JP2706300B2 - Engine air-fuel ratio control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an engine that feedback-controls an air-fuel ratio of an engine to a target air-fuel ratio.

<< Conventional Technology >> Conventionally, feedback control for controlling the air-fuel ratio of an engine to be constant has been performed (JP-B-61-56413, etc.). That is, an O ₂ sensor whose output voltage changes according to the air-fuel ratio is used as an air-fuel ratio sensor, and feedback control is performed toward an ideal air-fuel ratio (14.7) as a target value.

However, the O ₂ sensor has a considerable time delay until an electromotive force is generated after contact with the combustion gas. In addition, the responsiveness is different even when the air-fuel ratio is switched from lean to rich and vice versa. Due to such sensor characteristics, the O ₂ sensor may output a rich output signal or vice versa even though the air-fuel ratio has already shifted to the lean state. .

Therefore, the control set in advance certain delay time in anticipation of a response delay of the O ₂ sensor to stabilize, O ₂ at the transition point and then delay period elapse of the air-fuel ratio the air-fuel ratio has shifted from lean to rich The output signal from the sensor is compared with each other, and when these signals are in the same rich state, it is determined that the signal is rich and feedback control is performed, thereby suppressing the deviation of the air-fuel ratio.

<< Problems to be Solved by the Invention >> Conventionally, the delay period is simply set by considering only the response delay of the O ₂ sensor, and the relationship with the control gain is not considered.

According to the study of the inventor, for example, in the case of performing feedback control in a low-medium load engine operating state of a boost of 3500 to -150 mmHg, even in the same feedback zone, in the region where the intake air amount is small as in idle operation, fluctuation due to disturbance For example, the air-fuel ratio is deviated due to hunting in the fuel supply, the flammability changes, and vibration is sensed. Therefore, in such a region with a small amount of intake air, if the current air-fuel ratio is 15, if the difference is 1.3 minutes, which is the difference in order to correct the air-fuel ratio to the ideal air-fuel ratio, the control gain is increased and the control gain is corrected all at once. Stability will not be obtained. On the other hand, even in the middle load range, the engine output is relatively high in the region with a large intake air amount, so that the deterioration of the combustion stability due to the fluctuation of the air-fuel ratio does not become a problem, but rather the control is performed more than in the idle operation. It is desirable to increase the gain to increase the control response.

Although changing the control gain in accordance with the operating state of the engine has an advantage in this way, if the delay period is set separately from the change in the control gain as described above, the feedback period is changed as in the case of shifting to high-speed operation. Air-fuel ratio control is stable, for example, when the control gain reflected in the control increases, the control amount overshoots on the rich side, and conversely, the air-fuel ratio shifts to the lean side when shifting to low / medium speed operation. There was a problem not to do.

The present invention has been made in view of such circumstances, and the delay time can be changed in accordance with a change in the control gain based on the engine operating state, and a deviation in the air-fuel ratio is prevented to ensure control stability. It is an object of the present invention to provide an engine air-fuel ratio control device that can be achieved.

<< Means for Solving the Problems >> According to the present invention, the output value changes across the stoichiometric air-fuel ratio, and the stoichiometric air-fuel ratio has a constant value on the rich side and a constant value on the lean side different from the rich side. And an air-fuel ratio sensor that outputs the air-fuel ratio sensor, and a delay period from when the output value of the rich-lean transition from the air-fuel ratio sensor changes until a predetermined time elapses. Air-fuel ratio determining means for determining a change in the air-fuel ratio when the output value after the delay period has elapsed is identical; gain setting means for presetting a control gain of the air-fuel ratio according to the operating state of the engine; Feedback control means for performing feedback control of the air-fuel ratio in accordance with the gain set by the gain setting means based on the determination signal from the fuel ratio determination means; A delay period changing means for changing the delay period to be shorter when the period is longer is provided.

<< Operation >> According to the present invention, the feedback value is set based on the control gain of the air-fuel ratio according to the operating state of the engine, and the delay period is changed. For example, when the control gain is increased, the delay time is shortened, and when the control gain is decreased, the delay time is increased. For example, the air-fuel ratio is corrected in accordance with the delay time. Therefore, when the delay time changes in accordance with the control gain, an excessive correction value in a high-speed operation range where the control gain is large,
Problems such as overshoot are prevented, and approach to the target air-fuel ratio can be performed quickly, thereby improving responsiveness. Therefore,
Appropriate air-fuel ratio control can be performed, and deviation of the air-fuel ratio can be prevented to ensure control stability.

<< Example >> Hereinafter, an example of the present invention is described with reference to drawings.

 FIG. 1 shows a schematic configuration of an engine system.

In the present invention, basically, the air-fuel ratio sensor 13 for detecting the rich / lean state of the air-fuel ratio, the output value from the air-fuel ratio sensor 13 at the time of the state change, and the output value after the delay period T has elapsed are the same. Air-fuel ratio determining means for determining a change in the air-fuel ratio
20, gain setting means 21 in which the control gain of the air-fuel ratio according to the operating state of the engine 1 is preset, and air-fuel ratio determination means 20
The feedback control means 22 performs feedback control of the air-fuel ratio in accordance with the gain set by the gain setting means 21 based on the determination signal from the control unit, and the delay period changing means 23 changes the delay period T according to the control gain. You.

Here, the air-fuel efficiency sensor 13 changes its output value across the stoichiometric air-fuel ratio, and outputs a constant value on the rich side with respect to the stoichiometric air-fuel ratio, and outputs a constant value on the lean side different from the rich side. . The air-fuel ratio determination means 20 is an air-fuel ratio sensor.
An air-fuel ratio sensor is provided with a delay period until a predetermined time elapses from the output value change time of rich-lean transition from 13
A change in the air-fuel ratio is determined when the output value at the time when the output value changes from 13 and the output value after the delay period has elapsed are the same. The delay period changing means 23 changes the delay period for the control gain of the air-fuel ratio so as to shorten the delay period when the control gain is large.

On the intake side of the engine 1, an air cleaner 2 and an air flow meter 3 are connected via a surge tank 4 and an intake pipe 5, and a fuel tank 6 and a fuel pump 7 are connected via a fuel supply pipe 8 and an injector 9. ing. An exhaust pipe is provided on the exhaust side of the engine 1.
An exhaust gas purifier 11 and a silencer 12 are connected via 10, and the exhaust pipe 10 is provided with an O ₂ sensor 13 as an air-fuel ratio sensor.

The air-fuel ratio controller 14 receives an intake air amount signal 101 from the air flow meter 3, an air-fuel ratio signal 12 from the O ₂ sensor 13, other engine speed signals 103, and signals such as intake air temperature and cooling water temperature. The fuel supply amount control signal 104 is output to the injector 9 based on the calculation.
Reference numeral 15 denotes a battery power supply.

FIG. 2 schematically shows a circuit configuration of the air-fuel ratio control device 14.

Air-fuel ratio control system 14, as shown in FIG. 2, O ₂ sensor 13
The air-fuel ratio determining means 20 for determining a change in the air-fuel ratio when a predetermined delay period has elapsed after the output of the engine has reached a predetermined determination value, and a gain for setting a control gain according to the operating state of the engine 1 Setting means 21 and a gain setting means for calculating a feedback value calculated based on the output of the air-fuel ratio determining means 20.
A feedback control unit 22 that performs feedback control of the air-fuel ratio by outputting based on the output of the output unit 21 and a delay period changing unit 23 that changes the delay period according to the control gain are provided. These are configured as a control program in this embodiment.

FIG. 3 is a flowchart showing the entire operation of the air-fuel ratio control device 14, FIG. 4 is a flowchart showing the details of the operation, and FIG. 5 is a time chart.

First, the flow of the entire fuel injection control will be described with reference to FIG.

After device startup, air flow meter, an engine speed sensor, O ₂ sensor, water temperature gauge, signal read (step a) from the intake air temperature meter or the like, calculation of the basic injection amount of fuel (Tp = Q · k /
N) is performed (step b). Here, Tp is the basic injection amount, Q is the intake amount, N is the engine speed, and k is a constant, which is determined by the input value of step a.

Next, a correction amount C is obtained (step c). Correction amount C
Is determined based on the cooling water temperature or the intake air temperature. Thereafter, the determination of the feedback zone is performed (step d), that is, a stable temperature state (for example, the cooling water temperature 70
(° C. or more), it is determined whether the zone is established or not. If this condition is satisfied and the zone is established, feedback control is performed 4 (step e), and the correction amount C and the feedback correction amount CFB are added to the previously obtained basic injection amount Tp.
The final injection amount Ti is obtained by multiplying the sum by (step f) and output to the injector 9 (step g).

If it is determined in step d that it is not the feedback zone, the feedback correction amount is set to zero (CFB =
0) (step h).

Next, a flow for determining the feedback correction value CFB will be described with reference to FIG.

As feedback control, PI control is performed, and P value and I value are changed depending on the engine speed by proportional and integral control. As described above, it is necessary to increase the responsiveness as the rotation speed increases. For this reason, both the P value and the I value are increased. Further, the delay time is changed according to the PI value.

In Figure 4, after the start, to set the PI value according to the engine speed (step i), followed by determination actual output A of the O ₂ sensor 13 is rich or lean (eg: A> 0.45 V)
(Step j). If rich (YES),
Previous O output A of the _second sensor 13 'is determined whether rich or lean (A'performs> 0.45 V) (step k). Here, if it is determined that this time the first rich (NO), PI
A delay period T according to the value is set (step 1),
The timer is decremented during this period T (step m). During this subtraction, an increment ΔI of the I value is added to the previous feedback correction value CFB (i−1) to shift the air-fuel ratio to the rich side (step n). . Thereafter, the current sensor output A is replaced by the previous sensor output A ', and the control is returned. Thus, when the previous air-fuel ratio state is lean, a flag described later is set to 0.

In the next loop in which the timer is being subtracted, if the rich state continues, steps i and k have elapsed, and the flag F is determined (step p). Here, the flag F is 0
(NO), it is then determined whether or not the timer is subtracting the delay period T (step q).
, The same processing as described above is continuously executed. On the other hand, if the delay period T has elapsed after the timer subtraction ends (YES), it is determined that the rich state has been maintained as a result, and in order to bring the air-fuel ratio closer to the ideal air-fuel ratio from the rich side, the previous time is determined. The required feedback correction value CFB is obtained by subtracting the control value P from the feedback correction value CFB (i-1) (step r). At this time, the flag F is replaced with 1 to indicate that the control is on the rich side. Further, when the air-fuel ratio is on the rich side, in order to gradually decrease the fuel from the judgment (YES) of the flag F in step p, the increment Δ
Control for subtracting I is executed.

Thereafter, when the air-fuel ratio shifts from rich to lean, steps k 'to s', n are executed.

Considering the time chart of FIG. 5, FIG.
When the air-fuel ratio shifts from the lean side to the rich side as shown in the above, the O ₂ sensor 13 outputs a predetermined electric signal as shown in FIG. D, and the timer is set as shown in FIG. The timer then counts down, and if the timer is still rich after the end of the timing, the flag F rises as shown in FIG. The feedback correction value CFB increases in accordance with the PI value as shown in FIG. 3E, but is first reduced by the P value with the rise of the flag F, and further gradually reduced in accordance with the I value. Here, conventionally, the air-fuel ratio is shifted by an error (region C) based on the delay period T when the I value is large (curve A) and when the I value is small (curve B). In the above embodiment, this PI
In addition to the setting of the value, the delay period T is further changed in accordance with the I value (gain), so that the feedback correction value CFB due to the I value set depending on the engine speed is suppressed from being excessive or too small. It has become. Therefore, for example, when the control gain is large, the delay time is short, and when the control gain is small, the delay time is long. For example, the correction of the air-fuel ratio is performed in correspondence with the delay period T. Therefore, since the delay time changes in accordance with the control gain, problems such as excessive correction values and overshoot in a high-speed operation range where the control gain is large can be prevented, and the approach to the target air-fuel ratio can be performed quickly, and the response can be improved. The performance is improved. Therefore, appropriate air-fuel ratio control can be performed, and a deviation in the air-fuel ratio can be prevented to ensure control stability.

<< Effects of the Invention >> As described above, according to the air-fuel ratio control apparatus for an engine according to the present invention, the delay time is changed in accordance with the change in the control gain of the air-fuel ratio based on the engine operating state. Thus, an excellent effect is achieved in that the air-fuel ratio control can be performed smoothly, the deviation of the air-fuel ratio can be prevented, and the control stability can be ensured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram, FIG.
The figure is a flowchart showing the detailed operation, and FIG. 5 is a time chart showing the operation. 1 ...... engine 13 ...... air-fuel ratio sensor (O ₂ sensor) 20 ...... air determining means 21 ...... gain setting means 22 ...... feedback control means 23 ...... delay period changing means

Claims (1)

(57) [Claims] An air-fuel ratio sensor that changes its output value across a stoichiometric air-fuel ratio and outputs a constant value on the rich side and a constant value on the lean side different from the rich side with respect to the stoichiometric air-fuel ratio. Providing a delay period from when the output value of the rich / lean transition from the air-fuel ratio sensor changes until a predetermined time elapses,
Air-fuel ratio determining means for determining a change in the air-fuel ratio when the output value from the air-fuel ratio sensor at the time of the output value change and the output value after the delay period have elapsed are determined. Gain setting means for setting a control gain of the air-fuel ratio in advance; feedback control means for feedback-controlling the air-fuel ratio in accordance with the gain set by the gain setting means based on a determination signal from the air-fuel ratio determining means; An air-fuel ratio control device for an engine, comprising: a delay period changing unit that changes the delay period to shorten the delay period when the control gain is large.