JPS63143373A - Exhaust gas recirculation device for engine - Google Patents

Abstract

PURPOSE:To reduce the NOx exhaust quantity furthermore by increase- correcting the recirculation quantity of exhaust gas when the temperature of the exhaust gas the recirculation of which does not give influences onto the combustion faculty and stability of an engine is high. CONSTITUTION:In an exhaust gas recirculation device, a portion of the exhaust gas in an exhaust passage A is allowed to recirculate into an intake passage B by an exhaust recirculation means C, which is controlled by an exhaust recirculation control means D according to the engine operation state. In this case, an exhaust temperature detecting means E for detecting the temperature of the exhaust gas (or the related temperature) is installed. A recirculation quantity correcting means F corrects the exhaust gas recirculation quantity by the exhaust quantity recirculation control means D or the exhaust recirculation means C according to the detected exhaust temperature. The correction is executed so that the exhaust gas recirculation flow rate is increased when the exhaust gas temperature is higher than the standard temperature corresponding to the engine operation state.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an engine exhaust gas recirculation system that reduces NOx (nitrogen oxide) emissions by recirculating a part of the exhaust gas to the intake passage. Regarding equipment.

(Prior Art) Engines for automobiles, etc. are equipped with exhaust gas recirculation devices that reduce NOx emissions by recirculating part of the exhaust gas into the intake passage to suppress combustion temperature. However, on the one hand, this exhaust gas recirculation causes deterioration in the combustibility, stability, or output performance of the engine. Therefore, for example, JP-A-57-148
As shown in Publication No. 049, the optimal recirculation amount (recirculation rate) of exhaust gas is set in advance according to the operating range of the engine, and the recirculation is controlled to reach the set amount. While sufficiently reducing NOx emissions in the area,
The effect on engine stability and output performance is minimized.

(Problem to be solved by the invention) However, even if the optimal exhaust gas recirculation amount is set in each operating range as described above, the reduction of NOx emission hanging due to exhaust gas recirculation and the stability of the engine are not achieved. Since these two requirements are essentially incompatible, it is difficult to always satisfy these two requirements. In particular, due to variations in the engine itself and external conditions, in some cases NOx emissions may not be reduced sufficiently and in others. In this case, a problem arises in that engine stability etc. are needlessly sacrificed.

The present invention addresses the above-mentioned situation when reducing NOx emissions by recirculating exhaust gas, and reduces NOx emissions while maintaining required engine stability and output performance.
The aim is to reduce OX emissions as much as possible.

(Means for Solving the Problems) That is, the exhaust gas recirculation device for an engine according to the present invention has an exhaust gas recirculation system that recirculates part of the exhaust gas in the exhaust passage A to the intake passage B, as shown in FIG. In a configuration including a means C and an exhaust recirculation control means for controlling the amount of recirculation of exhaust gas by the means C according to the operating state of the engine, the temperature of the exhaust gas (or a temperature related thereto, hereinafter the same) is provided. )
and an inter-recirculation correction means F for correcting the amount of exhaust gas recirculated by the exhaust gas recirculation control means or the exhaust gas recirculation means C according to the exhaust gas temperature detected by the means E. It is characterized by: Specifically, this recirculation period correction means F adjusts the exhaust gas recirculation R when the exhaust gas temperature is higher than a standard temperature depending on the operating state of the engine.
It works to increase the amount of

(Operation) According to the above configuration, the exhaust gas recirculation period is controlled according to the operating condition by the exhaust gas recirculation control means, and is set to the optimal one preset for each operating condition. When the temperature of the exhaust gas is higher than the standard temperature, the recirculation amount correction means F increases the amount relative to the above-mentioned set value.

By the way, when the temperature of exhaust gas is high, part of it is recirculated to the intake passage, which has the effect of heating the fuel and promoting vaporization and atomization, and this effect has a negative effect on combustibility due to exhaust gas recirculation. will be eliminated or weakened. Therefore, when the exhaust gas temperature is higher than the standard temperature, increasing the far am as described above has little effect on combustibility, engine stability, output performance, etc., and NOx emissions are reduced accordingly. That will happen.

(Example of implementation) Examples of the present invention will be described below.

As shown in FIG. 2, the engine 1 includes an intake passage 5 and an exhaust passage 6, which communicate with the combustion chamber 4 via intake and exhaust valves 2.3, respectively.
An air cleaner 7, an air flow meter 8, and a throttle valve 9 are arranged in the intake passage 5 from the upstream side, and in this embodiment, the downstream part of the intake passage 5 has a small passage cross-sectional area and a low-load It is branched into a passage 5a for use and a passage 5b for high load with a large passage cross-sectional area. The high-load passage 5b is equipped with a shutter valve 11 that is opened and closed by an actuator 10, and a fuel injection valve 12 is installed downstream thereof.

Further, between the intake passage 5 and the exhaust passage 6, both passages 5
．． An exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 13 is provided which communicates the exhaust gas recirculation passage 1 (EGR amount) from the exhaust passage 6 side to the intake passage 5 side on the passage 13.
An exhaust gas recirculation control valve (EGR valve) 14 is provided to control the exhaust gas recirculation, and an exhaust temperature sensor 15 is installed upstream of the valve 14 (on the exhaust passage 6 side) to detect the temperature of the exhaust gas.

On the other hand, this engine 1 has functions such as opening/closing control of the shutter valve 11, fuel injection amount control from the fuel injection valve 12, and E
A control unit 20 is provided that performs EGRffl control using the GR valve 14, and the unit 20 receives an intake air amount signal a from the air flow meter 8, an engine rotational speed signal from the distributor 21, and receives an intake air amount signal a from the exhaust temperature sensor 15. The exhaust gas temperature signal C is inputted.

Then, this control unit 20 calculates the amount of air supplied to the combustion chamber 4 per cycle corresponding to the engine load based on the intake air amount signal a and the engine speed signal S, and also calculates the amount of air supplied to the combustion chamber 4 per cycle corresponding to the engine load. After setting the corresponding fuel injection M and adding a predetermined correction to this, fuel injection signals d...d are output to the fuel injection valves 12...12 of each cylinder. Further, when the engine load corresponding to the amount of air per cycle is low, a drive signal e is output to the actuator 10 of the shutter valve 11 to shut off the high load passage 5b. Low-load passage 5a with a small passage cross-sectional area when loaded
Air is supplied from the combustion chamber 4 to form a swirl in the combustion air 4, thereby improving combustion performance at low loads.

On the other hand, regarding EGR control, which is a characteristic part of the present invention,
The control unit 20 operates according to the flowchart shown in FIG. Next, to explain this operation, the control unit 20 first reads the engine speed and engine load based on the above signals a and b in step S1 of the flowchart, and then reads the actual engine speed indicated by these values in step S2. It is determined whether or not the operating range belongs to a preset EGR range.

And EGRiii! If it does not belong to step S
3, set EGRffiV to zero. On the other hand, the driving range is EG
When it belongs to the R region, the reference EGRIVo is determined from a map preset according to the rotation speed and load in step S4.
and the reference exhaust temperature TO. These maps basically have a lot of IEGRfiVo on the high-load, high-speed side,
Further, the reference exhaust temperature To is set high, and the various engine conditions are standard.

Further, the control unit 20 controls the EGR passage 13 based on the signal C from the exhaust gas temperature sensor 15 in step S5.
Detects the temperature T of the exhaust gas inside.

Then, in step S6, this temperature T is compared with the reference exhaust gas temperature TO read from the map, and if the two are equal, then in step S7 EGRfMV is set to the reference EGR amount vO also read from the map.

Then, in step S8, the above E is set so that this arrogance becomes 0.
A control signal f is output to the EGR valve 14 on the GR passage 13.

On the other hand, if the actual exhaust gas temperature T and the reference exhaust gas temperature TO read from the map are not equal in step S6, step S9. According to S10, the difference AT (T-To
) is calculated, and the EGR correction amount AV per 1° C. temperature difference, which is preset according to the engine speed and load, is read from the map.

In this map as well, where is the high load, high rotation side?
The AV is set to be large.

Then, the control unit 20 performs step S11.
Then, using the above temperature difference AT and EGR correction amount AV, the reference E
The final EGRffiV is obtained by correcting the GR value Vo according to the following formula.
is calculated, and in step S8, the above EGR is
A control signal "is output to the valve 14.

Formula: V=Vo+AT-AV As a result, when the exhaust gas temperature T is higher than the reference temperature TO, EGRffiV is increased according to the difference. Also, if the exhaust gas temperature T is lower than the reference temperature TO (
AT<O), the EGR amount V is reduced.

By the way, there is a relationship between the stability of the engine operating state and the EGR rate as shown in Figure 4, and when the EGR reaches its stability limit,
The R amount increases as the exhaust temperature increases. Therefore, as mentioned above, even if the EGR amount V is increased when the exhaust gas temperature T is high, the stability of the engine operating condition will not be impaired, and the EGR
Since the relationship between the rate and the amount of NOx emissions is shown in Figure 5, by increasing the EGR amount V when the exhaust temperature T is high, NOx can be reduced while maintaining the stability of the engine operating condition.
It becomes possible to reduce x emissions.

In this embodiment, when the exhaust temperature T is higher than the reference temperature To in the high load, high rotation region, when the temperature difference WIT) is 1°C,
It becomes possible to effectively suppress the emission of NOx. Furthermore, if the exhaust gas temperature T is lower than the reference temperature To, E
While reducing GRIV will ensure the required engine stability, it will also increase NOx emissions; however, by setting the standard EGR amount Vo to a sufficient value in advance, NOx emissions can be reduced. It can be within the permissible limits.

Further, in this embodiment, the exhaust temperature sensor 15 is
Although it was arranged in the GR passage 13 to directly detect the exhaust gas temperature, a temperature sensor was installed in the intake passage near the combustion chamber after the exhaust gas was recirculated, and the EGR The amount may be corrected, and in this case, it is more preferable to perform the correction in consideration of the influence of the intake air temperature.

(Effects of the Invention) As described above, according to the present invention, in an engine in which the amount of recirculation of exhaust gas is controlled according to the operating state of the engine, the recirculation of exhaust gas affects the combustibility, stability, or output of the engine. Since the amount of recirculation of exhaust gas is increased when the exhaust gas is at high temperature, which has little effect on performance, NOxOx can be reduced without impairing the stability of the engine.
This makes it possible to further reduce emissions. This makes it possible to realize an engine that is excellent in both engine performance such as stability and output performance, and exhaust purification performance.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of the present invention, FIG. 2 is a diagram of an engine control system according to an embodiment of the present invention, FIG. 3 is a flow chart diagram showing the operation of exhaust gas recirculation control in the embodiment, and FIG. A graph showing the relationship between the EGR rate and engine stability, which is a premise of the present invention, and FIG. 5 are graphs showing the relationship between the EGR rate and the NOx emissions. 1... Engine, 5... Intake passage, 6... Exhaust passage, 13.14... Exhaust gas recirculation means (EGR passage, EG
R valve), 15...Exhaust temperature detection means (exhaust temperature sensor), 20...Exhaust gas recirculation control means, recirculation amount correction means (control unit). Figure 3 Figure 4 Figure 15

Claims (1)

[Claims] (1) an exhaust gas recirculation device that recirculates part of the exhaust gas to the intake passage; and an exhaust gas recirculation control device that controls the amount of exhaust gas recirculated by the exhaust gas recirculation device according to the operating state of the engine;
an exhaust gas temperature detection means for detecting a temperature related to the exhaust gas temperature; and an exhaust gas temperature detection means for detecting a temperature related to the exhaust gas temperature; An exhaust gas recirculation device for an engine, comprising a recirculation amount correction means for increasing a recirculation amount.