JPH02211344A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To maintain the air-fuel ratio control precision at high level and accelerate the stabilization of revolution by fixing the feedback correction coefficient at 1.0 by suspending the air-fuel ratio feedback control for a certain time when the external load varies in idling operation and carrying out open loop control. CONSTITUTION:If air-fuel ratio feedback control is carried out in parallel when external load is increased by the turning-ON of an air conditioner switch, hunting is generated, and a long time is necessary for the convergence to an aimed revolution speed. Therefore, when the external load is varied, air-fuel ratio feedback control is suspended for a certain time by a control unit 20, and open loop control in which the feedback correction coefficient is fixed at 1.0 is carried out, and the variation of the revolution speed due to the air-fuel ratio control is excluded, and the convergence performance to the aimed revolution speed in the actual revolution speed is improved. In this case, the feedback correction coefficient is fixed at 1.0, and the control in the lean side or rich side direction can be carried out with high responsiveness when feedback control is restarted after the lapse of a certain time.

Description

DETAILED DESCRIPTION OF THE INVENTION ('fIi Industrial Application Field) The present invention relates to an air-fuel ratio control device for an engine.

(Prior art) In general, in engines, as shown in Fig. 6, air-fuel ratio control is performed in which the air-fuel ratio converges to the stoichiometric air-fuel ratio by feedback control of the fuel amount in a specific operating range in relation to engine load, etc. During operation, idle control is performed to converge the engine speed to a target speed set in accordance with the engine load by feedback control of the intake air amount.

However, in such a system in which the 1': idle control 9++ and the air-fuel ratio control are performed simultaneously, for example, when the target engine speed increases due to application of an external load, the engine performance is increased by increasing the amount of intake air and adjusting the mIA. Idle control is performed to increase the engine speed and converge it to the target engine speed, but on the other hand, since the engine speed fluctuates in relation to air-fuel ratio control, this air-fuel ratio control There was a problem in that hunting occurred due to the influence of rotational fluctuations caused by engine rotation, and it took time for the engine rotational speed to stabilize.

One way to deal with this problem is to stop feedback control of the air-fuel ratio during idle operation, as disclosed in Japanese Patent Publication No. 7051/1983, for example.

(Problem to be solved by the invention) However, if the feedback control of the air-fuel ratio is stopped during idling operation in this way, it is possible to stabilize the engine speed when an external load is applied during idling operation. However, there is a risk that the control accuracy of the air-fuel ratio will be greatly reduced and the emission characteristics will be adversely affected, and this cannot be said to be preferable from the viewpoint of the overall operating characteristics of the engine.

SUMMARY OF THE INVENTION Therefore, the present invention provides an engine air-fuel ratio control device that can effectively suppress engine rotational fluctuations due to changes in external load without significantly reducing air-fuel ratio control accuracy in the idling operating range. That is.

(Means for Solving the Problem) In the present invention, as a means for solving the problem, an air-fuel ratio control device for an engine that performs feedback control of the air-fuel ratio in a specific operating range of the engine is provided. , when the external load changes, the air-fuel ratio feedback control is stopped for a certain period of time from the external load change, and the feedback correction coefficient is fixed at 1.0 to perform open loop control. It is something to do.

(Function) In the present invention having such a configuration, (1) Since the feedback control of the air-fuel ratio is stopped for a certain period of time when the external load changes, the feedback control stop time in the air-fuel ratio control region is minimized as much as possible. (2) Since open-loop control is performed with the feedback correction coefficient fixed at 1.0 for a certain period of time after the external load changes, if feedback control is restarted after the certain period of time has elapsed, lean (3) When external load changes, air-fuel ratio feedback control is stopped and rotational fluctuations based on air-fuel ratio control are eliminated. Therefore, the rotation speed control by idle control is performed easily and efficiently, and hunting, overshoot, and undershoot of the rotation speed are suppressed as much as possible.

(Effects of the Invention) Therefore, according to the engine air-fuel ratio control device of the present invention, (+) The shortening of the air-fuel ratio feedback control period when external load changes can be suppressed to the shortest possible time, and the feedback control Since the responsiveness of air-fuel ratio control at the time of recovery is good, air-fuel ratio control accuracy is maintained at a high level. (2) Fluctuations in engine speed based on air-fuel ratio when external load changes are eliminated. Therefore, the engine speed can be easily and efficiently controlled by idle control, and the stabilization of the engine speed can be promoted.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 1 to 5.

FIG. 1 shows an intake/exhaust system diagram of an automobile engine equipped with an air-fuel ratio control device according to an embodiment of the present invention, in which reference numeral 1 is the engine, 2 is an intake passage, and 3 is an exhaust passage, 4 is an air cleaner, 5 is an air flow meter that detects the intake air m, 6 is a throttle valve, and the opening degree of the throttle valve 6 is determined by the throttle sensor 1.
Detected by 2. Also, 7 is a distributor that detects the engine speed, 8 is a crank angle sensor,
9 is the injector! 0 is a water temperature sensor, and lI is a 0 sensor that detects the degree of acidity in exhaust gas.

Furthermore, the intake passage 2 includes the throttle valve 6.
A bypass air passage 13 is provided to bypass the air, and this bypass air passage 13 is also provided with a bypass air valve 14 that opens and closes the bypass air passage 13 by duty control. This bypass air valve 14 opens and closes in response to a bypass air signal B from a control unit 20, which will be described later.
By increasing or decreasing the idling speed of the engine I, the idling speed of the engine I is increased or decreased and is made to converge to a predetermined target speed.

Further, the control unit 20 is for performing fuel control and rotation speed control, and the control unit 20 has an intake air amount signal A1, a throttle opening signal A, and an engine rotation speed signal as control element signals. A
3, a crank angle signal A4, a water temperature signal A, and an oxygen concentration signal A are input, respectively. Based on these input signals, this control unit outputs a fuel supply signal I3t and a bypass air signal B, respectively, to perform fuel supply control, air-fuel ratio control, and idle control.

Each of these controls will be explained later in the flowchart (
2 to 4), but prior to that, two types of control, air-fuel ratio control and idle control, will be specifically explained based on FIG. 5.

In this example, the operating region (air-fuel ratio feedback control zone, hereinafter referred to as 0.F'/n zone) where the intake air amount and engine speed are each below a predetermined value and the cooling water temperature is above a predetermined value. In addition to performing feedback control of the air-fuel ratio in the operating range where the engine speed is below a predetermined value and the throttle valve 6 is at idle opening (idle speed control zone, hereinafter referred to as the ISC control zone), feedback control of the engine speed is performed. It is designed to take control. Therefore, as shown in FIG. 5, in the ISC control zone, feedback control of the air-fuel ratio and feedback control of the engine speed may be performed simultaneously and in parallel. In this operating state where air-fuel ratio control and idle control are being performed in parallel using feedback control, if the external load increases due to, for example, turning on the air conditioner switch, the system will respond to the change in external load. As the target engine speed increases, the intake air m
is increased and the actual rotation speed of engine I is made to converge to the target rotation speed.In this case, if feedback control of the air-fuel ratio is performed in parallel, the engine rotation speed due to this air-fuel ratio control will be As described above, hunting occurs due to the influence of fluctuations, and it takes time for the actual rotation speed to converge to the target rotation speed. Therefore, in this embodiment, the present invention is applied, and when the external load changes, the feedback control of the air-fuel ratio is stopped for a certain period of time, and the feedback correction coefficient is fixed at a predetermined value. This eliminates fluctuations in engine speed due to engine speed changes, thereby increasing the convergence of the actual engine speed to the target engine speed. Furthermore, the feedback correction coefficient in this case is fixed at 1.0, so that when the feedback control is restarted after the above-mentioned certain period of time has elapsed, control can be performed with good responsiveness even in the direction of the lean side and the ridge side. This is what I did.

Hereinafter, the actual operations of each of the above controls will be explained according to the flowcharts shown in FIGS. 2 to 4.

In this embodiment, the control flow includes a main routine (see Figure 2) that performs startup control, and an interrupt subroutine (see Figure 2) that performs air-fuel ratio control and idle control.
(Fig. 3) and an interrupt subroutine (see Fig. 4) for controlling fuel supply.

In the main routine shown in Fig. 2, first, a basic fuel pulse +lJT p is given, which takes into account the increase in the amount of fuel at the time of starting. Output (step S,).Furthermore, the fuel feedback coefficient C
Set BF to 1.0 (i.e., do not perform fuel correction) and initialize the counter to 0 (
Step S,). Note that this counter is a timer for stopping the feedback control of the air-fuel ratio when the load changes.

Next, various elements that are prerequisites for control are read (step S4). Here, the output values of the water temperature sensor, throttle sensor, and O sensor are used to determine the engine operating status, and the 0N-01 of the air conditioner switch, headlamp switch, fan switch, and power steering switch are used to determine the external load application. ? 'Read each F signal. After the engine is started, these various elements are read repeatedly so that the latest information is always prepared.

In the subroutine shown in FIG. 3, air-fuel ratio control and idle control are performed. That is, first, after the interrupt, a change in the load switch from ON to OFF is determined (step Q).

As a result of the judgment, when there is a 0N-OFF' change in the load switch this time, the counter is set to a predetermined value (i.e., the time during which feedback control of the air-fuel ratio is stopped), and from then on, the counter is set to 0. The feedback correction coefficient CI? B is fixed at 1.0 and open loop control is performed (steps Q, Q5). On the other hand, as a result of the judgment, 0N-OF+? If there is no change (remains ON state or OI?F state), the counter is sequentially decremented until it reaches 0 (step Q). Therefore, when there is a change in external load, the feedback correction coefficient CFB is set to 1.0 regardless of whether it is in the O*F/B zone, and this prevents fluctuations in engine speed based on air-fuel ratio control. will be excluded.

On the other hand, when the above counter reaches 0 (that is, when it is possible to restart Fitoback control), first step Q
4, it is determined whether the zone is OtF/I3. This OFF'/[3 zone determination is made based on the intake air m, engine speed, and water temperature as described above. As a result of the determination, if the zone is not 0°F/[3, the feedback correction coefficient CFB is set to 1. Open loop control is performed by fixing the voltage to O (step Qa). On the other hand, 0! If it is determined to be in the F/n zone, P of the actual rotational speed CF'B with O and sensor output values as parameters.
・Perform I control (proportional/integral control) (step Q1)
.

Next, moving to idle control, first, in step Q6, it is determined whether or not it is in the ISO control zone, and if it is not in the IsC control zone, the duty of bypass air valve I4 is set to a predetermined fixed value. , outputs the duty (step Q,).

On the other hand, if it is determined that it is an ISO control zone,
In step Q,) to calculate the target engine speed based on the engine load condition, duty control (integral control) is performed using the deviation between the actual engine speed and this target speed as a parameter, and this is output. (Steps Q,,Qe).

In the subroutine shown in FIG. 4, the fuel supply amount is controlled. That is, first, at step P, the current actual rotational speed is read, and at step P.

Read the current intake air amount at . Then, the basic fuel pulse width 'rp is calculated from this actual rotation speed and intake air amount, and the basic fuel pulse width 'rp is multiplied by the feedback correction coefficient CFB obtained in the subroutine shown in FIG. The fuel pulse width T inj is determined (step P4), and this final fuel pulse width T inj is output to the injector 9 (step pH).

Note that the method of setting the predetermined value set by the counter, that is, the feedback correction coefficient CFB, at 1.0 for a certain period of time is, for example, changing it according to the deviation of the target rotation speed before and after the change in load, or Various setting methods can be considered, such as setting the time from when the target rotation speed is changed to when a predetermined period of time has elapsed after the engine rotation speed reaches a rotation speed within a minute range centered on the target rotation speed after this change. .

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an engine equipped with an air-fuel ratio control device according to an embodiment of the present invention, FIGS. 2 to 4 are control flowcharts thereof, FIG. 5 is a control characteristic diagram thereof, and FIG. It is a control characteristic diagram in a conventional air-fuel ratio control device. 1φΦ Sanzenkai engine 2... Intake passage 3... Exhaust passage 4... Air cleaner 5... Air flow meter 6... Throttle valve 7... Distributor 8...Crank angle sensor 9...ms, injector, water temperature sensor, O, sensor, throttle sensor, bypass air passage, bypass air valve

Claims (1)

[Claims] 1. An engine air-fuel ratio control device that performs feedback control of the air-fuel ratio in a specific operating range of the engine. An air-fuel ratio control device for an engine, comprising control means for stopping fuel ratio feedback control and fixing a feedback correction coefficient to 1.0 to perform open-loop control.