JPH063304A - Air/fuel ratio detecting device for internal combustion engine - Google Patents

Abstract

PURPOSE:To correct the output fluctuation of an air/fuel ratio sensor in an actual-machine state without performing any calibrating work by providing the sensor, an output converting means, air/fuel ratio control means, response detecting means, and conversion characteristic correcting means. CONSTITUTION:An air/fuel sensor responds to the concentration of a specific component contained in an exhaust gas which changes depending upon the air ratio of the intake air-fuel mixture of an engine and the output value of the sensor varies. An output converting means converts the output value of the sensor into air/fuel ratio data. An air/fuel ratio control means forcibly changes the air-fuel ratio of the intake air-fuel mixture of the engine by a prescribed value. A response detecting means detects the parameter indicating the response of the sensor during the fluctuation of the output value following the variation of air-fuel ratio caused by the air/fuel ratio control means. A conversion characteristic correcting means corrects the conversion characteristics of the output converting means based on the parameter indicating the response detected by means of the response detecting means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio detecting device for an internal combustion engine, and more particularly to a technique for correcting variations in output characteristics of a sensor for detecting the air-fuel ratio of an engine intake air-fuel mixture based on exhaust gas component concentration.

[0002]

2. Description of the Related Art Conventionally, an air-fuel ratio of an engine intake air-fuel mixture is indirectly detected by detecting an oxygen concentration in engine exhaust with an oxygen sensor, and the air-fuel ratio detected by the oxygen sensor is set as a target air-fuel ratio. Air-fuel ratio feedback control is known in which the fuel supply amount is feedback-controlled so as to be closer (see Japanese Patent Laid-Open No. 60-240840, etc.).

In such air-fuel ratio feedback control, conventionally, control has been generally performed in which the target air-fuel ratio is set to the theoretical air-fuel ratio using an oxygen sensor capable of detecting rich / lean with respect to the theoretical air-fuel ratio. In response to the growing demand for improved fuel efficiency, lean-burn engines have been developed with a target air-fuel ratio that is significantly higher than the theoretical air-fuel ratio (for example, 20 to 24). A full range air-fuel ratio sensor that can detect a range has been used.

As the full range air-fuel ratio sensor, one realized by a signal processing circuit as shown in FIG. 4, for example, is known. In FIG. 4, a portion surrounded by a dotted line shows an equivalent circuit of the sensor element portion, and the sensor element has a sensor current generated according to a difference in oxygen partial pressure between the exhaust side and the diffusion chamber side, which are separated by the stabilized zirconia. The sensor output voltage Vs is generated by Ips, and in the processing circuit, the deviation from the equilibrium point (450 mV in FIG. 4) of the output voltage Vs becomes zero, that is, the equivalent sensor current Ipe.
A feedback processing circuit is configured to flow (or suck) a current Ip (pump current) that makes zero to the sensor element side from the error amplifier based on the comparison between the output voltage Vs and the equilibrium point. Here, as the sensor output, the current Ip is converted into a voltage by the resistor Rs and taken out.

That is, an oxygen pump function is added to the function of a conventionally known zirconia type oxygen sensor, and the zirconia element part is maintained so that the output voltage obtained at the reference oxygen partial pressure difference is maintained. The current is forcibly flown into (or sucked out from) the air-fuel ratio, and the air-fuel ratio is detected based on the equilibrium point based on the level of the current required to maintain the output voltage.

[0006]

By the way, in the air-fuel ratio sensor as described above, the relationship between the sensor output value (current Ip) and the oxygen concentration in the exhaust gas is slightly different for each sensor due to the variation of the sensor. It was unavoidable to show. Therefore, for example, the target air-fuel ratio is set to an extremely high value (for example, 20 to 24) compared to the theoretical air-fuel ratio, and feedback control is executed using the air-fuel ratio sensor so that such a lean air-fuel ratio is actually obtained. In this case, the air-fuel ratio actually obtained by the variation of the individual air-fuel ratio sensor varies with respect to the target lean air-fuel ratio, and NOx
There were cases where the concentration increased or combustion became unstable and a surge was generated.

As a method of compensating for variations in individual air-fuel ratio sensors, the output signal is previously verified for each air-fuel ratio sensor,
A resistor with a resistance value corresponding to the variation of the output signal is attached to the sensor, and the value is read on the unit side to correct the sensor output signal according to the characteristics of each sensor, or the sensor circuit uses the above-mentioned verification result. The method of adding the adjustment resistance of the corresponding resistance value was performed.

However, according to the above variation compensation method, since it is necessary to verify the output signal for each air-fuel ratio sensor in advance, the number of man-hours is significantly increased, and the output in the state of being actually attached to the engine is However, there is a problem in that deviation from the output under the test condition may occur, and accurate variation compensation cannot be performed. By the way, the variation of the sensor output with respect to the oxygen concentration in the exhaust, that is, the variation of the static characteristic correlates with the response characteristic of the sensor output value when the oxygen concentration in the exhaust changes, and as shown in FIG. 6, for example, It was confirmed from the experiment that the static deviation tends to increase as the deviation of the actual response characteristic from the expected response characteristic corresponding to the predetermined air-fuel ratio change increases.

The present invention has been made in view of the above circumstances, and utilizes the fact that the response characteristic of the air-fuel ratio sensor correlates with the static variation as described above, and therefore the air-fuel ratio in the actual state without performing the verification work. An object of the present invention is to provide an air-fuel ratio detection device capable of correcting the output variation of the sensor, thereby enabling highly accurate air-fuel ratio feedback control.

[0010]

Therefore, an air-fuel ratio detecting device for an internal combustion engine according to the present invention is constructed as shown in FIG. 1 or 2. In FIG. 1, the air-fuel ratio sensor is
It is a sensor whose output value changes in response to the concentration of a specific component in the exhaust which changes depending on the air-fuel ratio of the engine intake air-fuel mixture,
The output conversion means converts the output value of the air-fuel ratio sensor into air-fuel ratio data.

Further, the air-fuel ratio control means forcibly changes the air-fuel ratio of the engine intake air-fuel mixture by a predetermined value, and the responsiveness detection means causes the air-fuel ratio generated by the change of the air-fuel ratio by the air-fuel ratio control means. A parameter indicating responsiveness to changes in the output value of the air-fuel ratio sensor is detected. Then, the conversion characteristic correction unit corrects the conversion characteristic of the output conversion unit based on the parameter indicating the response detected by the response detection unit.

On the other hand, in FIG. 2, the region-by-region air-fuel ratio control means controls the air-fuel ratio of the engine intake air-fuel mixture according to the air-fuel ratio assigned to each engine operating region. Further, the air-fuel ratio sensor is a sensor whose output value changes in response to the concentration of a specific component in the exhaust which changes depending on the air-fuel ratio of the engine intake air-fuel mixture, and the output conversion means changes the output value of this air-fuel ratio sensor. Convert to air-fuel ratio data.

The expected value storage means stores the expected value of the output value change of the air-fuel ratio sensor according to the step difference between the operating regions of the air-fuel ratio assigned for each operating region.
Here, the output sampling means, when the actual air-fuel ratio controlled by the area-specific air-fuel ratio control means changes according to the step difference in the assigned air-fuel ratio between the operating areas, the output value of the air-fuel ratio sensor Sample changes.

Then, the correction means based on the expected value compares the change in the output value sampled by the output sampling means with the corresponding expected value stored in the expected value storage means, and based on the comparison result. The conversion characteristic of the output conversion means is corrected.

[0015]

With this configuration, the output response of the air-fuel ratio sensor is forcibly generated by forcibly changing the air-fuel ratio of the engine intake air-fuel mixture by a predetermined value, and the parameter indicating the actual response characteristic is detected. . Since the response characteristic correlates with the variation in the sensor output value with respect to the exhaust gas component concentration, the characteristic for converting the sensor output into the air-fuel ratio data is corrected based on the parameter indicating the response characteristic.

Further, in the air-fuel ratio control for each operating region according to the air-fuel ratio assigned to each operating region, when a step occurs in the air-fuel ratio, the response of the air-fuel ratio sensor corresponding to the occurrence of the air-fuel ratio step. To sample. Then, the expected value (expected response characteristic) of the output change of the air-fuel ratio sensor stored in advance according to the step is compared with the sampled actual sensor response, and the difference between the actual response and the expected value is compared. The characteristic of converting the output value into the air-fuel ratio data is corrected based on the above.

[0017]

EXAMPLES Examples of the present invention will be described below. In FIG. 3 showing an embodiment, air is drawn into an internal combustion engine 1 from an air cleaner 2 through an intake duct 3, a throttle valve 4 and an intake manifold 5. At each branch portion of the intake manifold 5, a fuel injection valve 6 is provided for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that is energized by a solenoid to open the valve, is deenergized and is closed, and is energized by an injection pulse signal from a control unit 12 described later to open the valve. Fuel, which is pumped from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator, is injected and supplied to the engine 1.

A spark plug 7 is provided in each combustion chamber of the engine 1 to spark-ignite and ignite and burn the air-fuel mixture. Exhaust gas is discharged from the engine 1 through the exhaust manifold 8, the exhaust duct 9, the catalyst 10 and the muffler 11. The control unit 12 that electronically controls fuel supply to the engine includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like, and receives input signals from various sensors. Upon receipt, the fuel injection amount of the fuel injection valve 6 is calculated as described later, and the operation of the fuel injection valve 6 is controlled based on the fuel injection amount.

As the various sensors, the intake duct 3 is used.
An air flow meter 13 is provided therein and outputs a signal according to the intake air flow rate Q of the engine 1. Further, a crank angle sensor 14 is provided and outputs a rotation signal for each predetermined crank angle. Here, by measuring the cycle of the rotation signal or the number of occurrences within a predetermined time,
The engine rotation speed Ne can be calculated.

Further, a water temperature sensor 15 for detecting the cooling water temperature Tw of the water jacket of the engine 1 is provided.
Further, an air-fuel ratio sensor 16 is provided at the collecting portion of the exhaust manifold 8. This air-fuel ratio sensor 16 is oxygen (specific component) in exhaust gas that changes depending on the air-fuel ratio of the engine intake air-fuel mixture.
A sensor whose output voltage (output value) changes in response to the concentration is used. In the present embodiment, a sensor configured by the processing circuit as shown in FIG. 4 described above and capable of detecting a wide air-fuel ratio region is used. .

Since FIG. 4 has already been described, a detailed description thereof will be omitted. However, the air-fuel ratio sensor 16 of this embodiment is
An oxygen pump function is added to the function of the zirconia-type oxygen sensor, and a current Ip that causes zero deviation from the equilibrium point of the electromotive force generated by the oxygen partial pressure difference is flown (or sucked) into the zirconia element portion. By
The air-fuel ratio is detected based on the level of the current Ip. The sensor output is the pump current Ip.
Is converted into a voltage Vout and outputted.

Here, the CPU of the microcomputer incorporated in the control unit 12 calculates the fuel injection amount (injection pulse width) Ti according to the air-fuel ratio pre-assigned for each operating region, as shown below, and the calculation is performed. The fuel supply to the engine is electronically controlled by controlling the opening and driving of the fuel injection valve 6 at a predetermined timing based on the fuel injection amount Ti thus obtained.

In the present embodiment, the stoichiometric air-fuel ratio region for controlling the air-fuel ratio of the engine intake air-fuel mixture to near the stoichiometric air-fuel ratio, and the lean air-fuel ratio extremely higher than the stoichiometric air-fuel ratio (for example, 20 to
The operating range is roughly divided into two, the lean burn range controlled in 24) and the operating range corresponding to the air-fuel ratio assigned to each subdivided range that divides the two operating ranges. The air-fuel ratio correction coefficient KMR is set.

The intake air flow rate Q and the engine speed N
The basic fuel injection amount Tp calculated based on e is corrected by the air-fuel ratio correction coefficient KMR corresponding to the assigned air-fuel ratio for each operating region, and the actual air-fuel ratio detected by the air-fuel ratio sensor 16 and the target The final fuel injection amount T is set by comparing the air-fuel ratio with the air-fuel ratio feedback correction coefficient LMD for correcting the basic fuel injection amount Tp.
By calculating i, the fuel injection amount Ti corresponding to the air-fuel ratio assigned for each operating region can be obtained.

The control unit 12 has a function as a control unit of the electronically controlled fuel injection device as described above, and a function for compensating the output characteristic variation of the air-fuel ratio sensor 16 according to the present invention is shown in the flowchart of FIG. To prepare. In the flowchart of FIG. 5, first, step 1 (denoted as S1 in the figure. The same applies hereinafter).
Then, it is determined whether or not the current operating conditions (engine load, engine speed) are included in the lean burn region.

When the operating condition is within the lean burn region, the routine proceeds to step 2, where the lean burn is preliminarily divided for each operating region divided by the basic fuel injection amount Tp (engine load equivalent value) and the engine speed Ne. The map that stores the air-fuel ratio correction coefficient KMR corresponding to the air-fuel ratio allocation within the region is referred to, and the air-fuel ratio correction coefficient KMR _L corresponding to the current operating conditions is obtained.

Then, the basic fuel injection amount Ti is corrected by the air-fuel ratio correction coefficient KMR _L , and the fuel injection amount T corresponding to the lean air-fuel ratio assigned in accordance with the operating conditions.
i is calculated and output. On the other hand, if it is determined in step 1 that it is not in the lean burn region, the process proceeds to step 3 and similarly, the air-fuel ratio correction coefficient KMR _S corresponding to the air-fuel ratio assigned to the operating condition included in the theoretical air-fuel ratio control region. Is calculated, and based on this, the fuel injection amount Ti is calculated and output.

That is, the air-fuel ratio of the engine intake air-fuel mixture is controlled according to the air-fuel ratio assigned to each engine operating region (in this embodiment, it is largely divided into a theoretical air-fuel ratio and a lean air-fuel ratio). Steps 1 to 3 correspond to the region-by-region air-fuel ratio control means, and switching between the stoichiometric air-fuel ratio and the lean air-fuel ratio in accordance with the allocation for each operating region means to forcibly change the air-fuel ratio by a predetermined value. Therefore, the steps 1 to 3 also correspond to the air-fuel ratio control means.

In step 4, it is determined whether or not it is the switching timing between the lean burn region and the stoichiometric air-fuel ratio control region, that is, the air-fuel ratio of the engine intake air-fuel mixture has a large step with a change in operating conditions. Then, it is determined whether or not it is the timing to forcibly change. When it is not the switching timing, the variation learning of the air-fuel ratio sensor 16 which will be described later cannot be performed, so this program is ended as it is.

On the other hand, when it is the switching timing between the lean burn and the stoichiometric air-fuel ratio, the routine proceeds to step 5, where the output voltage Vout of the air-fuel ratio sensor 16 which changes in response to the air-fuel ratio change having this large step is sampled. To do. The sampled output voltage Vout is stored in the memory in the next step 6. The steps 5 and 6 correspond to the output sampling means and the response detecting means.

In step 7, the air-fuel ratio sensor 16 which is expected when the air-fuel ratio is greatly changed in accordance with the switching between the lean burn region and the stoichiometric air-fuel ratio control region this time.
Set the output change characteristics of. That is, the air-fuel ratio step difference given at the switching timing is, for example, when the lean air-fuel ratio is switched to the stoichiometric air-fuel ratio, the lean-burn air-fuel ratio correction coefficient KMR _L before switching and the stoichiometric air-fuel ratio after switching. Since it is determined from the fuel ratio correction coefficient KMR _S , the expected value of the output change of the air-fuel ratio sensor 16 is stored in advance according to the combination of the correction coefficients KMR _L and KMR _S , and the expected characteristic of the output change is calculated as described above. Correction coefficient KM
The reading can be performed based on the combination of R _L and KMR _S. Therefore, the part of the above step 7 shows the function as the expected value storage means of the control unit 12, and in reality, the memory built in the control unit 12 corresponds to the expected value storage means. .

In the next step 8, the output Vout sampled at the switching timing between the lean air-fuel ratio and the stoichiometric air-fuel ratio and the expected change characteristic (expected value of the response characteristic) are compared and expected. The data Δt representing the response deviation time of the actual output Vout with respect to the changing characteristic is obtained. That is, the deviation with respect to the reference response characteristic is detected by comparing the actually obtained change characteristic of the output Vout with the reference output change characteristic when the same air-fuel ratio step is given. For this, the average or maximum deviation time at each output Vout point, the deviation time at the intermediate output Vout time, and the time from the start to the end of the response change may be obtained.

Although the response shift time Δt corresponds to the parameter indicating the response, the changing speed of the output Vout may be obtained instead of the time Δt. In the next step 9, the response deviation time Δt (or the changing speed of the output Vout) and the output value Vout correlated with the response deviation time Δt.
(Starting point output, ending point output when an air-fuel ratio step is generated,
A true air-fuel ratio corresponding to the correlation output Vout [A /
F] is obtained from the map.

That is, when the response deviation time Δt is substantially zero, it is judged that the output voltage Vout is output as a standard corresponding to the oxygen concentration in the exhaust gas (air-fuel ratio). When Δt occurs, it is estimated that the larger the response deviation time Δt is, the larger the deviation of the static characteristics is. Therefore, based on the response deviation time Δt, the air-fuel ratio [A / F].

At the next step 10, the true air-fuel ratio data [A / A corresponding to the output Vout obtained at the step 9 is obtained.
F], the air-fuel ratio corresponding to the corresponding output Vout in the conversion table for converting the output Vout into the air-fuel ratio data is rewritten. The step 10 corresponds to the conversion characteristic correction means and the correction means based on the expected value, and the conversion table to be corrected corresponds to the output conversion means.

As described above, if the static characteristic of the air-fuel ratio sensor 16 is corrected from the response characteristic when a predetermined air-fuel ratio change occurs, the variation in the static characteristic of the air-fuel ratio sensor 16 can be reduced. Thus, it becomes possible to correct in the actual machine state without the need to perform the verification in advance, and it becomes possible to absorb the error in the actual machine of the variation characteristic obtained by performing the verification in advance. Therefore, it is possible to correct the static characteristic variation of the air-fuel ratio sensor 16 with high accuracy and easily, and thereby improve the accuracy of air-fuel ratio feedback control.

By the way, in the above embodiment, a large air-fuel ratio step generated when switching between the lean burn region and the stoichiometric air-fuel ratio region is utilized, and a change in the sensor output Vout caused by the air-fuel ratio step is sampled. However, the air-fuel ratio is forcibly changed only to detect the response characteristic of the air-fuel ratio sensor 16, and the output Vou at this time is changed.
The response characteristic of t may be obtained. However, in the case where the air-fuel ratio is forcibly changed for learning the sensor variation as described above, it is preferable that the air-fuel ratio is limited to during the idling operation so that the drivability is not significantly affected.

In this embodiment, as the air-fuel ratio sensor 16, the zirconia type oxygen sensor constructed by adding an oxygen pump function is shown. However, the air fuel ratio sensor 16 is not limited to this, and oxygen sensors of various configurations are shown. Is applicable to.

[0039]

As described above, according to the air-fuel ratio detecting apparatus for an internal combustion engine according to the present invention, a correction is performed to detect a single product variation of the air-fuel ratio sensor in a state where the air-fuel ratio sensor is mounted on the actual machine and to compensate for this. Since it is performed, it is not necessary to individually calibrate the output of the air-fuel ratio sensor in advance, or it is possible to absorb the nonconformity of the variation characteristics obtained by performing the calibration in advance on the actual machine, and it is possible to perform high-precision emptying without increasing man-hours. This has the effect of being able to compensate for variations in the individual fuel ratio sensors.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention.

FIG. 2 is a block diagram showing the basic configuration of the present invention.

FIG. 3 is a system schematic diagram of an embodiment.

FIG. 4 is a circuit diagram showing a processing circuit of the air-fuel ratio sensor in the embodiment.

FIG. 5 is a flowchart showing how air-fuel ratio sensor variation learning is performed in the embodiment.

FIG. 6 is a time chart showing a comparison between actual response characteristics of an air-fuel ratio sensor and expected response values.

[Explanation of symbols]

 1 Internal Combustion Engine 6 Fuel Injection Valve 12 Control Unit 13 Air Flow Meter 14 Crank Angle Sensor 16 Air-Fuel Ratio Sensor

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G01N 27/419

Claims (2)

[Claims] 1. An air-fuel ratio sensor whose output value changes in response to the concentration of a specific component in exhaust gas that changes depending on the air-fuel ratio of an engine intake air-fuel mixture, and an output value of the air-fuel ratio sensor converted into air-fuel ratio data. Output conversion means, an air-fuel ratio control means for forcibly changing the air-fuel ratio of the engine intake air-fuel mixture by a predetermined value, and an output value of the air-fuel ratio sensor generated with the change of the air-fuel ratio by the air-fuel ratio control means. Responsiveness detecting means for detecting a parameter indicating responsiveness in change, and conversion characteristic correcting means for correcting the conversion characteristic of the output converting means based on the parameter indicating responsiveness detected by the responsiveness detecting means. An air-fuel ratio detection device in an internal combustion engine configured to include. 2. An air-fuel ratio detecting device for an internal combustion engine, comprising: region-specific air-fuel ratio control means for controlling the air-fuel ratio of an engine intake air-fuel mixture according to the air-fuel ratio assigned to each engine operating region. An air-fuel ratio sensor whose output value changes in response to the concentration of a specific component in the exhaust gas that changes depending on the air-fuel ratio, output conversion means for converting the output value of the air-fuel ratio sensor into air-fuel ratio data, and the operating region Expected value storage means for storing the expected value of the output value change of the air-fuel ratio sensor according to the step difference between the operating areas of the air-fuel ratio assigned for each, and the actual air controlled by the area-specific air-fuel ratio control means Output sampling means for sampling a change in the output value of the air-fuel ratio sensor when the fuel ratio changes in accordance with the step difference in the assigned air-fuel ratio between the operating regions; and the sampling means by the output sampling means. The change in the output value and the corresponding expected value stored in the expected value storage means are compared, and based on the result of the comparison, the correction means based on the expected value for correcting the conversion characteristic of the output conversion means, An air-fuel ratio detection device in an internal combustion engine configured to include.