JPH09126060A - Exhaust gas recirculation control method and device thereof - Google Patents

Abstract

(57) [Abstract] [Problem] It is difficult to control NOx reduction with high accuracy by control based on the EGR rate and the like, and smoke has been exacerbated depending on operating conditions and the like. Exhaust gas recirculation control is performed by adjusting the opening of an EGR valve according to the operating condition of an engine. EGR
The oxygen concentration R _O2 in the total intake air including gas and the ratio between the oxygen amount Q _O2 in the total intake air and the fuel injection amount Q _F are calculated, and the oxygen fuel ratio (Q _O2 / Q _F ) and the allowable smoke limit When the oxygen fuel ratio (Q _O2 / Q _F ) is small, the EGR valve is controlled so as to be equal to the smoke allowable limit value K, and when it is large, the oxygen concentration R _O2 is the target oxygen concentration D _O2. The EGR valve is controlled so as to be equal to. This will ensure the amount of oxygen needed to maintain the target smoke level, keeping smoke emissions within acceptable levels while maximizing NOx.
Can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EGR for appropriately recirculating exhaust gas of an engine to an intake system, that is, an exhaust gas recirculation control method and a device therefor.

[0002]

2. Description of the Related Art Recently, exhaust gas recirculation (EGR) has been widely used to reduce NOx by returning a part of exhaust gas to an intake system. The amount of recirculation (EGR
It is necessary to control with high accuracy so as to be compatible with the stability of combustion. Especially when applied to a diesel engine, if EGR is excessive, smoke will be generated greatly. Highly accurate EGR control is required.

[0003]

By the way, the conventional EGR
The control is performed based on the EGR rate (= EGR gas amount / fresh air intake amount + EGR gas amount), as disclosed in, for example, Japanese Patent Laid-Open No. 5-18324. The control accuracy was not sufficient. That is, as shown in FIG. 12, the relationship between the EGR rate and the NOx reduction rate (the emission rate when the NOx emission amount without EGR is 100) greatly differs depending on the operating conditions, and at high load. The NOx reduction rate drastically changes with a slight change in the EGR rate. This is low
This is because the exhaust gas contains a large amount of oxygen at the time of medium load because it burns with rich air, and it decreases when the load becomes high. Therefore, it is difficult to control the NOx reduction to the target value with high accuracy, and further, depending on the operating condition, for example, if there is a boost delay in the transition period of the supercharging engine, the oxygen shortage easily causes the deterioration of smoke. was there.

[0004]

In order to solve the above problems, the present invention performs EGR control to maintain low smoke in accordance with changes in the absolute oxygen amount in the total intake air containing EGR gas. The EGR control is performed to reduce NOx according to the change of the oxygen concentration in the inside. In devising this exhaust gas recirculation control method, the present inventors experimentally determined that the NOx level represented by the NOx reduction rate is uniquely determined depending on the intake oxygen concentration regardless of the operating condition (Fig. 11). It has been found that the smoke level represented by the exhaust smoke concentration depends on the excess air ratio λa in consideration of the amount of oxygen in the EGR gas (see FIG. 9). Further, it has been found that the oxygen concentration in the exhaust gas changes depending on the EGR rate (see FIG. 10), and the oxygen concentration in the exhaust gas greatly changes depending on the engine load and the engine speed operating conditions (see FIG. 8). There is. Furthermore, it has been found that the smoke level has a strong correlation with the ratio between the oxygen amount and the fuel injection amount, and that the smoke becomes worse even with the same oxygen concentration when the intake air amount decreases (see FIG. 7). Based on these research results, the present invention uses EGR as a control parameter in place of the conventional EGR rate or excess air ratio.
It proposes the oxygen concentration and the absolute oxygen amount in the total intake air including gas. According to this control method, the smoke emission amount does not exceed the allowable limit value, and the NOx can be maximally reduced.

Further, according to the present invention, when the exhaust gas recirculation control is performed by adjusting the opening degree of the EGR valve according to the operating condition of the engine, the oxygen concentration in the total intake air including the EGR gas and the total intake air The ratio between the oxygen amount and the fuel injection amount is calculated, the oxygen fuel ratio is compared with the smoke allowable limit value, and when the oxygen fuel ratio is small, the EGR valve is controlled so as to be equal to the smoke allowable limit value, When it is large, the EGR valve is controlled so that the oxygen concentration becomes equal to the target oxygen concentration. By controlling in this way, it is possible to secure the amount of oxygen required to maintain the target smoke level, while suppressing the smoke emission amount within the allowable value at all times.
The maximum reduction of NOx can be achieved.

Further, the present invention is an apparatus for carrying out the above control method, which is more preferable than a connection position between an EGR valve provided in an exhaust gas recirculation path for recirculating exhaust gas and an exhaust gas recirculation path of an intake passage. The control unit is provided on the downstream side to detect the amount of air and the oxygen concentration, and the control unit that operates the EGR valve according to the detection value of the detection unit and the engine operating condition. A storage unit that stores the limit value and the set value of the target oxygen concentration, the oxygen concentration in the total intake air containing the EGR gas, and the ratio between the oxygen amount in the total intake air and the fuel injection amount are calculated based on the detected value. A comparison calculation unit that calculates and compares the calculated value with a set value to determine the optimum opening of the EGR valve, and an output unit that outputs a control signal so that the EGR valve has the optimum opening. Those digits. With this configuration, the detection means detects the total intake air amount including the EGR gas and the oxygen concentration. The controller obtains the oxygen concentration in the total intake air and the ratio between the amount of oxygen in the total intake air and the fuel injection amount from these detected values and operating conditions. Then, the oxygen fuel ratio is compared with the smoke allowable limit value, and the EGR valve is controlled to an optimum opening degree depending on the size. As a result, highly accurate EGR control that achieves the maximum reduction of NOx is achieved while always suppressing the smoke emission amount within the allowable value.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, an exhaust gas recirculation control device to which the present invention is applied will be described with reference to FIG. This exhaust gas recirculation control device is provided with an EGR provided in an exhaust gas recirculation passage 1 for recirculating exhaust gas.
The valve 2, the detection means 4 provided in the intake passage 3 for detecting the air amount and the oxygen concentration thereof, and the control unit 5 for operating the EGR valve 2 according to the detection value of the detection means 4 and the engine operating condition. It is mainly composed.

The exhaust gas recirculation passage is composed of an exhaust passage 6 and an intake passage 3.
Are connected to short-circuit them. Exhaust passage 6
Extends from the exhaust manifold 8 of the engine 7 via the muffler 9 so as to exhaust the exhaust gas. The intake passage 3 is configured to guide the outside air to the intake manifold 11 of the engine 7 via the air cleaner 10. The EGR valve 2 is a control unit 5
It is operated by an actuator 13 connected to the output section 12 of the above, and a part of the exhaust gas flowing through the exhaust passage 6 is merged with the intake passage 3 according to the opening degree thereof and is recirculated to the engine 7. .

The detecting means 4 is provided in the intake passage 3 on the downstream side of the connection position (merging position) 22 with the exhaust gas recirculation passage 2, and detects the EGR gas that has merged with the fresh air by detecting the pressure or the like. An air flow sensor 14 for measuring the flow rate V _A of the total intake air, an oxygen concentration sensor 15 for measuring the oxygen concentration R _O2 in the total intake air using the electromotive force of the solid electrolyte, and the specific gravity of oxygen are corrected. Intake air temperature Ti for
And a suction temperature sensor 16 for measuring
These sensors 14, 15 and 16 are connected to the input section 17 of the control unit 5, respectively. When a sensor that measures the mass flow rate of air is used as the air flow sensor 14, the suction temperature sensor 16 may be omitted. In addition, as a sensor for detecting the operating condition, a rotation sensor 18 for measuring the rotation speed Ne of the engine 7 and an accelerator opening sensor 19 for measuring the accelerator opening _VL are provided. It is connected to the input unit 17.

The control unit 5 stores, in addition to the input section 17 and the output section 12, a smoke allowable limit value (smoke limit) determined by the exhaust gas regulation value and commercial characteristics, and a set value of the target oxygen concentration D _O2. A unit 20 and a comparison calculation unit (CPU) 21 that performs a predetermined calculation and comparison judgment based on the detected value are provided. The storage unit 20 stores the fuel injection amount Q based on the engine speed Ne and the accelerator opening degree _VL.
Fuel injection quantity map for calculating the _F (see FIG. 3), the oxygen concentration map for determining the target oxygen concentration D _O2 from the engine speed Ne and the fuel injection amount Q _F (see FIG. 4), oxy-fuel ratio ( Q _O2 / Q _F ) Smoke level map (see FIG. 5) showing the relationship with the smoke concentration, and oxygen fuel ratio map (FIG. 6) for obtaining the smoke allowable limit value K from the engine speed Ne and the fuel injection amount Q _F. See) and are provided. Among them, the fuel injection amount Q _F is the fuel injection amount per unit time (liter / 1 hour). In addition, the intake air amount Q at the oxygen fuel ratio (Q _O2 / Q _F )
_O2 is calculated by the following formula.

Q _O2 = V _A × γ × R _O2 / 100 Here, γ; oxygen specific gravity at temperature Ti. Then, the comparison calculation unit 21 obtains the oxygen fuel ratio finally obtained by the search and calculation using these maps. (Q _O2 /
Q _F ), smoke limit value K, and inhaled oxygen concentration R _O2
And the target oxygen concentration D _O2 are compared and determined, the optimum opening of the EGR valve 2 at that time is obtained, and an operation signal to the actuator 13 is output via the output unit 12.

Next, an embodiment of the exhaust gas recirculation control method of the present invention will be described as an operation when the opening degree control of the EGR valve 2 is performed by the exhaust gas recirculation control device having the above-mentioned configuration (see FIG. 2).

First, in order to grasp the operating condition, the engine speed Ne is detected by the engine speed sensor 18 (ST
1) The accelerator opening sensor 19 detects the accelerator opening _VL (ST2). In parallel with this, the intake air temperature Ti passing through the intake passage 3 by the intake temperature sensor 16
Is detected (ST 3), the oxygen concentration sensor 15 detects the oxygen concentration R _O2 of the intake air (ST 4), and the air flow sensor 14 detects the intake air amount V _A (ST 5).
These detections target not only fresh air but also all intake air to which EGR gas is added when the EGR valve 2 is open.

Next, these detected values Ne, V _L , Ti,
The comparison operation unit 21 of the control unit 5, which has received R _O2 and V _A , performs a predetermined operation and search. That is, FIG.
The fuel injection amount Q _F is searched from the accelerator opening _VL and the engine speed Ne by the fuel injection amount map shown in (ST6). For example, in the figure, when the engine speed Ne is "n" and the accelerator opening _VL is 70%, the fuel injection amount Q
_F is calculated as “q”. Then, according to the oxygen concentration map shown in FIG. 4, the fuel injection amount Q _F and the engine speed Ne
The target oxygen concentration D _O2 is searched from (ST 7). For example, in the figure, if the engine speed Ne is "n" and the fuel injection amount Q _F is "q", then D _O2 = 17%. Next, the target oxygen concentration D _O2 obtained from this oxygen concentration map is
Whether or not it is a region, for example, whether or not D _O2 ≠ 21% is judged (ST 8). If the target oxygen concentration D _O2 is 21%, the EGR valve 2
Is completely closed (ST 9), exhaust gas recirculation is not performed,
Return to the initial detection and search of the flow. Then, in the EGR region, the intake oxygen amount Q _O2 is calculated by the above formula (ST10), and the oxygen fuel ratio (K) corresponding to the smoke allowable limit value is calculated from the oxygen fuel ratio map shown in FIG. 6 ( ST11). For example, in the figure, the engine speed Ne is "n",
If the fuel injection amount Q is “q”, the oxygen fuel ratio of the smoke allowable limit value is calculated as “K ₂ ”. The smoke allowable limit value K and the oxygen fuel ratio (Q _O2 / Q _F ) based on the detected value
(ST12). In this comparison, when the oxygen fuel ratio (Q _O2 / Q _F ) is larger than the smoke allowable limit value K, that is, when the amount of oxygen that provides good smoke is secured, the oxygen concentration R _O2 is the target oxygen concentration D O. _The EGR valve 2 is controlled so that it becomes _O2 (ST13). For example R _O2 ＞
If it is D _O2 , increase the opening degree of the EGR valve 2 and
Increase the amount so that R _O2 = D _O2 . Also R _O2 <
If it is D _O2 , the opening degree of the EGR valve 2 is reduced to reduce the EGR amount. When the EGR amount decreases, the intake air amount of fresh air increases accordingly, so the oxygen concentration R _O2 of the total intake air increases,
Finally, the opening is reduced until R _O2 = D _O2 . When the oxygen fuel ratio (Q _O2 / Q _F ) is smaller than the smoke allowable limit value K, that is, when “a” is located on the left side of “K” in FIG. 5, it is indicated by An in the figure. As described above, since there is an operation (rotation) region that exceeds the smoke limit, EG should be set so that Q _O2 / Q _F = K.
The opening of the R valve 2 is reduced to secure the required oxygen amount Q _O2 (ST14).

In this way, the opening degree of the EGR valve 2 is controlled in accordance with the oxygen concentration R _O2 in the total intake air containing the EGR gas and the change in the ratio between the oxygen amount Q _O2 and the fuel injection amount Q _F. When the oxygen amount Q _O2 is smaller than the smoke allowable limit value K, the absolute oxygen amount is increased to secure the target smoke level, and when the oxygen amount Q _O2 is large, it is necessary to reduce it to the target NOx level. Since the oxygen concentration is set to R _O2 , both low smoke and maximum NOx reduction can be reliably achieved, and highly accurate EGR control according to all operating conditions can be achieved. For example, when applied to a supercharged diesel engine, a boost delay occurs in a transient state such as acceleration,
As shown in FIG. 7, although the intake air is less than in the steady state, the required oxygen amount (Q _O2 / Q _F ) with respect to the fuel injection amount Q _F
Since the control is performed in consideration of the above, it is possible to instantaneously respond to the change in the operating condition, and the smoke emission amount does not exceed the allowable limit value K. Further, even if there is a situation unique to each device such that intake resistance increases and intake air amount decreases due to clogging of the air cleaner, highly accurate EGR control can be performed without being affected by this.

Although the smoke allowable limit value K is changed according to the driving condition (ST11) in FIG. 2, it may be fixedly set as the target level. Further, in the control maps of FIGS. 4 and 6, one parameter is set to the fuel injection amount Q.
_Although it is set to _F , the accelerator opening degree V _L may be used. Further, as a technique to be compared with the present invention, there is Japanese Utility Model Laid-Open No. 4-116654 in which EGR control is performed so that the amount of smoke generated does not exceed an allowable limit. However, this proposal compares the smoke limit air amount with the target fresh air intake amount, and does not consider the oxygen in the EGR gas. Therefore, the oxygen content in the EGR gas is too large or too small and the EGR gas is too small. It is considered that the EGR control with high precision is difficult due to the variation in the way of applying. In the present invention, since the oxygen in the EGR gas is taken into consideration, the highly accurate E that prevents the deterioration of smoke due to the change in the operating conditions can be obtained.
GR control can be achieved.

[0018]

In summary, according to the present invention, it is possible to perform highly accurate EGR control that copes with rapid changes in operating conditions, etc., and achieve maximum NOx reduction while always suppressing smoke emissions within the allowable value. Demonstrate the excellent effect of being.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an exhaust gas recirculation control device of the present invention.

FIG. 2 is a flowchart showing an embodiment of an exhaust gas recirculation control method of the present invention.

FIG. 3 is a diagram showing a fuel injection amount map in FIG.

FIG. 4 is a diagram showing an oxygen concentration map in FIG.

5 is a diagram showing the relationship between the oxygen fuel ratio and the smoke concentration in FIG.

FIG. 6 is a diagram showing an oxygen fuel ratio map in FIG.

FIG. 7 is a diagram showing a relationship among oxygen concentration, smoke emission amount, and oxygen fuel ratio.

FIG. 8 is a diagram showing changes in oxygen concentration depending on operating conditions.

FIG. 9 is a diagram showing a relationship between an excess air ratio and exhaust smoke concentration.

FIG. 10 is a diagram showing a relationship between an EGR rate and an oxygen concentration in exhaust gas.

FIG. 11 is a diagram showing the relationship between the intake oxygen concentration and the NOx reduction rate.

FIG. 12 is a diagram showing the relationship between the EGR rate and the NOx reduction rate for explaining the problems of the conventional technique.

[Explanation of symbols]

1 exhaust gas recirculation passage 2 EGR valve 3 intake passage 4 detection means 5 control unit 20 storage unit 21 comparison calculation unit 22 connection position K smoke allowable limit value D _O2 target oxygen concentration R _O2 oxygen concentration Q _O2 oxygen amount Q _F fuel injection amount

Claims (3)

[Claims] 1. EGR control is performed to maintain low smoke in accordance with a change in absolute oxygen amount in total intake air containing EGR gas, and N is controlled in accordance with a change in oxygen concentration in the total intake air.
An exhaust gas recirculation control method comprising performing EGR control to reduce Ox. 2. When performing exhaust gas recirculation control by adjusting the opening degree of the EGR valve according to the operating condition of the engine, the oxygen concentration in the total intake air including the EGR gas and the oxygen amount in the total intake air. Then, the oxygen injection ratio is compared with the smoke allowable limit value, and when the oxygen fuel ratio is small, the EGR valve is controlled so as to be equal to the smoke allowable limit value. When it is larger, the above E concentration is adjusted so that the oxygen concentration becomes equal to the target oxygen concentration.
An exhaust gas recirculation control method characterized by controlling a GR valve. 3. An EGR valve provided in an exhaust gas recirculation path for recirculating exhaust gas and a downstream side of a connection position between the intake passage and the exhaust gas recirculation path for detecting the air amount and oxygen concentration thereof. And a control unit for operating the EGR valve according to the detection value of the detection means and the engine operating condition, and the control unit stores a smoke allowable limit value and a target oxygen concentration set value. And the oxygen concentration in the total intake air containing EGR gas and the ratio between the oxygen amount in the total intake air and the fuel injection amount based on the detected value and the calculated value and the set value. An exhaust gas recirculation control system comprising: a comparison calculation unit for comparing and determining the optimum opening of the EGR valve; and an output unit for outputting a control signal so that the EGR valve has the optimum opening. Control device.