JPS6332140A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To prevent the generation of misfire and engine stall by correcting the control signal for the feedback control for the air-fuel ratio on the basis of the correction quantity corresponding to the fundamental air-fuel ratio characteristic in each operation state and reducing the width of the feedback correction quantity within a prescribed range. CONSTITUTION:Each detection value of the ignition signal supplied from an ignition coil 2, negative pressure sensor 7, O2 sensor 11, atmospheric pressure switch 12, etc. is input into a control unit 1. The air-fuel ratio is feedback- controlled through an air-fuel ratio controlling actuator 3 according to the operation state. The control unit 1 judges if the car is on a highland or lowland according to the detection value supplied from the atmospheric pressure switch 12, and reads out the limit value of the control quantity for feedback correction from a data map corresponding to the intake negative pressure and the number of revolution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an engine that performs feedback control of an air-fuel ratio based on an air-fuel ratio sensor.

(Prior art) In general, air-fuel ratio control using a feedback control method is based on the output of an air-fuel ratio sensor (such as an oxygen sensor) on a basic air-fuel ratio determined by venturi negative pressure, etc. in a carburetor engine, for example. The air-fuel ratio is controlled by generating a signal and varying, for example, the air bleed opening area and the fuel jet opening area in response to the control signal. On the other hand, in a fuel injection engine, the basic injection amount determined by the intake air amount and the engine rotational speed is corrected based on the output of the air-fuel ratio sensor, and air-fuel ratio control is achieved using the corrected injection amount.

In this case, in the case of a carburetor type engine, the conventional feedback control amount is, for example, the opening ratio or duty ratio of the air bleed, and the device that controls the fuel supply amount is, for example, an air bleed solenoid. .

By the way, the basic air-fuel ratio changes greatly and complicatedly depending on the operating state of the engine. For example, the air-fuel ratio characteristics when the feedback control signal is electrically swung to its maximum width (for example, the air bleed opening area is fully opened) are not constant as shown in FIG. 8, but vary greatly depending on the operating range.

Figure 8 shows the relationship between the engine speed and the engine speed when the intake negative pressure is kept constant (-200,11 Hg, -4001,1 Hg) and the air bleed opening area, etc. is maximized in a carburetor type engine. Shows air-fuel ratio characteristics.

Ideally, if the negative pressure is constant and the air bleed opening ratio is constant, the above air-fuel ratio characteristics should be flat, but in reality, even if the negative pressure is constant, if the rotation speed changes, the air-fuel ratio will change, and even if the negative pressure is constant, the air-fuel ratio will change. Under two different negative pressures, there are complex changes as shown in Figure 8.

(Problem to be solved by the invention) Therefore, in FIG.
(When the air-fuel ratio is at the stoichiometric air-fuel ratio (=14.7) under feedback control in the g (high load) state (rotational speed N+)
, the air bleed is fully open. Then, when the operating condition changes at the next moment and the negative pressure changes to -400 mmHg, the air-fuel ratio of the maximum control amount is lean in the area after that change, so the engine may misfire or run into a ninja strike. . This is an example of overleaning.

In addition, when the load state changes from the high load state on the high speed side to the low load state in Fig. 8, the feedback control signal cannot respond immediately as shown in Fig. 9, so the air-fuel ratio after control changes as shown in the figure. Therefore, it becomes overrich. In addition, in FIG. 9, the horizontal axis is time (1), and when the load shifts from high load to low load, the basic air-fuel ratio, the feedback control signal, the air-fuel ratio after sterilization, and the target air-fuel ratio -14, 7(
) are shown respectively.

Therefore, the present invention was proposed in order to solve the above-mentioned problems of the prior art, and its purpose is to correct the feedback control amount so that it does not exceed a predetermined value, thereby improving the operating state of the engine. An object of the present invention is to propose an air-fuel ratio control device for an engine that can appropriately control the air-fuel ratio even if the engine changes, for example, without causing engine misfire or engine stoppage, and that can quickly achieve air-fuel ratio control even after changes in operating conditions. .

(Means for Solving the Problems) The configuration of the present invention for achieving the above-mentioned problems is based on a control signal for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to a target value based on an air-fuel ratio sensor. a signal generating means for generating a signal, a correction amount setting means for presetting a correction amount corresponding to the basic air-fuel ratio characteristic of each operating state, a correction means for correcting the control signal with the correction amount, and a fuel supply means that supplies fuel based on a control signal.

(Function) In the present invention having the above configuration, the correction amount set by the correction amount setting means is such that the correction amount set by the correction amount setting means is such that the control signal for controlling the fuel supply amount is set by the correction amount to cause engine operation to worsen in each operating state, even if any operating state change occurs. Since the air-fuel ratio is kept within a range that does not occur, engine misfires, etc., for example, are eliminated, and the air-fuel ratio can be controlled smoothly even after the change.

(Example) Examples of the present invention will be described in detail below with reference to the accompanying drawings.

<Configuration of Embodiment> FIG. 1 shows an embodiment for engine control centered on the engine 8. In FIG. Fuel supply to the engine of this embodiment uses a carburetor system. 4 is a carburetor, 5 is a choke valve, 6 is a throttle valve, 7 is a negative pressure sensor that detects the negative pressure in the intake pipe 9, 11 is an oxygen (02) sensor, 1 is a control unit that controls the engine, 2 is a This is an ignition coil that determines the engine speed based on the ignition signal. The air-fuel ratio of the mixture is determined by the A/F according to the signal Cn0w (feedback control amount) from the control unit 1.
This is done by changing the opening area of the air bleed in the carburetor 4 via the control actuator 3. Further, 12 is an atmospheric pressure switch. In this embodiment, attention is paid to the fact that the air density varies depending on the altitude above sea level, and that this change in density affects the air-fuel ratio. It is for controlling.

The human input signals to the control unit 1 include the signal o2 from the oxygen sensor 11 and the signal BOO3 indicating the intake pipe negative pressure.
T, ■G pulse, etc. to know the engine rotation speed.

Control unit in Figure 2! An example of the circuit configuration is shown below. Its general configuration is CPU20, BoosT, O
A/D converter 21 that manually converts 40 into a digital value.
, an input boat 22 for manually controlling the output of the atmospheric pressure switch 7;
A timer 23 for setting the delay time necessary for engine control, a ROM 24 for storing a control procedure program as shown in FIG. 4, and a RAM 25 for storing calculation data, etc.
, output port 26 latching signal Cnow, signal Cn
The output driver 27 and the like drive the A/F control actuator 3 according to the ow.

<Control of Example> The air-fuel ratio control of the example described below divides the operating state into, for example, a high-load operating state, a low-load operating state, a feedback operating state, etc., and controls the air-fuel ratio of each operating state. It is. Here, in this embodiment, the signal for feedback controlling the air-fuel ratio is sent to the A/F control actuator 3.
The control amount Cnow is manually inputted to Cnow. Also, this Know
In order to prevent ICnov from swinging beyond a predetermined value, limit control is performed on the control ICnov in each operating state. If this limit control is always performed, the control amount Cnow will not fluctuate beyond a certain range. Therefore, even if the operating condition changes, the control amount C9aw before the change can be quickly changed to the after change Cnow, and Overrich as there was in the past,
Over-leaning, misfires, engine stalls, etc. will be eliminated.

Among the various maps stored in the ROM 24, FIG. 3(a) shows those that are particularly relevant to the fruitful 'X example. In the figure, )IIGHLIMIT is a map of limit values for highlands, and LOWLIMIT is a map of limit values for lowlands. These maps are engine speed and negative pressure BOO
Optimal limit values are set in advance and stored in accordance with the 5T.

Therefore, a combination of one BOO3T value and rotation speed determines one set of limit values for high altitude and low altitude. Figure 5 shows an example of a limit map. The numbers in the figure indicate the duty ratio of the solenoid 3 when the A/F control actuator 3 is a duty solenoid. For example, when the duty ratio is 100, it is fully open (lean).

FIG. 3(b) shows a storage area of data related to the embodiment in the RAM 25. In the figure, C and p are limit values corresponding to a certain rotation speed and BOO3T value selected from the limit map, and Cn (+w is the aforementioned feedback control amount at that time, and A/ F
Control actuator 3 is driven.

FIG. 4 is a flowchart of the control procedure according to the embodiment. First, in step S1, in order to know the current y-turn height,
The logic value of the high altitude switch 12 is taken in. Step 32~
In step S4, depending on the logic value of this high altitude switch, the switch is set for high altitude (HIGHLIMIT) or low altitude (LOWLIM).
Select one of the limit maps (IT). Step S5. In S6, negative pressure BO0ST and engine speed N
is taken in, and in step S7 the negative pressure BOO3T at that time is
and the limit value Cmap corresponding to the engine speed N is indexed.

In step S8, the operating range is determined from the various quantities obtained above, and it is determined whether the operating range is a feedback control range or not. If the operating range is outside the feedback range, the process proceeds to step S9, where open control is performed. In other words, in this embodiment, which is a carburetor engine, the
Without driving the /F control actuator 3, the air-fuel ratio is arbitrarily determined according to the amount of fuel discharged according to the venturi negative pressure.

On the other hand, if it is determined that the judgment in step S8 is in the feedback control region, the oxygen sensor 11
Capture the output of In step S11, according to this signal 02, a feedback control signal C1o1 is calculated so as to achieve, for example, the stoichiometric air-fuel ratio. Next, in step S12,
It is checked whether the calculated signal amount Cnow exceeds the limit value C1!2 determined in step S7. If it exceeds, in step S13, correction is made so as not to exceed C1ov h' Cmap. In step S14, the above-determined Cl
The A/F control actuator 3 is driven according to ow.

That is, according to this embodiment, as long as it is in the feedback control region, Cnow is the limit Cm according to the operating region.
ap will not be exceeded, so even if the operating range changes,
After the change, overrich or overlean air-fuel ratio can be prevented, and the target air-fuel ratio can be quickly reached.

<Modification> FIG. 6 shows a modification of the above embodiment. In the above embodiment, one of the two limit maps was selected depending on the high altitude switch, but in this modification, there is only one limit map, and the limit map is selected from that one map according to the engine speed and negative pressure. The limit value Cll1ap is corrected according to the altitude. Step S21 in the figure is the seventh
The high altitude correction coefficient chac having the characteristics as shown in the figure is calculated, and in step S25, this Cha is calculated. Correct C□2 based on.

As yet another modification, instead of having two limit maps, one for highlands and one for lowlands, for example, only one map for lowlands is provided, and when the highland switch 12 detects a highland, a constant coefficient K is set for that lowland. It may be added to the limit value C□2.

In addition, the following is proposed as a modification regarding feedback control. In the control shown in FIG. 4, Cnow
The limit control of Cn is always performed only when it is in the feedback control region, and if it is determined in step S8 that it is not in the feedback control region, in step S9, an arbitrary Cn
ow was set, and the amount of fuel discharged was left to the venturi negative pressure. Therefore, in this modification, step S8
If it is not in the feedback control region, instead, C now is determined according to the engine speed and negative pressure at that time, and the process proceeds from step S9 to step S12, so that limit control is performed even outside the feedback control region. It is. In this way, although the feeling of output is slightly reduced, it is possible to improve the followability of the air-fuel ratio control and to prevent over-rich and over-lean conditions even with changes in operating conditions in all operating ranges.

Furthermore, in the above embodiment, the feedback control amount Cnov
exceeds the predetermined value C□2, the predetermined value C01al
The idea was to perform limit control to suppress the value to 1, but in addition to the upper limit, there is also a modified example in which a lower limit is provided, and instead of limit control, a predetermined value is added or subtracted. A modification example that performs such correction is also conceivable.

Although the above embodiment has been explained using a carburetor engine using a digital computer for convenience of explanation, it is also possible to use a so-called analog computer in the control unit section.
Similar effects can also be obtained with fuel injection engines.

(Effects of the Invention) As explained above, according to the present invention, by correcting the width of the feedback control amount based on the air-fuel ratio sensor so that it falls within a predetermined value, the control response on the fuel supply side is improved. As a result, even if the operating state of the engine changes, engine misfire, engine stop, etc. will not occur, and air-fuel ratio control can be quickly achieved even after the operating state changes.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment in which the present invention is applied to a carburetor engine, Fig. 2 is a diagram of an example of the circuit of the engine control 4-unit unit of the embodiment, and Figs. 3 (a) and (b) respectively. , ROM and RA of the embodiment
FIG. 4 is a flowchart of a control procedure according to the embodiment; FIG. 5 is a diagram of a limit map configuration example; FIG. 6 is a flowchart of a control procedure according to a modified example; The figure is a characteristic diagram of the coefficient for high altitude correction according to the modified example, and FIGS. 8 and 9 are diagrams explaining the drawbacks of the conventional example. In the figure, 1... Control unit, 2... Ignition coil, 3... A/F control actuator, 4... Carburetor, 5... Choke #, 6... Throttle valve, 7 ...Negative pressure sensor, 8...Cylinder,
9... Intake pipe, 10... Exhaust pipe, 11... Oxygen sensor, 12... Atmospheric pressure switch, 20... CPU,
21... A/D converter, 22... Input board, 23
...Timer, 24...ROM, 25. RAM, 2
6... Output boat, 27... Output driver. Figure 1 Figure 3 (0) Figure 3 (b) Figure 6 Figure 7 Figure 8 Figure 9

Claims (4)

[Claims] (1) Signal generation means for generating a control signal for feedback controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to a target value based on an air-fuel ratio sensor, and correction corresponding to the basic air-fuel ratio characteristics of each operating state. Air-fuel ratio control for an engine, comprising a correction amount setting means for presetting an amount, a correction means for correcting the control signal by the correction amount, and a fuel supply means for supplying fuel based on the corrected control signal. Device. (2) The correction amount setting means sets a limit value according to each operating state, and the correction means performs limit correction so that the control signal does not exceed the range of the limit value. An air-fuel ratio control device for an engine according to scope 1. (3) The engine according to claim 1, wherein the correction amount setting means includes storage means for storing the correction amount previously set according to the engine speed and intake negative pressure. air-fuel ratio control device. (4) The correction means corrects the control signal based on a correction amount when the signal generation means generates a control signal for feedback control to the stoichiometric air-fuel ratio. The air-fuel ratio control device for an engine according to item 1.