JP2010261387A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of restraining the amount of NOx discharged to the outside without being purified during cold start or the like of an internal combustion engine, while restraining device cost and fuel consumption. <P>SOLUTION: This exhaust emission control device has a NOx catalyst 35, a NOx adsorption catalyst 25 for temporarily adsorbing-holding NOx, and a burner 60 as a heating means capable of heating exhaust gas. For relatively increasing a NOx adsorption amount for possibly adsorbing the NOx adsorption catalyst 25 during cold start of the internal combustion engine, bed temperature thereof is raised by the burner 60 to a first temperature region in first stage temperature rise control, and for desorbing NOx adsorbed to the NOx adsorption catalyst 25 and relatively increasing a NOx purification rate of the NOx catalyst 35, the bed temperature of the NOx catalyst 25 is raised to a second temperature region higher than the first temperature region. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  As an exhaust purification device that purifies nitrogen oxides (NOx) contained in exhaust gas discharged from an internal combustion engine, Patent Literature 1 heats a NOx adsorption catalyst that adsorbs NOx, a NOx catalyst that purifies NOx, and a NOx adsorption catalyst. And a high-temperature gas generator that supplies combustion gas for the purpose. In this exhaust purification device, NOx in the exhaust gas is adsorbed by the NOx adsorption catalyst, and when the amount of NOx adsorbed by the NOx adsorption catalyst reaches a certain level, the combustion gas is transferred from the high temperature gas generator to the NOx adsorption catalyst. To be supplied. Thereby, NOx adsorbed on the NOx adsorption catalyst is desorbed. The desorbed NOx is purified by the NOx catalyst.

Japanese Patent Laid-Open No. 3-135417

  Incidentally, the NOx adsorption catalyst and the NOx catalyst each have an active temperature range in which NOx is adsorbed efficiently or NOx can be purified efficiently. For this reason, at the time of cold start of the internal combustion engine or the like, if the NOx adsorption catalyst and the NOx catalyst are not warmed up early, NOx may be discharged outside without being purified. If the heating means is provided for each of the NOx adsorption catalyst and the NOx catalyst for early warming, there is a problem that the cost of the apparatus is significantly increased and the fuel consumption is also deteriorated.

  An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can suppress the amount of NOx released to the outside without being purified at the time of cold start of the internal combustion engine and the like and can reduce the cost and fuel consumption of the device. It is in.

  An exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust passage of the internal combustion engine, is provided on the upstream side of the NOx catalyst in the exhaust passage, and is included in the exhaust gas. NOx adsorption catalyst that temporarily adsorbs and retains NOx, a heating means that is provided upstream of the NOx adsorption catalyst in the exhaust passage and that can heat exhaust gas, and the NOx adsorption catalyst can be adsorbed when the internal combustion engine is started In order to relatively increase the NOx adsorption amount, the first stage temperature rise control for raising the bed temperature of the NOx adsorption catalyst to the first temperature range by the heating means, and NOx adsorbed on the NOx adsorption catalyst In order to desorb and relatively increase the NOx purification rate of the NOx catalyst, the bed temperature of the NOx catalyst is increased by the heating means to a second temperature range higher than the first temperature range. And having a control means for executing a second stage temperature rise control for raising the temperature.

  In the above configuration, the first temperature range is a temperature range in which the NOx adsorption catalyst is activated, and the second temperature range is a temperature range in which the NOx catalyst is activated.

  The said structure WHEREIN: The said heating means can employ | adopt the structure containing the burner which supplies fuel and air and supplies the combustion gas as waste gas to the said exhaust passage.

  In the above configuration, a filter for collecting particulate matter contained in the exhaust gas is further provided between the NOx adsorption catalyst and the NOx catalyst in the exhaust passage, and the heating means regenerates the purification function of the filter It is possible to employ a configuration used for filter regeneration processing.

  According to the present invention, it is possible to suppress the amount of NOx released to the outside without being purified at the time of cold start of the internal combustion engine or the like while suppressing the apparatus cost and fuel consumption.

1 is a schematic diagram illustrating a configuration of an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention. It is a graph which shows an example of the relationship between the adsorption amount of a NOx adsorption catalyst, the purification rate of a NOx catalyst, and temperature. It is a timing chart for demonstrating 1st step temperature rising control and 2nd step temperature rising control. It is a graph which shows an example of the change of the NOx amount in temperature rising control. It is a flowchart which shows an example of the temperature rising control by ECU.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a configuration diagram of an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention.
In FIG. 1, the internal combustion engine 10 is a diesel engine, for example, and a burner 60 as a heating unit is provided on the upstream side of the exhaust passage 15 of the internal combustion engine 10. An air supply path 61 for supplying air and a fuel supply path 62 for supplying fuel are connected to the burner 60 from the internal combustion engine 10 side. The burner 60 combusts the fuel supplied from the fuel supply path 62 and supplies the combustion gas to the exhaust passage 15. Further, by controlling the amount of air from the air supply path 61 and the amount of fuel from the fuel supply path 62, the air-fuel ratio of the combustion gas is controlled. The burner 60 is used to raise the bed temperature of the NOx adsorption catalyst 25, the DPF 30, and the NOx catalytic converter 35 described later.

  The combustion gas exhausted from the burner 60 may be exhausted to the exhaust passage 15 in a completely burned state, or may be exhausted to the exhaust passage 15 in a state containing unburned fuel.

  On the downstream side of the burner 60 in the exhaust passage 15, a NOx adsorption catalyst 25, a DPF (diesel particulate filter) 30 as a filter, and a NOx catalyst 35 are provided in this order.

  In the exhaust passage 15, a NOx sensor 95 </ b> A that detects the concentration of nitrogen oxides is provided downstream of the NOx catalyst 35, and a NOx sensor 95 </ b> B is provided upstream of the NOx catalyst 35. An exhaust temperature sensor 90 is provided at each of the inlet of the NOx adsorption catalyst 25, the inlet / outlet of the DPF 30, and the inlet of the NOx catalyst 35, and detection signals from these sensors are input to the ECU 100 as control means.

  Further, in the exhaust passage 15, a urea water addition valve 70 for adding a urea aqueous solution to the exhaust passage 15 and a downstream of the urea water addition valve 70 are provided between the DPF 30 and the NOx catalyst 35. And an addition valve downstream mixer 80 for mixing the urea aqueous solution.

  The NOx adsorption catalyst 25 is composed of an adsorption catalyst such as zeolite, and temporarily adsorbs NOx contained in the exhaust gas EG. Note that the maximum NOx adsorption amount that can be adsorbed by the NOx adsorption catalyst 25 varies according to the bed temperature, as will be described later.

  The DPF 30 is a filter that collects particulate matter (PM) contained in the exhaust gas EG. As is well known, the structure of the DPF 30 is composed of, for example, a honeycomb body made of metal or ceramics. The DPF 30 needs to be regenerated when a predetermined amount of PM is deposited. Specifically, the exhaust gas EG and unburned fuel heated by the burner 060 are supplied to the DPF 30. As a result, the collected PM is burned and the filter function is regenerated. The temperature of the DPF 30 in this regeneration process is, for example, about 600 to 700 ° C. Note that the determination of whether a predetermined amount of PM has accumulated on the DPF 30 is a well-known technique, and a description thereof will be omitted. Further, the DPF 30 may be configured to carry an oxidation catalyst made of a noble metal.

  The urea water addition valve 70 is supplied with urea water from a tank 75 that stores a urea aqueous solution, and adds an amount of urea water according to a control signal from the ECU 100 to the exhaust passage 15.

  The NOx catalyst 35 selectively reduces NOx contained in the exhaust gas EG into nitrogen gas and water using the urea aqueous solution added from the urea addition valve 70 as a reducing agent. Specifically, the urea aqueous solution added to the exhaust gas EG is hydrolyzed by the heat of the exhaust gas EG to change to ammonia, and is adsorbed and held by the NOx catalyst 35. The ammonia adsorbed and held by the NOx catalyst 35 reacts with NOx and is reduced to water and harmless nitrogen. If the ammonia adsorption amount of the NOx catalyst 35 exceeds the saturated adsorption amount, ammonia slip may occur, and if it is too small, NOx may not be sufficiently purified. As a reducing agent, ammonia can be directly supplied instead of urea.

  The NOx catalyst 35 has a well-known structure. For example, the NOx catalyst 35 is composed of zeolite containing Si, O, and Al as main components and containing Fe ions, for example, a vanadium catalyst on the surface of a base material made of aluminum oxide alumina. A material carrying (V2O5) or the like can be used, and is not particularly limited thereto.

  The ECU 100 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a backup memory such as an EEPROM (Electronically Erasable and Programmable Read Only Memory), an A / D converter, a buffer, and the like. It comprises hardware including an output interface circuit including an input interface circuit, a drive circuit, etc., and necessary software. ECU 100 controls urea water addition amount control for controlling the amount of urea water added as a reducing agent from urea water addition valve 70 based on signals from exhaust temperature sensors 90A to 90D, NOx sensors 95A and 95B, and the like. The bed temperature of the NO adsorption catalyst 25 and the bed temperature of the NOx catalyst 35 are controlled by the burner 60.

Next, the principle of the present invention will be described with reference to FIGS.
First, as shown in FIG. 2, the adsorption amount (maximum adsorption amount) of the NOx adsorption catalyst 25 and the NOx purification rate (maximum purification rate) of the NOx catalyst 35 change according to the bed temperature. Specifically, as the temperature of the NOx adsorption catalyst 25 rises from the cold start, the adsorption amount becomes maximum at the temperature Ta, and the adsorption amount decreases as the temperature rises thereafter. The NOx purification rate of the NOx catalyst 35 increases as the temperature increases from the cold start, reaches a maximum at a temperature T2 higher than the temperature Ta, and then decreases as the temperature increases.

  In the present invention, by utilizing the properties of the NOx adsorption catalyst 25 and the NOx catalyst 35 as described above, as shown in FIG. 3, the NOx adsorption that can be adsorbed by the NOx adsorption catalyst 25 at the time of cold start (during cold start). In order to increase the amount relatively, the NOx adsorption catalyst 25 is adsorbed by the NOx adsorption catalyst 25 and the first stage temperature rise control in which the bed temperature of the NOx adsorption catalyst 25 is raised to the first temperature range (near temperature Ta) using the burner 60. In order to desorb NOx and to relatively increase the NOx purification rate of the NOx catalyst 35, the bed temperature of the NOx catalyst 25 is set to a second temperature range (temperature T2) higher than the first temperature range (near temperature Ta). The second stage temperature rise control is performed to raise the temperature using the burner 60 until the vicinity).

  That is, in the present invention, in order to quickly increase the NOx adsorption amount of the NOx adsorption catalyst 25 at the cold start, the temperature is forcibly increased to a temperature range where NOx is most easily adsorbed, and NOx is adsorbed efficiently, (Section A in FIG. 3). When the bed temperature of the NOx adsorption catalyst 25 is raised, the bed temperature of the NOx catalyst 35 is raised accordingly. At this time, as shown in FIG. 3, when the bed temperature of the NOx catalyst reaches a predetermined threshold temperature T1 (in the vicinity of B shown in FIG. 3), the temperature control target is changed from the NOx adsorption catalyst 25 to the NOx catalyst. Instead of 35, the temperature of the NOx catalyst 35 is raised to the second temperature range T2. Here, it is preferable that the temperature range T1 is a temperature range in which the purification rate α is obtained such that the amount of NOx discharged to the outside shown in FIG. 2 can be suppressed to a predetermined NOx amount X (ppm) or less.

  Alternatively, the switching timing from the first stage temperature rise control to the second stage temperature rise control is the timing when the estimated amount of NOx adsorbed by the NOx adsorption catalyst 25 exceeds a predetermined threshold Th. It is also possible to do.

  Here, FIG. 4 shows an example of changes in the amount of NOx detected before the NOx catalyst 25 and the amount of NOx released to the outside (released from the tail pipe) when the temperature raising control as described above is executed. The description will be given with reference.

  Since the purification of NOx is not progressing near the cold start time, the amount of NOx before the NOx catalyst 25 and the amount of NOx released from the tail pipe are relatively large. Since the temperature of the NOx adsorption catalyst 25 rises and the adsorption capacity increases, the amount of NOx before the NOx catalyst 25 and the amount of NOx released from the tail pipe are rapidly reduced. When the section A is reached and the second stage temperature increase control is switched at the point B, the NOx adsorbed by the NOx adsorption catalyst 25 is purged, so that the amount of NOx before the NOx catalyst 25 increases. However, the amount of NOx released from the tail pipe does not exceed the predetermined NOx amount X even at the maximum. Α (T1) shown in FIG. 4 corresponds to the NOx purification rate obtained at least in the temperature range T1.

  Next, an example of the temperature increase control by the ECU 100 will be described with reference to a flowchart shown in FIG. The processing routine shown in FIG. 5 is executed when the internal combustion engine is cold started.

  First, the burner 60 is activated to heat the NOx adsorption catalyst 25 to the activation temperature (near the temperature Ta) (step S1). That is, the first stage temperature increase control is executed. The temperature of the NOx adsorption catalyst 25 can be estimated from the output of the exhaust temperature sensor, for example.

  Next, it is determined whether the bed temperature of the NOx adsorption catalyst 25 has exceeded the temperature T1 (step S2). The bed temperature of the NOx adsorption catalyst 25 can be estimated from the output of the exhaust temperature sensor.

  When the bed temperature of the NOx adsorption catalyst 25 exceeds the temperature T1, it is determined whether the estimated value of the NOx adsorption amount of the NOx adsorption catalyst 25 exceeds a predetermined threshold value Th (step S3). When exceeding, the NOx catalyst 35 is heated to the activation temperature (near temperature T2) (step S4). That is, the second stage temperature increase control is executed.

  In the above embodiment, the case where the DPF 30 is provided and the selective reduction catalyst is heated using the regeneration process of the DPF 30 has been described, but the present invention is not limited to this. A configuration without the DPF 30 is also possible. When the DPF 30 is provided on the downstream side of the NOx catalytic converter 35, the selective reduction catalyst may be heated using a burner or a heater, or during rapid acceleration, etc. It is also possible to raise the temperature to a high temperature region by utilizing the temperature rise of the exhaust gas when a high load is applied to the internal combustion engine.

  In the above embodiment, the burner 60 is used as the heating means. However, for example, other heating means such as a heater for heating the exhaust gas itself may be used.

DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine 15 ... Exhaust passage 25 ... NOx adsorption catalyst 30 ... DPF (filter)
35 ... NOx catalyst 60 ... Burner 70 ... Urea water addition valve 100 ... ECU
90A to 90D ... exhaust temperature sensors 95A, 95B ... NOx sensors

Claims (4)

A NOx catalyst provided in an exhaust passage of the internal combustion engine for purifying NOx contained in the exhaust gas;
A NOx adsorption catalyst provided upstream of the NOx catalyst in the exhaust passage and temporarily adsorbing and holding NOx contained in the exhaust gas;
A heating means provided upstream of the NOx adsorption catalyst in the exhaust passage and capable of heating exhaust gas;
First-stage temperature rise control for raising the bed temperature of the NOx adsorption catalyst to a first temperature range by the heating means in order to relatively increase the NOx adsorption amount that can be adsorbed by the NOx adsorption catalyst when the internal combustion engine is started. In order to desorb NOx adsorbed on the NOx adsorption catalyst and relatively increase the NOx purification rate of the NOx catalyst, a bed temperature of the NOx catalyst is set to a second temperature higher than the first temperature range. Control means for performing second-stage temperature rise control for raising the temperature by the heating means to a temperature range;
An exhaust emission control device for an internal combustion engine, comprising:   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the heating unit includes a burner that is supplied with fuel and air and supplies combustion gas as exhaust gas to the exhaust passage. A filter for collecting particulate matter contained in the exhaust gas between the NOx adsorption catalyst and the NOx catalyst in the exhaust passage;
The exhaust purification device for an internal combustion engine according to claim 1 or 2, wherein the heating means is used for a filter regeneration process for regenerating the purification function of the filter.   The first temperature range is a temperature range in which the NOx adsorption catalyst is activated, and the second temperature range is a temperature range in which the NOx catalyst is activated. 4. An exhaust emission control device for an internal combustion engine according to any one of 3 above.

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