JP5310166B2 - Engine exhaust purification system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit heat damage to a urea water injection valve by a simpler structure. <P>SOLUTION: This exhaust emission control device for an engine includes an injection valve control means 51 controlling an injection quantity of urea water from the urea water injection valve 25, a temperature decision means 53 deciding whether the urea water injection valve 25 is in a high temperature state where a heat damage countermeasure is necessary or not based on a temperature (Tn) detected by being correlated with the urea water injection valve 25, and a target injection quantity calculation means 52 calculating a first target injection quantity Q1 necessary for reducing NOx at an NOx elimination catalyst 23 with an injection quantity from the urea water injection valve 25 set as a target value and calculating a second target injection quantity Q2 purposing the inhibition of heat damage to the urea water injection valve 25. When the urea water injection valve 25 is in a high temperature state, the injection valve control means 51 injects the urea water of a larger injection quantity out of the first and second target injection quantities Q1, Q2 from the urea water injection valve (SB10 or SB13). <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a selective reduction type NOx purification catalyst provided on an exhaust passage of an engine, a urea water injection valve for injecting urea water into an exhaust passage upstream of the NOx purification catalyst, and the urea water injection The present invention relates to an engine exhaust purification device including an injection valve control means for controlling an injection amount of urea water from a valve.

  Conventionally, for example, as shown in Patent Document 1 below, a selective reduction catalyst provided on an exhaust passage of an engine and urea water as a reducing agent is injected into an exhaust passage upstream of the selective reduction catalyst. And a urea water injection valve that promotes the reduction reaction of nitrogen oxides (NOx) in the selective catalytic reduction catalyst by the action of urea water injected from the urea water injection valve into the exhaust passage. Exhaust treatment devices are known.

JP 2007-321647 A

  As the urea water injection valve, an electromagnetically driven valve (electromagnetic valve) is generally used as described in Patent Document 1. However, when such an electromagnetic valve is used as a urea water injection valve, there is a concern about the occurrence of heat damage. That is, it is assumed that the urea water injection valve provided in the exhaust passage through which the high-temperature exhaust gas passes has a considerably high temperature. However, a solenoid (an electromagnetic coil, a magnetic circuit, or the like provided in the urea water injection valve) is provided. The heat-resistant temperature of the mechanism) is considerably lower than the temperature of exhaust gas, which is about 500 ° C. at the maximum, so that the operability of the urea water injection valve may be deteriorated due to excessive rise in the temperature of the solenoid.

  As a measure for preventing the occurrence of such heat damage, in Patent Document 1, a cooling chamber surrounding the urea water injection valve is formed in the injection valve holder that holds the urea water injection valve. By cooling the cooling medium in the cooling chamber, the urea water injection valve is cooled. However, in this case, the structure of the injection valve holder becomes complicated, and a new system for circulating the cooling medium in the cooling chamber inside the injection valve holder is required, and an increase in the number of parts is inevitable. There is a problem.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine exhaust purification device capable of suppressing thermal damage of a urea water injection valve with a simpler configuration. .

In order to solve the above problems, the present invention injects urea water into a selective reduction type NOx purification catalyst provided on an exhaust passage of an engine and an exhaust passage upstream of the NOx purification catalyst. An exhaust emission control device for an engine comprising a urea water injection valve and an injection valve control means for controlling an injection amount of urea water from the urea water injection valve, which is detected in association with the urea water injection valve Based on a predetermined temperature, temperature determining means for determining whether or not the urea water injection valve is in a high temperature state that requires countermeasures against heat damage, and the NOx purification as a target value of the injection amount from the urea water injection valve A target injection amount calculating means for calculating a first target injection amount necessary for reducing NOx by the catalyst and calculating a second target injection amount for the purpose of suppressing thermal damage of the urea water injection valve; and an engine Discharged from the combustion chamber and a NOx concentration adjusting means for adjusting the x concentration, when the urea water injection valve is confirmed to be in a high temperature state by said temperature determination means as the predetermined temperature is higher, is the target injection amount calculating means The second target injection amount is calculated as a large value, and the injection valve control means injects urea water from the urea water injection valve at a larger injection amount of the first and second target injection amounts. When the temperature determination unit confirms that the urea water injection valve is in a high temperature state and the second target injection amount calculated by the target injection amount calculation unit is larger than the first target injection amount, The NOx concentration is adjusted to be higher by the NOx concentration adjusting means (claim 1).

  According to the present invention, when the urea water injection valve is in a high temperature state, a relatively large amount of urea water is injected from the urea water injection valve at the second target injection amount for the purpose of suppressing thermal damage. It is possible to sufficiently cool the urea water injection valve by injecting urea water and cooling it, and it is possible to effectively prevent the operability of the urea water injection valve from being deteriorated due to heat damage. Also, depending on the engine operating condition, it is assumed that the first target injection amount originally required for reducing NOx is calculated to be larger than the second target injection amount for heat damage countermeasures. However, even in such a case, according to the above configuration, since the larger one of the first and second target injection amounts is adopted, it is always possible regardless of the operating state of the engine or the like. A large amount of injection from the urea water injection valve is ensured, and the urea water injection valve can be sufficiently cooled by the injection. In addition, according to the above-described configuration in which the cooling amount is controlled by controlling the injection amount from the urea water injection valve, it is not necessary to provide a dedicated cooling system or the like for cooling the urea water injection valve. There is an advantage that heat damage of the urea water injection valve can be suppressed with a simple configuration.

Further, in the present invention, when the urea water injection valve is in a high temperature state, the second target injection amount is calculated as a larger value as the predetermined temperature is higher, so the temperature of the urea water injection valve is higher and measures against heat damage. By injecting a larger amount of urea water as the required level is higher, there is an advantage that the heat damage of the urea water injection valve can be surely suppressed by exerting an appropriate cooling action according to the required level.

Further, in the present invention, when the urea water injection valve is in a high temperature state and the second target injection amount is larger than the first target injection amount, the NOx concentration is adjusted to be higher by the NOx concentration adjusting means. Even when a relatively large amount of urea water is injected into the exhaust passage based on the second target injection amount for harm prevention, the NOx concentration in the exhaust gas is increased in accordance with this, so that it is not used for the reduction reaction. There is an advantage that the amount of ammonia discharged to the outside can be effectively suppressed.

In the present invention, it is preferable that the temperature determination unit confirms that the urea water injection valve is in a high temperature state, and the second target injection amount calculated by the target injection amount calculation unit is greater than the first target injection amount. Is larger, the greater the difference between the two target injection amounts, the greater the increase in the NOx concentration by the NOx adjusting means ( Claim 2 ).

  According to this configuration, the NOx concentration can be increased as the amount of urea water injected excessively for countermeasures against heat damage increases, and sufficient cooling of the urea water injection valve is achieved by a large amount of urea water injection. There is an advantage that the amount of ammonia discharged to the outside can be effectively suppressed.

When the EGR control means for controlling the amount of exhaust gas recirculated to the engine intake system is provided as the NOx concentration adjusting means, when the NOx concentration is adjusted to be higher, the EGR control means returns the exhaust gas. The flow rate is preferably reduced ( claim 3 ).

  According to this configuration, there is an advantage that the NOx concentration can be appropriately increased when necessary by increasing the peak temperature of combustion in accordance with the reduction in the recirculation amount of the exhaust gas.

In the case where the NOx concentration adjusting means includes an injector control means for controlling the injection timing of fuel injected from the injector into the combustion chamber of the engine, when the NOx concentration is adjusted to be high, the injector control means the injection timing is changed in the direction to promote the generation of NOx it is preferable (claim 4).

  According to this configuration, there is an advantage that the NOx concentration can be appropriately increased when necessary by promoting the generation of NOx according to the change of the fuel injection timing.

  As described above, according to the engine exhaust gas purification apparatus of the present invention, there is an advantage that the heat damage of the urea water injection valve can be suppressed with a simpler configuration.

1 is a diagram illustrating an overall configuration of an engine to which an engine exhaust gas purification apparatus according to an embodiment of the present invention is applied. It is a block diagram which shows the control system of the said engine. It is a figure which shows the example of a setting of the EGR rate according to the driving | running state of an engine. It is a flowchart which shows the content of the control regarding filter reproduction | regeneration processing. It is a flowchart which shows the content of the control regarding injection of urea water. It is a graph which shows the relationship between the temperature of a NOx purification catalyst, and the 2nd target injection quantity. It is a graph which shows the relationship between the difference of the 1st, 2nd target injection quantity, and the increase width of NOx concentration.

  FIG. 1 is a diagram showing an overall configuration of an engine to which an engine exhaust gas purification apparatus according to an embodiment of the present invention is applied. The engine shown in this figure includes an engine body 1 including a piston 2 and a cylinder 3, an intake passage 11 for supplying combustion air (fresh air) to the engine body 1, and exhaust from the engine body 1. And an exhaust passage 20 serving as a passage for the exhaust gas.

  The engine body 1 directly injects fuel into the piston 2 and the cylinder 3, as well as a crankshaft 5 that rotates about the axis according to the reciprocating motion of the piston 2, and a combustion chamber 4 formed above the piston 2. And an injector 10. An intake port 6 and an exhaust port 7 are opened in the combustion chamber 4, and an intake valve 8 and an exhaust valve 9 for opening and closing these ports are provided in the upper part of the engine body 1.

  The intake passage 11 and the exhaust passage 20 are connected to the intake port 6 and the exhaust port 7 of the engine body 1, respectively. When the engine body 1 is started, air is taken into the combustion chamber 4 through the intake passage 11, and the taken-in air (intake air) is mixed with fuel injected from the injector 10 to generate an air-fuel mixture. . The generated air-fuel mixture burns in the combustion chamber 4 and the burned gas (exhaust gas) is discharged to the outside through the exhaust passage 20.

  The injector 10 incorporates a needle valve, a solenoid for electromagnetically opening and closing the valve, and the like. When a pulse signal from the ECU 50 described later is input to the solenoid, the needle valve is driven to open for a time corresponding to the pulse width, and an amount of fuel corresponding to the valve opening time is injected from the needle valve. It has become so. In addition, the engine of this embodiment shall be a diesel engine. For this reason, light oil is injected from the injector 10 as fuel.

  Further, the engine body 1 is provided with a water temperature sensor 38 that detects the temperature of the cooling water of the engine and an engine rotation speed sensor 39 that detects the rotation speed of the crankshaft 5.

  Next, the intake system of the engine including the intake passage 11 will be described. From the upstream side (opposite side to the engine body 1) to the intake passage 11, the air cleaner 12 that removes foreign matters and dust in the intake air, and the intake air that has been compressed and heated by a supercharger 19 described later. An intercooler 13 for cooling, a throttle valve 14 for adjusting the intake flow rate, and a surge tank 15 for pressure regulation are provided.

  An air flow sensor 35 for detecting the intake air flow rate is provided on the downstream side of the air cleaner 12. The surge tank 15 is provided with an intake air temperature sensor 36 for detecting the intake air temperature and an intake pressure sensor 37 for detecting the intake air pressure.

  Between the air cleaner 12 and the intercooler 13, a compressor 19 a as one component of the supercharger 19 is provided. In addition, the supercharger 19 of this embodiment is what is called a turbocharger which supercharges using the energy of exhaust gas. That is, a turbine 19b that is rotationally driven by the energy of exhaust gas is provided in the exhaust passage 20, and the turbine 19b and the compressor 19a are connected to each other via a connecting shaft, whereby the supercharger 19 is configured. ing. During operation of the engine, the compressor 19a rotates at a high speed in conjunction with the turbine 19b, whereby the intake air is compressed and a larger amount of air is sent to the engine body 1.

  The throttle valve 14 is linked to an unillustrated accelerator pedal that is depressed by the driver, and the throttle valve 14 is driven to open and close in accordance with the operation amount (opening) of the accelerator pedal. Yes. The accelerator pedal is provided with an accelerator opening sensor 45 (FIG. 2) for detecting the opening thereof.

  Next, the exhaust system of the engine including the exhaust passage 20 will be described. The exhaust passage 20 is provided with an oxidation catalyst 21, a particulate filter 22 (hereinafter abbreviated as DPF 22), and a NOx purification catalyst 23 in that order from the upstream side (engine body 1 side). The functions and structures of these catalysts and filters will be described in detail later.

  A first temperature sensor 40 that detects the temperature of the oxidation catalyst 21 by detecting the temperature of the exhaust gas flowing into the oxidation catalyst 21 is provided on the upstream side of the oxidation catalyst 21. Similarly, a second temperature sensor 41 for detecting the temperature of the DPF 22 is provided on the upstream side of the DPF 22, and a third temperature sensor for detecting the temperature of the NOx purification catalyst 23 on the upstream side of the NOx purification catalyst 23. 42 is provided.

  The exhaust passage 20 is provided with a narrow tube 46 that communicates the upstream side and the downstream side of the DPF 22, and a differential pressure sensor 43 that detects the differential pressure before and after the DPF 22 is provided in the narrow tube 46.

  Further, on the downstream side of the NOx purification catalyst 23, a NOx concentration sensor that detects the NOx concentration in the exhaust gas after passing through the NOx purification catalyst 23, that is, the NOx concentration after NOx is reduced by the NOx purification catalyst 23. 44 is provided.

  Here, an exhaust gas recirculation system is employed in the engine of the present embodiment. For this reason, the intake passage 11 and the exhaust passage 20 communicate with each other via the EGR passage 16. That is, one end portion of the EGR passage 16 is connected to the upstream side of the turbine 19b in the exhaust passage 20 and the other end portion of the EGR passage 16 is connected to the installation portion of the surge tank 15 in the intake passage 11. The intake passage 11 and the exhaust passage 20 communicate with each other.

  The EGR passage 16 is provided with an EGR valve 17, and when the EGR valve 17 is opened, a part of the exhaust gas passing through the exhaust passage 20 is recirculated to the intake passage 11. Yes. The exhaust gas recirculated to the intake passage 11 in this way (this is particularly referred to as EGR gas) merges with the intake air (fresh air) that has passed through the throttle valve 14 and is introduced into the combustion chamber 4 again. The EGR valve 17 is opened and closed in accordance with an operation signal from the ECU 50 described later, and the amount of EGR gas (EGR amount) is adjusted in accordance with the opening degree.

  The EGR passage 16 is provided with an EGR cooler 18. The EGR cooler 18 is a water cooling type cooling device for cooling the EGR gas passing through the EGR passage 16. That is, if the hot EGR gas joins fresh air as it is, the intake air temperature rises and the intake air density decreases. Therefore, the EGR gas is cooled by the EGR cooler 18 to suppress the rise in the intake air temperature. ing.

  As described above, in the engine of the present embodiment, the intake passage 11 and the exhaust passage 20 are communicated with each other via the EGR passage 16, whereby a part of the exhaust gas passing through the exhaust passage 20 is used as the EGR gas. To reflux. Thereby, the effect etc. which reduce the quantity of NOx produced by combustion of the air-fuel | gaseous mixture in the combustion chamber 4 are acquired. That is, since the exhaust gas after combustion contains only a small amount of oxygen, this oxygen-diluted exhaust gas is mixed with the intake air, thereby reducing the oxygen concentration in the intake air. Then, combustion occurs in a state where the oxygen concentration is lower than usual, so that the peak combustion temperature is lowered, thereby suppressing generation of NOx.

  Next, an exhaust emission control device applied to the engine of the present embodiment having the above-described configuration will be described. The engine exhaust purification apparatus of the present embodiment includes the oxidation catalyst 21, the DPF 22, and the NOx purification catalyst 23 provided on the exhaust passage 20, and the upstream side of the NOx purification catalyst 23 (that is, the DPF 22 and the NOx purification catalyst). 23) and a urea water injection valve 25 for injecting urea water into the exhaust passage 20 and a urea water supply device 27 for supplying urea water to the urea water injection valve 25.

  The oxidation catalyst 21 is formed by supporting a catalyst layer made of, for example, rhodium, cerium oxide, platinum, alumina or the like on a carrier such as a honeycomb structure, and includes HC (hydrocarbon) and CO (one-piece) contained in the exhaust gas. It has a function of purifying carbon oxide) by an oxidation reaction.

  The DPF 22 has a catalyst layer made of, for example, platinum or alumina supported on a carrier such as a honeycomb structure, and has a function of collecting particulates (hereinafter abbreviated as PM) contained in exhaust gas. And, it has a function of detoxifying the collected PM periodically by burning.

  The NOx purification catalyst 23 is a catalyst in which a catalyst layer made of, for example, titania-vanadium, zeolite, chromium oxide, manganese oxide, molybdenum oxide, titanium oxide, tungsten oxide or the like is supported on a carrier such as a honeycomb structure. The urea water injected from the urea water injection valve 25 has a function of selectively reducing NOx contained in the exhaust gas and decomposing it into nitrogen and water. That is, the NOx purification catalyst 23 is configured as a selective reduction type NOx catalyst (urea SCR catalyst) that can efficiently purify NOx by utilizing the reduction action of urea water.

  This point will be described in more detail. When urea water is injected into the exhaust passage 20 from the urea water injection valve 25, hydrolysis is performed by the heat of the exhaust gas, and the resulting ammonia is converted into the NOx purification catalyst 23 (catalyst layer) on the downstream side. ). A denitration reaction occurs between the ammonia adsorbed on the NOx purification catalyst 23 and NOx in the exhaust gas, so that NOx is selectively reduced (that is, decomposed into nitrogen and water) and rendered harmless. It has become so.

  The urea water injection valve 25 has substantially the same structure as the injector 10 provided in the engine body 1. That is, the urea water injection valve 25 incorporates a needle valve, a solenoid, and the like. The solenoid valve temporarily opens the needle valve in response to a pulse signal from the ECU 50, which will be described later. An amount of urea water corresponding to the above is injected from the needle valve.

  The urea water supply device 27 includes a urea water tank 28 that stores urea water, an electric pump 29 that pumps the urea water from the urea water tank 28 and pumps it, and the urea water that is pumped from the electric pump 29. And a supply pipe 30 for supplying the water injection valve 25. The supply pipe 30 is provided with a pressure control valve 32 so that the pressure of the urea water supplied to the urea water injection valve 25 through the supply pipe 30 is maintained constant by the pressure control valve 32. Yes.

  FIG. 2 is a block diagram showing a control system of the engine of the present embodiment. The ECU 50 shown in the figure is a control device for comprehensively controlling each part of the engine, and includes a well-known CPU, ROM, RAM, and the like.

  The ECU 50 includes the air flow sensor 35, the intake air temperature sensor 36, the intake air pressure sensor 37, the water temperature sensor 38, the engine rotational speed sensor 39, the first temperature sensor 40, the second temperature sensor 41, the third temperature sensor 42, and the differential pressure sensor. 43, a NOx concentration sensor 44, and an accelerator opening sensor 45 are electrically connected, and detection signals from these various sensors are sequentially input to the ECU 50. Here, in particular, the rotational speed of the engine inputted from the engine rotational speed sensor 39 is Ne, the temperature of the NOx purification catalyst 23 inputted from the third temperature sensor 42 is Tn, and before and after the DPF 22 inputted from the differential pressure sensor 43 Is represented by ΔP, the NOx concentration downstream of the NOx purification catalyst 23 input from the NOx concentration sensor is represented by Dnr, and the opening of the accelerator pedal input by the accelerator opening sensor 45 is represented by θ.

  The ECU 50 is also electrically connected to the injector 10, the EGR valve 17, the urea water injection valve 25, and the electric pump 29, and is configured to output drive control signals to these devices. ing.

  Next, specific functions of the ECU 50 configured as described above will be described. Here, mainly the functions of the ECU 50 will be described focusing on the functions related to the control of the urea water injection valve 25 and the functions related to the filter regeneration process for burning the PM deposited on the DPF 22.

  In relation to the above functions, the ECU 50 functionally includes an injection valve control means 51, a target injection amount calculation means 52, a temperature determination means 53, an EGR control means 54, and an injector control means 55. .

  The injection valve control means 51 controls the urea water injection operation by the urea water injection valve 25 to thereby control the injection amount and the injection timing of the urea water injected from the urea water injection valve 25 into the exhaust passage 20. It is something to control.

  The target injection amount calculating means 52 calculates a target value of the urea water injection amount to be injected from the urea water injection valve 25 based on various parameter values relating to the engine operating state.

  The temperature determination means 53 determines whether or not a countermeasure against heat damage of the urea water injection valve 25 is necessary based on the temperature detected in relation to the urea water injection valve 25. That is, since the urea water injection valve 25 is exposed to high-temperature exhaust gas that is as high as about 500 ° C., the temperature of the built-in solenoid becomes higher than the heat-resistant temperature, and the operability may be deteriorated. is there. Therefore, before such heat damage of the urea water injection valve 25 occurs, it is determined whether or not countermeasures for heat damage of the urea water injection valve 25 are necessary based on the magnitude of the temperature related to the urea water injection valve 25. .

  Specifically, in this embodiment, as the temperature related to the urea water injection valve 25, the magnitude of the temperature Tn of the NOx purification catalyst 23 input from the third temperature sensor 42 disposed on the downstream side is determined, Based on the result, it is determined whether or not countermeasures against heat damage of the urea water injection valve 25 are necessary. That is, in this embodiment, the temperature Tn of the NOx purification catalyst 23 corresponds to the predetermined temperature according to the present invention.

  The EGR control means 54 controls the amount of exhaust gas (EGR gas) recirculated from the exhaust system to the intake system by controlling the opening and closing of the EGR valve 17 in the EGR passage 16 according to the operating state of the engine. Is. FIG. 3 is a diagram showing a change in the EGR rate (the ratio of EGR gas to fresh air) set by the EGR control means 54. As shown in the figure, the EGR rate is set to a higher value as the engine rotational speed Ne or the required torque (load) Te is smaller, and is set to zero in a high rotation or high load range (that is, the exhaust gas recirculation is reduced). Will be stopped). That is, the EGR control means 54 opens the EGR valve 17 more widely as the engine rotational speed Ne or the required torque Te is smaller, and recirculates a large amount of exhaust gas to the intake system, while the EGR valve 17 is in a high speed or high load range. Is fully closed to stop the exhaust gas recirculation, thereby setting the EGR rate as shown in FIG.

  The injector control means 55 controls the injection amount and timing of fuel injected from the injector 10 into the combustion chamber 4 by controlling the fuel injection operation by the injector 10.

  Next, control operations relating to the injection of urea water and the regeneration of the DPF 22 executed by the ECU 50 including the means 51 to 55 will be described with reference to the flowcharts of FIGS. 4 and 5.

  First, the control operation regarding the regeneration of the DPF 22 shown in FIG. 4 will be described. When the flowchart shown in the figure starts, first, control for reading the differential pressure ΔP across the DPF 22 from the differential pressure sensor 43 is executed (step SA1).

  Next, control for calculating the amount of PM accumulated in the DPF 22 (PM accumulation amount) M is executed based on the differential pressure ΔP across the DPF 22 read in step SA1 (step SA2). That is, it can be determined that the larger the differential pressure ΔP across the DPF 22 is, the more PM is accumulated in the DPF 22 (that is, the PM accumulation amount M is large). Using the relationship, the value of the PM deposition amount M is calculated.

  Next, it is determined whether or not the value of the PM deposition amount M calculated in step SA2 is equal to or less than a predetermined first threshold value Me (step SA3). Here, the threshold value Me is a threshold value for determining whether or not to terminate the filter regeneration process (the process of burning PM accumulated in the DPF 22) in step SA6 described later.

  When it is determined YES in Step SA3 and it is confirmed that the PM accumulation amount M ≦ Me, “0” is input to the filter regeneration execution flag F (Step SA8). The filter regeneration execution flag F indicates whether or not a filter regeneration process (SA6), which will be described later, is executed. F = 0 stops the filter regeneration process and F = 1 executes the filter regeneration process. Represents. Therefore, after “0” is input to the flag F in step SA8, the filter regeneration process is not executed (step SA9).

  On the other hand, if it is determined NO in step SA4 and it is confirmed that the PM accumulation amount M> Me, the value of the PM accumulation amount M calculated in step SA2 is the second predetermined value. It is determined whether or not it is larger than the threshold value Ms (step SA4). Specifically, the second threshold value Ms used here is for determining whether or not to start a filter regeneration process (SA6) described later, and is based on the first threshold value Me used in step SA3. Is also set to a large value.

  When it is determined YES in Step SA4 and it is confirmed that the PM accumulation amount M> Ms, that is, the PM accumulation amount M exceeds the first threshold value Me and exceeds the second threshold value Ms larger than this. If it is confirmed that the value exceeds the threshold value, “1” is input to the filter regeneration execution flag F (step SA5), and then a filter regeneration process for burning PM accumulated in the DPF 22 is performed (step S5). SA6).

  Specifically, in step SA6, in order to combust PM accumulated in the DPF 22, control for injecting fuel from the injector 10 in the expansion stroke of the engine (control for performing so-called post injection) is performed by the injector control means 55. The EGR control means 54 executes control for closing the EGR valve 17 and stopping the recirculation of the exhaust gas.

  That is, in step SA6, in addition to normal fuel injection in which fuel is injected from the injector 10 near the compression top dead center of the engine, post injection in which fuel is injected from the injector 10 in the expansion stroke of the engine is executed. As a result, most of the post-injected fuel remains unburned, and the exhaust gas contains many unburned components of the fuel. Then, the unburned component of the fuel undergoes an oxidation reaction in the oxidation catalyst 21 on the exhaust passage 20, whereby the temperature of the exhaust gas rises and the exhaust gas whose temperature has been increased flows into the downstream DPF 22. Due to the action of the exhaust gas thus heated and the catalyst (PM oxidation catalyst layer) in the DPF 22, the PM deposited on the DPF 13 causes an oxidation reaction (combustion) and burns out.

  On the other hand, the recirculation of the exhaust gas is stopped by the EGR control means 54 together with the control for burning the PM by the post injection as described above in order to ensure the combustion stability of the engine. . That is, if the exhaust gas recirculates continuously despite the post injection being executed, the unburned components (mainly unburned HC) of the fuel contained in the exhaust gas flow into the combustion chamber 4 again. As a result, combustion stability is impaired, and unburned components of the fuel may adhere to the EGR cooler 18 to cause clogging. Therefore, the EGR valve 17 is closed and exhaust gas is exhausted during post injection. By stopping the recirculation of the fuel, deterioration of combustion stability, clogging of the EGR cooler 18 and the like are prevented.

  When the regeneration process of the DPF 22 is started as described above, the PM accumulation amount M soon decreases and becomes equal to or less than the second threshold value Ms, and therefore the determination result in step SA4 becomes NO. Then, in step SA7, it is determined whether or not the filter regeneration execution flag F = 1. If YES is determined here, the filter regeneration process is continued (step SA6), while NO is determined and F is determined. If it is confirmed that = 0, the filter regeneration process is stopped (step SA9).

  That is, the filter regeneration execution flag F determined in step SA7 remains “1” until YES is determined in step SA3 and F = 0 is set in SA8, so the determination result in step SA3 is YES. Unless it becomes (that is, unless PM accumulation amount M ≦ Me), it is determined as YES in step SA7, and the filter regeneration process (SA6) is continuously executed during that time. Then, when the filter regeneration process is continued to some extent, when the PM deposition amount M decreases to the first threshold value Me or less, the determination result in step SA7 becomes NO for the first time, and the filter regeneration process is stopped ( SA9).

  Next, a control operation relating to the injection of urea water will be described based on the flowchart of FIG. The control flow in FIG. 5 is executed in parallel with the control flow shown in FIG.

  When the flowchart of FIG. 5 starts, first, from the engine speed sensor 39, the accelerator opening sensor 45, the third temperature sensor 42, and the NOx concentration sensor 44, the detected values of these sensors are the engine speed Ne, the accelerator opening. Control for reading the degree θ, the temperature Tn of the NOx purification catalyst 23, and the NOx concentration Dnr on the downstream side of the NOx purification catalyst 23 is executed (step SB1).

  Next, control for calculating the required torque Te of the engine is executed based on the engine rotational speed Ne and the accelerator opening degree θ acquired in step SB1 (step SB2). The calculated required torque Te and the above Based on the engine rotational speed Ne acquired in step SB1, control for calculating the NOx concentration upstream of the NOx purification catalyst 23 (that is, the value of the raw NOx concentration discharged from the combustion chamber 4 of the engine) Dnf is executed. (Step SB3).

  The NOx concentration Dnf on the upstream side of the NOx purification catalyst 23 can of course be detected using a NOx concentration sensor, like the NOx concentration Dnr on the downstream side, but the raw exhaust discharged from the combustion chamber 4 is also possible. The NOx concentration Dnf can be estimated relatively accurately based on the operating state of the engine, and therefore the NOx concentration Dnf is calculated here.

  Next, based on the temperature Tn of the NOx purification catalyst 23 acquired in step SB1 and the downstream NOx concentration Dnr and the upstream NOx concentration Dnf calculated in step SB3, the NOx purification catalyst 23 Control for calculating the first target injection amount Q1 as the injection amount of urea water to be injected from the urea water injection valve 25 for the reduction of NOx is executed by the target injection amount calculation means 52 (step SB4). ).

  That is, the target injection amount calculation means 52 obtains the NOx purification rate in the NOx purification catalyst 23 based on the NOx concentrations Dnf and Dnr upstream and downstream of the NOx purification catalyst 23, and for reducing NOx from the purification rate. The amount of ammonia consumed (ammonia consumption amount) is calculated, and the amount of ammonia that can be adsorbed by the NOx purification catalyst 23 (ammonia adsorption amount) is calculated based on the temperature Tn of the NOx purification catalyst 23. Based on the calculated ammonia consumption amount and ammonia adsorption amount, the amount of urea water to be supplied (supplemented) to the NOx purification catalyst 23 is estimated, and the estimated value is calculated as the first target injection amount Q1. To do.

  When the first target injection amount Q1 is calculated in this way, subsequently, the control for determining whether or not the urea water injection valve 25 is in a high temperature state (a state that requires countermeasures against heat damage) is performed. It is executed by the determination means 53 (step SB5). Specifically, when the temperature Tn of the NOx purification catalyst 23 acquired in step SB1 is equal to or higher than a predetermined threshold value Tn0, it is determined that the urea water injection valve 25 disposed on the upstream side thereof is in a high temperature state. Is done.

  When it is determined YES in Step SB5 and it is confirmed that the urea water injection valve 25 is in a high temperature state, the first target injection amount described above is used as the target value of the injection amount from the urea water injection valve 25. Control for calculating the second target injection amount Q2 having a different calculation standard from Q1 is executed by the target injection amount calculation means 52 (step SB6). The second target injection amount Q2 is for the purpose of suppressing thermal damage to the urea water injection valve 25, and is calculated based on the temperature Tn of the NOx purification catalyst 23.

  Specifically, as shown in FIG. 6, the second target injection amount Q2 is calculated as a larger value as the temperature Tn of the NOx purification catalyst 23 greatly exceeds the threshold value Tn0. That is, in a state where the temperature Tn of the NOx purification catalyst 23 reaches a high temperature equal to or higher than Tn0 and there is a concern about thermal damage of the urea water injection valve 25 located downstream thereof, a large amount of urea water proportional to the temperature Is injected from the urea water injection valve 25, it is expected that the temperature of the urea water injection valve 25 is lowered by the cooling action of the urea water injection itself, thereby suppressing the heat damage of the urea water injection valve 25. The Therefore, the second target injection amount Q2 for the purpose of suppressing thermal damage to the urea water injection valve 25 is set to a larger value as the temperature Tn related to the urea water injection valve 25 is higher.

  When the calculation of the second target injection amount Q2 is completed as described above, subsequently, whether the calculated second target injection amount Q2 is larger than the first target injection amount Q1 calculated in step SB4. Is determined (step SB7). When the urea water injection valve 25 is in a high temperature state, in many cases, the second target injection amount Q2 for the purpose of suppressing heat damage is more suitable for ammonia consumption in the NOx purification catalyst 23, etc. This is considered to be greater than the first target injection amount Q1 (that is, the injection amount of urea water necessary and sufficient for reducing NOx), and YES is determined in step SB7. However, depending on the operating state of the engine, the amount of ammonia consumed by the NOx purification catalyst 23 becomes considerably large. In such a case, the first target injection amount Q1 is larger than the second target injection amount Q2. In this case, the determination result in step SB7 is NO.

  When it is determined YES in step SB7 and it is confirmed that the second target injection amount Q2> the first target injection amount Q1, the filter regeneration process (PM accumulated in the DPF 22) described in step SA6 in FIG. It is determined whether or not the process of burning is performed (step SB8). Specifically, it is determined that the filter regeneration process is being executed when the filter regeneration execution flag F = 1 shown in FIG.

  When it is determined NO in step SB8 and it is confirmed that the filter regeneration process is not executed, based on the difference (Q2-Q1) between the second target injection amount Q2 and the first target injection amount Q1. Thus, control for adjusting the NOx concentration Dnf on the upstream side of the NOx purification catalyst 23 in the increasing direction is executed (step SB9). Specifically, in step SB9, as shown in FIG. 7, the larger the difference between the first and second target injection amounts (Q2-Q1), the larger the increase in the NOx concentration Dnf is set. It has become.

  The increase control of the NOx concentration Dnf is executed by at least one of the EGR control means 54 and the injector control means 55. For example, the EGR control means 54 returns to the intake system of the engine by setting the opening degree of the EGR valve 17 to a lower opening degree (including fully closed) than the normal time when the NOx concentration Dnf does not need to be increased. The amount of exhaust gas (EGR amount) is reduced, thereby increasing the NOx concentration Dnf. That is, when the EGR amount is reduced by the EGR control means 54, the oxygen concentration in the intake air increases, so the combustion peak temperature increases, more NOx is generated, and the NOx concentration discharged from the combustion chamber 4 is increased. Dnf increases.

  Further, the injector control means 55 increases the NOx concentration Dnf discharged from the combustion chamber 4 by changing the injection timing of the fuel injected from the injector 10 into the combustion chamber 4 in a direction that promotes the generation of NOx. . For example, in a diesel engine, in general, the injection timing of fuel injected from the injector 10 is shifted to the retard side with respect to the timing at which combustion is most likely to occur to slow down combustion, thereby suppressing the peak temperature of combustion and reducing NOx. Is trying to reduce. Thus, if the fuel injection timing set to the retard side for NOx reduction is returned to the advance side, the NOx concentration Dnf can be increased by promoting the generation of NOx.

  The increase control of the NOx concentration Dnf by the EGR control means 54 and the increase control of the NOx concentration Dnf by the injector control means 55 are properly used according to the required increase range of the NOx concentration Dnf and the operating state of the engine. For example, as shown in FIG. 3, since the exhaust gas recirculation is not performed by the EGR control means 54 in the high engine speed or high load range (EGR rate = 0), the EGR control means 54 performs NOx concentration. It is impossible to increase Dnf. Therefore, in such a case, the NOx concentration Dnf may be increased by changing the fuel injection timing based on the control of the injector control means 55. On the other hand, in the operating region other than the high engine speed or high load region, the NOx concentration Dnf can be increased by reducing the EGR amount based on the control of the EGR control means 54.

  Further, when the difference (Q2−Q1) between the second target injection amount Q2 and the first target injection amount Q1 is large and the NOx concentration Dnf needs to be increased significantly in response thereto, the EGR control means It is also conceivable to simultaneously perform the reduction of the EGR amount by 54 and the change of the fuel injection timing by the injector control means 55.

  From the above, in this embodiment, the NOx concentration control means for adjusting the NOx concentration Dnf exhausted from the combustion chamber 4 of the engine controls the EGR control means 54 for controlling the amount of exhaust gas recirculated to the engine intake system. And injector control means 55 for controlling the timing of fuel injection into the combustion chamber 4 of the engine.

  When the control for increasing the NOx concentration Dnf is completed as described above, subsequently, the control for injecting the urea water in an amount corresponding to the second target injection amount Q2 calculated in step SB6 from the urea water injection valve 25 is performed. This is executed by the injection valve control means 51 (step SB10). That is, here, since the second target injection amount Q2> the first target injection amount Q1, the larger second target injection amount Q2 is adopted as the urea water injection amount from the urea water injection valve 25. The

  On the other hand, if it is determined YES in step SB8 and it is confirmed that the filter regeneration process is being performed, the control in step SB9 for increasing the NOx concentration Dnf is omitted, and the process directly proceeds to step SB10, and the first The urea water is injected at the 2 target injection amount Q2. That is, as described with reference to the flowchart of FIG. 4, the exhaust gas recirculation to the intake system is stopped during the filter regeneration process. Therefore, the combustion can be performed without performing the NOx concentration increase control as in step SB9. The value of the NOx concentration Dnf discharged from the chamber 4 is originally high. Therefore, during the filter regeneration process, the NOx concentration Dnf increase control (step SB9) is omitted, and urea water injection (step SB10) is immediately performed.

  Next, the control operation that is performed when it is determined NO in Step SB7, that is, when the second target injection amount Q2 is equal to or less than the first target injection amount Q1 (Q2 ≦ Q1) will be described. In this case, first, as in step SB8, it is determined whether the filter regeneration process is being executed (step SB11).

  When it is determined NO in step SB11 and it is confirmed that the filter regeneration process is not executed, normal EGR control is executed (step SB12). That is, based on the EGR rate setting map as shown in FIG. 3, the EGR control means 54 performs control to adjust the opening of the EGR valve 17 and recirculate a desired amount of exhaust gas to the intake system.

  Next, the injection valve control means 51 performs control for injecting the urea water in an amount corresponding to the first target injection amount Q1 calculated in step SB4 from the urea water injection valve 25 (step SB13). That is, since the first target injection amount Q1 ≧ the second target injection amount Q2 here, the larger first target injection amount Q1 is adopted as the urea water injection amount from the urea water injection valve 25. The

  On the other hand, if it is determined YES in step SB11 and it is confirmed that the filter regeneration process is being performed, the exhaust gas recirculation is not performed, and thus the EGR control in step SB12 is omitted and step SB13 is directly performed. Then, the urea water is injected at the first target injection amount Q1.

  Further, when it is determined NO in Step SB5, that is, when it is confirmed that the temperature Tn of the NOx purification catalyst 23 is smaller than the threshold value Tn0 (Tn <Tn0) and the urea water injection valve 25 is not in a high temperature state. Also, the same control as in steps SB11 to SB13 is executed. That is, when the urea water injection valve 25 is not in a high temperature state, it is not necessary to consider the heat damage of the urea water injection valve 25. Therefore, it is sufficient to inject sufficient urea water for NOx reduction. As the injection amount, urea water for the first target injection amount Q1 is injected from the urea water injection valve 25.

  As described above, the engine exhaust purification apparatus of the present embodiment includes the selective reduction type NOx purification catalyst 23 provided on the exhaust passage 20 of the engine and the exhaust passage 20 upstream of the NOx purification catalyst 23. Detected in relation to the urea water injection valve 25 for injecting urea water therein, the injection valve control means 51 for controlling the injection amount of urea water from the urea water injection valve 25, and the urea water injection valve 25. Based on the temperature (here, the temperature Tn of the NOx purification catalyst 23), temperature determining means 53 for determining whether or not the urea water injection valve 25 is in a high temperature state that requires countermeasures against heat damage, and the urea water injection valve As a target value of the injection amount from 25, the first target injection amount Q1 necessary for reducing NOx by the NOx purification catalyst 23 is calculated, and the purpose is to suppress thermal damage of the urea water injection valve 25. Second target injection And a target injection quantity calculating means 52 for calculating the Q2. In this embodiment, when it is confirmed by the temperature determination means 53 that the urea water injection valve 25 is in a high temperature state (YES in step SB5), the injection valve control means 51 performs the first and second operations. The urea water is injected from the urea water injection valve at the larger one of the target injection amounts Q1, Q2 (step SB10 or SB13). According to such a structure, there exists an advantage that the heat damage of the urea water injection valve 25 can be suppressed with a simpler structure.

  That is, in the above embodiment, when the urea water injection valve 25 is in a high temperature state, by injecting the urea water from the urea water injection valve 25 at the second target injection amount Q2 for the purpose of suppressing the heat damage, The urea water injection valve 25 can be sufficiently cooled by injecting a relatively large amount of urea water and its cooling action, and the operability of the urea water injection valve 25 is effectively prevented from deteriorating due to heat damage. be able to. It is also assumed that the first target injection amount Q1, which is originally necessary for reducing NOx, is calculated to be larger than the second target injection amount Q2 for measures against heat damage depending on the operating state of the engine. However, even in such a case, according to the above configuration, since the larger one of the first and second target injection amounts Q1, Q2 is adopted, the operating state of the engine Regardless of the above, a large injection amount from the urea water injection valve 25 is always secured, and the urea water injection valve 25 can be sufficiently cooled by the injection. In addition, according to the above configuration in which the injection amount from the urea water injection valve 25 is controlled to cool the urea water injection valve 25, it is not necessary to provide a dedicated cooling system or the like for cooling the urea water injection valve 25. There is an advantage that the heat damage of the urea water injection valve 25 can be suppressed with a simpler configuration.

  In particular, in the above embodiment, as shown in FIG. 6, the higher the temperature Tn of the NOx purification catalyst 23 detected in relation to the urea water injection valve 25, the higher the second target injection for heat damage countermeasures. Since the amount Q2 is calculated as a large value, a larger amount of urea water is injected as the temperature of the urea water injection valve 25 is higher and the required level of countermeasures against heat damage is higher. There is an advantage that heat damage of the urea water injection valve 25 can be surely suppressed by exerting an appropriate cooling action.

  Moreover, in the said embodiment, it is confirmed by the temperature determination means 53 that the urea water injection valve 25 is in a high temperature state, and the said 2nd target injection quantity Q2 calculated by the target injection quantity calculation means 52 is 1st target. When the injection amount is greater than Q1 (that is, when both of steps SB5 and SB7 are YES), the NOx concentration Dnf discharged from the combustion chamber 4 of the engine by the NOx concentration adjusting means comprising the EGR control means 54 and the injector control means 55. Is adjusted in the increasing direction (step SB9). According to such a configuration, even when a relatively large amount of urea water is injected into the exhaust passage 20 based on the second target injection amount Q2 for measures against heat damage, the NOx concentration in the exhaust gas is also adjusted accordingly. By increasing Dnf, there is an advantage that the amount of ammonia discharged outside without being used in the reduction reaction can be effectively suppressed.

  That is, more urea water is injected from the urea water injection valve 25 than the amount originally required for NOx reduction (first target injection amount Q1) based on the second target injection amount Q2 for measures against heat damage. If this is done, a large amount of ammonia that has not been used for the reduction reaction may be discharged to the outside as it is (ammonia slip). However, when injecting urea water at the second target injection amount Q2, the NOx concentration Dnf is set. According to the above-described configuration that is adjusted to be higher, by appropriately balancing the increased injection amount of urea water and the value of the NOx concentration Dnf, NOx can be sufficiently obtained using the injected urea water. There is an advantage that the above-described external discharge of ammonia can be effectively suppressed while reducing.

  In particular, in the above embodiment, as shown in FIG. 7, the greater the difference (Q2−Q1) between the second target injection amount Q2 and the first target injection amount Q1, the greater the increase in the NOx concentration Dnf. Therefore, as the amount of extra urea water injected as a countermeasure against heat damage increases, the NOx concentration Dnf can be increased. There is an advantage that the amount of ammonia discharged to the outside can be effectively suppressed while achieving proper cooling.

  Further, as shown in the above embodiment, when the amount of exhaust gas recirculated to the intake system of the engine is reduced by the EGR control means 54, thereby adjusting the NOx concentration Dnf in the increasing direction. There is an advantage that the NOx concentration Dnf can be appropriately increased when necessary by increasing the peak temperature of combustion according to the reduction of the recirculation amount of the exhaust gas.

  Further, as shown in the above embodiment, the fuel injection timing is made to promote the generation of NOx by the injector control means 55 that controls the injection timing of the fuel injected from the injector 10 into the combustion chamber 4 of the engine. If the NOx concentration Dnf is adjusted to increase in this way, the NOx concentration Dnf can be appropriately increased when necessary by promoting the generation of NOx according to the change in the fuel injection timing. There are advantages.

  In the above embodiment, as the NOx concentration adjusting means for adjusting the NOx concentration Dnf discharged from the combustion chamber 4 of the engine in the increasing direction, the EGR control means 54 for controlling the recirculation amount of the exhaust gas, and the fuel injection timing. The injector control means 55 to be controlled is properly used according to the operating state of the operation, etc., but if possible, the NOx concentration Dnf is set using only one of the means 54 and 55. You may make it adjust to an increase direction.

  Further, in the above embodiment, the temperature Tn of the NOx purification catalyst 23 arranged on the downstream side is detected by the third temperature sensor 42 as the temperature related to the urea water injection valve 25, and the detection of the third temperature sensor 42 is performed. Based on the magnitude of the temperature Tn, the necessity of countermeasures against heat damage of the urea water injection valve 25 is determined. However, the temperature of the urea water injection valve 25 is directly detected, and the temperature is necessary for countermeasures against heat damage. Of course, it can also be used as a criterion for determining whether or not. However, if it does in this way, in order to detect the temperature of the urea water injection valve 25 directly, a temperature sensor for exclusive use will be needed, and problems, such as increase in part cost, will arise. On the other hand, when the temperature Tn of the NOx purification catalyst 23 that originally needs to be detected to determine the injection amount of urea water or the like is used as a determination criterion as in the above embodiment, a temperature sensor is added. Since it is not necessary, there is an advantage that the temperature state of the urea water injection valve 25 can be determined with a lower cost configuration.

4 Combustion chamber 10 Injector 20 Exhaust passage 23 NOx purification catalyst 25 Urea water injection valve 51 Injection valve control means 52 Target injection amount calculation means 53 Temperature judgment means 54 EGR control means 55 Injector control means Tn temperature (predetermined temperature)
Q1 First target injection amount Q2 Second target injection amount Dnf NOx concentration

Claims (4)

A selective reduction type NOx purification catalyst provided on the exhaust passage of the engine, a urea water injection valve for injecting urea water into the exhaust passage upstream of the NOx purification catalyst, and urea from the urea water injection valve An exhaust emission control device for an engine, comprising an injection valve control means for controlling a water injection amount,
Temperature determining means for determining whether or not the urea water injection valve is in a high temperature state requiring countermeasures against heat damage based on a predetermined temperature detected in relation to the urea water injection valve;
As a target value of the injection amount from the urea water injection valve, the first target injection amount required for reducing NOx by the NOx purification catalyst is calculated, and the purpose is to suppress thermal damage of the urea water injection valve. Target injection amount calculation means for calculating the second target injection amount ,
A NOx concentration adjusting means for adjusting the NOx concentration discharged from the combustion chamber of the engine ,
When it is confirmed by the temperature determination means that the urea water injection valve is in a high temperature state, the target injection amount calculation means calculates the second target injection amount as a larger value as the predetermined temperature is higher. the injector control means is injected urea water from the urea water injection valve in the injection amount with the larger of the first and second target injection quantity,
When it is confirmed by the temperature determination means that the urea water injection valve is in a high temperature state, and the second target injection amount calculated by the target injection amount calculation means is larger than the first target injection amount, An exhaust purification device for an engine, wherein the NOx concentration is adjusted to be higher by the NOx concentration adjusting means . The exhaust emission control device for an engine according to claim 1 ,
When it is confirmed by the temperature determination means that the urea water injection valve is in a high temperature state and the second target injection amount calculated by the target injection amount calculation means is larger than the first target injection amount, these An exhaust emission control device for an engine, characterized in that the greater the difference between the two target injection amounts, the greater the increase in the NOx concentration by the NOx adjusting means. The engine exhaust gas purification apparatus according to claim 1 or 2 ,
The NOx concentration adjusting means includes an EGR control means for controlling the amount of exhaust gas recirculated to the engine intake system,
An exhaust gas purifying apparatus for an engine, wherein when the NOx concentration is adjusted to be high, the recirculation amount of the exhaust gas is reduced by the EGR control means. The engine exhaust gas purification apparatus according to any one of claims 1 to 3 ,
The NOx concentration adjusting means includes an injector control means for controlling the injection timing of fuel injected from the injector into the combustion chamber of the engine,
An exhaust emission control device for an engine, wherein when the NOx concentration is adjusted to be higher, the fuel injection timing is changed by the injector control means in a direction that promotes the generation of NOx.

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