KR20200069502A - Air fuel ratio control method - Google Patents

Abstract

The present invention relates to an air-fuel ratio control method for reducing exhaust gas through more robust fuel control using a rear oxygen sensor when maintaining a constant driving state for a long time. According to the present invention, the method comprises: a lambda offset value securing step of securing a lambda offset value according to the degree of deterioration of a catalyst when a driving situation, in which an engine load is kept constant, is determined; a correction target lambda value calculating step of calculating a correction target lambda value by adding the lambda offset value to a target lambda value required by the oxygen sensor behind the catalyst; and a correction feedback control step of performing feedback control so that an actual lambda value measured by the oxygen sensor behind the catalyst converges to the correction target lambda value.

Description

Air-fuel ratio control method {AIR FUEL RATIO CONTROL METHOD}

The present invention relates to an air-fuel ratio control method for reducing exhaust gas through more robust fuel control using a rear oxygen sensor when maintaining a constant driving state for a long time.

In the case of gasoline vehicles, fuel control logic using a front/rear oxygen sensor is used to respond to enhanced emissions.

In particular, the rear oxygen sensor measures the richness/leanness of the exhaust gas after the oxidation/reduction reaction in the catalyst to enable more precise fuel feedback control, and also corrects the change and deterioration of the front oxygen sensor to help reduce emissions. Gives

Fuel control using the rear oxygen sensor is performed through PID control when a difference between a target lambda value and a measured lambda value required by the rear oxygen sensor occurs. At this time, the PID control value reduces the exhaust gas by moving the stoichiometric point of the front oxygen sensor to change the overall exhaust gas richness/leanness.

That is, PID control is performed so that the lambda value of the rear oxygen sensor is maintained in the region where the exhaust gas is the best, and an appropriate gain amount and deadband value are set at this time.

However, in the area where the variation in the amount of oxygen loaded in the catalyst is small, such as general driving conditions that include acceleration/deceleration of the vehicle, the effect of the exhaust gas is relatively affected because the catalyst plays a damping role even if the gain/deadband value is not optimized. not big.

However, in a driving condition that maintains a constant driving state for a long time, such as a cruise on a highway, when the oxygen amount is loaded in excess of the catalyst limit because the amount of oxygen loaded in the catalyst is continuously biased in one direction, the exhaust gas A problem occurs in which the amount of generated is rapidly increased.

The above descriptions as background arts are only for improving understanding of the background of the present invention, and should not be taken as an admission that they correspond to the prior arts already known to those skilled in the art.

KR 10-2011-0116581 A

The present invention has been made to solve the problems as described above, and when maintaining a constant driving state for a long time, to provide an air-fuel ratio control method for reducing exhaust gas through more robust fuel control using a rear oxygen sensor. .

The configuration of the present invention for achieving the above object, the controller determines the lambda offset value securing a lambda offset value according to the degree of deterioration of the catalyst, when the engine load is determined to be a constant driving condition; A correction target lambda value calculating step of calculating a correction target lambda value by adding the lambda offset value to a target lambda value required by the controller at the oxygen sensor behind the catalyst; And a correction feedback control step in which the controller feedback-controls the actual lambda value measured by the oxygen sensor behind the catalyst to converge to the correction target lambda value.

By checking the engine speed and the amount of intake air, when the rate of change of the engine speed and the rate of change of the amount of intake air are equal to or less than a predetermined value above a certain vehicle speed, it can be determined as a driving situation in which the load of the engine is kept constant.

In the step of securing the lambda offset value, when the rate of change of the engine speed and the rate of change of the intake air amount are equal to or less than a predetermined vehicle speed, the cumulative intake air amount per unit time of the intake air amount and the target lambda value and the actual lambda value error is a lambda error. Calculating a cumulative lambda error value per unit time of the value; Calculating a fuel correction factor by multiplying the cumulative suction air amount and a cumulative lambda error value; It may include; when the absolute value of the fuel correction factor exceeds a certain value, the lambda offset value is determined by a function of the degree of catalyst degradation.

In the step of securing the lambda offset value, when the rate of change of engine speed or the rate of change of intake air exceeds a predetermined value, feedback control may be performed so that the actual lambda value converges to the target lambda value.

After the correction feedback control step, if the actual lambda value measured by the rear oxygen sensor is out of a predetermined range, feedback control may be performed so that the actual lambda value converges to the target lambda value.

The present invention through the above-described problem solving means, by controlling the feedback so that the actual lambda value measured by the rear oxygen sensor converges the correction target lambda value, the oxygen loading amount in the catalyst is maintained at an appropriate level, thereby generating the amount of exhaust gas. This has the effect of preventing the rapid increase.

In addition, by correcting the lambda offset value considering the deterioration degree of the catalyst by reflecting it in the target lambda value, the correction control time point and the amount of correction are differentiated according to the catalyst deterioration degree, and thus, emissions that may occur depending on the deviation and deterioration degree of the catalyst It is also possible to appropriately respond to the strengthened emission regulations by reducing gas deviation.

1 is a view showing an example of a system configuration for air-fuel ratio control according to the present invention.
2 is a view showing the flow of the air-fuel ratio control process according to the present invention.

If described in detail with reference to the accompanying drawings, preferred embodiments of the present invention.

1 shows an air-fuel ratio control system applied to the present invention. Referring to the drawings, a catalyst 1 (ex: a three-way catalyst) is provided on an exhaust line, and the front and rear ends of the catalyst 1 are provided. The front oxygen sensor 3 and the rear oxygen sensor are provided.

Then, the front oxygen sensor 3 and the rear oxygen sensor 5 is connected to the controller (CLR), the output value measured at each oxygen sensor is input to the controller (CLR), the controller (CLR) engine speed and The amount of intake air is input, so that the driving state of the vehicle can be determined.

On the other hand, the present invention is a method for controlling the air-fuel ratio using the air-fuel ratio control system, and includes a lambda offset value calculating step, a lambda value calculating step, and a correction feedback control step.

Referring to FIGS. 1 and 2, first, in the step of securing the lambda offset value, when it is determined as a driving situation in which the load of the engine is kept constant through the controller CLR, the lambda according to the degree of deterioration of the catalyst 1 The offset value is secured.

At this time, the engine speed and the amount of intake air can be used as conditions for determining whether the engine load is a driving situation in which the load is kept constant.

That is, by checking the engine speed and the amount of intake air, when the rate of change of the engine speed is equal to or less than a certain value at a predetermined vehicle speed or higher, and the rate of change of the amount of intake air is equal to or less than the predetermined value, it is determined as a driving situation in which the engine load is kept constant. .

In addition, in the step of calculating the target lambda value, the controller CLR calculates the target lambda value by adding the lambda offset value to the target lambda value required by the oxygen sensor behind the catalyst 1. Here, the target lambda value may be a value obtained by adding a feedback control amount to an actual lambda value.

In the correction feedback control step, the controller CLR feedback-controls the actual lambda value measured by the oxygen sensor behind the catalyst 1 to converge to the correction target lambda value.

That is, in general, in the case of an operation condition in which acceleration/deceleration is repeated, feedback control is performed such that the measured lambda value of the rear oxygen sensor 5 converges the target lambda value.

However, in this process, if a driving condition that maintains a constant driving condition for a long time, such as cruise driving on a highway, is satisfied, the target lambda is added to the target lambda value by adding a lambda offset value (+/-) that reflects catalyst deterioration. By correcting the value, a new correction target lambda value is calculated.

Accordingly, by controlling the actual lambda value measured by the rear oxygen sensor 5 to converge the correction target lambda value, the oxygen loading amount in the catalyst 1 is maintained at an appropriate level, and thus the amount of generated exhaust gas It prevents a sharp increase.

In addition, with reference to FIG. 2, the method for securing the lambda offset value will be described in detail. When the engine speed change rate and the change rate of the intake air amount are less than or equal to a predetermined value at a predetermined vehicle speed or more, the accumulated amount of the intake air amount per unit time The intake air amount is calculated, and the cumulative lambda error value per unit time of the lambda error value which is an error between the target lambda value and the actual lambda value is calculated. This can be expressed as Equation (1) and Equation (2) below.

Cumulative suction air volume (kg/h) = suction air volume (n-1) + suction air volume (n)......(1)

Accumulated lambda error value = lambda error value (n-1) + lambda error value (n-1) .....(2)

Then, the fuel correction factor is calculated by multiplying the cumulative suction air amount and the cumulative lambda error value. This can be expressed as Equation (3) below.

Fuel correction factor = cumulative suction air amount × cumulative lambda error value............(3)

Subsequently, when the absolute value of the fuel correction factor exceeds a certain value, the lambda offset value can be determined as a function of the degree of catalyst deterioration. Here, the lambda offset value may be a predetermined value as a function of the degree of catalyst degradation, and a method for detecting the degree of catalyst degradation will be omitted by a known technique.

Lambda offset value = f (Catalyst OSC)

OSC: Oxygen Storage Capacity

That is, since the generation time of the exhaust gas is different depending on the degree of deterioration of the catalyst 1, the correction and control time according to the degree of catalyst deterioration by correcting the lambda offset value considering the deterioration degree of the catalyst 1 to be reflected in the target lambda value The over-correction amount is differentiated, and accordingly, the variation in the emission gas that may occur depending on the variation and the degree of deterioration of the catalyst 1 is reduced, thereby making it possible to appropriately respond to the strengthened emission regulation.

On the other hand, the present invention is configured to perform fuel control using the rear oxygen sensor 5 through the existing feedback control when the engine load is not a constant driving condition.

Specifically, in the step of securing the lambda offset value, when the rate of change of the engine speed or the rate of change of the intake air exceeds a predetermined value, feedback control is performed so that the actual lambda value converges to the target lambda value.

In addition, after the correction feedback control step, if the actual lambda value measured by the rear oxygen sensor 5 is out of a predetermined range, feedback control may be performed so that the actual lambda value converges to the target lambda value.

Of course, in this case, the accumulated values accumulated in Equations (1) and (2) are all initialized, and the same control as the existing feedback control logic is performed.

Hereinafter, the air-fuel ratio control method according to the present invention will be sequentially described.

Referring to FIG. 2, first, the engine speed, the intake air amount, and the measured lambda value and the target lambda value of the front and rear oxygen sensors 5 are input from the controller CLR (S10), and the input rear oxygen sensor 5 is input. The difference between the target lambda value and the actual lambda value is calculated to obtain a lambda error value (S20).

Subsequently, it is determined whether the rate of change of the engine speed is less than A and the rate of change of the intake air amount is less than B (S30).

As a result of the determination of S30, if these conditions are satisfied, the cumulative suction air amount is calculated by accumulating the intake air amount per unit time, and the cumulative lambda error value per unit time is calculated to calculate the cumulative lambda error value (S40).

Then, the fuel correction factor is calculated by multiplying the calculated cumulative suction air amount and the cumulative lambda error value (S50).

Subsequently, it is determined whether the calculated absolute value of the fuel correction factor exceeds C (S60), and when the determination result of S60 exceeds C, a lambda offset value determined by a function of catalyst deterioration is secured (S70).

Thereafter, the actual measured lambda value measured by the rear oxygen sensor 5, the feedback control amount (a feedback control amount required to converge the existing target lambda value), and the lambda offset value are summed to calculate a new correction target lambda value. (S80).

Accordingly, the fuel is feedback-controlled so that the actual lambda value measured by the rear oxygen sensor 5 converges the correction target lambda value (S90).

Subsequently, it is determined whether the measured lambda value measured by the rear oxygen sensor 5 is within a certain range between D and E (S100), and if it is within the above range, the process proceeds to step S70 to circulate.

However, when the measured lambda value measured by the rear oxygen sensor 5 deviates between D and E, the cumulative suction air amount and cumulative lambda error value calculated in step S40 are reset to 0 (S110).

Then, a target lambda value with a feedback control amount added to the measured lambda value is calculated (S120), and the fuel is feedback-controlled to converge the calculated target lambda value (S130).

As described above, the present invention provides feedback control so that the actual lambda value measured by the rear oxygen sensor 5 converges the correction target lambda value, thereby maintaining the oxygen loading amount in the catalyst 1 at an appropriate level and discharging it. The amount of gas generated is prevented from increasing rapidly.

In addition, by correcting the lambda offset value considering the deterioration degree of the catalyst 1 to the target lambda value, the correction control time point and the amount of correction are differentiated according to the catalyst deterioration degree, and thus the deviation and deterioration degree of the catalyst 1 Accordingly, it is possible to appropriately respond to the strengthened emission regulations by reducing the fluctuations in emissions that may occur.

On the other hand, the present invention has been described in detail only with respect to the specific examples described above, but it is obvious to those skilled in the art that various modifications and variations are possible within the technical scope of the present invention, and it is natural that such modifications and modifications belong to the appended claims. .

1: Catalyst
3: Forward oxygen sensor
5: rear oxygen sensor
CLR: Controller

Claims (5)

When the controller determines that the engine load is a constant driving condition, a lambda offset value securing step of securing a lambda offset value according to the degree of deterioration of the catalyst;
A correction target lambda value calculating step of calculating a correction target lambda value by adding the lambda offset value to a target lambda value required by the controller at the oxygen sensor behind the catalyst; And
And a correction feedback control step in which the controller feedback-controls the actual lambda value measured by the oxygen sensor at the rear of the catalyst to converge to the correction target lambda value. The method according to claim 1,
Air-fuel ratio control method, characterized in that by checking the engine speed and the amount of intake air, when the rate of change of the engine speed and the rate of change of the amount of intake air is less than or equal to a predetermined value at a predetermined vehicle speed or higher, the engine load is determined as a driving condition. The method according to claim 2,
The step of securing the lambda offset value,
When the rate of change of the engine speed and the rate of change of the intake air amount below a certain value above a certain vehicle speed, the accumulated intake air amount per unit time of the intake air amount and the cumulative lambda error value per unit time of the lambda error value which is an error between the target lambda value and the actual lambda value Calculating a;
Calculating a fuel correction factor by multiplying the cumulative suction air amount and a cumulative lambda error value;
And when the absolute value of the fuel correction factor exceeds a certain value, determining a lambda offset value as a function of the degree of catalyst deterioration. The method according to claim 3,
In the step of securing the lambda offset value, the air-fuel ratio control method characterized in that when the rate of change of the engine speed or the rate of change of the intake air exceeds a certain value, the actual lambda value is feedback-controlled to converge to the target lambda value. The method according to claim 3,
After the correction feedback control step, if the actual lambda value measured by the rear oxygen sensor is within a certain range, feedback control is performed so that the actual lambda value converges to the target lambda value.

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