KR100895276B1 - Exhaust gas recirculation system for reducing nox - Google Patents

Abstract

The present invention relates to an exhaust gas recirculation system for reducing nitrogen oxides (NOx) in which some of the exhaust gas of the engine is introduced into the cooler (EGR Cooler), cooled, and then flowed back into the intake port of the engine. An EGR valve installed at an inlet side of the cooler to open and close to control an inflow amount of the exhaust gas; A pressure sensor installed in the engine to measure intake air pressure [mmHg] flowing into the engine; An RPM sensor installed in the engine to measure a rotation speed [rpm] of the engine; And based on a plurality of operation modes selected on a standard test mode for exhaust gas measurement for the engine, setting valve opening conditions based on the intake air pressure relative to the rotational speed, and through the pressure sensor and the RPM sensor, respectively. And an EGR control unit for controlling the opening of the EGR valve only when the current suction air pressure and the rotation speed value measured satisfy the valve opening condition. As a result, the amount of nitrogen oxide generated can be effectively suppressed by operating properly in accordance with the state of the engine.

Exhaust Gas Recirculation (EGR), Boost Pressure Sensor, RPM Sensor

Description

Exhaust gas recirculation system for reducing nitrogen oxides {EXHAUST GAS RECIRCULATION SYSTEM FOR REDUCING NOx}

The present invention relates to an exhaust gas recirculation apparatus applied to a vehicle engine, and more particularly, to an exhaust gas recirculation apparatus for reducing nitrogen oxides (NOx).

Exhaust gas recirculation system refers to a device that circulates a part of the exhaust gas generated from a vehicle to an engine mixer by circulating it from the exhaust system to the intake machine.

Exhaust gases from automobiles contain many harmful substances. Among them, the amount of nitrogen oxide (NOx) is more regulated for the protection of the air environment.

However, according to the conventional exhaust gas recirculation apparatus mainly using a temperature sensor, there is a problem that the generation of nitrogen oxides cannot be effectively controlled as described below.

1 is a graph showing the correlation between the exhaust gas temperature and the NOx generation amount as data of an engine of a construction machine. The horizontal axis shows the operation mode, and the vertical axis shows the exhaust temperature [° C.] (left) and the NOx generation amount [ g / h] (right).

At this time, in the case of the conventional exhaust gas recirculation apparatus using the temperature sensor, for example, if the amount of nitrogen oxide generation exceeds 40 [g / h] to operate the exhaust gas recirculation apparatus to lower it, the engine state The exhaust gas recirculation device must be operated when is in the first, second, third and fifth modes indicated by " 0 " in the graph of FIG.

Since a conventional exhaust gas recirculation apparatus is operated through a temperature sensor, in the graph of FIG. 1, a temperature for operating the exhaust gas recirculation apparatus includes a value including all of the first, second, third and fifth modes described above. In other words, it should be seen that it should be set to at least 340 [° C.].

However, when set as such, there was a problem that the exhaust gas recirculation apparatus is operated in the sixth and seventh modes as well as in the first, second, third and fifth modes.

That is, according to FIG. 1, in the sixth and seventh modes, since the amount of nitrogen oxide generation does not reach the standard (that is, 40 [g / h]), the waste gas is recycled despite being recycled. As a result, environmentally harmful substances such as PM (Particulate Matter), which is in a trade off relationship with nitrogen oxide, are excessively discharged in the sixth and seventh modes.

In addition, according to the conventional exhaust gas recirculation apparatus operated through the temperature sensor, there was a problem that it is affected by the ambient temperature environment.

That is, when considering the environment of the construction machinery engine used outside the four seasons, especially considering the summer and winter weather, the engine may have a temperature difference of up to 50 to 60 [℃], the conventional exhaust gas As in the recirculator, there is a problem that using the temperature value as a control factor leads to a failure to properly control the exhaust gas recirculator.

An object of the present invention is to provide an exhaust gas recirculation apparatus for reducing nitrogen oxides, which can effectively suppress the amount of nitrogen oxides generated by operating properly according to the engine condition.

In order to achieve the above object, the present invention is exhaust gas recirculation apparatus for reducing nitrogen oxides (NOx) for receiving a portion of the exhaust gas of the engine flows into the cooler (EGR Cooler) and then cools it to the intake port of the engine (Exhaust) A gas recirculation system, comprising: an EGR valve installed at an inlet side of the cooler to open and close to control an inflow amount of the exhaust gas; A pressure sensor installed in the engine to measure intake air pressure [mmHg] flowing into the engine; An RPM sensor installed in the engine to measure a rotation speed [rpm] of the engine; And based on a plurality of operation modes selected on a standard test mode for exhaust gas measurement for the engine, setting valve opening conditions based on the intake air pressure relative to the rotational speed, and through the pressure sensor and the RPM sensor, respectively. It provides an exhaust gas recirculation device for reducing nitrogen oxides, characterized in that it comprises an EGR control unit for controlling the opening of the EGR valve only when the current intake air pressure and the rotation speed value measured satisfy the valve opening condition. do.

Here, the standard test mode for measuring the exhaust gas has a plurality of operation modes with a load rate [%] and a rotation speed [rpm] as variables, wherein the plurality of operation modes have a load rate of 50% and the rotation speed of the engine The third operation mode, which is the rated speed at maximum output, and the fifth operation mode, in which the load factor is 100% and the rotation speed are the intermediate speeds of the engine, may be used.

At this time, the valve opening condition is the current measured by the pressure sensor and the RPM sensor than the value on the line connecting the third operation mode and the fifth operation mode on the graph based on the rotational speed and the suction air pressure The value of the intake air pressure relative to the number of revolutions may be equal to or greater than.

Alternatively, the valve opening condition may be represented by the following relationship.

_{E min = {(A 3mode -A} 5mode) / (Rp-Rt)} * (Rn-Rt) + A 5mode ... (1)

Rn ≥ Rt ... (2)

E _A ≥ E _min ... (3)

Where E _min is the minimum suction air pressure [mmHg] that satisfies the valve opening condition,

A _3mode : Intake air pressure [mmHg] in the third operation mode,

A _5mode : Intake air pressure [mmHg] in the fifth operation mode,

         Rp: RPM at maximum output [rpm], Rt: RPM at maximum torque [rpm],

Rn: current rotation speed [rpm], E _A : current suction air pressure [mmHg])

According to the exhaust gas recirculation apparatus for reducing nitrogen oxides according to the present invention as described above, the valve opening condition based on the intake air pressure relative to the engine speed based on a plurality of operation modes selected from the standard operation mode for the exhaust gas test The exhaust gas recirculation apparatus is configured to open the EGR valve when the intake air pressure compared to the current rotational speed of the engine measured using the pressure sensor and the RPM sensor satisfies the valve opening condition. By properly operating in accordance with the state it is possible to effectively suppress the amount of nitrogen oxide generated.

As shown in FIG. 2, the nitrogen gas reducing exhaust gas recirculation apparatus 10 according to the embodiment of the present invention has a cooler (EGR Cooler) connected to the inlet and exhaust ports of the engine 1, respectively. ), The EGR valve 12 installed at the inlet side of the cooler 11, the pressure pressure sensor 13 and the RPM sensor 14 installed in the engine 1, and these sensors 13, 14. EGR control unit 15 for controlling the opening and closing of the EGR valve 12 on the basis of the signal received from the).

The inlet side of the cooler 11 communicates with the exhaust port of the engine 1, and the outlet side thereof communicates with the intake port of the engine 1.

Accordingly, when the EGR valve 12 is opened, the cooler 11 receives some of the exhaust gas from the exhaust port of the engine 1, cools it, and then discharges it back to the intake port side of the engine 1 to recirculate it to the engine 1. Let's go.

The EGR valve 12 is opened and closed by the EGR control unit 15 to control the entry and exit of the exhaust gas flowing into the cooler 11.

The pressure sensor 13 is for measuring the pressure of the gas flowing into the engine 1, that is, the intake air pressure [mmHg], and the RPM sensor 14 measures the rotation speed [rpm] of the engine 1. It is used as a purpose for.

The EGR control unit 15 has an EGR valve 12 only when the current intake air pressure and rotational speed of the engine 1 measured by the pressure sensor 13 and the RPM sensor 14 satisfy a predetermined valve opening condition. ) To open.

That is, the exhaust gas circulation system 10 according to the embodiment of the present invention, unlike the conventional exhaust gas circulation system that was operated based on the temperature value of the engine 1, the pressure sensor 13 and the RPM sensor 14 It is operated based on the intake air pressure [mmHg] and the rotation speed [rpm] measured through.

Hereinafter, the operation algorithm of the exhaust gas circulation system 10 according to the embodiment of the present invention will be described.

In order to regulate the exhaust gas of the engine 1, a standard for measuring it must be presented. For example, the "KC1-8" mode is an international standard (ISO 8178). Standard test mode used when

Table 1 below shows the configuration of the "KC1-8" mode.

[Table 1] KC1-8 mode

Operation mode One 2 3 4 5 6 7 8  Prime mover condition Load rate (%) 100 75 50 10 100 75 50 0 Prime mover Rated Speed at Maximum Output Intermediate rotation speed (maximum torque part) Idling

Meanwhile, FIGS. 3 and 4 show graphs measured by applying the "KC1-8" mode to the 175 [kW] / 2700 [rpm] engine mounted on a construction machine (crane).

FIG. 3 is a graph showing intake air pressure [mmHg] and nitrogen oxide (NOx) generation amount [g / h] for each mode constituting the "KC1-8" mode, and FIG. 4 is a rotation speed [rpm] of the engine 1. ] It is a graph showing the intake air pressure [mmHg] compared to the load (100%, 75%, 50%).

Through the graph of FIG. 3, it is possible to grasp the correlation between the amount of intake air and the amount of NOx generated.

Here, if the NOx generation amount should be lowered by opening the EGR valve 12 to operate the cooler 11 when the NOx generation amount is 40 [g / h] or more, the state of the engine 1 is in the "KC1-8" mode described above. The EGR valve 12 should be controlled to open only when in the first, second, third and fifth operation modes.

Table 2 below is a graph of the graph of FIG. 3 divided by operation modes, and the operation mode to which the EGR valve 12 should be opened is indicated by underlining in bold letters.

[Table 2] Rotational Speed (Load), Intake Air Pressure, NOx Generation by Operation Mode

Operation mode RPM [rpm] (load) Suction air pressure [mmHg] NOx generation amount [g / h] One 2700 (100%) 665.164 107.156 2 2700 (75%) 554.936 78.971 3 2700 (50%) 481.904 53.322 4 2700 (10%)  208.893  13.505 5 1700 (100%) 597.381 48.677 6 1700 (75%)  422.519 36.91 7 1700 (50%)  254.038  25.617 8  700 (IDLE)  26.088   5.987

That is, in Table 2, when the engine state is included in the area indicated by the underlined in bold letters, the EGR valve 12 may be opened.

If the area defined by Table 2 is shown in FIG. 4, a graph as shown in FIG. 5 can be obtained.

In the embodiment of the present invention, the third operation mode and the fifth operation mode on the graph of FIG. 5 are described as an algorithm relating to the valve opening condition of operating the exhaust gas recirculation apparatus 10, that is, opening the EGR valve 12. It is characterized by using.

That is, in FIG. 5, the EGR valve 12 is limited to the case where the current engine state exists in the area S above the line segment based on the line segment connecting both the third and fifth driving modes. To control the opening.

In this case, the valve opening condition can be expressed by the following equations.

_{E min = {(A 3mode -A} 5mode) / (Rp-Rt)} * (Rn-Rt) + A 5mode ... (1)

Rn ≥ Rt ... (2)

E _A ≥ E _min ... (3)

(here,

E _min : Minimum suction air pressure [mmHg], which satisfies the valve opening condition.

A _3mode : Intake air pressure [mmHg] in the third operation mode,

A _5mode : Intake air pressure [mmHg] in the fifth operation mode,

Rp: RPM at maximum output [rpm],

Rt: revolutions at maximum torque [rpm],

Rn: current rotation speed [rpm],

E _A : Current suction air pressure [mmHg])

In the formula (1), the intake air pressure (A _5mode) in the intake air pressure (A _3mode) and a fifth operation mode in the third operating mode, as well as measured through the test (Base Test) of the engine (1) Values.

The formula (1) at least to satisfy the third operation mode, and the a relational expression of the line segment connecting the both points of the 5 operation modes, all points present on a line segment (E _min) is the valve-opening condition in Figure 5 Means the intake air pressure. That is, the intake air pressure E _A currently measured from the engine 1 must be greater than or equal to the value of E _min relative to the current measured rotation speed Rn before the EGR valve 12 can be opened. 3)).

In addition, the valve opening condition requires that the rotational speed Rn currently measured is greater than or equal to the rotational speed Rt at the maximum output of the engine 1 (Equation (2)).

Therefore, in FIG. 1, the EGR control unit 15 has an engine state measured by the pressure sensor 13 and the RPM sensor 14 only in relation to the valve opening condition, that is, the relational expression of the above formulas (1) to (3). The control is performed so as to open the EGR valve 12 only when sufficient.

On the other hand, the exhaust gas recirculation apparatus 10 for reducing nitrogen oxides described above is only an embodiment for helping the understanding of the present invention, but the scope of the present invention is not limited thereto.

The scope of the invention to the technical scope is defined by the claims and equivalents described below.

1 is a graph for explaining the principle of operation of the exhaust gas recirculation device for reducing nitrogen oxide in the prior art,

2 is a conceptual view schematically showing an exhaust gas recirculation apparatus for reducing nitrogen oxides according to an embodiment of the present invention;

3 to 5 are graphs for explaining the operating principle of the exhaust gas recirculation apparatus for reducing nitrogen oxides of FIG.

        <Explanation of symbols for the main parts of the drawings>

10: exhaust gas recirculation device for reducing nitrogen oxides

11: cooler 12: EGR valve

13: pressure sensor 14: RPM sensor

15: EGR control unit

Claims (4)

In an exhaust gas recirculation system for reducing nitrogen oxides (NOx), which receives some of the engine exhaust gas through an EGR cooler, cools it, and then flows it back into the intake port of the engine. An EGR valve installed at an inlet side of the cooler to open and close to control an inflow amount of the exhaust gas; A pressure sensor installed in the engine to measure intake air pressure [mmHg] flowing into the engine; An RPM sensor installed in the engine to measure a rotation speed [rpm] of the engine; And Based on a plurality of operation modes selected from the standard test mode for exhaust gas measurement for the engine, the valve opening condition is set based on the intake air pressure to the rotational speed, and measured by the pressure sensor and the RPM sensor, respectively. And an EGR control unit for controlling the opening of the EGR valve only when the current suction air pressure and the rotational speed value satisfy the valve opening condition. The method of claim 1, The standard test mode for measuring exhaust gas has a plurality of operation modes with load factor [%] and rotation speed [rpm] as variables, wherein the plurality of operation modes include: The third operation mode in which the load ratio is 50% and the rotation speed is the rated speed at the maximum output of the engine, and the fifth operation mode in which the load ratio is 100% and the rotation speed is the intermediate rotation speed of the engine An exhaust gas recirculation apparatus for reducing nitrogen oxides, characterized in that. The method of claim 2, The valve opening condition is, The value of the intake air pressure compared to the current rotation speed measured by the pressure sensor and the RPM sensor than the value on the line connecting the third operation mode and the fifth operation mode on the graph based on the rotation speed and the intake air pressure The exhaust gas recirculation apparatus for reducing nitrogen oxides, characterized in that greater than or equal to. The method of claim 2, The valve opening condition is an exhaust gas recirculation device for reducing nitrogen oxides, characterized in that represented by the following relationship. _{E min = {(A 3mode -A} 5mode) / (Rp-Rt)} * (Rn-Rt) + A 5mode ... (1) Rn ≥ Rt ... (2) E _A ≥ E _min ... (3) Where E _min is the minimum suction air pressure [mmHg] that satisfies the valve opening condition, A _3mode : Intake air pressure [mmHg] in the third operation mode, A _5mode : Intake air pressure [mmHg] in the fifth operation mode,          Rp: RPM at maximum output [rpm], Rt: RPM at maximum torque [rpm], Rn: current rotation speed [rpm], E _A : current suction air pressure [mmHg])

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