JP2011106313A - Exhaust emission control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit deposition of a reducing agent component in an engine exhaust pipe. <P>SOLUTION: Temperature of exhaust gas flowing into an SCR catalyst, engine speed and load are acquired respectively (S1, S2), and addition flow rate of liquid reducing agent or precursor thereof injected and supplied from an injection nozzle to an exhaust gas upstream side of the SCR catalyst according to an engine operation state is calculated (S3). Temperature of a wall surface of an exhaust pipe positioned between the injection nozzle and the SCR catalyst is acquired (S4), and addition flow rate of the liquid reducing agent and the precursor thereof is reduced and compensated if the temperature of the wall surface is less than prescribed temperature (S5, S6). Flow rate of the liquid reducing agent or the precursor thereof injected and supplied from the injection nozzle is controlled base on the calculated or compensated flow rate of the liquid reducing agent or the precursor thereof (S7). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust purification device that selectively reduces and purifies NOx (nitrogen oxides) contained in engine exhaust.

  As a catalyst purification system for purifying NOx contained in engine exhaust, an exhaust purification device as described in JP 2009-127472 A (Patent Document 1) has been proposed. This exhaust purification device injects and supplies a liquid reducing agent or a precursor thereof at a flow rate according to the engine operating state upstream of the exhaust of an SCR (Selective Catalytic Reduction) catalyst disposed in an engine exhaust pipe, and NOx is supplied by the SCR catalyst. By performing a selective reduction reaction, NOx is purified to harmless components.

  By the way, in such an exhaust purification device, when the liquid reducing agent or its precursor injected and supplied upstream of the exhaust of the SCR catalyst adheres to the inner wall of the engine exhaust pipe, only the solvent evaporates depending on the engine operating state. There is a possibility that the solute as the reducing agent component is deposited. For this reason, when the exhaust temperature is lower than the predetermined temperature, the injection supply of the liquid reducing agent or its precursor is stopped to suppress the deposition of the reducing agent component in the engine exhaust pipe.

JP 2009-127472 A

  However, since the wall surface temperature of the engine exhaust pipe decreases due to the outside air temperature, the attachment of a liquid reducing agent or its precursor, etc., even if the exhaust temperature is higher than a predetermined temperature, the reducing agent component is deposited on the engine exhaust pipe. There was a risk of it happening.

  Therefore, in view of the problems of the prior art, the present invention reduces or stops the injection supply of the liquid reducing agent or its precursor when the wall surface temperature of the engine exhaust pipe is lower than a predetermined temperature, regardless of the level of the exhaust temperature. Thus, it is an object of the present invention to provide an engine exhaust purification device that suppresses precipitation of a reducing agent component on an engine exhaust pipe.

  For this reason, an exhaust emission control device for an engine according to the present invention includes an SCR catalyst that selectively reduces and purifies NOx using a reducing agent, an injection device that injects and supplies a liquid reducing agent or a precursor thereof upstream of the exhaust, and an engine A calculating means for calculating the flow rate of the liquid reducing agent or its precursor according to the operating state, a temperature detecting means for detecting the wall surface temperature of the engine exhaust pipe located between the injector and the SCR catalyst, and a temperature detecting means. Based on the correction means for correcting the flow rate calculated by the calculation means and the flow rate calculated by the calculation means or the flow rate corrected by the correction means when the detected wall surface temperature is lower than the predetermined temperature And a control means for controlling the flow rate of the liquid reducing agent or the precursor thereof injected and supplied from the control unit.

  According to the present invention, the flow rate of the liquid reducing agent or the precursor thereof according to the engine operating state is calculated, and the wall surface temperature of the engine exhaust pipe positioned between the injector and the SCR catalyst is less than a predetermined temperature. Sometimes, the flow rate of the liquid reducing agent or its precursor according to the engine operating state is corrected. Then, based on the flow rate according to the engine operating state or the flow rate corrected because the wall surface temperature is lower than the predetermined temperature, the flow rate of the liquid reducing agent or its precursor supplied from the injection device is controlled. . For this reason, when the wall surface temperature is lower than the predetermined temperature, the absolute amount of the liquid reducing agent or its precursor adhering to the inner wall of the engine exhaust pipe is reduced by appropriately correcting the flow rate of the liquid reducing agent or its precursor. The precipitation of the reducing agent component in the engine exhaust pipe can be suppressed.

Schematic showing an example of an exhaust emission control device embodying the present invention Flow chart showing an example of a control program Explanatory diagram of a preferred wall temperature sensor

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an embodiment of an exhaust emission control device embodying the present invention.
The intake pipe 14 connected to the intake manifold 12 of the diesel engine 10 is heated by the air cleaner 16 that removes dust in the air, the compressor 18A of the turbocharger 18 and the turbocharger 18 along the intake air circulation direction. An intercooler 20 for cooling the intake air and an intake collector 22 for smoothing the intake pulsation are arranged in this order.

On the other hand, the exhaust pipe 26 connected to the exhaust manifold 24 of the diesel engine 10 has a turbine 18B of the turbocharger 18, a continuously regenerating DFP (Diesel Particulate Filter) device 28, and a reducing agent precursor along the exhaust circulation direction. An injection nozzle 30 for supplying and supplying the urea aqueous solution, an SCR catalyst 32 for selectively reducing and purifying NOx using ammonia generated from the urea aqueous solution, and an oxidation catalyst 34 for oxidizing the ammonia that has passed through the SCR catalyst 32 are arranged in this order. Established. The continuous regeneration type DPF device 28 includes a DOC (Diesel Oxidation Catalyst) 28A that oxidizes at least NO (nitrogen monoxide) into NO ₂ (nitrogen dioxide), and a DPF 28B that collects and removes PM (Particulate Matter) in the exhaust gas. , Including. Instead of DPF 28B, a CSF (Catalyzed Soot Filter) having a catalyst (active component and additive component) supported on the surface thereof may be used. Here, the injection nozzle 30 is mentioned as an example of an injection device.

  The aqueous urea solution stored in the reducing agent tank 36 is supplied to the injection nozzle 30 via a reducing agent addition unit 38 having a built-in pump and flow control valve. Here, the reducing agent addition unit 38 may have a structure divided into two, that is, a pump module with a built-in pump and a dosing module with a built-in flow control valve. The injection nozzle 30 may be integrated with the reducing agent addition unit 38.

  As a control system of the exhaust purification device, an exhaust temperature sensor 40 that detects an exhaust temperature as an example of an engine operating state is attached to the exhaust pipe 26 positioned between the continuous regeneration type DPF device 28 and the injection nozzle 30. A wall surface temperature sensor 42 (temperature detection means) for detecting the wall surface temperature of the exhaust pipe 26 is attached to the exhaust pipe 26 located between the injection nozzle 30 and the SCR catalyst 32. Here, in order to reliably detect that the wall surface temperature has decreased due to the adhesion of the urea aqueous solution, the wall surface temperature sensor 42 can detect the wall surface temperature of the portion to which the urea aqueous solution supplied from the injection nozzle 30 is likely to adhere. desirable.

  The output signals of the exhaust temperature sensor 40 and the wall surface temperature sensor 42 are input to a reducing agent addition control unit (DCU) 44 incorporating a computer. Further, the reducing agent addition control unit 44 electronically controls the diesel engine 10 via an in-vehicle network such as a CAN (Controller Area Network) so that the rotation speed and load as an example of the engine operating state can be appropriately read. An engine control unit (ECU) 46 is connected. The reducing agent addition control unit 44 executes a control program stored in a ROM (Read Only Memory) or the like, thereby electronically controlling the reducing agent addition unit 38 in accordance with the exhaust temperature, the wall surface temperature, the rotation speed, and the load. To do.

  Here, as the load of the diesel engine 10, for example, a state quantity closely related to the torque, such as a fuel injection flow rate, an intake air flow rate, an intake pressure, a supercharging pressure, an accelerator opening degree, and a throttle opening degree, can be applied. . The rotational speed and load of the diesel engine 10 are not limited to the configuration read from the engine control unit 46, and may be directly detected by a known sensor.

  The reducing agent addition control unit 44 embodies calculation means and correction means by executing a control program. Further, the reducing agent addition control unit 44 and the reducing agent addition unit 38 cooperate to implement a control means.

FIG. 2 shows the contents of a control program that the reducing agent addition control unit 44 repeatedly executes every predetermined time when the diesel engine 10 is started.
In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the exhaust temperature is read from the exhaust temperature sensor 40.

In step 2, the rotational speed and load of the diesel engine 10 are read from the engine control unit 46.
In step 3, the reducing agent addition flow rate is calculated according to the exhaust temperature, the rotational speed, and the load as the engine operating state. That is, the NOx emission amount corresponding to the engine operating state is estimated, and the addition flow rate of the urea aqueous solution required to selectively reduce and purify this NOx is calculated.

In step 4, the wall surface temperature is read from the wall surface temperature sensor 42.
In step 5, it is determined whether the wall surface temperature is lower than a predetermined temperature. Here, the predetermined temperature is a threshold value for determining whether or not there is a possibility that only the solvent evaporates and the reducing agent component is deposited when the urea aqueous solution adheres to the inner wall of the exhaust pipe 26. The temperature is slightly higher than the melting point of urea (about 135 ° C.). If the wall surface temperature is lower than the predetermined temperature, the process proceeds to step 6 (Yes), and correction for reducing the reducing agent addition flow rate calculated in step 3 by a predetermined flow rate is performed. On the other hand, if the wall surface temperature is equal to or higher than the predetermined temperature, the process proceeds to Step 7 (No).

In step 7, a control signal corresponding to the reducing agent addition flow rate is output to the reducing agent addition unit 44, whereby the urea aqueous solution is injected and supplied (added) upstream of the exhaust of the SCR catalyst 32.
In such an exhaust purification device, the exhaust from the diesel engine 10 is introduced into the DOC 28A of the continuous regeneration type DPF device 28 via the exhaust manifold 24 and the turbine 18B of the turbocharger 18. Exhaust introduced into DOC28A flows to DPF28B being oxidized NO is to NO _2. In the DPF 28B, PM in the exhaust gas is collected and the PM is oxidized using NO ₂ generated by the DOC 28A.

Further, the urea aqueous solution injected and supplied from the injection nozzle 30 in accordance with the engine operating state is hydrolyzed using exhaust heat and water vapor in the exhaust, and converted into ammonia that functions as a reducing agent. It has been known that this ammonia is selectively reduced with NOx in the exhaust gas in the SCR catalyst 32 and is purified to H ₂ O (water) and N ₂ (nitrogen), which are harmless components. On the other hand, the ammonia that has passed through the SCR catalyst 32 is oxidized by the oxidation catalyst 34 disposed downstream of the exhaust gas, so that it is possible to suppress the ammonia from being released into the atmosphere as it is.

  At this time, when the wall surface temperature of the exhaust pipe 26 is lower than a predetermined temperature, the reducing agent addition flow rate corresponding to the engine operating state is corrected to decrease, so that the absolute amount of urea aqueous solution adhering to the inner wall of the exhaust pipe 26 decreases. It becomes. For this reason, precipitation of the reducing agent component (urea) in the exhaust pipe 26 can be suppressed.

  Here, instead of correcting the decrease in the reducing agent addition flow rate, the reducing agent addition flow rate may be set to 0 so that the injection supply of the urea aqueous solution is stopped. In this way, when the wall surface temperature of the exhaust pipe 26 is lower than the predetermined temperature, the urea aqueous solution is not injected and supplied from the injection nozzle 30, so that the precipitation of the reducing agent component on the exhaust pipe 26 can be effectively suppressed. it can. Even if the urea aqueous solution injection supply is temporarily stopped, the ammonia is adsorbed on the SCR catalyst 32, and therefore the NOx purification is less affected.

  By the way, it is assumed that the attachment position of the urea aqueous solution to the exhaust pipe 26 changes due to an increase or decrease in the exhaust flow rate. For this reason, as shown in FIG. 3, the wall surface temperature sensor 42 detects the wall surface temperature that has become the lowest among a plurality of locations of the exhaust pipe 26 located between the injection nozzle 30 and the SCR catalyst 32. May be. In this way, even if the urea aqueous solution adheres and the wall surface temperature partially decreases, injection supply control of the urea aqueous solution is performed based on the wall surface temperature, so that precipitation of the reducing agent component on the exhaust pipe 26 is suppressed. Can be effective. The wall surface temperature sensor 42 is not limited to one that detects wall surface temperatures at four locations.

  In the embodiment described above, the urea aqueous solution is injected and supplied from the injection nozzle 30. However, the reducing agent addition unit 38 may directly supply the urea aqueous solution without using the injection nozzle 30. Good. In this case, the reducing agent addition unit 38 is an example of an injection device.

  The present invention can be applied not only to an exhaust gas purification device using an aqueous urea solution, but also to an exhaust gas purification device using alcohol, gasoline, light oil, or the like mainly containing hydrocarbons as a liquid reducing agent or a precursor thereof. . Further, the present invention can be applied not only to the diesel engine 10 but also to a gasoline engine or the like.

DESCRIPTION OF SYMBOLS 10 Diesel engine 26 Exhaust pipe 30 Injection nozzle 32 SCR catalyst 38 Reductant addition unit 40 Exhaust temperature sensor 42 Wall surface temperature sensor 44 Reductant addition control unit 46 Engine control unit

Claims (4)

An SCR catalyst that selectively reduces and purifies nitrogen oxides using a reducing agent;
An injection device for injecting and supplying a liquid reducing agent or a precursor thereof upstream of the SCR catalyst exhaust;
Calculating means for calculating the flow rate of the liquid reducing agent or its precursor according to the engine operating state;
Temperature detecting means for detecting a wall surface temperature of an engine exhaust pipe located between the injector and the SCR catalyst;
Correction means for correcting the flow rate calculated by the calculation means when the wall surface temperature detected by the temperature detection means is less than a predetermined temperature;
Control means for controlling the flow rate of the liquid reducing agent or its precursor supplied from the injection device based on the flow rate calculated by the calculation means or the flow rate corrected by the correction means;
An exhaust emission control device for an engine characterized by comprising:   2. The exhaust emission control device for an engine according to claim 1, wherein the correction means reduces or reduces the flow rate calculated by the calculation means.   The temperature detection means detects a wall surface temperature of a portion of the engine exhaust pipe positioned between the injection device and the SCR catalyst, to which the liquid reducing agent injected from the injection device or a precursor thereof easily adheres. The engine exhaust gas purification device according to claim 1 or 2, wherein the engine exhaust gas purification device is provided.   The said temperature detection means detects the wall surface temperature used as the minimum temperature among the several places of the engine exhaust pipe located between the said injection device and the said SCR catalyst, The Claim 1 or Claim 2 characterized by the above-mentioned. An exhaust emission control device for an engine according to 1.

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