JP2016173037A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise a temperature of a selective catalyst reduction type NOx catalyst or a particulate filter with the usage of an intake heater.SOLUTION: An exhaust emission control system according to an embodiment of the invention includes a selective catalyst reduction type NOx catalyst 24 provided in an exhaust passage 4 of an engine 1, an intake heater 50 provided in an intake passage 3, and a control unit 100 for operating the intake heater when a temperature of the NOx catalyst is lower than a prescribed activation start temperature. The exhaust emission control system according to another embodiment of this invention includes a particulate filter 23 provided in the exhaust passage and having a catalyst, the intake heater provided in the intake passage, and the control unit 100 for operating the intake heater when execution of regeneration control for regenerating the particulate filter is requested and a temperature of the particulate filter is lower than a prescribed temperature required for regeneration.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification system, and more particularly to a system for purifying exhaust gas of an engine (internal combustion engine).

  Generally, the exhaust passage of a diesel engine captures a selective catalytic reduction type NOx catalyst for purifying nitrogen oxide (NOx) in exhaust gas and particulate matter (PM) contained in the exhaust gas. A particulate filter that collects and removes is installed.

  Patent Document 1 discloses that an intake heater, that is, an intake heater, is controlled in accordance with the exhaust gas temperature in order to improve the cold startability of the diesel engine and suppress white smoke emission after the cold start. Have been described.

JP-A-61-76755

  In order to set the NOx purification rate of the selective catalytic reduction type NOx catalyst to a certain level or higher, it is necessary to raise the temperature of the NOx catalyst to a predetermined temperature or higher.

  Further, when the amount of PM accumulated in the particulate filter exceeds a predetermined amount, regeneration control is performed so as to forcibly remove the accumulated PM to recover the PM trapping ability. Also in this regeneration control, it is necessary to raise the temperature of the particulate filter to a predetermined temperature or higher in order to improve the regeneration efficiency.

  On the other hand, the intake heater is generally used for improving the startability of the engine and improving the combustibility immediately after the start, and is not used for the purpose of raising the temperature of the selective catalytic reduction type NOx catalyst or the particulate filter. There wasn't.

  Accordingly, the present invention has been made in view of such circumstances, and an object thereof is to provide an exhaust gas purification system capable of raising the temperature of a selective catalytic reduction type NOx catalyst and a particulate filter using an intake heater. .

According to one aspect of the invention,
A selective catalytic reduction type NOx catalyst provided in the exhaust passage of the engine;
An intake heater provided in the intake passage of the engine;
A control unit that controls the intake heater to operate the intake heater when the temperature of the NOx catalyst is lower than a predetermined activation start temperature;
An exhaust gas purification system comprising: is provided.

According to another aspect of the invention,
A particulate filter provided in the exhaust passage of the engine and having a catalyst;
An intake heater provided in the intake passage of the engine;
The intake heater is operated so as to operate the intake heater when there is a regeneration control execution request for regenerating the particulate filter and the temperature of the particulate filter is lower than a predetermined temperature required for regeneration of the particulate filter. A control unit for controlling
An exhaust gas purification system comprising: is provided.

  According to the present invention, an excellent effect that the temperature of the selective catalytic reduction type NOx catalyst and the particulate filter can be raised using the intake heater is exhibited.

1 is a schematic view of an exhaust gas purification system according to an embodiment of the present invention. 3 is a flowchart showing a control routine of first control in the present embodiment. 6 is a flowchart showing a control routine of second control in the present embodiment.

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

  FIG. 1 is a schematic view of an exhaust gas purification system according to an embodiment of the present invention. The engine (internal combustion engine) 1 is a multi-cylinder compression ignition internal combustion engine mounted on a vehicle, that is, a diesel engine.

  The engine 1 includes an engine body 2, an intake passage 3 and an exhaust passage 4 connected to the engine body 2, and a fuel injection device 5. The engine body 2 includes structures such as a cylinder head, a cylinder block, and a crankcase, and a piston, a crankshaft, a valve mechanism, and the like housed therein.

  The fuel injection device 5 includes a common rail fuel injection device, and includes a fuel injection valve, that is, an injector 7 provided in each cylinder, and a common rail 8 connected to the injector 7. The injector 7 directly injects fuel into the cylinder 9. The common rail 8 stores the fuel injected from the injector 7 in a high pressure state.

  The intake passage 3 is mainly defined by an intake manifold 10 connected to the engine body 2 (particularly a cylinder head) and an intake pipe 11 connected to the upstream end of the intake manifold 10. The intake manifold 10 distributes and supplies the intake air sent from the intake pipe 11 to the intake ports of each cylinder. The intake pipe 11 is provided with an air cleaner 12, an air flow meter 13, a compressor 14 </ b> C of the turbocharger 14, an intercooler 15, and an electronically controlled throttle valve 16 in order from the upstream side. The air flow meter 13 is a sensor (intake air amount sensor) for detecting the intake air amount (intake air flow rate) per unit time of the engine 1.

  The exhaust passage 4 is mainly defined by an exhaust manifold 20 connected to the engine body 2 (particularly a cylinder head) and an exhaust pipe 21 disposed on the downstream side of the exhaust manifold 20. The exhaust manifold 20 collects exhaust gas sent from the exhaust port of each cylinder. A turbine 14 </ b> T of the turbocharger 14 is provided between the exhaust pipe 21 or between the exhaust manifold 20 and the exhaust pipe 21. In the exhaust pipe 21 downstream of the turbine 14T, an oxidation catalyst 22, a particulate filter (hereinafter referred to as “DPF”) 23, and a NOx catalyst 24 are provided in this order from the upstream side.

An oxidation catalyst (DOC: Diesel Oxidation Catalyst) 22 oxidizes and purifies unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust gas. The oxidation catalyst 22 has a function of heating and raising the temperature of exhaust gas with heat generated during oxidation of HC and CO. The oxidation catalyst 22 has oxidizes NO in the exhaust to NO _2, also the function of increasing the NO ₂ concentration in the exhaust gas.

  The DPF 23 collects and removes particulate matter (PM) contained in the exhaust gas. The DPF 23 will be described later.

  The NOx catalyst 24 is a catalyst for purifying nitrogen oxide NOx in the exhaust gas. The NOx catalyst 24 is composed of a selective catalytic reduction type NOx catalyst (SCR: Selective Catalytic Reduction), and can continuously reduce NOx when a reducing agent is added. An addition valve 25 for adding urea water as a reducing agent to the NOx catalyst 24 is provided on the upstream side of the NOx catalyst 24, particularly in the exhaust passage 4 near the inlet. In particular, the NOx catalyst 24 reduces and purifies NOx when the catalyst temperature (catalyst bed temperature) is in the active temperature range and urea water is added. When the urea water is added, the urea water is hydrolyzed in the exhaust pipe and on the catalyst to generate ammonia. This ammonia reacts with NOx to reduce NOx.

  The engine 1 also includes an EGR device 30. The EGR device 30 includes an EGR passage 31 for returning a part of exhaust gas (referred to as “EGR gas”) in the exhaust passage 4 (especially in the exhaust manifold 20) to the intake passage 3 (particularly in the intake manifold 10). The EGR cooler 32 that cools the EGR gas flowing through the EGR passage 31 and the EGR valve 33 for adjusting the flow rate of the EGR gas are provided.

  Further, in the present embodiment, an electronic control unit (hereinafter referred to as “ECU”) 100 serving as a control unit or a controller is provided. ECU 100 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like. The ECU 100 controls the injector 7, the throttle valve 16, and the EGR valve 33.

  Regarding the sensors, in addition to the air flow meter 13 described above, a rotational speed sensor 40 for detecting the rotational speed (rpm) of the engine and an accelerator opening sensor 41 for detecting the accelerator opening are provided. Further, exhaust temperature sensors 42, 43, and 44 are provided for detecting the exhaust temperature upstream of each of the oxidation catalyst 22, the DPF 23, and the NOx catalyst 24 or in the vicinity of the inlet. Further, a differential pressure sensor 45 for detecting a differential pressure between the exhaust pressure upstream and downstream of the DPF 23 is provided. Output signals from these sensors are sent to the ECU 100.

  ECU 100 estimates the temperatures of oxidation catalyst 22, DPF 23 (particularly, the catalyst), and NOx catalyst 24 based on the exhaust temperatures detected by exhaust temperature sensors 42, 43, 44, respectively. Each temperature may be directly detected by a temperature sensor provided in each of the oxidation catalyst 22, the DPF 23, and the NOx catalyst 24, or estimation and detection may be combined. These estimation and detection are collectively referred to as acquisition. Further, the ECU 100 estimates the PM accumulation amount of the DPF 23 based on the differential pressure detected by the differential pressure sensor 45. The PM accumulation amount can also be estimated based on the travel distance of the vehicle, the engine operation time, the fuel injection amount integrated value, and the like.

  Particularly in the present embodiment, an intake heater 50 is provided in the intake passage 3. The intake heater 50 is an electric heater provided with an electric heater, and is on / off controlled by the ECU 100. Intake heater 50 is installed in intake pipe 11 just before intake manifold 10 in this embodiment. Normally, the intake heater 50 is turned off. When the intake heater 50 is turned on, the intake heater 50 heats the intake air in the intake pipe 11. Thus, the heated intake air can be distributed to all the cylinders through the intake manifold 10.

  In the present embodiment, a so-called wall flow type DPF 23 is used in which both end openings of a honeycomb-shaped heat-resistant substrate are alternately closed in a checkered pattern. However, any type of filter that physically collects PM can be used, such as a mesh-shaped foam shape.

  The DPF 23 is a so-called continuous regeneration type DPF with a catalyst in which a noble metal (catalyst) such as Pt is supported on the inner wall thereof. In this case, during normal operation of the engine, HC in the exhaust gas supplied to the DPF is oxidized and burned by catalytic action, and at this time, PM accumulated in the DPF is burned and removed.

  However, as the engine operation time elapses, PM gradually accumulates inside the DPF. Therefore, when the PM accumulation amount in the DPF exceeds a predetermined amount, regeneration control for forcibly removing the accumulated PM to recover the PM trapping ability (that is, regenerating the DPF) ("DPF regeneration control"). ECU100 is performed by ECU100. At this time, for example, multi-injection such as post-injection is executed by the injector 7, and the air-fuel ratio of the exhaust gas is temporarily enriched. Then, a relatively large amount of HC contained in the exhaust gas reacts with the catalyst in the DPF, and the deposited PM is oxidized and burned by the reaction heat at this time. Instead of post injection or the like, a separate exhaust injector may be provided in the exhaust passage 4 to directly inject fuel into the exhaust passage 4.

  By the way, in order to set the NOx purification rate of the NOx catalyst 24 to a sufficiently high constant value or more, the temperature of the NOx catalyst 24 must be at least the activation start temperature or more. Here, the activation start temperature refers to the minimum temperature (for example, 200 ° C.) in the activation temperature range (for example, 200 to 400 ° C.) of the NOx catalyst 24.

  Therefore, the ECU 100 controls the intake heater 50 to operate (turn on) the intake heater 50 when the temperature of the NOx catalyst 24 is lower than a predetermined activation start temperature. As a result, the intake air temperature can be raised, and hence the exhaust gas temperature can be raised, and the temperature of the NOx catalyst 24 can be raised. And the temperature of the NOx catalyst 24 can be raised to the activation start temperature or higher at an early stage. The activation start temperature is experimentally obtained in advance and stored in the ECU 100.

  On the other hand, when the ECU 100 determines that the PM accumulation amount of the DPF 23 has exceeded the predetermined upper limit accumulation amount, the ECU 100 executes the DPF regeneration control on the condition that the DPF regeneration temperature condition described later is satisfied, assuming that there is a request for executing the DPF regeneration control. To do. The determination as to whether or not the PM deposition amount has exceeded the upper limit deposition amount is performed by comparing the PM deposition amount estimated from the detection value of the differential pressure sensor 45 with the upper limit deposition amount as described above.

  The DPF regeneration temperature condition is satisfied when the temperature of the DPF 23 (particularly its catalyst) is equal to or higher than a temperature necessary for regeneration of the DPF, that is, a predetermined lower limit temperature at which a desired regeneration efficiency can be obtained. If the DPF regeneration temperature condition is not satisfied when there is a request for executing the DPF regeneration control, the DPF regeneration control cannot be performed substantially, or the desired regeneration efficiency can be obtained even if the DPF regeneration control is performed. I can't.

  Therefore, when there is a DPF regeneration control execution request and the DPF regeneration temperature condition is not satisfied, the ECU 100 controls the intake heater 50 to operate (turn on) the intake heater 50. As a result, the intake air temperature can be raised, and consequently the exhaust gas temperature can be raised, and the temperature of the DPF 23 can be raised. And the temperature of DPF23 can be raised to a minimum temperature or more early. The lower limit temperature is also experimentally obtained in advance and stored in ECU 100.

  As described above, it is possible to raise the temperature of the selective catalytic reduction type NOx catalyst 24 and the DPF 23 using the intake heater 50.

  Next, the control routine of the first control in the present embodiment will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 100 at every predetermined calculation cycle τ (for example, 10 msec).

  First, in step S101, it is determined whether or not the estimated catalyst temperature Tc of the NOx catalyst 24 is lower than a predetermined activation start temperature Tcs.

  When the catalyst temperature Tc is lower than the activation start temperature Tcs, the intake heater 50 is turned on in step S102. Thereby, the catalyst temperature Tc can be raised to the activation start temperature Tcs at an early stage. On the other hand, when the catalyst temperature Tc is equal to or higher than the activation start temperature Tcs, the intake heater 50 is turned off (stopped) in step S103.

  Next, the control routine of the second control in the present embodiment will be described with reference to FIG. The illustrated routine is also repeatedly executed by the ECU 100 at every predetermined calculation cycle τ (for example, 10 msec).

  First, in step S201, it is determined whether there is a request for executing DPF regeneration control. If there is no execution request, the routine is terminated.

  If there is an execution request, it is determined in step S202 whether or not the estimated DPF temperature Td is lower than a predetermined lower limit temperature Tds.

  When the DPF temperature Td is lower than the lower limit temperature Tds, the intake heater 50 is turned on in step S203. Thereby, the DPF temperature Td can be raised to the lower limit temperature Tds at an early stage. On the other hand, when the DPF temperature Td is equal to or higher than the lower limit temperature Tds, the intake heater 50 is turned off in step S204.

  According to this routine, when the DPF regeneration control is requested and the DPF temperature Td is lower than the lower limit temperature Tds, the intake heater 50 is turned on, so that the DPF temperature Td can be raised to the lower limit temperature Tds early. . When the DPF temperature Td reaches the lower limit temperature Tds, DPF regeneration control is started or executed in another routine, and the DPF is regenerated. The intake heater 50 is turned off after the DPF temperature Td reaches the lower limit temperature Tds.

  Although the basic embodiment of the present invention has been described in detail above, the present invention can be applied to other embodiments as described below.

  (1) In the basic embodiment described above, when there is a request for execution of DPF regeneration control and the DPF temperature Td is lower than the lower limit temperature Tds, the intake heater 50 is turned on, and the DPF temperature Td is set without executing the DPF regeneration control. Waiting for the temperature to become equal to or higher than the lower limit temperature Tds, DPF regeneration control was executed when the DPF temperature Td became equal to or higher than the lower limit temperature Tds, and the intake heater 50 was also turned off.

  On the other hand, in this other embodiment, when there is a request for executing the DPF regeneration control and the DPF temperature Td is lower than the lower limit temperature Tds, the intake heater 50 is turned on and the DPF regeneration control is executed. When the temperature reaches the lower limit temperature Tds or more, the DPF regeneration control is continuously executed, and the intake heater 50 is also turned off.

  In this way, when the DPF temperature Td is lower than the lower limit temperature Tds, the exhaust gas is enriched by executing the DPF regeneration control. However, since the DPF temperature Td is not a high temperature necessary for regeneration, high regeneration efficiency is obtained. Is difficult. However, it is still possible to raise the DPF temperature Td to the lower limit temperature Tds more quickly by executing the DPF regeneration control than when the intake heater 50 is merely turned on. Therefore, the DPF temperature required for DPF regeneration can be realized earlier, and DPF regeneration control can be performed with high efficiency at an earlier timing.

  (2) The installation position and configuration of the intake heater 50 are arbitrary. For example, the intake heater 50 may be installed in the intake pipe 11 downstream of the intercooler 15 and upstream of the throttle valve 16. The intake heater 50 may be composed of a gas burner that heats intake air by burning fuel.

  The configurations of the above-described embodiments can be combined partially or wholly unless there is a particular contradiction. The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 Engine 3 Intake passage 4 Exhaust passage 23 Particulate filter (DPF)
24 NOx catalyst 50 Intake heater 100 Electronic control unit (ECU)

Claims (2)

A selective catalytic reduction type NOx catalyst provided in the exhaust passage of the engine;
An intake heater provided in the intake passage of the engine;
A control unit that controls the intake heater to operate the intake heater when the temperature of the NOx catalyst is lower than a predetermined activation start temperature;
An exhaust gas purification system comprising: A particulate filter provided in the exhaust passage of the engine and having a catalyst;
An intake heater provided in the intake passage of the engine;
The intake heater is operated so as to operate the intake heater when there is a regeneration control execution request for regenerating the particulate filter and the temperature of the particulate filter is lower than a predetermined temperature required for regeneration of the particulate filter. A control unit for controlling
An exhaust gas purification system comprising:

Images