JP3739684B2 - Method for estimating catalyst temperature of engine exhaust gas purification device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a diagnostic method and apparatus for an engine exhaust gas purification apparatus that uses an air-fuel ratio sensor, an oxygen concentration sensor (hereinafter, representatively referred to as an air-fuel ratio sensor) or a catalytic converter.
[0002]
[Prior art]
A device for purifying engine exhaust mainly comprises a catalytic converter and an air-fuel ratio feedback control device. The catalytic converter is installed in the exhaust pipe part to remove HC, NOx, and CO contained in the exhaust gas. In addition, since the air-fuel ratio feedback control device needs to keep the air-fuel ratio constant in order to fully perform the function of the catalytic converter, an oxygen sensor is installed upstream of the catalytic converter to control the fuel supply amount of the air-fuel ratio. Is to do. In the three-way catalyst system, if the performance of the oxygen sensor provided upstream of the catalytic converter deteriorates, the air-fuel ratio deviates from a narrow range centered on the stoichiometric air-fuel ratio, and the conversion efficiency of harmful components decreases. In addition, when the catalytic converter itself deteriorates in performance, the conversion efficiency of harmful components decreases even if the air-fuel ratio is accurately controlled. Such a technique for determining catalyst deterioration is described in, for example, Japanese Patent Laid-Open No. 5-171924. A pre-air-fuel ratio sensor for detecting an air-fuel ratio upstream of the exhaust gas of the catalyst, a post-air-fuel ratio sensor for detecting an air-fuel ratio downstream of the exhaust gas of the catalyst, a pre-air-fuel ratio sensor, and a post-air-fuel ratio sensor Feature waveform extraction means for attenuating a signal in a frequency band lower than the air-fuel ratio control frequency band of the air-fuel ratio control device from the output signal, and correlation function calculation for calculating a correlation function of the signal that has passed through the feature waveform extraction means There is provided a diagnostic device for an engine exhaust gas purifying device, characterized in that it has means and catalyst state determination means for determining the deterioration state of the catalyst based on the value of the correlation function.
[0003]
[Problems to be solved by the invention]
Catalytic converter performance is affected by catalyst temperature. The conversion efficiency decreases when the catalyst temperature is low. Therefore, if this catalyst temperature is not taken into account when diagnosing catalyst performance degradation, the catalyst temperature may change and become low depending on operating conditions such as engine speed and load, and may be misdiagnosed without being distinguished from performance degradation. was there. In order to solve this, it is necessary to install a temperature sensor and correct the diagnosis result as described in the above-mentioned JP-A-5-171924. However, since this catalyst temperature sensor requires a wide measurement range of 0 to 800 ° C., there has been a technical problem in that the cost of the diagnostic system is increased.
[0004]
In order to solve this problem, it is necessary to perform estimation using a signal that has already been measured in another application, for example, without using a catalyst temperature sensor. However, a means for accurately estimating the catalyst temperature for diagnosing this catalyst performance deterioration during operation has not yet been established.
[0005]
The present invention has been made in order to solve such a conventional problem. By executing catalyst temperature estimation during operation, an engine exhaust capable of accurately diagnosing whether or not performance degradation has occurred in a catalytic converter. An object of the present invention is to provide a diagnostic method and diagnostic apparatus for a gas purification apparatus.
[0006]
[Means for Solving the Problems]
The present invention has been made to achieve the above object, and detects a plurality of engine parameters;
Obtaining a catalyst temperature or an exhaust gas temperature near the catalyst installation based on the plurality of engine parameters;
The deterioration of the catalyst is judged using the catalyst temperature or the exhaust gas temperature in the vicinity of the catalyst installation as an index.
[0007]
As one aspect of the present invention, there is provided means for estimating the steady-state catalyst temperature using the rotational speed and load used for engine fuel injection control. This steady temperature estimation means is easily created by storing the test results during steady operation with an actual engine as two-dimensional map data of the rotational speed and load. Next, in order to correctly obtain the catalyst temperature even while the vehicle is running, a means for estimating the catalyst temperature in the transient state is provided, and the result obtained by the steady temperature estimating means is corrected. Furthermore, in this transient temperature estimation means, in order to facilitate adjustment and improve accuracy, the nonlinear characteristic is described by combining a plurality of linear characteristics. An engine exhaust gas purification apparatus comprising: catalyst state determination means for estimating the temperature of a catalyst based on values obtained by the steady temperature estimation means and the transient temperature estimation means, and correctly determining a deterioration state A diagnostic device is provided.
[0008]
In addition, when the catalyst temperature estimation means estimates the temperature of the catalyst by the steady temperature estimation means and the transient temperature estimation means, the catalyst temperature estimation means has the moisture accumulated in the catalyst and piping when starting the engine in order to further improve the estimation accuracy. There is provided a diagnostic device for an engine exhaust gas purifying apparatus, characterized in that a dead time means for temperature rise corresponding to latent heat is provided and a catalyst state determining means for determining a deterioration state of the catalyst.
[0009]
The transient temperature estimation means includes a means for switching a delay time constant between a temperature increase process heated by exhaust gas and a temperature decrease process cooled by heat radiation to the atmosphere, and a catalyst for determining a deterioration state of the catalyst A diagnostic device for an engine exhaust gas purification device is provided, characterized in that it has a state determination means.
[0010]
Further, the catalyst temperature estimation means includes catalyst temperature estimated value correction means corresponding to changes in engine coolant temperature, intake air temperature, and vehicle speed,
There is provided a diagnostic device for an engine exhaust gas purification device characterized by comprising:
[0011]
[Action]
First, a catalyst diagnosis is executed by means described in JP-A-2-3091.
[0012]
The front air-fuel ratio sensor and the rear air-fuel ratio sensor detect and output the air-fuel ratio between the upstream side and the downstream side of the catalyst corresponding to the crank angle detected by the crank angle detecting means. The characteristic waveform extraction means attenuates a signal in a frequency band lower than the air-fuel ratio control frequency band of the air-fuel ratio control apparatus from the output signal.
[0013]
The autocorrelation function calculating means calculates and outputs the autocorrelation function φ _xx of the signal that has passed through the characteristic waveform extracting means. On the other hand, the cross-correlation function means calculates and outputs a cross-correlation function φ _xy between the output signal of the front air-fuel ratio sensor and the output signal of the rear air-fuel ratio sensor that has passed through the characteristic waveform extraction means.
[0014]
For each predetermined period, the deterioration index calculation means includes a maximum value (φ _xy ) _max of the cross-correlation function φ _xy within the period, and a maximum value (φ _xx ) _{max of the} autocorrelation function φ _xx within the period, Is calculated as a sequential degradation index Φ _i . Further, the average value of the sequential deterioration index Φ _{i for} a predetermined number of times in the past is calculated and output as a deterioration index.
[0015]
The engine speed and the intake air amount are detected, and in accordance with these, first, the steady temperature estimating means outputs the catalyst temperature when the engine operating state (rotation speed, load) is stabilized. The catalyst temperature corresponding to the operating condition is output by the transient temperature estimating means via the temperature rise dead time means at the time of starting the engine. Next, an accurate catalyst temperature estimated value corresponding to changes in the engine coolant temperature, the intake air temperature, and the vehicle speed is output by the catalyst temperature estimated value correcting means.
[0016]
When the estimated catalyst temperature exceeds a predetermined value set in advance by the catalyst temperature comparison means, a deterioration index as a result of catalyst diagnosis is output.
[0017]
【Example】
An embodiment of the present invention will be described with reference to the drawings.
[0018]
First, the concept of the present invention will be described with reference to FIG.
[0019]
The diagnostic apparatus of the present embodiment includes a catalytic converter 2, O ₂ sensors 3 and 4 as air / fuel ratio sensors arranged before and after the catalytic converter 2, and fuel injection control by air / fuel ratio feedback based on the output of the O ₂ sensor 3. It is intended for systems that perform
[0020]
The diagnostic apparatus of this embodiment uses the air-fuel ratio perturbation by the air-fuel ratio feedback control as a test signal for the catalytic converter deterioration diagnosis. That is, if the catalytic converter 2 is not deteriorated, the air-fuel ratio perturbation is reduced in the downstream of the catalytic converter 2 due to the oxidation / reduction action of the catalyst. On the other hand, when the catalytic converter 2 deteriorates, the downstream air-fuel ratio perturbation approaches the upstream one. Thus, deterioration is diagnosed by paying attention to the similarity of the air-fuel ratio perturbation before and after the catalytic converter.
[0021]
Then, this similarity is evaluated using a correlation function.
[0022]
First, a method for diagnosing a catalyst in an embodiment of the present invention will be described.
[0023]
An output signal of the front O ₂ sensor 3 (hereinafter referred to as “front O ₂ sensor signal”) 114;
An output signal (hereinafter referred to as “rear O ₂ sensor signal”) 102 of the rear O ₂ sensor 4 is converted into digital data by the A / D converter 18 in synchronization.
[0024]
Next, a DC component that causes disturbance in diagnosis is removed from each signal by a high-frequency band pass filter (blocks 12A and 12B). Here, both filters have the same characteristics. Any signal removes a lower frequency component than the air-fuel ratio feedback control frequency which causes disturbance in diagnosis.
[0025]
Subsequently, an autocorrelation function φ _xx (0) at time t = 0 of the signal x (t) 105 obtained from the previous O ₂ sensor signal 114 is obtained (block 13). Here, φ _xx (0) is obtained because the autocorrelation function φ _xx takes the maximum value (φ _xx ) _max at t = 0.
[0026]
[Expression 1]
φ _xx (τ) = ∫x (t) x (t−τ) dt
Further, the cross-correlation function φ _xy (τ) is obtained from the signal x (t) obtained from the front O ₂ sensor signal 114 and the signal y (t) obtained from the rear O ₂ sensor signal 102 by a certain integration interval. Determine at T (block 14).
[0027]
[Expression 2]
φ _xy (τ) = ∫x (t) y (t−τ) dt
Here, the integration interval T is set in advance so that the fluctuation of the engine speed does not exceed a predetermined range in that interval.
[0028]
Then, locate the maximum of φ _xy (τ) in the integration interval T a (φ _{xy) max,} using the (φ _{xy) max,} sequential deterioration index _{Φ i (= (φ xy)} max / φ xx (0 ), (See Equation 5) (block 16A, see FIG. 5).
[0029]
[Equation 3]
Φ _i = (φ _xy ) _max / (φ _xx ) _max
The phase τ of the sequential deterioration index [Phi _i, in other words, the phase τ where _{(φ xy) / φ xx (} 0) takes the maximum value, to varying operating conditions and machine differences, [Phi _i actually data Obtain by searching.
[0030]
Then, Φ _i is stored in a memory (RAM), and Φ _{i + 1} is obtained by the same processing in the next integration interval T.
[0031]
The above operation is repeated n times to obtain the average value of Φ _i . The average value is used as the final deterioration index I of the catalytic converter 2. Note that the final deterioration index I is calculated in consideration of correction coefficients k ₁ and k _{2 according} to various operating conditions (blocks 16B, 16C, and 16D, see Equation 4 below).
[0032]
[Expression 4]
I = (Σk ₁ k ₂ Φ _i ) / n
I: Final degradation index k ₁ : Correction system number by engine load k ₂ : Correction system number by catalyst temperature Φ _i : Sequential degradation index n: Number of measurements Note that k ₁ and k ₂ are stored in advance in the memory (ROM) as map data Keep it.
[0033]
Subsequently, the deterioration index I is compared with a predetermined deterioration determination level _ID to determine a deterioration state. If the deterioration index I is greater than the deterioration determination level _ID , it is determined that the deterioration is in progress (block 16E).
[0034]
Here, the sequential deterioration index Φ _i is not used as it is, but the average value thereof, that is, the final deterioration index I is used. When the engine speed or load fluctuates during normal driving, the sequential deterioration index Φ _i is also affected. Because it fluctuates. In other words, by sequentially calculating and accumulating the degradation index Φ _i for each constant time, a certain number of revolutions, or a certain load band, and making the average value the final degradation index I, it is possible to determine the degradation in the entire operation region. However, when the operating state is limited to some extent, the determination may be performed using the sequential deterioration index Φ _i as it is.
[0035]
Now it is an embodiment lies in the means 20 for estimating the catalyst temperature T _CAT for obtaining the correction coefficient k _2. An embodiment of the catalyst temperature estimating means 20 is shown in FIG. The operation of the estimation means will be described below.
[0036]
First, the steady catalyst temperature T _{CAT, 0} is obtained by the steady model 201. Here, in the steady model 201, the catalyst temperature is measured in advance in a state where the engine speed and the load (for example, the intake air amount) are constant, and stored in the storage device as map data. Alternatively, the heat generation amount of the engine as a function of the engine speed and load may be calculated in advance and stored as map data.
[0037]
The predetermined time mask 202 measures the time after the engine is started, outputs zero until the predetermined time elapses, and outputs 1 thereafter. This dead time t ₀ is determined according to the operating state before and after the start. The engine water temperature T _w and the intake air temperature T _A are stored as map data. Basically define larger the dead time t ₀ according to the difference in the engine coolant temperature T _w and the intake air temperature T _A is reduced. As another method, the fuel amount integrated value SF _i after the start is sequentially calculated, and when the predetermined value is reached, the dead time t ₀ is terminated, and the predetermined value is used as the engine water temperature T _w and the intake air temperature T _A. There is also a way to make it larger as the difference in the number decreases. Here, the integrated fuel amount value SF _i may be an integrated value of the load.
[0038]
In any case, the output T _{CAT, 1} of the multiplier 203 is expressed by Equation 5.
[0039]
[Equation 5]
T _{CAT, 1} = T _w (t ≦ t ₀ )
T _{CAT, 1} = T _{CAT, 0} (t> t ₀ )
Here, the engine water temperature _Tw is detected by a sensor (not shown).
[0040]
The delay models 204 (1) and 204 (2) are obtained by calculation according to Equations 6 and 7.
[0041]
[Formula 6]
T _{CAT, 2, 1} = (1-1 / τ) T _{CAT, 2, 1} + ξ / τ T _{CAT, 1}
[0042]
[Expression 7]
T _{CAT, 2,2} = (1-1 / ζτ) T _{CAT, 2,2} + (1-ξ) / ζτT _{CAT, 1}
Here, the initial values of T _{CAT, 2,1} and T _{CAT, 2,2} are T _{CAT, 1} .
[0043]
FIG. 3 shows how to obtain τ, ξ, and ζ. FIG. 3 shows measured values of the catalyst temperature when the throttle is suddenly changed. The measurement conditions are the same as when measuring a stationary model. A plurality of time constants of the catalyst temperature change are measured, for example, two places of a rising time constant τ and a time constant multiplied by ζ. As a guide, ζ = 10. From these, ξ is obtained as shown in FIG.
[0044]
In FIG. 3, the temperature rise is shown, but the delay time constant of the temperature drop when the throttle is closed in a stepwise manner is obtained in the same manner, and the temperature drop delay time τ _d 206 is defined as the temperature rise delay time τ _u 207. These are stored separately, and these are switched by the positive / negative determination 205.
[0045]
[Equation 8]
τ = τ _u (T _{CAT, 2-} T _{CAT, 1} <0)
[0046]
[Equation 9]
τ = τ _d (T _{CAT, 2-} T _{CAT, 1} ≧ 0)
The adder 209 adds the outputs of the delay models 204 (1) and 204 (2) to obtain the estimated catalyst temperature T _{CAT, 3} (Equation 10).
[0047]
[Expression 10]
T _{CAT, 3} = T _{CAT, 2, 1} + T _{CAT, 2, 2}
Next, the estimated catalyst temperature T _{CAT, 3} is corrected according to Equations 11 to 12 in consideration of the effects of the engine water temperature T _w , the intake air temperature T _A , and the vehicle speed V _sp detected by a sensor (not shown). _Find T _CAT .
[0048]
## EQU11 ##
T _{CAT, 4} = T _{CAT, 3-} (T _w- T _{w, 0} )
Here, T _{w, 0} is the engine water temperature T _w when the steady model is measured.
[0049]
[Expression 12]
_{T CAT, 5 = T CAT,} 4 -η (T A -T A, 0)
Here, T _{A, 0} is the intake air temperature T _A when the steady model is measured.
[0050]
Η is a sensitivity coefficient set in advance according to the vehicle speed (Equation 13).
[0051]
[Formula 13]
η = F (V _sp )
Here F (V _sp) in the measurement conditions of the intake air temperature T _A at the time of measuring the steady-state model, measures the catalyst temperature when varying speed or air flow rate, and stores the empirical formula or map data.
[0052]
【The invention's effect】
FIG. 4 shows the effect of the catalyst temperature estimation according to the present invention in comparison with actual measurement values. The operating condition is the US test mode. The estimated temperature is in good agreement with the measured values throughout.
[0053]
As described above, according to the present invention, it is possible to accurately estimate the catalyst temperature during normal driving of an automobile and diagnose the deterioration of the catalytic converter, which is an engine exhaust gas purification control device, without error.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a detailed block diagram of a characteristic part of the present embodiment.
FIG. 3 is an explanatory diagram for determining parameters in the embodiment.
FIG. 4 is a characteristic diagram for explaining the operation of catalyst temperature estimation.
[Explanation of symbols]
2 ... catalytic converter 3 ... front O ₂ sensor, 4 ... rear O ₂ sensor, 13 ... autocorrelation function calculating unit, 14 ... cross-correlation function calculation means, 16 ... catalytic converter deterioration judging unit, 17 ... judgment result output means, 20 ... temperature estimation means, Φ _i ... sequential deterioration index, I ... final deterioration index, I _D ... deterioration determination level, x ... output of an air-fuel ratio sensor (pre-O ₂ sensor) provided upstream of the catalytic converter, y ... catalyst Output of an air-fuel ratio sensor (rear O ₂ sensor) provided downstream of the converter, φ _xx ... autocorrelation function of signal x, φ _xy ... cross-correlation function of signal x and signal y.

Claims (5)

In what detects the air-fuel ratio in the exhaust gas of the engine, adjusts the fuel injection amount so as to keep the air-fuel ratio in the exhaust gas at a predetermined value, and purifies the exhaust gas with a catalyst,
Detect engine parameters,
In steady state, the catalyst temperature under steady state is estimated by a steady state model based on the engine parameters,
A catalyst for an engine exhaust gas purifying apparatus characterized in that, in a transient state, the catalyst temperature under the transient state is estimated based on two different catalyst temperatures obtained by two transient state models having different time constants based on the engine parameters. Temperature estimation method. In claim 1,
A catalyst temperature estimation method for an engine exhaust gas purifying apparatus, characterized in that in a transient state, two different catalyst temperatures obtained by the transient state model are added to estimate the catalyst temperature under the transient state. In claim 1,
An initial value of the transient state model is a catalyst temperature obtained by the steady state model. In claim 1,
An engine parameter used in the steady state model is an engine speed and a load. In claim 1,
The transient state model has a linear output, and is a catalyst temperature estimation method for an engine exhaust gas purification device.

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