JPH0742883B2 - Air-fuel ratio controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for controlling, for example, an engine for a vehicle equipped with an electronically controlled fuel injection device, particularly in accordance with a warm-up state.

In order to perform air-fuel ratio control of the engine, an air-fuel ratio sensor that generates an analog output signal according to the oxygen concentration in the exhaust gas of the engine is used. As an air-fuel ratio control system using such an air-fuel ratio sensor, for example, as disclosed in Japanese Patent Laid-Open No. 57-165643, the output of the air-fuel ratio sensor becomes a preset reference value. Feedback control is used. In this case, a predetermined reference output, that is, a target air-fuel ratio at the time of feedback is used as a map with a value representing the engine speed and load, for example, intake pressure. However, this is good in steady-state operating conditions, but lean-burn engines generally do not rely on purifying the catalyst for nitrogen oxide NOx, so if the set air-fuel ratio deviates, Emissions are significantly worse, especially
Since the characteristics of NOx emitted from the engine become maximum in the vicinity of 16 on the lean side of the theoretical air-fuel ratio, even a slight deviation of the air-fuel ratio causes a problem of NOx emission increase in a lean burn engine. In addition, carbon monoxide CO in the exhaust gas is approximately the theoretical air-fuel ratio.
Since the increase starts in the darker state than 15, it is important to set the air-fuel ratio to a value thinner than the theoretical air-fuel ratio in consideration of the variation in the air-fuel ratio control.

Further, as a factor of the deviation (dispersion) of the air-fuel ratio when the feedback control is not performed, a change in the evaporation rate due to the difference in gasoline properties, a variation in the intake air amount sensor, a variation in the fuel injection valve, a variation in the engine, and the like are considered.

Next, when the engine is at a higher temperature than usual, in addition to the above-mentioned variation, the variation in the injection amount due to the generation of gasoline vapor in the fuel injection valve has a large influence, and the variation in the air-fuel ratio becomes large above the low temperature. As a result, deterioration of exhaust emission is promoted. That is, in order to suppress the generation of vapor, the fuel injection device generally increases the fuel pressure to about 250 kPa to 310 kPa, but when the temperature of the fuel and the fuel injection valve becomes high, vapor is generated, In particular, since the fuel is intermittently injected in the fuel injection valve, a pressure drop occurs immediately after the start of injection, vapor is generated, and the fuel injection amount is likely to decrease. The temperature at which this injection amount reduction occurs has a large individual difference due to variations in manufacturing of the fuel injection valve, which promotes variations in the air-fuel ratio of the engine.

Therefore, the present invention has been made in view of the above points, and an object thereof is to reliably prevent deterioration of exhaust emission by executing air-fuel ratio control with improved control accuracy even when the engine temperature is high. Is.

Therefore, the present invention is directed to an air-fuel ratio sensor whose detection signal changes in an analog manner in accordance with the air-fuel ratio, and a target air-fuel ratio set in a side thinner than the stoichiometric air-fuel ratio corresponding to the engine operating state corresponding to the air-fuel ratio feedback region. Means for storing fuel ratio data, means for determining a warmed-up state of the engine in the active state of the air-fuel ratio sensor, and a state in which the temperature of the engine is higher than a normal warm-up temperature corresponding to the warmed-up state Sometimes, means for storing corrected air-fuel ratio data that is richer than the normal target air-fuel ratio and thinner than the theoretical target air-fuel ratio set on the side thinner than the theoretical air-fuel ratio, and the target air-fuel ratio data corresponding to the operating state of the engine. Further, the corrected air-fuel ratio data corresponding to the warm-up state is read out, and the read target air-fuel ratio data is corrected by the corrected air-fuel ratio data to correct the target air-fuel ratio The present invention provides an air-fuel ratio control device including a lock control unit.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows a schematic configuration of an engine system in which an air-fuel ratio control device is provided. An air flow meter 12, a throttle valve 13, a throttle sensor 14, etc. are provided in an intake system of the engine 11. The air drawn from this intake system is
The fuel is supplied to the manifold 15, mixed with the fuel injected from the fuel injection valve 16, and supplied to the combustion chamber 17. In this combustion chamber 17, the mixture of fuel and air is transferred to the cylinder head 18
It is ignited and burned by a spark plug 19 provided in the exhaust gas, and the combustion gas is discharged to an exhaust pipe 21 via an exhaust valve 20. The exhaust pipe 21 is provided with an air-fuel ratio sensor 22 that detects the air-fuel ratio from the oxygen concentration in the exhaust gas, and the air-fuel ratio is feedback controlled by the detection output of the air-fuel ratio sensor 22. The air-fuel ratio sensor 22 is, for example, a limiting current detection type oxygen sensor, and the sensor has a built-in heater for keeping it at a predetermined temperature (for example, 500 ° C. to 600 ° C.) or higher.

A cylinder block 23 of the engine 11 is provided with a water temperature sensor 24 for detecting an engine cooling water temperature, and a distributor 26 for distributing an ignition signal from the igniter 25 to each cylinder is provided with a cylinder discrimination sensor 27 and rotation sensors.
28 built-in. Then, the detection signals from the respective sensors that detect the respective operating states of the engine 11 are supplied to the control device 29.

The control device 29 is constructed by using, for example, a microcomputer, and FIG. 2 shows its configuration. That is, a RAM 31 that temporarily stores data for a CPU 30 that performs arithmetic processing, and a ROM 32 that is used as a program memory or the like.
The CPU 30, RAM 31, ROM 32, etc. are connected by a data bus 33. Input / output ports 34, 35 and output ports 36, 37, 38 are connected to the data bus 33, and the air-fuel ratio sensor 22, the air flow meter 12,
The signal from the water temperature sensor 24 is taken out via the multiplexer 39, converted into a digital signal by the A / D converter 40, and supplied. The signals from the cylinder discrimination sensor 27 and the rotation angle sensor 28 are waveform-shaped by the waveform shaping circuit 41 and supplied to the input / output port 35, and the detection signal from the throttle sensor 15 is appropriately A / D converted by the input circuit 42. Supply to the input / output port 35. The output signal from each of the output ports 36, 37, 38 is
Igniter 25, fuel injection valve via drive circuits 43, 44, 45
16 and the heater 22a built in the air-fuel ratio sensor 22, and the ignition control and the fuel injection amount control and the temperature control of the air-fuel ratio sensor are performed. 46 is a clock oscillator,
A timing clock signal is given to the CPU 30 and the like.

Here, the ROM 32 stores map data in which the engine load area defined by the value Q / N based on the engine speed N and the intake air amount Q is divided into a feedback area and an open loop area. In addition, this ROM32 corresponds to the numerical data of the increase value in the open loop area, the numerical data of the set value for feedback correction in the feedback area, and the air-fuel ratio according to the operating conditions of various engines in the feedback area and open loop area. It stores the numerical data of the fuel injection time to be shifted.

Further, in the ROM 32, as shown in FIG. 3, in the air-fuel ratio feedback region with respect to the engine load region defined by the engine speed N and the value Q / N corresponding to the intake air amount Q corresponding to one revolution thereof. It stores various target air-fuel ratio data. Here, the normal theoretical air-fuel ratio data is about 14.7, and the target air-fuel ratio data stored in the ROM 32 here is set to a side thinner than the theoretical air-fuel ratio. In this case, the actual value of the ROM 32 is to convert the air-fuel ratio into the output of the air-fuel ratio sensor 22, and this target air-fuel ratio data corresponds to the fuel injection request amount F0 at that time.

In the control device 29 thus configured, the air flow meter is
12.When it is determined by the detection output of the rotation angle sensor 28 that the operating state of the engine 11 belongs to the feedback region, the air-fuel ratio of the air-fuel mixture is set to a predetermined target air-fuel ratio based on the detection output of the air-fuel ratio sensor 22. Feedback control is performed based on the fuel ratio.

Further, the correction amount F1 for the target air-fuel ratio related to the cooling water temperature as shown in FIG. 4 is set and stored in the ROM 32. Then, the correction amount F1 is read in accordance with the cooling water temperature obtained by the water temperature sensor 24, the target air-fuel ratio is corrected, and the feedback control of the air-fuel ratio is performed by the corrected value. For example, when the cooling water temperature is lower than 80 ° C., the target air-fuel ratio of each operation area shown in FIG. 3 is made thick as a function of the water temperature. Also, when the water temperature is high, it is usually a lean state that is sufficiently thinner than the stoichiometric air-fuel ratio, but when the water temperature becomes higher than 95 ° C, as is clear from FIG. The correction amount is slightly increased so that it is set between the normal target air-fuel ratio and the theoretical air-fuel ratio. Therefore, for example, even when vapor occurs in the fuel when the engine temperature is high, misfire is reliably prevented.

FIG. 5 illustrates the flow of the entire operation of the above-mentioned device. First, it is activated by a timer or an interrupt based on the crank angle of the engine. Then, in step 100, the engine speed N, the intake air amount Q, the water temperature, and other parameters are measured, and in the next step 101, the fuel injection amount F0 corresponding to the current operating region is measured by the measured and read parameters. calculate. This also corresponds to the target air-fuel ratio in each load region of the engine read from the map shown in FIG. Next, at step 102, if the engine is warming up, a correction amount F1 corresponding to the customer water temperature is calculated based on FIG. Further, in step 103, if the feedback control is being performed, the deviation correction amount F2 with respect to the target value is read, and the process proceeds to step 104. In this step 104, the total required amount F is calculated by summing the fuel required amount F0 and the correction amounts F1 and F2.
(F = F0 + F1 + F2) is calculated, and in step 105, the output is set to supply the fuel amount corresponding to this F to the engine.

FIG. 6 shows a flow of feedback processing corresponding to the above step 103. First, at step 200, it is judged whether or not the air-fuel ratio sensor 22 is active, and at step 201, the engine operating range can be fed back. It is determined whether it is a region. Then, when it is determined that the sensor 22 is active and is in the feedback possible region, the routine proceeds to step 202, where the value of the target air-fuel ratio according to the warm-up state is determined. This value coincides with “F = F1 + F2” and becomes the target value in the load region of the engine. Next in step 203 the current air-fuel ratio calculated from the output of the air-fuel ratio sensor 22 is obtained, and in step 204 this value is compared with the above target value to obtain the deviation, and the target air-fuel ratio and the current air-fuel ratio The correction amount F2 for leading the deviation between and to zero is calculated. When it is determined to be "NO" in steps 200 and 201, the process proceeds to step 205, and the correction amount F2 is set to "0". And
By using the correction amount obtained in this way,
The total required amount F can be obtained by the routine shown in FIG.

In the above embodiment, the target air-fuel ratio is continuously changed with respect to the water temperature, but the target air-fuel ratio may be changed stepwise so that the target air-fuel ratio changes above and below the water temperature of 70 ° C. .

In addition, although the warm-up state of the engine is detected by the cooling water temperature in the embodiment, the engine oil temperature may be used for this purpose.

As described above, according to the present invention, when the temperature of the engine is higher than normal, vapor is generated in the fuel, and even if the valve opening time of the fuel injection valve is constant, the amount of fuel injected into the cylinder Is not constant, the fuel injection amount varies and the control of the fuel injection amount becomes unstable, the air-fuel ratio fluctuates and misfire occurs, and a large amount of unfueled HC occurs,
Although the nitrogen oxide NOx may increase and the exhaust emission may deteriorate, in the present invention, when the engine is in a high temperature state, the air-fuel ratio is leaner than the normal state which is leaner than the theoretical air-fuel ratio. By performing feedback control to make the fuel richer and thinner than the stoichiometric air-fuel ratio, it is possible to reliably prevent misfire even if vapor occurs in the fuel, suppress the emission of unburned HC, and also generate NOx. Not only can it be suppressed, but also the generation of carbon monoxide CO can be suppressed satisfactorily, and there is an excellent effect that the deterioration of exhaust emission can be reliably prevented.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing an engine system for explaining an air-fuel ratio control device according to an embodiment of the present invention, and FIG. 2 is a configuration diagram explaining a control device used in the above embodiment,
FIG. 3 is a diagram for explaining a map of the target air-fuel ratio data stored in the ROM constituting the control device, FIG. 4 is a diagram for explaining the correction amount for the target air-fuel ratio, and FIG. 5 is a diagram for explaining the operation of the device. FIG. 6 is a flow chart for explaining the state, and FIG. 6 is a flow chart for explaining the feedback control state in the flow of the above operation. 11 …… Engine, 12 …… Air flow meter, 14 …… Throttle sensor, 16 …… Fuel injection valve, 22 …… Air-fuel ratio sensor,
24 …… Water temperature sensor, 27 …… Cylinder discrimination sensor, 28 …… Rotation angle sensor, 29 …… Control device.

Claims (4)

[Claims] 1. An air-fuel ratio sensor in which a detection signal is changed in an analog manner according to an air-fuel ratio, and a target air set in a side thinner than a theoretical air-fuel ratio corresponding to an engine operating state corresponding to an air-fuel ratio feedback region. Means for storing fuel ratio data, means for determining the engine warm-up state in the active state of the air-fuel ratio sensor, and when the engine temperature is higher than the normal warm-up temperature corresponding to the warm-up state , Means for storing corrected air-fuel ratio data that is richer than the normal target air-fuel ratio set to a side thinner than the theoretical air-fuel ratio and is higher than the theoretical air-fuel ratio, and reads out the target air-fuel ratio data corresponding to the operating state of the engine, Further, the corrected air-fuel ratio data corresponding to the warm-up state is read out, and the read-out target air-fuel ratio data is corrected by this corrected air-fuel ratio data to perform feedback control of the target air-fuel ratio. And an air-fuel ratio control device. 2. The air-fuel ratio control device according to claim 1, wherein the means for determining the warm-up state comprises a water temperature sensor for detecting a cooling water temperature of the engine. 3. The air-fuel ratio control device according to claim 1, wherein the means for determining the warm-up state is constituted by means for detecting the oil temperature of the engine. 4. The corrected air-fuel ratio data is set to a state richer than a normal target air-fuel ratio when the temperature of the engine is low, as claimed in claim 1, claim 2 or claim 3. The air-fuel ratio control device according to the item.