JP4601518B2 - EGR device - Google Patents

Description

  The present invention relates to an improvement of an EGR device.

  As a technique for reducing the NOx component in the exhaust gas, exhaust gas recirculation (hereinafter referred to as EGR) that recirculates the exhaust gas into the intake air is used. This recirculates exhaust gas into the intake air, thereby reducing the oxygen concentration in the intake air, increasing the specific heat of the intake air, lowering the combustion temperature, and suppressing the generation of NOx.

  However, by performing EGR, part of the intake air is replaced with EGR gas, the amount of intake air is reduced, the air excess rate is reduced, and smoke may be generated.

  For this reason, an EGR cooler for lowering the temperature of the EGR gas as disclosed in Patent Document 1 is provided in the middle of the route through which the EGR gas flows to cool the EGR gas, and the volumetric flow rate of the EGR gas is lowered to reduce the intake air. The filling efficiency is increased to prevent the excess air ratio from decreasing.

On the other hand, along with the tightening of exhaust gas regulations, demands for a high EGR rate and a high excess air ratio are increasing, and in order to respond to this, there is a technology for increasing the supercharging pressure using a turbocharger with a high pressure ratio. .
JP 2000-249003 A

  However, in such a conventional EGR system, it is necessary to increase the pressure ratio of the turbocharger compressor in order to increase the supercharging pressure, and the compressor outlet temperature rises. It is necessary to change the heat resistant material to withstand higher temperatures or to use a two-stage turbocharger. As a result, the use of heat-resistant materials causes a significant increase in cost, and the use of a two-stage turbocharger causes a problem in that a cooler is installed in each turbocharger, thus increasing costs and changing the in-vehicle layout. Furthermore, since the pressure in the intake manifold rises by increasing the supercharging pressure, and the in-cylinder pressure rises with this pressure rise, there is a problem that it is necessary to take measures against engine strength.

  The present invention has been made in view of the above-described problems, and provides an EGR device that achieves a high EGR rate and a high excess air ratio without increasing costs, changing the in-vehicle layout, and taking measures against engine strength. With the goal.

The present invention provides an EGR cooler that cools the recirculated EGR gas in the EGR passage in an EGR device that recirculates a part of the exhaust gas of the engine as EGR gas through the EGR passage into the intake air. A cooler section for cooling the gas, a catalyst section installed upstream in the EGR gas flow direction of the cooler section, and a fuel addition means for adding fuel to the catalyst section, and adding to the catalyst section to burn the fuel A controller for controlling the fuel addition means, an operating state detection sensor for detecting the operating state of the engine, a flow rate sensor for detecting the flow rate of the intake air, A pressure sensor that detects the pressure of the intake air mixed with air and EGR gas, and the controller controls the detected engine operation. The fuel addition amount to be added is calculated based on the state, and it is determined whether or not it is a fuel addition execution region based on the detected intake air flow rate and intake air pressure. The fuel is added to the catalyst part .

  In the present invention, the oxygen concentration in the EGR gas is reduced by adding fuel to the catalyst portion of the EGR cooler. For this reason, even if the flow rate of the EGR gas recirculated during intake is reduced, a high NOx reduction effect can be exhibited.

  In addition, since the flow rate of the recirculating EGR gas can be reduced, the intake air flow rate can be relatively increased, and the excess air ratio during intake can be increased.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  In FIG. 1, 1 is an engine, 2 is an intake passage for supplying intake air to the engine 1, and 3 is an exhaust passage for discharging exhaust gas generated by the engine downstream. A turbocharger 4 is disposed across the intake passage 2 and the exhaust passage 3. The turbocharger 4 is a variable nozzle turbocharger (hereinafter referred to as VNT) that rotates the turbine nozzle and adjusts the opening degree of the turbine nozzle in order to perform EGR control to be described later. An intercooler 5 is installed in the intake passage 2 downstream of the compressor of the VNT 4 to cool the intake air pressurized by the VNT 4 and supply it to the engine 1.

  An EGR passage 6 is provided that connects the VNT 4 upstream of the exhaust passage 3 and the intercooler 5 downstream of the intake passage 2 to recirculate exhaust gas to the intake passage 2. The EGR passage 6 is provided with an EGR cooler 7 and an EGR valve 8 that controls the amount of EGR gas into the intake air by adjusting the opening degree on the downstream side of the EGR cooler 7 in the EGR gas flow direction.

  The EGR cooler 7 is provided with a cooler portion 7b that cools the EGR gas, and oxygen (e.g., light oil) that is disposed on the upstream side of the cooler portion 7b and is injected from a fuel addition nozzle 9 described later. And a catalyst unit 7a for changing the carbon dioxide to carbon dioxide to reduce the oxygen concentration in the EGR gas. Further, a fuel addition nozzle 9 for adding fuel is installed upstream of the catalyst portion 7a. The fuel addition nozzle 9 is connected to a fuel supply device 10 to supply fuel.

  Therefore, the EGR gas that has flowed into the EGR cooler 7 temporarily rises in temperature in the catalyst portion 7a, but is cooled in the cooler portion 7b, and when the EGR cooler 7 is discharged, the temperature is lower than that at the time of inflow. Oxygen concentration in the EGR gas is lowered by the oxidation reaction in the part 7a as compared with the inflow, and is recirculated into the intake air.

  The fuel addition amount and the addition timing of the fuel addition nozzle 9 are controlled by the ECU 11. The ECU 11 performs integrated control of the engine 1, and the ECU 11 includes an engine operation state detection sensor 12 that detects an engine operation state such as an engine rotation speed and an engine load (fuel injection amount), a flow rate sensor 13 that detects an intake air flow rate, Output signals of a concentration sensor 14 that detects the oxygen concentration in the intake air, a pressure sensor 15 that detects the pressure of the intake air, and a temperature sensor 16 that detects the temperature of the EGR gas in the EGR cooler 7 are input. The ECU 11 performs EGR control by controlling the fuel addition amount and addition timing of the fuel injection nozzle 9 and the opening degree of the EGR valve 8 and the VNT 4 based on the input detection value.

  FIG. 2 is a flowchart for explaining the EGR control performed by the ECU 11. This control is performed at predetermined intervals, and as described above, the fuel is added to the EGR cooler 7 to reduce the oxygen concentration in the EGR gas, while increasing the carbon dioxide concentration.

  First, in step S1, the engine speed Ne, the fuel injection amount Gf, the intake air flow rate Ga, the EGR gas temperature Tex, the oxygen concentration in the intake air, and the intake pressure Pin are read from each sensor 12-16.

  In step S2, the excess air ratio λ is calculated from the read engine rotational speed Ne, fuel injection amount Gf, and intake air flow rate Ga.

  In the subsequent step S3, the target excess air ratio and the target oxygen concentration are calculated from the read engine rotational speed Ne and the fuel injection amount Gf using a map as shown in FIG. A map for calculating the target excess air ratio and the target oxygen concentration is provided.

  In step S4, it is determined from the read intake air flow rate Ga and the intake pressure Pin using a map as shown in FIG. 4 whether or not it is a region where the fuel is added to the EGR gas.

  In FIG. 4, the fuel addition execution region exceeds the upper limit of the normal control region that achieves the target excess air ratio and the target oxygen concentration calculated in step S3 only by opening control of the VNT 4 and the EGR valve 8, and the compressor of the VNT 4 Surge limit pressure, limit rotation speed of VNT4, in-cylinder pressure, intake manifold internal pressure, and the like are set in a region that is less than the structural limit pressure of the engine 1. That is, when the determination result is the normal control region, when the target excess air ratio and the target oxygen concentration can be achieved only by opening control of the VNT 4 and the EGR valve 8, the catalyst portion 7a of the EGR cooler 7 is achieved. Do not add fuel.

  When it is determined that the region is the fuel addition execution region, the process proceeds to step S5 to determine whether the EGR gas temperature Tex is equal to or higher than the predetermined temperature Tst. Here, the predetermined temperature Tst is set to, for example, the activation temperature (for example, 180 ° C.) of the catalyst unit 7a. If the condition of step S5 is satisfied, the process proceeds to step S6, the amount of fuel added to the EGR gas is calculated from the intake air flow rate Ga and the intake pressure Pin using a map as shown in FIG. A predetermined amount of fuel is added to the cooler 7. The fuel is injected into the catalyst part 7a, and the fuel reacts with oxygen in the catalyst part 7a, whereby the concentration of oxygen in the EGR gas is lowered and the concentration of carbon dioxide, which is an inert gas, is raised. Therefore, since the EGR cooler 7 is provided with the catalyst portion 7a and the fuel injection nozzle 9 for injecting fuel into the catalyst portion 7a, the EGR gas having a lower oxygen concentration can be recirculated into the intake air.

  On the other hand, if the condition of step S5 is not satisfied, the process proceeds to step S7.

  After the fuel addition in step S6, the opening degree of the EGR valve 8 and the VNT 5 is feedback controlled in step S7 so as to achieve the target excess air ratio and the target oxygen concentration set in step S3.

  Therefore, in the present invention, in the region where fuel can be added to the EGR cooler 7, by adding fuel to the catalyst portion 7a in the EGR cooler 7, oxygen in the EGR gas is converted to carbon dioxide which is an inert gas. The oxygen concentration in the EGR gas is lowered and the carbon dioxide concentration is raised. For this reason, even if the flow rate of the EGR gas recirculated into the intake air is reduced, a high NOx reduction effect can be exhibited with a small flow rate of the EGR gas as shown in FIG.

  In addition, since the flow rate of the recirculating EGR gas can be reduced, the intake air flow rate can be relatively increased, and the excess air ratio during intake can be increased.

  Moreover, the catalyst part 7a and the fuel addition nozzle 9 should just be provided in the EGR cooler 7, and the target high excess air ratio and high EGR rate can be achieved without requiring major changes to the VNT 3 or the engine 1. NOx can be reduced without increasing smoke.

  The fuel added to the catalyst portion 7a of the EGR cooler 7 is not limited to light oil, and may be any fuel that consumes oxygen by reaction with the catalyst. The catalyst unit 7a may be provided with a soot trap function. Further, as a fuel addition control method, feedback control based on the oxygen concentration of the intake manifold may be used. Further, the opening control of the EGR valve 8 and the VNT 5 is not limited to feedback control but may be open control.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  This is useful for increasing the excess air ratio of an EGR system equipped with an EGR cooler.

The block diagram of the engine which shows embodiment of this invention. The flowchart figure explaining EGR control. A map for calculating a target excess air ratio and a target oxygen concentration from the engine speed Ne and the fuel injection amount Gf. The figure explaining a fuel addition implementation area | region. A map for calculating the fuel addition amount from the engine rotation speed Ne and the fuel injection amount Gf. The figure which shows the relationship between the NOx reduction rate by EGR, and oxygen concentration. The figure which shows the relationship between smoke and an excess air ratio.

Explanation of symbols

1 Engine 2 Intake passage 3 Exhaust passage 4 VNT
5 Intercooler 6 EGR passage 7 EGR cooler 7a Catalyst part 7b Cooler part 8 EGR valve 9 Fuel injection nozzle 10 Fuel supply device 11 ECU
12 Engine operation state detection sensor 13 Flow rate sensor 14 Concentration sensor 15 Pressure sensor 16 Temperature sensor

Claims (4)

In an EGR device that recirculates a part of engine exhaust gas into intake air as EGR gas through an EGR passage,
An EGR cooler for cooling the recirculating EGR gas is provided in the EGR passage,
The EGR cooler includes a cooler section that cools EGR gas, a catalyst section that is installed upstream in the EGR gas flow direction of the cooler section, and a fuel addition unit that adds fuel to the catalyst section.
By adding to the catalyst part and burning the fuel, the oxygen concentration in the EGR gas is lowered ,
A controller for controlling the fuel addition means;
An operating state detection sensor for detecting the operating state of the engine;
A flow sensor for detecting the flow rate of the intake air;
A pressure sensor for detecting the pressure of the intake air mixed with the intake air and the EGR gas,
The controller calculates a fuel addition amount to be added based on the detected operating state of the engine, determines whether or not it is a fuel addition execution region based on the detected intake air flow rate and intake pressure, and is a fuel addition execution region. In this case, the EGR device is characterized in that the calculated fuel addition amount of fuel is added to the catalyst unit . A temperature sensor for detecting the temperature of the EGR gas flowing into the EGR cooler;
The EGR apparatus according to claim 1, wherein the fuel is added to the catalyst unit when the detected EGR gas temperature is equal to or higher than the activation temperature of the catalyst unit . The engine is equipped with a variable nozzle turbocharger,
An EGR valve for controlling the flow rate of EGR gas in the EGR passage;
The controller calculates a target excess air ratio and a target oxygen concentration according to the detected engine operating state, and the variable nozzle turbocharger and the EGR so as to achieve the calculated target excess air ratio and the target oxygen concentration. Control the opening of the valve,
2. The EGR device according to claim 1 , wherein when the target excess air ratio and the target oxygen concentration exceed the excess air ratio and the oxygen concentration that can be achieved by the opening degree control, it is determined that the fuel addition is performed . The EGR device according to any one of claims 1 to 3, wherein the fuel addition amount is set based on an operating state of the engine .

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