JPH07247914A - Exhaust reflux quantity control device of diesel engine - Google Patents

Abstract

PURPOSE:To make an EGR efficiently practicable in a steady driving state of an engine. CONSTITUTION:An electronic control unit 20 which is an exhaust reflux quantity control device of a diesel engine 1 having an EGR system 5 and fitted with a catalyst on an exhaust system 3 is constituted to be furnished with a catalyst activation detection means to detect an activating state of the catalyst, an engine steady driving state detection means to detect a steady driving state of the engine and an exhaust reflux quantity control means to make an EGR work at the time when the engine drives steadily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine exhaust gas recirculation amount control device, and more particularly to a diesel engine exhaust gas recirculation amount control device capable of effectively reducing NO _x while suppressing the generation of smoke.

[0002]

Exhaust gas recirculation (EGR) in diesel engines to reduce NO _x in the exhaust gas
Is being implemented. Then, in order to further reduce NO _{x due} to the recent demand for clean engines, it is necessary to carry out EGR (mass EGR) with a large amount of exhaust gas recirculation amount, and in addition, there is a need for automatic diesel engine-equipped vehicles. Due to the shift type (AT shift), the engine work load increases by 5 to 10% as compared with the manual type (MT) vehicle, so that it is necessary to increase the EGR amount.

However, even if the large amount of EGR is simply performed, NO _x can be reduced, but during acceleration operation of the engine, the EGR valve cutoff delay is compared with the quick response of fuel injection. However, there is a problem that the air-fuel mixture becomes temporarily rich due to the delay of air and smoke is generated. Therefore, in order to minimize the generated smoke, it is necessary to limit the EGR amount to the maximum allowable amount according to the transient operating state of the engine to improve the combustion state.

In order to reduce NO _x , it is also effective to retard the injection timing, which is also implemented, but the smoke is not increased as shown by the solid line in FIG. 6, for example. Even if NO _x is reduced in the range, H
The emission amount of C will increase. In order to avoid such an increase in HC emissions, an oxidation catalyst is attached to the exhaust system,
As shown by the dotted line in FIG. 6, reducing the HC emissions is implemented.

Therefore, this injection timing control and the above-mentioned EGR are performed.
The quantity control is carried out using a fixed map that regulates the fixed relationship without catalyst, and soluble organic matter (SOF) at light load due to low exhaust temperature.
The problem of temporary poisoning due to is likely to occur. For example, when driving in an urban area, SOF is adsorbed on the surface of the catalyst and covers the catalyst, which causes a problem that the function of the catalyst is temporarily impaired. Further, when the control is executed by using the map fixed so as to retard the injection timing so as to effectively utilize the oxidation catalyst and to increase the EGR, S
Although this is advantageous for the temporary poisoning of OF, it tends to cause a problem that odor and white smoke are generated when the catalyst is not warm.

In this respect, it is proposed that the EGR is executed only during warm-up when the catalyst has not reached the activation temperature to prevent deterioration of combustibility and to improve exhaust gas purification performance. (JP-A-57-146)
041 publication).

[0007]

However, in the above proposal, since the propriety of the EGR execution is judged only by the catalyst activation temperature, the running temperature is lower than the catalyst activation temperature and the transient operation is performed. EGR even inside
However, there is a problem that smoke is generated.

Therefore, according to the present invention, not only during warm-up, but also during steady engine operation, EGR is executed to reduce NO _x and suppress smoke.
Moreover, it is an object of the present invention to provide an exhaust gas recirculation amount control device for a diesel engine that can avoid poisoning of the catalyst. Specifically, it is an object of the present invention to provide an exhaust gas recirculation amount control device for a diesel engine, which is capable of executing EGR when the catalyst is inactive and in a steady operation.

[0009]

According to the present invention, EGR
In addition, the exhaust gas recirculation control device for a diesel engine having a catalyst installed in the exhaust system has a catalyst activation detecting means for detecting an activation state of the catalyst, and a steady operation state of the engine. The engine steady-state operation state detection means and the exhaust gas recirculation amount control means that executes EGR when the catalyst is inactive and the engine is in the steady-state operation are configured.

It is also possible to retard the fuel injection timing together with EGR. Specifically, the vehicle detects the vehicle speed and the fuel injection amount indicating a steady operation state, and determines whether the detected engine operating state remains within a specific area on the vehicle speed / fuel injection amount map for a predetermined time. By monitoring, the activation state of the catalyst can be detected. Further, in executing the EGR, increase control is executed to the basic EGR amount according to the time of staying in the specific area. Further, similarly, the retard control for the fuel injection timing can be executed.

[0011]

For example, when the exhaust temperature is low even in the steady operation state such as continuous low speed running or light load operation, EGR is executed to reduce NO _x and reduce EGR. By executing the above, it is possible to activate the catalyst, suppress the discharge of HC and the like, and avoid the poisoning by SOF. Moreover, it is possible to suppress the occurrence of smoke by not executing EGR during transient operation.

By keeping the catalyst active, it is possible to retard the fuel injection timing and further reduce NO _x . Further, by executing the EGR operation control during steady operation using the vehicle speed / fuel injection amount map, it becomes possible to effectively incorporate it into the electronic control system of the engine.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual configuration diagram showing main components of a diesel engine to which an exhaust gas recirculation amount control system for a diesel engine according to the present invention is applied. In the figure, 1 is a diesel engine body, 2 is an intake system, 3 is an exhaust system, 4
Is a turbocharger, 5 is an EGR system, 6 is a fuel injection valve,
Reference numeral 7 is an intake throttle valve, 8 is an accelerator pedal, 10 is a fuel feeder, 11 is an intake temperature sensor, 12 is a water temperature sensor, 13 is a crank position sensor, and 20 is an electronic control unit. The electronic control unit 20 receives the intake air temperature, the water temperature, and the crank position from the illustrated sensors 11, 12 and 13, respectively, the intake throttle valve 7 through the accelerator opening degree, and the sensors (not shown) through the engine speed. , Vehicle speed, fuel temperature, brake on / off, shift signal, etc. are input, and after performing necessary calculations, fuel injection timing control output to the fuel feeder 10 and EGR system 5
EGR control output is sent to. Although not shown, an oxidation catalyst is attached to the tip of the exhaust system 3.

First, the electronic control unit 20 activates a large amount of EGR, that is, idle EGR in order to reduce NO _x at the time of idling, and idle EG at the time of starting.
Control to reduce R. For example, in the case of an AT car,
When the engine speed NE is the idle speed and the accelerator opening is 0%, the idle EGR is operated. After that, either the brake off signal or the vehicle speed signal in addition to the brake off signal changes from 0 to 1,
Moreover, when the shift signal is in the neutral (N) or parking (P) range, the accelerator is now stepped on,
That is, it is predicted that the vehicle will start, and the idle EGR is reduced. Further, when the vehicle speed is zero and the accelerator opening is zero again, the reduction of the idle EGR is reset to reduce the NO _x at the time of idling and to effectively suppress the starting smoke.

Next, while the vehicle is running, control is executed based on the map of fuel injection timing / EGR amount adapted to the state where no catalyst is attached. For example, the vehicle speed is 60 to 100 km / h.
(Low exhaust temperature of 150-350 ° C) and 0-load
40% (light load) in a certain time (for example, 5 seconds)
If it continues, it is judged that the catalyst is warm,
The fuel injection timing is retarded and the EGR amount is increased stepwise so that the catalyst temperature approaches 400 ° C., for example. This enables effective use of the catalyst, and S
Temporary poisoning due to OF can be prevented.

From the viewpoint of effective utilization of the catalyst,
If the catalyst is warm, the fuel injection timing delay and EG
Even if you increase the R amount, there is no problem of odor or white smoke,
Further, NO _x can be reduced without increasing the particulates. From the viewpoint of temporary poisoning by SOF, generally, when the catalyst temperature exceeds 400 ° C, the sulfate increases and the catalyst is warm (for example, the vehicle speed is 60 km / h or more and the accelerator opening is 0% or more. ),
Then, a region where the temperature does not rise excessively (for example, a vehicle speed of 10
0 km / h or less and accelerator opening 40% or less)
When it continues for a fixed time (for example, 5 seconds), the catalyst temperature can be brought close to 400 ° C. by retarding the fuel injection timing and increasing the EGR amount, and temporary poisoning due to SOF can be prevented.

If the above conditions are not satisfied, the retard angle of the fuel injection timing and the EGR amount increase are reset to zero. Needless to say, the above-mentioned conditions need to be changed according to the components of the catalyst, the amount of sulfur components in the fuel, and the like. The control described above will be described by way of example. FIG. 2 is a characteristic diagram illustrating the purification characteristics of the oxidation catalyst. For the two catalysts A and B, the reduction rates of CO, HC and SOF with respect to the catalyst inlet gas temperature, and further, sulfide (sulfate) and particulates. (PM)
Shows the change in the amount of emissions. Further, FIG. 3 is a characteristic diagram showing an example of an engine temperature vs. engine temperature exhaust gas temperature, that is, a catalyst incoming gas temperature map, in which the vehicle speed as an actual traveling load is plotted.

From the viewpoint of the purification characteristics of the catalyst A, for example, the temperature of gas entering the catalyst is 270 ° C. at which the purification rate of SOF becomes 80%.
Is preferable, and higher temperature is desirable for burning the accumulated SOF. However, when the temperature is raised, 350
Sulfate is generated from around ℃, and the particulates increase. That is, there is a limit to the temperature rise,
Even if the temperature is increased by retarding the fuel injection timing and increasing the EGR amount, for example, 380 ° C. becomes the upper limit. Therefore, in the case of this catalyst A, it is preferable to keep it in the temperature range of 270 ° C to 380 ° C.

In the catalyst incoming gas temperature map, the EGR is operated up to an engine speed of 2800 rpm, but it is cut off at higher speeds. Therefore, 1
00-120 km / h (engine speed NE: 2600
.About.3200 rpm), the difference between the catalyst inlet gas temperatures is small. In the case of catalyst A, it is necessary to control the temperature so that it does not exceed 380 ° C.
Moreover, the accelerator opening is about 40%. As to the lower limit, as is clear from the purification characteristics of the catalyst A in FIG. 2, since HC, which is the main cause of odor, is purified only at 200 ° C. or higher, the vehicle speed corresponding to this is 60 km / h or higher, and
The accelerator opening becomes 0% or more.

The above-described exhaust gas recirculation amount control is executed in the electronic control unit 20, and FIG. 4 is a flowchart showing an example of software for realizing the control. This routine is periodically executed as, for example, an independent EGR and fuel injection timing control routine, or is periodically interrupted by the control main loop executed in the electronic control unit 20. First, after performing necessary initial settings, in step 101, the accelerator opening, engine speed NE, and vehicle speed are read, and in step 102, the fuel injection amount NQ is set to the engine speed N.
It is calculated based on E and the accelerator opening. continue,
In step 103, the basic EGR amount and the basic injection timing are calculated based on the engine speed NE and the injection amount NQ, for example, using a map that defines a normal control mode when a catalyst is not used.

Next, at step 104, depending on the detected vehicle speed and the calculated injection amount NQ, for example, within the area AREA where the above-mentioned control conditions are plotted on the vehicle speed / NQ map shown in FIG. Determine whether to do. If Yes, the time T within AREA is counted (T = T + ΔT), the time T is guarded by the guard time D in steps 106 and 107, and then the EGR amount increase and the injection timing retarding control are executed in step 108. It is determined whether or not the start time C has been reached (T ≧ C?). If Yes, in step 109, EG is set so as to be proportional to the elapsed time (TC) from the start time C with the respective slopes A (increase coefficient) and B (retard coefficient).
The R increase amount (ΔEGR) and the injection timing retard amount (Δ injection timing) are calculated. That is, ΔEGR = A (TC) Δinjection timing = B (TC) is calculated.

If it is not within AREA in step 104 (No), in step 110 the initial setting of EGR amount increase and injection timing retard control (ΔEGR = 0, Δ
Injection timing = 0, T = 0), and step 108
If the start time C is not reached in AREA, the control amount is initially set (ΔEGR = 0, Δinjection timing = 0) in step 111.

Then, using the calculated or initialized ΔEGR and Δinjection timing, step 11
At 2, the final EGR amount and the final injection timing are determined. That is, final EGR = basic EGR + ΔEGR final injection timing = basic injection timing−Δinjection timing is calculated. After that, based on the obtained final EGR and final injection timing, an EGR control and injection timing control execution step 113 that is provided independently, or the EGR in the control main loop executed in the electronic control unit 20 is executed. In the execution step of the control and the injection timing control, the control to which the necessary amount of increase and retard are added is executed.

In the above-described embodiment of the present invention, when the operating state of the engine stays within the specific area AREA obtained from the fuel injection amount NQ and the vehicle speed for a certain time or more,
Although the EGR amount increase and the injection timing retarding control are executed, the exhaust gas recirculation amount control device for a diesel engine according to the present invention is such that the engine is in a steady operation state, and
To realize the desired control by providing a steady operation state detecting means and a catalyst activation detecting means for separately detecting that the catalyst is in the inactive state or that the catalyst temperature is in a specific range. It goes without saying that you can do it.

Further, in the above embodiment, EGR
Although the retard control of the fuel injection timing is executed at the same time as the increase control, the target exhaust gas purification and SOF poisoning avoidance can be realized by executing at least the EGR increase control.

[0026]

As described above, according to the exhaust gas recirculation amount control system for a diesel engine of the present invention, the E ratio can be obtained not only when the engine is warmed up but also when the engine is in a steady operation.
GR can be executed, NO _x can be effectively reduced, smoke generation during transition can be suppressed, and poisoning by SOF of the catalyst can be avoided.

[Brief description of drawings]

FIG. 1 is a conceptual configuration diagram showing main components of a diesel engine to which an exhaust gas recirculation amount control device for a diesel engine according to the present invention is applied.

FIG. 2 is a characteristic diagram illustrating a purification characteristic of an oxidation catalyst.

FIG. 3 is a characteristic diagram showing an example of an exhaust temperature map on engine characteristics of engine speed vs. torque.

FIG. 4 is a flowchart showing an example of software for realizing exhaust gas recirculation amount control of a diesel engine according to the present invention.

FIG. 5 is a characteristic diagram showing a vehicle speed / injection amount map in which control conditions of exhaust gas recirculation amount control of a diesel engine according to the present invention are plotted.

FIG. 6 is a characteristic diagram showing the relationship between the ignition timing and the emission amounts of various exhaust gas components.

[Explanation of symbols]

 1 ... Diesel engine main body 2 ... Intake system 3 ... Exhaust system 4 ... Turbocharger 5 ... EGR system 6 ... Fuel injection valve 7 ... Intake throttle valve 8 ... Accelerator pedal 10 ... Fuel feeder 11 ... Intake temperature sensor 12 ... Water temperature sensor 13 ... Crank position sensor 20 ... Electronic control unit

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Claims (1)

[Claims] 1. An exhaust gas recirculation amount control device for a diesel engine having an EGR and having a catalyst mounted in an exhaust system, the catalyst activation detecting means for detecting an activation state of the catalyst, Engine steady-state operating state detecting means for detecting the steady-state operating state of the engine, based on the detection results of the catalyst activation detecting means and the engine steady-state operating state detecting means, the catalyst in an inactive state, and An apparatus provided with exhaust gas recirculation amount control means for executing the EGR during steady operation of the engine.