JPS6260945A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To prevent the generation of engine miss fire due to overlean state by setting an aimed air-fuel ratio to the lean side in comparison with a prescribed value and carrying out feedback control when the air-fuel ratio deflects to the lean side, while suspending the feedback control when the air-fuel ratio deflects to the rich side. CONSTITUTION:A control unit 30 sets the aimed air-fuel ratio corresponding to the operation state, and compares said aimed air-fuel ratio with the output voltage of an air-fuel ratio sensor 20, and feedback-controls the fuel injection quantity of a fuel injection valve 8. Though the air-fuel ratio is feedback- controlled in the operation region in which the aimed air-fuel ratio is set in the vicinity of the theoretical air-fuel ratio, no bad influence is given to the operation of an engine. Further, though fuel is increased in the lean state in comparison with the aimed air-fuel ratio in the region in which the aimed air- fuel ratio is set to the lean side from a prescribed value, the reduction of fuel through feedback control is not carried out, in a little rich state in comparison with the aimed air-fuel ratio, and the deflection to the lean side of the air-fuel ratio is prevented. Therefore, the engine stall due to the overlean state is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine air-fuel ratio control device that performs feedback control by changing a target air-fuel ratio depending on operating conditions.

(Prior Art) Conventionally, as shown in Japanese Unexamined Patent Publication No. 58-59330, an air-fuel ratio system detects the oxygen concentration in exhaust gas and outputs a signal corresponding to the air-fuel ratio (for example, a signal proportional to the air-fuel ratio). Air-fuel ratio feedback control that uses a sensor, sets a target air-fuel ratio according to the operating state, and controls the fuel supply amount by comparing the output of the air-fuel ratio sensor with a value corresponding to the target air-fuel ratio. There is a device. In this device, the air-fuel ratio can be detected over a wide range with the air-fuel ratio sensor, and by changing the target air-fuel ratio depending on the operating condition, the air-fuel ratio is controlled to suit various operating conditions. The fuel ratio is sometimes set near the stoichiometric air-fuel ratio and sometimes set on the lean side.

By the way, in this type of conventional device, the air-fuel ratio detected by the air-fuel ratio sensor is richer than the target air-fuel ratio, regardless of whether the target air-fuel ratio is set near the stoichiometric air-fuel ratio or on the lean side. When the condition is reached, the amount of fuel is decreased, and when the condition is leaner than the target air-fuel ratio, the amount of fuel is increased. Therefore, the air-fuel ratio is controlled to fluctuate somewhat around the target air-fuel ratio. However, when the target air-fuel ratio is set near the lean ignition limit for economical driving, etc., if the air-fuel ratio swings leaner than this, misfires may occur, and the frequency of swings towards the lean side may increase. The higher the temperature, the more likely misfires will occur. Therefore, at this time, there is a demand to suppress the air-fuel ratio i, lJ from swinging to the lean side from the target air-fuel ratio as much as possible through feedback control.

(Object of the Invention) In view of the above circumstances, the present invention provides an engine air-fuel ratio control device that is capable of suppressing overlean due to feedback control and preventing misfires in an operating range where the target air-fuel ratio is set to the lean side. It provides:

(Structure of the Invention) The present invention includes an air-fuel ratio sensor that detects the oxygen concentration in exhaust gas and outputs a signal corresponding to the air-fuel ratio, and a target air-fuel ratio sensor that detects the oxygen concentration in exhaust gas and outputs a signal corresponding to the air-fuel ratio. In the engine air-fuel ratio control device, the engine air-fuel ratio control device includes feedback control means for controlling at least one of the fuel supply amount or the air amount by comparing the value corresponding to the fuel ratio with a value corresponding to the fuel ratio. a first control means that performs feedback control to increase or decrease at least one of the fuel supply amount or the air amount in accordance with fluctuations in the air-fuel ratio around the target air-fuel ratio when the fuel ratio is set near the target air-fuel ratio; and a second control means that performs feedback control when the air-fuel ratio becomes leaner than the target air-fuel ratio and stops the feedback control when the air-fuel ratio becomes richer than the target air-fuel ratio when is set leaner than a predetermined value. It is something that

In other words, when the target air-fuel ratio is set to a leaner side than a predetermined value, if the condition becomes leaner than that, the amount of fuel is increased and the air-fuel ratio is controlled in the rich direction, but if the condition becomes leaner than the predetermined value, the air-fuel ratio is controlled to be richer. In this case, the fuel consumption is not reduced by feedback control, and the air-fuel ratio is prevented from swinging in the lean direction.

(Embodiment) FIG. 1 shows an embodiment of the apparatus of the present invention. In this figure, 11 is a cylinder of an engine 10, and 12 is a cylinder 11.
13 is an intake passage, and 14 is an exhaust passage.

In the intake passage 13, an air cleaner 1 is installed in order from the upstream side.
5, an air flow meter 16, a throttle valve 17, and a fuel injection valve 18 are provided. Furthermore, an air-fuel ratio sensor 20 is provided in the exhaust passage 14 upstream of one exhaust purification device. In addition, as detection elements necessary for controlling the amount of fuel injection gA, there is a rotation speed sensor 21 that detects the engine rotation speed based on changes in the engine crank angle, a pressure sensor 22 that detects the intake negative pressure corresponding to the engine load, and an intake pressure sensor 22 that detects the intake negative pressure corresponding to the engine load. An intake temperature sensor 23 that detects the air temperature and a water temperature sensor 24 that detects the engine cooling water temperature are provided.

The air-fuel ratio sensor 20 detects the air-fuel ratio by detecting the oxygen concentration in the exhaust gas, and outputs a signal corresponding to the air-fuel ratio. For example, as shown in FIG. ) is designed to generate an output voltage proportional to

30 is a control unit, CPtJ31, memory 3
2, includes an input section 33 and a drive circuit 34 for the fuel injection valve 18, and includes the air flow meter 16 and each sensor 20 to 2.
4 and outputs a drive signal to the fuel injection valve 18. This drive signal is given by an injection pulse, and the fuel injection amount (fuel supply amount) is determined by the pulse width of this injection pulse. is now under control.

The control unit 30 constitutes a feedback control means that sets a target air-fuel ratio according to the operating state, compares the output voltage of the air-fuel ratio sensor 20 with the target air-fuel ratio, and controls the fuel injection amount based on the output voltage of the air-fuel ratio sensor 20. However, in particular, in the present invention, the first control means performs control when the target air-fuel ratio is set near the stoichiometric air-fuel ratio by performing control as will be described in detail later; and second control means for performing control when set to a leaner side. As shown in FIG. 2, the predetermined air-fuel ratio Y1, which is the boundary between the control range by the first control means and the control range by the second control means, is considerably leaner than the stoichiometric air-fuel ratio (λ=1). For example, Δ/F=18. In addition, in FIG. 2, the target air-fuel ratio Yt and the corresponding target voltage Vt during lean operation where the predetermined air-fuel ratio Y1 is leaner (for example, A / F = 20 >), and the target voltage Vt corresponding to this are also shown. It shows the output voltage fluctuation permissible range α and its lower limit value (Vt-α) corresponding to the permissible range in the direction in which the air-fuel ratio shifts to the rich side (Y- is the permissible limit),
These will be explained later in the flowchart.

A specific example of control by the control unit 30 will be explained with reference to the flowchart in FIG. 3. In this specific example, the fuel injection amount is corrected by feedback control based on the output of the air-fuel ratio sensor 20 and the target voltage, and the average value of correction values obtained by, for example, multiple feedback controls is calculated for each operating state category. , store this as a learning value in memory 3
This learned value is reflected in the feedback control, that is, the correction value by the feedback control and the learned value are used together to control the fuel injection amount.

In this flowchart, the system is first initialized in step S1, and then the engine speed, intake negative pressure, water temperature, intake air temperature, air-fuel ratio sensor output, and air flow meter output are input in step S2. Next, in step S3, a basic injection pulse width Tp is calculated based on the engine speed and the air flow meter output, and in step S4, a target air-fuel ratio Yt is calculated based on the engine speed and the basic injection pulse width Tp. In this case, the basic injection pulse width To and the target air-fuel ratio Yt are stored in the memory 32 by using a map in advance of values according to the operating state that can be determined from the engine speed and the air flow meter output, or the engine speed and the basic injection pulse width Tp. It is only necessary to memorize it and calculate it based on this. Subsequently, in step S5, a target voltage Vt corresponding to the target air-fuel ratio Yt is determined based on the output characteristics of the air-fuel ratio sensor 20 shown in FIG.

Next, in step S6, it is checked whether or not the cooling water temperature and the operating state have become conditions for performing feedback control. If the determination result is No, in step S7, the learned value C
After setting s and the correction value Of for feedback control to O, the process moves to step S 1a described later.

If the determination result in step S6 is YES, it is checked in step S8 whether learning has been completed, that is, whether the learning value O3 has already been stored in the storage area of the learning value map corresponding to the current driving state. Find out. Although the process of calculating this learning value O5 is not shown in the flowchart,
For example, in the same operating state classification, step 812 described below
The average value of the correction values Cf may be calculated when the processing in steps S14 to S14 is repeated a plurality of times, and this may be stored as a learning value in the learning value map. Above step S8
If the determination result in step S9 is No, the learning value CS is
is set to 0, and then feedback control is performed in steps S12 to S14, which will be described later. In this way, in this embodiment, after completing the initial stage processing for determining the learning value C8,
The following processing, which is the main part of the present invention, is performed.

If the determination result in step S8 is YES, the learning value C8 corresponding to the operating state is read out from the map in step S1o, and then the process proceeds to step S11 to determine whether the target air-fuel ratio is equal to or higher than the predetermined air-fuel ratio (18 in the embodiment). Find out. If the determination result is NO, the first control means processes to determine whether the difference between the output voltage VS of the air-fuel ratio sensor 20 and the target voltage is positive or negative, so that the actual air-fuel ratio becomes the target air-fuel ratio. Check whether the state is lean or rich (step 512);
If it is in a lean state, the correction value C for feedback control
f is increased by a constant value ΔC (step 513), and if the condition is rich, the correction 1iacf is decreased by a constant value ΔC (step $14). In other words, feedback control is performed to increase or decrease the correction value Cf based on the deviation of the air-fuel ratio around the target air-fuel ratio.

Then, the process moves to step S18.

On the other hand, if the determination result in step S11 is YES,
As a process of the second control means, based on the determination whether the difference between the output voltage Vs and the target voltage Vt is positive or negative (step 515), if the actual air-fuel ratio is leaner than the target air-fuel ratio, step S13 Then, feedback control is performed to increase the correction value Cf, and if the air-fuel ratio is richer than the target air-fuel ratio, the feedback control is stopped, that is, the correction value Cf is not changed. However, in this case, in this embodiment, in order to prevent the air-fuel ratio from shifting transiently to the rich side, the output voltage Vs is lower than the target voltage Vt, as shown in FIG. A permissible range is set on the richer side than the fuel ratio), and feedback control is stopped within this permissible range. That is, when the rich state is determined in step Sts, the difference between the output voltage VS and the lower limit voltage of the allowable range (Vt-α) is further checked in step S16, and based on this, if it is within the allowable range, the step 81 is continued.
8, if the value is on the richer side than the allowable range, the correction value Cf is decreased by a constant value ΔC (step 517), and then the process moves to step 31a.

In step S18, the final injection pulse width 7i is set to [[ Ti=Tpxcx (1+Of+
C8)], and then in step S19, an injection pulse having the final injection pulse width T1 is output to control the fuel injector.

According to such control, as shown in FIG. 4, the way the air-fuel ratio changes is determined by the operating range B in which the target air-fuel ratio Yt is set near the stoichiometric air-fuel ratio and the operating range B in which the target air-fuel ratio is set on the lean side. are different. That is, in the former operating range A, by performing the processing as the first control means in steps 812 to S14 described above, when the state becomes richer than the target voltage Vt, the amount of fuel is increased until the state becomes one full. Once the lean state is reached, the process of reducing the amount of fuel is repeated until the rich state is reached, so the actual air-fuel ratio is equal to the target air-fuel ratio Yt.
It swings around. In this case, near the stoichiometric air-fuel ratio, the air-fuel ratio of 1lJt[l does not adversely affect the operation of the engine, and the air-fuel ratio is controlled so that the target air-fuel ratio Yt is achieved on average.

On the other hand, in the latter operating range B, the fuel is increased by 1 when the state becomes leaner than the target air-fuel ratio Yt, but the fuel is increased by 1 when the state becomes leaner than the target air-fuel ratio Yt. When the state is slightly richer than Yt, the amount of fuel is not reduced by feedback control, and the air-fuel ratio is prevented from leaning towards the lean side. Therefore, in the operating range B in which the target air-fuel ratio Yt is set to the lean side, the air-fuel ratio is prevented from becoming leaner than the target air-fuel ratio Yt, and misfires due to over-lean are prevented.

Also, operate the above as in the example! l! ! At B, if the fuel is reduced when the air-fuel ratio deviates richer than the target air-fuel ratio Yt by more than the allowable range, the air-fuel ratio becomes the target air-fuel ratio Yt.
There is no significant deviation from t.

In general, if the above-mentioned learned value Cs is reflected in the control, the responsiveness of the air-fuel ratio control to changes in the operating state can be improved, and it is possible to suppress deviations in the air-fuel ratio when the feedback control is stopped. can.

In addition, although the fuel supply amount is controlled in the above embodiment, in an engine using a carburetor, for example, a bypass passage that bypasses a throttle valve is provided in the intake passage and the flow rate of the bypass passage is controlled. may be controlled gD1'' according to the above embodiment.

(Effects of the Invention) As described above, the present invention provides the following advantages when performing feedback control of the air-fuel ratio by setting a target air-fuel ratio according to the operating state.
When the target air-fuel ratio is set to leaner than the predetermined value,
If the air-fuel ratio shifts to the lean side in the vicinity, feedback control is performed, but if it shifts to the switch side, feedback control is stopped, which prevents misfires due to over-lean. It is.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the output characteristics of the air-fuel ratio sensor, Fig. 3 is a control flowchart, and Fig. 4 shows that the target air-fuel ratio is near the stoichiometric air-fuel ratio. FIG. 4 is an explanatory diagram showing air-fuel ratio fluctuations when set to the lean side and when set to the lean side. 18...Fuel injection valve, 20...Air-fuel ratio sensor, 30
...control unit (feedback control means including first control means and second control means). Patent applicant Mazda Co., Ltd. Agent
Patent Attorney Etsushi Kotani Patent Attorney
Long 1) Masamukai Patent Attorney Itaya University of Tokyo Figure 2

Claims (1)

[Claims] 1. An air-fuel ratio sensor that detects the oxygen concentration in exhaust gas and outputs a signal corresponding to the air-fuel ratio, and a value corresponding to the target air-fuel ratio set according to the output of this air-fuel ratio sensor and the operating state. In an engine air-fuel ratio control device comprising a feedback control means for controlling at least one of a fuel supply amount or an air amount by comparison, when the target air-fuel ratio is set in the vicinity of the stoichiometric air-fuel ratio in the feedback control means. a first control means that performs feedback control to increase or decrease at least one of the fuel supply amount or the air amount in accordance with fluctuations in the air-fuel ratio around the target air-fuel ratio; An engine characterized in that it is provided with a second control means that performs feedback control when the air-fuel ratio becomes leaner than the target air-fuel ratio, and stops the feedback control when the air-fuel ratio becomes richer than the target air-fuel ratio. air-fuel ratio control device.