JP2002004838A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for a diesel engine for which no accumulation of PM occurs by surely burning PM collected by a DPF over the whole operating region of the engine. SOLUTION: An oxidizing catalyst 20, a DPF 21 for collecting PM in exhaust gas, and an exhaust gas temperature sensor 55 for detecting the temperature of the exhaust gas are situated in an exhaust passage 13. A controller 60 is provided control the air amount regulating mechanism disposed in a suction passage 12, so that the exhaust gas temperature is adjusted to be within a prescribed temperature range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for a diesel engine, and more particularly to an exhaust gas purifying apparatus for removing particulates in exhaust gas.

[0002]

2. Description of the Related Art Exhaust gas regulations of diesel engine vehicles have been strengthened year by year, and there is an urgent need to reduce particulate matter (hereinafter, PM) containing carbon as a main component. As a device for removing PM, a diesel particulate filter (hereinafter, DPF) is known, and a movement to require a DPF to be mounted on a diesel engine vehicle is in full swing. By the way, since PM collected by the repeated operation of the engine accumulates in the DPF mounted on the diesel engine vehicle, it is necessary to burn the collected PM to regenerate the DPF. As a means for this regeneration, there is a method of burning PM by heating with an electric heater, a burner, or the like. According to this method, a system in which a plurality of DPFs are arranged in parallel in an exhaust passage to alternately perform collection and combustion. Becomes Further, as another means for regenerating the DPF, an oxidation catalyst is provided in an exhaust passage upstream of the DPF, and NO in the exhaust gas is oxidized to NO ₂ by the oxidation catalyst, and PM is burned by NO ₂ . A method, a so-called continuous regeneration method, is also being studied, and is disclosed in, for example, Japanese Patent No. 301,249. In this continuous regeneration type DPF, since PM burns at a low temperature of 400 ° C. or less, there is no need to provide a special heating means such as an electric heater or a burner, and there is no need to provide a plurality of DPFs. It has the advantage of being simple and compact.

[0003]

FIG. 2 shows a continuous regeneration type D
5 is a graph showing the relationship between the exhaust gas temperature in PF and the combustion characteristics of PM. The combustion characteristic of PM in FIG.
It is shown by the amount of CO ₂ emitted by the combustion of M. As shown in FIG.
It shows a tendency that PM combustion becomes active in the range of 00 ° C. FIG. 3 is a graph showing the relationship between the operating state of the diesel engine and the exhaust gas temperature. As shown in FIG. 3, the exhaust gas temperature is lower than 250 ° C. in the low-load low-rotation region including the idling state (the lower left region in FIG. 3).
Conversely, the exhaust gas temperature is higher than 400 ° C. in the high-load high-rotation region (upper right region in FIG. 3). Therefore, in these operating regions, the combustion of the trapped PM does not proceed, and the PM is added to the DPF.
Is deposited, which causes a problem that the exhaust performance becomes large and the engine performance is greatly reduced. Furthermore, when a high-temperature exhaust gas of 600 ° C. or more is circulated to the DPF on which a large amount of PM is deposited, the PM burns rapidly, the temperature of the DPF itself rises to 2000 ° C. or more, and the DPF burns. Problems arise.

[0004] The present invention has been made in view of the above points,
The main technical problem is to provide an exhaust gas purifying apparatus for a diesel engine in which PM trapped in a DPF is reliably burned in the entire operation range of the engine and PM is not deposited.

[0005]

According to the present invention, in order to solve the above-mentioned main technical problems, an oxidation catalyst and a diesel particulate filter for collecting particulates in exhaust gas are provided in an exhaust passage of a diesel engine. In the exhaust gas purifying apparatus for a diesel engine, the air amount adjusting mechanism arranged in the intake passage of the diesel engine for adjusting the amount of air taken into the cylinder of the diesel engine, and detecting the temperature of the exhaust gas Exhaust gas temperature detecting means, and a controller for controlling an air amount adjusting mechanism based on the exhaust gas temperature detected by the exhaust gas temperature detecting means, wherein the controller controls the air flow so that the exhaust gas temperature falls within a predetermined temperature range. An exhaust gas purification device for a diesel engine is provided, which controls an amount adjustment mechanism.

The air amount adjusting mechanism includes air amount reducing means for reducing the amount of air taken into the cylinder, and air amount increasing means for increasing the amount of air taken into the cylinder. When the exhaust gas temperature is lower than the lower limit of the predetermined temperature range, the air amount reducing means is controlled, and when the exhaust gas temperature is higher than the upper limit value of the predetermined temperature range, the air amount increasing means is controlled. The air amount reducing means is constituted by an intake throttle valve, and the air amount increasing means is constituted by a supercharger. Further, it is desirable that a NOx catalyst be disposed in the exhaust passage of the diesel engine, and the lower limit of the predetermined temperature range be set to 300 ° C.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of an exhaust gas purification device for a diesel engine according to the present invention. A diesel engine 10 shown in FIG. 1 includes an engine body 11 including a cylinder block and a cylinder head, an intake passage 12 for introducing air into a cylinder formed in the engine body 11, and exhaust gas from a cylinder of the engine body 11. Exhaust passage 13 for exhausting air. The intake passage 12 includes an intake pipe 14 and an intake manifold 15.
The intake manifold 15 is connected to the engine body 11. On the other hand, the exhaust passage 13 includes an exhaust pipe 16 and an exhaust manifold 17, and the exhaust manifold 17 is connected to the engine body 11.

An oxidation catalyst 20, a DPF 21, and a NOx catalyst 22 are arranged in the exhaust pipe 16 from the upstream side. The oxidation catalyst 20 is formed, for example, by coating activated alumina or the like on the surface of a carrier made of honeycomb cordierite or heat-resistant steel to form a wash coat layer, and forming a noble metal such as platinum, palladium, or rhodium on the coat layer. What carried the catalytically active component which consists of is used. The oxidation catalyst 20 oxidizes NO in the exhaust gas to generate NO _2, and forms HC and C in the exhaust gas.
O is oxidized to produce H ₂ O and CO ₂ . Also, DP
F21 is a so-called wall flow type honeycomb filter in which many cells are formed in parallel with, for example, porous cordierite or silicon carbide, and the inlet and outlet of the cells are alternately closed. A fibrous filter wound in multiple layers around a perforated tube is used to trap PM in exhaust gas. NO
The x catalyst 22 may have the same structure and components as those of the oxidation catalyst 20, and reduce NOx (nitrogen oxide) such as NO in exhaust gas to N ₂ or H ₂ O.

The intake pipe 14 is provided with an intake throttle valve 30 for adjusting the amount of air taken into the cylinder of the engine body 11. The intake throttle valve 30 is opened and closed by a negative pressure diaphragm actuator 31. The actuator 31 adjusts the opening of the intake throttle valve 30 by adjusting the ratio of the negative pressure introduced from a vacuum pump (not shown) into the negative pressure chamber. It should be noted that the intake throttle valve 30 is normally kept at the fully open position. The exhaust pipe 16 on the upstream side of the oxidation catalyst 20 is provided with an exhaust throttle valve 32 for adjusting the amount of exhaust gas flowing from the exhaust manifold 17 to the outlet of the exhaust pipe 16. The exhaust throttle valve 32 is, similarly to the intake throttle valve 30, a negative pressure diaphragm type actuator 3.
3 is opened and closed. The actuator 33 adjusts the opening of the exhaust throttle valve 32 by adjusting the ratio of the negative pressure introduced from a vacuum pump (not shown) into the negative pressure chamber. The exhaust throttle valve 32 is also normally kept at the fully open position.

The intake pipe 1 on the upstream side of the intake throttle valve 30
4, a bypass passage 14a that bypasses a part of the intake pipe 14 is provided, and a supercharger 40 that forcibly sends air into a cylinder of the engine body 11 is provided in the bypass passage 14a. I have. As the supercharger 40, for example, a positive displacement supercharger such as a screw type or a roots type can be used, and any of a compression type and a non-compression type can be used. The supercharger 40 is driven by the rotational driving force of the crankshaft 18 of the engine body 11. That is, the rotor shaft 40 a of the supercharger 40 is operatively connected to the crankshaft 18 via a power transmission mechanism including the electromagnetic clutch 41, the supercharger driving pulley 42, the belt 43, and the crank pulley 19.
Therefore, when the electromagnetic clutch 41 is deenergized, power transmission to the rotor shaft 40a of the supercharger 40 is interrupted, and when the electromagnetic clutch 41 is energized, the rotor shaft 40a of the supercharger 40 is driven. Can be The electromagnetic clutch 41 is normally kept in a disconnected state so that the supercharger 40 is not driven. In the illustrated embodiment, the intake throttle valve 30 and the supercharger 40 function as an air amount adjusting mechanism for adjusting the amount of air taken into the cylinder of the engine body 11.

An on-off valve 34 is provided in the intake pipe 14 between the inlet and the outlet of the bypass passage 14a. On-off valve 3
4 is opened and closed by a diaphragm actuator 35 of a negative pressure type. The actuator 35 closes the on-off valve 34 by introducing a negative pressure from a vacuum pump (not shown) into the negative pressure chamber. The on-off valve 34 is normally kept open.

The diesel engine 10 in the illustrated embodiment has an EGR device 5 for recirculating a part of the exhaust gas to the intake passage 12 to reduce the amount of NOx in the exhaust gas.
0 is provided. The EGR device 50 includes an EGR passage 51 that communicates between the exhaust manifold 17 and the intake pipe 14,
An EGR valve 52 is provided in the EGR passage 51. The end of the EGR passage 51 on the side of the intake pipe 14 is connected to the downstream side of the intake throttle valve 30. The EGR valve 52 employs a diaphragm type,
The opening is adjusted by adjusting the ratio of the negative pressure introduced from a vacuum pump (not shown) to the negative pressure chamber. EG
The opening of the R valve 51 is normally determined according to the operating state (the number of revolutions, load, etc.) of the diesel engine 10.

The exhaust manifold 17 is provided with an exhaust gas temperature sensor 55 for detecting the temperature of exhaust gas discharged from a cylinder of the engine body 11. The signal detected by the exhaust gas temperature sensor 55 is input to a controller 60 that controls the above-described devices constituting the diesel engine 10. The controller 60 controls the actuator 31 of the intake throttle valve 30, the actuator 33 of the exhaust throttle valve 32, the actuator 35 of the on-off valve 34, the electromagnetic clutch 41, and the EGR valve based on the exhaust gas temperature detected by the exhaust gas temperature sensor 55. The control signal is output to 52 and the like.

The exhaust gas purifying apparatus for a diesel engine 10 shown in FIG. 1 is configured as described above.
The exhaust gas discharged from one cylinder is purified by the oxidation catalyst 20, the DPF 21 and the NOx catalyst 22 arranged in the exhaust pipe 16. Hereinafter, PM in exhaust gas,
And the process of purifying NOx will be described. First, the exhaust gas is NO in the exhaust gas passing through the oxidation catalyst 20 is oxidized to form NO _2. Next, the exhaust gas is DPF
After passing through the PM 21, PM in the exhaust gas is collected by the DPF 21. Here, NO ₂ + C → NO + CO, 2N by the trapped PM and NO ₂ generated by the oxidation catalyst 20.
A chemical reaction occurs due to O ₂ + 2C → N ₂ + 2CO ₂ . That is, the trapped PM is oxidized (burned) to CO or CO ₂ by NO ₂ . Finally, if the exhaust gas is N
When passing the Ox catalyst 22, NO generated in the reaction in the DPF21 are reduced to harmless _{N 2} and _{H 2} O. By the above process, PM and N in the exhaust gas
Ox is purified.

Further, as shown in FIG. 2, when the exhaust gas temperature is other than 250 ° C. to 400 ° C., the reaction between PM and NO ₂ does not proceed, so that the collected PM is not burned. Thus, the diesel engine 10 in the illustrated embodiment
The following control is executed in the exhaust gas purifying apparatus of the first embodiment. First, when the exhaust gas temperature detected by the exhaust gas temperature sensor 55 is lower than a preset lower limit temperature, for example, 250 ° C., the controller 60 causes the actuator 31 to close the intake throttle valve 30 by a predetermined amount from the fully open position. Outputs control signal. When the intake throttle valve 30 is throttled and the amount of air taken into the cylinder of the engine body 11 decreases, the combustion is performed in a state where the amount of air is too small (fuel rich) with respect to the amount of fuel injection. Rises. As described above, the intake throttle valve 30 functions as an air amount reducing unit that reduces the amount of air taken into the cylinder of the engine body 11.
When the exhaust gas temperature is lower than the lower limit side set temperature, the intake throttle valve 30 is throttled and the engine body 11
Is controlled so as to reduce the amount of air taken into the cylinder and increase the temperature of the exhaust gas until the temperature at which the collected PM burns, that is, the lower limit set temperature. The relationship between the exhaust gas temperature and the degree of opening of the intake throttle valve 30 may be set in advance, and the closing amount of the intake throttle valve 30 may be changed according to the exhaust gas temperature.

When the air amount is adjusted by the intake throttle valve 30, the temperature in the combustion chamber at the compression top dead center may decrease due to the decrease in the air amount, and the ignitability of the injected fuel may deteriorate. The control unit 60 may output a control signal to the EGR valve 52 so as to open the EGR valve 52. That is, when the EGR valve 52 is opened and the EGR gas is sucked into the cylinder of the engine body 11, a small amount of unburned fuel component contained in the EGR gas becomes a fire source, and the ignitability is improved. When performing such EGR control, the controller 60 may output a control signal to the actuator 33 so as to close the exhaust throttle valve 32 by a predetermined amount from the fully open position. That is, when the exhaust throttle valve 32 is throttled, the pressure in the exhaust passage 13 increases, and the EGR gas is easily recirculated to the intake passage 12, so that the EGR gas amount can be increased.

On the other hand, when the exhaust gas temperature detected by the exhaust gas temperature sensor 55 is higher than a preset upper limit temperature, for example, 400 ° C., the controller 60 connects the electromagnetic clutch 41 and further opens and closes the on-off valve 34. A control signal is output to the electromagnetic clutch 41 and the actuator 35 so as to be in the fully closed position. When the supercharger 40 is driven by the connection of the electromagnetic clutch 41 and the amount of air sucked into the cylinder of the engine body 11 increases, combustion is performed in a state where the amount of air is excessive with respect to the fuel injection amount (fuel lean). So that
The exhaust gas temperature decreases. As described above, the supercharger 40 functions as an air amount reducing unit that increases the amount of air taken into the cylinder of the engine body 11, and the controller 60 determines that the exhaust gas temperature is lower than the upper limit set temperature. If it is high, the supercharger 40 is driven to
The amount of air taken into the cylinder of
Control is performed to reduce the exhaust gas temperature until the temperature at which M burns, that is, the upper limit side set temperature. As described above, the exhaust purification device of the diesel engine 10
An air amount adjusting mechanism composed of the intake throttle valve 30 and the supercharger 40 adjusts the amount of air sucked into the cylinder of the engine body 11, so that the exhaust gas temperature is always kept within the temperature range in which PM burns. be able to. Therefore, DP
F21 is always effectively regenerated and PM is not deposited on DPF21.

FIG. 4 shows the relationship between the exhaust gas temperature and the NOx reduction characteristics of the NOx catalyst. As shown in FIG.
The Ox reduction rate is shown. Therefore, it is preferable to set the lower limit temperature to 300 ° C. in the exhaust gas temperature control. The set temperature at which the exhaust gas temperature control is performed is not limited to the above-described temperature, and may be changed according to the characteristics of the oxidation catalyst 20, the DPF 21, and the NOx catalyst 22.

The intake throttle valve 30 and the exhaust throttle valve 32 are used not only when the above-mentioned exhaust gas temperature control is executed, but the intake throttle valve 30 is used in combination with a fuel injection device (not shown) in a diesel engine. The exhaust throttle valve 32 can be used, for example, for improving the warm-up property when the diesel engine 10 is started at a low temperature or as an exhaust brake.

Although the present invention has been described based on the illustrated embodiment, the present invention is not limited to the embodiment. For example, as the DPF and the oxidation catalyst, a device in which a catalytically active component is carried on the DPF and the DPF and the oxidation catalyst are integrated into one unit may be used. In the illustrated embodiment, the exhaust gas temperature is detected by an exhaust gas temperature sensor disposed in the exhaust passage as exhaust gas temperature detecting means. However, the relationship shown in the graph of FIG. The rotation may be detected to determine the exhaust gas temperature from the map. Further, the supercharger may use not only a device using a rotational driving force of a crankshaft as a driving source but also a device using a motor as a driving source. Further, a fuel injection valve may be newly provided in the exhaust pipe on the upstream side of the NOx catalyst, and fuel may be administered as a reducing agent for promoting the reduction reaction in the NOx catalyst. In other words, any embodiment may be used as long as it has the requirements of the present invention and performs the same function.

[0021]

According to the present invention, there is provided an exhaust gas purifying apparatus for a diesel engine in which an oxidation catalyst and a diesel particulate filter are disposed in an exhaust passage, and an air amount adjusting mechanism disposed in an intake passage of the diesel engine. And exhaust gas temperature detecting means for detecting the temperature of the exhaust gas, and a controller, since the controller controls the air amount adjusting mechanism so that the exhaust gas temperature is within a predetermined temperature range,
PM collected by the DPF in all engine operating ranges
Can be reliably burned.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an exhaust gas purification device for a diesel engine according to the present invention.

FIG. 2 Exhaust gas temperature and PM in a continuous regeneration type DPF
4 is a graph showing the relationship between the combustion characteristics and the combustion characteristics.

FIG. 3 is a graph showing a relationship between an operating state of a diesel engine and an exhaust gas temperature.

FIG. 4 is a graph showing a relationship between exhaust gas temperature and NOx reduction characteristics in a NOx catalyst.

[Explanation of symbols]

 10: Diesel engine 11: Engine main body 12: Intake passage 13: Exhaust passage 14: Intake pipe 16: Exhaust pipe 20: Oxidation catalyst 21: DPF 22: NOx catalyst 30: Intake throttle valve 32: Exhaust throttle valve 34: Open / close valve 40 : Supercharger 41: Electromagnetic clutch 50: EGR device 51: EGR passage 52: EGR valve 55: Exhaust gas temperature sensor 60: Controller

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 23/02 F02D 23/02 C 41/04 360 41/04 360A F-term (Reference) 3G090 AA02 BA01 CA01 CB21 CB23 DA12 EA02 EA05 EA06 EA07 3G091 AA10 AA11 AA18 AA28 AB02 AB05 AB13 BA00 BA04 BA14 BA15 BA19 CA13 CB07 CB08 CB08 DA01 DA02 DB10 EA01 EA03 EA17 FB10 GA06 GB01X GB05W GB06W GB07W GB10H GBA HA3 H10 A DC03 DG06 EA01 EA02 EA09 FA17 FA18 HD01Z 3G301 HA02 HA11 HA13 JA24 JA25 LA00 LA03 LC07 NE01 NE06 NE17 NE19 PD11Z

Claims (5)

[Claims] An exhaust purification device for a diesel engine in which an oxidation catalyst and a diesel particulate filter for trapping particulates in exhaust gas are disposed in an exhaust passage of the diesel engine. An air amount adjusting mechanism provided for adjusting the amount of air taken into the cylinder of the diesel engine; exhaust gas temperature detecting means for detecting the temperature of exhaust gas; and exhaust gas detected by the exhaust gas temperature detecting means A controller that controls the air amount adjusting mechanism based on the temperature, wherein the controller controls the air amount adjusting mechanism so that the exhaust gas temperature falls within a predetermined temperature range. Exhaust gas purification device. 2. The air amount adjusting mechanism includes an air amount reducing unit that reduces an amount of air sucked into the cylinder, and an air amount increasing unit that increases an amount of air sucked into the cylinder. The controller controls the air amount reducing means when the exhaust gas temperature is lower than the lower limit of the predetermined temperature range, and increases the air amount when the exhaust gas temperature is higher than the upper limit of the predetermined temperature range. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein the means is controlled. 3. The exhaust gas purifying apparatus for a diesel engine according to claim 2, wherein said air amount reducing means is constituted by an intake throttle valve. 4. The exhaust gas purifying apparatus for a diesel engine according to claim 2, wherein said air amount increasing means is constituted by a supercharger. 5. The exhaust passage of a diesel engine has NO
x catalyst is disposed, and the lower limit of the predetermined temperature range is 300
The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein the temperature is set to ° C.