JP2001295686A - Engine air-fuel ratio control device - Google Patents

Abstract

(57) [Summary] [Object] To suppress variation in air-fuel ratio while suppressing variation in torque generated between cylinders. [Solution] A wide-range air-fuel ratio sensor provided for each cylinder detects an air-fuel ratio and sets a target. The shift amount with respect to the air-fuel ratio is calculated (S1, S2), and the valve timing of the electromagnetically driven intake / exhaust valve (mainly the closing of the intake valve) is adjusted so that the intake air amount is corrected based on the shift amount of the air-fuel ratio. Is controlled (S3, S4). Further, when the air-fuel ratio learning condition is satisfied, the corrected valve timing is updated and stored (S5, S6).

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 control of an engine, and more particularly to a technique for suppressing a variation in an air-fuel ratio while maintaining a constant generated torque for each cylinder.

[0002]

2. Description of the Related Art In a gasoline engine for a vehicle, an air-fuel ratio is controlled by controlling a fuel injection amount based on an intake air amount and an intake pressure. However, the air-fuel ratio may vary from cylinder to cylinder. .

Conventionally, in order to eliminate the variation in the air-fuel ratio of each cylinder, there has been proposed an apparatus in which an air-fuel ratio is detected for each cylinder and feedback control is performed. Similarly, since the air-fuel ratio is equalized by increasing or decreasing the fuel injection amount with respect to the intake air amount or intake pressure detected for each cylinder,
The fuel injection amount differs between cylinders, and the generated torque varies.

On the other hand, there is a type in which the valve timing of the intake / exhaust valve is variably controlled in accordance with the engine operating conditions. In particular, in the case where the intake / exhaust valve is of an electromagnetic drive type, the valve timing (mainly the intake valve closing timing) is controlled. ), It is possible to control the intake air amount for each cylinder.
-303122 etc.).

The present invention has been made in view of such a conventional problem, and is based on the control of the intake air amount for each cylinder.
It is an object of the present invention to provide an air-fuel ratio control device for an engine that suppresses variations in the air-fuel ratio while maintaining a constant generated torque for each cylinder.

[0006]

SUMMARY OF THE INVENTION Therefore, according to the present invention, in an engine capable of controlling the intake air amount for each cylinder, the fuel injection amount for each cylinder is detected while detecting the air-fuel ratio for each cylinder. The air-fuel ratio is controlled to the target air-fuel ratio by correcting and controlling the intake air amount for each cylinder while maintaining the same.

According to the first aspect of the present invention, if a change in operating conditions or a variation in characteristics between cylinders occurs while detecting the air-fuel ratio, a deviation occurs in the air-fuel ratio and the fuel injection amount. At this time, the amount of intake air is corrected and controlled while maintaining the same amount of fuel injection with the same amount of control of the fuel injection valve for each cylinder.

In this manner, by maintaining the same amount of fuel injection for each cylinder, it is possible to suppress variations in the air-fuel ratio by controlling the correction of the intake air amount while suppressing variations in the generated torque.

The invention according to claim 2 is characterized in that the intake air amount is corrected and controlled based on the difference between the air-fuel ratio detected for each cylinder and the target air-fuel ratio.

According to the second aspect of the present invention, when a difference between the air-fuel ratio detected for each cylinder and the target air-fuel ratio occurs due to a change in operating conditions or a change over time in characteristics, the deviation based on the air-fuel ratio is determined. To correct the intake air amount.

With this configuration, the intake air amount is corrected and controlled in accordance with the difference between the actual air-fuel ratio and the target air-fuel ratio, so that the air-fuel ratio can converge on the target air-fuel ratio with high accuracy.

The invention according to claim 3 is characterized in that the detection of the air-fuel ratio in the invention according to claim 2 is performed using a wide-range air-fuel ratio sensor.

According to the third aspect of the present invention, since the air-fuel ratio of each cylinder is detected in a wide range by using the wide-range air-fuel ratio sensor, the deviation between the detected air-fuel ratio and the target air-fuel ratio is obtained. be able to. Therefore, while performing normal air-fuel ratio feedback control for controlling the fuel injection amount with respect to the intake air amount detected commonly for each cylinder, the air-fuel ratio variation among the cylinders is controlled by first correcting the intake air amount. Can be corrected, and the air-fuel ratio can be switched while suppressing the torque fluctuation even when the target air-fuel ratio is switched.

According to a fourth aspect of the present invention, the air-fuel ratio of each cylinder is feedback-controlled to a reference air-fuel ratio, and the deviation of the fuel injection amount is determined for each operating region based on the deviation of the fuel injection amount from the reference value. Is corrected to control the intake air amount for each cylinder.

According to the fourth aspect of the invention, when the characteristics of the intake / exhaust valves change, when the air-fuel ratio of each cylinder is feedback-controlled to a reference air-fuel ratio (for example, a stoichiometric air-fuel ratio), the fuel injection amount is increased. A shift occurs with respect to the reference value for each area.

Therefore, the deviation of the fuel injection amount is obtained and the intake air amount for each cylinder is corrected and controlled so as to correct the deviation of the fuel injection amount. Variations in the torque generated between the cylinders can be suppressed in accordance with the reference value. Also, by correcting the intake air amount in accordance with the difference between the actual fuel injection amount and the reference value in the changed operation region even during the transition when the operating state changes, converging the fuel injection amount to the reference value, Good transient response can be ensured while suppressing changes in the air-fuel ratio.

According to a fifth aspect of the present invention, the air-fuel ratio of each cylinder is detected while detecting the air-fuel ratio in the fourth aspect of the present invention as rich or lean with respect to a reference air-fuel ratio using an oxygen sensor. Is feedback-controlled to the reference air-fuel ratio.

According to the fifth aspect of the present invention, even when the air-fuel ratio is detected using an oxygen sensor that detects the air-fuel ratio as rich or lean with respect to the reference air-fuel ratio, a change in characteristics or a deviation of the air-fuel ratio during transient operation is determined. As a result, it is possible to simultaneously suppress variations in the air-fuel ratio between the cylinders and the generated torque, and also satisfy transient operation performance.

The invention according to claim 6 is characterized in that the correction control amount of the intake air amount for each cylinder is learned and updated and stored for each operating region.

According to the invention of claim 6, the correction control amount of the intake air amount for each cylinder is learned for each operation region, the learned value is updated and stored, and the initial value is set when a new operation region is entered. By using this, the responsiveness of the air-fuel ratio control can be improved.

According to a seventh aspect of the present invention, the engine is provided with a variable valve timing means for varying the valve timing of the intake / exhaust valve for each cylinder, and the control of the intake air amount for each cylinder is performed by the valve timing. Suction by variable means
It is performed at the valve timing of the exhaust valve.

According to the seventh aspect of the present invention, the intake air amount can be variably controlled with good responsiveness in a portion closest to the combustion chamber by controlling the intake air amount based on the valve timing. Changes in the air-fuel ratio during operation can be absorbed with good responsiveness.

The invention according to claim 8 is characterized in that the variable valve timing means electromagnetically drives the intake / exhaust valve to vary the valve timing.

According to the eighth aspect of the present invention, the valve timing can be controlled in a wide range and with good responsiveness by using an electromagnetically driven intake / exhaust valve.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1 showing an entire configuration of an embodiment, an engine 1 mounted on a vehicle includes an electromagnetically driven intake valve 3 and an exhaust valve whose opening and closing are electronically controlled by a valve driving device 2 as a valve timing variable means. 4 is attached. A fuel injection valve 6 is mounted on an intake port 5 of each cylinder, and an ignition plug 8 and an ignition coil 9 are mounted on a combustion chamber 7.

FIG. 2 shows the structure of the valve driving device 2. In FIG. 2, a valve driving device 2 is provided integrally with a housing 21 made of a non-magnetic material provided on a cylinder head and a stem of an intake valve 3 (or an exhaust valve 4, hereinafter represented by the intake valve 3). An armature 22 that is freely movable in the armature 21 and an armature 22 that can draw the armature 22 and exert an electromagnetic force for closing the intake valve 3.
A valve-closing electromagnet 23 fixedly disposed in the housing 21 at a position facing the upper surface of the armature 22 and a lower surface of the armature 22 so as to exert an electromagnetic force for attracting the armature 22 and opening the intake valve 3. A valve-opening electromagnet 24 fixedly arranged in the housing 21 at an opposing position, a valve-closing-side return spring 25 for urging the armature 22 in the valve-closing direction of the intake valve 3, and a valve-opening direction of the intake valve 3 And a valve-opening-side return spring 26 for urging the armature 22 toward the valve. And when both the valve closing electromagnet 23 and the valve opening electromagnet 24 are demagnetized,
The spring force of the valve-closing-side return spring 25 and the valve-opening-side return spring 26 is set so that the intake valve 3 is located substantially at the center between the fully open position and the valve closed position. When excited, the intake valve 3 is closed, and when only the valve-opening electromagnet 24 is excited, the intake valve 3 is driven to open (fully open). In detail, before starting, the valve closing electromagnet 23 and the valve opening electromagnet
24 are alternately energized to resonate the armature 22 at a neutral position between the electromagnets, and the amplitude is increased so that the valve-closing electromagnet 23 is sufficiently close to the valve-closing electromagnet 23 or the valve-opening electromagnet 24. Alternatively, energization of the valve-opening electromagnet 24 is started, and the electromagnet 24 is attracted and held by one of the electromagnets. Thereafter, the energization of the electromagnet on the attraction side is cut off according to the opening and closing of the valve, and the armature 22 is moved by the biasing force of the return spring. As a result, the power of the electromagnet can be reduced, miniaturization and power consumption can be reduced, and fuel consumption can be reduced.

Returning to FIG. 1, an air flow meter 11 for detecting an intake air flow rate is mounted in the intake passage 10 at an upstream portion thereof.
An electronically controlled throttle valve 13 that is electronically controlled to an arbitrary opening degree via an actuator 12 is mounted on the downstream side. The electronically controlled throttle valve 13 is provided with a throttle opening sensor 14 for detecting a valve opening.

A crank angle sensor 15 which outputs a reference signal to the engine body at a reference crank angle of each cylinder and outputs a unit angle signal for each minute crank angle, a water temperature for detecting an engine cooling water temperature (hereinafter referred to as a water temperature). The sensor 16 is mounted.

An accelerator opening sensor 17 for detecting the amount of depression of the accelerator pedal (accelerator opening) is provided. On the other hand, a wide-range air-fuel ratio sensor 31 that detects the air-fuel ratio in a wide range based on the oxygen concentration in the exhaust gas and the like is attached to the exhaust port 30 of each cylinder.

The signals from the various sensors are output to a control unit 18, and the control unit 18
Based on these detection signals, a fuel injection signal is output to the fuel injection valve 6 to perform fuel injection control, an ignition signal is output to the ignition coil 9 to perform ignition control, and further, the actuator 12 is driven. In addition to controlling the opening of the electronically controlled throttle valve 13, a valve drive signal is output to the valve drive device 2 to control the opening and closing of the intake valve 3 and the exhaust valve 4.

Here, the control of the opening of the electronically controlled throttle valve 13 and the control of the valve timing of the intake and exhaust valves, in particular, the control of the closing timing of the intake valve 3 are performed based on the required torque based on the accelerator opening and the engine speed. Is controlled so that a target air amount commensurate with is obtained. That is, the electronically controlled throttle valve 13 is controlled so that the opening degree increases in accordance with an increase in the target air amount (required torque). However, the throttle control is performed only in the low / medium load region where the target air amount is less than the predetermined value. Then, the intake air pressure is generated to perform a control requiring an intake air negative pressure such as purge of evaporative fuel or EGR. It is controlled to keep it near.

The air-fuel ratio is feedback-controlled to the target air-fuel ratio for each cylinder based on the air-fuel ratio detected by the air-fuel ratio sensor 31 of each cylinder, and the fuel injection amount between the cylinders is kept constant. -By controlling the valve timing of the exhaust valve (mainly the closing timing of the intake valve), control is performed to suppress the variation in the air-fuel ratio while suppressing the variation in the generated torque.

Hereinafter, the air-fuel ratio control will be described with reference to the flowchart of FIG. In step 1, the air-fuel ratio is detected for each cylinder based on the signal from the air-fuel ratio sensor 31 of each cylinder.

In step 2, the deviation of the actual air-fuel ratio detected for each cylinder from the target air-fuel ratio is calculated. Here, the shift margin is calculated as a positive or negative value according to the rich / lean direction with respect to the target air-fuel ratio.

In step 3, the valve timing of the intake / exhaust valve for each cylinder (mainly the closing timing of the intake valve) is adjusted so that the intake air amount is corrected based on the calculated air-fuel ratio deviation.
Is corrected. Specifically, as the deviation of the air-fuel ratio from the target air-fuel ratio to the rich (lean) side becomes larger, the intake air is corrected by shifting the closing timing of the intake valve to the lower dead center side (top dead center side). Decrease (increase) the volume.

In step 4, the intake and exhaust valves are controlled in accordance with the corrected valve timing. Thus, the deviation of the air-fuel ratio from the target air-fuel ratio for each cylinder is corrected, and the variation in the air-fuel ratio between the cylinders is suppressed. On the other hand, the fuel injection amount is controlled to the common fuel injection amount so as to have the target air-fuel ratio based on the common intake air amount detected by the air flow meter 11, so that the variation in the torque generated between the cylinders can be avoided. .

Also, when the target air-fuel ratio is switched, the target air amount is switched, and at the same time, the deviation of the air-fuel ratio is adjusted by the intake air amount, thereby preventing a rapid change in the fuel injection amount. Torque fluctuation can be suppressed.

When the wide-range air-fuel ratio sensor is used as described above, it is possible to quantitatively detect the deviation from the target air-fuel ratio and thus correct it with high accuracy. , The valve timing may be corrected by a fixed amount at a time in accordance with the increase / decrease correction of the intake air amount.

Basically, the flow may be ended by this. However, in order to suppress the variation of the air-fuel ratio with good responsiveness,
The following air-fuel ratio learning is performed. In step 5, it is determined whether conditions for performing the air-fuel ratio learning such as a stable operation state are satisfied.

If not, the flow ends.
When the condition is satisfied, the process proceeds to step 6. In step 6, the corrected valve timing (mainly the intake valve closing timing) in the operating region determined by the current intake air amount and the engine rotation speed is set in the RAM of the microcomputer constituting the control unit 18. It is updated and stored as a learning value in the corresponding operation area of the map. Then, the next time the vehicle enters the same operation range, the intake air amount control by valve timing control is performed with the learning value as an initial value, and when a new air-fuel ratio learning condition is satisfied, the learning is performed and updated and stored.

This makes it possible to absorb variations in the air-fuel ratio with good responsiveness. Next, a second embodiment will be described. In this embodiment, the air-fuel ratio is detected as rich / lean with respect to the stoichiometric air-fuel ratio (reference air-fuel ratio) by using an oxygen sensor (indicated as 21 'in FIG. 1) instead of the wide-range type air-fuel ratio sensor. Applies to those that perform feedback control on the stoichiometric air-fuel ratio. The rest of the hardware configuration is the same as in the first embodiment.

In the present embodiment, it is not possible to directly detect the deviation from the stoichiometric air-fuel ratio, which is the target air-fuel ratio, but it is possible to suppress the variation in the air-fuel ratio between the cylinders, the variation in the generated torque, and the transient. The deviation of the air-fuel ratio at the time can be detected and corrected indirectly.

Hereinafter, the air-fuel ratio control of this embodiment will be described with reference to the flowchart of FIG. Step 11
Then, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio based on the signal from the oxygen sensor for each cylinder.

In step 12, the air-fuel ratio feedback correction coefficient α is averaged. In step 13, a deviation Δα between the averaged air-fuel ratio feedback correction coefficient α and the reference value α0 is calculated. Here, the reference value is set when the fuel injection amount is controlled so as to be a stoichiometric air-fuel ratio with respect to the intake air amount detected by the air flow meter, that is, the feedback correction amount is set to a value corresponding to 0. . Therefore, the deviation Δα is caused by a deviation of the actual fuel injection amount from the fuel injection amount corresponding to the stoichiometric air-fuel ratio due to a deviation of the actual intake air amount to the cylinder from the intake air amount detected by the air flow meter. It is caused by things. That is, the deviation Δα is calculated as a value corresponding to a deviation of the actual fuel injection amount from the fuel injection amount corresponding to the stoichiometric air-fuel ratio (reference air-fuel ratio).

In step 14, the valve timing (mainly the closing timing of the intake valve) for each cylinder is corrected so that the intake air amount is corrected according to the deviation Δα. Specifically, as Δα is a positive (negative) value, the fuel injection amount is increased (decreased) and corrected, and the intake air amount of the cylinder is increased (decreased) from the value detected by the air flow meter. Therefore, to correct this, for example, a correction is made to shift the closing timing of the intake valve to the top dead center side (bottom dead center side).

In step 15, the intake and exhaust valves are controlled according to the corrected valve timing. As a result, the air-fuel ratio is fed back to the stoichiometric air-fuel ratio for each cylinder, and at the same time, the deviation of the fuel injection amount is also corrected, so that the variation in the generated torque between the cylinders can be suppressed. , The valve timing may be simply corrected by a fixed amount in accordance with the sign of the difference Δα.

Further, similarly to the first embodiment, basically, the flow may be terminated by this, but the following learning is performed to improve the responsiveness at the time of transition. Step 16
Then, it is determined whether or not conditions for performing air-fuel ratio learning such as a stable operating state are satisfied.

If not, the flow is terminated,
When the condition is satisfied, the process proceeds to step 6. In step 17, the corrected valve timing (mainly the intake valve closing timing) in the operation region determined by the current intake air amount and the engine rotation speed is learned in the corresponding operation region of the map set in the RAM. Update and store as a value. And
The next time the vehicle enters the same operation region, the intake air amount control by valve timing control is performed with the learning value as an initial value, and when a new learning condition is satisfied, the learning is performed and updated and stored.

As a result, the air-fuel ratio and the target torque can be followed with good responsiveness even during a transition. Particularly, since the intake air amount is controlled at the position closest to the combustion chamber by controlling the valve timing and the system is of an electromagnetic drive type, substantially the same responsiveness as in learning a normal fuel injection amount can be secured.

In the above embodiment, the air-fuel ratio sensor or the oxygen sensor is provided for each cylinder to detect the air-fuel ratio for each cylinder. However, although the accuracy is inferior, one air-fuel ratio sensor is provided downstream of the exhaust manifold. A configuration in which a fuel ratio sensor or an oxygen sensor is provided, and a time delay in which combustion exhaust gas from each cylinder reaches the sensor is predicted based on an engine rotation speed, an intake air amount, and the like, and an air-fuel ratio for each cylinder is detected by timing control. Well, cost can be reduced.

Further, strictly speaking, variations in the characteristics of the fuel injection valve for each cylinder can be considered. Therefore, by applying the present invention after correcting the variations (correction by measurement or the like before shipping), it is possible to achieve a higher level. Variation in accuracy can be suppressed.

The means for variably controlling the intake air amount for each cylinder may be a means for variably controlling the valve timing, or a means for variably controlling the valve lift amount in an electromagnetically driven intake / exhaust valve. .

[Brief description of the drawings]

FIG. 1 is a system configuration diagram according to an embodiment.

FIG. 2 is a sectional view showing a configuration of a valve driving device used in the embodiment.

FIG. 3 is a flowchart showing an air-fuel ratio control routine in the embodiment.

FIG. 4 is a flowchart illustrating an air-fuel ratio control routine according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 2 Valve drive 3 Intake valve 4 Exhaust valve 18 Control unit 21 Air-fuel ratio sensor 21 'Oxygen sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 320 F02D 41/04 320 (72) Inventor Hatsugu Nagaishi 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan F-term (reference) within Automobile Co., Ltd. HC09Z HD05X HD05Z HD07X HD07Z HE03Z HE08Z HF08Z 3G301 HA01 HA06 HA13 HA19 JA04 JA05 JA15 JA17 KA11 LA03 LA07 LB02 LC01 MA01 ND01 ND22 NE13 NE14 NE15 PA01Z PA07Z PA11Z PB03Z PD03A PD03Z PD04 PE03Z10 PDZPE03Z08

Claims (8)

[Claims] In an engine capable of controlling an intake air amount for each cylinder, an intake air amount for each cylinder is corrected and controlled while maintaining the same fuel injection amount for each cylinder while detecting an air-fuel ratio for each cylinder. An air-fuel ratio control device for an engine, wherein the air-fuel ratio is controlled to a target air-fuel ratio. 2. An air-fuel ratio control device for an engine, wherein an intake air amount is corrected and controlled based on a difference between an air-fuel ratio detected for each cylinder and a target air-fuel ratio. 3. The air-fuel ratio control device for an engine according to claim 2, wherein the detection of the air-fuel ratio is performed using a wide-range air-fuel ratio sensor. 4. An air-fuel ratio of each cylinder is feedback-controlled to a reference air-fuel ratio, and a deviation of the fuel injection amount for each cylinder is corrected based on a deviation of the fuel injection amount from a reference value for each operation region. 3. The air-fuel ratio control device for an engine according to claim 2, wherein the intake air amount is corrected and controlled. 5. While detecting the air-fuel ratio as rich or lean with respect to a reference air-fuel ratio using an oxygen sensor,
The air-fuel ratio control device for an engine according to claim 4, wherein the air-fuel ratio of each cylinder is feedback-controlled to a reference air-fuel ratio. 6. The engine idle engine according to claim 1, wherein the correction control amount of the intake air amount for each cylinder is learned and updated and stored for each operating region. Fuel ratio control device. 7. The engine includes valve timing variable means for varying valve timing of intake and exhaust valves for each cylinder.
7. The engine according to claim 1, wherein the control of the intake air amount for each cylinder is performed at a valve timing of an intake / exhaust valve by the valve timing variable unit. Fuel ratio control device. 8. An intake control system for an engine according to claim 7, wherein said variable valve timing means electromagnetically drives intake and exhaust valves to change valve timing.