control unit (ECU) 40, and opens and closes based on a fuel injection command from the ECU 40. The fuel in the common rail can be injected into each combustion chamber at high pressure at a desired timing. It is. The common rail system is publicly known, and detailed description of the configuration of the common rail system is omitted here.

An intake pipe 8 is connected to an intake port of the engine 1 via an intake manifold 6, and an intercooler 9 is provided in the intake pipe 8. The intake pipe 8 is provided with an air flow sensor 7 for detecting the amount of intake air, that is, the amount of fresh air.
On the other hand, an exhaust pipe 12 is connected to the exhaust port via an exhaust manifold 10.
An EGR passage 14 extends from the exhaust manifold 10, and an end of the EGR passage 14 is connected to the intake manifold 6, and an electromagnetic EGR valve 16 is interposed in the EGR passage 14.

  A post-treatment device 20 is interposed in the exhaust pipe 12. The aftertreatment device 20 is an exhaust gas purification device comprising a catalytic converter or a diesel particulate filter (DPF) for purifying harmful components (HC, CO, NOx, etc.) and PM (particulate matter) contained in exhaust gas. In this example, a catalytic converter 26 is provided upstream of the DPF 24.

Further, an oxygen sensor 22 for detecting the excess air ratio λ in the exhaust gas by detecting the oxygen concentration in the exhaust gas is provided in the upstream portion of the exhaust pipe 12 from the catalytic converter 26.
The ECU 40 is a control device for performing comprehensive control of the fuel injection control device for the diesel engine according to the present invention including the engine 1.
On the input side of the ECU 40, in addition to the air flow sensor 7 and the oxygen sensor 22, an Ne sensor 42 that detects the engine rotational speed Ne, an operation amount of the accelerator pedal 46, that is, an accelerator position sensor (APS) that detects the accelerator opening θacc. Various sensors such as 44 are connected.

On the other hand, various devices such as the injector 2 and the EGR valve 16 are connected to the output side of the ECU 40. Based on various input information, the air-fuel ratio, fuel injection amount, intake air amount, ignition timing, etc. are set and commanded. Output as a value.
Referring to FIG. 2, there is shown a block diagram of the fuel injection control according to the present invention executed in the ECU 40. Hereinafter, the control procedure of the fuel injection control according to the present invention will be described based on the block diagram.

First, in block B10, the minimum value (Minimum value) among the basic injection amount, the maximum injection amount, the overboost injection amount, the overheat injection amount, and the overrun injection amount is selected as the normal injection amount (normal fuel injection amount) Qc.
Here, the basic injection amount is a reference value of the fuel injection amount read from a preset map based on the engine speed Ne and the accelerator opening θacc, the maximum injection amount is the clip value, and the over boost injection amount The overheat injection amount and the overrun injection amount are fuel injection amounts set for the purpose of fail-safe according to the boost pressure (supercharging pressure), the coolant temperature, and the engine rotational speed Ne, respectively.

Actually, after the normal injection amount Qc is set based on the basic injection amount, the basic injection amount is further limited by the maximum injection amount, the over boost injection amount, the overheat injection amount, and the overrun injection amount.
When the normal injection amount Qc is set in this way, the target value of the excess air ratio λ (λ = unit intake air weight / 14.3 · unit fuel weight) based on the normal injection amount Qc in block B12, that is, the target λ. (Target excess air ratio) is set (target excess air ratio setting means), and the EGR gas flow rate is set based on the target λ in block B14. Thereby, the EGR valve 16 is controlled to obtain the EGR gas flow rate (EGR control means).

  In block B20, an excess air ratio λ at which smoke starts to be generated, that is, a limit λ (limit excess air ratio) is set based on the normal injection amount Qc and the engine speed Ne (limit excess air ratio setting means). . In practice, the limit λ is set in advance as a limit λ map by experiments or the like according to the fuel injection amount and the engine rotational speed Ne, and is read from the limit λ map.

When the limit λ is obtained, in block B22, a λ limit injection amount (limit fuel injection amount) Qr is calculated based on the limit λ, the normal injection amount Qc and the estimated in-cylinder λ (limit fuel injection amount calculation means). .
Here, the estimated in-cylinder λ is an excess air ratio λ estimated to be realized in each cylinder with respect to the target λ, and the intake air amount, boost pressure, fuel injection amount, etc. detected by the airflow sensor 7 (In-cylinder excess air ratio estimating means).

Specifically, the λ limited injection amount Qr is calculated from the following equation (1).
λ limit injection amount Qr = normal injection amount Qc × estimated in-cylinder λ / limit λ (1)
That is, the λ limit injection amount Qr is obtained by multiplying the normal injection amount Qc by the limit ratio (estimated in-cylinder λ / limit λ).
When the λ limited injection amount Qr is calculated, the λ limited injection amount Qr is input to the value 1 side of SW2. On the other hand, the normal injection amount Qc is input to the value 0 side of SW2. That is, in SW2, the λ-limited injection amount Qr is output when it is positioned on the value 1 side, and the normal injection amount Qc is output when it is positioned on the value 0 side.

Specifically, switching between the value 0 side and the value 1 side of SW2 is performed by comparing the size of the estimated in-cylinder λ and the limit λ. Specifically, SW2 is switched to the value 1 side when the limit λ is greater than or equal to the estimated in-cylinder λ (limit λ ≧ estimated in-cylinder λ), and the limit λ is smaller than the estimated in-cylinder λ (limit λ <estimated In the case of in-cylinder λ), it is switched to the value 0 side.
That is, when the limit λ is greater than or equal to the estimated in-cylinder λ, the limiting ratio (estimated in-cylinder λ / limit λ) is 1.0 or less, and the λ-limited injection amount Qr is the normal injection amount Qc from the above equation (1). On the other hand, when the limit λ is smaller than the estimated in-cylinder λ, the limiting ratio (estimated in-cylinder λ / limit λ) exceeds 1.0, and from the above equation (1), the λ-limited injection amount Qr is Since it becomes larger than the normal injection amount Qc, the λ limited injection amount Qr is clipped with the normal injection amount Qc in the SW2. As a result, the λ-limited injection amount Qr is limited so as not to be larger than the normal injection amount Qc.

  In block B30, a smaller value (Minimum value) of either the normal injection amount Qc or the λ limited injection amount Qr is selected and output. That is, here, when the λ limited injection amount Qr limited by the limit λ is smaller than the normal injection amount Qc, the λ limited injection amount Qr is selected. Note that the λ-limited injection amount Qr is clipped to the normal injection amount Qc by the previous switching of SW2, so the λ-limited injection amount Qr does not become larger than the normal injection amount Qc, and the normal injection amount Qc is selected at the maximum. Is done. That is, the block B30 is executed for confirmation.

  The λ limited injection amount Qr selected in block B30 (which may be the normal injection amount Qc, but hereinafter referred to as λ limited injection amount Qr for convenience) is input to the value 1 side of SW1. On the other hand, the normal injection amount Qc is input to the value 0 side of SW1. That is, in SW1, the λ-limited injection amount Qr is output when it is positioned on the value 1 side, and the normal injection amount Qc is output when it is positioned on the value 0 side.

  Specifically, based on the accelerator opening information θacc from the APS 44, an accelerator opening change rate θacc ′, that is, a normal injection amount change rate Qc ′ that is a change degree of the normal injection amount Qc is detected (injection amount change degree detection means). Switching between the value 0 side and the value 1 side of SW1 is performed by determining whether or not the EGR gas flow rate is controllable and whether or not the normal injection amount change rate Qc ′ is equal to or greater than a predetermined value. .

Here, the state where the EGR gas flow rate can be controlled means that all of the following EGR control permission conditions 1) to 5) are satisfied for a predetermined time and the EGR valve 16 can be controlled. Whether or not the gas flow rate can be controlled is determined by determining whether or not all of the following EGR control permission conditions are satisfied for a predetermined time.
1) Coolant temperature ≧ predetermined value 2) Not in engine mode 3) Not in engine start mode 4) Boost pressure sensor (not shown) is normal 5) Drive of EGR valve 16 is normal Specifically, SW1 is an EGR gas flow rate When the normal injection amount change rate Qc ′ is equal to or greater than a predetermined value (Qc ′ ≧ predetermined value), it is switched to the value 1 side, but the EGR gas flow rate is not in a controllable state. Alternatively, when the normal injection amount change rate Qc ′ is smaller than the predetermined value (Qc ′ <predetermined value), the value is switched to the value 0 side.

In other words, from the SW1, when the EGR gas flow rate can be controlled and the engine 1 is in a predetermined acceleration state, the λ-limited injection amount Qr is output as the final injection amount Qf, and the EGR gas flow rate can be controlled. When the engine 1 is not in a proper situation or when the engine 1 is not in a predetermined acceleration state, the normal injection amount Qc is output as the final injection amount Qf (fuel injection means).
Thus, in the fuel injection control according to the present invention, when the EGR gas flow rate can be controlled and the engine 1 is in a predetermined acceleration state, the excess air ratio λ at which smoke starts to be generated, that is, the limit λ The fuel injection is performed with the λ-limited injection amount Qr obtained from the final injection amount Qf, while the EGR gas flow rate is set based on the target λ instead of the limit λ.

  Accordingly, for example, in the case of acceleration operation (for example, in a free accelerator state) in a low rotation and low load region, the fuel injection amount can be limited to the extent that no smoke is generated by the λ limited injection amount Qr, and the λ limited injection amount Qr is reduced. Correspondingly, it is possible to satisfactorily prevent the EGR gas flow rate from increasing and the amount of fresh air in the intake air from decreasing, and smoke discharge can be reliably suppressed with a simple configuration. In addition, when the fuel injection with the λ-limited injection amount Qr is returned to the fuel injection with the normal injection amount Qc, the EGR gas flow rate does not immediately decrease and the fresh air amount cannot follow the increase in the fuel injection amount. This can be prevented well, and smoke emission can be reliably suppressed.

  Further, here, fuel injection is performed at the λ-limited injection amount Qr on condition that the normal injection amount change rate Qc ′ is equal to or greater than a predetermined value and the EGR gas flow rate can be controlled. For example, when the diesel engine is in the engine stall mode or the start mode and the control of the EGR gas flow rate is unstable, or when the EGR gas flow rate is large and the fresh air amount is small, for example, when the boost sensor fails It is possible to prevent the fuel injection amount from being suppressed carelessly, and to prevent deterioration of combustion, inability to start, engine stall (engine stall), and the like.

Further, when the SW1 is the value 1 side, the switching to the value 0 side is, for example, that the λ-limited injection amount Qr becomes equal to or greater than the normal injection amount Qc due to an increase in the engine speed Ne, or the λ-limited This is performed after a predetermined time has elapsed after the start of fuel injection at the injection amount Qr.
As a result, the fuel injection is performed at the normal injection amount Qc thereafter, the fuel injection at the λ-restricted injection amount Qr is suppressed to the minimum necessary, and the exhaust of the engine 1 is reliably suppressed while suppressing the smoke discharge. The output performance can be prevented from being impaired.

This is the end of the description of the embodiment of the fuel injection control device for a diesel engine according to the present invention, but the embodiment is not limited to the above embodiment.
For example, in the above-described embodiment, the acceleration operation is mainly performed in the low rotation and low load region, but the present invention can also be applied to the idling operation during the idling operation.

It is a schematic block diagram of the fuel-injection control apparatus of the diesel engine which concerns on this invention mounted in the vehicle. It is a block diagram of fuel injection control concerning the present invention.

Explanation of symbols

1 diesel engine 2 injector 14 EGR passage 16 EGR valve 40 ECU (electronic control unit)
42 Ne sensor 44 APS

Claims (4)

A target air excess ratio setting means for setting a normal fuel injection amount based on the engine rotation speed and the accelerator operation amount, and setting a target excess air ratio based on the normal fuel injection amount and the engine rotation speed;
An EGR passage that recirculates a part of the exhaust gas as EGR gas to the intake system;
EGR control means for controlling the flow rate of EGR gas flowing through the EGR passage based on the target excess air ratio;
Limit excess air ratio setting means for setting a limit excess air ratio that does not generate smoke according to the normal fuel injection amount and the engine rotation speed;
Limiting fuel injection amount calculating means for obtaining a limiting fuel injection amount based on the limit excess air ratio;
An injection amount change degree detecting means for detecting a change degree of the normal fuel injection amount;
Fuel injection means for injecting fuel based on the limited fuel injection amount instead of the normal fuel injection amount when the change degree of the normal fuel injection amount becomes a predetermined value or more ;
The fuel injection for a diesel engine, wherein the EGR control means controls an EGR gas flow rate based on the target excess air ratio even when the limit excess air ratio is set by the limit excess air ratio setting means. Control device. In-cylinder excess air ratio estimating means for estimating the excess air ratio in the cylinder is further provided,
The limit fuel injection amount calculating means obtains a limit ratio of the excess air ratio by dividing the estimated excess air ratio in the cylinder by the limit excess air ratio, and calculates the product of the limit ratio and the normal fuel injection amount. 2. The fuel injection control device for a diesel engine according to claim 1, wherein a limit fuel injection amount is obtained.   The fuel injection means can control the EGR gas flow rate by the EGR control means, and when the degree of change of the normal fuel injection amount is equal to or greater than a predetermined value, the limited fuel is replaced with the normal fuel injection amount. The fuel injection control device for a diesel engine according to claim 1 or 2, wherein fuel injection is performed based on an injection amount.   The fuel injection means sets the limit fuel injection amount when the limit fuel injection amount becomes equal to or greater than the normal fuel injection amount or when a predetermined time has elapsed after starting fuel injection based on the limit fuel injection amount. The fuel injection control device for a diesel engine according to any one of claims 1 to 3, wherein the fuel injection based on the normal fuel injection amount is performed after finishing the fuel injection based on the fuel injection.

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