JPS63219842A - Air-fuel ratio controlling method - Google Patents

Abstract

PURPOSE:To trace the appropriately set target of air fuel ratio and maintain it in the air fuel ratio feedback control system by calculating a feedback gain by an I-PD control mechanism. CONSTITUTION:A reference fuel calculator 2 calculates a reference fuel injection amount Tp according to an intake air quantity Q3 and a revolution number N using a formula of K1Q3/N (K1 meaning a constant) and also calculates an injection pulse width T1 according to both feedback gain alpha from an I-PD control mechanism 3 and battery compensating pulse width TS using a formula of T1=KQ3/N.alpha+TS. Using an error between both value (c) obtained by dividing the counted air fuel ratio by a theory air fuel ratio and a value (r) obtained by dividing the target air fuel ratio by the theory air fuel ratio, the I-PD control mechanism 3 arithmetically operates an I control element Ialpha via an I operation element 31, also arithmetically operates both the P control element Palpha and the D control element PD via the P operation part 32 and the D operation part 33, and generates a feedback gain (alpha).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electronic fuel injection control device, and particularly to an air-fuel ratio control method suitable for performing feedback control of the air-fuel ratio over the entire operating range.

[Conventional technology]

The conventional air-fuel ratio feedback correction is as follows: Toyota Corona New Model Car Manual (October 1982) 3-71 [Problems to be Solved by the Invention] The above conventional technology requires that the air-fuel ratio be controlled to be close to the stoichiometric air-fuel ratio. This is good sometimes, but consider setting the target value of the air-fuel ratio not only to the stoichiometric air-fuel ratio but also to an arbitrary value during warm-up, acceleration, fuel cut, etc. to control torque output and fuel consumption. Therefore, there was a problem that feedback correction could not be performed appropriately when the target air-fuel ratio was set arbitrarily.

Since the air-fuel ratio sensor measures the oxygen concentration in exhaust gas, there is a delay between when fuel is injected and when the air-fuel ratio is measured. This delay changes depending on the operating condition of the engine. Therefore, the feedback gain (parameter) needs to be changed depending on the operating state of the engine.

The main purpose of the air-fuel ratio feedback correction is to maintain and stabilize the measured air-fuel ratio at the target air-fuel ratio. In normal PID control, which is often used in conventional process control, there may be a jump in the fuel injection amount, which is the manipulated variable, when the target air-fuel ratio setting is changed, so some kind of ingenuity is required for air-fuel ratio control. It is.

Furthermore, there is a problem in that the parameters of each of the P action, the mechanical action, and the D action required when performing PID control must be set in some way.

An object of the present invention is to provide an air-fuel ratio feedback correction control system when using a wide-range linear air-fuel ratio sensor for exhaust gas.

[Means for solving problems]

In order to achieve the above object, a feedback gain is calculated based on the I-PD control method, and the basic fuel injection pulse width is multiplied by the feedback gain to perform air-fuel ratio feedback correction.

In the I-PD control method, in order to reduce the influence of noise on the D operation, a method is used in which the slope of the control amount is averaged.

Furthermore, a method is provided in which the parameters of the P, I, and D operations are set by changing the target air-fuel ratio in steps from the normal operating state and from the corresponding air-fuel ratio response.

[Effect]

When calculating the feedback gain of the air-fuel ratio, it is determined by an I-PD control mechanism that leaves only the I operation in the main loop and forms the P operation and D operation as separate loops, and corrects it as follows using the obtained feedback gain. do.

Q&T1=KX-・α+Ts...(1) Here, Q heat: Intake air amount N: Engine speed KI: Constant α determined by injector characteristics: Feedback gain Ts: Battery correction pulse width T1: Injection pulse width TP: Basic fuel injection pulse width As a result, the target value of the air-fuel ratio is reflected in the feedback gain α without affecting the basic injection pulse width, and since the feedback gain α is formed by the I-PD control mechanism, stabilization Uke can have a function.

〔Example〕

An embodiment of the present invention will be described below. First, an overview of the configuration and operation of the embodiment will be explained with reference to FIG.

The basic fuel injection pulse width is determined from the measured intake air amount Q& and engine speed N as follows.

a T p = K r - (2) Here, Kr is a constant determined by the characteristics of the injector, and also includes a coefficient calculated to achieve the stoichiometric air-fuel ratio (A/F). In FIG. 1, the knee PD control mechanism 3 operates as follows. The measured air-fuel ratio A/F is calculated as the stoichiometric air-fuel ratio (
A/F) and normalize the control amount as follows.

The value obtained by dividing the target air-fuel ratio (A/F) r by the stoichiometric air-fuel ratio is determined as r (hereinafter referred to as target value) as follows.

From the deviation between the target value r and C, the control component (1) is calculated as follows through the machining operation 31 in FIG.

E(k)=Iα(k-1)+I(k)・E(k)・
...(5) Here, E(k): I component at time (I component value calculated at time by I operation unit 31 in FIG. 1) E(k)=r(k)-c (k) (k): I operation parameters The P operation unit 32 in FIG. 1 performs the P operation as follows.

Pα(k)=Px(k)・C(k)・
(6) Here, Pα(k): P component at time Pg(k): P operation parameter The D operation unit 33 in FIG. 1 performs the D operation as follows.

Dα(k) = D(C(k) −〇(k−1))
...(7) Here, Dα(k): D at time
Component Dsc(k): Feedback gain α(k) is obtained as follows from the components α(k), Pα(k), and Dα(k) obtained above the D operating parameter.

α(k)=Iα(k)−(Pα(k)+Dα(k))・
(8) In this way, in the I-PD control mechanism, the machining operation is the main loop, and the remaining P operations are in the form of a sub-loop.

Using the feedback gain α(k) obtained by the I-PD controller @3 in FIG. 1, the basic fuel injection pulse width is corrected as follows to determine the injection pulse width.

T*=Tp・a 10Ts - (9) As mentioned above, in order to improve the control performance, 1-I, P, and D operating parameters in the PD control mechanism 3 are set to the second
As shown in Figures (a), (b), and (c), the table is maintained in advance in the form of a table representing engine operating conditions.In this embodiment, the axis of the table is the engine speed N and the intake air amount Q&. be.

Search the table from the engine rotational speed N(k) and intake air amount Q,(k) operating at time k, and calculate the I, P, and D operating parameters at each time (k).

Obtain PK(k) and DK(k).

Next, how to determine the values of the I, P, and D operating parameters will be explained. As shown in Figure 3, until time 0, r
=1.0 is set as the target value, and the target value is changed in steps at k=o. In the change in air-fuel ratio measured at this time, ΔC(k) of step response C(k) = C:(k)-C
(k-1) ... (10) Find the maximum value ΔC, tax among the changes, and calculate the slope R as R:! :ΔCmax
/t-(11) where τ: obtained as sampling synchronization. Further, by extending the straight line of slope R to the left as shown in Fig. 3, a delay L is obtained at the point where it intersects with the line of r=1.0.

In this way, this step response is measured under all engine conditions (all combinations of Q and N), and R and L are determined.

Next, from the obtained R and L, I and P are obtained as follows.

D Calculate operating parameters.

Rτ In the manner described above, the values of the three tables shown in FIG. 2 are determined.

Noise is added to the air-fuel ratio measured by the sensor, and the D operation may disturb controllability. As a countermeasure, (7)
When determining the difference between the control amounts C(k) and C(k-1) in the equation, the average value of the differences at the following four points is used.

ΔC(k) = C(k)-C: (k-1) where, te=
-(c(k)+c(k-1)+C(k-2)+C(k-
3)) [Effects of the Invention] According to the present invention, even if the target value of the air-fuel ratio is changed, the I-
Since the target air-fuel ratio can be achieved through feedback correction of the PD@control mechanism, there is an effect that the target air-fuel ratio can be set arbitrarily.

This has the effect of increasing the target air-fuel ratio to increase torque output in driving ranges where torque output is desired, and reducing the target air-fuel ratio during deceleration when no torque is needed to improve fuel efficiency.

By using the I-PD control mechanism, the air-fuel ratio can be maintained and stabilized, improving exhaust gas performance during steady driving.
This has the effect of improving drivability because variations in 1-lux are reduced.

Similarly, since the I, P, and D operating parameters are searched and used according to the operating conditions, air-fuel ratios matching various operating modes can be obtained.

Further, even if measurement noise is added to the air-fuel ratio, the operation is performed to reduce the influence of the noise, which has the effect of suppressing deterioration of controllability due to noise.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a diagram showing an example of a table holding I, P, and D operating parameters, and FIG. 3 is a diagram showing a step response for determining the I, P, and D operating parameters. Kaya/Figure

Claims (1)

[Scope of Claims] 1. An air-fuel ratio control method in an engine electronic control system having an air-fuel ratio sensor, characterized in that a feedback gain is determined to follow and stably maintain an arbitrarily set target air-fuel ratio. 2. The air-fuel ratio control method according to item 1, wherein the feedback gain is calculated by an I-PD control mechanism. 3. I operation, P operation, and D in the above I-PD control mechanism
2. The air-fuel ratio control method according to item 2, wherein each operating parameter is changed depending on the engine state. 4. The air-fuel ratio control method according to item 3, characterized in that an average value of four-point differences in control amounts is used to calculate the difference in control amounts in the D operation.