JPH08246962A - Egr diagnosing device for internal combustion engine - Google Patents

Abstract

PURPOSE: To perform diagnosis of a flow rate of an EGR device onboard by a method wherein an EGR flow rate is determined from a relation between an internal combustion engine control parameter when the opening of an EGR valve is changed from a given value to other given value and an intake pressure, in an internal combustion engine having an exhaust gas reflux device. CONSTITUTION: During operation of a vehicle, an EGR diagnosis region is decided by a control device 107 and when EGR is within a diagnosis region, a given time elapses, and the opening of an EGR valve 108 is set to a given value 1. A given time then elapses for stabilization, the valve opening of the EGR valve 108 is set to a given value 2. When, during operation in a case setting to the given values 1 and 2 is executed, based on a difference between an intake pressure detected by a pressure detecting means 109 when EGR is actually applied and an intake pressure estimated from the number of revolutions and an air amount when EGR is not applied, EGR partial pressures are respectively determined and from a difference between the two EGR partial pressures, a flow rate of the EGR device is diagnosed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate diagnostic device for an EGR system installed to reduce NOx in an internal combustion engine.

[0002]

2. Description of the Related Art A three-way catalyst is installed in the exhaust system of an internal combustion engine,
In the technology for purifying hydrocarbons HC, carbon monoxide CO, and nitrogen oxides NOx in exhaust gas, in order to control the actual air-fuel ratio centering on the theoretical air-fuel ratio at which the purification capacity of the three-way catalyst becomes efficient, It is a known technique to install the fuel ratio detecting means in the exhaust system upstream of the three-way catalyst and feed back the oxygen concentration in the exhaust gas to the internal combustion engine controller. Also,
If the exhaust gas containing CO ₂ gas, which has a larger heat capacity than N ₂ in the air, is mixed in the air-fuel mixture, the combustion temperature will be lower than in the case where the exhaust gas is not mixed, even if combustion with the same calorific value is performed. It can suppress the generation of NOx. This is exhaust gas recirculation (hereinafter referred to as EGR), and as a known technique for EGR diagnosis, Japanese Patent Publication No. 6-31571 discloses a method of opening and closing an EGR valve and performing EGR diagnosis from operating states before and after the closing operation.

[0003]

[Problems to be Solved by the Invention] Air Resour in California, USA
Law Proposed by ces Board On-Board Diagnosis Ph
With aseII, vehicles with EGR devices will be obliged to monitor the amount of EGR recirculation. The present invention has an object of a means for detecting the EGR flow rate corresponding thereto.

[0004]

The pressure detecting means for detecting the pressure of the intake system and the EGR valve varying means, the rotational speed detecting means, the air flow rate detecting means and the internal combustion engine control parameter calculating means are provided.

[0005]

The intake pressure when the EGR is applied is detected by the pressure detection means, and the intake pressure (internal combustion engine control parameter) when the EGR is not applied at that time is calculated by the internal combustion engine control parameter calculation means, and the difference between them is calculated. The EGR partial pressure is detected from. Then, the EGR partial pressure when the EGR valve is set to the predetermined value 1 by the EGR valve varying means and the predetermined value 2
The EGR flow rate diagnosis is performed based on the difference in EGR partial pressure when set to.

[0006]

FIG. 1 shows an internal combustion engine system having an EGR device which is the subject of the present invention. It is composed of an internal combustion engine, an intake system, and an exhaust system, and an ignition device 101, a fuel injection device 102, and a rotation speed detection means 103 are attached to the internal combustion engine. Also, the intake system has an air cleaner and a flow rate detecting means 1.
04, and an air-fuel ratio sensor 105 and a three-way catalyst 106 are attached to the exhaust system. Internal combustion engine control device 1
07 takes in the output signal Qa of the flow rate detection means 104 and the output signal Ne of the rotation speed detection means 103, and the fuel injection amount Ti
Is calculated and the injection amount of the fuel injection device is controlled. Further, the internal combustion engine control device 107 detects the air-fuel ratio in the internal combustion engine from the air-fuel ratio sensor 105, and performs an air-fuel ratio feedback control for correcting the fuel injection amount Ti so that the air-fuel ratio in the internal combustion engine becomes the stoichiometric air-fuel ratio. To do. In addition, the mixture contains N ₂ in the air.
When the exhaust gas containing CO ₂ gas having a larger heat capacity is mixed in appropriately, the combustion temperature is lower than that in the case where the exhaust gas is not mixed, and the generation of NOx can be suppressed even if the combustion of the same calorific value is performed. This is called exhaust gas recirculation EGR, and the present invention relates to detection of the recirculation amount of this EGR.

The EGR is a device for reducing NOx by circulating a part of the exhaust gas to the intake system, and the ratio of the EGR flow rate to the intake air amount is generally called the EGR rate and defined by the equation 1.

[0008]

[Equation 1]

Here, by rearranging Equation 1, Equation 2 is obtained,
From this, the EGR recirculation amount is obtained.

[0010]

[Equation 2] Q _EGR ≈k1 · P _EGR · N (Equation 2) Next, a method of detecting P _EGR will be described.

In order to obtain P _EGR , the intake pressure when the EGR is actually applied is detected by the pressure detecting means 109. Then, the intake pressure when EGR is not applied at that time is estimated from the rotational speed and the air amount at that time. Then, P _EGR is detected from the difference. Now, a method for estimating the intake pressure Pa ₀ that will not be applied with EGR will be described with the EGR applied.

In the intake system, the following relational expression is established among the intake air amount Qa, the intake pressure Pa ₀ and the cylinder inflow air amount Qc.

[0013]

(Equation 3)

From the equation of state of gas, Qc can be assumed to be a function (map) of the rotational speed N and the intake pressure Pa ₀ . That is,

[0015]

[Formula 4] Pa ₀ = ∫k 2 · (Qa−f (N, Pa ₀ )) dt (Formula 4), and Pa ₀ can be obtained from this. FIG. 2 shows a block diagram of Equation 4. It can be regarded as a low-pass filter in which the cutoff frequency changes with a kind of rotation speed.
In this embodiment, this Pa ₀ becomes the internal combustion engine control parameter.

Further, this flow chart is shown in FIG.
The rotation speed is detected in step 301, and the intake air amount is detected in step 302. Next, in steps 303 and 304, P
Then, a ₀ is obtained, and in step 305, Qc is searched for from Pa ₀ , N. Then, in step 306, the current Pa _0
Will be Pa _0old to be used next time.

As described above, in the state where the EGR is applied, the intake pressure Pa at that time is detected by the pressure detecting means 109, and the intake pressure Pa ₀ which may not be applied the EGR.
By calculating from FIG. 3, P _EGR is calculated from the difference (Equation 5).

[0018]

[Equation 5] P _EGR = Pa−Pa ₀ (Equation 5) Then, Equation 5 is substituted into Equation 2 to obtain Q _EGR .

[0019]

[Equation 6] Q _EGR ≈k1 · (Pa−Pa ₀ ) · N (Equation 6) The above flowchart is shown in FIG. The intake pressure Pa is detected in step 401, and the estimated pressure Pa ₀ is calculated in step 402. Next, in step 403, the rotation speed is detected, and in step 404, Q _EGR is obtained.

According to the above method, Q _EGR can be detected. However, considering the influence of pulsation of Qa, the influence of temperature, the influence of atmospheric pressure, etc., the detection accuracy of Q _EGR is not necessarily high. Therefore, a method of canceling the influence of the pulsation of Qa, the influence of temperature, the influence of atmospheric pressure, etc. will be described below.

This is a method of using Q _EGR obtained according to the equation 6 as the correction amount when the EGR valve is fully closed. Originally, when the EGR valve is fully closed, Q _EGR must be zero. However, due to the influence of pulsation of Qa, the influence of temperature, the influence of atmospheric pressure, etc., Q _EGR when the EGR valve is fully closed is not necessarily zero. Therefore, this amount is used as a correction amount. In practice, the EGR valve opening is set to a predetermined value 1, Q _EGR is calculated from _Equation 6, and then it is set to a predetermined value 2 to calculate the correction amount of the EGR valve opening. Then, the EGR recirculation amount QQ _EGR is calculated from Equation 7.

[0022]

[ _Equation 7] QQ _EGR = Q _EGR1 −Q _EGR2 ( _Equation 7) However, Q _EGR1 : Q _EGR when the predetermined value is 1 Q _EGR Q _EGR2 : Q _EGR when the predetermined value is 2 The predetermined value 2 is set for correction Because of the EGR valve opening that was set, it is set near zero.

The above flow chart is shown in FIG. In step 501, the EGR diagnosis area is determined. If it is within the area, the processing from step 502 is performed, and if it is outside the area, diagnosis is not performed. If it is in the diagnostic area, step 50
At step 503, the EGR valve opening is set to the predetermined value 1 at step 503. Next, in order to stabilize, a predetermined time is passed in step 504, and Q _{EGR is performed in} step 505.
From Eq. 6 and set it as Q _EGR1 . Next, at step 506, the EGR valve opening is set to a predetermined value 2. A predetermined time is passed for stabilization (step 507), and step 50
In step 8, _find Q _EGR from _equation 6 and set it as Q _EGR2 . Next, in step 509, the EGR recirculation amount is obtained, and in step 510,
If it is larger than the judgment value, normal processing (step 51
2) is performed, and if smaller, abnormal processing (step 511) is performed.

FIG. 6 shows Q _EGR and QQ _EGR when the EGR valve opening is changed from the predetermined value 1 to the predetermined value 2. Further, FIG. 7 shows the change in QQ _EGR when the predetermined value 1 of the EGR valve opening is changed. Although the rotational speed and the load were changed, QQ _EGR proportional to the EGR valve opening was obtained in any region. From the above, it becomes possible to diagnose the recirculation amount of EGR.

As a function of the load L of the estimated pressure Pa ₀ ,
Similar diagnoses can be made. Also, here, EG
Although the diagnosis is made from the EGR partial pressure difference when the R valve has the predetermined value 1 and the predetermined value 2, the EGR partial pressure ratio when the EGR valve has the predetermined value 1 and the predetermined value 2 may be used.

[0026]

According to the present invention, it is possible to diagnose the EGR recirculation amount.

[Brief description of drawings]

FIG. 1 is a block diagram of an internal combustion engine system having an EGR device that is the subject of the present invention.

FIG. 2 is a block diagram for estimating intake pressure without EGR.

FIG. 3 is a flowchart for estimating an intake pressure that does not apply EGR.

FIG. 4 is a flowchart for obtaining Q _EGR from the actual intake pressure and the estimated intake pressure.

FIG. 5 is an EGR recirculation amount diagnosis flowchart.

FIG. 6 is a waveform diagram of Q _EGR and QQ _EGR when the EGR valve opening is changed from a predetermined value 1 to a predetermined value 2.

FIG. 7 is a characteristic diagram of QQ _EGR with respect to EGR valve opening.

[Explanation of symbols]

101 ... Ignition device, 102 ... Fuel injection device, 103 ... Rotation speed detection device, 104 ... Flow rate detection device, 105 ... Air-fuel ratio detection device, 106 ... Catalyst, 107 ... Internal combustion engine control device,
108, 601 ... EGR valve, 109 ... Pressure detection device, 602 ... EGR flow rate, 603 ... Corrected EGR flow rate.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Akito Numata 2477 Kashima Yatsu, Hitachi Takanaka, Ibaraki Pref. 3 within Hitachi Automotive Engineering Ring Co., Ltd. (72) Takanobu Ichihara 2520, Takanaka, Hitachinaka, Ibaraki Address Company Hitachi Ltd., Automotive Equipment Division (72) Inventor Toshio Ishii 2520 Takaba, Hitachinaka City, Ibaraki Prefecture Incorporated Hitachi, Ltd. Automotive Equipment Division, Hitachi Ltd. (72) Seiji Asano 2520 Takata, Hitachinaka City, Ibaraki Prefecture Bachi Co., Ltd.Hitachi Ltd., Automotive Equipment Division

Claims (8)

[Claims] 1. In an internal combustion engine having an exhaust gas recirculation system EGR, an EGR flow rate is obtained from a relationship between an internal combustion engine control parameter and intake pressure when the valve opening degree of the EGR is changed from a predetermined value 1 to a predetermined value 2. An EGR flow rate diagnostic device for an internal combustion engine, comprising: 2. The EGR diagnostic device for an internal combustion engine according to claim 1, wherein the EGR flow rate is obtained from the difference or ratio between the internal combustion engine control parameter and the intake pressure. 3. The EGR diagnostic device for an internal combustion engine according to claim 1, wherein the internal combustion engine control parameter is a function of an intake air amount and a rotational speed of the internal combustion engine. 4. The EGR diagnostic device for an internal combustion engine according to claim 1, wherein the internal combustion engine control parameter is a function of a load of the internal combustion engine. 5. The control parameter according to claim 1, 2, 3 or 4, wherein the control parameter when the EGR valve opening is set to a predetermined value 1 and the control parameter when a difference 1 between intake pressure and a predetermined value 2 is set. Using the difference 2 of the intake pressure, the difference 1-the difference 2 to E
An EGR diagnostic device for an internal combustion engine that obtains a GR partial pressure difference. 6. The control parameter according to claim 1, 2, 3 or 4, wherein the control parameter when the EGR valve opening is set to a predetermined value 1 and the control parameter when the ratio 1 of the intake pressure to the predetermined value 2 is set. Using the ratio 2 of the intake pressure, the ratio 1 / ratio 2 to E
An EGR diagnostic device for an internal combustion engine that obtains a GR partial pressure ratio. 7. The method according to claim 5, wherein the difference 1-difference 2 and the ratio 1 / ratio 2 are corrected by the number of revolutions.
An EGR diagnostic device for an internal combustion engine that obtains a flow rate for GR and reduces variations between operating regions. 8. The EG of an internal combustion engine according to claim 7, wherein EGR diagnosis is not performed when the flow rate of another bypass system changes.
R diagnostic device.