JP2016020637A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent excessive temperature rise of exhaust in supplying HC (unburned hydrocarbon) to an oxidation catalyst, and effectively suppress heat deterioration of an SCR catalyst.SOLUTION: An exhaust emission control system includes: a first oxidation catalyst 31 that is provided in an exhaust system of an internal combustion engine 10; a second oxidation catalyst 32 that is provided on the exhaust system on a downstream side with respect to the first oxidation catalyst 31; a selective reduction catalyst 41 that is provided on the downstream side with respect to the second oxidation catalyst 32 and reduces and purifies NOx in exhaust with NH3 generated from urea water as reductant; a third exhaust temperature sensor 53 detecting a temperature of exhaust inflowing to the selective reduction catalyst 41; a temperature rise control unit 62 periodically executing temperature rise control of supplying HC (unburned hydrocarbon) to the first oxidation catalyst 31 and increasing the exhaust temperature detected by the third exhaust temperature sensor 53 to a predetermined target temperature; and a target temperature correction unit 63 correcting a target temperature in temperature rise control executed next to the current temperature rise control, on the basis of the exhaust temperature detected by the third exhaust temperature sensor 53 during execution of temperature rise control and the target temperature.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an exhaust purification system.

  As an engine exhaust purification system, for example, Patent Document 1 discloses, in order from the exhaust upstream side, a pre-stage oxidation catalyst, a diesel particulate filter (hereinafter referred to as DPF), a middle-stage oxidation catalyst, a selective reduction catalyst (hereinafter referred to as SCR catalyst), The structure which has arrange | positioned the back | latter stage oxidation catalyst is disclosed.

  In the technology described in Patent Document 1, particulate matter (hereinafter referred to as PM) and nitrogen compound (hereinafter referred to as NOx) in exhaust gas are simultaneously purified, and high-temperature exhaust gas is introduced into a bypass passage at high exhaust temperature to form a middle-stage oxidation catalyst. By absorbing the heat, the thermal degradation of the SCR catalyst is prevented.

JP 2013-2283 A

  By the way, in the technique described in Patent Document 1, since the DPF is arranged between the front-stage oxidation catalyst and the middle-stage oxidation catalyst and the middle-stage oxidation catalyst is arranged in the bypass passage, the entire structure becomes complicated and the apparatus becomes larger. There is a problem that leads to an increase in costs.

  In addition, when the accumulation of sulfate (sulfate poisoning) proceeds on the front-stage oxidation catalyst, unburned hydrocarbons (HC) supplied by post-injection during DPF forced regeneration slip from the front-stage oxidation catalyst and react with the middle-stage oxidation catalyst. Further, by excessively raising the exhaust gas temperature, there is a possibility that thermal degradation of the SCR catalyst arranged immediately downstream cannot be prevented.

  In addition to sulfate poisoning, if the catalyst metal is poisoned by, for example, thermal deterioration of the oxidation catalyst over time or phosphorus (P) in the engine oil that has flowed into the exhaust gas, exhaust excess due to HC slip as described above will occur. There is a possibility that the temperature rises and thermal deterioration of the SCR catalyst cannot be prevented.

  An object of the present invention is to prevent an excessive exhaust temperature rise when supplying unburned hydrocarbon (HC) to an oxidation catalyst, and effectively suppress thermal degradation of the SCR catalyst.

  In order to achieve the above-described object, an exhaust purification system of the present invention includes a first oxidation catalyst that is provided in an exhaust system of an internal combustion engine and that can oxidize unburned hydrocarbons (HC), and is downstream of the first oxidation catalyst. A second oxidation catalyst provided in the exhaust system on the side and capable of oxidizing soluble organic components (SOF), and ammonia (NH 3) provided from the urea water provided in the exhaust system downstream from the second oxidation catalyst A selective reduction catalyst for reducing and purifying nitrogen compounds (NOx) in the exhaust gas using a reducing agent, temperature detection means for detecting an exhaust temperature flowing into the selective reduction catalyst, and unburned hydrocarbons in the first oxidation catalyst (HC) is supplied and the temperature rise control means for periodically executing the temperature rise control for raising the exhaust gas temperature detected by the temperature detection means to a predetermined target temperature; and the temperature detection during the temperature rise control. The exhaust temperature detected by the means Based on the difference between the target temperature, and a target temperature correction means for correcting the target temperature of the temperature increase control performed in the following the Atsushi Nobori control.

  Further, the target temperature correction means is a value obtained by subtracting the target temperature from the peak value when the peak value of the exhaust temperature detected by the temperature detection means is higher than the target temperature during the temperature increase control. Is preferably subtracted from the target temperature of the temperature increase control to be executed next.

  Further, the target temperature correction means is a value obtained by subtracting the peak value from the target temperature when the peak value of the exhaust gas temperature detected by the temperature detection means is lower than the target temperature during the temperature increase control. Is preferably added to the target temperature of the temperature increase control to be executed next.

  Further, it may further comprise combustion control means for controlling the fuel injection of the internal combustion engine by multistage injection to reduce the soot component in the exhaust discharged from the internal combustion engine.

  According to the exhaust purification system of the present invention, it is possible to prevent an excessive exhaust temperature rise when supplying unburned hydrocarbon (HC) to the oxidation catalyst, and to effectively suppress thermal degradation of the SCR catalyst.

It is a typical whole block diagram which shows the exhaust gas purification system of this embodiment. It is a functional block diagram which shows the electronic control unit (ECU) of this embodiment. It is a flowchart figure explaining the temperature rising control by the exhaust gas purification system of this embodiment. It is a figure explaining the target temperature correction | amendment of the temperature rising control by the exhaust gas purification system of this embodiment. It is the figure which compared the DOC exit temperature when HC slip arises, and the SCR entrance temperature.

  Hereinafter, an exhaust purification system according to an embodiment of the present invention will be described with reference to the accompanying drawings. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  As shown in FIG. 1, each cylinder of a diesel engine (hereinafter simply referred to as an engine) 10 is provided with an injector 11 that directly injects high-pressure fuel pressured by a common rail (not shown) into each cylinder. . The fuel injection amount and fuel injection timing of each injector 11 are controlled according to an instruction signal input from an electronic control unit (hereinafter referred to as ECU) 60.

  An intake passage 12 for introducing fresh air is connected to the intake manifold 10 </ b> A of the engine 10. An exhaust passage 16 for leading the exhaust is connected to the exhaust manifold 10B. The exhaust passage 16 is provided with a pre-stage post-treatment device 30, a post-stage post-treatment device 40, and the like in order from the exhaust upstream side.

  The pre-stage post-processing apparatus 30 is configured by arranging a first oxidation catalyst 31 and a second oxidation catalyst 32 in order from the upstream side in a case 30A. A case 30 </ b> A upstream of the first oxidation catalyst 31 is provided with a first exhaust temperature sensor 50 that detects an inlet exhaust temperature of the first oxidation catalyst 31 (hereinafter referred to as a DOC inlet temperature). The case 30A between the first oxidation catalyst 31 and the second oxidation catalyst 32 is provided with a second exhaust temperature sensor 51 that detects the outlet exhaust temperature of the first oxidation catalyst 31 (hereinafter referred to as DOC outlet temperature). It has been. The sensor values of these sensors 50 and 51 are transmitted to the electrically connected ECU 60.

  The first oxidation catalyst 31 is formed, for example, by supporting a NO2 generating catalyst or the like on a porous ceramic carrier, and functions to generate NO2 from NO contained in the exhaust, and unburned hydrocarbons supplied by post injection. It has a function of oxidizing (HC).

  The second oxidation catalyst 32 is formed, for example, by supporting a SOF oxidation catalyst on a porous ceramic carrier, and has a function of oxidizing and purifying mainly SOF components in PM contained in exhaust gas.

  The post-stage post-treatment device 40 is configured by arranging an SCR catalyst 41 and a third oxidation catalyst 42 in order from the upstream side in the case 40A. The exhaust passage 16 upstream of the SCR catalyst 41 is provided with a urea addition valve 44 of the urea water injector 43 and a NOx sensor 52 that detects the NOx value in the exhaust gas flowing into the SCR catalyst 41. Further, a third exhaust temperature sensor 53 for detecting an inlet exhaust temperature of the SCR catalyst 41 (hereinafter referred to as SCR inlet temperature) is provided in the exhaust passage 16 upstream of the SCR catalyst 41. The sensor values of these sensors 52 and 53 are transmitted to the electrically connected ECU 60.

  The urea water injection device 43 opens and closes the urea addition valve 44 in response to an instruction signal input from the ECU 60, so that the urea water is supplied from the urea water tank 45 into the exhaust passage 16 upstream of the SCR catalyst 41. The urea water pumped by the pump 46 is injected. The injected urea water is hydrolyzed by exhaust heat to be generated as NH3, and supplied to the SCR catalyst 41 on the downstream side as a reducing agent.

  The SCR catalyst 41 is formed, for example, by supporting zeolite or the like on a porous ceramic carrier. The SCR catalyst 41 adsorbs NH3 supplied as a reducing agent from the urea water injection device 43, and selectively reduces and purifies NOx from the exhaust gas passing through the adsorbed NH3.

  The third oxidation catalyst 42 is formed, for example, by supporting an oxidation catalyst on a porous ceramic carrier, and has a function of oxidizing NH 3 slipped downstream from the SCR catalyst 41.

  The ECU 60 performs various controls of the engine 10 and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like. Further, as shown in FIG. 2, the ECU 60 includes a PM reduction combustion control unit 61, a temperature increase control unit 62, and a target temperature correction unit 63 as some functional elements. In the present embodiment, these functional elements are described as being included in the ECU 60, which is an integral piece of hardware. However, any one of these functional elements may be provided in separate hardware.

  The PM reduction combustion control unit 61 executes PM reduction injection control that mainly reduces soot components in PM contained in exhaust gas by controlling the fuel injection of each injector 11 by multi-injection. As described above, in the present embodiment, the soot component in the PM is reduced by the combustion control of the engine 10, and the SOF component in the PM is oxidized and purified by the second oxidation catalyst 32, so that the DPM is omitted even if the DPF is omitted. It is configured to effectively suppress the release to the atmosphere. In addition to the PM reduction injection control, control for increasing the supercharging pressure by adjusting the opening of a variable capacity supercharger or EGR device (not shown) may be executed.

  The temperature raising control unit 62 (1) removes the sulfate deposited on the first oxidation catalyst 31, (2) removes white deposits generated from the urea water, and (3) is discharged from the engine 10 to the SCR catalyst 41. The temperature increase control is performed for the purpose of correcting the error between the estimated NH3 occlusion amount and the actual NH3 occlusion amount by removing the accumulated HC and (4) removing NH3 occluded in the SCR catalyst 41. In this embodiment, this temperature increase control supplies unburned hydrocarbons (HC) to the first oxidation catalyst 31 by post injection that injects a predetermined amount of fuel in the exhaust stroke, and raises the exhaust temperature with oxidation reaction heat. This is realized. Hereinafter, the details of the temperature rise control will be described based on the flowchart of FIG.

  In step (hereinafter, simply referred to as S) 100, it is determined whether or not an elapsed time (hereinafter referred to as an interval) from the completion of the previous temperature increase control to the present has reached a predetermined first threshold time. When the interval reaches the first threshold time (Yes), the present control proceeds to S110 and the purge flag F is turned on.

  In S120, it is determined whether or not the DOC inlet temperature detected by the first exhaust temperature sensor 50 is equal to or higher than a predetermined first threshold temperature indicating a catalyst active state. Further, in S130, it is determined whether or not the DOC outlet temperature detected by the second exhaust temperature sensor 51 is equal to or higher than the first threshold temperature. If any of these conditions is satisfied (Yes), the process proceeds to S140. On the other hand, if any of these conditions is not satisfied (No), the purge flag F is kept on and a standby state is entered.

In S140, the post-injection SCR inlet temperature detected by the third exhaust temperature sensor 53 is the exhaust gas temperature is raised to a predetermined target temperature T _n is started. The target temperature T _n is corrected as necessary by a target temperature correction unit 63 described later.

  In S150, it is determined whether or not the DOC inlet temperature detected by the first exhaust temperature sensor 50 is equal to or higher than the first threshold temperature. In S160, the DOC outlet detected by the second exhaust temperature sensor 51 is determined. It is determined whether or not the temperature maintains the first threshold temperature. If any of these conditions is satisfied (Yes), the process proceeds to S170. If any of these conditions is not satisfied (No), post injection is interrupted until the condition is satisfied again.

  In S170, it is determined whether or not the cumulative injection amount of post injection has reached a predetermined upper limit injection amount. If the cumulative injection amount has reached the upper limit injection amount (Yes), the purge flag F is turned off in S200, and the present control ends (temperature increase control: failure). On the other hand, when the cumulative injection amount has not reached the upper limit injection amount (No), the process proceeds to S180.

  In S180, termination determination of the temperature rise control is executed. The end of the temperature increase control was measured by the second exhaust temperature sensor 51 at a predetermined second threshold temperature or higher that can remove the sulfate, white deposit, HC, and NH3 defined in the above (1) to (4). It is determined based on the accumulated time. When the accumulated time reaches the predetermined second threshold time (Yes), the process proceeds to S190, the purge flag F is turned off, and the present control ends (temperature increase control: success). On the other hand, when the accumulated time has not reached the second threshold time (No), the present control is returned to S140 to continue the temperature increase control.

The target temperature correction unit 63 performs temperature correction for increasing or decreasing the target temperature T _n based on the SCR inlet temperature detected by the third exhaust temperature sensor 53 during the temperature rise control. Specifically, the peak value _{Tpeak_n} of the SCR inlet temperature detected by the third temperature sensor 53 during the n-th (n is a natural number of 1 or more) temperature increase control is recorded in a recording unit (not shown ₎ of the ECU 60. when performing n + 1 th temperature increase control is increased or decreased in accordance with the target temperature T _{n + 1} in the difference _{ΔT n (= T n -T peak_n} ) the n-th target temperature T _n and the peak value T _{Peak_n} to correct. For example, as shown in FIG. 4, when n-th peak value T _{Peak_n} is higher than the target temperature T _n, decreases the target temperature T _{n + 1} of the (n + 1) th by the difference [Delta] T _n (T n _{+ 1 = T n - (T peak_n -T} n)). Furthermore, if (n + 1) th peak value _T peak_n _{+ 1} is lower than the target temperature T _{n + 1,} to increase the difference [Delta] T n _{+ 1} by n + 2 th target temperature T _{n + 2} (T n _{+ 2} = _{T n + 1 + (T n} + 1 -T peak_n + 1)). As described above, the excessive increase in the temperature of the SCR catalyst 41 is effectively suppressed by correcting the target temperature from the next time stepwise in accordance with the difference between the SCR inlet temperature during the temperature increase control and the target temperature. Can do.

  Next, the effect of the exhaust gas purification system according to this embodiment will be described.

  The exhaust purification system of this embodiment includes a first oxidation catalyst 31 that generates NO2 in order from the exhaust upstream side, and a second oxidation catalyst 32 that oxidizes and purifies SOF components in PM mainly composed of unburned fuel, lubricating oil, and the like. , A SCR catalyst 41 for reducing and purifying NOx and a third oxidation catalyst 42 for preventing NH3 slip are arranged. Furthermore, fuel injection of the engine 10 is controlled by PM reduction injection that mainly reduces soot components in PM by multi-injection. That is, the exhaust emission performance can be effectively maintained without using the DPF by reducing the soot component in the PM by the combustion control of the engine 10 and purifying the SOF component by the second oxidation catalyst 32. ing. Therefore, it is possible to omit the DPF, and it is possible to effectively suppress an increase in size and cost of the apparatus.

  Further, by omitting the DPF, it is not necessary to perform forced regeneration by post injection or in-pipe injection, and fuel efficiency can be improved effectively. Further, the omission of the DPF eliminates the need for periodic cleaning of the DPF for removing ash, and the maintenance performance can be effectively improved.

  In addition, the sulfate poisoning of the first oxidation catalyst 31 can be removed by periodic temperature increase control, but there is a problem that it is not possible to cope with phosphorus poisoning and thermal degradation over time. Therefore, if temperature rise control is performed without considering the effects of phosphorus poisoning and aging heat deterioration, as shown in FIG. 5, the SCR inlet temperature becomes higher than the DOC outlet temperature due to HC slip, and the exhaust gas is excessively heated. There is a possibility that deterioration of the SCR catalyst 41 due to temperature cannot be prevented.

  The exhaust purification system of the present embodiment reliably removes sulfate poisoning by periodically performing temperature rise control, while appropriately setting a target temperature for temperature rise control for phosphorus poisoning and aging deterioration. By correcting, it is configured to effectively prevent HC slip during temperature rise control. Therefore, it is possible to effectively suppress the exhaust excessive temperature rise during the temperature rise control, and the thermal deterioration of the SCR catalyst 41 can be surely prevented.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, although the temperature increase control has been described as being performed by post injection, a fuel injection device may be provided in the exhaust passage 16 upstream of the first oxidation catalyst 31 and may be performed by exhaust pipe injection.

DESCRIPTION OF SYMBOLS 10 Engine 11 Injector 16 Exhaust passage 30 Pre-stage post-processing apparatus 31 1st oxidation catalyst 32 2nd oxidation catalyst 40 Post-stage post-treatment apparatus 41 SCR catalyst 42 3rd oxidation catalyst 50 1st exhaust temperature sensor 51 2nd exhaust temperature sensor 53 3rd Exhaust temperature sensor 60 ECU
61 PM reduction combustion control unit 62 Temperature rise control unit 63 Target temperature correction unit

Claims (4)

A first oxidation catalyst provided in an exhaust system of an internal combustion engine and capable of oxidizing unburned hydrocarbon (HC);
A second oxidation catalyst provided in an exhaust system downstream of the first oxidation catalyst and capable of oxidizing soluble organic components (SOF);
A selective reduction catalyst that is provided in an exhaust system downstream of the second oxidation catalyst and that reduces and purifies nitrogen compounds (NOx) in the exhaust gas using ammonia (NH3) generated from urea water as a reducing agent;
Temperature detecting means for detecting an exhaust temperature flowing into the selective reduction catalyst;
A temperature increase control means for periodically performing a temperature increase control for supplying unburned hydrocarbon (HC) to the first oxidation catalyst and increasing the exhaust temperature detected by the temperature detection means to a predetermined target temperature;
Based on the difference between the exhaust temperature detected by the temperature detection means and the target temperature during the temperature increase control, the target temperature correction means corrects the target temperature of the temperature increase control executed next to the temperature increase control. And an exhaust purification system. The target temperature correction means includes
When the peak value of the exhaust temperature detected by the temperature detection means is higher than the target temperature during the temperature increase control, the temperature increase control is executed next by subtracting the target temperature from the peak value. The exhaust gas purification system according to claim 1, wherein the exhaust gas purification system is subtracted from a target temperature. The target temperature correction means includes
When the peak value of the exhaust temperature detected by the temperature detection means during execution of the temperature increase control is lower than the target temperature, the temperature increase control is executed next by subtracting the peak value from the target temperature. The exhaust gas purification system according to claim 1 or 2, wherein the exhaust gas purification system is added to the target temperature. The exhaust emission control system according to any one of claims 1 to 3, further comprising combustion control means for controlling fuel injection of the internal combustion engine by multi-stage injection to reduce a soot component in exhaust discharged from the internal combustion engine.

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