JPS6355339A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To maintain the output of an engine in an area where target air-fuel ratio increases, by bringing the reduction correcting rate of a density correcting means for reducing fuel supply as the density of intake air decreases to a low level or to zero when the operating condition of engine is in said area. CONSTITUTION:A control unit 100 operates a basic fuel injection quantity based on an intake air quantity fed from an air flow meter 20 and a rotation fed from a rotation sensor 30, then makes various corrections based on the values detected through an intake air temperature sensor 19, a throttle opening sensor 18, an atmospheric pressure sensor 23, a water temperature sensor 24, an O2 sensor, etc. In other word, fuel supply is decrementally corrected as the density of intake air decreases based on the intake air temperature and the atmospheric pressure, and feedback correction to a target air-fuel ratio is made corresponding to an operating area being determined based on the throttle opening and the rotation. In an operating area where the target air-fuel ratio increases, reduction correcting rate of fuel supply corresponding to the density of intake air is brought to a low level or to zero.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides control to match the air-fuel ratio of an air-fuel mixture in an engine in which different target air-fuel ratios are set for a plurality of operating regions to each target air-fuel ratio. The present invention relates to an air-fuel ratio control device.

(Prior art) Conventionally, with the aim of improving fuel efficiency, different target air-fuel ratios are set for multiple operating regions, and the air-fuel ratio of the air-fuel mixture used for combustion is set as a target for each region. It is known to perform control to change the ratio of the amount of fuel supplied to the amount of intake air taken into the engine in order to improve the air-fuel ratio.

For example, one of the engines to which such control is performed is:
JP-A No. 60-30443 discloses that the target air-fuel ratio is set to an air-fuel ratio leaner than the stoichiometric air-fuel ratio (hereinafter referred to as lean air-fuel ratio) when the operating state is in the light load region, When the air-fuel ratio is on the Lynch side than the stoichiometric air-fuel ratio (
In addition to setting the target air-fuel ratio to the output air-fuel ratio (hereinafter referred to as the output air-fuel ratio), the proposed system also changes the target air-fuel ratio from the lean air-fuel ratio to the stoichiometric air-fuel ratio when the load is accelerated in the light load range. has been done.

By the way, in -M, the amount of fuel supplied to the engine is set based on the amount of intake air, and the air-fuel ratio is determined by the ratio of the weight of fuel to the weight of intake air. Therefore,
If the fuel supply amount is set regardless of the intake air density,
Since the air-fuel ratio deviates from the target air-fuel ratio when the density of the intake air changes, the fuel supply amount is usually corrected according to the density of the intake air.

(Problems to be Solved by the Invention) However, in an engine in which different target air-fuel ratios are set for each of a plurality of operating ranges as described above,
If the fuel supply amount is corrected to the same degree (ratio) in each region in accordance with the density of intake air, the following problem may occur.

That is, for example, if the density of intake air at low altitudes is used as a reference, and the fuel supply amount is corrected to the same degree in each region according to the density of intake air, the intake air density at high altitudes will be lower than that at low altitudes. The amount of fuel supplied will be reduced to the same extent in all regions as the density of the air becomes smaller. However, the operating condition of the engine is
When the target air-fuel ratio is in a region considered to be a lean air-fuel ratio, in addition to the fact that the ratio of the fuel supply amount to the intake air amount at low altitudes is smaller than when it is in other regions,
At high altitudes, this ratio will be even smaller, resulting in a situation where the desired engine output cannot be obtained unless the amount of accelerator pedal depression is increased compared to normal, thereby ensuring sufficient driving performance. There is a risk that it will not be possible to do so. In order to eliminate this inconvenience, by reducing the degree to which the fuel supply amount is reduced in accordance with the density of intake air in all regions, the engine operating state will be adjusted so that the target air-fuel ratio is the stoichiometric air-fuel ratio or the output air-fuel ratio. When it is in the range, the actual air-fuel ratio shifts to the Lynch side, which may cause problems such as misfire of the air-fuel mixture.

In view of the above, the present invention provides an engine in which different target air-fuel ratios are set in a plurality of operating regions, and for each operating region, the air-fuel ratio of the air-fuel mixture used for combustion is made to match the target air-fuel ratio. The fuel supply amount is corrected according to the density of the intake air, and the target air-fuel ratio of the engine is set to a relatively large (lean side) in a state where the change in the intake air is small. An object of the present invention is to provide an air-fuel ratio control device for an engine that can obtain a desired engine output without increasing the amount of depression of the accelerator pedal and ensure sufficient driving performance when the engine is in the driving range. shall be.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the air-fuel pressure control device for an engine according to the present invention, as shown in the basic configuration in FIG. a fuel supply amount setting means for setting the fuel supply amount based on the amount of intake air taken into the engine so that the air-fuel ratio of the air-fuel mixture in the engines, each of which has a different target air-fuel ratio set, is the same as the target air-fuel ratio;
an air density detection means for detecting the density of intake air taken into the engine; and the smaller the density of the intake air detected by the air density detection means, the smaller the fuel supply amount set by the fuel supply amount setting means. The density correction limiting means controls the density correction means to adjust the degree of weight loss correction to the density correction means depending on the operating state of the engine. When the target air-fuel ratio is in a large range, it is made smaller or zero than when it is in a small range.

(Function) In the air-fuel ratio control device for an engine according to the present invention configured as described above, the fuel supply amount set by the fuel supply amount setting means is adjusted according to the density of intake air by the density correction means. Corrected. In this case, the density correction means performs a reduction correction such that the smaller the density of the intake air, the smaller the fuel supply amount.

In this way, when the density correction means performs the reduction correction of the fuel supply amount, the density correction limiting means sets the degree of the reduction correction to the density correction means, depending on the operating state of the engine.
When the target air-fuel ratio is in a large range, it is made smaller or zero than when it is in a small range.

By doing this, when the density of the intake air is small and the engine operating state is in a region where the target air-fuel ratio is large, the desired air-fuel ratio can be achieved even if the amount of depression of the accelerator pedal is not increased. Engine output will be obtained.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an example of an engine air-fuel ratio control device according to the present invention, together with an engine to which the device is applied. In FIG. 2, an intake passage 12 that guides intake air from an air cleaner 11 into a combustion chamber 14 of an engine body 10 is provided with a throttle valve 16 that is interlocked with an accelerator pedal. The opening degree of this throttle valve 16 is determined by the throttle opening sensor 18.
A detection signal St corresponding to the opening of the throttle valve 16 is obtained from the throttle opening sensor 18, and is supplied to the control unit 100, which will be described in detail later.

An air flow meter 20 for detecting intake air is disposed upstream of the portion of the intake passage 12 located at the throttle valve 16. From this air flow meter 20,
A detection signal Sa corresponding to the detected intake air amount is supplied to the control unit 100. In addition, the intake passage 12
A surge tank 22 having a relatively large capacity is provided downstream of the part where the throttle valve 16 is arranged, and a fuel injection valve 25 is temporarily provided further downstream from the surge tank 22. There is. Fuel injection valve 25
The valve is electronically controlled, and the valve is opened according to the pulse width (duty) of the injection pulse signal Pc supplied from the control unit 100, and the fuel is pressure-regulated and pumped from the fuel supply system. The mixture is intermittently injected toward the intake port of the combustion chamber 14 at a predetermined timing, for example, in synchronization with the rotation of the engine, to create an air-fuel mixture for combustion within the combustion chamber 14. The air-fuel mixture is supplied to the combustion chamber 14 via the intake valve 27, ignited by the spark plug 28, and combusted. Exhaust gas generated by combustion of the air-fuel mixture in the combustion chamber 14 is discharged into the exhaust passage 26 via the exhaust valve 29.

Furthermore, in relation to the crank mechanism 33 that changes the reciprocating motion of the piston 31 in the engine body 10 into rotational motion,
A rotation speed sensor 30 that detects the engine rotation speed is arranged, and a detection signal Sn corresponding to the engine rotation speed is supplied from the rotation speed sensor 30 to the control unit 100.

The control unit) 100 has the above-mentioned detection signal Sa.
, Sn and St, 02 arranged in the exhaust passage 26
A detection signal So obtained from the sensor 35, a detection signal Sf corresponding to the temperature of the intake air obtained from the intake air temperature sensor 19 provided between the air cleaner 11 and the air flow meter 20 in the intake passage 12, and a detection signal Sf obtained from the atmospheric pressure sensor 23. Various detection signals are supplied, such as a detection signal Sp corresponding to the atmospheric pressure, and a detection signal Sw corresponding to the engine cooling water temperature obtained from the water temperature sensor 24 provided in the engine main body 10. The control unit 100 controls the fuel injection amount in the fuel injection valve 25, that is, controls the air-fuel ratio of the air-fuel mixture provided for combustion in the combustion chamber 14, based on the various detection signals described above.

Here, in this example, target air-fuel ratios are set in advance for each of a plurality of regions divided according to the operating state of the engine.

That is, in FIG. 3, the vertical axis shows the throttle opening corresponding to the engine load, and the horizontal axis shows the engine speed, and each region is shown. The engine rotation speed is the predetermined rotation speed N1
In region ■ below, the target air-fuel ratio is the stoichiometric air-fuel ratio (1
4, 7), and a region J in which the throttle opening is equal to or greater than the predetermined opening T2 (the throttle valve 16 is fully open or close to it), and the engine rotational speed is the predetermined rotational speed N2. In the range H where the throttle opening exceeds the idling opening T but is less than the predetermined opening T8, the target air-fuel ratio becomes the output air-fuel ratio (approximately 13).
Furthermore, in a region where the throttle opening exceeds the idling opening T but is less than the predetermined opening T2 and the engine speed is below the predetermined rotation speed N2, the target air-fuel ratio is set to a lean air-fuel ratio (approximately 18). be done. However, even if the operating state of the engine is within the range, when the engine is in an accelerating state, it is necessary to increase the engine output, so the target air-fuel ratio is set to the stoichiometric air-fuel ratio.

Note that in FIG. 3, a region C in which the throttle opening is less than the idling opening Tl and the engine speed exceeds a predetermined rotational speed NI is defined as a fuel cut region, and when the engine operating state is in this region, Air-fuel ratio control is not performed.

The control unit 100 then outputs the detection signal Sa.
, Sf, Sns So, Sp, St, SW, etc., the operating state of the engine is in region I.

J, H, and L, the pulse width of the injection pulse signal Pc supplied to the fuel injection valve 25 is set to match the air-fuel ratio of the air-fuel mixture provided for combustion with the target air-fuel ratio set for each region. The amount of fuel injection is controlled by changing the amount of fuel.

At that time, the control unit 100 controls the detection signal Sa
and Sn calculate the basic fuel injection amount based on the intake air amount and engine rotation speed, respectively. Then, the control unit 100 determines that the operating state of the engine is in region I.
0□ sensor 3 to set the target air-fuel ratio to the stoichiometric air-fuel ratio.
The basic fuel injection amount is corrected based on the detection signal So supplied from 5, an injection pulse signal Pc having a pulse width corresponding to the obtained fuel injection amount is formed, and this is supplied to the fuel injection valve 25. . As a result, feedback control of the air-fuel ratio is performed, and the actual air-fuel ratio converges to the stoichiometric air-fuel ratio, which is the target air-fuel ratio.

When such feedback control is performed, the control unit 100 aggregates the feedback correction values calculated for correcting the basic fuel injection amount a predetermined number of times, obtains the average value, and stores the average value in the built-in memory. To,
The average value is stored in place of the previously determined average value, and the average value is updated.

Furthermore, when the operating state of the engine is in regions J and H, the control unit 100 multiplies the basic fuel injection amount calculated as described in 5 above by a predetermined coefficient in order to adjust the air-fuel ratio to the output air-fuel ratio. A fuel injection amount larger than the basic fuel injection amount is calculated, and the calculated fuel injection amount is corrected by adjusting the detected signal Sp obtained from the atmospheric pressure sensor 23 to the atmospheric pressure. Such correction is performed by multiplying the fuel injection amount by an atmospheric pressure correction coefficient, which takes a smaller value as the atmospheric pressure becomes smaller, as shown in FIG. 4, for example, and thereby, As the density of the intake air decreases, a reduction correction is performed to decrease the fuel injection amount. Note that the vocal tract of the intake air changes depending on not only the atmospheric pressure but also the intake temperature, but in this example, the correction based on the atmospheric pressure and the correction based on the intake temperature are performed separately.

Then, the control unit 100 further corrects the fuel injection amount corrected according to the atmospheric pressure according to the intake air temperature detected by the detection signal Sf, the engine cooling water temperature detected by the detection signal Sw, etc., and generates a new fuel injection amount. The fuel injection amount is calculated, and an injection pulse signal Pc having a pulse width corresponding to the calculated fuel injection amount is formed and supplied to the fuel injection valve 25. As a result, the ratio of the fuel injection amount to the intake air amount is increased compared to the feedback control described above.
The actual air-fuel ratio becomes the target air-fuel ratio and the output air-fuel ratio.

Further, the control unit 100 performs basic fuel injection in order to make the air-fuel ratio a lean air-fuel ratio when the engine operating state is in the range, the engine cooling water temperature is higher than a predetermined temperature, and the engine is not in an acceleration state. This was corrected by multiplying the amount by the average value of the feedback correction coefficients stored in the built-in memory. The basic fuel injection amount is multiplied by a predetermined coefficient to calculate a fuel injection amount smaller than the basic fuel injection amount, and the calculated fuel injection amount is corrected according to intake air temperature, engine cooling water temperature, etc. to generate new fuel. Calculate the injection amount. Therefore, in this case, control unit 1
00 calculates the fuel injection amount without finally correcting the fuel injection amount based on the atmospheric pressure, forms an injection pulse signal Pc with a pulse width corresponding to the fuel injection amount, and uses this as the fuel injection amount. It is supplied to the injection valve 25. As a result, the ratio of the fuel injection amount to the intake air amount is reduced compared to the feedback control described above, and the actual air-fuel ratio becomes a lean air-fuel ratio, but since no correction is performed based on atmospheric pressure, for example, In a descendant where the air density is low, the air-fuel ratio takes a value closer to Lynch than the target air-fuel ratio. Therefore, even if the amount of depression of the accelerator pedal is not increased at high altitudes compared to low altitudes, the desired engine output can be obtained and sufficient driving performance can be ensured.

In addition, if the engine operating condition is too high and the engine cooling water temperature is below the specified temperature, setting the air-fuel ratio to a lean air-fuel ratio may worsen the combustibility of the air-fuel mixture. In this case, the control unit 100 sets the fuel injection amount so that the air-fuel ratio becomes, for example, a value near the stoichiometric air-fuel ratio.

The control unit 100 that performs the above-described control is configured using, for example, a microcomputer, and FIGS. 5 and 6 show an example of a program for fuel injection control executed by the microcomputer in such a case. This will be explained with reference to the flowchart.

FIG. 5 shows a program for fuel injection amount control,
After this program starts, the detection signals Sa, Sf, Sn, So, and Sp are generated in process 101.

St and 3w are taken in, and in the subsequent process 102, a basic fuel injection amount 'rp is set according to the intake air amount Q, which is detected by the detection signal Sa, and the engine rotational speed N, which is detected by the detection signal Sn. That is, the calculation Tp=KXQ/N (where K is a constant) is performed.

In the next decision 103, the throttle opening Th
It is determined whether or not the throttle opening Th is less than or equal to the idling opening T, and if it is determined that the throttle opening Th is less than or equal to the idling opening N. Determine whether or not it is less than or equal to N. In decision 104, engine speed N
If it is determined that the engine speed is not less than the predetermined rotation speed N, the engine operating state is in region C, so the process proceeds to process 105 to cut fuel, sets the fuel injection amount Ti to zero, and returns to the original state. Further, if it is determined that the engine speed N is less than or equal to the predetermined speed N1, the engine operating state is in the region (3), so the process proceeds to decision 107.

In addition, in decision 103, the throttle opening T
If it is determined that h is not less than the idling opening T, the process proceeds to decision 106, where the detection signal St determines whether the rate of change ΔTh of the throttle opening is greater than or equal to the predetermined value β, that is, the engine is accelerating. If it is determined that the engine is in an accelerating state, the process advances to decision 107.

In decision 107, based on the detection signal SO obtained from the 0□ sensor 35, it is determined whether the actual air-fuel ratio (A/F) is smaller (Lynch side) than the stoichiometric air-fuel ratio (14,7). , if it is determined that the actual air-fuel ratio is smaller than the stoichiometric air-fuel ratio, the process proceeds to process 108, in which a constant value is calculated from the previous feedback correction value Fb' stored in the built-in memory, as will be described later. Set a new feedback correction value Fb by subtracting α and process 112
If it is determined that the actual air-fuel ratio is larger (on the lean side) than the stoichiometric air-fuel ratio, the process proceeds to process 109, where a new feedback is added by adding -constant value α to the feedback correction value Fb''. The correction value Fb is set and the process proceeds to process 112.

In process 112, the basic fuel injection amount Tp set in process 102 is multiplied by the new feedback correction value Fb set in processes 108 to 110 to set the fuel injection amount Ti, and then the process proceeds to process 113. In process 113, the feedback correction value Fb used in process 112 is stored in the built-in memory in place of the previous feedback correction value Fb', and after updating the feedbank correction value Fb, the process proceeds to process 114. , In process 114, an injection pulse signal Pc having a pulse width corresponding to the fuel injection amount Ti set in process 112 is formed, and this is supplied to the fuel injection valve 25, and the process returns to the original state. As a result, feedback control is performed, and the air-fuel ratio converges to the stoichiometric air-fuel ratio, which is the target air-fuel ratio.

On the other hand, if it is determined in decision 106 that the engine is not in an accelerating state, the process proceeds to decision 116, where it is determined whether or not the throttle opening Th is equal to or greater than the predetermined opening T2, that is, the operating state of the engine is in the region J. If it is determined that it is in area J, the process advances to process 118; if it is determined that it is not in area J, the process advances to decision 119. In decision 119, it is determined whether the engine rotation speed N is equal to or higher than a predetermined rotation speed N2, that is, whether the engine operating state is in the region H,
If it is determined that the area is in area H, the process advances to process 118.

In process 118, in order to set the air-fuel ratio to the output air-fuel ratio, the basic fuel injection amount 'rp set in process 102 is multiplied by the rich air-fuel ratio correction coefficient A (A>1) to determine the fuel injection amount Ti. After setting, proceed to process 120. In process 120, in order to correct the fuel injection amount Ti set in process 118 according to atmospheric pressure, the relationship between atmospheric pressure and atmospheric pressure correction coefficient as shown in FIG. , reads the atmospheric pressure correction coefficient Px corresponding to the atmospheric pressure at which the detection signal Sp occurs, and adjusts the fuel injection l
After multiplying Ti by this atmospheric pressure correction coefficient Px and setting the obtained fuel injection amount as a new fuel injection amount Ti, the process proceeds to process 121. In process 121, process 1
The fuel injection amount obtained by multiplying the fuel injection amount Ti set in 20 by a correction coefficient Ct that is set according to the intake air temperature at which the detection signal Sf is detected, the engine cooling water temperature at which the detection signal Sw is detected, etc. After setting the new fuel injection ITi, the process proceeds to process 114.

In process 114, an injection pulse signal P having a pulse width corresponding to the fuel injection amount Ti set in process 121 is used.
c and supplies it to the fuel injection valve 25 and returns to the original state. Thereby, the air-fuel ratio becomes the output air-fuel ratio which is the target air-fuel ratio. □On the other hand, if it is determined in decision 119 that the engine rotation speed N is not equal to or higher than the predetermined rotation speed N, in this case, the engine operating state is within the range (however, it is not in an acceleration state), so decision 1
Proceed to step 22. In decision 122, it is determined whether the cooling water temperature W of the engine in which the detection signal Sw is detected is equal to or higher than a predetermined temperature W1, and the cooling water temperature W of the engine is determined to be a predetermined temperature W1.
If it is determined that the amount is not higher than , the process proceeds to process 123, where the fuel injection amount Ti is set to, for example, the basic fuel injection amount 'rp set in process 102. Then, in subsequent processes 120, 121 and 11''4, the fuel injection amount Ti set in process 123 is corrected according to the atmospheric pressure and the operating state of the engine, and the corrected fuel injection amount iTi is An injection pulse signal Pc having a pulse width corresponding to the pulse width is formed and supplied to the fuel injection valve 25, and then returns to light.

Further, if it is determined in decision 122 that the engine cooling water temperature W is equal to or higher than the predetermined temperature W1, the process proceeds to step 124, where feedback is calculated by an average value calculation routine described later and stored in the built-in memory. Process 12 takes in the average value MFb of the correction value Fb.
Proceed to step 5. In process 125, the basic fuel injection amount Tp set in process 102 is multiplied by the average value MFb of the feedback correction values Fb taken in in process 124 and the lean air-fuel ratio correction coefficient B (B<1). After that, the fuel injection amount Ti is set without going through the process 120, and therefore without performing the atmospheric pressure correction, the process proceeds to the process □. fuel injection amount Ti
, a new fuel injection flTi is set by adding correction according to the operating state of the engine, and the process □ then proceeds to process 114.

In process 114, an injection pulse signal Pc having a pulse width corresponding to the set fuel injection amount Ti is formed without performing atmospheric pressure correction, and this is supplied to the fuel injection valve 25, and the process returns to the original state. As a result, when the operating state of the engine is in the range and is not in an acceleration state, and the cooling water temperature W is above the predetermined temperature W8, the fuel injection amount is not reduced at high altitudes, so it is In comparison, the air-fuel ratio will be slightly richer.

FIG. 6 shows a program in a routine for calculating the average value MFb of the feedback correction value Fb.
, Sp and St, and in the subsequent decision 132, the detection signal St.

Based on Sn, it is determined whether air-fuel ratio feedback control (F/B) is being performed in the fuel injection control routine described above, and if it is determined that feedback control is not being performed, the process returns to the original state. , if it is determined that feedback control is being performed, decision 1
Proceed to step 33.

In decision 133, it is determined whether the atmospheric pressure is a reference value based on the detection signal Sp, that is, whether or not it is a lowland. If it is determined that this is the case, the process proceeds to process 134. In process 134, the previous feedback correction value Fb" stored in the memory in process 113 in the fuel injection control routine described above is taken in. In subsequent process 135, 1 is added to the count number U and this is used as a new count number. Then, the process proceeds to decision 136. In decision 136, it is determined whether the count number U is equal to or greater than the predetermined number of times X. If it is determined that the count number U is not equal to or greater than the predetermined number of times is the predetermined number of times X or more, process 13
Proceed to step 7.

In process 137, the
The average value MFb of the feedback correction values Fb is calculated and the process proceeds to process 138. In process 138, the average value MFb calculated in process 137 is stored in the built-in memory instead of the previously calculated average value MFb, and the average value M
Update the memory of Fb and return to the original state.

In the above example, when the engine operating state is in the range where the target air-fuel ratio is a lean air-fuel ratio,
When the fuel supply amount is not corrected according to the atmospheric pressure and the target air-fuel ratio is in a range where the air-fuel ratio is other than the lean air-fuel ratio, the fuel supply amount is corrected according to the atmospheric pressure. The air-fuel ratio control device for an engine according to the present invention does not necessarily have to be configured in this way; for example, as shown in FIG.
A correction coefficient that takes 1 when the target air-fuel ratio is a lean air-fuel ratio (for example, 18) is set, and the atmospheric pressure correction coefficient Px in the above example is multiplied by such a correction coefficient to increase the target air-fuel ratio. By correcting the atmospheric pressure correction coefficient Px so that it takes a larger value, the degree of reduction in the amount of fuel supplied at high altitudes may be made smaller as the target air-fuel ratio increases.

Further, in the above example, when the operating state of the engine is in the range where the target air-fuel ratio is the stoichiometric air-fuel ratio, the fuel injection amount is set by feedback control based on the detection signal obtained from the 0□ sensor, and When the operating state of the engine is in a region where the target air-fuel ratio is a lean air-fuel ratio, the average value of the feedback correction values calculated during the feedback control described above is used to set the fuel injection amount. However, the engine air-fuel ratio control device according to the present invention does not necessarily have to set the fuel injection amount in this way, and the engine air-fuel ratio control device according to the present invention does not necessarily have to set the fuel injection amount in this way, and can set the engine air-fuel ratio even when the engine operating state is in either of the above two ranges. The fuel injection amount may be set by loop control.

(Effects of the Invention) As is clear from the above description, in the engine air-fuel ratio control device according to the present invention, different target air-fuel ratios are set for each of a plurality of regions divided according to the operating state of the engine. In order to make the air-fuel ratio of the mixture used for combustion match the target air-fuel ratio, the fuel supply amount is corrected according to the density of the intake air. Therefore, when the engine operating state is in a region where the target air-fuel ratio is set to a relatively large (lean side), the amount of fuel supply is reduced to a greater degree than when the intake air density is high. Therefore, the desired engine output can be obtained and sufficient driving performance can be ensured without increasing the amount of depression of the accelerator pedal.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram showing the present invention in accordance with the claims, FIG. 2 is a schematic configuration diagram showing an example of an engine air-fuel ratio control device according to the present invention, and FIGS. 3 and 4 are Figures 2, 5, and 6, which are used to explain the operation of the example shown in Figure 2, respectively show programs executed by a microcomputer when the control unit shown in Figure 2 uses a microcomputer. FIG. 7 is a flowchart showing an example of the above, and is a characteristic diagram for explaining an example in which the control mode is different from the example shown in FIG. In the figure, 10 is the engine body, 18 is the throttle opening sensor, 19 is the intake temperature sensor, 20 is the air flow meter, 2
3 is an atmospheric pressure sensor, 24 is a water temperature sensor, 25 is a fuel injection valve, 30 is a rotation speed sensor, 35 is a 0□ sensor, and 100 is a control unit. Figure 2

Claims (1)

[Claims] A fuel supply amount is set based on the amount of intake air taken into the engine in order to match the air-fuel ratio of the air-fuel mixture in the engine, in which different target air-fuel ratios are set for a plurality of operating regions, to the target air-fuel ratio. supply amount setting means; air density detection means for detecting the density of intake air taken into the engine; density correction means for performing a reduction correction to reduce the amount of fuel supplied; An air-fuel ratio control device for an engine, comprising a density correction limiting means for making the density correction smaller or zero than when it is in a region where it is small.