JPH0734853A - Exhaust gas purifying device for diesel engine - Google Patents

Abstract

PURPOSE:To calculate correctly a pressure difference between pressure on upstream side and downstream side of a filter under its reference operating condition. CONSTITUTION:A filter 8 for collecting particulates is provided in the exhaust system of a diesel engine 1. A pressure difference under the state of reference operation is found out by a CPU 21 on the basis of an intake air flow to a diesel engine 1 shown by a hot-wire type flow sensor 5 and the flow at the time of reference operation in reference to a pressure difference between pressure on the upstream side and downstream side from the filter 8 known by pressure sensors 17, 18. In the CPU 21, the fuel injection amount of the diesel engine 1 is then found out from an acceleration opening degree and engine rotational speed by using a governor pattern, and the pressure difference in reference operating condition is corrected on the basis of the fuel injection amount. In the CPU 21, when a particulate collecting amount according to the pressure difference in the reference operating condition increases to a prescribed amount or more, an electric heater 9 and an electrically driven type air pump 12 are driven so as to regenerate the filter 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device for a diesel engine.

[0002]

2. Description of the Related Art D as a measure against black smoke in diesel engines
A PF (diesel particulate filter) system is adopted. As shown in FIG. 3, a DPF 32 for collecting particulates is provided in the exhaust system of the diesel engine 31, and the CPU is used during filter regeneration.
By energizing the electric heater 34 at 33, the DPF 3
The particulate matter collected in 2 is ignited and the air pump 35 is driven to supply secondary air to the DPF 32 to incinerate the particulate matter collected in the DPF 32. At this time, the CPU 33 determines whether the pressure sensor 36,
With respect to the pressure difference between the upstream side and the downstream side in the DPF 32 by 37, the pressure difference in the standard operation state is obtained from the intake air flow rate to the diesel engine by the intake air flow rate sensor 38 and the flow rate in the standard operation.

That is, since the DPF 32 has a laminar flow characteristic, a differential pressure proportional to the ventilation resistance of the DPF 32 is generated with respect to the volume flow rate. However, the ventilation resistance is determined by the initial pressure loss of the DPF 32 and the amount of particulate collection. It is assumed that the differential pressure before and after the DPF 32 generated when the volume flow rate V flows into the DPF 32 under a certain collection amount is ΔP. At this time, the value detected by the intake air flow rate sensor 38 was used as the volume flow rate V. When the reference volume flow rate Vstd is based on a certain operating condition, the pressure difference ΔP1 in the standard operating condition is calculated by the equation (1).

ΔP1 = ΔP · (Vstd / V) (1) Then, when the particulate collection amount according to the pressure difference ΔP1 in the standard operating state becomes a predetermined value or more, regeneration is performed. Was there.

[0005]

However, the DPF 32
The volumetric flow rate V of the exhaust gas flowing into the diesel engine 31 is
Since it is calculated based only on the intake air flow rate flowing into the intake air,
Since the volumetric flow rates of the exhaust gas flowing into F32 do not match,
An error will occur in the pressure difference in the standard operation state.

Therefore, an object of the present invention is to provide an exhaust emission control device for a diesel engine which can accurately calculate the pressure difference between the upstream side and the downstream side of the filter in the standard operation state.

[0007]

According to the present invention, there is provided a filter provided in an exhaust system of a diesel engine for collecting particulates, and for burning the particulates collected by the filter to regenerate the filter. Regenerating means, a pressure sensor for detecting the pressure difference between the upstream side and the downstream side in the filter, an intake air flow rate sensor provided in the intake system of the diesel engine, for detecting the intake air flow rate to the diesel engine, For the pressure difference between the upstream side and the downstream side in the filter by the pressure sensor, obtain the pressure difference in the standard operating state from the intake air flow rate to the diesel engine by the intake air flow rate sensor and the flow rate in the standard operation, When the particulate collection amount according to the pressure difference becomes a predetermined value or more, a control circuit for regenerating the filter by the regenerating means is provided. In the exhaust purification apparatus example was a diesel engine, in which the exhaust gas purification device for a diesel engine by correcting the pressure difference between the reference operating state at said control circuit based on the fuel injection amount of the diesel engine and its gist.

Here, the fuel injection amount of the diesel engine is stored in advance as a governor pattern, which is the injection characteristic of the fuel injection pump, and the accelerator opening and the engine speed are detected to open the accelerator using the governor pattern. Alternatively, it may be obtained from the engine speed and the engine speed.

The fuel injection amount of a diesel engine is
It may be obtained by taking in the injection amount signal from the engine control computer. Further, the fuel injection amount of the diesel engine may be directly obtained by the spill position sensor or the control rack position sensor.

[0010]

[Operation] The control circuit controls the pressure difference between the upstream side and the downstream side of the filter by the pressure sensor, and the pressure difference in the standard operating state from the intake air flow rate to the diesel engine by the intake air flow rate sensor and the standard operation flow rate. Ask for. At this time,
The pressure difference in the standard operation state is corrected based on the fuel injection amount of the diesel engine. That is, the amount of change in the amount of intake and exhaust due to the combustion of fuel in the diesel engine is obtained according to the amount of fuel injection, and is reflected in the calculation of the pressure difference in the standard operating state. Then, the control circuit causes the regeneration means to regenerate the filter when the amount of collected particulates according to the pressure difference becomes equal to or larger than a predetermined value.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an overall configuration diagram of an exhaust emission control device for a diesel engine.

The vehicle is equipped with a diesel engine 1. The diesel engine 1 has an intake pipe 2 and an exhaust pipe 3
And are connected. An engine air cleaner 4 is provided on the most upstream side of the intake pipe 2. Further, a hot-wire type flow rate sensor 5 is provided in the middle of the intake pipe 2, and the sensor 5 detects the intake air flow rate (volume flow rate).

The exhaust pipe 3 of the diesel engine 1 is provided with a housing 7 of an exhaust gas purification device 6. The housing 7 communicates with the exhaust pipe 3, and the diesel engine 1
Exhaust gas of the above passes through the inside of the housing 7. In the housing 7, a filter made of porous ceramic (DP
F) 8 is provided, and the particulate matter discharged from the diesel engine 1 is collected by the filter 8. Further, an electric heater 9 is provided at the upstream end of the filter 8, and the electric heater 9 is heated by energization of the electric heater 9 to ignite the particulates collected by the filter 8.

A secondary air supply pipe 10 is branched on the upstream side of the housing 7 in the exhaust pipe 3, and an electromagnetic valve 11 is arranged in the middle of the secondary air supply pipe 10. The electromagnetic valve 11 is provided to prevent exhaust gas from flowing back into the secondary air supply path during normal operation. The discharge side of the electric air pump 12 is connected to the tip of the secondary air supply pipe 10. Further, an air pump air cleaner 13 is provided on the intake side of the electric air pump 12. Then, when the electromagnetic valve 11 is opened, the secondary air is supplied to the intake pipe 3 of the diesel engine 1 by driving the electric air pump 12.

A fuel injection pump governor 14 is attached to the diesel engine 1, and an accelerator opening sensor 15 is provided in the governor 14. Further, the diesel engine 1 is provided with a rotation speed sensor 16, which detects the engine rotation speed.

A pressure sensor 17 is provided on the upstream side of the filter 8, and the sensor 17 detects the absolute pressure (pre-pressure) on the upstream side of the filter 8. A pressure sensor 18 is provided on the downstream side of the filter 8, and the sensor 18 detects an absolute pressure (post-pressure) on the downstream side of the filter 8. A temperature sensor 19 is provided in the exhaust pipe 3, and the sensor 19 detects the absolute temperature of exhaust gas (inlet gas temperature) flowing into the filter 8.

The electronic control unit (ECU) 20 has a CP
U21 is provided. The CPU 21 is connected to the electric heater 9 via the semiconductor relay 22,
The energization of the electric heater 9 is controlled according to the control signal from 1. Further, the CPU 21 is connected to the electric air pump 12 via the semiconductor relay 23, and the drive of the electric air pump 12 is controlled according to a control signal from the CPU 21.

The hot wire type flow sensor 5, accelerator opening sensor 15, rotation speed sensor 16, pressure sensor 17, pressure sensor 18 and temperature sensor 19 are connected to the CPU 21,
Output signals from these sensors are fetched by the CPU 21.

Further, the CPU 21 is provided with a memory 21a, and a governor pattern which is the injection characteristic of the fuel injection pump is stored in advance in this memory 21a. Then, using this governor pattern, the fuel injection amount can be detected from the accelerator opening and the engine speed.

Next, a method of calculating the pressure difference of the filter 8 in the standard operating condition in consideration of the fuel injection amount will be described. First,
The influence of the fuel injection amount on the volumetric flow rate of exhaust will be described.

About 80% of the inhaled air is nitrogen (N
₂ ) and the remaining about 20% is oxygen (O ₂ ). Therefore, the molecular formula of inhaled air is represented by the following chemical formula. A (8N ₂ + 2O ₂ ) ... (2) However, A is a constant and is determined by the suction volume flow rate.

The molecular formula of fuel gas oil is expressed by the following chemical formula. _{B (C x H y O z} ) ··· (3) However, B is a constant and is determined by the fuel injection amount.

The volume flow rate of the exhaust gas is obtained by the chemical reaction of the chemical formula (2) and the chemical reaction of the chemical formula (3). The components produced by the chemical reaction are NO ₂ , NO, CO ₂ ,
CO, H ₂ O, etc. However, if only oxygen and fuel are taken into consideration in order to simplify the explanation, the chemical reaction formula is as follows.

[0024]

[Equation 1]

However, a = 2 · A and b = B. a,
b, x, y, z are constants. a is determined by the suction volume flow rate. b is determined by the fuel injection amount. x, y and z are determined by the fuel component.

From the equation (4), the number of molecules of the exhaust gas changes from the number of molecules of the intake gas by the amount represented by the equation (5). n1 = (b / 4) · (y + 2z) (5) The change amount ΔV of the volumetric flow rate caused by the fuel injection is (6)
It becomes like a formula.

ΔV = n1 RT / P (6) where T is the gas temperature, R is the gas constant, and P is the pressure on the upstream side of the filter 8.

Therefore, the formula for calculating the pressure difference of the filter 8 in the standard operating condition in which the fuel injection amount is taken into consideration is as shown in formula (7). ΔP1 = ΔP · Vstd / (V + ΔV) (7) where ΔP is the pressure difference between the upstream side and the downstream side of the filter 8,
V is the volumetric flow rate flowing into the filter 8 obtained from the intake air amount, and Vstd is the reference volumetric flow rate under the standard operating conditions.

In the present embodiment, the electric heater 9 and the electric air pump 12 constitute a regeneration means, the hot wire type flow sensor 5 constitutes an intake air flow rate sensor, and the CPU 21
The control circuit is composed of.

Next, the operation of the exhaust emission control system of the diesel engine thus constructed will be described. CPU during playback
The operation in 21 will be described with reference to the flowchart of FIG.

First, during the operation of the diesel engine 1, the CPU 21 determines in step 100 the sensor signals of the hot-wire flow sensor 5, accelerator opening sensor 15, revolution sensor 16, pressure sensor 17, pressure sensor 18, and temperature sensor 19. Take in. Then, the CPU 21 determines the intake air flow rate, the accelerator opening degree, the engine speed, the upstream side pressure (front pressure) and the downstream side pressure (post pressure) of the filter 8, and the incoming gas temperature by the signal from the sensor. Detect. Then C
The PU 21 determines in step 101 whether or not the reproduction condition is satisfied.

That is, the CPU 21 uses the hot wire type flow sensor 5
Based on the intake air flow rate (volume flow rate), the temperature of the gas input by the temperature sensor 19 and the pre-pressure by the pressure sensor 17, the volume flow rate V flowing into the filter 8 determined from the intake air amount is determined. Further, the CPU 21 obtains the pressure difference ΔP between the upstream side and the downstream side of the filter 8 by subtracting the rear pressure from the front pressure.
Further, the CPU 21 obtains the fuel injection amount from the accelerator opening and the engine speed using the governor pattern of the memory 21a. Then, the CPU 21 obtains the pressure difference .DELTA.P1 of the filter 8 in the standard operating condition from the above equation (7) from the value of the standard volumetric flow rate Vstd under the standard operating condition.
That is, in the equation (5), the b value is obtained from the fuel injection amount, and the y value and the z value are obtained from the fuel component.
By substituting it into the equation, the change amount n1 of the number of molecules is obtained. By substituting this n1 value, the gas temperature T and the upstream side pressure P of the filter 8 into the equation (6), the change amount ΔV of the volume flow rate is obtained. And the pressure difference ΔP between the upstream and downstream of the filter 8, the reference volumetric flow rate Vstd, and the volumetric flow rate V flowing into the filter 8 obtained from the intake air amount.
And are substituted into the equation (7) to obtain the pressure difference ΔP1 of the filter 8 in the standard operating condition. The reference volume flow rate Vstd is obtained in advance and is the volume flow rate in a certain reference operation state.

When the CPU 21 determines that the particulate collection amount according to the pressure difference .DELTA.P1 in the standard operation state is less than the predetermined value and the regeneration is not necessary, this routine is ended. On the other hand, the CPU 21 starts the regeneration when the particulate collection amount according to the pressure difference ΔP1 in the standard operation state becomes equal to or larger than a predetermined value and the regeneration is necessary.

When the regeneration is started when the diesel engine 1 is stopped, the CPU 21 opens the electromagnetic valve 11 in step 102 so that air (oxygen) can be supplied from the electric air pump 12. Furthermore, CPU2
In step 103, the regeneration condition for regenerating the exhaust gas purification device 6 is determined. Here, the target control flow rate of the electric air pump 12 and the target control power of the electric heater 9 are determined.

Next, the CPU 21 controls energization of the electric heater 9 and drive control of the electric air pump 12 in step 104. That is, when the electric heater 9 is energized, the particulates collected in the filter 8 are ignited, the secondary air is supplied by driving the electric air pump 12, the particulates are incinerated, and the filter 8 is regenerated.

Then, the CPU 21 determines the elapsed time after the start of reproduction in step 105, and terminates the reproduction if the set time has elapsed. Thus, in this embodiment,
Based on the pressure difference ΔP between the upstream side and the downstream side in the filter 8 by the pressure sensors 17 and 18, the reference operation is performed from the intake air flow rate to the diesel engine 1 and the reference volume flow rate Vstd by the hot wire flow rate sensor 5 (intake air flow rate sensor). At the time of obtaining the pressure difference ΔP1 in the state, based on the fuel injection amount of the diesel engine 1, the change amount ΔV of the volume flow rate caused by the fuel injection of the formula (6) is obtained, and the change amount ΔV is used (7) As shown in the equation, ΔP1 is corrected.
That is, the amount of change ΔV in the intake / exhaust amount due to the combustion of fuel in the diesel engine 1 is obtained according to the fuel injection amount, and is reflected in the calculation of the pressure difference ΔP1 in the standard operating state. Therefore,
It is possible to accurately calculate the pressure difference between the upstream side and the downstream side of the filter 8 in the standard operation state.

The present invention is not limited to the above-mentioned embodiment. For example, when the fuel injection amount control of the diesel engine is electronically controlled as a method for detecting the fuel injection amount, an engine control computer is used. The fuel injection amount may be detected by taking in the injection amount signal from Further, as a method of detecting the fuel injection amount, when the distribution type injection pump is used, the fuel injection amount may be directly obtained by the spill position sensor. Alternatively, when a row-type injection pump is used, the fuel injection amount may be directly obtained by the control rack position sensor.

[0038]

As described above in detail, according to the present invention,
The excellent effect of accurately calculating the pressure difference between the upstream side and the downstream side of the filter in the standard operation state is exhibited.

[Brief description of drawings]

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

FIG. 2 is a flowchart for explaining the operation.

FIG. 3 is an overall configuration diagram of a conventional diesel engine exhaust emission control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine 5 Hot wire type flow rate sensor as intake air flow rate sensor 8 Filter 9 Electric heater constituting regeneration means 12 Electric air pump constituting regeneration means 18 CPU as control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiichi Kato 1-1, Showa-cho, Kariya city, Aichi Prefecture Nihon Denso Co., Ltd. (72) Inventor Naoji Morita 1-1-1, Showa-cho, Kariya city, Aichi prefecture Nidec Within the corporation

Claims (4)

[Claims] 1. A filter provided in an exhaust system of a diesel engine for collecting particulates, a regeneration means for burning the particulates captured by the filter to regenerate the filter, and the filter. A pressure sensor for detecting the pressure difference between the upstream side and the downstream side, an intake air flow rate sensor provided in the intake system of the diesel engine for detecting the intake air flow rate to the diesel engine, and a filter by the pressure sensor. For the pressure difference between the upstream side and the downstream side, the pressure difference in the standard operation state is calculated from the intake air flow rate to the diesel engine by the intake air flow rate sensor and the flow rate in the standard operation, and the particulate trap according to the pressure difference is obtained. A diesel engine provided with a control circuit for regenerating the filter by the regenerating means when the amount of collected water reaches a predetermined value or more. In the exhaust purification apparatus, the exhaust gas purification system for a diesel engine, characterized in that the correction of the pressure difference between the reference operating state at said control circuit based on the fuel injection amount of the diesel engine. 2. The fuel injection amount of the diesel engine stores a governor pattern, which is an injection characteristic of a fuel injection pump, in advance, detects an accelerator opening and an engine speed, and opens the accelerator using the governor pattern. The exhaust emission control device for a diesel engine according to claim 1, which is obtained from the engine speed and the engine speed. 3. The exhaust emission control device for a diesel engine according to claim 1, wherein the fuel injection amount of the diesel engine is obtained by taking in an injection amount signal from an engine control computer. 4. The exhaust emission control device for a diesel engine according to claim 1, wherein the fuel injection amount of the diesel engine is directly obtained by a spill position sensor or a control rack position sensor.