JP2978494B2 - Engine air-fuel ratio control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an engine in which idling speed control is performed so that the engine speed during idling falls within a target speed range. The present invention relates to an air-fuel ratio control device for an engine that controls a fuel supply amount and the like so that an air-fuel ratio of a supplied air-fuel mixture is a predetermined value.

2. Description of the Related Art In an engine mounted on a vehicle or the like, an idling air amount or an ignition timing is changed so that an engine speed during idling is within a target speed range to enhance operation stability. It is known to perform speed control.

In addition to controlling the idling speed in this manner, the air-fuel ratio of the air-fuel mixture used for combustion is varied by changing the fuel supply amount, etc., in order to reduce the fluctuation range of the engine speed and increase the operation stability of the engine. Controlled engines are also known, for example, as described in JP-A-62-255546.

(Problems to be Solved by the Invention) However, in the engine in which the idle speed control and the air-fuel ratio control as described above are performed, the engine is used for combustion so as to improve the fuel efficiency at the time of idling. Assuming that the air-fuel ratio of the air-fuel mixture is lean, depending on the value of the air-fuel ratio, the fluctuation range of the engine speed is limited by the upper and lower speeds that define the target speed range in idle speed control. , Ie, larger than the width of the dead zone in idle speed control. As described above, if the fluctuation range of the engine speed is set to be larger than the width of the dead zone in the idle speed control, there arises a problem that a stable operation state required for the engine cannot be obtained.

In view of the above, the present invention provides an engine in which the engine speed during idling is controlled to be within a target speed range, and the fuel supply amount is controlled to suppress the fluctuation of the engine speed during idling. Alternatively, it is an object of the present invention to provide an air-fuel ratio control device for an engine in which a control for changing an intake air amount is performed to improve a fuel efficiency while securing a stable operation state required for the engine. I do.

(Means for Solving the Problems) In order to achieve the above-mentioned object, an air-fuel ratio control device for an engine according to the present invention, as shown in FIG. For an engine provided with idle speed control means for performing idle speed control for changing an intake air amount or an ignition timing to be within a range, a rotation fluctuation detecting means for detecting a fluctuation width of the engine speed, Control means for controlling the air-fuel ratio of the air-fuel mixture provided for combustion during idling of the engine, the fluctuation range detected by the rotation fluctuation detection means to a target rotation speed range in idle speed control. The fuel supply to the engine must be the largest of the values that will be kept below the difference between the upper and lower speed limits. Control to change the amount or intake air amount is performed.

(Operation) In the air-fuel ratio control device for an engine according to the present invention having the above-described configuration, when the engine is in an idling state, the idle speed control means for controlling the idle speed provided in the engine provides: Under the condition that the intake air amount or the ignition timing is changed so that the engine speed is within the target speed range, the control means
The value of the air-fuel ratio of the air-fuel mixture supplied to the combustion is such that the fluctuation range of the engine speed is controlled to be equal to or less than the difference between the upper limit speed and the lower limit speed that defines the target speed range in the idle speed control. This is the maximum value.

By doing so, the air-fuel ratio takes the value on the leanest side under the condition that the engine speed during idling is within the target speed range in the idle speed control. You. Therefore, a stable operation state required for the engine is ensured, and the fuel efficiency is improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows an example of an air-fuel ratio control apparatus for an engine according to the present invention, together with an engine to which the apparatus is applied. In FIG. 2, a throttle valve 13 interlocked with an accelerator pedal is disposed in an intake passage 12 for guiding intake air from an air cleaner 11 to a combustion chamber 14 in an engine body 10, and a portion where the throttle valve 13 is disposed. On the more upstream side, an air flow meter 15 for detecting the intake air amount is arranged, and on the downstream side from the portion where the throttle valve 13 is arranged, a surge tank 16 is provided. On the downstream side, a fuel injection valve 20 is provided.

The fuel injection valve 20 is electronically controlled, opens according to the pulse width of the injection pulse signal Cp supplied from the control unit 100 described later, and is regulated by the fuel supply system to feed the fuel. The fuel to be injected is intermittently injected at a predetermined timing, for example, in synchronization with the rotation of the engine, toward the intake port portion with respect to the combustion chamber 14,
Create an air-fuel mixture to be burned within 14. The mixture is in the combustion chamber
The fuel gas is supplied to the fuel cell 14 via an intake valve 21, and is ignited by a spark plug 23 and burned. The exhaust gas generated by burning the air-fuel mixture in the combustion chamber 14 is discharged to the exhaust passage 26 via the exhaust valve 24.

In addition, a portion between the throttle valve 13 and the air flow meter 15 in the intake passage 12 is connected to a start end of the bypass portion 17 for the throttle valve 13, and an end portion of the bypass portion 17 is connected to the surge tank 16. I have. Bypass unit 17
Is provided with a flow regulating valve 19,
Opens and closes the bypass unit 17 according to the pulse width of the valve drive pulse signal Cq supplied from the control unit 100,
Thereby, the amount of intake air sucked into the combustion chamber 14 is adjusted.

On the other hand, in connection with the crank mechanism 30 that changes the reciprocating motion of the piston 25 in the engine body 10 into a rotational motion, a rotational speed sensor 31 that detects an engine rotational speed is provided.
From the rotation speed sensor 31, a detection signal Sn corresponding to the engine rotation speed is supplied to the control unit 100.

In addition to the detection signal Sn, the control unit 100
The detection signal St corresponding to the opening of the throttle valve 13 obtained from the throttle opening sensor 27, the detection signal Sa corresponding to the intake air amount obtained from the air flow meter 15, and the detection signal Sa near the stoichiometric air-fuel ratio disposed in the exhaust passage 26. O ₂ sensor 28 whose output characteristics change
Signal So depending on the oxygen concentration in the exhaust gas obtained from
A detection signal Sw corresponding to the cooling water temperature of the engine obtained from a water temperature sensor 29 provided in the engine body 10 is supplied, and also includes a detection signal indicating an operating state of an external load such as an air conditioner applied to the engine. , And another detection signal group Sx required for controlling the engine is also supplied. The control unit 100 controls the intake air amount and the fuel injection based on these various detection signals.

In controlling the intake air amount of the engine by the control unit 100, based on the throttle opening degree represented by the detection signal St and the engine speed N represented by the detection signal Sn, the engine is set to the fully closed state of the throttle valve 13, and is detected that the engine speed N is in the idling state is assumed to take the predetermined value N ₁ or less, further, the feedback control condition, for example, cooling water temperature of the engine indicated by the detection signal Sw is higher than a predetermined temperature When it is detected that such a condition is satisfied, it is determined according to the difference between the engine speed N and the target idle speed No set based on the engine cooling water temperature and the load imposed on the engine. Thus, a feedback correction value GF for the intake air amount is set.

In setting the feedback correction value GF, a rotation speed difference ΔN which is an absolute value of a difference between the engine rotation speed N and the target idle rotation speed No is calculated, and the calculated rotation speed difference ΔN
Is larger than a predetermined value α, for example, 10 (rpm), and when the engine speed N is equal to or greater than the target idle speed No, the predetermined value β is subtracted from the previously set feedback correction value GF. And a new feedback correction value GF is set, and when the rotation speed difference ΔN is larger than the value α and the engine rotation speed N is less than the target idle rotation speed No, the previously set feedback correction value GF is set. The value β is added to the value GF, and a new feedback correction value GF is set.
While the feedback correction value GF is updated and stored, if the rotation speed difference ΔN is equal to or smaller than the value α, the engine speed N is set to the upper limit obtained by adding the target idle speed No and the value α. At idle speed Na or less, target idle speed No
Is within the target rotational speed range that is equal to or higher than the lower limit rotational speed Nb obtained by subtracting the value α from the feedback correction value.
GF is not updated. Then, the feedback correction value GF set as described above and another correction value GX according to the load imposed on the engine and the like are added to the basic control value GB set according to the engine coolant temperature and the like. A control value G is set, and a valve drive pulse signal Cq having a pulse width corresponding to the set control value G is transmitted to the control unit 10.
From 0, it is supplied to the flow control valve 19. Thereby, the engine speed N is set to be within the target speed range.
Alternatively, feedback control on the amount of intake air is performed so as to be maintained within the target rotation speed range.

Further, when the engine is not in the idling state or the deceleration state, that is, when the throttle valve 13 is open, the control value G is set to the fixed value D, and
When the engine is in the idling state but the feedback control condition is not satisfied, and when the engine is in the decelerating state, the feedback control value GF is set to zero, and the control value G is set to the basic control value GB and other correction values. GX is added and set, and a valve drive pulse signal Cq having a pulse width corresponding to the set control value G is generated by the control unit.
From 100, it is supplied to the flow control valve 19.

In controlling the fuel injection amount by the control unit 100, the basic fuel injection amount Tp is set based on the engine speed N and the intake air amount represented by the detection signals Sn and Sa, and the engine coolant temperature represented by the detection signal Sw. Correction value BX according to the operating state of the engine
Is set. Then, when the feedback control condition such as that the cooling water temperature of the engine is equal to or higher than a predetermined temperature is satisfied without the engine being in the idling state, the detection signal So is determined according to the oxygen concentration in the exhaust gas represented by the detection signal So. When the feedback correction value BF is set and the feedback control condition is not satisfied, the feedback correction value BF is set to a fixed value, for example, 1, and the fuel injection amount Ti is set to the basic fuel injection amount Tp, the correction value. BX and the feedback correction value BF are multiplied and set. Then, an injection pulse signal Cp having a pulse width corresponding to the fuel injection amount Ti is formed, and is supplied to the fuel injection valve 20 at a predetermined timing synchronized with the rotation of the engine.

On the other hand, when the engine is idling,
It is determined whether or not an optimum air-fuel ratio control condition such as that the engine cooling water temperature is equal to or higher than a predetermined temperature is satisfied. If it is determined that the optimum air-fuel ratio control condition is satisfied, the optimum air-fuel ratio control condition is determined. The idle feedback correction value ID is set as described later to search for the fuel ratio, and if it is determined that the optimum air-fuel ratio control condition is not satisfied, the idle feedback correction value ID is set first. The fuel injection amount Ti is set by multiplying the set value by the basic fuel injection amount Tp, the correction value BX, and the set idle feedback correction value ID. Then, an injection pulse signal Cp having a pulse width corresponding to the fuel injection amount Ti is formed, and is supplied to the fuel injection valve 20 at a predetermined timing synchronized with the rotation of the engine.

As a result, the fuel injection valve 20 opens for a period corresponding to the pulse width of the injection pulse signal Cp, and injects an amount of fuel corresponding to the operating state of the engine toward the intake port.

When such fuel injection control is performed, the fluctuation range of the engine speed N within a predetermined period is calculated based on the detection signal Sn under the condition that the engine satisfies the optimum air-fuel ratio control condition. And, the fluctuation range is the upper limit rotational speed that determines the target rotational speed range in the idle rotational speed control.
When the difference between the Na and the lower limit rotational speed Nb is equal to or less than 2α, for example, 20 (rpm), the idle feedback correction value ID is searched for the optimum value that is the leanest one of the air-fuel ratio values. A memory update is performed.

In updating the storage of the idling feedback correction value ID, the idling feedback correction value previously set until the fluctuation range DN of the engine speed N is calculated after the engine satisfies the optimum air-fuel ratio control condition. The fuel injection amount Ti is set using the ID, and the fuel injection amount Ti
Is performed. Then, the fluctuation width DN is calculated, and as shown by a point a in FIG. 3, the calculated fluctuation width DN is larger than 2α when the value of the air-fuel ratio A / F takes a relatively rich value. When the value becomes, the value Ib is subtracted from the idle feedback correction value ID, a new idle feedback correction value ID is set, and the fuel injection amount Ti is set using the newly set idle feedback correction value ID. Then, fuel injection with the fuel injection amount Ti is performed. When the predetermined value Ib is subtracted from the idle feedback correction value ID, the air-fuel ratio A / F is shifted to the lean side, and the fluctuation width DN is changed to the point b.
As shown in the above, when the fluctuation width DN is reduced from the previously calculated fluctuation width DN, thereafter, the fluctuation feedback DN is calculated every time the fluctuation width DN is calculated from the idle feedback correction value ID until the fluctuation width DN becomes 2α or less. The value Ib is reduced and a new idle feedback correction value ID is set. Then, the fuel injection amount is calculated by using the set idle feedback correction value ID.
Ti is set, and fuel injection with the fuel injection amount Ti is repeatedly performed.

Thus, the value Ib is calculated from the idle feedback correction value ID.
Is reduced, as shown by points c and d, the air-fuel ratio A / F is shifted to the lean side, the fluctuation width DN gradually decreases, and the fluctuation width DN becomes 2α or less. Thereafter, the idle feedback correction value ID is calculated every time the fluctuation width DN is calculated until the fluctuation width DN becomes larger than 2α.
Is subtracted from the value Ic, and a new idle feedback correction value ID is set. Then, the fuel injection amount Ti is set based on the set idle feedback correction value ID, and the fuel injection with the fuel injection amount Ti is repeatedly performed. Each time the idle feedback correction value ID is set, the air-fuel ratio A / F is gradually shifted to the lean side, and the fluctuation width DN draws a parabola as shown by points e, f, g ,. Will change as follows.

In such a case, when a predetermined period Tx has elapsed from the point in time when the fluctuation width DN has become 2α or less, when the fluctuation width DN is smaller than 2α, for example, when the fluctuation width DN is at a point u, it is subtracted from the idle feedback correction value ID The value Ic is changed to the value 2Ic, and as shown by points v, w and x, the fluctuation width DN and the air-fuel ratio A
The change in / F is made large, and the fluctuation width DN is quickly made larger than 2α. Then, as shown by the point x, when the fluctuation width DN becomes larger than 2α, the value 2Ic is added to the idle feedback correction value ID at that time, and as shown by the point w, the fluctuation width DN becomes When the air-fuel ratio A / F is equal to or less than 2α, an optimum value Rx that is the leanest one among the values of the air-fuel ratio A / F is obtained, and the idle feedback correction value ID that can obtain the optimum value Rx is stored in the built-in memory Is done. On the other hand, when the period Tx does not elapse before the fluctuation width DN becomes larger than 2α, the fluctuation width DN and the air-fuel ratio A / F show changes when the value Ic is subtracted from the idle feedback correction value ID, The value Ic is added to the idle feedback correction value ID when the fluctuation width DN is larger than 2α, and the air-fuel ratio when the fluctuation width DN is 2α or less.
An optimum value that is the leanest one of the A / F values is obtained, and an idle feedback correction value ID that provides such an optimum value is stored in the built-in memory.

As described above, after the idle feedback correction value ID at which the optimum value is obtained is stored in the built-in memory, if the engine is idling and the optimum air-fuel ratio control condition is satisfied, the ignition Until the switch is turned off, the fuel injection amount Ti is set using the idle feedback correction ID that provides the optimum value x.

On the other hand, when the storage of the idle feedback correction value ID is updated, after the engine is in a state of satisfying the optimum air-fuel ratio control condition, the calculated fluctuation width DN is changed to the air-fuel ratio as shown by a point a 'in FIG. When the value of A / F takes a value larger than 2α under a relatively lean value, the value Ib is subtracted from the idle feedback correction value ID and a new idle feedback correction value ID is set, Newly set idle feedback correction value ID
Is used to set the fuel injection amount Ti, and the fuel injection amount
Fuel injection with Ti is performed. Then, the predetermined value Ib is subtracted from the idle feedback correction value ID, whereby the air-fuel ratio A / F is shifted to the lean side, and the fluctuation width DN is calculated first as shown by the point b '. If the fluctuation width DN is larger than the fluctuation width DN, then the fluctuation width DN becomes 2
Until it becomes equal to or less than α, the value Ib is added to the idle feedback correction value ID every time the fluctuation width DN is calculated, a new idle feedback correction value ID is set, and the fuel injection amount Ti
Is set based on the set idle feedback correction value ID.

By adding the value Ia to the idle feedback correction value ID in this way, the air-fuel ratio A / F is shifted to the rich side, and as shown by points c ', d', e 'and f'. After the fluctuation width DN gradually decreases and the fluctuation width DN becomes 2α or less, every time the fluctuation width DN is calculated, a value Ic smaller than the value Ib is subtracted from the idle feedback correction value ID to generate a new value. Each time the idle feedback correction value ID is set, and the idle feedback correction value ID is set, the air-fuel ratio A / F is shifted to the lean side so that the fluctuation range DN is indicated by points g ′ and h ′. Change. When the fluctuation width DN becomes larger than 2α as shown by the point h ′, the idle feedback correction value ID at that time
And the value Ic is added to the
When the DN is equal to or less than 2α, an optimum value Rx ′ that is the leanest one of the values of the air-fuel ratio A / F is obtained, and the idle feedback correction value ID at which the optimum value Rx ′ is obtained is It is set and stored in the built-in memory.

As described above, after the idle feedback correction value ID at which the optimum value is obtained is stored in the built-in memory, if the engine is idling and the optimum air-fuel ratio control condition is satisfied, the ignition Until the switch is turned off, the fuel injection amount Ti is set using the idle feedback correction ID that provides such an optimum value.

In addition, when the idle feedback correction value ID is updated as described above, when the set idle feedback correction value ID exceeds the upper limit value Fu and the lower limit value Fv defined for it, Instead of the idle feedback correction value ID, the upper limit value Fu or the lower limit value Fv is stored in the built-in memory as the idle feedback correction value ID for obtaining the optimum air-fuel ratio.

Thus, when the engine is in the idling state and the optimum air-fuel ratio control condition is satisfied, the fluctuation width DN of the engine speed N becomes equal to the upper limit speed Na and the lower limit speed which define the target speed range. The air-fuel ratio A / F is assumed to be the leanest value under the condition that the difference from the number Nb is kept below, so that the stable operation state required for the engine is obtained and the fuel efficiency is improved. Will be done.

Control unit 100 that performs control as described above
Is configured using, for example, a microcomputer. In such a case, an example of a program executed by the microcomputer for controlling the amount of intake air and controlling fuel injection is shown in the flowcharts of FIGS. 5 and 6. This will be described with reference to FIG.

The program for controlling the amount of intake air shown in the flowchart of FIG. 5 starts, for example, when the ignition switch is turned on. After the start, the detection signals Sn, St, Sw, and Sx in process 101 are started.
And in the following decision 102, the detection signal S
Based on the throttle opening indicated by t, the throttle valve 13
Is in a fully closed state. If it is determined that the throttle valve 13 is in the fully closed state, a basic control value GB is set in process 103 according to the engine coolant temperature or the like represented by the detection signal Sw. A correction value GX according to the load imposed on the engine represented by Sx is set, and the process proceeds to decision 107.

In decision 107, the engine speed N representing the detection signal Sn is the predetermined value N _1, for example, 1200 (rpm)
If the engine speed N is determined to be equal to or less than the value N ₁ , the engine is in an idling state. It is determined whether the feedback (F / B) control condition is satisfied. When it is determined that the feedback control condition is satisfied, the process proceeds to a process 109, in which a target idle speed No is set according to a cooling water temperature of the engine, a load imposed on the engine, and the like. The absolute value of the difference between the engine speed N and the target idle speed No is calculated and set as a speed difference ΔN. In the following decision 112, it is determined whether or not the speed difference ΔN is equal to or smaller than a predetermined value α. to decide.
If it is determined that the rotational speed difference ΔN is equal to or smaller than the value α, the process directly proceeds to the process 117 because the engine speed N is within the target rotational speed range, and it is determined that the rotational speed difference ΔN is not smaller than the value α. In this case, at decision 114, it is determined whether the engine speed N is equal to or higher than the target idle speed No. If it is determined that the engine speed N is equal to or higher than the target idle speed No, Process 115
In, a predetermined value β is subtracted from the feedback correction value GF to set a new feedback correction value GF. If it is determined in decision 114 that the engine speed N is less than the target idle speed No, in process 116, the value β is added to the feedback correction value GF, and a new feedback correction value GF is calculated. After setting, proceed to process 117.

In the process 117, the control value G is calculated by the equation G = GB + GF
In a subsequent process 118, a valve drive pulse signal Cq having a pulse width corresponding to the control value G calculated in the process 117 is formed, and is sent to the flow regulating valve 19 to return to the original state.

On the other hand, if it is determined in decision 108 that the feedback control condition is not satisfied, in process 121, the feedback correction value GF is set to zero, the process proceeds to process 117, and the processes after process 117 are executed in the same manner as described above. And go back.

Also, in decision 107, the engine speed N
If but that is determined that is greater than the value N _1, since the engine is in a deceleration state, in the process 121 proceeds to process 117 sets the feedback correction value GF zero, the process 117 after the step Execute in the same manner as described above and return to the original. Further, when it is determined in the decision 102 that the throttle valve 13 is not in the fully closed state, in the process 123, the control value G is set to the fixed value D, the process proceeds to the process 118, and the process 118 is executed in the same manner as described above. And go back.

In the program for controlling the fuel injection shown in the flowchart of FIG. 6, for example, the process is started when the ignition switch is turned on, and after the start, the detection signals Sn, Sa, St, So, Sw, and In a process 132 for capturing Sx, the basic fuel injection amount Tp is calculated by using the engine speed N represented by the detection signal Sn and the intake air amount Q represented by the detection signal Sa, as follows: Tp = K
× N / Q (where K is a constant), and in process 134, a correction value BX is set based on the engine cooling water temperature represented by the detection signal Sw, the load imposed on the engine represented by the detection signal Sx, and the like.

Next, in decision 135, the detection signals Sn and St
It is determined whether or not the engine is in an idling state based on the, if it is determined that the engine is not in the idling state, it is determined in decision 137 whether or not the feedback control condition is satisfied, the feedback control When it is determined that the condition is satisfied, in process 138, a feedback correction value BF is set according to the oxygen concentration in the exhaust gas represented by the detection signal So, and the process proceeds to process 140, where the feedback control condition is determined. If it is determined that the condition is not established, the process proceeds to step 139 to set the feedback correction value BF to 1
Go to 140.

In the process 140, the fuel injection amount Ti is calculated by the equation: Ti = Tp
× BX × BF, and in the following process 142, an injection pulse signal Cp having a pulse value corresponding to the fuel injection amount Ti
Is sent to the fuel injection valve 20 at a predetermined timing synchronized with the rotation of the engine, and then returns to the original state.

On the other hand, if it is determined in decision 135 that the engine is idling,
Proceeding to 144, it is determined whether or not the optimal air-fuel ratio control condition is satisfied.If it is determined that the optimal air-fuel ratio control condition is not satisfied, each step after decision 137 is performed in the same manner as described above. When it is determined that the optimum air-fuel ratio control condition is satisfied at decision 144, the process returns to step 145 to set an idle feedback correction value as shown in FIG. Execute the application program and proceed to process 146,
At 46, the fuel injection amount Ti is set by the formula: Ti = Tp × BX × ID, and then the process 142 is executed in the same manner as described above, and the process returns.

The flowchart of FIG. 7 shows a program for setting an idle feedback correction value. In this program, a flag J is used to determine the completion of the search for the optimum air-fuel ratio, and a flag W is used to determine the fluctuation range of the engine speed N. A value 2α where DN is the difference between the upper limit rotation speed Na and the lower limit rotation speed Nb that defines the target rotation speed range in idle speed control.
The flag V is used to determine whether the idle feedback correction value ID has been increased.The flags J, W, and V are used to determine whether the idle feedback correction value ID has been increased. , Is set to zero when the ignition switch is turned on. In the idle feedback correction value setting program, after the start, it is determined whether or not the flag J is 1 at a decision 151. If the flag J is determined to be 1, the program is terminated. When it is determined that the flag J is zero, in a process 152, a variation width DN of the engine speed N in a predetermined period is calculated, and in a decision 153, it is determined whether or not the flag W is one. If it is determined that the flag W is not 1, the decision 154 determines whether or not the flag V is 1, and if it is determined that the flag V is not 1, the decision 156 determines whether the flag V is It is determined whether or not the variation width DN has decreased. If it is determined that the variation width DN has decreased, it is determined in decision 157 whether or not the variation width DN is greater than 2α. Then, when it is determined that the fluctuation width DN is larger than 2α, in a process 158, a predetermined value Ib is subtracted from the idle feedback correction value ID to set a new idle feedback correction value ID, and At step 159, the flag V is set to zero and the decision 166 is made.
Proceed to.

In addition, when it is determined in decision 154 that the flag V is 1, in decision 162,
It is determined whether or not the fluctuation width DN has decreased, and if it is determined that the fluctuation width DN has decreased, in decision 163,
It is determined whether the fluctuation width DN is greater than 2α, and the fluctuation width DN is determined.
Is determined to be greater than 2α, the process 16
In step 4, a new idle feedback correction value is obtained by adding the value Ib to the idle feedback correction value ID.
The ID is set, and in the subsequent process 165, the flag V is set to 1 and the process proceeds to decision 166.

In the decision 166, it is determined whether or not the idle feedback correction value ID is larger than an upper limit value Fu defined for the idle feedback correction value ID.
Is determined to be larger than the upper limit Fu, the process 167 sets the idle feedback correction value ID to the upper limit Fu and ends the program, and the idle feedback correction value ID is equal to or less than the upper limit Fu. If it is determined that the idle feedback correction value ID is less than the lower limit value Fv determined for it in decision 168, the idle feedback correction value
When it is determined that the ID is less than the lower limit Fv, the program is terminated as it is, and when it is determined that the ID is less than the lower limit Fv, the idle feedback correction value ID is set to the lower limit Fv in the process 169. Set and exit this program.

On the other hand, when it is determined in decision 156 that the fluctuation width DN has increased, it is determined in decision 163 whether the fluctuation width DN is larger than 2α, and it is determined that the fluctuation width DN is larger than 2α. If so, process 164
The following steps are executed in the same manner as described above to end this process. If it is determined that the fluctuation width DN is equal to or smaller than 2α, the process 170 sets the flag W to 1, and then proceeds to the process 171. Also, in decision 162,
If it is determined that the fluctuation width DN has decreased, it is determined in decision 157 whether the fluctuation width DN is larger than 2α. If it is determined that the fluctuation width DN is larger than 2α, The process 158 and the subsequent steps are executed in the same manner as described above, and this process is terminated.
After setting to 1, the process proceeds to the process 171. Further, if the flag W is determined to be 1 in the decision 153, the process proceeds to the process 171.

In the process 171, a new count m is set by adding 1 to the count m, and in the subsequent process 172, a predetermined value Ic smaller than the value Ib is subtracted from the idle feedback correction value ID to obtain a new idle feedback. A correction value ID is set, and in decision 174, it is determined whether or not the idle feedback correction value ID is less than the lower limit value Fv.
If it is determined that the idle feedback correction value ID is not less than the lower limit value Fv in the process 175, the process proceeds to the decision 177. Proceed directly to decision 177. In decision 177, it is determined whether or not the fluctuation width DN is equal to or less than 2α, and the fluctuation width is determined.
When it is determined that the DN is equal to or smaller than 2α, it is determined whether or not the count number m is equal to or greater than the count number Ma corresponding to the predetermined period Tx in decision 178, and the count number m is determined as the count number. If it is determined that it is equal to or greater than Ma, the value Ic is doubled in process 179 to obtain a new value Ic.
Is set, the count number m is reset to zero in the subsequent process 180, and the program is terminated. If it is determined in decision 178 that the count number m is less than the count number Ma, the program is terminated as it is. I do.

When it is determined in the decision 177 that the fluctuation width DN is larger than 2α, the idle feedback correction value ID is added to the idle feedback correction value ID in the process 181 to obtain the optimum air-fuel ratio. After setting the correction value ID, setting the count number m to zero in the process 182, and setting the flag J to 1 in the process 183, the program ends.

In the above-described example, the idle speed control is performed by changing the intake air amount, and the control of the air-fuel ratio A / F of the air-fuel mixture provided for combustion is performed by changing the fuel supply amount. Although it is made to be performed, it is not necessary to be so, the idle speed control may be performed by changing the ignition timing, and the control of the air-fuel ratio A / F may be performed. This may be performed by changing the amount of intake air.

(Effects of the Invention) As is apparent from the above description, according to the engine air-fuel ratio control apparatus of the present invention, the intake air amount or the ignition timing is set so that the engine speed during idling is within the target speed range. Is changed, the air-fuel ratio of the mixture supplied to the combustion, the variation range of the engine speed, the upper speed limit and the lower limit that determine the target speed range in the idle speed control It is assumed that the maximum value of the values that will be kept below the difference with the rotation speed is taken, so that the engine rotation speed is within the target rotation speed range and the stable operation state required for the engine is obtained. Thus, the fuel economy can be improved under such a stable operation state.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram showing an air-fuel ratio control device for an engine according to the present invention according to the claims, and FIG. 2 is an example of an air-fuel ratio control device for an engine according to the present invention. FIG. 3 and FIG. 4 are characteristic diagrams used to explain the operation of the example shown in FIG. 1, and FIGS. 5 to 7 are examples shown in FIG. 4 is a flowchart illustrating an example of a program executed by a microcomputer when the microcomputer is used in the control unit in FIG. In the figure, 15 is an air flow meter, 17 is a bypass section, 19 is a flow control valve, 20 is a fuel injection valve, 27 is a throttle opening sensor, 31 is a rotation speed sensor, and 100 is a control unit.

Claims (1)

(57) [Claims] An engine provided with idle speed control means for performing idle speed control for changing an intake air amount or an ignition timing so that an engine speed during idling is within a target speed range. A rotation fluctuation detecting means for detecting a fluctuation width of the rotation speed; an air-fuel ratio of an air-fuel mixture used for combustion during idling of the engine; a fluctuation width detected by the rotation fluctuation detection means in the idle speed control. In order to take the maximum value of the values that will be kept below the difference between the upper limit speed and the lower limit speed that define the target speed range,
Control means for controlling the amount of fuel supplied to the engine or the amount of intake air to change the air-fuel ratio of the engine.