JP2000038918A - 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 capable of reducing regeneration time with filter burning preventing and stably operating by reducing the leakage current of a heater. SOLUTION: Current carrying to electric heating means is controlled at the given maximum duty ratio (S132), lower than 100% when detected temperature is equal to the given minimum threshold value (threshold value temperature at the low temperature side). PWM control (S144) is employed at the given minimum duty ratio, lower than the maximum duty ratio and higher than 0%, when the detected temperature is equal to the given maximum threshold value (threshold value temperature at the high temperature side) S144 higher than the minimum threshold value. This reduces regeneration time with filter burning preventing to increase the insulation resistance of the electric heating means, resulting in decreasing the leakage current. The equal temperature control width of the detected temperature T reduces the maximum temperature of a heater to increase the insulation resistance, resulting in reducing the leakage current.

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 collecting and regenerating particulate components (particulates) contained in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art In an exhaust gas purifying apparatus for a diesel engine, a heater, a temperature sensor, and a filter are provided in the exhaust path of a diesel engine from an upstream side in this order, and outside air (supply air) is supplied from an upstream side of the heater. The supply air heated by the heater is blown and supplied to the filter to ignite the particulates at the front end face of the filter. Thereafter, the particulates of the filter are sequentially spread from the upstream side to the downstream side.

[0003] Ceramics (for example, cordierite) constituting a filter cause burning such as cracks when the temperature exceeds a predetermined maximum allowable temperature. Therefore, it is necessary to prevent the filter temperature from exceeding the maximum allowable temperature. Therefore, if the temperature of the filter decreases, the required time for regeneration increases due to misfire or a decrease in the rate of fire spread. ing.

Specifically, in order to simplify the control, when the temperature detected by the temperature sensor rises to a predetermined high-side threshold temperature, the electric heating means is turned off, and the detected temperature is lowered to a predetermined low-temperature side. Binary on / off control is adopted to restart the energization of the heater when the temperature drops to the threshold temperature. The heater is constructed by extending a heating resistance wire such as a nichrome wire in the exhaust path in a direction perpendicular to the air supply direction (axial direction), or wrapping the nichrome wire with an insulator such as MgO. It is housed in a stainless steel sheath tube.

[0005] Since the supply air heating power (heating power) supplied to the heater is relatively large, it is usually supplied from a commercial AC power supply rather than from a vehicle-mounted battery.

[0006]

However, in the conventional power supply control to the heater in the exhaust gas purifying apparatus of a diesel engine, the temperature of the heated air supplied to the filter fluctuates greatly. It is not easy to keep the filter temperature high as long as the temperature does not exceed the allowable temperature, and the supply air temperature is set low for safety in order to prevent filter burnout when the heated air rises due to temperature fluctuations. However, as a result, there is a problem that the fire spread speed is reduced and the regeneration takes time.

[0007] In addition, when the heater is supplied from a commercial AC power supply, electric leakage occurs due to deterioration of the insulation resistance of the heater, etc.
There was also a troublesome problem that the electric leakage alarm was activated and the reproduction was interrupted. The present invention has been made in view of the above problems, and a first object of the present invention is to provide a diesel engine exhaust gas purification device that can reduce the regeneration time while preventing filter burnout. It is a second object of the present invention to provide a diesel engine exhaust gas purifying apparatus capable of performing stable operation by reducing leakage current of a heater.

[0008]

According to the exhaust gas purifying apparatus for a diesel engine, the power supply to the electric heating means is performed when the detected temperature reaches a predetermined minimum threshold value (low temperature threshold temperature). If the detected temperature is equal to a predetermined maximum threshold value (high-side threshold temperature) higher than the minimum threshold value at a predetermined maximum duty ratio smaller than 100% when equal, and smaller than the maximum duty ratio and 0% PWM control is performed at a predetermined larger minimum duty ratio.

In this case, the regeneration time can be shortened while preventing the filter from burning, and the leakage current can be reduced by increasing the insulation resistance of the electric heating means. Before describing the operation of the present configuration, problems in the conventional binary on / off control will be described below.

[0010] The control of the conventional binary on / off control will be described in detail. When the temperature detected by the temperature detecting means (temperature sensor) reaches the high-side threshold temperature, the power supply to the electric heating means (heater) is turned off. Then, the temperature of the heater is decreased by being cooled by the supply air, and the temperature of the supply air (heated air) heated by the heater is reduced. descend.

Thereafter, when the detected temperature drops to the lower threshold temperature, the power supply to the heater is turned on. Then
Despite being cooled by the air supply, the temperature of the heater rises due to its own heat generation, and the temperature of the air supply (heated air) heated by the heater rises. Is heated and its detected temperature rises. A conventional temperature sensor is configured such that a temperature detecting section (usually a thermocouple) is insulated and coated with a ceramic for protection.

Therefore, the thermocouple of the temperature sensor is heated to the high temperature side threshold temperature with the heated air higher than the temperature sensor, or the thermocouple of the temperature sensor is heated with the heated air lower than the temperature sensor. In order to cool the heating air, the temperature change width of the heated air becomes larger than the change width (temperature control width) of the detected temperature of the thermocouple. The width is even larger.

As a result, when the detected temperature rises and reaches the high-side threshold temperature, the current is completely cut off, and when the detected temperature decreases and reaches the low-side threshold temperature as in the prior art. In the conventional binary on / off control in which the power supply is completely restarted, the temperature change width of the supply air (heating air) introduced into the filter and the heater becomes considerably larger than the temperature control width of the detected temperature.

Therefore, it is necessary to lower the average temperature of the filter so that the change in the filter temperature due to the large temperature change width of the heated air does not exceed the maximum allowable temperature. The temperature can be maintained much lower than the maximum allowable temperature, and the rate of spread of the particulates decreases by that much, and the regeneration time becomes longer.

On the other hand, in the present configuration, even when the detected temperature reaches the high-side threshold temperature, the power supply to the heater is completely 0%.
Rather, even when the detected temperature reaches the lower threshold temperature, the power supply to the heater is not completely set to 100%. Therefore, in the heating power control at the time of the fire spread in this configuration, the temperature change width of the heater can be made smaller than that of the conventional binary on / off control, and the temperature change width of the heated air can be reduced accordingly, and the filter temperature becomes the highest. The temperature change width of the filter can be reduced within the range not reaching the permissible temperature, so that the average temperature of the filter can be maintained higher than before. It is known that a slight change in the filter temperature greatly changes the burning speed of the particulate.

Next, as described above, in the present configuration, the temperature change width and the temperature change speed of the heater can be made smaller than those in the conventional binary on / off control. The maximum heater temperature can be significantly lower than the conventional maximum heater temperature employing binary on / off control. It has also been found that when the temperature change width of the heater is reduced and the maximum temperature is reduced, the insulation resistance of the heater can be increased and the leakage current can be reduced.

The reason for this is that the inventors of the present invention have made it possible to reduce the temperature change width of the heater as described above, and when the maximum temperature (maximum heater temperature) is lowered, the heater adheres to the surface of the insulating support material and the insulation resistance of the heater is reduced. If the electrical resistance of the particulates or denatured products that lower the temperature increases due to the temperature drop, or if the heating resistor is housed in a metal sheath tube (ground potential) via an insulating material such as MgO, the insulation of MgO may be reduced. It is speculated that the resistance significantly decreases at high temperatures.

Since the amount of heating electric power supplied to the heater is considerably large, it is generally supplied from a commercial AC power supply instead of a vehicle-mounted battery. However, if the leakage current is large, the leakage breaker may operate or the safety control may be reduced. Not preferred. This problem is improved by employing this configuration. According to a second aspect of the present invention, in the exhaust gas purifying apparatus for a diesel engine according to the first aspect, further, when the detected temperature is within a temperature control range between a minimum threshold value and a maximum threshold value, the PWM may be used. The duty ratio of the controlled energization power increases as the detected temperature approaches the minimum threshold, and decreases as the detected temperature approaches the maximum threshold.

According to this structure, the effect of claim 1 can be further improved, in which the temperature change width of the heater and the heated air heated by the heater can be further reduced. According to the configuration of claim 3, the exhaust gas purifying apparatus for a diesel engine according to claim 1 or 2, further comprises:
The duty ratio is changed so as to eliminate the deviation between the detected temperature and the intermediate threshold temperature between the minimum threshold value (lower temperature threshold value) and the maximum threshold value (higher temperature threshold temperature). .

According to this configuration, the effect of claim 1 can be further improved, in which the temperature change width of the heater and the heated air heated by the heater can be further reduced. According to the fourth aspect of the present invention, in the exhaust gas purifying apparatus for a diesel engine according to any one of the first to third aspects, the electric heating means is further supplied with power from a commercial AC power supply.

With this configuration, since the leakage current can be reduced, the interruption of the regeneration operation due to the operation of the leakage breaker on the commercial AC power supply side can be suppressed.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to examples. Note that the duty ratio referred to in this specification may be an average value of a plurality of duty ratios sampled in a predetermined period immediately before. For example, a DC voltage obtained by full-wave rectifying a commercial AC power supply voltage includes a large ripple voltage. When the DC voltage is reduced by the ripple voltage, the duty ratio is increased, and when the DC voltage is increased, the duty ratio is reduced. You can also. By doing so, it is possible to suppress the heat generation fluctuation of the heater due to the ripple voltage.

[0023]

Embodiment 1 An embodiment of an exhaust gas purifying apparatus according to the present invention will be described with reference to a block diagram shown in FIG. This exhaust gas purifying apparatus has a metal filter housing case 1 and a ceramic honeycomb filter 2 in the filter housing case 1.
Is housed. A heater 3 made of a thermocouple is arranged facing the upstream end face of the filter 2 at a small interval, and a temperature sensor 4 is provided between the filter 2 and the heater 3. The temperature sensor 4 may be in close contact with the upstream end face of the filter 2 or the downstream end face of the heater 3.

The heater 3 uses a bare nichrome wire and the case 1
The filter 2 is stretched in a direction perpendicular to the axial direction of the filter 2 while being supported by an electrically insulating ceramic member (insulating support) fixed to the filter 2. The heater 3 is supplied with electric power from a commercial 200 V AC power supply through a controller 9 described below. In the heater 3, the ground insulation resistance may be reduced due to soiling of the surface of the ceramic member (insulating support material) or the like, and a ground leakage current may flow.

An exhaust main pipe 101 of the diesel engine 100 and an air supply branch pipe 102 are connected to an upstream end wall of the filter housing case 1. Or, the air supply branch pipe 102
May be connected to the exhaust main pipe 101. 5 is an electromagnetic valve, 6 is an air flow meter, 7 is an air pump.
02 to the filter 2.

A pressure hose 103 extends from the air supply branch pipe 102, and a pressure sensor 8 is provided at an end of the pressure hose 103. 104 is a filter and 10
Reference numeral 5 denotes a tail pipe that discharges exhaust gas from the downstream end wall of the filter housing case 1 to the outside. The signals from the temperature sensor 4, the air flow meter 6, and the pressure sensor 8 are input to a controller 9, and the controller 9 controls the driving of the heater 3, the solenoid valve 5, and the motor M based on the calculation result.

The controller 9 is a control device having a microcomputer (not shown) built therein. The microcomputer converts various kinds of input data into digital data, performs arithmetic processing on the converted data, and performs processing on the heater 3, the solenoid valve 5, and the air pump 7 The reproduction is executed by controlling the drive of the motor M for driving. Reference numeral 12 denotes an alarm buzzer that issues an alarm when an abnormality occurs. Reference numeral 13 denotes a lamp that notifies the arrival of the regeneration time. Reference numeral 14 denotes a manual switch that instructs the controller 9 to perform a filter regeneration operation. Reference numeral 15 denotes an on-vehicle battery.

The filter 2 is a honeycomb ceramic filter, and is fired in a cylindrical shape using cordierite as a material. The filter 2 has a number of vents penetrating both end faces, one of the adjacent vents is plugged at the upstream end and the other is plugged at the downstream end. Exhaust gas passes through the porous partition between adjacent vents, and
Only the downstream end plug vent and the porous septum are trapped.

The power supply control to the heater 3 by the controller 9 will be described in more detail with reference to FIG. 90 is an earth leakage breaker, 91 is a commercially available full-wave rectifier diode bridge, which performs full-wave rectification of a commercial 200V AC voltage. The full-wave rectified DC voltage contains the pulsating flow and the heater 3 and the IG
The IGBT 92 is applied to a heater drive circuit that is connected in series with the BT 92, and the IGBT 92 is PWM-controlled by appropriately controlling the duty ratio at a carrier frequency of about 1 kHz according to the input situation. If the IGBT 92 is changed to a triac,
The full-wave rectifier diode bridge 91 can be omitted.

Hereinafter, the operation of the exhaust gas purifying apparatus for a diesel engine will be described. (Particle collection operation) Diesel engine 10
The exhaust gas discharged from the exhaust pipe 0 is introduced into the filter housing case 1 through the exhaust pipe 101, particulates in the exhaust gas are collected by the filter 2, and the purified exhaust gas is discharged from the tail pipe 105 to the outside. You. During the particulate collection operation, it is natural that the power supply to the solenoid valve 5 is cut off and closed, and the power supply to the heater 3 and the air pump 7 is cut off.

(Filter Reproduction Timing Judgment Operation) Next, the regeneration timing judgment operation of the filter 2 executed by the controller 9 will be described. When an ignition switch (not shown) is turned on, the battery 9
Are supplied with a power supply voltage, which are initially reset and start operating. At the same time, a starter (not shown) starts the engine.

Next, the pressure P is read from the pressure sensor 8 and the temperature T is read from the temperature sensor 4. Next, if the engine is operating, it is determined whether or not the pressure P exceeds a predetermined threshold pressure, and if so, the lamp 13 is turned on to request the filter to be regenerated. (Filter Regenerating Operation) Next, a filter regenerating routine for regenerating the filter 3 will be described below.

The filter regeneration includes preheating, heat spread,
It is performed in the order of cooling. When the operator confirms that the filter regeneration is necessary by observing the light emission of the lamp 13 and turns on the switch 14 for the filter regeneration during the engine stop period, the controller 9 starts the heater 3 in the first preheating temperature rising period. Then, power is supplied to the motor M so that the filter 2 is preheated and heated to ignite the particulates, so that the temperature detected by the temperature sensor 4 is maintained within a preset temperature control width during the subsequent fire spread period. The intermittent control of the heater 3 is executed to spread the particulates from the upstream side to the downstream side. During the cooling period, the supply air flow rate is greatly increased, the power supply to the heater 3 is cut off, and the remaining particulates are burned. After burning out the filter, the filter 2 is cooled.

(Heater Control) Next, a method of controlling the heater 3 which is a feature of the present embodiment will be described below with reference to flowcharts shown in FIGS. First, switch 1
By detecting the input of No. 4, the PWM control energization to the heater 3 is started (S100). At this time, the duty ratio is set to 100%, and the filter 3 is preheated quickly.

Next, the detected temperature T is read from the temperature sensor 4 (S102), and it waits until it reaches a first threshold value T1 (here, 720 ° C.) (S104).
If it has reached, the detected temperature increase rate dT / dt is calculated (S1).
06). Note that the detected temperature increase rate dT / dt is calculated by dividing the temperature difference between the previous value and the current value of the detected temperature T by the required time therebetween.

Next, the calculated detected temperature increase rate dT / dt
Is checked between the minimum allowable increase rate L and the maximum allowable increase rate H (S108). If it is smaller than L, the duty ratio is increased by a small value ΔD (S110), and a predetermined time is waited ( (S112), and then return to S102. Similarly, if the calculated detected temperature increase rate dT / dt is larger than H, the duty ratio is reduced by a small value ΔD (S114), and waits for a predetermined time (S116), and then returns to S102.

Thus, when the detected temperature reaches the vicinity of the temperature control range (here, 785 to 795 ° C.) during the fire spread period, the temperature control range can be slowly approached. At S108, detected temperature increase rate dT / dt
Is within the above range (L to H), the detected temperature T is read again (S118), and the process waits until the detected temperature T reaches the high-side threshold temperature TH of the temperature control width (S12).
0), when it reaches, the duty ratio is reduced by a predetermined value to lower the temperature of the heater 3 (S122), and the timer is started (S124). The predetermined value is set to be slightly larger so that the temperature of the heater 3 is surely lowered and the detected temperature T is lowered.

Next, the detected temperature T is read again (S12).
6) Wait until the read detected temperature T reaches the low temperature side threshold temperature TL of the temperature control width (S128), and when it reaches, read the count value (temperature fall time) of the timer (S130) and read the read temperature. The amount of increase in the current duty ratio is determined based on the fall time and the amount of decrease in the duty ratio (S132), and the duty ratio is increased (S132).
134), and start the timer (S136).

The amount of increase in the duty ratio in S132 is determined as follows. If the temperature decrease time Δt is shorter than a predetermined value due to the previous decrease ratio ΔDdown of the duty ratio, it is determined that the heat generation amount change corresponding to the decrease amount ΔDdown is too large, and the current duty ratio increase amount ΔDup is set to the previous decrease amount ΔDdown. Make it much smaller. The duty ratio increase amount ΔDup and the previous decrease amount ΔDup are determined according to the length of the temperature decrease time Δt.
The difference from Ddown can also be determined.

The previous duty ratio down amount ΔDdow
If the temperature fall time Δt is longer than a predetermined value due to n, it is determined that the change in the heat generation amount corresponding to the down amount ΔDdown is appropriate, and the current duty ratio increase amount ΔDup is made equal to the previous down amount ΔDdown. Next, the detected temperature T is read again (S138), and the read detected temperature T is read.
Waits until the temperature reaches the high-side threshold temperature TH of the temperature control width (S140). When the temperature reaches the threshold value, the timer count value (temperature fall time) is read (S142), and the read temperature rise time and duty ratio increase amount are read. The amount of reduction of the current duty ratio is determined based on this (S144), and S12
Return to 2.

In the power supply control routine for the heater 3 shown in FIGS. 3 and 4, whether or not a power supply cutoff command accompanying the end of the filter regeneration operation is input is confirmed by a periodic interruption routine. 3 is completely cut off.

[0042]

Second Embodiment (Heater Control) Next, another embodiment of a method for controlling the heater 3 which is a feature of the present embodiment will be described below with reference to a flowchart shown in FIG. In the heater control of this embodiment, the routine shown in the flowchart of FIG. 4 in the first embodiment is changed to the routine shown in the flowchart of FIG.

If the detected temperature increase rate dT / dt falls within the above range (L to H) in S108, the detected temperature T is read again (S200), and the intermediate temperature Tm (Tm) of the temperature control width (TL to TH) is read. = (TL + TH) / 2) and the temperature deviation α (= T−Tm) between the detected temperature TT (S202), and further, the difference between the current value of the detected temperature T calculated in S200 and the previous value stored is stored. The detected temperature change rate dT / dt is obtained by dividing by the time between the two (S204).

Next, based on the obtained temperature deviation α (= T−Tm) and the detected temperature change rate dT / dt, the current change amount ΔD of the duty ratio D is determined from a map stored in advance (S206). . This map is a ternary map, and includes a temperature deviation α (= T−Tm) and a detected temperature increase rate dT.
The relationship between / dt and the change amount ΔD of the duty ratio is stored.

More specifically, the temperature deviation α (= T−
If (Tm) is positive (the detected temperature T is higher than Tm), and if the detected temperature change rate dT / dt is positive (temperature rise), the duty ratio is reduced by a predetermined amount. The detected temperature change rate dT
The predetermined amount can be adjusted according to the magnitude of / dt. For example, if the detected temperature change rate dT / dt is large, the predetermined amount is increased, and if the detected temperature change rate dT / dt is small, the predetermined amount is reduced.

If the temperature deviation α (= T−Tm) is positive (the detected temperature T is higher than Tm), the detected temperature change rate dT /
If dt is negative (temperature drop), the duty ratio is kept or slightly reduced. It should be noted that the predetermined amount can be adjusted according to the magnitude of the detected temperature change rate dT / dt. For example, if the detected temperature change rate dT / dt is large, the predetermined amount is increased and the duty ratio is greatly reduced, and if the detected temperature change rate dT / dt is small, the predetermined amount is reduced or left unchanged.

Conversely, when the temperature deviation α (= T−Tm) is negative (the detected temperature T is lower than Tm), the detected temperature change rate dT /
If dt is negative (temperature drop), the duty ratio is increased by a predetermined amount. It should be noted that the predetermined amount can be adjusted according to the magnitude of the detected temperature change rate dT / dt. For example, if the detected temperature change rate dT / dt is large, the predetermined amount is increased, and if the detected temperature change rate dT / dt is small, the predetermined amount is reduced.

When the temperature deviation α (= T−Tm) is negative (the detected temperature T is lower than Tm), the detected temperature change rate dT /
If dt is positive (temperature rise), the duty ratio is kept or slightly reduced. It should be noted that the predetermined amount can be adjusted according to the magnitude of the detected temperature change rate dT / dt. For example, if the detected temperature change rate dT / dt is large, the predetermined amount is increased and the duty ratio is greatly reduced, and if the detected temperature change rate dT / dt is small, the predetermined amount is reduced or left unchanged.

Next, it is checked whether or not an energization cutoff command has been input upon completion of the filter regeneration operation (S210). If so, energization of the heater 3 is completely cut off (S212). Otherwise, the flow returns to S200. Then, the above-described temperature control is repeated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an exhaust gas purifying apparatus for a diesel engine of the present invention.

FIG. 2 is a circuit diagram showing a heater control circuit section of the controller 9 shown in FIG.

FIG. 3 is a flowchart illustrating a temperature control routine of a heater 3 in the embodiment 1;

FIG. 4 is a flowchart illustrating a temperature control routine of the heater 3 according to the first embodiment.

FIG. 5 is a flowchart showing a temperature control routine of a heater 3 shown in FIG. 1 in a second embodiment.

[Explanation of symbols]

1 is a filter housing case (case), 2 is a filter, 3
Is a heater (electric heating means), 4 is a temperature sensor (temperature detecting means), 5 is a solenoid valve, 6 is an air flow meter, 7 is an air pump (air supply means), 8 is a pressure sensor (pressure detecting means),
9 is a controller (reproduction control means)

Claims (4)

[Claims] 1. A metal case provided in an exhaust path of a diesel engine, a filter provided in the case to collect particulates, and a filter provided in the case near an end face of the filter. An electric heating means for igniting the particulate by energization; an air supplying means for introducing air into the case for the burning of the particulate; a gas supply means provided in the case downstream of the electric heating means. A diesel engine comprising: temperature detection means for detecting the temperature of the air supply; and regeneration control means for controlling the drive of the electric heating means based on the air supply temperature to control the regeneration of the filter by incineration of the particulates. In the exhaust gas purifying apparatus for an engine, the regeneration control means may be smaller than 100% when a temperature detected by the temperature detection means is equal to a predetermined minimum threshold value. At a constant maximum duty ratio, when the temperature detected by the temperature detecting means is equal to a predetermined maximum threshold value larger than the minimum threshold value, at a predetermined minimum duty ratio smaller than the maximum duty ratio and larger than 0%, An exhaust gas purifying apparatus for a diesel engine, wherein a power supply to the electric heating means is PWM-controlled. 2. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein said regeneration control means controls a temperature at which a temperature detected by said temperature detection means falls between said minimum threshold value and said maximum threshold value. When the detected temperature is within the width, the duty ratio of the PWM-controlled energized power increases as the detected temperature approaches the minimum threshold, and decreases as the detected temperature approaches the maximum threshold. Exhaust gas purification equipment for diesel engines. 3. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein said regeneration control means comprises: an intermediate threshold between said minimum threshold and said maximum threshold; and said detected temperature. An exhaust gas purifying apparatus for a diesel engine, which calculates a deviation from the duty ratio and changes the duty ratio in a direction to eliminate the deviation. 4. An exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein said electric heating means is supplied with electric power from a commercial AC power supply.