JP2004316569A - False deterioration signal generating device for air-fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To conduct control variable adjusting work under consideration of a deteriorated state of an air-fuel sensor at low cost and with high precision. <P>SOLUTION: As a new air-fuel ratio sensor is installed on an engine, the air-fuel ratio is forcedly changed in steps. Based on air-fuel ratio operation quantity and detection signals of the air-fuel ratio sensor at this time, parameters for a plant model from a fuel injection valve to the air-fuel ratio sensor is identified. Next, correction characteristics (transmission functions) for generating false deterioration signals representing response delay in the deteriorated state are set based on the parameters. The detection signals are corrected based on the correction characteristics to generate transitive delay corresponding to the deteriorated state. Air-fuel ratio feedback control is conducted based on the detection signals corrected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sensor for detecting an operating state of an internal combustion engine, and to a pseudo-deterioration signal generation device for generating a detection signal in a state where the sensor is degraded.
[0002]
[Prior art]
Conventionally, an air-fuel ratio sensor that detects an air-fuel ratio of a combustion air-fuel mixture based on an oxygen concentration in exhaust gas of an internal combustion engine is provided in an exhaust pipe, and an actual air-fuel ratio detected by the air-fuel ratio sensor and a target air-fuel ratio are compared. There is known an air-fuel ratio feedback control in which a fuel supply amount to an engine is feedback-controlled based on a deviation.
[0003]
Further, in the air-fuel ratio feedback control disclosed in Patent Document 1, a configuration is disclosed in which a change in a time constant due to deterioration of an air-fuel ratio sensor is detected, and a target air-fuel ratio is changed in accordance with the change in the time constant. I have.
[0004]
[Patent Document 1]
JP-A-08-128347 [0005]
[Problems to be solved by the invention]
By the way, in order to optimally perform the process corresponding to the deterioration of the air-fuel ratio sensor as described above, it is necessary to experimentally perform the operation in a state where the air-fuel ratio sensor is deteriorated and to adapt various parameters in advance. .
[0006]
Therefore, conventionally, for the adaptation work, an air-fuel ratio sensor showing an output characteristic in a deteriorated state has been manufactured, and the deteriorated air-fuel ratio sensor is mounted on an engine to detect the air-fuel ratio.
[0007]
However, it is difficult to manufacture an air-fuel ratio sensor having deteriorated characteristics as required, and there has been a problem that the manufacturing cost of the deteriorated air-fuel ratio sensor increases.
In addition, during the experiment in which the deteriorated air-fuel ratio sensor is mounted on the engine, the degree of deterioration of the deteriorated air-fuel ratio sensor advances, and it is difficult to perform the adaptation work under a constant deterioration condition. was there.
[0008]
The present invention has been made in view of the above problems, and has as its object to enable low-cost and high-accuracy adjustment of a control parameter corresponding to a state in which an air-fuel ratio sensor has deteriorated.
[0009]
[Means for Solving the Problems]
Therefore, according to the first aspect of the present invention, a transmission characteristic until an air-fuel ratio change is detected by the air-fuel ratio sensor is obtained based on the air-fuel ratio manipulated variable and a detection signal of the air-fuel ratio sensor. By setting a correction characteristic of the detection signal corresponding to the degree of deterioration of the request and correcting the detection signal of the air-fuel ratio sensor with the set correction characteristic, a transient delay corresponding to the degree of deterioration of the request is forcibly generated. Configuration.
[0010]
According to such a configuration, the response characteristic of the actual air-fuel ratio detection in the new state is obtained by detecting the transfer characteristic until the air-fuel ratio change is detected by the air-fuel ratio sensor, and the response characteristic (in the new air-fuel ratio sensor). Based on the responsiveness, a correction characteristic of the detection signal is set to simulate the responsiveness at the time of deterioration.
[0011]
Then, by correcting the detection signal of the air-fuel ratio sensor with the set correction characteristic, a pseudo deterioration signal indicating a transient delay corresponding to the required degree of deterioration is generated.
Therefore, a pseudo deteriorated air-fuel ratio detection signal can be generated while using a new air-fuel ratio sensor, and a correction characteristic for pseudo-deterioration based on the actual response characteristic of the new air-fuel ratio sensor. Is set, it is possible to simulate the required deterioration state with high accuracy.
[0012]
According to the second aspect of the present invention, the air-fuel ratio manipulated variable for stepwise changing the air-fuel ratio is forcibly given, and the air-fuel ratio change is detected by the air-fuel ratio sensor based on the detection signal of the air-fuel ratio sensor at that time. The transfer characteristics were determined.
[0013]
According to this configuration, the air-fuel ratio is forcibly changed in steps, and a transfer characteristic until a change corresponding to this step change appears in the detection signal of the air-fuel ratio sensor is obtained.
Therefore, it is possible to easily detect a change in the detection signal corresponding to the air-fuel ratio operation amount, and it is possible to accurately determine the transfer characteristic.
[0014]
According to a third aspect of the present invention, the transfer characteristic is determined by identifying a parameter of a plant model that is controlled from a fuel injection valve that injects fuel to the engine to an air-fuel ratio sensor.
[0015]
According to this configuration, a plant model is set from the fuel injection valve to the air-fuel ratio sensor as a control target, and the parameters of the plant model are identified based on the air-fuel ratio operation amount and the detection signal of the air-fuel ratio sensor.
[0016]
Therefore, a model from the fuel injection valve to the air-fuel ratio sensor can be modeled to accurately set a correction characteristic corresponding to the required degree of deterioration.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a system configuration diagram of an internal combustion engine to which a pseudo degradation signal generating device according to the present invention is applied.
[0018]
In FIG. 1, an intake pipe 12 of an internal combustion engine 11 is provided with an air flow meter 13 for measuring an intake air flow rate Qa and an intake throttle valve 14 for controlling the intake air flow rate Qa.
[0019]
An electromagnetic fuel injection valve 15 is provided for each cylinder in a manifold portion downstream of the intake throttle valve 14.
The fuel injection valve 15 is driven to open by a drive pulse signal set in the control unit 50 as described later, and injects fuel controlled to a predetermined pressure.
[0020]
Further, a water temperature sensor 16 for detecting a cooling water temperature Tw in the cooling jacket of the engine 11 is provided.
On the other hand, an air-fuel ratio sensor 18 that detects the air-fuel ratio of the intake air-fuel mixture based on the oxygen concentration in the exhaust gas is provided near the collecting portion of the exhaust manifold 17.
[0021]
Downstream of the air-fuel ratio sensor 18, a three-way catalyst 19 for purifying exhaust gas by oxidizing CO and HC in the exhaust gas and reducing NOx in the vicinity of the stoichiometric air-fuel ratio is disposed.
[0022]
Here, the structure of the air-fuel ratio sensor 18 and the principle of detecting the air-fuel ratio will be described.
FIG. 2 shows the structure of the air-fuel ratio sensor 18.
The main body 1 of the air-fuel ratio sensor 18 is made of, for example, a heat-resistant porous insulating material such as zirconia Zr ₂ O ₃ having oxygen ion conductivity, and the main body 1 is provided with a heater section 2.
[0023]
Further, the main body 1 is provided with an air introduction hole 3 communicating with the atmosphere (standard gas), and a gas diffusion layer 6 communicating with the engine exhaust side via the gas introduction hole 4 and the protective layer 5.
[0024]
The sensing portion electrodes 7A and 7B are provided facing the air introduction hole 3 and the gas diffusion layer 6, and the oxygen pump electrodes 8A and 8B are provided around the gas diffusion layer 6 and the periphery of the main body 1 corresponding thereto. .
[0025]
A voltage corresponding to the ratio between the oxygen ion concentration (oxygen partial pressure) in the gas diffusion layer 6 and the oxygen ion concentration in the atmosphere is generated between the sensing portion electrodes 7A and 7B, and the gas is generated based on the voltage. Rich / lean of the air-fuel ratio in the diffusion layer 6 with respect to the stoichiometric air-fuel ratio is detected.
[0026]
On the other hand, a voltage generated between the sensing portion electrodes 7A, 7B, that is, a voltage is applied to the oxygen pump electrodes 8A, 8B in accordance with rich / lean in the gas diffusion layer 6.
[0027]
When a predetermined voltage is applied to the oxygen pump electrode portions 8A and 8B, oxygen ions in the gas diffusion layer 6 move accordingly, and a current flows between the oxygen pump electrode portions 8A and 8B.
[0028]
Here, the current value (limit current) Ip flowing between the oxygen pump electrode portions 8A and 8B when a predetermined voltage is applied is affected by the oxygen ion concentration in the exhaust gas. By detecting the current (Ip), the air-fuel ratio can be detected.
[0029]
That is, as shown in the table (A) of FIG. 3, a correlation between the current / voltage between the oxygen pump electrodes and the air-fuel ratio is obtained, and based on the rich / lean output of the sensing unit electrodes 7A and 7B, the oxygen pump is operated. By reversing the direction in which the voltage is applied to the electrode portions 8A and 8B, the current value (limit current) Ip flowing between the oxygen pump electrode portions 8A and 8B in both the lean and rich air-fuel ratio regions is calculated. The air-fuel ratio can be detected.
[0030]
The air-fuel ratio can be detected over a wide range by detecting the current value Ip between the oxygen pump electrode portions based on the above-described air-fuel ratio detection principle and referring to, for example, the table (B) in FIG.
[0031]
However, the structure of the air-fuel ratio sensor 18 and the principle of detecting the air-fuel ratio are not limited to those described above, and a so-called stoichiometric sensor that detects only rich / lean with respect to the stoichiometric air-fuel ratio may be used.
[0032]
Here, the description returns to FIG.
The engine 11 is provided with a crank angle sensor 20 for detecting the angle of the crankshaft. The control unit 50 outputs a crank unit angle signal output from the crank angle sensor 20 in synchronization with the engine rotation for a predetermined time. The engine speed Ne is detected by counting or measuring the cycle of the crank reference angle signal.
[0033]
The control unit 50 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like. The above-described air-fuel ratio sensor 18, air flow meter 13, water temperature sensor 16, crank Upon receiving an input signal from the angle sensor 20 or the like, the fuel injection amount of the fuel injection valve 15 is controlled as follows.
[0034]
The control unit 50 calculates a basic fuel injection pulse width Tp = k × Qa / Ne (k is a constant) from the intake air flow rate Qa detected by the air flow meter 13 and the engine rotation speed Ne obtained from the signal of the crank angle sensor 20. ) Is calculated, and a water temperature correction coefficient Kw forcibly correcting to the rich side when the water temperature is low, a start and post-start increase correction coefficient Kas, an air-fuel ratio feedback correction coefficient LAMBDA, a voltage correction amount Ts, and a target corresponding to the target air-fuel ratio. The final fuel injection pulse width Ti = Tp × (1 + Kw + Kas +...) × LAMBDA × Z + Ts is calculated from the equivalent ratio Z and the like.
[0035]
Then, the fuel injection pulse width Ti is sent to the fuel injection valve 15 as a drive pulse signal, and an amount of fuel proportional to the effective injection pulse width Te obtained by removing the voltage correction amount Ts from the fuel injection pulse width Ti is injected. Is done.
[0036]
The air-fuel ratio feedback correction coefficient LAMBDA is a coefficient for correcting a deviation of the actual air-fuel ratio detected by the air-fuel ratio sensor 18 from the target air-fuel ratio, and is used to correct the basic fuel pulse width Tp. Is made equal to a target air-fuel ratio (for example, a stoichiometric air-fuel ratio).
[0037]
The air-fuel ratio feedback correction coefficient LAMBDA is set by proportional / integral / differential control based on the deviation between the actual air-fuel ratio detected by the air-fuel ratio sensor 18 and the target air-fuel ratio.
[0038]
Here, the control unit 50 has a built-in function as a pseudo-deterioration signal generator of the air-fuel ratio sensor according to the present invention, so that the pseudo-deterioration signal generator can be selectively operated. ing.
[0039]
That is, the air-fuel ratio feedback control is normally performed using the detection signal of the air-fuel ratio sensor 18 as it is, and the air-fuel ratio feedback control is performed to adapt various control variables at the time of developing and designing the engine control specifications. The detection signal of the sensor 18 is processed by the pseudo deterioration signal generation device to switch to a state in which the air-fuel ratio feedback control is performed by a switch operation.
[0040]
In generating a pseudo deterioration signal of the air-fuel ratio sensor 18, a request for the degree of deterioration can be given to the control unit 50 from outside.
[0041]
The degree of deterioration is specified by a vehicle travel distance such as a travel distance of 100,000 km or 200,000 km.
Further, the air-fuel ratio sensor 18 in the case where the pseudo deterioration signal generating device is made to function is a new air-fuel ratio sensor having standard output characteristics, and does not use a deteriorated air-fuel ratio sensor showing output characteristics in a deteriorated state.
[0042]
The flowchart of FIG. 4 shows the processing contents of the pseudo deterioration signal generator. In step S1, it is determined whether or not there is a request to pseudo-degrade the detection signal of the air-fuel ratio sensor 18, and the pseudo deterioration signal is determined. If there is a request, the process proceeds to step S2.
[0043]
In step S2, it is determined whether or not the identification of the parameters of the plant model in which the control is performed from the fuel injection valve 15 to the air-fuel ratio sensor 18 has been completed.
If the parameter identification has not been completed, the process proceeds to step S3, and it is determined whether or not the conditions for executing the identification are satisfied.
[0044]
As the execution condition of the identification, it is determined that the failure determination of each component or system is not performed, and that the air-fuel ratio sensor 18 is in an active state.
If the identification execution condition is satisfied, the process proceeds to step S4, and it is determined whether the engine is in a steady operation state.
[0045]
For example, a change amount ΔQ of the intake air amount Q per unit time is obtained, and a state where the absolute value of the change amount ΔQ is equal to or less than a predetermined value is determined as a steady operation state.
If the engine is in the steady operation state, the process proceeds to step S5, and the air-fuel ratio is forcibly changed in steps. The step change of the air-fuel ratio is, for example, periodically reversed from rich to lean to lean to rich.
[0046]
If a function of diagnosing the response deterioration of the air-fuel ratio sensor 18 as a delay time until the forcible step change of the air-fuel ratio is detected by the air-fuel ratio sensor 18 is provided, the response deterioration diagnosis is executed. Thus, a stepwise change in the air-fuel ratio can be generated.
[0047]
In step S6, the parameters of the plant model are identified based on the air-fuel ratio rich / lean switching signal (air-fuel ratio operation amount) and the detection signal of the air-fuel ratio sensor 18 at that time.
[0048]
The plant model is described, for example, by a second-order ARX model (Auto-Regressive eXogenous model) in which dead time due to exhaust transportation is compensated, and parameters of the model are sequentially least-squares (recursive least-squares method). Identify.
[0049]
When it is determined that the identification is completed in step S2 by the identification, the process proceeds to step S7, and it is determined whether or not the identification is the first time after the identification is completed. If the identification is the first time, the process proceeds to step S8.
[0050]
In step S8, based on the identified parameters (plant model), a transfer function (time constant) for correcting the detection signal so as to exhibit a response corresponding to the deterioration state is set for each predetermined deterioration degree. Then, the setting result is stored as table data corresponding to each degree of deterioration.
[0051]
That is, the identified parameter (plant model) indicates the responsiveness when the air-fuel ratio sensor 18 is in a new state, and the degree of deterioration set in advance is, for example, a time constant that increases by a predetermined ratio with respect to a new state. Therefore, a transfer function (time constant) as a correction characteristic for correcting the detection signal for each preset deterioration degree can be set based on the identified parameter (plant model).
[0052]
If it is determined in step S7 that it is not the first time, the transfer function (time constant) for correcting the detection signal corresponding to each degree of deterioration is already stored. Proceed to S9.
[0053]
In step S9, the required degree of deterioration (for example, a travel distance of 100,000 km, a travel distance of 200,000 km, etc.) is read.
In step S10, a transfer function (time constant) for correcting the detection signal, which is stored corresponding to the degree of deterioration of the request read in step S9, is searched.
[0054]
In step S11, the detection signal of the air-fuel ratio sensor 18 is corrected based on the searched transfer function (time constant) to forcibly generate a transient delay corresponding to the required deterioration state. In step S12, the transient delay is determined. Is output as a pseudo degradation signal.
[0055]
The correction can be performed by a process using an analog circuit and also by a digital signal process (arithmetic process).
The simulated deterioration signal is used for air-fuel ratio feedback control, thereby simulating an air-fuel ratio feedback control state when the air-fuel ratio sensor 18 is deteriorated while using a new air-fuel ratio sensor 18.
[0056]
Then, based on the engine operating state (exhaust properties and the like) at this time, various parameters are adjusted in consideration of the deterioration state.
As described above, if the configuration is such that the detection signal of the new air-fuel ratio sensor 18 is degraded in a pseudo manner, it is not necessary to manufacture an air-fuel ratio sensor having deterioration characteristics, and the air-fuel ratio is detected at the required response deterioration degree. Thus, the adaptation operation in a state where the air-fuel ratio sensor has deteriorated can be performed accurately at low cost.
[0057]
Furthermore, since the correction characteristic for pseudo degradation is set based on the actual response characteristic of the air-fuel ratio sensor 18, the required degradation state can be simulated with high accuracy.
[0058]
Instead of incorporating the pseudo deterioration signal generator in the control unit 50, a separate pseudo deterioration signal generator may be interposed between the air-fuel ratio sensor 18 and the control unit 50.
[0059]
Further, when the response deterioration of the air-fuel ratio sensor differs between the rich change direction and the lean change direction, the correction characteristics may be set individually for the rich change direction and the lean change direction.
[0060]
Here, technical ideas other than the claims that can be grasped from the above embodiment will be described below together with their effects.
(A) A pseudo deterioration signal generating device for an air-fuel ratio sensor according to any one of claims 1 to 3,
A pseudo-deterioration signal generator for an air-fuel ratio sensor, wherein the correction characteristics are set individually in a rich change direction and a lean change direction.
[0061]
According to this configuration, when the deterioration characteristic of the air-fuel ratio sensor is different between the rich change direction and the lean change direction, a correction corresponding to this is performed, and a pseudo deterioration signal close to the actual deterioration state can be generated.
(B) In the pseudo deterioration signal generating device for an air-fuel ratio sensor according to any one of claims 1 to 3,
A pseudo deterioration signal generator for an air-fuel ratio sensor, wherein the degree of deterioration of the request is specified based on a traveling distance.
[0062]
According to this configuration, the degree of deterioration of the sensor is specified based on the travel distance, for example, equivalent to 100,000 km or 200,000 km, and a transient delay corresponding to the standard sensor degradation at the travel distance is forcibly generated. Let it.
[0063]
Therefore, it is possible to simulate the state of deterioration of the air-fuel ratio sensor while traveling over a certain traveling distance, and it is possible to easily perform an adaptation operation based on the traveling distance.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an internal combustion engine according to an embodiment.
FIG. 2 is a structural diagram of an air-fuel ratio sensor.
FIG. 3 is a diagram for explaining an air-fuel ratio detection principle of an air-fuel ratio sensor.
FIG. 4 is a flowchart showing pseudo degradation signal generation control.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Internal combustion engine, 13 ... Air flow meter, 15 ... Fuel injection valve, 17 ... Exhaust manifold, 18 ... Air-fuel ratio sensor, 20 ... Crank angle sensor, 50 ... Control unit

Claims (3)

A pseudo-deterioration signal generator for an air-fuel ratio sensor that detects an air-fuel ratio based on a component concentration in engine exhaust,
Based on the air-fuel ratio operation amount and the detection signal of the air-fuel ratio sensor, determine a transfer characteristic until an air-fuel ratio change is detected by the air-fuel ratio sensor,
Based on the transfer characteristics, set the correction characteristics of the detection signal corresponding to the degree of degradation of the request,
A pseudo-deterioration signal generation device for an air-fuel ratio sensor, wherein the correction signal corrects a detection signal of the air-fuel ratio sensor to forcibly generate a transient delay corresponding to the degree of deterioration of the request. An air-fuel ratio manipulated variable for stepwise changing the air-fuel ratio is forcibly given, and a transmission characteristic until an air-fuel ratio change is detected by the air-fuel ratio sensor is determined based on a detection signal of the air-fuel ratio sensor at that time. The apparatus for generating a pseudo deterioration signal for an air-fuel ratio sensor according to claim 1. 3. The pseudo air-fuel ratio sensor according to claim 1, wherein the transfer characteristic is obtained by identifying a parameter of a plant model in which control is performed from a fuel injection valve that injects fuel to an engine to the air-fuel ratio sensor. Deterioration signal generator.

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