JP3163696B2 - Exhaust gas recirculation control device for diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation control device for a diesel engine used in a vehicle such as an automobile, and more particularly to an exhaust gas recirculation control device capable of avoiding generation of smoke during a transition.

[0002]

2. Description of the Related Art In a diesel engine, in order to reduce the NOx concentration in exhaust gas, exhaust gas recirculation (hereinafter referred to as EGR) for replacing a part of surplus air in the intake air into a combustion chamber with the exhaust gas. It is running. This EG
The recirculation amount of the exhaust gas at R is controlled according to the engine load and the number of revolutions.

However, during rapid acceleration of the engine, particularly during rapid acceleration operation from a low load to a high load, smoke increases more easily than in a steady state because the fuel injection amount increases rapidly and EGR gas remains. Therefore, the fact that exhaust gas recirculation is performed at the same flow rate as during steady operation even during rapid acceleration operation is as follows.
It is not preferable for smoke prevention.

For this reason, conventionally, the EGR execution region is limited to a low load region where smoke is not a serious problem, or the EGR is instantaneously stopped when the load change is large (for example, see 63-198766), and a technique of reducing the fuel injection amount in conjunction with the stop of EGR during acceleration transition (Japanese Patent Application Laid-Open No. 63-143343) is known.

[0005]

However, in the technique in which the execution of EGR is limited to a low load region, the smoke reduction at the time of acceleration can be realized, but the reduction of the NOx concentration in the exhaust gas in the entire operation region of the diesel engine is reduced. Was not performed sufficiently. Further, in the technique of Japanese Patent Application Laid-Open No. 63-198766, since EGR is not performed during acceleration irrespective of the level of the load, there is a problem that the suppression of NOx during acceleration cannot be realized. On the other hand, in the technique of Japanese Patent Application Laid-Open No. 63-143343, it is possible to suppress an increase in NOx while suppressing an increase in smoke during acceleration, but on the other hand, there is a new problem that acceleration performance is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and it is an object of the present invention to reduce the generation of smoke without impairing the operation performance during transient operation and to suppress the increase in NOx in a wide load range. It is an object of the present invention to provide an exhaust gas recirculation control device for a diesel engine that can be used.

[0007]

The exhaust gas recirculation control device for a diesel engine according to the present invention, which has been made to achieve the above object, comprises: an exhaust gas recirculation means for recirculating exhaust gas to an engine combustion chamber; Recirculation command value instructing means for instructing an exhaust gas recirculation command value according to a load state; and recirculation control means for controlling an operation state of the exhaust gas recirculation means in accordance with the designated exhaust gas recirculation command value. In the exhaust gas recirculation control device for a diesel engine, a transient quantity calculating means for calculating a transient quantity of the engine speed, a change speed term is calculated based on the calculated transient quantity, and the recirculation command value indicating means is provided. Based on the exhaust gas recirculation command value
A response time term that becomes larger as the exhaust gas recirculation command value becomes larger is calculated, and the exhaust gas recirculation command value of the recirculation control unit is corrected from the change speed term and the response time term. Correction means.

As a result of adopting this configuration, according to the exhaust gas recirculation control device for a diesel engine of the present invention, during steady running, an amount of exhaust gas is recirculated in accordance with the load condition of the engine, but the engine speed is changed. In the state, the exhaust gas is recirculated in an amount taking into account the transient state by the correction. This correction also takes into account the control state (for example, valve lift amount) of the recirculation means that is controlled in accordance with the engine load, so that even if acceleration or deceleration is performed in any load range, the correction is quickly performed. A later state can be realized.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a diesel engine equipped with EGR and its peripheral devices. In the figure,
Reference numeral 1 denotes a diesel engine body, in which a piston 5 is slidably fitted in a cylinder block 3, and a combustion chamber 7 surrounded by the cylinder block 3 and the piston 5 is provided. An intake passage 11 and an exhaust passage 13 mounted on the cylinder head 9 communicate with the combustion chamber 7. A recirculation passage 15 for recirculating exhaust gas is connected between the exhaust passage 13 and the intake passage 11. The exhaust passage 13 is connected to a port 17, while the intake passage 11 is connected to a port 19. Each is connected. An EGR control valve 21 is provided in the middle of the recirculation passage 15.

The EGR control valve 21 includes a housing 25
The inside is divided into an atmosphere chamber 29 and a negative pressure chamber 31 by a diaphragm 27, and a valve element 33 is attached to a surface of the diaphragm 27 on the atmosphere chamber 29 side via a rod 31, and a valve seat 35 is formed by the valve element 33. It opens and closes, and opens and closes the return passage 15. On the other hand, a spring force is applied to the surface of the diaphragm 27 on the side of the negative pressure chamber 31 by a compression spring 35, and the diaphragm 27 moves against the spring force due to a pressure difference between the atmosphere chamber 29 and the negative pressure chamber 31. Thus, the opening of the valve is adjusted.
The negative pressure chamber 31 of the EGR control valve 21 is connected to a negative pressure adjusting valve 37 via a pipe 36, and the negative pressure adjusting valve 37
, The negative pressure supplied from the negative pressure supply device 39 is adjusted.

Further, a passage 40 in the EGR control valve 21 is provided.
Is connected to the conduit 41 of the return passage 15. Further, the diesel engine includes various sensors and switches, that is, as sensors, a water temperature sensor 51 for detecting the temperature of the cooling water, and an accelerator opening sensor 53 for outputting a signal corresponding to the amount of depression of an accelerator pedal. ,
Speed sensor 5 for detecting the speed of the diesel engine
And an idle switch 57 that operates in conjunction with the accelerator pedal and detects an idle state as a switch.
and so on.

The detection signals from the various sensors and switches are input to an electronic control unit 61, and the electronic control unit 6
The drive of the actuator such as the negative pressure regulating valve 37 is controlled by 1. The electronic control unit 61 is composed of a well-known microcomputer, that is, an input / output interface 63 that processes input signals of various sensors into digital signals that can be processed by a computer and converts the input signals into drive signals to an actuator. CPU
65, a RAM 67 as temporary storage means, a ROM 69 in which various control programs are stored in advance, and the like.

The operation of the exhaust gas recirculation control device is as follows.
The arithmetic processing is performed according to the control program stored in the ROM 69, that is, the water temperature Tw, the accelerator opening Ac
The exhaust gas recirculation amount is calculated based on cp and the rotation speed NE,
A signal according to this result is sent to the negative pressure regulating valve 37,
The pressure in the negative pressure chamber 31 of the GR control valve 21 is controlled. As a result, the diaphragm 27 moves and the valve opening is adjusted, so that the recirculation amount of the exhaust gas is changed.

Next, control executed according to a program stored in the ROM 69 of the electronic control unit 61 will be described in detail with reference to the flowchart of FIG. FIG.
First, the engine speed NE (hereinafter abbreviated as NE), accelerator opening Accp, fuel injection amount command value QFI
N (hereinafter abbreviated as QFIN) and other various data indicating the engine state are read (S10), and a two-dimensional map (FIG. 3) of the ROM 69 is searched and interpolated based on NE and QFIN, thereby obtaining an EGR command value. (Hereinafter DF
IN is abbreviated) (S20).

Subsequently, it is determined whether or not a transition state such as acceleration or deceleration is present (S30). In particular,
Based on the difference between the previous and current rotational speeds, if the difference is equal to or greater than a predetermined value (for example, 20 rpm), it is determined that the vehicle is in the transient state. If it is determined that the state is not the transient state, the process proceeds to S90 and thereafter to perform the normal EGR control.

On the other hand, if the transition state is determined, the NE change speed "DNE" is calculated from the previous and current NEs (S40). Then, based on the NE change speed DNE, the map shown in FIG. 4 is referred to to calculate a change speed term TDD (S50). Further, based on the current DFIN, the map shown in FIG. Is calculated (S
60). Subsequently, the EGR command correction amount TD is calculated by multiplying the calculated change speed term TDD by the response time term KTD.
Is calculated (S70), and the EGR command correction amount TD is calculated as EG
It is added to the R command value DFIN (S80). Then, the corrected EGR command value DFIN is stored in the output compare (S90), and the EGR valve is driven based on this (S100).

It is to be noted that, instead of using only the change speed term TDD corresponding to the NE change speed DNE, this change speed term TDD is multiplied by the response time term KTD to obtain the correction amount TD by the current EGR valve lift. This is for compensating, for example, that the response delay time until the valve is fully closed differs depending on the amount.

As a result of the above configuration, according to the apparatus of the embodiment, as shown in FIG. 6, when the acceleration transient state is determined at time T1, the EGR command value DFIN is reduced by the correction amount TD. Accordingly, the EGR valve lift amount decreases, and the EGR amount decreases. Therefore, the acceleration is completed and EG
At the time T2 outside the R region, the EGR amount is also reduced to substantially zero, and the actual EGR amount can be made to coincide with the target EGR amount. Note that the dotted line in the figure indicates a case where the above-described processing is not performed during the acceleration transition. If the above processing is not performed, the actual EGR amount is still considerable at the time T2, which causes an increase in smoke.

As described above, according to the present embodiment, the target EGR amount and the actual EGR amount can be matched even during the acceleration transition, so that the EGR can be executed even during acceleration. Further, even if EGR is performed during acceleration, smoke does not increase, so that it is not necessary to suppress the fuel injection amount and the acceleration performance is not impaired.

As a result, as shown in FIG. 7, the EGR region can be set to a wide range including the region where the fuel injection amount is considerably large, and is wider than the conventional EGR possible region indicated by the dotted line. The EGR can be performed over a wide range, and the emission of NOx and the like can be improved over a wide load range. Moreover, this emission improvement is performed to the maximum during acceleration, and the generation of smoke can be suppressed without lowering the acceleration performance during the acceleration. In addition, since a correction value is used in consideration of the response time term KTD reflecting the valve lift, any situation can be dealt with promptly.

In addition, during deceleration, the EGR amount can be increased quickly and accurately, and NOx reduction can be sufficiently performed. Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modes can be adopted without departing from the gist of the present invention.

For example, the determination as to whether or not the vehicle is in the transition to the acceleration may be made based on the change state of the accelerator opening. It may be configured to execute. Further, the configuration may be such that the change speed term TDD is calculated using a parameter that indicates an acceleration / deceleration state other than the NE change speed DNE.

[0023]

As described above, according to the exhaust gas recirculation control device for a diesel engine of the present invention, EGR can be executed over a wide load range as long as there is a surplus in the intake air amount. Moreover, in such a case, even if a state such as a sudden acceleration or a deceleration occurs, it is possible to prevent a problem such as an increase in the amount of generated smoke accompanying the state. As a result, a remarkable effect that it is possible to prevent the deterioration of the driving performance while suppressing both the deterioration of the emission of NOx and the like at the time of acceleration or deceleration and the generation of smoke, and to execute the EGR in a wide load region. Play.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an apparatus of an embodiment.

FIG. 2 is a flowchart of an EGR control process executed by the embodiment.

FIG. 3 is a map for calculating an EGR command value DFIN used in the embodiment.

FIG. 4 is a map for calculating a change speed term TDD used in the embodiment.

FIG. 5 is a map for calculating a response time term KTD used in the embodiment.

FIG. 6 is a graph showing the responsiveness of an EGR valve according to the embodiment.

FIG. 7 is an explanatory diagram showing an enlargement of an EGR region in the embodiment.

[Explanation of symbols]

1 ... diesel engine body, 7 ... combustion chamber, 1
DESCRIPTION OF SYMBOLS 1 ... Intake passage, 13 ... Exhaust passage, 15 ... Recirculation passage, 21 ... EGR control valve, 37 ... Negative pressure regulating valve, 39 ... Negative pressure supply device, 51 ...・ Water temperature sensor,
53: accelerator opening degree sensor, 55: rotation speed sensor, 57: idle switch, 61: electronic control unit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-2459 (JP, A) JP-A-3-134256 (JP, A) JP-A-2-119666 (JP, A) JP-A-59-24 221467 (JP, A) JP-A-2-271061 (JP, A) JP-A 61-21858 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02M 25/07 550 F02M 25/07 570

Claims (1)

(57) [Claims] 1. An exhaust gas recirculation means for recirculating exhaust gas to an engine combustion chamber, a recirculation command value instructing means for instructing an exhaust gas recirculation command value according to a load state of an engine, and the indicated exhaust gas recirculation command. In a diesel engine exhaust gas recirculation control device provided with a recirculation control means for controlling an operation state of the exhaust gas recirculation means in accordance with a value, a transient state quantity calculating means for calculating a transient state quantity of an engine speed; The change speed term is calculated based on the obtained transient state quantity, and the larger the exhaust gas recirculation command value is based on the exhaust gas recirculation command value of the recirculation command value indicating means, the larger the change speed term is.
And a correction means for calculating an exhaust gas recirculation command value of the recirculation control means from the change speed term and the response time term. Exhaust gas recirculation control device.