JPH074318A - Egr device of diesel engine - Google Patents

Abstract

PURPOSE:To provide an EGR device which can correct difference of output characteristics of pressure sensors. CONSTITUTION:This EGR device of a diesel engine is provided with a means 16 by which the opening of an EGR valve 4 is controlled so that a target EGR rate according to an operating condition can be obtained based on difference of signal output Va-Vb of first and second pressure sensors 12, 13. It is provided with a means 17 by which the signal output error DELTAV of the first and second pressure sensors 12, 13 is computed based on the detected signals Va, Vb of the first and second pressure sensors 12, 13 read under a plurality of intake pressure conditions when EGR is cut by full close of the EGR valve 4, and a means 18 by which difference of signal output Va-Vb of the first and the second pressure sensors 12, 13 is corrected based on the signal output error DELTAV.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved EGR device for diesel engines.

[0002]

2. Description of the Related Art In automobile engines and the like, in order to suppress the generation of NOx which is a harmful component in exhaust gas,
Recirculating inert exhaust gas to the intake pipe, so-called E
A GR device is provided.

An example of this EGR device is shown in FIG. 6 (see Japanese Patent Application Laid-Open No. 57-165656).

In the figure, 20 is a diesel engine,
Reference numeral 21 is an intake passage, 22 is an exhaust passage, and 23 is an intake passage 21.
An exhaust gas recirculation passage (hereinafter, referred to as an EGR passage) 24 returns an EGR gas, which is a part of the exhaust gas from the exhaust passage 22, to the intake passage 21 on the downstream side of the intake throttle valve 23. , 25 are EGR flow rate (exhaust gas recirculation amount)
The EGR valve (control valve) which controls the is shown.

The intake throttle valve 23 and the EGR valve 25 are interlocked with the diaphragm actuators and operate in accordance with the negative pressure supplied from the vacuum modulators 26 and 27. The vacuum modulators 26 and 27 are supplied from the control unit 28. The control negative pressure is adjusted based on the signal. The opening degrees of the intake throttle valve 23 and the EGR valve 25 are controlled according to a command from the control unit 28,
By returning a certain amount of EGR gas to the intake passage 21,
The maximum temperature during combustion is lowered to reduce the amount of NOx in the exhaust gas.

The EGR passage 2 is used to detect the EGR flow rate.
4, a bypass passage 30 is provided in parallel with the bypass passage 30, and a venturi portion (throttle) for measuring the flow rate is provided in the bypass passage 30.
It is supposed to be taken out in 2.

The control unit 28 includes the intake throttle valve 2
An intake air amount signal from an air flow meter 40 that is provided on the upstream side of 3 to measure the intake air amount and an EGR flow rate signal from a differential pressure sensor 32 that measures the EGR flow rate are input.
In addition, a distance sensor 41 that detects the traveling distance of the vehicle and transmits a signal to the control unit 28 at every constant distance traveling.
Is provided. The control unit 28 controls the EGR rate (= EGR flow rate / intake air amount × 100) according to the operating state.
The control target value of (%) is selected by a table lookup, and the opening of the EGR valve 25 and the intake throttle valve 23 is subjected to open loop control using this as a command value. Air volume and EGR
The EGR rate is obtained from the detected value of the flow rate, the error of the detected EGR rate with respect to the control target value is detected, and the control command value is corrected so as to eliminate this error.

By detecting the intake air amount through the air flow meter 40, the EGR rate does not change due to changes in the intake air amount due to running of the vehicle at high altitudes or clogging of the air cleaner.

[0009]

However, such a conventional EGR device is provided with the differential pressure sensor 32 for detecting the EGR flow rate and the air flow meter 40 for measuring the intake air amount. Is provided, there is a problem that the structure is complicated and the cost of the product is increased.

As a countermeasure against this, the EGR passage 24 and the intake passage 21 are provided with first and second pressure sensors for detecting the absolute pressure respectively, and the EGR flow rate is obtained from the signal output difference between the two, and the pressure in the intake passage 21 is calculated. It is conceivable that the intake air amount is obtained.

However, if there is an error in the initial setting of the output characteristics of the first and second pressure sensors that detect absolute pressure, or if there is deterioration over time, the output values of the first and second pressure sensors will be mutually different. Differently, the actual EGR rate may deviate from the target value.

It is an object of the present invention to provide an EGR device capable of correcting the output characteristic difference of the pressure sensor, focusing on the above problems.

[0013]

According to the present invention, as shown in FIG. 1, an EGR passage 3 connecting an exhaust passage 2 and an intake passage 1 of a diesel engine, and an EGR valve 4 provided in the middle of the EGR passage 3 are provided. A first pressure sensor 12 that outputs a signal Va corresponding to the pressure in the EGR passage 3, a second pressure sensor 13 that outputs a signal Vb corresponding to the pressure in the intake passage 1,
In an EGR device for a diesel engine, which is provided with means 16 for controlling the opening degree of the EGR valve 4 so as to obtain a target EGR rate according to the operating state based on the signal output difference Va-Vb of the second pressure sensors 12, 13. , The detection signal V of the first and second pressure sensors 12 and 13 read under a plurality of intake pressure conditions when the EGR valve 4 is fully closed and EGR is cut.
Means 17 for calculating a signal output error ΔV (= mVb + n) of the first and second pressure sensors 12 and 13 based on a and Vb.
And a means 18 for correcting the signal output difference Va-Vb of the first and second pressure sensors 12, 13 based on the signal output error ΔV.

[0014]

[Operation] EGR at EGR cut when the EGR valve is fully closed
Since the pressure in the passage and the pressure in the intake passage are equal regardless of the pressure condition in the intake passage, the first and second pressure sensors 12, 1
The output characteristics of the signal outputs Va and Vb of 3 are essentially the same.

Therefore, the first and second pressure sensors 12, 1 read under a plurality of intake pressure conditions during EGR cut.
The signal output error ΔV (= mVb + n) of the first and second pressure sensors 12 and 13 is calculated based on the detection signals Va and Vb of 3.

Based on this signal output error ΔV, the signal output difference Va-Vb between the first and second pressure sensors 12 and 13 is calculated.
By correcting the first and second pressure sensors 12, 1
A target EGR rate according to the engine operating state can be obtained regardless of the variation in the output characteristic of No. 3.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 shows an outline of the EGR device. EG connecting the exhaust passage 2 and the intake passage 1 of the diesel engine
An R passage 3 is provided, and an orifice 10 is provided in the middle of the EGR passage 3. Since the flow of the EGR gas is throttled by the orifice 10, the EGR flow rate that returns to the intake passage 1 through the EGR passage 3 increases according to the pressure difference between the EGR passage 3 and the intake passage 1.

In the middle of the EGR passage 3, a diaphragm type EG is provided on the exhaust passage 2 side, that is, the upstream side of the orifice 10.
The R valve 4 is interposed. Diaphragm chamber 13 of EGR valve 4
A signal negative pressure passage 5 is connected to. This signal negative pressure passage 5
Is communicated with the vacuum pump 7, and a duty control valve 8 is interposed in the middle thereof. The duty control valve 8 appropriately dilutes the negative pressure introduced into the diaphragm chamber 46 of the EGR valve 4 to control the opening degree of the EGR valve 4.

As the opening degree of the EGR valve 4 increases, the EG
The pressure in the EGR passage 3 on the downstream side of the R valve 4 is increased, and the EGR flow rate recirculated to the intake passage 1 via the orifice 10 is increased.

A butterfly type intake throttle valve 9 is provided in the intake passage 1 upstream of the confluence of the EGR passage 3. The intake throttle valve 9 is opened and closed via an actuator 10. In the intake passage 1 downstream of the intake throttle valve 9, an intake negative pressure is generated as the opening degree of the intake throttle valve 9 becomes smaller, and is returned to the intake passage 1 through the orifice 10.
GR flow rate increases.

The control unit 11 uses, for example, the engine speed, as a signal representing the engine operating state.
Input signals indicating accelerator pedal opening (position of fuel injection pump control sleeve or control rack), fuel injection timing, engine cooling water temperature, engine oil temperature, etc., and preset based on these signals to correspond to operating conditions. So that the desired target EGR rate is obtained.
The opening degrees of the valve 4 and the intake throttle valve 9 are controlled. In addition, when the engine water temperature is cold after the engine starts until it reaches a certain value,
Alternatively, the EGR valve 4 is fully closed during a predetermined high load operation E
GR cut control is performed.

A first pressure sensor 12 for detecting the pressure Pa in the EGR passage 3 between the orifice 10 and the EGR valve 4 and an intake throttle valve for detecting the EGR flow rate returned to the intake passage 1 via the orifice 10. A second pressure sensor 13 that detects the pressure Pb in the intake passage 1 downstream of 9 is provided.

The control unit 11 inputs the detection signals Va and Vb of the first and second pressure sensors 12 and 13,
The EGR flow rate is calculated from the signal output difference Va-Vb of both,
The intake air amount is calculated from the detection signal Vb of the second pressure sensor 13 and the EGR rate (= EGR flow rate / intake air amount × 100%) is calculated, and the calculated EGR rate matches the target EGR rate. Feedback control is performed so as to perform. As a result, for example, the deviation of the EGR rate due to the clogging of the air filter provided on the upstream side of the intake passage 1 or the adhesion of carbon to the EGR valve 4 is corrected.

By the way, the EGR in which the EGR valve 4 is fully closed
Since the flow of EGR gas is stopped via the orifice 10 at the time of cutting, the pressure in the EGR passage 3 and the pressure in the intake passage 1 are equal regardless of the pressure condition in the intake passage 1, and
The output characteristics of the second pressure sensors 12 and 13 are essentially the same.

FIG. 3 shows a case where the output characteristics of the first and second pressure sensors 12 and 13 vary depending on the pressure condition of the intake passage 1 when the EGR valve 4 is fully closed and EGR is cut. Each signal output error ΔV of the first and second pressure sensors 12 and 13 has a proportional relationship with one signal output Vb as shown in FIG. 4, and is represented as ΔV = mVb + n.

As described above, the first and second pressure sensors 12,
In order to deal with the case where the output characteristic of the control valve 13 has a variation, the control unit is utilized by utilizing the fact that the pressure in the EGR passage 3 is equal to the intake pressure condition in the intake passage 1 at the time of EGR cut when the EGR valve 4 is fully closed. 28 is the first read under a plurality of intake pressure conditions during EGR cut,
The signal output error Δ of the first and second pressure sensors 12 and 13 based on the detection signals Va and Vb of the second pressure sensors 12 and 13.
V (= mVb + n) is obtained, and the signal output difference V between the first and second pressure sensors 12 and 13 is calculated based on this signal output error ΔV.
Correct a-Vb.

The flowchart of FIG. 5 shows a control program executed in the control unit 11 for correcting the signal output error ΔV of the first and second pressure sensors 12 and 13, which is executed at regular time intervals. It

First, when it is determined that the EGR cut condition is satisfied, the intake throttle valve 9 is fully opened, and under this pressure condition 1, the signal outputs Va of the first and second pressure sensors 12 and 13 are obtained.
₁ and Vb ₁ are read and the signal output error ΔV ₁ between them is calculated (steps 1, 2, 3, 4).

Subsequently, the intake throttle valve 8 is set to the maximum throttle position,
Under this pressure condition 2, the first and second pressure sensors 12,
The signal outputs Va ₂ and Vb ₂ of 13 are read, and the signal output error ΔV ₂ between them is calculated (steps 5, 6, 7, and 8).

In this way, the signal outputs Va ₁ , Va ₂ , Vb ₁ and Vb ₂ obtained under the two pressure conditions 1 and 2 are obtained.
And m and n in the equation of ΔV = mVb + n based on
The value of is calculated (step 8).

On the other hand, under the operating conditions in which exhaust gas recirculation is performed,
The signal output Va of the first pressure sensor 12 is read and the pressure Pa in the EGR passage 3 is calculated by the formula Pa = pVa + q (steps 1, 9, 10).

Subsequently, the signal output V of the second pressure sensor 13
b is read, and the signal output error ΔV with the first pressure sensor 12
Is calculated by the formula of ΔV = mVb + n, the correction value Vb of the signal output Vb is calculated by the formula of Vb = Vb + ΔV, and the pressure Pb of the intake passage 1 is calculated by the formula of Pb = pVb + q (steps 11, 12, 13, 14).

With the above arrangement, the signal output error ΔV
By correcting the signal output difference Va-Vb of the first and second pressure sensors 12 and 13 on the basis of the above, the engine operating state is maintained regardless of the variation in the output characteristics of the first and second pressure sensors 12 and 13. A corresponding target EGR rate is obtained.

The first and second pressure sensors 12 and 13 read under two intake pressure conditions during EGR cut.
Although the signal output error ΔV (= mVb + n) of the first and second pressure sensors 12 and 13 was calculated based on the detection signals Va and Vb of, the pressure condition also changes when the engine speed changes, and therefore, for example, when the engine starts. The accuracy of correction can be improved by reading the detection signals Va and Vb under as many conditions as possible during EGR cut until the engine water temperature reaches a constant value later.

[0036]

As described above, according to the present invention, the EGR passage connecting the exhaust passage and the intake passage of the diesel engine,
An EGR valve interposed in the middle of the EGR passage, and a first pressure sensor that outputs a signal Va according to the pressure in the EGR passage,
A signal output difference Va-Vb between the second pressure sensor that outputs a signal Vb corresponding to the pressure in the intake passage and the first and second pressure sensors.
In an EGR device for a diesel engine equipped with a means for controlling the opening degree of the EGR valve so as to obtain a target EGR rate according to the operating state based on the above, a plurality of intake pressure conditions at the time of EGR cut with the EGR valve fully closed. The signal output error ΔV (= mVb) of the first and second pressure sensors based on the detection signals Va and Vb of the first and second pressure sensors that have been read.
+ N) and a signal output difference Va-Vb of the first and second pressure sensors based on the signal output error ΔV.
EGR control can be performed accurately without being affected by the difference in the output characteristics of the pressure sensors.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the present invention.

FIG. 2 is a schematic configuration diagram of an EGR device showing an embodiment of the present invention.

FIG. 3 is a diagram showing a specific example of signal output of the pressure sensor.

FIG. 4 is a diagram similarly showing a relationship between a signal output error and a signal output of the pressure sensor.

FIG. 5 is a flow chart showing control contents for similarly correcting a signal output error of the pressure sensor.

FIG. 6 is a schematic configuration diagram of an EGR device similarly showing a conventional example.

[Explanation of symbols]

 1 Intake Passage 2 Exhaust Passage 3 EGR Passage 4 EGR Valve 12 First Pressure Sensor 13 Second Pressure Sensor 16 EGR Valve Opening Control Means 17 Signal Output Error Calculation Means 18 Correcting Means

Claims (1)

[Claims] 1. An EGR passage connecting an exhaust passage and an intake passage of a diesel engine, an EGR valve provided in the middle of the EGR passage, and a first pressure sensor for outputting a signal Va corresponding to the pressure in the EGR passage, Signal V according to the pressure in the intake passage
Means for controlling the opening degree of the EGR valve so that a target EGR rate according to the operating state can be obtained based on the signal output difference Va-Vb between the second pressure sensor that outputs b and the first and second pressure sensors. In the EGR device of the diesel engine including the first and second pressure sensors, which are read under a plurality of intake pressure conditions at the time of EGR cut with the EGR valve fully closed, And a means for calculating a signal output error ΔV (= mVb + n) of the two pressure sensors, and a means for correcting the signal output difference Va-Vb of the first and second pressure sensors based on the signal output error ΔV. Characteristic diesel engine EGR device.