JP2017044112A - Exhaust emission control system and fuel supply method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system and a fuel supply method capable of suppressing variation of purification performance caused by an individual difference of an electromagnetic pump for pressure-feeding unburned fuel to an injector inserted in an exhaust passage.SOLUTION: When a regeneration request of a PM collection filter 7 is made, an ECU 14 starts an electromagnetic pump 11 for pressure-feeding unburned fuel 10 to an injector 8 after closing a flow regulating valve 12, and then, performs control for adjusting rotational frequency of the electromagnetic pump 11 on the basis of preset map data so that a measurement value X of a pressure sensor 13 corresponds to a target pressure value A within a predetermined range.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification system, and more particularly, an exhaust gas purification system and a fuel supply capable of suppressing variations in purification performance due to individual differences of electromagnetic pumps that pump unburned fuel to an injector inserted in an exhaust passage. Regarding the method.

  A vehicle using a diesel engine as a drive source is equipped with an exhaust gas purification system for removing harmful substances such as particulate matter (PM) and nitrogen oxide (NOx) contained in the exhaust gas.

  As for the former PM, a PM collection filter that collects and purifies PM by a filter made of a honeycomb-like porous body made of ceramics is mainly used (for example, see Patent Document 1). In order to prevent clogging by the collected PM, the PM collection filter needs to burn and remove PM before reaching the collection limit amount. When the temperature of the exhaust gas is a high temperature such as 500 ° C. or higher, PM spontaneously burns continuously. However, when the temperature of the exhaust gas is low, unburned fuel is supplied into the exhaust gas, and the hydrocarbon (HC) of the unburned fuel is burned by the oxidation catalyst (DOC) arranged in the front stage of the filter, and the oxidation reaction The forced regeneration which heats exhaust gas by heating DOC to about 600 degreeC using heat and forcibly burns the collected PM is required.

  As for the latter NOx, a NOx occlusion reduction catalyst has been put into practical use (see, for example, Patent Document 2). This NOx occlusion reduction catalyst temporarily stores NOx in exhaust gas in the NOx occlusion material when the air-fuel ratio is in a lean state, and then supplies unburned fuel to the exhaust gas to make it rich (rich spike). The NOx occluded in is desorbed and reduced by a three-way function to purify the exhaust gas.

  Further, in order to prevent the NOx occlusion material from being poisoned by the sulfur content contained in the supplied unburned fuel or lubricating oil and reducing the NOx purification rate, the exhaust gas is made rich and the exhaust gas temperature is reduced. It is necessary to appropriately perform a desulfurization operation (S purge) that promotes sulfur desorption by raising the temperature to a high temperature (for example, 600 to 700 ° C. or the like).

  In general, the supply of unburned fuel into the exhaust gas in the exhaust gas purification system using the above-described PM collection filter and NOx occlusion reduction catalyst is performed by injecting unburned fuel from an injector inserted in the exhaust passage. Normally, pumps for supplying fuel to the engine body are used for pumping unburned fuel to the injector. However, in recent years, a dedicated electromagnetic pump has come to be used from the viewpoint of improving the exhaust gas purification rate by precisely controlling the injection pressure of unburned fuel from the injector at a high level and atomizing it. Yes.

  This electromagnetic pump has a function of adjusting the delivery pressure by controlling the rotation speed. However, because there is an individual difference in performance due to manufacturing tolerances in the electromagnetic pump that is an off-the-shelf product, there is a difference in the delivery pressure even at the same rotation speed, and the purification performance of the exhaust gas purification system varies between vehicles. There is a problem of being stuck.

JP 2005-16317 A JP 2001-355485 A

  An object of the present invention is to provide an exhaust gas purification system and a fuel supply method that can suppress variations in purification performance caused by individual differences of electromagnetic pumps that pump unburned fuel to an injector inserted in an exhaust passage. is there.

  The exhaust gas purification system of the present invention that achieves the above object includes a fuel supply means for supplying unburned fuel into an exhaust passage of an engine, and a catalytic converter interposed in the exhaust passage on the downstream side of the fuel supply means. Control means, and the fuel supply means is installed between an injector inserted into the exhaust passage, an electromagnetic pump for pumping the unburned fuel to the injector, and between the injector and the electromagnetic pump In the exhaust gas purification system having a flow rate adjustment valve, a pressure sensor for measuring the pressure of the unburned fuel is provided between the electromagnetic pump and the flow rate adjustment valve, and the control means is configured to request an operation of the fuel supply means. If so, after the flow rate adjustment valve is closed and the electromagnetic pump is started, the measured value of the pressure sensor is matched with the target pressure value within a predetermined range. It is characterized in performing control for adjusting the rotational speed of the electromagnetic pump.

  The fuel supply method of the present invention that achieves the above object is provided with an injector inserted into an exhaust passage of an engine, an electromagnetic pump that pumps the unburned fuel to the injector, and a space between the injector and the electromagnetic pump. In the fuel supply method using the flow rate adjusting valve, when there is a request to supply unburned fuel from the injector to the exhaust passage, the flow rate adjusting valve is closed, the electromagnetic pump is started, and the electromagnetic pump The rotational speed of the electromagnetic pump is adjusted so that the measured value of the pressure of unburned fuel between the flow rate adjustment valve and the target pressure value matches within a predetermined range, and the flow rate adjustment valve is opened to Unburned fuel is supplied from the injector to the exhaust passage.

  According to the exhaust gas purification system and the fuel supply method of the present invention, the delivery pressure of unburned fuel to the injector by the electromagnetic pump is corrected to a preset target pressure value. Variations in the purification performance of the exhaust gas purification system to be performed can be suppressed.

1 is a configuration diagram of an exhaust gas purification system according to a first embodiment of the present invention. It is a graph which shows the characteristic of an electromagnetic pump. It is a flowchart explaining the control content of ECU. It is a graph which shows the example of the map data which concerns on correction | amendment of the rotation speed of an electromagnetic pump. It is a block diagram of the exhaust gas purification system which consists of the 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an exhaust gas purification system according to the first embodiment of the present invention.

  This exhaust gas purification system 1A is installed in a large-diameter catalytic converter 4 interposed in an exhaust passage 3 through which exhaust gas G from a diesel engine 2 mounted on a vehicle flows, and in an exhaust passage 3 upstream of the catalytic converter 4. The fuel supply means 5 is provided.

  In the catalytic converter 4, a PM collection filter 7 in which an oxidation catalyst (DOC) 6 is disposed in the previous stage is stored. The DOC 6 is formed by supporting rhodium, cerium oxide, platinum, aluminum oxide or the like on a metal carrier formed into a structure having a function of mixing the exhaust gas G of the diesel engine 2. The PM collection filter 7 is formed of a monolith honeycomb wall flow type filter in which the inlet and outlet of a porous ceramic honeycomb channel (cell) are alternately plugged. In the configuration example of FIG. 1, the DOC 6 and the PM collection filter 7 are separated from each other. However, the DOC 6 and the PM collection filter 7 may be integrally used as a CSF in which an oxidation catalyst substance is supported on the filter.

  The fuel supply means 5 is installed between an injector 8 inserted into the exhaust passage 3, an electromagnetic pump 11 that pumps unburned fuel 10 from the fuel tank 9 to the injector 8, and the injector 8 and the electromagnetic pump 11. The flow rate adjusting valve 12 is provided. As shown in the example of FIG. 2, the electromagnetic pump 11 controls the liquid delivery pressure by adjusting the rotational speed. Further, the flow rate adjustment valve 12 has a function of controlling the injection amount and injection timing of the unburned fuel 10 injected from the injector 8.

  In this fuel supply means 5, a pressure sensor 13 that measures the pressure of the unburned fuel 10 is provided between the electromagnetic pump 11 and the flow rate adjustment valve 12.

  The electromagnetic pump 11 is connected to an ECU 14 as control means through an in-vehicle network (shown by a one-dot chain line), and the flow rate adjusting valve 12 and the pressure sensor 13 through hard wiring (shown by a solid line).

  The fuel supply method which consists of embodiment of this invention is demonstrated below based on FIG. 3 as control content of ECU14 in 1 A of exhaust gas purification systems mentioned above.

  The ECU 14 confirms whether or not there is a regeneration request for the PM collection filter 7 (S10). If there is a regeneration request, the ECU 14 closes the flow rate adjustment valve 12 assuming that there is an operation request for the fuel supply means 5. The valve is opened (zero opening) (S20), and the electromagnetic pump 11 is started at the initial rotational speed (S30). Examples of the trigger for the regeneration request of the PM collection filter 7 include a differential pressure of the catalytic converter 4 and an elapsed time since the previous regeneration. The initial rotational speed is set in advance based on the catalog value of the electromagnetic pump 11 or the like.

  Next, the ECU 14 inputs the measured value X of the pressure sensor 13 (S40), and compares it with the target pressure value A after a lapse of time until the measured value X becomes stable (S50) (S60). This target pressure value A is set to a high pressure value for each vehicle type so that the unburned fuel 10 injected from the injector 8 is atomized as much as possible, as long as each component of the fuel supply means 5 is not damaged. It is set in advance.

  Then, if the measured value X is significantly different from the target pressure value A, the ECU 14 adjusts the rotational speed of the electromagnetic pump 11 based on the map data so as to match within a predetermined range (S70).

  FIG. 4 shows an example of map data. This map data indicates the relationship between the deviation ΔP (= A−X) between the target pressure value A and the measured value X and the rotational speed of the electromagnetic pump 11, and is based on the performance specifications of the electromagnetic pump 11 in advance. Is set. Specifically, when the measured value X falls below the target pressure value A (ΔP is a positive value), the rotational speed of the electromagnetic pump 11 is increased, while the measured value X exceeds the target pressure value A (ΔP Is a negative value), the rotational speed of the electromagnetic pump 11 is decreased.

  In addition, after the process of step 70, you may perform the process which further makes deviation (DELTA) P of the target pressure value A and the measured value X smaller by increasing or decreasing rotation speed by the preset increment or decrement.

  When the measured value X matches the target pressure value P within a predetermined range, the ECU 14 ends the control. Thereafter, the ECU 14 performs control to adjust the opening degree of the flow rate adjustment valve 12 in accordance with the temperature of the exhaust gas G and the driving state of the vehicle, and starts injection of the unburned fuel 10 from the injector 8 into the exhaust passage 3. To do.

  By performing such control, the delivery pressure of the unburned fuel 10 to the injector 8 by the electromagnetic pump 11 can be corrected so as to approach the target pressure value A. Therefore, exhaust gas caused by individual differences of the electromagnetic pump 11 Variations in the purification performance of the purification system 1A can be suppressed.

  FIG. 5 shows a configuration of an exhaust gas purification system according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same part as FIG. 1, and the description is abbreviate | omitted.

  In this exhaust gas purification system 1B, an LNT catalyst 15 is stored in the catalytic converter 4. The LNT catalyst 15 is formed by supporting a catalyst metal and a NOx storage material on the surface of a cell support of a monolith honeycomb cell formed of γ alumina or the like. Pt or Pd is used as the catalyst metal. Further, as the NOx storage material, any one of alkali metals such as K, Na, Li, and Cs, and alkaline earth metals such as Ba and Ca, or a combination thereof is used.

  In such an exhaust gas purification system 1B, the ECU 14 performs the control of “rich spike or S purge” instead of the “regeneration request” in step 10 of FIG. 3, as in the case of the first embodiment. Thus, variation in the purification performance of the exhaust gas purification system 1B due to individual differences in the electromagnetic pump 11 can be suppressed.

1A, 1B Exhaust gas purification system 2 Diesel engine 3 Exhaust passage 4 Catalytic converter 5 Fuel supply means 6 DOC
7 PM collection filter 8 Injector 10 Unburned fuel 11 Electromagnetic pump 12 Flow rate adjusting valve 13 Pressure sensor 14 ECU
15 LNT catalyst

Claims (4)

A fuel supply means for supplying unburned fuel into the exhaust passage of the engine, a catalytic converter interposed in the exhaust passage on the downstream side of the fuel supply means, and a control means,
The fuel supply means includes an injector inserted into the exhaust passage, an electromagnetic pump for pumping the unburned fuel to the injector, and a flow rate adjusting valve installed between the injector and the electromagnetic pump. In the purification system,
A pressure sensor for measuring the pressure of the unburned fuel is provided between the electromagnetic pump and the flow control valve;
When there is a request for operation of the fuel supply means, the control means closes the flow rate adjusting valve and activates the electromagnetic pump, and then the measured value of the pressure sensor is within a predetermined range from the target pressure value. The exhaust gas purification system is characterized in that control is performed to adjust the rotational speed of the electromagnetic pump so as to agree with each other. A PM collection filter is stored in the catalytic converter,
The exhaust gas purification system according to claim 1, wherein the operation request for the fuel supply means is made simultaneously with the regeneration request for the PM collection filter. A NOx occlusion reduction catalyst is stored in the catalytic converter,
The exhaust gas purification system according to claim 1, wherein the operation request for the fuel supply means is made simultaneously with a request for a rich spike or a sulfur purge. In a fuel supply method using an injector inserted into an exhaust passage of an engine, an electromagnetic pump for pumping the unburned fuel to the injector, and a flow rate adjustment valve installed between the injector and the electromagnetic pump,
When there is a request to supply unburned fuel from the injector to the exhaust passage, the flow regulating valve is closed, the electromagnetic pump is started, and the pressure of unburned fuel between the electromagnetic pump and the flow regulating valve The fuel supply for supplying unburned fuel from the injector to the exhaust passage by adjusting the number of revolutions of the electromagnetic pump and opening the flow rate adjustment valve so that the measured value of the pressure coincides with the target pressure value within a predetermined range Method.

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