JPH08296426A - Exhaust particulates purifying device - Google Patents

Abstract

PURPOSE: To control the energization of an electric heater so that the combustion residue of exhaust particulates at the outer circumference of a filter can be eliminated. CONSTITUTION: A central heater 5a and a peripheral heater 5b are provided to a heater-side end surface of a filter 3 for collecting exhaust particulates, and when the filter 3 is reproduced, both the central heater 5a and the peripheral heater 5b are simultaneously energized so that the exhaust particulates can be ignited, and at the time of propagated combustion after the ignition, the energization to the central heater 5a is stopped. Further, the energization to the peripheral heater 5b is maintained. At the time of this propagated combusion, a secondary air from an air pump (not shown) is supplied to the filter 3, and the heating energy from the peripheral heater 5b is conveyed to the combustion surface by the secondary air. Thus, a combustion residue of exhaust particulates at the outer circumference of the filter can be eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to exhaust particulate matter (particulates) contained in exhaust gas of a diesel engine.
The present invention relates to an exhaust particle purification device that collects exhaust gas using a filter and burns the collected exhaust particles to regenerate the filter.

[0002]

2. Description of the Related Art In this type of exhaust gas purification apparatus, a filter arranged in the exhaust passage of a diesel engine collects exhaust particles in exhaust gas and detects the amount of the collected exhaust particles. The regeneration time is determined, and exhaust particulates adhering to the filter are burned to regenerate the filter.

In order to regenerate the filter, first, an electric heater provided on the end face of the filter on the heater side is energized for a predetermined ignition period to ignite exhaust particulates, and after the ignition period is completed, the heater energization is cut off, and the air pump is connected to the filter. This is performed by sending secondary air to propagate and burn the combustion surface from the end surface on the heater side to the other end of the filter.

[0004]

However, in the regeneration of the filter, since the peripheral portion of the outer periphery of the filter radiates heat to the outside air through the filter case, the regeneration temperature of the peripheral portion lowers, and unburned residue may occur. Then, once the unburned residue is generated, the amount of collection in the outer peripheral portion increases in the next collection. Therefore, when the collection and regeneration are repeated, the collection amount in the peripheral portion increases, and when it exceeds the limit, regenerative combustion is also performed in the peripheral portion. The regeneration temperature (peak value) at this time is considerably higher than that in the central portion at a portion slightly inside the outer peripheral portion, and therefore there is a possibility of filter cracking.

The present invention has been made in view of the above problems, and it is an object of the present invention to control the energization of an electric heater so as to eliminate the unburned residue of exhaust particles on the outer peripheral portion of the filter.

[0006]

To achieve the above object, in the invention described in claim 1, a filter (1) provided in an exhaust passage of a diesel engine for collecting exhaust particulates, and one of the filters are provided. Electric heater (5) provided on the end face side to heat and ignite the collected exhaust particulates
An air supply means (6, 7, 12) for supplying secondary air for propagating and burning the ignited exhaust particles; and a filter for controlling the electric heater and the air supply means during regeneration of the filter. In the exhaust particulate purifying device, comprising: a control means (17, 9) for burning the exhaust particulates collected in the electric heater, the electric heater includes a central heater (5a) for heating a central portion on one end face side of the filter and a peripheral portion. And a peripheral heater (5b) for heating the portion, the control means energizes the peripheral heater and supplies electric power to the central heater during a propagation combustion period after igniting the exhaust particulates. It is characterized by stopping energization.

According to a second aspect of the present invention, in the exhaust particulate purifying apparatus according to the first aspect, the control means simultaneously energizes the central heater and the peripheral heater during an ignition period in which the exhaust particulate is ignited. It is characterized by that. According to a third aspect of the invention, in the exhaust gas purification apparatus according to the first or second aspect, the control means is
It is characterized in that energization to the peripheral heater is maintained while the air supply means is operated.

The reference numerals in parentheses of the above-mentioned means indicate the correspondence with the concrete means described in the embodiments described later. An electric heater separated for heating the peripheral portion and the central portion of the filter is disclosed in Japanese Patent Laid-Open No. 141141/1993.
There is one disclosed in Japanese Laid-Open Patent Publication No. 225, but when this is ignited, the electric currents to the two separated electric heaters are shifted in time,
It is intended to improve the ignitability at the time of ignition,
As described above, the present invention differs from the present invention in which only the peripheral heater for heating the peripheral portion is energized during the propagating combustion to eliminate the unburned residue in the peripheral portion during the propagating burning.

[0009]

According to the invention described in claims 1 to 3, the peripheral heaters are energized and the central heaters are deenergized during the propagation combustion period after the exhaust particulates are ignited. ing. Therefore, at the time of propagation combustion, the heating energy due to the energization of the peripheral heater is carried to the combustion surface by the secondary air, and the heat radiation at the outer peripheral portion is replenished, so that the lowering of the regeneration temperature at the outer peripheral portion is prevented,
It is possible to eliminate the unburned residue of exhaust particulates on the outer peripheral portion.

Further, since the energization of the central heater is stopped during the propagating combustion, excessive heating energy is prevented from being injected into the central portion where heat is easily accumulated, and cracks are generated due to excessive temperature rise of the filter. Can be prevented.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of an exhaust particulate purifying apparatus showing an embodiment of the present invention. The exhaust pipe 2 of the diesel engine 1 is provided with a filter case 4 having a filter 3, and the exhaust gas passing through the filter inlet 4a of the filter case 4 through the filter 3 causes exhaust gas in the exhaust gas to be exhausted. The fine particles are collected by the filter 3. Further, the exhaust gas that has passed through the filter 3 has a filter outlet 4b.
Is emitted from a muffler (not shown).

The filter 3 has a honeycomb-shaped cell structure made of ceramic materials alternately plugged,
A large number of pores of several microns are formed on the wall surface of each cell, and when the exhaust gas passes through the pores, the exhaust fine particles in the exhaust gas are trapped on the wall surface and filtered. An electric heater 5 is provided on the heater-side end surface of the filter 3, and the exhaust particulates collected by the electric heater 5 are heated and ignited.

FIG. 2 shows a sectional structure of the heater-side end surface of the filter 3. The filter 3 has a honeycomb-shaped cell structure in which both end surfaces are alternately plugged as described above, and the plug 3a has a heater wire (nichrome wire) 5'of the electric heater 5.
Is buried. The electric power is supplied to the electric heater 5 by supplying the battery voltage from the battery 8 via the heater relay 9. Although only one electric heater 5 and one heater relay 9 are shown in FIG. 1, since the peripheral portion and the central portion of the filter 3 are separately heated, the electric heater 5 and the heater relay 9 are separated. Two relays 9 are provided respectively for the peripheral part and the central part. This will be described later.

Further, an air pump (A / A) for supplying secondary air to the filter 3 in order to perform propagation combustion during filter regeneration.
P) 6 is provided. Secondary air from the air pump 6 is supplied to the filter 3 via the air introduction pipe 7.
Also, to form the exhaust gas flow path during filter regeneration,
A bypass pipe 10 is provided. This bypass pipe 10
The selection of the flow path to the filter and the flow path to the filter 3 is performed by switching the exhaust switching valve 11. The supply of the secondary air from the air introduction pipe 7 is performed by switching the air switching valve 12. The exhaust switching valve 11 and the air switching valve 12 are each driven to be switched by an actuator (not shown), and the actuator operates upon receiving a drive signal from an ECU 17 described later.

Further, in order to detect the trapped amount of the filter 3, the pressure sensor 1 for detecting the pressure at the filter inlet 4a.
3, a pressure sensor 1 for detecting the pressure at the filter outlet 4b
4, an exhaust temperature sensor 15 that detects the exhaust temperature, and an intake flow rate sensor 1 that detects the intake flow rate of the diesel engine 1
6 is provided. The signals from these sensors are input to the electronic control unit (ECU) 17. This ECU
Reference numeral 17 is provided with a microcomputer system composed of a CPU, a ROM, a RAM, an I / O circuit and the like. Then, as will be described later, the amount of collected exhaust particulates is detected to determine the regeneration timing, and a calculation process for regenerating the filter 3 is executed when the regeneration timing is determined. This ECU 17
Performs the arithmetic processing by turning on the key switch 18.

FIG. 3 shows the configuration of the electric heater 5 and the heater relay 9. As shown in the figure, the electric heater 5 is composed of a central heater 5a arranged in the central portion of the filter 3 and a peripheral heater 5b arranged in the peripheral portion. Also,
A central heater relay 9a and a peripheral heater relay 9b for energizing the central heater 5a and the peripheral heater 5b are provided.

In the above structure, the operation is performed by the ECU 1
This will be described with reference to the flowchart of FIG. First, sensor signals from the sensors 13 to 16 are fetched (step 101), and then collection control is performed (step 102). Specifically, the exhaust switching valve 1
1 is opened to the filter inlet 4a side and the exhaust switching valve drive signal is output so as to close the bypass pipe 10 so that the exhaust gas of the diesel engine 1 is introduced into the filter 3.

Next, based on the sensor signal captured in step 101, the trapped amount is calculated as follows (step 103). First, the pressure P2 detected by the pressure sensor 14 is subtracted from the pressure P1 detected by the pressure sensor 13 to obtain the differential pressure ΔP (= P1−P2) of the filter 3, and then the intake flow rate sensor 16 detects the pressure difference. Intake flow rate G
a and the exhaust temperature Tex detected by the exhaust temperature sensor 15, the exhaust volume flow rate V of the exhaust gas is V = f (Ga, Te
x). Then, from the filter differential pressure ΔP and the exhaust volume flow rate V, the collection amount C of exhaust particulates is g (ΔP,
V). The function g is basically set so as to obtain a value obtained by dividing the differential pressure ΔP by the exhaust volume flow rate V. The value obtained using this function is the ventilation resistance,
That is, it indicates the amount of clogging of the filter, which is taken as the collection amount C.

Next, it is judged whether or not the collected amount C has reached a predetermined set value (that is, a limit value at which regeneration is required) C _O (step 104). Then, the above process is repeated until the collected amount C reaches the predetermined value C _O. Therefore, in this state, the collection by the filter 3 is promoted. Further, the heater relay 9 and the air pump 6 are not driven, and the air switching valve 12 also closes the air introduction pipe 7.

After that, when the amount of the exhaust particulates collected by the filter 3 becomes large and the collected amount C reaches the predetermined value C _O , it is judged in step 104 that the regeneration is started. Based on this regeneration start determination, ignition control is first performed (step 10
5). Specifically, an exhaust switching valve drive signal for switching and driving the exhaust switching valve 11 so as to close the filter inlet 4a and open the passage to the bypass pipe 10 is output. Further, the heater relays 9a and 9b are driven to close the respective relay contacts so that the voltage of the battery 8 is applied to the central heater 5a and the peripheral heater 5b at the same time. Further, the timer t _F for measuring the ignition time is reset to 0. The value of this timer t _F (and timer t _R described later) is updated by a counting process not shown.

The central heater 5a and the peripheral heater 5b are energized at the time of ignition until the timer t _F reaches t _FO corresponding to a constant ignition time, and the central heater 5a and the peripheral heater 5b generate heat by energization. . In this case, filter 3
In order to heat and ignite the exhaust particulate matter collected in, it is necessary to heat up to an ignition temperature of about 600 ° C.,
A fixed ignition period t _{FO for the} central heater 5a and the peripheral heater 5b
It is possible to exceed the ignition temperature by energizing only.

Then, when it is determined that the value of the timer t _F has reached t _FO (step 106), the ignition control is ended and the next regeneration control is performed (step 107). In this regeneration control, an air switching valve drive signal is output to open the air switching valve 12, and a driving voltage is applied to the air pump 6 to operate the air pump 6. Further, the timer t _R for measuring the reproduction time of the filter 3 is reset to 0. Therefore, by this regeneration control, the secondary air is supplied from the air pump 6 to the filter via the air introduction pipe 7, and the regeneration is started. Further, the drive of the central heater relay 9a is turned off, and the energization of the central heater 5a is stopped. By this, the secondary air is introduced from the air pump 6, and the ignition surface of the filter 3 moves from the end surface close to the filter inlet 4a to the other surface. Propagating combustion that moves toward the end face is started.

Further, during this propagation combustion, the outer peripheral portion of the filter 3 is radiated to the atmosphere through the filter case 4, so that the regeneration temperature tends to be lower than the regeneration temperature of the central portion, but the peripheral heater 5b is not energized. Since the heating energy is maintained, the heating energy is carried to the combustion surface by the secondary air, and the heat radiation at the outer peripheral portion is replenished. Therefore, it is possible to prevent the regeneration temperature from decreasing at the outer peripheral portion, and it is possible to eliminate the unburned residue of the exhaust particulate matter at the outer peripheral portion.

Further, by stopping the energization of the central heater 5a during the propagating combustion, excessive heating energy is prevented from being injected into the central portion where heat is easily accumulated, and cracks are generated due to excessive temperature rise of the filter 3. Can be prevented. After that, when the reproduction time t _R reaches t _RO and the reproduction end time is reached, it is determined that the reproduction is ended and the determination in step 108 is Y.
When ES occurs, the operation of the peripheral heater 5b and the air pump 6 is stopped, and the regeneration end control for outputting the air switching valve drive signal to close the air switching valve 12 is performed (step 109). Three
Resumes collection of.

FIG. 5 shows the operation timings of the central heater relay 9a, the peripheral heater relay 9b and the air pump 6 during filter regeneration. In the above embodiment,
The exhaust pipe 2 has been shown with the bypass pipe 10 provided.
The present invention can also be applied to a so-called dual type exhaust particulate purification device in which two branch flow paths are provided in parallel with each other, and filters are provided in each, and collection and regeneration are alternately performed.

Further, since the electric power of the electric heaters 5a and 5b is set to a predetermined value regardless of the fluctuation of the terminal voltage of the battery 8,
Duty control may be performed to control the ON-OFF duty ratio in accordance with the battery voltage during the ON period of each of the heater relays 9a and 9b. further,
In the above-described embodiment, the central heater relay 9a and the peripheral heater relay 9b are turned on at the same time during the ignition period to perform ignition. However, as shown in JP-A-5-141225, they are staggered in time. It may be turned on to improve the ignitability.
You may make it ignite by making N.

In the above embodiment, each step shown in the flowchart of FIG. 4 is understood as a function realizing means for realizing each function.
Step 103 is grasped as a trapping amount detecting means for detecting the trapped amount of exhaust particulates, and step 104 is grasped as a regeneration timing judging means.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an exhaust emission control device for a diesel engine showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a cross-sectional structure of a heater-side end surface of a filter 3.

FIG. 3 is a configuration diagram showing a configuration of an electric heater 5 and a heater relay 9.

FIG. 4 is a flowchart showing a calculation process of a CPU in an ECU 17 in FIG.

FIG. 5: Central heater relay 9 during filter regeneration
FIG. 6 is a diagram showing the operation timings of a, a peripheral heater relay 9b, and an air pump 6. Is.

[Explanation of Codes] 1 ... Diesel engine, 2 ... Exhaust pipe, 3 ... Filter,
4 ... Filter case, 5 ... Electric heater, 5a ... Central heater, 5b ... Peripheral heater, 6 ... Air pump, 9 ... Heater relay, 9a ... Central heater relay, 9b ... Peripheral heater relay, 11 ... Exhaust switching valve, 12 ... Air Switching valve, 13, 14
... pressure sensor, 15 ... exhaust temperature sensor, 16 ... intake flow sensor, 17 ... ECU.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shoji Morita, 1-1, Showa-cho, Kariya city, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor, Terutaka Kageyama, 1-1, Showa-cho, Kariya city, Aichi prefecture Co., Ltd. (72) Inventor Toshiharu Kondo 1-1-1, Showa-cho, Kariya city, Aichi Prefecture Nihondenso Co., Ltd.

Claims (3)

[Claims] 1. A filter provided in an exhaust passage of a diesel engine for collecting exhaust particles, an electric heater provided on one end surface side of the filter for heating and igniting the collected exhaust particles, and an ignited exhaust gas. Air supply means for supplying secondary air for propagating and burning the particles, and control means for controlling the electric heater and the air supply means to burn the exhaust particles collected by the filter when the filter is regenerated. In the exhaust particulate purifying apparatus comprising: the electric heater, the electric heater is configured to have a central heater that heats a central portion of the one end surface side of the filter and a peripheral heater that heats a peripheral portion, and the control unit is the exhaust gas. In the propagation combustion period after igniting the fine particles, the peripheral heater is energized and the central heater is deenergized. Exhaust particulate emission control device. 2. The exhaust particulate purifying apparatus according to claim 1, wherein the control means simultaneously energizes the central heater and the peripheral heater during an ignition period in which the exhaust particulate is ignited. 3. The exhaust particulate purifying apparatus according to claim 1, wherein the control means maintains the energization of the peripheral heater while operating the air supply means.