JP2861599B2 - Diesel engine exhaust purification system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to control the energization of a diesel particulate incineration heater and the opening of a waste gate valve so that the NOx catalyst can be controlled to a temperature range in which a high NOx purification rate can be exhibited. A diesel engine exhaust purification device.

[0002]

2. Description of the Related Art A diesel engine exhaust purification system in which a NOx reduction catalyst is disposed in an exhaust system of a diesel engine and the temperature of the NOx reduction catalyst is controlled by using an electric heater for regenerating a particulate filter. 61-1 Kaisho
No. 12715.

[0003]

However, the conventional apparatus has the following problems. I. Since the electric heater is used for both the filter regeneration and the catalyst temperature control, the power consumption increases. B. If the particulates of the filter are ignited and incinerated halfway during catalyst bed temperature control, subsequent filter regeneration control will not be successful.

An object of the present invention is to provide an exhaust gas purifying apparatus for a diesel engine, which can reduce the amount of electric power consumed by an electric heater as compared with the prior art and can prevent ignition of particulates during non-regeneration. is there.

[0005]

According to the present invention, the above object is attained by the following exhaust purification system for a diesel engine. That is, a diesel engine with a supercharger equipped with a wastegate valve, an electric heater for regenerating a filter with a variable amount of electricity provided in an exhaust system of the diesel engine, a particulate filter, a lean NOx catalyst,
Temperature detection means for detecting a temperature representative of the catalyst bed temperature of the lean NOx catalyst, regeneration time detection means for detecting a time to regenerate the particulate filter, and the regeneration time detection means has determined that the filter regeneration time has been reached. Sometimes the electric heater is energized and the regeneration of the filter is executed,
By controlling the opening of the waste gate valve when the regeneration timing detection means determines that the filter is not regeneration, and controlling the amount of current supplied to the electric heater to a range smaller than the amount of current supplied during the filter regeneration period. An exhaust purification device for a diesel engine, comprising: determination means for executing catalyst bed temperature control.

[0006]

In a diesel engine with a supercharger having a wastegate valve, the exhaust gas temperature can be controlled by changing the opening of the wastegate valve. In other words, opening the waste gate valve reduces the supercharging amount,
The amount of intake air, and hence the amount of exhaust gas, can be reduced without reducing the amount of fuel, and as a result, the temperature of exhaust gas can be increased. Since the exhaust gas temperature can be increased by means other than the electric heater, the catalyst bed temperature can be increased by the electric heater with less electric power than before, and the power consumption in the catalyst bed temperature control can be reduced. In addition, when the catalyst bed temperature is controlled during non-regeneration of the filter, the amount of power supplied to the electric heater is set smaller than during regeneration, so that ignition of the particulates during non-regeneration is prevented.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the exhaust gas purifying apparatus for a diesel engine according to the present invention will be described below with reference to the drawings. In FIG. 1, a diesel engine 1 includes a supercharger 2. The compressor 18 of the supercharger 2 is connected to the intake manifold 15 of the diesel engine 1, and the turbine 17 is connected to the exhaust manifold 16. An exhaust pipe 14 of the diesel engine 1 is connected to a downstream side of the turbine 17 of the supercharger 2. Turbine 1 of turbocharger 2
A wastegate valve 3 is provided in a bypass passage that bypasses the valve 7, and the opening of the wastegate valve 3 is changed by a valve driving device 4. Valve drive 4
Is provided with a duty control solenoid valve in the middle of a negative pressure supply passage to the diaphragm chamber, and the waste gate valve 3 can be controlled to an arbitrary opening degree by controlling the solenoid valve. .

A catalyst (lean NOx catalyst) 9 capable of reducing NOx even in a lean air-fuel ratio region is provided in the exhaust pipe 14. Such a catalyst 9 is composed of a zeolite catalyst having a transition metal ion-exchanged on zeolite and exhibiting NOx reduction ability in the presence of HC (hydrocarbon), or a catalyst having alumina or zeolite carrying a noble metal.

The lean NOx catalyst 9 has a particulate filter 1 for trapping diesel particulates (fine particles such as soot discharged from a diesel engine).
3 are provided. In this case, the lean NOx catalyst 9 and the particulate filter 13 may be integrally formed by supporting the catalyst 9 on the particulate filter 13.

For the particulate filter 13,
The diesel particulates trapped by the particulate filter 13 are ignited and burned, and the filter 1
Filter regeneration electric heater 8 for regenerating filter 3
(Hereinafter, simply referred to as an electric heater 8). A heater voltage control device 10 is connected to the electric heater 8 to control the voltage applied to the electric heater 8, that is, the current flowing through the electric heater 8, so that the amount of electric power (generated heat) consumed by the electric heater 8 can be controlled. It has become.

When the lean NOx catalyst 9 is made of a zeolite catalyst, it is necessary to supply HC as a reducing agent in order for the lean NOx catalyst 9 to exhibit NOx reducing ability. The HC supply device is provided for a portion of the exhaust pipe 14 on the upstream side of the lean NOx catalyst 9. The HC supply device includes, for example, an HC source 5 and an HC addition amount control valve 6 (hereinafter, referred to as an HC control valve 6) provided on a path from the HC source 5 to the exhaust pipe 14.

The above-described valve driving device 4, heater voltage control device 10, and HC control valve 6 are controlled by an electronic control device (electronic control unit, ECU) 12
Controlled. Outputs of various sensors are supplied to the ECU 12 as inputs. Various sensors include a pressure sensor 7 provided at a portion of the exhaust pipe 14 on the upstream side of the lean NOx catalyst 9 and an exhaust pipe 1 on the downstream side of the lean NOx catalyst 9.
4 includes the temperature sensor 11 provided in the portion of FIG. The pressure sensor 7 is a sensor for detecting that the particulates are captured and the pressure on the upstream side of the particulate filter 13 is increased. The pressure sensor 7 is used to determine whether or not the regeneration time has come. Is configured. Also,
The temperature sensor 11 is used to determine whether or not the catalyst bed temperature is in an optimum temperature range for the NOx purification rate, and constitutes a temperature detecting means. The ECU 12 also receives input signals of the engine speed and the torque.

The lean NOx catalyst 9 is not activated if the catalyst bed temperature is too low, so the NOx purification rate decreases. If the catalyst bed temperature is too high, the reducing agent HC is directly oxidized to water and carbon dioxide. Since the amount of HC is insufficient, the NOx purification rate also decreases. For this reason, the lean NOx catalyst 9
To indicate the x purification rate, it is necessary to control the temperature within a certain temperature range, for example, it is necessary to control the temperature within a temperature range of 400 to 500 ° C.

The ECU 12 comprises, for example, a microcomputer, an input / output interface, an analog / digital converter (A / D converter) for converting an analog amount into a digital amount, a read-only memory (ROM) for reading only, It has an access random memory (RAM) for temporary storage and a central processor unit (CPU) for executing operations. The ROM stores a control routine that constitutes the determination means as shown in FIG.
This is read out by the CPU and the operation is executed.

The routine of FIG. 2 is interrupted at regular intervals. First, at step 102, the engine speed NE and the torque, for example, the accelerator opening ACCP are read. Next, at step 104, the HC addition amount necessary for NOx purification in the engine operating state of NE and ACCP is read from a predetermined map.

[0016] Subsequently, at step 106, along with reading the engine back pressure P from the output of the pressure sensor 7, the back pressure P to determine whether large or not than a predetermined value P ₁ which defines because Ji pre.
Since P> increasing number particulate catcher rates trapped P ₁ if the particulate filter 13 is the engine back pressure went up, particulate incineration control proceeds to step 108 it is determined that the filter regeneration timing has come If P ≦ P _1, it is determined that it is the filter non-regeneration time, and the routine proceeds to step 118, where catalyst bed temperature control is performed.

When the routine proceeds to step 108, the HC control valve 6 is turned off at step 108 to stop the supply of HC. This is because if HC is supplied, it burns and the temperature rises too much, so it is better not to supply HC during incineration of soot. Subsequently, the routine proceeds to step 110, where the duty ratio DTW for opening and closing the waste gate valve 3 is set to 0, and the waste gate valve 3 is fully opened, so that the engine exhaust gas temperature becomes the highest. Subsequently, step 112
And the voltage control duty DTH is set to 100 so that the current flowing through the electric heater 8 is maximized. As a result, the particulate is ignited, and burning of the particulate and regeneration of the filter are started.

Subsequently, the routine proceeds to step 114, where it is determined whether or not a set time, for example, 30 seconds, has elapsed. If not, the routine proceeds to the return step. If 30 seconds have elapsed, it is determined that the burning of the particulates has been completed. Considering this, the process proceeds to step 116, where the heater voltage is set to 0, and the energization to the electric heater 8 is stopped.

If it is determined in step 106 that it is the filter non-regeneration time and the process proceeds to step 118, step 118
Is a temperature T representing the catalyst bed temperature (for example, temperature sensor 1
1 output), it is determined whether the higher than the lower limit value T ₁ of the temperature range T ₁ -T ₂ for the lean NOx catalyst 9 can show a high NOx purification rate, the upper limit of the temperature range proceeds to atmospheric if step 120 to determine lower or not than the value T _2. If the current temperature T is in the temperature range of T ₁ -T ₂ , there is no need to perform temperature control, so the routine proceeds to step 122, where the HC control valve 6 is turned on, HC is added, and NOx reduction proceeds as it is. .

If it is determined in step 118 that T ≦ T ₁ , the catalyst bed temperature is too low.
The control is executed to increase the catalyst bed temperature. That is,
In step 132, the HC control valve 6 is turned off. In step 134, the DTW is reduced by a constant value, and the waste gate valve 3 is gradually opened to gradually increase the exhaust gas temperature. Then, the process proceeds to a step 136, wherein it is determined whether or not DTW <0.
≦ T that it ₁ wastegate valve 3 only the open side determines not possible to increase the catalyst bed temperature, step 13
8, the DTH is increased by a constant value, and the current flowing through the electric heater 8 is increased. Then, the process proceeds to step 130, in which the waste gate valve control duty ratio SDW is set to DWT, the electric heater power amount control duty SDH is set to DTH, control is performed, and the process returns.

If it is determined in step 120 that T ≧ T ₂ , the catalyst bed temperature is too high.
Control is performed so that the catalyst bed temperature becomes low. That is,
In step 124, the HC control valve 6 is turned off, and in step 1
In step 26, the exhaust gas temperature is gradually decreased by increasing the DTW by a constant value and gradually closing the waste gate valve 3. Subsequently, the routine proceeds to step 128, where DTH is set to 0, and the current flowing through the electric heater 8 is set to 0. Subsequently, the process proceeds to step 130, where the SDW is set to DT as described above.
W, SDH as DTH, execute control, and return.

In the routine of FIG. 2 described above, when the regeneration timing detecting means (for example, the pressure sensor 7) determines that the filter regeneration timing is reached, the electric heater 8 is energized to execute the regeneration of the filter. The catalyst bed temperature control is performed by controlling the opening of the wastegate valve 3 when the means 7 determines that the filter is not to be regenerated, and by controlling the amount of power supplied to the electric heater 8 to a range smaller than the amount of power supplied during the filter regeneration time. Is determined.

The operation of the exhaust gas purifying apparatus for a diesel engine is performed according to the routine shown in FIG. In such control, the catalyst bed temperature control is performed not only by the electric heater 8 but also by the opening degree control of the waste gate valve 3. The temperature control by the heater 8 is used together. Therefore, the temperature control by the electric heater 8 is reduced by the temperature control by the waste gate valve 3, and the amount of power consumed by the electric heater 8 is reduced.

Further, when the catalyst bed temperature control is executed, the amount of electricity supplied to the electric heater 8 is smaller than the amount of electricity supplied to the electric heater 8 during particulate incineration. This prevents the particulates from being ignited. For example, under the severest condition of T ≧ T ₂ , DTH is set to 0 and the power supply to the electric heater 8 is stopped, so that the electric heater 8 does not cause particulate ignition.

[0025]

According to the present invention, since the determination means is provided, when the regeneration timing detecting means determines that the filter regeneration timing has been reached, the electric heater 8 is energized to execute the regeneration of the filter.
The catalyst bed is controlled by controlling the opening of the waste gate valve 3 when the regeneration timing detecting means determines that the filter is not regenerating, and controlling the amount of current supplied to the electric heater 8 within a range smaller than the amount of current supplied during the filter regeneration period. By controlling the temperature, the power consumption in the catalyst bed temperature control can be reduced, and particulate ignition by the electric heater during non-regeneration can be prevented.

[Brief description of the drawings]

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

FIG. 2 is a control flowchart of a determining means for controlling the exhaust gas purification device of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Supercharger 3 Waste gate valve 4 Valve drive device 5 HC source 6 HC control valve 7 Pressure sensor 8 Electric heater 9 Lean NOx catalyst 10 Heater voltage control device 11 Temperature sensor 12 ECU 13 Particulate filter 14 Exhaust pipe 15 Intake manifold 16 Exhaust manifold 17 Turbine 18 Compressor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01N 3/02 341 F01N 3/20 F01N 3/24 F01N 3/28 301 F01N 9/00

Claims (1)

(57) [Claims] 1. A diesel engine with a supercharger having a wastegate valve, an electric heater for regenerating a filter, a particulate filter, and a lean NOx catalyst, provided in an exhaust system of the diesel engine, the amount of which is variable, and Temperature detection means for detecting a temperature representative of the catalyst bed temperature of the NOx catalyst; regeneration time detection means for detecting a time at which the particulate filter should be regenerated; and when the regeneration time detection means determines that the filter regeneration time is required. The electric heater is energized to perform regeneration of the filter, and when the regeneration timing detecting means determines that the filter is not regeneration timing, the opening degree of the waste gate valve is controlled, and the amount of electricity supplied to the electric heater is controlled by the filter. Judgment to execute catalyst bed temperature control by controlling within a range smaller than the amount of electricity during regeneration Exhaust purification apparatus for a diesel engine, characterized in that it comprises a stage, a.