JP2847454B2 - Air-fuel ratio detection device for internal combustion engine - Google Patents

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 an air-fuel ratio of an engine intake air-fuel mixture based on exhaust gas component concentration.

[0002]

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

In such air-fuel ratio feedback control, control for setting a target air-fuel ratio to a stoichiometric air-fuel ratio by using an oxygen sensor capable of detecting rich / lean with respect to a stoichiometric air-fuel ratio has been generally performed. In response to the increasing demand for improved fuel efficiency, lean-burn engines have been developed that use an air-fuel ratio that is much higher than the stoichiometric air-fuel ratio (for example, 20 to 24) as the target air-fuel ratio. An all-area air-fuel ratio sensor capable of detecting an area has been used.

As the full-range air-fuel ratio sensor, for example, a sensor realized by a signal processing circuit as shown in FIG. 4 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 generates a sensor current generated according to a difference in oxygen partial pressure between the exhaust side and the diffusion chamber side separated by stabilized zirconia. A sensor output voltage Vs is generated by Ips. In the processing circuit, the deviation of the output voltage Vs from the equilibrium point (450 mV in FIG. 4) becomes zero, that is, the equivalent sensor current Ipe
A current Ip (pump current) which makes zero zero is supplied from the error amplifier to the sensor element 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 a zirconia element section is provided so that an output voltage obtained at a reference oxygen partial pressure difference is maintained. A current is forced to flow into (or out of) 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 above-described air-fuel ratio sensor, the relationship between the sensor output value (current Ip) and the oxygen concentration in the exhaust is slightly different from sensor to sensor due to variations in individual sensors. Showing was inevitable. For this reason, for example, the target air-fuel ratio is set to an extremely high value (for example, 20 to 24) as compared with the stoichiometric air-fuel ratio, and the feedback control is executed using the air-fuel ratio sensor so that the lean air-fuel ratio is actually obtained. In this case, the air-fuel ratio actually obtained due to the single-unit variation of the air-fuel ratio sensor varies with respect to the target lean air-fuel ratio.
In some cases, the concentration increased, or combustion became unstable, causing a surge.

[0007] As a method of compensating for the variation of the single unit of the air-fuel ratio sensor, an output signal is tested in advance for each air-fuel ratio sensor.
A resistance having 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 characteristic of each sensor, or the sensor circuit adds the test result to the test result. A method of adding an adjustment resistor having a corresponding resistance value has been performed.

However, according to the above-described variation compensation method, it is necessary to test the output signal for each air-fuel ratio sensor in advance, so that the number of man-hours is greatly increased, and the output in the state actually attached to the engine is reduced. In some cases, a deviation may occur from the output under the test conditions, and accurate dispersion compensation cannot be performed. By the way, the variation in the sensor output with respect to the oxygen concentration in the exhaust gas, that is, the variation in the static characteristics correlates with the response characteristic of the sensor output value when the oxygen concentration in the exhaust gas changes, for example, as shown in FIG. It has been confirmed from experiments 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 performs the air-fuel ratio operation in the actual machine state without performing a test operation. An object of the present invention is to provide an air-fuel ratio detection device capable of correcting output variations of a sensor, thereby enabling high-precision air-fuel ratio feedback control.

[0010]

Therefore, an air-fuel ratio detecting device for an internal combustion engine according to the present invention is configured as shown in FIG. 1 or FIG. In FIG. 1, the air-fuel ratio sensor is
A sensor whose output value changes in response to the concentration of a specific component in exhaust gas that changes according to the air-fuel ratio of the engine intake air-fuel mixture,
The output converter converts the output value of the air-fuel ratio sensor into data of the air-fuel ratio.

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 detecting means includes the air-fuel ratio generated by the air-fuel ratio control means. A parameter indicating responsiveness to a change 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 responsiveness detected by the responsiveness detection unit.

On the other hand, in FIG. 2, the region-specific 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 operation region. The air-fuel ratio sensor is a sensor whose output value changes in response to the concentration of a specific component in the exhaust gas which changes according to the air-fuel ratio of the engine intake air-fuel mixture, and the output conversion means converts the output value of this air-fuel ratio sensor to Convert to air-fuel ratio data.

The expected value storage means stores an expected value of a change in the output value of the air-fuel ratio sensor in accordance with a step between the operating regions of the air-fuel ratio assigned to each of the operating regions.
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 of the assigned air-fuel ratio between the operation areas, the output value of the air-fuel ratio sensor Sample the change.

[0014] The correction means based on the expected value compares a change in the output value sampled by the output sampling means with a 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 a parameter indicating the actual response characteristic is detected. . Since the response characteristic correlates with the variation of the sensor output value with respect to the exhaust gas component concentration, the characteristic for converting the sensor output into air-fuel ratio data is corrected based on the parameter indicating the response characteristic.

Further, when a step occurs in the air-fuel ratio in the air-fuel ratio control for each operation region according to the air-fuel ratio assigned to each operation region, the response of the air-fuel ratio sensor corresponding to the occurrence of the air-fuel ratio step Is sampled. Then, an 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 a 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.

[0017]

Embodiments of the present invention will be described below. In FIG. 3 showing one embodiment, air is sucked into an internal combustion engine 1 from an air cleaner 2 via an intake duct 3, a throttle valve 4 and an intake manifold 5. In each branch 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 and opens, and is deenergized and closed by being energized by an injection pulse signal from a control unit 12, which will be described later. Fuel that is pressure-fed from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator is injected and supplied to the engine 1.

Each combustion chamber of the engine 1 is provided with an ignition plug 7 for igniting a mixture by igniting a spark. Then, exhaust gas is discharged from the engine 1 through the exhaust manifold 8, the exhaust duct 9, the catalyst 10, and the muffler 11. A control unit 12 for electronically controlling 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. Then, the fuel injection amount by 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.

The various sensors include an intake duct 3
An air flow meter 13 is provided therein, and outputs a signal corresponding 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 speed Ne can be calculated.

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

Although FIG. 4 has already been described, a detailed description thereof will be omitted, but 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 the deviation of an electromotive force generated by an oxygen partial pressure difference from an equilibrium point to flow into (or sucks out of) a zirconia element unit. By doing
The air-fuel ratio is detected based on the level of the current Ip. The sensor output is the pump current Ip
Is converted to a voltage Vout and output.

Here, the CPU of the microcomputer built in the control unit 12 calculates the fuel injection amount (injection pulse width) Ti in accordance with the air-fuel ratio assigned in advance for each operation region, as described below. The fuel supply to the engine is electronically controlled by controlling the opening 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 in which the air-fuel ratio of the engine intake air-fuel mixture is controlled near the stoichiometric air-fuel ratio, and a lean air-fuel ratio that is extremely high with respect to the stoichiometric air-fuel ratio (for example, 20 to
24), the operating region is roughly divided into two regions, that is, the lean burn region to be controlled, and the operating region corresponding to the air-fuel ratio assigned to each sub-region that divides the two operating regions. The air-fuel ratio correction coefficient KMR is set.

Then, the intake air flow rate Q and the engine speed N
e, the basic fuel injection amount Tp calculated based on the air fuel ratio is corrected by the air fuel ratio correction coefficient KMR corresponding to the air fuel ratio allocated to each operating region, and the actual air fuel ratio detected by the air fuel ratio sensor 16 and the target fuel injection amount Tp are corrected. The air-fuel ratio is compared with the air-fuel ratio to set an air-fuel ratio feedback correction coefficient LMD for correcting the basic fuel injection amount Tp.
By calculating i, a fuel injection amount Ti corresponding to the air-fuel ratio assigned to each operation 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 of compensating for variations in output characteristics of the air-fuel ratio sensor 16 according to the present invention, as shown in the flowchart of FIG. So prepared. In the flowchart of FIG. 5, first, step 1 (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.

If the operating condition is within the lean burn range, the routine proceeds to step 2, where the lean burn is performed for each of the operating ranges previously classified by the basic fuel injection amount Tp (engine load equivalent value) and the engine speed Ne. referring to a map that stores the air-fuel ratio correction coefficient KMR corresponding to the air-fuel ratio assignment in the region, determining the air-fuel ratio correction coefficient KMR _L corresponding to the current operating conditions.

[0027] Then, the through air-fuel ratio correction coefficient KMR _L by correcting the basic fuel injection amount Ti, the fuel injection amount corresponding to the lean air-fuel ratio assigned to correspond to the operating conditions T
i is calculated and output. On the other hand, when it is determined in step 1 that the engine 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 stoichiometric air-fuel ratio control region. Is calculated, and the fuel injection amount Ti is calculated and output based on this.

That is, the air-fuel ratio of the engine intake air-fuel mixture is controlled in accordance with the air-fuel ratio assigned to each engine operating region (in this embodiment, the air-fuel ratio is roughly divided into a stoichiometric air-fuel ratio and a lean air-fuel ratio). Steps 1 to 3 correspond to the air-fuel ratio control means for each area, and switching between the stoichiometric air-fuel ratio and the lean air-fuel ratio in accordance with the assignment for each operation area means forcibly changing the air-fuel ratio by a predetermined value. Therefore, the steps 1 to 3 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 due to a change in the operating conditions. Then, it is determined whether or not it is time to forcibly change. If it is not the switching timing, the variation learning of the air-fuel ratio sensor 16, which will be described later, cannot be performed.

On the other hand, when it is the switching timing between the lean burn and the stoichiometric air-fuel ratio, the process 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. I do. The sampled output voltage Vout is stored in the memory in the next step 6. Steps 5 and 6 correspond to output sampling means and responsiveness detecting means.

In step 7, the air-fuel ratio sensor 16 expected when the air-fuel ratio is largely changed in accordance with the current switching between the lean burn region and the stoichiometric air-fuel ratio control region.
Set the output change characteristics. That is, the air-fuel ratio step given by the switching timing, for example, a lean from the air-fuel ratio when switching to a stoichiometric air-fuel ratio, the air-fuel ratio correction coefficient KMR _L for lean-burn before switching, empty for 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 in accordance with 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 data can be read out based on a combination of R _L and KMR _S. Therefore, the step 7 described above indicates the function of the control unit 12 as the expected value storage means, and the memory built in the control unit 12 actually 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 is compared with the expected change characteristic (expected value of the response characteristic). Data .DELTA.t representative of a response delay time of the actual output Vout with respect to the change characteristics is obtained. That is, the change characteristic of the actually obtained output Vout is compared with the reference output change characteristic when the same air-fuel ratio step is given, and a deviation from the reference response characteristic is detected. For example, the average or maximum of the shift time at each output Vout point, the shift time at the intermediate output Vout point, and the time from the start of the response change to the end thereof may be obtained.

Although the response delay time Δt corresponds to a parameter indicating the response, the change speed of the output Vout may be obtained instead of the time Δt. In the next step 9, the response delay time Δt (or the changing speed of the output Vout) and the output value Vout correlated to the response delay time Δt are determined.
(Start output, end output when air-fuel ratio step is generated,
The average air-fuel ratio corresponding to the correlation output Vout [A / A
F] is obtained from the map.

That is, when the response delay time Δt is substantially zero, it is determined that the output voltage Vout is output as a reference 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 characteristic is. Therefore, based on the response deviation time Δt, the air-fuel ratio [A / F].

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

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 is caused, the variation of the static characteristic of the air-fuel ratio sensor 16 can be reduced. This makes it possible to make corrections in the actual machine state without having to perform the test in advance, and to absorb errors in the actual machine in the variation characteristics obtained by performing the test in advance. Therefore, it is possible to easily and accurately correct the static characteristic variation of the air-fuel ratio sensor 16, and to improve the accuracy of the air-fuel ratio feedback control.

In the above embodiment, the change in the sensor output Vout caused by the air-fuel ratio step is sampled by utilizing the large air-fuel ratio step generated when switching between the lean burn region and the stoichiometric air-fuel ratio region. 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, when the air-fuel ratio is forcibly changed for learning the sensor variation as described above, it is preferable that the air-fuel ratio be limited to an idling operation or the like so as not to greatly affect the drivability.

In this embodiment, the air-fuel ratio sensor 16 is constructed by adding an oxygen pump function to a zirconia type oxygen sensor. However, the present invention is not limited to this. It can be applied 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 for compensating for a variation in the air-fuel ratio sensor by detecting a single component of the air-fuel ratio sensor in a state where the air-fuel ratio sensor is mounted on the actual machine. Therefore, it is not necessary to individually verify the output of the air-fuel ratio sensor in advance, or it is possible to absorb the inconsistency of the variation characteristics obtained by performing the verification in advance on the actual machine, and to accurately perform the air measurement without increasing the number of steps. There is an effect that it is possible to compensate for variations in the single fuel ratio sensor.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a 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 a state of learning variation of the air-fuel ratio sensor in the embodiment.

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

[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 the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/419 G01N 27/26 G01N 27/409

Claims (2)

(57) [Claims] An air-fuel ratio sensor whose output value changes in response to the concentration of a specific component in exhaust gas that changes according to the air-fuel ratio of an engine intake air-fuel mixture, and the output value of the air-fuel ratio sensor is 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 for an internal combustion engine configured to include: 2. An air-fuel ratio detecting device for an internal combustion engine, comprising: a region-specific air-fuel ratio control means for controlling an air-fuel ratio of an engine intake air-fuel mixture according to an air-fuel ratio assigned to each engine operation region. An air-fuel ratio sensor whose output value changes in response to the concentration of a specific component in exhaust gas that changes according to the air-fuel ratio of the air-fuel ratio; an output conversion unit that converts an output value of the air-fuel ratio sensor into air-fuel ratio data; Expectation value storage means for storing an expected value of an output value change of the air-fuel ratio sensor in accordance with a step between operation areas of the air-fuel ratio assigned to each of the air-fuel ratios; and 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 of the assigned air-fuel ratio between the operation regions; Correction means for comparing the change in the output value with the corresponding expected value stored in the expected value storage means, and correcting the conversion characteristic of the output conversion means based on the comparison result. An air-fuel ratio detection device for an internal combustion engine configured to include: