JP2014015871A - Egr device - Google Patents

Abstract

An EGR apparatus capable of controlling the NOx concentration with higher accuracy than conventional ones is provided.
A NOx sensor 17 for detecting the concentration of NOx contained in exhaust gas 8 discharged from an engine 1 is provided, and the amount of change per unit time of the fuel injection amount of the engine 1 is maintained within an allowable range. Only when the control value based on the detection value of the airflow sensor 14 is switched to the control based on the detection value of the NOx sensor 17, the target NOx concentration is determined according to the operating state, and the NOx concentration actually measured by the NOx sensor 17 is changed to the target NOx concentration. The controller 18 is configured to control the EGR valve 12 as much as possible.
[Selection] Figure 1

Description

  The present invention relates to an EGR device that reduces NOx by recirculating a part of exhaust gas to the intake side.

  2. Description of the Related Art Conventionally, in an automobile engine or the like, a part of exhaust gas is extracted from the exhaust side and returned to the intake side, and combustion of fuel in the engine is suppressed by the exhaust gas returned to the intake side so that the combustion temperature is increased. So-called exhaust gas recirculation (EGR) is performed in which the generation of NOx is reduced by lowering.

  In general, when this type of exhaust gas recirculation is performed, an EGR pipe is used between an appropriate position of the exhaust passage extending from the exhaust manifold to the exhaust pipe and an appropriate position of the intake passage extending from the intake pipe to the intake manifold. The exhaust gas is recirculated through the EGR pipe.

  In addition, if the exhaust gas recirculated to the engine is cooled in the middle of the EGR pipe, the exhaust gas temperature decreases and its volume decreases, which effectively reduces the combustion temperature without significantly reducing the engine output. Since the generation of nitrogen oxides can be reduced, a water-cooled EGR cooler is provided in the middle of an EGR pipe for recirculating exhaust gas to the engine.

  However, reducing NOx by exhaust gas recirculation is in a trade-off relationship with the occurrence of black smoke due to poor combustion in the cylinder, so the amount of exhaust gas recirculation is simply reduced. From the viewpoint of suppressing the generation of black smoke, it is necessary to appropriately control the EGR valve provided in the EGR pipe to limit the recirculation amount of the exhaust gas.

  The control of the EGR valve so far is performed by a control device equipped with a target air amount map, and the air amount detected by an airflow sensor with good response to load fluctuation (intake flow rate taken into the engine) However, the control is performed so that the target air amount is read from the target air amount map based on the fuel injection amount and the engine speed at the time of detection.

  As prior art document information related to this type of EGR apparatus, there is the following Patent Document 1 and the like.

JP 2006-9745 A

  However, in general, in the existing airflow sensor, a hot wire type in which a current is supplied so that the temperature of the wire exposed to the flow of intake air becomes constant and the amount of air is detected by reading the current value. (The more air the more the wire is cooled, the more current is required to maintain a constant temperature). However, in the detection of the air amount by such a hot wire type airflow sensor, the intake pipe Since the robustness with respect to the piping layout or the like is small, there is a large variation, and even if the EGR valve is controlled based on the detection value of the airflow sensor, it is difficult to suppress the NOx concentration as intended.

  In other words, the target air amount map of the control device indicates the amount of air that can most effectively suppress the NOx concentration within the range where black smoke is not generated while measuring NOx at the engine tuning stage as the fuel injection amount. It is created by investigating the relationship with the engine speed, but for example, if a flow of intake air different from the engine at the time of map creation is formed due to the accuracy of assembly of the intake pipe etc., it hits the wire in each operating condition Since the flow velocity changes, there is a possibility that the NOx concentration cannot be suppressed as intended even if the EGR valve is controlled so that the target air amount matches the target air amount map.

  Moreover, in the control based on the detection value of the air flow sensor, it is expected that the NOx concentration should be suppressed most effectively if the EGR valve is controlled so that the air amount actually measured by the air flow sensor becomes the target air amount. However, there is an aspect that it is difficult to control with high accuracy in that whether or not the NOx concentration is actually suppressed is not reflected in the control.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an EGR device capable of controlling the NOx concentration with higher accuracy than in the past.

The present invention includes an EGR pipe that extracts a part of exhaust gas from the exhaust side and recirculates it to the intake side, an EGR valve that is provided in the middle of the EGR pipe and adjusts the recirculation amount of the exhaust gas, and takes in the engine EGR provided with an airflow sensor that detects the amount of air that is generated, and a control device that controls the EGR valve to determine a target air amount according to the operating state and to use the air amount actually measured by the airflow sensor as the target air amount A device,
The airflow sensor includes a NOx sensor that detects the concentration of NOx contained in the exhaust gas discharged from the engine, and the airflow sensor only when the change amount per unit time of the fuel injection amount of the engine is maintained within an allowable range. The control based on the detected value of the NOx sensor is switched to the control based on the detected value of the NOx sensor, the target NOx concentration is determined according to the operating state, and the EGR valve is set so that the NOx concentration actually measured by the NOx sensor becomes the target NOx concentration. The control device is configured to control.

  Thus, in this way, when the amount of change in the fuel injection amount of the engine per unit time is maintained within an allowable range during constant speed driving on a highway, the load is almost constant. The control device detects that the load condition is stable and changes, and the control of the EGR valve in the control device is switched from the control based on the detection value of the airflow sensor to the control based on the detection value of the NOx sensor. The target NOx concentration is determined according to the operating state, the EGR valve is controlled so that the NOx concentration actually measured by the NOx sensor becomes the target NOx concentration, and the EGR valve is fed back while monitoring the NOx concentration itself in the exhaust gas. It becomes possible to control.

  However, while the NOx sensor has the advantage of being able to monitor the NOx concentration itself in the exhaust gas, the NOx concentration is detected as the result of the accelerator operation (load fluctuation) on the most downstream side, so the accelerator operation (load fluctuation) ) Is not suitable for controlling the EGR valve under an unstable load condition in which the engine load increases or decreases sharply, but under such an unstable load condition, The amount of change per unit time in the fuel injection amount of the engine deviates from the allowable range, and the control based on the detected value of the NOx sensor returns to the control based on the detected value of the airflow sensor, so the accelerator operation (load fluctuation) is most upstream. The air flow that fluctuates immediately in response to the air flow sensor is detected with good responsiveness, and the control of the EGR valve following the load fluctuation is performed. .

  Further, in the present invention, the target air amount that can read out the air amount that can most effectively suppress the NOx concentration without generating black smoke in the current operating state based on the fuel injection amount and the engine speed. A map, and a target NOx concentration map that can read out the lowest NOx concentration that can be realized without generating black smoke in the current operating state based on the fuel injection amount and the engine speed, and these target air amount map and The controller can be configured to determine the target air amount and the target NOx concentration using the target NOx concentration map.

  Furthermore, in the present invention, an intake air temperature sensor for detecting the temperature of intake air taken into the engine and an atmospheric pressure sensor for detecting atmospheric pressure are provided, and the target air is based on the detected values of the intake air temperature sensor and the atmospheric pressure sensor. Preferably, the control device is configured to correct the temperature and atmospheric pressure for the amount and the target NOx concentration.

  According to the EGR device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the first and second aspects of the present invention, the control of the EGR valve by the control device is performed when the stable load condition such as when driving at a constant speed on an expressway is achieved. Switching from control based on the detection value of the sensor to control based on the detection value of the NOx sensor, the EGR valve can be feedback controlled while monitoring the NOx concentration itself in the exhaust gas, so the airflow can be controlled under all conventional load conditions. The NOx concentration can be controlled with higher accuracy than when the control based on the detection value of the sensor is performed.

  (II) According to the invention described in claim 3 of the present invention, when the target air amount and the target NOx concentration are determined by the control device, the optimum target is considered in consideration of the temperature of the intake air taken into the engine and the atmospheric pressure. The amount of air and the target NOx concentration can be corrected, and the EGR valve can be controlled with higher accuracy.

It is the schematic which shows an example of the form which implements this invention. It is a graph explaining the example of control switching by the control apparatus of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes an engine that is a diesel engine. The engine 1 includes a turbocharger 2 and intake air guided from an air cleaner (not shown). 3 is sent to the compressor 2 a of the turbocharger 2 through the intake pipe 4, the intake air 3 pressurized by the compressor 2 a is sent to the intercooler 5 to be cooled, and the intake air 3 is further supplied from the intercooler 5 to the intake manifold 6. It is guided and distributed to each cylinder 7 of the engine 1.

  The exhaust gas 8 discharged from each cylinder 7 of the engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 9, and the exhaust gas 8 driving the turbine 2b is discharged out of the vehicle through the exhaust pipe 10. I have to do it.

  An end portion of the exhaust manifold 9 in the arrangement direction of the cylinders 7 and one end portion of the intake pipe 4 connected to the intake manifold 6 are connected by an EGR pipe 11. A part of 8 can be extracted and recirculated to the intake pipe 4.

  Here, in the middle of the EGR pipe 11, an EGR valve 12 for adjusting the recirculation amount of the exhaust gas 8 and an EGR cooler 13 for cooling the recirculated exhaust gas 8 are provided. In the EGR cooler 13, the temperature of the exhaust gas 8 can be decreased by exchanging heat between the cooling water (not shown) and the exhaust gas 8.

  Further, upstream of the compressor 2 a of the intake pipe 4, an airflow sensor 14 for detecting the amount of air taken into the engine 1 (the flow rate of the intake air 3 taken into the engine 1) and the temperature of the intake air 3 taken into the engine 1 are detected. An intake air temperature sensor 15 is provided, and an atmospheric pressure sensor 16 for detecting atmospheric pressure is provided at an appropriate place where the influence of traveling wind is small. An exhaust gas 8 is provided downstream of the turbine 2b of the exhaust pipe 10. The NOx sensor 17 for detecting the NOx concentration in the engine is equipped. The airflow sensor 14, the intake air temperature sensor 15, the atmospheric pressure sensor 16, and the detection signals 14a, 15a, 16a, 17a from the NOx sensor 17 are engine control computers It is input to a control device 18 constituting an ECU (Electronic Control Unit).

  However, here, for convenience of explanation, the airflow sensor 14 and the intake air temperature sensor 15 are described separately, but actually, the temperature of the intake air 3 is used when determining the flow rate of the intake air 3 (fresh air). Since temperature correction is applied to the detected flow rate, the intake air temperature sensor 15 is usually built in the airflow sensor 14.

  Further, the NOx sensor 17 may be newly installed for controlling the EGR valve 12, but the selective reduction having the property of selectively reacting NOx with the reducing agent on the downstream side of the exhaust pipe 10 even in the presence of oxygen. When a type catalyst (not shown) and a reducing agent addition device for adding a necessary amount of reducing agent to the upstream side of the selective catalytic reduction catalyst are equipped, the addition amount of the reducing agent is determined. Since the NOx sensor 17 is already installed, the detection signal 17a of the NOx sensor 17 may be used for the control of the EGR valve 12.

  In the control device 18, the target air amount is determined according to the operating state, and the EGR valve 12 is controlled by the control signal 12a so that the air amount actually measured by the airflow sensor 14 becomes the target air amount. However, only when the amount of change in the fuel injection amount of the engine 1 per unit time is maintained within an allowable range, the detected value of the NOx sensor 17 is controlled based on the control based on the detected value of the airflow sensor 14. The EGR valve 12 is controlled so that the target NOx concentration is determined according to the operating state, and the NOx concentration actually measured by the NOx sensor 17 is set to the target NOx concentration.

  Further, when the control device 18 determines the target air amount and the target NOx concentration, the control device 18 is most likely to generate black smoke in the current operating state based on the fuel injection amount and the engine speed. Based on the target air amount map that can read out the air amount that can effectively suppress the NOx concentration, the fuel injection amount, and the engine speed, the lowest that can be achieved without generating black smoke in the current operating state A target NOx concentration map from which the NOx concentration can be read out is provided, and the target air amount and the target NOx concentration are determined using these target air amount map and target NOx concentration map.

  Here, in the target air amount map, the amount of air that can most effectively suppress the NOx concentration within the range in which black smoke is not generated while measuring NOx at the tuning stage of the engine 1 is the fuel injection amount and the engine. The target NOx concentration map was created by investigating the relationship between the engine speed and the fuel injection with the lowest NOx concentration that can be achieved within the range where black smoke is not generated while measuring NOx at the tuning stage of the engine 1. It was created by investigating the relationship between quantity and engine speed.

  Note that the control device 18 is also responsible for fuel injection control of the engine 1, and information on an accelerator opening and an engine speed (not shown) is inputted as a signal, and an instruction value for the fuel injection amount is determined by these information. Therefore, the information of the fuel injection amount and the engine speed is updated and grasped every moment in the control device 18, and the target is based on the information of the fuel injection amount and the engine speed. The target air amount and the target NOx concentration are read from the air amount map and the target NOx concentration map.

  At this time, the target air amount and the target NOx concentration read from the target air amount map and the target NOx concentration map are based on the temperature and the atmospheric pressure of the intake air 3 detected by the intake air temperature sensor 15 and the atmospheric pressure sensor 16. More specifically, correction is applied. More specifically, a correction coefficient is determined based on the actually measured temperature and atmospheric pressure, and the map value is multiplied.

  Thus, in this way, when the amount of change in the fuel injection amount of the engine 1 per unit time is maintained within an allowable range during constant speed driving on a highway, the load is almost constant. It is detected by the control device 18 that the load condition is stable, and the control of the EGR valve 12 in the control device 18 is detected by the NOx sensor 17 from the control based on the detection value of the airflow sensor 14. The control is switched to the control based on the value, the target NOx concentration is determined according to the operating state, the EGR valve 12 is controlled so that the NOx concentration actually measured by the NOx sensor 17 becomes the target NOx concentration, and the NOx concentration in the exhaust gas 8 is controlled. The EGR valve 12 can be feedback controlled while monitoring itself.

  However, the NOx sensor 17 has an advantage that the NOx concentration itself in the exhaust gas 8 can be monitored. However, since the NOx concentration is detected as a result of the accelerator operation (load fluctuation) on the most downstream side, the accelerator operation ( However, it is not suitable for controlling the EGR valve 12 under an unstable load condition in which the load of the engine 1 increases or decreases sharply. Then, the change amount per unit time of the fuel injection amount of the engine 1 is out of the allowable range, and the control based on the detection value of the airflow sensor 14 is returned from the control based on the detection value of the NOx sensor 17. The EGR valve 1 that detects the air amount that fluctuates immediately in response to the accelerator operation (load variation) by the air flow sensor 14 with good responsiveness and follows the load variation. 2 control will be implemented.

  For example, FIG. 2 shows an example of control switching by the control device 18. The time zone of an unstable load condition in which the change amount ΔQ per unit time Δt of the fuel injection amount of the engine 1 deviates from the allowable range. In A and C, the control based on the detection value of the airflow sensor 14 is performed, and the stable load condition is such that the change amount ΔQ per unit time Δt of the fuel injection amount of the engine 1 is maintained within the allowable range. In the time zone B, control based on the detected value of the NOx sensor 17 is performed.

  Therefore, according to the above embodiment, the control of the EGR valve 12 by the control device 18 is performed based on the detection value of the airflow sensor 14 when a stable load condition such as when driving at a constant speed on an expressway is met. Since the EGR valve 12 can be feedback-controlled while monitoring the NOx concentration itself in the exhaust gas 8 by switching to the control based on the detected value of the NOx sensor 17, the detection of the airflow sensor 14 under all load conditions as in the prior art. The NOx concentration can be controlled with higher accuracy than in the case of performing control based on the value.

  Further, in this embodiment, when the control device 18 determines the target air amount and the target NOx concentration, the optimum target air amount and the target NOx concentration in consideration of the temperature of the intake air 3 taken into the engine 1 and the atmospheric pressure. Therefore, the EGR valve 12 can be controlled with higher accuracy.

  It should be noted that the EGR apparatus of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Engine 3 Intake 8 Exhaust gas 11 EGR pipe 12 EGR valve 12a Control signal 14 Airflow sensor 14a Detection signal 15 Intake temperature sensor 15a Detection signal 16 Atmospheric pressure sensor 16a Detection signal 17 NOx sensor 17a Detection signal 18 Control device

Claims (3)

An EGR pipe that extracts a part of the exhaust gas from the exhaust side and recirculates it to the intake side, an EGR valve that is provided in the middle of the EGR pipe and adjusts the recirculation amount of the exhaust gas, and the amount of air taken into the engine An EGR device comprising: an airflow sensor to detect; and a control device for determining a target air amount according to an operating state and controlling the EGR valve so that an air amount actually measured by the airflow sensor is the target air amount. ,
The airflow sensor includes a NOx sensor that detects the concentration of NOx contained in the exhaust gas discharged from the engine, and the airflow sensor only when the change amount per unit time of the fuel injection amount of the engine is maintained within an allowable range. The control based on the detected value of the NOx sensor is switched to the control based on the detected value of the NOx sensor, the target NOx concentration is determined according to the operating state, and the EGR valve is set so that the NOx concentration actually measured by the NOx sensor becomes the target NOx concentration. An EGR device characterized in that the control device is configured to control.   A target air amount map that can read out an air amount that can most effectively suppress the NOx concentration without generating black smoke in the current operating state based on the fuel injection amount and the engine speed, and a fuel injection amount A target NOx concentration map that can read out the lowest NOx concentration that can be realized without generating black smoke in the current operating state based on the engine speed, and using these target air amount map and target NOx concentration map The EGR device according to claim 1, wherein the control device is configured to determine a target air amount and a target NOx concentration.   Equipped with an intake air temperature sensor that detects the temperature of intake air taken into the engine and an atmospheric pressure sensor that detects atmospheric pressure. Based on the detection values of these intake air temperature sensor and atmospheric pressure sensor, The EGR device according to claim 1 or 2, wherein the control device is configured to correct the temperature and the atmospheric pressure.

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