JPH07180529A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PURPOSE:To prevent the supercooling of filters by calculating the minimum required regenerating exhaust gas flow from the maximum exhaust gas flow that filters can make flow without supercooling based on exhaust gas temperature and the concentration of oxygen in the exhaust gas and, based on both exhaust gas flow values, determining the opening of an exhaust gas flow control valve on the side of filter to be regenerated. CONSTITUTION:A control unit 30 inputs signals from a vehicle speed sensor 35 in addition to those from a speed sensor 32, a control lever sensor 33, and a water temperature sensor 34. Based on these inputted signals, the maximum exhaust gas flow that filters 13 and 23 can supplying within the range that they are not cooled and the concentration of oxygen in the exhaust gas are calculated and, during exhausting, the maximum required regenerating exhaust gas flow is calculated from the oxygen concentration value. Then current flow to heaters 12 and 22 on the filters 13 and 23 sides and the opening of exhaust gas flow control valves 14 are controlled based on the maximum exhaust gas flow value an regenerating exhaust gas flow value. Thus the supercooling of the filters 13 and 23 can be prevented, and thus power consumption can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter regeneration that collects exhaust particulates discharged from a diesel engine by a filter and burns and removes the exhaust particulates deposited when the exhaust particulates deposited on the filter reach a predetermined amount. The present invention relates to an exhaust emission control device for a diesel engine having a function.

[0002]

2. Description of the Related Art Conventionally, as an exhaust emission control device of a diesel engine having a filter regeneration function of collecting fine particles discharged from a diesel engine with a filter and burning and removing the collected fine particles with an electric heater to regenerate the filter. Is, for example, as shown in SAE920139.

In such a conventional device, the exhaust passage is divided into four,
An electric heater for regeneration is provided in each passage with a heater-integrated filter wound with ceramic fiber as a filter material, a poppet valve is provided in series with each filter, and exhaust gas is supplied to the filter seat of the poppet valve during regeneration. An orifice is provided for this purpose. Then, during regeneration, the poppet valve in series with the filter to be regenerated is closed and the heater is energized for a predetermined time.

However, in such a conventional exhaust gas purification apparatus for a diesel engine, when the exhaust gas is supplied to the filter at the time of regeneration, in order to efficiently raise the temperature of the filter by the heater, the filter being regenerated It is necessary to limit the amount of exhaust leakage flow to the appropriate amount, but since there is no means to adjust the leakage flow, a large amount of exhaust exceeding the required amount flows into the filter and the time required for regeneration is extended. Or, there is a problem that reliable reproduction cannot be performed.

As a means for solving such a problem,
For example, a method has been proposed in which the exhaust flow rate control valve controls the flow rate of exhaust gas flowing into the filter during regeneration according to engine operating conditions (for example, Japanese Patent Application No. 5-224501). Here, in order to burn the collected exhaust particulates, it is necessary to supply oxygen to the filter to be regenerated, but when the exhaust gas flow rate increases to secure the required oxygen amount, it is given to the filter by the heater. Heat is taken away, the time required for regeneration is extended, and the amount of energy used for regeneration is increased. Since the energy loss due to the exhaust flow is determined by the exhaust flow rate flowing to the filter, the exhaust temperature, and the filter temperature, the exhaust flow rate characteristic is set in the conventional device so that the exhaust flow rate is obtained from these.

[0006]

However, in the above-mentioned conventional apparatus, the exhaust flow rate is set only from the viewpoint of preventing the cooling of the filter, so the exhaust flow rate supplied to the filter being regenerated is exhausted from the engine. The flow rate was controlled to be approximately proportional to the exhaust flow rate. In other words, at a certain engine speed, it is sufficient to set the flow rate of the air flowing to the filter at a low load with a low exhaust temperature, and the exhaust temperature rises as the load increases, so cooling of the filter is said to be no problem. . Therefore, the exhaust temperature is high, such as low rotation and high load, but the exhaust flow rate is low, and under conditions where the oxygen concentration in the exhaust is low, the amount of oxygen supplied to the filter being regenerated is insufficient, so the combustion of particulates deposited on the filter However, there was a problem that the heater energization time required for regeneration was extended or regeneration was defective and the pressure loss was not recovered.

The present invention has been made by paying attention to such a conventional problem, and it is possible to prevent regeneration of the filter and to control the exhaust flow rate so as to secure the required oxygen amount, thereby regenerating the regeneration. An object of the present invention is to provide an exhaust emission control device for a diesel engine, which is capable of ensuring and reducing electric power required for regeneration.

[0008]

Therefore, in the exhaust emission control system for a diesel engine of the present invention, as shown in FIG. 1, the exhaust passage of the diesel engine is branched into a plurality of exhaust passages, and the exhaust passage is exhausted from the engine into each branch passage. A filter for collecting fine particles to be collected,
An electric heater for burning and removing the particulates trapped by the filter, and an exhaust flow rate control valve that is provided in series with the filter and controls the exhaust flow rate that flows through the filter are provided, while the engine operating state detection means is provided, Exhaust temperature detecting means, and a maximum exhaust flow rate calculating means for calculating the maximum exhaust flow rate that can be flown to the filter side in a range where the filter to be regenerated does not become supercooled when the filters are regenerated, based on the detection value of the exhaust temperature detecting means. An oxygen concentration calculating means for calculating the oxygen concentration in the exhaust gas according to the engine operating state detected by the engine operating state detecting means, and an oxygen amount necessary for regeneration based on the calculated value of the oxygen concentration calculating means Regeneration exhaust flow rate calculation means for calculating the regeneration exhaust flow rate necessary for the regeneration, and a branch passage on the filter side for regeneration based on the calculation values of the front and rear exhaust flow rate calculation means And valve opening control means for controlling the exhaust gas flow rate control valve opening, constructed by a heater energization control means for energizing the filter side of the electric heater to be played during filter regeneration.

Further, when the exhaust flow rate calculated by the regeneration exhaust flow rate calculation means is larger than the exhaust flow rate calculated by the maximum exhaust flow rate calculation means, the exhaust flow rate control valve is fully closed for a predetermined time. It is preferable to have a configuration including.

[0010]

In such a construction, from the viewpoint of preventing the cooling of the filter to be regenerated, from the viewpoint of calculating the maximum exhaust flow rate that can flow in the range where the filter does not become supercooled, based on the exhaust temperature, and in order to satisfactorily burn the exhaust particulates, The oxygen concentration in the exhaust gas is calculated, and the minimum required regeneration exhaust gas flow rate is calculated from this oxygen concentration value in the exhaust gas. Then, the opening degree of the exhaust gas flow rate control valve on the filter side to be regenerated is determined based on both the exhaust gas flow rate values.

As described above, according to the present invention, the exhaust gas flow rate is controlled from the viewpoints of both the supercooling of the filter and the combustibility of the exhaust particulates, so that the exhaust particulates deposited on the filter can be favorably prevented while preventing the supercooling of the filter. It is possible to combust, and it is possible to prevent waste of electric power because the heater energization time is not extended more than necessary. Further, the pressure loss can be recovered by the good filter regeneration.

Further, according to the present invention, when the minimum required exhaust flow rate for regeneration calculated from the viewpoint of excellent combustion of exhaust particulates exceeds the maximum exhaust flow rate calculated from the viewpoint of preventing cooling of the filter to be regenerated. , The exhaust flow rate control valve on the filter side for regeneration is controlled to be fully closed for a predetermined time. As a result, the exhaust flow rate exceeding the maximum exhaust flow rate in consideration of the filter cooling prevention is not supplied to the filter, and the reliability of the filter cooling prevention can be enhanced.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram showing the system configuration of an embodiment of the present invention. In FIG. 2, an intake passage 2 and an exhaust passage 3 are connected to the engine body 1. The exhaust passage 3 branches into two branch passages 11 and 21 on the way. Inside each of the branch passages 11 and 21, heaters 12 and 22 and filters 13 and 23 for collecting exhaust particulates are sequentially provided from the upstream side after enlarging the passage area. In addition, each filter 1
Exhaust flow control valve 1 is provided on the further downstream side of 3, 23, respectively.
4, 24 are interposed. Then, the exhaust flow control valve 1
The exhaust passages 3 are joined again on the downstream side of 4, 24.
Each of the heaters 12 and 22 has a control unit 30.
ON / OFF controlled heater relays 15 and 2
Energization is controlled via 5. Further, the opening degree of the exhaust flow rate control valves 14 and 24 is controlled via drive actuators 16 and 26 that are also controlled by the control unit 30. Here, as the material of the filters 13 and 23, any of ceramic fiber, ceramic foam, metal foam, and sintered metal may be used. Also,
The exhaust flow rate control valves 14 and 24 are butterfly
A valve, a slide valve, a poppet valve, etc. can be used.

The exhaust passage 3 has branch passages 11 and 21.
An exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 4 that branches on the upstream side of the EGR passage 4 and is connected to the intake passage 2 is provided, and an EGR valve 5 is provided in the EGR passage 4 to receive a signal from the control unit 30. Based on this, drive control is performed via the drive actuator 6. An exhaust temperature sensor 31 as exhaust temperature detecting means is provided between the EGR passage 4 and the branch passages 11 and 21 of the exhaust passage 3. Also, the engine body 1
Includes a rotation speed sensor 32 for detecting the engine rotation speed N, a control lever sensor 33 for detecting the engine load Q from the control lever opening of the fuel injection pump,
A water temperature sensor 34 for detecting the engine water temperature is provided.

The control unit 30 receives the signals from the vehicle speed sensor 35 in addition to the signals from the sensors, and based on the signals input from the sensors constituting the engine operating state detecting means, As shown in the flow chart described later, the filter 13 or 23 for performing regeneration such as calculation of oxygen concentration in exhaust gas, regeneration exhaust flow rate, maximum exhaust flow rate, etc., and determining regeneration time of each filter.
For energizing the exhaust side heater 12 or 22 and the exhaust flow control valve 1
The opening degree of 4 or 24 is controlled. Therefore, the control unit 30 has the functions of the maximum exhaust flow rate calculation means, the oxygen concentration calculation means, the regeneration exhaust flow rate calculation means, the valve opening control means, and the heater energization control means, and these functions are shown in the flowchart described later. It is provided as software.

Next, the operation of the exhaust gas purification apparatus of this embodiment will be described based on the flow charts shown in FIGS. FIG. 3 and FIG. 4 are basic control flowcharts of the particulate collection operation and the filter regeneration operation by the filter of the apparatus of this embodiment. Since the filter regeneration operation is alternately performed here, for convenience, the heater 12 on the side of the branch passage 11, the filter 13, and the exhaust flow control valve 14 are connected to the first heater,
The heater 22, the filter 23, and the exhaust flow rate control valve 24 on the side of the branch passage 21 will be referred to as a first heater and a second control valve, respectively.

First, in step 1 (indicated by S1 in the drawing, the same applies hereinafter), the engine speed N and the engine load Q are read from the speed sensor 32 and the control lever sensor 33. In Step 2, based on the engine speed N and the engine load Q read in Step 1,
Emission amount of exhaust particulate per unit time ΔP
Calculate M.

In step 3, it is determined whether the reproduction flag 1 is ON. When the reproduction flag 1 is ON, the first
It is determined that the filter is being regenerated, and exhaust particulate matter is collected only by the second filter. In step 7, a value obtained by multiplying the exhaust particulate quantity ΔPM calculated in step 2 by a preset filter collection efficiency is used. The total deposition amount β ₂ of the second filter is detected by adding to the current deposition amount of the second filter,
Further, the opening degree of the first control valve on the side of the first filter which is being regenerated in step 9 corresponds to the change in the operating condition during the regeneration as shown in FIG.
Adjust as shown in the flow chart.

If the determination in step 3 is NO (reproduction flag 1 is OFF), the process proceeds to step 4 and reproduction flag 2 is set to 0.
It is determined whether it is N or not. When the reproduction flag 2 is ON, the second
It is determined that the filter is being regenerated, and in the same manner as in steps 7 and 9, the total deposition amount β ₁ of the first filter is detected in step 6, and the opening degree of the second control valve is adjusted in step 8. When it is determined in step 4 that the regeneration flag 2 is not ON, it is determined in step 5 that neither the first filter nor the second filter is being regenerated, and the exhaust particulate deposition amount ΔPM is set to
The total deposition amounts β ₁ and β ₂ of both filters are detected by dividing and adding to the first and second filters.

Next, in steps 10 and 11, it is judged whether or not the total accumulation amounts β ₁ and β ₂ of the respective filters have reached a predetermined amount βRe which is judged to be the regeneration time. Then, when β ₁ ≧ βRe, that is, when it is determined that the regeneration time is on the first filter side, in steps 13, 15, and 17,
The regeneration flag 1 is turned on, the opening degree of the first control valve is adjusted, and the first heater is turned on (energized). Also, β ₂ ≧ β
When Re, that is, when it is determined that the second filter side is the regeneration time, the regeneration flag 2 is set to ON in steps 12, 14 and 16, the opening degree of the second control valve is adjusted, and the second heater is turned on. (Energized).

Then, when the heater is turned on in step 16 or 17, the heater energization time starts to be measured,
Energization is performed until the determination in step 18 or 19 is YES, that is, until the heater energization time Th ₂ (second heater side) or Th ₁ (first heater side) on the filter side during regeneration reaches a predetermined time Tre. . When it is determined in step 18 or 19 that the heater energization time has reached the predetermined time, it is determined that the regeneration is finished, and if the regeneration is the first filter, the first heater is turned on in steps 21, 23, 25 and 27. Turn it off,
The first control valve is fully opened, the regeneration flag 1 is turned off, the value of the total deposition amount β ₁ of exhaust particulates is cleared to 0, and the regeneration operation is ended. If the regeneration is the second filter, in steps 20, 22, 24, and 26, the second heater is turned off, the second control valve is fully opened, the regeneration flag 2 is turned off, and the total accumulation amount β of exhaust particulates β a value of ₂ is cleared to 0, the reproduction operation is ended.

In the above-mentioned regeneration operation, when it is judged that it is time to regenerate the filter, the opening of the control valve is adjusted (see FIG. 3).
Steps 14 and 16) of the flow chart of the above are, when regenerating, the exhaust flow rate according to the cooling prevention of the filter on the regenerating side and the required oxygen amount required for combustion of fine particles,
This is for supplying to the filter on the reproduction side. Details of the opening degree adjusting operation of the control valve will be described with reference to the flowchart shown in FIG.

First, in step 31, the rotation speed sensor 3
2, the engine speed N and the engine load Q are read from the control lever sensor 33. In step 32,
The exhaust flow rate is calculated from the map shown in FIG. 8 based on the engine speed N read in step 31. In step 33, the exhaust temperature Tex is read from the exhaust temperature sensor 31. The exhaust temperature Tex may be calculated using a map as shown in FIG. 7 instead of being read from the exhaust temperature sensor.

In step 34, the maximum exhaust flow rate Vmax which is determined from the exhaust temperature Tex read in step 33 and which takes into account the cooling prevention of the filter is calculated. The maximum exhaust flow rate Vmax is calculated based on the difference between 700 ° C., which is the temperature under which the filter is heated by the heater, and the exhaust temperature Tex, and is calculated by the following equation. _{Vmax = K 1 + K 2 (} Tex-700) K 1, K 2 is the constant step 35, it opens up the exhaust flow control valve in consideration of the filter cooling prevention from Vmax calculated by the exhaust flow rate and the step 34 obtained at step 32 The degree Otp is calculated from the map shown in FIG.

Next, in step 36, the EGR condition is judged from the operating state of the engine, and in step 37, step 3
On the basis of the EGR condition determination of No. 6, the exhaust gas oxygen concentration in consideration of the EGR condition is calculated. Here, the EGR is set according to the engine speed, the engine load, the water temperature, the vehicle speed, etc. However, when the EGR is present, the target EGR rate is generally set. By switching the maps of FIGS. 9 and 10, the oxygen concentration in the exhaust gas is calculated.

In step 38, the minimum exhaust flow rate Vmin for securing the required oxygen amount required for combustion of fine particles, which is determined from the oxygen concentration in the exhaust gas obtained in step 37, is calculated. This minimum exhaust flow rate Vmin is calculated by the following equation. Vmin = (AIR / Rt) × (0.21 / EO ₂ ), where AIR: Atmospheric condition necessary to burn the exhaust gas particles of βRe (21% O ₂ ) Rt: Regeneration time (for example, 5 minutes) EO ₂ : In step 39 of the oxygen concentration in exhaust gas, the opening degree Oo ₂ of the control valve considering the combustibility of fine particles is calculated from the exhaust flow rate obtained in step 32 and the minimum exhaust flow rate Vmin obtained in step 38 in the same manner as in step 35. It is calculated from the map shown in FIG.

In step 40, it is judged whether or not there is a compatible range (overlap range) between the control valve opening degrees Otp and Oo ₂ obtained in step 35 and step 39, respectively. The routine proceeds to step 44, where the actual valve opening degree Ore is set within the range of both valve opening degrees compatible with each other. This valve opening O
Re may be any opening as long as it is within the compatibility range, but it is preferable to set it to a value close to the valve opening Oo ₂ from the viewpoint of preventing temperature rise and cooling.

However, depending on the characteristics of the control valve, there is a case where the calculated valve opening degrees Otp and Oo ₂ are not compatible with each other.
If there is no compatible region, it is necessary to control separately the temperature rise by the heater and the combustion of the fine particles by the oxygen supply, and in order to give priority to the temperature rise control by the heater, step 41
To fully close the control valve and turn on the fully closed flag in step 42.
Then, in step 43, the count of the valve closing timer is started in order to fully close the control valve for the required time. In this way, when the valve opening degree Otp considering the filter cooling prevention and the valve opening degree Oo ₂ considering the combustibility of the fine particles do not overlap, in other words, the minimum amount of oxygen required to burn the fine particles can be secured. When the exhaust flow rate of is larger than the maximum exhaust flow rate that can be supplied in the range where the filter does not cool, priority is given to the temperature rise control by the heater, so that the cooling of the filter is prevented and the power consumption due to the extension of the energization time of the heater can be prevented. .

Further, in the above-described regeneration operation shown in FIG. 3, the control valve opening on the regeneration side is adjusted during filter regeneration (steps 8 and 9 in the flowchart of FIG. 3) is the operation of the engine during the regeneration operation. Due to the change of state, the filter is overcooled and the combustion propagation of exhaust particulates is obstructed,
This is to prevent the combustion of exhaust particulates from falling into a misfire state due to insufficient oxygen supply. The details of the operation of adjusting the opening of the control valve during regeneration will be described with reference to the flowchart shown in FIG.

Steps 51 to 54 show the operation from the execution of the fully closed control of the control valve to the start of the oxygen supply after a predetermined time in the flowchart of FIG. That is, in step 51, it is determined whether or not the valve closing flag is ON, and when it is ON, it is determined that the control valve full closing control is being performed, and in step 52, it is determined whether or not the count value of the valve closing timer reaches a predetermined value. Is determined, and until the predetermined value is reached, step 5
At 4, the valve close timer is incremented. When the predetermined value is reached, the valve closing flag is turned off in step 53 to complete the fully closed control of the control valve, and steps 55 to 64 are executed to supply oxygen.

Steps 55 to 63 are the same as the control operation of the control valve opening shown in steps 31 to 39 of the flowchart of FIG. Then, the valve opening control shown in the flowchart of FIG. 6, when determining the actual valve opening Ore each valve opening Otp, after Oo ₂ calculates, both valve opening Otp, Oo ₂
Both regions within the the absence, the valve opening Oo ₂ considering flammability priority, sets the actual valve opening Ore to Oo ₂ in.
The reason for this is that the control valve was fully closed,
This is because it is necessary to supply a sufficient amount of oxygen because the temperature of the filter has been sufficiently raised and the exhaust particulates have been sufficiently heated and ignited.

[0032]

As described above, according to the present invention, the maximum exhaust flow rate that can be supplied within the range where the filter is not overcooled is calculated based on the exhaust temperature, and the oxygen in the exhaust is calculated based on the engine operating condition. Obtain the concentration, calculate the minimum exhaust flow rate that can supply an amount of oxygen sufficient to burn the exhaust particulates based on this oxygen concentration, and open the exhaust flow control valve on the filter side that regenerates from both of these exhaust flow values. Since the degree is determined, it is possible to allow the exhaust gas flow rate to flow through the filter at the time of filter regeneration not only from the viewpoint of preventing overcooling of the filter but also considering the combustibility of exhaust particulates. Therefore, even in an engine operating state where the exhaust temperature is high but the exhaust flow rate is small, such as low rotation and high load, a sufficient amount of oxygen can be supplied to the filter during regeneration, combustion of exhaust particulate becomes good, and the filter can be swiftly discharged. Can be played. Further, it is possible to prevent the energization time of the heater from being extended and reduce the power consumption.

Further, when the cooling of the filter proceeds when the exhaust flow rate for ensuring the combustibility of the exhaust particulates is passed, if the exhaust flow rate control valve is fully closed and the temperature rise of the filter is prioritized. It is possible to increase the certainty of preventing overcooling of the.

[Brief description of drawings]

FIG. 1 is a block configuration diagram for explaining a configuration of the present invention.

FIG. 2 is a configuration diagram of a system according to an embodiment of the present invention.

FIG. 3 is a flowchart explaining the basic operation of the above embodiment.

FIG. 4 is a flowchart following FIG.

FIG. 5 is a flowchart illustrating a valve opening adjustment operation.

FIG. 6 is a flowchart illustrating a valve opening adjustment operation during filter regeneration.

[Fig. 7] Exhaust temperature characteristic diagram depending on engine speed and engine load

FIG. 8 is a characteristic diagram of exhaust flow rate with respect to engine speed

FIG. 9 is a characteristic diagram of exhaust gas oxygen concentration with respect to engine speed and engine load without EGR

FIG. 10 is a characteristic diagram of exhaust gas oxygen concentration with respect to engine speed and engine load when EGR is present.

FIG. 11 is a characteristic diagram of exhaust particulate emission according to engine speed and engine load.

FIG. 12 is a flow characteristic diagram of the exhaust flow control valve.

[Explanation of symbols]

 1 Engine Main Body 3 Exhaust Passage 11,21 Branch Passage 12,22 Heater 13,23 Filter 14,24 Exhaust Flow Control Valve 30 Control Unit 31 Exhaust Temperature Sensor 32 Rotation Speed Sensor 33 Control Lever Sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F01N 9/00 ZAB Z

Claims (2)

[Claims] 1. An exhaust passage of a diesel engine is branched into a plurality of filters, and a filter for collecting fine particles discharged from the engine in each branch passage, and an electricity for burning and removing the fine particles collected by the filter. A heater and an exhaust flow rate control valve that is provided in series with the filter and controls the exhaust flow rate flowing through the filter are provided, while an engine operating state detection unit, an exhaust temperature detection unit, and a filter that is regenerated when each filter is regenerated. The maximum exhaust flow rate calculation means for calculating the maximum exhaust flow rate that can flow to the filter side in the range that does not become supercooling based on the detection value of the exhaust temperature detection means, and the engine operating state detected by the engine operating state detecting means. According to the oxygen concentration calculation means for calculating the oxygen concentration in the exhaust gas, and the regeneration necessary to secure the amount of oxygen required for regeneration based on the calculated value of the oxygen concentration calculation means. An exhaust flow rate calculation means for regeneration for calculating the exhaust flow rate of, and a valve opening degree control means for controlling the exhaust flow rate control valve opening degree of the branch passage on the filter side for regeneration based on the calculated values of the front and rear exhaust flow rate calculation means, An exhaust emission control device for a diesel engine, comprising: a heater energization control unit that energizes an electric heater on the filter side that is regenerated during filter regeneration. 2. A control means for fully closing the exhaust flow rate control valve for a predetermined time when the exhaust flow rate calculated by the regeneration exhaust flow rate calculation means is larger than the exhaust flow rate calculated by the maximum exhaust flow rate calculation means. The exhaust emission control device for a diesel engine according to claim 1, further comprising: