JPH11236813A - Regeneration system for exhaust gas purifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a regeneration system for exhaust gas purifying device capable of effectively regenerating a honeycomb filter for purifying the exhaust gas by capturing the particulates contained in the exhaust gas, while the vehicle is running. SOLUTION: A regeneration system for an exhaust gas purifying device is installed in an exhaust gas passage 11 of a Diesel engine 10 and is composed of three gas purifying devices 20 equipped with honeycomb filters 22 consisting of porous sintered silicon carbide, a heater 24 installed ahead on the gas inlet side of the filter 22 for its regeneration, a flow regulating valve 26 installed on the gas outlet side of the filter 22, and a control unit 30 to control the power supplied to heater 24 and the flow regulating valve 26.

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 purifying exhaust gas discharged from an internal combustion engine such as a diesel engine. It relates to a reproduction system.

[0002]

2. Description of the Related Art An exhaust gas purifying apparatus provided with an exhaust gas purifying honeycomb filter used for removing particulates and the like discharged from an internal combustion engine such as a diesel engine is known. In this filter, as the service time increases, the load on the engine increases due to the accumulation of particulates, and in the worst case, the filter is destroyed. Such a phenomenon is remarkable in a diesel vehicle such as a bus, a truck, or a forklift.

[0003] Therefore, by burning the particulates captured by the honeycomb filter for exhaust gas purification,
Although it is necessary to regenerate the filter, cordierite used in the conventional honeycomb filter for purifying exhaust gas has poor maximum operating temperature and thermal conductivity, so the durability is poor, and the maximum operating temperature is low. There is a problem that the amount of particulates that can be burned in one regeneration is limited.

The applicant of the present invention has disclosed a regeneration system for an exhaust gas purifying apparatus employing a porous silicon carbide sintered body having a high maximum operating temperature and a high thermal conductivity in an exhaust gas purifying honeycomb filter, as disclosed in JP-A-3-23307. It has already been proposed in the official gazette. As shown in FIG. 6, in an exhaust gas purifying apparatus 1 provided in an exhaust passage 5, a heater 3 is arranged on the outer periphery of an exhaust gas purifying honeycomb filter 2. Regeneration of the exhaust gas purifying honeycomb filter 2 is performed by heating the filter 2 by the heater 3 and supplying auxiliary combustion air from an inlet 4 provided in front of the exhaust gas purifying device 1 to incinerate the particulates. Will be Note that this regeneration system is normally operated in a state where the operation of the internal combustion engine is stopped after the vehicle has run.

However, according to this device, a pipe for supplying auxiliary combustion air into the exhaust gas purifying honeycomb filter 2, a pump unit for supplying the auxiliary combustion air, a power supply for driving the pump unit, and a drive control Control unit (neither shown) is required,
The mounting of these members has the disadvantage that the interior space is restricted and the structure is complicated.

Further, since the heater 3 is provided on the outer periphery of the exhaust gas purifying honeycomb filter 2, the temperature distribution when the particulates start to burn becomes uniform along the outer peripheral surface of the filter 2. It takes a long time (heating time) to heat the entire filter 2 to the particulate combustion temperature. Further, as the combustion proceeds by supplying the auxiliary combustion air to the heated filter 2,
The front surface of the exhaust gas purifying honeycomb filter 2 is cooled by the supporting air, and a temperature distribution is generated in which the temperature rises in the rear part (right side in the drawing) of the filter 2, and the resulting stress distribution sometimes reduces the allowable stress of the filter 2. As a result, cracks are generated in the filter 2, and in order to prevent the cracks from occurring, the amount of incinerated particulates is set lower than the permissible capacity of the filter.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been developed in consideration of the fact that particulate matter contained in exhaust gas discharged from an internal combustion engine is not used even when a vehicle is running without using auxiliary combustion air. It is an object of the present invention to provide a regeneration system for an exhaust gas purifying apparatus that can efficiently regenerate an exhaust gas purifying honeycomb filter that captures air.

[0008]

According to a first aspect of the present invention, there is provided a regeneration system for an exhaust gas purifying apparatus, which is provided in an exhaust passage of an internal combustion engine and carries a catalyst for purifying an exhaust gas. At least two exhaust gas purifying devices each having a honeycomb filter for purifying exhaust gas of a silicon carbide sintered body, a heater disposed in front of a gas inflow side of the filter to regenerate the filter, A flow control valve disposed on the gas outflow side of the honeycomb filter for use, and a control unit for controlling power supplied to the heater and the flow control valve.

In the regeneration system of the present invention, the heater is heated in accordance with a command from the control unit, and the flow rate is reduced by the flow control valve disposed on the gas outflow side of the exhaust gas purifying honeycomb filter. Reduce the flow rate of exhaust gas passing through the filter. For this reason, the exhaust gas from the internal combustion engine gently passes through the exhaust gas purifying device, and the particulates captured by the exhaust gas purifying honeycomb filter are incinerated by reacting with the oxygen contained in the exhaust gas. You.

At this time, since the heater is disposed in front of the exhaust gas purifying honeycomb filter on the gas inflow side, the highest temperature heated by the heater is the front end of the filter, and the inside of the filter is heated. Since the highest temperature position coincides with the combustion start point, the time required for temperature rise can be significantly reduced. Further, the front end of the exhaust gas purifying honeycomb filter is not cooled by the exhaust gas from the internal combustion engine, and the heat conduction in the filter is caused by the exhaust gas passing through the filter along the longitudinal direction. Since it is performed uniformly and efficiently, the combustion is propagated with less stress distribution.

Therefore, according to the reproducing system of the present invention,
Since it is not necessary to use the auxiliary air for supplying the exhaust gas purifying honeycomb filter used in the conventional regeneration system and the pump for supplying the auxiliary air, the structure is simplified, and the members are simplified. Wide mounting space can be secured. Further, even while the vehicle is running, continuous operation can be performed by alternately switching the operation of the exhaust gas purification device. Further, the exhaust gas purifying honeycomb filter can be safely regenerated in a short time.

As a configuration for achieving the excellent combustion mechanism of the regeneration system, the present invention employs, for example, a porous silicon carbide sintered body as a material for a honeycomb filter for purifying exhaust gas. This sintered body has a very high thermal conductivity and helps to efficiently transmit the heat directly from the heater and the heat of the exhaust gas passing through the heater surface to the rear and radial direction of the filter. Even if combustion occurs, heat can be safely diffused. For this reason, the variation in the temperature distribution that occurs when burning the particulates adhered to the exhaust gas purifying honeycomb filter is eliminated, and the time required for incineration of the particulates can be further reduced. The amount of particulates that can be incinerated can also be increased. Furthermore, in the case of a silicon carbide sintered body, the maximum use temperature is higher than that of cordierite, and the thickness of the cell wall can be reduced. For this reason, the size of the filter can be reduced.

Further, since the high-temperature exhaust gas from the internal combustion engine is activated by the exhaust gas purifying catalyst carried by the exhaust gas purifying honeycomb filter, the burning temperature of the particulates is lowered and the power consumption of the heater is reduced. The amount can be reduced.

Further, the regeneration system of the exhaust gas purifying apparatus according to the second aspect is characterized in that, in the first aspect, a regeneration unit in which the exhaust gas purifying apparatus, the heater, and the flow control valve are integrated. It is assumed that.

In this case, since the exhaust gas purifying device, the heater and the flow control valve can be replaced as a single unit, workability in assembling or removing in the exhaust passage is improved.

Further, in the regeneration system of the exhaust gas purifying apparatus according to the third aspect, the exhaust gas purifying apparatus according to the first or second aspect, wherein the flow rate adjusting valve causes the flow rate of exhaust gas flowing out of the flow rate adjusting valve to the exhaust gas purifying apparatus. The flow rate is set so as to be 1/20 to 1/40, preferably 1/30 of the flow rate of the exhaust gas to be flowed.

In this case, if the flow rate of the exhaust gas flowing out of the flow control valve is larger than 1/20 of the flow rate of the exhaust gas flowing into the exhaust gas purifying device, the honeycomb filter for purifying the exhaust gas is cooled, which is necessary for regeneration. Heater power becomes large. On the other hand, if it is smaller than 1/40, the amount of oxygen flowing through the filter is reduced, so that the particulates are less likely to be burned.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a first embodiment of a regeneration system for an exhaust gas purification device according to the present invention. The illustrated regeneration system is a device for regenerating an exhaust gas purifying device that purifies exhaust gas discharged from an internal combustion engine (in this embodiment, the diesel engine 10). The regeneration system branches midway in an exhaust passage 11 from the engine 10. 3 installed
The exhaust gas purifying honeycomb filter includes a plurality of regenerating units 12-1, 12-2, and 12-3, and each unit is made of a sintered body of porous silicon carbide (SiC) and carries an exhaust gas purifying catalyst. Exhaust Gas Purification Device 20 with 22
And the filter 22 for heating the filter 22.
And a flow control valve 26 disposed on the gas outflow side of the filter 22. Further, the regeneration system includes a control unit 30 that controls the power supplied to the heater 24 and the flow control valve 26. A control unit 30 connected to a vehicle-mounted battery 28 controls the heater 24 and the flow control valve 26 independently.

The controller unit 30 includes an input section 32 to which measured values of the engine speed Ne (rpm), the pressure loss Pd (mmAq) in the exhaust gas purifier 20 and the temperature T in the exhaust gas purifier 20 are inputted, CPU (Central Processing Unit) 34 for arithmetically processing the output signal from input unit 32 to control the operation of 24 and flow regulating valve 26
And a heater operation control unit 36 for operating the heater 24 based on the result of the arithmetic processing by the CPU 34, and an output unit 38 for operating the flow control valve 26 to the throttle position (see the valve element 26a in FIG. 1). .

The heater 24 is a spiral resistance heater arranged at a predetermined distance from the end face of the filter 22 on the gas inflow side. The shape of the heater 24 is not limited to a spiral shape, and any shape may be used as long as the heater 24 allows the supplied exhaust gas from the engine 10 to pass through when disposed in front of the filter 22. .

In this case, since the gas inlet side end face of the exhaust gas purifying honeycomb filter 22 is not in direct contact with the heater 24, the gas inlet side end face of the filter 22 does not exhibit an abnormally high temperature due to the heating of the heater 24. . Accordingly, it is possible to prevent a crack from being generated near the gas inflow side end face of the exhaust gas purifying honeycomb filter 22 due to a rapid temperature change. In addition, since the front end of the exhaust gas purifying honeycomb filter 22 is not blocked, the pressure loss does not increase. When the regeneration system is mounted on a vehicle, the heater 24 and the front end of the filter 22 are vibrated due to vibration. And no damage is caused.

In particular, if the heater 24 is arranged at a distance of 0.2 to 15 cm from the end face of the exhaust gas purifying honeycomb filter 22 to the exhaust gas purifying honeycomb filter 22, the exhaust gas purifying honeycomb filter 22 can be easily removed. A good balance between heat propagation, heat exchange with exhaust gas, and avoidance of contact vibration is desirable.

Here, the exhaust gas purifying honeycomb filter 22 will be described in detail. FIG. 2 is a schematic sectional view showing the first regeneration unit 12-1 among the regeneration units 12-1, 12-2, and 12-3 of the three exhaust gas purification devices. As shown in FIG. 2, the exhaust gas purifying honeycomb filter 22 is formed in a honeycomb shape by a porous silicon carbide sintered body. The exhaust gas purifying honeycomb filter 22 is formed with a plurality of exhaust gas flow holes 23 extending in parallel with the longitudinal direction, and one end of each of the flow holes 23 on the gas inflow side or the discharge side is formed of porous silicon carbide. It is sealed alternately with small pieces 23a of the sintered body. In this manner, the flow holes on the gas inlet side end face and the gas outlet side end face of the exhaust gas purifying honeycomb filter 22 have a checkered pattern.

On the inner wall surface of the exhaust gas flow hole 23, an exhaust gas purifying catalyst is carried. As the exhaust gas purifying catalyst, various conventionally known catalysts can be used. Here, an oxidation catalyst will be described as an example.
Further, the exhaust gas purifying honeycomb filter 22 is connected to the exhaust gas purifying device 2 via a heat insulating material 23b provided on the outer peripheral surface thereof.
0 is tightly held in the casing.

In this case, assuming that the regeneration unit has the exhaust gas purifying device 20, the heater 24 and the flow control valve 26 integrally formed, the exhaust gas purifying device 20, the heater 24 and the flow control valve 26 need to be replaced as a single unit. Therefore, there is an advantage that workability such as assembly or removal in the exhaust passage 11 is improved.

The exhaust gas (Gin) discharged from the diesel engine 10 is supplied to the exhaust gas purifying honeycomb filter 2.
2, the particulates (particulate matter such as soot) in the exhaust gas are filtered at the surface of the exhaust gas flow holes 23, and HC is oxidized by the oxidation catalyst. The exhaust gas (Gout) that has been purified by passing through the exhaust gas purifying honeycomb filter 22 is returned to the exhaust passage 11 again.
It is discharged out of the vehicle via.

However, if the diesel engine 10 is operated for a long period of time, the particulates will
3 on the inner wall surface. For this reason, during the operation of the diesel engine 10, after the elapse of a predetermined time, the exhaust gas purifying device 20
The exhaust gas purifying honeycomb filter 22 in the inside is regenerated by using the regeneration system according to the present invention.

While the vehicle is running, the three regeneration systems 12-
Reference numerals 1, 12-2 and 12-3 are in a non-operating state, and while exhaust gas from the engine 10 passes through the three exhaust gas purification devices 20, particulates in the exhaust gas are exhausted and the exhaust gas purification honeycomb filter is used. Filtered through 22.

However, when the particulates are captured, the three reproduction units 12-1 and 12-1 shown in FIG.
-2 and 12-3, for example, the reproduction unit 12-1
Only the other playback units 12-2, 12-3
Remain inactive. That is, in response to a command from the control unit 30, the heater 24 is controlled via the circuit R1.
Is turned ON, thereby heating the end face of the exhaust gas purifying honeycomb filter 22 on the gas inflow side, and operating the valve body 26a of the flow control valve 26 to narrow the rear side of the filter 22 on the gas outflow side. For this reason, in the exhaust gas purifying apparatus 20, the exhaust gas heated by the heater 24 slowly passes through the exhaust gas purifying honeycomb filter 22, and the particulates captured by the filter 22 during this time are contained in the exhaust gas. It is incinerated by reacting with oxygen.

During the regeneration of the exhaust gas purifying honeycomb filter 22 by controlling only the heater 24 and the flow control valve 26 of the regeneration system by the control unit 30,
The exhaust gas is purified by the remaining regeneration units 12-2 and 12-3.

After the reproduction of the reproduction unit 12-1 is completed, the remaining reproduction units 12-2 and 12-3 are sequentially reproduced by the instructions from the control unit 30 in the same manner as described above. Therefore, while the vehicle is running, the reproduction unit 1
Since the reproduction of 2-1 to 12-2 and 12-3 is performed individually and sequentially, it is much more economical than the case where the operation of the vehicle is stopped and these reproduction units are reproduced.

The exhaust gas purifying honeycomb filter 2
The effect of supporting the oxidation catalyst on the inner wall surface of the exhaust gas flow hole 23 in 2 will be described in detail below.

FIGS. 3A to 3C are time charts exemplifying time periods until a predetermined pressure loss occurs depending on the presence or absence of an oxidation catalyst in the exhaust gas purifying apparatus. FIG. 3A shows a case where a diesel bus equipped with an exhaust gas purifying device without an oxidation catalyst travels at a normal low speed in an urban area, for example, when 40 g of particulates serving as a standard for starting regeneration are captured. Pressure loss of 3000mm
The regeneration cycle of the exhaust gas purifying honeycomb filter 22 at Aq is 2 hours. On the other hand, FIG.
(C) shows a case in which an exhaust gas purification device having an oxidation catalyst is used, and a regeneration cycle based on a pressure loss of 3000 mmAq takes 4 hours as shown in FIG. In the case of high-speed running on a suburb or a toll road, the time is 8 hours as shown in FIG.

As is apparent from these time charts, when the oxidation catalyst is carried on the inner wall surface of the exhaust gas passage hole 23 in the exhaust gas purifying honeycomb filter 22,
Since the operation start cycle of the regeneration system of the present invention can be delayed when the vehicle is running, it is effective to improve the durability of the heater 24 and the flow control valve 26. Since the running mode of the vehicle is usually a mixture of low speed and high speed, the operation start cycle of the reproduction system should be every 3 to 4 hours, as is clear from FIGS. Is desirable.

By the way, the minimum power consumption of the heater required for one reproduction is 500 Wh on average. FIG. 4 is a characteristic diagram in which the electric energy E (Wh) necessary for incinerating particulates is plotted on the vertical axis, and the engine speed Ne (rpm) is plotted on the horizontal axis. However, curve A shows curve B when the catalyst has an oxidation catalyst.
Is a case without an oxidation catalyst.

As is clear from the curve B, when the oxidation catalyst is not present, the heater needs a high electric energy when the engine speed Ne is low because the temperature in the exhaust gas is low when the engine speed Ne is low. Although the electric energy E decreases, when the engine speed exceeds a predetermined engine speed No, even if the temperature of the exhaust gas increases, the electric energy E for operating the heater needs to be increased again.

On the other hand, in the curve A having the oxidation catalyst, when the engine speed Ne is low, a high amount of electric power is required because the temperature of the exhaust gas is not enough to incinerate the particulates. As the engine speed Ne increases, the temperature of the exhaust gas rises, and the exhaust gas is activated by the oxidation catalyst. This promotes incineration of the trapped particulates. it can.

For this reason, when the oxidation catalyst is supported, the amount of power E required for heating the heater can be suppressed lower than when the oxidation catalyst is not supported, and the exhaust gas purifying honeycomb can be maintained in a state of high power efficiency. The filter 22 can be regenerated.

The first embodiment of the regeneration system of the present invention shown in FIG. 1 is generally applied to a 12 to 13 L class diesel engine.

FIG. 5 shows a second embodiment of the regeneration system of the present invention, which is usually applied to a 6-7L class diesel engine. The same members as those in the first embodiment will be described with the same reference numerals. The flow control valve 26 forms a throttle by a gap formed between the rotary valve body 26a and the inner wall of the pipe.

As in the first embodiment, this regeneration system has two regeneration units 12-1 and 12- while the vehicle is running.
2 is inactive, but when particulates are captured, one of the two playback units 12-1 and 12-2 is first played back in the same manner as in the example of FIG. Play the playback unit of.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle equipped with a 12L class diesel engine has a heater 24 in the regeneration system shown in FIG.
Cell structure supporting a 2000 W DC (direct current) heater and a conventionally known exhaust gas purifying catalyst as an exhaust gas purifying honeycomb filter 22: 12/300, size: φ165 × L150 (mm), and capacity 3.2 A filter made of the silicon carbide sintered body of (L) is used.

The total exhaust gas flow rate of the above engine is:
4000 to 13500 L / mi depending on engine speed
n and 3000 mmAq in the exhaust gas purifying device 20.
When the pressure loss of the filter was detected, the regeneration of the filter was started by squeezing the flow control valve 26 to reduce the flow rate of the exhaust gas passing through the apparatus to 1/30.

The above description is only a preferred embodiment of the present invention, and various changes can be made within the scope of the present invention. For example, the playback system according to the present invention is not limited to running the vehicle, but is also possible in an idling state.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a first embodiment of a reproduction system of the present invention.

FIG. 2 is a sectional view of a main part of a reproducing unit used in the reproducing system of the present invention.

FIG. 3 is a time chart illustrating a time cycle until a predetermined pressure loss occurs depending on the presence or absence of an exhaust gas purifying catalyst in the exhaust gas purifying device.

FIG. 4 is a characteristic diagram showing a relationship between an amount of electric power E required to incinerate particulates and an engine speed Ne depending on the presence or absence of an exhaust gas purifying catalyst in the exhaust gas purifying device.

FIG. 5 is a system diagram showing a second embodiment of the reproduction system of the present invention.

FIG. 6 is a system diagram showing a conventional reproduction system.

[Explanation of symbols]

 Reference Signs List 20 exhaust gas purification device 22 honeycomb filter for exhaust gas purification 23 exhaust gas circulation hole 24 heater 26 flow rate regulating valve 28 battery 30 control unit 32 input unit 34 CPU (central processing unit) 36 heater operation control unit 38 output unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 53/86 ZAB B01J 35/04 301Z B01J 35/04 301 B01D 53/36 ZABK

Claims (3)

[Claims] At least two exhaust gas purifying devices are provided in an exhaust passage of an internal combustion engine and provided with an exhaust gas purifying honeycomb filter of a porous silicon carbide sintered body carrying an exhaust gas purifying catalyst; A heater disposed in front of the gas inflow side of the filter to regenerate the filter, a flow control valve disposed on the gas outflow side of the exhaust gas purifying honeycomb filter, and electric power supplied to the heater and the flow control valve And a control unit for controlling the exhaust gas purification system. 2. The regeneration system for an exhaust gas purifying apparatus according to claim 1, wherein a regeneration unit is formed by integrating the exhaust gas purifying apparatus, the heater, and the flow control valve. 3. The flow control valve is set such that the flow rate of exhaust gas flowing out of the flow control valve is 1/20 to 1/40 of the flow rate of exhaust gas flowing into the exhaust gas purification device. The exhaust gas purifying apparatus regeneration system according to claim 1 or 2, wherein: